BACKGROUND. NAFLD affects 25-30% of the US and European populations and is associated with insulin resistance (IR), T2D, increased cardiovascular risk and is defined by hepatic triglyceride content (HTG) > 5.56%. However, it is unknown whether HTG content less than 5.56% is associated with cardiometabolic risk factors and whether there are ethnic [Asian Indian (AI) vs. non-Asian Indian (non-AI)] and/or gender differences in these parameters in lean individuals. METHODS. We prospectively recruited 2,331 individuals and measured HTG, using 1H MRS, and plasma concentrations of triglycerides, total cholesterol, LDL cholesterol, HDL cholesterol, and uric acid. Insulin sensitivity was assessed using HOMA-IR and the Matsuda Insulin Sensitivity Index (ISI). RESULTS. The 95th percentile for HTG in lean non-AI individuals was 1.85%. Plasma insulin, triglycerides, total cholesterol, LDL cholesterol and uric acid concentrations were increased and HDL decreased in individuals with HTG content > 1.85% and ≤ 5.56% compared to those individuals with HTG content ≤ 1.85% and was associated with increased IR. Mean HTG was lower in lean non-AI women compared to lean non-AI men, whereas lean AI men and women had a 40-100% increase in HTG when compared to non-AI men and women which was associated with increased cardiometabolic risk factors. CONCLUSIONS. We found that the 95th percentile of HTG in lean non-AI individuals was 1.85% and that HTG concentrations above this threshold were associated with IR and cardiovascular risk factors. Premenopausal women are protected from these changes whereas young lean AI men and women manifest increased HTG content and associated cardiometabolic risk factors. FUNDING. Supported by grants from the United States Department of Health and Human Resources (NIH/NIDDK): R01 DK113984, P30 DK45735, U24 DK59635 and UL1 RR024139 and the Novo Nordisk Foundation (NNF18CC0034900).
Kitt Falk Petersen, Sylvie Dufour, Fangyong Li, Douglas L. Rothman, Gerald I. Shulman
Ammonia is a cytotoxic metabolite with pleiotropic molecular and metabolic effects, including senescence induction. During dysregulated ammonia metabolism, which occurs in chronic diseases, skeletal muscle becomes a major organ for nonhepatocyte ammonia uptake. Muscle ammonia disposal occurs in mitochondria via cataplerosis of critical intermediary metabolite α-ketoglutarate, a senescence-ameliorating molecule. Untargeted and mitochondrially targeted data were analyzed by multiomics approaches. These analyses were validated experimentally to dissect the specific mitochondrial oxidative defects and functional consequences, including senescence. Responses to ammonia lowering in myotubes and in hyperammonemic portacaval anastomosis rat muscle were studied. Whole-cell transcriptomics integrated with whole-cell, mitochondrial, and tissue proteomics showed distinct temporal clusters of responses with enrichment of oxidative dysfunction and senescence-related pathways/proteins during hyperammonemia and after ammonia withdrawal. Functional and metabolic studies showed defects in electron transport chain complexes I, III, and IV; loss of supercomplex assembly; decreased ATP synthesis; increased free radical generation with oxidative modification of proteins/lipids; and senescence-associated molecular phenotype–increased β-galactosidase activity and expression of p16INK, p21, and p53. These perturbations were partially reversed by ammonia lowering. Dysregulated ammonia metabolism caused reversible mitochondrial dysfunction by transcriptional and translational perturbations in multiple pathways with a distinct skeletal muscle senescence-associated molecular phenotype.
