Human geneSLC41A1encodes for the Na+/Mg2+exchanger

Renal diseases that course with hypomagnesemia. Comments on a new hereditary hypomagnesemic tubulopathy

Renal diseases associated with hypomagnesemia are a complex and diverse group of tubulopathies caused by mutations in genes encoding proteins that are expressed in the thick ascending limb of the loop of Henle and in the distal convoluted tubule. In this paper, we review the initial description, the clinical expressiveness and etiology of four of the first hypomagnesemic tubulopathies described: type 3 Bartter and Gitelman diseases, Autosomal recessive hypomagnesemia with secondary hypocalcemia and Familial hypomagnesemia with hypercalciuria and nephrocalcinosis. The basic biochemical patterns observed in renal tubular hypomagnesemias and the modalities of transport and interaction that occur between the transporters involved in the reabsorption of magnesium in the distal convoluted tubule are described below. Finally, the recent report of a new renal disease with hypomagnesemia, type 2 hypomagnesemia with secondary hypocalcemia caused by reduced TRPM7 channel activity is described.

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.

Molecular-based phenotype variations in amelogenesis imperfecta

Amelogenesis imperfecta (AI) is one of the typical dental genetic diseases in human. It can occur isolatedly or as part of a syndrome. Previous reports have mainly clarified the types and mechanisms of nonsyndromic AI. This review aimed to compare the phenotypic differences among the hereditary enamel defects with or without syndromes and their underlying pathogenic genes. We searched the articles in PubMed with different strategies or keywords including but not limited to amelogenesis imperfecta, enamel defects, hypoplastic/hypomaturation/hypocalcified, syndrome, or specific syndrome name. The articles with detailed clinical information about the enamel and other phenotypes and clear genetic background were used for the analysis. We totally summarized and compared enamel phenotypes of 18 nonsyndromic AI with 17 causative genes and 19 syndromic AI with 26 causative genes. According to the clinical features, radiographic or ultrastructural changes in enamel, the enamel defects were basically divided into hypoplastic and hypomineralized (hypomaturated and hypocalcified) and presented a higher heterogeneity which were closely related to the involved pathogenic genes, types of mutation, hereditary pattern, X chromosome inactivation, incomplete penetrance, and other mechanisms.The gene-specific enamel phenotypes could be an important indicator for diagnosing nonsyndromic and syndromic AI.

Intracellular Mg2+ protects mitochondria from oxidative stress in human keratinocytes

Reactive oxygen species (ROS) are harmful for the human body, and exposure to ultraviolet irradiation triggers ROS generation. Previous studies have demonstrated that ROS decrease mitochondrial membrane potential (MMP) and that Mg2+ protects mitochondria from oxidative stress. Therefore, we visualized the spatio-temporal dynamics of Mg2+ in keratinocytes (a skin component) in response to H2O2 (a type of ROS) and found that it increased cytosolic Mg2+ levels. H2O2-induced responses in both Mg2+ and ATP were larger in keratinocytes derived from adults than in keratinocytes derived from newborns, and inhibition of mitochondrial ATP synthesis enhanced the H2O2-induced Mg2+ response, indicating that a major source of Mg2+ was dissociation from ATP. Simultaneous imaging of Mg2+ and MMP revealed that larger Mg2+ responses corresponded to lower decreases in MMP in response to H2O2. Moreover, Mg2+ supplementation attenuated H2O2-induced cell death. These suggest the potential of Mg2+ as an active ingredient to protect skin from oxidative stress.

Low Magnesium Concentration Enforces Bone Calcium Deposition Irrespective of 1,25-Dihydroxyvitamin D3 Concentration

Efficient coordination between Mg²⁺ and vitamin D maintains adequate Ca²⁺ levels during lactation. This study explored the possible interaction between Mg²⁺ (0.3, 0.8, and 3 mM) and 1,25-dihydroxyvitamin D₃ (1,25D; 0.05 and 5 nM) during osteogenesis using bovine mesenchymal stem cells. After 21 days, differentiated osteocytes were subjected to OsteoImage analysis, alkaline phosphatase (ALP) activity measurements, and immunocytochemistry of NT5E, ENG (endoglin), SP7 (osterix), SPP1 (osteopontin), and the BGLAP gene product osteocalcin. The mRNA expression of NT5E, THY1, ENG, SP7, BGLAP, CYP24A1, VDR, SLC41A1, SLC41A2, SLC41A3, TRPM6, TRPM7, and NIPA1 was also assessed. Reducing the Mg²⁺ concentration in the medium increased the accumulation of mineral hydroxyapatite and ALP activity. There was no change in the immunocytochemical localization of stem cell markers. Expression of CYP24A1 was higher in all groups receiving 5 nM 1,25D. There were tendencies for higher mRNA abundance of THY1, BGLAP, and NIPA1 in cells receiving 0.3 mM Mg²⁺ and 5 nM 1,25D. In conclusion, low levels of Mg²⁺ greatly enhanced the deposition of bone hydroxyapatite matrix. The effect of Mg²⁺ was not modulated by 1,25D, although the expression of certain genes (including BGLAP) tended to be increased by the combination of low Mg²⁺ and high 1,25D concentrations.

Magnesium reabsorption in the kidney

Mg²⁺ is essential for many cellular and physiological processes, including muscle contraction, neuronal activity, and metabolism. Consequently, the blood Mg²⁺ concentration is tightly regulated by balanced intestinal Mg²⁺ absorption, renal Mg²⁺ excretion, and Mg²⁺ storage in bone and soft tissues. In recent years, the development of novel transgenic animal models and identification of Mendelian disorders has advanced our current insight in the molecular mechanisms of Mg²⁺ reabsorption in the kidney. In the proximal tubule, Mg²⁺ reabsorption is dependent on paracellular permeability by claudin-2/12. In the thick ascending limb of Henle's loop, the claudin-16/19 complex provides a cation-selective pore for paracellular Mg²⁺ reabsorption. The paracellular Mg²⁺ reabsorption in this segment is regulated by the Ca²⁺-sensing receptor, parathyroid hormone, and mechanistic target of rapamycin (mTOR) signaling. In the distal convoluted tubule, the fine tuning of Mg²⁺ reabsorption takes place by transcellular Mg²⁺ reabsorption via transient receptor potential melastatin-like types 6 and 7 (TRPM6/TRPM7) divalent cation channels. Activity of TRPM6/TRPM7 is dependent on hormonal regulation, metabolic activity, and interacting proteins. Basolateral Mg²⁺ extrusion is still poorly understood but is probably dependent on the Na⁺ gradient. Cyclin M2 and SLC41A3 are the main candidates to act as Na⁺/Mg²⁺ exchangers. Consequently, disturbances of basolateral Na⁺/K⁺ transport indirectly result in impaired renal Mg²⁺ reabsorption in the distal convoluted tubule. Altogether, this review aims to provide an overview of the molecular mechanisms of Mg²⁺ reabsorption in the kidney, specifically focusing on transgenic mouse models and human hereditary diseases.

Functional characteristics and therapeutic potential of SLC41 transporters

Magnesium (Mg²⁺) plays an important role in various cellular functions such as protein synthesis, DNA stability, energy metabolism, enzyme and channel activities, and muscle contractility. Therefore, intracellular Mg²⁺ concentration is tightly regulated by multiple Mg²⁺ transporters and channels. So far, various candidate genes of Mg²⁺ transporters have been identified, and the research on their structure and function is currently in progress. The Solute Carrier 41 (SLC41) family, which is related to the bacterial Mg²⁺ transporter/channel MgtE, comprises three isoforms of SLC41A1, SLC41A2, and SLC41A3. Based on recent studies, SLC41A1 is thought to mediate Mg²⁺ influx or Na⁺-dependent Mg²⁺ efflux across the plasma membrane, whereas SLC41A2 and SLC41A3 may mediate Mg²⁺ fluxes across either the plasma membrane or organellar membranes. Intriguingly, SLC41A1 variants have been identified in patients with Parkinson's disease (PD) and nephronophthisis-related ciliopathies. Further genetic analyses reveal the association of SLC41A1 polymorphisms with PD risks. This review highlights the recent advances in the understanding of the molecular and functional characteristics of SLC41 family towards its therapeutic and diagnostic applications.

