Neuregulin improves response to glucose tolerance test in control and diabetic rats

Neuregulin-1β increases glucose uptake and promotes GLUT4 translocation in palmitate-treated C2C12 myotubes by activating PI3K/AKT signaling pathway

Insulin resistance (IR) is a feature of type 2 diabetes (T2DM) accompanied by reduced glucose uptake and glucose transporter 4 (GLUT4) translocation by skeletal muscle. Neuregulin-1β (NRG-1β) is essential for myogenesis and the regulation of skeletal muscle metabolism. Neuregulin-1β increases insulin sensitivity, promotes glucose uptake and glucose translocation in normal skeletal muscle. Here, we explored whether Neuregulin-1β increased glucose uptake and GLUT4 translocation in palmitate (PA)-treated C2C12 myotubes. After C2C12 myoblasts differentiated into myotubes, we used palmitate to induce cellular insulin resistance. Cells were incubated with or without Neuregulin-1β and glucose uptake was determined using the 2-NBDG assay. The expression level of glucose transporter 4 (GLUT4) was measured via immunofluorescence and Western blotting. MK2206, an inhibitor of AKT, was employed to reveal the important role played by AKT signaling in PA-treated C2C12 myotubes. We then established an animal model with T2DM and evaluated the effects of Neuregulin-1β on body weight and the blood glucose level. The GLUT4 level in the gastrocnemius of T2DM mice was also measured. NRG-1β not only increased glucose uptake by PA-treated myotubes but also promoted GLUT4 translocation to the plasma membrane. The effect of NRG-1β on PA-treated C2C12 myotubes was associated with AKT activation. In T2DM mice, Neuregulin-1β not only improved diabetes-induced weight loss and diabetes-induced hyperglycemia, but also promoted GLUT4 translocation in the gastrocnemius. In summary, Neuregulin-1β increased glucose uptake and promoted translocation of GLUT4 to the plasma membrane in PA-treated C2C12 myotubes by activating the PI3K/AKT signaling pathway.

Serum neuregulin 4 is negatively correlated with insulin sensitivity in humans and impairs mitochondrial respiration in HepG2 cells

Neuregulin 4 (NRG4) has been described to improve metabolic disturbances linked to obesity status in rodent models. The findings in humans are controversial. We aimed to investigate circulating NRG4 in association with insulin action in humans and the possible mechanisms involved. Insulin sensitivity (euglycemic hyperinsulinemic clamp) and serum NRG4 concentration (ELISA) were analysed in subjects with a wide range of adiposity (n = 89). In vitro experiments with human HepG2 cell line were also performed. Serum NRG4 was negatively correlated with insulin sensitivity (r = −0.25, p = 0.02) and positively with the inflammatory marker high-sensitivity C reative protein (hsCRP). In fact, multivariant linear regression analyses showed that insulin sensitivity contributed to BMI-, age-, sex-, and hsCRP-adjusted 7.2% of the variance in serum NRG4 (p = 0.01). No significant associations were found with adiposity measures (BMI, waist circumference or fat mass), plasma lipids (HDL-, LDL-cholesterol, or fasting triglycerides) or markers of liver injury. Cultured hepatocyte HepG2 treated with human recombinant NRG4 had an impact on hepatocyte metabolism, leading to decreased gluconeogenic- and mitochondrial biogenesis-related gene expression, and reduced mitochondrial respiration, without effects on expression of lipid metabolism-related genes. Similar but more pronounced effects were found after neuregulin 1 administration. In conclusion, sustained higher serum levels of neuregulin-4, observed in insulin resistant patients may have deleterious effects on metabolic and mitochondrial function in hepatocytes. However, findings from in vitro experiments should be confirmed in human primary hepatocytes.

