Calpains play a role in insulin secretion and action

Calpain and Cardiometabolic Diseases

Calpain is defined as a member of the superfamily of cysteine proteases possessing the CysPC motif within the gene. Calpain-1 and -2, which are categorized as conventional isozymes, execute limited proteolysis in a calcium-dependent fashion. Accordingly, the calpain system participates in physiological and pathological phenomena, including cell migration, apoptosis, and synaptic plasticity. Recent investigations have unveiled the contributions of both conventional and unconventional calpains to the pathogenesis of cardiometabolic disorders. In the context of atherosclerosis, overactivation of conventional calpain attenuates the barrier function of vascular endothelial cells and decreases the immunosuppressive effects attributed to lymphatic endothelial cells. In addition, calpain-6 induces aberrant mRNA splicing in macrophages, conferring atheroprone properties. In terms of diabetes, polymorphisms of the calpain-10 gene can modify insulin secretion and glucose disposal. Moreover, conventional calpain reportedly participates in amino acid production from vascular endothelial cells to induce alteration of amino acid composition in the liver microenvironment, thereby facilitating steatohepatitis. Such multifaceted functionality of calpain underscores its potential as a promising candidate for pharmaceutical targets for the treatment of cardiometabolic diseases. Consequently, the present review highlights the pivotal role of calpains in the complications of cardiometabolic diseases and embarks upon a characterization of calpains as molecular targets.

Association of Calpain10 polymorphisms with polycystic ovarian syndrome susceptibility: a systematic review and meta-analysis with trial sequential analysis

Insulin resistance plays an important role in the pathogenesis of polycystic ovarian syndrome (PCOS). Calpain10 (CAPN10) gene was the first identified susceptibility gene for type 2 diabetes mellitus and closely related to insulin sensitivity. A lot of research attention has been attracted on the relationship between CAPN10 polymorphisms and PCOS risk, but they didn't reach a consistent conclusion. We therefore performed this systematic review and meta-analysis to assess the association of CAPN10 common variants with PCOS susceptibility. A total of 21 studies were eligible for inclusion. Meta-analyses were done for 5 variants that had at least two data sources: UCSNP-19, -43, -44, -56 and -63. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated under five genetic models. Subgroup analyses by ethnicity, PCOS diagnostic criteria, and source of controls were conducted. Moreover, false-positive report probability (FPRP) test and trial sequential analysis (TSA) were performed to assess the significant associations. The results showed a possible negative association between UCSNP-19 and PCOS risk (ins/ins vs. del/del + del/ins: OR = 0.84, 95% CI: 0.72-0.98). In subgroup analyses, FPRP test indicated that noteworthy associations were observed in mixed ethnicities for UCSNP-43 (A vs. G: OR = 1.81, 95% CI: 1.17-2.79; AA + AG vs. GG: OR = 2.14, 95% CI: 1.20-3.80) and in Asians for UCSNP-44 (CC vs. TT: OR = 2.07, 95% CI: 1.21-3.51; CC vs. CT + TT: OR = 2.19, 95% CI: 1.31-3.69), but TSA plots showed that the accumulated sample sizes of these associations were insufficient to draw firm conclusions. In summary, our study suggested that UCSNP-19, UCSNP-43, and UCSNP-44 in CAPN10 gene may be involved in PCOS susceptibility. These findings warrant further studies.

RELA governs a network of islet-specific metabolic genes necessary for beta cell function

AIMS/HYPOTHESIS

NF-κB activation unites metabolic and inflammatory responses in many diseases yet less is known about the role that NF-κB plays in normal metabolism. In this study we investigated how RELA impacts the beta cell transcriptional landscape and provides network control over glucoregulation.

METHODS

We generated novel mouse lines harbouring beta cell-specific deletion of either the Rela gene, encoding the canonical NF-κB transcription factor p65 (βp65KO mice), or the Ikbkg gene, encoding the NF-κB essential modulator NEMO (βNEMOKO mice), as well as βA20Tg mice that carry beta cell-specific and forced transgenic expression of the NF-κB-negative regulator gene Tnfaip3, which encodes the A20 protein. Mouse studies were complemented by bioinformatics analysis of human islet chromatin accessibility (assay for transposase-accessible chromatin with sequencing [ATAC-seq]), promoter capture Hi-C (pcHi-C) and p65 binding (chromatin immunoprecipitation-sequencing [ChIP-seq]) data to investigate genome-wide control of the human beta cell metabolic programme.

RESULTS

Rela deficiency resulted in complete loss of stimulus-dependent inflammatory gene upregulation, consistent with its known role in governing inflammation. However, Rela deletion also rendered mice glucose intolerant because of functional loss of insulin secretion. Glucose intolerance was intrinsic to beta cells as βp65KO islets failed to secrete insulin ex vivo in response to a glucose challenge and were unable to restore metabolic control when transplanted into secondary chemical-induced hyperglycaemic recipients. Maintenance of glucose tolerance required Rela but was independent of classical NF-κB inflammatory cascades, as blocking NF-κB signalling in vivo by beta cell knockout of Ikbkg (NEMO), or beta cell overexpression of Tnfaip3 (A20), did not cause severe glucose intolerance. Thus, basal p65 activity has an essential and islet-intrinsic role in maintaining normal glucose homeostasis. Genome-wide bioinformatic mapping revealed the presence of p65 binding sites in the promoter regions of specific metabolic genes and in the majority of islet enhancer hubs (~70% of ~1300 hubs), which are responsible for shaping beta cell type-specific gene expression programmes. Indeed, the islet-specific metabolic genes Slc2a2, Capn9 and Pfkm identified within the large network of islet enhancer hub genes showed dysregulated expression in βp65KO islets.

CONCLUSIONS/INTERPRETATION

These data demonstrate an unappreciated role for RELA as a regulator of islet-specific transcriptional programmes necessary for the maintenance of healthy glucose metabolism. These findings have clinical implications for the use of anti-inflammatories, which influence NF-κB activation and are associated with diabetes.

Multiomics Analysis-Based Biomarkers in Diagnosis of Polycystic Ovary Syndrome

Polycystic ovarian syndrome is an utmost communal endocrine, psychological, reproductive, and metabolic disorder that occurs in women of reproductive age with extensive range of clinical manifestations. This may even lead to long-term multiple morbidities including obesity, diabetes mellitus, insulin resistance, cardiovascular disease, infertility, cerebrovascular diseases, and ovarian and endometrial cancer. Women affliction from PCOS in midst assemblage of manifestations allied with menstrual dysfunction and androgen exorbitance, which considerably affects eminence of life. PCOS is recognized as a multifactorial disorder and systemic syndrome in first-degree family members; therefore, the etiology of PCOS syndrome has not been copiously interpreted. The disorder of PCOS comprehends numerous allied health conditions and has influenced various metabolic processes. Due to multifaceted pathophysiology engaging several pathways and proteins, single genetic diagnostic tests cannot be supportive to determine in straight way. Clarification of cellular and biochemical pathways and various genetic players underlying PCOS could upsurge our consideration of pathophysiology of this syndrome. It is requisite to know pathophysiological relationship between biomarker and their reflection towards PCOS disease. Biomarkers deliver vibrantly and potent ways to apprehend the spectrum of PCOS with applications in screening, diagnosis, characterization, and monitoring. This paper relies on the endeavor to point out many candidates as potential biomarkers based on omics technologies, thus highlighting correlation between PCOS disease with innovative technologies. Therefore, the objective of existing review is to encapsulate more findings towards cutting-edge advances in prospective use of biomarkers for PCOS disease. Discussed biomarkers may be fruitful in guiding therapies, addressing disease risk, and predicting clinical outcomes in future.

