TMEM174 Deficiency Reduces Longevity by Promoting Phosphate-Driven Vascular Calcification

Dysregulation of phosphate homeostasis contributes to reduced longevity and vascular complications in chronic kidney disease and aging. This study investigates the role of TMEM174, a proximal tubule-specific protein, in regulating the phosphate co-transporter NPT2A and its subsequent impact on lifespan and vascular health. TMEM174 knockout (KO) mice (C57BL6/J and DBA/2J) were fed diets with varying phosphate concentrations (0.6% vs. 1.2%). In OKP cells, TIRF and FRET microscopy, alongside immunoprecipitation, were used to identify the TMEM174 protein regions essential for NPT2A binding and endocytosis. TMEM174 KO mice exhibited significantly shorter lifespans than wild-type controls. High phosphate diets exacerbated vascular calcification, stiffness, and mortality, while low phosphate diets rescued these phenotypes. In vitro, TMEM174 siRNA blocked PTH-induced NPT2A endocytosis, increasing its apical membrane retention. FRET and biochemical assays revealed that the C-terminal region of TMEM174 is essential for its association with NPT2A. While intact TMEM174 and N-terminal mutants (TMEM174ΔN) facilitated NPT2A degradation, C-terminal deletions (TMEM174ΔC) failed to associate with or degrade NPT2A. TMEM174 is a critical regulator of phosphate homeostasis and longevity. The C-terminal region of TMEM174 is specifically required for NPT2A endocytosis and degradation, identifying it as a potential therapeutic target for managing phosphate-related vascular complications.