Magnesium homeostasis in deoxygenated sickle erythrocytes is modulated by endothelin-1 via Na+ /Mg2+ exchange

Painful crises in sickle cell disease (SCD) are associated with increased plasma cytokines levels, including endothelin-1 (ET-1). Reduced red cell magnesium content, mediated in part by increased Na⁺ /Mg²⁺ exchanger (NME) activity, contributes to erythrocyte K⁺ loss, dehydration and sickling in SCD. However, the relationship between ET-1 and the NME in SCD has remained unexamined. We observed increased NME activity in sickle red cells incubated in the presence of 500 nM ET-1. Deoxygenation of sickle red cells, in contrast, led to decreased red cell NME activity and cellular dehydration that was reversed by the NME inhibitor, imipramine. Increased NME activity in sickle red cells was significantly blocked by pre-incubation with 100 nM BQ788, a selective blocker of ET-1 type B receptors. These results suggest an important role for ET-1 and for cellular magnesium homeostasis in SCD. Consistent with these results, we observed increased NME activity in sickle red cells of three mouse models of sickle cell disease greater than that in red cells of C57BL/J6 mice. In vivo treatment of BERK sickle transgenic mice with ET-1 receptor antagonists reduced red cell NME activity. Our results suggest that ET-1 receptor blockade may be a promising therapeutic approach to control erythrocyte volume and magnesium homeostasis in SCD and may thus attenuate or retard the associated chronic inflammatory and vascular complications of SCD.

SLC41A1 knockout mice display normal magnesium homeostasis

Transcellular Mg²⁺ reabsorption in the distal convoluted tubule (DCT) of the kidneys plays an important role in maintaining systemic Mg²⁺ homeostasis. SLC41A1 is a Na⁺/Mg²⁺ exchanger that mediates Mg²⁺ efflux from cells and is hypothesized to facilitate basolateral extrusion of Mg²⁺ in the DCT. In this study, we generated a SLC41A1 knockout mouse model to examine the role of SLC41A1 in Mg²⁺ homeostasis. Slc41a1^-/- mice exhibited similar serum and urine Mg²⁺ levels as their wild-type littermates. Dietary restriction of Mg²⁺ resulted in reduced serum Mg²⁺ concentration and urinary Mg²⁺ excretion, which was similar in the wild-type and knockout groups. Expression of genes encoding Mg²⁺ channels and transporters such as transient receptor potential melastatin 6 (Trpm6), transient receptor potential melastatin 7 (Trpm7), cyclin and CBS domain divalent metal cation transport mediator 2 (Cnnm2), and Slc41a3 were unchanged based on genotype. We investigated the potential redundancy of SLC41A1 and its homolog SLC41A3 by generating a double knockout mouse. Although Slc41a3^-/- knockout mice showed significantly reduced serum Mg²⁺ compared with wild-type and Slc41a1^-/- knockout groups, double knockout mice displayed similar serum Mg²⁺ levels as Slc41a3^-/- knockout mice. In conclusion, our data show that SLC41A1 is not involved in the regulation of systemic Mg²⁺ homeostasis in mice. Our data also demonstrate that SLC41A1 does not compensate for the loss of SLC41A3, suggesting different functions of these SLC41 proteins in vivo.NEW & NOTEWORTHY SLC41A1 has been hypothesized to mediate Mg²⁺ extrusion in the distal convoluted tubule and thus regulate Mg²⁺ homeostasis. This study investigated the role of SLC41A1 in Mg²⁺ homeostasis in vivo using a transgenic mouse model. Our results demonstrate that SLC41A1 is not required to maintain normal Mg²⁺ balance in mice. We also show that SLC41A3 is more important than SLC41A1 in regulating systemic Mg²⁺ levels.

Recent Advances in the Structural Biology of Mg2+ Channels and Transporters

Magnesium ions (Mg²⁺) are the most abundant divalent cations in living organisms and are essential for various physiological processes, including ATP utilization and the catalytic activity of numerous enzymes. Therefore, the homeostatic mechanisms associated with cellular Mg²⁺ are crucial for both eukaryotic and prokaryotic organisms and are thus strictly controlled by Mg²⁺ channels and transporters. Technological advances in structural biology, such as the expression screening of membrane proteins, in meso phase crystallization, and recent cryo-EM techniques, have enabled the structure determination of numerous Mg²⁺ channels and transporters. In this review article, we provide an overview of the families of Mg²⁺ channels and transporters (MgtE/SLC41, TRPM6/7, CorA/Mrs2, CorC/CNNM), and discuss the structural biology prospects based on the known structures of MgtE, TRPM7, CorA and CorC.

Structural and functional comparison of magnesium transporters throughout evolution

Magnesium (Mg²⁺) is the most prevalent divalent intracellular cation. As co-factor in many enzymatic reactions, Mg²⁺ is essential for protein synthesis, energy production, and DNA stability. Disturbances in intracellular Mg²⁺ concentrations, therefore, unequivocally result in delayed cell growth and metabolic defects. To maintain physiological Mg²⁺ levels, all organisms rely on balanced Mg²⁺ influx and efflux via Mg²⁺ channels and transporters. This review compares the structure and the function of prokaryotic Mg²⁺ transporters and their eukaryotic counterparts. In prokaryotes, cellular Mg²⁺ homeostasis is orchestrated via the CorA, MgtA/B, MgtE, and CorB/C Mg²⁺ transporters. For CorA, MgtE, and CorB/C, the motifs that form the selectivity pore are conserved during evolution. These findings suggest that CNNM proteins, the vertebrate orthologues of CorB/C, also have Mg²⁺ transport capacity. Whereas CorA and CorB/C proteins share the gross quaternary structure and functional properties with their respective orthologues, the MgtE channel only shares the selectivity pore with SLC41 Na⁺/Mg²⁺ transporters. In eukaryotes, TRPM6 and TRPM7 Mg²⁺ channels provide an additional Mg²⁺ transport mechanism, consisting of a fusion of channel with a kinase. The unique features these TRP channels allow the integration of hormonal, cellular, and transcriptional regulatory pathways that determine their Mg²⁺ transport capacity. Our review demonstrates that understanding the structure and function of prokaryotic magnesiotropic proteins aids in our basic understanding of Mg²⁺ transport.

Membrane Transport Proteins Expressed in the Renal Tubular Epithelial Cells of Seawater and Freshwater Teleost Fishes

The kidney is an important organ that maintains body fluid homeostasis in seawater and freshwater teleost fishes. Seawater teleosts excrete sulfate and magnesium in small amounts of isotonic urine, and freshwater teleosts excrete water in large amounts of hypo-osmotic urine. The volume, osmolality, and ionic compositions of the urine are regulated mainly by membrane transport proteins expressed in the renal tubular epithelial cells. Gene expression, immunohistochemical, and functional analyses of the fish kidney identified membrane transport proteins involved in the secretion of sulfate and magnesium ions by the proximal tubules and reduction of urine volume by the collecting ducts in seawater teleosts, and excretion of water as hypotonic urine by the distal tubules and collecting ducts in freshwater teleosts. These studies promote an understanding of how the kidney contributes to the seawater and freshwater acclimation of teleosts at the molecular level.

