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Petra Henning,1 Sofia Movérare-Skrtic,1 Anna Westerlund,1 Pedro Paulo Chaves de Souza,2,3 Thais Floriano-Marcelino,3 Karin H Nilsson,1 Maha El Shahawy,1,4 Claes Ohlsson,1 Ulf H Lerner1 1Department of Internal Medicine and Clinical Nutrition, Institute of Medicine, Sahlgrenska Osteoporosis Centre and Centre for Bone and Arthritis Research at the Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; 2The Innovation in Biomaterials Laboratory, School of Dentistry, Federal University of Goiás, Goiânia, Brazil; 3Department of Physiology and Pathology, São Paulo State University (UNESP), School of Dentistry, Araraquara, Brazil; 4Department of Oral Biology, Faculty of Dentistry, Minia University, Minia, 61511, EgyptCorrespondence: Ulf H LernerUniversity of Gothenburg, Klin Farm Lab, Vita Straket 11, Gothenburg, 41345, SwedenTel +46 70 651 91 03Email ulf.lerner@gu.seBackground: Bone loss is often observed adjacent to inflammatory processes. The WNT signaling pathways have been implicated as novel regulators of both immune responses and bone metabolism. WNT16 is important for cortical bone mass by inhibiting osteoclast differentiation, and we have here investigated the regulation of WNT16 by several members of the pro-inflammatory gp130 cytokine family.Methods: The expression and regulation of Wnt16 in primary murine cells were studied by qPCR, scRNAseq and in situ hybridization. Signaling pathways were studied by siRNA silencing. The importance of oncostatin M (OSM)-induced WNT16 expression for osteoclastogenesis was studied in cells from Wnt16-deficient and wild-type mice.Results: We found that IL-6/sIL-6R and OSM induce the expression of Wnt16 in primary mouse calvarial osteoblasts, with OSM being the most robust stimulator. The induction of Wnt16 by OSM was dependent on gp130 and OSM receptor (OSMR), and downstream signaling by the SHC1/STAT3 pathway, but independent of ERK. Stimulation of the calvarial cells with OSM resulted in enhanced numbers of mature, oversized osteoclasts when cells were isolated from Wnt16 deficient mice compared to cells from wild-type mice. OSM did not affect Wnt16 mRNA expression in bone marrow cell cultures, explained by the finding that Wnt16 and Osmr are expressed in distinctly different cells in bone marrow, nor was osteoclast differentiation different in OSM-stimulated bone marrow cell cultures isolated from Wnt16−/- or wild-type mice. Furthermore, we found that Wnt16 expression is substantially lower in cells from bone marrow compared to calvarial osteoblasts.Conclusion: These findings demonstrate that OSM is a robust stimulator of Wnt16 mRNA in calvarial osteoblasts and that WNT16 acts as a negative feedback regulator of OSM-induced osteoclast formation in the calvarial bone cells, but not in the bone marrow.Keywords: oncostatin M, WNT16, osteoclast, osteoblast

Background and Purpose Bone resorption induced by interleukin-1β ( IL-1β) and tumour necrosis factor ( TNF-α) is synergistically potentiated by kinins, partially due to enhanced kinin receptor expression. Inflammation-induced bone resorption can be impaired by IL-4 and IL-13. The aim was to investigate if expression of B1 and B2 kinin receptors can be affected by IL-4 and IL-13. Experimental Approach We examined effects in a human osteoblastic cell line ( MG-63), primary human gingival fibroblasts and mouse bones by IL-4 and IL-13 on mRNA and protein expression of the B1 and B2 kinin receptors. We also examined the role of STAT6 by RNA interference and using Stat6-/- mice. Key Results IL-4 and IL-13 decreased the mRNA expression of B1 and B2 kinin receptors induced by either IL-1β or TNF-α in MG-63 cells, intact mouse calvarial bones or primary human gingival fibroblasts. The burst of intracellular calcium induced by either bradykinin ( B2 agonist) or des- Arg10-Lys-bradykinin ( B1 agonist) in gingival fibroblasts pretreated with IL-1β was impaired by IL-4. Similarly, the increased binding of B1 and B2 ligands induced by IL-1β was decreased by IL-4. In calvarial bones from Stat6-deficient mice, and in fibroblasts in which STAT6 was knocked down by siRNA, the effect of IL-4 was decreased. Conclusions and Implications These data show, for the first time, that IL-4 and IL-13 decrease kinin receptors in a STAT6-dependent mechanism, which can be one important mechanism by which these cytokines exert their anti-inflammatory effects and impair bone resorption. [ABSTRACT FROM AUTHOR]

Unlabelled: Interleukin-6 (IL-6)-type cytokines are pleiotropic molecules capable of stimulating bone resorption and expressed by numerous cell types. In the present study, we tested the hypothesis that gingival fibroblasts may exert local osteotropic effects through production of IL-6 and related cytokines. IL-6-type cytokine expression and regulation by IL-1beta and tumor necrosis factor-alpha (TNF-alpha) were studied in fibroblasts from the non-inflamed gingiva of healthy individuals. Constitutive mRNA expression of IL-6, IL-11, and leukemia inhibitory factor (LIF), but not of oncostatin M (OSM), was demonstrated, as was concentration-dependent stimulation of IL-6 and LIF mRNA and of protein by IL-1beta and TNF-alpha. IL-11 mRNA and protein were concentration-dependently stimulated by IL-1beta. The signaling pathway involved in IL-6 and LIF mRNA stimulation involved MAP kinases, but not NF-kappaB. The findings support the view that resident cells may influence the pathogenesis of periodontal disease through osteotropic IL-6-type cytokine production mediated by activation of MAP kinases.Abbreviations: IL-1alpha (interleukin-1alpha); IL-1beta (interleukin-1beta); IL-6 (interleukin-6); IL-11 (interleukin-11); LIF (leukemia inhibitory factor); OSM (oncostatin M); alpha(1)-coll. I (alpha(1)-collagen I); ALP (alkaline phosphatase); BMP-2 (bone morphogenetic protein-2); OC (osteocalcin); BSP (bone sialoprotein); TNFR I (tumor necrosis factor receptor I); TNFR II (tumor necrosis factor receptor II); IL-1R1 (interleukin-1 receptor 1); GAPDH (glyceraldehyde-3-phosphate dehydrogenase); RPL13A (ribosomal protein L13A); mRNA (messenger ribonucleic acid); cDNA (complementary deoxyribonucleic acid); PCR (polymerase chain-reaction); BCA (bicinchoninic acid); ELISA (enzyme-linked immunosorbent assay); alpha-MEM (alpha modification of Minimum Essential Medium); and FCS (fetal calf serum). [ABSTRACT FROM AUTHOR]

BACKGROUND: The aim of the present study was to investigate bone resorption activity (BRA), interleukin-1 alpha (IL-1 alpha), IL-1 beta and interleukin-1 receptor antagonist (IL-1ra) in gingival crevicular fluid (GCF) in sites with no signs of periodontal disease and in sites with horizontal or angular loss of periodontal bone. These assessments were performed before and after periodontal treatment. METHODS: GCFs were collected from 10 individuals with filter strips from two healthy sites and four sites with deep pathological periodontal pockets, two of which showed horizontal bone loss and two with angular bone loss. All diseased pockets were treated with flap surgery and systemic Doxyferm. Twelve months later GCF was collected again and treatment outcome evaluated. BRA in GCFs was assessed in a bone organ culture system by following the release of (45)Ca from neonatal mouse calvariae. The amounts of IL-1 alpha, IL-1 beta and IL-1ra in GCFs were quantified by enzyme-linked immunosorbent assay (ELISA). RESULTS: Treatment resulted in reduction of pocket depths with 3.5+/-0.5 mm in sites with angular bone loss and 2.8+/-0.3 mm in sites with horizontal bone loss. Initially, BRA, IL-1 alpha, IL-1 beta and IL-1ra were significantly higher in GCFs from diseased sites compared with healthy sites. No differences in BRA and cytokine levels were seen between GCFs from pockets with horizontal and angular bone losses. The levels of IL-1 alpha, IL-1 beta and IL-1ra were significantly reduced after treatment of diseased pockets. Pocket depths were significantly correlated to BRA only in pre-treatment sites with angular bone loss. BRA was correlated to Il-1 alpha, IL-1 beta, but not to IL-1ra, in diseased sites with angular bone loss, before and after treatment. The reductions of BRA in the individual sites, seen after treatment, were not correlated to the reductions of Il-1 alpha, IL-1 beta or IL-1ra. CONCLUSIONS: These data show that BRA and cytokine levels are increased in GCFs from sites with periodontal disease and that periodontal treatment results in reduction of the cytokines. Our findings further indicate that IL-1 alpha and IL-1 beta play important roles for the BRA present in GCFs, but that other factors also contribute to this activity. [ABSTRACT FROM AUTHOR]