Reduction in the Dietary VA Status Prevents Type 2 Diabetes and Obesity in Zucker Diabetic Fatty Rats

We hypothesized that the vitamin A (VA) status regulates type 2 diabetes (T2D) development in Zucker diabetic fatty (ZDF) rats. Zucker Lean and ZDF rats at weaning were fed a VA deficient with basal fat (VAD-BF, no VA and 22.1% fat energy), VA marginal with BF (VAM-BF, 0.35 mg retinyl palmitate (RP)/kg), VA sufficient with BF (VAS-BF, 4.0 mg RP/kg), VAD with high fat (VAD-HF, 60% fat energy), VAM-HF or VAS-HF diet for 8 weeks, including an oral glucose tolerance test (OGTT) at week 7.5. The hepatic mRNA and proteins levels were determined using real-time PCR and Western blot, respectively. The VAD-BF/HF and VAM-BF/HF diets prevented peripheral hyperglycemia and attenuated obesity in ZDF rats, which occurred in the presence of the VAS-BF/HF diets. This lowered VA status reduced venous blood hyperglycemia, hyperinsulinemia and hyperlipidemia, and improved OGTT and homeostasis model assessment for insulin resistance results in ZDF rats. The expression levels of key hepatic genes for glucose and fat metabolism were regulated by VA status and dietary fat contents. An interaction between VA and HF condition was also observed. We conclude that the reduction in the dietary VA status in both BF and HF conditions prevents T2D and obesity in ZDF rats.

Leptin Receptor-Deficient db/db Mice Show Significant Heterogeneity in Response to High Non-heme Iron Diet

Recent studies have shown an association between iron homeostasis, obesity and diabetes. In this work, we investigated the differences in the metabolic status and inflammation in liver, pancreas and visceral adipose tissue of leptin receptor-deficient db/db mice dependent on high iron concentration diet. 3-month-old male BKS-Leprdb/db/JOrlRj (db/db) mice were divided into two groups, which were fed with different diets containing high iron (29 g/kg, n = 57) or standard iron (0.178 g/kg; n = 42) concentrations for 4 months. As anticipated, standard iron-fed db/db mice developed obesity and diabetes. However, high iron-fed mice exhibited a wide heterogeneity. By dividing into two subgroups at the diabetes level, non-diabetic subgroup 1 (<13.5 mmol/l, n = 30) significantly differed from diabetic subgroup two (>13.5 mmol/l, n = 27). Blood glucose concentration, HbA1c value, inflammation markers interleukin six and tumor necrosis factor α and heme oxygenase one in visceral adipose tissue were reduced in subgroup one compared to subgroup two. In contrast, body weight, C-peptide, serum insulin and serum iron concentrations, pancreatic islet and signal ratio as well as cholesterol, LDL and HDL levels were enhanced in subgroup one. While these significant differences require further studies and explanation, our results might also explain the often-contradictory results of the metabolic studies with db/db mice.

Neuregulins: protective and reparative growth factors in multiple forms of cardiovascular disease

Neuregulins (NRGs) are protein ligands that act through ErbB receptor tyrosine kinases to regulate tissue morphogenesis, plasticity, and adaptive responses to physiologic needs in multiple tissues, including the heart and circulatory system. The role of NRG/ErbB signaling in cardiovascular biology, and how it responds to physiologic and pathologic stresses is a rapidly evolving field. While initial concepts focused on the role that NRG may play in regulating cardiac myocyte responses, including cell survival, growth, adaptation to stress, and proliferation, emerging data support a broader role for NRGs in the regulation of metabolism, inflammation, and fibrosis in response to injury. The constellation of effects modulated by NRGs may account for the findings that two distinct forms of recombinant NRG-1 have beneficial effects on cardiac function in humans with systolic heart failure. NRG-4 has recently emerged as an adipokine with similar potential to regulate cardiovascular responses to inflammation and injury. Beyond systolic heart failure, NRGs appear to have beneficial effects in diastolic heart failure, prevention of atherosclerosis, preventing adverse effects on diabetes on the heart and vasculature, including atherosclerosis, as well as the cardiac dysfunction associated with sepsis. Collectively, this literature supports the further examination of how this developmentally critical signaling system functions and how it might be leveraged to treat cardiovascular disease.