Dysregulated Erythroid Mg2+ Efflux in Type 2 Diabetes

Hyperglycemia is associated with decreased Mg²⁺ content in red blood cells (RBC), but mechanisms remain unclear. We characterized the regulation of Mg²⁺ efflux by glucose in ex vivo human RBC. We observed that hemoglobin A_1C (HbA_1C) values correlated with Na⁺-dependent Mg²⁺ efflux (Na⁺/Mg²⁺ exchange) and inversely correlated with cellular Mg content. Treatment of cells with 50 mM D-glucose, but not with sorbitol, lowered total cellular Mg (2.2 ± 0.1 to 2.0 ± 0.1 mM, p < 0.01) and enhanced Na⁺/Mg²⁺ exchange activity [0.60 ± 0.09 to 1.12 ± 0.09 mmol/10¹³ cell × h (flux units, FU), p < 0.05]. In contrast, incubation with selective Src family kinase inhibitors PP2 or SU6656 reduced glucose-stimulated exchange activation (p < 0.01). Na⁺/Mg²⁺ exchange activity was also higher in RBC from individuals with type 2 diabetes (T2D, 1.19 ± 0.13 FU) than from non-diabetic individuals (0.58 ± 0.05 FU, p < 0.01). Increased Na⁺/Mg²⁺ exchange activity in RBC from T2D subjects was associated with lower intracellular Mg content. Similarly increased exchange activity was evident in RBC from the diabetic db/db mouse model as compared to its non-diabetic control (p < 0.03). Extracellular exposure of intact RBC from T2D subjects to recombinant peptidyl-N-glycosidase F (PNGase F) reduced Na⁺/Mg²⁺ exchange activity from 0.98 ± 0.14 to 0.59 ± 0.13 FU (p < 0.05) and increased baseline intracellular Mg content (1.8 ± 0.1 mM) to normal values (2.1 ± 0.1 mM, p < 0.05). These data suggest that the reduced RBC Mg content of T2D RBC reflects enhanced RBC Na⁺/Mg²⁺ exchange subject to regulation by Src family kinases and by the N-glycosylation state of one or more membrane proteins. The data extend our understanding of dysregulated RBC Mg²⁺ homeostasis in T2D.

Transcriptional Control of Trpm6 by the Nuclear Receptor FXR

Farnesoid x receptor (FXR) is a nuclear bile acid receptor that belongs to the nuclear receptor superfamily. It plays an essential role in bile acid biosynthesis, lipid and glucose metabolism, liver regeneration, and vertical sleeve gastrectomy. A loss of the FXR gene or dysregulations of FXR-mediated gene expression are associated with the development of progressive familial intrahepatic cholestasis, tumorigenesis, inflammation, and diabetes mellitus. Magnesium ion (Mg²⁺) is essential for mammalian physiology. Over 600 enzymes are dependent on Mg²⁺ for their activity. Here, we show that the Trpm6 gene encoding a Mg²⁺ channel is a direct FXR target gene in the intestinal epithelial cells of mice. FXR expressed in the intestinal epithelial cells is absolutely required for sustaining a basal expression of intestinal Trpm6 that can be robustly induced by the treatment of GW4064, a synthetic FXR agonist. Analysis of FXR ChIP-seq data revealed that intron regions of Trpm6 contain two prominent FXR binding peaks. Among them, the proximal peak from the transcription start site contains a functional inverted repeat 1 (IR1) response element that directly binds to the FXR-RXRα heterodimer. Based on these results, we proposed that an intestinal FXR-TRPM6 axis may link a bile acid signaling to Mg²⁺ homeostasis.

Alzheimer's Disease-Associated SNP rs708727 in SLC41A1 May Increase Risk for Parkinson's Disease: Report from Enlarged Slovak Study

SLC41A1 (A1) SNPs rs11240569 and rs823156 are associated with altered risk for Parkinson's disease (PD), predominantly in Asian populations, and rs708727 has been linked to Alzheimer's disease (AD). In this study, we have examined a potential association of the three aforementioned SNPs and of rs9438393, rs56152218, and rs61822602 (all three lying in the A1 promoter region) with PD in the Slovak population. Out of the six tested SNPs, we have identified only rs708727 as being associated with an increased risk for PD onset in Slovaks. The minor allele (A) in rs708727 is associated with PD in dominant and completely over-dominant genetic models (OR_D = 1.36 (1.05-1.77), p = 0.02, and OR_COD = 1.34 (1.04-1.72), p = 0.02). Furthermore, the genotypic triplet GG_(rs708727) + AG_(rs823156) + CC_(rs61822602) might be clinically relevant despite showing a medium (h ≥ 0.5) size difference (h = 0.522) between the PD and the control populations. RandomForest modeling has identified the power of the tested SNPs for discriminating between PD-patients and the controls to be essentially zero. The identified association of rs708727 with PD in the Slovak population leads us to hypothesize that this A1 polymorphism, which is involved in the epigenetic regulation of the expression of the AD-linked gene PM20D1, is also involved in the pathoetiology of PD (or universally in neurodegeneration) through the same or similar mechanism as in AD.

circSLC41A1 Resists Porcine Granulosa Cell Apoptosis and Follicular Atresia by Promoting SRSF1 through miR-9820-5p Sponging

Ovarian granulosa cell (GC) apoptosis is the major cause of follicular atresia. Regulation of non-coding RNAs (ncRNAs) was proved to be involved in regulatory mechanisms of GC apoptosis. circRNAs have been recognized to play important roles in cellular activity. However, the regulatory network of circRNAs in follicular atresia has not been fully validated. In this study, we report a new circRNA, circSLC41A1, which has higher expression in healthy follicles compared to atretic follicles, and confirm its circular structure using RNase R treatment. The resistant function of circSLC41A1 during GC apoptosis was detected by si-RNA transfection and the competitive binding of miR-9820-5p by circSLC41A1 and SRSF1 was detected with a dual-luciferase reporter assay and co-transfection of their inhibitors or siRNA. Additionally, we predicted the protein-coding potential of circSLC41A1 and analyzed the structure of circSLC41A1-134aa. Our study revealed that circSLC41A1 enhanced SRSF1 expression through competitive binding of miR-9820-5p and demonstrated a circSLC41A1–miR-9820-5p–SRSF1 regulatory axis in follicular GC apoptosis. The study adds to knowledge of the post-transcriptional regulation of follicular atresia and provides insight into the protein-coding function of circRNA.

Clinical and Genetic Approach to Renal Hypomagnesemia

Magnesium (Mg²⁺) is an important intracellular cation and essential to maintain cell function including cell proliferation, immunity, cellular energy metabolism, protein and nucleic acid synthesis, and regulation of ion channels. Consequences of hypomagnesemia affecting multiple organs can be in overt or subtle presentations. Besides detailed history and complete physical examination, the assessment of urinary Mg²⁺ excretion is help to differentiate renal from extra-renal (gastrointestinal, tissue sequestration, and shifting) causes of hypomagnesemia. Renal hypomagnesemia can be caused by an increased glomerular filtration and impaired reabsorption in proximal tubular cells, thick ascending limb of the loop of Henle or distal convoluted tubules. A combination of renal Mg²⁺ wasting, familial history, age of onset, associated features, and exclusion of acquired etiologies point to inherited forms of renal hypomagnesemia. Based on clinical phenotypes, its definite genetic diagnosis can be simply grouped into specific, uncertain, and unknown gene mutations with a priority of genetic approach methods. An unequivocal molecular diagnosis could allow for prediction of clinical outcome, providing genetic counseling, avoiding unnecessary studies or interventions, and possibly uncovering the pathogenic mechanism. Given numerous identified genes responsible for Mg²⁺ transport in renal hypomagnesemia over the past two decades, several potential and specific molecular and cellular therapeutic strategies to correct hypomagnesemia are promising.

