Transient receptor potential melastatin 7 (TRPM7) cation channels, magnesium and the vascular system in hypertension

Cordyceps: Alleviating ischemic cardiovascular and cerebrovascular injury - A comprehensive review

ETHNOPHARMACOLOGICAL RELEVANCE

Cordyceps has a long medicinal history as a nourishing herb in traditional Chinese medicine (TCM). Ischemic cardio-cerebrovascular diseases (CCVDs), including cerebral ischemic/reperfusion injury (CI/RI) and myocardial ischemic/reperfusion injury (MI/RI), are major contributors to mortality and disability in humans. Numerous studies have indicated that Cordyceps or its artificial substitutes have significant bioactivity on ischemic CCVDs, however, there is a lack of relevant reviews.

AIM OF THE STUDY

This review was conducted to investigate the chemical elements, pharmacological effects, clinical application and drug safety of Cordycepson ischemic CCVDs.

MATERIALS AND METHODS

A comprehensive search was conducted on the Web of Science, PubMed, Chinese National Knowledge Infrastructure (CNKI), and Wanfang databases using the keywords "Cordyceps", "Cerebral ischemic/reperfusion injury", and "Myocardial ischemic/reperfusion injury" or their synonyms. The retrieved literature was then categorized and summarized.

RESULTS

The study findings indicated that Cordyceps and its bioactive components, including adenosine, cordycepin, mannitol, polysaccharide, and protein, have the potential to protect against CI/RI and MI/RI by improving blood perfusion, mitigating damage from reactive oxygen species, suppressing inflammation, preventing cellular apoptosis, and promoting tissue regeneration. Individually, Cordyceps could reduce neuronal excitatory toxicity and blood-brain barrier damage caused by cerebral ischemia. It can also significantly improve cardiac energy metabolism disorders and inhibit calcium overload caused by myocardial ischemia. Additionally, Cordyceps exerts a significant preventive or curative influence on the factors responsible for heart/brain ischemia, including hypertension, thrombosis, atherosclerosis, and arrhythmia.

CONCLUSION

This study demonstrates Cordyceps' prospective efficacy and safety in the prevention or treatment of CI/RI and MI/RI, providing novel insights for managing ischemic CCVDs.

Review Article on Molecular Mechanism of Regulation of Hypertension by Macro-elements (Na, K, Ca and Mg), Micro-elements/Trace Metals (Zn and Cu) and Toxic Elements (Pb and As)

Hypertension (HT) is a medical condition arising due to increase in blood pressure (BP) prevalent worldwide. The balanced dietary intakes of macro-elements and micro-elements including Na, K, Ca, Mg, Zn, and Cu have been described to maintain BP in humans by regulating the osmolarity of blood, cells/tissues, prevention of generation of oxidative and nitrosative stress (OANS), and endothelial damage through their functioning as important components of renin-angiotensin-aldosterone system (RAAS), antioxidant enzyme defense system, and maintenance of blood vascular-endothelial and vascular smooth muscle cell (VSMC) functions. However, inadequate/excess dietary intakes of Na/K, Ca/Mg, and Zn/Cu along with higher Pb and As exposures recognized to induce HT through common mechanisms including the followings: endothelial dysfunctions due to impairment of vasodilatation, increased vasoconstriction and arterial stiffness, blood clotting, inflammation, modification of sympathetic activity and higher catecholamine release, increased peripheral vascular resistance, and cardiac output; increased OANS due to reduced and elevated activities of extracellular superoxide dismutase and NAD(P)H oxidase, less nitric oxide bioavailability, decrease in cGMP and guanylate cyclase activity, increase in intracellular Ca2+ ions in VSMCs, and higher pro-inflammatory cytokines; higher parathyroid and calcitriol hormones; activation/suppression of RAAS resulting imbalance in blood Na+, K+, and water regulated by renin, angiotensin II, and aldosterone through affecting natriuresis/kaliuresis/diuresis; elevation in serum cholesterol and LDL cholesterol, decrease in HDL cholesterol due to defect in lipoprotein metabolism. The present study recommends the need to review simple dietary mineral intervention studies/supplementation trials before keeping their individual dietary excess intakes/exposures in consideration because their interactions lead to elevation and fall of their concentrations in body affecting onset of HT.

Magnesium and the Hallmarks of Aging

Magnesium is an essential ion in the human body that regulates numerous physiological and pathological processes. Magnesium deficiency is very common in old age. Age-related chronic diseases and the aging process itself are frequently associated with low-grade chronic inflammation, called 'inflammaging'. Because chronic magnesium insufficiency has been linked to excessive generation of inflammatory markers and free radicals, inducing a chronic inflammatory state, we formerly hypothesized that magnesium inadequacy may be considered among the intermediaries helping us explain the link between inflammaging and aging-associated diseases. We show in this review evidence of the relationship of magnesium with all the hallmarks of aging (genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, disabled autophagy, dysbiosis, and chronic inflammation), which may positively affect the human healthspan. It is feasible to hypothesize that maintaining an optimal balance of magnesium during one's life course may turn out to be a safe and economical strategy contributing to the promotion of healthy aging. Future well-designed studies are necessary to further explore this hypothesis.

Involvement of TRPM7 in Alcohol-Induced Damage of the Blood-Brain Barrier in the Presence of HIV Viral Proteins

Ethanol (EtOH) exerts its effects through various protein targets, including transient receptor potential melastatin 7 (TRPM7) channels, which play an essential role in cellular homeostasis. We demonstrated that TRPM7 is expressed in rat brain microvascular endothelial cells (rBMVECs), the major cellular component of the blood-brain barrier (BBB). Heavy alcohol drinking is often associated with HIV infection, however mechanisms underlying alcohol-induced BBB damage and HIV proteins, are not fully understood. We utilized the HIV-1 transgenic (HIV-1Tg) rat to mimic HIV-1 patients on combination anti-retroviral therapy (cART) and demonstrated TRPM7 expression in rBMVECs wass lower in adolescent HIV-1Tg rats compared to control animals, however control and HIV-1Tg rats expressed similar levels at 9 weeks, indicating persistent presence of HIV-1 proteins delayed TRPM7 expression. Binge exposure to EtOH (binge EtOH) decreased TRPM7 expression in control rBMVECs in a concentration-dependent manner, and abolished TRPM7 expression in HIV-1Tg rats. In human BMVECs (hBMVECs), TRPM7 expression was downregulated after treatment with EtOH, HIV-1 proteins, and in combination. Next, we constructed in vitro BBB models using BMVECs and found TRPM7 antagonists enhanced EtOH-mediated BBB integrity changes. Our study demonstrated alcohol decreased TRPM7 expression, whereby TRPM7 could be involved in the mechanisms underlying BBB alcohol-induced damage in HIV-1 patients on cART.

Potential of the TRPM7 channel as a novel therapeutic target for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an intractable vascular disease characterized by a progressive increase in pulmonary vascular resistance caused by pulmonary vascular remodeling, which ultimately leads to right-sided heart failure. PAH remains incurable, despite the development of PAH-targeted therapeutics centered on pulmonary artery relaxants. It is necessary to identify the target molecules that contribute to pulmonary artery remodeling. Transient receptor potential (TRP) channels have been suggested to modulate pulmonary artery remodeling. Our study focused on the transient receptor potential ion channel subfamily M, member 7, or the TRPM7 channel, which modulates endothelial-to-mesenchymal transition and smooth muscle proliferation in the pulmonary artery. In this review, we summarize the role and expression profile of TRPM7 channels in PAH progression and discuss TRPM7 channels as possible therapeutic targets. In addition, we discuss the therapeutic effect of a Chinese herbal medicine, Ophiocordyceps sinensis (OCS), on PAH progression, which partly involves TRPM7 inhibition.

