Background: Histone deacetylase (HDAC) enzymes inhibit gene expression through chromatin compaction and exacerbate myocyte death following ischemia-reperfusion (IR) in the heart. In our prior study, disinhibition of antioxidant gene and protein expression was achieved through 24 hour pretreatment with entinostat, a class I HDAC inhibitor, and was correlated with improved heart contractile recovery from IR. Additionally, ERK1/2 was phosphorylated, indicating activation of the reperfusion injury survival kinase (RISK) pathway. HDAC inhibitors also enhance posttranslational acetylation of nonhistone proteins through unmasking of acetyltransferase activity, which may influence heart survival from injury.
Hypothesis: We hypothesized that inhibition of class I HDACs during reperfusion in postischemic hearts would activate the RISK pathway and improve contractile recovery.
Methods: Hearts from male Sprague-Dawley rats (n=4/group) were isolated and perfused in Langendorff mode. Global ischemia was induced by cessation of perfusion for 30 min, followed by 60 min of reperfusion, during which hearts were perfused with vehicle or 10, 100 or 1000 nM entinostat. Results are reported vs vehicle as mean±SE.
Results: At the end of reperfusion, rate pressure product (mm hg/min) was improved with 10 nM entinostat (17226±1187, p<0.001) vs vehicle (11024±1810), as were +dP/dtmax, -dP/dtmax, and developed pressure. The improvement in pressure development with 10 nM entinostat was due primarily to prevention of end diastolic dysfunction in reperfusion. LV function was not significantly preserved in hearts treated with 100 or 1000 nM entinostat. Hearts reperfused with 10 nM entinostat showed reduced infarct area (35%) vs vehicle (64%), along with increased shuttling of 14-3-3 protein, Akt and phospho-ERK from cytoplasm to nucleus. These effects were reduced with higher concentrations of inhibitor. Notably, histone acetylation was increased with higher concentrations of entinostat, but not with 10 nM.
Conclusions: Inhibition of class I HDACs during reperfusion resulted in specific activation of RISK members without acetylation of histone, indicating that acetyltransferase enzymes may mediate activation of pro-survival kinases in the IR heart.