The sequalae of periodontitis include irreversible degradation of tooth-supporting structures and circulatory spread of inflammatory mediators. However, the serum protein profile in periodontitis is not well described, which is partly attributable to the limited number of studies based on large and well-characterized periodontitis cohorts. This study aims to identify novel, circulating inflammation-related proteins associated with periodontitis within the PerioGene North case-control study, which includes 478 cases with severe periodontitis and 509 periodontally healthy controls. The serum concentrations of high-sensitivity C-reactive protein (hs-CRP) and a panel of 45 inflammation-related proteins were analyzed using targeted proteomics. A distinguishable serum protein profile was evident in periodontitis cases. The protein pattern could separate cases from controls with a sensitivity of 0.81 and specificity of 0.81 (area under the curve = 0.87). Adjusted levels for hs-CRP and 24 of the 45 proteins were different between cases and controls. High levels of hs-CRP and matrix metalloproteinase-12, and low levels of epidermal growth factor (EGF) and oxidized low-density lipoprotein receptor 1 (OLR-1) were detected among the cases. Furthermore, the levels of C-C motif chemokine-19, granulocyte colony-stimulating factor-3 (CSF-3), interleukin-7 (IL-7), and hs-CRP were significantly higher in cases with a high degree of gingival inflammation. The levels of CSF-3 and tumor necrosis factor ligand superfamily member-10 TNFSF-10 were higher in cases with many deep periodontal pockets. The PerioGene North study includes detailed clinical periodontal data and uncovers a distinct serum protein profile in periodontitis. The findings of lower EGF and OLR-1 among the cases are highlighted, as this has not been presented before. The role of EGF and OLR-1 in periodontitis pathogenesis and as possible future biomarkers should be further explored., Competing Interests: Declaration of Conflicting InterestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Osteoporosis is a common skeletal disease affecting millions of individuals world-wide, with an increased risk of fracture, and a decreased quality of life. Despite its well-known consequences, the etiology of osteoporosis and optimal treatment methods are not fully understood. Human genetic studies have identified genetic variants within the FMN2/GREM2 locus to be associated with trabecular volumetric bone mineral density (vBMD) and vertebral and forearm fractures, but not with cortical bone parameters. GREM2 is a bone morphogenetic protein (BMP) antagonist. In this study, we employed Grem2-deficient mice to investigate whether GREM2 serves as the plausible causal gene for the fracture signal at the FMN2/GREM2 locus. We observed that Grem2 is moderately expressed in bone tissue and particularly in osteoblasts. Complete Grem2 gene deletion impacted mouse survival and body growth. Partial Grem2 inactivation in Grem2 +/- female mice led to increased trabecular BMD of femur and increased trabecular bone mass in tibia due to increased trabecular thickness, with an unchanged cortical thickness, as compared with wildtype littermates. Furthermore, Grem2 inactivation stimulated osteoblast differentiation, as evidenced by higher alkaline phosphatase (Alp), osteocalcin (Bglap), and osterix (Sp7) mRNA expression after BMP-2 stimulation in calvarial osteoblasts and osteoblasts from the long bones of Grem2 -/- mice compared to wildtype littermates. These findings suggest that GREM2 is a possible target for novel osteoporotic treatments, to increase trabecular bone mass and prevent osteoporotic fractures., (© 2024. The Author(s).)

A deleterious effect of elevated levels of vitamin A on bone health has been reported in clinical studies. Mechanistic studies in rodents have shown that numbers of periosteal osteoclasts are increased, while endocortical osteoclasts are simultaneously decreased by vitamin A treatment. The present study investigated the in vitro and in vivo effect of all-trans retinoic acid (ATRA), the active metabolite of vitamin A, on periosteal osteoclast progenitors. Mouse calvarial bone cells were cultured in media containing ATRA, with or without the osteoclastogenic cytokine receptor activator of nuclear factor kappa B-ligand (RANKL), on plastic dishes or bone discs. Whereas ATRA did not stimulate osteoclast formation alone, the compound robustly potentiated the formation of RANKL-induced bone resorbing osteoclasts. This effect was due to stimulation by ATRA (half-maximal stimulation ∼3 nM) on the numbers of macrophages/osteoclast progenitors in the bone cell cultures, as assessed by mRNA and protein expression of several macrophage and osteoclast progenitor cell markers, such as macrophage colony-stimulating factor receptor, receptor activator of nuclear factor kappa B, F4/80, and CD11b, as well as by flow cytometry (FACS) analysis of CD11b + /F480 + /Gr1 - cells. The stimulation of macrophage numbers in the periosteal cell cultures was not mediated by increased macrophage colony-stimulating factor or interleukin-34. In contrast, ATRA did not enhance macrophages in bone marrow cell cultures. Importantly, ATRA treatment upregulated the mRNA expression of several macrophage-related genes in the periosteum of tibia in adult mice. These observations demonstrate a novel mechanism by which vitamin A enhances osteoclast formation specifically on periosteal surfaces., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The first evidence of the existence of vitamin A was the observation 1881 that a substance present in small amounts in milk was necessary for normal development and life. It was not until more than 100 years later that it was understood that vitamin A acts as a hormone through nuclear receptors. Unlike classical hormones, vitamin A cannot be synthesized by the body but needs to be supplied by the food as retinyl esters in animal products and ß-carotene in vegetables and fruits. Globally, vitamin A deficiency is a huge health problem, but in the industrialized world excess of vitamin A has been suggested to be a risk factor for secondary osteoporosis and enhanced susceptibility to fractures. Preclinical studies unequivocally have shown that increased amounts of vitamin A cause decreased cortical bone mass and weaker bones due to enhanced periosteal bone resorption. Initial clinical studies demonstrated a negative association between intake of vitamin A, as well as serum levels of vitamin A, and bone mass and fracture susceptibility. In some studies, these observations have been confirmed, but in other studies no such associations have been observed. One meta-analysis found that both low and high serum levels of vitamin A were associated with increased relative risk of hip fractures. Another meta-analysis also found that low levels of serum vitamin A increased the risk for hip fracture but could not find any association with high serum levels of vitamin A and hip fracture. It is apparent that more clinical studies, including large numbers of incident fractures, are needed to determine which levels of vitamin A that are harmful or beneficial for bone mass and fracture. It is the aim of the present review to describe how vitamin A was discovered and how vitamin A is absorbed, metabolized and is acting as a ligand for nuclear receptors. The effects by vitamin A in preclinical studies are summarized and the clinical investigations studying the effect by vitamin A on bone mass and fracture susceptibility are discussed in detail., Competing Interests: The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Lerner.)

It is well established that inflammatory processes in the vicinity of bone often induce osteoclast formation and bone resorption. Effects of inflammatory processes on bone formation are less studied. Therefore, we investigated the effect of locally induced inflammation on bone formation. Toll-like receptor (TLR) 2 agonists LPS from Porphyromonas gingivalis and PAM2 were injected once subcutaneously above mouse calvarial bones. After five days, both agonists induced bone formation mainly at endocranial surfaces. The injection resulted in progressively increased calvarial thickness during 21 days. Excessive new bone formation was mainly observed separated from bone resorption cavities. Anti-RANKL did not affect the increase of bone formation. Inflammation caused increased bone formation rate due to increased mineralizing surfaces as assessed by dynamic histomorphometry. In areas close to new bone formation, an abundance of proliferating cells was observed as well as cells robustly stained for Runx2 and alkaline phosphatase. PAM2 increased the mRNA expression of Lrp5 , Lrp6 and Wnt7b , and decreased the expression of Sost and Dkk1 . In situ hybridization demonstrated decreased Sost mRNA expression in osteocytes present in old bone. An abundance of cells expressed Wnt7b in Runx2-positive osteoblasts and ß-catenin in areas with new bone formation. These data demonstrate that inflammation, not only induces osteoclastogenesis, but also locally activates canonical WNT signaling and stimulates new bone formation independent on bone resorption., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Henning, Kassem, Westerlund, Lundberg, Engdahl, Lionikaite, Wikström, Wu, Li, Lindholm, de Souza, Movérare-Skrtic and Lerner.)

It has previously been demonstrated that the polybisphosphonate osteodex (ODX) inhibits bone resorption in organ-cultured mouse calvarial bone. In this study, we further investigate the effects by ODX on osteoclast differentiation, formation, and function in several different bone organ and cell cultures. Zoledronic acid (ZOL) was used for comparison. In retinoid-stimulated mouse calvarial organ cultures, ODX and ZOL significantly reduced the numbers of periosteal osteoclasts without affecting Tnfsf11 or Tnfrsf11b mRNA expression. ODX and ZOL also drastically reduced the numbers of osteoclasts in cell cultures isolated from the calvarial bone and in vitamin D3-stimulated mouse crude bone marrow cell cultures. These data suggest that ODX can inhibit osteoclast formation by inhibiting the differentiation of osteoclast progenitor cells or by directly targeting mature osteoclasts. We therefore assessed if osteoclast formation in purified bone marrow macrophage cultures stimulated by RANKL was inhibited by ODX and ZOL and found that the initial formation of mature osteoclasts was not affected, but that the bisphosphonates enhanced cell death of mature osteoclasts. In agreement with these findings, ODX and ZOL did not affect the mRNA expression of the osteoclastic genes Acp5 and Ctsk and the osteoclastogenic transcription factor Nfatc1. When bone marrow macrophages were incubated on bone slices, ODX and ZOL inhibited RANKL-stimulated bone resorption. In conclusion, ODX does not inhibit osteoclast formation but inhibits osteoclastic bone resorption by decreasing osteoclast numbers through enhanced cell death of mature osteoclasts., (© 2024. The Author(s).)

