Shedding Light on Neuromelanin: Optogenetic Probing in a Mouse Model of Early Parkinson’s Disease

Neurodegenerative diseases such as Parkinson’s and Alzheimer’s are unique to humans and share aging as their primary risk factor. Neuromelanin - a neuroprotective pigment formed in human catecholaminergic neurons - accumulates over the lifespan but is believed to become neurotoxic in later life. Our understanding of neuromelanin’s contribution to proteinopathies remains limited, primarily because standard preclinical model organisms do not naturally produce neuromelanin. In this talk, I will introduce a novel, cell-specific approach that enables the controlled, dose-dependent induction of human-like neuromelanin in catecholaminergic neurons. This model provides a powerful tool to investigate the pathological consequences of neuromelanin accumulation and its contribution to neuronal vulnerability. For example, accumulation of neuromelanin in the locus coeruleus, the brain’s principal source of norepinephrine, leads to a range of non-motor impairments that mirror early-stage symptoms of Parkinson’s disease. I will describe a distinct neurodegenerative phenotypes associated with neuromelanin buildup, along with transcriptomic changes that reveal shifts in the molecular identity of both noradrenergic and dopaminergic neurons. Importantly, our findings suggest that the early-stage loss of catecholaminergic neurons observed in Parkinson’s disease may have been misinterpreted as cell death. Instead, we provide evidence for a transition to a dormant neuronal state, marked by the loss of classical cell-type markers. Finally, I will present data showing that optogenetic reactivation of these dormant dopaminergic neurons can reverse key pathological features and alleviate symptoms.