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Anterior cruciate ligament (ACL) injuries often result in post-traumatic osteoarthritis (PTOA). To better understand the molecular mechanisms behind PTOA development following ACL injury, we profiled ACL injury-induced transcriptional changes in knee joints of three mouse strains with varying susceptibility to OA: STR/ort (highly susceptible), C57BL/6J (moderately susceptible) and super-healer MRL/MpJ (not susceptible). Right knee joints of the mice were injured using a non-invasive tibial compression injury model and global gene expression was quantified before and at 1-day, 1-week, and 2-weeks post-injury using RNA-seq. Following injury, injured and uninjured joints of STR/ort and injured C57BL/6J joints displayed significant cartilage degeneration while MRL/MpJ had little cartilage damage. Gene expression analysis suggested that prolonged inflammation and elevated catabolic activity in STR/ort injured joints, compared to the other two strains may be responsible for the severe PTOA phenotype observed in this strain. MRL/MpJ had the lowest expression values for several inflammatory cytokines and catabolic enzymes activated in response to ACL injury. Furthermore, we identified several genes highly expressed in MRL/MpJ compared to the other two strains including B4galnt2 and Tpsab1 which may contribute to enhanced healing in the MRL/MpJ. Overall, this study has increased our knowledge of early molecular changes associated with PTOA development.

Patients with anterior cruciate ligament (ACL) rupture are two times as likely to develop posttraumatic osteoarthritis (PTOA). Annually, there are ∼900,000 knee injuries in the United States, which account for ∼12% of all osteoarthritis (OA) cases. PTOA leads to reduced physical activity, deconditioning of the musculoskeletal system, and in severe cases requires joint replacement to restore function. Therefore, treatments that would prevent cartilage degradation post-injury would provide attractive alternatives to surgery. Sclerostin (Sost), a Wnt antagonist and a potent negative regulator of bone formation, has recently been implicated in regulating chondrocyte function in OA. To determine whether elevated levels of Sost play a protective role in PTOA, we examined the progression of OA using a noninvasive tibial compression overload model in SOST transgenic (SOSTTG ) and knockout (Sost-/- ) mice. Here we report that SOSTTG mice develop moderate OA and display significantly less advanced PTOA phenotype at 16 weeks post-injury compared with wild-type (WT) controls and Sost-/- . In addition, SOSTTG built ∼50% and ∼65% less osteophyte volume than WT and Sost-/- , respectively. Quantification of metalloproteinase (MMP) activity showed that SOSTTG had ∼2-fold less MMP activation than WT or Sost-/- , and this was supported by a significant reduction in MMP2/3 protein levels, suggesting that elevated levels of SOST inhibit the activity of proteolytic enzymes known to degrade articular cartilage matrix. Furthermore, intra-articular administration of recombinant Sost protein, immediately post-injury, also significantly decreased MMP activity levels relative to PBS-treated controls, and Sost activation in response to injury was TNFα and NF-κB dependent. These results provide in vivo evidence that sclerostin functions as a protective molecule immediately after joint injury to prevent cartilage degradation. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Joint injury causes post-traumatic osteoarthritis (PTOA). About ∼50% of patients rupturing their anterior cruciate ligament (ACL) will develop PTOA within 1-2 decades of the injury, yet the mechanisms responsible for the development of PTOA after joint injury are not well understood. In this study, we examined whole joint gene expression by RNA sequencing (RNAseq) at 1 day, 1-, 6-, and 12 weeks post injury, in a non-invasive tibial compression (TC) overload mouse model of PTOA that mimics ACL rupture in humans. We identified 1446 genes differentially regulated between injured and contralateral joints. This includes known regulators of osteoarthritis such as MMP3, FN1, and COMP, and several new genes including Suco, Sorcs2, and Medag. We also identified 18 long noncoding RNAs that are differentially expressed in the injured joints. By comparing our data to gene expression data generated using the surgical destabilization of the medial meniscus (DMM) PTOA model, we identified several common genes and shared mechanisms. Our study highlights several differences between these two models and suggests that the TC model may be a more rapidly progressing model of PTOA. This study provides the first account of gene expression changes associated with PTOA development and progression in a TC model. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. J Orthop Res 35:474-485, 2017.

