TRPM6 and TRPM7--Gatekeepers of human magnesium metabolism

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.

Improving diagnosis and treatment of hypomagnesemia

Magnesium is one of the most abundant cations in the body and acts as a cofactor in more than 600 biochemical reactions. Hypomagnesemia is a highly prevalent condition, especially in subjects with comorbid conditions, but has received less attention than other electrolyte disturbances. This review will discuss magnesium physiology, absorption, storage, distribution across the body, and kidney excretion. After reviewing the regulation of magnesium homeostasis, we will focus on the etiology and clinical presentation of hypomagnesemia. The role of laboratory medicine in hypomagnesemia will be the main purpose of this review, and we will discuss the laboratory tests and different samples and methods for its measurement. Although free magnesium is physiologically active, total serum magnesium is the most commonly used measurement in laboratory medicine and is apt for clinical purposes; however, it is not appropriately used, and many patients with hypomagnesemia remain undiagnosed and not treated. Using information technologies, laboratory medicine can largely improve the diagnosis and treatment of hypomagnesemia through the design and establishment of automatic demand management and result management interventions by acting in the first and last steps of the laboratory cycle, test requests, and actions taken after test results, to unmask patients with hypomagnesemia and improve the number of patients undergoing treatment.

Magnesium and Vascular Calcification in Chronic Kidney Disease: Current Insights

Magnesium (Mg) plays crucial roles in multiple essential biological processes. As the kidneys are the primary organ responsible for maintaining the blood concentration of Mg, people with chronic kidney disease (CKD) may develop disturbances in Mg. While both hyper- and hypomagnesemia may lead to adverse effects, the consequences associated with hypomagnesemia are often more severe and lasting. Importantly, observational studies have shown that CKD patients with hypomagnesemia have greater vascular calcification. Vascular calcification is accelerated and contributes to a high mortality rate in the CKD population. Both in vitro and animal studies have demonstrated that Mg protects against vascular calcification via several potential mechanisms, such as inhibiting the formation of both hydroxyapatite and pathogenic calciprotein particles as well as limiting osteogenic differentiation, a process in which vascular smooth muscle cells in the media layer of the arteries transform into bone-like cells. These preclinical findings have led to several important clinical trials that have investigated the effects of Mg supplementation on vascular calcification in people with CKD. Interestingly, two major clinical studies produced contradictory findings, resulting in a state of equipoise. This narrative review provides an overview of our current knowledge in the renal handling of Mg in health and CKD and the underlying mechanisms by which Mg may protect against vascular calcification. Lastly, we evaluate the strength of evidence from clinical studies on the efficacy of Mg supplementation and discuss future research directions.

Cannabigerolic Acid (CBGA) Inhibits the TRPM7 Ion Channel Through its Kinase Domain

Cannabinoids are a major class of compounds produced by the plant Cannabis sativa. Previous work has demonstrated that the main cannabinoids cannabidiol (CBD) and tetrahydrocannabinol (THC) can have some beneficial effects on pain, inflammation, epilepsy, and chemotherapy-induced nausea and vomiting. While CBD and THC represent the two major plant cannabinoids, some hemp varieties with enzymatic deficiencies produce mainly cannabigerolic acid (CBGA). We recently reported that CBGA has a potent inhibitory effect on both Store-Operated Calcium Entry (SOCE) via inhibition of Calcium Release-Activated Calcium (CRAC) channels as well as currents carried by the channel-kinase TRPM7. Importantly, CBGA prevented kidney damage and suppressed mRNA expression of inflammatory cytokines through inhibition of these mechanisms in an acute nephropathic mouse model. In the present study, we investigate the most common major and minor cannabinoids to determine their potential efficacy on TRPM7 channel function. We find that approximately half of the tested cannabinoids suppress TRPM7 currents to some degree, with CBGA having the strongest inhibitory effect on TRPM7. We determined that the CBGA-mediated inhibition of TRPM7 requires a functional kinase domain, is sensitized by both intracellular Mg⋅ATP and free Mg2+ and reduced by increases in intracellular Ca2+. Finally, we demonstrate that CBGA inhibits native TRPM7 channels in a B lymphocyte cell line. In conclusion, we demonstrate that CBGA is the most potent cannabinoid in suppressing TRPM7 activity and possesses therapeutic potential for diseases in which TRPM7 is known to play an important role such as cancer, stroke, and kidney disease.

Magnesium Status, Genetic Variants of Magnesium-Related Ion Channel Transient Receptor Potential Membrane Melastatin 6 (TRPM6) and the Risk of Gestational Diabetes Mellitus in Chinese Pregnant Women: A Nested Case-Control Study

SCOPE

Magnesium plays an important role in regulating glucose metabolism. The study attempts to explore association between magnesium status and single nucleotide polymorphisms (SNPs) of gene involved in magnesium absorption-transient receptor potential membrane melastatin 6 (TRPM6) and gestational diabetes mellitus (GDM) risk METHODS AND RESULTS: A nested case-control study including 170 GDM cases and matched 340 controls is conducted based on Tongji Birth Cohort. Dietary, serum, and urine magnesium are evaluated before the diagnosis of GDM. Compared to the lowest tertile, women in the highest tertile of serum magnesium are at a lower risk of GDM (adjusted odds ratio [aOR] 0.42, 95% confidence intervals [CI] 0.21-0.84). Serum magnesium is inversely associated with insulin and homeostatic model assessment of insulin resistance (β = -0.05, p = 0.002; β = -0.04, p = 0.001, respectively). The aOR for GDM in carriers of the CT or CC genotypes of TRPM6 rs2274924 compared with carriers of the TT genotype is 2.76 (95% CI 1.78-4.26). Dietary magnesium is positively associated with serum magnesium (β = 0.02, p = 0.004), but not with GDM risk.

CONCLUSION

Serum magnesium and the TRPM6 rs2274924 polymorphism are associated with the risk of GDM.

Cell death induction and protection by activation of ubiquitously expressed anion/cation channels. Part 3: the roles and properties of TRPM2 and TRPM7

Cell volume regulation (CVR) is a prerequisite for animal cells to survive and fulfill their functions. CVR dysfunction is essentially involved in the induction of cell death. In fact, sustained normotonic cell swelling and shrinkage are associated with necrosis and apoptosis, and thus called the necrotic volume increase (NVI) and the apoptotic volume decrease (AVD), respectively. Since a number of ubiquitously expressed ion channels are involved in the CVR processes, these volume-regulatory ion channels are also implicated in the NVI and AVD events. In Part 1 and Part 2 of this series of review articles, we described the roles of swelling-activated anion channels called VSOR or VRAC and acid-activated anion channels called ASOR or PAC in CVR and cell death processes. Here, Part 3 focuses on therein roles of Ca2+-permeable non-selective TRPM2 and TRPM7 cation channels activated by stress. First, we summarize their phenotypic properties and molecular structure. Second, we describe their roles in CVR. Since cell death induction is tightly coupled to dysfunction of CVR, third, we focus on their participation in the induction of or protection against cell death under oxidative, acidotoxic, excitotoxic, and ischemic conditions. In this regard, we pay attention to the sensitivity of TRPM2 and TRPM7 to a variety of stress as well as to their capability to physicall and functionally interact with other volume-related channels and membrane enzymes. Also, we summarize a large number of reports hitherto published in which TRPM2 and TRPM7 channels are shown to be involved in cell death associated with a variety of diseases or disorders, in some cases as double-edged swords. Lastly, we attempt to describe how TRPM2 and TRPM7 are organized in the ionic mechanisms leading to cell death induction and protection.

