Metabolism
Abstract
Bile acids are signaling molecules that critically control hepatocellular function. Disrupted bile acid homeostasis may be implicated in the pathogenesis of chronic liver diseases. Glutathione is an important antioxidant that protects the liver against oxidative injury. Various forms of liver disease share the common characteristics of reduced cellular glutathione and elevated oxidative stress. This study reports a potentially novel physiological function of bile acids in regulating hepatic sulfur amino acid and glutathione metabolism. We found that bile acids strongly inhibited the cysteine dioxygenase type-1–mediated (CDO1-mediated) cysteine catabolic pathway via a farnesoid X receptor–dependent mechanism. Attenuating this bile acid repressive effect depleted the free cysteine pool and reduced the glutathione concentration in mouse liver. Upon acetaminophen challenge, cholestyramine-fed mice showed impaired hepatic glutathione regeneration capacity and markedly worsened liver injury, which was fully prevented by N-acetylcysteine administration. These effects were recapitulated in CDO1-overexpressing hepatocytes. Findings from this study support the importance of maintaining bile acid homeostasis under physiological and pathophysiological conditions, as altered hepatic bile acid signaling may negatively impact the antioxidant defense mechanism and sensitivity to oxidative injury. Furthermore, this finding provides a possible explanation for the reported mild hepatotoxicity associated with the clinical use of bile acid sequestrants in human patients.
Authors
Yifeng Wang, Jibiao Li, David Matye, Yuxia Zhang, Katie Dennis, Wen-Xing Ding, Tiangang Li
Abstract
Adiponectin, an adipocyte-derived circulating protein, accumulates in vasculature, heart, and skeletal muscles through interaction with a unique glycosylphosphatidylinositol-anchored cadherin, T-cadherin. Recent studies have demonstrated that such accumulation is essential for adiponectin-mediated cardiovascular protection. Here, we demonstrate that the adiponectin/T-cadherin system enhances exosome biogenesis and secretion, leading to the decrease of cellular ceramides. Adiponectin accumulated inside multivesicular bodies, the site of exosome generation, in cultured cells and in vivo aorta, and also in exosomes in conditioned media and in blood, together with T-cadherin. The systemic level of exosomes in blood was significantly affected by adiponectin or T-cadherin in vivo. Adiponectin increased exosome biogenesis from the cells, dependently on T-cadherin, but not on AdipoR1 or AdipoR2. Such enhancement of exosome release accompanied the reduction of cellular ceramides through ceramide efflux in exosomes. Consistently, the ceramide reduction by adiponectin was found in aortas of WT mice treated with angiotensin II, but not in T-cadherin–knockout mice. Our findings provide insights into adiponectin/T-cadherin–mediated organ protection through exosome biogenesis and secretion.
Authors
Yoshinari Obata, Shunbun Kita, Yoshihisa Koyama, Shiro Fukuda, Hiroaki Takeda, Masatomo Takahashi, Yuya Fujishima, Hirofumi Nagao, Shigeki Masuda, Yoshimitsu Tanaka, Yuto Nakamura, Hitoshi Nishizawa, Tohru Funahashi, Barbara Ranscht, Yoshihiro Izumi, Takeshi Bamba, Eiichiro Fukusaki, Rikinari Hanayama, Shoichi Shimada, Norikazu Maeda, Iichiro Shimomura
Abstract
Clinical and experimental data indicate a beneficial effect of estrogens on energy and glucose homeostasis associated with improved insulin sensitivity and positive effects on insulin secretion. The aim of the study was to investigate the impact of estrogens on proglucagon-producing cells, pancreatic α cells, and enteroendocrine L cells. The consequences of sexual hormone deprivation were evaluated in ovariectomized mice (ovx). Ovx mice exhibited impaired glucose tolerance during oral glucose tolerance tests (OGTT), which was associated with decreased GLP-1 intestinal and pancreatic secretion and content, an effect that was reversed by estradiol (E2) treatment. Indeed, E2 increased oral glucose–induced GLP-1 secretion in vivo and GLP-1 secretion from primary culture of mouse and human α cells through the activation of all 3 estrogen receptors (ERs), whereas E2-induced GLP-1 secretion from mouse and human intestinal explants occurred only by ERβ activation. Underlying the implication of ERβ, its selective agonist WAY20070 was able to restore glucose tolerance in ovx mice at least partly through plasma GLP-1 increase. We conclude that E2 directly controls both α- and L cells to increase GLP-1 secretion, in addition to its effects on insulin and glucagon secretion, highlighting the potential beneficial role of the estrogenic pathway and, more particularly, of ERβ agonists to prevent type 2 diabetes.