Lipoproteins are immunostimulatory bacterial components suggested to participate in inflammation-induced bone loss in periodontal disease through stimulation of osteoclast differentiation. Toll-like receptor 2 activation by Pam2CSK4 (PAM2), known to mimic bacterial lipoproteins, was previously shown to enhance periodontal bone resorption in mice. The anti-inflammatory cytokine interleukin-4 (IL-4) is a known inhibitor of RANKL-induced bone resorption in vitro. Here, we have investigated whether IL-4 could decrease PAM2-induced periodontal bone loss and osteoclastogenesis in vivo. In a model of periodontitis induced by gingival injections of PAM2 in mice, concomitant injections of IL-4 reduced bone loss. Histologically, IL-4 reduced the recruitment of inflammatory cells and the formation of TRAP+ osteoclasts stimulated by PAM2. Mouse bone marrow macrophages (BMMs) and neonatal calvarial osteoblasts were used to assess the effect of IL-4 on PAM2-induced osteoclastogenesis in vitro. In RANKL-primed BMMs stimulated by PAM2 Nfatc1, Ctsk, and Acp5 gene expression was up-regulated and resulted in robust formation of TRAP+ multinucleated osteoclasts, effects which were impaired by IL-4. These effects were mediated by impairment in PAM2-induced c-fos expression. In primary calvarial osteoblast cultures, IL-4 decreased PAM2-induced Tnfsf11 (encoding RANKL) mRNA and enhanced Tnfrsf11b (encoding OPG) expression. Our data demonstrate that the osteoprotective effect by IL-4 on lipoprotein-induced periodontal disease occurs through the inhibition of osteoclastogenesis by three mechanisms, one by acting directly on osteoclast progenitors, another by acting indirectly through decreasing the expression of osteoclast-regulating cytokines in osteoblasts and a third by decreasing inflammation., Competing Interests: Declaration of Competing Interest The authors have no conflicts of interest to declare., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Vitamin A refers to a group of fat-soluble compounds with retinol activity, including all- trans retinol and pro-vitamin A carotenoids. Bioactive compounds include retinal and all- trans retinoic acid with important functions in vision, immune function, growth, and development. The literature search that was performed for the current scoping review yielded a total of seven publications relevant to setting the recommended daily intake for vitamin A. In total, six publications assessed the relationship of serum retinol and/or dietary vitamin A intake with fracture risk ( n = 2), cancer ( n = 3), and deficiency after bariatric surgery ( n = 1). One additional report by the European Food Safety Administration (EFSA) with updated average requirements was included. The outcomes-based systematic reviews and meta-analyses showed positive associations for vitamin A intake and serum retinol with risk of hip fracture. Weak or inconclusive associations were observed for cancer or obesity. One publication by EFSA with updated estimated average requirements and population reference intakes for dietary vitamin A intakes was published in 2015. The EFSA recommendations and estimated average requirements are based on a European reference population, with body weights derived from an assumed body mass index of 22, which might be too low and not representative of the Nordic and Baltic populations, and consequently resulting in lower estimated average requirements and recommendations. In conclusion, there were limited new outcomes-based data for vitamin A and health outcomes., (© 2023 Thomas Olsen and Ulf H. Lerner.)

Osteoporotic fracture is among the most common and costly of diseases. While reasonably heritable, its genetic determinants have remained elusive. Forearm fractures are the most common clinically recognized osteoporotic fractures with a relatively high heritability. To establish an atlas of the genetic determinants of forearm fractures, we performed genome-wide association analyses including 100,026 forearm fracture cases. We identified 43 loci, including 26 new fracture loci. Although most fracture loci associated with bone mineral density, we also identified loci that primarily regulate bone quality parameters. Functional studies of one such locus, at TAC4, revealed that Tac4 -/- mice have reduced mechanical bone strength. The strongest forearm fracture signal, at WNT16, displayed remarkable bone-site-specificity with no association with hip fractures. Tall stature and low body mass index were identified as new causal risk factors for fractures. The insights from this atlas may improve fracture prediction and enable therapeutic development to prevent fractures., (© 2023. The Author(s).)

Background: Global sclerostin inhibition reduces fracture risk efficiently but has been associated with cardiovascular side effects. The strongest genetic signal for circulating sclerostin is in the B4GALNT3 gene region, but the causal gene is unknown. B4GALNT3 expresses the enzyme beta-1,4-N-acetylgalactosaminyltransferase 3 that transfers N-acetylgalactosamine onto N-acetylglucosaminebeta-benzyl on protein epitopes (LDN-glycosylation)., Methods: To determine if B4GALNT3 is the causal gene, B4galnt3 -/- mice were developed and serum levels of total sclerostin and LDN-glycosylated sclerostin were analysed and mechanistic studies were performed in osteoblast-like cells. Mendelian randomization was used to determine causal associations., Findings: B4galnt3 -/- mice had higher circulating sclerostin levels, establishing B4GALNT3 as a causal gene for circulating sclerostin levels, and lower bone mass. However, serum levels of LDN-glycosylated sclerostin were lower in B4galnt3 -/- mice. B4galnt3 and Sost were co-expressed in osteoblast-lineage cells. Overexpression of B4GALNT3 increased while silencing of B4GALNT3 decreased the levels of LDN-glycosylated sclerostin in osteoblast-like cells. Mendelian randomization demonstrated that higher circulating sclerostin levels, genetically predicted by variants in the B4GALNT3 gene, were causally associated with lower BMD and higher risk of fractures but not with higher risk of myocardial infarction or stroke. Glucocorticoid treatment reduced B4galnt3 expression in bone and increased circulating sclerostin levels and this may contribute to the observed glucocorticoid-induced bone loss., Interpretation: B4GALNT3 is a key factor for bone physiology via regulation of LDN-glycosylation of sclerostin. We propose that B4GALNT3-mediated LDN-glycosylation of sclerostin may be a bone-specific osteoporosis target, separating the anti-fracture effect of global sclerostin inhibition, from indicated cardiovascular side effects., Funding: Found in acknowledgements., Competing Interests: Declaration of interests CO has two patents/patent applications in the field of probiotics and bone health. All other authors declare that they have no conflict of interest., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

This study includes 1005 men from the Gothenburg part of the Osteoporotic Fracture in Men Study (MrOS). Included are 66 men with anemia (hemoglobin < 130 g/L). The follow-up time was up to 16 years, and the main results are that anemia is associated with all fractures and non-vertebral osteoporotic fractures., Introduction: Anemia and osteoporotic fractures are conditions that are associated with increased morbidity and mortality. Clinical studies have suggested that anemia can be used as a predictor of future osteoporotic fractures., Method: Men from the Osteoporotic Fractures in Men Study (MrOS) Sweden, Gothenburg, with available hemoglobin (Hb) values (n = 1005, median age 75.3 years (SD 3.2)), were included in the current analyses. Of these, 66 suffered from anemia, defined as Hb < 130 g/L. Median follow-up time for fracture was 10.1 years and the longest follow-up time was 16.1 years., Results: Men with anemia had, at baseline, experienced more falls and had a higher prevalence of diabetes, cancer, prostate cancer, hypertension, and stroke. Anemia was not statistically significantly associated with bone mineral density (BMD). Men with anemia had higher serum levels of fibroblast growth factor 23 (iFGF23) (p < 0.001) and phosphate (p = 0.001) and lower serum levels of testosterone (p < 0.001) and estradiol (p < 0.001). Moreover, men with anemia had an increased risk of any fracture (hazard ratio (HR) 1.97, 95% CI 1.28-3.02) and non-vertebral osteoporotic fracture (HR 2.15, 95% CI 1.18-3.93), after adjustment for age and total hip BMD, in 10 years. The risk for any fracture was increased in 10 and 16 years independently of falls, comorbidities, inflammation, and sex hormones. The age-adjusted risk of hip fracture was increased in men with anemia (HR 2.32, 95% CI 1.06-5.12), in 10 years, although this was no longer statistically significant after further adjustment for total hip BMD., Conclusions: Anemia is associated with an increased risk for any fracture and non-vertebral osteoporotic fracture in elderly men with a long follow-up time. The cause is probably multifactorial and our results support that anemia can be used as a predictor for future fracture., (© 2022. The Author(s).)

