Search

Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene. Despite recent progress in conditioning, an important number of patients are not eligible for allogeneic stem cell transplantation because of the severity of the disease and significant transplant-related morbidity. We exploited peripheral CD34(+) cells, known to circulate at high frequency in the peripheral blood of TCIRG1-deficient patients, as a novel cell source for autologous transplantation of gene corrected cells. Detailed phenotypical analysis showed that circulating CD34(+). cells have a cellular composition that resembles bone marrow (BM), supporting their use in gene therapy protocols. Transcriptomic profile revealed enrichment in genes expressed by hematopoietic stem and progenitor cells (HSPC). To overcome the limit of BM harvest/HSPC mobilization and serial blood drawings in TCIRG1 patients, we applied UM171-based ex vivo expansion of HSPC coupled with lentiviral gene transfer. Circulating CD34(+). cells from TCIRG1-defective patients were transduced with a clinically-optimized lentiviral vector expressing TCIRG1 under the control of phosphoglycerate promoter and expanded ex vivo. Expanded cells maintained long-term engraftment capacity and multi-lineage repopulating potential when transplanted in vivo both in primary and secondary NOD scid gamma common chain (NSG) recipients. Moreover, when CD34(+) cells were differentiated in vitro, genetically corrected osteoclasts resorbed the bone efficiently. Overall, we provide evidence that expansion of circulating HSPC coupled to gene therapy can overcome the limit of stem cell harvest in osteopetrotic patients, thus opening the way to future gene-based treatment of skeletal diseases caused by BM fibrosis.

Acrofrontofacionasal dysostosis type 1 (AFFND1) is an extremely rare disorder characterized by several dysmorphic features, skeletal abnormalities and intellectual disability, and described only in seven patients in the literature. A biallelic variant in the Neuroblastoma Amplified Sequence (NBAS) gene was recently identified in two Indian patients with AFFND1. Here we report genetic investigation of AFFND1 in the originally described Brazilian families and the identification of an extremely rare, recessively-inherited, intronic variant in the Phosphatidylinositol Glycan class B (PIGB) gene NC_000015.10 (NM_004855.4): c.795-19T > G) in the affected individuals. The PIGB gene encodes an enzyme involved in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor, which is required for the post-translational modification of a large variety of proteins, enabling their correct cellular localization and function. Recessive variants in PIGB have previously been reported in individuals with a neurodevelopmental syndrome having partial overlap with AFFND1. In vitro assays demonstrated that the intronic variant leads to exon skipping, suggesting the Brazilian AFFND1 patients may be null for PIGB, in agreement with their severe clinical phenotype. These data increase the number of pathogenic variants in the PIGB gene, place AFFND1 among GPI deficiencies and extend the spectrum of phenotypes associated with GPI biosynthesis defects.

ClC-7 is a chloride-proton antiporter of the CLC protein family. In complex with its accessory protein Ostm-1, ClC-7 localizes to lysosomes and to the osteoclasts' ruffled border, where it plays a critical role in acidifying the resorption lacuna during bone resorption. Gene inactivation in mice causes severe osteopetrosis, neurodegeneration, and lysosomal storage disease. Mutations in the human CLCN7 gene are associated with diverse forms of osteopetrosis. The functional evaluation of ClC-7 variants might be informative with respect to their pathogenicity, but the cellular localization of the protein hampers this analysis. Here we investigated the functional effects of 13 CLCN7 mutations identified in 13 new patients with severe or mild osteopetrosis and a known ADO2 mutation. We mapped the mutated amino acid residues in the homology model of ClC-7 protein, assessed the lysosomal colocalization of ClC-7 mutants and Ostm1 through confocal microscopy, and performed patch-clamp recordings on plasma-membrane-targeted mutant ClC-7. Finally, we analyzed these results together with the patients' clinical features and suggested a correlation between the lack of ClC-7/Ostm1 in lysosomes and severe neurodegeneration. © 2020 American Society for Bone and Mineral Research (ASBMR).

