Glucosylceramide synthase regulates adipo???osteogenic differentiation through synergistic activation of PPAR?? with GlcCer

Dysregulation of the adipo-osteogenic differentiation balance of mesenchymal stem cells (MSCs), which are common progenitor cells of adipocytes and osteoblasts, has been associated with many pathophysiologic diseases, such as obesity, osteopenia, and osteoporosis. Growing evidence suggests that lipid metabolism is crucial for maintaining stem cell homeostasis and cell differentiation; however, the detailed underlying mechanisms are largely unknown. Here, we demonstrate that glucosylceramide (GlcCer) and its synthase, glucosylceramide synthase (GCS), are key determinants of MSC differentiation into adipocytes or osteoblasts. GCS expression was increased during adipogenesis and decreased during osteogenesis. Targeting GCS using RNA interference or a chemical inhibitor enhanced osteogenesis and inhibited adipogenesis by controlling the transcriptional activity of peroxisome proliferator-activated receptor gamma (PPAR gamma). Treatment with GlcCer sufficiently rescued adipogenesis and inhibited osteogenesis in GCS knockdown MSCs. Mechanistically, GlcCer interacted directly with PPAR gamma through A/B domain and synergistically enhanced rosiglitazone-induced PPAR gamma activation without changing PPAR gamma expression, thereby treatment with exogenous GlcCer increased adipogenesis and inhibited osteogenesis. Animal studies demonstrated that inhibiting GCS reduced adipocyte formation in white adipose tissues under normal chow diet and high-fat diet feeding and accelerated bone repair in a calvarial defect model. Taken together, our findings identify a novel lipid metabolic regulator for the control of MSC differentiation and may have important therapeutic implications