Metabolism
Abstract
The t-SNARE protein SNAP23 conventionally functions as a component of the cellular machinery required for intracellular transport vesicle fusion with target membranes and has been implicated in the regulation of fasting glucose levels, BMI, and type 2 diabetes. Surprisingly, we observed that adipocyte-specific KO of SNAP23 in mice resulted in a temporal development of severe generalized lipodystrophy associated with adipose tissue inflammation, insulin resistance, hyperglycemia, liver steatosis, and early death. This resulted from adipocyte cell death associated with an inhibition of macroautophagy and lysosomal degradation of the proapoptotic regulator BAX, with increased BAX activation. BAX colocalized with LC3-positive autophagic vacuoles and was increased upon treatment with lysosome inhibitors. Moreover, BAX deficiency suppressed the lipodystrophic phenotype in the adipocyte-specific SNAP23-KO mice and prevented cell death. In addition, ATG9 deficiency phenocopied SNAP23 deficiency, whereas ATG7 deficiency had no effect on BAX protein levels, BAX activation, or apoptotic cell death. These data demonstrate a role for SNAP23 in the control of macroautophagy and programmed cell death through an ATG9-dependent, but ATG7-independent, pathway regulating BAX protein levels and BAX activation.
Authors
Daorong Feng, Dulguun Amgalan, Rajat Singh, Jianwen Wei, Jennifer Wen, Tszki Peter Wei, Timothy E. McGraw, Richard N. Kitsis, Jeffrey E. Pessin
Abstract
Prostate cancer is an androgen-dependent disease subject to interactions between the tumor epithelia and its microenvironment. Here, we found epigenetic changes in cancer-associated prostatic fibroblasts (CAF) initiated a cascade of stromal-epithelial interactions. This facilitated lethal prostate cancer growth and development of resistance to androgen signaling deprivation therapy (ADT). We identified that a Ras inhibitor, RASAL3, is epigenetically silenced in human prostatic CAF, leading to oncogenic Ras activity driving macropinocytosis-mediated glutamine synthesis. Interestingly, ADT further promoted RASAL3 epigenetic silencing and glutamine secretion by prostatic fibroblasts. In a orthotopic xenograft model, subsequent inhibition of macropinocytosis and glutamine transport resulted in antitumor effects. Stromal glutamine served as a source of energy through anaplerosis and as a mediator of neuroendocrine differentiation for prostate adenocarcinoma. Antagonizing the uptake of glutamine restored sensitivity to ADT in a castrate resistant xenograft model. In validating these findings, we found that prostate cancer patients on ADT with therapeutic resistance had elevated blood glutamine levels compared to those with therapeutically responsive disease (odds ratio = 7.451, P = 0.02). Identification of epigenetic regulation of RAS activity in prostatic CAF revealed RASAL3 as a sensor for metabolic and neuroendocrine reprogramming in prostate cancer patients failing ADT.
Authors
Rajeev Mishra, Subhash Haldar, Veronica Placencio, Anisha Madhav, Krizia Rohena-Rivera, Priyanka Agarwal, Frank Duong, Bryan Angara, Manisha Tripathi, Zhenqiu Liu, Roberta A. Gottlieb, Shawn Wagner, Edwin M. Posadas, Neil A. Bhowmick
Abstract
Movement of circulating fatty acids (FAs) to parenchymal cells requires their transfer across the endothelial cell (EC) barrier. The multi-ligand receptor cluster of differentiation 36 (CD36) facilitates tissue FA uptake and is expressed in ECs and parenchymal cells such as myocytes and adipocytes. Whether tissue uptake of FAs is dependent on EC or parenchymal cell CD36, or both, is unknown. Using a cell-specific deletion approach, we show that EC, but not parenchymal cell CD36 deletion increased fasting plasma FAs and postprandial triglycerides. EC-Cd36 knockout mice had reduced uptake of radiolabeled long chain FAs into heart, skeletal muscle, and brown adipose tissue; these uptake studies were replicated using [11C]palmitate PET scans. High fat diet-fed EC-CD36 deficient mice had improved glucose tolerance and insulin sensitivity. Both EC and cardiomyocyte (CM) deletion of CD36 reduced heart lipid droplet accumulation after fasting, but CM deletion did not affect heart glucose or FA uptake. Heart expression of several genes modulating glucose metabolism and insulin action increased with EC-CD36 deletion, but decreased with CM deletion. In conclusion, EC CD36 acts as a gatekeeper for parenchymal cell FA uptake, with important downstream effects on glucose utilization and insulin action.
