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Genomics of human fatty liver disease reveal mechanistically linked lipid droplet-associated gene regulations in bland steatosis and nonalcoholic steatohepatitis. Transl Res 2016; 177:41-69. [PMID: 27376874 DOI: 10.1016/j.trsl.2016.06.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Revised: 05/13/2016] [Accepted: 06/08/2016] [Indexed: 12/11/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is a common disorder hallmarked by excessive lipid deposits. Based on our recent research on lipid droplet (LD) formation in hepatocytes, we investigated LD-associated gene regulations in NAFLD of different grades, that is, steatosis vs steatohepatitis by comparing liver biopsies from healthy controls (N = 13) and NAFLD patients (N = 102). On average, more than 700 differentially expressed genes (DEGs) were identified of which 146 are mechanistically linked to LD formation. We identified 51 LD-associated DEGs frequently regulated in patient samples (range ≥5 to ≤102) with the liver-receptor homolog-1(NR5A2), that is, a key regulator of cholesterol metabolism being commonly repressed among 100 patients examined. With bland steatosis, notable regulations involved hypoxia-inducible lipid droplet-associated-protein and diacylglycerol-O-acyltransferase-2 renowned for their role in LD-growth. Conversely, nonalcoholic steatohepatitis-associated DEGs coded for epidermal growth factor receptor and TLR4 signaling with decreased expression of the GTPase Rab5 and the lipid phosphohydrolase PPAP2B thus highlighting adaptive responses to inflammation, LDL-mediated endocytosis and lipogenesis, respectively. Studies with steatotic primary human hepatocyte cultures demonstrated induction of LD-associated PLIN2, CIDEC, DNAAF1, whereas repressed expression of CPT1A, ANGPTL4, and PKLR informed on burdened mitochondrial metabolism. Equally, repressed expression of the B-lymphocyte chemoattractant CXCL13 and STAT4 as well as induced FGF21 evidenced amelioration of steatosis-related inflammation. In-vitro/in-vivo patient sample comparisons confirmed C-reactive protein, SOCS3, NR5A2, and SOD2 as commonly regulated. Lastly, STRING network analysis highlighted potential "druggable" targets with PLIN2, CIDEC, and hypoxia-inducible lipid droplet-associated-protein being confirmed by immunofluorescence microscopy. In conclusion, steatosis and steatohepatitis specific gene regulations informed on the pathogenesis of NAFLD to broaden the perspective of targeted therapies.
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52
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Caveolin-1 Function in Liver Physiology and Disease. Trends Mol Med 2016; 22:889-904. [DOI: 10.1016/j.molmed.2016.08.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 08/14/2016] [Accepted: 08/17/2016] [Indexed: 12/18/2022]
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ROR1 sustains caveolae and survival signalling as a scaffold of cavin-1 and caveolin-1. Nat Commun 2016; 7:10060. [PMID: 26725982 PMCID: PMC4777216 DOI: 10.1038/ncomms10060] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Accepted: 10/28/2015] [Indexed: 01/03/2023] Open
Abstract
The receptor tyrosine kinase-like orphan receptor 1 (ROR1) sustains prosurvival signalling directly downstream of the lineage-survival oncogene NKX2-1/TTF-1 in lung adenocarcinoma. Here we report an unanticipated function of this receptor tyrosine kinase (RTK) as a scaffold of cavin-1 and caveolin-1 (CAV1), two essential structural components of caveolae. This kinase-independent function of ROR1 facilitates the interactions of cavin-1 and CAV1 at the plasma membrane, thereby preventing the lysosomal degradation of CAV1. Caveolae structures and prosurvival signalling towards AKT through multiple RTKs are consequently sustained. These findings provide mechanistic insight into how ROR1 inhibition can overcome EGFR-tyrosine kinase inhibitor (TKI) resistance due to bypass signalling via diverse RTKs such as MET and IGF-IR, which is currently a major clinical obstacle. Considering its onco-embryonic expression, inhibition of the scaffold function of ROR1 in patients with lung adenocarcinoma is an attractive approach for improved treatment of this devastating cancer.