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.

Deficiency of the Mg2+-permeable channel/α-kinase TRPM7 in mice increases susceptibility to cardiovascular and renal fibrosis induced by aldosterone and salt.

On the Connections between TRPM Channels and SOCE

Plasma membrane protein channels provide a passageway for ions to access the intracellular milieu. Rapid entry of calcium ions into cells is controlled mostly by ion channels, while Ca2+-ATPases and Ca2+ exchangers ensure that cytosolic Ca2+ levels ([Ca2+]cyt) are maintained at low (~100 nM) concentrations. Some channels, such as the Ca2+-release-activated Ca2+ (CRAC) channels and voltage-dependent Ca2+ channels (CACNAs), are highly Ca2+-selective, while others, including the Transient Receptor Potential Melastatin (TRPM) family, have broader selectivity and are mostly permeable to monovalent and divalent cations. Activation of CRAC channels involves the coupling between ORAI1-3 channels with the endoplasmic reticulum (ER) located Ca2+ store sensor, Stromal Interaction Molecules 1-2 (STIM1/2), a pathway also termed store-operated Ca2+ entry (SOCE). The TRPM family is formed by 8 members (TRPM1-8) permeable to Mg2+, Ca2+, Zn2+ and Na+ cations, and is activated by multiple stimuli. Recent studies indicated that SOCE and TRPM structure-function are interlinked in some instances, although the molecular details of this interaction are only emerging. Here we review the role of TRPM and SOCE in Ca2+ handling and highlight the available evidence for this interaction.

Transient Receptor Potential Melastatin 7 Promotes Vascular Adventitial Fibroblasts Phenotypic Transformation and Inflammatory Reaction Induced by Mechanical Stretching Stress via p38 MAPK/JNK Pathway

Remodeling of the arteries is one of the pathological bases of hypertension. We have previously shown that transient receptor potential melastatin 7 (TRPM7) aggravates the vascular adventitial remodeling caused by pressure overload in the transverse aortic constriction (TAC) model. In this study, we sought to explore the functional expression and downstream signaling of TRPM7 in vascular adventitial fibroblasts (AFs) stimulated by mechanical stretching stress (MSS). The expression of TRPM7 was upregulated with a concomitant translocation to the cytoplasm in the AFs stimulated with 20% MSS. Meanwhile, the expression of α-smooth muscle actin (α-SMA), a marker of transformation from AFs to myofibroblasts (MFs) was also increased. Moreover, AF-conditioned medium caused a significant migration of macrophages after treatment with MSS and contained high levels of monocyte chemotactic protein-1 (MCP-1), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α). Pharmacological and RNA interference approaches using the TRPM7 inhibitor 2-aminoethoxydiphenyl borate (2-APB) and specific anti-TRPM7 small interfering RNA (si-RNA-TRPM7) abrogated these changes significantly. Further exploration uncloaked that inhibition of TRPM7 reduced the phosphorylation of p38 MAP kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) in the AFs stimulated with MSS. Furthermore, inhibition of the phosphorylation of p38MAPK or JNK could also alleviate the MSS-induced expression of α-SMA and secretion of inflammatory factors. These observations indicate that activated TRPM7 participates in the phenotypic transformation and inflammatory action of AFs in response to MSS through the p38MAPK/JNK pathway and suggest that TRPM7 may be a potential therapeutic target for vascular remodeling caused by hemodynamic changes in hypertension.

Magnesium Supplementation Attenuates Pulmonary Hypertension via Regulation of Magnesium Transporters

Pulmonary hypertension (PH) is characterized by profound vascular remodeling and altered Ca²⁺ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Magnesium ion (Mg²⁺), a natural Ca²⁺ antagonist and a cofactor for numerous enzymes, is crucial for regulating diverse cellular functions, but its roles in PH remains unclear. Here, we examined the roles of Mg²⁺ and its transporters in PH development. Chronic hypoxia and monocrotaline induced significant PH in adult male rats. It was associated with a reduction of [Mg²⁺]_i in PASMCs, a significant increase in gene expressions of Cnnm2, Hip14, Hip14l, Magt1, Mmgt1, Mrs2, Nipa1, Nipa2, Slc41a1, Slc41a2 and Trpm7; upregulation of SLC41A1, SLC41A2, CNNM2, and TRPM7 proteins; and downregulation of SLC41A3 mRNA and protein. Mg²⁺ supplement attenuated pulmonary arterial pressure, right heart hypertrophy, and medial wall thickening of pulmonary arteries, and reversed the changes in the expression of Mg²⁺ transporters. Incubation of PASMCs with a high concentration of Mg²⁺ markedly inhibited PASMC proliferation and migration, and increased apoptosis, whereas a low level of Mg²⁺ produced the opposite effects. siRNA targeting Slc41a1/2, Cnnm2, and Trpm7 attenuated PASMC proliferation and migration, but promoted apoptosis; and Slc41a3 overexpression also caused similar effects. Moreover, siRNA targeting Slc41a1 or high [Mg²⁺] incubation inhibited hypoxia-induced upregulation and nuclear translocation of NFATc3 in PASMCs. The results, for the first time, provide the supportive evidence that Mg²⁺ transporters participate in the development of PH by modulating PASMC proliferation, migration, and apoptosis; and Mg²⁺ supplementation attenuates PH through regulation of Mg²⁺ transporters involving the NFATc3 signaling pathway.

Magnesium, Oxidative Stress, Inflammation, and Cardiovascular Disease

Hypomagnesemia is commonly observed in heart failure, diabetes mellitus, hypertension, and cardiovascular diseases. Low serum magnesium (Mg) is a predictor for cardiovascular and all-cause mortality and treating Mg deficiency may help prevent cardiovascular disease. In this review, we discuss the possible mechanisms by which Mg deficiency plays detrimental roles in cardiovascular diseases and review the results of clinical trials of Mg supplementation for heart failure, arrhythmias and other cardiovascular diseases.

Epidermal growth factor signaling through transient receptor potential melastatin 7 cation channel regulates vascular smooth muscle cell function

OBJECTIVE

Transient receptor potential (TRP) melastatin 7 (TRPM7) cation channel, a dual-function ion channel/protein kinase, regulates vascular smooth muscle cell (VSMC) Mg2+ homeostasis and mitogenic signaling. Mechanisms regulating vascular growth effects of TRPM7 are unclear, but epidermal growth factor (EGF) may be important because it is a magnesiotropic hormone involved in cellular Mg2+ regulation and VSMC proliferation. Here we sought to determine whether TRPM7 is a downstream target of EGF in VSMCs and if EGF receptor (EGFR) through TRPM7 influences VSMC function. Approach and results: Studies were performed in primary culture VSMCs from rats and humans and vascular tissue from mice deficient in TRPM7 (TRPM7+/Δkinase and TRPM7R/R). EGF increased expression and phosphorylation of TRPM7 and stimulated Mg2+ influx in VSMCs, responses that were attenuated by gefitinib (EGFR inhibitor) and NS8593 (TRPM7 inhibitor). Co-immunoprecipitation (IP) studies, proximity ligation assay (PLA) and live-cell imaging demonstrated interaction of EGFR and TRPM7, which was enhanced by EGF. PP2 (c-Src inhibitor) decreased EGF-induced TRPM7 activation and prevented EGFR-TRPM7 association. EGF-stimulated migration and proliferation of VSMCs were inhibited by gefitinib, PP2, NS8593 and PD98059 (ERK1/2 inhibitor). Phosphorylation of EGFR and ERK1/2 was reduced in VSMCs from TRPM7+/Δkinase mice, which exhibited reduced aortic wall thickness and decreased expression of PCNA and Notch 3, findings recapitulated in TRPM7R/R mice.