Plants produce considerable amounts of volatile organic compounds (VOCs) with several biological functions, including protection against biotic agents such as viruses and their vectors. In citrus species, these metabolites can be related with their different susceptibility/tolerance toward the Tristeza virus (CTV), one of the main biotic constraints for the citrus industry. The objective of this study was to compare the VOCs pattern from the leaves of a CTV-susceptible citrus variety such as Citrus aurantium and from three CTV-tolerant varieties: Citrus volkameriana, Carrizo citrange, and Forner-Alcaide no. 5. The VOCs emitted were analyzed via the headspace SPME method, while plant metabolites sequestered in the leaves were analyzed by heptane extraction followed by GC-MS. The results indicated that the majority of the VOCs emitted and sequestered in the leaves of the varieties tolerant and susceptible to CTV are constituted mainly by volatile terpenes (VTs) that exhibit strong qualitative/quantitative differences among the profiles of the four citrus species. In detail, the VOC emission indicated different patterns between C. aurantium and C. volkameriana and from both of them in comparison with Forner-Alcaide no. 5 and Carrizo citrange that exhibited more similarities, with the last two characterized by a higher presence of sesquiterpenes. The data obtained from the analysis of the VOCs sequestered in leaf tissues of the CTV-tolerant varieties indicated a higher presence of monoterpenes such as limonene, α-pinene, and p-cymene, known to be the main components of several plant extracts showing deterrent properties toward viruses and insect vectors. As VOC evaluation is a fast and noninvasive measure of phenotypic dynamics, allowing the association of plant phenotypes in accordance to plant disease resistance and/or stress tolerance, the possible implications of such differences in terms of tolerance grade to CTV and/or its related vectors are discussed.

Biomimetic scaffolds are extremely versatile in terms of chemical composition and physical properties, which can be defined to accomplish specific applications. One property that can be added is the production/release of bioactive soluble factors, either directly from the biomaterial, or from cells embedded within the biomaterial. We reasoned that pursuing this strategy would be appropriate to setup a cell-based therapy for RANKL-deficient autosomal recessive osteopetrosis, a very rare skeletal genetic disease in which lack of the essential osteoclastogenic factor RANKL impedes osteoclast formation. The exogenously administered RANKL cytokine is effective in achieving osteoclast formation and function in vitro and in vivo, thus, we produced murine Rankl−/− mesenchymal stromal cells (MSCs) overexpressing human soluble RANKL (hsRL) following lentiviral transduction (LVhsRL). Here, we described a three-dimensional (3D) culture system based on a magnesium-doped hydroxyapatite/collagen I (MgHA/Col) biocompatible scaffold closely reproducing bone physicochemical properties. MgHA/Col-seeded murine MSCs showed improved properties, as compared to two-dimensional (2D) culture, in terms of proliferation and hsRL production, with respect to LVhsRL-transduced cells. When implanted subcutaneously in Rankl−/− mice, these cell constructs were well tolerated, colonized by host cells, and intensely vascularized. Of note, in the bone of Rankl−/− mice that carried scaffolds with either WT or LVhsRL-transduced Rankl−/− MSCs, we specifically observed formation of TRAP+ cells, likely due to sRL released from the scaffolds into circulation. Thus, our strategy proved to have the potential to elicit an effect on the bone; further work is required to maximize these benefits and achieve improvements of the skeletal pathology in the treated Rankl−/− mice. Stem Cells Translational Medicine 2019;8:22–34

Autosomal recessive osteopetrosis (ARO) is a severe bone disease characterized by increased bone density due to impairment in osteoclast resorptive function or differentiation. Hematopoietic stem cell transplantation is the only available treatment; however, this therapy is not effective in RANKL-dependent ARO, since in bone this gene is mainly expressed by cells of mesenchymal origin. Of note, whether lack of RANKL production might cause a defect also in the bone marrow (BM) stromal compartment, possibly contributing to the pathology, is unknown. To verify this possibility, we generated and characterized BM mesenchymal stromal cell (BM-MSC) lines from wild type and Rankl−/− mice, and found that Rankl−/− BM-MSCs displayed reduced clonogenicity and osteogenic capacity. The differentiation defect was significantly improved by lentiviral transduction of Rankl−/− BM-MSCs with a vector stably expressing human soluble RANKL (hsRANKL). Expression of Rankl receptor, Rank, on the cytoplasmic membrane of BM-MSCs pointed to the existence of an autocrine loop possibly activated by the secreted cytokine. Based on the close resemblance of RANKL-defective osteopetrosis in humans and mice, we expect that our results are also relevant for RANKL-dependent ARO patients. Data obtained in vitro after transduction with a lentiviral vector expressing hsRANKL would suggest that restoration of RANKL production might not only rescue the defective osteoclastogenesis of this ARO form, but also improve a less obvious defect in the osteoblast lineage, thus possibly achieving higher benefit for the patients, when the approach is translated to clinics.