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Guan X, Wang N, Cui F, Liu Y, Liu P, Zhao J, Han C, Li X, Leng Z, Li Y, Ji X, Zou W, Liu J. Caveolin-1 is essential in the differentiation of human adipose-derived stem cells into hepatocyte-like cells via an MAPK pathway-dependent mechanism. Mol Med Rep 2015; 13:1487-94. [PMID: 26717806 PMCID: PMC4732856 DOI: 10.3892/mmr.2015.4743] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 09/25/2015] [Indexed: 12/20/2022] Open
Abstract
Human adipose-derived stem cells (hADSCs), widely present in the adult human body, are an emerging and attractive tool for the establishment of stem cell-based therapies for the treatment of liver disease. However, the mechanism underlying hADSCs hepatic differentiation remains to be elucidated. Caveolin-1 (Cav-1), a 21–24 kDa membrane structural protein, is important in liver regeneration and development. In the present study, fluorescence immuno-cytochemistry and western blotting were used to analyze the expression levels of Cav-1 and evaluate its effects on the hepatic differentiation of hADSCs. The results revealed that primary hADSCs preserved the ability to proliferate and differentiate into hepatocyte-like cells. As demonstrated by semiquantitative reverse transcription-polymerase chain reaction, hepatocyte-inducing factors significantly increased the expression of Cav-1 in a time-dependent manner, as indicated by increased expression levels of the albumin (ALB) and α-fetoprotein (AFP) markers. In addition the expression levels of ALB and HNF1A significantly decreased following small interfering RNA-mediated knockdown of Cav-1. The mitogen-activated protein kinase (MAPK) signaling pathway was activated during hepatic differentiation and inhibited following Cav-1 knockdown. These results suggested that Cav-1 may regulate the hepatocyte-like differentiation of hADSCs by modulating mitogen-activated protein kinase kinase/MAPK signaling. The results of the present study will provide experimental and theoretical basis for further clinical studies on stem cell transplantation in the treatment of liver disease.
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Affiliation(s)
- Xin Guan
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Nan Wang
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Fenggong Cui
- Liaoning Key Laboratories of Biotechnology and Molecular Drug Research and Development, College of Life Science, Liaoning Normal University, Dalian, Liaoning 116029, P.R. China
| | - Yang Liu
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Peng Liu
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Jingyuan Zhao
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Chao Han
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Xiaoyan Li
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Zhiqian Leng
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Ying Li
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Xiaofei Ji
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
| | - Wei Zou
- Liaoning Key Laboratories of Biotechnology and Molecular Drug Research and Development, College of Life Science, Liaoning Normal University, Dalian, Liaoning 116029, P.R. China
| | - Jing Liu
- Regenerative Medicine Centre, The First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning 116011, P.R. China
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Khan SA, Wollaston-Hayden EE, Markowski TW, Higgins L, Mashek DG. Quantitative analysis of the murine lipid droplet-associated proteome during diet-induced hepatic steatosis. J Lipid Res 2015; 56:2260-72. [PMID: 26416795 DOI: 10.1194/jlr.m056812] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Indexed: 01/17/2023] Open
Abstract
Hepatic steatosis is characterized by the accumulation of lipid droplets (LDs), which are composed of a neutral lipid core surrounded by a phospholipid monolayer embedded with many proteins. Although the LD-associated proteome has been investigated in multiple tissues and organisms, the dynamic changes in the murine LD-associated proteome in response to obesity and hepatic steatosis have not been studied. We characterized the hepatic LD-associated proteome of C57BL/6J male mouse livers following high-fat feeding using isobaric tagging for relative and absolute quantification. Of the 1,520 proteins identified with a 5% local false discovery rate, we report a total of 48 proteins that were increased and 52 proteins that were decreased on LDs in response to high-fat feeding. Most notably, ribosomal and endoplasmic reticulum proteins were increased and extracellular and cytosolic proteins were decreased in response to high-fat feeding. Additionally, many proteins involved in fatty acid catabolism or xenobiotic metabolism were enriched in the LD fraction following high-fat feeding. In contrast, proteins involved in glucose metabolism and liver X receptor or retinoid X receptor activation were decreased on LDs of high-fat-fed mice. This study provides insights into unique biological functions of hepatic LDs under normal and steatotic conditions.
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Affiliation(s)
- Salmaan Ahmed Khan
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108
| | | | - Todd W Markowski
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - LeeAnn Higgins
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Douglas G Mashek
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108
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Aranda JF, Canfrán-Duque A, Goedeke L, Suárez Y, Fernández-Hernando C. The miR-199-dynamin regulatory axis controls receptor-mediated endocytosis. J Cell Sci 2015; 128:3197-209. [PMID: 26163491 DOI: 10.1242/jcs.165233] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 07/02/2015] [Indexed: 12/19/2022] Open
Abstract
Small non-coding RNAs (microRNAs) are important regulators of gene expression that modulate many physiological processes; however, their role in regulating intracellular transport remains largely unknown. Intriguingly, we found that the dynamin (DNM) genes, a GTPase family of proteins responsible for endocytosis in eukaryotic cells, encode the conserved miR-199a and miR-199b family of miRNAs within their intronic sequences. Here, we demonstrate that miR-199a and miR-199b regulate endocytic transport by controlling the expression of important mediators of endocytosis such as clathrin heavy chain (CLTC), Rab5A, low-density lipoprotein receptor (LDLR) and caveolin-1 (Cav-1). Importantly, miR-199a-5p and miR-199b-5p overexpression markedly inhibits CLTC, Rab5A, LDLR and Cav-1 expression, thus preventing receptor-mediated endocytosis in human cell lines (Huh7 and HeLa). Of note, miR-199a-5p inhibition increases target gene expression and receptor-mediated endocytosis. Taken together, our work identifies a new mechanism by which microRNAs regulate intracellular trafficking. In particular, we demonstrate that the DNM, miR-199a-5p and miR-199b-5p genes act as a bifunctional locus that regulates endocytosis, thus adding an unexpected layer of complexity in the regulation of intracellular trafficking.