Effects of obesity and diabesity on heart rhythm in the Zucker rat

Obesity and type 2 diabetes mellitus are risk factors for hypertension, coronary heart disease, cardiac arrhythmias including atrial fibrillation, heart failure and sudden cardiac death. The effects of obesity and diabesity on heart rhythm were investigated in the Zucker diabetic fatty (ZDF) and Zucker fatty (ZF) compared to the Zucker lean (ZL) control rat. In vivo biotelemetry techniques were used to assess the electrocardiogram and other cardiac and metabolic parameters. ZDF rats were characterized by age-dependent elevations in fasting and non-fasting blood glucose, glucose intolerance and weight gain and ZF rats were characterized by smaller elevations in fasting and non-fasting blood glucose and greater weight gain compared to ZL rats. Heart rate (HR) was progressively reduced in ZDF, ZF and ZL rats. At 195 days (6.5 months) of age there were significant differences in HR between ZDF (265 ± 8 bpm, n = 10), ZF (336 ± 9 bpm, n = 10) and ZL (336 ± 10 bpm, n = 10) rats and significant differences in HRV between ZDF (22 ± 1 bpm, n = 10), ZF (27 ± 1 bpm, n = 10) and ZL (31 ± 1 bpm, n = 10) rats. Power spectral analysis revealed no significant (P > 0.05) differences in HRV at low frequencies, reduced HRV at high frequencies and increased sympathovagal balance in ZDF compared to ZF and ZL rats. HR was reduced by ageing and additionally reduced by diabesity in the absence of changes in physical activity and body temperature. Reductions in HRV associated with altered sympathovagal drive might partly underlie disturbed HR in the ZDF rat. Possible explanations for reduced HR and future mechanistic studies are discussed.

Roles and mechanisms of NRG1 in modulating the pathogenesis of NAFLD through ErbB3 signaling in hepatocytes (NRG1 modulates NAFLD through ErbB3 signaling)

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is an emerging chronic liver disease. However, the underlying mechanisms remained poorly understood. Neuregulin (NRG) family participate in energy metabolism, and might be related to NAFLD.

METHODS

L02 cells were exposed to oleic acid to establish a cellular model of NAFLD. We analyzed the NAFLD cells with NRG1 and subsequent ErbB3 siRNA treatment. Cellular total lipid was stained by Oil Red O, while triglyceride content and inflammation markers were measured by enzymatic kits. The expressions of down-stream molecules were evaluated by western blot.

RESULTS

In vitro, NRG1 could alleviate the steatosis of NAFLD, and inhibit the expression of IL-6 and TNF-α. The downregulation of ErbB3 aggravated steatosis, improved the levels of triglyceride, IL-6 and TNF-α in NRG1-treated NAFLD. Moreover, NRG1 treatment up-regulated ErbB3 phosphorylation, and increased the expression of PI3K and phosphorylation-AKT. When NRG1-treated NAFLD cells were transfected with ErbB3 siRNA, the expressions of ErbB3, p-ErbB3, p-AKT and PI3K were all reduced.

CONCLUSION

NRG1 might play a protective role in the pathogenesis of NAFLD through ErbB3 phosphorylation to modulate the activation of PI3K-AKT pathway. The findings will expand the understanding of the mechanisms of NAFLD, and provide potential therapeutic targets.

Neuregulin 1 treatment improves glucose tolerance in diabetic db/db mice, but not in healthy mice

Context: Neuregulin 1 (NRG1) and ErbB receptors are involved in glucose homeostasis. However, the effects of the neuregulin 1-ErbB pathway activation on glucose metabolism in liver are controversial.Objective: Assess NRG1 and ErbB signalling in liver and the effects of 8-week treatment with NRG1 on glucose homeostasis in diabetic db/db mice and in control healthy mice.Results: NRG1 improved glucose, insulin and insulin sensitivity index during OGTT in db/db mice, but not in control mice. Compared with healthy mice, phosphorylation of p38, ErbB-1 and ErbB-3 was increased in diabetic mice, and neuregulin 1 treatment increased phosphorylation of p38 and ErbB-4. Conversely, the AKT/FOXO1 pathway was not affected by the 8-week treatment with NRG1.Conclusion: Diabetic mice showed altered NRG1-ErbB pathway in the liver compared with healthy mice. Moreover, chronic NRG1 treatment increased p38 phosphorylation in liver and improved glucose tolerance in diabetic mice, but not in control mice.

