Impaired mitochondrial-endoplasmic reticulum interaction and mitophagy in Miro1-mutant neurons in Parkinson's disease.

Anne Grünewald,Clara Berenguer-Escuder,Dajana Grossmann,François Massart,Giuseppe Arena,Javier Jarazo,Jens C Schwamborn,Jonas Walter,Kobi Wasner,Paul Antony,Rejko Krüger

doi:10.1093/hmg/ddaa066

Abstract

Mitochondrial Rho GTPase 1 (Miro1) protein is a well-known adaptor for mitochondrial transport and also regulates mitochondrial quality control and function. Furthermore, Miro1 was associated with mitochondrial-endoplasmic reticulum (ER) contact sites (MERCs), which are key regulators of cellular calcium homeostasis and the initiation of autophagy. Impairments of these mechanisms were linked to neurodegeneration in Parkinson’s disease (PD). We recently revealed that PD fibroblasts harboring Miro1 mutations displayed dysregulations in MERC organization and abundance, affecting mitochondrial homeostasis and clearance. We hypothesize that mutant Miro1 impairs the function of MERCs and mitochondrial dynamics, altering neuronal homeostasis and integrity in PD. PD skin fibroblasts harboring the Miro1-R272Q mutation were differentiated into patient-derived neurons. Live-cell imaging and immunocytochemistry were used to study mitophagy and the organization and function of MERCs. Markers of autophagy or mitochondrial function were assessed by western blotting. Quantification of organelle juxtapositions revealed an increased number of MERCs in patient-derived neurons. Live-cell imaging results showed alterations of mitochondrial dynamics and increased sensitivity to calcium stress, as well as reduced mitochondrial clearance. Finally, western blot analysis indicated a blockage of the autophagy flux in Miro1-mutant neurons. Miro1-mutant neurons display altered ER-mitochondrial tethering compared with control neurons. This alteration likely interferes with proper MERC function, contributing to a defective autophagic flux and cytosolic calcium handling capacity. Moreover, mutant Miro1 affects mitochondrial dynamics in neurons, which may result in disrupted mitochondrial turnover and altered mitochondrial movement.

Highlights

Parkinson’s disease (PD) is a chronic neurodegenerative disorder, the cause of which currently remains elusive [1]
We recently revealed that PD fibroblasts harboring Mitochondrial Rho GTPase 1 (Miro1) mutations displayed dysregulations in mitochondrial-endoplasmic reticulum (ER) contact sites (MERCs) organization and abundance, affecting mitochondrial homeostasis and clearance
To develop a closer-todisease patient-based cellular model, we used these fibroblasts to generate induced-pluripotent stem cell-derived Miro1R272Q mutant neurons, and we provide the first insights into the pathogenic effect of PD-associated mutant Miro1 in human midbrain neurons

Summary

Introduction

Parkinson’s disease (PD) is a chronic neurodegenerative disorder, the cause of which currently remains elusive [1]. Most cases of PD are idiopathic and only ∼10% are caused by genetic mutations [2]. 23 loci have been identified, in which mutations are proposed to cause PD [3], and >20 risk factors are suggested to be involved in the pathogenesis of the disorder [4]. The key histopathological hallmark of PD is the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta [5]. The molecular mechanisms underlying the neuronal cell death are still under debate. Animal- and patientbased cellular models of genetic PD forms help identify common molecular pathways involved in the pathogenesis of PD [6,7]

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Conclusion