NGF and Its Role in Immunoendocrine Communication during Metabolic Syndrome.

Nerve growth factor (NGF) was the first neurotrophin described. This neurotrophin contributes to organogenesis by promoting sensory innervation and angiogenesis in the endocrine and immune systems. Neuronal and non-neuronal cells produce and secrete NGF, and several cell types throughout the body express the high-affinity neurotrophin receptor TrkA and the low-affinity receptor p75NTR. NGF is essential for glucose-stimulated insulin secretion and the complete development of pancreatic islets. Plus, this factor is involved in regulating lipolysis and thermogenesis in adipose tissue. Immune cells produce and respond to NGF, modulating their inflammatory phenotype and the secretion of cytokines, contributing to insulin resistance and metabolic homeostasis. This neurotrophin regulates the synthesis of gonadal steroid hormones, which ultimately participate in the metabolic homeostasis of other tissues. Therefore, we propose that this neurotrophin's imbalance in concentrations and signaling during metabolic syndrome contribute to its pathophysiology. In the present work, we describe the multiple roles of NGF in immunoendocrine organs that are important in metabolic homeostasis and related to the pathophysiology of metabolic syndrome.

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.

The effects of sucrose and arsenic on muscular insulin signaling pathways differ between the gastrocnemius and quadriceps muscles.

Introduction: Insulin resistance in muscle can originate from a sedentary lifestyle, hypercaloric diets, or exposure to endocrine-disrupting pollutants such as arsenic. In skeletal muscle, insulin stimulates glucose uptake by translocating GLUT4 to the sarcolemma. This study aimed to evaluate the alterations induced by sucrose and arsenic exposure in vivo on the pathways involved in insulinstimulated GLUT4 translocation in the quadriceps and gastrocnemius muscles. Methods: Male Wistar rats were treated with 20% sucrose (S), 50 ppm sodium arsenite (A), or both (A+S) in drinking water for 8 weeks. We conducted an intraperitoneal insulin tolerance (ITT) test on the seventh week of treatment. The quadriceps and gastrocnemius muscles were obtained after overnight fasting or 30 min after intraperitoneal insulin injection. We assessed changes in GLUT4 translocation to the sarcolemma by cell fractionation and abundance of the proteins involved in GLUT4 translocation by Western blot. Results: Male rats consuming S and A+S gained more weight than control and Atreated animals. Rats consuming S, A, and A+S developed insulin resistance assessed through ITT. Neither treatments nor insulin stimulation in the quadriceps produced changes in GLUT4 levels in the sarcolemma and Akt phosphorylation. Conversely, A and A+S decreased protein expression of Tether containing UBX domain for GLUT4 (TUG), and A alone increased calpain-10 expression. All treatments reduced this muscle's protein levels of VAMP2. Conversely, S and A treatment increased basal GLUT4 levels in the sarcolemma of the gastrocnemius, while all treatments inhibited insulin-induced GLUT4 translocation. These effects correlated with lower basal levels of TUG and impaired insulin-stimulated TUG proteolysis. Moreover, animals treated with S had reduced calpain-10 protein levels in this muscle, while A and A+S inhibited insulin-induced Akt phosphorylation. Conclusion: Arsenic and sucrose induce systemic insulin resistance due to defects in GLUT4 translocation induced by insulin. These defects depend on which muscle is being analyzed, in the quadriceps there were defects in GLUT4 retention and docking while in the gastrocnemius the Akt pathway was impacted by arsenic and the proteolytic pathway was impaired by arsenic and sucrose.

The potential role of COVID-19 in the induction of DNA damage.

The coronavirus disease-2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is challenging global health and economic systems. In some individuals, COVID-19 can cause a wide array of symptoms, affecting several organs, such as the lungs, heart, bowels, kidneys and brain, causing multiorgan failure, sepsis and death. These effects are related in part to direct viral infection of these organs, immunological deregulation, a hypercoagulatory state and the potential for development of cytokine storm syndrome. Since the appearance of COVID-19 is recent, the long-term effects on the health of recovered patients remain unknown. In this review, we focused on current evidence of the mechanisms of DNA damage mediated by coronaviruses. Data supports that these viruses can induce DNA damage, genomic instability, and cell cycle deregulation during their replication in mammalian cells. Since the induction of DNA damage and aberrant DNA repair mechanisms are related to the development of chronic diseases such as cancer, diabetes, neurodegenerative disorders, and atherosclerosis, it will be important to address similar effects and outcomes in recovered COVID-19 patients.

Cryptic splicing events result in unexpected protein products from calpain-10 (CAPN10) cDNA.

