TRPM7 deficiency exacerbates cardiovascular and renal damage induced by aldosterone-salt.

Hyperaldosteronism causes cardiovascular disease as well as hypomagnesemia. Mechanisms are ill-defined but dysregulation of TRPM7, a Mg2+-permeable channel/α-kinase, may be important. We examined the role of TRPM7 in aldosterone-dependent cardiovascular and renal injury by studying aldosterone-salt treated TRPM7-deficient (TRPM7+/Δkinase) mice. Plasma/tissue [Mg2+] and TRPM7 phosphorylation were reduced in vehicle-treated TRPM7+/Δkinase mice, effects recapitulated in aldosterone-salt-treated wild-type mice. Aldosterone-salt treatment exaggerated vascular dysfunction and amplified cardiovascular and renal fibrosis, with associated increased blood pressure in TRPM7+/Δkinase mice. Tissue expression of Mg2+-regulated phosphatases (PPM1A, PTEN) was downregulated and phosphorylation of Smad3, ERK1/2, and Stat1 was upregulated in aldosterone-salt TRPM7-deficient mice. Aldosterone-induced phosphorylation of pro-fibrotic signaling was increased in TRPM7+/Δkinase fibroblasts, effects ameliorated by Mg2+ supplementation. TRPM7 deficiency amplifies aldosterone-salt-induced cardiovascular remodeling and damage. We identify TRPM7 downregulation and associated hypomagnesemia as putative molecular mechanisms underlying deleterious cardiovascular and renal effects of hyperaldosteronism.

Substantial involvement of TRPM7 inhibition in the therapeutic effect of Ophiocordyceps sinensis on pulmonary hypertension.

Ophiocordyceps sinensis (OCS), an entomopathogenic fungus, is known to exert antiproliferative and antitissue remodeling effects. Vascular remodeling and vasoconstriction play critical roles in the development of pulmonary hypertension (PH). The therapeutic potential of OCS for PH was investigated using rodent PH models, and cultured pulmonary artery endothelial and smooth muscle cells (PAECs and PASMCs), with a focus on the involvement of TRPM7. OCS ameliorated the development of PH, right ventricular hypertrophy and dysfunction in the monocrotaline-induced PH rats. The genetic knockout of TRPM7 attenuated the development of PH in mice with monocrotaline pyrrole-induced PH. TRPM7 was associated with medial hypertrophy and the plexiform lesions in rats and humans with PH. OCS suppressed proliferation of PASMCs derived from the PH patients. Ethanol extracts of OCS inhibited TRPM7-like current, TGF-ß2-induced endothelial-mesenchymal transition, IL-6-induced STAT3 phosphorylation, and PDGF-induced Akt phosphorylation in PAECs or PASMCs. These inhibitory effects were recapitulated by either siRNA-mediated TRPM7 knockdown or treatment with TRPM7 antagonist FTY-720. OCS and FTY-720 induced vasorelaxation in the isolated normal human pulmonary artery. As a result, the present study proposes the therapeutic potential of OCS for the treatment of PH. The inhibition of TRPM7 is suggested to underlie the therapeutic effect of OCS.

Defects in TRPM7 channel function deregulate thrombopoiesis through altered cellular Mg(2+) homeostasis and cytoskeletal architecture.

Mg(2+) plays a vital role in platelet function, but despite implications for life-threatening conditions such as stroke or myocardial infarction, the mechanisms controlling [Mg(2+)]i in megakaryocytes (MKs) and platelets are largely unknown. Transient receptor potential melastatin-like 7 channel (TRPM7) is a ubiquitous, constitutively active cation channel with a cytosolic α-kinase domain that is critical for embryonic development and cell survival. Here we report that impaired channel function of TRPM7 in MKs causes macrothrombocytopenia in mice (Trpm7(fl/fl-Pf4Cre)) and likely in several members of a human pedigree that, in addition, suffer from atrial fibrillation. The defect in platelet biogenesis is mainly caused by cytoskeletal alterations resulting in impaired proplatelet formation by Trpm7(fl/fl-Pf4Cre) MKs, which is rescued by Mg(2+) supplementation or chemical inhibition of non-muscle myosin IIA heavy chain activity. Collectively, our findings reveal that TRPM7 dysfunction may cause macrothrombocytopenia in humans and mice.

Ca²âº entry via Trpm2 is essential for cardiac myocyte bioenergetics maintenance.

