Background. Sphingolipids are important components of cellular membranes and functionally associated with fundamental processes such as cell differentiation, neuronal signaling and myelin sheath formation. Defects in the synthesis or degradation of sphingolipids leads to various neurological pathologies, however, the entire spectrum of sphingolipid metabolism disorders remained elusive. Methods. A combined approach of genomics and lipidomics was applied to identify and characterize a human sphingolipid metabolism disorder.Results. By whole-exome sequencing in a patient with a multisystem neurological disorder of both the central and peripheral nervous system, we identified a homozygous p.(Ala280Val) variant in DEGS1, which catalyzes the last step in the ceramide synthesis pathway. The blood sphingolipid profile in the patient showed a significant increase in dihydro sphingolipid species which was further recapitulated in patient-derived fibroblasts, in CRISPR/Cas9-derived DEGS1 knockout cells, and by pharmacological inhibition of DEGS1. The enzymatic activity in patient fibroblasts was reduced by 80% compared to wild type cells which was in line with a reduced expression of mutant DEGS1 protein. Moreover, an atypical and potentially neurotoxic sphingosine isomer was identified in patient plasma and in cells expressing mutant DEGS1. Conclusion. We report DEGS1 dysfunction as cause for a novel sphingolipid disorder with hypomyelination and degeneration of both the central and peripheral nervous system.Trial registration. Not applicable.Funding. RESOLVE: Project number 305707; SNF: Project 31003A_153390/1; Rare Disease Initiative Zurich.
Gergely Karsai, Florian Kraft, Natja Haag, G. Christoph Korenke, Benjamin Hänisch, Alaa Othman, Saranya Suriyanarayanan, Regula Steiner, Cordula Knopp, Michael Mull, Markus Bergmann, J. Michael Schröder, Joachim Weis, Miriam Elbracht, Matthias Begemann, Thorsten Hornemann, Ingo Kurth
Peroxisomes perform essential functions in lipid metabolism, including fatty acid oxidation and plasmalogen synthesis. Here, we describe a role for peroxisomal lipid metabolism in mitochondrial dynamics in brown and beige adipocytes. Adipose tissue peroxisomal biogenesis was induced in response to cold exposure through activation of the thermogenic co-regulator PRDM16. Adipose-specific knockout of the peroxisomal biogenesis factor Pex16 (Pex16-AKO) in mice impaired cold tolerance, decreased energy expenditure, and increased diet-induced obesity. Pex16 deficiency blocked cold-induced mitochondrial fission, decreased mitochondrial copy number, and caused mitochondrial dysfunction. Adipose-specific knockout of the peroxisomal beta-oxidation enzyme acyl CoA oxidase 1 (Acox1-AKO) was not sufficient to affect adiposity, thermogenesis or mitochondrial copy number, but knockdown of the plasmalogen synthetic enzyme glyceronephosphate O-acyltransferase (GNPAT) recapitulated the effects of Pex16 inactivation on mitochondrial morphology and function. Plasmalogens are present in mitochondria and decreased with Pex16 inactivation. Their dietary supplementation increased mitochondrial copy number, improved mitochondrial function, and rescued thermogenesis in Pex16-AKO mice. These findings support a surprising interaction between peroxisomes and mitochondria to regulate mitochondrial dynamics and thermogenesis.
