title: Histone methylation patterns in astrocytes are influenced by age following ischemia.
abstract: In animal models, middle-aged females sustain greater ischemia-induced infarction as compared to adult females. This age difference in infarct severity is associated with reduced functional capacity of astrocytes, a critical neural support cell. The impaired response of astrocytes following stroke in middle-aged females may be related to epigenetic alterations, including histone acetylation or methylation. The present study measured the activity of enzymes that regulate histone acetylation and methylation in cerebral cortical astrocytes of adult (6 month) and middle-aged (11+ month) female rats 48 h following middle cerebral artery occlusion. H3K4 histone methyltransferase activity was decreased in astrocytes from middle-aged females. The next experiment therefore examined H3K4me3 (transcriptional enhancer) and H3K9me3 (transcriptional repressor) in astrocytes from adult and middle-aged females using ChIP-seq analysis. Adult females had more enriched H3K4me3 peaks (304 vs. 26) at transcriptional start sites and fewer H3K9me3 enriched peaks than middle-aged females (4 vs. 22), indicating a pattern of less active chromatin in astrocytes in the older group following ischemia. DAVID clustering analysis of H3K4me3 enriched genes found several functional categories, including cell motility, regulation of apoptosis and the vascular endothelial growth factor (VEGF) pathway. H3K4me3 was enriched at the miR-17-20 cluster and VEGFa, and analysis of a separate set of astrocytes confirmed that VEGF protein expression and miR-20 mRNA expression were significantly greater following ischemia in adult females compared to middle-aged females. These data indicate that astrocytes display less active chromatin with aging and provide new insight into possible mechanisms for differences in stroke severity observed during aging.
authors.affiliation: a Women's Health in Neuroscience Program; Department of Neuroscience and Experimental Therapeutics; Texas A & M Health Science Center College of Medicine ; Bryan , TX USA ;
authors.forename: Nioka C
authors.initials: NC
authors.lastname: Chisholm
authors.forename: Michael L
authors.initials: ML
authors.lastname: Henderson
authors.forename: Amutha
authors.initials: A
authors.lastname: Selvamani
authors.forename: Min Jung
authors.initials: MJ
authors.lastname: Park
authors.forename: Scott
authors.initials: S
authors.lastname: Dindot
authors.forename: Rajesh C
authors.initials: RC
authors.lastname: Miranda
authors.forename: Farida
authors.initials: F
authors.lastname: Sohrabji
mesh_terms: D000107:Acetylation; D000123:Acetyltransferases / Q000378:metabolism; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002545:Brain Ischemia / Q000378:metabolism*; D002540:Cerebral Cortex / Q000098:blood supply / Q000166:cytology / Q000378:metabolism*; D005260:Female; D006657:Histones / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D017207:Rats, Sprague-Dawley
chemical_list: D006657:Histones; D008780:Methyltransferases; D000123:Acetyltransferases; D008239:Lysine
keywords: BCA, bicinchoninic acid; ChIP, chromatin immunoprecipitation; DNA, deoxyribonucleic acid; DNMT1, DNA methyltransferase 1; DTT, Dithiothreitol; FDR, false discovery rate; GFAP, glial fibrillary acidic protein; GLAST, glutamate–aspartate transporter; GLT-1, glial glutamate transporter 1; H3K4, histone 3 lysine 4; H3K4me3; H3K9, histone 3 lysine 9; HAT, histone acetyltransferase; HBSS, hank's balanced salt solution; HDAC; HDAC, histone deacetyltransferase; IGF-1, insulin-like growth factor-1; Iba-1, ionized calcium binding adaptor molecule 1; MACS, model-based analysis of ChIP-seq; NeuN, neuronal nuclei; PECAM, platelet endothelial cell adhesion molecule; SICER, spatial clustering for identification of ChIP-enriched regions; SIRT, sirtuin; VEGF, vascular endothelial growth factor, mRNA; acetylation; aging; epigenetics; histone 3 lysine 4 trimethylation; me3, trimethylation; messenger ribonucleic acid; qPCR, quantitative polymerase chain reaction; stroke; transcription