Publications by authors named "Isabella R Straub"

4 Publications

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Multi-OMICS study of a CHCHD10 variant causing ALS demonstrates metabolic rewiring and activation of endoplasmic reticulum and mitochondrial unfolded protein responses.

Hum Mol Genet 2021 May;30(8):687-705

Department of Human Genetics, McGill University, Montreal, Quebec, Canada.

Mutations in CHCHD10, coding for a mitochondrial intermembrane space protein, are a rare cause of autosomal dominant amyotrophic lateral sclerosis. Mutation-specific toxic gain of function or haploinsufficiency models have been proposed to explain pathogenicity. To decipher the metabolic dysfunction associated with the haploinsufficient p.R15L variant, we integrated transcriptomic, metabolomic and proteomic data sets in patient cells subjected to an energetic stress that forces the cells to rely on oxidative phosphorylation for ATP production. Patient cells had a complex I deficiency that resulted in an increased NADH/NAD+ ratio, diminished TCA cycle activity, a reorganization of one carbon metabolism and an increased AMP/ATP ratio leading to phosphorylation of AMPK and inhibition of mTORC1. These metabolic changes activated the unfolded protein response (UPR) in the ER through the IRE1/XBP1 pathway, upregulating downstream targets including ATF3, ATF4, CHOP and EGLN3, and two cytokine markers of mitochondrial disease, GDF15 and FGF21. Activation of the mitochondrial UPR was mediated through an upregulation of the transcription factors ATF4 and ATF5, leading to increased expression of mitochondrial proteases and heat shock proteins. There was a striking transcriptional up regulation of at least seven dual specific phosphatases, associated with an almost complete dephosphorylation of JNK isoforms, suggesting a concerted deactivation of MAP kinase pathways. This study demonstrates that loss of CHCHD10 function elicits an energy deficit that activates unique responses to nutrient stress in both the mitochondria and ER, which may contribute to the selective vulnerability of motor neurons.
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http://dx.doi.org/10.1093/hmg/ddab078DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8127406PMC
May 2021

Loss of CHCHD10-CHCHD2 complexes required for respiration underlies the pathogenicity of a CHCHD10 mutation in ALS.

Hum Mol Genet 2018 01;27(1):178-189

Department of Human Genetics, McGill University, Montreal, QC H3A 2B4, Canada.

Coiled-helix coiled-helix domain containing protein 10 (CHCHD10) and its paralogue CHCHD2 belong to a family of twin CX9C motif proteins, most of which localize to the intermembrane space of mitochondria. Dominant mutations in CHCHD10 cause amyotrophic lateral sclerosis (ALS)/frontotemporal dementia, and mutations in CHCHD2 have been associated with Parkinson's disease, but the function of these proteins remains unknown. Here we show that the p.R15L CHCHD10 variant in ALS patient fibroblasts destabilizes the protein, leading to a defect in the assembly of Complex I, impaired cellular respiration, mitochondrial hyperfusion, an increase in the steady-state level of CHCHD2, and a severe proliferation defect on galactose, a substrate that forces cells to synthesize virtually all of their ATP aerobically. CHCHD10 and CHCHD2 appeared together in distinct foci by immunofluorescence analysis and could be quantitatively immunoprecipitated with antibodies against either protein. Blue native polyacrylamide gel electrophoresis analyses showed that both proteins migrated in a high molecular weight complex (220 kDa) in control cells, which was, however, absent in patient cells. CHCHD10 and CHCHD2 levels increased markedly in control cells in galactose medium, a response that was dampened in patient cells, and a new complex (40 kDa) appeared in both control and patient cells cultured in galactose. Re-entry of patient cells into the cell cycle, which occurred after prolonged culture in galactose, was associated with a marked increase in Complex I, and restoration of the oxygen consumption defect. Our results indicate that CHCHD10-CHCHD2 complexes are necessary for efficient mitochondrial respiration, and support a role for mitochondrial dysfunction in some patients with ALS.
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http://dx.doi.org/10.1093/hmg/ddx393DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5886208PMC
January 2018

Significance of [2Fe-2S] Cluster N1a for Electron Transfer and Assembly of Escherichia coli Respiratory Complex I.

