The neuregulin system of ligands and their receptors in rat islets of langerhans

Novel secreted regulators of glucose and lipid metabolism in the development of metabolic diseases

The tight regulation of glucose and lipid metabolism is crucial for maintaining metabolic health. Dysregulation of these processes can lead to the development of metabolic diseases. Secreted factors, or hormones, play an essential role in the regulation of glucose and lipid metabolism, thus also playing an important role in the development of metabolic diseases such as type 2 diabetes and obesity. Given the important roles of secreted factors, there has been significant interest in identifying new secreted factors and new functions for existing secreted factors that control glucose and lipid metabolism. In this review, we evaluate novel secreted factors or novel functions of existing factors that regulate glucose and lipid metabolism discovered in the last decade, including secreted isoform of endoplasmic reticulum membrane complex subunit 10, vimentin, cartilage intermediate layer protein 2, isthmin-1, lipocalin-2, neuregulin-1 and neuregulin-4. We discuss their discovery, tissues of origin, mechanisms of action and sex differences, emphasising their potential to regulate metabolic processes central to diabetes. Additionally, we discuss the translational barriers, particularly the absence of identified receptors, that hamper their functional characterisation and further therapeutic development. Ultimately, the identification of new secreted factors may give insights into previously unidentified pathways of disease progression and mechanisms of glucose and lipid homeostasis.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Leukocyte Telomere Length and Neuregulin-4 Levels in Female Patients with Acromegaly: The Relationship between Disease Activity and Body Fat Distribution

The study aimed to examine leukocyte telomere length (LTL) and serum neuregulin-4 levels and their relationship with disease activity, co-morbidities and body fat distribution in female acromegaly patients. Forty female patients with acromegaly and thirty-nine age and body mass index (BMI) similar healthy female volunteers were included in the study. Patients were classified into two groups: active acromegaly (AA) and controlled acromegaly (CA). The quantitative polymerase chain reaction (PCR) method was used to study LTL, and T/S ratio < 1 was accepted as shortened telomere length. Neuregulin-4 was studied by ELISA. There was no difference in median LTL between acromegaly and the control group (p = 0.530). The percentage of T/S < 1 in patients with acromegaly (60.0%) was similar to that of the control group (43.6%) (p = 0.144). However, serum neuregulin-4 was significantly higher in patients with acromegaly than those in the control group (p = 0.037). There were no significant differences concerning LTL, percentage of T/S < 1 and neuregulin-4 levels between active and controlled acromegaly groups (p > 0.05). Neuregulin-4 correlated positively with fasting glucose, triglyceride (TG), triglyceride/glucose (TyG) index, and lean body mass in the acromegaly group. A negative correlation was observed between LTL and neuregulin-4 in the control group (p = 0.039). When the factors affecting neuregulin-4 were evaluated by multivariate linear regression analysis with an enter method, TG (β: 0.316, p = 0.025) was independently and positively associated with neuregulin-4. Our findings indicate that acromegaly is associated with unchanged LTL and high neuregulin-4 levels in female patients. However, the relationship between acromegaly, the aging process, and neuregulin-4 involves complex mechanisms, and further studies are needed.

Correlation of asprosin and Nrg-4 with type 2 diabetes Mellitus Complicated with Coronary Heart Disease and the Diagnostic Value

PURPOSE

Asprosin is a newly discovered adipose factor secreted by white fat, which is involved in glucose metabolism and inflammation. Neuregulin-4 (Nrg-4) is a new adipose factor released from brown adipose tissue and is considered to play an important role in metabolism. This study aims to explore the association between serum Asprosin, Nrg-4 level and coronary heart disease(CHD) in patients with type 2 diabetes mellitus(T2DM) and the diagnostic value.

PATIENTS AND METHODS

157 patients with T2DM were enrolled from Affiliated Hospital of Chengde Medical University between December 2020 to July 2021. These patients were divided into T2DM without CHD group (T2DM-0, n = 80) and T2DM with CHD (T2DM-CHD, n = 77). Serum Asprosin and Nrg-4 expression was detected by enzyme-linked immunosorbent assay, and the correlations between Asprosin or Nrg-4 and clinical and biochemical indicators were analyzed. A receiver operating characteristics curve analysis and area under the curve (AUC) were used to evaluate diagnostic accuracy.

