Miro1 mutations disrupt cellular calcium homeostasis via dysregulation of mitochondria-ER-contact-sites, rendering iPSC-derived neurons more susceptible to lipid peroxidation.

The pathogenesis of Parkinson's disease is multifactorial, but disruption of calcium and iron is a common feature. The mitochondrial Rho GTPase Miro1 is a component of the mitochondrial-endoplasmic reticulum contact sites and a key regulator of calcium homeostasis. Heterozygous variants in the Miro1-encoding gene RHOT1 were identified in Parkinson's disease patients. Neurons harboring Parkinson's disease-associated variants show defects in mitochondrial calcium regulation and mitochondria-ER contact sites organization which we hypothesize to contribute to neuronal vulnerability. However, the exact mechanism is not fully understood. We systematically assessed the role of Miro1 and its different domains by using a set of isogenic lines with gene edited mutations S156A and K572R in PINK1/Parkin regulatory elements and the Parkinson's disease-associated mutation R272Q. This showed us a general role of Miro1 in the regulation of cellular calcium homeostasis and the regulation of mitochondrial-ER contact sites, but more importantly, a domain-specific involvement of local calcium distribution, impaired store operated calcium entry and vulnerability to ferroptosis. These findings indicate that Miro1-mutant specific impairments in cellular calcium handling contributes to neuronal vulnerability via mitochondria-ER contact sites and provides further insights in the mechanism how impaired regulation of Miro1 impacts neurons in the context of Parkinson's disease.