Beyond Ion Homeostasis: Hypomagnesemia, Transient Receptor Potential Melastatin Channel 7, Mitochondrial Function, and Inflammation

As the second most abundant intracellular divalent cation, magnesium (Mg2+) is essential for cell functions, such as ATP production, protein/DNA synthesis, protein activity, and mitochondrial function. Mg2+ plays a critical role in heart rhythm, muscle contraction, and blood pressure. A significant decline in Mg2+ intake has been reported in developed countries because of the increased consumption of processed food and filtered/deionized water, which can lead to hypomagnesemia (HypoMg). HypoMg is commonly observed in cardiovascular diseases, such as heart failure, hypertension, arrhythmias, and diabetic cardiomyopathy, and HypoMg is a predictor for cardiovascular and all-cause mortality. On the other hand, Mg2+ supplementation has shown significant therapeutic effects in cardiovascular diseases. Some of the effects of HypoMg have been ascribed to changes in Mg2+ participation in enzyme activity, ATP stabilization, enzyme kinetics, and alterations in Ca2+, Na+, and other cations. In this manuscript, we discuss new insights into the pathogenic mechanisms of HypoMg that surpass previously described effects. HypoMg causes mitochondrial dysfunction, oxidative stress, and inflammation. Many of these effects can be attributed to the HypoMg-induced upregulation of a Mg2+ transporter transient receptor potential melastatin 7 channel (TRMP7) that is also a kinase. An increase in kinase signaling mediated by HypoMg-induced TRPM7 transcriptional upregulation, independently of any change in Mg2+ transport function, likely seems responsible for many of the effects of HypoMg. Therefore, Mg2+ supplementation and TRPM7 kinase inhibition may work to treat the sequelae of HypoMg by preventing increased TRPM7 kinase activity rather than just altering ion homeostasis. Since many diseases are characterized by oxidative stress or inflammation, Mg2+ supplementation and TRPM7 kinase inhibition may have wider implications for other diseases by acting to reduce oxidative stress and inflammation.

Study Based on the Alliance Between Serum Magnesium Levels and Preterm Labor: An Inclusive Review

Preterm labor, regarded as the onset of labor before 37 weeks of gestation, is a highly prevalent issue in obstetrics with repercussions for neonatal health. This review article presents an in-depth analysis of the alliance between serum magnesium levels and preterm labor. The review explores the physiological roles of magnesium right through pregnancy, including its significance for energy metabolism, smooth muscle contraction, deoxyribonucleic acid (DNA), and protein synthesis. It addresses cellular transport and the homeostasis of magnesium. The pathophysiological processes encompassing inflammation, oxidative stress, calcium regulation, smooth muscle contractility, and neuroendocrine pathways are investigated. The review evaluates epidemiological studies investigating the alliance between serum magnesium levels and preterm labor. The review incorporates an assortment of study varieties, such as observational studies, case-control studies, prospective cohort studies, and meta-analyses. In the course of reviewing the prognostic relevance of serum magnesium levels in premature labor, therapeutic implications involving diagnostic precision, prognostic significance, and therapeutic response assessment have additionally been addressed. Therapeutic interventions targeting magnesium levels, such as magnesium supplementation, tocolytic therapy, and the role of magnesium in antenatal corticosteroid administration, are explored. This review provides an in-depth evaluation of the correlation between serum magnesium levels and preterm labor, stressing its therapeutic significance and repercussions for future research and treatment strategies.

The Benefits of Nanosized Magnesium Oxide in Fish Megalobrama amblycephala: Evidence in Growth Performance, Redox Defense, Glucose Metabolism, and Magnesium Homeostasis

This study evaluated the effects of dietary magnesium oxide nanoparticles (MgO NPs) on the growth, redox defense, glucose metabolism, and magnesium homeostasis in blunt snout bream. Fish (12.42 ± 0.33 g) were fed seven diets containing graded levels of MgO NPs (0, 60, 120, 240, 480, 960, and 1920 mg/kg) for 12 weeks. Whole-body Mg retention decreased significantly as the dietary Mg increased. As dietary MgO NPs levels reached 120 mg/kg, the growth performance and feed utilization remarkably improved. When added at 240 mg/kg, oxidative stress was significantly reduced evidenced by the increased Mn-sod transcription and the decreased CAT and GSH-Px activities and the MDA content. Meanwhile, it enhanced glucose transport, glycolysis, and glycogen synthesis, while inhibiting gluconeogenesis, as was characterized by the increased transcriptions of glut2, gk, and pk, and the decreased transcriptions of fbpase and g6pase. In addition, the supplementation of 120 mg/kg MgO NPs promoted Mg transport marked by a significant increase in the protein expressions of TRMP7, S41A3, and CNNM1. In conclusion, the moderate supplementation of MgO NPs improved the growth performance, reduced hepatic oxidative stress, and promoted glucose transport, glycolysis, glycogen synthesis, and magnesium homeostasis in fish while inhibiting glu.

Gene-nutrient interactions that impact magnesium homeostasis increase risk for neural tube defects in mice exposed to dolutegravir

In 2018, data from a surveillance study in Botswana evaluating adverse birth outcomes raised concerns that women on antiretroviral therapy (ART) containing dolutegravir (DTG) may be at increased risk for neural tube defects (NTDs). The mechanism of action for DTG involves chelation of Mg²⁺ ions in the active site of the viral integrase. Plasma Mg²⁺ homeostasis is maintained primarily through dietary intake and reabsorption in the kidneys. Inadequate dietary Mg²⁺ intake over several months results in slow depletion of plasma Mg²⁺ and chronic latent hypomagnesemia, a condition prevalent in women of reproductive age worldwide. Mg²⁺ is critical for normal embryonic development and neural tube closure. We hypothesized that DTG therapy might slowly deplete plasma Mg²⁺ and reduce the amount available to the embryo, and that mice with pre-existing hypomagnesemia due to genetic variation and/or dietary Mg²⁺ insufficiency at the time of conception and initiation of DTG treatment would be at increased risk for NTDs. We used two different approaches to test our hypothesis: 1) we selected mouse strains that had inherently different basal plasma Mg²⁺ levels and 2) placed mice on diets with different concentrations of Mg²⁺. Plasma and urine Mg²⁺ were determined prior to timed mating. Pregnant mice were treated daily with vehicle or DTG beginning on the day of conception and embryos examined for NTDs on gestational day 9.5. Plasma DTG was measured for pharmacokinetic analysis. Our results demonstrate that hypomagnesemia prior to conception, due to genetic variation and/or insufficient dietary Mg²⁺ intake, increases the risk for NTDs in mice exposed to DTG. We also analyzed whole-exome sequencing data from inbred mouse strains and identified 9 predicted deleterious missense variants in Fam111a that were unique to the LM/Bc strain. Human FAM111A variants are associated with hypomagnesemia and renal Mg²⁺ wasting. The LM/Bc strain exhibits this same phenotype and was the strain most susceptible to DTG-NTDs. Our results suggest that monitoring plasma Mg²⁺ levels in patients on ART regimens that include DTG, identifying other risk factors that impact Mg²⁺ homeostasis, and correcting deficiencies in this micronutrient might provide an effective strategy for mitigating NTD risk.

Magnesium Deficiency and Cardiometabolic Disease

Magnesium (Mg²⁺) has many physiological functions within the body. These include important roles in maintaining cardiovascular functioning, where it contributes to the regulation of cardiac excitation-contraction coupling, endothelial functioning and haemostasis. The haemostatic roles of Mg²⁺ impact upon both the protein and cellular arms of coagulation. In this review, we examine how Mg²⁺ homeostasis is maintained within the body and highlight the various molecular roles attributed to Mg²⁺ in the cardiovascular system. In addition, we describe how nutritional and/or disease-associated magnesium deficiency, seen in some metabolic conditions, has the potential to influence cardiac and vascular outcomes. Finally, we also examine the potential for magnesium supplements to be employed in the prevention and treatment of cardiovascular disorders and in the management of cardiometabolic health.

On the modulation of TRPM channels: Current perspectives and anticancer therapeutic implications

The transient melastatin receptor potential (TRPM) ion channel subfamily functions as cellular sensors and transducers of critical biological signal pathways by regulating ion homeostasis. Some members of TRPM have been cloned from cancerous tissues, and their abnormal expressions in various solid malignancies have been correlated with cancer cell growth, survival, or death. Recent evidence also highlights the mechanisms underlying the role of TRPMs in tumor epithelial-mesenchymal transition (EMT), autophagy, and cancer metabolic reprogramming. These implications support TRPM channels as potential molecular targets and their modulation as an innovative therapeutic approach against cancer. Here, we discuss the general characteristics of the different TRPMs, focusing on current knowledge about the connection between TRPM channels and critical features of cancer. We also cover TRPM modulators used as pharmaceutical tools in biological trials and an indication of the only clinical trial with a TRPM modulator about cancer. To conclude, the authors describe the prospects for TRPM channels in oncology.