Oncostatin M (OSM), which belongs to the IL-6 family of cytokines, is the most potent and effective stimulator of osteoclast formation in this family, as assessed by different in vitro assays. Osteoclastogenesis induced by the IL-6 type of cytokines is mediated by the induction and paracrine stimulation of the osteoclastogenic cytokine receptor activator of nuclear factor κ-B ligand (RANKL), expressed on osteoblast cell membranes and targeting the receptor activator of nuclear factor κ-B (RANK) on osteoclast progenitor cells. The potent effect of OSM on osteoclastogenesis is due to an unusually robust induction of RANKL in osteoblasts through the OSM receptor (OSMR), mediated by a JAK-STAT/MAPK signaling pathway and by unique recruitment of the adapter protein Shc1 to the OSMR. Gene deletion of Osmr in mice results in decreased numbers of osteoclasts and enhanced trabecular bone caused by increased trabecular thickness, indicating that OSM may play a role in physiological regulation of bone remodeling. However, increased amounts of OSM, either through administration of recombinant protein or of adenoviral vectors expressing Osm , results in enhanced bone mass due to increased bone formation without any clear sign of increased osteoclast numbers, a finding which can be reconciled by cell culture experiments demonstrating that OSM can induce osteoblast differentiation and stimulate mineralization of bone nodules in such cultures. Thus, in vitro studies and gene deletion experiments show that OSM is a stimulator of osteoclast formation, whereas administration of OSM to mice shows that OSM is not a strong stimulator of osteoclastogenesis in vivo when administered to adult animals. These observations could be explained by our recent finding showing that OSM is a potent stimulator of the osteoclastogenesis inhibitor WNT16, acting in a negative feedback loop to reduce OSM-induced osteoclast formation.

Osteoporosis is an age-dependent serious skeletal disease that leads to great suffering for the patient and high social costs, especially as the global population reaches higher age. Decreasing estrogen levels after menopause result in a substantial bone loss and increased fracture risk, whereas estrogen treatment improves bone mass in women. RSPO3, a secreted protein that modulates WNT signaling, increases trabecular bone mass and strength in the vertebrae of mice, and is associated with trabecular density and risk of distal forearm fractures in humans. The aim of the present study was to determine if RSPO3 is involved in the bone-sparing effect of estrogens. We first observed that estradiol (E2) treatment increases RSPO3 expression in bone of ovariectomized (OVX) mice, supporting a possible role of RSPO3 in the bone-sparing effect of estrogens. As RSPO3 is mainly expressed by osteoblasts in the bone, we used a mouse model devoid of osteoblast-derived RSPO3 ( Runx2-creRspo3 flox/flox mice) to determine if RSPO3 is required for the bone-sparing effect of E2 in OVX mice. We confirmed that osteoblast-specific RSPO3 inactivation results in a substantial reduction in trabecular bone mass and strength in the vertebrae. However, E2 increased vertebral trabecular bone mass and strength similarly in mice devoid of osteoblast-derived RSPO3 and control mice. Unexpectedly, osteoblast-derived RSPO3 was needed for the full estrogenic response on cortical bone thickness. In conclusion, although osteoblast-derived RSPO3 is a crucial regulator of vertebral trabecular bone, it is required for a full estrogenic effect on cortical, but not trabecular, bone in OVX mice. Thus, estradiol and RSPO3 regulate vertebral trabecular bone mass independent of each other. NEW & NOTEWORTHY Osteoblast-derived RSPO3 is known to be a crucial regulator of vertebral trabecular bone. Our new findings show that RSPO3 and estrogen regulate trabecular bone independent of each other, but that RSPO3 is necessary for a complete estrogenic effect on cortical bone.

Periodontal disease (PD) is a polymicrobial chronic inflammatory condition of the supporting tissues around the teeth, leading to the destruction of surrounding connective tissue. During the progression of PD, osteoclasts play a crucial role in the resorption of alveolar bone that eventually leads to the loss of teeth if the PD is left untreated. Therefore, the development of antiresorptive therapies targeting bone-resorbing cells will significantly benefit the treatment of PD. Here, we demonstrate the inhibitory effect of CsinCPI-2, a novel cysteine peptidase inhibitor from the orange tree, on periodontitis-induced inflammation, alveolar bone loss, and osteoclast differentiation. Using the ligature-induced periodontitis model in mice, we show that treatment with CsinCPI-2 (0.8 µg/g of body weight) significantly reduced inflammatory cell infiltrate in the connective tissue and prevented the loss of alveolar bone mass (BV/TV) caused by PD, effects associated with diminished numbers of TRAP-positive multinucleated cells. Furthermore, CsinCPI-2 significantly downregulated the numbers of inflammatory cells expressing CD3, CD45, MAC387, and IL-1β. In vitro, CsinCPI-2 inhibited RANKL-induced TRAP+ multinucleated osteoclast formation in mouse bone marrow macrophage cultures in a concentration-dependent manner. This effect was not due to cytotoxicity, as demonstrated by the MTT assay. CsinCPI-2 inhibited RANKL-induced mRNA expression of Acp5 , Calcr , and Ctsk , as well as the RANKL-induced upregulation of Nfatc1, a crucial transcription factor for osteoclast differentiation. Based on our findings, CsinCPI-2 prevents bone loss induced by PD by controlling the inflammatory process and acting directly on osteoclastogenesis, suggesting an interesting potential for CsinCPI-2 in the strategy for PD treatment.

Osteoporosis is a significant health problem, with skeletal fractures increasing morbidity and mortality. Excess glucocorticoids (GC) represents the leading cause of secondary osteoporosis. The first phase of glucocorticoid-induced osteoporosis is increased bone resorption. In this Chapter, in vitro studies of the direct glucocorticoid receptor (GR) mediated cellular effects of GC on osteoclasts to affect bone resorption and indirect effects on osteoblast lineage cells to increase the RANKL/OPG ratio and stimulate osteoclastogenesis and bone resorption are reviewed in detail, together with detailed descriptions of in vivo effects of GC in different portions of the skeleton in research animals and humans. Brief sections are devoted to contrasting functions of GC in osteonecrosis, vitamin D formation, in vitro and in vivo bone resorptive actions dependent on vitamin D receptor and vitamin D toxicity, as well as the molecular basis of GR action. Included are also more detailed assessments of the interactions of GC with the major calcium regulating hormones, 1,25(OH) 2 -vitamin D3 and parathyroid hormone, describing the in vitro increases in RANKL/OPG ratios, osteoclastogenesis and synergistic bone resorption that occurs when GC is combined with either 1,25(OH) 2 -vitamin D3 or parathyroid hormone. Additionally, a molecular basic for the synergistic interaction of GC with 1,25(OH) 2 -vitamin D3 is provided along with a suggested molecular basic for the interaction between GC and parathyroid hormone., (Copyright © 2022 Elsevier Inc. All rights reserved.)

With increasing age of the population, countries across the globe are facing a substantial increase in osteoporotic fractures. Genetic association signals for fractures have been reported at the RSPO3 locus, but the causal gene and the underlying mechanism are unknown. Here we show that the fracture reducing allele at the RSPO3 locus associate with increased RSPO3 expression both at the mRNA and protein levels, increased trabecular bone mineral density and reduced risk mainly of distal forearm fractures in humans. We also demonstrate that RSPO3 is expressed in osteoprogenitor cells and osteoblasts and that osteoblast-derived RSPO3 is the principal source of RSPO3 in bone and an important regulator of vertebral trabecular bone mass and bone strength in adult mice. Mechanistic studies revealed that RSPO3 in a cell-autonomous manner increases osteoblast proliferation and differentiation. In conclusion, RSPO3 regulates vertebral trabecular bone mass and bone strength in mice and fracture risk in humans., (© 2021. The Author(s).)

