Polymorphisms in the gene encoding the voltage-dependent Ca(2+) channel Ca (V)2.3 (CACNA1E) are associated with type 2 diabetes and impaired insulin secretion

Identification of rare variants in candidate genes associated with monogenic diabetes in polish mody-x patients

Purpose

Monogenic diabetes (MD) is caused by a mutation in a single gene and accounts for approximately 2.5-6% of all diabetes cases. Maturity-onset diabetes of the young (MODY) is the most common form of MD. To date, 14 different genes have been identified and associated with the presence of MODY phenotype. However, the number of potential candidate genes with relevance to beta cell function and glucose metabolism is increasing as more research is published. The aim of the study was to identify potentially causative variants in selected candidate genes in patients with a clinical diagnosis of MD.

Methods

Targeted Next-Generation Sequencing (tNGS) on Illumina NextSeq 550 platform involving Agilent SureSelectQXT Target Enrichment protocol for 994 patients with suspected MD was performed. In the next step, the sequencing data of 617 patients with no pathogenic variants in main MD-related genes were reanalysed for the presence of causative variants in six candidate genes (MTOR, TBC1D4, CACNA1E, MNX1, SLC19A2, KCNH6). The presence of the selected variants was confirmed by Sanger sequencing.

Results

Seven heterozygous possibly damaging variants were identified in four candidate genes (MTOR, TBC1D4, CACNA1E, MNX1). Five changes were assessed as novel variants, not previously described in available databases. None of the described variants were present among patients previously diagnosed with MODY diabetes due to causative, pathogenic variants in known MODY-related genes.

Conclusions

The results obtained seem to confirm the effectiveness of the NGS method in identifying potentially causative variants in novel candidate genes associated with MODY diabetes.

Role of High Voltage-Gated Ca2+ Channel Subunits in Pancreatic β-Cell Insulin Release. From Structure to Function

The pancreatic islets of Langerhans secrete several hormones critical for glucose homeostasis. The β-cells, the major cellular component of the pancreatic islets, secrete insulin, the only hormone capable of lowering the plasma glucose concentration. The counter-regulatory hormone glucagon is secreted by the α-cells while δ-cells secrete somatostatin that via paracrine mechanisms regulates the α- and β-cell activity. These three peptide hormones are packed into secretory granules that are released through exocytosis following a local increase in intracellular Ca2+ concentration. The high voltage-gated Ca2+ channels (HVCCs) occupy a central role in pancreatic hormone release both as a source of Ca2+ required for excitation-secretion coupling as well as a scaffold for the release machinery. HVCCs are multi-protein complexes composed of the main pore-forming transmembrane α1 and the auxiliary intracellular β, extracellular α2δ, and transmembrane γ subunits. Here, we review the current understanding regarding the role of all HVCC subunits expressed in pancreatic β-cell on electrical activity, excitation-secretion coupling, and β-cell mass. The evidence we review was obtained from many seminal studies employing pharmacological approaches as well as genetically modified mouse models. The significance for diabetes in humans is discussed in the context of genetic variations in the genes encoding for the HVCC subunits.

Cav2.3 channel function and Zn2+-induced modulation: potential mechanisms and (patho)physiological relevance

Voltage-gated calcium channels (VGCCs) are critical for Ca²⁺ influx into all types of excitable cells, but their exact function is still poorly understood. Recent reconstruction of homology models for all human VGCCs at atomic resolution provides the opportunity for a structure-based discussion of VGCC function and novel insights into the mechanisms underlying Ca²⁺ selective flux through these channels. In the present review, we use these data as a basis to examine the structure, function, and Zn²⁺-induced modulation of Ca_v2.3 VGCCs, which mediate native R-type currents and belong to the most enigmatic members of the family. Their unique sensitivity to Zn²⁺ and the existence of multiple mechanisms of Zn²⁺ action strongly argue for a role of these channels in the modulatory action of endogenous loosely bound Zn²⁺, pools of which have been detected in a number of neuronal, endocrine, and reproductive tissues. Following a description of the different mechanisms by which Zn²⁺ has been shown or is thought to alter the function of these channels, we discuss their potential (patho)physiological relevance, taking into account what is known about the magnitude and function of extracellular Zn²⁺ signals in different tissues. While still far from complete, the picture that emerges is one where Ca_v2.3 channel expression parallels the occurrence of loosely bound Zn²⁺ pools in different tissues and where these channels may serve to translate physiological Zn²⁺ signals into changes of electrical activity and/or intracellular Ca²⁺ levels.

