Authors: Suryanarayan Biswal Debashree Das Kalpana Barhwal Ashish Kumar Tapas Chandra Nag Mahendra Kumar Thakur Sunil Kumar Hota Bhuvnesh Kumar
Publish Date: 2016/10/03
Volume: 54, Issue: 8, Pages: 6133-6147
Abstract
Exposure to global hypoxia and ischemia has been reported to cause neurodegeneration in the hippocampus with CA3 neurons This neuronal damage is progressive during the initial phase of exposure but maintains a plateau on prolonged exposure The present study on Sprague Dawley rats aimed at understanding the underlying molecular and epigenetic mechanisms that lead to hypoxic adaptation of CA3 neurons on prolonged exposure to a global hypoxia Our results show stagnancy in neurodegeneration in CA3 region beyond 14 days of chronic exposure to hypobaria simulating an altitude of 25000 ft Despite increased synaptosomal glutamate and higher expression of NR1 subunit of NMDA receptors we observed decrease in postsynaptic density and accumulation of synaptic vesicles at the presynaptic terminals Molecular investigations involving western blot and realtime PCR showed durationdependent decrease in the expression of SNAP25 resulting in reduced vesicular docking and synaptic remodeling ChIP assays for epigenetic factors showed decreased expression of H3K9Ac and H3K14Ac resulting in SNAP25 promoter silencing during prolonged hypoxia Administration of sodium butyrate a nonspecific HDAC inhibitor during 21 days hypoxic exposure prevented SNAP25 downregulation but increased CA3 neurodegeneration This epigenetic regulation of SNAP25 promoter was independent of increased DNMT3b expression and promoter methylation Our findings provide a novel insight into epigenetic factorsmediated synaptic remodeling to prevent excitotoxic neurodegeneration on prolonged exposure to global hypobaric hypoxia
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