Publications by authors named "Sander M Houten"

122 Publications

An integrative multiomic network model links lipid metabolism to glucose regulation in coronary artery disease.

Nat Commun 2021 01 22;12(1):547. Epub 2021 Jan 22.

Department of Genetics and Genomic Science and Institute for Multiscale Biology, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA.

Elevated plasma cholesterol and type 2 diabetes (T2D) are associated with coronary artery disease (CAD). Individuals treated with cholesterol-lowering statins have increased T2D risk, while individuals with hypercholesterolemia have reduced T2D risk. We explore the relationship between lipid and glucose control by constructing network models from the STARNET study with sequencing data from seven cardiometabolic tissues obtained from CAD patients during coronary artery by-pass grafting surgery. By integrating gene expression, genotype, metabolomic, and clinical data, we identify a glucose and lipid determining (GLD) regulatory network showing inverse relationships with lipid and glucose traits. Master regulators of the GLD network also impact lipid and glucose levels in inverse directions. Experimental inhibition of one of the GLD network master regulators, lanosterol synthase (LSS), in mice confirms the inverse relationships to glucose and lipid levels as predicted by our model and provides mechanistic insights.
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http://dx.doi.org/10.1038/s41467-020-20750-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7822923PMC
January 2021

Glutaric aciduria type 3 is a naturally occurring biochemical trait in inbred mice of 129 substrains.

Mol Genet Metab 2021 02 12;132(2):139-145. Epub 2021 Jan 12.

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA. Electronic address:

The glutaric acidurias are a group of inborn errors of metabolism with different etiologies. Glutaric aciduria type 3 (GA3) is a biochemical phenotype with uncertain clinical relevance caused by a deficiency of succinyl-CoA:glutarate-CoA transferase (SUGCT). SUGCT catalyzes the succinyl-CoA-dependent conversion of glutaric acid into glutaryl-CoA preventing urinary loss of the organic acid. Here, we describe the presence of a GA3 trait in mice of 129 substrains due to SUGCT deficiency, which was identified by screening of urine organic acid profiles obtained from different inbred mouse strains including 129S2/SvPasCrl. Molecular and biochemical analyses in an F2 population of the parental C57BL/6J and 129S2/SvPasCrl strains (B6129F2) confirmed that the GA3 trait occurred in Sugct animals. We evaluated the impact of SUGCT deficiency on metabolite accumulation in the glutaric aciduria type 1 (GA1) mouse model. We found that GA1 mice with SUGCT deficiency have decreased excretion of urine 3-hydroxyglutaric acid and decreased levels glutarylcarnitine in urine, plasma and kidney. Our work demonstrates that SUGCT contributes to the production of glutaryl-CoA under conditions of low and pathologically high glutaric acid levels. Our work also highlights the notion that unexpected biochemical phenotypes can occur in widely used inbred animal lines.
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http://dx.doi.org/10.1016/j.ymgme.2021.01.004DOI Listing
February 2021

NLRX1 Deletion Increases Ischemia-Reperfusion Damage and Activates Glucose Metabolism in Mouse Heart.

Front Immunol 2020 11;11:591815. Epub 2020 Dec 11.

Laboratory of Experimental Intensive Care and Anesthesiology, Department of Anesthesiology, Amsterdam UMC, University of Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, Netherlands.

Background: NOD-like receptors (NLR) are intracellular sensors of the innate immune system, with the NLRP3 being a pro-inflammatory member that modulates cardiac ischemia-reperfusion injury (IRI) and metabolism. No information is available on a possible role of anti-inflammatory NLRs on IRI and metabolism in the intact heart. Here we hypothesize that the constitutively expressed, anti-inflammatory mitochondrial NLRX1, affects IRI and metabolism of the isolated mouse heart.

Methods: Isolated C57Bl/6J and NLRX1 knock-out (KO) mouse hearts were perfused with a physiological mixture of the essential substrates (lactate, glucose, pyruvate, fatty acid, glutamine) and insulin. For the IRI studies, hearts were subjected to either mild (20 min) or severe (35 min) ischemia and IRI was determined at 60 min reperfusion. Inflammatory mediators (IL-6, TNFα) and survival pathways (mito-HKII, p-Akt, p-AMPK, p-STAT3) were analyzed at 5 min of reperfusion. For the metabolism studies, hearts were perfused for 35 min with either 5.5 mM C-glucose or 0.4 mM C-palmitate under normoxic conditions, followed by LC-MS analysis and integrated, stepwise, mass-isotopomeric flux analysis (MIMOSA).

Results: NLRX1 KO significantly increased IRI (infarct size from 63% to 73%, end-diastolic pressure from 59 mmHg to 75 mmHg, and rate-pressure-product recovery from 15% to 6%), following severe, but not mild, ischemia. The increased IRI in NLRX1 KO hearts was associated with depressed Akt signaling at early reperfusion; other survival pathways or inflammatory parameters were not affected. Metabolically, NLRX1 KO hearts displayed increased lactate production and glucose oxidation relative to fatty acid oxidation, associated with increased pyruvate dehydrogenase flux and 10% higher cardiac oxygen consumption.

Conclusion: Deletion of the mitochondrially-located NOD-like sensor NLRX1 exacerbates severe cardiac IR injury, possibly through impaired Akt signaling, and increases cardiac glucose metabolism.
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http://dx.doi.org/10.3389/fimmu.2020.591815DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7759503PMC
December 2020

Empagliflozin Decreases Lactate Generation in an NHE-1 Dependent Fashion and Increases α-Ketoglutarate Synthesis From Palmitate in Type II Diabetic Mouse Hearts.

Front Cardiovasc Med 2020 4;7:592233. Epub 2020 Dec 4.

Laboratory of Experimental Intensive Care and Anesthesiology, Department of Anesthesiology, Amsterdam Cardiovascular Sciences, Amsterdam Universitair Medische Centra, University of Amsterdam, Amsterdam, Netherlands.

