Telomerase Reverse Transcriptase Regulates Intracellular Ca2+ Homeostasis and Mitochondrial Function via the p53/PGC-1α Pathway in HL-1 Cells

Background: Telomere shortening is strongly associated with cardiovascular aging and disease, and patients with shorter telomeres in peripheral blood leukocytes are at higher risk of cardiovascular diseases such as heart failure and atrial fibrillation (AF). Telomerase Reverse Transcriptase (TERT) maintains telomere length, and overexpression of TERT has been shown to reduce cardiomyocyte Apoptosis and myocardial infarct size, and extend the lifespan of aged mice. However, the specific impact of TERT on the electrophysiology of cardiomyocytes remains to be elucidated. The aims of this study were to evaluate the role of TERT in Ca2+ homeostasis and mitochondrial function in atrial myocytes as well as the underlying mechanisms.

Methods: TERT overexpressed and silenced HL-1 cells were constructed with lentiviruses, and the respective empty lentiviral vectors were used as negative controls. Then the patch clamp technique was used to record the electrophysiological characteristics such as cell action potential duration (APD) and L-type Ca2+ currents (ICa,L), flow cytometry was used to detect intracellular Ca2+ concentration and mitochondrial membrane potential (MMP), and the Seahorse assay was used to measure the oxygen consumption rate (OCR).

Results: TERT silencing led to intracellular Ca2+ overload, shortened APD, decreased ICa,L current density, altered Ca2+ gating mechanism, decreased MMP and OCR, and increased Reactive Oxygen Species (ROS), whereas TERT overexpression led to the reverse effects. Additionally, TERT silencing resulted in intracellular Ca2+ overload with decreased expression of the SERCA2a, CaV1.2, and NCX1.1, whereas TERT overexpression had opposing effects. Furthermore, we discovered that TERT could regulate the expression of p53 and Peroxisome Proliferator-activated Receptor gamma coactivator 1-alpha (PGC-1α). The expression of PGC-1α was downregulated by the p53 agonist Tenovin-6 but upregulated by the p53 inhibitor PFTα. The effects of the PGC-1α inhibitor SR-18292 on intracellular Ca2+ and cell electrophysiology were similar to those of silencing TERT, whereas the PGC-1α agonist ZLN005 produced comparable outcomes to TERT overexpression.

Conclusions: TERT silencing-induced Ca2+ overload and mitochondrial dysfunction may be one mechanism of age-related AF. Overexpression of TERT reduced the basis for arrhythmia formation such as AF, suggesting a favorable safety profile for TERT therapy. TERT regulated intracellular Ca2+ homeostasis and mitochondrial function through the p53/PGC-1α pathway. In addition, PGC-1α might be a novel target for AF, suggesting that intervention for AF should be not limited to abnormal cation handling.

Ca2+ homeostasis; atrial fibrillation; electrophysiology; mitochondrial function; p53/PGC-1α pathway; telomerase reverse transcriptase.