Ubiquitously expressed Trpm2 channel limits oxidative stress and preserves mitochondrial function. We first demonstrated that intracellular Ca(2+) concentration increase after Trpm2 activation was due to direct Ca(2+) influx and not indirectly via reverse Na(+)/Ca(2+) exchange. To elucidate whether Ca(2+) entry via Trpm2 is required to maintain cellular bioenergetics, we injected adenovirus expressing green fluorescent protein (GFP), wild-type (WT) Trpm2, and loss-of-function (E960D) Trpm2 mutant into left ventricles of global Trpm2 knockout (gKO) or WT hearts. Five days post-injection, gKO-GFP heart slices had higher reactive oxygen species (ROS) levels but lower oxygen consumption rate (OCR) than WT-GFP heart slices. Trpm2 but not E960D decreased ROS and restored OCR in gKO hearts back to normal levels. In gKO myocytes expressing Trpm2 or its mutants, Trpm2 but not E960D reduced the elevated mitochondrial superoxide (O2(.-)) levels in gKO myocytes. After hypoxia-reoxygenation (H/R), Trpm2 but not E906D or P1018L (inactivates Trpm2 current) lowered O2(.-) levels in gKO myocytes and only in the presence of extracellular Ca(2+), indicating sustained Ca(2+) entry is necessary for Trpm2-mediated preservation of mitochondrial function. After ischemic-reperfusion (I/R), cardiac-specific Trpm2 KO hearts exhibited lower maximal first time derivative of LV pressure rise (+dP/dt) than WT hearts in vivo. After doxorubicin treatment, Trpm2 KO mice had worse survival and lower +dP/dt. We conclude 1) cardiac Trpm2-mediated Ca(2+) influx is necessary to maintain mitochondrial function and protect against H/R injury; 2) Ca(2+) influx via cardiac Trpm2 confers protection against H/R and I/R injury by reducing mitochondrial oxidants; and 3) Trpm2 confers protection in doxorubicin cardiomyopathy.

TRPM3 is a nociceptor channel involved in the detection of noxious heat.

Transient receptor potential melastatin-3 (TRPM3) is a broadly expressed Ca(2+)-permeable nonselective cation channel. Previous work has demonstrated robust activation of TRPM3 by the neuroactive steroid pregnenolone sulfate (PS), but its in vivo gating mechanisms and functions remained poorly understood. Here, we provide evidence that TRPM3 functions as a chemo- and thermosensor in the somatosensory system. TRPM3 is molecularly and functionally expressed in a large subset of small-diameter sensory neurons from dorsal root and trigeminal ganglia, and mediates the aversive and nocifensive behavioral responses to PS. Moreover, we demonstrate that TRPM3 is steeply activated by heating and underlies heat sensitivity in a subset of sensory neurons. TRPM3-deficient mice exhibited clear deficits in their avoidance responses to noxious heat and in the development of inflammatory heat hyperalgesia. These experiments reveal an unanticipated role for TRPM3 as a thermosensitive nociceptor channel implicated in the detection of noxious heat.

TRPM channels mediate zinc homeostasis and cellular growth during Drosophila larval development.

TRPM channels have emerged as key mediators of diverse physiological functions. However, the ionic permeability relevant to physiological function in vivo remains unclear for most members. We report that the single Drosophila TRPM gene (dTRPM) generates a conductance permeable to divalent cations, especially Zn(2+) and in vivo a loss-of-function mutation in dTRPM disrupts intracellular Zn(2+) homeostasis. TRPM deficiency leads to profound reduction in larval growth resulting from a decrease in cell size and associated defects in mitochondrial structure and function. These phenotypes are cell-autonomous and can be recapitulated in wild-type animals by Zn(2+) depletion. Both the cell size and mitochondrial defect can be rescued by extracellular Zn(2+) supplementation. Thus our results implicate TRPM channels in the regulation of cellular Zn(2+) in vivo. We propose that regulation of Zn(2+) homeostasis through dTRPM channels is required to support molecular processes that mediate class I PI3K-regulated cell growth.

SLC41A2 encodes a plasma-membrane Mg2+ transporter.

The TRPM7 (transient receptor potential melastatin 7) ion channel has been implicated in the uptake of Mg2+ into vertebrate cells, as elimination of TRPM7 expression through gene targeting in DT40 B-lymphocytes renders them unable to grow in the absence of supplemental Mg2+. However, a residual capacity of TRPM7-deficient cells to accumulate Mg2+ and proliferate when provided with supplemental Mg2+ suggests the existence of Mg2+ uptake mechanism(s) other than TRPM7. Evaluation of the expression of several members of the SLC41 (solute carrier family 41) family, which exhibit homology with the MgtE class of prokaryotic putative bivalent-cation transporters, demonstrated that one, SLC41A2 (solute carrier family 41 member 2), is expressed in both wild-type and TRPM7-deficient DT40 cells. Characterization of heterologously expressed SLC41A2 protein indicated that it is a plasma-membrane protein with an N-terminus-outside/C-terminus-inside 11-TM (transmembrane)-span topology, consistent with its functioning as a trans-plasma-membrane transporter. In contrast with a previous report of ion-channel activity associated with SLC41A2 expression in oocytes, investigation of whole cell currents in SLC41A2-expressing DT40 cells revealed no novel currents of any type associated with SLC41A2 expression. However, expression of SLC41A2 in TRPM7-deficient cells under the control of a doxycycline-inducible promoter was able to conditionally enhance their net uptake of 26Mg2+ and conditionally and dose-dependently provide them with the capacity to grow in the absence of supplemental Mg2+, observations strongly supporting a model whereby SLC41A2 directly mediates trans-plasma-membrane Mg2+ transport. Overall, our results suggest that SLC41A2 functions as a plasma-membrane Mg2+ transporter in vertebrate cells.