Magnesium Homeostasis: Lessons from Human Genetics

Mg2+, the fourth most abundant cation in the body, serves as a co-factor for about 600 cellular enzymes. One third of ingested Mg2+ is absorbed from the gut through a saturable transcellular process and a concentration-dependent paracellular process. Absorbed Mg2+ is excreted by the kidney and maintains serum Mg2+ within a narrow range of 0.7 to 1.25 mmol/L. The reabsorption of Mg2+ by the nephron is characterized by paracellular transport in the proximal tubule and thick ascending limb. The nature of the transport pathways in the gut epithelia and thick ascending limb has emerged from an understanding of the molecular mechanisms responsible for rare monogenetic disorders presenting with clinical hypomagnesemia. These human disorders due to loss-of function mutations, in concert with mouse models have led to a deeper understanding of Mg2+ transport in the gut and renal tubule. This review focuses on the nature of the transporters and channels revealed by human and mouse genetics and how they are integrated into an understanding of human Mg2+ physiology.

Sodium-Glucose Cotransporter 2 Inhibitors and Management of Refractory Hypomagnesemia Without Overt Urinary Magnesium Wasting: A Report of 2 Cases

Sodium-glucose cotransporter 2 (SGLT2) inhibitor have become widely used in patients with diabetes, heart failure, and kidney disease to improve clinical outcomes and diminish hospitalizations. They have also been associated with increased serum magnesium levels in patients with type 2 diabetes. The use of SGLT2 inhibitors resulted in improved magnesium homeostasis in a series of patients with refractory hypomagnesemia with urinary magnesium wasting. However, the role of SLGT2 inhibitors in patients with hypomagnesemia without urinary magnesium wasting remains unexplored. We report 2 cases with refractory hypomagnesemia without significant urinary magnesium wasting and dramatically improved serum magnesium levels after the initiation of SGLT2 inhibitors. Case 1 achieved independence from weekly intravenous magnesium infusions and reached sustainably greater serum magnesium levels with decreased oral magnesium supplementation and increased urinary fractional excretion of magnesium. Case 2 demonstrated improved serum magnesium levels with reduced oral magnesium supplementation without significant reduction in urinary fractional excretion of magnesium. These findings not only expand the use of SGLT2 inhibitors but also open the door for further studies to better understand the pathophysiology of how magnesium homeostasis is altered with inhibition of SGLT2.

TRPM7 via calcineurin/NFAT pathway mediates metastasis and chemotherapeutic resistance in head and neck squamous cell carcinoma

The exact mechanisms of Head and neck squamous carcinoma (HNSCC) chemoresistance and metastatic transformation remain unclear. In recent decades, members of the transient receptor potential (TRP) channel family have been proposed as potential biomarkers and/or drug targets in cancer treatment. First, in a TCGA cohort of HNSCC, TRPM7 is highly expressed in cancer tissues, especially the expression in invasive cancer tissues is statistically significant (p>0.001). In GEO and TCGA cohort, patients with high expression of TRPM7 and NFATC2 have poor overall survival rates. The expression of TRPM7 and NFATC2 showed a positive correlation. Compared to human normal oral keratinocytes (hNOK), TRPM7 is overexpressed in FaDU, SAS, and TW2.6 cell lines. Similarly, patients with HNSCC exhibited higher TRPM7 expression than non-HNSCC subjects, and this high TRPM7 expression was associated with worse 5-year overall survival. Furthermore, TRPM7 inversely correlated with E-cadherin, but positively correlated with Vimentin, NANOG, and BMI-1 mRNA levels. Consistent with this, we demonstrated the overexpression of TRPM7 in cisplatin-resistant subjects, compared to the cisplatin-sensitive counterparts. Moreover, shRNA-mediated silencing of TRPM7 significantly suppressed the migration, invasion, colony formation, and tumorsphere formation of SAS cells, with associated downregulation of Snail, c-Myc, cyclin D1, SOX2, OCT4, and NANOG proteins expression. Finally, compared with the untreated wild-type SAS cells or cisplatin-treated cells, shTRPM7 alone or in combination with cisplatin significantly inhibited tumorsphere and colony formation. These findings serving as the basis for development of novel therapeutic strategies against metastasis and chemoresistance, while providing new insights into TRPM7 biology and activity in HNSCC.

Identification of novel off targets of baricitinib and tofacitinib by machine learning with a focus on thrombosis and viral infection

As there are no clear on-target mechanisms that explain the increased risk for thrombosis and viral infection or reactivation associated with JAK inhibitors, the observed elevated risk may be a result of an off-target effect. Computational approaches combined with in vitro studies can be used to predict and validate the potential for an approved drug to interact with additional (often unwanted) targets and identify potential safety-related concerns. Potential off-targets of the JAK inhibitors baricitinib and tofacitinib were identified using two established machine learning approaches based on ligand similarity. The identified targets related to thrombosis or viral infection/reactivation were subsequently validated using in vitro assays. Inhibitory activity was identified for four drug-target pairs (PDE10A [baricitinib], TRPM6 [tofacitinib], PKN2 [baricitinib, tofacitinib]). Previously unknown off-target interactions of the two JAK inhibitors were identified. As the proposed pharmacological effects of these interactions include attenuation of pulmonary vascular remodeling, modulation of HCV response, and hypomagnesemia, the newly identified off-target interactions cannot explain an increased risk of thrombosis or viral infection/reactivation. While further evidence is required to explain both the elevated thrombosis and viral infection/reactivation risk, our results add to the evidence that these JAK inhibitors are promiscuous binders and highlight the potential for repurposing.

Role of mechanosensitive channels/receptors in atherosclerosis

Mechanical forces are critical physical cues that can affect numerous cellular processes regulating the development, tissue maintenance, and functionality of cells. The contribution of mechanical forces is especially crucial in the vascular system where it is required for embryogenesis and for maintenance of physiological function in vascular cells including aortic endothelial cells, resident macrophages, and smooth muscle cells. Emerging evidence has also identified a role of these mechanical cues in pathological conditions of the vascular system such as atherosclerosis and associated diseases like hypertension. Of the different mechanotransducers, mechanosensitive ion channels/receptors are gaining prominence due to their involvement in numerous physiological and pathological conditions. However, only a handful of potential mechanosensory ion channels/receptors have been shown to be involved in atherosclerosis, and their precise role in disease development and progression remains poorly understood. Here, we provide a comprehensive account of recent studies investigating the role of mechanosensitive ion channels/receptors in atherosclerosis. We discuss the different groups of mechanosensitive proteins and their specific roles in inflammation, endothelial dysfunction, macrophage foam cell formation, and lesion development, which are crucial for the development and progression of atherosclerosis. Results of the studies discussed here will help in developing an understanding of the current state of mechanobiology in vascular diseases, specifically in atherosclerosis, which may be important for the development of innovative and targeted therapeutics for this disease.

Sequential activation of M1 and M2 phenotypes in macrophages by Mg degradation from Ti-Mg alloy for enhanced osteogenesis

BACKGROUND

Even though the modulatory effects of Magnisum (Mg) and its alloys on bone-healing cells have been widely investigated during the last two decades, relatively limited attention has been paid on their inflammation-modulatory properties. Understanding the activation process of macrophages in response to the dynamic degradation process of Mg as well as the relationship between macrophage phenotypes and their osteogenic potential is critical for the design and development of advanced Mg-based or Mg-incorporated biomaterials.

METHODS

In this work, a Ti-0.625 Mg (wt.%) alloy fabricated by mechanical alloying (MA) and subsequent spark plasma sintering (SPS) was employed as a material model to explore the inflammatory response and osteogenic performance in vitro and in vivo by taking pure Ti as the control. The data analysis was performed following Student's t-test.

RESULTS

The results revealed that the macrophages grown on the Ti-0.625 Mg alloy underwent sequential activation of M1 and M2 phenotypes during a culture period of 5 days. The initially increased environmental pH (~ 8.03) was responsible for the activation of M1 macrophages, while accumulated Mg²⁺ within cells contributed to the lateral M2 phenotype activation. Both M1 and M2 macrophages promoted osteoblast-like SaOS-2 cell maturation. In vivo experiment further showed the better anti-inflammatory response, regenerative potentiality and thinner fibrous tissue layer for the Ti-0.625 Mg alloy than pure Ti.