A brief insight into the etiology, genetics, and immunology of polycystic ovarian syndrome (PCOS)

Polycystic ovarian syndrome (PCOS) is a prevailing endocrine and metabolic disorder occurring in about 6-20% of females in reproductive age. Most symptoms of PCOS arise early during puberty. Since PCOS involves a combination of signs and symptoms, thus it is considered as a heterogeneous disorderliness. The most accepted diagnostic criteria is Rotterdam criteria which involves two of the latter three features: (a) hyperandrogenism, (b) oligo- or an-ovulation, and (c) polycystic ovaries. The persistent hormonal imbalance leads to multiple small antral follicles formation and irregular menstrual cycle, ultimately causing infertility among females. Insulin resistance, cardiovascular diseases, abdominal obesity, psychological disorders, infertility, and cancer are also related to PCOS. These pathophysiologies associated with PCOS are interrelated with each other. Hyperandrogenism causes insulin resistance and hyperglycemia, leading to ROS formation, oxidative stress, and abdominal adiposity. In consequence, inflammation, ROS production, insulin resistance, and hyperandrogenemia also increase. Elevation of AGEs in the body either produced endogenously or consumed from diet exaggerates PCOS symptoms and is also related to ovarian dysfunction. This review summarizes how AGE formation, inflammation, and oxidative stress are significantly essential in PCOS progression. Alterations during prenatal development like exposure to excess AMH, androgens, or toxins (bisphenol-A, endocrine disruptors, etc.) may also be the etiologic mechanism behind PCOS. Although the etiology of this disorder is unclear, environmental and genetic factors are primarily involved. Physical inactivity, as well as unhealthy eating habits, has a vital role in the progression of PCOS. This review outlines a collection of specific genes phenotypically linked with PCOS. Furthermore, beneficial effect of metformin in maintaining endocrine abnormalities and ovarian function is also mentioned. Kisspeptin is a protein which helps in onset of puberty and increases GnRH pulsatile release during ovulation as well as role of KNDy neurons in GnRH pulsatile signal required for reproduction are also elaborated. This review also focuses on the immunology related to PCOS involving chronic low-grade inflammation, and how the alterations within the follicular microenvironment are intricated in the development of infertility in PCOS patients. How PCOS develops following antiepileptic and psychiatric medication is also expanded in this review. Initiation of antiandrogen treatment in early age (≤ 25 years) might be helpful in spontaneous conception in PCOS women. The role of BMP (bone morphogenetic proteins) in folliculogenesis and their expression in oocytes and granulosa cells are also explained. GDF8 and SERPINE1 expression in PCOS is given in detail.

Pathophysiologic Mechanisms of Insulin Secretion and Signaling-Related Genes in Etiology of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrinopathy in women. PCOS is characterized by anovulation, hyperandrogenism, polycystic ovaries, insulin resistance, and obesity. Despite the finding that the genetic origin of PCOS is well demonstrated in previous twin and familial clustering studies, genes and factors that can exactly explain the PCOS pathophysiology are not known. Objective(s). In this review, we attempted to identify genes related to secretion and signaling of insulin aspects of PCOS and their physiological functions in order to explain the pathways that are regulated by these genes which can be a prominent function in PCOS predisposition. Materials and Methods. For this purpose, published articles and reviews dealing with genetic evaluation of PCOS in women from peer-reviewed journals in PubMed and Google Scholar databases were included in this review. Results. The genomic investigations in women of different populations identified many candidate genes and loci that are associated with PCOS. The most important of them are INSR, IRS1-2, MTNR1A, MTNR1B, THADA, PPAR-γ2, ADIPOQ, and CAPN10. These are mainly associated with metabolic aspects of PCOS. Conclusions. In this review, we proposed that each of these genes may interrupt specific physiological pathways by affecting them and contribute to PCOS initiation. It is clear that the role of genes involved in insulin secretion and signaling is more critical than other pathways.

A genetic screen for Drosophila social isolation mutants and analysis of sex pistol

Prolonged periods of forced social isolation is detrimental to well-being, yet we know little about which genes regulate susceptibility to its effects. In the fruit fly, Drosophila melanogaster, social isolation induces stark changes in behavior including increased aggression, locomotor activity, and resistance to ethanol sedation. To identify genes regulating sensitivity to isolation, I screened a collection of sixteen hundred P-element insertion lines for mutants with abnormal levels of all three isolation-induced behaviors. The screen identified three mutants whose affected genes are likely central to regulating the effects of isolation in flies. One mutant, sex pistol (sxp), became extremely aggressive and resistant to ethanol sedation when socially isolated. sxp also had a high level of male–male courtship. The mutation in sxp reduced the expression of two minor isoforms of the actin regulator hts (adducin), as well as mildly reducing expression of CalpA, a calcium-dependent protease. As a consequence, sxp also had increased expression of the insulin-like peptide, dILP5. Analysis of the social behavior of sxp suggests that these minor hts isoforms function to limit isolation-induced aggression, while chronically high levels of dILP5 increase male–male courtship.

Arsenic impairs GLUT1 trafficking through the inhibition of the calpain system in lymphocytes

Exposure to arsenic is associated with increased risk of developing insulin resistance and type 2 diabetes. The proteases calpain-1 (CAPN1), calpain-2 (CAPN2) and calpain-10 (CAPN10) and their endogenous inhibitor calpastatin (CAST) regulate glucose uptake in skeletal muscle and adipocytes. We investigated whether arsenic disrupts GLUT1 trafficking and function through calpain inhibition, using lymphocytes as a cell model. Lymphocytes from healthy subjects were treated with 0.1 or 1 μM of sodium arsenite for 72 h and challenged with 3.9 or 11.1 mM of glucose. Our results showed that arsenite inhibited GLUT1 trafficking, glucose uptake, and calpain activity in the presence of 11.1 mM of glucose. These correlated with a decrease in the autolytical fragment of 50 kDa of CAPN1 and increased levels of CAST, but there were no changes in CAPN2 and CAPN10. We used a cell-free system to evaluate the effect of arsenite over CAPN1, finding that arsenite induced CAPN1 autolysis. To confirm that calpains are involved in GLUT1 trafficking and glucose uptake in lymphocytes, we generated stable CAPN1 or CAPN10 knockdowns in Jurkat cells using short hairpin RNA (shRNA). CAPN1 knockdown induced glucose uptake, while CAPN10 knockdown diminished glucose uptake, which correlated with a significant reduction of calpain activity after the pulse with 11.1 mM of glucose. These data showed that CAPN10 was responsible for the induction of calpain activity after the challenge with 11.1 mM of glucose and that CAPN1 and CAPN10 regulate glucose uptake in lymphocytes. Altogether, our results suggest that arsenite impairs GLUT1 trafficking and function through calpain dysregulation.

Calpain-10 regulates actin dynamics by proteolysis of microtubule-associated protein 1B

Calpain-10 (CAPN10) is the calpain family protease identified as the first candidate susceptibility gene for type 2 diabetes mellitus (T2DM). However, the detailed molecular mechanism has not yet been elucidated. Here we report that CAPN10 processes microtubule associated protein 1 (MAP1) family proteins into heavy and light chains and regulates their binding activities to microtubules and actin filaments. Immunofluorescent analysis of Capn10^−/− mouse embryonic fibroblasts shows that MAP1B, a member of the MAP1 family of proteins, is localized at actin filaments rather than at microtubules. Furthermore, fluorescence recovery after photo-bleaching analysis shows that calpain-10 regulates actin dynamics via MAP1B cleavage. Moreover, in pancreatic islets from CAPN10 knockout mice, insulin secretion was significantly increased both at the high and low glucose levels. These findings indicate that deficiency of calpain-10 expression may affect insulin secretion by abnormal actin reorganization, coordination and dynamics through MAP1 family processing.