Magnesium transport in the aglomerular kidney of the Gulf toadfish (Opsanus beta)

Despite having an aglomerular kidney, Gulf toadfish can survive in water ranging from nearly fresh up to 70 parts per thousand salinity. In hyperosmotic environments, the major renal function is to balance the passive Mg²⁺ load from the environment with an equal excretion. However, the molecular transporters involved in Mg²⁺ secretion are poorly understood. We investigated whether environmental MgCl₂ alone or in combination with elevated salinity affected transcriptional regulation of genes classically involved in renal Mg²⁺ secretion (slc41a1, slc41a3, cnnm3) together with three novel genes (trpm6, trpm7, claudin-19) and two isoforms of the Na⁺/K⁺-ATPase α-subunit (nka-α1a, nka-α1b). First, toadfish were acclimated to 5, 9, 35, or 60 ppt water (corresponding to ~ 7, 13, 50 and 108 mmol L^-1 ambient [Mg²⁺], respectively) and sampled at 24 h or 9 days. Next, the impact of elevated ambient [Mg²⁺] was explored by exposing toadfish to control (50 mmol L^-1 Mg²⁺), or elevated [Mg²⁺] (100 mmol L^-1) at a constant salinity for 7 days. Mg²⁺ levels in this experiment corresponded with levels in control and hypersaline conditions in the first experiment. A salinity increase from 5 to 60 ppt stimulated the level of all investigated transcripts in the kidney. In Mg²⁺-exposed fish, we observed a 14-fold increase in the volume of intestinal fluids and elevated plasma osmolality and [Mg²⁺], suggesting osmoregulatory challenges. However, none of the renal gene targets changed expression compared with the control group. We conclude that transcriptional regulation of renal Mg²⁺ transporters is induced by elevated [Mg²⁺] in combination with salinity rather than elevated ambient [Mg²⁺] alone.

Study of cognitive impairment and genetic polymorphism of SLC41A1 (rs11240569 allele) in Parkinson’s disease in Upper Egypt: case-control study

Background

Parkinson’s disease is one of the neurodegenerative disorders that is caused by genetic and environmental factors or interaction between them. Solute carrier family 41 member 1 within the PARK16 locus has been reported to be associated with Parkinson’s disease. Cognitive impairment is one of the non-motor symptoms that is considered a challenge in Parkinson’s disease patients. This study aimed to investigate the association of rs11240569 polymorphism; a synonymous coding variant in SLC41A1 in Parkinson’s disease patients in addition to the assessment of cognitive impairment in those patients.

Results

In a case -control study, rs11240569 single nucleotide polymorphisms in SLC41A1, genes were genotyped in 48 Parkinson’s disease patients and 48 controls. Motor and non-motor performance in Parkinson's disease patients were assessed by using the Movement Disorder Society-Sponsored Revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS). The genotype and allele frequencies were compared between the two groups and revealed no significant differences between case and control groups for rs11240569 in SLC41A1 gene with P value .523 and .54, respectively. Cognition was evaluated and showed the mean ± standard deviation (SD) of WAIS score of PD patients 80.4 ± 9.13 and the range was from 61 to 105, in addition to MMSE that showed mean ± SD 21.96 ± 3.8.

Conclusion

Genetic testing of the present study showed that rs11240569 polymorphism of SLC41A1 gene has no significant differences in distributions of alleles and genotypes between cases and control group, in addition to cognitive impairment that is present in a large proportion of PD patients and in addition to the strong correlation between cognitive impairment and motor and non-motor symptoms progression.

The Combined Influence of Magnesium and Insulin on Central Metabolic Functions and Expression of Genes Involved in Magnesium Homeostasis of Cultured Bovine Adipocytes

At the onset of lactation, dairy cows suffer from insulin resistance, insulin deficiency or both, similar to human diabetes, resulting in lipolysis, ketosis and fatty liver. This work explored the combined effects of different levels of magnesium (0.1, 0.3, 1 and 3 mM) and insulin (25, 250 and 25,000 pM) on metabolic pathways and the expression of magnesium-responsive genes in a bovine adipocyte model. Magnesium starvation (0.1 mM) and low insulin (25 pM) independently decreased or tended to decrease the accumulation of non-polar lipids and uptake of the glucose analog 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-deoxyglucose (6-NBDG). Activity of glycerol 3-phosphate dehydrogenase (GPDH) was highest at 25 pM insulin and 3 mM magnesium. Expression of SLC41A1 and SLC41A3 was reduced at 0.1 mM magnesium either across insulin concentrations (SLC41A1) or at 250 pM insulin (SLC41A3). MAGT1 expression was reduced at 3 mM magnesium. NIPA1 expression was reduced at 3 mM and 0.1 mM magnesium at 25 and 250 pM insulin, respectively. Expression of SLC41A2, CNNM2, TRPM6 and TRPM7 was not affected. We conclude that magnesium promotes lipogenesis in adipocytes and inversely regulates the transcription of genes that increase vs. decrease cytosolic magnesium concentration. The induction of GAPDH activity by surplus magnesium at low insulin concentration can counteract excessive lipomobilization.

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.

The structure of MgtE in the absence of magnesium provides new insights into channel gating

MgtE is a Mg2+ channel conserved in organisms ranging from prokaryotes to eukaryotes, including humans, and plays an important role in Mg2+ homeostasis. The previously determined MgtE structures in the Mg2+-bound, closed-state, and structure-based functional analyses of MgtE revealed that the binding of Mg2+ ions to the MgtE cytoplasmic domain induces channel inactivation to maintain Mg2+ homeostasis. There are no structures of the transmembrane (TM) domain for MgtE in Mg2+-free conditions, and the pore-opening mechanism has thus remained unclear. Here, we determined the cryo-electron microscopy (cryo-EM) structure of the MgtE-Fab complex in the absence of Mg2+ ions. The Mg2+-free MgtE TM domain structure and its comparison with the Mg2+-bound, closed-state structure, together with functional analyses, showed the Mg2+-dependent pore opening of MgtE on the cytoplasmic side and revealed the kink motions of the TM2 and TM5 helices at the glycine residues, which are important for channel activity. Overall, our work provides structure-based mechanistic insights into the channel gating of MgtE.

Differential impact of imipramine on thapsigargin- and tunicamycin-induced endoplasmic reticulum stress and mitochondrial dysfunction in neuroblastoma SH-SY5Y cells

The aim of our work was to study effect of antidepressant imipramine on both thapsigargin- and tunicamycin-induced ER stress and mitochondrial dysfunction in neuroblastoma SH-SY5Y cells. ER stress in SH-SY5Y cells was induced by either tunicamycin or thapsigargin in the presence or absence of imipramine. Cell viability was tested by the MTT assay. Splicing of XBP1 mRNA was studied by RT-PCR. Finally, expression of Hrd1 and Hsp60 was determined by Western blot analysis. Our findings provide evidence that at high concentrations imipramine potentiates ER stress-induced death of SH-SY5Y cells. The effect of imipramine on ER stress-induced death of SH-SY5Y cells was stronger in combination of imipramine with thapsigargin. In addition, we have found that treatment of SH-SY5Y cells with imipramine in combination of either thapsigargin or tunicamycin is associated with the alteration of ER stress-induced IRE1α-XBP1 signalling. Despite potentiation of ER stress-induced XBP1 splicing, imipramine suppresses both thapsigargin- and tunicamycin-induced expression of Hrd1. Finally, imipramine in combination with thapsigargin, but not tunicamycin, aggravates ER stress-induced mitochondrial dysfunction without significant impact on intracellular mitochondrial content as indicated by the unaltered expression of Hsp60. Our results indicate the possibility that chronic treatment with imipramine might be associated with a higher risk of development and progression of neurodegenerative disorders, in particular those allied with ER stress and mitochondrial dysfunction like Parkinson's and Alzheimer's disease.