Wnt3a is a major regulator of bone metabolism however, very few of its target genes are known in bone. Wnt3a preferentially signals through transmembrane receptors Frizzled and co-receptors Lrp5/6 to activate the canonical signaling pathway. Previous studies have shown that the canonical Wnt co-receptors Lrp5 and Lrp6 also play an essential role in normal postnatal bone homeostasis, yet, very little is known about specific contributions by these co-receptors in Wnt3a-dependent signaling. We used high-throughput sequencing technology to identify target genes regulated by Wnt3a in osteoblasts and to elucidate the role of Lrp5 and Lrp6 in mediating Wnt3a signaling. Our study identified 782 genes regulated by Wnt3a in primary calvarial osteoblasts. Wnt3a up-regulated the expression of several key regulators of osteoblast proliferation/ early stages of differentiation while inhibiting genes expressed in later stages of osteoblastogenesis. We also found that Lrp6 is the key mediator of Wnt3a signaling in osteoblasts and Lrp5 played a less significant role in mediating Wnt3a signaling.

Type 1 diabetes mellitus (T1DM) patients have osteopenia and impaired fracture healing due to decreased osteoblast activity. Further, no adequate treatments are currently available that can restore impaired healing in T1DM; hence a significant need exists to investigate new therapeutics for treatment of orthopedic complications. Sclerostin (SOST), a WNT antagonist, negatively regulates bone formation, and SostAb is a potent bone anabolic agent. To determine whether SOST antibody (SostAb) treatment improves fracture healing in streptozotocin (STZ) induced T1DM mice, we administered SostAb twice weekly for up to 21days post-fracture, and examined bone quality and callus outcomes at 21days and 42days post-fracture (11 and 14weeks of age, respectively). Here we show that SostAb treatment improves bone parameters; these improvements persist after cessation of antibody treatment. Markers of osteoblast differentiation such as Runx2, collagen I, osteocalcin, and DMP1 were reduced, while an abundant number of SP7/osterix-positive early osteoblasts were observed on the bone surface of STZ calluses. These results suggest that STZ calluses have poor osteogenesis resulting from failure of osteoblasts to fully differentiate and produce mineralized matrix, which produces a less mineralized callus. SostAb treatment enhanced fracture healing in both normal and STZ groups, and in STZ+SostAb mice, also reversed the lower mineralization seen in STZ calluses. Micro-CT analysis of calluses revealed improved bone parameters with SostAb treatment, and the mineralized bone was comparable to Controls. Additionally, we found sclerostin levels to be elevated in STZ mice and β-catenin activity to be reduced. Consistent with its function as a WNT antagonist, SostAb treatment enhanced β-catenin activity, but also increased the levels of SOST in the callus and in circulation. Our results indicate that SostAb treatment rescues the impaired osteogenesis seen in the STZ induced T1DM fracture model by facilitating osteoblast differentiation and mineralization of bone.

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder whose most debilitating pathology is progressive and cumulative heterotopic ossification (HO) of skeletal muscles, ligaments, tendons, and fascia. FOP is caused by mutations in the type I BMP receptor gene ACVR1, which enable ACVR1 to utilize its natural antagonist, activin A, as an agonistic ligand. The physiological relevance of this property is underscored by the fact that HO in FOP is exquisitely dependent on activation of FOP-mutant ACVR1 by activin A, an effect countered by inhibition of anti-activin A via monoclonal antibody treatment. Hence, we surmised that anti-ACVR1 antibodies that block activation of ACVR1 by ligands should also inhibit HO in FOP and provide an additional therapeutic option for this condition. Therefore, we generated anti-ACVR1 monoclonal antibodies that block ACVR1's activation by its ligands. Surprisingly, in vivo, these anti-ACVR1 antibodies stimulated HO and activated signaling of FOP-mutant ACVR1. This property was restricted to FOPmutant ACVR1 and resulted from anti-ACVR1 antibody-mediated dimerization of ACVR1. Conversely, wild-type ACVR1 was inhibited by anti-ACVR1 antibodies. These results uncover an additional property of FOP-mutant ACVR1 and indicate that anti-ACVR1 antibodies should not be considered as therapeutics for FOP., Introduction Fibrodysplasia ossificans progressiva (FOP) (OMIM #135100) is a rare, autosomal dominant disorder characterized by congenital skeletal dysplasias and progressive and cumulative heterotopic ossification (HO) of skeletal muscles, tendons, ligaments, [...]

