No abstract

Redox imbalance is a primary cause for endothelial dysfunction (ED). Under oxidant stress, many critical proteins regulating endothelial function undergo oxidative modifications that lead to ED. Cellular levels of GSH, the primary reducing source in cells, can significantly regulate cell function via reversible protein thiol modification. N-Acetyl cysteine (NAC), a precursor for GSH biosynthesis, is beneficial for many vascular diseases; however, the detailed mechanism of these benefits is still not clear. From HPLC analysis, NAC significantly increases both cellular GSH and BH4 levels. Immunoblotting of eNOS and DUSP4, a dual-specificity phosphatase with a cysteine as its active residue, revealed that both enzymes are up-regulated by NAC. EPR spin-trapping further demonstrated that NAC enhances NO generation from cells. Long-term exposure to Cd2+ contributes to DUSP4 degradation and the uncontrolled activation of p38 and ERK1/2, leading to apoptosis. Treatment with NAC prevents DUSP4 degradation and protects cells against Cd2+-induced apoptosis. Moreover, the increased DUSP4 expression can redox regulate p38 and ERK1/2 pathways from hyper-activation, providing a survival mechanism against the toxicity of Cd2+. DUSP4 gene knockdown further supports the hypothesis that DUSP4 is an antioxidant gene, critical in the modulation of eNOS translation, and thus protects against Cd2+-induced stress. Depletion of intracellular GSH by BSO makes cells more susceptible to Cd2+-induced apoptosis. Pre-treatment with NAC prevents p38 over-activation and thus protects the endothelium from this oxidative stress. Therefore, the identification of DUSP4 activation by NAC provides a novel target for future drug design.

No abstract

Background: Redox imbalance is the primary cause for endothelial dysfunction (ED), obstructed blood flow, and subsequent heart attack and failure. Under oxidant stress, many critical proteins regulating endothelial function undergo oxidative modifications that lead to ED. Cellular levels of glutathione (GSH), the primary reducing source, can significantly regulate cell function via reversible protein thiol modification. N-Acetyl cysteine (NAC), a precursor for GSH biosynthesis, is beneficial for many vascular diseases; however, the detailed mechanism of these benefits is still not clear. Methods: We employed EPR spin-trapping, HPLC, fluorescent microscopy, immunoblotting, and qPCR of both in vitro and ex vivo experiments using either cultured cells or the Langendorff heart preparation. Results: NAC treatment increases NO generation from endothelial cells, as well as the enzyme and cofactor responsible for its production, ie eNOS and BH4. Interestingly, NAC treatment also increased the expression of DUSP4, an inducible nuclear dual-specificity phosphatase implicated in cardiovascular function. We hereby establish that DUSP4 redox modulates two important kinases (p38 and ERK1/2) of MAPK signaling pathways and provides protection against Cd2+-induced ROS damage as well as hypoxia-reoxygenation insult to endothelial cells. Furthermore, a four week oral NAC pre-treatment promotes DUSP4 both protein and mRNA expression in the rat myocardium and renders the heart less susceptible to ex vivo ischemia-reperfusion injury. Protein expression profiles in the myocardium closely mimic those observed with cultured endothelial cells. The infarct size of NAC-treated hearts is significantly reduced. The myocardial rate pressure product is much improved above vehicle treated rats. Conclusion: NAC serves as a direct antioxidant and as a regulator of transcription and translation of DUSP4, modulating the activity of its downstream effectors: ERK1/2 and p38, and thus protects against ROS-induced damage both in vitro and ex vivo. As such, NAC-derived drugs can provide a novel therapy to oxidant-induced diseases via the specific up-regulation of protective proteins such as DUSP4 and eNOS.