Authors
Ni-Huiping Son, Debapriya Basu, Dmitri Samovski, Terri A. Pietka, Vivek S. Peche, Florian Willecke, Xiang Fang, Shui-Qing Yu, Diego Scerbo, Hye Rim Chang, Fei Sun, Svetlana Bagdasarov, Konstantinos Drosatos, Steve T. Yeh, Adam E. Mullick, Kooresh I. Shoghi, Namrata Gumaste, KyeongJin Kim, Lesley-Ann M. Huggins, Tenzin Lhakhang, Nada A. Abumrad, Ira J. Goldberg
Abstract
Control of cellular metabolism is critical for efficient cell function, although little is known about the interplay between cell subset-specific metabolites in situ, especially in the tumor setting. Here, we determine how a macrophage-specific metabolite, itaconic acid, can regulate tumor progression in the peritoneum. We show peritoneal tumors (B16 melanoma or ID8 ovarian carcinoma) elicited a fatty acid oxidation-mediated increase in oxidative phosphorylation (OXPHOS) and glycolysis in peritoneal tissue-resident macrophages (pResMφ). Unbiased metabolomics identified itaconic acid, the product of Irg1-mediated catabolism of mitochondrial cis-aconitate, among the most highly upregulated metabolites in pResMφ of tumor-bearing mice. Administration of lentivirally-encoded Irg1 shRNA significantly reduced peritoneal tumors. This resulted in reductions in OXPHOS and OXPHOS-driven production of reactive oxygen species (ROS) in pResMφ and ROS-mediated MAP kinase activation in tumor cells. Our findings demonstrate that tumors profoundly alter pResMφ metabolism, leading to the production of itaconic acid, which potentiates tumor growth. Monocytes isolated from ovarian carcinoma patient ascites fluid expressed significantly elevated levels of Irg1. Therefore, Irg1 in pResMφ represents a potential therapeutic target for peritoneal tumors.
Authors
Jonathan M. Weiss, Luke C. Davies, Megan Karwan, Lilia Ileva, Michelle K. Ozaki, Robert Y.S. Cheng, Lisa A. Ridnour, Christina M. Annunziata, David A. Wink, Daniel W. McVicar
Abstract
Jumonji D3 (JMJD3) histone demethylase epigenetically regulates development and differentiation, immunity, and tumorigenesis by demethylating a gene repression histone mark, H3K27-me3, but a role for JMJD3 in metabolic regulation has not been described. SIRT1 deacetylase maintains energy balance during fasting by directly activating both hepatic gluconeogenic and mitochondrial fatty acid β-oxidation genes, but the underlying epigenetic and gene-specific mechanisms remain unclear. In this study, JMJD3 was identified unexpectedly as a gene-specific transcriptional partner of SIRT1 and epigenetically activated mitochondrial β-oxidation, but not gluconeogenic, genes during fasting. Mechanistically, JMJD3, together with SIRT1 and the nuclear receptor PPARα, formed a positive autoregulatory loop upon fasting-activated PKA signaling and epigenetically activated β-oxidation–promoting genes, including Fgf21, Cpt1a, and Mcad. Liver-specific downregulation of JMJD3 resulted in intrinsic defects in β-oxidation, which contributed to hepatosteatosis as well as glucose and insulin intolerance. Remarkably, the lipid-lowering effects by JMJD3 or SIRT1 in diet-induced obese mice were mutually interdependent. JMJD3 histone demethylase may serve as an epigenetic drug target for obesity, hepatosteatosis, and type 2 diabetes that allows selective lowering of lipid levels without increasing glucose levels.