Autosomal recessive osteopetroses (AROs) are rare, genetically heterogeneous skeletal diseases with increased bone density that are often lethal if left untreated. A precise molecular classification is relevant for the patient's management, because in some subgroups hematopoietic stem cell transplantation (HSCT), which is the only curative therapy, is contraindicated. In two unrelated ARO patients, the molecular analysis revealed the presence of a synonymous variant in known ARO genes, namely in the TCIRG1 gene in one patient and in the CLCN7 in the other patient, predicted to impact on the splicing process. In the latter case, sequencing of the transcript confirmed the splicing defect, whereas in the former, for whom an RNA sample was not available, the defect was reconstructed in vitro by the minigene technology. These results strongly suggest that these synonymous changes were responsible for the disease in our patients. Our findings are novel with respect to ARO and add to the few reports in literature dealing with different diseases, underlining the importance of cDNA analysis for the correct assessment of exonic changes, even when exome sequencing is performed. In particular, we highlight the possibility that at least in some cases ARO is due to synonymous changes, erroneously considered clinically silent, in the genes already described in literature, and suggest carefully reevaluating the sequencing results of these genes when mutations are not found at a first analysis. In addition, with respect to the CLCN7 gene, we suggest that synonymous variants might also contribute to the large spectrum of severity typical of CLCN7-dependent osteopetrosis through more subtle, but not negligible, effects on protein availability and functionality. © 2016 American Society for Bone and Mineral Research.

Controlling oxidative stress through the activation of antioxidant pathways is crucial in bone homeostasis, and impairments of the cellular defense systems involved contribute to the pathogenesis of common skeletal diseases. In this work we focused on the dipeptidyl peptidase 3 (DPP3), a poorly investigated ubiquitous zinc-dependent exopeptidase activating the Keap1-Nrf2 antioxidant pathway. We showed Dpp3 expression in bone and, to understand its role in this compartment, we generated a Dpp3 knockout (KO) mouse model and specifically investigated the skeletal phenotype. Adult Dpp3 KO mice showed a mild growth defect, a significant increase in bone marrow cellularity, and bone loss mainly caused by increased osteoclast activity. Overall, in the mouse model, lack of DPP3 resulted in sustained oxidative stress and in alterations of bone microenvironment favoring the osteoclast compared to the osteoblast lineage. Accordingly, in vitro studies revealed that Dpp3 KO osteoclasts had an inherent increased resorptive activity and ROS production, which on the other hand made them prone to apoptosis. Moreover, absence of DPP3 augmented bone loss after estrogen withdrawal in female mice, further supporting its relevance in the framework of bone pathophysiology. Overall, we show a nonredundant role for DPP3 in the maintenance of bone homeostasis and propose that DPP3 might represent a possible new osteoimmunological player and a marker of human bone loss pathology. © 2019 American Society for Bone and Mineral Research.

Oral cancer (OC) is a largely asymptomatic disease, resulting in one of the highest mortality rates of any cancer. OC is currently ranked as the sixth most common cancer in the world, according to a recent World Health Organization analysis, and its prevalence is increasing, both in western and developing regions. Depending on the stage of OC, treatment strategies include surgery, radiation therapy and chemotherapy, or a combination thereof. As with numerous other types of cancer, resistance to conventional chemotherapeutic drugs is increasing in oral squamous cell carcinoma (OSCC). The present study aimed to investigate the use of a novel group of compounds, the pyrrolo‑1,5‑benzoxazepines (PBOXs), as a therapeutic alternative for the treatment of OC. PBOXs are microtubule‑targeting agents that are able to induce apoptosis in numerous cancer cell types, thereby preventing tumour cell proliferation. Ca9.22 gingival and TR146 buccal cell lines were used as models for OSSC. Cell viability and proliferation in the presence of two PBOXs: PBOX‑6 and PBOX‑15, was monitored using an AlamarBlueTM assay. Flow cytometric analysis of propidium iodide‑stained cells was used to determine the DNA content, and therefore the percentage of cells in each phase of the cell cycle. Microtubule disruption was determined by indirect immunofluorescence staining. Changes in protein expression and degradation were determined by western blotting. The results of the present study indicated that both PBOX‑6 and ‑15 were able to induce apoptotic cell death by disrupting the microtubule network in both cell lines. The EC50 values were subsequently calculated for both PBOX‑6 and ‑15, and PBOX‑15 was shown to possess a higher potency. Both compounds displayed anti‑proliferative effects mediated through sustained G2/M arrest accompanied by tubulin disruption, and a decrease in DNA repair protein poly (ADP ribose) polymerase expression. These findings suggest that PBOXs may prove useful, either alone or in combination with other agents, in the treatment of chemotherapeutic resistant OSCC.

