Lorenzo-Ramos, E. | bioRxiv Science

bioRxiv2026

Tier-specific location of Lewy body pathology and related neuromelanin levels drive dopaminergic cell vulnerability in pigmented non-human primates

Although a differential vulnerability of dopaminergic neurons to degeneration based on their specific location within the dorsal and ventral tiers of the substantia nigra pars compacta (SNcD and SNcV, respectively) has long been postulated, the underlying mechanisms sustaining these tier-specific differences remain poorly understood. Here, upon inducing a viral-mediated enhancement of neuromelanin (NMel) accumulation within dopaminergic neurons in non-human primates, the distribution of Lewy body-like inclusions (LBs) was analyzed within identified SNcD and SNcV neurons, together with their intracellular NMel levels. Results showed that the vast majority of intracytoplasmic inclusions were found in SNcV neurons, and indeed correlated to higher pigmentation levels. By contrast, only very few LBs were found in calbindin-positive neurons of the SNcD, which in parallel exhibited very low levels of NMel accumulation. These results postulate an additive effect made of a tier-specific location of LB burden together with high pigmentation levels as synergistic drivers sustaining the preferential vulnerability of SNcV dopaminergic neurons. Moreover, the evidence obtained here supported that NMel accumulation beyond a given threshold triggers the aggregation of endogenous -Syn in the form of LBs; therefore, approaches intended to reduce pigmentation levels in SNcV neurons would likely induce a neuroprotective effect by preventing the subsequent aggregation of -Syn.

neuroscience↗

bioRxiv2025

Introducing PIGMO, a novel PIGmented MOuse model of Parkinson's disease (V1)

There is a pressing need for the development, characterization, and standardization of animal models of Parkinsons disease (PD) that properly mimic the cardinal features of this disorder, comprising both the motor phenotype and neuropathological signatures. In the past few years, animal modeling has moved from neurotoxin-based approaches toward viral vectors carrying a given genetic payload of interest. Here, to induce pigmentation of the mouse brain upon systemic delivery, we took advantage of a modified adeno-associated viral vector capsid engineered to bypass the blood-brain barrier and coding for the human tyrosinase gene (AAV9-P31-hTyr). Obtained results revealed an ongoing pigmentation of catecholaminergic centers related to the pathophysiology of PD, such as the substantia nigra pars compacta, ventral tegmental area, and locus coeruleus. Moreover, pigmented dopaminergic neurons exhibited Lewy body-like intracytoplasmic inclusions, a progressive nigrostriatal degeneration, and a time-dependent PD motor phenotype. The bilateral pigmented mouse model of PD generated this way is highly reproducible, does not require stereotaxic surgery for viral vector deliveries, and opens unprecedented possibilities for preclinical testing of therapeutic candidates designed to reduce disease progression rates.

neuroscience↗