CONCLUSIONS

We show that EGFR directly interacts with TRPM7 through c-Src-dependent processes. Functionally these phenomena regulate [Mg2+]i homeostasis, ERK1/2 signaling and VSMC function. Our findings define a novel signaling cascade linking EGF/EGFR and TRPM7, important in vascular homeostasis.

TRPM7 channel inhibition exacerbates pulmonary arterial hypertension through MEK/ERK pathway

Cellular senescence is an important mechanism of autonomous tumor suppression, while its consequence such as the senescence-associated secretory phenotype (SASP) may drive tumorigenesis and age-related diseases. Therefore, controlling the cell fate optimally when encountering senescence stress is helpful for anti-cancer or anti-aging treatments. To identify genes essential for senescence establishment or maintenance, we carried out a CRISPR-based screen with a deliberately designed single-guide RNA (sgRNA) library. The library comprised of about 12,000 kinds of sgRNAs targeting 1378 senescence-associated genes selected by integrating the information of literature mining, protein-protein interaction network, and differential gene expression. We successfully detected a dozen gene deficiencies potentially causing senescence bypass, and their phenotypes were further validated with a high true positive rate. RNA-seq analysis showed distinct transcriptome patterns of these bypass cells. Interestingly, in the bypass cells, the expression of SASP genes was maintained or elevated with CHEK2, HAS1, or MDK deficiency; but neutralized with MTOR, CRISPLD2, or MORF4L1 deficiency. Pathways of some age-related neurodegenerative disorders were also downregulated with MTOR, CRISPLD2, or MORF4L1 deficiency. The results demonstrated that disturbing these genes could lead to distinct cell fates as a consequence of senescence bypass, suggesting that they may play essential roles in cellular senescence.

Chanzyme TRPM7 protects against cardiovascular inflammation and fibrosis

AIMS

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

Magnesium Regulates Endothelial Barrier Functions through TRPM7, MagT1, and S1P1

Mg2+-deficiency is linked to hypertension, Alzheimer's disease, stroke, migraine headaches, cardiovascular diseases, and diabetes, etc., but its exact role in these pathophysiological conditions remains elusive. Mg2+ can regulate vascular functions, yet the mechanistic insight remains ill-defined. Data show that extracellular Mg2+ enters endothelium mainly through the TRPM7 channel and MagT1 transporter. Mg2+ can act as an antagonist to reduce Ca2+ signaling in endothelium. Mg2+ also reduces the intracellular reactive oxygen species (ROS) level and inflammation. In addition, Mg2+-signaling increases endothelial survival and growth, adhesion, and migration. Endothelial barrier integrity is significantly enhanced with Mg2+-treatment through S1P1-Rac1 pathways and barrier-stabilizing mediators including cAMP, FGF1/2, and eNOS. Mg2+ also promotes cytoskeletal reorganization and junction proteins to tighten up the barrier. Moreover, Mg2+-deficiency enhances endothelial barrier permeability in mice, and Mg2+-treatment rescues histamine-induced transient vessel hyper-permeability in vivo. In summary, Mg2+-deficiency can cause deleterious effects in endothelium integrity, and Mg2+-treatment may be effective in the prevention or treatment of vascular dysfunction.

TRPM7, Magnesium, and Signaling

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a ubiquitously expressed chanzyme that possesses an ion channel permeable to the divalent cations Mg2+, Ca2+, and Zn2+, and an α-kinase that phosphorylates downstream substrates. TRPM7 and its homologue TRPM6 have been implicated in a variety of cellular functions and is critically associated with intracellular signaling, including receptor tyrosine kinase (RTK)-mediated pathways. Emerging evidence indicates that growth factors, such as EGF and VEGF, signal through their RTKs, which regulate activity of TRPM6 and TRPM7. TRPM6 is primarily an epithelial-associated channel, while TRPM7 is more ubiquitous. In this review we focus on TRPM7 and its association with growth factors, RTKs, and downstream kinase signaling. We also highlight how interplay between TRPM7, Mg2+ and signaling kinases influences cell function in physiological and pathological conditions, such as cancer and preeclampsia.

Zinc regulates vascular endothelial cell activity through zinc-sensing receptor ZnR/GPR39

Zn2+ is an essential element for cell survival/growth, and its deficiency is linked to many disorders. Extracellular Zn2+ concentration changes participate in modulating fundamental cellular processes such as proliferation, secretion, ion transport, and cell signal transduction in a mechanism that is not well understood. Here, we hypothesize that the Zn2+-sensing receptor ZnR/G protein-coupled receptor 39 (GPR39), found in tissues where dynamic Zn2+ homeostasis takes place, enables extracellular Zn2+ to trigger intracellular signaling pathways regulating key cell functions in vascular cells. Thus, we investigated how extracellular Zn2+ regulates cell viability, proliferation, motility, angiogenesis, vascular tone, and inflammation through ZnR/GPR39 in endothelial cells. Knockdown of GPR39 through siRNA largely abolished Zn2+-triggered cellular activity changes, Ca2+ responses, as well as the downstream activation of Gαq-PLC pathways. Extracellular Zn2+ promoted vascular cell survival/growth through activation of cAMP and Akt as well as overexpressing of platelet-derived growth factor-α receptor and vascular endothelial growth factor A. It also enhanced cell adhesion and mobility, endothelial tubule formation, and cytoskeletal reorganization. Such effects from extracellular Zn2+ were not observed in GPR39-/- endothelial cells. Zn2+ also regulated inflammation-related key molecules such as heme oxygenase-1, selectin L, IL-10, and platelet endothelial cell adhesion molecule 1, as well as vascular tone-related prostaglandin I2 synthase and nitric oxide synthase-3. In sum, extracellular Zn2+ regulates endothelial cell activity in a ZnR/GPR39-dependent manner and through the downstream Gαq-PLC pathways. Thus, ZnR/GPR39 may be a therapeutic target for regulating endothelial activity.

Magnesium Reduces Blood-Brain Barrier Permeability and Regulates Amyloid-β Transcytosis

Poor Mg status is a risk factor for Alzheimer's disease (AD), and the underlying mechanisms remain elusive. Here, we provided the first evidence that elevated Mg levels significantly reduced the blood-brain barrier (BBB) permeability and regulated its function in vitro. Transient receptor potential melastatin 7 (TRPM7) and magnesium transporter subtype 1 (MagT1) were two major cellular receptors mediating entry of extracellular Mg²⁺ into the cells. Elevated Mg levels also induced an accelerated clearance of amyloid-β peptide (Aβ) from the brain to the blood side via BBB transcytosis through low-density lipoprotein receptor-related protein (LRP) and phosphatidylinositol binding clathrin assembly protein (PICALM), while reduced the influx of Aβ from the blood to the brain side involving receptor for advanced glycation end products (RAGE) and caveolae. Mg enhanced BBB barrier properties and overall expression of LRP1 and PICALM whereas reduced that of RAGE and caveolin-1. Apical-to-basolateral and vice versa steady-state Aβ flux achieved an equilibrium of 18 and 0.27 fmol/min/cm², respectively, about 30 min after the initial addition of physiological levels of free Aβ. Knockdown of caveolin-1 or disruption of caveolae membrane microdomains reduced RAGE-mediated influx significantly, but not LRP1-mediated efflux of Aβ. Stimulating endothelial cells with vascular endothelial growth factor (VEGF) enhanced caveolin-1 phosphorylation and RAGE expression. Co-immunoprecipitation demonstrated that RAGE, but not LRP1, was physically associated with caveolin-1. Thus, Mg can reduce BBB permeability and promote BBB clearance of Aβ from the brain by increasing the expression of LRP1 and PICALM while reducing the level of RAGE and caveolin-1.