Hongsuk Park, Anyuan He, Min Tan, Jordan M. Johnson, John M. Dean, Terri A. Pietka, Yali Chen, Xiangyu Zhang, Fong-Fu Hsu, Babak Razani, Katsuhiko Funai, Irfan J. Lodhi
The lipin phosphatidic acid phosphatase (PAP) enzymes are required for triacylglycerol (TAG) synthesis from glycerol 3-phosphate in most mammalian tissues. The 3 lipin proteins (lipin 1, lipin 2, and lipin 3) each have PAP activity, but have distinct tissue distributions, with lipin 1 being the predominant PAP enzyme in many metabolic tissues. One exception is the small intestine, which is unique in expressing exclusively lipin 2 and lipin 3. TAG synthesis in small intestinal enterocytes utilizes 2-monoacylglycerol and does not require the PAP reaction, making the role of lipin proteins in enterocytes unclear. Enterocyte TAGs are stored transiently as cytosolic lipid droplets or incorporated into lipoproteins (chylomicrons) for secretion. We determined that lipin enzymes are critical for chylomicron biogenesis, through regulation of membrane phospholipid composition and association of apolipoprotein B48 with nascent chylomicron particles. Lipin 2/3 deficiency caused phosphatidic acid accumulation and mammalian target of rapamycin complex 1 (mTORC1) activation, which were associated with enhanced protein levels of a key phospholipid biosynthetic enzyme (CTP:phosphocholine cytidylyltransferase α) and altered membrane phospholipid composition. Impaired chylomicron synthesis in lipin 2/3 deficiency could be rescued by normalizing phospholipid synthesis levels. These data implicate lipin 2/3 as a control point for enterocyte phospholipid homeostasis and chylomicron biogenesis.
Peixiang Zhang, Lauren S. Csaki, Emilio Ronquillo, Lynn J. Baufeld, Jason Y. Lin, Alexis Gutierrez, Jennifer R. Dwyer, David N. Brindley, Loren G. Fong, Peter Tontonoz, Stephen G. Young, Karen Reue
Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme detoxifying acetaldehyde and endogenous lipid aldehydes; previous studies suggest a protective role of ALDH2 against cardiovascular disease (CVD). Around 40% of East Asians carrying a single nucleotide polymorphism (SNP) ALDH2 rs671 have increased incidences of CVD. However, the role of ALDH2 in CVD beyond alcohol consumption remains poorly defined. Here we report that ALDH2/LDLR DKO mice have decreased atherosclerosis compared to LDLR KO mice, whereas ALDH2/APOpoE DKO have increased atherosclerosis, suggesting an unexpected interaction of ALDH2 with LDLR. Further studies demonstrate that in the absence of LDLR, AMPK phosphorylates ALDH2 at threonine 356 and enables its nuclear translocation. Nuclear ALDH2 interacts with HDAC3 and represses transcription of a lysosomal proton pump protein ATP6Vv0Ee2, critical for maintaining lysosomal function, autophagy and degradation of oxLDL. Interestingly, an interaction of cytosolic LDLR C-terminus with AMPK blocks ALDH2 phosphorylation and subsequent nuclear translocation, whereas ALDH2 rs671 mutant in human macrophages attenuates this interaction, which releases ALDH2 to nucleus to suppress ATP6Vv0Ee2 expression, resulting in increased foam cells due to impaired lysosomal function. Our studies reveal a novel role of ALDH2 and LDLR in atherosclerosis and provide a molecular mechanism by which ALDH2 rs671 SNP increases CVD.
Shanshan Zhong, Luxiao Li, Yu-Lei Zhang, Lili Zhang, Jianhong Lu, Shuyuan Guo, Ningning Liang, Jing Ge, Mingjiang Zhu, Yongzhen Tao, Yun-Cheng Wu, Huiyong Yin
Notch signaling regulates differentiation of the pancreatic endocrine lineage during embryogenesis, but the role of Notch in mature β cells is unclear. We found that islets derived from lean mice show modest β cell Notch activity, which increases in obesity and in response to high glucose. This response appeared maladaptive, as mice with β cell-specific deficient Notch transcriptional activity (β-Rbpj, β-DNMAML) showed improved glucose tolerance when subjected to high-fat diet feeding. Conversely, mice with β cell-specific expression of constitutively-active Notch1 (β-NICD) had a progressive loss of β cell maturity, due to proteasomal degradation of MafA, leading to impaired glucose-stimulated insulin secretion and glucose intolerance with aging or obesity. Surprisingly, Notch-active β cells had increased proliferative capacity, leading to increased but dysfunctional β cell mass. These studies demonstrate a dynamic role for Notch in developed β cells to simultaneously regulate β cell function and proliferation.