The calcium channel subunit gamma-4 is regulated by MafA and necessary for pancreatic beta-cell specification

Voltage-gated Ca2+ (CaV) channels trigger glucose-induced insulin secretion in pancreatic beta-cell and their dysfunction increases diabetes risk. These heteromeric complexes include the main subunit alpha1, and the accessory ones, including subunit gamma that remains unexplored. Here, we demonstrate that CaV gamma subunit 4 (CaVγ4) is downregulated in islets from human donors with diabetes, diabetic Goto-Kakizaki (GK) rats, as well as under conditions of gluco-/lipotoxic stress. Reduction of CaVγ4 expression results in decreased expression of L-type CaV1.2 and CaV1.3, thereby suppressing voltage-gated Ca2+ entry and glucose stimulated insulin exocytosis. The most important finding is that CaVγ4 expression is controlled by the transcription factor responsible for beta-cell specification, MafA, as verified by chromatin immunoprecipitation and experiments in beta-cell specific MafA knockout mice (MafA Δβcell ). Taken together, these findings suggest that CaVγ4 is necessary for maintaining a functional differentiated beta-cell phenotype. Treatment aiming at restoring CaVγ4 may help to restore beta-cell function in diabetes.

1,25-Dihydroxyvitamin D3 enhances glucose-stimulated insulin secretion in mouse and human islets: a role for transcriptional regulation of voltage-gated calcium channels by the vitamin D receptor

AIM

Vitamin D deficiency in rodents negatively affects glucose-stimulated insulin secretion (GSIS) and human epidemiological studies connect poor vitamin D status with type 2 diabetes. Previous studies performed primarily in rat islets have shown that vitamin D can enhance GSIS. However the molecular pathways linking vitamin D and insulin secretion are currently unknown. Therefore, experiments were undertaken to elucidate the transcriptional role(s) of the vitamin D receptor (VDR) in islet function.

METHODS

Human and mouse islets were cultured with vehicle or 1,25-dihydroxyvitamin-D₃ (1,25D₃) and then subjected to GSIS assays. Insulin expression, insulin content, glucose uptake and glucose-stimulated calcium influx were tested. Microarray analysis was performed. In silico analysis was used to identify VDR response elements (VDRE) within target genes and their activity was tested using reporter assays.

RESULTS

Vdr mRNA is abundant in islets and Vdr expression is glucose-responsive. Preincubation of mouse and human islets with 1,25D₃ enhances GSIS and increases glucose-stimulated calcium influx. Microarray analysis identified the R-type voltage-gated calcium channel (VGCC) gene, Cacna1e, which is highly upregulated by 1,25D₃ in human and mouse islets and contains a conserved VDRE in intron 7. Results from GSIS assays suggest that 1,25D₃ might upregulate a variant of R-type VGCC that is resistant to chemical inhibition.

CONCLUSION

These results suggest that the role of 1,25D₃ in regulating calcium influx acts through the R-Type VGCC during GSIS, thereby modulating the capacity of beta cells to secrete insulin.

Chemical genetic-based phenotypic screen reveals novel regulators of gluconeogenesis in human primary hepatocytes

Insulin resistance is a pathophysiological hallmark of type 2 diabetes and nonalcoholic fatty liver disease. Under the condition of fat accumulation in the liver, suppression of hepatic glucose production by insulin is diminished. In order to gain deeper understanding of dysregulation of glucose production in metabolic diseases, in the present study, we performed an unbiased phenotypic screening in primary human hepatocytes to discover novel mechanisms that regulate gluconeogenesis in the presence of insulin. To optimize phenotypic screening process, we used a chemical genetic screening approach by building a small-molecule library with prior knowledge of activity-based protein profiling. The “positive hits” result from the screen will be small molecules with known protein targets. This makes downstream deconvolution process (i.e., determining the relevant biological targets) less time-consuming. To unbiasedly decipher the molecular targets, we developed a novel statistical method and discovered a set of genes, including DDR3 and CACNA1E that suppressed gluconeogenesis in human hepatocytes. Further investigation, including transcriptional profiling and gene network analysis, was performed to understand the molecular functions of DRD3 and CACNA1E in human hepatocytes.

A high-throughput screening protocol helped identify two novel genes involved in sugar metabolism that could be druggable targets for treating type 2 diabetes. Haiqing Hua and colleagues from the Lilly China Research and Development Center, a division of Eli Lilly & Company in Shanghai, evaluated the ability of human liver cells to produce glucose when exposed to a library of more than 1500 small-molecule drugs with known molecular targets. The researchers distinguished a set of genes that, when inhibited, dramatically suppressed glucose production. Two of these genes had not previously been implicated in liver function. The researchers began to dissect that molecular function through studies of gene expression and gene network analysis. The results demonstrate a way to combine chemical genetics and phenotypic screening to identify novel drug targets, revealing two for diabetes.