Biological Responses and Mechanisms of Human Bone Marrow Mesenchymal Stem Cells to Zn and Mg Biomaterials

Zn biomaterials attract strong attentions recently for load-bearing medical implants because of their mechanical properties similar to bone, biocompatibility, and degradability at a more matched rate to tissue healing. It has been shown previously that Zn alloys are beneficial for bone regeneration, but the supporting mechanisms have not been explored in detail. Here, we studied the biological responses of human bone marrow mesenchymal stem cells (hMSC) to Zn and the underlying cellular signaling mechanisms. Typical Mg material AZ31 was used as a comparative benchmark control. Direct culture of cells on the materials revealed that cell adhesion, proliferation, and motility were higher on Zn than on AZ31. Significant cytoskeletal reorganizations induced by Zn or AZ31 were also observed. Mineralization of extracellular matrix (ECM) and hMSC osteogenic differentiation, measured by Alizarin red and ALP staining and activities, were significantly enhanced when cells were cultured with Zn or AZ31. Quantitative PCR also showed the increased expression of bone-related genes including ALP, collagen I, and osteopontin. Using small RNA interference to knockdown related key molecules, we illustrated the mechanisms of Zn-induced cellular signaling. TRPM7 and GPR39 appear to be the major cellular receptors facilitating Zn²⁺-entry into hMSC. The intracellular Zn²⁺ then activates the cAMP-PKA pathway and triggers intracellular Ca²⁺ responses, leading to activation of MAPK. In addition, Zn²⁺ activates the Gαq-PLC-AKT pathway as well. Eventually, all of this signaling would lead to enhanced differential regulation of genes, cell survival/growth and differentiation, ECM mineralization, osteogenesis, and other cellular activities.

Muscling in on TRP channels in vascular smooth muscle cells and cardiomyocytes

The human TRP protein family comprises a family of 27 cation channels with diverse permeation and gating properties. The common theme is that they are very important regulators of intracellular Ca²⁺ signaling in diverse cell types, either by providing a Ca²⁺ influx pathway, or by depolarising the membrane potential, which on one hand triggers the activation of voltage-gated Ca²⁺ channels, and on the other limits the driving force for Ca²⁺ entry. Here we focus on the role of these TRP channels in vascular smooth muscle and cardiac striated muscle. We give an overview of highlights from the recent literature, and highlight the important and diverse roles of TRP channels in the pathophysiology of the cardiovascular system. The discovery of the superfamily of Transient Receptor Potential (TRP) channels has significantly enhanced our knowledge of multiple signal transduction mechanisms in cardiac muscle and vascular smooth muscle cells (VSMC). In recent years, multiple studies have provided evidence for the involvement of these channels, not only in the regulation of contraction, but also in cell proliferation and remodeling in pathological conditions. The mammalian family of TRP cation channels is composed by 28 genes which can be divided into 6 subfamilies groups based on sequence similarity: TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipins), TRPV (Vanilloid), TRPP (Policystin) and TRPA (Ankyrin-rich protein). Functional TRP channels are believed to form four-unit complexes in the plasma, each of them expressed with six transmembrane domain and intracellular N and C termini. Here we review the current knowledge on the expression of TRP channels in both muscle types, and discuss their functional properties and role in physiological and pathophysiological processes.

Perspective: The Case for an Evidence-Based Reference Interval for Serum Magnesium: The Time Has Come

The 2015 Dietary Guidelines Advisory Committee indicated that magnesium was a shortfall nutrient that was underconsumed relative to the Estimated Average Requirement (EAR) for many Americans. Approximately 50% of Americans consume less than the EAR for magnesium, and some age groups consume substantially less. A growing body of literature from animal, epidemiologic, and clinical studies has demonstrated a varied pathologic role for magnesium deficiency that includes electrolyte, neurologic, musculoskeletal, and inflammatory disorders; osteoporosis; hypertension; cardiovascular diseases; metabolic syndrome; and diabetes. Studies have also demonstrated that magnesium deficiency is associated with several chronic diseases and that a reduced risk of these diseases is observed with higher magnesium intake or supplementation. Subclinical magnesium deficiency can exist despite the presentation of a normal status as defined within the current serum magnesium reference interval of 0.75-0.95 mmol/L. This reference interval was derived from data from NHANES I (1974), which was based on the distribution of serum magnesium in a normal population rather than clinical outcomes. What is needed is an evidenced-based serum magnesium reference interval that reflects optimal health and the current food environment and population. We present herein data from an array of scientific studies to support the perspective that subclinical deficiencies in magnesium exist, that they contribute to several chronic diseases, and that adopting a revised serum magnesium reference interval would improve clinical care and public health.

The relationship between elevated magnesium levels and coronary artery ectasia

Backround

Coronary artery ectasia (CAE) without specific symptoms is the localised or diffuse swelling of the epicardial coronary arteries. Magnessium (Mg) plays an important role in cardiac excitability, vascular tonus, contractibility, reactivity and vasodilatation. In our research, we aimed to study the vasodilatory effect of Mg in the aetiopathogenesis of ectasia.

Methods

Patients identified during routine coronary angiograms in our clinic between January 2010 and 2013 were included in the study. Sixty-two patients with isolated CAE, 57 with normal coronary angiograms (NCA), 73 with severe coronary artery disease (CAD), and 95 with stenosis of at least one coronary artery and CAE (CAD + CAE) were included in the study. Serum Mg levels were measured in mg/ dl after 12 hours of fasting.

Results

There were no statistically significant differences between the groups in terms of age, hypertension, smoking, hyperlipidaemia, diabetes mellitus, family history of coronary artery disease and medications used. Serum glucose, thyroid stimulating hormone (TSH), urea, total cholesterol, triglyceride, low-density lipoprotein (LDL) cholesterol, sodium and potassium levels were similar in all groups. Serum Mg levels were 1.90 ± 0.19 mg/dl in patients with isolated CAE, 1.75 ± 0.19 mg/dl in those with CAD, 1.83 ± 0.20 mg/dl in those with CAD + CAE, and 1.80 ± 0.16 mg/dl in the NCA group. These results show that Mg levels were higher in ectasia patients with or without CAD.

Conclusions

The histopathological characteristics of patients with CAE were similar to those with CAD. The specific mechanism of abnormal luminal dilatation seen in CAE however remains to be elucidated. Mg is a divalent cation with powerful vasodilatory effects. In our study, serum Mg levels were found to be statistically higher in ectasia patients with or without CAD.