Neuregulin, an Effector on Mitochondria Metabolism That Preserves Insulin Sensitivity

Various external factors modulate the metabolic efficiency of mitochondria. This review focuses on the impact of the growth factor neuregulin and its ErbB receptors on mitochondria and their relationship with several physiopathological alterations. Neuregulin is involved in the differentiation of heart, skeletal muscle, and the neuronal system, among others; and its deficiency is deleterious for the health. Information gathered over the last two decades suggests that neuregulin plays a key role in regulating the mitochondrial oxidative machinery, which sustains cell survival and insulin sensitivity.

Mechanisms of the Multitasking Endothelial Protein NRG-1 as a Compensatory Factor During Chronic Heart Failure

Heart failure is a complex syndrome whose phenotypic presentation and disease progression depends on a complex network of adaptive and maladaptive responses. One of these responses is the endothelial release of NRG (neuregulin)-1—a paracrine growth factor activating ErbB2 (erythroblastic leukemia viral oncogene homolog B2), ErbB3, and ErbB4 receptor tyrosine kinases on various targets cells. NRG-1 features a multitasking profile tuning regenerative, inflammatory, fibrotic, and metabolic processes. Here, we review the activities of NRG-1 on different cell types and organs and their implication for heart failure progression and its comorbidities. Although, in general, effects of NRG-1 in heart failure are compensatory and beneficial, translation into therapies remains unaccomplished both because of the complexity of the underlying pathways and because of the challenges in the development of therapeutics (proteins, peptides, small molecules, and RNA-based therapies) for tyrosine kinase receptors. Here, we give an overview of the complexity to be faced and how it may be tackled.

Neuregulin 4 Is a Novel Marker of Beige Adipocyte Precursor Cells in Human Adipose Tissue

Background: Nrg4 expression has been linked to brown adipose tissue activity and browning of white adipocytes in mice. Here, we aimed to investigate whether these observations could be translated to humans by investigating NRG4 mRNA and markers of brown/beige adipocytes in human visceral (VAT) and subcutaneous adipose tissue (SAT). We also studied the possible association of NRG4 with insulin action.

Methods: SAT and VAT NRG4 and markers of brown/beige (UCP1, UCP3, and TMEM26)-related gene expression were analyzed in two independent cohorts (n = 331 and n = 59). Insulin resistance/sensitivity was measured using HOMA_IR and glucose infusion rate during euglycemic hyperinsulinemic clamp.

Results: In both cohort 1 and cohort 2, NRG4 and thermogenic/beige-related gene expression were significantly increased in VAT compared to SAT. Adipogenic-related genes followed an opposite pattern. In cohort 1, VAT NRG4 gene expression was positively correlated with BMI and expression of UCP1, UCP3, TMEM26, and negatively with adipogenic (FASN, PPARG, and SLC2A4)- and inflammatory (IL6 and IL8)-related genes. In SAT, NRG4 gene expression was negatively correlated with HOMA_IR and positively with UCP1 and TMEM26 gene expression. Multiple linear regression analysis revealed that expression of TMEM26 gene was the best predictor of NRG4 gene expression in both VAT and SAT. Specifically, NRG4 and TMEM26 gene expression was significantly increased in VAT, but not in SAT stromal vascular fraction cells (p < 0.001). In cohort 2, the significant association between NRG4 and TMEM26 gene expression in both VAT and SAT was confirmed, and SAT NRG4 gene expression also was positively correlated with insulin action and the expression of UCP1.

Conclusion: Current findings suggest NRG4 gene expression as a novel marker of beige adipocytes in human adipose tissue.

ErbB4 deletion predisposes to development of metabolic syndrome in mice

ErbB4, a member of the EGF receptor family, plays a variety of roles in physiological and pathological states. Genetic studies have indicated a link between ErbB4 and type 2 diabetes and obesity, but its role in metabolic syndrome (MetS) has not been reported. In the current study we found that mice with ErbB4 deletion developed MetS after 24 wk on a medium-fat diet (MFD), as indicated by development of obesity, dyslipidemia, hepatic steatosis, hyperglycemia, hyperinsulinemia, and insulin resistance, compared with wild-type mice. ErbB4 deletion mice also exhibited increased amounts of subcutaneous and visceral fat, with increased serum leptin levels, compared with wild-type mice, whereas levels of adiponectin were not significantly different. Histologically, severe inflammation, indicated by F4/80 immunostaining and M1 macrophage polarization, was detected in inguinal and epididymal white adipose tissue in ErbB4 deletion mice. ErbB4 expression decreased during 3T3-L1 preadipocyte differentiation. Administration of neuroregulin 4, a specific ligand for ErbB4, to 3T3-L1 adipocytes had no effect on adipogenesis and lipolysis but significantly inhibited lipogenesis, promoted browning, induced GLUT4 redistribution to the cell membrane, and increased glucose uptake. Neuroregulin 4 also significantly increased glucose uptake in adipocytes isolated from wild-type mice, while these effects were significantly decreased in adipocytes isolated from ErbB4 deletion mice. In conclusion, our results indicate that ErbB4 may play an important role in glucose homeostasis and lipogenesis. ErbB4 deficiency-related obesity and adipose tissue inflammation may contribute to the development of MetS.