Emerging roles of the solute carrier family in pancreatic cancer

Pancreatic cancer is a gastrointestinal tumor with a high mortality rate, and advances in surgical procedures have only resulted in limited improvements in the prognosis of patients. Solute carriers (SLCs), which rank second among membrane transport proteins in terms of abundance, regulate cellular functions, including tumor biology. An increasing number of studies focusing on the role of SLCs in tumor biology have indicated their relationship with pancreatic cancer. The mechanism of SLC transporters in tumorigenesis has been explored to identify more effective therapies and improve survival outcomes. These transporters are significant biomarkers for pancreatic cancer, the functions of which include mainly proliferative signaling, cell death, angiogenesis, tumor invasion and metastasis, energy metabolism, chemotherapy sensitivity and other functions in tumor biology. In this review, we summarize the different roles of SLCs and explain their potential applications in pancreatic cancer treatment.

Sodium Transporters in Human Health and Disease

Sodium (Na+) electrochemical gradients established by Na+/K+ ATPase activity drives the transport of ions, minerals, and sugars in both excitable and non-excitable cells. Na+-dependent transporters can move these solutes in the same direction (cotransport) or in opposite directions (exchanger) across both the apical and basolateral plasma membranes of polarized epithelia. In addition to maintaining physiological homeostasis of these solutes, increases and decreases in sodium may also initiate, directly or indirectly, signaling cascades that regulate a variety of intracellular post-translational events. In this review, we will describe how the Na+/K+ ATPase maintains a Na+ gradient utilized by multiple sodium-dependent transport mechanisms to regulate glucose uptake, excitatory neurotransmitters, calcium signaling, acid-base balance, salt-wasting disorders, fluid volume, and magnesium transport. We will discuss how several Na+-dependent cotransporters and Na+-dependent exchangers have significant roles in human health and disease. Finally, we will discuss how each of these Na+-dependent transport mechanisms have either been shown or have the potential to use Na+ in a secondary role as a signaling molecule.

Modeling Distal Convoluted Tubule (Patho)Physiology: An Overview of Past Developments and an Outlook Toward the Future

The kidneys are essential for maintaining electrolyte homeostasis. Blood electrolyte composition is controlled by active reabsorption and secretion processes in dedicated segments of the kidney tubule. Specifically, the distal convoluted tubule (DCT) and connecting tubule are important for regulating the final excretion of sodium, magnesium, and calcium. Studies unravelling the specific function of these segments have greatly improved our understanding of DCT (patho)physiology. Over the years, experimental models used to study the DCT have changed and the field has advanced from early dissection studies with rats and rabbits to the use of various transgenic mouse models. Developments in dissection techniques and cell culture methods have resulted in immortalized mouse DCT cell lines and made it possible to specifically obtain DCT fragments for ex vivo studies. However, we still do not fully understand the complex (patho)physiology of this segment and there is need for advanced human DCT models. Recently, kidney organoids and tubuloids have emerged as new complex cell models that provide excellent opportunities for physiological studies, disease modeling, drug discovery, and even personalized medicine in the future. This review presents an overview of cell models used to study the DCT and provides an outlook on kidney organoids and tubuloids as model for DCT (patho)physiology. Impact statement This study provides a detailed overview of past and future developments on cell models used to study kidney (patho)physiology and specifically the distal convoluted tubule (DCT) segment. Hereby, we highlight the need for an advanced human cell model of this segment and summarize recent advances in the field of kidney organoids and tubuloids with a focus on DCT properties. The findings reported in this review are significant for future developments toward an advanced human model of the DCT that will help to increase our understanding of DCT (patho)physiology.

Mechanisms coupling sodium and magnesium reabsorption in the distal convoluted tubule of the kidney

Hypomagnesaemia is a common feature of renal Na⁺ wasting disorders such as Gitelman and EAST/SeSAME syndrome. These genetic defects specifically affect Na⁺ reabsorption in the distal convoluted tubule, where Mg²⁺ reabsorption is tightly regulated. Apical uptake via TRPM6 Mg²⁺ channels and basolateral Mg²⁺ extrusion via a putative Na⁺ -Mg²⁺ exchanger determines Mg²⁺ reabsorption in the distal convoluted tubule. However, the mechanisms that explain the high incidence of hypomagnesaemia in patients with Na⁺ wasting disorders of the distal convoluted tubule are largely unknown. In this review, we describe three potential mechanisms by which Mg²⁺ reabsorption in the distal convoluted tubule is linked to Na⁺ reabsorption. First, decreased activity of the thiazide-sensitive Na⁺ /Cl^- cotransporter (NCC) results in shortening of the segment, reducing the Mg²⁺ reabsorption capacity. Second, the activity of TRPM6 and NCC are determined by common regulatory pathways. Secondary effects of NCC dysregulation such as hormonal imbalance, therefore, might disturb TRPM6 expression. Third, the basolateral membrane potential, maintained by the K⁺ permeability and Na⁺ -K⁺ -ATPase activity, provides the driving force for Na⁺ and Mg²⁺ extrusion. Depolarisation of the basolateral membrane potential in Na⁺ wasting disorders of the distal convoluted tubule may therefore lead to reduced activity of the putative Na⁺ -Mg²⁺ exchanger SLC41A1. Elucidating the interconnections between Mg²⁺ and Na⁺ transport in the distal convoluted tubule is hampered by the currently available models. Our analysis indicates that the coupling of Na⁺ and Mg²⁺ reabsorption may be multifactorial and that advanced experimental models are required to study the molecular mechanisms.

Mg2+ Transporters in Digestive Cancers

Despite magnesium (Mg²⁺) representing the second most abundant cation in the cell, its role in cellular physiology and pathology is far from being elucidated. Mg²⁺ homeostasis is regulated by Mg²⁺ transporters including Mitochondrial RNA Splicing Protein 2 (MRS2), Transient Receptor Potential Cation Channel Subfamily M, Member 6/7 (TRPM6/7), Magnesium Transporter 1 (MAGT1), Solute Carrier Family 41 Member 1 (SCL41A1), and Cyclin and CBS Domain Divalent Metal Cation Transport Mediator (CNNM) proteins. Recent data show that Mg²⁺ transporters may regulate several cancer cell hallmarks. In this review, we describe the expression of Mg²⁺ transporters in digestive cancers, the most common and deadliest malignancies worldwide. Moreover, Mg²⁺ transporters’ expression, correlation and impact on patient overall and disease-free survival is analyzed using Genotype Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) datasets. Finally, we discuss the role of these Mg²⁺ transporters in the regulation of cancer cell fates and oncogenic signaling pathways.

Lactate as a new second messenger shaping intracellular Mg2+ dynamics and bioenergetics

Mg²⁺ is an essential cation controlling many biochemical reactions. Recently, Daw et al. [1] have shown that l-lactate acts as a second messenger triggering a dynamic exchange of Mg²⁺ between the endoplasmic reticulum and mitochondria to shape energy metabolism. This discovery changes our view on the cellular role of Mg²⁺.