Ras homologous guanosine triphosphatases (RhoGTPases) control several cellular functions, including cytoskeletal actin remodeling and cell migration. Their activities are downregulated by GTPase-activating proteins (GAPs). Although RhoGTPases are implicated in bone remodeling and osteoclast and osteoblast function, their significance in human bone health and disease remains elusive. Here, we report defective RhoGTPase regulation as a cause of severe, early-onset, autosomal-dominant skeletal fragility in a three-generation Finnish family. Affected individuals ( n  = 13) presented with multiple low-energy peripheral and vertebral fractures despite normal bone mineral density (BMD). Bone histomorphometry suggested reduced bone volume, low surface area covered by osteoblasts and osteoclasts, and low bone turnover. Exome sequencing identified a novel heterozygous missense variant c.652G>A (p.G218R) in ARHGAP25 , encoding a GAP for Rho-family GTPase Rac1. Variants in the ARHGAP25 5' untranslated region (UTR) also associated with BMD and fracture risk in the general population, across multiple genomewide association study (GWAS) meta-analyses (lead variant rs10048745). ARHGAP25 messenger RNA (mRNA) was expressed in macrophage colony-stimulating factor (M-CSF)-stimulated human monocytes and mouse osteoblasts, indicating a possible role for ARHGAP25 in osteoclast and osteoblast differentiation and activity. Studies on subject-derived osteoclasts from peripheral blood mononuclear cells did not reveal robust defects in mature osteoclast formation or resorptive activity. However, analysis of osteosarcoma cells overexpressing the ARHGAP25 G218R-mutant, combined with structural modeling, confirmed that the mutant protein had decreased GAP-activity against Rac1, resulting in elevated Rac1 activity, increased cell spreading, and membrane ruffling. Our findings indicate that mutated ARHGAP25 causes aberrant Rac1 function and consequently abnormal bone metabolism, highlighting the importance of RhoGAP signaling in bone metabolism in familial forms of skeletal fragility and in the general population, and expanding our understanding of the molecular pathways underlying skeletal fragility. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research., (© 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.)

Immunoglobulin G (IgG) is important in clearance and recognition of previously presented antigens and after activation, IgGs can interact with the Fc gamma receptors (FcγRs) on haematopoietic cells, including bone-resorbing osteoclasts. The pathogenicity of IgG, that is the ability to elicit stimulatory effects via FcγRs, can be modulated by attachment of sugar moieties, including sialic acids. Human IgGs and autoantibodies are associated with bone loss in autoimmune disease. However, the impact of polyclonal murine IgG via FcγRs on bone loss is poorly understood. Here, we investigate if heat-aggregated activated murine polyclonal IgG complexes have any direct effects on murine osteoclasts and if they modulate arthritis-mediated bone loss. Using cell cultures of murine osteoclasts, we show that IgG complexes without sialic acids (de-IgG complexes) enhance receptor activator of nuclear factor kappa-Β ligand (RANKL)-stimulated osteoclastogenesis, an effect associated with increased FcγRIII expression. Using an in vivo model of arthritis-mediated bone loss, where IgG complexes were injected into arthritic knees, no effect on the severity of arthritis or the degree of arthritis-mediated bone loss was detected. Interestingly, injection of de-IgG complexes into non-arthritic knees increased osteoclast formation and enhanced bone erosions. Our findings show that activated de-IgG complexes have no additive effect on arthritis-mediated bone loss. However, de-IgG complexes potentiate murine osteoclastogenesis and enhance local bone erosion in non-arthritic bones, further confirming the link between the adaptive immune system and bone., (© 2020 The Authors. Scandinavian Journal of Immunology published by John Wiley & Sons Ltd on behalf of The Scandinavian Foundation for Immunology.)

In elderly ambulatory men, high platelet and high neutrophil counts are related to low bone mineral density (BMD), after adjustment for relevant covariates. Low hemoglobin (hgb) is even associated with low BMD, but this relationship seems to be dependent on estradiol and osteocalcin., Purpose: Blood and bone cells exist in close proximity to each other in the bone marrow. Accumulating evidence, from both preclinical and clinical studies, indicates that these cell types are interconnected. Our hypothesis was that BMD measurements are associated with blood count variables and bone remodeling markers., Methods: We analyzed blood count variables, bone remodeling markers, and BMD, in subjects from the MrOS cohort from Gothenburg, Sweden. Men with at least one blood count variable (hgb, white blood cell count, or platelet count) analyzed were included in the current analysis (n = 1005), median age 75.3 years (range 69-81 years)., Results: Our results show that high platelet counts were related to low BMD at all sites (total hip BMD; r = - 0.11, P = 0.003). No statistically significant association was seen between platelet counts and bone remodeling markers. Neutrophil counts were negatively associated with total body BMD (r = - 0.09, P = 0.006) and total hip BMD (r = - 0.08, P = 0.010), and positively related to serum ALP (r = 0.15, P < 0.001). Hgb was positively related to total hip BMD (r = 0.16, P < 0.001), and negatively to serum osteocalcin (r = - 0.13, P < 0.001). The association between platelet and neutrophil counts and total hip BMD was statistically significant after adjustments for other covariates, but the association between hgb and total hip BMD was dependent on estradiol and osteocalcin., Conclusions: Our observations support the hypothesis of an interplay between blood and bone components.

Osteoporosis is a common skeletal disease, with increased risk of fractures. Currently available osteoporosis treatments reduce the risk of vertebral fractures, mainly dependent on trabecular bone, whereas the effect on nonvertebral fractures, mainly dependent on cortical bone, is less pronounced. WNT signaling is a crucial regulator of bone homeostasis, and the activity of WNTs is inhibited by NOTUM, a secreted WNT lipase. We previously demonstrated that conditional inactivation of NOTUM in all osteoblast lineage cells increases the cortical but not the trabecular bone mass. The aim of the present study was to determine if NOTUM increasing cortical bone is derived from osteoblast precursors/early osteoblasts or from osteocytes/late osteoblasts. First, we demonstrated Notum mRNA expression in Dmp1- expressing osteocytes and late osteoblasts in cortical bone using in situ hybridization. We then developed a mouse model with inactivation of NOTUM in Dmp1 -expressing osteocytes and late osteoblasts ( Dmp1-creNotum flox/flox mice). We observed that the Dmp1-creNotum flox/flox mice displayed a substantial reduction of Notum mRNA in cortical bone, resulting in increased cortical bone mass and decreased cortical porosity in femur but no change in trabecular bone volume fraction in femur or in the lumbar vertebrae L5 in Dmp1-creNotum flox/flox mice as compared with control mice. In conclusion, osteocytes and late osteoblasts are the principal source of NOTUM in cortical bone, and NOTUM derived from osteocytes/late osteoblasts reduces cortical bone mass. These findings demonstrate that inhibition of osteocyte/late osteoblast-derived NOTUM might be an interesting pharmacological target to increase cortical bone mass and reduce nonvertebral fracture risk. NEW & NOTEWORTHY NOTUM produced by osteoblasts is known to regulate cortical bone mass. Our new findings show that NOTUM specifically derived by DMP1 -expressing osteocytes and late osteoblasts regulates cortical bone mass and not trabecular bone mass.

Preclinical studies on the role of erythropoietin (EPO) in bone metabolism are contradictory. Regeneration models indicate an anabolic effect on bone healing, whereas models on physiologic bone remodeling indicate a catabolic effect on bone mass. No human studies on EPO and fracture risk are available. It is known that fibroblast growth factor 23 (FGF23) affects bone mineralization and that serum concentration of FGF23 is higher in men with decreased estimated glomerular filtration rate (eGFR). Recently, a direct association between EPO and FGF23 has been shown. We have explored the potential association between EPO and bone mineral density (BMD), fracture risk, and FGF23 in humans. Plasma levels of EPO were analyzed in 999 men (aged 69 to 81 years), participating in the Gothenburg part of the population-based Osteoporotic Fractures in Men (MrOS) study, MrOS Sweden. The mean ± SD EPO was 11.5 ± 9.0 IU/L. Results were stratified by eGFR 60 mL/min. For men with eGFR ≥60 mL/min (n = 728), EPO was associated with age (r = 0.13, p < 0.001), total hip BMD (r = 0.14, p < 0.001), intact (i)FGF23 (r = 0.11, p = 0.004), and osteocalcin (r = -0.09, p = 0.022). The association between total hip BMD and EPO was independent of age, body mass index (BMI), iFGF23, and hemoglobin (beta = 0.019, p < 0.001). During the 10-year follow-up, 164 men had an X-ray-verified fracture, including 117 major osteoporotic fractures (MOF), 39 hip fractures, and 64 vertebral fractures. High EPO was associated with higher risk for incident fractures (hazard ratio [HR] = 1.43 per tertile EPO, 95% confidence interval [CI] 1.35-1.63), MOF (HR = 1.40 per tertile EPO, 95% CI 1.08-1.82), and vertebral fractures (HR = 1.42 per tertile EPO, 95% CI 1.00-2.01) in a fully adjusted Cox regression model. In men with eGFR<60 mL/min, no association was found between EPO and BMD or fracture risk. We here demonstrate that high levels of EPO are associated with increased fracture risk and increased BMD in elderly men with normal renal function. © 2019 American Society for Bone and Mineral Research., (© 2019 American Society for Bone and Mineral Research.)

