Hyperglycemia enhances adipogenic induction of lipid accumulation: involvement of extracellular signal-regulated protein kinase 1/2, phosphoinositide 3-kinase/Akt, and peroxisome proliferator-activated receptor gamma signaling

The molecular events of hyperglycemia-triggered increase in adipogenic induction of lipid accumulation remain unclear. We examined the effects of hyperglycemia on adipogenic induction of lipid accumulation and its involved signaling molecules, such as phosphoinositide 3-kinase (PI3K), ERKs, and peroxisome proliferator-activated receptor gamma (PPAR gamma). Bone marrow-derived mesenchymal stem cells (MSCs) isolated from FVB/N mice were capable of differentiating into adipocytes in adipogenic medium. The effects of high glucose (HG) (25.5 mm) were assessed in vitro by RT-PCR, ELISA, flow cytometry, immunostaining, and immunoblotting. The in vivo effect of hyperglycemia was further studied in streptozotocin (STZ)-induced diabetic FVB/N mice. Exposure of MSCs to HG enhanced adipogenic induction of lipid accumulation as compared with 5.5 mm glucose. HG increased PPAR gamma expression and PI3K activity and its downstream effector Akt phosphorylation during adipogenesis. Inhibition of PI3K/Akt activity with PI3K inhibitor LY294002 or by expressing the dominant negative p85 or Akt prevented the HG-enhanced PPAR gamma-dependent adipogenic induction of lipid accumulation. Moreover, HG increased the phosphorylation of ERK1/2 during adipogenesis. MAPK/ERK inhibitor PD98059 inhibited the PI3K activity, Akt phosphorylation, and lipid accumulation triggered by HG. PI3K inhibitor LY294002 did not affect the HG-increased ERK1/2 phosphorylation during adipogenesis. We next observed that adipogenic induction of lipid accumulation of MSCs isolated from STZ-induced diabetic mice is enhanced. Moreover, triglyceride, PPAR gamma expression, phosphorylated Akt and ERK1/2, and marrow fat in bones of STZ-diabetic mice were also increased. These results suggest that hyperglycemia enhances the adipogenic induction of lipid accumulation through an ERK1/2-activated PI3K/Akt-regulated PPAR gamma pathway.