The interaction between DNA methylation and long non-coding RNA during the onset of puberty in goats

Epigenetics plays an important role in controlling female puberty. Both DNA methylation and long non-coding RNAs (lncRNA) regulate the initiation of puberty by affecting the expression of genes related to puberty. While recent studies have indicated that DNA methylation of lncRNA represses the expression of lncRNA, its role in regulating puberty remains unclear. To explore the mechanism between DNA methylation and lncRNAs during puberty onset, we performed whole-genome bisulphite sequencing (WGBS) and RNA-sequencing (RNA-seq). We found that DNA methylation was inversely correlated to gene expression levels during puberty. Methylation levels gradually decreased near the transcription initiation site and were present at high levels in the exon, intron and 3' untranslated regions. In the promoter, lncRNA expression was negatively related to DNA methylation. We reported hypermethylation in the gene body and downstream of the lncRNA compared with upstream regions. In GO and KEGG analyses, we found enriched target genes of lncRNA, XLOC_960044 and XLOC_767346. During puberty, methylation of these genes increased while expression decreased. Our study indicates that DNA methylation of the promoter is negatively correlated with lncRNA during puberty onset, and methylation regulates the initiation of puberty via lncRNA, which provides new insight into the epigenetic mechanism of puberty onset.

DNA polymorphisms predict time to progression from uncomplicated to complicated Crohn's disease

OBJECTIVE

Most patients with Crohn's disease (CD) are diagnosed with the uncomplicated inflammatory form of the disease (Montreal stage B1). However, the majority of them will progress to complicated stricturing (B2) and penetrating (B3) CD during their lifetimes. The aim of our study was to identify the genetic factors associated with time to progression from uncomplicated to complicated CD.

PATIENTS AND METHODS

Patients with an inflammatory phenotype at diagnosis were followed up for 10 years. Genotyping was carried out using Illumina ImmunoChip. After quality control, association analyses, Bonferroni's adjustments, linear and Cox's regression, and Kaplan-Meier analysis were carried out for 111 patients and Manhattan plots were constructed.

RESULTS

Ten years after diagnosis, 39.1% of the patients still had the inflammatory form and 60.9% progressed to complicated disease, with an average time to progression of 5.91 years. Ileal and ileocolonic locations were associated with the complicated CD (P=1.08E-03). We found that patients with the AA genotype at single-nucleotide polymorphism rs16857259 near the gene CACNA1E progressed to the complicated form later (8.80 years) compared with patients with the AC (5.11 years) or CC (2.00 years) genotypes (P=3.82E-07). In addition, nine single-nucleotide polymorphisms (near the genes RASGRP1, SULF2, XPO1, ZBTB44, HLA DOA/BRD2, HLA DRB1/HLA DQA1, PPARA, PUDP, and KIAA1614) showed a suggestive association with disease progression (P<10). Multivariate Cox's regression analysis on the basis of clinical and genetic data confirmed the association of the selected model with disease progression (P=5.73E-16).

CONCLUSION

Our study confirmed the association between the locus on chromosome 1 near the gene CACNA1E with time to progression from inflammatory to stricturing or penetrating CD. Predicting the time to progression is useful to the clinician in terms of individualizing patients' management.

Identifying heterogeneous subtypes of gastric cancer and subtype‑specific subpaths of microRNA‑target pathways

The present study aimed to classify gastric cancer (GC) into subtypes and to screen the subtype-specific genes, their targeted microRNAs (miRNAs) and enriched pathways to explore the putative mechanism of each GC subtypes. The GSE13861 data set was downloaded from the Gene Expression Omnibus and used to screen differential expression genes (DEGs) in GC samples based on the detection of imbalanced differential signal algorithm. The specific genes in each subtype were identified with the cut-off criterion of U>0.04, pathway enrichment analysis was performed and the subtype-specific subpaths of miRNA-target pathway were determined. A total of 1,263 DEGs were identified in the primary gastric adenocarcinoma (PGD) samples, which were subsequently divided into four subtypes, according to the hierarchy cluster analysis. Identification of the subpaths of each subtype indicated that the subpath related to subtype 1 was miRNA (miR)-202/calcium voltage-gated channel subunit α1 (CACNA1E)/type II diabetes mellitus. The nuclear factor-κB signaling pathway was the most significantly specific pathway and subpath identified for subtype 2, which was regulated by miR-338-targeted suppression of C-C motif chemokine ligand 21 (CCL21). For subtype 3, significant related pathways included ubiquitin-mediated proteolysis and proteasome, and the important subpath was miR-146B/proteasome 26S subunit, non-ATPase 3 (PSMD3)/proteasome; focal adhesion was the significant pathway indicated for subtype 4, and the subpaths were miR-34A/vinculin (VCL)/focal adhesion and miR-34C/VCL/focal adhesion. In addition, Helicobacter pylori infection was higher in GC subtype 1 than in other subtypes. Specific genes, such as CACNA1E, CCL21, PSMD3 and VCL, may be used as potential feature genes to identify different subtypes of GC, and their associated subpaths may partially explain the pathogenetic mechanism of each GC subtype.