Changes in cardiac metabolism and ion homeostasis precede and drive cardiac remodeling and heart failure development. We previously demonstrated that sodium/glucose cotransporter 2 inhibitors (SGLT2i's) have direct cardiac effects on ion homeostasis, possibly through inhibition of the cardiac sodium/hydrogen exchanger (NHE-1). Here, we hypothesize that Empagliflozin (EMPA) also possesses direct and acute cardiac effects on glucose and fatty acid metabolism of isolated type II diabetes mellitus () mouse hearts. In addition, we explore whether direct effects on glucose metabolism are nullified in the presence of an NHE-1 inhibitor. Langendorff-perfused type II diabetic db/db mouse hearts were examined in three different series: : C glucose perfusions ( = 32); : C palmitate perfusions ( = 13); and : C glucose + 10 μM Cariporide (specific NHE-1 inhibitor) perfusions ( = 17). Within each series, EMPA treated hearts (1 μM EMPA) were compared with vehicle-perfused hearts (0.02% DMSO). Afterwards, hearts were snap frozen and lysed for stable isotope analysis and metabolomics using LC-MS techniques. Hearts from series 1 were also analyzed for phosphorylation status of AKT, STAT3, AMPK, ERK, and eNOS ( = 8 per group). Cardiac mechanical performance, oxygen consumption and protein phosphorylation were not altered by 35 min EMPA treatment. EMPA was without an overall acute and direct effect on glucose or fatty acid metabolism. However, EMPA did specifically decrease cardiac lactate labeling in the C glucose perfusions (C labeling of lactate: 58 ± 2% vs. 50 ± 3%, for vehicle and EMPA, respectively; = 0.02), without changes in other glucose metabolic pathways. In contrast, EMPA increased cardiac labeling in α-ketoglutarate derived from C palmitate perfusions (C labeling of α-KG: 79 ± 1% vs. 86 ± 1% for vehicle and EMPA, respectively; = 0.01). Inhibition of the NHE by Cariporide abolished EMPA effects on lactate labeling from C glucose. The present study shows for the first time that the SGLT2 inhibitor Empagliflozin has acute specific metabolic effects in isolated diabetic hearts, i.e., decreased lactate generation from labeled glucose and increased α-ketoglutarate synthesis from labeled palmitate. The decreased lactate generation by EMPA seems to be mediated through NHE-1 inhibition.
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http://dx.doi.org/10.3389/fcvm.2020.592233DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7746656PMC
December 2020

Intestinal Inflammation Modulates the Expression of ACE2 and TMPRSS2 and Potentially Overlaps With the Pathogenesis of SARS-CoV-2-related Disease.

Gastroenterology 2021 01 25;160(1):287-301.e20. Epub 2020 Sep 25.

The Dr. Henry D. Janowitz Division of Gastroenterology, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York; Precision Institute of Immunology, Icahn School of Medicine at Mount Sinai, New York, New York. Electronic address:

Background And Aims: The presence of gastrointestinal symptoms and high levels of viral RNA in the stool suggest active severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication within enterocytes.

Methods: Here, in multiple, large cohorts of patients with inflammatory bowel disease (IBD), we have studied the intersections between Coronavirus Disease 2019 (COVID-19), intestinal inflammation, and IBD treatment.

Results: A striking expression of ACE2 on the small bowel enterocyte brush border supports intestinal infectivity by SARS-CoV-2. Commonly used IBD medications, both biologic and nonbiologic, do not significantly impact ACE2 and TMPRSS2 receptor expression in the uninflamed intestines. In addition, we have defined molecular responses to COVID-19 infection that are also enriched in IBD, pointing to shared molecular networks between COVID-19 and IBD.

Conclusions: These data generate a novel appreciation of the confluence of COVID-19- and IBD-associated inflammation and provide mechanistic insights supporting further investigation of specific IBD drugs in the treatment of COVID-19. Preprint doi: https://doi.org/10.1101/2020.05.21.109124.
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http://dx.doi.org/10.1053/j.gastro.2020.09.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7516468PMC
January 2021

The lysine degradation pathway: Subcellular compartmentalization and enzyme deficiencies.

Mol Genet Metab 2020 Sep - Oct;131(1-2):14-22. Epub 2020 Jul 30.

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA. Electronic address:

Lysine degradation via formation of saccharopine is a pathway confined to the mitochondria. The second pathway for lysine degradation, the pipecolic acid pathway, is not yet fully elucidated and known enzymes are localized in the mitochondria, cytosol and peroxisome. The tissue-specific roles of these two pathways are still under investigation. The lysine degradation pathway is clinically relevant due to the occurrence of two severe neurometabolic disorders, pyridoxine-dependent epilepsy (PDE) and glutaric aciduria type 1 (GA1). The existence of three other disorders affecting lysine degradation without apparent clinical consequences opens up the possibility to find alternative therapeutic strategies for PDE and GA1 through pathway modulation. A better understanding of the mechanisms, compartmentalization and interplay between the different enzymes and metabolites involved in lysine degradation is of utmost importance.
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http://dx.doi.org/10.1016/j.ymgme.2020.07.010DOI Listing
July 2020

Inhibition and Crystal Structure of the Human DHTKD1-Thiamin Diphosphate Complex.

ACS Chem Biol 2020 08 9;15(8):2041-2047. Epub 2020 Jul 9.

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029, United States.

DHTKD1 is the E1 component of the 2-oxoadipate dehydrogenase complex, which is an enzyme involved in the catabolism of (hydroxy-)lysine and tryptophan. Mutations in DHTKD1 have been associated with 2-aminoadipic and 2-oxoadipic aciduria, Charcot-Marie-Tooth disease type 2Q and eosinophilic esophagitis, but the pathophysiology of these clinically distinct disorders remains elusive. Here, we report the identification of adipoylphosphonic acid and tenatoprazole as DHTKD1 inhibitors using targeted and high throughput screening, respectively. We furthermore elucidate the DHTKD1 crystal structure with thiamin diphosphate bound at 2.25 Å. We also report the impact of 10 disease-associated missense mutations on DHTKD1. Whereas the majority of the DHTKD1 variants displayed impaired folding or reduced thermal stability in combination with absent or reduced enzyme activity, three variants showed no abnormalities. Our work provides chemical and structural tools for further understanding of the function of DHTKD1 and its role in several human pathologies.
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http://dx.doi.org/10.1021/acschembio.0c00114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7890914PMC
August 2020

Deletion of 2-aminoadipic semialdehyde synthase limits metabolite accumulation in cell and mouse models for glutaric aciduria type 1.

J Inherit Metab Dis 2020 11 26;43(6):1154-1164. Epub 2020 Jul 26.

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA.

