Gene variation of the transient receptor potential cation channel, subfamily M, members 6 (TRPM6) and 7 (TRPM7), and type 2 diabetes mellitus: a case-control study

Molecular Regulations and Functions of the Transient Receptor Potential Channels of the Islets of Langerhans and Insulinoma Cells

Insulin secretion from the β-cells of the islets of Langerhans is triggered mainly by nutrients such as glucose, and incretin hormones such as glucagon-like peptide-1 (GLP-1). The mechanisms of the stimulus-secretion coupling involve the participation of the key enzymes that metabolize the nutrients, and numerous ion channels that mediate the electrical activity. Several members of the transient receptor potential (TRP) channels participate in the processes that mediate the electrical activities and Ca²⁺ oscillations in these cells. Human β-cells express TRPC1, TRPM2, TRPM3, TRPM4, TRPM7, TRPP1, TRPML1, and TRPML3 channels. Some of these channels have been reported to mediate background depolarizing currents, store-operated Ca²⁺ entry (SOCE), electrical activity, Ca²⁺ oscillations, gene transcription, cell-death, and insulin secretion in response to stimulation by glucose and GLP1. Different channels of the TRP family are regulated by one or more of the following mechanisms: activation of G protein-coupled receptors, the filling state of the endoplasmic reticulum Ca²⁺ store, heat, oxidative stress, or some second messengers. This review briefly compiles our current knowledge about the molecular mechanisms of regulations, and functions of the TRP channels in the β-cells, the α-cells, and some insulinoma cell lines.

Genetic basis for the establishment of endosymbiosis in Paramecium

The single-celled ciliate Paramecium bursaria is an indispensable model for investigating endosymbiosis between protists and green-algal symbionts. To elucidate the mechanism of this type of endosymbiosis, we combined PacBio and Illumina sequencing to assemble a high-quality and near-complete macronuclear genome of P. bursaria. The genomic characteristics and phylogenetic analyses indicate that P. bursaria is the basal clade of the Paramecium genus. Through comparative genomic analyses with its close relatives, we found that P. bursaria encodes more genes related to nitrogen metabolism and mineral absorption, but encodes fewer genes involved in oxygen binding and N-glycan biosynthesis. A comparison of the transcriptomic profiles between P. bursaria with and without endosymbiotic Chlorella showed differential expression of a wide range of metabolic genes. We selected 32 most differentially expressed genes to perform RNA interference experiment in P. bursaria, and found that P. bursaria can regulate the abundance of their symbionts through glutamine supply. This study provides novel insights into Paramecium evolution and will extend our knowledge of the molecular mechanism for the induction of endosymbiosis between P. bursaria and green algae.

TRP channels: potential drug target for neuropathic pain

Neuropathic pain is a debilitating disease which affects central as well as peripheral nervous system. Transient receptor potential (TRP) channels are ligand-gated ion channels that detect physical and chemical stimuli and promote painful sensations via nociceptor activation. TRP channels have physiological role in the mechanisms controlling several physiological responses like temperature and mechanical sensations, response to painful stimuli, taste, and pheromones. TRP channel family involves six different TRPs (TRPV1, TRPV2, TRPV3, TRPV4, TRPM8, and TRPA1) which are expressed in pain sensing neurons and primary afferent nociceptors. They function as transducers for mechanical, chemical, and thermal stimuli into inward currents, an essential first step for provoking pain sensations. TRP ion channels activated by temperature (thermo TRPs) are important molecular players in acute, inflammatory, and chronic pain states. Different degree of heat activates four TRP channels (TRPV1-4), while cold temperature ranging from affable to painful activate two indistinctly related thermo TRP channels (TRPM8 and TRPA1). Targeting primary afferent nociceptive neurons containing TRP channels that play pivotal role in revealing physical stimuli may be an effective target for the development of successful pharmacotherapeutics for clinical pain syndromes. In this review, we highlighted the potential role of various TRP channels in different types of neuropathic pain. We also discussed the pharmacological activity of naturally and synthetically originated TRP channel modulators for pharmacotherapeutics of nociception and neuropathic pain.