The triggering pathway to insulin secretion: Functional similarities and differences between the human and the mouse β cells and their translational relevance

In β cells, stimulation by metabolic, hormonal, neuronal, and pharmacological factors is coupled to secretion of insulin through different intracellular signaling pathways. Our knowledge about the molecular machinery supporting these pathways and the patterns of signals it generates comes mostly from rodent models, especially the laboratory mouse. The increased availability of human islets for research during the last few decades has yielded new insights into the specifics in signaling pathways leading to insulin secretion in humans. In this review, we follow the most central triggering pathway to insulin secretion from its very beginning when glucose enters the β cell to the calcium oscillations it produces to trigger fusion of insulin containing granules with the plasma membrane. Along the way, we describe the crucial building blocks that contribute to the flow of information and focus on their functional role in mice and humans and on their translational implications.

Differential expression of genes and differentially perturbed pathways associated with very high evening fatigue in oncology patients receiving chemotherapy

PURPOSE

Fatigue is the most common symptom associated with cancer and its treatment. Investigation of molecular mechanisms associated with fatigue in oncology patients may identify new therapeutic targets. The objectives of this study were to evaluate the relationships between gene expression and perturbations in biological pathways and evening fatigue severity in oncology patients who received chemotherapy (CTX).

METHODS

The Lee Fatigue Scale (LFS) and latent class analysis were used to identify evening fatigue phenotypes. We measured 47,214 ribonucleic acid transcripts from whole blood collected prior to a cycle of CTX. Perturbations in biological pathways associated with differential gene expression were identified from public data sets (i.e., Kyoto Encyclopedia Gene and Genomes, BioCarta).

RESULTS

Patients were classified into Moderate (n = 65, mean LFS score 3.1) or Very High (n = 195, mean LFS score 6.4) evening fatigue groups. Compared to patients with Moderate fatigue, patients with Very High fatigue exhibited differential expression of 29 genes. A number of the perturbed pathways identified validated prior mechanistic hypotheses for fatigue, including alterations in immune function, inflammation, neurotransmission, energy metabolism, and circadian rhythms. Based on our findings, energy metabolism was further divided into alterations in carbohydrate metabolism and skeletal muscle energy. Alterations in renal function-related pathways were identified as a potential new mechanism.

CONCLUSIONS

This study identified differential gene expression and perturbed biological pathways that provide new insights into the multiple and likely inter-related mechanisms associated with evening fatigue in oncology patients.

Genetic findings in sport-related concussions: potential for individualized medicine?

Concussion is a traumatic transient disturbance of the brain. In sport, the initial time and severity of concussion is known giving an opportunity for subsequent analysis. Variability in susceptibility and recovery between individual athletes depends, among other parameters, on genetic factors. The genes-encoding polypeptides that determine incidence, severity and prognosis for concussion are the primary candidates for genetic analysis. Genetic polymorphisms in the genes contributing to plasticity and repair (APOE), synaptic connectivity (GRIN2A), calcium influx (CACNA1E), uptake and deposit of glutamate (SLC17A7) are potential biomarkers of concussion incidence and recovery rate. With catalogued genetic variants, prospective genotyping of athletes at the beginning of their career will allow medical professionals to improve concussion management and return-to-play decisions.

FTO Inhibits Insulin Secretion and Promotes NF-κB Activation through Positively Regulating ROS Production in Pancreatic β cells

FTO (Fat mass and obesity-associated) is associated with increased risk of obesity and type 2 diabetes incurrence. Pancreas islet β cells dysfunction and insulin resistance are major causes of type 2 diabetes. However, whether FTO plays an important functional role in pancreatic β cells as well as the related molecular mechanism is still unclear. In the present study, the tissue expression profile of FTO was firstly determined using quantitative PCR and western blot. FTO is widely expressed in various tissues and presented with relative high expression in pancreas tissue, especially in endocrine pancreas. FTO overexpression in MIN6 cells achieved by lentivirus delivery significantly inhibits insulin secretion in the presence of glucose stimulus as well as KCl. FTO silence has no effect on insulin secretion of MIN6 cells. However, FTO overexpression doesn’t affect the transcription of insulin gene. Furthermore, reactive oxygen species (ROS) production and NF-κB activation are significantly promoted by FTO overexpression. Inhibition of intracellular ROS production by N-acetyl-L-cysteine (NAC) can alleviate NF-κB activation and restore the insulin secretion mediated by FTO overexpression. A whole transcript-microarray is employed to analyze the differential gene expression mediated by FTO overexpression. The genes which are modulated by FTO are involved in many important biological pathways such as G-protein coupled receptor signaling and NF-κB signaling. Therefore, our study indicates that FTO may contribute to pancreas islet β cells dysfunction and the inhibition of FTO activity is a potential target for the treatment of diabetes.