Glucocorticoid (GC) therapy decreases bone mass and increases the risk of fractures. We investigated interactions between the GC dexamethasone (DEX) and the bone resorptive agents 1,25(OH) 2 -vitamin D 3 (D3) and parathyroid hormone (PTH) on osteoclastogenesis. We observed a synergistic potentiation of osteoclast progenitor cell differentiation and formation of osteoclasts when DEX was added to either D3- or PTH-treated mouse bone marrow cell (BMC) cultures. Cotreatment of DEX with D3 or PTH increased gene encoding calcitonin receptor ( Calcr ), acid phosphatase 5, tartrate resistant ( Acp5 ), cathepsin K ( Ctsk ), and TNF superfamily member 11 ( Tnfsf11 ) mRNA, receptor activator of NF-κB ligand protein (RANKL), numbers of osteoclasts on plastic, and pit formation and release of C-terminal fragment of type I collagen from cells cultured on bone slices. Enhanced RANKL protein expression caused by D3 and DEX was absent in BMC from mice in which the GC receptor (GR) was deleted in stromal cells/osteoblasts. Synergistic interactions between DEX and D3 on RANKL and osteoclast formation were present in BMC from mice with attenuated GR dimerization. These data demonstrate that the GR cooperates with D3 and PTH signaling, causing massive osteoclastogenesis, which may explain the rapid bone loss observed with high dosages of GC treatment.-Conaway, H. H., Henning, P., Lie, A., Tuckermann, J., Lerner, U. H. Glucocorticoids employ the monomeric glucocorticoid receptor to potentiate vitamin D 3 and parathyroid hormone-induced osteoclastogenesis.

Osteoclasts are multinucleated, giant cells originating from myeloid hematopoetic stem cells. These are the only cells in nature which can resorb bone. Differentiation of mononucleated osteoclast progenitor cells requires stimulation with M-CSF (macrophage colony-stimulating factor) for the cells to proliferate and survive and with RANKL (receptor activator of nuclear factor kappa B ligand) for differentiation along the osteoclastic lineage to cells which eventually fuse to the mature, multinucleated osteoclasts. Therefore, most hormones and cytokines stimulating osteoclastogenesis do so indirectly by regulating the expression in osteoblasts of RANKL and its inhibitory decoy receptor OPG. Antibodies neutralizing RANKL is a common therapy to inhibit excessive osteoclast formation in diseases such as osteoporosis and malignant tumors with skeletal metastasis. Mature osteoclasts resorb bone by stimulating acid release into the resorption lacunae, followed by proteolytic degradation of bone matrix proteins. Loss-of-function mutations of proteins involved in acidification and proteolysis cause osteopetrosis, a disease with sclerotic bone due to non-functional osteoclasts. Osteoclasts are important for a healthy skeleton by removing damaged bone during remodeling of the skeleton, but are also important for modeling of bone, calcium homeostasis and tooth eruption, and possibly also for glucose and fat metabolism. Loss of bone in inflammatory disease, metastasizing tumors and osteoporosis is due to increased RANKL expression and enhanced osteoclast formation. The present overview aims to summarize how osteoclasts are formed and resorb bone in health and disease., (Copyright© of YS Medical Media ltd.)

In bone, sclerostin is mainly osteocyte-derived and plays an important local role in adaptive responses to mechanical loading. Whether circulating levels of sclerostin also play a functional role is currently unclear, which we aimed to examine by two-sample Mendelian randomization (MR). A genetic instrument for circulating sclerostin, derived from a genomewide association study (GWAS) meta-analysis of serum sclerostin in 10,584 European-descent individuals, was examined in relation to femoral neck bone mineral density (BMD; n = 32,744) in GEFOS and estimated bone mineral density (eBMD) by heel ultrasound (n = 426,824) and fracture risk (n = 426,795) in UK Biobank. Our GWAS identified two novel serum sclerostin loci, B4GALNT3 (standard deviation [SD]) change in sclerostin per A allele (β = 0.20, p = 4.6 × 10 -49 ) and GALNT1 (β  = 0.11 per G allele, p = 4.4 × 10 -11 ). B4GALNT3 is an N-acetyl-galactosaminyltransferase, adding a terminal LacdiNAc disaccharide to target glycocoproteins, found to be predominantly expressed in kidney, whereas GALNT1 is an enzyme causing mucin-type O-linked glycosylation. Using these two single-nucleotide polymorphisms (SNPs) as genetic instruments, MR revealed an inverse causal relationship between serum sclerostin and femoral neck BMD (β = -0.12, 95% confidence interval [CI] -0.20 to -0.05) and eBMD (β = -0.12, 95% CI -0.14 to -0.10), and a positive relationship with fracture risk (β = 0.11, 95% CI 0.01 to 0.21). Colocalization analysis demonstrated common genetic signals within the B4GALNT3 locus for higher sclerostin, lower eBMD, and greater B4GALNT3 expression in arterial tissue (probability >99%). Our findings suggest that higher sclerostin levels are causally related to lower BMD and greater fracture risk. Hence, strategies for reducing circulating sclerostin, for example by targeting glycosylation enzymes as suggested by our GWAS results, may prove valuable in treating osteoporosis. © 2019 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc., (© 2019 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc.)

Osteoporosis is a common skeletal disease, affecting millions of individuals worldwide. Currently used osteoporosis treatments substantially reduce vertebral fracture risk, whereas nonvertebral fracture risk, mainly caused by reduced cortical bone mass, has only moderately been improved by the osteoporosis drugs used, defining an unmet medical need. Because several wingless-type MMTV integration site family members (WNTs) and modulators of WNT activity are major regulators of bone mass, we hypothesized that NOTUM, a secreted WNT lipase, might modulate bone mass via an inhibition of WNT activity. To characterize the possible role of endogenous NOTUM as a physiologic modulator of bone mass, we developed global, cell-specific, and inducible Notum -inactivated mouse models. Notum expression was high in the cortical bone in mice, and conditional Notum inactivation revealed that osteoblast lineage cells are the principal source of NOTUM in the cortical bone. Osteoblast lineage-specific Notum inactivation increased cortical bone thickness via an increased periosteal circumference. Inducible Notum inactivation in adult mice increased cortical bone thickness as a result of increased periosteal bone formation, and silencing of Notum expression in cultured osteoblasts enhanced osteoblast differentiation. Large-scale human genetic analyses identified genetic variants mapping to the NOTUM locus that are strongly associated with bone mineral density (BMD) as estimated with quantitative ultrasound in the heel. Thus, osteoblast-derived NOTUM is an essential local physiologic regulator of cortical bone mass via effects on periosteal bone formation in adult mice, and genetic variants in the NOTUM locus are associated with BMD variation in adult humans. Therapies targeting osteoblast-derived NOTUM may prevent nonvertebral fractures.-Movérare-Skrtic, S., Nilsson, K. H., Henning, P., Funck-Brentano, T., Nethander, M., Rivadeneira, F., Coletto Nunes, G., Koskela, A., Tuukkanen, J., Tuckermann, J., Perret, C., Souza, P. P. C., Lerner, U. H., Ohlsson, C. Osteoblast-derived NOTUM reduces cortical bone mass in mice and the NOTUM locus is associated with bone mineral density in humans.

M-CSF and RANKL are two crucial cytokines stimulating differentiation of mature, bone resorbing, multinucleated osteoclasts from mononucleated progenitor cells in the monocyte/macrophage lineage. In addition to the receptors for M-CSF and RANKL, osteoclast progenitor cells express receptors for several other pro- and anti-osteoclastogenic cytokines, which also regulate osteoclast formation by affecting signaling downstream M-CSF and RANKL receptors. Similar to many other cells originating from myeloid hematopoetic stem cells, also osteoclast progenitors express toll-like receptors (TLRs). Nine murine TLRs are expressed in the progenitors and all, with the exception of TLR2 and TLR4, are downregulated during osteoclastogenesis. Activation of TLR2, TLR4, and TLR9, but not TLR5, in osteoclast progenitors stimulated with M-CSF and RANKL arrests differentiation along the osteoclastic lineage and keeps the cells at a macrophage stage. When the progenitors are primed with M-CSF/RANKL and then stimulated with agonists for TLR2, TLR4, or TLR9 in the presence of M-CSF, but in the absence of RANKL, the cells differentiate to mature, bone resorbing osteoclasts. TLR 2, 4, 5, and 9 are also expressed on osteoblasts and their activation increases osteoclast differentiation by an indirect mechanism through stimulation of RANKL. In mice, treatment with agonists for TLR2, 4, and 5 results in osteoclast formation and extensive bone loss. It remains to be shown the relative importance of inhibitory and stimulatory effects by TLRs on osteoclast progenitors and the role of RANKL produced by TLR stimulated osteoblasts, for the bone resorbing effects in vivo .

