The role of Miro at endoplasmic reticulum-mitochondria contacts in health and disease

Endoplasmic reticulum-mitochondria contacts (ERMCs) play a key role in a range of physiological processes including calcium homeostasis, autophagy, apoptosis, and lipid metabolism (Shirokova et al., 2020). The dysregulation of both the function and ultrastructure of these inter-organellar contacts has been observed in diseases such as Amyotrophic lateral sclerosis, Alzheimer's, and Parkinson's disease (PD) (De Mario et al., 2017). Indeed, it is postulated that the malfunction of ERMCs is a major early contributor to the pathogenic end-point in neurodegenerative disease. Despite these observations, our understanding of the mechanisms underpinning the regulation of ERMCs is still limited, particularly in neurons. This knowledge could provide clarity to dysfunction in disease and help identify new targets for therapeutics.

The Mitochondrial Rho GTPase (Miro) family are outer mitochondrial membrane proteins that localize at ERMCs. Miro is known to interact with several proteins which accumulate at ERMCs, such as the Mitofusins (Misko et al.,2010), and both the Drosophila and Yeast homologs are associated with regulatory roles at ERMCs (Lee et al., 2016; Kornmann et al., 2011). Moreover, Miro knock-out and PD-related Miro1-mutants altered ERMC ultrastructure whilst simultaneously dysregulating calcium homeostasis in human cell lines (Modi et al., 2019; Berenguer-Escuder et al., 2019).

While there is growing evidence of a regulatory mechanism controlling the number of contacts and their components, potentially underpinned by Miro, the types of contacts targeted and the mechanism by which Miro regulates them remains unclear. Thus, we aim to utilise confocal, super resolution, and electron microscopy to explore the role of Miro in ERMC regulation in primary cultured neurons and ex vivo brain tissue. Moreover, we will apply molecular and cell biology techniques to explore the functional and structural implications of Miro dysfunction on specific protein contacts. Our investigation will utilise pre-existing in-lab mouse Miro1/2 knock-out lines (López-Doménech et al., 2018) and Miro1-constructs, including PD-related mutants and signaling mutants. We hope to provide further insight into the regulatory processes at ERMCs and their dysregulation in the neurodegenerative process.