Interplay of microRNA‐503 and N‐acetylcysteine in regulating hypoxia‐reoxygenation injury in cardiomyocyte H9C2 cells

Abstract

microRNAs(miRs) are involved in many cardiovascular diseases including myocardial ischemia / reperfusion injury (IRI). Myocardial IRI can lead to oxidative stress, many miRs are regulated in response to oxidative stress. N‐acetylcysteine (NAC) –a known antioxidant, is reported to have protective effects against myocardial IRI. Previously, we and others observed that cardiac miR‐503 was down‐regulated during myocardial IRI in vivo in rodents or in cardiomyocyte H9C2 cells subjected to hypoxia and reoxygenation (H/R). This study is aimed to explore the interplay of miR503 and NAC in the regulation of hypoxia‐reoxygenation injury and possible molecular mechanisms in cardiomyocyte H9C2 cells. Here, H9C2 cells were subjected to hypoxia for 10 hours followed by reoxygenation 6 hours as simulated myocardial IRI. Results showed that cell viability was decreased and lactate dehydrogenase (LDH) activity was increased upon H/R; Pretreatment with NAC (1mM) to H9C2 cells for 30 hours can improve cell viability and reduce LDH activity in both normoxia and H/R states, while pretreatment with NAC (2mM) decreased cell viability and increased LDH activity. We also found that NAC (1mM) can down‐regulate miR‐503 expression level in H9C2 cells subjected to normoxia, it also down‐regulated miR‐503 expression level upon H/R. In order to inhibit endogenous miR‐503, H9C2 cells was transfected with Antagomir‐503, inhibition of miR‐503 can improve cell viability and reduce LDH activity upon H/R; Western blotting results showed that there was no significant difference among control, HR, HR+negative control of Antagomir‐503(NC) or HR+Antagomir‐503 groups for proapoptotic Bax protein, while anti‐apoptotic Bcl2 protein was increased after transfection of Antagomir‐503 compared with HR+NC. Target‐Scan software showed that Phosphoinositide‐3‐kinase, regulatory subunit 1(PI3K p85) is one of miR‐503 target genes, and P85 protein was decreased after H/R, but it was increased significantly after administration of Antagomir‐503, its down‐stream protein phospho‐AKT (Thr450) was also significantly increased. However, Antagomir‐503 and NAC (1mM) used in combination to H9C2 cells upon H/R, did not provide an additional advantage in protecting cell injury. It is concluded that administration of NAC (1mM) or Antagomir‐503 alone can alleviate cell injury, while the combination of NAC (1mM) and Antagomir‐503 has no synergistic cytoprotective effects, the possible molecular mechanisms need to be further explored.Support or Funding InformationSupported by Hong Kong RGC(17158616 M) and HMRF (05161826)grants.