Telomerase Reverse Transcriptase in Aortic Valve Calcification

PROJECT SUMMARY Calcific aortic valve disease is a common disorder that causes substantial medical care costs and health burden. The only current therapy is aortic valve replacement. Without replacement, mortality rates approach 50% within 2-3-years of diagnosis. Aortic valve replacement does not come without risks, as mechanical valves, while stable,

require life-long anticoagulation therapy, and bioprosthetic valves last only a decade. Thus, there is a great need for early non-surgical therapeutic interventions. Our long-term goal is to dissect the mechanisms that transform a healthy valve into a calcifying valve, to identify potential targets for the development of non-surgical therapies.

For calcification to occur, the aortic valve interstitial cell must undergo extensive changes to alter its chromatin structure and transcriptome. We recently made the discovery that telomerase reverse transcriptase (TERT) is required for the osteogenic reprogramming of valve interstitial cells. TERT is well known for its critical role in

elongating telomeres, however we and others have identified non-canonical transcriptional regulatory and chro- matin remodeling functions of TERT, yet the understanding of these non-canonical roles is in its nascency. We have found TERT transcript and protein levels are elevated in human calcified aortic valves. Our in vitro studies

show that genetic deletion/reduction of TERT reduces calcification in valve interstitial cells from human and mouse. We have demonstrated that TERT initiates osteogenic transcriptional programs by coupling with tran- scription factor STAT5 to bind and activate the promoter of the osteogenic master regulator RUNX2. Osteogenic

treatment or inflammatory stimuli elevated transcription and protein levels of TERT and STAT5 in valve interstitial cells. We also identified that TERT co-localized with the chromatin remodeling protein BRG1 in these calcifying cells. From these data we hypothesize that inflammatory stress initiates TERT-mediated osteogenic reprogram-

ming of valve interstitial cells by scaffolding the STAT5 transcription factor with proteins required for chromatin remodeling and histone modification. To test this hypothesis, Aim 1 will investigate the epigenetic and transcrip- tional changes directed by TERT during osteogenic reprogramming of aortic valve interstitial cells, Aim 2 will

visualize the dynamics of TERT/STAT5 interaction and identify epigenome-modifying binding partners of TERT, and Aim3 will utilize 3D in vitro cell co-cultures of valve interstitial cells and inflammatory cells and spatial RNA sequencing on a spectrum of diseased human aortic valves to define the contribution of specific inflammatory

cell types in valve calcification. With these integrated multi-omics and disease modeling approaches we will be able to identify the key drivers of the initial switch that triggers osteogenic cellular reprogramming of valve cells. Understanding these mechanisms may enable us to develop noninvasive therapies to halt, prevent, or even

reverse aortic valve calcification.