The role of the mitochondrial outer membrane protein SLC25A46 in mitochondrial fission and fusion

Abstract

Mutations inSLC25A46underlie a wide spectrum of neurodegenerative diseases associated with alterations in mitochondrial morphology. We established an SLC25A46 knock-out cell line in human fibroblasts and studied the pathogenicity of three variants (p.T142I, p.R257Q, and p.E335D). Mitochondria were fragmented in the knock-out cell line and hyperfused in all pathogenic variants. The loss of SLC25A46 led to abnormalities in the mitochondrial cristae ultrastructure that were not rescued by the expression of the variants. SLC25A46 was present in discrete puncta at mitochondrial branch points and tips of mitochondrial tubules, co-localizing with DRP1 and OPA1. Virtually, all fission/fusion events were demarcated by a SLC25A46 focus. SLC25A46 co-immunoprecipitated with the fusion machinery, and loss of function altered the oligomerization state of OPA1 and MFN2. Proximity interaction mapping identified components of the ER membrane, lipid transfer proteins, and mitochondrial outer membrane proteins, indicating that it is present at interorganellar contact sites. SLC25A46 loss of function led to altered mitochondrial lipid composition, suggesting that it may facilitate interorganellar lipid flux or play a role in membrane remodeling associated with mitochondrial fusion and fission.

Identification of SLC25A46 interaction interfaces with mitochondrial membrane fusogens Opa1 and Mfn2

“…One possible mode of inhibitory action may be SLC25A46 binding would be sufficient to result in steric competition for Opa1 self-assembly, which relies on the BSE and stalk regions to mediate formation of helical filaments (52)(53)(54). Consistent with this prediction, levels of Opa1 oligomeric complexes were found to increase upon loss of SLC25A46 (8).…”

“…A cluster of SLC25A46 disease mutations face the IMS ( Figure 4A ). While many mutations were reported to destabilize the protein, certain disease-causing mutations (T142I and R340C) cause a hyper-fused mitochondrial phenotype (6, 8, 9, 15, 24). We co-expressed these SLC25A46 mutants with Opa1, and found these disease mutants still bound Opa1 ( Figure 4B ).…”

“…SLC25A46 protein-protein interactions also may regulate cristae morphology, which is dramatically affected upon loss of SLC25A46 (6,8,24,26,27,29). Proteomics studies have also implicated SLC25A46 endoplasmic reticulum interaction partners in maintaining ER-mitochondria contacts facilitating lipid flux (6)(7)(8). Future mechanistic structure-activity studies are necessary to explore these other roles of SLC25A46 in cristae regulation and lipid metabolism.…”

SLC-25A46 Regulates Mitochondrial Fusion through FZO-1/Mitofusin and is Essential for Maintaining Neuronal Morphology

“…All of these studies support the function of SLC25A46 as a fission factor. In contrast, the complete loss of SLC25A46 in the knock-out Hela cell results in the fragmentation of the mitochondrial network 16 . In a separate study using a knockout mouse model, loss of SLC25A46 function led to the formation of small mitochondrial fragments in the nervous system 17 .…”

Mitochondria in depression: The dysfunction of mitochondrial energy metabolism and quality control systems

“…Mitochondrial fusion is a process that allows content mixing between intact and dysfunctional mitochondria, whereas fission is the process that includes sequestration of irreversibly damaged, fusionincompetent mitochondria and their subsequent elimination by autophagy. 82 As replacement of damaged mitochondria contributes to the integrity and homogeneity of the mitochondrial population in a cell, both mitochondrial fusion and fission are coordinated to maintain homeostasis of the mitochondria in the cellular stress response.…”