CONCLUSION

The results highlighted the roles of Mg degradation in the Ti-0.625 Mg alloy on the sequential activation of macrophage phenotypes and the importance of modulating M1-to-M2 transition in macrophage phenotypes for the design and development of inflammation-modulatory biomaterials.

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.

Roles of Intramolecular Interactions in the Regulation of TRP Channels

The transient receptor potential (TRP) channels, classified into six (-A, -V, -P, -C, -M, -ML, -N and -Y) subfamilies, are important membrane sensors and mediators of diverse stimuli including pH, light, mechano-force, temperature, pain, taste, and smell. The mammalian TRP superfamily of 28 members share similar membrane topology with six membrane-spanning helices (S1-S6) and cytosolic N-/C-terminus. Abnormal function or expression of TRP channels is associated with cancer, skeletal dysplasia, immunodeficiency, and cardiac, renal, and neuronal diseases. The majority of TRP members share common functional regulators such as phospholipid PIP2, 2-aminoethoxydiphenyl borate (2-APB), and cannabinoid, while other ligands are more specific, such as allyl isothiocyanate (TRPA1), vanilloids (TRPV1), menthol (TRPM8), ADP-ribose (TRPM2), and ML-SA1 (TRPML1). The mechanisms underlying the gating and regulation of TRP channels remain largely unclear. Recent advances in cryogenic electron microscopy provided structural insights into 19 different TRP channels which all revealed close proximity of the C-terminus with the N-terminus and intracellular S4-S5 linker. Further studies found that some highly conserved residues in these regions of TRPV, -P, -C and -M members mediate functionally critical intramolecular interactions (i.e., within one subunit) between these regions. This review provides an overview on (1) intramolecular interactions in TRP channels and their effect on channel function; (2) functional roles of interplays between PIP2 (and other ligands) and TRP intramolecular interactions; and (3) relevance of the ligand-induced modulation of intramolecular interaction to diseases.

Case Report: A Novel Non-Canonical Splice Site Variant (c.1638+7T>C) in TRPM6 Cause Primary Homagnesemia With Secondary Hocalcemia

OBJECTIVE

Primary hypomagnesemia with secondary hypocalcemia (HSH) is caused by loss-of-function mutations in the TRPM6 gene encoding the epithelial magnesium channel. It is characterized by hypomagnesemia and secondary hypocalcemia associated with neurological symptoms. Here, we aimed to investigate the genetic defects of the TRPM6 gene found in a girl from China.

METHODS

The genomic DNA of the proband and the parents was extracted for whole-exome sequencing. Sanger sequencing was further performed to validate the candidate variants. Subsequently, the TRPM6 gene deletion was verified by quantitative PCR (qPCR) experiment. The effect of the variant on mRNA splicing was analyzed through a minigene splice assay and reverse transcription PCR (RT-PCR) in vitro.

RESULTS

The proband presented with the symptoms of generalized seizures, tetany, and muscle spasms, which were refractory to anticonvulsant treatment. Phenotypic data indicated that the patient had hypomagnesemia, poor parathyroid hormone response, and resultant hypocalcemia. The trio whole-exome sequencing identified that the proband carried compound heterozygous variants in the TRPM6 gene, a paternally derived exon 6 deletion, and a maternally derived splicing variant (c.1638+7T>C) in exon 14. The minigene splice assay confirmed that the c.1638+7T>C variant resulted in exon 14 skipping, which caused the alteration of TRPM6 mRNA splicing.

CONCLUSION

Our results support that the compound heterozygous variants in TRPM6 are responsible for HSH in this patient. A novel pathogenic splicing variant (c.1638+7T>C) in the intron 14 disturbs the normal TRPM6 mRNA splicing, suggesting that the non-classical splice variant plays a critical role in HSH. This variant is essential for future effective genetic diagnosis.

Case Report: Recurrent Hemiplegic Migraine Attacks Accompanied by Intractable Hypomagnesemia Due to a de novo TRPM7 Gene Variant

Transient receptor potential melastatin 7 (TRPM7) is a ubiquitously expressed chanzyme comprised of a divalent cation channel permeable to calcium and magnesium and a cytosolic serine-threonine α-kinase domain. TRPM7 has a crucial role in magnesium ion homeostasis and anoxic neuronal death, which was identified as a potential non-glutamate target for hypoxic-ischemic neuronal injury. TRPM7 is implicated in ischemic stroke and hypomagnesemia in many studies, but it has not been associated with disease in the OMIM database. No clinical cases between TRPM7 gene variants and hypomagnesemia have been reported, so far. One patient with recurrent hemiplegic migraine attacks accompanied by intractable hypomagnesemia was followed up at Tianjin Children's Hospital from 2018 to 2021. We systematically summarized and analyzed the clinical manifestations, imaging features, and serum magnesium changes of the patient. Genetic analysis was performed by whole-exome sequencing and Sanger sequencing to infer the etiology of hemiplegic migraine attacks and hypomagnesemia in this patient. Gene sequencing revealed a novel heterozygous variant of the TRPM7 gene (c.2998A>G, p. Met1000Val), which has not been reported previously; this is also a de novo variant that is not inherited from his parents. We described a novel variant p. Met1000Val (c.2998A>G) located in the transmembrane region of TRPM7 protein, which is possibly crucial for the normal function of the ion channel. Our study expands the variation spectrum of the TRPM7 gene, highlights the importance of molecular genetic evaluation in patients with TRPM7 gene deficiency, and demonstrates the causal relationship between TRPM7 gene variants and disease manifestations.

Anatomophysiology of the Henle's Loop: Emphasis on the Thick Ascending Limb

The loop of Henle plays a variety of important physiological roles through the concerted actions of ion transport systems in both its apical and basolateral membranes. It is involved most notably in extracellular fluid volume and blood pressure regulation as well as Ca²⁺ , Mg²⁺ , and acid-base homeostasis because of its ability to reclaim a large fraction of the ultrafiltered solute load. This nephron segment is also involved in urinary concentration by energizing several of the steps that are required to generate a gradient of increasing osmolality from cortex to medulla. Another important role of the loop of Henle is to sustain a process known as tubuloglomerular feedback through the presence of specialized renal tubular cells that lie next to the juxtaglomerular arterioles. This article aims at describing these physiological roles and at discussing a number of the molecular mechanisms involved. It will also report on novel findings and uncertainties regarding the realization of certain processes and on the pathophysiological consequences of perturbed salt handling by the thick ascending limb of the loop of Henle. Since its discovery 150 years ago, the loop of Henle has remained in the spotlight and is now generating further interest because of its role in the renal-sparing effect of SGLT2 inhibitors. © 2022 American Physiological Society. Compr Physiol 12:1-21, 2022.

TRPM7 Ion Channel: Oncogenic Roles and Therapeutic Potential in Breast Cancer

Simple Summary

Breast cancer is the most frequently diagnosed malignant tumor and the second leading cause of cancer death in women worldwide. The risk of developing breast cancer is 12.8%, i.e., 1 in 8 people, and a woman’s risk of dying is approximately 1 in 39. Calcium signals play an important role in various cancers and transport calcium ions may have altered expression in breast cancer, such as the TRPM7 calcium permeant ion channel, where overexpression may be associated with a poor prognosis. This review focuses on the TRPM7 channel, and the oncogenic roles studied so far in breast cancer. The TRPM7 ion channel is suggested as a potential and prospective target in the diagnosis and treatment of breast cancer.

Abstract

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a divalent cations permeant channel but also has intrinsic serine/threonine kinase activity. It is ubiquitously expressed in normal tissues and studies have indicated that it participates in important physiological and pharmacological processes through its channel-kinase activity, such as calcium/magnesium homeostasis, phosphorylation of proteins involved in embryogenesis or the cellular process. Accumulating evidence has shown that TRPM7 is overexpressed in human pathologies including breast cancer. Breast cancer is the second leading cause of cancer death in women with an incidence rate increase of around 0.5% per year since 2004. The overexpression of TRPM7 may be associated with a poor prognosis in breast cancer patients, so more efforts are needed to research a new therapeutic target. TRPM7 regulates the levels of Ca²⁺, which can alter the signaling pathways involved in survival, cell cycle progression, proliferation, growth, migration, invasion, epithelial-mesenchymal transition and thus determines cell behavior, promoting tumor development. This work provides a complete overview of the TRPM7 ion channel and its main involvements in breast cancer. Special consideration is given to the modulation of the channel as a potential target in breast cancer treatment by inhibition of proliferation, migration and invasion. Taken together, these data suggest the potential exploitation of TRPM7 channel-kinase as a therapeutic target and a diagnostic biomarker.