Glutaric aciduria type 1 (GA1) is an inborn error of lysine degradation characterized by acute encephalopathy that is caused by toxic accumulation of lysine degradation intermediates. We investigated the efficacy of substrate reduction through inhibition of 2-aminoadipic semialdehyde synthase (AASS), an enzyme upstream of the defective glutaryl-CoA dehydrogenase (GCDH), in a cell line and mouse model of GA1. We show that loss of AASS function in GCDH-deficient HEK-293 cells leads to an approximately fivefold reduction in the established GA1 clinical biomarker glutarylcarnitine. In the GA1 mouse model, deletion of Aass leads to a 4.3-, 3.8-, and 3.2-fold decrease in the glutaric acid levels in urine, brain, and liver, respectively. Parallel decreases were observed in urine and brain 3-hydroxyglutaric acid levels, and plasma, urine, and brain glutarylcarnitine levels. These in vivo data demonstrate that the saccharopine pathway is the main source of glutaric acid production in the brain and periphery of a mouse model for GA1, and support the notion that pharmacological inhibition of AASS may represent an attractive strategy to treat GA1.
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http://dx.doi.org/10.1002/jimd.12276DOI Listing
November 2020

DHTKD1 and OGDH display substrate overlap in cultured cells and form a hybrid 2-oxo acid dehydrogenase complex in vivo.

Hum Mol Genet 2020 05;29(7):1168-1179

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.

Glutaric aciduria type 1 (GA1) is an inborn error of lysine degradation characterized by a specific encephalopathy that is caused by toxic accumulation of lysine degradation intermediates. Substrate reduction through inhibition of DHTKD1, an enzyme upstream of the defective glutaryl-CoA dehydrogenase, has been investigated as a potential therapy, but revealed the existence of an alternative enzymatic source of glutaryl-CoA. Here, we show that loss of DHTKD1 in glutaryl-CoA dehydrogenase-deficient HEK-293 cells leads to a 2-fold decrease in the established GA1 clinical biomarker glutarylcarnitine and demonstrate that oxoglutarate dehydrogenase (OGDH) is responsible for this remaining glutarylcarnitine production. We furthermore show that DHTKD1 interacts with OGDH, dihydrolipoyl succinyltransferase and dihydrolipoamide dehydrogenase to form a hybrid 2-oxoglutaric and 2-oxoadipic acid dehydrogenase complex. In summary, 2-oxoadipic acid is a substrate for DHTKD1, but also for OGDH in a cell model system. The classical 2-oxoglutaric dehydrogenase complex can exist as a previously undiscovered hybrid containing DHTKD1 displaying improved kinetics towards 2-oxoadipic acid.
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http://dx.doi.org/10.1093/hmg/ddaa037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7206849PMC
May 2020

Metabolic interactions between peroxisomes and mitochondria with a special focus on acylcarnitine metabolism.

Biochim Biophys Acta Mol Basis Dis 2020 05 10;1866(5):165720. Epub 2020 Feb 10.

Department of Genetics and Genomic Sciences, Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, Box 1498, New York, NY 10029, USA.

Carnitine plays an essential role in mitochondrial fatty acid β-oxidation as a part of a cycle that transfers long-chain fatty acids across the mitochondrial membrane and involves two carnitine palmitoyltransferases (CPT1 and CPT2). Two distinct carnitine acyltransferases, carnitine octanoyltransferase (COT) and carnitine acetyltransferase (CAT), are peroxisomal enzymes, which indicates that carnitine is not only important for mitochondrial, but also for peroxisomal metabolism. It has been demonstrated that after peroxisomal metabolism, specific intermediates can be exported as acylcarnitines for subsequent and final mitochondrial metabolism. There is also evidence that peroxisomes are able to degrade fatty acids that are typically handled by mitochondria possibly after transport as acylcarnitines. Here we review the biochemistry and physiological functions of metabolite exchange between peroxisomes and mitochondria with a special focus on acylcarnitines.
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http://dx.doi.org/10.1016/j.bbadis.2020.165720DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146961PMC
May 2020

Slc22a5 haploinsufficiency does not aggravate the phenotype of the long-chain acyl-CoA dehydrogenase KO mouse.

J Inherit Metab Dis 2020 05 23;43(3):486-495. Epub 2019 Dec 23.

Department of Genetics and Genomic Sciences, Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, New York, New York.

Secondary carnitine deficiency is commonly observed in inherited metabolic diseases characterised by the accumulation of acylcarnitines such as mitochondrial fatty acid oxidation (FAO) disorders. It is currently unclear if carnitine deficiency and/or acylcarnitine accumulation play a role in the pathophysiology of FAO disorders. The long-chain acyl-CoA dehydrogenase (LCAD) KO mouse is a model for long-chain FAO disorders and is characterised by decreased levels of tissue and plasma free carnitine. Tissue levels of carnitine are controlled by SLC22A5, the plasmalemmal carnitine transporter. Here, we have further decreased carnitine availability in the LCAD KO mouse through a genetic intervention by introducing one defective Slc22a5 allele (jvs). Slc22a5 haploinsufficiency decreased free carnitine levels in liver, kidney, and heart of LCAD KO animals. The resulting decrease in the tissue long-chain acylcarnitines levels had a similar magnitude as the decrease in free carnitine. Levels of cardiac deoxycarnitine, a carnitine biosynthesis intermediate, were elevated due to Slc22a5 haploinsufficiency in LCAD KO mice. A similar increase in heart and muscle deoxycarnitine was observed in an independent experiment using Slc22a5 mice. Cardiac hypertrophy, fasting-induced hypoglycemia and increased liver weight, the major phenotypes of the LCAD KO mouse, were not affected by Slc22a5 haploinsufficiency. This may suggest that secondary carnitine deficiency does not play a major role in the pathophysiology of these phenotypes. Similarly, our data do not support a major role for toxicity of long-chain acylcarnitines in the phenotype of the LCAD KO mouse.
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http://dx.doi.org/10.1002/jimd.12204DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7205564PMC
May 2020

Liver disease predominates in a mouse model for mild human Zellweger spectrum disorder.

Biochim Biophys Acta Mol Basis Dis 2019 10 15;1865(10):2774-2787. Epub 2019 Jun 15.