Exploring the associations between genetic variants in genes encoding for subunits of calcium channel and subtypes of bipolar disorder

BACKGROUND

Associations of two voltage-gated calcium channel (Cav) genes, CACNA1C and CACNB2, were identified for bipolar disorder (BP) in different ethnic groups in recent genome-wide association studies. The current study aimed to evaluate the associations of several Cav genes and subtypes of BP in genetically more homogeneous Taiwanese samples. Additionally, we tested interaction effects among genes that encode for α1, β and γ-subunits of calcium channel.

METHODS

8 Cav genes were selected based on evidence in prior association studies and significant linkage regions for BP. 280 BP patients and 200 controls were recruited. Multifactor dimensionality reduction was performed for interaction testing in these discovery samples. Replication was conducted for two markers using additional 495 Taiwanese cases and 1341 controls.

RESULTS

Weak associations for CACNA1C (rs10848635), CACNA1E (rs10848635), CACNB2 (rs11013860), and CACNG2 (rs2284018) genes were observed. Joint analysis of four markers revealed higher accumulative risk with increasing numbers of risk genotypes an individual endorsed for BP-I (Ptrend=0.006) and BP-II (Ptrend=0.017) disorders. Combined analysis with independent replication samples further supported the association of rs11013860 in CACNB2 with BP subtype I (P=1×10(-6)). Suggestive interactions were found between genes encoded for different subunits of calcium channel (α1, β, and γ).

LIMITATIONS

Moderate sample size and incomplete markers coverage for the chosen Cav genes.

CONCLUSIONS

Our results support the involvement of different calcium channel genes in bipolar illness, in particular the beta-subunit in the Asian population. Further investigation of functional property of these genes can contribute on understanding the etiological mechanisms of bipolar illness.

Association between genetic polymorphisms in Ca(v)2.3 (R-type) Ca2+ channels and fentanyl sensitivity in patients undergoing painful cosmetic surgery

Individual differences in the sensitivity to fentanyl, a widely used opioid analgesic, lead to different proper doses of fentanyl, which can hamper effective pain treatment. Voltage-activated Ca(2+) channels (VACCs) play a crucial role in the nervous system by controlling membrane excitability and calcium signaling. Ca(v)2.3 (R-type) VACCs have been especially thought to play critical roles in pain pathways and the analgesic effects of opioids. However, unknown is whether single-nucleotide polymorphisms (SNPs) of the human CACNA1E (calcium channel, voltage-dependent, R type, alpha 1E subunit) gene that encodes Cav2.3 VACCs influence the analgesic effects of opioids. Thus, the present study examined associations between fentanyl sensitivity and SNPs in the human CACNA1E gene in 355 Japanese patients who underwent painful orofacial cosmetic surgery, including bone dissection. We first conducted linkage disequilibrium (LD) analyses of 223 SNPs in a region that contains the CACNA1E gene using genomic samples from 100 patients, and a total of 13 LD blocks with 42 Tag SNPs were observed within and around the CACNA1E gene region. In the preliminary study using the same 100 genomic samples, only the rs3845446 A/G SNP was significantly associated with perioperative fentanyl use among these 42 Tag SNPs. In a confirmatory study using the other 255 genomic samples, this SNP was also significantly associated with perioperative fentanyl use. Thus, we further analyzed associations between genotypes of this SNP and all of the clinical data using a total of 355 samples. The rs3845446 A/G SNP was associated with intraoperative fentanyl use, 24 h postoperative fentanyl requirements, and perioperative fentanyl use. Subjects who carried the minor G allele required significantly less fentanyl for pain control compared with subjects who did not carry this allele. Although further validation is needed, the present findings show the possibility of the involvement of CACNA1E gene polymorphisms in fentanyl sensitivity.

How "Pharmacoresistant" is Cav2.3, the Major Component of Voltage-Gated R-type Ca2+ Channels?

Membrane-bound voltage-gated Ca²⁺ channels (VGCCs) are targets for specific signaling complexes, which regulate important processes like gene expression, neurotransmitter release and neuronal excitability. It is becoming increasingly evident that the so called “resistant” (R-type) VGCC Ca_v2.3 is critical in several physiologic and pathophysiologic processes in the central nervous system, vascular system and in endocrine systems. However its eponymous attribute of pharmacologic inertness initially made in depth investigation of the channel difficult. Although the identification of SNX-482 as a fairly specific inhibitor of Ca_v2.3 in the nanomolar range has enabled insights into the channels properties, availability of other pharmacologic modulators of Ca_v2.3 with different chemical, physical and biological properties are of great importance for future investigations. Therefore the literature was screened systematically for molecules that modulate Ca_v2.3 VGCCs.