Aim: In this article, the interplay between bone resorbing and bone forming cells is reviewed., Method: This review examines the comprehensive literature on the interaction between bone resorption and bone formation., Results: Coupling between bone resorption and bone formation refers to the process within basic multicellular units, in which osteoclastic bone resorption is met by the differentiation of osteoblasts and their bone forming activity. There are many possible signalling molecules that contribute to coupling at the asynchronously working remodelling sites throughout our skeleton. These include growth factors released from the bone matrix during bone resorption, soluble and membrane products of the osteoclasts and their precursors and signals from osteocytes., Conclusions: In this review, we describe the potential roles of a number of these factors, whose interactions are essential for a tight control of coupling within individual remodelling units, in order to control skeletal mass. Both pre-clinical evidence and clinical evidence pinpoint that molecules in the WNT signalling pathway could be promising bone augmentation therapeutic targets. Regarding oral implications, there is support, from preclinical studies in rats, that anti-sclerostin antibodies can restore alveolar bone mass., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background and Purpose: The gp130 family of cytokines signals through receptors dimerizing with the gp130 subunit. Downstream signaling typically activates STAT3 but also SHP2/Ras/MAPK pathways. Oncostatin M (OSM) is a unique cytokine in this family since the receptor (OSMR) activates a non-redundant signaling pathway by recruitment of the adapter Shc1. We have studied the functional relevance of Shc1 for OSM-induced bone resorption. Experimental Approach: Osteoblasts were stimulated with OSM and STAT3 and Shc1 activations were studied using real-time PCR and Western blots. The role of STAT3 and Shc1 for OSM-induced RANKL expression and osteoclast formation was studied by silencing their mRNA expressions. Effects of OSM were compared to those of the closely related cytokine leukemia inhibitory factor (LIF). Key Results: OSM, but not LIF, induced the mRNA and protein expression of Shc1 and activated phosphorylation of Shc1 in the osteoblasts. Silencing of Shc1 decreased OSM-induced activation of STAT3 and RANKL expression. Silencing of STAT3 had no effect on activation of Shc1, but prevented the OSM-mediated increase of RANKL expression. Silencing of either Shc1 or STAT3 in osteoblasts decreased formation of osteoclasts in OSM-stimulated co-cultures of osteoblasts and macrophages. In agreement with these observations, OSM was a more potent and robust stimulator than LIF of RANKL formation and bone resorption in mouse calvariae and osteoclast formation in bone marrow cultures. Conclusions and Implications: Activation of the Shc1-dependent STAT3 signaling is crucial for OSM-induced osteoclast formation. Inhibition of Shc1 is a potential mechanism to specifically inhibit OSM-induced bone resorption.

Mechanisms leading to osteoporosis are incompletely understood. Genetic disorders with skeletal fragility provide insight into metabolic pathways contributing to bone strength. We evaluated 6 families with rare skeletal phenotypes and osteoporosis by next-generation sequencing. In all the families, we identified a heterozygous variant in SGMS2, a gene prominently expressed in cortical bone and encoding the plasma membrane-resident sphingomyelin synthase SMS2. Four unrelated families shared the same nonsense variant, c.148C>T (p.Arg50*), whereas the other families had a missense variant, c.185T>G (p.Ile62Ser) or c.191T>G (p.Met64Arg). Subjects with p.Arg50* presented with childhood-onset osteoporosis with or without cranial sclerosis. Patients with p.Ile62Ser or p.Met64Arg had a more severe presentation, with neonatal fractures, severe short stature, and spondylometaphyseal dysplasia. Several subjects had experienced peripheral facial nerve palsy or other neurological manifestations. Bone biopsies showed markedly altered bone material characteristics, including defective bone mineralization. Osteoclast formation and function in vitro was normal. While the p.Arg50* mutation yielded a catalytically inactive enzyme, p.Ile62Ser and p.Met64Arg each enhanced the rate of de novo sphingomyelin production by blocking export of a functional enzyme from the endoplasmic reticulum. SGMS2 pathogenic variants underlie a spectrum of skeletal conditions, ranging from isolated osteoporosis to complex skeletal dysplasia, suggesting a critical role for plasma membrane-bound sphingomyelin metabolism in skeletal homeostasis.

Increased vitamin A consumption is associated with decreased cortical bone mass and increased fracture risk in humans. Rodent studies have demonstrated that hypervitaminosis A increases cortical bone resorption, whereas the importance of the effects on bone formation is less well defined. We used an experimental model of increased bone formation by loading of the tibiae to investigate the effect of vitamin A on bone formation. Control [retinol activity equivalents (RAE) 4.5 µg/g chow] or vitamin A (RAE 60 µg/g chow) diets were given to female C57BL/6N mice for 4 wk, after which the tibiae were subjected to axial loading on alternate days for 2 wk, while the diets were continued. Vitamin A inhibited the loading-induced increase in trabecular and cortical bone volume. This was attributed to inhibition of loading-induced increase in osteoblast number and activity, and expression of osteoblastic genes Sp7, Alpl, and Col1a1 in cortical bone. Vitamin A, loading, and combination thereof also resulted in site-specific effects on bone composition measured by Raman spectroscopy. In summary, a clinically relevant dose of vitamin A suppresses the loading-induced gain of bone mass by decreasing bone formation. These observations may have implications for regulation of bone mass caused by physical activity and the risk of osteoporosis in humans.-Lionikaite, V., Henning, P., Drevinge, C., Shah, F. A., Palmquist, A., Wikström, P., Windahl, S. H., Lerner, U. H. Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation.

The regulation of the kallikrein-kinin system is an important mechanism controlling vasodilation and promoting inflammation. We aimed to investigate the role of Toll-like receptor 2 (TLR2) in regulating kinin B 1 and B 2 receptor expression in human gingival fibroblasts and in mouse gingiva. Both P. gingivalis LPS and the synthetic TLR2 agonist Pam 2 CSK 4 increased kinin receptor transcripts. Silencing of TLR2, but not of TLR4, inhibited the induction of kinin receptor transcripts by both P. gingivalis LPS and Pam 2 CSK 4 . Human gingival fibroblasts (HGF) exposed to Pam 2 CSK 4 increased binding sites for bradykinin (BK, B 2 receptor agonist) and des-Arg 10 -Lys-bradykinin (DALBK, B 1 receptor agonist). Pre-treatment of HGF for 24 h with Pam 2 CSK 4 resulted in increased PGE 2 release in response to BK and DALBK. The increase of B1 and B2 receptor transcripts by P. gingivalis LPS was not blocked by IL-1β neutralizing antibody; TNF-α blocking antibody did not affect B 1 receptor up-regulation, but partially blocked increase of B 2 receptor mRNA. Injection of P. gingivalis LPS in mouse gingiva induced an increase of B 1 and B 2 receptor mRNA. These data show that activation of TLR2 in human gingival fibroblasts as well as in mouse gingival tissue leads to increase of B 1 and B 2 receptor mRNA and protein.

The disability, mortality and costs caused by non-vertebral osteoporotic fractures are enormous. Existing osteoporosis therapies are highly effective at reducing vertebral but not non-vertebral fractures. Cortical bone is a major determinant of non-vertebral bone strength. To identify novel osteoporosis drug targets, we phenotyped cortical bone of 3 366 viable mouse strains with global knockouts of druggable genes. Cortical bone thickness was substantially elevated in Notum -/- mice. NOTUM is a secreted WNT lipase and we observed high NOTUM expression in cortical bone and osteoblasts but not osteoclasts. Three orally active small molecules and a neutralizing antibody inhibiting NOTUM lipase activity were developed. They increased cortical bone thickness and strength at multiple skeletal sites in both gonadal intact and ovariectomized rodents by stimulating endocortical bone formation. Thus, inhibition of NOTUM activity is a potential novel anabolic therapy for strengthening cortical bone and preventing non-vertebral fractures., Competing Interests: The authors declare no competing interests.

Increased intake of vitamin A (retinoids) is associated with decreased bone mass and increased fracture risk in humans. Mechanistic studies in rodents have shown that hypervitaminosis A results in decreased bone mass caused by an increase in periosteal osteoclasts while simultaneously decreasing endocortic osteoclasts. In vivo and ex vivo bone organ cultures have demonstrated that excess retinoids increase osteoclast formation due to increased receptor activator of nuclear factor kappa B-ligand (RANKL) expression. In vitro, studies using murine bone marrow macrophages (BMM) have shown that retinoids inhibit osteoclast formation induced by recombinant RANKL. These opposing in vivo/ex vivo versus in vitro effects may elucidate why excess retinoids affect periosteal and endocortic osteoclast formation differently. In addition, it has been reported that retinoids can inhibit osteoclast formation under inflammatory conditions such as experimentally induced arthritis in mice. In the present study, we have compared the effect of all-trans-retinoic acid (ATRA) on physiologically and inflammatory induced osteoclastogenesis. ATRA inhibited physiologically induced (RANKL) osteoclast formation of human peripheral blood monocytes and mouse BMM as well as human monocytes stimulated with the pro-inflammatory compounds, TNF-α and LPS. The inhibition was due to impeded differentiation, rather than fusion, of mononucleated progenitor cells. ATRA disrupted differentiation by interfering with osteoclastogenic intracellular signaling. In line with this view, overexpression of Tnfrsf11a (encodes for RANK) in BMM could not overcome the inhibition of osteoclastogenesis by ATRA. The data suggest that ATRA inhibits both physiologic and inflammatory osteoclast differentiation of progenitors from the bone marrow and peripheral blood., (©2018 Society for Leukocyte Biology.)