RESULTS

Serum Asprosin level of the T2DM-CHD group were significantly higher and Nrg-4 level significantly lower than those of the T2DM-0 group.Spearman correlation analysis showed that serum Asprosin levels were significantly positively correlated with diabetes course,history of hypertension, fasting plasma glucose(FPG), glycosylated hemoglobin A1c(HbA1C), triglycerides(TG),triglyceride glucose index(TyG index) and urea, and negatively correlated with ALT (all p < 0.05). Nrg-4 was negatively correlated with history of hypertension, body mass index(BMI), FPG, HbA1C, TG, and TyG indexes (all p < 0.05), and positively correlated with high-density lipoprotein cholesterol(HDL-C)(p < 0.05).Logistic regression analysis showed that after adjusting potential confounders, Asprosin was a risk factor for diabetes mellitus, Nrg-4 was a protective factor.The AUC of Asprosin for diagnosing T2DM-CHD was 0.671 (95% confidence interval [CI] 0.584-0.759), and the AUC of the Nrg4 index for diagnosing T2DM-CHD was 0.772 (95% CI 0.700-0.844). The AUC of Asprosin and Nrg-4 for the combined diagnosis of T2DM-CHD was 0.796 (95% CI 0.726-0.864).

CONCLUSION

Asprosin and Nrg-4 may be novel diagnostic biomarkers for T2DM with CHD, as they effectively improved the diagnostic accuracy for T2DM-CHD.

Neuregulin 4 as a novel adipokine in energy metabolism

Adipose tissue has been shown to play a key role in energy metabolism and it has been shown to regulate metabolic homeostasis through the secretion of adipokines. Neuregulin 4 (Nrg4), a novel adipokine secreted mainly by brown adipose tissue (BAT), has recently been characterized as having an important effect on the regulation of energy homeostasis and glucolipid metabolism. Nrg4 can modulate BAT-related thermogenesis by increasing sympathetic innervation of adipose tissue and therefore has potential metabolic benefits. Nrg4 improves metabolic dysregulation in various metabolic diseases such as insulin resistance, obesity, non-alcoholic fatty liver disease, and diabetes through several mechanisms such as anti-inflammation, autophagy regulation, pro-angiogenesis, and lipid metabolism normalization. However, inconsistent findings are found regarding the effects of Nrg4 on metabolic diseases in clinical settings, and this heterogeneity needs to be further clarified by future studies. The potential metabolic protective effect of Nrg4 suggests that it may be a promising endocrine therapeutic target.

New Discovered Adipokines Associated with the Pathogenesis of Obesity and Type 2 Diabetes

Obesity is defined as abnormal or excessive accumulation of adipose tissue, closely associated with the increased risk of various comorbidities, especially type 2 diabetes mellitus (T2DM). Adipose tissue is a complex structure responsible for not only fat storage but also releasing adipokines which may play roles in the pathogenesis and could be developed into biomarkers for diagnosis, treatment and prognosis of obesity-related metabolic diseases. This review aims to summarize several adipokines discovered recently that have promising functions in obesity and T2DM. Among them, the levels of FSTL1, WISP1 and Asprosin in subjects with obesity or diabetes are commonly higher than in normal controls, suggesting that they may be pathogenic. Inversely, SFRP5, Metrnl, NRG4 and FAM19A5 may serve as the protective factors.

