Gene expression of iPSC-derived neurons from patient with Mohr-Tranebjaerg syndrome and healthy control
Ontology highlight
ABSTRACT: Mohr-Tranebjaerg syndrome (MTS) is a neurodegenerative disease caused by mutations in Translocase of Inner Mitochondrial Membrane 8A/Deafness Dystonia Protein 1 (TIMM8A/DDP1), which encodes TIMM8a/DDP1 located in the intermembrane space (IMS) of mitochondria. Up to now, the pathophysiology of MTS remains unclear. In this study, we established induced pluripotent stem cells (iPSCs) derived from MTS patient carrying the TIMM8a loss-of-function pathogenic variant, p.Q75fs95* to study the mechanism of MTS. We found that MTS-iPSCs presented defects in neuronal differentiation, exhibited smaller somata, fewer branches and shorter neurites, accompanied by mitochondrial dysfunction including fragmented mitochondria, reduced ATP and elevated ROS.
Project description:Recent studies have linked bioenergetic regulation to cellular differentiation. However, the contribution of metabolic communication among subcellular components to the fate of progenitor cells remains unclear. Adenylate kinase 2 (AK2) is an adenylate phosphotransferase localized in the mitochondrial intermembrane space. Although AK2 mutations in human can cause a severe combined immunodeficiency with neutropenia, named reticular dysgenesis (RD), underlying mechanisms have not yet been elucidated. To address these questions, we established induced pluripotent stem cells (iPSCs) from two RD patients. Metabolic flux analysis revealed that AK2 mediates the distribution of glycolytic metabolites into the tricarbon acid cycle in mitochondria. Hematopoietic differentiation from RD-iPSCs was profoundly impaired. Intriguingly, RD-iPSC-derived hematopoietic progenitors exhibited an immature mitochondrial morphology, discordant ATP distribution among the mitochondria and nucleus, and alteration of global transcriptional profiles. These results highlight the importance of stage-specific intracellular energy communication for controlling the fate of multipotential progenitors.
Project description:Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria can be disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in adenine nucleotide translocase 1 (Ant1), and its yeast homolog Aac2, cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis and cell viability independent of Ant1’s nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/Ant1 cause severe clogging primarily at the Translocase of the Outer Membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger Ant1 variant led to neurodegeneration and an age-dependent dominant myopathy that phenocopy Ant1-induced human disease, suggesting clogging as a mechanism of disease. More broadly, this work implies the existence of uncharacterized amino acid requirements for mitochondrial carrier proteins to avoid clogging and subsequent disease.
Project description:Mitochondrial functions are essential for cell viability and rely on protein import into the organelle. Various disease and stress conditions can lead to mitochondrial import defects. We find that inhibition of mitochondrial import in budding yeast activates a surveillance mechanism, mitoCPR, that is aimed at ameliorating mitochondrial import and protecting mitochondria during import stress. mitoCPR induces expression of Cis1 which associates with the mitochondrial translocase to reduce the accumulation of mitochondrial precursor proteins at the organelle surface. Clearance of precursor proteins depends on the Cis1 interacting AAA+ ATPase Msp1 and the proteasome suggesting that Cis1 facilitates degradation of un-imported proteins at the mitochondrial surface.
Project description:Mitophagy is essential to maintain mitochondrial function and prevent diseases. It activates upon mitochondria depolarization, which causes PINK1 stabilization on the mitochondrial outer membrane. Strikingly, a number of conditions, including mitochondrial protein misfolding, can induce mitophagy without a loss in membrane potential. The underlying molecular details remain unclear. Here, we report that a loss of mitochondrial protein import, mediated by the pre-sequence translocase-associated motor complex PAM, is sufficient to induce mitophagy in polarized mitochondria. A genome-wide CRISPR/Cas9 screen for mitophagy inducers identifies components of the PAM complex. Protein import defects are able to induce mitophagy without a need for depolarization. Upon mitochondrial protein misfolding, PAM dissociates from the import machinery resulting in decreased protein import and mitophagy induction. Our findings extend the current mitophagy model to explain mitophagy induction upon conditions that do not affect membrane polarization, such as mitochondrial protein misfolding.
Project description:Mitochondria are complex organelles with different compartments, each harboring their own protein quality control factors. While the chaperones of the mitochondrial matrix have been well characterized, it is poorly understood which chaperones protect the mitochondrial intermembrane space. We show that cytosolic small heat shock proteins are imported under basal conditions into the mitochondrial intermembrane space, where they operate as molecular chaperones. To identify chaperone substrates with MS/MS, we used a molecular trap variant of HSPB1/Hsp27 (S135F mutant). Through affinity-enrichment co-immunoprecipitation we identified significantly enriched substrates versus GFP-negative control.