Avinash Kumar, Nicole Welch, Saurabh Mishra, Annette Bellar, Rafaella Nasciemento Silva, Ling Li, Shashi Shekhar Singh, Mary Sharkoff, Alexis Kerr, Aruna Kumar Chelluboyina, Jinendiran Sekar, Amy H. Attaway, Charles Hoppel, Belinda Willard, Gangarao Davuluri, Srinivasan Dasarathy
Tristetraprolin (TTP), an important immunosuppressive protein regulating mRNA decay through recognition of the AU-rich elements (AREs) within the 3′-UTRs of mRNAs, participates in the pathogenesis of liver diseases. However, whether TTP regulates mRNA stability through other mechanisms remains poorly understood. Here, we report that TTP was upregulated in acute liver failure (ALF), resulting in decreased mRNA stabilities of CCL2 and CCL5 through promotion of N6-methyladenosine (m6A) mRNA methylation. Overexpression of TTP could markedly ameliorate hepatic injury in vivo. TTP regulated the mRNA stabilization of CCL2 and CCL5. Interestingly, increased m6A methylation in CCL2 and CCL5 mRNAs promoted TTP-mediated RNA destabilization. Moreover, induction of TTP upregulated expression levels of WT1 associated protein, methyltransferase like 14, and YT521-B homology N6-methyladenosine RNA binding protein 2, which encode enzymes regulating m6A methylation, resulting in a global increase of m6A methylation and amelioration of liver injury due to enhanced degradation of CCL2 and CCL5. These findings suggest a potentially novel mechanism by which TTP modulates mRNA stabilities of CCL2 and CCL5 through m6A RNA methylation, which is involved in the pathogenesis of ALF.
Pingping Xiao, Mingxuan Li, Mengsi Zhou, Xuejun Zhao, Cheng Wang, Jinglin Qiu, Qian Fang, Hong Jiang, Huifen Dong, Rui Zhou
Monocarboxylates, such as lactate and pyruvate, are precursors for biosynthetic pathways, including those for glucose, lipids, and amino acids via the tricarboxylic acid (TCA) cycle and adjacent metabolic networks. The transportation of monocarboxylates across the cellular membrane is performed primarily by monocarboxylate transporters (MCTs), the membrane localization and stabilization of which are facilitated by the transmembrane protein basigin (BSG). Here, we demonstrate that the MCT/BSG axis sits at a crucial intersection of cellular metabolism. Abolishment of MCT1 in the plasma membrane was achieved by Bsg depletion, which led to gluconeogenesis impairment via preventing the influx of lactate and pyruvate into the cell, consequently suppressing the TCA cycle. This net anaplerosis suppression was compensated in part by the increased utilization of glycogenic amino acids (e.g., alanine and glutamine) into the TCA cycle and by activated ketogenesis through fatty acid β-oxidation. Complementary to these observations, hyperglycemia and hepatic steatosis induced by a high-fat diet were ameliorated in Bsg-deficient mice. Furthermore, Bsg deficiency significantly improved insulin resistance induced by a high-fat diet. Taken together, the plasma membrane–selective modulation of lactate and pyruvate transport through BSG inhibition could potentiate metabolic flexibility to treat metabolic diseases.
Akihiro Ryuge, Tomoki Kosugi, Kayaho Maeda, Ryoichi Banno, Yang Gou, Kei Zaitsu, Takanori Ito, Yuka Sato, Akiyoshi Hirayama, Shoma Tsubota, Takashi Honda, Kazuki Nakajima, Tomoya Ozaki, Kunio Kondoh, Kazuo Takahashi, Noritoshi Kato, Takuji Ishimoto, Tomoyoshi Soga, Takahiko Nakagawa, Teruhiko Koike, Hiroshi Arima, Yukio Yuzawa, Yasuhiko Minokoshi, Shoichi Maruyama, Kenji Kadomatsu
The signaling mechanisms by which dietary fat and cholesterol signals regulate central pathways of glucose homeostasis are not completely understood. By using a hepatocyte-specific PKCβ-deficient (PKCβHep–/–) mouse model, we demonstrated the role of hepatic PKCβ in slowing disposal of glucose overload by suppressing glycogenesis and increasing hepatic glucose output. PKCβHep–/– mice exhibited lower plasma glucose under the fed condition, modestly improved systemic glucose tolerance and mildly suppressed gluconeogenesis, increased hepatic glycogen accumulation and synthesis due to elevated glucokinase expression and activated glycogen synthase (GS), and suppressed glucose-6-phosphatase expression compared with controls. These events were independent of hepatic AKT/GSK-3α/β signaling and were accompanied by increased HNF-4α transactivation, reduced FoxO1 protein abundance, and elevated expression of GS targeting protein phosphatase 1 regulatory subunit 3C in the PKCβHep–/– liver compared with controls. The above data strongly imply that hepatic PKCβ deficiency causes hypoglycemia postprandially by promoting glucose phosphorylation via upregulating glucokinase and subsequently redirecting more glucose-6-phosphate to glycogen via activating GS. In summary, hepatic PKCβ has a unique and essential ability to induce a coordinated response that negatively affects glycogenesis at multiple levels under physiological postprandial conditions, thereby integrating nutritional fat intake with dysregulation of glucose homeostasis.
