Autosomal Dominant Optic Atrophy (ADOA), a disease that causes blindness and other neurological disorders, is linked to mutations. OPA1, dependent on its GTPase and GED domains, governs inner mitochondrial membrane (IMM) fusion and cristae organization, which are central to oxidative metabolism. Mitochondrial dynamics and IMM organization have also been implicated in Ca homeostasis and signaling but the specific involvements of OPA1 in Ca dynamics remain to be established. Here we studied the possible outcomes of OPA1 and its ADOA-linked mutations in Ca homeostasis using rescue and overexpression strategies in -deficient and murine embryonic fibroblasts (MEFs), respectively and in human ADOA-derived fibroblasts. MEFs lacking required less Ca mobilization from the endoplasmic reticulum (ER) to induce a mitochondrial matrix [Ca] rise ([Ca]). This was associated with closer ER-mitochondria contacts and no significant changes in the mitochondrial calcium uniporter complex. Patient cells carrying GTPase or GED domain mutations also exhibited altered Ca homeostasis, and the mutations associated with lower OPA1 levels displayed closer ER-mitochondria gaps. Furthermore, in MEF background, we found that acute expression of GTPase mutants but no GED mutants, partially restored cytosolic [Ca] ([Ca]) needed for a prompt [Ca] rise. Finally, mutants’ overexpression in WT MEFs disrupted Ca homeostasis, partially recapitulating the observations in ADOA patient cells. Thus, OPA1 modulates functional ER-mitochondria coupling likely through the OPA1 GED domain in MEFs. However, the co-existence of WT and mutant forms of OPA1 in patients promotes an imbalance of Ca homeostasis without a domain-specific effect, likely contributing to the overall ADOA progress.
Copyright © 2022 Cartes-Saavedra, Macuada, Lagos, Arancibia, Andrés, Yu-Wai-Man, Hajnóczky and Eisner.