Authors
Sunmi Seok, Young-Chae Kim, Sangwon Byun, Sunge Choi, Zhen Xiao, Naoki Iwamori, Yang Zhang, Chaochen Wang, Jian Ma, Kai Ge, Byron Kemper, Jongsook Kim Kemper
Abstract
BACKGROUND. Recombinant leptin (metreleptin) ameliorates hyperphagia and metabolic abnormalities in leptin-deficient humans with lipodystrophy. We aimed to determine whether metreleptin improves glucose and lipid metabolism in humans when food intake is held constant. METHODS. Patients with lipodystrophy were hospitalized for 19 days with food intake held constant by controlled diet in an inpatient metabolic ward. In a non-randomized cross-over design, previously metreleptin-treated patients (n = 8) were continued on-metreleptin for five days, and off-metreleptin for the next 14 days (withdrawal cohort). This order was reversed in metreleptin-naïve patients (n = 14), who were restudied after six months of metreleptin treatment on an ad libitum diet (initiation cohort). Outcomes included insulin sensitivity by hyperinsulinemic-euglycemic clamp, fasting glucose and triglycerides, lipolysis measured using isotopic tracers, and liver fat by magnetic resonance spectroscopy. RESULTS. With food intake constant, peripheral insulin sensitivity decreased by 41% after stopping metreleptin for 14 days (withdrawal cohort) and increased by 32% after starting metreleptin for 14 days (initiation cohort). In the initiation cohort only, metreleptin decreased fasting glucose by 11%, triglycerides by 41%, and increased hepatic insulin sensitivity. Liver fat decreased from 21.8% to 18.7%. In the initiation cohort, lipolysis did not change independent of food intake, but decreased after six months on metreleptin on an ad libitum diet by 30% (palmitate turnover) to 35% (glycerol turnover). CONCLUSION. Using lipodystrophy as a human model of leptin deficiency and replacement, we showed that metreleptin improves insulin sensitivity, and decreases hepatic and circulating triglycerides, independent of its effects on food intake. TRIAL REGISTRATION. ClinicalTrials.gov, NCT01778556. FUNDING. This research was supported by the intramural research program of the National Institute of Diabetes and Digestive and Kidney Diseases.
Authors
Rebecca J. Brown, Areli Valencia, Megan Startzell, Elaine Cochran, Peter J. Walter, H. Martin Garraffo, Hongyi Cai, Ahmed M. Gharib, Ronald Ouwerkerk, Amber B. Courville, Shanna Bernstein, Robert J. Brychta, Kong Y. Chen, Mary Walter, Sungyoung Auh, Phillip Gorden
Abstract
Complications of diabetes affect tissues throughout body, including central nervous system. Epidemiological studies show that diabetic patients have increased risk of depression, anxiety, age-related cognitive decline and Alzheimer’s disease. Mice lacking insulin receptor in brain or on hypothalamic neurons display an array of metabolic abnormalities, however, the role of insulin action on astrocytes and neurobehaviors remains less well-studied. Here, we demonstrate that astrocytes are a direct insulin target in the brain and that knockout of IR on astrocytes causes increased anxiety and depressive-like behaviors in mice. This can be reproduced in part by deletion of IR on astrocytes in the nucleus accumbens. At a molecular level, loss of insulin signaling in astrocytes impaired tyrosine phosphorylation of Munc18c. This led to decreased exocytosis of ATP from astrocytes, resulting in decreased purinergic signaling on dopaminergic neurons. These reductions contributed to decreased dopamine release from brain slices. Central administration of ATP analogues could reverse depressive-like behaviors in mice with astrocyte IR knockout. Thus, astrocytic insulin signaling plays an important role in dopaminergic signaling, providing a potential mechanism by which astrocytic insulin action may contribute to increased rates of depression in people with diabetes, obesity and other insulin resistant states.