Authors
Sandra Handgraaf, Rodolphe Dusaulcy, Florian Visentin, Jacques Philippe, Yvan Gosmain
Abstract
Nonalcoholic fatty liver disease (NAFLD), a metabolic predisposition for development of hepatocellular carcinoma (HCC), represents a disease spectrum ranging from steatosis to steatohepatitis to cirrhosis. Acox1, a rate-limiting enzyme in peroxisomal fatty acid β-oxidation, regulates metabolism, spontaneous hepatic steatosis, and hepatocellular damage over time. However, it is unknown whether Acox1 modulates inflammation relevant to NAFLD pathogenesis or if Acox1-associated metabolic and inflammatory derangements uncover and accelerate potential for NAFLD progression. Here, we show that mice with a point mutation in Acox1 (Acox1Lampe1) exhibited altered cellular metabolism, modified T cell polarization, and exacerbated immune cell inflammatory potential. Further, in context of a brief obesogenic diet stress, NAFLD progression associated with Acox1 mutation resulted in significantly accelerated and exacerbated hepatocellular damage via induction of profound histological changes in hepatocytes, hepatic inflammation, and robust upregulation of gene expression associated with HCC development. Collectively, these data demonstrate that β-oxidation links metabolism and immune responsiveness and that a better understanding of peroxisomal β-oxidation may allow for discovery of mechanisms central for NAFLD progression.
Authors
Maria E. Moreno-Fernandez, Daniel A. Giles, Traci E. Stankiewicz, Rachel Sheridan, Rebekah Karns, Monica Cappelletti, Kristin Lampe, Rajib Mukherjee, Christian Sina, Anthony Sallese, James P. Bridges, Simon P. Hogan, Bruce J. Aronow, Kasper Hoebe, Senad Divanovic
Abstract
Alport syndrome is a rare hereditary renal disorder with no etiologic therapy. We found that osteopontin (OPN) is highly expressed in the renal tubules of the Alport mouse and plays a causative pathological role. OPN genetic deletion ameliorated albuminuria, hypertension, tubulointerstitial proliferation, renal apoptosis, and hearing and visual deficits in the Alport mouse. In Alport renal tubules we found extensive cholesterol accumulation and increased protein expression of dynamin-3 (DNM3) and LDL receptor (LDLR) in addition to dysmorphic mitochondria with defective bioenergetics. Increased pathological cholesterol influx was confirmed by a remarkably increased uptake of injected DiI-LDL cholesterol by Alport renal tubules, and by the improved lifespan of the Alport mice when crossed with the Ldlr–/– mice with defective cholesterol influx. Moreover, OPN-deficient Alport mice demonstrated significant reduction of DNM3 and LDLR expression. In human renal epithelial cells, overexpressing DNM3 resulted in elevated LDLR protein expression and defective mitochondrial respiration. Our results suggest a potentially new pathway in Alport pathology where tubular OPN causes DNM3- and LDLR-mediated enhanced cholesterol influx and impaired mitochondrial respiration.