Regulation of Energy Metabolism by Receptor Tyrosine Kinase Ligands

Metabolic diseases, such as diabetes, obesity, and fatty liver disease, have now reached epidemic proportions. Receptor tyrosine kinases (RTKs) are a family of cell surface receptors responding to growth factors, hormones, and cytokines to mediate a diverse set of fundamental cellular and metabolic signaling pathways. These ligands signal by endocrine, paracrine, or autocrine means in peripheral organs and in the central nervous system to control cellular and tissue-specific metabolic processes. Interestingly, the expression of many RTKs and their ligands are controlled by changes in metabolic demand, for example, during starvation, feeding, or obesity. In addition, studies of RTKs and their ligands in regulating energy homeostasis have revealed unexpected diversity in the mechanisms of action and their specific metabolic functions. Our current understanding of the molecular, biochemical and genetic control of energy homeostasis by the endocrine RTK ligands insulin, FGF21 and FGF19 are now relatively well understood. In addition to these classical endocrine signals, non-endocrine ligands can govern local energy regulation, and the intriguing crosstalk between the RTK family and the TGFβ receptor family demonstrates a signaling network that diversifies metabolic process between tissues. Thus, there is a need to increase our molecular and mechanistic understanding of signal diversification of RTK actions in metabolic disease. Here we review the known and emerging molecular mechanisms of RTK signaling that regulate systemic glucose and lipid metabolism, as well as highlighting unexpected roles of non-classical RTK ligands that crosstalk with other receptor pathways.

A systematic review of the association of neuregulin 4, a brown fat-enriched secreted factor, with obesity and related metabolic disturbances

Neuregulin 4 (Nrg4), a novel brown fat-enriched hormone, plays a key role in the modulation of glucose and lipid metabolism and energy balance. Recent data have demonstrated that the expression of Nrg4 is substantially down-regulated in mouse and human obesity, making its regulatory aspect intriguing. Because of the close relationship between Nrg4, obesity, and associated metabolic diseases, this systematic review aimed to assess the association of Nrg4 with obesity and related metabolic disturbances, emphasizing its possible mechanisms of action in these disorders. We searched PubMed/Medline, ScienceDirect, Scopus, EMBASE, ProQuest, and Google Scholar up until June 2019. The evidence reviewed here indicates that Nrg4 may contribute to the prevention of obesity and related metabolic complications by elevating brown adipose tissue activity, increasing the expression of thermogenic markers, decreasing the expression of lipogenic/adipogenic genes, exacerbating white adipose tissue browning, increasing the number of brite/beige adipocytes, promoting hepatic fat oxidation and ketogenesis, inducing neurite outgrowth, enhancing blood vessels in adipose tissue, increasing the circulatory levels of healthy adipokines, and improving glucose homeostasis. Thus, Nrg4 appears to be a novel therapeutic strategy for the treatment of obesity and associated metabolic complications. However, prospective cohort studies are warranted to confirm these outcomes.

Association between circulating neuregulin4 levels and diabetes mellitus: A meta-analysis of observational studies

INTRODUCTION

Neuregulin 4 (Nrg4) was proven as a brown fat-enriched secreted factor that can regulate glucose and lipid metabolism. However, the association between circulating Nrg4 levels and diabetes mellitus (DM) in human remains unclear. We conducted a meta-analysis to investigate association of circulating Nrg4 with DM.

METHODS

Observational studies comparing circulating Nrg4 levels in diabetes patients and health controls were included. Circulating Nrg4, correlation coefficients of clinical indices and circulating Nrg4 were pooled by meta-analysis.

RESULTS

Seven studies were included. The pooled results indicated there were no significant difference in the circulating Nrg4 between diabetes patients and controls (SMD = 0.18, 95%CI = -0.06 to 0.42, P = 0.143). However, diabetes patients had higher circulating Nrg4 than their controls in cross-sectional studies (SMD = 0.55, 95%CI = 0.36 to 0.73, P<0.001). None of the renal function and metabolic syndrome markers were correlated with circulating Nrg4, whereas the HbA1c and BMI were positively correlated (rs = 0.09, 95%CI = 0.03 to 0.16, P = 0.005; rs = 0.20, 95%CI = 0.07 to 0.34, P = 0.003; respectively).

CONCLUSION

Our findings suggested circulating Nrg4 may play a role in in the development of DM in cross-sectional studies and circulating Nrg4 might be associated with imbalance in glucose metabolism and obesity.

