Dissection of telomere-independent functions of nuclear and mitochondrial Telomerase Reverse Transcriptase ex vivo and in vivo

• Applicants: Professor Dr. Joachim Altschmied; Professorin Dr. Judith Haendeler
• Subject Area: Cardiac and Vascular Surgery ; Biogerontology and Geriatric Medicine
• Term: from 2012 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226386019

• Final Report Year: 2017

Final Report Abstract

Over the last years, it has become evident that Telomerase Reverse Transcriptase (TERT) is expressed in all cells of the cardiovascular system and plays an important role in cardiovascular diseases as well as in aging processes. TERT is not only present in the nucleus, but also in the mitochondria of those cells. A drawback of all previous approaches to assess the functions of nuclear and mitochondrial TERT was, that these experiments were based on overexpression of nuclear and mitochondrially targeted TERT on a background of endogenous TERT or on cells and animals completely devoid of the protein. To unequivocally dissect the functions of TERT in the two organelles, we have created cells and mice, which express nuclear or mitochondrially localized TERT on an otherwise TERT-deficient background. In this project we found important differences, but also similarities, between nuclear and mitochondrially localized TERT in cells of the cardiovascular system and in whole animals. Nuclear as well as mitochondrial TERT can increase NO bioavailability in the endothelium. Furthermore, we observed no differences in endothelium-dependent vasodilation under basal conditions in adult, 6 months old mice, irrespective of the presence or localization of TERT. With respect to the differences, we found that mitochondrially localized TERT, but not nuclear TERT, reduces mitochondrial reactive oxygen species (ROS) production in fibroblasts. Furthermore, we have analyzed the ability of cardiac fibroblasts to differentiate into myofibroblasts, which is required after myocardial infarction to fill the gaps resulting from cardiomyocyte death. In this regard we analyzed e.g. upregulation of α Smooth Muscle Actin and Matrix Metalloproteinase 2, which are important steps in this differentiation and demonstrated that mitochondrial TERT is required and sufficient for cardiac fibroblasts to differentiate into myofibroblasts. Moreover, mitochondrially localized TERT, but not nuclear TERT, can improve respiration in isolated heart mitochondria, compared to TERT-deficient mice as well as to wildtype littermates. In an open chest model for ischemia reperfusion injury of the heart, adult, 6 months old TERT-deficient mice showed significantly increased infarct size com-pared to age-matched wildtype littermates. Strikingly, infarct size in animals containing TERT exclusively in the mitochondria was significantly smaller than in TERT-deficient mice. Moreover, there is a trend towards reduced infarct size in these mitoTERT mice also in comparison to wildtype animals. Thus, one could speculate that identifying strategies to enhance specifically mitochondrially localized, but not nuclear TERT, could serve as a potential therapeutic approach in myocardial infarction injury in humans.

Publications

• (2013). Unhealthy diet and ultrafine carbon black particles induce senescence and disease associated phenotypic changes. Exp Gerontol 48, 8-16
  Büchner, N., Ale-Agha, N., Jakob, S., Sydlik, U., Kunze, K., Unfried, K., Altschmied, J., and Haendeler, J.
  
• (2014) Cellular functions of the dual-targeted catalytic subunit of telomerase, telomerase reverse transcriptase - Potential role in senescence and aging. Exp Gerontol 56, 189-193
  Ale-Agha, N., Dyballa-Rukes, N., Jakob, S., Altschmied, J., Haendeler, J.
  
• (2014). Outfielders playing in the infield: functions of aging-associated "nuclear" proteins in the mitochondria. Curr Mol Med 14, 1247-1251
  Czypiorski, P., Altschmied, J., Rabanter, L.L., Goy, C., Jakob, S., and Haendeler, J.
  
• (2015) Endothelial cells in health and disease. Antioxid Redox Signal 22, 1209-1211
  Eckers, A., Haendeler, J.
  
• (2016). Role of Telomerase in the Cardiovascular System. Genes (Basel) 7
  Zurek, M., Altschmied, J., Kohlgrüber, S., Ale-Agha, N., and Haendeler, J.
  
• (2017) Nuclear factor (erythroid-derived 2)-like 2 and Thioredoxin-1 in atherosclerosis and ischemia/reperfusion injury in the heart. Antioxid Redox Signal 26, 630-644
  Jakobs, P., Serbulea, V., Leitinger, N., Eckers, A., Haendeler, J.
  
• (2017) Regulation of transcription factors by reactive oxygen species and nitric oxide in vascular physiology and pathology, Antioxid Redox Signal 26, 679-699
  Kohlgrüber, S., Upadhye, A., Dyballa-Rukes, N., McNamara, C.A., Altschmied, J.
  
• (2017) The anti-apoptotic properties of APEX1 in the endothelium require the first twenty amino acids and converge on Thioredoxin-1. Antioxid Redox Signal 26, 616-629
  Dyballa-Rukes, N., Jakobs, P., Eckers, A., Ale-Agha, N., Serbulea, V., Aufenvenne, K., Zschauer, T.C., Rabanter, L.L., Jakob, S., von Ameln, F., Eckermann, O., Leitinger, N., Goy, C., Altschmied, J., Haendeler, J.