NRG4 Human
Description
Biochemical Characteristics and Expression
NRG4 is characterized by an epidermal growth factor (EGF)-like domain, enabling receptor binding. Its primary isoforms are secreted, though some membrane-bound variants exist . Key features include:
| Property | Details |
|---|---|
| Gene Location | Chromosome 15q24.2 |
| Primary Receptor | ERBB4 (with ERBB1/ERBB2 coreceptors) |
| Tissue Distribution | Brown adipose tissue (BAT), liver, pancreas, breast, and prostate tissue |
| Subcellular Localization | Secreted (majority), intracellular (minor isoforms) |
Physiological Roles in Metabolic Regulation
NRG4 functions as a novel adipokine, influencing energy homeostasis and lipid metabolism.
Anti-Obesity and Insulin-Sensitizing Effects
Overexpression of NRG4 via hydrodynamic gene transfer in mice prevents high-fat diet (HFD)-induced obesity by:
-
Suppressing hepatic lipogenesis: Inhibiting de novo lipid synthesis (e.g., downregulating ACACA) .
-
Reducing chronic inflammation: Lowering macrophage markers (F4/80, Cd68) and chemokines (Mcp1) .
-
Enhancing BAT thermogenesis: Increasing body temperature by 1°C and upregulating Ucp1 and Dio2 .
Table 1: NRG4’s Preventive vs. Therapeutic Effects
Dual Role in Insulin Sensitivity
Paradoxically, NRG4 shows context-dependent effects on glucose metabolism:
-
Negative correlation: Elevated serum NRG4 levels are associated with insulin resistance in humans, particularly in obesity and polycystic ovary syndrome (PCOS) .
-
Mechanistic insights: In vitro studies show NRG4 reduces mitochondrial respiration and gluconeogenic gene expression (PEPCK, G6PC) in hepatocytes, potentially exacerbating insulin resistance .
Obesity and NAFLD
-
Hepatic NRG4/ERBB4 downregulation: Observed in obese individuals, correlating with increased ACACA (a lipogenic enzyme) .
-
Genetic mutations: NRG4 variants (e.g., E47Q) disrupt fat distribution, leading to subcutaneous fat accumulation and reduced visceral adiposity .
Table 2: NRG4 Mutations and Metabolic Outcomes
| Mutation | Phenotype |
|---|---|
| R44H | Dyslipidemia, liver dysfunction |
| E47Q | Severe obesity (BMI >40) with subcutaneous fat dominance, normal glucose |
| Data from . |
Diabetes and Cardiovascular Complications
-
Autophagy modulation: NRG4 upregulates AMPK/mTOR pathways, attenuating diabetic cardiomyopathy .
-
NASH/HCC protection: Reduces hepatic immune dysregulation and fibrosis by inhibiting pro-inflammatory T-cell infiltration .
Targeted Interventions
-
Gene therapy: Hydrodynamic NRG4 transfer shows promise in preclinical models but lacks efficacy in established obesity .
-
Small-molecule agonists: ERBB4 activation remains a potential strategy, though specificity challenges persist .
Limitations and Controversies
Product Specs
Q&A
How has serum NRG4 been associated with metabolic parameters in different human studies?
The literature presents conflicting associations between circulating NRG4 and metabolic parameters. Some studies report an inverse association between NRG4 concentration and characteristics of metabolic syndrome or non-alcoholic fatty liver disease. Contrastingly, other investigations have documented increased NRG4 levels in patients with type 2 diabetes, altered glucose tolerance, or obesity. A meta-analysis including seven studies concluded that circulating NRG4 was positively associated with alterations in glucose metabolism and obesity, suggesting a more complex relationship than initially theorized from animal models .
What cellular mechanisms have been implicated in NRG4 function in human hepatocytes?
In human hepatocyte models (HepG2 cells), NRG4 administration impacts cellular metabolism by decreasing gluconeogenic-related gene expression and reducing mitochondrial biogenesis-related gene expression. Additionally, NRG4 reduces mitochondrial respiration in palmitate-treated hepatocytes. Unlike observations in mouse models, human hepatocytes treated with NRG4 show no significant effects on expression of lipid metabolism-related genes, suggesting species-specific metabolic responses to this growth factor .
How does insulin sensitivity correlate with circulating NRG4 levels in humans with varying degrees of adiposity?
Research utilizing gold-standard euglycemic hyperinsulinemic clamp methodology has demonstrated a significant negative correlation between serum NRG4 and insulin sensitivity (r = −0.25, p = 0.02). Multivariate linear regression analyses revealed that insulin sensitivity contributed to 7.2% of the variance in serum NRG4 (p = 0.01) after controlling for BMI, age, sex, and the inflammatory marker hsCRP. This suggests NRG4 may play a role in insulin resistance independent of adiposity measures .
What are the comparative effects of NRG4 versus NRG1 on human hepatocyte metabolism?
Both NRG4 and NRG1 exert similar but quantitatively different effects on human hepatocytes. In vitro experiments show both neuregulins decrease gluconeogenic- and mitochondrial biogenesis-related gene expression, with NRG1 producing more pronounced effects. Specifically, NRG4 administration reduces basal and maximal respiration without significantly affecting oxygen consumption for ATP production and proton leak. NRG1 demonstrates broader effects, reducing basal and maximal respiration, proton leak, and spare respiratory capacity. These findings indicate potentially overlapping but distinct metabolic impacts between neuregulin family members .