Association of Circulating Neuregulin-4 with Presence and Severity of Coronary Artery Disease

Neuregulin-4 (Nrg4) is a newly discovered adipokine that is synthesized in many tissues and plays an important role in modulating systemic energy metabolism and in the development of metabolic disorders. However, little is known about the relationship between Nrg4 and coronary artery disease (CAD). In this study, we investigated the association between Nrg4 and the presence and severity of CAD.We enrolled 73 patients diagnosed by coronary angiography (CAG) as having CAD and 32 controls. The CAD group was divided into two subgroups according to their SYNTAX score. Plasma levels of Nrg4 were measured in all participants and compared among different groups. The relationship between Nrg4 and CAD was analyzed. Receiver operating characteristic (ROC) analysis was conducted to evaluate the usefulness Nrg4 in assessing the presence and severity of CAD.Nrg4 levels were negatively associated with the SYNTAX score (r = -0.401, P = 0.000). The patients with a higher SYNTAX score had significantly lower Nrg4 levels as compared with the low SYNTAX score subgroup and the controls (P < 0.05). The Nrg4 levels of the low SYNTAX score subgroup were much lower than controls (P < 0.05). Furthermore, an association between Nrg4 and CAD (odds ratio, 0.279; 95% confidence interval, 0.088-0.882) was observed. Nrg4 had 43.8% sensitivity and 96.9% specificity for identifying CAD, and 73.1% sensitivity and 87.3% specificity for identifying patients who had severe coronary artery lesions.Nrg4 levels were found to be inversely associated with the presence and severity of CAD.

Plasma Neuregulin 4 Levels Are Associated with Metabolic Syndrome in Patients Newly Diagnosed with Type 2 Diabetes Mellitus

Neuregulin 4 (Nrg4) has been proposed to play a role in the pathogeneses of obesity, insulin resistance, and dyslipidemia. However, information about the link between Nrg4 and metabolic syndrome (MetS) is scarce, especially in patients with newly diagnosed type 2 diabetes mellitus (nT2DM). This study aimed at investigating whether Nrg4 is associated with MetS in nT2DM patients. A total of 311 patients with nT2DM were recruited. Plasma Nrg4 concentration was determined by ELISA. Plasma Nrg4 concentration was lower in nT2DM patients with MetS than in nT2DM patients without MetS (P = 0.001). Nrg4 concentration showed negative correlations with most of the analyzed indicators of MetS. MetS was less prevalent among subjects in the highest quartile of plasma Nrg4 concentration than among those in the lowest quartile (P < 0.01). Age- and sex-adjusted plasma Nrg4 concentrations were positively correlated with concentrations of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A (both P < 0.05) and negatively correlated with triglyceride, high-sensitivity C-reactive protein (hs-CRP), and gamma-glutamyltransferase concentrations, neutrophil count, and white blood cell (WBC) count (all P < 0.05). In multivariate analysis, Nrg4 was independently associated with hs-CRP level, WBC count, and HDL-C level (P = 0.001 or P < 0.05). Multiple logistic regression analysis of MetS prediction by Nrg4 revealed an odds ratio of 0.560 (95% CI: 0.374-0.837; P < 0.01). Decreased plasma Nrg4 levels, which may be associated with augmented oxidative stress, inflammation, and dyslipidemia, might be involved in the development of MetS in nT2DM patients.

Nonalcoholic Fatty Liver Disease Progresses into Severe NASH when Physiological Mechanisms of Tissue Homeostasis Collapse

Phenotypic modulation of NAFLD-severity by molecules derived from white (adipokines) and brown (batokines) adipose tissue may be important in inducing or protecting against the progression of the disease. Adipose tissue-derived factors can promote the progression of NAFLD towards severe histological stages (NASH-fibrosis and NASHcirrhosis). This effect can be modulated by the release of adipokines or batokines that directly trigger an inflammatory response in the liver tissue or indirectly modulate related phenotypes, such as insulin resistance. Metabolically dysfunctional adipose tissue, which is often infiltrated by macrophages and crown-like histological structures, may also show impaired production of anti-inflammatory cytokines, which may favor NAFLD progression into aggressive phenotypes by preventing its protective effects on the liver tissue.