Transient Receptor Potential Melastatin 7 Cation Channel Kinase: New Player in Angiotensin II-Induced Hypertension

Transient receptor potential melastatin 7 (TRPM7) is a bifunctional protein comprising a magnesium (Mg(2+))/cation channel and a kinase domain. We previously demonstrated that vasoactive agents regulate vascular TRPM7. Whether TRPM7 plays a role in the pathophysiology of hypertension and associated cardiovascular dysfunction is unknown. We studied TRPM7 kinase-deficient mice (TRPM7Δkinase; heterozygous for TRPM7 kinase) and wild-type (WT) mice infused with angiotensin II (Ang II; 400 ng/kg per minute, 4 weeks). TRPM7 kinase expression was lower in heart and aorta from TRPM7Δkinase versus WT mice, effects that were further reduced by Ang II infusion. Plasma Mg(2+) was lower in TRPM7Δkinase versus WT mice in basal and stimulated conditions. Ang II increased blood pressure in both strains with exaggerated responses in TRPM7Δkinase versus WT groups (P<0.05). Acetylcholine-induced vasorelaxation was reduced in Ang II-infused TRPM7Δkinase mice, an effect associated with Akt and endothelial nitric oxide synthase downregulation. Vascular cell adhesion molecule-1 expression was increased in Ang II-infused TRPM7 kinase-deficient mice. TRPM7 kinase targets, calpain, and annexin-1, were activated by Ang II in WT but not in TRPM7Δkinase mice. Echocardiographic and histopathologic analysis demonstrated cardiac hypertrophy and left ventricular dysfunction in Ang II-treated groups. In TRPM7 kinase-deficient mice, Ang II-induced cardiac functional and structural effects were amplified compared with WT counterparts. Our data demonstrate that in TRPM7Δkinase mice, Ang II-induced hypertension is exaggerated, cardiac remodeling and left ventricular dysfunction are amplified, and endothelial function is impaired. These processes are associated with hypomagnesemia, blunted TRPM7 kinase expression/signaling, endothelial nitric oxide synthase downregulation, and proinflammatory vascular responses. Our findings identify TRPM7 kinase as a novel player in Ang II-induced hypertension and associated vascular and target organ damage.

Association of hypermagnesemia and blood pressure in the critically ill

BACKGROUND

Although magnesium is important in the biology of blood pressure regulation, little clinical data exist on the association of hypermagnesemia and blood pressure.

METHOD

We examined the association of hypermagnesemia and SBP in a cross-sectional study of 10 521 ICU patients from a single tertiary care medical center, 6% of whom had a serum magnesium above 2.6 mg/dl at time of admission.

RESULTS

In a multivariable analysis, hypermagnesemia was associated with SBP 6.2 mmHg lower [95% confidence interval (CI) -8.2, -4.2, P < 0.001] than in patients with admission values of serum magnesium 2.6 mg/dl or less. Each mg/dl increase in serum magnesium was associated with a decrease in SBP of 4.3 mmHg (95% CI -5.5, -3.1, P < 0.001). In addition, hypermagnesemic patients had a 2.48-fold greater likelihood (95% CI 2.06, 3.00, P < 0.001) of receiving intravenous vasopressors during the first 24 h of ICU care, independent of admission SBP.

CONCLUSION

Our findings add support to the biologic importance of magnesium regulation in blood pressure control.

Intracellular magnesium level determines cell viability in the MPP(+) model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder resulting from mitochondrial dysfunction in dopaminergic neurons. Mitochondria are believed to be responsible for cellular Mg²⁺ homeostasis. Mg²⁺ is indispensable for maintaining ordinal cellular functions, hence perturbation of the cellular Mg²⁺ homeostasis may be responsible for the disorders of physiological functions and diseases including PD. However, the changes in intracellular Mg²⁺ concentration ([Mg²⁺]i) and the role of Mg²⁺ in PD have still been obscure. In this study, we investigated [Mg²⁺]i and its effect on neurodegeneration in the 1-methyl-4-phenylpyridinium (MPP⁺) model of PD in differentiated PC12 cells. Application of MPP⁺ induced an increase in [Mg²⁺]i immediately via two different pathways: Mg²⁺ release from mitochondria and Mg²⁺ influx across cell membrane, and the increased [Mg²⁺]i sustained for more than 16 h after MPP⁺ application. Suppression of Mg²⁺ influx decreased the viability of the cells exposed to MPP⁺. The cell viability correlated highly with [Mg²⁺]i. In the PC12 cells with suppressed Mg²⁺ influx, ATP concentration decreased and the amount of reactive oxygen species (ROS) increased after an 8h exposure to MPP⁺. Our results indicate that the increase in [Mg²⁺]i inhibited cellular ROS generation and maintained ATP production, which resulted in the protection from MPP⁺ toxicity.

TRPM7 regulates vascular endothelial cell adhesion and tube formation

Transient receptor potential melastatin 7 (TRPM7) is a nonselective cation channel with an α-kinase domain in its COOH terminal, known to play a role in diverse physiological and pathological processes such as Mg2+ homeostasis, cell proliferation, and hypoxic neuronal injury. Increasing evidence suggests that TRPM7 contributes to the physiology/pathology of vascular systems. For example, we recently demonstrated that silencing TRPM7 promotes growth and proliferation and protects against hyperglycemia-induced injury in human umbilical vein endothelial cells (HUVECs). Here we investigated the potential effects of TRPM7 on morphology, adhesion, migration, and tube formation of vascular endothelial cells and the potential underlying mechanism. We showed that inhibition of TRPM7 function in HUVECs by silencing TRPM7 decreases the density of TRPM7-like current and cell surface area and inhibits cell adhesion to Matrigel. Silencing TRPM7 also promotes cell migration, wound healing, and tube formation. Further studies showed that the extracellular signal-regulated kinase (ERK) pathway is involved in the change of cell morphology and the increase in HUVEC migration induced by TRPM7 silencing. We also demonstrated that silencing TRPM7 enhances the phosphorylation of myosin light chain (MLC) in HUVECs, which might be involved in the enhancement of cell contractility and motility. Collectively, our data suggest that the TRPM7 channel negatively regulates the function of vascular endothelial cells. Further studies on the underlying mechanism may facilitate the development of the TRPM7 channel as a target for the therapeutic intervention of vascular diseases.

Magnesium physiology and clinical therapy in veterinary critical care

OBJECTIVE

To review magnesium physiology including absorption, excretion, and function within the body, causes of magnesium abnormalities, and the current applications of magnesium monitoring and therapy in people and animals.

ETIOLOGY

Magnesium plays a pivotal role in energy production and specific functions in every cell in the body. Disorders of magnesium can be correlated with severity of disease, length of hospital stay, and recovery of the septic patient. Hypermagnesemia is seen infrequently in people and animals with significant consequences reported. Hypomagnesemia is more common in critically ill people and animals, and can be associated with platelet, immune system, neurological, and cardiovascular dysfunction as well as alterations in insulin responsiveness and electrolyte imbalance.

DIAGNOSIS

Measurement of serum ionized magnesium in critically or chronically ill veterinary patients is practical and provides information necessary for stabilization and treatment. Tissue magnesium concentrations may be assessed using nuclear magnetic resonance spectroscopy as well as through the application of fluorescent dye techniques.

THERAPY

Magnesium infusions may play a therapeutic role in reperfusion injury, myocardial ischemia, cerebral infarcts, systemic inflammatory response syndromes, tetanus, digitalis toxicity, bronchospasms, hypercoagulable states, and as an adjunct to specific anesthetic or analgesic protocols. Further veterinary studies are needed to establish the frequency and importance of magnesium disorders in animals and the potential benefit of magnesium infusions as a therapeutic adjunct to specific diseases.

PROGNOSIS

The prognosis for most patients with magnesium disorders is variable and largely dependent on the underlying cause of the disorder.