Amsterdam UMC, University of Amsterdam, Laboratory Genetic Metabolic Diseases, Amsterdam Gastroenterology & Metabolism, the Netherlands. Electronic address:

Zellweger spectrum disorders (ZSDs) are autosomal recessive diseases caused by defective peroxisome assembly. They constitute a clinical continuum from severe early lethal to relatively milder presentations in adulthood. Liver disease is a prevalent symptom in ZSD patients. The underlying pathogenesis for the liver disease, however, is not fully understood. We report a hypomorphic ZSD mouse model, which is homozygous for Pex1-c.2531G>A (p.G844D), the equivalent of the most common pathogenic variant found in ZSD, and which predominantly presents with liver disease. After introducing the Pex1-G844D allele by knock-in, we characterized homozygous Pex1-G844D mice for survival, biochemical parameters, including peroxisomal and mitochondrial functions, organ histology, and developmental parameters. The first 20 post-natal days (P20) were critical for survival of homozygous Pex1-G844D mice (~20% survival rate). Lethality was likely due to a combination of cholestatic liver problems, liver dysfunction and caloric deficit, probably as a consequence of defective bile acid biosynthesis. Survival beyond P20 was nearly 100%, but surviving mice showed a marked delay in growth. Surviving mice showed similar hepatic problems as described for mild ZSD patients, including hepatomegaly, bile duct proliferation, liver fibrosis and mitochondrial alterations. Biochemical analyses of various tissues showed the absence of functional peroxisomes accompanied with aberrant levels of peroxisomal metabolites predominantly in the liver, while other tissues were relatively spared. ur findings show that homozygous Pex1-G844D mice have a predominant liver disease phenotype, mimicking the hepatic pathology of ZSD patients, and thus constitute a good model to study pathogenesis and treatment of liver disease in ZSD patients.
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http://dx.doi.org/10.1016/j.bbadis.2019.06.013DOI Listing
October 2019

Mild inborn errors of metabolism in commonly used inbred mouse strains.

Mol Genet Metab 2019 04 24;126(4):388-396. Epub 2019 Jan 24.

Department of Genetics and Genomic Sciences, Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, Box 1498, New York, NY 10029, USA. Electronic address:

Inbred mouse strains are a cornerstone of translational research but paradoxically many strains carry mild inborn errors of metabolism. For example, α-aminoadipic acidemia and branched-chain ketoacid dehydrogenase deficiency are known in C57BL/6J mice. Using RNA sequencing, we now reveal the causal variants in Dhtkd1 and Bckdhb, and the molecular mechanism underlying these metabolic defects. C57BL/6J mice have decreased Dhtkd1 mRNA expression due to a solitary long terminal repeat (LTR) in intron 4 of Dhtkd1. This LTR harbors an alternate splice donor site leading to a partial splicing defect and as a consequence decreased total and functional Dhtkd1 mRNA, decreased DHTKD1 protein and α-aminoadipic acidemia. Similarly, C57BL/6J mice have decreased Bckdhb mRNA expression due to an LTR retrotransposon in intron 1 of Bckdhb. This transposable element encodes an alternative exon 1 causing aberrant splicing, decreased total and functional Bckdhb mRNA and decreased BCKDHB protein. Using a targeted metabolomics screen, we also reveal elevated plasma C5-carnitine in 129 substrains. This biochemical phenotype resembles isovaleric acidemia and is caused by an exonic splice mutation in Ivd leading to partial skipping of exon 10 and IVD protein deficiency. In summary, this study identifies three causal variants underlying mild inborn errors of metabolism in commonly used inbred mouse strains.
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http://dx.doi.org/10.1016/j.ymgme.2019.01.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6535113PMC
April 2019

PLPHP deficiency: clinical, genetic, biochemical, and mechanistic insights.

Brain 2019 03;142(3):542-559

British Columbia Children's Hospital Research Institute, Vancouver, BC, Canada.

Biallelic pathogenic variants in PLPBP (formerly called PROSC) have recently been shown to cause a novel form of vitamin B6-dependent epilepsy, the pathophysiological basis of which is poorly understood. When left untreated, the disease can progress to status epilepticus and death in infancy. Here we present 12 previously undescribed patients and six novel pathogenic variants in PLPBP. Suspected clinical diagnoses prior to identification of PLPBP variants included mitochondrial encephalopathy (two patients), folinic acid-responsive epilepsy (one patient) and a movement disorder compatible with AADC deficiency (one patient). The encoded protein, PLPHP is believed to be crucial for B6 homeostasis. We modelled the pathogenicity of the variants and developed a clinical severity scoring system. The most severe phenotypes were associated with variants leading to loss of function of PLPBP or significantly affecting protein stability/PLP-binding. To explore the pathophysiology of this disease further, we developed the first zebrafish model of PLPHP deficiency using CRISPR/Cas9. Our model recapitulates the disease, with plpbp-/- larvae showing behavioural, biochemical, and electrophysiological signs of seizure activity by 10 days post-fertilization and early death by 16 days post-fertilization. Treatment with pyridoxine significantly improved the epileptic phenotype and extended lifespan in plpbp-/- animals. Larvae had disruptions in amino acid metabolism as well as GABA and catecholamine biosynthesis, indicating impairment of PLP-dependent enzymatic activities. Using mass spectrometry, we observed significant B6 vitamer level changes in plpbp-/- zebrafish, patient fibroblasts and PLPHP-deficient HEK293 cells. Additional studies in human cells and yeast provide the first empirical evidence that PLPHP is localized in mitochondria and may play a role in mitochondrial metabolism. These models provide new insights into disease mechanisms and can serve as a platform for drug discovery.
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http://dx.doi.org/10.1093/brain/awy346DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6391652PMC
March 2019

Saccharopine, a lysine degradation intermediate, is a mitochondrial toxin.

J Cell Biol 2019 02 16;218(2):391-392. Epub 2019 Jan 16.

Department of Genetics and Genomic Sciences and Icahn Institute for Data Science and Genomic Technology, Icahn School of Medicine at Mount Sinai, New York, NY

Saccharopine, a nonproteinogenic amino acid originally isolated from the yeast , is an intermediate in lysine metabolism. In this issue, Zhou et al. (2019. https://doi.org./10.1083/jcb.201807204) show that abnormal accumulation of saccharopine results in defective mitochondrial dynamics and function in worm and mouse models.
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http://dx.doi.org/10.1083/jcb.201901033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363453PMC
February 2019

Peroxisomes can oxidize medium- and long-chain fatty acids through a pathway involving ABCD3 and HSD17B4.

FASEB J 2019 03 12;33(3):4355-4364. Epub 2018 Dec 12.

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA.