Yaoling Shu, Faizule Hassan, Michael C. Ostrowski, Kamal D. Mehta
Xanthine oxidoreductase (XOR) is an enzyme that catalyzes hypoxanthine to xanthine and xanthine to uric acid, respectively. However, the underlying mechanisms of increased plasma XOR and its pathological roles in systemic diseases, such as atherosclerosis, are not fully understood. In this study, we found that changes in plasma XOR activity after bariatric surgery closely associated with those in liver enzymes, but not with those in BMI. In a mouse model of nonalcoholic fatty liver disease/steatohepatitis (NAFLD/NASH), plasma XOR activity markedly increased. Besides, purine catabolism was accelerated in the plasma per se of NASH mice and human patients with high XOR activity. In our NASH mice, we observed an increased vascular neointima formation consisting of dedifferentiated vascular smooth muscle cells (SMCs), which was significantly attenuated by topiroxostat, a selective XOR inhibitor. In vitro, human liver S9–derived XOR promoted proliferation of SMCs with phenotypic modulation and induced ROS production by catabolizing hypoxanthine released from human endothelial cells. Collectively, the results from human and mouse models suggest that increased plasma XOR activity, mainly explained by excess hepatic leakage, was involved in the pathogenesis of vascular injury, especially in NAFLD/NASH conditions.
Yusuke Kawachi, Yuya Fujishima, Hitoshi Nishizawa, Takashi Nakamura, Seigo Akari, Takayo Murase, Takuro Saito, Yasuhiro Miyazaki, Hirofumi Nagao, Shiro Fukuda, Shunbun Kita, Naoto Katakami, Yuichiro Doki, Norikazu Maeda, Iichiro Shimomura
Alcohol-associated liver disease (ALD) represents a spectrum of histopathological changes, including alcoholic steatosis, steatohepatitis, and cirrhosis. One of the early responses to excessive alcohol consumption is lipid accumulation in the hepatocytes. Lipid ω-hydroxylation of medium- and long-chain fatty acid metabolized by the cytochrome P450 4A (CYP4A) family is an alternative pathway for fatty acid metabolism. The molecular mechanisms of CYP4A in ALD pathogenesis have not been elucidated. In this study, WT and Shp−/− mice were fed with a modified ethanol-binge, National Institute on Alcohol Abuse and Alcoholism model (10 days of ethanol feeding plus single binge). Liver tissues were collected every 6 hours for 24 hours and analyzed using RNA-Seq. The effects of REV-ERBα agonist (SR9009, 100 mg/kg/d) or CYP4A antagonist (HET0016, 5 mg/kg/d) in ethanol-fed mice were also evaluated. We found that hepatic Cyp4a10 and Cyp4a14 expression were significantly upregulated in WT mice, but not in Shp−/− mice, fed with ethanol. ChIP quantitative PCR and promoter assay revealed that REV-ERBα is the transcriptional repressor of Cyp4a10 and Cyp4a14. Rev-Erbα−/− hepatocytes had a marked induction of both Cyp4a genes and lipid accumulation. REV-ERBα agonist SR9009 or CYP4A antagonist HET0016 attenuated Cyp4a induction by ethanol and prevented alcohol-induced steatosis. Here, we have identified a role for the SHP/REV-ERBα/CYP4A axis in the pathogenesis of ALD. Our data also suggest REV-ERBα or CYP4A as the potential therapeutic targets for ALD.
