Objective: We explored mitochondria as integrators of genetics and environment in LRRK2 G2019S neuronal models. Specifically, we aimed to unravel mitochondrial mechanisms that define the penetrance of this mutation.

Background: The LRRK2 G2019S mutation shows incomplete penetrance, i.e. while some carriers develop PD, others never manifest any signs of the disease. However, the molecular factors defining penetrance in these individuals currently remain elusive. Mitochondrial dysfunction plays a central role in PD. Our previous work in fibroblasts showed that LRRK2 G2019S mutation carriers affected by PD (LRRK2+/PD+) presented higher levels of mitochondrial major arc deletions compared to unaffected G2019S carriers (LRRK2+/PD-). In addition, cells from manifesting carriers displayed impaired mitophagy and altered antioxidant signaling.

Method: IPSCs from healthy, LRRK2+/PD+ and LRRK2+/PD- individuals were converted into neural progenitor cells (NPCs) and subsequently differentiated into dopaminergic neurons for 48 hrs or 30 days. To test the influence of environmental factors on mitochondria, neurons were cultured for 24h in medium deprived of antioxidants. Untreated and treated neurons were subjected to RNA sequencing and mtDNA integrity assays.

Results: Preliminary results from NPCs differentiated for 48h revealed elevated deletion levels in LRRK2+/PD+ cultures compared to controls. While in controls the formation of mtDNA major arc deletions could be induced by ROS, mtDNA deletion levels did not increase further in LRRK2+/PD+ upon antioxidant deprivation. Moreover, this treatment increased mtDNA release into the cytosol in all cell lines independent of genotype and PD status. The results from the RNA sequencing are still pending, as are the phenotyping analyses in 30-day-old neurons. In mature neurons, we will be able to further characterize mitochondrial signaling alterations in response to ROS by assessing morphological and functional parameters.

Conclusion: Even during the early stages of neuronal differentiation, we observed differences in mtDNA integrity when comparing cultures from controls, unaffected and affected LRRK2 G2019S carriers. Interestingly, the mtDNA deletion phenotype could be mirrored in ROS-exposed control cultures, warranting further experiments that will allow uncovering of involved mitochondrial pathways.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/exploring-mitochondrial-mechanisms-defining-parkinsons-disease-penetrance-in-lrrk2-g2019s-neuronal-cultures/