An exploratory study of the association between KCNB1 rs1051295 and type 2 diabetes and its related traits in Chinese Han population

Since the KCNB1 encoding Kv2.1 channel accounts for the majority of Kv currents modulating insulin secretion by pancreatic islet beta-cells, we postulated that KCNB1 is a plausible candidate gene for genetic variation contributing to the variable compensatory secretory function of beta-cells in type-2 diabetes (T2D). We conducted two studies, a case-control study and a cross-section study, to investigate the association of common single-nucleotide polymorphisms (SNPs) in KCNB1 with T2D and its linking traits. In the case-control study, we first examined the association of 20 tag SNPs of KCNB1 with T2D in a population with 226 T2D patients and non-diabetic subjects (screening study). We then identified the association in an enlarged population of 412 T2D patients and non-diabetic subjects (replication study). In the cross-sectional study, we investigated the linkage between the candidate SNP rs1051295 and T2D by comparing beta-cell function and insulin sensitivity among rs1051295 genotypes in a general population of 1051 subjects at fasting and after glucose loading (oral glucose tolerance tests, OGTT) in 84 fasting glucose impaired subjects, and several T2D-related traits. We found that among the 19 available tag SNPs, only the KCNB1 rs1051295 was associated with T2D (P = 0.027), with the rs1051295 TT genotype associated with an increased risk of T2D compared with genotypes CC (P = 0.009). At fasting, rs1051295 genotype TT was associated with a 9.8% reduction in insulin sensitivity compared to CC (P = 0.008); along with increased plasma triglycerides (TG) levels (TT/CC: P = 0.046) and increased waist/hip (W/H) ratio (TT/CC: P = 0.013; TT/TC: P = 0.002). OGTT confirmed that genotype TT exhibited reduced insulin sensitivity by 16.3% (P = 0.030) compared with genotype TC+CC in a fasting glucose impaired population. The KCNB1 rs1051295 genotype TT in the Chinese Han population is associated with decreased insulin sensitivity and increased plasma TG and W/H ratio, which together contribute to an increased risk for T2D.

Regulation of insulin secretion in human pancreatic islets

Pancreatic β cells secrete insulin, the body's only hormone capable of lowering plasma glucose levels. Impaired or insufficient insulin secretion results in diabetes mellitus. The β cell is electrically excitable; in response to an elevation of glucose, it depolarizes and starts generating action potentials. The electrophysiology of mouse β cells and the cell's role in insulin secretion have been extensively investigated. More recently, similar studies have been performed on human β cells. These studies have revealed numerous and important differences between human and rodent β cells. Here we discuss the properties of human pancreatic β cells: their glucose sensing, the ion channel complement underlying glucose-induced electrical activity that culminates in exocytotic release of insulin, the cellular control of exocytosis, and the modulation of insulin secretion by circulating hormones and locally released neurotransmitters. Finally, we consider the pathophysiology of insulin secretion and the interactions between genetics and environmental factors that may explain the current diabetes epidemic.

CACNA1E variants affect beta cell function in patients with newly diagnosed type 2 diabetes. the Verona newly diagnosed type 2 diabetes study (VNDS) 3

Background

Genetic variability of the major subunit (CACNA1E) of the voltage-dependent Ca²⁺ channel Ca_V2.3 is associated to risk of type 2 diabetes, insulin resistance and impaired insulin secretion in nondiabetic subjects. The aim of the study was to test whether CACNA1E common variability affects beta cell function and/or insulin sensitivity in patients with newly diagnosed type 2 diabetes.

Methodology/Principal Findings

In 595 GAD-negative, drug naïve patients (mean±SD; age: 58.5±10.2 yrs; BMI: 29.9±5 kg/m², HbA1c: 7.0±1.3) with newly diagnosed type 2 diabetes we: 1. genotyped 10 tag SNPs in CACNA1E region reportedly covering ∼93% of CACNA1E common variability: rs558994, rs679931, rs2184945, rs10797728, rs3905011, rs12071300, rs175338, rs3753737, rs2253388 and rs4652679; 2. assessed clinical phenotypes, insulin sensitivity by the euglycemic insulin clamp and beta cell function by state-of-art modelling of glucose/C-peptide curves during OGTT. Five CACNA1E tag SNPs (rs10797728, rs175338, rs2184945, rs3905011 and rs4652679) were associated with specific aspects of beta cell function (p<0.05−0.01). Both major alleles of rs2184945 and rs3905011 were each (p<0.01 and p<0.005, respectively) associated to reduced proportional control with a demonstrable additive effect (p<0.005). In contrast, only the major allele of rs2253388 was related weakly to more severe insulin resistance (p<0.05).