Autosomal recessive osteopetrosis (ARO) is a rare genetic bone disease with genotypic and phenotypic heterogeneity, sometimes translating into delayed diagnosis and treatment. In particular, cases of intermediate severity often constitute a diagnostic challenge and represent good candidates for exome sequencing. Here, we describe the tortuous path to identification of the molecular defect in two siblings, in which osteopetrosis diagnosed in early childhood followed a milder course, allowing them to reach the adult age in relatively good conditions with no specific therapy. No clearly pathogenic mutation was identified either with standard amplification and resequencing protocols or with exome sequencing analysis. While evaluating the possible impact of a 3'UTR variant on the TCIRG1 expression, we found a novel single nucleotide change buried in the middle of intron 15 of the TCIRG1 gene, about 150 nucleotides away from the closest canonical splice site. By sequencing a number of independent cDNA clones covering exons 14 to 17, we demonstrated that this mutation reduced splicing efficiency but did not completely abrogate the production of the normal transcript. Prompted by this finding, we sequenced the same genomic region in 33 patients from our unresolved ARO cohort and found three additional novel single nucleotide changes in a similar location and with a predicted disruptive effect on splicing, further confirmed in one of them at the transcript level. Overall, we identified an intronic region in TCIRG1 that seems to be particularly prone to splicing mutations, allowing the production of a small amount of protein sufficient to reduce the severity of the phenotype usually associated with TCIRG1 defects. On this basis, we would recommend including TCIRG1 not only in the molecular work-up of severe infantile osteopetrosis but also in intermediate cases and carefully evaluating the possible effects of intronic changes. © 2015 American Society for Bone and Mineral Research.

Purpose of Review: The term osteopetrosis refers to a group of rare skeletal diseases sharing the hallmark of a generalized increase in bone density owing to a defect in bone resorption. Osteopetrosis is clinically and genetically heterogeneous, and a precise molecular classification is relevant for prognosis and treatment. Here, we review recent data on the pathogenesis of this disorder. Recent Findings: Novel mutations in known genes as well as defects in new genes have been recently reported, further expanding the spectrum of molecular defects leading to osteopetrosis. Summary: Exploitation of next-generation sequencing tools is ever spreading, facilitating differential diagnosis. Some complex phenotypes in which osteopetrosis is accompanied by additional clinical features have received a molecular classification, also involving new genes. Moreover, novel types of mutations have been recognized, which for their nature or genomic location are at high risk being neglected. Yet, the causative mutation is unknown in some patients, indicating that the genetics of osteopetrosis still deserves intense research efforts.

Acrofrontofacionasal Dysostosis type 1 (AFFND1) is an extremely rare, autosomal recessive syndrome, comprising facial and skeletal abnormalities, short stature and intellectual disability. We analyzed an Indian family with two affected siblings by exome sequencing and identified a novel homozygous truncating mutation in the Neuroblastoma-Amplified Sequence (NBAS) gene in the patients' genome. Mutations in the NBAS gene have recently been associated with different phenotypes mainly involving skeletal formation, liver and cognitive development. The NBAS protein has been implicated in two key cellular processes, namely the non-sense mediated decay and the Golgi-to-Endoplasmic Reticulum retrograde traffic. Both functions were impaired in HEK293T cells overexpressing the truncated NBAS protein, as assessed by Real-Time PCR, Western blot analysis, co-immunoprecipitation, and immunofluorescence analysis. We examined the expression of NBAS protein in mouse embryos at various developmental stages by immunohistochemistry, and detected expression in developing chondrogenic and osteogenic structures of the skeleton as well as in the cortex, hippocampus and cerebellum, which is compatible with a role in bone and brain development. Functional genetics in the zebrafish model showed that depletion of endogenous z-nbas in fish embryos results in defective morphogenesis of chondrogenic cranial skeletal elements. Overall, our data point to a conserved function of NBAS in skeletal morphogenesis during development, support the hypothesis of a causative role of the mutated NBAS gene in the pathogenesis of AFFND1 and extend the spectrum of phenotypes associated with defects in this gene.