The effects of sustained aerobic swimming on osmoregulatory pathways in Atlantic salmon Salmo salar smolts

Atlantic salmon Salmo salar smolts were exposed to one of the four different aerobic exercise regimens for 10 weeks followed by a 1 week final smoltification period in fresh water and a subsequent eight-day seawater transfer period. Samples of gill and intestinal tissue were taken at each time point and gene expression was used to assess the effects of exercise training on both branchial and intestinal osmoregulatory pathways. Real-time polymerase chain reaction (PCR) analysis revealed that exercise training up-regulated the expression of seawater relevant genes in the gills of S. salar smolts, including Na(+) , K(+) ATPase (nka) subunit α1b, the Na(+) , K(+) , 2 Cl(-) co-transporter (nkcc1) and cftr channel. These findings suggest that aerobic exercise stimulates expression of seawater ion transport pathways that may act to shift the seawater transfer window for S. salar smolts. Aerobic exercise also appeared to stimulate freshwater ion uptake mechanisms probably associated with an osmorespiratory compromise related to increased exercise. No differences were observed in plasma Na(+) and Cl(-) concentrations as a consequence of exercise treatment, but plasma Na(+) was lower during the final smoltification period in all treatments. No effects of exercise were observed for intestinal nkcc2, nor the Mg(2+) transporters slc41a2 and transient receptor protein M7 (trpm7); however, expression of both Mg(2+) transporters was affected by salinity transfer suggesting a dynamic role in Mg(2+) homeostasis in fishes.

Hypomagnesemia in brachycephalic dogs

Background

Brachycephalic dogs are at risk for arterial hypertension and obstructive sleep apnea, which are both associated with chronic magnesium (Mg) depletion.

Hypothesis/Objectives

To compare the period prevalence of hypomagnesemia between Boxers and Bulldogs presented to a referral teaching hospital. To screen a group of Bulldogs for evidence of hypomagnesemia, and to obtain pilot data regarding the utility of parenteral Mg tolerance testing (PMgTT) in the diagnosis of whole‐body Mg deficiency.

Animals

Chemistry laboratory submissions were retrospectively analyzed for serum total Mg (tMg) in Boxers and Bulldogs. Prospectively, 16 healthy client‐owned Bulldogs were enrolled.

Methods

Retrospective case study. tMg concentrations were compared between Boxers and Bulldogs. Dogs with low serum albumin or high serum creatinine concentrations were excluded. Prospectively, ionized Mg (iMg), tMg, and arterial blood pressure were measured and iMg‐to‐tMg ratio (iMg : tMg) was calculated. Parenteral Mg tolerance testing (PMgTT) was performed in 3/16 dogs.

Results

In the retrospective study, period prevalence of hypomagnesemia was 4.7% in Boxers and 15% in Bulldogs (P = .02). The risk ratio for hypomagnesemia in Bulldogs was 1.8 when compared to Boxers (CI: 1.3–2.7). In the prospective study, iMg was [median (interquartile)] 0.43 (0.42–0.46) mmol/L (reference range 0.4–0.52), tMg was 1.9 (1.8–1.9) mg/dL (reference range 1.9–2.5). iMg : tMg was [mean (±SD)] 0.59 ± 0.04. Percentage retention after PMgTT were 55%, 95%, and 67%, respectively.

Conclusions and Clinical Importance

Mg deficiency is common in Bulldogs and could contribute to comorbidities often observed in this breed. iMg : tMg and PMgTT might prove helpful in detecting chronic subclinical Mg deficiency.

The Pathophysiologic Roles of TRPM7 Channel

Transient receptor potential melastatin 7 (TRPM7) is a member of the melastatin-related subfamily and contains a channel and a kinase domain. TRPM7 is known to be associated with cell proliferation, survival, and development. It is ubiquitously expressed, highly permeable to Mg²⁺ and Ca²⁺, and its channel activity is negatively regulated by free Mg²⁺ and Mg-complexed nucleotides. Recent studies have investigated the relationships between TRPM7 and a number of diseases. TRPM7 regulates cell proliferation in several cancers, and is associated with ischemic cell death and vascular smooth muscle cell (VSMC) function. This review discusses the physiologic and pathophysiologic functions and significance of TRPM7 in several diseases.

Functional properties of ion channels and transporters in tumour vascularization

Vascularization is crucial for solid tumour growth and invasion, providing metabolic support and sustaining metastatic dissemination. It is now accepted that ion channels and transporters play a significant role in driving the cancer growth at all stages. They may represent novel therapeutic, diagnostic and prognostic targets for anti-cancer therapies. On the other hand, although the expression and role of ion channels and transporters in the vascular endothelium is well recognized and subject of recent reviews, only recently has their involvement in tumour vascularization been recognized. Here, we review the current literature on ion channels and transporters directly involved in the angiogenic process. Particular interest will be focused on tumour angiogenesis in vivo as well as in the different steps that drive this process in vitro, such as endothelial cell proliferation, migration, adhesion and tubulogenesis. Moreover, we compare the 'transportome' system of tumour vascular network with the physiological one.

TRPM7

The channel kinases TRPM6 and TRPM7 are fusion proteins with an ion transport domain and an enzymatically active kinase domain. TRPM7 has been found in every mammalian tissue investigated to date. The two-in-one protein structure, the ubiquitous expression profile, and the protein's unique biophysical characteristics that enable divalent ion transport involve TRPM7 in a plethora of (patho)physiological processes. With its prominent role in cellular and systemic magnesium homeostasis, TRPM7 emerges as a key player in embryonic development, global ischemia, cardiovascular disease, and cancer.

Emerging role of TRP channels in cell migration: from tumor vascularization to metastasis

Transient Receptor Potential (TRP) channels modulate intracellular Ca(2+) concentrations, controlling critical cytosolic and nuclear events that are involved in the initiation and progression of cancer. It is not, therefore, surprising that the expression of some TRP channels is altered during tumor growth and metastasis. Cell migration of both epithelial and endothelial cells is an essential step of the so-called metastatic cascade that leads to the spread of the disease within the body. It is in fact required for both tumor vascularization as well as for tumor cell invasion into adjacent tissues and intravasation into blood/lymphatic vessels. Studies from the last 15 years have unequivocally shown that the ion channles and the transport proteins also play important roles in cell migration. On the other hand, recent literature underlies a critical role for TRP channels in the migration process both in cancer cells as well as in tumor vascularization. This will be the main focus of our review. We will provide an overview of recent advances in this field describing TRP channels contribution to the vascular and cancer cell migration process, and we will systematically discuss relevant molecular mechanism involved.

The interaction of transient receptor potential melastatin 7 with macrophages promotes vascular adventitial remodeling in transverse aortic constriction rats

Transient receptor potential melastatin 7 (TRPM7), a novel channel kinase, has been recently identified in the vasculature. However, its regulation and function in vascular diseases remain poorly understood. To address this lack of knowledge, we sought to examine whether TRPM7 can mediate the vascular remodeling process induced by pressure overload in the right common carotid artery proximal to the band (RCCA-B) in male Sprague-Dawley rats with transverse aortic constriction (TAC). The contribution of TRPM7 to amplified vascular remodeling after TAC was tested using morphometric and western blot analyses. Pressure overload-induced vascular wall thickening, especially in the adventitia, was readily detected in RCCA-B. The TRPM7 level was increased with a simultaneous accumulation of macrophages in the adventitia of RCCA-B, whereas the anti-inflammatory molecule annexin-1, a TRPM7 downstream target, was decreased. After the addition of the TRPM7 inhibitor 2-aminoethoxydiphenyl borate (2-APB), significant reductions in macrophage accumulation as well as the expression of monocyte chemotactic protein-1, SM-22-α and collagen I were observed, whereas annexin-1 was rescued. Finally, in cultured vascular adventitial fibroblasts treated with macrophage-conditioned medium, there were marked increases in the expression of TRPM7 and SM-22-α with a concurrent reduction in annexin-1 expression; these effects were largely prevented by treatment with 2-APB and specific anti-TRPM7 small interfering RNA. Our findings provide the first demonstration of the potential regulatory roles of TRPM7 in the vascular inflammation, pressure overload-mediated vascular adventitial collagen accumulation and cell phenotypic transformation in TAC rats. The targeting of TRPM7 has potential therapeutic importance for vascular diseases.