How does NRG4 expression differ across the progression of metabolic disease in humans?
NRG4 expression appears to vary according to the stage of metabolic disease progression. Studies have observed increased levels of NRG4 in situations of altered glucose tolerance or early diabetes but decreased levels in patients with advanced diabetes as reflected by microalbuminuria. This biphasic pattern suggests NRG4 may serve different functions depending on disease stage, potentially including an initial compensatory role in maintaining insulin action and glucose metabolism during early disease development before declining in advanced stages .
What are the gold-standard techniques for measuring NRG4 levels in clinical studies?
For accurate quantification of circulating NRG4 in human subjects, enzyme-linked immunosorbent assay (ELISA) kits specifically validated for human NRG4 detection are the method of choice. Research indicates that high-sensitivity assays with detection limits around 0.25 ng/ml provide reliable measurements. When selecting assays, researchers should verify both intra- and inter-assay variations are below 10% to ensure reproducibility. Statistical analyses should include normality testing (such as Kolmogorov-Smirnov test) before selecting appropriate statistical approaches .
What study design elements are critical when investigating NRG4's relationship with metabolic parameters in humans?
Robust NRG4 research requires careful consideration of several methodological factors. Studies should include participants with a wide range of adiposity to capture the full spectrum of potential NRG4 effects. Exclusion criteria should address confounding factors including type 2 diabetes, liver dysfunction, significant systemic diseases, recent infections, cardiovascular events, and medications that interfere with insulin action. Gold-standard techniques like euglycemic hyperinsulinemic clamp should be employed for insulin sensitivity assessment rather than surrogate indices. Multivariate analyses should control for key covariates including BMI, age, sex, and inflammatory markers .
How can researchers reconcile contradictory findings regarding NRG4's role in human metabolic health?
The contradictory literature on NRG4 requires careful methodological evaluation when interpreting findings. Researchers should consider:
-
Population characteristics: Studies in prediabetic, diabetic, and obese populations show different NRG4 relationships than those in healthy subjects
-
Disease progression: NRG4 levels appear to depend on the evolution and stage of metabolic disease development
-
Measurement techniques: Variations in assay sensitivity and specificity may contribute to discrepancies
-
Species differences: Effects observed in rodent models may not translate directly to humans due to fundamental differences in metabolic regulation
Comprehensive analysis across multiple metabolic parameters rather than isolated associations provides more reliable interpretation of NRG4's metabolic role .
What key methodological improvements would advance our understanding of NRG4 function in humans?
Future research on NRG4 would benefit from several methodological refinements:
-
Longitudinal studies tracking NRG4 levels across disease progression stages
-
Studies combining tissue-specific expression analysis with circulating levels
-
Experiments in human primary hepatocytes rather than transformed cell lines
-
Protein-level validation of gene expression findings
-
Investigation of potential compensatory mechanisms in insulin resistance
-
Assessment of NRG4's effects on specific insulin signaling pathways in human tissues
-
Studies examining potential NRG4 resistance similar to insulin and leptin resistance
These approaches would help resolve contradictions in the current literature and establish more definitive understanding of NRG4's role in human metabolism .
What cellular mechanisms warrant investigation to better understand species-specific effects of NRG4?
Given the discrepancy between rodent and human NRG4 effects, several cellular mechanisms deserve focused investigation:
-
Receptor expression and binding affinity differences between species
-
Post-receptor signaling pathway variations
-
Interactions between NRG4 and inflammatory mediators in human tissues
-
Effects on mitochondrial function in primary human cells
-
Cross-talk between NRG4 signaling and insulin signaling pathways
-
Tissue-specific responses to NRG4 in humans versus rodents
-
Potential compensatory mechanisms in insulin resistant states
Understanding these mechanisms would clarify why NRG4 appears to have different effects in humans compared to the beneficial effects observed in rodent models .
Product Science Overview
NRG4 contains one EGF-like domain and is a low-affinity ligand for the ERBB4 tyrosine kinase receptor. It activates type-1 growth factor receptors, initiating cell-to-cell signaling through tyrosine phosphorylation . NRG4 also recruits ERBB1 and ERBB2 coreceptors, resulting in ligand-stimulated tyrosine phosphorylation and activation of the ERBB receptors .
Recent studies have shown that NRG4 serum levels are associated with insulin resistance, metabolic syndrome, nonalcoholic fatty liver disease, and the severity of atherosclerosis . Additionally, loss of expression of NRG4 is frequently seen in advanced bladder cancer, while increased NRG4 expression correlates with better survival .
Recombinant human NRG4 is typically produced using bacterial, yeast, baculovirus-insect, or mammalian expression systems. The recombinant protein is often purified to a high degree of purity, with endotoxin levels kept low to ensure its suitability for research and therapeutic applications .
The recombinant human NRG4 consists of 63 amino acids and has a calculated molecular mass of approximately 6.7 kDa as estimated in SDS-PAGE under reducing conditions . It is usually provided as a lyophilized powder, which can be reconstituted for use in various experimental setups .
