Abstract T MP20: Histone Methylation Patterns in Astrocytes are Influenced by Age Following Ischemia
Introduction: In animal models, ischemia results in larger infarcts in middle-aged females as compared to adult females. This age difference in infarct severity is associated with reduced functional capacity of astrocytes, a critical support cell. Astrocytes from middle-aged females synthesize less IGF-1, a neuroprotective growth factor, and display reduced ability to clear glutamate. The impaired response of astrocytes following stroke in middle-aged females may be related to epigenetic alterations, including histone methylation, that occur during aging.
Hypothesis: We evaluated the hypothesis that astrocytes from middle-aged females would have a distinctive pattern of histone methylation following ischemia as compared to astrocytes from younger females, resulting in differential protein expression.
Methods: The middle cerebral artery was occluded in adult (6 month) and middle-aged (11+ month) female Sprague Dawley rats (n=9-15). Astrocytes were extracted from the ischemic hemisphere 48 hours after ischemia. ChIP-seq was used to measure H3K4 and H3K9 trimethylation (me3) across the genome. In a second set of astrocytes, the expression of genes/proteins with highly methylated promoters was measured with either qPCR or ELISA immunoassays (n=6-7).
Results: Adult females had more H3K4me3 peaks (912 vs 72) and fewer H3K9me3 (4 vs 22) peaks than middle-aged females. Increased H3K4me3 was found at promoters for genes encoding the mir17-20 cluster and vascular endothelial growth factor (VEGF). In agreement with the methylation data, astrocytes from adult females had higher protein levels of VEGF and greater expression of mir20 than middle-aged females (p<.05).
Conclusions: This study found more H3K4me3 and less H3K9me3 in astrocytes from adult females indicating a general increase in gene transcription following ischemia. Increased trimethylation of mir20 was accompanied with increased expression of mir20 in astrocytes from adult females. Importantly, trimethylation of lysine 4 on histone 3 results in increased gene transcription whereas mir20 negatively regulates translation. This complex interaction of epigenetic modifications provides insight into possible mechanisms for differences in stroke severity observed during aging.
Author Disclosures: N. Chisholm: None. A. Selvamani: None. M. Park: None. F. Sohrabji: Research Grant; Significant; AG042189.
- © 2015 by American Heart Association, Inc.