Alberto Bartolome, Changyu Zhu, Lori Sussel, Utpal B. Pajvani
Levothyroxine (LT4) is a form of thyroid hormone used to treat hypothyroidism. In the brain, T4 is converted to the active form T3 by the type 2 deiodinase (D2). Thus, it is intriguing that carriers of the Thr92Ala polymorphism in the D2 gene (DIO2) exhibit clinical improvement when liothyronine (LT3) is added to LT4 therapy. Here we report that D2 is a cargo protein in endoplasmic reticulum Golgi intermediary compartment (ERGIC) vesicles, recycling between ER and Golgi. The Thr92 to Ala substitution (Ala92-D2) caused ER stress and activated the unfolded protein response (UPR); Ala92-D2 accumulated in the trans-Golgi and generated less T3, all of which was restored by eliminating ER stress with the chemical chaperone 4-phenyl butyric acid (4-PBA). An Ala92-Dio2 polymorphism-carrying mouse exhibited UPR and hypothyroidism in distinct brain areas. The mouse refrained from physical activity, slept more and required additional time to memorize objects. Enhancing T3 signaling in the brain with LT3 improved cognition, whereas restoring proteostasis with 4-PBA eliminated the Ala92-Dio2 phenotype. In contrast, primary hypothyroidism intensified the Ala92-Dio2 phenotype, with only partial response to LT4 therapy. Disruption of cellular proteostasis and reduced Ala92-D2 activity may explain the failure of LT4 therapy in carriers of Thr92Ala-DIO2.
Sungro Jo, Tatiana L. Fonseca, Barbara M.L. Da Costa Bocco, Gustavo W. Fernandes, Elizabeth A. McAninch, Anaysa P. Bolin, Rodrigo R. Da Conceição, Joao Pedro W.S. De Castro, Daniele L. Ignacio, Péter Egri, Dorottya Németh, Csaba Fekete, Maria Martha Bernardi, Victoria D. Leitch, Naila S. Mannan, Katharine F. Curry, Natalie C. Butterfield, J.H. Duncan Bassett, Graham R. Williams, Balázs Gereben, Miriam O. Ribeiro, Antonio C. Bianco
Immune nonresponder (INR) HIV-1–infected subjects are characterized by their inability to reconstitute the CD4+ T cell pool after antiretroviral therapy. This is linked to poor clinical outcome. Mechanisms underlying immune reconstitution failure are poorly understood, although, counterintuitively, INRs often have increased frequencies of circulating CD4+ T cells in the cell cycle. While cycling CD4+ T cells from healthy controls and HIV+ patients with restored CD4+ T cell numbers complete cell division in vitro, cycling CD4+ T cells from INRs do not. Here, we show that cells with the phenotype and transcriptional profile of Tregs were enriched among cycling cells in health and in HIV infection. Yet there were diminished frequencies and numbers of Tregs among cycling CD4+ T cells in INRs, and cycling CD4+ T cells from INR subjects displayed transcriptional profiles associated with the impaired development and maintenance of functional Tregs. Flow cytometric assessment of TGF-β activity confirmed the dysfunction of Tregs in INR subjects. Transcriptional profiling and flow cytometry revealed diminished mitochondrial fitness in Tregs among INRs, and cycling Tregs from INRs had low expression of the mitochondrial biogenesis regulators peroxisome proliferator–activated receptor γ coactivator 1-α (PGC1α) and transcription factor A for mitochondria (TFAM). In vitro exposure to IL-15 allowed cells to complete division, restored the expression of PGC1α and TFAM, and regenerated mitochondrial fitness in the cycling Tregs of INRs. Our data suggest that rescuing mitochondrial function could correct the immune dysfunction characteristic of Tregs in HIV-1–infected subjects who fail to restore CD4+ T cells during antiretroviral therapy.