Magnesium-permeable TRPM6 polymorphisms in patients with meningomyelocele

BACKGROUND

To evaluate whether there is an association between single nucleotide polymorphisms in magnesium-permeable TRPM6 ion channel and development of meningomyelocele (MMC). Therefore, we examined a total of 150 children with MMC, along with age- and gender-matched controls. DNA collected from whole blood was analyzed for the presence of two polymorphisms, rs2274924 (A > G; K1579E; Leu1579Glu) and rs3750425 (G > A; Val1393Ile), in TRPM6. Serum Mg²⁺ and calcium levels were also examined.

RESULTS

A statistically significant difference in the distribution of rs2274924 genotypes (p = 0.049) was observed between the groups. Decreases in the AA genotype, and increases in the AG heterozygous genotype were also detected in the study group. The distribution of polymorphisms in the rs3750425 genotype and alleles was not statistically different between groups. Serum Mg²⁺ levels were lower in the GG genotype of rs3750425 compared with the GA and AA genotypes (p = 0.003).

CONCLUSIONS

A statistically significant difference in rs3750425 genotypes was observed between the patients with MMC and the controls, which corresponded to lower serum Mg²⁺ concentrations in these patients. Taken together, these results suggest that genetic variations in the Mg²⁺-permeable TRPM6 ion channel may play a role in the etiopathogenesis of MMC during embryonic development.

Hypomagnesemia in Type 2 Diabetes: A Vicious Circle?

Over the past decades, hypomagnesemia (serum Mg(2+) <0.7 mmol/L) has been strongly associated with type 2 diabetes mellitus (T2DM). Patients with hypomagnesemia show a more rapid disease progression and have an increased risk for diabetes complications. Clinical studies demonstrate that T2DM patients with hypomagnesemia have reduced pancreatic β-cell activity and are more insulin resistant. Moreover, dietary Mg(2+) supplementation for patients with T2DM improves glucose metabolism and insulin sensitivity. Intracellular Mg(2+) regulates glucokinase, KATP channels, and L-type Ca(2+) channels in pancreatic β-cells, preceding insulin secretion. Moreover, insulin receptor autophosphorylation is dependent on intracellular Mg(2+) concentrations, making Mg(2+) a direct factor in the development of insulin resistance. Conversely, insulin is an important regulator of Mg(2+) homeostasis. In the kidney, insulin activates the renal Mg(2+) channel transient receptor potential melastatin type 6 that determines the final urinary Mg(2+) excretion. Consequently, patients with T2DM and hypomagnesemia enter a vicious circle in which hypomagnesemia causes insulin resistance and insulin resistance reduces serum Mg(2+) concentrations. This Perspective provides a systematic overview of the molecular mechanisms underlying the effects of Mg(2+) on insulin secretion and insulin signaling. In addition to providing a review of current knowledge, we provide novel directions for future research and identify previously neglected contributors to hypomagnesemia in T2DM.

Genetic variations in magnesium-related ion channels may affect diabetes risk among African American and Hispanic American women

BACKGROUND

Prospective studies consistently link low magnesium intake to higher type 2 diabetes (T2D) risk.

OBJECTIVE

We examined the association of common genetic variants [single nucleotide polymorphisms (SNPs)] in genes related to magnesium homeostasis with T2D risk and potential interactions with magnesium intake.

METHODS

Using the Women's Health Initiative-SNP Health Association Resource (WHI-SHARe) study, we identified 17 magnesium-related ion channel genes (583 SNPs) and examined their associations with T2D risk in 7287 African-American (AA; n = 1949 T2D cases) and 3285 Hispanic-American (HA; n = 611 T2D cases) postmenopausal women. We performed both single- and multiple-locus haplotype analyses.

