bims-mecmid 2022-06-05 papers

Issue of 2022‒06‒05
four papers selected by
Mauricio Cardenas Rodriguez
University of Padova

Front Cell Dev Biol. 2022 ;10 868465

Reciprocal Regulation of Mitofusin 2-Mediated Mitophagy and Mitochondrial Fusion by Different PINK1 Phosphorylation Events.

Jiajia Li, Xiawei Dang, Antonietta Franco, Gerald W Dorn.

Mitochondrial repair is essential to metabolic homeostasis. Outer mitochondrial membrane mitofusin (MFN) proteins orchestrate mitochondrial fusion that opposes mitochondrial degeneration caused by senescence. Depending upon physiological context, MFN2 can either mediate mitochondrial fusion or recruit cytosolic Parkin to initiate mitophagic elimination. Because it is not clear how these events are counter-regulated we engineered and expressed MFN2 mutants that mimic phosphorylated or non-phosphorylatable MFN2 at its PINK1 phosphorylation sites: T111, S378, and S442. By interrogating mitochondrial fusion, polarization status, and Parkin binding/mitophagy as a function of inferred MFN2 phosphorylation, we discovered that individual MFN2 phosphorylation events act as a biological "bar-code", directing mitochondrial fate based on phosphorylation site state. Experiments in Pink1 deficient cells supported a central role for PINK1 kinase as the pivotal regulator of MFN2 functionality. Contrary to popular wisdom that Parkin-mediated ubiquitination regulates MFN-mediated mitochondrial fusion, results in Prkn null cells demonstrated the dispensability of Parkin for MFN2 inactivation. These data demonstrate that PINK1-mediated phosphorylation is necessary and sufficient, and that Parkin is expendable, to switch MFN2 from fusion protein to mitophagy effector.

Keywords: MFN2; PINK1 kinase; Parkin; fusion; mitochondrial quality control; mitofusin regulation; phosphorylation

DOI: https://doi.org/10.3389/fcell.2022.868465

Hum Mol Genet. 2022 Jun 02. pii: ddac128. [Epub ahead of print]

Modelling autosomal dominant optic atrophy associated with OPA1 variants in iPSC-derived retinal ganglion cells.

Paul E Sladen, Katarina Jovanovic, Rosellina Guarascio, Daniele Ottaviani, Grace Salsbury, Tatiana Novoselova, J Paul Chapple, Patrick Yu-Wai-Man, Michael E Cheetham.

Autosomal dominant optic atrophy (DOA) is the most common inherited optic neuropathy, characterised by the preferential loss of retinal ganglion cells (RGCs), resulting in optic nerve degeneration and progressive bilateral central vision loss. Over 60% of genetically confirmed DOA patients carry variants in the nuclear OPA1 gene, which encodes for a ubiquitously expressed, mitochondrial GTPase protein. OPA1 has diverse functions within the mitochondrial network, facilitating inner membrane fusion and cristae modelling, regulating mitochondrial DNA maintenance and coordinating mitochondrial bioenergetics. There are currently no licensed disease-modifying therapies for DOA and the disease mechanisms driving RGC degeneration are poorly understood. Here, we describe the generation of isogenic, heterozygous OPA1 null iPSC (OPA1+/-) through CRISPR/Cas9 gene editing of a control cell line, in conjunction with the generation of DOA patient-derived iPSC carrying OPA1 variants, namely, the c.2708_2711delTTAG variant (DOA iPSC), and previously reported missense variant iPSC line (c.1334G>A, DOA+ iPSC) and CRISPR/Cas9 corrected controls. A two-dimensional (2D) differentiation protocol was used to study the effect of OPA1 variants on iPSC-RGC differentiation and mitochondrial function. OPA1+/-, DOA and DOA+ iPSC showed no differentiation deficit compared to control iPSC lines, exhibiting comparable expression of all relevant markers at each stage of differentiation. OPA1+/- and OPA1 variant iPSC-RGCs exhibited impaired mitochondrial homeostasis, with reduced bioenergetic output and compromised mitochondrial DNA maintenance. These data highlight mitochondrial deficits associated with OPA1 dysfunction in human iPSC-RGCs, and establish a platform to study disease mechanisms that contribute to RGC loss in DOA, as well as potential therapeutic interventions.

DOI: https://doi.org/10.1093/hmg/ddac128

Brain. 2022 Jun 03. pii: awac197. [Epub ahead of print]

CHCHD10 and SLP2 control the stability of the PHB complex: a key factor for motor neuron viability.

