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‐Cre^ERT2 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‐CreER^T2;Rosa26‐tdTomato^flox/wt mice were sacrificed at different time points for tracing the fate of Gli1⁺ cells in both intact and fracture bone. Gli1‐CreER^T2‐mediated Tgfbr2 knockout (Gli1‐CreER^T2;Tgfbr2^flox/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‐Cre^ERT2 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.

TGF-β signaling is crucial for modulating osteoarthritis (OA), and protein phosphatase magnesium–dependent 1A (PPM1A) has been reported as a phosphatase of SMAD2 and regulates TGF-β signaling, while the role of PPM1A in cartilage homeostasis and OA development remains largely unexplored. In this study, we found increased PPM1A expression in OA chondrocytes and confirmed the interaction between PPM1A and phospho-SMAD2 (p-SMAD2). Importantly, our data show that PPM1A KO substantially protected mice treated with destabilization of medial meniscus (DMM) surgery against cartilage degeneration and subchondral sclerosis. Additionally, PPM1A ablation reduced the cartilage catabolism and cell apoptosis after the DMM operation. Moreover, p-SMAD2 expression in chondrocytes from KO mice was higher than that in WT controls with DMM induction. However, intraarticular injection with SD-208, repressing TGF-β/SMAD2 signaling, dramatically abolished protective phenotypes in PPM1A-KO mice. Finally, a specific pharmacologic PPM1A inhibitor, Sanguinarine chloride (SC) or BC-21, was able to ameliorate OA severity in C57BL/6J mice. In summary, our study identified PPM1A as a pivotal regulator of cartilage homeostasis and demonstrated that PPM1A inhibition attenuates OA progression via regulating TGF-β/SMAD2 signaling in chondrocytes and provided PPM1A as a potential target for OA treatment.

Articular cartilage degeneration plays a key role in the pathogenesis of osteoarthritis (OA). Bushenhuoxue formula (BSHXF) has been widely used in the treatment of OA in clinics. However, the molecular mechanisms responsible for the chondroprotective effect of BSHXF remain to be elucidated. The purpose of this study was to explore the effects of BSHXF on OA mice model. In this study, we investigated the effects of BSHXF on destabilization of the medial meniscus (DMM)-induced chondrocyte degradation in OA mice model. At 12 weeks post-surgery, the joints were harvested for tissue analyses, including histology, histomorphometry, TUNEL, OARSI scoring, micro-CT and immunohistochemistry for COL2, TGFBR2, pSMAD2 and MMP13. Additionally, we also evaluated the effects of BSHXF on Mmp13 mRNA and protein expression in chondrogenic ATDC5 cells through real-time PCR and Western blot respectively. Moreover, we investigated the chondroprotective effect of BSHXF on mice with Tgfbr2 conditional knockout (Tgfbr2 Col2ER mice) in chondrocyte, including the relative experiments mentioned above. We transfected Tgfbr2 siRNA in ATDC5 to further evaluate the changes of Mmp13 mRNA and protein expression followed by BSHXF treatment. Amelioration of cartilage degradation and chondrocyte apoptosis were observed in DMM-induced mice, with increases in cartilage area and thickness, proteoglycan matrix, COL2 content and decreases in OARSI score at 12 weeks post surgery. Moreover, the elevated TGFBR2 and pSMAD2, and reduced MMP13 positive cells were also revealed in DMM-induced mice treated with BSHXF. Besides, decreased Mmp13 mRNA and protein expression were observed inchondrogenic ATDC5 cells culture in serum containing BSHXF. As expected, Tgfbr2 Col2ER mice exhibited significant OA-like phenotype. Interestingly, obvious improvement in articular cartilage structure was still observed in Tgfbr2 Col2ER mice after BSHXF treatment via up-regulated pSMAD2 and down-regulated MMP13 expressional levels in articular cartilage. BSHXF could inhibit cartilage degradation through TGF-β/MMP13 signaling, and be considered a good option for the treatment of OA.

