Abstract W P107: HDAC4 Shuttling in Interneurons and Pyramidal Neurons is Associated with Improved Axonal Density and Myelination after Stroke

Abstract

Background: We have previously demonstrated that stroke induces nuclear shuttling of histone deacetylase 4 (HDAC4) in neurons during stroke recovery. Further examination of the distribution of HDAC4 shuttling in interneurons and pyramidal neurons may provide new insights into mechanisms of HDAC4 mediated neuronal circuitry remodeling after stroke. In the current study, we measured nuclear shuttling of HDAC4 in these two populations of neurons in the peri-infarct cortical layers after stroke. Methods: Adult male Wistar rats (n=6/group) were subjected to permanent middle cerebral artery occlusion (MCAO) and sacrificed at 2 or 14 days after MCAO. Sham operated rats were used as a control. Double immunohistochemistry was performed with antibodies against HDAC4 along with microtubule-associated protein 2 (MAP2, neurons), parvalbumin (PV, interneurons), Ctip2 (pyramidal neurons), phosphorylated neurofilament heavy chain (pNFH, axons) and myelin basic protein (MBP, myelination). Results: HDAC4 nuclear immunoreactivity in MAP2+ neurons of the normal cortex was evenly distributed throughout the upper (L1-4) and lower cortical layers (L5-6). Stroke significantly (p<0.05) increased the percentage of neurons with nuclear HDAC4 in L5-6 at 2 (37%) and 14 days (73%) compared to sham (19%), whereas in L1-4, a significant increase in neurons with nuclear HDAC4 was detected only at 14 days after MCAO (49% vs 17%). Among neurons, stroke significantly increased the number of Ctip2+ and PV+ neurons with nuclear HDAC4 in L5-6 at 2 (Ctip2 57%, PV 66%) and 14 days after stroke (Ctip2 73%, PV 74%) compared to sham (Ctip2 33%, PV 12%). Furthermore, in L5-6, but not in L1-4, nuclear HDAC4 shuttling was positively and significantly correlated with increased axons and myelination as determined by pNFH (r = 0.84, p<0.05) and MBP (r = 0.76, p<0.05) densities, respectively. Conclusion: Stroke induces nuclear shuttling of HDAC4 in pyramidal neurons and interneurons of layers 5-6 of the peri-infarct cortex which is strongly correlated with enhanced axonal density and myelination, suggesting a role for HDAC4 in promoting pyramidal neuron and interneuron axon remodeling during stroke recovery.