Department of Anatomy, Biochemistry & Physiology, John A. Burns School of Medicine, University of Hawai'i at Manoa, HI, United States of America.
Department of Anatomy, Biochemistry & Physiology, John A. Burns School of Medicine, University of Hawai'i at Manoa, HI, United States of America; Department of Cardiology and Geriatrics, Kochi Medical School, Kochi University, Kochi, Japan.
Life Sci. 2019 Sep 1;232:116665. doi: 10.1016/j.lfs.2019.116665. Epub 2019 Jul 16.
Overexpression of the mechanistic target of rapamycin (mTOR), a member of the PIKK (phosphoinositide kinase-related kinase) family, protects cardiomyocytes from cell death induced by pathological stimuli such as ischemia. We previously reported that posttranslational modification of mTOR plays an important role in regulating cardiac mTOR expression. The aim of this study was to see if Tel2 (telomere maintenance 2), a protein that regulates the abundance of PIKKs, confers similar cardioprotective effects as mTOR. Tel2 is not well-characterized in cardiomyocytes, therefore we examined the effects of Tel2 on cardiomyocyte viability under ischemic stress conditions.
We overexpressed Tel2 or silenced Tel2 with siRNA in the HL-1 cardiomyocyte cell line to survey the effects of Tel2 overexpression and downregulation on cell survival during hypoxia. Adult mouse cardiomyocytes transfected with Tel2 adenoviruses were used to test whether Tel2 sufficiently prevented cardiomyocyte cell death against hydrogen peroxide (HO).
Overexpressing Tel2 increased mTOR expression with a concomitant increase in mTOR Complex 1 (mTORC1) and mTORC2 activity in HL-1 cells. Tel2 deletion decreased mTOR expression, and mTORC1 and mTORC2 activity accordingly. In both HL-1 cells and adult mouse cardiomyocytes, Tel2 overexpression protected cardiomyocytes under ischemic stress. These effects were mTOR-dependent, as mTOR inhibitors blunted the effects of Tel2. While gene silencing of Tel2 did not affect cell survival under normoxia, Tel2 silencing made cardiomyocytes more vulnerable to cell death under hypoxia.
Upregulating Tel2 expression increases mTOR-mediated cardiomyocyte survival and targeting Tel2 could be another therapeutic strategy against ischemic heart disease.
机械靶标雷帕霉素（mTOR）是 PIKK（磷脂酰肌醇激酶相关激酶）家族的成员，其过度表达可保护心肌细胞免受缺血等病理刺激引起的细胞死亡。我们之前的研究报告表明，mTOR 的翻译后修饰在调节心脏 mTOR 表达中起着重要作用。本研究的目的是观察调节 PIKK 丰度的蛋白质 Tel2 是否与 mTOR 具有相似的心脏保护作用。Tel2 在心肌细胞中的功能尚未得到充分表征，因此我们研究了 Tel2 在缺血应激条件下对心肌细胞活力的影响。
我们在 HL-1 心肌细胞系中过表达 Tel2 或用 siRNA 沉默 Tel2，以调查 Tel2 过表达和下调对缺氧期间细胞存活的影响。用 Tel2 腺病毒转染的成年小鼠心肌细胞用于测试 Tel2 是否足以防止心肌细胞因过氧化氢（HO）而死亡。
在 HL-1 细胞中，过表达 Tel2 增加了 mTOR 的表达，同时增加了 mTOR 复合物 1（mTORC1）和 mTORC2 的活性。Tel2 缺失降低了 mTOR 的表达，以及 mTORC1 和 mTORC2 的活性。在 HL-1 细胞和成年小鼠心肌细胞中，Tel2 过表达均可保护心肌细胞免受缺血应激。这些作用是 mTOR 依赖性的，因为 mTOR 抑制剂减弱了 Tel2 的作用。虽然 Tel2 的基因沉默在常氧条件下不影响细胞存活，但 Tel2 的沉默使心肌细胞在缺氧条件下更容易死亡。
上调 Tel2 表达可增加 mTOR 介导的心肌细胞存活，靶向 Tel2 可能是治疗缺血性心脏病的另一种策略。