Osteoarthritis (OA) is a common disease characterized by cartilage degeneration. In recent years much attention has been paid to Traditional Chinese Medicine (TCM) since its treatments have shown efficacy for ameliorating cartilage degradation with mild side effects. Osteoking is a TCM prescription that has long been used in OA treatment. However, the exact mechanism of Osteoking are not fully elucidated. In the current study, destabilization of the medial meniscus (DMM)-induced OA mice was introduced as a wild type animal model. After 8 weeks of administration of Osteoking, histomorphometry, OARSI scoring, gait analysis, micro-CT, and immunohistochemical staining for Col2, MMP-13, TGFβRII and pSmad-2 were conducted to evaluate the chondroprotective effects of Osteoking in vivo. Further in vitro experiments were then performed to detect the effect of Osteoking on chondrocytes. TGFβRII^Col2ER transgenic mice were constructed and introduced in the current study to validate whether Osteoking exerts its anti-OA effects via the TGF-β signaling pathway. Results demonstrated that in wild type DMM mice, Osteoking ameliorated OA-phenotype including cartilage degradation, subchondral bone sclerosis, and gait abnormality. Col2, TGFβRII, and pSmad-2 expressions were also found to be up-regulated after Osteoking treatment, while MMP-13 was down-regulated. In vitro, the mRNA expression of MMP-13 and ADAMTS5 decreased and the mRNA expression of Aggrecan, COL2, and TGFβRII were up-regulated after the treatment of Osteoking in IL-1β treated chondrocytes. The additional treatment of SB505124 counteracted the positive impact of Osteoking on primary chondrocytes. In TGFβRII^Col2ER mice, spontaneous OA-liked phenotype was observed and treatment of Osteoking failed to reverse the OA spontaneous progression. In conclusion, Osteoking ameliorates OA progression by decelerating cartilage degradation and alleviating subchondral bone sclerosis partly via the TGF-β signaling pathway.

Bushenhuoxue formula (BSHXF) has shown excellent clinical effects on the treatment of osteoporosis in China. The aim of this study is to determine the anti-osteoporosis effects and precise molecular mechanisms of BSHXF on mouse models. Ten-week-old female C57BL/6 J mice were subjected to ovariectomy and provided a daily treatment of BSHXF. At 8 weeks post-surgery, the femurs were harvested for tissue analyses including μCT, histology, qRT-PCR and immunohistochemical (IHC) staining of β-catenin, ALP and FABP4. To investigate the role of β-catenin in the anti-osteoporosis effects of BSHXF, relative experiments mentioned above were performed in β-catenin conditional knockout mice. Ovariectomized (OVX) mice presented severe bone loss and excessive fat accumulation in the chondro-osseous junction underneath the growth plate, with decreased expression of ALP and increased expression of FABP4. BSHXF significantly recovered the OVX-induced abnormal osteogenesis and adipogenesis with the activation of β-catenin in growth plate chondrocytes. Further, we generated growth plate chondrocyte-specific β-catenin knockout (β-cateninGli1ER) mice that exhibited bone loss and fat accumulation in the chondro-osseous junction, similar to the OVX mice. However, BSHXF failed to rescue the osteoporosis-like phenotype in β-cateninGli1ER mice, indicating the anti-osteoporosis effects of BSHXF act mainly through β-catenin signaling. No significant restoration of ALP and FABP4 was observed in β-cateninGli1ER mice after the treatment of BSHXF. BSHXF attenuates osteoporosis by promoting osteogenic differentiation of growth plate chondrocytes mainly in β-catenin-dependent manner. BSHXF is considered as a new candidate for the treatment of osteoporosis.

Osteoarthritis (OA) is a globally prevalent degenerative joint disease. Recent studies highlight the role of ferroptosis in OA progression. Targeting ferroptosis regulation presents a promising therapeutic strategy for OA; however, current research primarily focuses on single targets associated with ferroptosis. In this study, a reactive oxygen species (ROS)‐responsive nanoparticle is developed by linking deferasirox (DEF) and pterostilbene (PTE) with thioketal and incorporating cerium ions (Ce), creating Ce@D&P nanoparticles (NPs), which offer multitarget regulation of ferroptosis. The characteristics of Ce@D&P NPs are evaluated and their therapeutic effects on IL‐1β‐stimulated chondrocytes are verified. Results show that Ce@D&P NPs reduce ROS levels, mitigate inflammation, chelate iron to inhibit ferroptosis, and balance extracellular matrix (ECM) metabolism in chondrocytes. Mechanistically, transcriptomics and metabolomics analyses suggest that Ce@D&P NPs exerted their effects by regulating oxidative stress and lipid metabolism in chondrocytes. To better treat destabilization of the medial meniscus (DMM)‐induced OA in mice, Ce@D&P NPs via intra‐articular injection are delivered. The results show that Ce@D&P NPs alleviate cartilage matrix damage and slow OA progression. Overall, the findings indicate that Ce@D&P NPs represent a promising multitarget drug delivery system, and Ce@D&P NPs may be an effective strategy for OA treatment.