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Transient Receptor Potential Melastatin 7 (TRPM7) cation channel is a chanzyme (channel + kinase) that influences cellular Mg2+ homeostasis and vascular signalling. However, the pathophysiological significance of TRPM7 in the cardiovascular system is unclear. The aim of this study was to investigate the role of this chanzyme in the cardiovascular system focusing on inflammation and fibrosis.TRPM7-deficient mice with deletion of the kinase domain (TRPM7+/Δkinase) were studied and molecular mechanisms investigated in TRPM7+/Δkinase bone marrow-derived macrophages (BMDM) and co-culture systems with cardiac fibroblasts. TRPM7-deficient mice had significant cardiac hypertrophy, fibrosis, and inflammation. Cardiac collagen and fibronectin content, expression of pro-inflammatory mediators (SMAD3, TGFβ) and cytokines [interleukin (IL)-6, IL-10, IL-12, tumour necrosis factor-α] and phosphorylation of the pro-inflammatory signalling molecule Stat1, were increased in TRPM7+/Δkinase mice. These processes were associated with infiltration of inflammatory cells (F4/80+CD206+ cardiac macrophages) and increased galectin-3 expression. Cardiac [Mg2+]i, but not [Ca2+]i, was reduced in TRPM7+/Δkinase mice. Calpain, a downstream TRPM7 target, was upregulated (increased expression and activation) in TRPM7+/Δkinase hearts. Vascular functional and inflammatory responses, assessed in vivo by intra-vital microscopy, demonstrated impaired neutrophil rolling, increased neutrophil: endothelial attachment and transmigration of leucocytes in TRPM7+/Δkinase mice. TRPM7+/Δkinase BMDMs had increased levels of galectin-3, IL-10, and IL-6. In co-culture systems, TRPM7+/Δkinase macrophages increased expression of fibronectin, proliferating cell nuclear antigen, and TGFβ in cardiac fibroblasts from wild-type mice, effects ameliorated by MgCl2 treatment.We identify a novel anti-inflammatory and anti-fibrotic role for TRPM7 and suggest that its protective effects are mediated, in part, through Mg2+-sensitive processes.

TRPM7 is a bi-functional protein where an ion channel domain is fused with an atypical α-kinase domain. Impairment of the kinase domain leads to hypomagnesemia and sensitization to allergic reactions. We here investigate whether TRPM7 is involved in receptor-stimulated peritoneal mast cell degranulation and histamine release. Using the whole-cell patch clamp technique, we find that mimicking hypomagnesemic conditions by removal of extracellular Mg2+ shifts the degranulation response to intracellular Ca2+ from a graded to an all-or-none process independent of functional TRPM7 activity. In contrast, G-protein-induced mast cell degranulation requires higher intracellular Ca2+ levels in cells isolated from a mouse heterozygotic for a TRPM7 kinase domain knock-out (dKhet). Removal of extracellular Mg2+ compensates for this effect by both significantly increasing the degranulation amplitude and accelerating the rate of secretion in dKhet but not wild type (wt) cells. These observations are confirmed in a histamine release assay, where G-protein induced histamine secretion using MIP-1α is greatly enhanced in dKhet mast cells under hypomagensemic conditions, whereas Ca2+-induced degranulation by FcϵRI crosslinking is similar compared to wt. We conclude that Ca2+-induced mast cell activation is sensitive to extracellular Mg2+ concentrations independent of TRPM7 and that the TRPM7 kinase domain, but not the channel domain, is involved in G-protein-regulated degranulation.