Dysregulation of Calpain Proteolytic Systems Underlies Degenerative Vascular Disorders

Chronic vascular diseases such as atherosclerosis, aneurysms, diabetic angiopathy/retinopathy as well as fibrotic and proliferative vascular diseases are generally complicated by the progression of degenerative insults, which are characterized by endothelial dysfunction, apoptotic/necrotic cell death in vascular/immune cells, remodeling of extracellular matrix or breakdown of elastic lamella. Increasing evidence suggests that dysfunctional calpain proteolytic systems and defective calpain protein metabolism in blood vessels contribute to degenerative disorders. In vascular endothelial cells, the overactivation of conventional calpains consisting of calpain-1 and -2 isozymes can lead to the disorganization of cell-cell junctions, dysfunction of nitric oxide synthase, sensitization of Janus kinase/signal transducer and activator of transcription cascades and depletion of prostaglandin I₂, which contributes to degenerative disorders. In addition to endothelial cell dysfunctions, calpain overactivation results in inflammatory insults in macrophages and excessive fibrogenic/proliferative signaling in vascular smooth muscle cells. Moreover, calpain-6, a non-proteolytic unconventional calpain, is involved in the conversion of macrophages to a pro-atherogenic phenotype, leading to the pinocytotic deposition of low-density lipoprotein cholesterol in the cells. Here, we discuss the recent progress that has been made in our understanding of how calpain contributes to degenerative vascular disorders.

Emerging roles of calpain proteolytic systems in macrophage cholesterol handling

Calpains are Ca2+-dependent intracellular proteases that play central roles in the post-translational processing of functional proteins. In mammals, calpain proteolytic systems comprise the endogenous inhibitor calpastatin as well as 15 homologues of the catalytic subunits and two homologues of the regulatory subunits. Recent pharmacological and gene targeting studies in experimental animal models have revealed the contribution of conventional calpains, which consist of the calpain-1 and -2 isozymes, to atherosclerotic diseases. During atherogenesis, conventional calpains facilitate the CD36-dependent uptake of oxidized low-density lipoprotein (LDL), and block cholesterol efflux through ATP-binding cassette transporters in lesional macrophages, allowing the expansion of lipid-enriched atherosclerotic plaques. In addition, calpain-6, an unconventional non-proteolytic calpain, in macrophages reportedly potentiates pinocytotic uptake of native LDL, and attenuates the efferocytic clearance of apoptotic and necrotic cell corpses from the lesions. Herein, we discuss the recent progress that has been made in our understanding of how calpain contributes to atherosclerosis, in particular focusing on macrophage cholesterol handling.

Npas4 Transcription Factor Expression Is Regulated by Calcium Signaling Pathways and Prevents Tacrolimus-induced Cytotoxicity in Pancreatic Beta Cells

Cytosolic calcium influx activates signaling pathways known to support pancreatic beta cell function and survival by modulating gene expression. Impaired calcium signaling leads to decreased beta cell mass and diabetes. To appreciate the causes of these cytotoxic perturbations, a more detailed understanding of the relevant signaling pathways and their respective gene targets is required. In this study, we examined the calcium-induced expression of the cytoprotective beta cell transcription factor Npas4. Pharmacological inhibition implicated the calcineurin, Akt/protein kinase B, and Ca(2+)/calmodulin-dependent protein kinase signaling pathways in the regulation of Npas4 transcription and translation. Both Npas4 mRNA and protein had high turnover rates, and, at the protein level, degradation was mediated via the ubiquitin-proteasome pathway. Finally, beta cell cytotoxicity of the calcineurin inhibitor and immunosuppressant tacrolimus (FK-506) was prevented by Npas4 overexpression. These results delineate the pathways regulating Npas4 expression and stability and demonstrate its importance in clinical settings such as islet transplantation.

Cysteine proteases as therapeutic targets: does selectivity matter? A systematic review of calpain and cathepsin inhibitors

Cysteine proteases continue to provide validated targets for treatment of human diseases. In neurodegenerative disorders, multiple cysteine proteases provide targets for enzyme inhibitors, notably caspases, calpains, and cathepsins. The reactive, active-site cysteine provides specificity for many inhibitor designs over other families of proteases, such as aspartate and serine; however, a) inhibitor strategies often use covalent enzyme modification, and b) obtaining selectivity within families of cysteine proteases and their isozymes is problematic. This review provides a general update on strategies for cysteine protease inhibitor design and a focus on cathepsin B and calpain 1 as drug targets for neurodegenerative disorders; the latter focus providing an interesting query for the contemporary assumptions that irreversible, covalent protein modification and low selectivity are anathema to therapeutic safety and efficacy.

Common polymorphisms of calpain-10 and the risk of polycystic ovary syndrome in Tunisian population: a case-control study

Recent studies have suggested that calpain-10 (CAPN10) gene polymorphisms play a role in the susceptibility to polycystic ovary syndrome (PCOS). The aim of the present study was to evaluate the possible association between three single nucleotide polymorphisms (SNPs) in CAPN10 gene: UCSNP-43 (rs3792267), UCSNP-19 (rs3842570), and UCSNP-63 (rs5030952) and PCOS in Tunisian cases and control women. Study subjects included 127 women with PCOS (mean age 29.8 ± 4.7 year) and 150 healthy women (mean age 33.5 ± 5.6 year). CAPN10 genotyping was carried-out by direct PCR and PCR-RFLP. Linkage disequilibrium pattern in the genomic region explored was determined by HAPLOVIEW 4.2 while reconstruction of haplotypes was done using PHASE 2.1. The phylogenetic distribution of haplotypes in the population was determined by ARLEQUIN 2.000. Six haplotypes were observed. None of SNPs associated with PCOS or its components while the haplotype H4 associated with the phenotype PCOS-obese (P < 0.025). Moreover the pair of haplotypes H1/H4 strongly associated with high blood-pressure (OR = 14.4, P < 0.012). This work confirms the association of CAPN10 gene with metabolic components in PCOS and highlights the role of haplotypes as strong and efficient genetic markers.

The calpain system and diabetes

Diabetes mellitus is recognized as a clinical syndrome that is characterized by hyperglycemia due to deficiency of insulin. The global prevalence of diabetes has been estimated to increase from 4% (1995) to 5.4% by the year 2025. Insulin dependent diabetes mellitus (IDDM/Type-1) in human, generating hyperglycemia due to insulin deficiency as a consequence of destructing beta cells in the pancreatic islets. Non-insulin dependent diabetes mellitus (NIDDM/Type-II), is a multifactorial, exact biochemical and genetic defect which has not yet been elucidated completely. Calpains seem to play a role in NIDDM and IDDM. Positional cloning experiments revealed that there is a NIDDM susceptibility to calpain 10 (CAPN10). Increased calpain activity and leukocyte trafficking were noticed in the microcirculation in ZDF (Zuker diabetic fatty) rats. Exercise and low body weight play a significant role in reducing calpains expression or elevating the calpains degradation in the skeletal muscle of NIDDM rats. Numerous investigations have been reported that non-coding polymorphisms in CAPN10 proteins might be involved in the NIDDM. Calpain and its mRNA presence had been reported in tissues from many mammalian species. CAPN10 and other calpains seem to be linked to glucose metabolism, insulin secretion and action pathways. This review will give an overview of the role of calpain in NIDDM and IDDM.

Role of calpain-10 in the development of diabetes mellitus and its complications

Calpain activity has been implicated in several cellular processes such as cell signaling, apoptosis, exocytosis, mitochondrial metabolism and cytoskeletal remodeling. Evidence has indicated that the impairment of calpain expression and the activity of different calpain family members are involved in diverse pathologies. Calpain-10 has been implicated in the development of type 2 diabetes, and polymorphisms in the CAPN10 gene have been associated with an increased risk of developing this disease. The present work focused on the molecular biology of calpain-10, supporting its key participation in glucose metabolism. Current knowledge regarding the role of calpain-10 in the development of type 2 diabetes mellitus and diabetes-related diseases is additionally reviewed.

