Abstract 113: Nuclear Translocation of Neuronal Histone Deacetylase 4 (HDAC4) is Detrimental in Stroke

Abstract

HDAC4 has been identified as a transcriptional corepressor that catalyzes local histone deacetylation. It is highly expressed in neurons and usually trapped in cytosol. In vitro, translocation of HDAC4 from cytosol into nucleus induced neuronal death in response to glutamate toxicity. Here we assessed the hypothesis that accumulation of nuclear HDAC4 occurs after stroke, this translocation is detrimental in stroke outcome and regulated by calcium/calmodulin-dependent protein kinase IV (CaMK IV). Wild type (WT) and CaMK IV knockout (KO) mice were subjected to transient middle cerebral artery occlusion and were sacrificed 6 hours for molecule assessments or 72 hours post stroke for outcome assessments. Primary cortical neurons underwent oxygen-glucose deprivation (OGD) and viability was measured 24 hours after OGD. Lentiviral vectors were utilized in culture and mice. Stroke induced HDAC4 nuclear translocation in WT mice as assessed by both Western blots and immunohistochemistry. Knockdown of HDAC4 improved cell viability after OGD (HDAC4 SiRNA: 87.19±7.57% vs. control: 68.09±3.83%, p<0.05, n=6). Expression of a nuclear restricted HDAC4 mutant (Nuc) reduced cell viability after OGD (p<0.05), in contrast, no effect was seen for a cytoplasmic mutant HDAC4 (Cyto) (Nuc: 50.32±1.36% and Cyto: 68.95±2.17% vs. GFP control: 73.25±1.28%, n=6). In vivo nuclear HDAC4 mutant expression increased hemispheric infarcts (Nuc: 57.54±1.67% vs. Cyto: 36.98±3.26%) and worsened mice performance in rotarod test (Nuc: 12.38±3.50 seconds vs. Cyto: 33.65±2.98 seconds) compared with expression of cytoplasmic HDAC4 mutant after stroke (p<0.05, n=8-10). Percentage of nuclear HDAC4 positive neurons in penumbra was increased in CaMK IV KO mice (KO: 66.28±4.28% vs. WT: 37.08±2.44%, p<0.05, n=4) when compared to WT after stroke. Finally, overexpression of CaMK IV increased neuronal viability after OGD; however, this effect was lost when HDAC4 was inhibited by SiRNA. In conclusion, we showed that ischemia induces HDAC4 nuclear shuttling in neurons and this translocation is deleterious in stroke outcome. Our data suggested CaMK IV inhibits HDAC4 nuclear accumulation in stroke.