Reddy Marpadga A, Villeneuve Louisa M, Wang Mei, Lanting Linda, Natarajan Rama
Department of Diabetes, Beckman Research Institute of City of Hope, Duarte, CA 91010, USA.
Circ Res. 2008 Sep 12;103(6):615-23. doi: 10.1161/CIRCRESAHA.108.175190. Epub 2008 Aug 7.
Insulin resistance and type 2 diabetes are major risk factors for vascular complications. Vascular smooth muscle cells (VSMCs) derived from db/db mice, an established mouse model of type 2 diabetes, displayed enhanced inflammatory gene expression and proatherogenic responses. We examined the hypothesis that aberrant epigenetic chromatin events may the underlying mechanism for this persistent dysfunctional behavior and "memory" of the diabetic cells. Chromatin immunoprecipitation assays showed that levels of histone H3 lysine 4 dimethylation (H3K4me2), a key chromatin mark associated with active gene expression, were significantly elevated at the promoters of the inflammatory genes monocyte chemoattractant protein-1 and interleukin-6 in db/db VSMCs relative to db/+ cells. Tumor necrosis factor-alpha-induced inflammatory gene expression, H3K4me2 levels, and recruitment of RNA polymerase II at the gene promoters were also enhanced in db/db VSMCs, demonstrating the formation of open chromatin poised for transcriptional activation in diabetes. On the other hand, protein levels of lysine-specific demethylase1 (LSD1), which negatively regulates H3K4 methylation and its occupancy at these gene promoters, were significantly reduced in db/db VSMCs. High glucose (25 mmol/L) treatment of human VSMCs also increased inflammatory genes with parallel increases in promoter H3K4me2 levels and reduced LSD1 recruitment. LSD1 gene silencing with small interfering RNAs significantly increased inflammatory gene expression and enhanced VSMC-monocyte binding in nondiabetic VSMCs. In contrast, overexpression of LSD1 in diabetic db/db VSMCs inhibited their enhanced inflammatory gene expression. These results demonstrate novel functional roles for LSD1 and H3K4 methylation in VSMCs and inflammation. Dysregulation of their actions may be a major mechanism for vascular inflammation and metabolic memory associated with diabetic complications.
胰岛素抵抗和2型糖尿病是血管并发症的主要危险因素。源自db/db小鼠（一种已确立的2型糖尿病小鼠模型）的血管平滑肌细胞（VSMC）表现出增强的炎症基因表达和促动脉粥样硬化反应。我们检验了这样一种假设，即异常的表观遗传染色质事件可能是这种持续性功能失调行为以及糖尿病细胞“记忆”的潜在机制。染色质免疫沉淀分析表明，相对于db/+细胞，在db/db VSMC中，与活跃基因表达相关的关键染色质标记物组蛋白H3赖氨酸4二甲基化（H3K4me2）在炎症基因单核细胞趋化蛋白-1和白细胞介素-6的启动子处水平显著升高。肿瘤坏死因子-α诱导的炎症基因表达、H3K4me2水平以及RNA聚合酶II在基因启动子处的募集在db/db VSMC中也增强了，这表明在糖尿病中形成了易于转录激活的开放染色质。另一方面，赖氨酸特异性去甲基化酶1（LSD1）的蛋白水平在db/db VSMC中显著降低，LSD1负向调节H3K4甲基化及其在这些基因启动子处的占据。用高糖（25 mmol/L）处理人VSMC也增加了炎症基因，同时启动子H3K4me2水平升高且LSD1募集减少。用小干扰RNA沉默LSD1基因显著增加了非糖尿病VSMC中的炎症基因表达并增强了VSMC与单核细胞的结合。相反，在糖尿病db/db VSMC中过表达LSD1抑制了它们增强的炎症基因表达。这些结果证明了LSD1和H3K4甲基化在VSMC和炎症中的新功能作用。它们作用的失调可能是与糖尿病并发症相关的血管炎症和代谢记忆的主要机制。