Decreased plasma neuregulin 4 concentration is associated with increased high-sensitivity C-reactive protein in newly diagnosed type 2 diabetes mellitus patients: a cross-sectional study

AIMS

Inflammation has been reported to be involved in the pathogenesis of atherosclerosis. This principal objective of this study was to investigate if the secretion of neuregulin 4 (Nrg4), a soluble protein associated with metabolic syndrome and subclinical cardiovascular disease, is correlated with the inflammation marker high-sensitivity C-reactive protein (hs-CRP) in patients with newly diagnosed type 2 diabetes mellitus (nT2DM).

METHODS

A study group of 311 nT2DM patients was divided into three subgroups based on hs-CRP tertiles. Multiple linear regression was conducted to explore the association between plasma Nrg4 and hs-CRP levels.

RESULTS

The nT2DM patients with the highest hs-CRP levels (>2.46 mg/L) exhibited higher atherogenic coefficients and atherogenic index of plasma (AIP) levels, but lower levels of plasma Nrg4, as compared to those with the lowest hs-CRP levels (<0.63 mg/L). Plasma Nrg4 levels were inversely associated with white blood cell count, hs-CRP, and AIP and positively associated with high-density lipoprotein cholesterol (HDL-C), before and after adjustment for age, gender, body mass index (BMI), and body fat percentage (P < 0.01 or P < 0.05). hs-CRP was the factor most strongly associated with plasma Nrg4 levels.

CONCLUSIONS

These results indicate that lower plasma Nrg4 levels may be associated with elevated hs-CRP in nT2DM patients. It generates the hypothesis that decreased levels of Nrg4 may trigger the development of atherosclerosis through its proinflammatory effects. These findings need to be confirmed by further prospective studies.

Neuregulin 1 Improves Glucose Tolerance in db/db Mice

In vitro experiments using rodent skeletal muscle cells suggest that neuregulin 1 (NRG1) is involved in glucose metabolism regulation, although no study has evaluated the role of NRG1 in systemic glucose homeostasis. The purpose of this study was to investigate the effect of chronic and acute NRG1 treatment on glucose homeostasis in db/db mice. To this aim, glucose tolerance tests were performed in 8-week-old male db/db mice after treatment with NRG1 (50μg.kg^-1) or saline 3 times per week for 8 weeks. In other experiments, glucose tolerance and pyruvate tolerance tests were performed in db/db mice 15 minutes after a single NRG1 (50μg.kg^-1) or saline injection. Liver, adipose tissue, hypothalamus and skeletal muscle were also collected 30 minutes after acute NRG1 (50μg.kg^-1) or saline treatment, and the phosphorylation status of the ERBB receptors, AKT (on Ser473) and FOXO1 (on Ser256) was assessed by western blotting. Chronic treatment (8 weeks) with NRG1 improved glucose tolerance in db/db mice. Acute treatment also lowered glycemia and insulinemia during glucose or pyruvate tolerance tests. NRG1 acute injection induced activation of ERBB3 receptors and phosphorylation of AKT and FOXO1 only in liver. Altogether, this study shows that acute and chronic NRG1 treatments improve glucose tolerance in db/db mice. This effect could be mediated through inhibition of hepatic gluconeogenesis.

Structure and function of epigen, the last EGFR ligand

Epigen is the latest addition to the mammalian family of EGFR ligands. Epigen was initially identified as a novel expressed sequence tag with homology to the EGF family by high throughput sequencing of a mouse keratinocyte complementary DNA library, and received its name for its ability to act as an epithelial mitogen. In vitro studies attributed to epigen several unique features, such as persistent and potent biological actions involving low affinity receptor binding, as well as sub-maximal receptor activation and inactivation. Similarly to the other EGFR ligands, the expression of epigen is up-regulated by hormones and in certain cancer types. While the biological functions of epigen remain to be uncovered, it appears to play a role in epidermal structures, such as the mammary gland and the sebaceous gland. The latter organ, in particular, was greatly enlarged in transgenic mice overexpressing epigen. Interestingly, mice lacking epigen develop and grow normally, probably due to functional compensation by other EGFR ligands. Future studies are likely to reveal the biological roles of the unique receptor binding properties of epigen, as well as its potential harnessing during disease.