Abstract 12584: Transcription Factor EB Regulates Vascular Smooth Muscle Calcification
Introduction: Vascular calcification is a strong predictor of cardiovascular-related mortality. Hyperphosphatemia causes phenotypic switches of vascular smooth muscle cells (VSMCs), leading to medial calcification. Recent studies have suggested that dysfunction of the autophagy-lysosomal pathway in VSMCs is a cause of vascular calcification, but the process through which this pathway fails is elusive. Transcription factor EB (TFEB) is a master regulator of lysosome biogenesis; its function in VSMCs is unknown. Hypothesis: We assessed the hypothesis that the dysfunction of TFEB in VSMCs is a cause of vascular calcification. Methods and Results: We induced vascular calcification in wild type mouse aorta with an ex vivo hyperphosphatemia model . Addition of inorganic phosphate at a 1.7 mmol/L for five days decreased TFEB protein expression (0.23 ± 0.10-fold vs. day0, n = 5-7). Immunohistochemistry and alizarin red staining showed that a decrease in TFEB expression in the tunica media was correlated with the formation of calcification. VSMCs were isolated from rat aorta and were cultured for seven days in vitro . Addition of inorganic phosphate dose-dependently decreased TFEB protein expression both in whole cell lysate and in nuclear fraction (0.07± 0.03-fold vs. control, n = 5 ; 0.01 ± 0.003-fold vs. control, n = 4, respectively) while it rather increased mRNA expression of Tfeb (4.48 ± 0.95-fold, n = 7 vs. control). The Decrease in TFEB protein by inorganic phosphate was correlated with the accumulation of TFEB in the SDS-insoluble fraction, suggesting the formation of protein aggregates. The Knockdown of TFEB in VSMCs by siRNA exacerbated phosphate-induced calcium deposition (2.93 ± 0.85-fold, n = 4 vs. negative siRNA). The addition of inorganic phosphate significantly decreased lysosomal activity determined by LysoTracker dye; and treatment with 20 nmol/L of bafilomycin A, a lysosome inhibitor, further accelerated phosphate-induced calcium deposition (13.6 ± 3.69-fold, n = 7 vs. vehicle). Conclusion: In conclusion, TFEB expression in VSMCs is downregulated at the protein level by hyperphosphatemia. The diminution of functional TFEB predisposes to vascular calcification, presumably through downregulating lysosomal activity.