Nuclear accumulation of histone deacetylase 4 (HDAC4) by PP1-mediated dephosphorylation exerts neurotoxicity in Pb-exposed neural cells

Lead (Pb) is an environmental contaminant that primarily affects the central nervous system, particularly the developing brain. Recently, increasing evidence indicates the important roles of histone deacetylases (HDACs) in Pb-induced neurotoxicity. However, the precise molecular mechanisms involving HDAC4 remains unknown. The purpose of this study was to investigate the role of HDAC4 in Pb-induced neurotoxicity both in vivo and in vitro. In vitro study, PC12 cells were exposed to Pb (10 mu M) for 24 h, then the mRNA and protein levels of HDAC4 were analyzed. In vivo study, pregnant rats and their female offspring were treated with lead (50 ppm) until postnatal day 30. Then the pups were sacrificed and the mRNA and protein levels of HDAC4 in the hippocampus were analyzed. The results showed that HDAC4 was significantly increased in both PC12 cells and rat hippocampus upon Pb exposure. Blockade of HDAC4 with either LMK-235 (an inhibitor of HDAC4) or shHDAC4 (HDAC4-knocking down plasmid) ameliorated the Pb-induced neurite outgrowth deficits. Interestingly, HDAC4 was aberrantly accumulated in the nucleus upon Pb exposure. By contrast, blocking the HDAC4 shuffling from the cytosol to the nucleus with Delta NLS2-HDAC4 (the cytosol-localized HDAC4 mutant) was able to rescue the neuronal impairment. In addition, Pb increased PP1 (protein phosphatase 1) expression which in turn influenced the subcellular localization of HDAC4 by dephosphorylation of specific serine/threonine residues. What's more, blockade of PP1 with PP1-knocking down construct (shPP1) ameliorated Pb-induced neurite outgrowth deficits. Taken together, nuclear accumulation of HDAC4 by PP1-mediated dephosphorylation involved in Pb-induced neurotoxicity. This study might provide a promising molecular target for medical intervention with environmental cues.