Non-canonical Telomerase Reverse Transcriptase Controls Osteogenic Differentiation of Aortic Valve Cells Through STAT5

Abstract: Background: Calcific aortic valve disease (CAVD) is the pathological remodeling of the valve leaflets which leads to heart failure and high stroke risk. While several mechanisms are known to drive cardiovascular calcification, the initial steps orchestrating the osteogenic reprogramming of cells are not fully understood. Non-canonical functions of telomerase reverse transcriptase (TERT) include service as a cofactor to stimulate gene transcription, and TERT overexpression primes mesenchymal stem cells to differentiate into osteoblasts. We investigated whether TERT contributes to osteogenic reprogramming of valve interstitial cells. Methods: Baseline transcription of TERT and osteogenic markers, senescence, DNA damage, and telomere length in valve tissue and primary aortic valve interstitial cells (VICs) from control and CAVD patients were assessed. TERT expression was depleted in cells using lentiviral vectors. Cells from Tert+/+ and Tert-/- mice were used to validate human findings. Immunofluorescence staining, proximity ligation assay, and chromatin immunoprecipitation assay were used in mechanistic experiments. Results: TERT protein was highly expressed in calcified valve leaflets, without changes in telomere length, DNA damage, or senescence. These phenotypic features were retained in primary VICs isolated and cultured from those diseased tissues. TERT levels were increased with osteogenic or inflammatory stimuli, and genetic deletion or reduction of TERT prevented calcification of VICs isolated from humans and mice. Similar results were seen in smooth muscle cells (SMCs) and mesenchymal stem cells (MSCs). TERT and Signal Transducer and Activator of Transcription 5A/B (STAT5) colocalize and bind to the Runt-Related Transcription Factor 2 (RUNX2) gene promoter, and TERT and STAT5 co-localized in calcified valve tissues. Pharmacological inhibition of STAT5A prevented calcification in vitro. Conclusions: These data show that non-canonical TERT activity is required for the calcification of VICs. TERT partners with STAT5A to bind to and activate the RUNX2 gene promoter. These data identify a novel therapeutic target to abate vascular calcification.