Species-specific effects of neuregulin-1β (cimaglermin alfa) on glucose handling in animal models and humans with heart failure

Neuregulin-1β is a member of the neuregulin family of growth factors and is critically important for normal development and functioning of the heart and brain. A recombinant version of neuregulin-1β, cimaglermin alfa (also known as glial growth factor 2 or GGF2) is being investigated as a possible therapy for heart failure. Previous studies suggest that neuregulin-1β stimulation of skeletal muscle increases glucose uptake and, specifically, sufficient doses of cimaglermin alfa acutely produce hypoglycemia in pigs. Since acute hypoglycemia could be a safety concern, blood glucose changes in the above pig study were further investigated. In addition, basal glucose and glucose disposal were investigated in mice. Finally, as part of standard clinical chemistry profiling in a single ascending-dose human safety study, blood glucose levels were evaluated in patients with heart failure after cimaglermin alfa treatment. A single intravenous injection of cimaglermin alfa at doses of 0.8mg/kg and 2.6mg/kg in mice resulted in a transient reduction of blood glucose concentrations of approximately 20% and 34%, respectively, at 2h after the treatment compared to pre-treatment levels. Similar results were observed in diabetic mice. Treatment with cimaglermin alfa also increased blood glucose disposal following oral challenge in mice. However, no significant alterations in blood glucose concentrations were found in human heart failure patients at 0.5 and 2h after treatment with cimaglermin alfa over an equivalent human dose range, based on body surface area. Taken together, these data indicate strong species differences in blood glucose handling after cimaglermin alfa treatment, and particularly do not indicate that this phenomenon should affect human subjects.

Intrinsic and Antipsychotic Drug-Induced Metabolic Dysfunction in Schizophrenia

For decades, there have been observations demonstrating significant metabolic disturbances in people with schizophrenia including clinically relevant weight gain, hypertension, and disturbances in glucose and lipid homeostasis. Many of these findings pre-date the use of antipsychotic drugs (APDs) which on their own are also strongly associated with metabolic side effects. The combination of APD-induced metabolic changes and common adverse environmental factors associated with schizophrenia have made it difficult to determine the specific contributions of each to the overall metabolic picture. Data from drug-naïve patients, both from the pre-APD era and more recently, suggest that there may be an intrinsic metabolic risk associated with schizophrenia. Nevertheless, these findings remain controversial due to significant clinical variability in both psychiatric and metabolic symptoms throughout patients' disease courses. Here, we provide an extensive review of classic and more recent literature describing the metabolic phenotype associated with schizophrenia. We also suggest potential mechanistic links between signaling pathways associated with schizophrenia and metabolic dysfunction. We propose that, beyond its symptomatology in the central nervous system, schizophrenia is also characterized by pathophysiology in other organ systems directly related to metabolic control.

Nrg4 promotes fuel oxidation and a healthy adipokine profile to ameliorate diet-induced metabolic disorders

Objective

Brown and white adipose tissue exerts pleiotropic effects on systemic energy metabolism in part by releasing endocrine factors. Neuregulin 4 (Nrg4) was recently identified as a brown fat-enriched secreted factor that ameliorates diet-induced metabolic disorders, including insulin resistance and hepatic steatosis. However, the physiological mechanisms through which Nrg4 regulates energy balance and glucose and lipid metabolism remain incompletely understood. The aims of the current study were: i) to investigate the regulation of adipose Nrg4 expression during obesity and the physiological signals involved, ii) to elucidate the mechanisms underlying Nrg4 regulation of energy balance and glucose and lipid metabolism, and iii) to explore whether Nrg4 regulates adipose tissue secretome gene expression and adipokine secretion.