Thioamide-based fluorescent protease sensors

Thioamide quenchers can be paired with compact fluorophores to design “turn-on” fluorescent protease substrates. We have used this method to study a variety of serine-, cysteine-, carboxyl-, and metallo-proteases, including trypsin, chymotrypsin, pepsin, thermolysin, papain, and calpain. Since thioamides quench some fluorophores red-shifted from those naturally occurring in proteins, this technique can be used for real time monitoring of protease activity in crude preparations of virtually any protease. We demonstrate the value of this method in three model applications: (1) characterization of papain enzyme kinetics using rapid-mixing experiments, (2) selective monitoring of cleavage at a single site in a peptide with multiple proteolytic sites, and (3) analysis of the specificity of an inhibitor of calpain in cell lysates.

μ-Calpain as a Novel Target for Impairment of Nitric Oxide-Mediated Vascular Relaxation in Diabetes: A Mini Review

Diabetes is one of the most prevalent metabolic disorders. In diabetes, incidence of coronary artery diseases and peripheral vascular diseases is increased 2- to 4-fold and 10-fold, respectively, compared to healthy individuals. In spite of extensive studies, the underlying mechanisms of endothelial dysfunction (ED), an early event in the development of vascular diseases, remain incompletely understood in diabetes. This mini-review discusses the role and signaling pathways of calpains - a family of Ca²⁺-sensitive intracellular proteases in nitric oxide (NO)-mediated ED in diabetes. We conclude that activation of calpains, especially μ-calpain, plays an important role in the pathogenesis of NO-mediated ED and inflammatory responses in diabetes which is mainly via endothelial Nitric Oxide Synthase (eNOS) inactivation/degradation in macro- and micro-vasculature. We review existing literature demonstrating that hyperhomocysteinemia, elevated plasma homocysteine level, potentiates hyperglycemia-induced ED via μ-calpain/PKCβ₂ activation-induced eNOS-pThr497/495 and eNOS inactivation. μ-calpain may be a critical therapeutic target for NO-mediated ED in diabetes.

Phytochemicals targeting genes relevant for type 2 diabetes

Nutrigenomic approaches based on ethnopharmacology and phytotherapy concepts have revealed that type 2 diabetes mellitus (T2DM) may be susceptible to dietary intervention. Interaction between bioactive food components and the genome may influence cell processes and modulate the onset and progression of the disease. T2DM, characterized by insulin resistance and beta cell dysfunction, is one of the leading causes of death and disability. Despite the great advances that have been made in the understanding and management of this complex, multifactorial disease, T2DM has become a worldwide epidemic in the 21st century. Population and family studies have revealed a strong genetic component of T2DM, and a number of candidate genes have been identified in humans. Variations in the gene sequences such as single nucleotide polymorphisms, explain the individual differences in traits like disease susceptibility and response to treatment. A clear understanding of how nutrients affect the expression of genes should facilitate the development of individualized intervention and, eventually, treatment strategies for T2DM. Review of the literature identified many phytochemicals/extracts from traditional medicinal plants that can target diabetogenic genes. This review focuses on the genetic aspects of T2DM, nutrient modification of genes relevant for diabetes, and future prospects of nutritional therapy of T2DM.

Calpain-10 gene polymorphisms in type 2 diabetes and its micro- and macrovascular complications

Genetic variations in the calpain 10 gene (CAPN10) were previously implicated with increased risk of type 2 diabetes (T2DM). We studied the association of single nucleotide polymorphisms in the CAPN10 gene, SNP -43, SNP -19 and SNP -63, with T2DM and its complications. Overall, we examined 1440 individuals: 880 patients with diabetes and 560 healthy subjects, all Caucasians of Polish origin. All subjects were genotyped for the CAPN10 SNPs by polymerase chain reaction (PCR). The frequencies of alleles, genotypes and haplotypes at three studied loci were similar between the groups. However, the -43 SNP was significantly more frequent in T2DM patients with coexisting cardiovascular disease (CVD) than in patients without CVD (p=0.001). The -43 SNP was still significantly associated with the risk of CVD after adjusting for potential risk factors including male gender, age, BMI, dyslipidemia and hypertension. The odds ratio for G allele for CVD+ versus CVD- patients was 1.89, 95% CI 1.52-2.35. None of the studied SNPs was significantly associated with microvascular diabetic complications. There was a tendency to increased frequency of SNP -43 1/1 homozygotes in patients with diabetic retinopathy (p=0.057). The homozygous haplotype combination 121/121 was more frequent in T2DM patients than in non-diabetic controls (18.4% vs 10.5%, p=0.019). In conclusion, the results of our study suggest the significant association of SNP -43 with the risk of CVD coexisting with T2DM. We also observed that 121/121 haplotype was associated with T2DM in the studied population.

Development of α-helical calpain probes by mimicking a natural protein-protein interaction

We have designed a highly specific inhibitor of calpain by mimicking a natural protein-protein interaction between calpain and its endogenous inhibitor calpastatin. To enable this goal we established a new method of stabilizing an α-helix in a small peptide by screening 24 commercially available cross-linkers for successful cysteine alkylation in a model peptide sequence. The effects of cross-linking on the α-helicity of selected peptides were examined by CD and NMR spectroscopy, and revealed structurally rigid cross-linkers to be the best at stabilizing α-helices. We applied this strategy to the design of inhibitors of calpain that are based on calpastatin, an intrinsically unstable polypeptide that becomes structured upon binding to the enzyme. A two-turn α-helix that binds proximal to the active site cleft was stabilized, resulting in a potent and selective inhibitor for calpain. We further expanded the utility of this inhibitor by developing irreversible calpain family activity-based probes (ABPs), which retained the specificity of the stabilized helical inhibitor. We believe the inhibitor and ABPs will be useful for future investigation of calpains, while the cross-linking technique will enable exploration of other protein-protein interactions.

Human β-cell proliferation and intracellular signaling: driving in the dark without a road map

A major goal in diabetes research is to find ways to enhance the mass and function of insulin secreting β-cells in the endocrine pancreas to prevent and/or delay the onset or even reverse overt diabetes. In this Perspectives in Diabetes article, we highlight the contrast between the relatively large body of information that is available in regard to signaling pathways, proteins, and mechanisms that together provide a road map for efforts to regenerate β-cells in rodents versus the scant information in human β-cells. To reverse the state of ignorance regarding human β-cell signaling, we suggest a series of questions for consideration by the scientific community to construct a human β-cell proliferation road map. The hope is that the knowledge from the new studies will allow the community to move faster towards developing therapeutic approaches to enhance human β-cell mass in the long-term goal of preventing and/or curing type 1 and type 2 diabetes.

Advanced glycation end-products induce calpain-mediated degradation of ezrin

Advanced glycation end-products (AGEs) are important mediators of diabetic complications via incompletely understood pathways. AGEs bind to intracellular ERM proteins (ezrin, radixin and moesin) that modulate cell shape, motility, adhesion and signal transduction. AGEs bind to the N-terminal domain of ezrin but not full-length ezrin. The AGE binding site may be made accessible either by proteolysis releasing an N-terminal fragment or ezrin activation by phosphorylation. Increased intracellular calcium is a primary event in cell activation by high glucose or AGEs. Calpain activity is increased concomitantly, and ezrin is a calpain substrate. The present study assessed whether glycated proteins affect ezrin cleavage and activation in renal tubule epithelial cells. After 7 days, AGE-BSA decreased ezrin levels in MDCK renal tubular cells to 66 ± 4% of control. AGE-RNAse, ribosylated fetal bovine serum and methylglyoxal-BSA all had similar effects. The AGE-BSA-induced decrease in ezrin was abolished by calpastatin peptide, a specific calpain inhibitor, and 1,2-bis-aminophenoxyethane-tetraacetic acid acetoxymethyl ester (BAPTA-AM), a calcium chelator. Ezrin breakdown products were increased in AGE-BSA-treated cells, with a main fragment of ∼ 43 kDa. In vitro, calpain 1 cleaved recombinant human ezrin, generating breakdown fragments including an N-terminal fragment of ∼ 43 kDa. Studies with ezrin mutants showed that non-phosphorylated ezrin was more susceptible to calpain cleavage. AGE-BSA decreased phosphorylated ERM levels to 31 ± 12% in MDCK cells. Thus, AGE-BSA promotes calpain-mediated proteolysis of ezrin in MDCK cells by both increasing calpain activity and reducing phosphorylation. Therapies targeting both glycated proteins and calpain may provide protection against diabetic complications.