Peroxisomes are essential organelles for the specialized oxidation of a wide variety of fatty acids, but they are also able to degrade fatty acids that are typically handled by mitochondria. Using a combination of pharmacological inhibition and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein 9 genome editing technology to simultaneously manipulate peroxisomal and mitochondrial fatty acid β-oxidation (FAO) in HEK-293 cells, we identified essential players in the metabolic crosstalk between these organelles. Depletion of carnitine palmitoyltransferase (CPT)2 activity through pharmacological inhibition or knockout (KO) uncovered a significant residual peroxisomal oxidation of lauric and palmitic acid, leading to the production of peroxisomal acylcarnitine intermediates. Generation and analysis of additional single- and double-KO cell lines revealed that the D-bifunctional protein (HSD17B4) and the peroxisomal ABC transporter ABCD3 are essential in peroxisomal oxidation of lauric and palmitic acid. Our results indicate that peroxisomes not only accept acyl-CoAs but can also oxidize acylcarnitines in a similar biochemical pathway. By using an Hsd17b4 KO mouse model, we demonstrated that peroxisomes contribute to the plasma acylcarnitine profile after acute inhibition of CPT2, proving in vivo relevance of this pathway. We summarize that peroxisomal FAO is important when mitochondrial FAO is defective or overloaded.-Violante, S., Achetib, N., van Roermund, C. W. T., Hagen, J., Dodatko, T., Vaz, F. M., Waterham, H. R., Chen, H., Baes, M., Yu, C., Argmann, C. A., Houten, S. M. Peroxisomes can oxidize medium- and long-chain fatty acids through a pathway involving ABCD3 and HSD17B4.
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http://dx.doi.org/10.1096/fj.201801498RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6404569PMC
March 2019

Increased cardiac fatty acid oxidation in a mouse model with decreased malonyl-CoA sensitivity of CPT1B.

Cardiovasc Res 2018 08;114(10):1324-1334

Department of Genetics and Genomic Sciences, Icahn Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, Box 1498, New York, NY, USA.

Aims: Mitochondrial fatty acid oxidation (FAO) is an important energy provider for cardiac work and changes in cardiac substrate preference are associated with different heart diseases. Carnitine palmitoyltransferase 1B (CPT1B) is thought to perform the rate limiting enzyme step in FAO and is inhibited by malonyl-CoA. The role of CPT1B in cardiac metabolism has been addressed by inhibiting or decreasing CPT1B protein or after modulation of tissue malonyl-CoA metabolism. We assessed the role of CPT1B malonyl-CoA sensitivity in cardiac metabolism.

Methods And Results: We generated and characterized a knock in mouse model expressing the CPT1BE3A mutant enzyme, which has reduced sensitivity to malonyl-CoA. In isolated perfused hearts, FAO was 1.9-fold higher in Cpt1bE3A/E3A hearts compared with Cpt1bWT/WT hearts. Metabolomic, proteomic and transcriptomic analysis showed increased levels of malonylcarnitine, decreased concentration of CPT1B protein and a small but coordinated downregulation of the mRNA expression of genes involved in FAO in Cpt1bE3A/E3A hearts, all of which aim to limit FAO. In vivo assessment of cardiac function revealed only minor changes, cardiac hypertrophy was absent and histological analysis did not reveal fibrosis.

Conclusions: Malonyl-CoA-dependent inhibition of CPT1B plays a crucial role in regulating FAO rate in the heart. Chronic elevation of FAO has a relatively subtle impact on cardiac function at least under baseline conditions.
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http://dx.doi.org/10.1093/cvr/cvy089DOI Listing
August 2018

Protein moonlighting in inborn errors of metabolism: the case of the mitochondrial acylglycerol kinase.

Authors:
Sander M Houten

J Inherit Metab Dis 2017 11 21;40(6):755-756. Epub 2017 Sep 21.

Department of Genetics and Genomic Sciences, Icahn Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, Box 1498, New York, NY 10029, USA.

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http://dx.doi.org/10.1007/s10545-017-0090-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5743438PMC
November 2017

Germline deletion of Krüppel-like factor 14 does not increase risk of diet induced metabolic syndrome in male C57BL/6 mice.

Biochim Biophys Acta Mol Basis Dis 2017 12 28;1863(12):3277-3285. Epub 2017 Sep 28.

Department of Genetics and Genomic Sciences, Icahn Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, New York, NY, USA. Electronic address:

Objective: The transcription factor Krüppel-like factor 14 (KLF14) has been associated with type 2 diabetes and high-density lipoprotein-cholesterol (HDL-C) through genome-wide association studies. The mechanistic underpinnings of KLF14's control of metabolic processes remain largely unknown. We studied the physiological roles of KLF14 in a knockout (KO) mouse model.

Methods: Male whole body Klf14 KO mice were fed a chow or high fat diet (HFD) and diet induced phenotypes were analyzed. Additionally, tissue-specific expression of Klf14 was determined using RT-PCR, RNA sequencing, immunoblotting and whole mount lacZ staining. Finally, the consequences of KLF14 loss-of-function were studied using RNA sequencing in tissues with relatively high Klf14 expression levels.

Results: KLF14 loss-of-function did not affect HFD-induced weight gain or insulin resistance. Fasting plasma concentrations of glucose, insulin, cholesterol, HDL-C and ApoA-I were also comparable between Klf14 and Klf14 mice on chow and HFD. We found that in mice expression of Klf14 was the highest in the anterior pituitary (adenohypophysis), lower but detectable in white adipose tissue and undetectable in liver. Loss of KLF14 function impacted on the pituitary transcriptome with extracellular matrix organization as the primary affected pathway and a predicted link to glucocorticoid receptor signaling.

Conclusions: Whole body loss of KLF14 function in male mice does not result in metabolic abnormalities as assessed under chow and HFD conditions. Mostly likely there is redundancy for the role of KLF14 in the mouse and a diverging function in humans.
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http://dx.doi.org/10.1016/j.bbadis.2017.09.021DOI Listing
December 2017

Deficiency of the Mitochondrial NAD Kinase Causes Stress-Induced Hepatic Steatosis in Mice.

Gastroenterology 2018 01 18;154(1):224-237. Epub 2017 Sep 18.

Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan. Electronic address:

Background & Aims: The mitochondrial nicotinamide adenine dinucleotide (NAD) kinase (NADK2, also called MNADK) catalyzes phosphorylation of NAD to yield NADP. Little is known about the functions of mitochondrial NADP and MNADK in liver physiology and pathology. We investigated the effects of reduced mitochondrial NADP by deleting MNADK in mice.