Methods

We examined the correlation of adipose Nrg4 expression with obesity in a cohort of diet-induced obese mice and investigated the upstream signals that regulate Nrg4 expression. We performed metabolic cage and hyperinsulinemic-euglycemic clamp studies in Nrg4 transgenic mice to dissect the metabolic pathways regulated by Nrg4. We investigated how Nrg4 regulates hepatic lipid metabolism in the fasting state and explored the effects of Nrg4 on adipose tissue gene expression, particularly those encoding secreted factors.

Results

Adipose Nrg4 expression is inversely correlated with adiposity and regulated by pro-inflammatory and anti-inflammatory signaling. Transgenic expression of Nrg4 increases energy expenditure and augments whole body glucose metabolism. Nrg4 protects mice from diet-induced hepatic steatosis in part through activation of hepatic fatty acid oxidation and ketogenesis. Finally, Nrg4 promotes a healthy adipokine profile during obesity.

Conclusions

Nrg4 exerts pleiotropic beneficial effects on energy balance and glucose and lipid metabolism to ameliorate obesity-associated metabolic disorders. Biologic therapeutics based on Nrg4 may improve both type 2 diabetes and non-alcoholic fatty liver disease (NAFLD) in patients.

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Nrg4 is a target of pro-inflammatory and anti-inflammatory signaling in adipocytes.

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Transgenic expression of Nrg4 increased energy expenditure and glucose metabolism.

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Nrg4 stimulates hepatic fatty acid oxidation and ketogenesis during starvation.

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Nrg4 promotes a beneficial adipokine profile during obesity.

Neuregulin 1 improves complex 2-mediated mitochondrial respiration in skeletal muscle of healthy and diabetic mice

It has been reported that neuregulin1 (NRG1) improves glucose tolerance in healthy and diabetic rodents. In vitro studies also suggest that NRG1 regulates myocyte oxidative capacity. To confirm this observation in vivo, we evaluated the effect on mitochondrial function of an 8-week treatment with NRG1 in db/db diabetic mice and C57BL/6JRJ healthy controls. NRG1 treatment improved complex 2-mediated mitochondrial respiration in the gastrocnemius of both control and diabetic mice and increased mitochondrial complex 2 subunit content by 2-fold. This effect was not associated with an increase in mitochondrial biogenesis markers. Enhanced ERBB4 phosphorylation could mediate NRG1 effects on mitochondrial function through signalling pathways, independently of ERK1/2, AKT or AMPK.

Type I neuregulin1α is a novel local mediator to suppress hepatic gluconeogenesis in mice

Neuregulin1 is an epidermal growth factor (EGF)-like domain-containing protein that has multiple isoforms and functions as a local mediator in the control of various cellular functions. Here we show that type I isoform of neuregulin1 with an α-type EGF-like domain (Nrg1α) is the major isoform in mouse liver and regulates hepatic glucose production. Forced expression of Nrg1α in mouse liver enhanced systemic glucose disposal and decreased hepatic glucose production with reduced fasting blood glucose levels. Nuclear forkhead box protein O1 (FoxO1) and its downstream targets, PEPCK and G6Pase, were suppressed in liver and isolated hepatocytes by Nrg1α overexpression. In contrast, silencing of Nrg1α enhanced glucose production with increased PEPCK and G6Pase expressions in cAMP/dexamethasone-stimulated hepatocytes. Mechanistically, the recombinant α-type EGF-like domain of NRG1α (rNRG1α) stimulated the ERBB3 signalling pathway in hepatocytes, resulting in decreased nuclear FoxO1 accumulation via activation of both the AKT and ERK pathways. In addition, acute treatment with rNRG1α also suppressed elevation of blood glucose levels after both glucose and pyruvate challenge. Although a liver-specific deletion of Nrg1 gene in mice showed little effect on systemic glucose metabolism, these results suggest that NRG1α have a novel regulatory function in hepatic gluconeogenesis by regulating the ERBB3-AKT/ERK-FoxO1 cascade.