Dietary Mg2+ Intake and the Na+/Mg2+ Exchanger SLC41A1 Influence Components of Mitochondrial Energetics in Murine Cardiomyocytes

Cardiomyocytes are among the most energy-intensive cell types. Interplay between the components of cellular magnesium (Mg) homeostasis and energy metabolism in cardiomyocytes is poorly understood. We have investigated the effects of dietary Mg content and presence/functionality of the Na+/Mg2+ exchanger SLC41A1 on enzymatic functions of selected constituents of the Krebs cycle and complexes of the electron transport chain (ETC). The activities of aconitate hydratase (ACON), isocitrate dehydrogenase (ICDH), α-ketoglutarate dehydrogenase (KGDH), and ETC complexes CI-CV have been determined in vitro in mitochondria isolated from hearts of wild-type (WT) and Slc41a1-/- mice fed a diet with either normal or low Mg content. Our data demonstrate that both, the type of Mg diet and the Slc41a1 genotype largely impact on the activities of enzymes of the Krebs cycle and ETC. Moreover, a compensatory effect of Slc41a1-/- genotype on the effect of low Mg diet on activities of the tested Krebs cycle enzymes has been identified. A machine-learning analysis identified activities of ICDH, CI, CIV, and CV as common predictors of the type of Mg diet and of CII as suitable predictor of Slc41a1 genotype. Thus, our data delineate the effect of dietary Mg content and of SLC41A1 functionality on the energy-production in cardiac mitochondria.

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.

General Aspects of Metal Ions as Signaling Agents in Health and Disease

This review focuses on the current knowledge on the involvement of metal ions in signaling processes within the cell, in both physiological and pathological conditions. The first section is devoted to the recent discoveries on magnesium and calcium-dependent signal transduction-the most recognized signaling agents among metals. The following sections then describe signaling pathways where zinc, copper, and iron play a key role. There are many systems in which changes in intra- and extra-cellular zinc and copper concentrations have been linked to important downstream events, especially in nervous signal transduction. Iron signaling is mostly related with its homeostasis. However, it is also involved in a recently discovered type of programmed cell death, ferroptosis. The important differences in metal ion signaling, and its disease-leading alterations, are also discussed.

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.

Inhibition of Mg2+ Extrusion Attenuates Glutamate Excitotoxicity in Cultured Rat Hippocampal Neurons

Magnesium plays important roles in the nervous system. An increase in the Mg²⁺ concentration in cerebrospinal fluid enhances neural functions, while Mg²⁺ deficiency is implicated in neuronal diseases in the central nervous system. We have previously demonstrated that high concentrations of glutamate induce excitotoxicity and elicit a transient increase in the intracellular concentration of Mg²⁺ due to the release of Mg²⁺ from mitochondria, followed by a decrease to below steady-state levels. Since Mg²⁺ deficiency is involved in neuronal diseases, this decrease presumably affects neuronal survival under excitotoxic conditions. However, the mechanism of the Mg²⁺ decrease and its effect on the excitotoxicity process have not been elucidated. In this study, we demonstrated that inhibitors of Mg²⁺ extrusion, quinidine and amiloride, attenuated glutamate excitotoxicity in cultured rat hippocampal neurons. A toxic concentration of glutamate induced both Mg²⁺ release from mitochondria and Mg²⁺ extrusion from cytosol, and both quinidine and amiloride suppressed only the extrusion. This resulted in the maintenance of a higher Mg²⁺ concentration in the cytosol than under steady-state conditions during the ten-minute exposure to glutamate. These inhibitors also attenuated the glutamate-induced depression of cellular energy metabolism. Our data indicate the importance of Mg²⁺ regulation in neuronal survival under excitotoxicity.

Magnesium transporter protein solute carrier family 41 member 1 suppresses human pancreatic ductal adenocarcinoma through magnesium-dependent Akt/mTOR inhibition and bax-associated mitochondrial apoptosis

The aim of this study was to identify the function of the Mg²⁺ transporter protein solute carrier family 41 member 1 SLC41A1 in pancreatic ductal adenocarcinoma and the underlying mechanisms. A total of 27 solute carrier proteins were differentially expressed in pancreatic ductal adenocarcinoma. Three of these proteins were correlated with clinical outcomes in patients, among which SLC41A1 was downregulated in tumour. Overexpression of SLC41A1 suppressed orthotopic tumour growth in a mouse model and reduced the cell proliferation, colony formation, and invasiveness of KP3 and Panc-1 cells, which may have been associated with the increased population of apoptotic-prone cells. Overexpression of SLC41A1 reduced the mitochondrial membrane potential, induced Bax while suppressed Bcl-2 expression. Suppression of Bax abrogated the tumour-suppressive effects of SLC41A1. Furthermore, overexpression of SLC41A1 promoted Mg²⁺ efflux and suppressed Akt/mTOR activity, which is the upstream regulator of Bax and Bcl-2. An increase in Akt activity and supplementation with Mg²⁺ abolished SLC41A1-induced tumour suppression. The results of this study suggest that SLC41A1 may be a potential target for the treatment of pancreatic ductal adenocarcinoma.

Down-Regulated Expression of Magnesium Transporter Genes Following a High Magnesium Diet Attenuates Sciatic Nerve Crush Injury

BACKGROUND

Magnesium supplementation has potential for use in nerve regeneration. The expression of some magnesium transporter genes is reflective of the intracellular magnesium levels.

OBJECTIVE

To assess the expression of various magnesium transporter genes as they relate to neurological alterations in a sciatic nerve injury model.

METHODS

Sciatic nerve injury was induced in rats, which were then fed either basal or high magnesium diets. Magnesium concentrations and 5 magnesium transporter genes (SLC41A1, MAGT1, CNNM2, TRPM6, and TRPM7) were measured in the tissue samples.

RESULTS

The high magnesium diet attenuated cytoskeletal loss in a dose-dependent manner in isolated nerve explants. The high magnesium diet augmented nerve regeneration and led to the restoration of nerve structure, increased S-100, and neurofilaments. This increased regeneration was consistent with the improvement of neurobehavioral and electrophysiological assessment. The denervated muscle morphology was restored with the high magnesium diet, and that was also highly correlated with the increased expression of desmin and acetylcholine receptors in denervated muscle. The plasma magnesium levels were significantly elevated after the animals consumed a high magnesium diet and were reciprocally related to the down-regulation of CNNM2, MagT1, and SCL41A1 in the blood monocytes, nerves, and muscle tissues of the nerve crush injury model.

CONCLUSION

The increased plasma magnesium levels after consuming a high magnesium diet were highly correlated with the down-regulation of magnesium transporter genes in monocytes, nerves, and muscle tissues after sciatic nerve crush injury. The study findings suggest that there are beneficial effects of administering magnesium after a nerve injury.

A Comprehensive Prognostic and Immune Analysis of SLC41A3 in Pan-Cancer

SLC41A3, as a member of the 41^st family of solute carriers, participates in the transport of magnesium. The role of SLC41A3 in cancer prognosis and immune regulation has rarely been reported. This study was designed to analyze the expression status and prognostic significance of SLC41A3 in pan-cancers. The mRNA expression profiles of SLC41A3 were obtained from The Cancer Genome Atlas (TCGA), the Genotype-Tissue Expression (GTEx), the Broad Institute Cancer Cell Line Encyclopedia (CCLE), and the International Cancer Genome Consortium (ICGC). The Cox regression and Kaplan-Meier analyses were used to evaluate the prognostic value of SLC41A3 in pan-cancer. Furthermore, the correlation between SLC41A3 expression and immune cells infiltration, immune checkpoint, mismatch repair (MMR), DNA methyltransferase (DNMT), tumor mutation burden (TMB), and microsatellite instability (MSI) were calculated using data form TCGA database. The results showed that the expression of SLC41A3 was down-regulated in kidney renal clear cell carcinoma (KIRC), and was associated with poor overall survival and tumor-specific mortality. Whereas, the expression of SLC41A3 was up-regulated in liver hepatocellular carcinoma (LIHC), and the results of Cox regression analysis revealed that SLC41A3 was an independent factor for LIHC prognosis. Meanwhile, a nomogram including SLC41A3 and stage was built and exhibited good predictive power for the overall survival of LIHC patients. Additionally, correlation analysis suggested a significant correlation between SLC41A3 and TMB, MSI, MMR, DNMT, and immune cells infiltration in various cancers. The overall survival and disease-specific survival analysis revealed that the combined SLC41A3 expression and immune cell score, TMB, and MSI were significantly associated with clinical outcomes in ACC, LIHC, and UVM patients. Therefore, we proposed that SLC41A3 may serve as a potential prognostic biomarker for cancer.