Hepatocellular carcinoma (HCC) is a frequent neoplasia and a leading cause of inflammation-related cancer mortality. Despite most HCC arise from persistent inflammatory conditions; pathways linking chronic inflammation to cancer development are still incompletely elucidated. We dissected the role of adaptive immunity in the Mdr2-/- mouse, a model of inflammation-associated cancer, in which ablation of adaptive immunity has been induced genetically (Rag2-/-Mdr2-/- and μMt-Mdr2-/- mice) or with in vivo treatments using lymphocyte-specific depleting antibodies (anti-CD20 or anti-CD4/CD8). We found that activated B and T lymphocytes, secreting fibrogenic TNFα and other pro-inflammatory cytokines, infiltrated the liver of the Mdr2-/- mice, during chronic fibrosing cholangitis. Lymphocytes ablation, in the Rag2-/-Mdr2-/- and μMt-Mdr2-/- mice, strongly suppressed hepatic stellate cell (HSC) activation and extracellular matrix deposition, enhancing HSCs transition to cellular senescence. Moreover, lack of lymphocytes changed the intrahepatic metabolic/oxidative state, resulting in skewed macrophages polarization towards an anti-inflammatory M2 phenotype. Remarkably, hepatocarcinogenesis was significantly suppressed in the Rag2-/-Mdr2-/- mice, correlating with reduced TNFα–NF-κB pathway activation. Ablation of CD20+ B cells but not of CD4+/CD8+ T cells in the Mdr2-/- mice, promoted senescence-mediated fibrosis resolution and inhibited the pro-tumorigenic TNFα-NF-kB pathway. Interestingly, presence of infiltrating B cells correlated with increased tumor aggressiveness and reduced disease free survival in human HCC. Conclusion: Adaptive immunity sustains liver fibrosis and favors HCC growth in chronic injury, by modulating innate components of inflammation and limiting the extent of HSC senescence. Therapies designed to B cell targeting may be an effective strategy in liver fibrosis. This article is protected by copyright. All rights reserved.

Mesenchymal stem cells (MSCs) are multipotent stromal cells that are identified by in vitro plastic adherence, colony-forming capacity, expression of a panel of surface molecules, and ability to differentiate at least toward osteogenic, adipogenic, and chondrogenic lineages. They also produce trophic factors with immunomodulatory, proangiogenic, and antiapoptotic functions influencing the behavior of neighboring cells. On the other hand, a reciprocal regulation takes place; in fact, MSCs can be isolated from several tissues, and depending on the original microenvironment and the range of stimuli received from there, they can display differences in their essential characteristics. Here, we focus mainly on the bone tissue and how soluble factors, such as growth factors, cytokines, and hormones, present in this microenvironment can orchestrate bone marrow-derived MSCs fate. We also briefly describe the alteration of MSCs behavior in pathological settings such as hematological cancer, bone metastasis, and bone marrow failure syndromes. Overall, the possibility to modulate MSCs plasticity makes them an attractive tool for diverse applications of tissue regeneration in cell therapy. Therefore, the comprehensive understanding of the microenvironment characteristics and components better suited to obtain a specific MSCs response can be extremely useful for clinical use.

Sp140 is a nuclear leukocyte-specific protein involved in primary biliary cirrhosis and a risk factor in chronic lymphocytic leukemia. The presence of several chromatin related modules such as plant homeodomain (PHD), bromodomain and SAND domain suggests a role in chromatin-mediated regulation of gene expression; however, its real function is still elusive. Herein we present the solution structure of Sp140-PHD finger and investigate its role as epigenetic reader in vitro. Sp140-PHD presents an atypical PHD finger fold which does not bind to histone H3 tails but is recognized by peptidylprolyl isomerase Pin1. Pin1 specifically binds to a phosphopeptide corresponding to the L3 loop of Sp140-PHD and catalyzes cis-trans isomerization of a pThr-Pro bond. Moreover co-immunoprecipitation experiments demonstrate FLAG-Sp140 interaction with endogenous Pin1 in vivo. Overall these data include Sp140 in the list of the increasing number of Pin1 binders and expand the regulatory potential of PHD fingers as versatile structural platforms for diversified interactions.