Excess vitamin A has been associated with decreased cortical bone thickness and increased fracture risk. While most studies in rodents have employed high dosages of vitamin A for short periods of time, we investigated the bone phenotype in mice after longer exposure to more clinically relevant doses. For 1, 4 and 10 weeks, mice were fed a control diet (4.5 µg retinyl acetate/g chow), a diet modeled from the human upper tolerable limit (UTL; 20 µg retinyl acetate/g chow) and a diet three times UTL (supplemented; 60 µg retinyl acetate/g chow). Time-dependent decreases in periosteal circumference and bone mineral content were noted with the supplemented dose. These reductions in cortical bone resulted in a significant time-dependent decrease of predicted strength and a non-significant trend toward reduced bone strength as analyzed by three-point bending. Trabecular bone in tibiae and vertebrae remained unaffected when vitamin A was increased in the diet. Dynamic histomorphometry demonstrated that bone formation was substantially decreased after 1 week of treatment at the periosteal site with the supplemental dose. Increasing amount of vitamin A decreased endocortical circumference, resulting in decreased marrow area, a response associated with enhanced endocortical bone formation. In the presence of bisphosphonate, vitamin A had no effect on cortical bone, suggesting that osteoclasts are important, even if effects on bone resorption were not detected by osteoclast counting, genes in cortical bone or analysis of serum TRAP5b and CTX. In conclusion, our results indicate that even clinically relevant doses of vitamin A have a negative impact on the amount of cortical bone.

Because several studies have implicated serotonin as a regulator of bone mass, we here explore its potential association on fracture risk and falls, as on bone mineral density (BMD) and muscle strength, in humans. Serum levels of serotonin were analyzed in 950 men (aged 69 to 81 years), participating in the Gothenburg part of the population-based study MrOS Sweden. Men taking selective serotonin reuptake inhibitors (SSRIs) had a mean value of 31.2 μg/L compared with 159.4 μg/L in those not taking SSRIs. SSRI users were excluded from further analysis. During 10-year follow-up, 224 men exhibited fractures, including 97 nonvertebral osteoporotic fractures (57 hip fractures), and 86 vertebral fractures. Serotonin was associated with hip fracture in linear analysis (hazard ratio [HR] = 1.27, 95% confidence interval [CI] 1.03-1.58) and to all fractures in a nonlinear manner, when quintiles of serotonin was included in quadratic terms (HR = 1.12, 95% CI 1.04-1.21). Men in serotonin quintile 5 had, in multivariable analysis, a HR of 2.30 (95% CI 1.31-4.02) for hip fracture and 1.82 (95% CI 1.17-2.85) for nonvertebral fractures compared with men in quintiles 1 to 4. Men in quintile 1 had, in multivariable analysis, a HR of 1.76 (95% CI 1.03-2.99) for nonvertebral fractures compared with men in quintiles 2 to 4. No association was found with vertebral fractures. Individuals in serotonin quintile 1 had higher prevalence of falls compared with quintiles 2 to 5 (odds ratio = 1.90, 95% CI 1.26-2.87). Serotonin was positively associated with hand-grip strength (r = 0.08, p = 0.02) and inversely with hip BMD (r = -0.10, p = 0.003). To assess the association between SSRIs and falls and fractures, the total MrOS Sweden cohort was examined (n = 3014). SSRI users (n = 90) had increased prevalence of falls (16% versus 33%, p = 0.0001) and increased rate of incident fractures (28.0 versus 44.7 per 1000 person-years, p = 0.018). We present novel data showing that high levels of serotonin predict an increased risk for hip fracture and nonvertebral osteoporotic fractures. © 2018 American Society for Bone and Mineral Research., (© 2018 American Society for Bone and Mineral Research.)

WNT signaling is involved in the tumorigenesis of various cancers and regulates bone homeostasis. Palmitoleoylation of WNTs by Porcupine is required for WNT activity. Porcupine inhibitors are under development for cancer therapy. As the possible side effects of Porcupine inhibitors on bone health are unknown, we determined their effects on bone mass and strength. Twelve-week-old C57BL/6N female mice were treated by the Porcupine inhibitors LGK974 (low dose = 3 mg/kg/day; high dose = 6 mg/kg/day) or Wnt-C59 (10 mg/kg/day) or vehicle for 3 weeks. Bone parameters were assessed by serum biomarkers, dual-energy X-ray absorptiometry, µCT and histomorphometry. Bone strength was measured by the 3-point bending test. The Porcupine inhibitors were well tolerated demonstrated by normal body weight. Both doses of LGK974 and Wnt-C59 reduced total body bone mineral density compared with vehicle treatment ( P  < 0.001). Cortical thickness of the femur shaft ( P  < 0.001) and trabecular bone volume fraction in the vertebral body ( P  < 0.001) were reduced by treatment with LGK974 or Wnt-C59. Porcupine inhibition reduced bone strength in the tibia ( P  < 0.05). The cortical bone loss was the result of impaired periosteal bone formation and increased endocortical bone resorption and the trabecular bone loss was caused by reduced trabecular bone formation and increased bone resorption. Porcupine inhibitors exert deleterious effects on bone mass and strength caused by a combination of reduced bone formation and increased bone resorption. We suggest that cancer targeted therapies using Porcupine inhibitors may increase the risk of fractures., (© 2018 The authors.)

Therapeutic use of glucocorticoids (GCs) is a major cause of secondary osteoporosis, but the molecular mechanisms responsible for the deleterious effects of GCs in bone are only partially understood. WNT16 is a crucial physiological regulator of bone mass and fracture susceptibility, and we hypothesize that disturbed WNT16 activity might be involved in the deleterious effects of GC in bone. Twelve-week-old female Obl-Wnt16 mice (WNT16 expression driven by the rat procollagen type I α1 promoter) and wild-type (WT) littermates were treated with prednisolone (7.6 mg·kg -1 ·day -1 ) or vehicle for 4 wk. We first observed that GC treatment decreased the Wnt16 mRNA levels in bone of female mice (-56.4 ± 6.1% compared with vehicle, P < 0.001). We next evaluated if WNT16 overexpression protects against GC-induced bone loss. Dual-energy X-ray absorptiometry analyses revealed that GC treatment decreased total body bone mineral density in WT mice (-3.9 ± 1.2%, P = 0.028) but not in Obl-Wnt16 mice (+1.3 ± 1.4%, nonsignificant). Microcomputed tomography analyses showed that GC treatment decreased trabecular bone volume fraction (BV/TV) of the femur in WT mice ( P = 0.019) but not in Obl-Wnt16 mice. Serum levels of the bone formation marker procollagen type I N-terminal propeptide were substantially reduced by GC treatment in WT mice (-50.3 ± 7.0%, P = 0.008) but not in Obl-Wnt16 mice (-3.8 ± 21.2%, nonsignificant). However, the cortical bone thickness in femur was reduced by GC treatment in both WT mice and Obl-Wnt16 mice. In conclusion, GC treatment decreases Wnt16 mRNA levels in bone and WNT16 overexpression partly protects against GC-induced bone loss.

Substantial progress has been made in the therapeutic reduction of vertebral fracture risk in patients with osteoporosis, but non-vertebral fracture risk has been improved only marginally. Human genetic studies demonstrate that the WNT16 locus is a major determinant of cortical bone thickness and non-vertebral fracture risk and mouse models with life-long Wnt16 inactivation revealed that WNT16 is a key regulator of cortical thickness. These studies, however, could not exclude that the effect of Wnt16 inactivation on cortical thickness might be caused by early developmental and/or growth effects. To determine the effect of WNT16 specifically on adult cortical bone homeostasis, Wnt16 was conditionally ablated in young adult and old mice through tamoxifen-inducible Cre-mediated recombination using CAG-Cre-ER; Wnt16 flox/flox ( Cre-Wnt16 flox/flox ) mice. First, 10-week-old Cre-Wnt16 flox/flox and Wnt16 flox/flox littermate control mice were treated with tamoxifen. Four weeks later, Wnt16 mRNA levels in cortical bone were reduced and cortical thickness in femur was decreased in Cre-Wnt16 flox/flox mice compared to Wnt16 flox/flox mice. Then, inactivation of Wnt16 in 47-week-old mice (evaluated four weeks later) resulted in a reduction of Wnt16 mRNA levels, cortical thickness and cortical bone strength with no effect on trabecular bone volume fraction. Mechanistic studies demonstrated that the reduced cortical bone thickness was caused by a combination of increased bone resorption and reduced periosteal bone formation. In conclusion, WNT16 is a crucial regulator of cortical bone thickness in young adult and old mice. We propose that new treatment strategies targeting the adult regulation of WNT16 might be useful to reduce fracture risk at cortical bone sites., (© 2018 The authors.)