Exendin-4 differentially modulates essential functions of human dermal fibroblasts under normoglycemic and hyperglycemic conditions.

Abstract

Evidence that exendin-4, a glucagon-like peptide-1 analog, might be used to treat poorly healing wounds under diabetic and nondiabetic conditions has gained increasing interest. Little is known, however, about the effects of the drug on the production by dermal fibroblasts of key extracellular matrix and regulatory compounds. Therefore, we used human skin fibroblasts cultured in normo- (1 g/l = 5.6 mmol/l glucose) or hyperglycemic (4.5 g/l = 25 mmol/l glucose) culture medium to test the effects of exendin-4 (0 - 100 nmol/l) on fibroblast functions crucial for the wound healing process. Exendin-4 increased the proliferative and metabolic activities, as measured by the BrdU (bromodeoxyuridine) and MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assays, respectively, of fibroblasts cultured in normoglycemic medium. Under hyperglycemic conditions, the drug had no effect on proliferation and reduced metabolic fibroblast activity. Exendin-4 decreased metalloproteinase-9 (MMP-9) secretion in the normoglycemic milieu only and increased tissue inhibitor of metalloproteinase-1 (TIMP-1) concentration in fibroblast colonies under both normo- and hyperglycemic experimental conditions. Exendin-4 increased the fibroblast growth factor-1 (FGF-1) concentration in cell colonies maintained in the normoglycemic milieu but decreased FGF-1 release when fibroblasts were grown in hyperglycemic medium. High glucose caused lactic dehydrogenase (LDH) leakage when compared with normoglycemic conditions, and exendin-4 was not able to prevent this effect, although it reduced LDH release from fibroblasts cultured in normoglycemic medium. Finally, exendin-4 increased glycosaminoglycan (GAG) content under both experimental conditions. Our results indicate that exendin-4 effects on the production of the extracellular matrix and regulatory proteins differ in human skin fibroblasts exposed to either normal or high glucose. In general, the beneficial effects of the drug, which may be important for the improvement of wound healing, are more pronounced under normoglycemic conditions, thus indicating that hyperglycemia attenuates the positive effects of exendin-4 on fibroblasts.