Calpain-10 (CAPN10) belongs to the calpain superfamily. Genetic polymorphisms of the CAPN10 gene are associated with susceptibility to develop type 2 diabetes mellitus. Although the role of CAPN10 in the pathophysiology of diabetes has been extensively investigated, its biochemical properties are largely unknown. In this report, we made the surprising discovery that CAPN10 cDNA transcripts are subject to cryptic splicing and unexpected protein products were expressed. The same set of splicing products was reproducibly detected in four types of cultured cells including the primary culture of mouse myoblast. At least, one of the products was identical to a natural splicing variant. Sequence analysis of the splicing potential of CAPN10 cDNA, together with mutagenesis studies, resulted in the identification of a powerful splicing acceptor site at the junction of the sequences encoded by exons 9 and 10. We successfully extended the analysis to create expression construct resistant to splicing for both human and mouse CAPN10. The construct allowed us to analyze two major CAPN10 isoforms and reveal their difference in substrate proteolysis and potential cell functions. These results demonstrate that proteins produced from cDNA do not necessarily reflect the original nucleotide sequence. We provide insight into the property of recombinantly expressed CAPN10 proteins in cultured cells circumventing unexpected protein products.

Is Arsenic Exposure a Risk Factor for Metabolic Syndrome? A Review of the Potential Mechanisms.

Exposure to arsenic in drinking water is a worldwide health problem. This pollutant is associated with increased risk of developing chronic diseases, including metabolic diseases. Metabolic syndrome (MS) is a complex pathology that results from the interaction between environmental and genetic factors. This condition increases the risk of developing type 2 diabetes, cardiovascular diseases, and cancer. The MS includes at least three of the following signs, central obesity, impaired fasting glucose, insulin resistance, dyslipidemias, and hypertension. Here, we summarize the existing evidence of the multiple mechanisms triggered by arsenic to developing the cardinal signs of MS, showing that this pollutant could contribute to the multifactorial origin of this pathology.

Maternal overnutrition before and during pregnancy induces DNA damage in male offspring: A rabbit model.

Using a rabbit model, we investigated whether maternal intake of a high-fat and high-carbohydrate diet (HFCD) before and during pregnancy induces an increase in micronuclei frequency and oxidative stress in offspring during adulthood. Female rabbits received a standard diet (SD) or HFCD for two months before mating and during gestation. The offspring from both groups were nursed by foster mothers fed SD until postnatal day 35. After weaning, all the animals received SD until postnatal day 440. At postnatal day 370, the frequency of micronuclei in peripheral blood reticulocytes (MN-RETs) increased in the male offspring from HFCD-fed mothers compared with the male offspring from SD-fed mothers. Additionally, fasting serum glucose increased in the offspring from HFCD-fed mothers compared with the offspring from SD-fed mothers. At postnatal day 440, the offspring rabbits were challenged with HFCD or continued with SD for 30 days. There was an increase in MN-RET frequency in the male rabbits from HFCD-fed mothers, independent of the type of challenging diet consumed during adulthood. The challenge induced changes in serum cholesterol, LDL and HDL that were influenced by the maternal diet and offspring sex. We measured malondialdehyde in the liver of rabbits as an oxidative stress marker after diet challenge. Oxidative stress in the liver only increased in the female offspring from HFCD-fed mothers who were also challenged with this same diet. The data indicate that maternal overnutrition before and during pregnancy is able to promote different effects depending on the sex of the animals, with chromosomal instability in male offspring and oxidative stress and hypercholesterolemia in female offspring. Our data might be important in the understanding of chronic diseases that develop in adulthood due to in utero exposure to maternal diet.

TUG is a calpain-10 substrate involved in the translocation of GLUT4 in adipocytes.

The calpain-10 (CAPN10) protease is implicated in the translocation of the glucose transporter 4 (GLUT4), which is retained in the Golgi matrix via the Tether containing a UBX domain for GLUT4 (TUG) protein. Insulin stimulation induces the proteolytic processing of TUG, which leads to the translocation of GLUT4 to the cell membrane. We tested whether TUG is a CAPN10 substrate. Proteolysis of TUG by calpains was assessed using a cell-free system containing calpain-1 and TUG. In situ proteolysis of TUG by calpains was demonstrated in 3T3-L1 adipocytes in the presence of insulin or calpain inhibitors to modulate calpain activity. Proteolysis of TUG by CAPN10 was confirmed using transient or stable silencing of CAPN10 in 3T3-L1 adipocytes. Calpains proteolyzed the C-terminus of TUG in vitro. In adipocytes, insulin-induced cleavage of TUG was correlated with the activation of calpains. Treatment with calpain inhibitors reduced TUG cleavage, resulting in impaired GLUT4 translocation without altering Akt phosphorylation. Furthermore, CAPN10 but not calpain-1 or calpain-2 colocalized with GLUT4 in the absence of insulin, and their colocalization was reduced after stimulation with insulin. Finally, we demonstrated that CAPN10 knockdown reduced the proteolysis of TUG without altering the phosphorylation of Akt or the expression of the Usp25m protease. Thus, our results provide evidence that the TUG protein is cleaved by CAPN10 to regulate GLUT4 translocation.