Loss of calpain 10 causes mitochondrial dysfunction during chronic hyperglycemia

We showed that renal calpain 10, a mitochondrial and cytosolic Ca(2+)-regulated cysteine protease, is specifically decreased in kidneys of diabetic rats and mice, and is associated with diabetic nephropathy. The goals of this study were to examine renal calpain 10 and mitochondrial dysfunction in streptozotocin-induced hyperglycemic rats and determine the effects of siRNA-mediated knock down of renal calpain 10 on mitochondrial function. Four weeks after streptozotocin injection, calpain 10 protein and mRNA were decreased and calpain 10 substrates accumulated. We detected increased state 2 respiration in isolated renal mitochondria and increased markers of mitochondrial fission and mitophagy. All changes were prevented by daily insulin injection. Compared to scrambled siRNA, calpain 10 siRNA resulted in a marked decrease in renal calpain 10 at 2, 5 and 7 days. In concert with the loss of renal calpain 10, calpain 10 substrates accumulated, mitochondrial fusion decreased, mitochondrial fission and mitophagy increased. In summary, insulin-sensitive hyperglycemia induced loss of renal calpain 10 is correlated with renal mitochondrial dysfunction, fission and mitophagy, and specific depletion of renal calpain 10 produces similar mitochondrial defects. These results provide evidence that diabetes-induced renal mitochondrial dysfunction and renal injury may directly result from the loss of renal calpain 10.

Tau phosphorylation and μ-calpain activation mediate the dexamethasone-induced inhibition on the insulin-stimulated Akt phosphorylation

Evidence has suggested that insulin resistance (IR) or high levels of glucocorticoids (GCs) may be linked with the pathogenesis and/or progression of Alzheimer's disease (AD). Although studies have shown that a high level of GCs results in IR, little is known about the molecular details that link GCs and IR in the context of AD. Abnormal phosphorylation of tau and activation of μ-calpain are two key events in the pathology of AD. Importantly, these two events are also related with GCs and IR. We therefore speculate that tau phosphorylation and μ-calpain activation may mediate the GCs-induced IR. Akt phosphorylation at Ser-473 (pAkt) is commonly used as a marker for assessing IR. We employed two cell lines, wild-type HEK293 cells and HEK293 cells stably expressing the longest human tau isoform (tau-441; HEK293/tau441 cells). We examined whether DEX, a synthetic GCs, induces tau phosphorylation and μ-calpain activation. If so, we examined whether the DEX-induced tau phosphorylation and μ-calpain activation mediate the DEX-induced inhibition on the insulin-stimulated Akt phosphorylation. The results showed that DEX increased tau phosphorylation and induced tau-mediated μ-calpain activation. Furthermore, pre-treatment with LiCl prevented the effects of DEX on tau phosphorylation and μ-calpain activation. Finally, both LiCl pre-treatment and calpain inhibition prevented the DEX-induced inhibition on the insulin-stimulated Akt phosphorylation. In conclusion, our study suggests that the tau phosphorylation and μ-calpain activation mediate the DEX-induced inhibition on the insulin-stimulated Akt phosphorylation.

Four polymorphisms of the CAPN 10 gene and their relationship to polycystic ovary syndrome susceptibility: a meta-analysis

OBJECTIVE

  To investigate the association between CAPN 10 gene polymorphism and polycystic ovary syndrome (PCOS) susceptibility.

DESIGN

Meta-analysis of published case-control studies of four single nucleotide polymorphisms (SNPs) in CAPN 10 and PCOS susceptibility.

PATIENTS

  Women with PCOS.

MEASUREMENTS

  Odds ratios (ORs) and 95% confidence intervals (CIs) for heterozygous, homozygous, dominant model, recessive model and allele.

RESULTS

  A total of 11 studies were involved in the meta-analysis. UCSNP-63 was significantly associated with PCOS, with homozygous carriers (TT vs CC: OR = 0·64; 95% CI: 0·45-0·90) and recessive model (TT vs CC and CT: OR = 0·64; 95% CI: 0·45-0·90) being protective factors. In addition, UCSNP-19 was significantly associated with PCOS, with recessive model (ins/ins vs del/del and del/ins: OR = 0·72, 95% CI: 0·59-0·88) and insert allele (ins vs del: OR = 0·85, 95% CI: 0·76-0·96) being protective factors, while heterozygous carriers (del/ins vs del/del: OR = 1·56, 95% CI: 1·24-1·94) and deletion allele (del vs ins: OR = 1·18, 95% CI: 1·04-1·32) being risk factors. However, no significant associations were found between UCSNP-44, -43 and PCOS. Moreover, the results of the Rotterdam criteria subgroup analysis were similar with that of overall analysis.

CONCLUSIONS

  This is the first report on the association between CAPN 10 UCSNP-63 and PCOS in genotype, with homozygous carriers and recessive model being protective factors. Additionally, insert allele and recessive model of UCSNP-19 are protective factors, while deletion allele and heterozygous genotype are risk factors for PCOS development.

Association of CAPN10 SNPs and haplotypes with polycystic ovary syndrome among South Indian Women

Polycystic Ovary Syndrome (PCOS) is known to be characterized by metabolic disorder in which hyperinsulinemia and peripheral insulin resistance are central features. Given the physiological overlap between PCOS and type-2 diabetes (T2DM), and calpain 10 gene (CAPN10) being a strong candidate for T2DM, a number of studies have analyzed CAPN10 SNPs among PCOS women yielding contradictory results. Our study is first of its kind to investigate the association pattern of CAPN10 polymorphisms (UCSNP-44, 43, 56, 19 and 63) with PCOS among Indian women. 250 PCOS cases and 299 controls from Southern India were recruited for this study. Allele and genotype frequencies of the SNPs were determined and compared between the cases and controls. Results show significant association of UCSNP-44 genotype CC with PCOS (p = 0.007) with highly significant odds ratio when compared to TC (OR = 2.51, p = 0.003, 95% CI = 1.37–4.61) as well as TT (OR = 1.94, p = 0.016, 95% CI = 1.13–3.34). While the haplotype carrying the SNP-44 and SNP-19 variants (21121) exhibited a 2 fold increase in the risk for PCOS (OR = 2.37, p = 0.03), the haplotype containing SNP-56 and SNP-19 variants (11221) seems to have a protective role against PCOS (OR = 0.20, p = 0.004). Our results support the earlier evidence for a possible role of UCSNP-44 of the CAPN10 gene in the manifestation of PCOS.