Souheil-Antoine Younes, Aarthi Talla, Susan Pereira Ribeiro, Evgeniya V. Saidakova, Larisa B. Korolevskaya, Konstantin V. Shmagel, Carey L. Shive, Michael L. Freeman, Soumya Panigrahi, Sophia Zweig, Robert Balderas, Leonid Margolis, Daniel C. Douek, Donald. D. Anthony, Pushpa Pandiyan, Mark Cameron, Scott F. Sieg, Leonard H. Calabrese, Benigno Rodriguez, Michael M. Lederman
Non-alcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge signals from activated GPCRs, and modulate cell signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of Gα12 on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα12 level in mouse liver. Gα12 ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12 KO liver revealed that Gα12 signaling pathway regulated sirtuin 1 (SIRT1) and PPARα responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12 KO mice, which was reversed by lentivirus-mediated Gα12 overexpression in hepatocytes. Mechanistically, Gα12 stabilized SIRT1 protein through transcriptional induction of USP22 via HIF-1α increase. Gα12 levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12 KO mice fed high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα12 regulates SIRT1-dependent mitochondrial respiration through HIF-1α-dependent USP22 induction, identifying Gα12 as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.
Tae Hyun Kim, Yoon Mee Yang, Chang Yeob Han, Ja Hyun Koo, Hyunhee Oh, Su Sung Kim, Byoung Hoon You, Young Hee Choi, Tae-Sik Park, Chang Ho Lee, Hitoshi Kurose, Mazen Noureddin, Ekihiro Seki, Yu-Jui Yvonne Wan, Cheol Soo Choi, Sang Geon Kim
Atypical antipsychotics are highly effective antischizophrenic medications but their clinical utility is limited by adverse metabolic sequelae. We investigated whether upregulation of macrophage migration inhibitory factor (MIF) underlies the insulin resistance that develops during treatment with the most commonly prescribed atypical antipsychotic, olanzapine. Olanzapine monotherapy increased BMI and circulating insulin, triglyceride, and MIF concentrations in drug-naive schizophrenic patients with normal MIF expression, but not in genotypic low MIF expressers. Olanzapine administration to mice increased their food intake and hypothalamic MIF expression, which led to activation of the appetite-related AMP-activated protein kinase and Agouti-related protein pathway. Olanzapine also upregulated MIF expression in adipose tissue, which reduced lipolysis and increased lipogenic pathways. Increased plasma lipid concentrations were associated with abnormal fat deposition in liver and skeletal muscle, which are important determinants of insulin resistance. Global MIF-gene deletion protected mice from olanzapine-induced insulin resistance, as did intracerebroventricular injection of neutralizing anti–MIF antibody, supporting the role of increased hypothalamic MIF expression in metabolic dysfunction. These findings uphold the potential pharmacogenomic value of MIF genotype determination and suggest that MIF may be a tractable target for reducing the metabolic side effects of atypical antipsychotic therapy.
Donghong Cui, Yanmin Peng, Chengfang Zhang, Zezhi Li, Yousong Su, Yadan Qi, Mengjuan Xing, Jia Li, Grace E. Kim, Kevin N. Su, Jinjie Xu, Meiti Wang, Wenhua Ding, Marta Piecychna, Lin Leng, Michiru Hirasawa, Kaida Jiang, Lawrence Young, Yifeng Xu, Dake Qi, Richard Bucala
Adipocyte turnover in adulthood is low, suggesting that the cellular source of new adipocytes, the adipocyte progenitor (AP), resides in a state of relative quiescence. Yet the core transcriptional regulatory circuitry (CRC) responsible for establishing a quiescent state and the physiological significance of AP quiescence are incompletely understood. Here, we integrate transcriptomic data with maps of accessible chromatin in primary APs, implicating the orphan nuclear receptor NR4A1 in AP cell-state regulation. NR4A1 gain and loss of function in APs ex vivo decreased and enhanced adipogenesis, respectively. Adipose tissue of Nr4a1–/– mice demonstrated higher proliferative and adipogenic capacity compared with that of WT mice. Transplantation of Nr4a1–/– APs into the subcutaneous adipose tissue of WT obese recipients improved metrics of glucose homeostasis relative to administration of WT APs. Collectively, these data identify NR4A1 as a previously unrecognized constitutive regulator of AP quiescence and suggest that augmentation of adipose tissue plasticity may attenuate negative metabolic sequelae of obesity.
Yang Zhang, Alexander J. Federation, Soomin Kim, John P. O’Keefe, Mingyue Lun, Dongxi Xiang, Jonathan D. Brown, Matthew L. Steinhauser