A New Caco-2 Cell Model of in vitro Intestinal Barrier: Application for the Evaluation of Magnesium Salts Absorption

Experimental data concerning the bioavailability of the different Mg-salts in human organism is inconsistent. Mg-absorption reported by clinical studies largely varies depending on the method used for evaluation. The aim of this study was to evaluate the bioavailability and accessibility of magnesium bound in different Mg-salt compounds, using an in vitro model of intestinal cell barrier. The study included a variety of inorganic (oxide, sulphate, chloride, carbonate) and organic salts (lactate, citrate, pidolate). Caco-2 cells were cultivated in a complete culture medium with different magnesium salts treatments in ascending concentrations. The viability and quantity of cells was analysed by FACS. Mg-absorption was analysed by a direct colorimetric assay, measured by spectrometry. T-test identified a significant decrease in cell count treatment with mg-lactate compared with citrate. Mg-pidolate showed a significantly higher cell viability compared with Mg-citrate, Mg-lactate and Mg-chloride. Even though the difference was not significant, we showed that an increase in Mg2+ salt concentration progressively decreased the cell count and the viability and the effect was universal for all the used Mg-salt treatments. Mg-citrate, chloride, and sulphate showed a significantly lower absorption compared to Mg-carbonate, pidolate and oxide. Our in vitro monolayer model of human intestinal transport showed that viability and quantity of cell decreased with increasing Mg-concentration. We admit that our experiment model may have some limitations in accurately describing an in vivo Mg2+ absorption. Moreover, it is also necessary to assess the relevance of our data in vivo and especially in clinical practice.

Associations between gene expression of magnesium transporters and glucose metabolism in pregnancy

BACKGROUND/PURPOSE

To assess the relationship between gene expressions of the magnesium transporters and glucose parameters in pregnant women.

METHODS

A cohort of women without ongoing or prior medical illnesses was recruited at the start of an early singleton pregnancy. Expression levels of the magnesium transporters-SLC41A1, CNNM2, MAGT1, TRPM6, and TRPM7-were assessed in the peripheral leukocytes, while total calcium and magnesium were assessed in the serum between 10 and 13 weeks gestation. Glucose parameters were assessed between 24 and 28 weeks gestation using the 75 g oral glucose tolerance test.

RESULTS

A total of 208 patients were included in the study. The expressions of the magnesium transports were generally unrelated to age, body mass index (BMI), or serum levels of calcium and magnesium. The magnesium transporters were correlated with each other at baseline (correlation coefficients: 0.31 to 0.51). BMI was a strong predictor of fasting glucose levels, while both BMI and age were strong predictors of post-load glucose levels. The expression of TRPM7 was found to be predictive of 1-h post-load blood glucose after accounting for the effects of age and BMI (β = -0.196, p = 0.020).

CONCLUSION

The increased maternal expression of the magnesium transporter TRPM7 may be associated with decreased glucose tolerance in pregnant women. In particular, the association between TRPM7 and 1-h post-load glucose levels was found to be independent of the effects of age and BMI. Future studies are needed to determine whether a mechanistic relationship can be demonstrated between TRPM7 and glucose metabolism.

TRPM8 Channels: Advances in Structural Studies and Pharmacological Modulation

The transient receptor potential melastatin subtype 8 (TRPM8) is a cold sensor in humans, activated by low temperatures (>10, <28 °C), but also a polymodal ion channel, stimulated by voltage, pressure, cooling compounds (menthol, icilin), and hyperosmolarity. An increased number of experimental results indicate the implication of TRPM8 channels in cold thermal transduction and pain detection, transmission, and maintenance in different tissues and organs. These channels also have a repercussion on different kinds of life-threatening tumors and other pathologies, which include urinary and respiratory tract dysfunctions, dry eye disease, and obesity. This compendium firstly covers newly described papers on the expression of TRPM8 channels and their correlation with pathological states. An overview on the structural knowledge, after cryo-electron microscopy success in solving different TRPM8 structures, as well as some insights obtained from mutagenesis studies, will follow. Most recently described families of TRPM8 modulators are also covered, along with a section of molecules that have reached clinical trials. To finalize, authors provide an outline of the potential prospects in the TRPM8 field.

An overview of diagnosis and management of drug-induced hypomagnesemia

Magnesium (Mg) is commonly addressed as the "forgotten ion" in medicine. Nonetheless, hypomagnesemia should be suspected in clinical practice in patients with relevant symptomatology and also be considered a predisposing factor for the development of other electrolyte disturbances. Furthermore, chronic hypomagnesemia has been associated with diabetes mellitus and cardiovascular disease. Hypomagnesemia as a consequence of drug therapy is relatively common, with the list of drugs inducing low serum Mg levels expanding. Culprit medications linked to hypomagnesemia include antibiotics (e.g. aminoglycosides, amphotericin B), diuretics, antineoplastic drugs (cisplatin and cetuximab), calcineurin inhibitors, and proton pump inhibitors. In recent years, the mechanisms of drug-induced hypomagnesemia have been unraveled through the discovery of key Mg transporters in the gut and kidney. This narrative review of available literature focuses on the pathogenetic mechanisms underlying drug-induced hypomagnesemia in order to increase the insight of clinicians toward early diagnosis and effective management.

TRP channels in health and disease at a glance

The transient receptor potential (TRP) channel superfamily consists of a large group of non-selective cation channels that serve as cellular sensors for a wide spectrum of physical and environmental stimuli. The 28 mammalian TRPs, categorized into six subfamilies, including TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPA (ankyrin), TRPML (mucolipin) and TRPP (polycystin), are widely expressed in different cells and tissues. TRPs exhibit a variety of unique features that not only distinguish them from other superfamilies of ion channels, but also confer diverse physiological functions. Located at the plasma membrane or in the membranes of intracellular organelles, TRPs are the cellular safeguards that sense various cell stresses and environmental stimuli and translate this information into responses at the organismal level. Loss- or gain-of-function mutations of TRPs cause inherited diseases and pathologies in different physiological systems, whereas up- or down-regulation of TRPs is associated with acquired human disorders. In this Cell Science at a Glance article and the accompanying poster, we briefly summarize the history of the discovery of TRPs, their unique features, recent advances in the understanding of TRP activation mechanisms, the structural basis of TRP Ca2+ selectivity and ligand binding, as well as potential roles in mammalian physiology and pathology.

Disturbances of calcium homeostasis in a child with acute lymphoblastic leukemia

Hypercalcemia is a rare presentation of childhood acute lymphoblastic leukemia (ALL), and presents with nonspecific symptoms. A 11-year old boy developed severe hypercalcemia during initial presentation and relapse of ALL. Both times, he subsequently developed transient symptomatic hypocalcemia, associated with hypomagnesemia and renal tubulopathy. Disturbances in calcium homeostasis may rarely be the sole presenting feature of ALL in children, as a paraneoplastic syndrome, or may arise as a consequence of the malignancy and its treatment. Along with other measures, early recognition of malignancy and initiation of treatment play a key role in correcting calcium disturbances.

