EARLY ACTIVATION OF NECROPTOSIS IN NIGRAL DOPAMINERGIC NEURONS IN A MOUSE MODEL OF PARKINSON’S DISEASE

Inactivating mutations in the ubiquitin ligase PARKIN cause Autosomal Recessive Juvenile Parkinsonism (ARJP), a neurodegenerative disorder characterized by early dysfunction and progressive loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNpc). Understanding the mechanisms underlying neurodegeneration could inform the design of neuroprotective drugs, an unmet need in Parkinson’s disease. Recent evidence indicates that PARKIN inhibits necroptosis, a regulated inflammatory form of cell death that promotes astrocytic and microglial activation in the central nervous system. Necroptosis is mediated by a core pathway involving RIPK1, RIPK3 and MLKL, whose phosphorylation and membrane translocation lead to plasma membrane permeabilization and cell rupture.
Here, we investigated necroptosis in a preclinical model of ARJP, PrknR275W mice, which harbor a loss-of-function mutation corresponding to the most frequent missense variant found in PRKN-mutated patients. These mice exhibit progressive degeneration of SNpc DAergic neurons from 6 months of age, preceded by early neuronal defects at 1 month. We analyzed markers of necroptosis and neuroinflammation in the SNpc at 1 and 6 months of age.
Immunofluorescence analysis revealed increased RIPK3 and phosphorylated MLKL levels in DAergic neurons of PrknR275W mice at both ages, accompanied by upregulation of Ripk3 and Mlkl transcripts. Neuroinflammatory changes emerged at 6 months, with enhanced microglial and astrocytic activation. Consistently, bulk RNA sequencing analysis of SNpc tissue from 6-month-old mice showed enrichment of transcripts of the inflammatory pathways in mutant animals.
These findings suggest that necroptosis is activated in nigral DAergic neurons of PrknR275W mice, possibly playing a role in neurodegeneration.