Dengshun Miao

Previous studies have suggested that Bmi1 is a positive regulator of osteoblast formation and osteogenesis, while p27 is a negative regulator. Mice lacking p27 display larger mandibles which accompanied with the upregulated Bmi1. To clarify the interaction between p27 and Bmi1 in alveolar bone formation, we compared the mandible phenotypes of homozygous p27-deficient (p27 ^−/− ) mice, homozygous Bmi1-deficient (Bmi1 ^−/− ) mice, double homozygous p27 and Bmi1-deficient (p27 ^−/− Bmi1 ^−/− ) mice to those of their wild-type (WT) littermates at 4 weeks of age by radiograph, histochemistry and immunohistochemistry. Results showed the mandible mineral density, alveolar bone volume, cortical thickness, osteoblast number and surface, type I collagen positive area were all increased obviously in p27 ^−/− mice compared to WT mice, which implied p27 deletion activated alveolar bone formation. However, these parameters were decreased significantly in Bmi1 ^−/− and p27 ^−/− Bmi1 ^−/− mice compared to WT mice and similar between Bmi1 ^−/− and p27 ^−/− Bmi1 ^−/− mice. To explain the phenomenon of Bmi1 deficiency blocking p27 deletion induced active alveolar bone formation, Sonic hedgehog N-Terminus Protein (Shh-N) and Shh antagonist KAAD-cyclopamine were treated with the bone marrow mesenchymal stem cells (BMSCs) derived from alveolar bone in vitro. Bmi1 deletion blocked the cell proliferation and osteogenic effect of Shh agonist on BMSCs in vitro. In conclusion, this study indicated that Bmi1 was an essential effect molecule of p27-Shh signaling in regulation of alveolar bone formation which provided new evidence on alveolar bone anabolic action.

Objective: Osteoporosis is associated with reduced active vitamin D, but the molecular basis remains incompletely understood. This study investigated how active vitamin D preserves skeletal homeostasis and prevents bone loss. Design: Experimental mechanistic study using genetically modified mouse models and bone marrow mesenchymal stem cells (BMSCs). Methods: Mice with reduced active vitamin D production were examined for bone mass, skeletal aging, and osteogenic capacity. Mouse and human BMSCs were used to assess proliferation, osteogenic differentiation, and molecular signaling. Gene expression, protein turnover, and pathway analyses determined how active vitamin D regulates cell-cycle control in skeletal progenitors. Genetic deletion studies tested the functional contribution of P27 to bone loss. Results: Active vitamin D protected against osteoporosis by activating a vitamin D receptor (VDR)-dependent pathway that increased cyclin-dependent kinase 2 (CDK2) expression and promoted P27 degradation in BMSCs. Loss of this signaling caused P27 accumulation, reduced stem-cell proliferation, impaired osteogenic differentiation, and enhanced skeletal senescence, leading to bone loss. Active vitamin D promoted P27 phosphorylation at threonine 187 and its degradation via the ubiquitin-proteasome pathway. Importantly, P27 deletion partially rescued the osteoporotic phenotype in mice with reduced active vitamin D production. Conclusions: Active vitamin D maintains bone integrity through a VDR-dependent mechanism that enhances CDK2 expression and promotes P27 degradation in BMSCs. These findings identify a previously unrecognized mechanism linking vitamin D signaling to skeletal aging and suggest that targeting P27 turnover may offer a therapeutic strategy, provided tissue-specific approaches mitigate the oncogenic risks of P27 manipulation.