Project description:In this study, we show that within minutes of exposure to differentiation cues and activation of the electron transport chain, the mitochondrial outer membrane transiently fuses with the nuclear membrane of neural progenitors, leading to efflux of the nuclear-encoded RNAs (neRNA) into the positively charged mitochondrial intermembrane space. Subsequent degradation of mitochondrial neRNAs by Polynucleotide phosphorylase 1 (Pnpt1) residing in the intermembrane space curbs the transcriptomic memory of progenitor cells. Further, phosphorolysis by Pnpt1 indirectly suppresses ATP production by depriving ATP synthase of inorganic phosphate, resulting in delayed recovery of the attenuated transcriptomic memory. Collectively, these events force the progenitor cells towards a “tipping point” characterised by emergence of a competing neuronal differentiation program.
Project description:In this study, we show that within minutes of exposure to differentiation cues and activation of the electron transport chain, the mitochondrial outer membrane transiently fuses with the nuclear membrane of neural progenitors, leading to efflux of the nuclear-encoded RNAs (neRNA) into the positively charged mitochondrial intermembrane space. Subsequent degradation of mitochondrial neRNAs by Polynucleotide phosphorylase 1 (Pnpt1) residing in the intermembrane space curbs the transcriptomic memory of progenitor cells. Further, phosphorolysis by Pnpt1 indirectly suppresses ATP production by depriving ATP synthase of inorganic phosphate, resulting in delayed recovery of the attenuated transcriptomic memory. Collectively, these events force the progenitor cells towards a “tipping point” characterised by emergence of a competing neuronal differentiation program.
Project description:Mitochondria are the central metabolic hub of the cell and their function is vital for cellular activities. Mitochondrial autophagy, or mitophagy, is a quality control mechanism to surveille the fitness and functionality of mitochondria and is therefore essential for life. Both mitochondrial dysfunction and malfunctional DNA damage response (DDR) are a major etiology for tissue impairment and aging. ATR has been shown mainly as a nuclear factor to conduct DNA damage response under DNA replication stress. Paradoxically, the human Seckel syndrome caused by ATR mutations is characterized by premature aging and neuropathies, suggesting a role of ATR in non-replicating tissues. Here we report a previously unknown yet direct role of ATR at mitochondria. We find that HSP90 chaperones ATR and PINK1 to mitochondria, where ATR interacts with and thereby stabilizes PINK1 docking at the mitochondrial translocase TOM/TIM complex as well as with the electron transport chain (ETC). ATR mutant cells are refractory to mitophagy initiation, which can be reverted by an ectopic expression of full length, but not ATR-interaction mutant, PINK1. ATR deletion alters mitochondrial dynamics and OXPHOS functions producing aberrantly high reactive oxygen species (ROS) that attack cytosolic macromolecules prior to damaging nuclear DNA. Intriguingly, pharmacological intervention of mitochondrial metabolism to prevent ROS overproduction can mute ATR-mediated nuclear DDR. This study demonstrates that ATR is an integrated component of the mitochondrial membrane to ensure mitochondrial fitness as a primary physiological function, which, together with its essential DDR function, safeguards the cell fate under physiological and genotoxic conditions.
Project description:Leukemic stem cells (LSC) rely on oxidative metabolism and are differentially sensitive to targeting mitochondrial pathways, which spares normal hematopoietic cells. A subset of mitochondrial proteins are folded in the intermembrane space via the mitochondrial intermembrane assembly (MIA) pathway. We found increased mRNA expression of MIA pathway substrates in acute myeloid leukemia (AML) stem cells. Therefore, we evaluated the effects of inhibiting this pathway in AML. Genetic and chemical inhibition of ALR reduces AML growth and viability, disrupts LSC self-renewal and induces their differentiation. ALR inhibition preferentially decreases its substrate COX17, a mitochondrial copper chaperone and knockdown of COX17 phenocopies ALR loss. Inhibiting ALR and COX17 increases mitochondrial copper levels which in turn inhibit S-Adenosylhomocysteine Hydrolase (SAHH) and lower levels of S-adenosylmethionine (SAM), DNA methylation, and chromatin accessibility to lower LSC viability. These results provide insight into mechanisms through which mitochondrial copper controls epigenetic status and viability of LSCs.
Project description:Aberrant localization of proteins to mitochondria disturbs mitochondrial function and contributes to the pathogenesis of Huntington’s disease (HD). However, the crucial factors and the molecular mechanisms remain elusive. Here, we found that heat shock transcription factor 1 (HSF1) accumulates in the mitochondria of HD cell cultures, a YAC128 mouse model, and human striatal organoids derived from HD induced pluripotent stem cells (iPSCs). Overexpression of mitochondria-targeting HSF1 (mtHSF1) in the striatum causes neurodegeneration and HD-like behavior. Mechanistically, mtHSF1 facilitates mitochondrial fission by activating dynamin-related protein 1 (Drp1) phosphorylation at S616. Moreover, mtHSF1 suppresses single-stranded DNA binding protein 1 (SSBP1) oligomer formation, which results in mitochondrial DNA (mtDNA) deletion. Suppression of HSF1 mitochondrial localization by DH1, a unique peptide inhibitor, abolishes HSF1-induced mitochondrial abnormalities and ameliorates deficits in an HD animal model and human striatal organoids. Altogether, our findings describe an unsuspected role of HSF1 in contributing to mitochondrial dysfunction, which may provide a promising therapeutic target for HD.