Solute carrier transporters: the metabolic gatekeepers of immune cells

Solute carrier (SLC) transporters meditate many essential physiological functions, including nutrient uptake, ion influx/efflux, and waste disposal. In its protective role against tumors and infections, the mammalian immune system coordinates complex signals to support the proliferation, differentiation, and effector function of individual cell subsets. Recent research in this area has yielded surprising findings on the roles of solute carrier transporters, which were discovered to regulate lymphocyte signaling and control their differentiation, function, and fate by modulating diverse metabolic pathways and balanced levels of different metabolites. In this review, we present current information mainly on glucose transporters, amino-acid transporters, and metal ion transporters, which are critically important for mediating immune cell homeostasis in many different pathological conditions.

SNPs rs11240569, rs708727, and rs823156 in SLC41A1 Do Not Discriminate Between Slovak Patients with Idiopathic Parkinson's Disease and Healthy Controls: Statistics and Machine-Learning Evidence

Gene SLC41A1 (A1) is localized within Parkinson’s disease-(PD)-susceptibility locus PARK16 and encodes for the Na⁺/Mg²⁺-exchanger. The association of several A1 SNPs with PD has been studied. Two, rs11240569 and rs823156, have been associated with reduced PD-susceptibility primarily in Asian populations. Here, we examined the association of rs11240569, rs708727, and rs823156 with PD in the Slovak population and their power to discriminate between PD patients and healthy controls. The study included 150 PD patients and 120 controls. Genotyping was performed with the TaqMan^® approach. Data were analyzed by conventional statistics and Random Forest machine-learning (ML) algorithm. Individually, none of the three SNPs is associated with an altered risk for PD-onset in Slovaks. However, a combination of genotypes of SNP-triplet GG_(rs11240569)/AG_(rs708727)/AA_(rs823156) is significantly (p < 0.05) more frequent in the PD (13.3%) than in the control (5%) cohort. ML identified the power of the tested SNPs in isolation or of their singlets (joined), duplets and triplets to discriminate between PD-patients and healthy controls as zero. Our data further substantiate differences between diverse populations regarding the association of A1 polymorphisms with PD-susceptibility. Lack of power of the tested SNPs to discriminate between PD and healthy cases render their clinical/diagnostic relevance in the Slovak population negligible.

Magnesium is a critical element for competent development of bovine embryos

The study was designed to determine the impact of magnesium (Mg²⁺) on bovine embryo development. We found that two commercially available sources of bovine serum albumin (BSA) and fetal bovine serum (FBS) contained different amounts of Mg²⁺ residue: 4 ppm in ICPbio BSA, 114 ppm in Sigma BSA, and 44 ppm in FBS. When CR1 was used as basal medium, PVA and ICPbio BSA produced the lowest blastocyst yield (2.2-2.3%), whereas Sigma BSA increased blastocyst yield to 18.9% (P < 0.05). Supplementation of 1.4 mM MgCl₂ into the medium increased the blastocyst rate in the ICPbio BSA group (29.4%) but not in the PVA group (5.4%; P < 0.05) to a level comparable to that of the FBS group (33.7%; P > 0.05). We next found that increasing concentrations of MgCl₂ in the culture medium (ICPbio BSA) elevated blastocyst rate from 2.6% (0 mM), 38.4% (0.35 mM) to 50.2% (1.4 mM; P < 0.05), further maintained at 44.9% (2.1 mM) and 43.4% (2.8 mM) (P > 0.05). However, blastocyst rate was reduced to 31.4% (4.2 mM) and 29.4% (5.6 mM) when MgCl₂ supplement was increased (P < 0.05). Comparable blastocyst development was achieved in both ICPbio BSA (30.0-33.1%) and Sigma BSA (37.4-38.7%) groups when 1.4 mM Mg²⁺ was supplemented regardless of its source (MgCl₂ vs. MgSO₄; P > 0.05). In embryo transfer experiments, higher rates of pregnancy (54.3 vs. 41.5%) and calving (44.3 vs. 32.5%) were achieved in the CR1-Mg²⁺-supplemented BSA group compared with the FBS group with co-culture, respectively (P < 0.05). These results demonstrate that Mg²⁺ is a key ion that promotes competent blastocyst and term development. Therefore, a simple and efficient defined medium (CR1-Mg²⁺-BSA) can successfully replace complex serum and somatic cell co-culture.

Magnesium-responsive genes are downregulated in diabetic patients after a three-month exercise program on a bicycle ergometer

BACKGROUND

Exercise is an effective therapy for the management of diabetes because it helps regulate glucose and magnesium homeostasis. Nevertheless, the mechanisms by which exercise exerts effects on magnesium transport remain unclear. This study investigated the expression of genes encoding magnesium transporters (GMTs) after a three-month exercise program in diabetic patients.

METHODS

This study was conducted with a within-subject pre-post design. A total of 15 adult patients with type 2 diabetes mellitus (T2DM) were recruited and underwent a three-month indoor bicycle exercise program. The expression of five GMTs (CNNM2, TRPM6, TRPM7, SLC41A1, and SLC41A3) was determined in blood samples. Relevant anthropometric values and biochemical parameters were also determined.

RESULTS

Although the body weight and body mass index decreased after three months exercise, there were no significant differences. Fasting blood glucose, glycated hemoglobin (HbA1c), waist circumference, and magnesium levels decreased after the exercise program (p < 0.05). The expression of SLC41A1 and SLC41A3 were downregulated after exercise, but only CNNM2, TRPM6, and TRPM7 showed significantly decreased expression levels compared with those before the exercise program (p < 0.05).

CONCLUSION

The three-month exercise program ameliorated blood glucose levels and downregulated the expression of magnesium-responsive genes in patients with T2DM.

SLC41A1 is essential for magnesium homeostasis in vivo

Solute carrier family 41 member A1 (SLC41A1) has been suggested to mediate magnesium (Mg2+) transport by several in vitro studies. However, the physiological function of SLC41A1 remains to be elucidated. In this study, cellular Mg2+ transport assays combined with zebrafish slc41a1 knockdown experiments were performed to disclose SLC41A1 function and its physiological relevance. The gene slc41a1 is ubiquitously expressed in zebrafish tissues and is regulated by water and dietary Mg2+ availability. Knockdown of slc41a1 in zebrafish larvae grown in a Mg2+-free medium resulted in a unique phenotype characterized by a decrease in zebrafish Mg content. This decrease shows that SLC41A1 is required to maintain Mg2+ balance and its dysfunction results in renal Mg2+ wasting in zebrafish larvae. Importantly, the Mg content of the larvae is rescued when mouse SLC41A1 is expressed in slc41a1-knockdown zebrafish. Conversely, expression of mammalian SLC41A1-p.Asp262Ala, harboring a mutation in the ion-conducting SLC41A1 pore, did not reverse the renal Mg2+ wasting. 25Mg2+ transport assays in human embryonic kidney 293 (HEK293) cells overexpressing SLC41A1 demonstrated that SLC41A1 mediates cellular Mg2+ extrusion independently of sodium (Na+). In contrast, SLC41A1-p.Asp262Ala expressing HEK293 cells displayed similar Mg2+ extrusion activities than control (mock) cells. In polarized Madin-Darby canine kidney cells, SLC41A1 localized to the basolateral cell membrane. Our results demonstrate that SLC41A1 facilitates renal Mg2+ reabsorption in the zebrafish model. Furthermore, our data suggest that SLC41A1 mediates both Mg2+ uptake and extrusion.

