Protection of Myocytes From Hypoxia-Reoxygenation Injury by Nitric Oxide Is Mediated by Modulation of Transforming Growth Factor-β 1

Abstract

Background — Reoxygenation injury is a result of several complex events, including release of reactive oxygen species, protein kinase C (PKC) activation, and altered expression of transforming growth factor-β 1 (TGF-β 1 ). Nitric oxide (NO) generally protects tissues from reperfusion injury. Methods and Results — We examined the modulation of TGF-β 1 expression and activity and PKC activation in cultured rat heart myocytes exposed to a brief period of hypoxia-reoxygenation (H-R) by NO donor 3-morpholino-sydnonimine (SIN-1). H-R resulted in an increased expression of total TGF-β 1 (mRNA and protein) but a decrease in the release of active TGF-β 1 . Myocyte PKC-α protein level was not altered by H-R, but its phosphorylation was augmented. Pretreatment of myocytes with SIN-1 diminished myocyte injury quantified as lactate dehydrogenase release. Simultaneously, release of active TGF-β 1 increased and total TGF-β 1 expression decreased (all P <0.05 versus H-R alone). PKC-α phosphorylation increased further in cells treated with SIN-1. The effects of SIN-1 were blocked by the NO scavenger phenyl-tetramethyl-imidazoline-oxyl-oxide as well as by the PKC inhibitor staurosporine. To examine if another NO donor would have a similar effect, cardiomyocytes were treated with nitroglycerin before H-R. With nitroglycerin treatment, similar to SIN-1 treatment, myocyte injury was diminished, TGF-β 1 release increased, and total TGF-β 1 expression decreased. Conclusions — These observations suggest modulation of TGF-β 1 expression as a novel mechanism of salutary effect of NO donors. PKC-α activation may play an important role in the protective effect of NO against H-R injury.