Conclusions/Significance

In patients with newly diagnosed type 2 diabetes CACNA1E common variability is strongly associated to beta cell function. Genotyping CACNA1E might be of help to infer the beta cell functional phenotype and to select a personalized treatment.

Channeling dysglycemia: ion-channel variations perturbing glucose homeostasis

Maintaining blood glucose homeostasis is a complex process that depends on pancreatic islet hormone secretion. Hormone secretion from islets is coupled to calcium entry which results from regenerative islet cell electrical activity. Therefore, the ionic mechanisms that regulate calcium entry into islet cells are crucial for maintaining normal glucose homeostasis. Genome-wide association studies (GWAS) have identified single-nucleotide polymorphisms (SNPs), including five located in or near ion-channel or associated subunit genes, which show an association with human diseases characterized by dysglycemia. This review focuses on polymorphisms and mutations in ion-channel genes that are associated with perturbations in human glucose homeostasis and discusses their potential roles in modulating pancreatic islet hormone secretion.

Polymorphisms in CACNA1E and Camk2d are associated with seizure susceptibility of Sprague-Dawley rats

Seizures are associated with high intracellular calcium levels. However, conditions characterized by high intracellular calcium levels, such as stroke or traumatic brain injury, do not always evoke epilepsy. We hypothesized that polymorphisms in calcium-related genes CACNA1E and Camk2d contribute to the individual variability in seizure susceptibility. The distribution of one single nucleotide polymorphism (SNP) in the CACNA1E and one in the Camk2d gene was determined in Sprague-Dawley rats that were subjected to amygdala kindling or hyperthermia-induced seizures. The pre-kindling afterdischarge threshold was significantly lower in rats with the CACNA1E GG genotype (45.2+/-6.7microA) than in the GT genotyped animals (79.3+/-53.7microA). Among hyperthermia treated rats, the Camk2d G allele was more frequent among rats that did not display behavioral seizures during hyperthermia (67%) than in animals that did show behavioral seizures during hyperthermia (52%, chi(2)(1)=3.847, p=0.05). SNPs in CACNA1E and Camk2d genes are associated with the individual variability in seizure susceptibility in two experimental seizure models.

Calcium signaling in the islets

Easy access to rodent islets and insulinoma cells and the ease of measuring Ca(2+) by fluorescent indicators have resulted in an overflow of data that have clarified minute details of Ca(2+) signaling in the rodent islets. Our understanding of the mechanisms and the roles of Ca(2+) signaling in the human islets, under physiological conditions, has been hugely influenced by uncritical extrapolation of the rodent data obtained under suboptimal experimental conditions. More recently, electrophysiological and Ca(2+) studies have elucidated the ion channel repertoire relevant for Ca(2+) signaling in the human islets and have examined their relative importance. Many new channels belonging to the transient receptor potential (TRP) family are present in the beta-cells. Ryanodine receptors, nicotinic acid adenine dinucleotide phosphate channel, and Ca(2+)-induced Ca(2+) release add new dimension to the complexity of Ca(2+) signaling in the human beta-cells. A lot more needs to be learnt about the roles of these new channels and CICR, not because that will be easy but because that will be difficult. Much de-learning will also be needed. Human beta-cells do not have a resting state in the normal human body even under physiological fasting conditions. Their membrane potential under physiologically relevant resting conditions is approximately -50 mV. Biphasic insulin secretion is an experimental epiphenomenon unrelated to the physiological pulsatile insulin secretion into the portal vein in the human body. Human islets show a wide variety of electrical activities and patterns of [Ca(2+)](i) changes, whose roles in mediating pulsatile secretion of insulin into the portal vein remain questionable. Future studies will hopefully be directed toward a better understanding of Ca(2+) signaling in the human islets in the context of the pathogenesis and treatment of human diabetes.

Hyperinsulinism and diabetes: genetic dissection of beta cell metabolism-excitation coupling in mice

The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.

Comparative identification of Ca2+ channel expression in INS-1 and rat pancreatic beta cells

AIM

To identify and compare the profile of Ca(2+) channel subunit expression in INS-1 and rat pancreatic beta cells.

METHODS

The rat insulin-secreting INS-1 cell line was cultured in RPMI-1640 with Wistar rats employed as islet donors. Ca(2+) channel subunit expression in INS-1 and isolated rat beta cells were examined by reverse transcription polymerase chain reaction (RT-PCR). Absolute real-time quantitative PCR was performed in a Bio-Rad iQ5 Gradient Real Time PCR system and the data analyzed using an iQ5 system to identify the expression level of the Ca(2+) channel subunits.