Emmanuelle C Genin, Sylvie Bannwarth, Baptiste Ropert, Françoise Lespinasse, Alessandra Mauri-Crouzet, Gaelle Augé, Konstantina Fragaki, Charlotte Cochaud, Erminia Donnarumma, Sandra Lacas-Gervais, Timothy Wai, Véronique Paquis-Flucklinger.

CHCHD10 is an amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) gene that encodes a mitochondrial protein whose precise function is unclear. Here we show that CHCHD10 interacts with the Stomatin-Like Protein 2 (SLP2) and participates to the stability of the Prohibitin (PHB) complex in the inner mitochondrial membrane. By using patient fibroblasts and mouse models expressing the same CHCHD10 variant (p.Ser59Leu), we show that SLP2 forms aggregates with prohibitins, found in vivo in the hippocampus and as aggresome-like inclusions in spinal motor neurons of Chchd10S59L/+ mice. Affected cells and tissues display instability of the PHB complex which participates at least in part to the activation of the OMA1 cascade with OPA1 processing leading to mitochondrial fragmentation, abnormal mitochondrial cristae morphogenesis and neuronal death found in spinal cord and the hippocampus of Chchd10S59L/+ animals. Destabilization of the PHB complex leads to the instability of the mitochondrial contact site and cristae organizing system (MICOS) complex, likely via the disruption of OPA1/Mitofilin interaction. Thus, SLP2/PHB aggregates and destabilization of the PHB complex are critical in the sequence of events leading to motor neuron death in CHCHD10S59L-related disease.

Keywords: CHCHD10 ; amyotrophic lateral sclerosis; frontotemporal dementia; mitochondrion; motor neuron disease

DOI: https://doi.org/10.1093/brain/awac197

IUBMB Life. 2022 May 30.

Mitochondrial E3 ubiquitin ligase 1 (MUL1) as a novel therapeutic target for diseases associated with mitochondrial dysfunction.

Ximena Calle, Valeria Garrido-Moreno, Erik Lopez, Ignacio Norambuena-Soto, Daniela Martínez, Allan Peñaloza-Otárola, Angelo Troncossi, Alejandra Guerrero-Moncayo, Angélica Ortega, Vinicius Maracaja-Coutinho, Valentina Parra, Mario Chiong, Sergio Lavandero.

Mitochondrial E3 ubiquitin ligase (MUL1) is a mitochondrial outer membrane-anchored protein-containing transmembrane domains in both its N- and C-terminal regions, where both are exposed to the cytosol. Interestingly the C-terminal region has a RING finger domain responsible for its E3 ligase activity, as ubiquitin or in SUMOylation, interacting with proteins related to mitochondrial fusion and fission, cell survival, and tumor suppressor proteins, such as Akt. Therefore, MUL1 is involved in various cellular processes, such as mitochondrial dynamics, inter-organelle communication, proliferation, mitophagy, immune response, inflammation and cell apoptosis. MUL1 is expressed at a higher basal level in the heart, immune system organs, and blood. Here, we discuss the role of MUL1 in mitochondrial dynamics and its function in various pathological models, both in vitro and in vivo. In this context, we describe the role of MUL1 in: (1) the inflammatory response, by regulating NF-κB activity, (2) cancer, by promoting cell death and regulating exonuclear function of proteins, such as p53 (3) neurological diseases, by maintaining communication with other organelles and interacting with proteins to eliminate damaged organelles and (4) cardiovascular diseases, by maintaining mitochondrial fusion/fission homeostasis. In this review, we summarize the latest advances in the physiological and pathological functions of MUL1. We also describe the different substrates of MUL1, acting as a positive or negative regulator in various pathologies associated with mitochondrial dysfunction. In conclusion, MUL1 could be a potential key target for the development of therapies that focus on ensuring the functionality of the mitochondrial network and, furthermore, the quality control of intracellular components by synchronously modulating the activity of different cellular mechanisms involved in the aforementioned pathologies. This, in turn, will guide the development of targeted therapies. This article is protected by copyright. All rights reserved.

Keywords: Akt; C1orf166; FLJ12875; GIDE; MAPL; MULAN; Mitochondrial E3 ubiquitin ligase 1; RNF218; cell death; inflammation; mitochondria morphology

DOI: https://doi.org/10.1002/iub.2657