Methods: We generated MNADK knockout (KO) mice on a C57BL/6NTac background; mice with a wild-type Mnadk gene were used as controls. Some mice were placed on an atherogenic high-fat diet (16% fat, 41% carbohydrate, and 1.25% cholesterol supplemented with 0.5% sodium cholate) or given methotrexate intraperitoneally. We measured rates of fatty acid oxidation in primary hepatocytes using radiolabeled palmitate and in mice using indirect calorimetry. We measured levels of reactive oxygen species in mouse livers and primary hepatocytes. Metabolomic analyses were used to quantify serum metabolites, such as amino acids and acylcarnitines.

Results: The KO mice had metabolic features of MNADK-deficient patients, such as increased serum concentrations of lysine and C10:2 carnitine. When placed on the atherogenic high-fat diet, the KO mice developed features of nonalcoholic fatty liver disease and had increased levels of reactive oxygen species in livers and primary hepatocytes, compared with control mice. During fasting, the KO mice had a defect in fatty acid oxidation. MNADK deficiency reduced the activation of cAMP-responsive element binding protein-hepatocyte specific and peroxisome proliferator-activated receptor alpha, which are transcriptional activators that mediate the fasting response. The activity of mitochondrial sirtuins was reduced in livers of the KO mice. Methotrexate inhibited the catalytic activity of MNADK in hepatocytes and in livers in mice with methotrexate injection. In mice given injections of methotrexate, supplementation of a diet with nicotinamide riboside, an NAD precursor, replenished hepatic NADP and protected the mice from hepatotoxicity, based on markers such as increased level of serum alanine aminotransferase.

Conclusion: MNADK facilitates fatty acid oxidation, counteracts oxidative damage, maintains mitochondrial sirtuin activity, and prevents metabolic stress-induced non-alcoholic fatty liver disease in mice.
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http://dx.doi.org/10.1053/j.gastro.2017.09.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5742027PMC
January 2018

Biallelic Mutations in MRPS34 Lead to Instability of the Small Mitoribosomal Subunit and Leigh Syndrome.

Am J Hum Genet 2017 Aug;101(2):239-254

Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, VIC 3052, Australia; Department of Paediatrics, University of Melbourne, Melbourne, VIC 3052, Australia; Victorian Clinical Genetic Services, Royal Children's Hospital, Melbourne, VIC 3052, Australia. Electronic address:

The synthesis of all 13 mitochondrial DNA (mtDNA)-encoded protein subunits of the human oxidative phosphorylation (OXPHOS) system is carried out by mitochondrial ribosomes (mitoribosomes). Defects in the stability of mitoribosomal proteins or mitoribosome assembly impair mitochondrial protein translation, causing combined OXPHOS enzyme deficiency and clinical disease. Here we report four autosomal-recessive pathogenic mutations in the gene encoding the small mitoribosomal subunit protein, MRPS34, in six subjects from four unrelated families with Leigh syndrome and combined OXPHOS defects. Whole-exome sequencing was used to independently identify all variants. Two splice-site mutations were identified, including homozygous c.321+1G>T in a subject of Italian ancestry and homozygous c.322-10G>A in affected sibling pairs from two unrelated families of Puerto Rican descent. In addition, compound heterozygous MRPS34 mutations were identified in a proband of French ancestry; a missense (c.37G>A [p.Glu13Lys]) and a nonsense (c.94C>T [p.Gln32]) variant. We demonstrated that these mutations reduce MRPS34 protein levels and the synthesis of OXPHOS subunits encoded by mtDNA. Examination of the mitoribosome profile and quantitative proteomics showed that the mitochondrial translation defect was caused by destabilization of the small mitoribosomal subunit and impaired monosome assembly. Lentiviral-mediated expression of wild-type MRPS34 rescued the defect in mitochondrial translation observed in skin fibroblasts from affected subjects, confirming the pathogenicity of MRPS34 mutations. Our data establish that MRPS34 is required for normal function of the mitoribosome in humans and furthermore demonstrate the power of quantitative proteomic analysis to identify signatures of defects in specific cellular pathways in fibroblasts from subjects with inherited disease.
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http://dx.doi.org/10.1016/j.ajhg.2017.07.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5544391PMC
August 2017

Acute detachment of hexokinase II from mitochondria modestly increases oxygen consumption of the intact mouse heart.

Metabolism 2017 07 21;72:66-74. Epub 2017 Apr 21.

Laboratory of Experimental Intensive Care and Anesthesiology, Department of Anesthesiology, Academic Medical Center, Amsterdam, The Netherlands. Electronic address:

Objective: Cardiac hexokinase II (HKII) can translocate between cytosol and mitochondria and change its cellular expression with pathologies such as ischemia-reperfusion, diabetes and heart failure. The cardiac metabolic consequences of these changes are unknown. Here we measured energy substrate utilization in cytosol and mitochondria using stabile isotopes and oxygen consumption of the intact perfused heart for 1) an acute decrease in mitochondrial HKII (mtHKII), and 2) a chronic decrease in total cellular HKII.

Methods/results: We first examined effects of 200nM TAT (Trans-Activator of Transcription)-HKII peptide treatment, which was previously shown to acutely decrease mtHKII by ~30%. In Langendorff-perfused hearts TAT-HKII resulted in a modest, but significant, increased oxygen consumption, while cardiac performance was unchanged. At the metabolic level, there was a nonsignificant (p=0.076) ~40% decrease in glucose contribution to pyruvate and lactate formation through glycolysis and to mitochondrial citrate synthase flux (6.6±1.1 vs. 11.2±2.2%), and an 35% increase in tissue pyruvate (27±2 vs. 20±2pmol/mg; p=0.033). Secondly, we compared WT and HKII hearts (50% chronic decrease in total HKII). RNA sequencing revealed no differential gene expression between WT and HKII hearts indicating an absence of metabolic reprogramming at the transcriptional level. Langendorff-perfused hearts showed no significant differences in glycolysis (0.34±0.03μmol/min), glucose contribution to citrate synthase flux (35±2.3%), palmitate contribution to citrate synthase flux (20±1.1%), oxygen consumption or mechanical performance between WT and HKII hearts.

