Active vitamin D protects against osteoporosis by promoting VDR-dependent CDK2 transcription and P27 degradation

Area of Science:

• Molecular biology
• Endocrinology
• Skeletal biology

Background:

• Osteoporosis is linked to low active vitamin D levels, but the underlying molecular mechanisms are not fully understood.
• Understanding how vitamin D influences bone health is crucial for developing effective osteoporosis treatments.

Purpose of the Study:

• To investigate the molecular mechanisms by which active vitamin D maintains skeletal homeostasis and prevents bone loss.
• To elucidate the role of vitamin D signaling in regulating bone marrow mesenchymal stem cells (BMSCs) and skeletal aging.

Main Methods:

• Utilized genetically modified mouse models with reduced active vitamin D production.
• Examined bone mass, skeletal aging, and osteogenic capacity in mice.
• Assessed proliferation, osteogenic differentiation, and molecular signaling in mouse and human BMSCs.
• Conducted gene expression, protein turnover, and pathway analyses to identify key regulatory pathways.
• Employed genetic deletion studies to test the functional role of P27 in bone loss.

Main Results:

• Active vitamin D activates a vitamin D receptor (VDR)-dependent pathway, increasing cyclin-dependent kinase 2 (CDK2) expression and promoting P27 degradation in BMSCs.
• Disruption of this pathway leads to P27 accumulation, reduced stem cell proliferation, impaired osteogenic differentiation, and accelerated skeletal aging, resulting in bone loss.
• Active vitamin D facilitates P27 phosphorylation and subsequent degradation via the ubiquitin-proteasome pathway.
• Deletion of P27 partially ameliorated the osteoporotic phenotype in mice with diminished active vitamin D production.

Conclusions:

• Active vitamin D is essential for maintaining bone integrity through a VDR-mediated mechanism that boosts CDK2 expression and P27 degradation in BMSCs.
• This study reveals a novel link between vitamin D signaling, skeletal aging, and stem cell function.
• Targeting P27 turnover presents a potential therapeutic strategy for osteoporosis, emphasizing the need for tissue-specific approaches to manage oncogenic risks.