DUSP4 Is the Key Protein Modulating Cardiovascular Function in Response to NAC Pre-Treatment

Our previous work on the redox activation of DUSP4 by NAC in endothelial cells demonstrated that DUSP4 is an antioxidant protein, critical in the modulation of MAPK signal pathways and eNOS expression by protecting against oxidant-induced stress. More recently, we demonstrated that DUSP4 -/- mouse hearts suffer greater infarct than wild-type (WT) and have poor post-ischemic functional recovery when subjected to ischemia/reperfusion (I/R) injury. DUSP4 is an inducible nuclear phosphatase whose main function is to regulate MAPKs (ERK, JNK and p38) via dephosphorylation, and it has been demonstrated to be important for cardiovascular function. In this designed study, DUSP4 -/- mouse is used to test that DUSP4 is the critical gene in response to NAC activation, which provides a beneficial effect against oxidant stress. WT or DUSP4 -/- mice were first treated with NAC for two weeks, and subsequently hearts were isolated and subjected to 30 min ischemia and 30 min reperfusion. At the end of reperfusion period, the rate pressure product (RRP %) and coronary flow (CF %) were recorded to evaluate the functional recovery. The result indicated that WT hearts with NAC pre-treatment have a better functional recovery in both RPP (24.2% ± 7.7% vs 13.8% ± 2.9%) and CF (57.0% ±9.2% vs 36.8% ±2.8%) compared to non-treated WT hearts. However, DUSP4 -/- hearts with NAC treatment exhibited poor functional recovery (lower in RPP (5.1% ± 1.0% s 3.0% ±1.8%) and CF (33.8% ±1.5% vs 27.2 ±2.7%)) after I/R compared to DUSP4 -/- hearts without NAC treatment. Thus, these results further support our hypothesis that the activation of DUSP4 by NAC is important against I/R injury. From immunoblotting analysis, the results revealed that eNOS is up-regulated in WT hearts after two weeks of NAC treatment; however, eNOS is down-regulated in DUSP4 -/- hearts in response to NAC treatment. These results are consistent with the functional changes (RPP % and CF %) post-ischemia. Therefore, DUSP4 plays a critical role in response to NAC treatment against oxidant stress via the activation of eNOS for post-ischemic functional recovery, and is a potential target for the treatment of the oxidant-induced cardiovascular diseases.