Calpain Activity in Leukocytes Is Associated with Diabetes Biochemical Markers.

BACKGROUND AND AIMS: CAPN10 gene is associated with type 2 diabetes (T2D). Specific members of the calpain system (CAPN1, CAPN2 and CAPN10) are implicated in glucose metabolism. The aim of this study was to evaluate the calpain activity in leukocytes of control subjects and patients with T2D and its association with the calpain family members involved in glucose metabolism and with biochemical parameters that are altered in T2D. METHODS: Calpain activity under extracellular glucose concentrations (70-280 mg/dL) was evaluated in leukocytes from subjects with and without T2D. Protein and mRNA levels of CAPN1, CAPN2 and CAPN10 were evaluated. Calpain inhibitors assays were performed in leukocytes from subjects without T2D to evaluate glucose uptake. Calpain activity at 100 mg/dL glucose was correlated with biochemical parameters by multivariate regression. RESULTS: Calpain activity in control subjects increased with extracellular glucose concentration in a dose-dependent manner, showing a negative association with HbA1c levels and total amount of CAPN10 protein. In contrast, calpain activity is decreased in patients with T2D and do not respond to changes in glucose concentration. A reduction of CAPN1 autolytic fragments were observed in the subjects with diabetes. Calpain inhibitors decreased calpain activity but did not altered glucose uptake in leukocytes. CONCLUSIONS: Calpain activity induced by glucose in leukocytes was associated with biochemical markers of glucose metabolism and with CAPN10 protein abundance. Calpain activity is low in subjects with T2D. Thus, calpain activity induced by extracellular glucose in leukocytes could be a potential marker for T2D early risk detection.

Effects of arsenic on adipocyte metabolism: Is arsenic an obesogen?

The environmental obesogen model proposes that in addition to a high-calorie diet and diminished physical activity, other factors such as environmental pollutants and chemicals are involved in the development of obesity. Although arsenic has been recognized as a risk factor for Type 2 Diabetes with a specific mechanism, it is still uncertain whether arsenic is also an obesogen. The impairment of white adipose tissue (WAT) metabolism is crucial in the onset of obesity, and distinct studies have evaluated the effects of arsenic on it, however only in some of them for obesity-related purposes. Thus, the known effects of arsenic on WAT/adipocytes were integrated based on the diverse metabolic and physiological processes that occur in WAT and are altered in obesity, specifically: adipocyte growth, adipokine secretion, lipid metabolism, and glucose metabolism. The currently available information suggests that arsenic can negatively affect WAT metabolism, resulting in arsenic being a potential obesogen.

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.

The reduction of Calpain-10 expression is associated with risk polymorphisms in obese children.

Excessive weight gain and obesity are major public health concerns. Childhood obesity is growing at an alarming rate. Polymorphisms in the Calpain-10 gene and the reduced expression of this gene in muscle cells and adipocytes have been associated with an increased risk of type 2 diabetes mellitus in several populations. In the present study, we explored the contribution of Calpain-10 in the development of metabolic impairment in childhood. We evaluated the presence of risk polymorphisms in the CAPN10 gene (SNP-44, SNP-43, InDel-19 and SNP-63) and the associated changes in the Calpain-10 mRNA levels in a pediatric population. A total of 161 Mexican children between 4 and 18 years old were included in this study. This population was classified into three groups according to international growth references: healthy weight (HW), overweight (OW) and obese (OB). Association studies of the anthropometric data, clinical values, genotyping and expression assays showed a decrease in the Calpain-10 mRNA and protein expression in the OW and OB groups with respect to the HW group. This decrease in the Calpain-10 mRNA expression was more evident in individuals homozygous for SNP-44 (T/T) and InDel-19 (3/3), alone (p<0.001 and p=0.015, respectively) or in combination (p=0.017). These polymorphisms were also associated with elevated BMI, weight percentiles, z-scores, waist circumferences, fasting glucose levels and beta cell functions in the OW and OB groups (p<0.05). Moreover, our results indicate a statistically significant decrease in the expression of the 75-kDa Calpain-10 isoform in the OW+OB group. The presence of polymorphisms and alterations in the expression of the CAPN10 gene at early ages might result in metabolic impairment in adulthood and should be further investigated.