PPARG in osteocytes controls sclerostin expression, bone mass, marrow adiposity and mediates TZD-induced bone loss

Area of Science:

• Endocrinology
• Bone Biology
• Metabolic Regulation

Background:

• Peroxisome proliferator activated receptor gamma (PPARG) is a nuclear receptor crucial for energy metabolism and insulin sensitivity.
• Emerging evidence suggests a link between metabolic regulation and bone mass maintenance.
• Osteocytes, the most abundant cells in bone, play a critical role in bone remodeling and mechanosensing.

Purpose of the Study:

• To investigate the role of PPARG in osteocyte function and its regulation of sclerostin production.
• To explore the connection between PPARG-mediated energy metabolism and bone mass.
• To evaluate the therapeutic potential of targeting PPARG in osteocytes for osteoporosis treatment.

Main Methods:

• Generation of an osteocyte-specific PPARG knockout mouse model (γOT^KO).
• Analysis of bone mass, bone marrow adiposity, WNT signaling, and osteoblast activity in γOT^KO mice.
• Assessment of SOST/sclerostin transcript and protein levels in osteocytes.
• Pharmacological activation of PPARG using rosiglitazone and evaluation of TZD-induced bone loss.

Main Results:

• Osteocyte-specific PPARG deletion led to increased bone mass and reduced bone marrow adiposity.
• PPARG was found to be essential for sclerostin production in osteocytes, with a strong correlation between PPARG and SOST/sclerostin expression.
• The promoter region of the Sost gene contains PPARG binding elements, indicating direct transcriptional regulation.
• γOT^KO mice were protected from TZD-induced bone loss, demonstrating the pharmacologic relevance of PPARG in osteocytes.

Conclusions:

• Transcriptional activity of PPARG is critical for sclerostin expression in osteocytes.
• Targeting PPARG in osteocytes represents a promising therapeutic strategy for osteoporosis.
• The study supports the conjunction between energy metabolism regulation and bone mass maintenance through PPARG signaling.