Numerical data underlying graphs.

Telomerase Reverse Transcriptase (TERT), in addition to its well-known role in telomere lengthening, also has non-canonical functions, including gene regulation and protection against apoptosis. Beyond its nuclear functions, it is now recognized for its presence inside mitochondria. However, the biological role of TERT in mitochondrial physiological activity, with its specific mechanism of action, still needs to be clarified. This work clearly demonstrates the presence of TERT inside the mitochondrion under physiological conditions, in different cellular contexts, both with endogenous and ectopic TERT expression, and regardless of the presence of telomerase RNA counterpart TERC. TERT was shown to bind mitochondrial DNA, influencing mitochondrial replication and transcription. Furthermore, electron microscopy analysis of morphology revealed TERT-induced fragmentation of the mitochondrial network. Collectively, our findings suggest that TERT may play a role in regulating mitochondrial biogenesis and dynamics, and influencing processes such as fission and mitophagy, essential for maintaining mitochondrial homeostasis and closely connected to cellular states.