Fibroblast growth factor 21 protects the heart from apoptosis in a diabetic mouse model via extracellular signal-regulated kinase 1/2-dependent signalling pathway

This study investigated fibroblast growth factor 21 (FGF21)-mediated cardiac protection against apoptosis caused by diabetic lipotoxicity and explored the protective mechanisms involved. Cardiac Fgf21 mRNA expression was examined in a diabetic mouse model using real-time PCR. After pre-incubation of palmitate-treated cardiac H9c2 cells and primary cardiomyocytes with FGF21 for 15 h, apoptosis and Fgf21-induced cell-survival signalling were investigated using small interfering (si)RNA and/or pharmacological inhibitors. We also examined the cardiac apoptotic signalling and structural and functional indices in wild-type and Fgf21-knockout (Fgf21-KO) diabetic mice. In a mouse model of type 1 diabetes, cardiac Fgf21 expression was upregulated about 40-fold at 2 months and 3–1.5-fold at 4 and 6 months after diabetes. FGF21 significantly reduced palmitate-induced cardiac apoptosis. Mechanistically, palmitate downregulated, but FGF21 upregulated, phosphorylation levels of extracellular signal-regulated kinase (ERK)1/2, mitogen-activated protein kinase 14 (p38 MAPK) and AMP-activated protein kinase (AMPK). Inhibition of each kinase with its inhibitor and/or siRNA revealed that FGF21 prevents palmitate-induced cardiac apoptosis via upregulating the ERK1/2-dependent p38 MAPK–AMPK signalling pathway. In vivo administration of FGF21, but not FGF21 plus ERK1/2 inhibitor, to diabetic or fatty-acid-infused mice significantly prevented cardiac apoptosis and reduced inactivation of ERK1/2, p38 MAPK and AMPK and prevented cardiac remodelling and dysfunction. The Fgf21-KO mice were more susceptible to diabetes-induced cardiac apoptosis, and this could be prevented by administration of FGF21. Deletion of Fgf21 did not further exacerbate cardiac dysfunction. These results demonstrate that FGF21 prevents lipid- or diabetes-induced cardiac apoptosis by activating the ERK1/2–p38 MAPK–AMPK pathway. FGF21 may be a therapeutic target for the treatment of diabetes-related cardiac damage.