Autosomal recessive osteopetrosis (ARO) is a rare genetic bone disease with genotypic and phenotypic heterogeneity, sometimes translating into delayed diagnosis and treatment. In particular, cases of intermediate severity often constitute a diagnostic challenge and represent good candidates for exome sequencing. Here, we describe the tortuous path to identification of the molecular defect in two siblings, in which osteopetrosis diagnosed in early childhood followed a milder course, allowing them to reach the adult age in relatively good conditions with no specific therapy. No clearly pathogenic mutation was identified either with standard amplification and resequencing protocols or with exome sequencing analysis. While evaluating the possible impact of a 3'UTR variant on the TCIRG1 expression, we found a novel single nucleotide change buried in the middle of intron 15 of the TCIRG1 gene, about 150 nucleotides away from the closest canonical splice site. By sequencing a number of independent cDNA clones covering exons 14 to 17, we demonstrated that this mutation reduced splicing efficiency but did not completely abrogate the production of the normal transcript. Prompted by this finding, we sequenced the same genomic region in 33 patients from our unresolved ARO cohort and found three additional novel single nucleotide changes in a similar location and with a predicted disruptive effect on splicing, further confirmed in one of them at the transcript level. Overall, we identified an intronic region in TCIRG1 that seems to be particularly prone to splicing mutations, allowing the production of a small amount of protein sufficient to reduce the severity of the phenotype usually associated with TCIRG1 defects. On this basis, we would recommend including TCIRG1 not only in the molecular work-up of severe infantile osteopetrosis but also in intermediate cases and carefully evaluating the possible effects of intronic changes.

Osteoclast-poor RANKL-dependent Autosomal Recessive Osteopetrosis (ARO) is a rare bone disease characterized by an increase in bone density due to the failure of bone resorption by impaired osteoclast formation. Hematopoietic stem cell transplantation is not an effective therapy for this ARO form, since in bone RANKL is produced mainly by cells of mesenchymal origin. Therefore Mesenchymal Stromal Cells (MSC) transplantation together with a gene-therapy strategy to correct RANKL defect in MSC could represent a possible effective therapy. Of note, whether also MSC, besides the osteoclasts, are affected by RANKL deficiency is unknown. To verify this, we established and characterized bone marrow derived MSC (BM-MSC) lines from the Rankl−/− (KO) mouse model, which recapitulates the human disease, and from wild type (WT) mice. No differences were found between KO and WT MSC in terms of morphology, immunophenotype and proliferation capacity. However, KO MSC displayed a reduced clonogenic potential with a decrease in stemness genes expression. KO MSC were able to normally differentiate towards the adipogenic and chondrogenic lineages, while showed a significantly impaired osteogenic differentiation capacity compared to WT MSC, as demonstrated by reduced Alizarin Red staining (ARS) and expression of osteogenic genes. To confirm that this alteration was due to the lack of functional RANKL, we developed a third generation lentiviral vector expressing human soluble RANKL (hsRL) for the genetic correction of KO MSC. We first investigated lentiviral transduction in 293T cells to optimize transduction efficiency at different multiplicity of infection (MOI) ranging from 1 to 100. hsRL production increased proportionally to the MOI and was stable over time. However, the higher the MOI the higher the cytotoxicity observed. Based on these data, we performed a lentiviral hsRL transduction in KO MSC at 20 and 50 MOI, to define the optimal transduction conditions. After transduction 99.5% of MSC were GFP+. While in Rankl−/− control cells the cytokine was not detected, in corrected cells hsRL production and secretion was measurable and comparable to sRL levels in WT mouse. KO MSC stably expressing hsRL showed an improved osteogenic differentiation capacity compared to untransduced KO MSC, as demonstrated by increased ARS and expression of osteogenic genes. Moreover, the expression of RANK receptor in both MSC suggested an autocrine role of sRL as possible mechanism. Our data suggest that restoration of RANKL production in lentiviral-transduced KO MSC might not only allow osteoclast differentiation in Rankl−/− mice upon transplantation, but also improve the osteogenic differentiation defect of KO MSC.