Chronic high glucose downregulates mitochondrial calpain 10 and contributes to renal cell death and diabetes-induced renal injury

Whereas most calpains are cytosolic proteases, calpain 10 is resident in mitochondria and is important in mitochondrial homeostasis. Because calpain 10 has been implicated in type 2 diabetes, we studied its possible role in diabetes-induced renal dysfunction. We treated renal proximal tubular cells with high glucose (17 mmol/l) and found decreased mitochondrial calpain 10 mRNA and protein at 96 h compared with cells incubated with 0 or 5 mmol/l glucose or 17 mmol/l D-mannitol. High glucose increased mitochondrial calpain 10 substrates (NDUFB8 and ATP synthase β), decreased basal and uncoupled respiration, and initiated cell apoptosis as indicated by cleaved caspase 3 and nuclear condensation. Renal calpain 10 protein and mRNA were specifically decreased in streptozotocin-induced diabetic rats with kidney dysfunction, and in diabetic ob/ob mice. In agreement with our in vitro data, the kidneys of streptozotocin-induced diabetic rats had elevated calpain 10 substrates and cleaved caspase 3. Finally, specific siRNA-induced knockdown of calpain 10 in the proximal tubules of control rats resulted in decreased renal function as evidenced by increased serum creatinine, and increased caspase 3 cleavage compared with rats receiving scrambled siRNA. Thus, the glucose-induced loss of calpain 10 in vivo results in renal cell apoptosis and organ failure through accumulation of mitochondrial calpain 10 substrates and mitochondrial dysfunction. Whether this is a major cause of the decreased renal function in diabetic nephropathy will require further studies.

Pancreatic β-cell Raf-1 is required for glucose tolerance, insulin secretion, and insulin 2 transcription

Regulation of glucose homeostasis by insulin depends on pancreatic β-cell growth, survival, and function. Raf-1 kinase is a major downstream target of several growth factors that promote proliferation and survival of many cell types, including the pancreatic β cells. We have previously reported that insulin protects β cells from apoptosis and promotes proliferation by activating Raf-1 signaling in cultured human islets, mouse islets, and MIN6 cells. As Raf-1 activity is critical for basal apoptosis and insulin secretion in vitro, we hypothesized that Raf-1 may play an important role in glucose homeostasis in vivo. To test this hypothesis, we utilized the Cre-loxP recombination system to obtain a pancreatic β-cell-specific ablation of Raf-1 kinase gene (RIPCre(+/+):Raf-1(flox/flox)) and a complete set of littermate controls (RIPCre(+/+):Raf-1(wt/wt)). RIPCre(+/+):Raf-1(flox/flox) mice were viable, and no effects on weight gain were observed. RIPCre(+/+):Raf-1(flox/flox) mice had increased fasting blood glucose levels and impaired glucose tolerance but normal insulin tolerance compared to littermate controls. Insulin secretion in vivo and in isolated islets was markedly impaired, but there was no apparent effect on the exocytosis machinery. However, islet insulin protein and insulin 2 mRNA, but not insulin 1 mRNA, were dramatically reduced in Raf-1-knockout mice. Analysis of insulin 2 knockout mice demonstrated that this reduction in mRNA was sufficient to impair in vivo insulin secretion. Our data further indicate that Raf-1 specifically and acutely regulates insulin 2 mRNA via negative action on Foxo1, which has been shown to selectively control the insulin 2 gene. This work provides the first direct evidence that Raf-1 signaling is essential for the regulation of basal insulin transcription and the supply of releasable insulin in vivo.

The Genetic Basis of the Polycystic Ovary Syndrome: A Literature Review Including Discussion of PPAR-gamma

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder of the women of reproductive age. Familial clustering of PCOS has been consistently reported suggesting that genetic factors play a role in the development of the syndrome although PCOS cases do not exhibit a clear pattern of Mendelian inheritance. It is now well established that PCOS represents a complex trait similar to type-2 diabetes and obesity, and that both inherited and environmental factors contribute to the PCOS pathogenesis. A large number of functional candidate genes have been tested for association or linkage with PCOS phenotypes with more negative than positive findings. Lack of universally accepted diagnostic criteria, difficulties in the assignment of male phenotype, obscurity in the mode of inheritance, and particularly small sample size of the study populations appear to be major limitations for the genetic studies of PCOS. In the near future, utilizing the genome-wide scan approach and the HapMap project will provide a stronger potential for the genetic analysis of the syndrome.

New emerging role of protein-tyrosine phosphatase 1B in the regulation of glycogen metabolism in basal and TNF-α-induced insulin-resistant conditions in an immortalised muscle cell line isolated from mice

AIMS/HYPOTHESIS

Protein-tyrosine phosphatase 1B (PTP1B) negatively regulates insulin action, promoting attenuation of the insulin signalling pathway. The production of this phosphatase is enhanced in insulin-resistant states, such as obesity and type 2 diabetes, where high levels of proinflammatory cytokines (TNF-α, IL-6) are found. In these metabolic conditions, insulin action on glycogen metabolism in skeletal muscle is greatly impaired. We addressed the role of PTP1B on glycogen metabolism in basal and insulin-resistant conditions promoted by TNF-α.

METHODS

We studied the effect of TNF-α in the presence and absence of insulin on glycogen content and synthesis, glycogen synthase (GS) and glycogen phosphorylase (GP) activities and on glycogen synthesis and degradation signalling pathways. For this purpose we used immortalised cell lines isolated from skeletal muscle from mice lacking PTP1B.

RESULTS

Absence of PTP1B caused activation of GS and GP with a net glycogenolytic effect, reflected in lower amounts of glycogen and activation of the glycogenolytic signalling pathway, with higher rates of phosphorylation of cyclic adenosine monophosphate-dependent kinase (PKA), phosphorylase kinase (PhK) and GP phosphorylation. Nevertheless, insulin action was strongly enhanced in Ptp1b (also known as Ptpn1)(-/-) cells in terms of glycogen content, synthesis, GS activation rates and GS Ser641 dephosphorylation. Treatment with TNF-α augmented the activity ratios of both GS and GP, and impaired insulin stimulation of glycogen synthesis in wild-type myocytes, whereas Ptp1b (-/-) myocytes restored this inhibitory effect. We report a glycogenolytic effect of TNF-α, as demonstrated by greater activation of the degradation signalling cascade PKA/PhK/GP. In our model, this effect is mediated by the activation of PKA.

CONCLUSIONS/INTERPRETATION

We provide new data about the role of PTP1B in glycogen metabolism and confirm the beneficial effect that absence of the phosphatase confers against an insulin-resistant condition.

Protein-engineered biomaterials: nanoscale mimics of the extracellular matrix

BACKGROUND

Traditional materials used as in vitro cell culture substrates are rigid and flat surfaces that lack the exquisite nano- and micro-scale features of the in vivo extracellular environment. While these surfaces can be coated with harvested extracellular matrix (ECM) proteins to partially recapitulate the bio-instructive nature of the ECM, these harvested proteins often exhibit large batch-to-batch variability and can be difficult to customize for specific biological studies. In contrast, recombinant protein technology can be utilized to synthesize families of 3 dimensional protein-engineered biomaterials that are cyto-compatible, reproducible, and fully customizable.

SCOPE OF REVIEW

Here we describe a modular design strategy to synthesize protein-engineered biomaterials that fuse together multiple repeats of nanoscale peptide design motifs into full-length engineered ECM mimics.

MAJOR CONCLUSIONS

Due to the molecular-level precision of recombinant protein synthesis, these biomaterials can be tailored to include a variety of bio-instructional ligands at specified densities, to exhibit mechanical properties that match those of native tissue, and to include proteolytic target sites that enable cell-triggered scaffold remodeling. Furthermore, these biomaterials can be processed into forms that are injectable for minimally-invasive delivery or spatially patterned to enable the release of multiple drugs with distinct release kinetics.