A Magnesium Transport Protein Related to Mammalian SLC41 and Bacterial MgtE Contributes to Circadian Timekeeping in a Unicellular Green Alga

Circadian clocks in eukaryotes involve both transcriptional-translational feedback loops, post-translational regulation, and metabolic, non-transcriptional oscillations. We recently identified the involvement of circadian oscillations in the intracellular concentrations of magnesium ions (Mg²⁺_i) that were conserved in three eukaryotic kingdoms. Mg²⁺_i in turn contributes to transcriptional clock properties of period and amplitude, and can function as a zeitgeber to define phase. However, the mechanism-or mechanisms-responsible for the generation of Mg²⁺_i oscillations, and whether these are functionally conserved across taxonomic groups, remain elusive. We employed the cellular clock model Ostreococcustauri to provide a first study of an MgtE domain-containing protein in the green lineage. OtMgtE shares homology with the mammalian SLC41A1 magnesium/sodium antiporter, which has previously been implicated in maintaining clock period. Using genetic overexpression, we found that OtMgtE contributes to both timekeeping and daily changes in Mg²⁺_i. However, pharmacological experiments and protein sequence analyses indicated that critical differences exist between OtMgtE and either the ancestral MgtE channel or the mammalian SLC41 antiporters. We concluded that even though MgtE domain-containing proteins are only distantly related, these proteins retain a shared role in contributing to cellular timekeeping and the regulation of Mg²⁺_i.

Quantification of Mg2+, Ca2+ and H+ transport by the gastrointestinal tract of the goldfish, Carassius auratus, using the Scanning Ion-selective Electrode Technique (SIET)

An in vitro gut-sac technique and the scanning ion-selective electrode technique (SIET) were used to characterize Mg²⁺, Ca²⁺, and H⁺ transport at both the mucosal and serosal surfaces of non-everted and everted gastrointestinal tissues obtained from Carassius auratus. As part of the study, two magnesium ionophores were compared (II vs. VI). Unfed animals displayed uniform transport of all ions along the intestine. Feeding resulted in elevated Mg²⁺ and Ca²⁺ transport when the gut lumen contained chyme however, under symmetrical conditions this increased transport rate was absent. Furthermore, zonation of divalent cation transport was present for both Ca²⁺ and Mg²⁺ under non-symmetrical conditions while the zonation remained for Ca²⁺ alone under symmetrical conditions. High dietary Mg²⁺ decreased absorption and induced secretion of Mg²⁺ in the posterior intestine. Uptake kinetics in the esophagus suggest large diffusive and/or convective components based on a linear relationship between Mg²⁺ transport and concentration and lack of inhibition by ouabain, an inhibitor of Na⁺-K⁺-ATPase. In contrast, kinetics in the rectum were suggestive of a low affinity, saturable carrier-mediated pathway. A decrease in Mg²⁺ and Ca²⁺ transport was observed in the posterior intestine (both at the mucosal and serosal surfaces) in response to ouabain. This impact was greatest for Ca²⁺ transport and when applied to the mucosal fluid and measured in everted preparations. In contrast a putative Mg²⁺ transport inhibitor, cobalt(III)hexamine-chloride, did not affect Mg²⁺ transport. This is the first study to use SIET approaches to study ion transport in the gut of teleost fish. This is also the first study to provide characterization of Mg²⁺ transport in the gut of C. auratus. Due to the limited selectivity of Magnesium ionophore II, subsequent studies of tissues bathed in physiological saline should be made using Magnesium Ionophore VI.

Renal sodium and magnesium reabsorption are not coupled in a mouse model of Gordon syndrome

Active reabsorption of magnesium (Mg2+ ) in the distal convoluted tubule (DCT) of the kidney is crucial for maintaining Mg2+ homeostasis. Impaired activity of the Na+ -Cl- -cotransporter (NCC) has been associated with hypermagnesiuria and hypomagnesemia, while increased activity of NCC, as observed in patients with Gordon syndrome, is not associated with alterations in Mg2+ balance. To further elucidate the possible interrelationship between NCC activity and renal Mg2+ handling, plasma Mg2+ levels and urinary excretion of sodium (Na+ ) and Mg2+ were measured in a mouse model of Gordon syndrome. In this model, DCT1-specific expression of a constitutively active mutant form of the NCC-phosphorylating kinase, SPAK (CA-SPAK), increases NCC activity and hydrochlorothiazide (HCTZ)-sensitive Na+ reabsorption. These mice were normomagnesemic and HCTZ administration comparably reduced plasma Mg2+ levels in CA-SPAK mice and control littermates. As inferred by the initial response to HCTZ, CA-SPAK mice exhibited greater NCC-dependent Na+ reabsorption together with decreased Mg2+ reabsorption, compared to controls. Following prolonged HCTZ administration (4 days), CA-SPAK mice exhibited higher urinary Mg2+ excretion, while urinary Na+ excretion decreased to levels observed in control animals. Surprisingly, CA-SPAK mice had unaltered renal expression of Trpm6, encoding the Mg2+ -permeable channel TRPM6, or other magnesiotropic genes. In conclusion, CA-SPAK mice exhibit normomagnesemia, despite increased NCC activity and Na+ reabsorption. Thus, Mg2+ reabsorption is not coupled to increased thiazide-sensitive Na+ reabsorption, suggesting a similar process explains normomagnesemia in Gordon syndrome. Further research is required to unravel the molecular underpinnings of this phenomenon and the more pronounced Mg2+ excretion after prolonged HCTZ administration.

The rise and fall of novel renal magnesium transporters

Body Mg2+ balance is finely regulated in the distal convoluted tubule (DCT), where a tight interplay among transcellular reabsorption, mitochondrial exchange, and basolateral extrusion takes place. In the last decades, several research groups have aimed to identify the molecular players in these processes. A multitude of proteins have been proposed to function as Mg2+ transporter in eukaryotes based on phylogenetic analysis, differential gene expression, and overexpression studies. However, functional evidence for many of these proteins is lacking. The aim of this review is, therefore, to critically reconsider all putative Mg2+ transporters and put their presumed function in context of the renal handling of Mg2+. Sufficient experimental evidence exists to acknowledge transient receptor potential melastatin (TRPM) 6 and TRPM7, solute carrier family 41 (SLC41) A1 and SLC41A3, and mitochondrial RNA splicing 2 (MRS2) as Mg2+ transporters. TRPM6/7 facilitate Mg2+ influx, SLC41A1 mediates Mg2+ extrusion, and MRS2 and SLC41A3 are implicated in mitochondrial Mg2+ homeostasis. These proteins are highly expressed in the DCT. The function of cyclin M (CNNM) proteins is still under debate. For the other proposed Mg2+ transporters including Mg2+ transporter subtype 1 (MagT1), nonimprinted in Prader-Willi/Angelman syndrome (NIPA), membrane Mg2+ transport (MMgT), Huntingtin-interacting protein 14 (HIP14), and ATP13A4, functional evidence is limited, or functions alternative to Mg2+ transport have been suggested. Additional characterization of their Mg2+ transport proficiency should be provided before further claims about their role as Mg2+ transporter can be made.