Abstract 1686: Mitochondrial Telomerase Reverse Transcriptase Binds to and Protects Mitochondrial DNA from Damage
Telomerase prevents aging and is important for synthesis and maintenance of telomere length in the nucleus. The catalytic subunit, the telomerase reverse transcriptase (TERT), has recently been detected in the mitochondria. Therefore, the aim of this study was to investigate the import mechanism and the functional role of mitochondrially localized TERT. TERT is imported into the mitochondria via the translocase of outer membrane 20 (Tom20) and the translocase of inner membrane 23 (Tim 23). After establishing a modified chromatin immunoprecipitation assay using mitochondrial specific primers to detect mtDNA bound to immunoprecipitated TERT and a modified EMSA specific for mitochondrial DNA, we verified that TERT binds to mitochondrial DNA at the coding region for ND1 and ND2 of complex I of the respiratory chain. To get further insights into the functional role of mitochondrial DNA bound TERT, we in vitro transcribed and translated TERT and coincubated TERT with mitochondrial DNA prior to UV light damaging. Binding of TERT to mitochondrial DNA protects against UV light induced damage (53 +/− 5 % rescue of mitochondrial DNA from damage). The binding and protection of mitochondrial DNA by TERT in vitro is independent of its reverse transcriptase activity. However, serum-induced respiratory chain activity is only increased in cells overexpressing TERTwt, but not by overexpressing the reverse transcriptase dead mutant TERT(D868A) (TERTwt: 2.3 +/− 0.4; TERT(D868A): 0.95 +/− 0.8 fold increase in activity). TERTwt, but not TERT(D868A) reduced ethidiume bromide-induced formation of reactive oxygen species in mitochondria. Next, we cloned TERT into a mitochondrial- as well as nuclear-targeted vector to exclusively overexpress TERT in the mitochondria or in the nucleus. Strikingly, mitochondrially targeted TERT revealed the most prominent protective effect on H2O2-induced apoptosis (TERTnuc: 31 +/− 4 %; TERTmito: 51 +/− 3 % inhibition compared to TERTwt). These data demonstrate that mitochondrial TERT exerts a novel, protective function by binding to mitochondrial DNA, increasing respiratory chain activity, reducing mitochondrially produced reactive oxygen species and, thereby, protecting against oxidative stress- and UV-induced damage.