Ion Transporters and Osmoregulation in the Kidney of Teleost Fishes as a Function of Salinity

Euryhaline teleosts exhibit major changes in renal function as they move between freshwater (FW) and seawater (SW) environments, thus tolerating large fluctuations in salinity. In FW, the kidney excretes large volumes of water through high glomerular filtration rates (GFR) and low tubular reabsorption rates, while actively reabsorbing most ions at high rates. The excreted product has a high urine flow rate (UFR) with a dilute composition. In SW, GFR is greatly reduced, and the tubules reabsorb as much water as possible, while actively secreting divalent ions. The excreted product has a low UFR, and is almost isosmotic to the blood plasma, with Mg²⁺, SO₄^2–, and Cl^– as the major ionic components. Early studies at the organismal level have described these basic patterns, while in the last two decades, studies of regulation at the cell and molecular level have been implemented, though only in a few euryhaline groups (salmonids, eels, tilapias, and fugus). There have been few studies combining the two approaches. The aim of the review is to integrate known aspects of renal physiology (reabsorption and secretion) with more recent advances in molecular water and solute physiology (gene and protein function of transporters). The renal transporters addressed include the subunits of the Na⁺, K⁺- ATPase (NKA) enzyme, monovalent ion transporters for Na⁺, Cl^–, and K⁺ (NKCC1, NKCC2, CLC-K, NCC, ROMK2), water transport pathways [aquaporins (AQP), claudins (CLDN)], and divalent ion transporters for SO₄^2–, Mg²⁺, and Ca²⁺ (SLC26A6, SLC26A1, SLC13A1, SLC41A1, CNNM2, CNNM3, NCX1, NCX2, PMCA). For each transport category, we address the current understanding at the molecular level, try to synthesize it with classical knowledge of overall renal function, and highlight knowledge gaps. Future research on the kidney of euryhaline fishes should focus on integrating changes in kidney reabsorption and secretion of ions with changes in transporter function at the cellular and molecular level (gene and protein verification) in different regions of the nephrons. An increased focus on the kidney individually and its functional integration with the other osmoregulatory organs (gills, skin and intestine) in maintaining overall homeostasis will have applied relevance for aquaculture.

TRPM3 in Brain (Patho)Physiology

Already for centuries, humankind is driven to understand the physiological and pathological mechanisms that occur in our brains. Today, we know that ion channels play an essential role in the regulation of neural processes and control many functions of the central nervous system. Ion channels present a diverse group of membrane-spanning proteins that allow ions to penetrate the insulating cell membrane upon opening of their channel pores. This regulated ion permeation results in different electrical and chemical signals that are necessary to maintain physiological excitatory and inhibitory processes in the brain. Therefore, it is no surprise that disturbances in the functions of cerebral ion channels can result in a plethora of neurological disorders, which present a tremendous health care burden for our current society. The identification of ion channel-related brain disorders also fuel the research into the roles of ion channel proteins in various brain states. In the last decade, mounting evidence has been collected that indicates a pivotal role for transient receptor potential (TRP) ion channels in the development and various physiological functions of the central nervous system. For instance, TRP channels modulate neurite growth, synaptic plasticity and integration, and are required for neuronal survival. Moreover, TRP channels are involved in numerous neurological disorders. TRPM3 belongs to the melastatin subfamily of TRP channels and represents a non-selective cation channel that can be activated by several different stimuli, including the neurosteroid pregnenolone sulfate, osmotic pressures and heat. The channel is best known as a peripheral nociceptive ion channel that participates in heat sensation. However, recent research identifies TRPM3 as an emerging new player in the brain. In this review, we summarize the available data regarding the roles of TRPM3 in the brain, and correlate these data with the neuropathological processes in which this ion channel may be involved.

Magnesium, Little Known But Possibly Relevant: A Link between NASH and Related Comorbidities

Non-alcoholic steatohepatitis (NASH) is characterized by an abnormal hepatic lipid accumulation accompanied by a necro-inflammatory process and a fibrotic response. It comprises from 10% to 30% of cases of patients with non-alcoholic liver disease, which is a global health problem affecting around a quarter of the worldwide population. Nevertheless, the development of NASH is often surrounded by a pathological context with other comorbidities, such as cardiovascular diseases, obesity, insulin resistance or type 2 diabetes mellitus. Dietary imbalances are increasingly recognized as the root cause of these NASH-related comorbidities. In this context, a growing concern exists about whether magnesium consumption in the general population is sufficient. Hypomagnesemia is a hallmark of the aforementioned NASH comorbidities, and deficiencies in magnesium are also widely related to the triggering of complications that aggravate NASH or derived pathologies. Moreover, the supplementation of this cation has proved to reduce mortality from hepatic complications. In the present review, the role of magnesium in NASH and related comorbidities has been characterized, unraveling the relevance of maintaining the homeostasis of this cation for the correct functioning of the organism.

The Perilous PPI: Proton Pump Inhibitor as a Cause of Clinically Significant Hypomagnesaemia

Proton pump inhibitors (PPIs) are the mainstay of therapy for all gastric acid related diseases and are commonly used in current clinical practice. Although widely regarded as safe, PPIs have been associated with a variety of adverse effects, including hypomagnesaemia. The postulated mechanism of PPI-related hypomagnesaemia involves inhibition of intestinal magnesium absorption via transient receptor potential melastin (TRPM) 6 and 7 cation channels. PPIinduced hypomagnesaemia (PPIH) has become a well recognized phenomenon since it was first reported in 2006. Clinical concerns arise from growing number of case reports presenting PPIH as a consequence of long-term PPI use, with more than 30 cases published to date.

In this article, we report 2 cases of PPIH associated with the use of pantoprazole. Both patients presented with severe hypomagnesaemia and hypocalcaemia. One of them had associated hypokalemia and cardiac arrhythmia. A casual relation with PPIs postulated and supported by resolution of electrolyte abnormalities after discontinuation of PPIs.

Magnesium bioavailability of dried and thinly shaved kombu in rats

BACKGROUND

Magnesium (Mg) is highly bioavailable in kombu compared with other edible seaweeds. However, a considerable amount of Mg is lost during industrial processing and cooking of kombu. We hypothesized that thinly shaved kombu (TSK), a traditional Japanese kombu product, is a suitable Mg source for daily diets because TSK hardly loses Mg during processing. Rats were fed diets containing TSK or magnesium oxide (MgO) to satisfy 25%, 50%, 75%, or 100% of their Mg requirements. We determined the relative Mg bioavailability of TSK compared to MgO and examined factors affecting Mg bioavailability in TSK.

RESULTS

The relative bioavailability of Mg in TSK compared with MgO was calculated as 92.3%, 111.4%, and 87.2% from apparent absorption, urinary excretion, and femoral concentration of Mg, respectively. The ultrafiltrable Mg concentration was lower in the cecal content of rats given TSK than those given MgO. However, the mRNA expression of TRPM6, an Mg channel responsible for Mg absorption, was higher in the cecum of rats given TSK than those given MgO.

CONCLUSION

Enhancement of TRPM6 expression in the large intestine negates the low bioaccessibility of Mg in TSK, and thus TSK shows Mg bioavailability comparable with MgO. © 2020 Society of Chemical Industry.

'Magnesium'-the master cation-as a drug-possibilities and evidences

Magnesium (Mg²⁺) is the 2nd most abundant intracellular cation, which participates in various enzymatic reactions; there by regulating vital biological functions. Magnesium (Mg²⁺) can regulate several cations, including sodium, potassium, and calcium; it consequently maintains physiological functions like impulse conduction, blood pressure, heart rhythm, and muscle contraction. But, it doesn't get much attention in account with its functions, making it a "Forgotten cation". Like other cations, maintenance of the normal physiological level of Mg²⁺ is important. Its deficiency is associated with various diseases, which point out to the importance of Mg²⁺ as a drug. The roles of Mg²⁺ such as natural calcium antagonist, glutamate NMDA receptor blocker, vasodilator, antioxidant and anti-inflammatory agent are responsible for its therapeutic benefits. Various salts of Mg²⁺ are currently in clinical use, but their application is limited. This review collates all the possible mechanisms behind the behavior of magnesium as a drug at different disease conditions with clinical shreds of evidence.

The Importance of Non-Coding RNAs in Neurodegenerative Processes of Diabetes-Related Molecular Pathways

Diabetes mellitus (DM) is a complex condition and serious health problem, with growing occurrence of DM-associated complications occurring globally. Persistent hyperglycemia is confirmed as promoting neurovascular dysfunction leading to irreversible endothelial cell dysfunction, increased neuronal cell apoptosis, oxidative stress and inflammation. These collaboratively and individually result in micro- and macroangiopathy as well as neuropathy demonstrated by progressive neuronal loss. Recently, major efforts have been pursued to select not only useful diagnostic and prognostic biomarkers, but also novel therapeutic approaches. Both microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) belong to a class of non-coding RNAs identified in most of the body fluids i.e., peripheral blood, cerebrospinal fluid, brain tissue and neurons. Numerous miRNAs, lncRNAs and their target genes are able to modulate signaling pathways known to play a role in the pathophysiology of progressive neuronal dysfunction. Therefore, they pose as promising biomarkers and treatment for the vast majority of neurodegenerative disorders. This review provides an overall assessment of both miRNAs’ and lncRNAs’ utility in decelerating progressive nervous system impairment, including neurodegeneration in diabetic pathways.

