TRPM7 is protective against hypertension, cardiovascular inflammation and fibrosis induced by aldosterone and salt

Abstract

Introduction : TRPM7 is a channel permeable to Mg2+, Ca2+ and Zn2+ bound to an alpha-kinase domain with essential role in cation homeostasis and cell cycle and activation. Hyperaldosteronism, which induces hypertension and cardiovascular fibrosis, is associated with Mg2+ wasting. Here we investigate the importance of TRPM7 in hypertension and fibrosis induced by aldosterone and salt. Methods Wild-type (WT) and TRPM7-deficient (M7+/Δ) mice were treated with aldosterone (600µg/Kg/day) and/or 1% NaCl (drinking water) (aldo, salt or aldo-salt) for 4 weeks. Blood pressure (BP) was evaluated by tail-cuff. Vessel structure was assessed by pressure myography. Inflammatory cell infiltrate was investigated by flow cytometry. Molecular mechanisms were investigated in cardiac fibroblasts (CF) from WT and M7+/Δ mice. Protein expression was assessed by western-blot and histology. Results M7+/Δ mice exhibited reduced TRPM7 expression (30%) and phosphorylation (62%), levels that were recapitulated in WT mice treated with aldo-salt. M7+/Δ exhibited increased BP by aldo, salt and aldo-salt (135-140mmHg) vs M7+/Δ veh (117mmHg) (p<0.05), whereas in WT, BP was increased only in the aldo-salt group (134mmHg). Mesenteric arteries from M7+/Δ aldo-salt exhibited thinner walls by reducing cross-sectional area (35%) vs WT aldo-salt (p<0.05). Aldo-salt induced greater collagen deposition in hearts (68%), kidneys (126%) and aortas (45%) from M7+/Δ vs WT. In kidneys from WT mice, aldo-salt increased frequency of macrophages (47% vs 32% WT veh) and CD4+T cells (33% vs 22% WT veh) (p<0.05), effects observed already in M7+/Δ veh (macrophages: 42%, CD4+T cells: 34%). Aldosterone increased CD8+T cells in kidneys from M7+/Δ (16% vs M7+/Δ-veh 9%). Hearts from M7+/Δ veh exhibited increased TGFβ, p-Smad3 and p-Stat1 (1.5-fold) whereas in WT these effects were only found after aldo-salt. Cardiac expression of PPM1A, a Mg2+-dependent phosphatase, was reduced (3-fold) only in M7+/Δ mice. CF from M7+/Δ mice showed reduced of proliferation (30%) and PPM1A (4-fold) and increased expression of TGFβ, IL-11, IL-6 (2-6-fold), p-Stat1 (2-fold), p-Smad3 (9-fold) and p-ERK1/2 (8-fold) compared with WT. Mg2+ supplementation normalized cell proliferation and reduced protein phosphorylation in M7+/Δ CF (p<0.05. Conclusions Our findings identify a protective role of TRPM7 in aldosterone-salt induced cardiovascular injury, which when downregulated, facilitates hypertension, vascular remodeling and cardiac fibrosis through Mg2+ -dependent mechanisms.