Zhihong Yang, Rana V. Smalling, Yi Huang, Yanchao Jiang, Praveen Kusumanchi, Will Bogaert, Li Wang, Don A. Delker, Nicholas J. Skill, Sen Han, Ting Zhang, Jing Ma, Nazmul Huda, Suthat Liangpunsakul
Development of primary liver cancer is a multi-stage process. Detailed understanding of sequential epigenetic alterations is largely missing. Here, we performed Infinium Human Methylation 450k BeadChips and RNA sequencing analyses for genome-wide methylome and transcriptome profiling of cirrhotic liver (n=7), low- (n=4) and high-grade (n=9) dysplastic lesions, early (n=5) and progressed (n=3) hepatocellular carcinomas (HCC) synchronously detected in eight HCC patients with chronic hepatitis B infection. Integrative analyses of epigenetically driven molecular changes were identified and validated in two independent cohorts comprising 887 HCC. Mitochondrial DNA sequencing was further employed for clonality analyses and indicates multi-clonal origin in the majority of investigated HCC. Alterations in DNA methylation progressively increased from CL to dysplastic lesions and reached a maximum in early HCC. Associated early alterations identified by IPA pathway analyses involved apoptosis, immune regulation and stemness pathways, while late changes centered on cell survival, proliferation and invasion. We further validated putative 23 epi-drivers with concomitant expression changes and associated with overall survival. Functionally, Striatin 4 (STRN4) was demonstrated to be epigenetically regulated and inhibition of STRN4 significantly suppressed tumorigenicity of HCC cell lines. Overall, application of integrative genomic analyses defines epigenetic driver alterations and provides promising targets for novel therapeutic approaches.
Carolin Czauderna, Alicia Poplawski, Colm J. O´Rourke, Darko Castven, Benjamín Pérez-Aguilar, Diana Becker, Stefanie Heilmann-Heimbach, Margarete Odenthal, Wafa Amer, Marcel Schmiel, Uta Drebber, Harald Binder, Dirk A. Ridder, Mario Schindeldecker, Beate K. Straub, Peter R. Galle, Jesper B. Andersen, Snorri S. Thorgeirsson, Young Nyun Park, Jens U. Marquardt
The liver is the major source of glucose production during fasting under normal physiological conditions. However, the kidney may also contribute to maintaining glucose homeostasis in certain circumstances. To test the ability of the kidney to compensate for impaired hepatic glucose production in vivo, we developed a stable isotope approach to simultaneously quantify gluconeogenic and oxidative metabolic fluxes in the liver and kidney. Hepatic gluconeogenesis from phosphoenolpyruvate was disrupted via liver-specific knockout of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; KO). 2H/13C isotopes were infused in fasted KO and WT littermate mice, and fluxes were estimated from isotopic measurements of tissue and plasma metabolites using a multicompartment metabolic model. Hepatic gluconeogenesis and glucose production were reduced in KO mice, yet whole-body glucose production and arterial glucose were unaffected. Glucose homeostasis was maintained by a compensatory rise in renal glucose production and gluconeogenesis. Renal oxidative metabolic fluxes of KO mice increased to sustain the energetic and metabolic demands of elevated gluconeogenesis. These results show the reciprocity of the liver and kidney in maintaining glucose homeostasis by coordinated regulation of gluconeogenic flux through PEPCK-C. Combining stable isotopes with mathematical modeling provides a versatile platform to assess multitissue metabolism in various genetic, pathophysiological, physiological, and pharmacological settings.
Mohsin Rahim, Clinton M. Hasenour, Tomasz K. Bednarski, Curtis C. Hughey, David H. Wasserman, Jamey D. Young
Obesity is a risk factor for gallbladder cancer (GBC) development and correlates with shorter overall survival. Leptin, derived from adipocytes, has been suggested to contribute to the growth of cancer cells. However, the detailed mechanism of leptin in GBC drug resistance remains uninvestigated. In this study, it is clinically relevant that GBC patients with a higher BMI (BMI ≥ 24 kg/m2) (n=30) were associated with increased GBC risks, including survival. Moreover, obese NOD/SCID mice exhibited a higher circulating concentration of leptin, which is associated with GBC growth and attenuated gemcitabine efficacy. We further revealed that leptin can inhibit gemcitabine-induced GBC cell death through myeloid cell leukemia 1 (MCL1) activation. The transcription factor CCAAT/enhancer-binding protein delta (CEBPD) is responsive to activated signal transducers and activators of transcription 3 (pSTAT3) and contributes to MCL1 transcriptional activation upon leptin treatment. In addition, MCL1 mediates leptin-induced mitochondrial fusion and is associated with GBC cell survival. This study suggests the involvement of the pSTAT3/CEBPD/MCL1 axis in leptin-induced mitochondrial fusion and survival. It provides a new therapeutic target to improve the efficacy of gemcitabine in GBC patients.
Wei-Jan Wang, Hong-Yue Lai, Fei Zhang, Wan-Jou Shen, Pei-Yu Chu, Hsin-Yin Liang, Ying-Bin Liu, Ju-Ming Wang
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