Hair magnesium, but not serum magnesium, is associated with left ventricular wall thickness in hemodialysis patients

BACKGROUND

Extracellular magnesium (Mg) accounts for approximately 1% of the total body Mg. Clinically, serum Mg concentration is measured, but it does not necessarily reflect total body Mg status. Although relationships have been reported between reduced Mg and cardiovascular disease in non-dialysis patients, there have been few such studies in hemodialysis patients. It was hypothesized that reduced Mg, as represented by lower Mg concentration in the hair, would be associated with echocardiographic parameters in chronic hemodialysis patients.

METHODS AND RESULTS

Hair Mg concentration was measured in 79 male hemodialysis patients using inductively coupled plasma mass spectrometry, and the relationships between hair Mg concentration and echocardiographic parameters were investigated. There was no significant correlation between Mg concentration in the hair and in serum. Hair Mg concentration in the patients with high-left ventricular mass index (LVMI) was significantly lower than that in the low-LVMI patients. Hair Mg concentration correlated significantly and negatively with posterior left ventricular wall thickness, interventricular septum thickness, left ventricular wall thickness (LVWT), and relative wall thickness. Serum Mg concentration, however, did not correlate with any of these echocardiographic parameters.

CONCLUSIONS

In hemodialysis patients, hair Mg concentration is a biomarker, independent of serum Mg concentration. Hair Mg, but not serum Mg, was significantly and negatively associated with LVWT. Reduced tissue Mg concentration, as measured in the hair, may be associated with left ventricular hypertrophy in hemodialysis patients.

Aldosterone signaling through transient receptor potential melastatin 7 cation channel (TRPM7) and its α-kinase domain

We demonstrated a role for the Mg(2+) transporter TRPM7, a bifunctional protein with channel and α-kinase domains, in aldosterone signaling. Molecular mechanisms underlying this are elusive. Here we investigated the function of TRPM7 and its α-kinase domain on Mg(2+) and pro-inflammatory signaling by aldosterone. Kidney cells (HEK-293) expressing wild-type human TRPM7 (WThTRPM7) or constructs in which the α-kinase domain was deleted (ΔKinase) or rendered inactive with a point mutation in the ATP binding site of the α-kinase domain (K1648R) were studied. Aldosterone rapidly increased [Mg(2+)]i and stimulated NADPH oxidase-derived generation of reactive oxygen species (ROS) in WT hTRPM7 and TRPM7 kinase dead mutant cells. Translocation of annexin-1 and calpain-II and spectrin cleavage (calpain target) were increased by aldosterone in WT hTRPM7 cells but not in α-kinase-deficient cells. Aldosterone stimulated phosphorylation of MAP kinases and increased expression of pro-inflammatory mediators ICAM-1, Cox-2 and PAI-1 in Δkinase and K1648R cells, effects that were inhibited by eplerenone (mineralocorticoid receptor (MR) blocker). 2-APB, a TRPM7 channel inhibitor, abrogated aldosterone-induced Mg(2+) responses in WT hTRPM7 and mutant cells. In 2-APB-treated ΔKinase and K1648R cells, aldosterone-stimulated inflammatory responses were unchanged. These data indicate that aldosterone stimulates Mg(2+) influx and ROS production in a TRPM7-sensitive, kinase-insensitive manner, whereas activation of annexin-1 requires the TRPM7 kinase domain. Moreover TRPM7 α-kinase modulates inflammatory signaling by aldosterone in a TRPM7 channel/Mg(2+)-independent manner. Our findings identify novel mechanisms for non-genomic actions of aldosterone involving differential signaling through MR-activated TRPM7 channel and α-kinase.

Whole grains, type 2 diabetes, coronary heart disease, and hypertension: links to the aleurone preferred over indigestible fiber

Higher whole grain cereal intakes are associated with substantially lower risks of type 2 diabetes, coronary heart disease, and hypertension. These reduced risks have been established in large prospective studies that now include millions of person-years of follow-up. We analyze the results of 11 major prospective studies to provide recommendations about whole grain consumption. The following review establishes the amount of whole grains that should ideally be consumed based on prospective evidence; defines the nature of whole grains; identifies that the whole grain evidence is robust and not due to confounding; and provides a detailed assessment of several potential mechanisms for the effect of whole grains on health. We draw the following conclusions. Firstly, to maintain health, 40 grams or more of whole grains should be consumed daily. This is about a bowl of whole grain breakfast cereal daily, but 80% of the population does not achieve this. Secondly, aleurone in bran is a critical grain component generally overlooked in favor of indigestible fiber. Live aleurone cells constitute 50% of millers' bran. They store minerals, protein, and the antioxidant ferulic acid, and are clearly more than just indigestible fiber. Finally, we suggest potential roles for magnesium, zinc, and ferulic acid in the development of chronic disease. If the results of prospective studies were applied to the life-style practices of modern societies there exists the potential for enormous personal health and public financial benefits.

Role of TRPM in melanocytes and melanoma

Transient receptor potential (TRP) cation channel superfamily plays important roles in variety cellular processes including polymodal cellular sensing, cell adhesion, cell polarity, proliferation, differentiation and apoptosis. One of its subfamilies are TRPM channels. mRNA expression of its founding member, TRPM1 (melastatin), correlates with terminal melanocytic differentiation and loss of its expression has been identified as an important diagnostic and prognostic marker for primary cutaneous melanoma. Because TRPM1 gene codes two transcripts: TRPM1 channel protein in its exons and miR-211 in one of its introns, we propose a dual role for TRPM1 gene where the loss of TRPM1 channel protein is an excellent marker of melanoma aggressiveness, while the expression of miR-211 is linked to the tumor suppressor function of TRPM1. In addition, three other members of this subfamily, TRPM 2, 7 and 8 are implicated in the regulation of melanocytic behaviour. TRPM2 is capable of inducing melanoma apoptosis and necrosis. TRPM7 can be a protector and detoxifier in both melanocytes and melanoma cells. TRPM8 can mediate agonist-induced melanoma cell death. Therefore, we propose that TRPM1, TRPM2, TRPM7 and TRPM8 play crucial roles in melanocyte physiology and melanoma oncology and are excellent diagnostic markers and theraputic targets.

Characterization of Mg²⁺-regulated TRPM7-like current in human atrial myocytes

BACKGROUND

TRPM7 (Transient Receptor Potential of the Melastatin subfamily) proteins are highly expressed in the heart, however, electrophysiological studies, demonstrating and characterizing these channels in human cardiomyocytes, are missing.

METHODS

We have used the patch clamp technique to characterize the biophysical properties of TRPM7 channel in human myocytes isolated from right atria small chunks obtained from 116 patients in sinus rhythm during coronary artery and valvular surgery. Under whole-cell voltage-clamp, with Ca²⁺ and K⁺ channels blocked, currents were generated by symmetrical voltage ramp commands to potentials between -120 and +80 mV, from a holding potential of -80 mV.