RESULTS

Among AA women, carriers of each additional copy of SNP rs6584273 in cyclin mediator 1 (CNNM1) had 16% lower T2D risk [OR: 0.84; false discovery rate (FDR)-adjusted P = 0.02]. Among HA women, several variants were significantly associated with T2D risk, including rs10861279 in solute carrier family 41 (anion exchanger), member 2 (SLC41A2) (OR: 0.54; FDR-adjusted P = 0.04), rs7174119 in nonimprinted in Prader-Willi/Angelman syndrome 1 (NIPA1) (OR: 1.27; FDR-adjusted P = 0.04), and 2 SNPs in mitochondrial RNA splicing 2 (MRS2) (rs7738943: OR = 1.55, FDR-adjusted P = 0.01; rs1056285: OR = 1.48, FDR-adjusted P = 0.02). Even with the most conservative Bonferroni adjustment, two 2-SNP-haplotypes in SLC41A2 and MRS2 region were significantly associated with T2D risk (rs12582312-rs10861279: P = 0.0006; rs1056285-rs7738943: P = 0.002). Among women with magnesium intake in the lowest 30% (AA: ≤0.164 g/d; HA: ≤0.185 g/d), 4 SNP signals were strengthened [rs11590362 in claudin 19 (CLDN19), rs823154 in SLC41A1, rs5929706 and rs5930817 in membra; HA: ≥0.313 g/d), rs6584273 in CNNM1 (OR: 0.71; FDR-adjusted P = 0.04) and rs1800467 in potassium inwardly rectifying channel, subfamily J, member 11 (KCNJ11) (OR: 2.50; FDR-adjusted P = 0.01) were significantly associated with T2D risk.

CONCLUSIONS

Our findings suggest important associations between genetic variations in magnesium-related ion channel genes and T2D risk in AA and HA women that vary by amount of magnesium intake.

Inherited disorders of renal hypomagnesaemia

The kidney plays a key role in the maintenance of normal magnesium balance. The distal tubule of the kidney, namely the thick ascending limb of the loop of Henle and the distal convoluted tubule, is crucial for the regulation of serum magnesium levels and body magnesium content. The identification of molecular defects related to rare inherited magnesium losing disorders has contributed greatly to a better understanding of the process of renal magnesium handling. Since the number of genetic defects related to magnesium metabolism is still increasing, it might be expected that our knowledge on magnesium physiology will further improve. This knowledge will hopefully lead to therapeutic strategies that enable specific therapies for patients suffering from the symptoms and possible sequelae of chronic magnesium depletion.

The association between single-nucleotide polymorphisms of TRPM7 gene and breast cancer in Han Population of Northeast China

Breast cancer is one of the most common cancer and remains the leading cause of cancer-related deaths in women. There is increasing evidence suggesting that TRPM7 plays a pivotal role in breast cancer progression and metastasis. In this study, a case-control study was carried out to investigate the effects of SNPs in TRPM7 genes in the development of breast cancer in Han Population of Northeast China. A total of six SNPs (rs8042919, rs4775899, rs11635825, rs7173321, rs616256, and rs11070795) were chosen and genotyped. Genotypes were analyzed using a single-base primer extension assay. Chi-square (χ (2)) test was used to analyze statistical difference between control and patient groups in genotype and allele frequencies. The genotype-specific risks and allele frequencies of haplotypes in breast cancer patients and controls were estimated by OR and 95 % confidence intervals. The G allele of rs8042919 was associated with a reduced disease risk. The G allele of rs7173321 and particularly its homozygous GG genotype are associated with an increased breast cancer risk. Two of the TRPM7 SNPs (rs8042919 and rs7173321) are associated with breast cancer patients in Han Population of Northeast China.

Dietary magnesium and genetic interactions in diabetes and related risk factors: a brief overview of current knowledge

Nutritional genomics has exploded in the last decade, yielding insights—both nutrigenomic and nutrigenetic—into the physiology of dietary interactions and our genes. Among these are insights into the regulation of magnesium transport and homeostasis and mechanisms underlying magnesium’s role in insulin and glucose handling. Recent observational evidence has attempted to examine some promising research avenues on interaction between genetics and dietary magnesium in relation to diabetes and diabetes risk factors. This brief review summarizes the recent evidence on dietary magnesium’s role in diabetes and related traits in the presence of underlying genetic risk, and discusses future potential research directions.