Authors
Weikang Cai, Chang Xue, Masaji Sakaguchi, Masahiro Konishi, Alireza Shirazian, Heather A. Ferris, Mengyao Li, Ruichao Yu, Andre Kleinridders, Emmanuel N. Pothos, C. Ronald Kahn
Abstract
In the brain, the ventral hypothalamus (VHT) regulates energy and bone metabolism. Whether this regulation uses the same or different neuronal circuits is unknown. Alteration of AP1 signaling in the VHT increases energy expenditure, glucose utilization, and bone density, yet the specific neurons responsible for each or all of these phenotypes are not identified. Using neuron-specific genetically targeted AP1 alterations as a tool in adult mice, we found that AgRP- or POMC- expressing neurons, predominantly present in the arcuate nucleus (ARC) within the VHT, stimulate whole body energy expenditure, glucose utilization and bone formation and density, although their effects on bone resorption differed. In contrast, AP1 alterations in Steroidogenic factor 1 (SF1)-expressing neurons, present in the ventromedial hypothalamus (VMH), increase energy, but decrease bone density, suggesting that these effects are independent. Altered AP1 signaling also increased the levels of the neuromediator galanin in the hypothalamus and global galanin deletion, VHT galanin silencing using shRNA, or pharmacological galanin receptor blockade, counteracted the observed effects on energy and bone. Thus, AP1 antagonism reveals that AgRP- and POMC- expressing neurons can stimulate body metabolism and increase bone density, with galanin acting as a central downstream effector. The results obtained with SF1-expressing neurons, however, indicate that bone homeostasis is not always dictated by the global energy status, and vice versa.
Authors
Anna Idelevich, Kazusa Sato, Kenichi Nagano, Glenn Rowe, Francesca Gori, Roland Baron
Abstract
Thiazolidinediones (TZDs) are PPARγ agonists with potent insulin-sensitizing effects. However, their use has been curtailed by significant adverse effects on weight, bone, heart, and hemodynamic balance. TZDs induce the deacetylation of PPARγ on K268 and K293 to cause the browning of white adipocytes. Here we showed that targeted PPARγ mutations resulting in constitutive deacetylation (K268R/K293R, 2KR) increased energy expenditure, and protected from visceral adiposity and diet-induced obesity by augmenting brown remodeling of white adipose tissues. Strikingly, when 2KR mice were treated with rosiglitazone, they maintained the insulin-sensitizing, glucose-lowering response to TZDs, while displaying little, if any, adverse effects on fat deposition, bone density, fluid retention, and cardiac hypertrophy. Thus, deacetylation appears to fulfill the goal of dissociating the metabolic benefits of PPARγ activation from its adverse effects. Strategies to leverage PPARγ deacetylation may lead to the design of safer, more effective agonists of this nuclear receptor in the treatment of metabolic diseases.
Authors
Michael J. Kraakman, Qiongming Liu, Jorge Postigo-Fernandez, Ruiping Ji, Ning Kon, Delfina Larrea, Maria Namwanje, Lihong Fan, Michelle Chan, Estela Area-Gomez, Wenxian Fu, Remi J. Creusot, Li Qiang
Abstract
Increasing evidence suggests a role for excessive intake of fructose in the Western diet as a contributor to the current epidemics of metabolic syndrome and obesity. Hereditary fructose intolerance (HFI) is a difficult and potentially lethal orphan disease associated with impaired fructose metabolism. In HFI, the deficiency of a particular aldolase, aldolase B, results in the accumulation of intracellular phosphorylated fructose thus leading to phosphate sequestration and depletion, increased ATP turnover and a plethora of conditions leading to clinical manifestations including fatty liver, hyperuricemia, Fanconi syndrome and severe hypoglycemia. Unfortunately, to date, there is no treatment for HFI and avoiding sugar and fructose in our society has become quite challenging. In this report, through use of genetically modified mice and pharmacological inhibitors, we demonstrate that the absence or inhibition of ketohexokinase (Khk), an enzyme upstream of aldolase B, is sufficient to prevent hypoglycemia and liver and intestinal injury associated with HFI using aldolase B knockout mice. We thus provide evidence for the first time of a potential therapeutic approach for this condition. Mechanistically, our studies suggest that it is the inhibition of the Khk C isoform, not the A isoform, that protects animals from HFI.
Authors
Miguel A. Lanaspa, Ana Andres-Hernando, David J. Orlicky, Christina Cicerchi, Cholsoon Jang, Nanxing Li, Tamara Milagres, Masanari Kuwabara, Michael F. Wempe, Joshua D. Rabinowitz, Richard J. Johnson, Dean R. Tolan
Copyright © 2018 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)