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-beta1 (TGF-beta(1)). Nitric oxide (NO) generally protects tissues from reperfusion injury.
Methods and results: We examined the modulation of TGF-beta1 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-beta1 (mRNA and protein) but a decrease in the release of active TGF-beta1. Myocyte PKC-alpha 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-beta1 increased and total TGF-beta1 expression decreased (all P<0.05 versus H-R alone). PKC-alpha 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-beta1 release increased, and total TGF-beta1 expression decreased.
Conclusions: These observations suggest modulation of TGF-beta1 expression as a novel mechanism of salutary effect of NO donors. PKC-alpha activation may play an important role in the protective effect of NO against H-R injury.