Zn2+跨膜转运异常在腹主动脉瘤发病中的作用和机制研究

Abdominal aortic aneurysm (AAA) is characterized by degradation of medial elastic layer with aortic rupture being the major cause of death. Unfortunately, no efficient drug therapy is presently available for this grave vascular disease. Surprisingly, we have previously shown that TRPM7 channel-mediated slight Zn2+ influx significantly enhanced the activation and transcription of extracellular matrix-degrading enzyme --- MMP (matrix metalloproteinase). We were inspired to embark on investigating Zn2+ transporters in AAA given that it is Zn2+ transporter protein that plays central roles in Zn2+ transmembrane transport. Our preliminary data showed that during AAA: 1) increased Zn2+ entry in vascular smooth muscle was due to enhanced ZIP6 function; 2) interestingly, the increase in ZIP6 function was not attributable to elevated ZIP6 expression, but rather was associated with ZIP6 homodimerization and AMPK α2-mediated phosphorylation. We thus hypothesized that ZIP6-mediated Zn2+ influx activated MMP and enhanced its expression through Zn2+-sensitive transcription factor --- MTF1, consequently degrading medial extracellular matrix and compromising medial integrity. ZIP6 knockout mice and AAA patient samples will be employed to explore the role of aberrant Zn2+ transport in the pathogenesis of AAA and dissect the underlying mechanisms. This study will provide novel insights into the pathogenesis of AAA and evaluate if ZIP6 could be therapeutically exploited to treat AAA.

腹主动脉瘤（abdominal aortic aneurysm，AAA）以中膜弹力层破坏为特征病理改变，血管破裂是主要死因；危害极大但有效药物防治靶点匮乏。申请人前期意外发现TRPM7通道介导少量锌离子（Zn2+）内流，但显著增强金属基质蛋白酶（MMP）活性与表达。受此启发且由于转运体是Zn2+跨膜转运的核心方式，本研究因此聚焦Zn2+转运体，首次发现AAA时：①血管平滑肌锌内流增强与ZIP6转运功能增强密切相关；②有意思的是，ZIP6功能增强与表达变化无关，而ZIP6同源二聚体化及AMPKα2介导的磷酸化可能是关键原因。因此假设：AAA时ZIP6介导锌内流增强，活化MMP或促进表达，降解中膜基质破坏结构。拟利用ZIP6基因敲除小鼠与病人标本多手段探讨Zn2+跨膜转运异常在AAA发病中的作用和机制。本研究将从“Zn2+失稳态”新角度为AAA发病机制提供新见解，评估靶向ZIP6的治疗学意义。

腹主动脉瘤（Abdominal aortic aneurysm, AAA）以中膜弹力层破坏为主要病理特征，危害大但发病机制未阐明、药物治疗手段缺乏。金属基质蛋白酶（MMP）是AAA致病关键酶，其结构维持和活化依赖锌离子（Zn2+）。本研究以“锌离子跨膜转运异常”为切入点，探讨锌离子转运体在AAA发病过程中的作用和机制。实验发现，除表达于细胞质膜的ZIP6外，另一类质膜表达的ZIP8及内质网膜表达的ZIP7均是AAA时胞浆内锌离子浓度升高的重要来源。ZIP6同源二聚体化增强锌离子跨膜转运，促进转录因子MTF1核转位，增强pro-MMP2转录。正致力于构建内皮特异性（ZIPfl/fl;Tie2-Cre）、血管平滑肌特异性（ZIPfl/fl;Myh11-CreERT2）、巨噬细胞特异性ZIP敲除（ZIPfl/fl;Lyz2-Cre）敲除小鼠品系，并进一步获得Apoe-/-背景小鼠，将复制CaCl2或AngII诱导的模型以确证锌转运体在AAA中的作用。多项GWAS提示ZIP8基因多样性与心血管疾病密切相关，但与AAA的关系不清楚。本研究已构建ZIP8A391T/+小鼠，拟从临床线索出发探究ZIP8多样性与AAA间的因果关系。衰老是AAA最重要的危险因素，本研究初步探讨了离子转运在衰老过程中的变化，为后期研究衰老与AAA间的关系积累经验。实验发现血管衰老时Trpm7表达与功能上调，促进血管平滑肌细胞向炎症表型转化，血管疾病易感性升高。本研究将全面论证锌离子转运体介导的离子稳态失衡在AAA发病中的关键作用，为确证AAA防治新靶点提供实验依据。本研究已标注发表论文4篇，共资助10名研究生开展学位论文，其中3名已毕业。