Authors
Wen Ding, Keyvan Yousefi, Stefania Goncalves, Bradley J. Goldstein, Alfonso L. Sabater, Amy Kloosterboer, Portia Ritter, Guerline Lambert, Armando J. Mendez, Lina A. Shehadeh
Abstract
Alterations in ectopic lipid deposition and circulating lipids are major risk factors for developing cardiometabolic diseases. Angiopoietin-like protein 4 (ANGPTL4), a protein that inhibits lipoprotein lipase (LPL), controls fatty acid (FA) uptake in adipose and oxidative tissues and regulates circulating triacylglycerol-rich (TAG-rich) lipoproteins. Unfortunately, global depletion of ANGPTL4 results in severe metabolic abnormalities, inflammation, and fibrosis when mice are fed a high-fat diet (HFD), limiting our understanding of the contribution of ANGPTL4 in metabolic disorders. Here, we demonstrate that genetic ablation of ANGPTL4 in adipose tissue (AT) results in enhanced LPL activity, rapid clearance of circulating TAGs, increased AT lipolysis and FA oxidation, and decreased FA synthesis in AT. Most importantly, we found that absence of ANGPTL4 in AT prevents excessive ectopic lipid deposition in the liver and muscle, reducing novel PKC (nPKC) membrane translocation and enhancing insulin signaling. As a result, we observed a remarkable improvement in glucose tolerance in short-term HFD-fed AT-specific Angptl4-KO mice. Finally, lack of ANGPTL4 in AT enhances the clearance of proatherogenic lipoproteins, attenuates inflammation, and reduces atherosclerosis. Together, these findings uncovered an essential role of AT ANGPTL4 in regulating peripheral lipid deposition, influencing whole-body lipid and glucose metabolism and the progression of atherosclerosis.
Authors
Binod Aryal, Abhishek K. Singh, Xinbo Zhang, Luis Varela, Noemi Rotllan, Leigh Goedeke, Balkrishna Chaube, Joao-Paulo Camporez, Daniel F. Vatner, Tamas L. Horvath, Gerald I. Shulman, Yajaira Suárez, Carlos Fernández-Hernando
Abstract
Although accumulation of lymphocytes in the white adipose tissue (WAT) in obesity is linked to insulin resistance, it remains unclear whether lymphocytes also participate in the regulation of energy homeostasis in the WAT. Here, we demonstrate enhanced energy dissipation in Rag1–/– mice, increased catecholaminergic input to subcutaneous WAT, and significant beige adipogenesis. Adoptive transfer experiments demonstrated that CD8+ T cell deficiency accounts for the enhanced beige adipogenesis in Rag1–/– mice. Consistently, we identified that CD8–/– mice also presented with enhanced beige adipogenesis. The inhibitory effect of CD8+ T cells on beige adipogenesis was reversed by blockade of IFN-γ. All together, our findings identify an effect of CD8+ T cells in regulating energy dissipation in lean WAT, mediated by IFN-γ modulation of the abundance of resident immune cells and of local catecholaminergic activity. Our results provide a plausible explanation for the clinical signs of metabolic dysfunction in diseases characterized by altered CD8+ T cell abundance and suggest targeting of CD8+ T cells as a promising therapeutic approach for obesity and other diseases with altered energy homeostasis.
Authors
Maria Moysidou, Sevasti Karaliota, Elisavet Kodela, Maria Salagianni, Yassemi Koutmani, Antonia Katsouda, Konstantia Kodella, Panagiotis Tsakanikas, Styliani Ourailidou, Evangelos Andreakos, Nikolaos Kostomitsopoulos, Dimitris Skokos, Antonios Chatzigeorgiou, Kyoung-Jin Chung, Stefan Bornstein, Mark W. Sleeman, Triantafyllos Chavakis, Katia P. Karalis
Abstract
Excess lipid accumulation is an early signature of nonalcoholic fatty liver disease (NAFLD). Although liver receptor homolog 1 (LRH-1) (encoded by NR5A2) is suppressed in human NAFLD, evidence linking this phospholipid-bound nuclear receptor to hepatic lipid metabolism is lacking. Here, we report an essential role for LRH-1 in hepatic lipid storage and phospholipid composition based on an acute hepatic KO of LRH-1 in adult mice (LRH-1AAV8-Cre mice). Indeed, LRH-1–deficient hepatocytes exhibited large cytosolic lipid droplets and increased triglycerides (TGs). LRH-1–deficient mice fed high-fat diet displayed macrovesicular steatosis, liver injury, and glucose intolerance, all of which were reversed or improved by expressing wild-type human LRH-1. While hepatic lipid synthesis decreased and lipid export remained unchanged in mutants, elevated circulating free fatty acid helped explain the lipid imbalance in LRH-1AAV8-Cre mice. Lipidomic and genomic analyses revealed that loss of LRH-1 disrupts hepatic phospholipid composition, leading to lowered arachidonoyl (AA) phospholipids due to repression of Elovl5 and Fads2, two critical genes in AA biosynthesis. Our findings reveal a role for the phospholipid sensor LRH-1 in maintaining adequate pools of hepatic AA phospholipids, further supporting the idea that phospholipid diversity is an important contributor to healthy hepatic lipid storage.