Conclusions: These results indicate that acute albeit not chronic changes in mitochondrial HKII modestly affect cardiac oxygen consumption and energy substrate metabolism.
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http://dx.doi.org/10.1016/j.metabol.2017.04.008DOI Listing
July 2017

Heterozygous Pathogenic Variant in DACT1 Causes an Autosomal-Dominant Syndrome with Features Overlapping Townes-Brocks Syndrome.

Hum Mutat 2017 04 2;38(4):373-377. Epub 2017 Feb 2.

Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York.

A heterozygous nonsense variant was identified in dapper, antagonist of beta-catenin, 1 (DACT1) via whole-exome sequencing in family members with imperforate anus, structural renal abnormalities, genitourinary anomalies, and/or ear anomalies. The DACT1 c.1256G>A;p.Trp419 variant segregated appropriately in the family consistent with an autosomal dominant mode of inheritance. DACT1 is a member of the Wnt-signaling pathway, and mice homozygous for null alleles display multiple congenital anomalies including absent anus with blind-ending colon and genitourinary malformations. To investigate the DACT1 c.1256G>A variant, HEK293 cells were transfected with mutant DACT1 cDNA plasmid, and immunoblotting revealed stability of the DACT1 p.Trp419 protein. Overexpression of DACT1 c.1256G>A mRNA in Xenopus embryos revealed a specific gastrointestinal phenotype of enlargement of the proctodeum. Together, these findings suggest that the DACT1 c.1256G>A nonsense variant is causative of a specific genetic syndrome with features overlapping Townes-Brocks syndrome.
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http://dx.doi.org/10.1002/humu.23171DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390682PMC
April 2017

Changes in the Metabolome in Response to Low-Dose Exposure to Environmental Chemicals Used in Personal Care Products during Different Windows of Susceptibility.

PLoS One 2016 28;11(7):e0159919. Epub 2016 Jul 28.

Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States of America.

The consequences of ubiquitous exposure to environmental chemicals remain poorly defined. Non-targeted metabolomic profiling is an emerging method to identify biomarkers of the physiological response to such exposures. We investigated the effect of three commonly used ingredients in personal care products, diethyl phthalate (DEP), methylparaben (MPB) and triclosan (TCS), on the blood metabolome of female Sprague-Dawley rats. Animals were treated with low levels of these chemicals comparable to human exposures during prepubertal and pubertal windows as well as chronically from birth to adulthood. Non-targeted metabolomic profiling revealed that most of the variation in the metabolites was associated with developmental stage. The low-dose exposure to DEP, MPB and TCS had a relatively small, but detectable impact on the metabolome. Multiple metabolites that were affected by chemical exposure belonged to the same biochemical pathways including phenol sulfonation and metabolism of pyruvate, lyso-plasmalogens, unsaturated fatty acids and serotonin. Changes in phenol sulfonation and pyruvate metabolism were most pronounced in rats exposed to DEP during the prepubertal period. Our metabolomics analysis demonstrates that human level exposure to personal care product ingredients has detectable effects on the rat metabolome. We highlight specific pathways such as sulfonation that warrant further study.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0159919PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4965097PMC
August 2017

Assessment of plasma acylcarnitines before and after weight loss in obese subjects.

Arch Biochem Biophys 2016 Sep 19;606:73-80. Epub 2016 Jul 19.

Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; Institute of Metabolic Science, Metabolic Research Laboratories, Cambridge University Hospital NHS Trust, Cambridge, UK. Electronic address: http://www.metabolism.maartensoeters.nl/

Acylcarnitines, fatty acid oxidation (FAO) intermediates, have been implicated in diet-induced insulin resistance and type 2 diabetes mellitus, as increased levels are found in obese insulin resistant humans. Moreover plasma acylcarnitines have been associated with clinical parameters related to glucose metabolism, such as fasting glucose levels and HbA1c. We hypothesized that plasma acylcarnitines would correlate with energy expenditure, insulin sensitivity and other clinical parameters before and during a weight loss intervention. We measured plasma acylcarnitines in 60 obese subjects before and after a 12 week weight loss intervention. These samples originated from three different interventions (diet alone (n = 20); diet and exercise (n = 21); diet and drug treatment (n = 19)). Acylcarnitine profiles were analysed in relation to clinical parameters of glucose metabolism, insulin sensitivity and energy expenditure. Conclusions were drawn from all 60 subjects together. Despite amelioration of HOMA-IR, plasma acylcarnitines levels increased during weight loss. HOMA-IR, energy expenditure and respiratory exchange ratio were not related to plasma acylcarnitines. However non-esterified fatty acids correlated strongly with several acylcarnitines at baseline and during the weight loss intervention (p < 0.001). Acylcarnitines did not correlate with clinical parameters of glucose metabolism during weight loss, questioning their role in insulin resistance and type 2 diabetes mellitus.
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http://dx.doi.org/10.1016/j.abb.2016.07.013DOI Listing
September 2016

A PPARγ-Bnip3 Axis Couples Adipose Mitochondrial Fusion-Fission Balance to Systemic Insulin Sensitivity.

Diabetes 2016 09 20;65(9):2591-605. Epub 2016 Jun 20.

Department of Medical Biochemistry, University of Amsterdam, Academic Medical Centre, Amsterdam, the Netherlands

Aberrant mitochondrial fission plays a pivotal role in the pathogenesis of skeletal muscle insulin resistance. However, fusion-fission dynamics are physiologically regulated by inherent tissue-specific and nutrient-sensitive processes that may have distinct or even opposing effects with respect to insulin sensitivity. Based on a combination of mouse population genetics and functional in vitro assays, we describe here a regulatory circuit in which peroxisome proliferator-activated receptor γ (PPARγ), the adipocyte master regulator and receptor for the thiazolidinedione class of antidiabetic drugs, controls mitochondrial network fragmentation through transcriptional induction of Bnip3. Short hairpin RNA-mediated knockdown of Bnip3 in cultured adipocytes shifts the balance toward mitochondrial elongation, leading to compromised respiratory capacity, heightened fatty acid β-oxidation-associated mitochondrial reactive oxygen species generation, insulin resistance, and reduced triacylglycerol storage. Notably, the selective fission/Drp1 inhibitor Mdivi-1 mimics the effects of Bnip3 knockdown on adipose mitochondrial bioenergetics and glucose disposal. We further show that Bnip3 is reciprocally regulated in white and brown fat depots of diet-induced obesity and leptin-deficient ob/ob mouse models. Finally, Bnip3(-/-) mice trade reduced adiposity for increased liver steatosis and develop aggravated systemic insulin resistance in response to high-fat feeding. Together, our data outline Bnip3 as a key effector of PPARγ-mediated adipose mitochondrial network fragmentation, improving insulin sensitivity and limiting oxidative stress.
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http://dx.doi.org/10.2337/db16-0243DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5001173PMC
September 2016

Malnutrition-associated liver steatosis and ATP depletion is caused by peroxisomal and mitochondrial dysfunction.