The Ion Channel and GPCR Toolkit of Brain Capillary Pericytes

Brain pericytes reside on the abluminal surface of capillaries, and their processes cover ~90% of the length of the capillary bed. These cells were first described almost 150 years ago (Eberth, 1871; Rouget, 1873) and have been the subject of intense experimental scrutiny in recent years, but their physiological roles remain uncertain and little is known of the complement of signaling elements that they employ to carry out their functions. In this review, we synthesize functional data with single-cell RNAseq screens to explore the ion channel and G protein-coupled receptor (GPCR) toolkit of mesh and thin-strand pericytes of the brain, with the aim of providing a framework for deeper explorations of the molecular mechanisms that govern pericyte physiology. We argue that their complement of channels and receptors ideally positions capillary pericytes to play a central role in adapting blood flow to meet the challenge of satisfying neuronal energy requirements from deep within the capillary bed, by enabling dynamic regulation of their membrane potential to influence the electrical output of the cell. In particular, we outline how genetic and functional evidence suggest an important role for G_s-coupled GPCRs and ATP-sensitive potassium (K_ATP) channels in this context. We put forth a predictive model for long-range hyperpolarizing electrical signaling from pericytes to upstream arterioles, and detail the TRP and Ca²⁺ channels and G_q, G_i/o, and G_12/13 signaling processes that counterbalance this. We underscore critical questions that need to be addressed to further advance our understanding of the signaling topology of capillary pericytes, and how this contributes to their physiological roles and their dysfunction in disease.

TRPM Channels in Human Diseases

The transient receptor potential melastatin (TRPM) subfamily belongs to the TRP cation channels family. Since the first cloning of TRPM1 in 1989, tremendous progress has been made in identifying novel members of the TRPM subfamily and their functions. The TRPM subfamily is composed of eight members consisting of four six-transmembrane domain subunits, resulting in homomeric or heteromeric channels. From a structural point of view, based on the homology sequence of the coiled-coil in the C-terminus, the eight TRPM members are clustered into four groups: TRPM1/M3, M2/M8, M4/M5 and M6/M7. TRPM subfamily members have been involved in several physiological functions. However, they are also linked to diverse pathophysiological human processes. Alterations in the expression and function of TRPM subfamily ion channels might generate several human diseases including cardiovascular and neurodegenerative alterations, organ dysfunction, cancer and many other channelopathies. These effects position them as remarkable putative targets for novel diagnostic strategies, drug design and therapeutic approaches. Here, we review the current knowledge about the main characteristics of all members of the TRPM family, focusing on their actions in human diseases.

NaCl cotransporter activity and Mg2+ handling by the distal convoluted tubule

The genetic disease Gitelman syndrome, knockout mice, and pharmacological blockade with thiazide diuretics have revealed that reduced activity of the NaCl cotransporter (NCC) promotes renal Mg²⁺ wasting. NCC is expressed along the distal convoluted tubule (DCT), and its activity determines Mg²⁺ entry into DCT cells through transient receptor potential channel subfamily M member 6 (TRPM6). Several other genetic forms of hypomagnesemia lower the drive for Mg²⁺ entry by inhibiting activity of basolateral Na⁺-K⁺-ATPase, and reduced NCC activity may do the same. Lower intracellular Mg²⁺ may promote further Mg²⁺ loss by directly decreasing activity of Na⁺-K⁺-ATPase. Lower intracellular Mg²⁺ may also lower Na⁺-K⁺-ATPase indirectly by downregulating NCC. Lower NCC activity also induces atrophy of DCT cells, decreasing the available number of TRPM6 channels. Conversely, a mouse model with increased NCC activity was recently shown to display normal Mg²⁺ handling. Moreover, recent studies have identified calcineurin and uromodulin (UMOD) as regulators of both NCC and Mg²⁺ handling by the DCT. Calcineurin inhibitors paradoxically cause hypomagnesemia in a state of NCC activation, but this may be related to direct effects on TRPM6 gene expression. In Umod^-/- mice, the cause of hypomagnesemia may be partly due to both decreased NCC expression and lower TRPM6 expression on the cell surface. This mini-review discusses these new findings and the possible role of altered Na⁺ flux through NCC and ultimately Na⁺-K⁺-ATPase in Mg²⁺ reabsorption by the DCT.

TRPM7 channel activity in Jurkat T lymphocytes during magnesium depletion and loading: implications for divalent metal entry and cytotoxicity

TRPM7 is a cation channel-protein kinase highly expressed in T lymphocytes and other immune cells. It has been proposed to constitute a cellular entry pathway for Mg²⁺ and divalent metal cations such as Ca²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Ni²⁺. TRPM7 channels are inhibited by cytosolic Mg²⁺, rendering them largely inactive in intact cells. The dependence of channel activity on extracellular Mg²⁺ is less well studied. Here, we measured native TRPM7 channel activity in Jurkat T cells maintained in external Mg²⁺ concentrations varying between 400 nM and 1.4 mM for 1-3 days, obtaining an IC₅₀ value of 54 μM. Maintaining the cells in 400 nM or 8 μM [Mg²⁺]_o resulted in almost complete activation of TRPM7 in intact cells, due to cytosolic Mg²⁺ depletion. A total of 1.4 mM [Mg²⁺]_o was sufficient to fully eliminate the basal current. Submillimolar concentrations of amiloride prevented cellular Mg²⁺ depletion but not loading. We investigated whether the cytotoxicity of TRPM7 permeant metal ions Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Sr²⁺, and Ba²⁺ requires TRPM7 channel activity. Mg²⁺ loading modestly reduced cytotoxicity of Zn²⁺, Co²⁺, Ni²⁺, and Mn²⁺ but not of Cd²⁺. Channel blocker NS8593 reduced Co²⁺ and Mn²⁺ but not Cd²⁺ or Zn²⁺ cytotoxicity and interfered with Mg²⁺ loading as evaluated by TRPM7 channel basal activity. Ba²⁺ and Sr²⁺ were neither detectably toxic nor permeant through the plasma membrane. These results indicate that in Jurkat T cells, entry of toxic divalent metal cations primarily occurs through pathways distinct from TRPM7. By contrast, we found evidence that Mg²⁺ entry requires TRPM7 channels.

Is There a Role for Absorbable Metals in Surgery? A Systematic Review and Meta-Analysis of Mg/Mg Alloy Based Implants

Magnesium (Mg) alloys have received attention in the literature as potential biomaterials for use as absorbable implants in oral and maxillofacial and orthopedic surgery applications. This study aimed to evaluate the available clinical studies related to patients who underwent bone fixation (patients), and received conventional fixation (intervention), in comparison to absorbable metals (comparison), in terms of follow-up and complications (outcomes). A systematic review and meta-analysis were performed in accordance with the PRISMA statement and PROSPERO (CRD42020188654), PICO question, ROBINS-I, and ROB scales. The relative risk (RR) of complications and failures were calculated considering a confidence interval (CI) of 95%. Eight studies (three randomized clinical trial (RCT), one retrospective studies, two case-control studies, and two prospective studies) involving 468 patients, including 230 Mg screws and 213 Titanium (Ti) screws, were analyzed. The meta-analysis did not show any significant differences when comparing the use of Mg and Ti screws for complications (p = 0.868). The estimated complication rate was 13.3% (95% CI: 8.3% to 20.6%) for the comparison group who received an absorbable Mg screw. The use of absorbable metals is feasible for clinical applications in bone surgery with equivalent outcomes to standard metal fixation devices.

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.

