Hyperglycemia upregulates translation of the fibroblast growth factor 2 mRNA in mouse aorta via internal ribosome entry site

Fibroblast growth factor 2 (FGF-2) is normally synthesized at low levels but is elevated in various pathophysiological conditions including diabetes-associated vascular diseases. FGF-2 expression is regulated translationally through an internal ribosome entry site (IRES) located in its mRNA, which allows a nonclassical cap-independent translation. We addressed the pathophysiological regulation of the IRES in vivo by using a streptozotocin-induced hyperglycemic model known to suppress markedly overall translation. Evaluation of FGF-2 IRES-dependent translation was performed with transgenic mice expressing dual luciferase bicistronic mRNA containing the FGF-2 IRES. FGF-2 IRES-dependent reporter activity increased 240% of control in the diabetic aorta although the reporter mRNA levels significantly decreased. Expression of endogenous FGF-2 protein in the aorta closely correlated with the IRES activity but not with FGF-2 mRNA levels. Moreover, the biosynthesis of endogenous FGF-2 protein was stimulated in an IRES-dependent manner by high glucose that significantly suppressed global protein synthesis in aortic smooth muscle cells from the transgenic mice. These results suggest that IRES-dependent translational regulation could play a pathological role in FGF-2 expression in vivo, especially in the cardiovascular consequences of diabetes.