Emerging evidence suggests that microRNAs (miRNAs) may be pathologically involved in osteoarthritis (OA). Subchondral bone (SCB) sclerosis is accounted for the knee osteoarthritis (KOA) development and progression. In this study, we aimed to screen the miRNA biomarkers of KOA and investigated whether these miRNAs regulate the differentiation potential of mesenchymal stem cells (MSCs) and thus contributing to SCB. We identified 48 miRNAs in the blood samples in KOA patients (n = 5) through microarray expression profiling detection. After validation with larger sample number, we confirmed hsa‐miR‐582‐5p and hsa‐miR‐424‐5p were associated with the pathology of SCB sclerosis. Target genes prediction and pathway analysis were implemented with online databases, indicating these two candidate miRNAs were closely related to the pathways of pluripotency of stem cells and pathology of OA. Surprisingly, mmu‐miR‐582‐5p (homology of hsa‐miR‐582‐5p) was downregulated in osteogenic differentiation and upregulated in adipogenic differentiation of mesenchymal progenitor C3H10T1/2 cells, whereas mmu‐mir‐322‐5p (homology of hsa‐miR‐424‐5p) showed no change through the in vitro study. Supplementing mmu‐miR‐582‐5p mimics blocked osteogenic and induced adipogenic differentiation of C3H10T1/2 cells, whereas silencing of the endogenous mmu‐miR‐582‐5p enhanced osteogenic and repressed adipogenic differentiation. Further mechanism studies showed that mmu‐miR‐582‐5p was directly targeted to Runx2. Mutation of putative mmu‐miR‐582‐5p binding sites in Runx2 3′ untranslated region (3′UTR) could abolish the response of the 3′UTR‐luciferase construct to mmu‐miR‐582‐5p supplementation. Generally speaking, our data suggest that miR‐582‐5p is an important biomarker of KOA and is able to regulate osteogenic and adipogenic differentiation of MSCs via targeting Runx2. The study also suggests that miR‐582‐5p may play a crucial role in SCB sclerosis of human KOA.

Objectives Most bone fracture heals through enchondral bone formation that relies on the involvement of periosteal progenitor cells. However, the identity of periosteal progenitor cells and the regulatory mechanism of their proliferation and differentiation remain unclear. The aim of this study was to investigate whether Gli1‐CreERT2 can identify a population of murine periosteal progenitor cells and the role of TGF‐β signalling in periosteal progenitor cells on fracture healing. Materials and methods Double heterozygous Gli1‐CreERT2;Rosa26‐tdTomatoflox/wt mice were sacrificed at different time points for tracing the fate of Gli1+ cells in both intact and fracture bone. Gli1‐CreERT2‐mediated Tgfbr2 knockout (Gli1‐CreERT2;Tgfbr2flox/flox) mice were subjected to fracture surgery. At 4, 7, 10, 14 and 21 days post‐surgery, tibia samples were harvested for tissue analyses including μCT, histology, real‐time PCR and immunofluorescence staining. Results Through cell lineage‐tracing experiments, we have revealed that Gli1‐CreERT2 can be used to identify a subpopulation of periosteal progenitor cells in vivo that persistently reside in periosteum and contribute to osteochondral elements during fracture repair. During the healing process, TGF‐β signalling is continually activated in the reparative Gli1+ periosteal cells. Conditional knockout of Tgfbr2 in these cells leads to a delayed and impaired enchondral bone formation, at least partially due to the reduced proliferation and chondrogenic and osteogenic differentiation of Gli1+ periosteal cells. Conclusions TGF‐β signalling plays an essential role on fracture repair via regulating enchondral bone formation process of Gli1+ periosteal cells.

Although osteoarthritis (OA) in the hip joint is a common and debilitating degenerative disease, the precise molecular mechanisms underlying its pathological process remains unclear. This study sets out to investigate whether β‐catenin plays a critical role in hip OA pathogenesis. Here, we showed overexpressed β‐catenin protein in human OA cartilage tissues. Then, we analyzed β‐cat(ex3) Col2ER mice, in which β‐catenin gene was conditionally activated in femoral head chondrocytes. At 2 months of age, β‐cat(ex3) Col2ER mice already showed a phenotype of severe cartilage degeneration in the femoral head. More changes observed in β‐cat(ex3) Col2ER mice with age included subchondral sclerosis and osteophyte formation along joint margins, resembling a hip OA phenotype in humans. In addition, cartilage degradation and chondrocyte apoptosis as the results of β‐catenin activation possibly contributed to this hip OA‐like phenotype. Overall our findings provide direct evidence about the importance of β‐catenin in hip OA pathogenesis.

No abstract