RESULTS

We demonstrate that activated native current has dual control by intracellular Mg²⁺ (free-Mg²⁺ or ATP-bound form), and shows up- or down-regulation by its low or high levels, respectively, displaying outward rectification in physiological extracellular medium. High extracellular Mg²⁺ and Ca²⁺ block the outward current, while Gd³⁺, SpM⁴⁺, 2-APB, and carvacrol inhibit both (inward and outward) currents. Besides, divalents also permeate the channel, and the efficacy sequence, at 20 mM, was Mg²⁺>Ni²⁺>Ca²⁺>Ba²⁺>Cd²⁺ for decreasing outward and Ni²⁺>Mg²⁺>Ba²⁺≥Ca²⁺>Cd²⁺ for increasing inward currents. The defined current bears many characteristics of heterologously expressed or native TRPM7 current, and allowed us to propose that current under study is TRPM7-like. However, the time of beginning and time to peak as well steady state magnitude (range from 1.21 to 11.63 pA/pF, n(cells/patients) = 136/77) of induced TRPM7-like current in atrial myocytes from different patients showed a large variability, while from the same sample of human atria all these parameters were very homogenous. We present new information that TRPM7-like current in human myocytes is less sensitive to Mg²⁺. In addition, in some myocytes (from 24 out of 77 patients) that current was already up-regulated at membrane rupture.

CONCLUSIONS

This study provides the first electrophysiological description of TRPM7-like current in native human atrial myocytes. Less sensitivity to intracellular Mg²⁺ suggests for channel operation under physiological conditions. The TRPM7-like current up-regulation indicates the pathophysiological evidence of that current in human heart.

Mechanoregulation of cytoskeletal dynamics by TRP channels

The ability of cells to respond to mechanical stimulation is crucial to a variety of biological processes, including cell migration, axonal outgrowth, perception of pain, cardiovascular responses and kidney physiology. The translation of mechanical cues into cellular responses, a process known as mechanotransduction, typically takes place in specialized multiprotein structures such as cilia, cell-cell or cell-matrix adhesions. Within these structures, mechanical forces such as shear stress and membrane stretch activate mechanosensitive proteins, which set off a series of events that lead to altered cell behavior. Members of the transient receptor potential (TRP) family of cation channels are emerging as important players in mechanotransductory pathways. Localized within mechanosensory structures, they are activated by mechanical stimuli and trigger fast as well as sustained cytoskeletal responses. In this review, we will provide an overview of how TRP channels affect cytoskeletal dynamics in various mechano-regulated processes.

The effect of acute magnesium loading on the maximal exercise performance of stable chronic obstructive pulmonary disease patients

OBJECTIVE

The potential influence of magnesium on exercise performance is a subject of increasing interest. Magnesium has been shown to have bronchodilatatory properties in asthma and chronic obstructive pulmonary disease patients. The aim of this study was to investigate the effects of acute magnesium IV loading on the aerobic exercise performance of stable chronic obstructive pulmonary disease patients.

METHODS

Twenty male chronic obstructive pulmonary disease patients (66.2 + 8.3 years old, FEV1: 49.3+19.8%) received an IV infusion of 2 g of either magnesium sulfate or saline on two randomly assigned occasions approximately two days apart. Spirometry was performed both before and 45 minutes after the infusions. A symptom-limited incremental maximal cardiopulmonary test was performed on a cycle ergometer at approximately 100 minutes after the end of the infusion.

RESULTS

Magnesium infusion was associated with significant reductions in the functional residual capacity (-0.41 l) and residual volume (-0.47 l), the mean arterial blood pressure (-5.6 mmHg) and the cardiac double product (734.8 mmHg.bpm) at rest. Magnesium treatment led to significant increases in the maximal load reached (+8 w) and the respiratory exchange ratio (0.06) at peak exercise. The subgroup of patients who showed increases in the work load equal to or greater than 5 w also exhibited significantly greater improvements in inspiratory capacity (0.29 l).

CONCLUSIONS

The acute IV loading of magnesium promotes a reduction in static lung hyperinflation and improves the exercise performance in stable chronic obstructive pulmonary disease patients. Improvements in respiratory mechanics appear to be responsible for the latter finding.

Identification of the phosphorylation sites on intact TRPM7 channels from mammalian cells

Transient receptor potential melastatin 7 (TRPM7) channels are divalent cation-selective ion channels that are permeable to Ca(2+) and Mg(2+). TRPM7 is ubiquitously expressed in vertebrate cells and contains both an ion channel and a kinase domain. TRPM7 plays an important role in regulating cellular homeostatic levels of Ca(2+) and Mg(2+) in mammalian cells. Although studies have shown that the kinase domain of TRPM7 is required for channel activation and can phosphorylate other target proteins, a systematic analysis of intact TRPM7 channel phosphorylation sites expressed in mammalian cells is lacking. We applied mass spectrometric proteomic techniques to identify and characterize the key phosphorylation sites in TRPM7 channels. We identified 14 phosphorylation sites in the cytoplasmic domain of TRPM7, eight of which have not been previously reported. The identification of phosphorylation sites using antibody-based immunopurification and mass spectrometry is an effective approach for defining the phosphorylation status of TRPM7 channels. The present results show that TRPM7 channels are phosphorylated at multiple sites, which serves as a mechanism to modulate the dynamic functions of TRPM7 channels in mammalian cells.

The role of magnesium in hypertension and cardiovascular disease

Magnesium intake of 500 mg/d to 1000 mg/d may reduce blood pressure (BP) as much as 5.6/2.8 mm Hg. However, clinical studies have a wide range of BP reduction, with some showing no change in BP. The combination of increased intake of magnesium and potassium coupled with reduced sodium intake is more effective in reducing BP than single mineral intake and is often as effective as one antihypertensive drug in treating hypertension. Reducing intracellular sodium and calcium while increasing intracellular magnesium and potassium improves BP response. Magnesium also increases the effectiveness of all antihypertensive drug classes. It remains to be conclusively proven that cardiovascular disease such as coronary heart disease, ischemic stroke, and cardiac arrhythmias can be prevented or treated with magnesium intake. Preliminary evidence suggests that insulin sensitivity, hyperglycemia, diabetes mellitus, left ventricular hypertrophy, and dyslipidemia may be improved with increased magnesium intake. Various genetic defects in magnesium transport are associated with hypertension and possibly with cardiovascular disease. Oral magnesium acts as a natural calcium channel blocker, increases nitric oxide, improves endothelial dysfunction, and induces direct and indirect vasodilation.

Ion channels and transporters in cancer. 6. Vascularizing the tumor: TRP channels as molecular targets

Tumor vascularization is a critical process that determines tumor growth and metastasis. In the last decade new experimental evidence obtained from in vitro and in vivo studies have challenged the classical angiogenesis model forcing us to consider new scenarios for tumor neovascularization. In particular, the genetic stability of tumor-derived endothelial cells (TECs) has been recently questioned in several studies, which show that TECs, as well as pericytes, differ significantly from their normal counterparts at genetic and functional levels. In addition to such an epigenetic action of tumor microenvironment on endothelial cells (ECs) commitment, the distinct characteristics of TECs could be due to differences in their origin compared with preexisting differentiated ECs. Intracellular Ca(2+) signals are involved at different critical phases in the regulation of the complex process of angiogenesis and tumor progression. These signals are generated by a wide variety of intrinsic and extrinsic factors. Several key components of Ca(2+) signaling including Ca(2+) channels in the plasma membrane, endoplasmic reticulum, calcium pumps, and mitochondria contribute to the generation, amplitude, and frequency of these Ca(2+) change. In particular, several members of the transient receptor potential (TRP) family of calcium-permeable channels have profound effects on the function of ECs. Because of its multifaceted role in the control of cell function, proliferation, and motility, TRP channels have been suggested as a potential molecular target for control of tumor neovascularization. Since plasma membrane Ca(2+) channels are easily and directly accessible via the bloodstream, they are potential targets for a number of pharmacological and antibody-targeted therapeutic strategies, with specificity being the main limitation. In this review we discuss recent advances in understanding the role of Ca(2+) channels, with specific reference to TRP channels, in tumor vascularization process.