The mechanisms of mitochondrial damage-dependentneuroinflammation in experimental models ofParkinson’s disease. The role of Parkin dysfunction.

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Parkinson's disease (PD) involves progressive death of dopaminergic neurons and is the second most common neurodegenerative disorder. Misfolding and deposition of α-synuclein (α-syn) as Lewy bodies is a hallmark of PD etiology, but the mechanisms of its neurotoxicity remain unclear. Another established PD-associated protein, the E3 ubiquitin ligase parkin is essential for mitochondrial quality control, and loss of its activity leads to accumulation of misfolded proteins and damaged mitochondria which can release damage-associated molecular patterns (DAMPs, including mtDNA) activating innate immune receptors to promote (neuro)inflammation, an important driver of PD pathology. However, the role of parkin in α-syn–induced, mitochondria-linked inflammation (mitoflammation) and dopaminergic cell death has not been elucidated in depth. Our main hypothesis is that parkin dysfunction contributes to α-syn–induced mitochondrial impairment that leads to neuroinflammation and neurodegeneration in PD. To test this hypothesis, we will investigate parkin’s involvement in α-syn–evoked mitochondrial damage, inflammatory response, and neurodegeneration in mouse and cellular models of synucleinopathy. To induce PD-like pathology, 12-week-old C57BL/6J mice, parkin knock-out mice (Park2-/-) or parkin overexpressing (Park2oe) mice will be stereotactically injected with human α-syn oligomers (5μg of protein/5μl/side) or vehicle, bilaterally into the dorsal striatum. In vitro and ex vivo models will be used for the investigation of specific aspects of mitochondrial damage, signaling pathways, and interactions between neurons, microglia and astrocytes: induced pluripotent stem cells (iPSC) from PD patients differentiated into microglia and astrocytes, conditionally immortalized human fetal mesencephalic cells (LUHMES) differentiated to exhibit dopamine neuron characteristics as well as microglia-depleted organotypic mouse midbrain slices. We assume that parkin prevents α-syn–induced inflammation and neurodegeneration by clearing damaged mitochondria in neurons, thereby preventing the release of DAMPs, and attenuating PD-linked glial inflammatory responses. We will analyze neuron survival, neuroinflammation, dopamine and its metabolites, brain tissue ultrastructure and animal behavior in control and parkin-overexpressing mice subjected to α-syn neurotoxicity and to potentially neuroprotective pharmacological treatments. This project will characterize the mechanisms by which α-syn–induced parkin dysfunction modulates mitochondrial damage and associated immune response in preclinical models of PD. The direct association between α-syn propagation, parkin dysfunction, mitoflammation, and dopaminergic cell death has not been investigated so far. Addressing the role of parkin at the crossroads of α-syn spreading and neuroinflammation holds the promise for better understanding of PD pathomechanism and identification of novel therapeutic targets.