The effects of Tel2 on cardiomyocyte survival

Aims: 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.

Materials and methods: 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 (H₂O₂).

Key findings: 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.

Significance: Upregulating Tel2 expression increases mTOR-mediated cardiomyocyte survival and targeting Tel2 could be another therapeutic strategy against ischemic heart disease.