RESULTS

In INS-1 cells, the L-type Ca(2+) channel 1C subunit had the highest expression level and the TPRM2 subunit had the second highest expression. In rat beta cells, the TPRC4beta subunit expression was dominant and the expression of the L-type 1C subunit exceeded the 1D subunit expression about two-fold. This result agreed with other studies, confirming the important role of the L-type 1C subunit in insulin-secreting cells, and suggested that non-voltage-operated Ca(2+) channels may have an important role in biphasic insulin secretion.

CONCLUSION

Twelve major Ca(2+) channel subunit types were identified in INS-1 and rat beta cells and significant differences were observed in the expression of certain subunits between these cells.

The type 2 diabetes associated minor allele of rs2237895 KCNQ1 associates with reduced insulin release following an oral glucose load

Background

Polymorphisms in the potassium channel, voltage-gated, KQT-like subfamily, member 1 (KCNQ1) have recently been reported to associate with type 2 diabetes. The primary aim of the present study was to investigate the putative impact of these KCNQ1 polymorphisms (rs2283228, rs2237892, rs2237895, and rs2237897) on estimates of glucose stimulated insulin release.

Methodology/Principal Findings

Genotypes were examined for associations with serum insulin levels following an oral glucose tolerance test (OGTT) in a population-based sample of 6,039 middle-aged and treatment-naïve individuals. Insulin release indices estimated from the OGTT and the interplay between insulin sensitivity and insulin release were investigated using linear regression and Hotelling T2 analyses.

Applying an additive genetic model the minor C-allele of rs2237895 was associated with reduced serum insulin levels 30 min (mean±SD: (CC) 277±160 vs. (AC) 280±164 vs. (AA) 299±200 pmol/l, p = 0.008) after an oral glucose load, insulinogenic index (29.6±17.4 vs. 30.2±18.7vs. 32.2±22.1, p = 0.007), incremental area under the insulin curve (20,477±12,491 vs. 20,503±12,386 vs. 21,810±14,685, p = 0.02) among the 4,568 individuals who were glucose tolerant. Adjustment for the degree of insulin sensitivity had no effect on the measures of reduced insulin release. The rs2237895 genotype had a similar impact in the total sample of treatment-naïve individuals. No association with measures of insulin release were identified for the less common diabetes risk alleles of rs2237892, rs2237897, or rs2283228.

Conclusion

The minor C-allele of rs2237895 of KCNQ1, which has a prevalence of about 42% among Caucasians was associated with reduced measures of insulin release following an oral glucose load suggesting that the increased risk of type 2 diabetes, previously reported for this variant, likely is mediated through an impaired beta cell function.

A genome scan for positive selection in thoroughbred horses

Thoroughbred horses have been selected for exceptional racing performance resulting in system-wide structural and functional adaptations contributing to elite athletic phenotypes. Because selection has been recent and intense in a closed population that stems from a small number of founder animals Thoroughbreds represent a unique population within which to identify genomic contributions to exercise-related traits. Employing a population genetics-based hitchhiking mapping approach we performed a genome scan using 394 autosomal and X chromosome microsatellite loci and identified positively selected loci in the extreme tail-ends of the empirical distributions for (1) deviations from expected heterozygosity (Ewens-Watterson test) in Thoroughbred (n = 112) and (2) global differentiation among four geographically diverse horse populations (F(ST)). We found positively selected genomic regions in Thoroughbred enriched for phosphoinositide-mediated signalling (3.2-fold enrichment; P<0.01), insulin receptor signalling (5.0-fold enrichment; P<0.01) and lipid transport (2.2-fold enrichment; P<0.05) genes. We found a significant overrepresentation of sarcoglycan complex (11.1-fold enrichment; P<0.05) and focal adhesion pathway (1.9-fold enrichment; P<0.01) genes highlighting the role for muscle strength and integrity in the Thoroughbred athletic phenotype. We report for the first time candidate athletic-performance genes within regions targeted by selection in Thoroughbred horses that are principally responsible for fatty acid oxidation, increased insulin sensitivity and muscle strength: ACSS1 (acyl-CoA synthetase short-chain family member 1), ACTA1 (actin, alpha 1, skeletal muscle), ACTN2 (actinin, alpha 2), ADHFE1 (alcohol dehydrogenase, iron containing, 1), MTFR1 (mitochondrial fission regulator 1), PDK4 (pyruvate dehydrogenase kinase, isozyme 4) and TNC (tenascin C). Understanding the genetic basis for exercise adaptation will be crucial for the identification of genes within the complex molecular networks underlying obesity and its consequential pathologies, such as type 2 diabetes. Therefore, we propose Thoroughbred as a novel in vivo large animal model for understanding molecular protection against metabolic disease.