Protection of the human aortic valve interstitial cells against radiation-induced remodeling by repression of the TRPM4 channel.

Abstract

Radiation-induced aortic valve deleterious remodeling may occur years after radiotherapy. The TRPM4 cation channel participates in aortic valve radiation-induced remodeling in mice in vivo. Valvular interstitial cells (VIC) are involved in valve leaflet thickening and calcification leading to aortic stenosis. TRPM4 favors their remodeling toward an osteogenic phenotype in vitro. Here, we evaluated whether radiation-induced remodeling involves TRPM4 in human VICs.

Methods: VICs were isolated from aortic valves and maintained in procalcifying media supplemented or not with 9-phenanthrol (a TRPM4 inhibitor) or shRNA-TRPM4. Cells were irradiated at 0 or 8 Gy. 10 days post-irradiation, cell surface, viability, cycle and proliferation were measured. Senescence was evaluated by β-galactosidase activity measurements. Osteogenic markers (BMP2, Runx2, ALP) and TRPM4 mRNA levels were quantified by qPCR.

Results: VIC surface increased after radiation while cell density decreased. Radiation had no effect on viability but induced an increase of the proportion of cells in G0 cell cycle phase. An increase of cell senescence was observed after irradiation. Finally, irradiation induced an increase of TRPM4, BMP2, Runx2 and ALP mRNA. All these effects were partly prevented by 9-phenanthrol or shRNA-TRPM4. Interestingly, VIC density on aortic valve leaflets from mice submitted to X ray treatment in vivo was decreased in treated animals compared to untreated ones and this was not observed in animals with disruption of the Trpm4 gene.

Conclusion: TRPM4 participates in radiation-induced hVICs remodeling by promoting cell senescence and osteogenic transition. TRPM4 may thus be evaluated as a therapeutic target to diminish valvular effects of radiotherapy.