Tsc1 Regulates the Balance Between Osteoblast and Adipocyte Differentiation Through Autophagy/Notch1/β-Catenin...

Area of Science:

• Bone Biology
• Cellular Metabolism
• Molecular Endocrinology

Background:

• Osteoporosis is characterized by reduced bone mass and increased marrow adiposity.
• The molecular mechanisms linking these changes remain unclear.
• Tuberous sclerosis 1 (Tsc1) plays a role in cellular growth and metabolism.

Purpose of the Study:

• To investigate the role of Tsc1 in regulating bone homeostasis.
• To elucidate the molecular mechanisms by which Tsc1 deficiency affects bone marrow stromal cells (BMSCs).

Main Methods:

• Mice lacking Tsc1 in Osterix-expressing cells were used for in vivo studies.
• Tsc1-deficient BMSCs were analyzed for proliferation, differentiation, and signaling pathways in vitro.
• Western blotting and molecular assays were employed to study protein levels and signaling.

Main Results:

• Tsc1 deficiency in vivo led to decreased trabecular bone mass, reduced osteoblastogenesis, increased osteoclastogenesis, and increased marrow adiposity.
• In vitro, Tsc1-deficient BMSCs exhibited decreased proliferation, osteogenic differentiation, and increased adipogenic differentiation.
• This was associated with Wnt/β-catenin signaling downregulation, autophagy suppression, and increased Notch1, leading to GSK3β-independent β-catenin degradation.

Conclusions:

• Tsc1 is a critical regulator of the balance between osteoblast and adipocyte differentiation in BMSCs.
• Tsc1 deficiency disrupts bone homeostasis by promoting adipogenesis and inhibiting osteogenesis.
• The findings provide insights into the molecular mechanisms underlying osteoporosis and marrow fat accumulation.