Fibroblast growth factor 21 (FGF-21) is expressed in numerous tissues, including liver, brown adipose tissue, white adipose tissue and pancreas, circulating levels of FGF-21 are derived specifically from the liver in mice. FGF-21 stimulates glucose uptake in adipocytes but not in other cell types.
Serum FGF-21 levels were significantly increased in patients with type 2 diabetes mellitus (T2DM) which may indicate a role in the pathogenesis of T2DM. Elevated levels also correlate with liver fat content in non-alcoholic fatty liver disease and positively correlate with BMI in humans suggesting obesity as a FGF21-resistant state.