Oxidative stress-induced, poly(ADP-ribose) polymerase-dependent upregulation of ET-1 expression in chronic diabetic complications

Hyperglycemia in diabetes induces increased endothelin-1 (ET-1) production in the retina, kidney, and heart that may lead to hemodynamic impairment, permeability alteration, and increased extracellular matrix (ECM) protein production. Chronically elevated blood glucose levels may cause oxidative stress in these target tissues of diabetic complications. Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme activated by DNA strand breaks due to oxidative stress. We investigated the role of PARP in regulating ET-1 expression and ET-1-induced abnormalities in the targets organs of diabetic complications. Male Sprague-Dawley rats were injected with streptozotocin to induce diabetes. Once diabetes was established, half of the diabetic rats were randomly chosen to receive PARP inhibitor 3-aminobenzamide for 4 months. In a second set of experiments, PARP(-/-) mice and their controls were fed for 2 months with either a normal rodent diet or a 30% galactose diet to induce a normoinsulinemic hyperhexosemic state. Tissues harvested at the conclusion of both experiments were then subjected to real-time RT-PCR analysis for mRNA expression and immunohistochemical assessrnent of oxidative stress. In both experiments, the hyperhexosernic state upregulated expression of ET-1 mRNA in the retina, kidney, and heart. Furthermore, upregulation of ET-1-dependent ECM transcripts, such as fibronectin and extradomain B-containing fibronectin, was noted in all tissues. These tissues also demonstrated oxidative stress, as evidenced by the presence of nuclei positive for 8-hydroxy-2'-deoxyguanosine. In contrast, inhibition of PARP, either through a chemical means in the diabetic rats or by genetic manipulation in the galactose-fed animals, prevented both oxidative stress and hyperhexoseinia-induced upregulation of these genes. These results suggest that, in diabetes, oxidative stress and PARP activation may produce their effects through ET-1. Hence, blockade of such pathways may constitute potential adjuvant treatment modalities in chronic diabetic complications.