Phylogenetics Identifies Two Eumetazoan TRPM Clades and an Eighth TRP Family, TRP Soromelastatin (TRPS)

Transient receptor potential melastatins (TRPMs) are most well known as cold and menthol sensors, but are in fact broadly critical for life, from ion homeostasis to reproduction. Yet, the evolutionary relationship between TRPM channels remains largely unresolved, particularly with respect to the placement of several highly divergent members. To characterize the evolution of TRPM and like channels, we performed a large-scale phylogenetic analysis of >1,300 TRPM-like sequences from 14 phyla (Annelida, Arthropoda, Brachiopoda, Chordata, Cnidaria, Echinodermata, Hemichordata, Mollusca, Nematoda, Nemertea, Phoronida, Priapulida, Tardigrada, and Xenacoelomorpha), including sequences from a variety of recently sequenced genomes that fill what would otherwise be substantial taxonomic gaps. These findings suggest: 1) the previously recognized TRPM family is in fact two distinct families, including canonical TRPM channels and an eighth major previously undescribed family of animal TRP channel, TRP soromelastatin; 2) two TRPM clades predate the last bilaterian-cnidarian ancestor; and 3) the vertebrate-centric trend of categorizing TRPM channels as 1-8 is inappropriate for most phyla, including other chordates.

Steroids and TRP Channels: A Close Relationship

Transient receptor potential (TRP) channels are remarkable transmembrane protein complexes that are essential for the physiology of the tissues in which they are expressed. They function as non-selective cation channels allowing for the signal transduction of several chemical, physical and thermal stimuli and modifying cell function. These channels play pivotal roles in the nervous and reproductive systems, kidney, pancreas, lung, bone, intestine, among others. TRP channels are finely modulated by different mechanisms: regulation of their function and/or by control of their expression or cellular/subcellular localization. These mechanisms are subject to being affected by several endogenously-produced compounds, some of which are of a lipidic nature such as steroids. Fascinatingly, steroids and TRP channels closely interplay to modulate several physiological events. Certain TRP channels are affected by the typical genomic long-term effects of steroids but others are also targets for non-genomic actions of some steroids that act as direct ligands of these receptors, as will be reviewed here.

Ion channels in capillary endothelium

Vascular beds are anatomically and functionally compartmentalized into arteries, capillaries, and veins. The bulk of the vasculature consists of the dense, anastomosing capillary network, composed of capillary endothelial cells (cECs) that are intimately associated with the parenchyma. Despite their abundance, the ion channel expression and function and Ca²⁺ signaling behaviors of capillaries have only recently begun to be explored in detail. Here, we discuss the established and emerging roles of ion channels and Ca²⁺ signaling in cECs. By mining a publicly available RNA-seq dataset, we outline the wide variety of ion channel genes that are expressed in these cells, which potentially imbue capillaries with a broad range of sensing and signal transduction capabilities. We also underscore subtle but critical differences between cEC and arteriolar EC ion channel expression that likely underlie key functional differences in ECs at these different levels of the vascular tree. We focus our discussion on the cerebral vasculature, but the findings and principles being elucidated in this area likely generalize to other vascular beds.

TRP Channels in Digestive Tract Cancers

Cancers of the digestive tract are among the most prevalent types of cancer. These types of cancers are often diagnosed at a late stage, which results in a poor prognosis. Currently, many biomedical studies focus on the role of ion channels, in particular transient receptor potential (TRP) channels, in cancer pathophysiology. TRP channels show mostly non-selective permeability to monovalent and divalent cations. TRP channels are often dysregulated in digestive tract cancers, which can result in alterations of cancer hallmark functions, such as enhanced proliferation, migration, invasion and the inability to induce apoptosis. Therefore, TRP channels could serve as potential diagnostic biomarkers. Moreover, TRP channels are mostly expressed on the cell surface and ion channel targeting drugs do not need to enter the cell, making them attractive candidate drug targets. In this review, we summarize the current knowledge about TRP channels in connection to digestive tract cancers (oral cancer, esophageal cancer, liver cancer, pancreatic cancer, gastric cancer and colorectal cancer) and give an outlook on the potential of TRP channels as cancer biomarkers or therapeutic targets.

Study of Magnesium Formulations on Intestinal Cells to Influence Myometrium Cell Relaxation

Background: Magnesium is involved in a wide variety of physiological processes including direct relaxation of smooth muscle. A magnesium imbalance can be considered the primary cause or consequence of many pathophysiological conditions. The smooth muscle tissue of the uterus, i.e., the myometrium, undergoes numerous physiological changes during life, fundamental for uterine activities, and it receives proven benefits from magnesium supplementation. However, magnesium supplements have poor absorption and bioavailability. Furthermore, no data are available on the direct interaction between intestinal absorption of magnesium and relaxation of the myometrium. Methods: Permeability in human intestinal cells (Caco-2 cells) and direct effects on myometrial cells (PHM1-41 cells) of two different forms of magnesium, i.e., sucrosomial and bisglycinate, were studied in order to verify the magnesium capacity of modulate contractility. Cell viability, reactive oxygen species (ROS) and nitric oxide (NO) production, magnesium concentration, contractility, and pathways involved were analyzed. Results: Data showed a better influence of buffered chelate bisglycinate on intestinal permeability and myometrial relaxation over time with a maximum effect at 3 h and greater availability compared to the sucrosomial form. Conclusions: Magnesium-buffered bisglycinate chelate showed better intestinal absorption and myometrial contraction, indicating a better chance of effectiveness in human applications.

Metformin regulates TRPM6, a potential explanation for magnesium imbalance in type 2 diabetes patients

Metformin therapy is associated with lower serum magnesium (Mg²⁺) levels in type 2 diabetes patients. The TRPM6 channel determines the fine-tuning of Mg²⁺ (re)absorption in intestine and kidney. Therefore, we aimed to investigate the short- and long-term effects of metformin on TRPM6. Patch clamp recordings and biotinylation assays were performed upon 1 h of incubation with metformin in TRPM6-transfected HEK293 cells. Additionally, 24 h of treatment of mDCT15 kidney and hCaco-2 colon cells with metformin was applied to measure the effects on endogenous TRPM6 expression by quantitative real-time PCR. To assess Mg²⁺ absorption, ²⁵Mg²⁺ uptake measurements were performed using inductively coupled plasma mass spectrometry. Short-term effects of metformin significantly increased TRPM6 activity and its cell surface trafficking. In contrast, long-term effects significantly decreased TRPM6 mRNA expression and ²⁵Mg²⁺ uptake. Metformin lowered TRPM6 mRNA levels independently of insulin- and AMPK-mediated pathways. Moreover, in type 2 diabetes patients, metformin therapy was associated with lower plasma Mg²⁺ concentrations and fractional excretion of Mg²⁺. Thereby, short-term metformin treatment increases TRPM6 activity explained by enhanced cell surface expression. Conversely, long-term metformin treatment results in downregulation of TRPM6 gene expression in intestine and kidney cells. This long-term effect translated in an inverse correlation between metformin and plasma Mg²⁺ concentration in type 2 diabetes patients.

Proton-Pump Inhibitors and Hypomagnesaemia in Kidney Transplant Recipients

Proton-pump inhibitors (PPIs) are commonly used after kidney transplantation and there is rarely an incentive to discontinue treatment. In the general population, PPI use has been associated with hypomagnesaemia. We aimed to investigate whether PPI use is associated with plasma magnesium, 24-h urinary magnesium excretion and hypomagnesaemia, in kidney transplant recipients (KTR). Plasma magnesium and 24-h urinary magnesium excretion were measured in 686 stable outpatient KTR with a functioning allograft for ≥1 year from the TransplantLines Food and Nutrition Biobank and Cohort-Study (NCT02811835). PPIs were used by 389 KTR (56.6%). In multivariable linear regression analyses, PPI use was associated with lower plasma magnesium (β: −0.02, P = 0.02) and lower 24-h urinary magnesium excretion (β: −0.82, P < 0.001). Moreover, PPI users had a higher risk of hypomagnesaemia (plasma magnesium <0.70 mmol/L), compared with non-users (Odds Ratio (OR): 2.12; 95% confidence interval (CI) 1.43–3.15, P < 0.001). This risk tended to be highest among KTR taking high PPI dosages (>20 mg omeprazole Eq/day) and was independent of adjustment for potential confounders (OR: 2.46; 95% CI 1.32–4.57, P < 0.005). No interaction was observed between PPI use and the use of loop diuretics, thiazide diuretics, tacrolimus, or diabetes (P_interaction > 0.05). These results demonstrate that PPI use is independently associated with lower magnesium status and hypomagnesaemia in KTR. The concomitant decrease in urinary magnesium excretion indicates that this likely is the consequence of reduced intestinal magnesium absorption. Based on these results, it might be of benefit to monitor magnesium status periodically in KTR on chronic PPI therapy.