Introduction/Background Children with moderate-to-severe atopic dermatitis (AD) are at increased risk of lower bone mineral density (BMD) and fractures. Peak bone mass achieved during prepubescence is a major determinant of lifetime risk of fractures and osteoporosis. Bone alkaline phosphatase (BALP) promotes bone mineralization and contributes to density and linear growth in children. Systemic corticosteroids (SCS) negatively impact growth and bone health. Objectives To describe the impact of dupilumab treatment on BALP in children aged 6–11 years with moderate-to-severe AD and prior history of SCS use. Methods BALP levels in sera from participants receiving dupilumab 300 mg every 4 weeks (q4w) or placebo in LIBERTY AD PEDS (NCT03345914) and dupilumab 300 mg q4w in LIBERTY AD PED-OLE (NCT02612454) were analyzed at baseline and at 8, 12, 16 (PEDS), and 52 weeks (PED-OLE). Serum BALP levels (mcg/L) were stratified by prior use (with SCS; n = 42) or with no prior use of SCS (without SCS; n = 203), as captured in PEDS patient history at baseline. Results Regardless of prior SCS use, dupilumab treatment led to significant increase in BALP levels in children with moderate-to-severe AD at Week 16 compared with the placebo group (with SCS: 300 mg q4w [n = 25] vs placebo [n = 17], mean change [standard deviation] in BALP levels of 15.1 mcg/L [16.5] vs −5.5 mcg/L [16.0], P = 0.0099; without SCS: 300 mg q4w [n = 97] vs placebo [n = 106], 11.8 mcg/L [18.8] vs 2.2 mcg/L [16.3], P = 0.0074). By Week 52, BALP levels further increased vs baseline regardless of prior SCS use and were comparable with reference intervals (with SCS: 24.5 mcg/L [16.8], P = 0.0044; without SCS: 13.4 mcg/L [19.4], P = 0.0002). Patients in the placebo group who switched to dupilumab in PED-OLE had improved to levels similar to those of patients continuing treatment by Week 52 (with SCS: 23.3 mcg/L [19.3], P = 0.0067 [vs baseline]; without SCS: 18.4 mcg/L [20.4], P < 0.0001 [vs baseline]). Conclusions Dupilumab treatment increased BALP levels in children aged 6-11 years with moderate-to-severe AD irrespective of prior history of SCS use. These results add to the body of evidence that moderate-to-severe AD can negatively impact BALP levels, and that this effect may be improved with dupilumab in this age group, regardless of history of SCS use. The increase in BALP levels suggests that dupilumab may help improve bone mineralization in children with moderate-to-severe AD when treated during prepubescence. [ABSTRACT FROM AUTHOR]

A considerable body of circumstantial data suggests that cyclin D1 is an attractive candidate to mediate the effects of [beta]-catenin in mammary tissue. To test the functional significance of these correlative findings, we investigated the genetic interaction between transcriptionally active [beta]-catenin ([DELTA]N89/[beta]-catenin) and its target gene cyclin D1 in the mouse mammary gland during pubertal development, pregnancy, and tumorigenesis. Our data demonstrate that cyclin D1 is dispensable for the [DELTA]N89/[beta]-catenin-stimulated initiation of alveologenesis in virgin females, for the de novo induction of alveoli in males, and for the formation of tumors. Indeed, lack of cyclin D1 accentuates and enhances these hyperplastic and tumorigenic [DELTA]N89[beta]-catenin phenotypes. Although alveologenesis is initiated by [DELTA]N89[beta]-catenin in a cyclin D1-independent fashion, up-regulation of cyclin D1 occurs in [DELTA]N89[beta]-catenin mice and its expression remains essential for the completion of alveolar development during the later stages of pregnancy. Thus, alveologenesis is a two-step process, and cyclin D1 activity during late alveologenesis cannot be replaced by the activity of other [beta]-catenin target genes that successfully drive proliferation at earlier stages. mammary tumor | Wnt | cell adhesion | cell cycle | cadherins

