Chronic Overexpression of Neuronal NRG1-III in Mice Causes Long-Term Detrimental Changes in Lower Motor Neurons, Neuromuscular Synapses and Motor Behaviour

Neuregulins (NRGs) are ligands for tyrosine kinase receptors from the ErbB family and serve multiple developmental functions in the nervous system. NRG1-ErbB signaling regulates myelination and is associated with amyotrophic lateral sclerosis (ALS) pathology. Given the potential therapeutic relevance of this pathway for motor neuron (MN) diseases, we employed a transgenic (TG) mouse model with persistent neuronal overexpression of NRG type III (NRG1-III) to investigate its long-term impact on the neuromuscular system. We examined MNs and their synaptic inputs, including cholinergic C-boutons, at which NRG1-III typically accumulates. MNs from TG mice exhibited persistent upregulation of C-bouton-associated postsynaptic proteins, as well as increased biogenesis of subsynaptic cistern-like ER-plasma membrane contacts. Following nerve injury, NRG1-III overexpression resulted in exacerbated neuroinflammation and disruption of enlarged NRG1 clusters. Calcium imaging revealed altered homeostasis in TG MNs, which upregulated molecules linked to axonal plasticity. At neuromuscular junctions, we observed regressive changes involving autophagic dysregulation. These alterations were accompanied by increased motor activity in behavioral tests. Overall, our findings indicate that persistently elevated NRG1-III signaling diminishes MN connectivity and long-term health, which must be considered when developing therapeutic strategies for neurodegenerative diseases, such as ALS.