Molecular determinants of FGF‐21 activity—synergy and cross‐talk with PPARγ signaling

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Abstract
Fibroblast growth factor (FGF)‐21 is a novel regulator of insulin‐independent glucose transport in 3T3‐L1 adipocytes and has glucose and triglyceride lowering effects in rodent models of diabetes. The precise mechanisms whereby FGF‐21 regulates metabolism remain to be determined. Here we describe the early signaling events triggered by FGF‐21 treatment of 3T3‐L1 adipocytes and reveal a functional interplay between FGF‐21 and peroxisome proliferator‐activated receptor gamma (PPARγ) pathways that leads to a marked stimulation of glucose transport. While the early actions of FGF‐21 on 3T3‐L1 adipocytes involve rapid accumulation of intracellular calcium and phosphorylation of Akt, GSK‐3, p70S6K, SHP‐2, MEK1/2, and Stat3, continuous treatment for 72 h induces an increase in PPARγ protein expression. Moreover, chronic activation of the PPARγ pathway in 3T3‐L1 adipocytes with the PPARγ agonist and anti‐diabetic agent, rosiglitazone (BRL 49653), enhances FGF‐21 action to induce tyrosine phosphorylation of FGF receptor‐2. Strikingly, treatment of cells with FGF‐21 and rosiglitazone in combination leads to a pronounced increase in expression of the GLUT1 glucose transporter and a marked synergy in stimulation of glucose transport. Together these results reveal a novel synergy between two regulators of glucose homeostasis, FGF‐21 and PPARγ, and further define FGF‐21 mechanism of action. J. Cell. Physiol. 210: 1–6, 2007.