Higher magnesium intake is associated with lower fasting glucose and insulin, with no evidence of interaction with select genetic loci, in a meta-analysis of 15 CHARGE Consortium Studies

Favorable associations between magnesium intake and glycemic traits, such as fasting glucose and insulin, are observed in observational and clinical studies, but whether genetic variation affects these associations is largely unknown. We hypothesized that single nucleotide polymorphisms (SNPs) associated with either glycemic traits or magnesium metabolism affect the association between magnesium intake and fasting glucose and insulin. Fifteen studies from the CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology) Consortium provided data from up to 52,684 participants of European descent without known diabetes. In fixed-effects meta-analyses, we quantified 1) cross-sectional associations of dietary magnesium intake with fasting glucose (mmol/L) and insulin (ln-pmol/L) and 2) interactions between magnesium intake and SNPs related to fasting glucose (16 SNPs), insulin (2 SNPs), or magnesium (8 SNPs) on fasting glucose and insulin. After adjustment for age, sex, energy intake, BMI, and behavioral risk factors, magnesium (per 50-mg/d increment) was inversely associated with fasting glucose [β = -0.009 mmol/L (95% CI: -0.013, -0.005), P < 0.0001] and insulin [-0.020 ln-pmol/L (95% CI: -0.024, -0.017), P < 0.0001]. No magnesium-related SNP or interaction between any SNP and magnesium reached significance after correction for multiple testing. However, rs2274924 in magnesium transporter-encoding TRPM6 showed a nominal association (uncorrected P = 0.03) with glucose, and rs11558471 in SLC30A8 and rs3740393 near CNNM2 showed a nominal interaction (uncorrected, both P = 0.02) with magnesium on glucose. Consistent with other studies, a higher magnesium intake was associated with lower fasting glucose and insulin. Nominal evidence of TRPM6 influence and magnesium interaction with select loci suggests that further investigation is warranted.

Role of oxidative stress and Ca²⁺ signaling on molecular pathways of neuropathic pain in diabetes: focus on TRP channels

Diabetes mellitus, a debilitating chronic disease, affects ~100 million people. Peripheral neuropathy is one of the most common early complications of diabetes in ~66 % of these patients. Altered Ca(2+) handling and Ca(2+) signaling were detected in a huge variety of preparations isolated from animals with experimentally induced type 1 and 2 diabetes as well as patients suffering from the disease. We reviewed the role of Ca(2+) signaling through cation channels and oxidative stress on diabetic neuropathic pain in sensory neurons. The pathogenesis of diabetic neuropathy involves the polyol pathway, advanced glycation end products, oxidative stress, protein kinase C activation, neurotrophism, and hypoxia. Experimental studies with respect to oxidative stress and Ca(2+) signaling, inhibitor roles of antioxidants in diabetic neuropathic pain are also summarized in the review. We hypothesize that deficits in insulin, triggers alterations of sensory neurone phenotype that are critical for the development of abnormal Ca(2+) homeostasis and oxidative stress and associated mitochondrial dysfunction. The transient receptor potential channels are a large family of proteins with six main subfamilies. The sheer number of different TRPs with distinct functions supports the statement that these channels are involved in a wide range of processes ranging in diabetic neuropathic pain and it seems that the TRPC, TRPM and TRPV groups are mostly responsible from diabetic neuropathic pain. In conclusion, the accumulating evidence implicating Ca(2+) dysregulation and over production of oxidative stress products in diabetic neuropathic pains, along with recent advances in understanding of genetic variations in cation channels such as TRP channels, makes modulation of neuronal Ca(2+) handling an increasingly viable approach for therapeutic interventions against the painful and degenerative aspects of many diabetic neuropathies.