GENERAL SIGNIFICANCE

Given the reproducibility and flexibility of these protein-engineered biomaterials, they are ideal substrates for reductionist biological studies of cell-matrix interactions, for in vitro models of physiological processes, and for bio-instructive scaffolds in regenerative medicine therapies. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

Calpain-10 is a component of the obesity-related quantitative trait locus Adip1

We previously mapped Adip1, an obesity quantitative trait locus (QTL), to the central portion of murine chromosome 1 containing the calpain-10 (Capn10) gene. Human studies have associated calpain-10 (CAPN10) variants with type 2 diabetes and various metabolic traits. We performed a quantitative hybrid complementation test (QHCT) to determine whether differences attributed to Adip1 are the result of variant Capn10 alleles in LG/J and SM/J mice. We crossed LG/J and SM/J to wild-type (C57BL/6J) and Capn10 knockout (Capn10(-/-)) mice to form four F(1) hybrid groups: LG/J by wild-type, LG/J by Capn10(-/-), SM/J by wild-type, and SM/J by Capn10(-/-). We performed a two-way ANOVA with the experimental strain, tester strain, and their interaction as the factors. Significant interaction indicates a quantitative failure to complement. We found failure to complement for fat, organ, and body weights, and leptin, female free fatty acid, and triglyceride levels. Capn10(-/-) resulted in heavier weights and higher serum levels in LG/J crosses but not in SM/J crosses. For glucose tolerance and insulin response tests, the Capn10(-/-) allele resulted in lower glucose levels in crosses with SM/J but had no effect in the LG/J crosses. Differences between the LG/J and SM/J Capn10 alleles are the likely source of some of the QTL effects mapped to Adip1 in the LG/J-by-SM/J cross. Capn10 plays an important role in regulating obesity and diabetes in mice.

The pseudokinase tribbles homolog 3 interacts with ATF4 to negatively regulate insulin exocytosis in human and mouse beta cells

Insufficient insulin secretion and reduced pancreatic beta cell mass are hallmarks of type 2 diabetes (T2DM). Here, we confirm that a previously identified polymorphism (rs2295490/Q84R) in exon 2 of the pseudokinase-encoding gene tribbles 3 (TRB3) is associated with an increased risk for T2DM in 2 populations of people of mixed European descent. Carriers of the 84R allele had substantially reduced plasma levels of C-peptide, the product of proinsulin processing to insulin, suggesting a role for TRB3 in beta cell function. Overexpression of TRB3 84R in mouse beta cells, human islet cells, and the murine beta cell line MIN6 revealed reduced insulin exocytosis, associated with a marked reduction in docked insulin granules visualized by electron microscopy. Conversely, knockdown of TRB3 in MIN6 cells restored insulin secretion and expression of exocytosis genes. Further analysis in MIN6 cells demonstrated that TRB3 interacted with the transcription factor ATF4 and that this complex acted as a competitive inhibitor of cAMP response element-binding (CREB) transcription factor in the regulation of key exocytosis genes. In addition, the 84R TRB3 variant exhibited greater protein stability than wild-type TRB3 and increased binding affinity to Akt. Mice overexpressing TRB3 84R in beta cells displayed decreased beta cell mass, associated with reduced proliferation and enhanced apoptosis rates. These data link a missense polymorphism in human TRB3 to impaired insulin exocytosis and thus increased risk for T2DM.

Impaired insulin secretion in transgenic mice over-expressing calpastatin in pancreatic β-cells

Calpains are a family of calcium-activated proteases involved in a number of cellular functions including cell death, proliferation and exocytosis. The finding that variation in the calpain-10 gene increases type 2 diabetes risk in some populations has increased interest in determining the potential role of calpains in pancreatic β-cell function. In the present study, transgenic mice (Cast (RIP)) expressing an endogenous calpain inhibitor, calpastatin, in pancreatic β-cells were used to dissect the role of the calpain system in the regulation insulin secretion in vivo and in vitro. Glucose concentrations after the administration of intraperitoneal glucose were significantly increased in Cast (RIP) mice compared with wildtype littermate controls. This was associated with a reduction in glucose-stimulated insulin secretion in vivo. Using pancreas perfusion, static islet incubation and islet perifusion, it was demonstrated that Cast (RIP) islets hypersecreted insulin at low glucose, but exhibited significantly impaired insulin responses to high glucose. Examination of insulin release and calcium signals from isolated islets indicated that distal components of the insulin exocytotic pathway were abnormal in Cast (RIP) mice. Cast (RIP) islets had modestly reduced expression of Rab3a and other critical components in the late steps of insulin exocytosis. These studies provide the first evidence that blocking endogenous calpain activity partially impairs insulin release in vivo and in vitro by targeting distal components of the insulin exocytotic machinery.

Calpain-mediated degradation of reversibly oxidized protein-tyrosine phosphatase 1B

Protein-tyrosine phosphatases (PTPs) are regulated by reversible inactivating oxidation of the catalytic-site cysteine. We have previously shown that reversible oxidation upon UVA irradiation is followed by calpain-mediated PTP degradation. Here, we address the mechanism of regulated cleavage and the physiological function of PTP degradation. Reversible oxidation of PTP1B in vitro strongly facilitated the association with calpain and led to greatly increased calpain-dependent inactivating cleavage. Both oxidation-induced association and cleavage depended exclusively on the presence of the catalytic (reversibly oxidized) cysteine residue 215. A major cleavage site was identified preceding amino acid position Ala77. In calpain-deficient cells, insulin signaling was apparently diminished, consistent with a possible role for calpain in removing a negative regulator of insulin signaling. Reversibly oxidized PTP1B may be a target of calpain in this context.

Calpain-10 expression is elevated in pancreatic islets from patients with type 2 diabetes

BACKGROUND

Calpain-10 was the first gene to be identified influencing the risk of type 2 diabetes (T2D) by positioning cloning. Studies in beta-cell lines and rodent islets suggest that calpain-10 may act as a regulator of insulin secretion. However, its role in human pancreatic islets remains unclear. The aim of this study was to examine if calpain-10 expression is altered in islets from patients with T2D and if the transcript level correlates with insulin release. We also tested if polymorphisms in the CAPN10 gene are associated with gene expression and insulin secretion in vitro.

METHODOLOGY/PRINCIPAL FINDINGS

Calpain-10 mRNA expression was analysed in human pancreatic islets from 34 non-diabetic and 10 T2D multi-organ donors. CAPN10 SNP-43 and SNP-44 were genotyped and related to gene expression and insulin release in response to glucose, arginine and glibenclamide. The mRNA level of calpain-10 was elevated by 64% in pancreatic islets from patients with T2D compared with non-diabetic donors (P = 0.01). Moreover, the calpain-10 expression correlated positively with arginine-stimulated insulin release in islets from non-diabetic donors (r = 0.45, P = 0.015). However, this correlation was lost in islets from patients with T2D (r = 0.09; P = 0.8). The G/G variant of SNP-43 was associated with reduced insulin release in response to glucose (P</=0.04) in non-diabetic donors.

CONCLUSIONS

While calpain-10 expression correlates with insulin release in non-diabetic human islets, this correlation is lost in T2D suggesting that a stimulatory effect of calpain-10 could be lost in patients with T2D.

A complex selection signature at the human AVPR1B gene

BACKGROUND

The vasopressin receptor type 1b (AVPR1B) is mainly expressed by pituitary corticotropes and it mediates the stimulatory effects of AVP on ACTH release; common AVPR1B haplotypes have been involved in mood and anxiety disorders in humans, while rodents lacking a functional receptor gene display behavioral defects and altered stress responses.

RESULTS

Here we have analyzed the two exons of the gene and the data we present suggest that AVPR1B has been subjected to natural selection in humans. In particular, analysis of exon 2 strongly suggests the action of balancing selection in African populations and Europeans: the region displays high nucleotide diversity, an excess of intermediate-frequency alleles, a higher level of within-species diversity compared to interspecific divergence and a genealogy with common haplotypes separated by deep branches. This relatively unambiguous situation coexists with unusual features across exon 1, raising the possibility that a nonsynonymous variant (Gly191Arg) in this region has been subjected to directional selection.