Authors
Diego A. Miranda, William C. Krause, Amaury Cazenave-Gassiot, Miyuki Suzawa, Hazel Escusa, Juat Chin Foo, Diyala S. Shihadih, Andreas Stahl, Mark Fitch, Edna Nyangau, Marc Hellerstein, Markus R. Wenk, David L. Silver, Holly A. Ingraham
Abstract
Insulin resistance is associated with increased incidence and enhanced progression of cancers. However, little is known about strategies that can effectively ameliorate insulin resistance and consequently halt cancer progression. Herein, we propose that the transcription factor Nrf2 (also known as Nfe2l2) may be such a target, given its central role in disease prevention. To this end, we developed a mouse that overexpresses the Notch intracellular domain in adipocytes (AdNICD), leading to lipodystrophy-induced severe insulin resistance and subsequent development of sarcomas, as a model reflecting that Notch signaling is deregulated in cancers and shows positive associations with insulin resistance and fatty liver disease in humans. Nrf2 pathway activation was achieved by knocking down Keap1, a repressor of Nrf2, in the AdNICD background. Constitutively enhanced Nrf2 signaling in this setting led to prevention of hepatic steatosis, dyslipidemia, and insulin resistance by repressing hepatic lipogenic pathways and restoration of the hepatic fatty acid profile to control levels. This protective effect of Nrf2 against diabetes extended to significant reduction and delay in sarcoma incidence and latency. Our study highlights that the Nrf2 pathway, which has been induced by small molecules in clinical trials, is a potential therapeutic target against insulin resistance and subsequent risk of cancer.
Authors
Dionysios V. Chartoumpekis, Yoko Yagishita, Marco Fazzari, Dushani L. Palliyaguru, Uma N.M. Rao, Apostolos Zaravinos, Nicholas K.H. Khoo, Francisco J. Schopfer, Kurt R. Weiss, George K. Michalopoulos, Ian Sipula, Robert M. O’Doherty, Thomas W. Kensler, Nobunao Wakabayashi
Abstract
Neuregulins (NRGs) are emerging as an important family of signaling ligands that regulate glucose and lipid homeostasis. NRG1 lowers blood glucose levels in obese mice, whereas the brown fat–enriched secreted factor NRG4 protects mice from high-fat diet–induced insulin resistance and hepatic steatosis. However, the therapeutic potential of NRGs remains elusive, given the poor plasma half-life of the native ligands. Here, we engineered a fusion protein using human NRG1 and the Fc domain of human IgG1 (NRG1-Fc) that exhibited extended half-life in circulation and improved potency in receptor signaling. We evaluated its efficacy in improving metabolic parameters and dissected the mechanisms of action. NRG1-Fc treatment triggered potent AKT activation in the liver, lowered blood glucose, improved insulin sensitivity, and suppressed food intake in obese mice. NRG1-Fc acted as a potent secretagogue for the metabolic hormone FGF21; however, the latter was largely dispensable for its metabolic effects. NRG1-Fc directly targeted the hypothalamic POMC neurons to promote membrane depolarization and increase firing rate. Together, NRG1-Fc exhibits improved pharmacokinetic properties and exerts metabolic benefits through dual inhibition of hepatic gluconeogenesis and caloric intake.
Authors
Peng Zhang, Henry Kuang, Yanlin He, Sharon O. Idiga, Siming Li, Zhimin Chen, Zhao Yang, Xing Cai, Kezhong Zhang, Matthew J. Potthoff, Yong Xu, Jiandie D. Lin
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