Chisholm Nioka C, Henderson Michael L, Selvamani Amutha, Park Min Jung, Dindot Scott, Miranda Rajesh C, Sohrabji Farida
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 ;
Epigenetics. 2015;10(2):142-52. doi: 10.1080/15592294.2014.1001219. Epub 2015 Feb 3.
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.
在动物模型中，与成年雌性相比，中年雌性遭受更大的缺血性梗死。梗死严重程度的这种年龄差异与星形胶质细胞（一种关键的神经支持细胞）功能能力下降有关。中年雌性中风后星形胶质细胞反应受损可能与表观遗传改变有关，包括组蛋白乙酰化或甲基化。本研究测量了成年（6个月）和中年）和中年（11个月以上）雌性大鼠大脑中动脉闭塞48小时后，调节大脑皮质星形胶质细胞中组蛋白乙酰化和甲基化的酶的活性。中年雌性星形胶质细胞中H3K4组蛋白甲基转移酶活性降低。因此，接下来的实验使用ChIP-seq分析检查了成年和中年雌性星形胶质细胞中的H3K4me3（转录增强子）和H3K9me3（转录抑制子）。成年雌性在转录起始位点有更多富集的H3K4me3峰（304个对26个），且比中年雌性有更少的H3K9me3富集峰（4个对22个），表明老年组缺血后星形胶质细胞中染色质活性较低的模式。对H3K4me3富集基因的DAVID聚类分析发现了几个功能类别，包括细胞运动、凋亡调节和血管内皮生长因子（VEGF）途径。H3K4me3在miR-17-20簇和VEGFa处富集，对另一组星形胶质细胞的分析证实，与中年雌性相比，成年雌性缺血后VEGF蛋白表达和miR-20 mRNA表达显著更高。这些数据表明，随着年龄增长，星形胶质细胞显示出染色质活性降低，并为衰老过程中观察到的中风严重程度差异的可能机制提供了新的见解。