Children with atopic dermatitis (AD) are at risk for low bone mineral density (BMD), which is associated with an increased prevalence of osteopenia, osteoporosis, and fracture risk.1,2 Factors such as restricted nutrition, vitamin D deficiency, poor sleep and corticosteroid use contribute to lower bone alkaline phosphatase (BALP) levels, a marker of bone mineralization, seen in children with moderate-to-severe AD compared with healthy children.³ A major determinant for the lifetime risk of fractures and osteoporosis is the magnitude of peak bone mass achieved during prepubescent years. Low BALP and BMD in children with moderate-to-severe AD could contribute to a higher prevalence of osteopenia and osteoporosis. The objective of this analysis is to report the impact of dupilumab treatment on markers of bone formation in children aged ≥ 6 to <12 years with moderate-to-severe AD. The analysis was performed retrospectively on sera from participants in LIBERTY AD PEDS (NCT03345914) and LIBERTY AD PED-OLE (NCT02612454). In LIBERTY AD PEDS, a double-blind, 16-week, phase 3 trial, children aged 6 to <12 years were randomized 1 : 1 : 1 to 300 mg dupilumab every 4 weeks (300 mg q4w), a weight-based regimen of dupilumab every 2 weeks (100 mg q2w for patients with baseline weight <30 kg, and 200 mg q2w for those with baseline weight ≥30 kg), or placebo; with concomitant medium-potency topical corticosteroids (TCS). After the initial 16-week trial, children aged 6 to <12 years were enrolled in the open-label extension study LIBERTY AD PED-OLE. Patients received dupilumab 300 mg q4w, which could be titrated up in case of inadequate clinical response at week 16 (200 mg q2w for patients with baseline weight <60 kg, and 300 mg q2w for those with baseline weight ≥60 kg); with concomitant medium-potency TCS. Bone biomarkers including BALP, procollagen type 1 N-terminal propeptide, C-terminal crosslinking telopeptide of type 1 collagen, osteocalcin, and insulin-like growth factor 1 were analysed at baseline, 8, 12, 16 and BALP only at 52 weeks. Dupilumab treatment led to a rapid and significant increase in geometric mean (standard error) levels of BALP in children with moderate-to-severe AD at 16 weeks compared with patients in the placebo group (77.7(1.02) μgL−1 vs. 65.0(1.04) μgL−1; P<0.0001). As well as a rapid and significant increase in BALP levels in children from the placebo group once they joined the OLE trial. BALP levels increased over 52 weeks in all treated children, reaching a level of 78–84 μgL−1 which constitutes a significant improvement compared with baseline, and is comparable to healthy reference intervals. An increasing trend from baseline to 16 weeks of dupilumab treatment was observed for other biomarkers, however, there was a limited number of data points due to insufficient volumes of serum available for analysis. These placebo-controlled results show, for the first time, a rapid and significant increase in BALP, and a possible trend in other biomarkers, in children with AD during treatment with dupilumab. These results suggest increased bone mineralization during the treatment period. [ABSTRACT FROM AUTHOR]

The article presents research conducted by Sarah J. Hatsell on the development of fibrodysplasia ossificans progressiva (FOP) due to ACVR1R206H receptor mutation. Topics discussed include mice models with mutated genes exhibited perinatal death; development of heterotropic ossification by mouse models that express Acvr1[R206H]; and therapeutic use of human antibody to activin A for FOP.