J Hepatol 2016 12 14;65(6):1198-1208. Epub 2016 Jun 14.

Department of Pediatrics, Center for Liver, Digestive and Metabolic Diseases, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands; Physiology and Experimental Medicine Program, Research Institute, The Hospital for Sick Children, Toronto, Canada; Division of Gastroenterology, Hepatology and Nutrition, The Hospital for Sick Children, Toronto, Canada; Centre for Global Child Health, The Hospital for Sick Children, Toronto, Canada. Electronic address:

Background & Aims: Severe malnutrition in young children is associated with signs of hepatic dysfunction such as steatosis and hypoalbuminemia, but its etiology is unknown. Peroxisomes and mitochondria play key roles in various hepatic metabolic functions including lipid metabolism and energy production. To investigate the involvement of these organelles in the mechanisms underlying malnutrition-induced hepatic dysfunction we developed a rat model of malnutrition.

Methods: Weanling rats were placed on a low protein or control diet (5% or 20% of calories from protein, respectively) for four weeks. Peroxisomal and mitochondrial structural features were characterized using immunofluorescence and electron microscopy. Mitochondrial function was assessed using high-resolution respirometry. A novel targeted quantitative proteomics method was applied to analyze 47 mitochondrial proteins involved in oxidative phosphorylation, tricarboxylic acid cycle and fatty acid β-oxidation pathways.

Results: Low protein diet-fed rats developed hypoalbuminemia and hepatic steatosis, consistent with the human phenotype. Hepatic peroxisome content was decreased and metabolomic analysis indicated peroxisomal dysfunction. This was followed by changes in mitochondrial ultrastructure and increased mitochondrial content. Mitochondrial function was impaired due to multiple defects affecting respiratory chain complex I and IV, pyruvate uptake and several β-oxidation enzymes, leading to strongly reduced hepatic ATP levels. Fenofibrate supplementation restored hepatic peroxisome abundance and increased mitochondrial β-oxidation capacity, resulting in reduced steatosis and normalization of ATP and plasma albumin levels.

Conclusions: Malnutrition leads to severe impairments in hepatic peroxisomal and mitochondrial function, and hepatic metabolic dysfunction. We discuss the potential future implications of our findings for the clinical management of malnourished children.

Lay Summary: Severe malnutrition in children is associated with metabolic disturbances that are poorly understood. In order to study this further, we developed a malnutrition animal model and found that severe malnutrition leads to an impaired function of liver mitochondria which are essential for energy production and a loss of peroxisomes, which are important for normal liver metabolic function.
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http://dx.doi.org/10.1016/j.jhep.2016.05.046DOI Listing
December 2016

Systems proteomics of liver mitochondria function.

Science 2016 Jun;352(6291):aad0189

Laboratory of Integrative and Systems Physiology, Interfaculty Institute of Bioengineering, École Polytechnique Fédérale de Lausanne, CH-1015, Switzerland.

Recent improvements in quantitative proteomics approaches, including Sequential Window Acquisition of all Theoretical Mass Spectra (SWATH-MS), permit reproducible large-scale protein measurements across diverse cohorts. Together with genomics, transcriptomics, and other technologies, transomic data sets can be generated that permit detailed analyses across broad molecular interaction networks. Here, we examine mitochondrial links to liver metabolism through the genome, transcriptome, proteome, and metabolome of 386 individuals in the BXD mouse reference population. Several links were validated between genetic variants toward transcripts, proteins, metabolites, and phenotypes. Among these, sequence variants in Cox7a2l alter its protein's activity, which in turn leads to downstream differences in mitochondrial supercomplex formation. This data set demonstrates that the proteome can now be quantified comprehensively, serving as a key complement to transcriptomics, genomics, and metabolomics--a combination moving us forward in complex trait analysis.
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http://dx.doi.org/10.1126/science.aad0189DOI Listing
June 2016

The impact of altered carnitine availability on acylcarnitine metabolism, energy expenditure and glucose tolerance in diet-induced obese mice.

Biochim Biophys Acta 2016 08 22;1862(8):1375-82. Epub 2016 Apr 22.

Department of Clinical Chemistry, Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105AZ Amsterdam, The Netherlands; Department of Genetics and Genomic Sciences, Icahn Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, Box 1498, New York, NY 10029, USA. Electronic address:

Aim: Acylcarnitines are fatty acid oxidation (FAO) intermediates, which have been implicated in diet-induced insulin resistance. Elevated acylcarnitine levels are found in obese, insulin resistant humans and rodents, and coincide with lower free carnitine. We hypothesized that increasing free carnitine levels by administration of the carnitine precursor γ-butyrobetaine (γBB) could facilitate FAO, thereby improving insulin sensitivity.

Methods: C57BL/6N mice were fed with a high fat or chow diet with or without γBB supplementation (n=10 per group). After 8weeks of diet, indirect calorimetry, glucose tolerance and insulin sensitivity tests were performed. AC profiles and carnitine biosynthesis intermediates were analyzed in plasma and tissues by tandem mass spectrometry (MS) and liquid chromatography tandem MS.

Results: γBB supplementation did not facilitate FAO, was unable to curb bodyweight and did not prevent impaired glucose homeostasis in the HFD fed mice in spite of marked alterations in the acylcarnitine profiles in plasma and liver. Remarkably, γBB did not affect the acylcarnitine profile in other tissues, most notably muscle. Administration of a bolus acetylcarnitine also caused significant changes in plasma and liver, but not in muscle acylcarnitine profiles, again without effect on glucose tolerance.

Conclusion: Altogether, increasing carnitine availability affects acylcarnitine profiles in plasma and liver but does not modulate glucose tolerance or insulin sensitivity. This may be due to the lack of an effect on muscle acylcarnitine profiles, as muscle tissue is an important contributor to whole body insulin sensitivity. These results warrant caution on making associations between plasma acylcarnitine levels and insulin resistance.
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http://dx.doi.org/10.1016/j.bbadis.2016.04.012DOI Listing
August 2016