CONCLUSION

Although the underlying selective pressure(s) remains to be identified, we consider this to be among the first documented examples of a gene involved in mood disorders and subjected to natural selection in humans; this observation might add support to the long-debated idea that depression/low mood might have played an adaptive role during human evolution.

Replication of calpain-10 genetic association with carotid intima-media thickness

OBJECTIVE

Diabetes and atherosclerosis may share common genetic determinants. A prior study in Hispanics found association of haplotypes in the diabetes gene calpain-10 (CAPN10) with carotid artery intima-media thickness (CIMT). This study sought to replicate this association in an independent cohort.

METHODS

Four CAPN10 SNPs were genotyped and haplotypes determined in 487 Hispanic Americans from 143 families ascertained via an index case with hypertension. CIMT was measured from B-mode ultrasound, and glycemic traits quantified from euglycemic clamps. Association of SNPs and haplotypes with CIMT was determined.

RESULTS

The minor alleles of SNP-56 and SNP-63 were associated with increased CIMT in dominant and additive models. The association of haplotype 1112 with increased CIMT was replicated. No associations with fasting insulin, insulin secretion, or insulin sensitivity were observed.

CONCLUSIONS

CAPN10 association with CIMT was replicated, further supporting its role as a common genetic determinant of diabetes and atherosclerosis in Hispanics.

Effect of exercise training on calpain systems in lean and obese Zucker rats

Exercise training plays a major role in the improving physiology of diabetes. Herein we aimed to investigate the influence of exercise upon the calcium-dependent calpain-isoform expressions of lean or obese Zucker rats, a model of obesity and type II diabetes (NIDDM). Five-month-old rats were divided: (1) obese sedentary (OS, n=7); (2) obese exercise (OE, n=7); (3) lean sedentary (LS, n=7); (4) lean exercise (LE, n=7). After 2-month exercise (treadmill running), the body weight (BW) and expression of calpain 10, mu-calpain, and m-calpain in skeletal muscles were determined by RT-PCR, using beta-actin as internal standard. We found exercise is useful for BW lossing, especially in the obese rats. The BW difference between OS and OE rats (69 g vs. 18.2 g) was more significantly than that between LS and LE rats (41.8 g vs. 28.7 g). The calpain 10 expression of LS rats (0.965) was lower than that of LE rats (1.006), whereas those of OS and OE were comparable. The mu- or m-calpain expressions of sedentary groups (OS, LS) was significantly higher than those of exercise groups (OE, LE). The mu-calpain expression (1.13/0.92) and m-calpain expression (1.01/0.99) of OS/LS rats was significantly higher than those of OE/LE rats [1.07/0.9 (micro-calpain); 0.97/0.95 (m-calpain)]. We concluded that the micro- or m-calpains in skeletal muscle are regulated by exercise in both lean and obese Zucker rats. Exercise and BW controlling might improve the physiopathology of obesity and diabetes. Both micro- or m-calpains might become useful markers for prognoses of diabetes.

Characterization of endogenous and recombinant human calpain-10

Calpain-10 is a novel ubiquitous calpain family member that has been implicated as a susceptibility gene for type 2 diabetes. One of the major challenges is that the function of calpain-10 is not yet known. To address this problem, we purified human calpain-10 from different sources, including the endogenous and the recombinant calpain-10 from HeLa S3 and 293F cells, respectively. Both endogenous and recombinant calpain-10 were present as two major forms with different origins. Interestingly, radiolabeled calpain-10 was found to be efficiently cleaved at the N-terminal region by calpain-2, but not by other proteases. None of these calpain-10 proteins have putative proteolytic activity under in vitro conditions when examined using different peptide substrates, including more than 70 in vitro translated, radiolabeled oligopeptides. Our results raise the possibility that calpain-10 may require a special intracellular localization or interacting partner(s) to acquire proteolytic activity, or it functions by interacting with other proteins rather than through its proteolytic activity.

Calpain-10 gene and protein expression in human skeletal muscle: effect of acute lipid-induced insulin resistance and type 2 diabetes

OBJECTIVE

Our objective was to investigate the effect of lipid-induced insulin resistance and type 2 diabetes on skeletal muscle calpain-10 mRNA and protein levels.

RESEARCH DESIGN AND METHODS

In the first part of this study, 10 healthy subjects underwent hyperinsulinemic euglycemic (4.5 mmol/liter) clamps for 6 h with iv infusion of either saline or a 20% Intralipid emulsion (Fresenius Kabi AG, Bad Homburg, Germany). Skeletal muscle biopsies were taken before and after 3- and 6-h insulin infusion and analyzed for calpain-10 mRNA and protein expression. In the second part of the study, muscle samples obtained after an overnight fast in 10 long-standing, sedentary type 2 diabetes patients, 10 sedentary, weight-matched, normoglycemic controls, and 10 age-matched, endurance-trained cyclists were analyzed for calpain-10 mRNA and protein content.

RESULTS

Intralipid infusion in healthy subjects reduced whole body glucose disposal by approximately 50% (P<0.001). Calpain-10 mRNA (P=0.01) but not protein content was reduced after 6-h insulin infusion in both the saline and Intralipid emulsion trials. Skeletal muscle calpain-10 mRNA and protein content did not differ between the type 2 diabetes patients and normoglycemic controls, but there was a strong trend for total calpain-10 protein to be greater in the endurance-trained athletes (P=0.06).

CONCLUSIONS

These data indicate that skeletal muscle calpain-10 expression is not modified by insulin resistance per se and suggest that hyperinsulinemia and exercise training may modulate human skeletal muscle calpain-10 expression.

Calpain proteolysis of insulin-like growth factor binding protein (IGFBP) -2 and -3, but not of IGFBP-1

Calpains are cytoplasmic Ca(2+)-regulated cysteine proteases that may regulate insulin-like growth factor (IGF)-independent actions of insulin-like growth factor binding proteins (IGFBPs) through IGFBP proteolysis. In this study, [(125)I]-labeled IGFBP-2 and -3, but not IGFBP-1, were proteolyzed by Ca(2+)-activated m-calpain in vitro. Degradation of higher concentrations of the recombinant proteins IGFBP-2 and -3 by m-calpain was dose-dependent, but was terminated within 20 min by autolysis. By subjecting proteolytic fragments to N-terminal amino acid sequence analysis, the primary cleavage sites in IGFBP-2 and -3 were localized to the non-conserved central linker regions. Using the biosensor technique, in vitro binding of m-calpain to IGFBP-3 was demonstrated to be a Ca(2+)-dependent reaction with a rapid on/off rate.

The activity of calpains in lymphocytes is glucose-dependent and is decreased in diabetic patients

Calpains are nonlysosomal calcium-dependent cysteine proteases that participate in insulin secretion and action. Polymorphisms in the calpain-10 gene have been shown to increase the risk for type 2 diabetes. Since white blood cells have been used to study glucose homeostasis, the present study was carried to find out if calpains have different activity and/or expression in accessible cells such as lymphocytes of individuals with or without type 2 diabetes. Fasting blood glucose concentration was significantly higher in diabetic subjects, whereas the difference in the activity of calpains evaluated in basal and stimulating extracellular glucose concentration was significantly higher in the lymphocytes from the control group. The mRNA expression of calpain-10 was similar in the lymphocytes of both patients and controls. The protein blots showed four bands that ranged between 75 and 50 kDa; however, no statistical differences were observed in the expression of the calpain-10 isoforms between controls and patients. Data obtained showed that human lymphocytes express calpain-10 mRNA and protein, showing a similar expression between diabetic and control subjects, nevertheless in the diabetic group calpain activity was less glucose-sensitive.