NRG1

Neuregulins (Nrgs) are a family of multifunctional polypeptide growth factors that primarily act by activating tyrosine kinase receptors, specifically the ErbB receptor family PMID 41213606.

• Signaling Hub: Activation of Nrgs triggers critical downstream signaling cascades, including the PI3K/Akt, MAPK/ERK, and mTOR pathways, which are essential for tissue development, regeneration, and maintenance PMID 39522716PMID 41213606.
• Metabolic and Thermogenic Regulation: In adipose tissue, NRG4 (a specific isoform) serves as a neurotrophic "batokine" that contributes to the remodeling of the sympathetic neural network and promotes the thermogenesis of brown and beige adipocytes PMID 38786764. It limits hepatic lipogenesis and regulates overall energy balance PMID 41213606.
• Neural and Cardiac Role: In the central nervous system (CNS), NRGs/ErbB4 signaling is widely distributed and contributes to the regulation of neuronal development, survival, and synaptic plasticity PMID 40818821. In the heart, it is involved in maintaining cardiovascular development and stress response PMID 40818821.

• Neuregulin is classified as an exerkine because its expression and secretion are upregulated in response to various physical activity stimuli across multiple tissues PMID 40818821:
• Cardiac and Skeletal Muscle Source: NRG1 is identified as an exercise-inducible factor secreted by both the heart and skeletal muscle following exercise training PMID 40818821PMID 38107476.
• Adipose Source: NRG4 is identified as an exercise-responsive adipokine/batokine; both aerobic and resistance training enhance its circulating levels, with high-intensity interval training (HIIT) and circuit resistance training being particularly effective stimuli PMID 41213606PMID 38786764.
• Endothelial Response: Neuregulin expression also elevates in human cardiac endothelial cells in response to exercise PMID 38107476.

• Cardiovascular Recovery: In myocardial infarction models, exercise-induced NRG1 promotes endogenous heart regeneration and contributes to cardiac functional recovery via the ErbB/PI3K/Akt signaling pathway PMID 40818821PMID 38107476.
• Metabolic Disease Management: NRG4 is viewed as a promising target for improving metabolic disorders, such as obesity, Type 2 Diabetes, and Non-alcoholic fatty liver disease (NAFLD), by increasing energy expenditure, reducing hepatic lipogenesis, and improving insulin sensitivity PMID 41213606PMID 38786764.
• Neuroprotection: Intracerebroventricular administration of NRG1 has been shown to alleviate synaptic loss and cognitive deficits in Alzheimer’s Disease (AD) models PMID 40818821. It is also being investigated as a potential biomarker for cognitive impairment in vascular dementia PMID 40818821.
• Osteoarthritis (OA): NeuregulinHind exerts a "positive correlation" with joint health by hindering OA progression. It reduces joint inflammation, safeguards chondrocytes from apoptosis, and mitigates the degradation of the extracellular matrix PMID 38107476.

Cardiovascular Disease

Recombinant NRG-1 has demonstrated beneficial effects in heart failure in both animal models and human clinical trials (1-5, PMID 33063822PMID 36120374PMID 23104879PMID 21631420PMID 23384772. Two distinct forms of recombinant NRG-1 improve cardiac function in patients with systolic heart failure (1, PMID 33063822. Phase I and II clinical trials have shown that NRG-1 is safe and improves cardiac function in chronic heart failure patients (4-5, PMID 21631420PMID 23384772. The therapeutic mechanisms include promoting cardiomyocyte survival and proliferation, maintaining myofibril structure, counterbalancing excessive β-adrenergic signaling, and promoting angiogenesis (4, 6, PMID 21631420PMID 22427524.

Beyond heart failure, NRG-1 shows promise in multiple cardiovascular conditions including diastolic heart failure, atherosclerosis prevention, diabetic cardiovascular complications, and sepsis-associated cardiac dysfunction (1, PMID 33063822. NRG-1 can repair the heart in atherosclerosis, myocardial infarction, ischemia-reperfusion injury, and cardiomyopathy by regulating cardiac inflammation, oxidative stress, and necrotic apoptosis (2, PMID 36120374.

Neurological and Neurodegenerative Diseases

NRG-1 represents a potential neuroprotective treatment for ischemic stroke, with a therapeutic window exceeding 13 hours in preclinical studies (7, PMID 38638304. It significantly reduces ischemia-induced neuronal death, neuroinflammation, and oxidative stress in rodent stroke models (7, PMID 38638304. NRG-1 has been shown to be safe in human patients in cardiac trials, supporting its potential translation to stroke treatment (7, PMID 38638304.

NRG/ErbB signaling shows therapeutic potential in neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) (8-9, PMID 33897409PMID 40254133. The pathway regulates differentiation, migration, and myelination, and plays roles in neuroprotection and remyelination following CNS injury (10, PMID 31229498. Recent discoveries include human pedigrees where autosomal dominant frontotemporal lobar degeneration/ALS potentially results from ERBB4 mutations (9, PMID 40254133.

Nervous System Injury and Repair

NRG-1/ErbB signaling is critical for both peripheral and central nervous system repair (10, PMID 31229498. It modulates glial and immune responses while fostering neuroprotection and remyelination in CNS injury (10, PMID 31229498. The pathway also regulates synaptic plasticity at glutamatergic, GABAergic, and dopaminergic synapses, which is essential for learning, memory, and complex behaviors (11-12, PMID 31906113PMID 39923224.