Biochemistry 2017 06 25;56(22):2770-2778. Epub 2017 May 25.

Spemann Graduate School of Biology and Medicine (SGBM), Albert-Ludwigs-University , Freiburg, Germany.

NADH:ubiquinone oxidoreductase, respiratory complex I, couples electron transfer from NADH to ubiquinone with proton translocation across the membrane. NADH reduces a noncovalently bound FMN, and the electrons are transported further to the quinone reduction site by a 95 Å long chain of seven iron-sulfur (Fe-S) clusters. Binuclear Fe-S cluster N1a is not part of this long chain but is located within electron transfer distance on the opposite site of FMN. The relevance of N1a to the mechanism of complex I is not known. To elucidate its role, we individually substituted the cysteine residues coordinating N1a of Escherichia coli complex I by alanine and serine residues. The mutations led to a significant loss of the NADH oxidase activity of the mutant membranes, while the amount of the complex was only slightly diminished. N1a could not be detected by electron paramagnetic resonance spectroscopy, and unexpectedly, the content of binuclear cluster N1b located on a neighboring subunit was significantly decreased. Because of the lack of N1a and the partial loss of N1b, the variants did not survive detergent extraction from the mutant membranes. Only the C97A variant retained N1a and was purified by chromatographic steps. The preparation showed a slightly diminished NADH/ferricyanide oxidoreductase activity, while the NADH:decyl-ubiquinone oxidoreductase activity was not affected. N1a of this preparation showed unusual spectroscopic properties indicating a different ligation. We discuss whether N1a is involved in the physiological electron transfer reaction.
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http://dx.doi.org/10.1021/acs.biochem.6b01058DOI Listing
June 2017

Serum 25-hydroxyvitamin D: a predictor of macrovascular and microvascular complications in patients with type 2 diabetes.

Diabetes Care 2015 Mar 18;38(3):521-8. Epub 2014 Dec 18.

National Health and Medical Research Council Clinical Trials Centre, University of Sydney, Sydney, Australia

Objective: People with diabetes frequently develop vascular disease. We investigated the relationship between blood 25-hydroxyvitamin D (25OH-D) concentration and vascular disease risk in type 2 diabetes.

Research Design And Methods: The relationships between blood 25OH-D concentration at baseline and the incidence of macrovascular (including myocardial infarction and stroke) and microvascular (retinopathy, nephropathy, neuropathy, and amputation) disease were analyzed with Cox proportional hazards models and logistic regression in an observational study of patients in the 5-year Fenofibrate Intervention and Event Lowering in Diabetes trial.

Results: A total of 50% of the patients had low vitamin D concentrations, as indicated by median blood 25OH-D concentration of 49 nmol/L. These patients with a blood 25OH-D concentration <50 nmol/L had a higher cumulative incidence of macrovascular and microvascular events than those with levels ≥50 nmol/L. Multivariate analysis, stratified by treatment and adjusted for relevant confounders, identified blood 25OH-D concentration as an independent predictor of macrovascular events. A 50 nmol/L difference in blood 25OH-D concentration was associated with a 23% (P = 0.007) change in risk of macrovascular complications during the study, and further adjustments for seasonality, hs-CRP, and physical activity level had little impact. The unadjusted risk of microvascular complications was 18% (P = 0.006) higher during the study, though the excess risk declined to 11-14% and lost significance with adjustment for HbA1c, seasonality, or physical activity.

Conclusions: Low blood 25OH-D concentrations are associated with an increased risk of macrovascular and microvascular disease events in type 2 diabetes. However, a causal link remains to be demonstrated.
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http://dx.doi.org/10.2337/dc14-0180DOI Listing
March 2015
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