Osteoarthritis (OA) is a widespread chronic joint disorder characterized by progressive cartilage degeneration, leading to substantial impairment in qualit

Background: Vitamin D is essential for skeletal health, but its role in redox homeostasis and cellular senescence during aging in vivo is unclear. We therefore investigated whether active vitamin D insufficiency accelerates bone loss via oxidative stress and senescence pathways. Methods: Male wild-type (WT) and Cyp27b1 haploinsufficient mice (modeling vitamin D insufficiency) were treated with N-acetylcysteine (NAC) or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Double-mutant p16-/-Cyp27b1+/- mice were used to assess the role of the tumor suppressor protein p16. Mice were maintained until 8 months of age in a specific pathogen-free facility. Outcomes included lifespan (n = variable per group, monitored daily); generation of oxidative stress (determined by serum malondialdehyde [MDA] levels via assay kit); generation of bone reactive oxygen species [ROS] (determined via flow cytometry), development of DNA damage (indicated by 8-hydroxy-2′-deoxyguanosine [8-OHdG] and γ-H2A.X generation and determined via immunohistochemistry and Western blot); and senescence (assessed by generation of β-galactosidase [β-gal], p16, and senescence-associated secretory phenotype [SASP] cytokines as determined via staining, blot, and real-time reverse transcription polymerase chain reaction). Additionally, bone microarchitecture was examined via micro-computed tomography and histomorphometry. Data from at least 5 mice per group were analyzed using unpaired Student’s t-test for two-group comparisons and two-way analysis of variance for multi-group comparisons, with significance at p < 0.05. Results: Compared with wild-type controls, Cyp27b1+/- mice showed a significantly shorter lifespan, higher oxidative stress, greater DNA damage, increased senescence markers, and lower trabecular bone volume (all p < 0.05). In Cyp27b1+/- mice, treatment with either N-acetylcysteine or 1,25(OH)2D3 significantly improved survival, reduced oxidative stress and DNA damage, attenuated senescence markers, and increased bone volume relative to untreated Cyp27b1+/- mice (p < 0.05 for all relevant comparisons; n = 5 per group). Genetic deletion of p16 in Cyp27b1+/-mice similarly increased bone volume and reduced senescence-associated readouts compared with Cyp27b1+/- controls (p < 0.05; n = 5). Conclusions: Active vitamin D insufficiency accelerates skeletal aging in vivo through a pathway involving reactive oxygen species-DNA damage-p16/senescence-associated secretory phenotype. Antioxidants, vitamin D repletion, or p16 inhibition rescued bone loss, highlighting redox-senescence axes as potential therapeutic targets for osteoporosis.

Background: Osteoarthritis (OA) is a prevalent chronic joint disease characterized by progressive cartilage degeneration, significantly impairing quality of life for millions worldwide. Cellular senescence has emerged as a pivotal driver of OA pathogenesis, with senescent chondrocytes exhibiting a senescence-associated secretory phenotype that exacerbates tissue degradation. Long non-coding RNAs (lncRNAs) play critical roles in cartilage homeostasis, yet their regulatory mechanisms in OA remain incompletely understood. This study aimed to investigate the expression patterns, biological functions, and underlying mechanisms of lncRNA HOXC-AS3 in chondrocyte biology and OA pathogenesis. Results: LncRNA HOXC-AS3 was significantly downregulated in both OA cartilage tissues and IL-1β-treated human chondrocytes. Functional experiments demonstrated that HOXC-AS3 knockdown inhibited chondrocyte proliferation, promoted cellular senescence, and caused extracellular matrix imbalance, while its overexpression effectively reversed IL-1β-induced chondrocyte dysfunction. Mechanistic investigations revealed that HOXC-AS3 functions through dual molecular mechanisms: serving as a competing endogenous RNA by directly binding to miR-615-3p, and interacting with ribosome-binding protein 1 (RRBP1). Both mechanisms converged to regulate the expression of citron rho-interacting serine/threonine kinase (CIT), a key cell cycle regulator. Notably, CIT knockdown recapitulated the cellular phenotypes observed with HOXC-AS3 deficiency, while HOXC-AS3 overexpression rescued chondrocyte function by maintaining CIT expression levels even under inflammatory conditions. Conclusions: Our study identifies lncRNA HOXC-AS3 as a critical regulator of chondrocyte homeostasis that protects against OA progression through novel dual mechanisms: miR-615-3p sponging and RRBP1 interaction, both converging to maintain CIT expression. These findings not only enhance our understanding of the complex regulatory networks underlying OA pathogenesis but also highlight HOXCAS3 and its downstream effectors as potential therapeutic targets for OA treatment.