TDAG51 (T-Cell Death Associated Gene 51) Is a Key Modulator of Vascular Calcification and Osteogenic Transdifferentiation of Arterial Smooth Muscle Cells

OBJECTIVE: Cardiovascular disease is the primary cause of mortality in patients with chronic kidney disease. Vascular calcification (VC) in the medial layer of the vessel wall is a unique and prominent feature in patients with advanced chronic kidney disease and is now recognized as an important predictor and independent risk factor for cardiovascular and all-cause mortality in these patients. VC in chronic kidney disease is triggered by the transformation of vascular smooth muscle cells (VSMCs) into osteoblasts as a consequence of elevated circulating inorganic phosphate (P_i) levels, due to poor kidney function. The objective of our study was to investigate the role of TDAG51 (T-cell death-associated gene 51) in the development of medial VC. METHODS AND RESULTS: Using primary mouse and human VSMCs, we found that TDAG51 is induced in VSMCs by P_i and is expressed in the medial layer of calcified human vessels. Furthermore, the transcriptional activity of RUNX2 (Runt-related transcription factor 2), a well-established driver of P_i-mediated VC, is reduced in TDAG51^-/- VSMCs. To explain these observations, we identified that TDAG51^-/- VSMCs express reduced levels of the type III sodium-dependent P_i transporter, Pit-1, a solute transporter, a solute transporter, a solute transporter responsible for cellular P_i uptake. Significantly, in response to hyperphosphatemia induced by vitamin D₃, medial VC was attenuated in TDAG51^-/- mice. CONCLUSIONS: Our studies highlight TDAG51 as an important mediator of P_i-induced VC in VSMCs through the downregulation of Pit-1. As such, TDAG51 may represent a therapeutic target for the prevention of VC and cardiovascular disease in patients with chronic kidney disease.