Biology subjects

Wai, T.

Publications and source records attributed to Wai, T..

4 recordsLinked to original sources

bioRxiv2021

Mitochondrial fission process 1 (MTFP1) controls bioenergetic efficiency and prevents inflammatory cardiomyopathy and heart failure in mice

Mitochondria are paramount to the metabolism and survival of cardiomyocytes. Here we show that Mitochondrial Fission Process 1 (MTFP1) is essential for cardiac structure and function. Constitutive knockout of cardiomyocyte MTFP1 in mice resulted in adult-onset dilated cardiomyopathy (DCM) characterized by sterile inflammation and cardiac fibrosis that progressed to heart failure and middle-aged death. Failing hearts from cardiomyocyte-restricted knockout mice displayed a general decline in mitochondrial gene expression and oxidative phosphorylation (OXPHOS) activity. Pre-DCM, we observed no defects in mitochondrial morphology, content, gene expression, OXPHOS assembly nor phosphorylation dependent respiration. However, knockout cardiac mitochondria displayed reduced membrane potential and increased non-phosphorylation dependent respiration, which could be rescued by pharmacological inhibition of the adenine nucleotide translocase ANT. Primary cardiomyocytes from pre-symptomatic knockout mice exhibited normal excitation-contraction coupling but increased sensitivity to programmed cell death (PCD), which was accompanied by an opening of the mitochondrial permeability transition pore (mPTP). Intriguingly, mouse embryonic fibroblasts deleted for Mtfp1 recapitulated PCD sensitivity and mPTP opening, both of which could be rescued by pharmacological or genetic inhibition of the mPTP regulator Cyclophilin D. Collectively, our data demonstrate that contrary to previous in vitro studies, the loss of the MTFP1 promotes mitochondrial uncoupling and increases cell death sensitivity, causally mediating pathogenic cardiac remodeling.

physiology↗

bioRxiv2021

Enhanced cGAS-STING-dependent interferon signaling associated with mutations in ATAD3A

Mitochondrial DNA (mtDNA) has been suggested to drive immune system activation, but the induction of interferon signaling by mtDNA has not been demonstrated in a Mendelian mitochondrial disease. We initially ascertained two patients, one with a purely neurological phenotype, and one with features suggestive of systemic sclerosis in a syndromic context, and found them both to demonstrate enhanced interferon-stimulated gene (ISG) expression in blood. We determined each to harbor a previously described de novo dominant-negative heterozygous mutation in ATAD3A, encoding ATPase family AAA domain-containing protein 3A (ATAD3A). We identified five further patients with mutations in ATAD3A, and recorded up-regulated ISG expression and interferon alpha protein in four of them. Knockdown of ATAD3A in THP-1 cells resulted in increased interferon signaling, mediated by cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING). Enhanced interferon signaling was abrogated in THP-1 cells and patient fibroblasts depleted of mtDNA. Thus, mutations in the mitochondrial membrane protein ATAD3A define a novel type I interferonopathy. SummaryDominant-negative mutations in ATAD3A, a ubiquitously expressed mitochondrial protein, cause mitochondrial DNA-dependent up-regulation of type I interferon signaling in the context of neurological disease and autoimmunity, thereby defining a novel type I interferonopathy.

immunology↗

bioRxiv2021

High-throughput phenotypic screen for genetic modifiers in patient-derived OPA1 mutant fibroblasts identifies PGS1 as a functional suppressor of mitochondrial fragmentation

Mutations affecting the mitochondrial fusion protein Optic Atrophy 1 (OPA1) cause autosomal dominant optic atrophy (DOA) - one of the most common form of mitochondrial disease. The majority of patients develop isolated optic atrophy, but about 20% of OPA1 mutation carriers manifest more severe neurological deficits as part of a "DOA+" phenotype. OPA1 deficiency causes mitochondrial fragmentation and also disrupts cristae organization, oxidative phosphorylation, mitochondrial DNA (mtDNA) maintenance, and cell viability. It has not yet been established whether phenotypic severity can be modulated by genetic modifiers of OPA1. To better understand the genetic regulation of mitochondrial dynamics, we established a high-throughput imaging pipeline using supervised machine learning (ML) to perform unbiased, quantitative mitochondrial morphology analysis that was coupled with a bespoke siRNA library targeting the entire known mitochondrial proteome (1531 genes), providing a detailed phenotypic screening of human fibroblasts. In control fibroblasts, we identified known and novel genes whose depletion promoted elongation or fragmentation of the mitochondrial network. In DOA+ patient fibroblasts, we identified 91 candidate genes whose depletion prevents mitochondrial fragmentation, including the mitochondrial fission genes DNM1L, MIEF1, and SLC25A46, but also genes not previously linked to mitochondrial dynamics such as Phosphatidyl Glycerophosphate Synthase (PGS1), which belongs to the cardiolipin (CL) synthesis pathway. PGS1 depletion reduces CL content in mitochondria and rebalances mitochondrial dynamics in OPA1-deficient fibroblasts by inhibiting mitochondrial fission, which improves defective respiration, but does not rescue mtDNA depletion, cristae dysmorphology or apoptotic sensitivity. Our data reveal that the multifaceted roles of OPA1 in mitochondria can be functionally uncoupled by modulating mitochondrial lipid metabolism, providing novel insights into the cellular relevance of mitochondrial fragmentation. This study illustrates the power of a first-in-kind objective automated imaging approach to uncover genetic modifiers of mitochondrial disease through high-throughput phenotypic screening of patient fibroblasts.

cell biology↗

bioRxiv2020

Distinct molecular signatures of fission predict mitochondrial degradation or proliferation

Mitochondrial fission is a highly regulated process which, when disrupted, can alter metabolism, proliferation and apoptosis1-3. The downstream effects have implications for many diseases, from neurodegeneration4-6 to cardiovascular disease7,8 and cancer9,10. Key components of the fission machinery have been identified: constriction sites are initiated by the endoplasmic reticulum (ER)11 and actin12 before dynamin-related protein 1 (Drp1)13 is recruited to the outer mitochondrial membrane via adaptor proteins14-17, where it drives constriction and scission of the membrane18. In the life cycle of mitochondria, fission is important for the biogenesis of new mitochondria as well as the clearance of dysfunctional mitochondria via mitophagy3,19. Global regulation of fission on the cellular level is insufficient to explain how fate decisions are made at the single organelle level, so it is unknown how those dual functions arise, blocking progress in developing therapies that target mitochondrial activity. However, systematically studying mitochondrial division to uncover fate determinants is challenging, since fission is unpredictable, and mitochondrial morphology is extremely heterogeneous. Furthermore, because their ultrastructure lies below the diffraction limit, the dynamic organization of mitochondria and their interaction partners are hard to study at the single organelle level. We used live-cell structured illumination microscopy (SIM) and instant SIM20 for fast multi-colour acquisition of mitochondrial dynamics in Cos-7 cells and mouse cardiomyocytes. We analysed hundreds of fission events, and discovered two functionally and mechanistically distinct types of fission. Mitochondria divide peripherally to shed damaged material into smaller daughter mitochondria that subsequently undergo mitophagy, whereas healthy mitochondria proliferate via midzone division. Both types are Drp1-mediated, but they rely on different membrane adaptors to recruit Drp1, and ER and actin mediated pre-constriction is only involved in midzone fission.

cell biology↗