1896-P: Adipocyte-Derived Fibroblast Growth Factor 21 (FGF21) Contributes to Circulating FGF21 Pools in Diet-Induced Obese Mice

Fibroblast growth factor 21 (FGF-21) is a hormone derived from hepatocytes and adipocytes that plays a role in energy homeostasis, and promotes weight loss when given pharmacologically. Nutritional stress such as fasting increases liver-derived FGF-21 expression, whereas over-nutrition (i.e., obesity) promotes adipocyte-derived FGF-21 (Ad-FGF-21) production. Despite the current dogma that Ad-FGF-21 acts only in a paracrine manner, obesity is associated with elevated circulating FGF-21 levels which correlate with adiposity and adipose tissue FGF-21 mRNA expression. To date, a concise role for Ad-FGF-21 in obesity-associated energy balance has not been identified. To determine whether Ad-FGF-21 plays a pathological role in obesity, and whether it contributes to circulating FGF-21 levels, we generated mice with Ad-FGF-21 deficiency (Ad-FGF-21 KO) and placed them on an obesogenic high fat high sucrose diet for 18 weeks. Body composition, energy expenditure, glucose and insulin tolerance were assessed. Male and female Ad-FGF-21 KO mice were protected from obesity, gained less body fat, and exhibited improved glucose metabolism over wild type (WT) controls. Circulating FGF-21 levels were higher in obese WT mice than age-matched chow-fed WT or obese Ad-FGF-21 KO mice with no changes in hepatic FGF-21, suggesting that adipocytes are a source of FGF-21 in obesity. Moreover, adipose tissue explants from obese WT mice secreted higher levels of FGF-21 than explants from chow-fed mice, an effect that was blunted in Ad-FGF-21 KO mice. Finally, expression of fibroblast activation protein (FAP), an enzyme that cleaves FGF-21 to blunt its activity, was reduced from obese adipose tissue, providing a potential mechanism by which adipocyte-derived FGF-21 circulates in obesity.

In summary, adipocyte-derived FGF-21 may contribute to obesity-associated increases in circulating FGF-21, with the potential to influence the pathology of obesity.