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Affiliation(s)
- Juan F Aranda
- Integrative Cell Signaling and Neurobiology of Metabolism Program, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT 06510, USA Vascular Biology and Therapeutics Program, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Alberto Canfrán-Duque
- Integrative Cell Signaling and Neurobiology of Metabolism Program, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT 06510, USA Vascular Biology and Therapeutics Program, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Leigh Goedeke
- Integrative Cell Signaling and Neurobiology of Metabolism Program, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT 06510, USA Vascular Biology and Therapeutics Program, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Yajaira Suárez
- Integrative Cell Signaling and Neurobiology of Metabolism Program, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT 06510, USA Vascular Biology and Therapeutics Program, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Carlos Fernández-Hernando
- Integrative Cell Signaling and Neurobiology of Metabolism Program, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT 06510, USA Vascular Biology and Therapeutics Program, Yale University School of Medicine, New Haven, CT 06510, USA
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57
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Ding L, Yang Y, Qu Y, Yang T, Wang K, Liu W, Xia W. Bile acid promotes liver regeneration via farnesoid X receptor signaling pathways in rats. Mol Med Rep 2015; 11:4431-7. [PMID: 25634785 DOI: 10.3892/mmr.2015.3270] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 10/29/2014] [Indexed: 11/05/2022] Open
Abstract
Bile acids, which are synthesized from cholesterol in the hepatocytes of the liver, are amphipathic molecules with a steroid backbone. Studies have shown that bile acid exhibits important effects on liver regeneration. However, the mechanism underlying these effects remains unclear. The aim of the present study was to investigate the effect of bile acid and the farnesoid X receptor (FXR) on hepatic regeneration and lipid metabolism. Rats were fed with 0.2% bile acid or glucose for 7 days and then subjected to a 50 or 70% hepatectomy. Hepatic regeneration rate, serum and liver levels of bile acid, and expression of FXR and Caveolin‑1, were detected at 24, 48 or 72 h following hepatectomy. The expression of proliferating cell nuclear antigen (PCNA) in the liver was measured using immunohistochemistry at the end of the study. Hepatocytes isolated from rats were treated with bile acid, glucose, FXR agonist and FXR antagonist, separately or in combination. Lipid metabolism, the expression of members of the FXR signaling pathway and energy metabolism‑related factors were measured using ELISA kits or western blotting. Bile acid significantly increased the hepatic regeneration rate and the expression of FXR, Caveolin‑1 and PCNA. Levels of total cholesterol and high density lipoprotein were increased in bile acid‑ or FXR agonist‑treated hepatocytes in vitro. Levels of triglyceride, low density lipoprotein and free fatty acid were decreased. In addition, bile acid and FXR agonists increased the expression of bile salt export pump and small heterodimer partner, and downregulated the expression of apical sodium‑dependent bile acid transporter, Na+/taurocholate cotransporting polypeptide and cholesterol 7α‑hydroxylase. These results suggested that physiological concentrations of bile acid may promote liver regeneration via FXR signaling pathways, and may be associated with energy metabolism.
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Affiliation(s)
- Long Ding
- The Second Department of General Surgery, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
| | - Yu Yang
- Department of Topographical Anatomy, College of Basic Medical Sciences, Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
| | - Yikun Qu
- The Second Department of General Surgery, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
| | - Ting Yang
- Department of Vascular Surgery, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
| | - Kaifeng Wang
- Department of Vascular Surgery, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
| | - Weixin Liu
- The Second Department of General Surgery, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
| | - Weibin Xia
- The Second Department of General Surgery, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154003, P.R. China
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58
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Li B, Zhang Z, Zhang H, Quan K, Lu Y, Cai D, Ning G. Aberrant miR199a-5p/caveolin1/PPARα axis in hepatic steatosis. J Mol Endocrinol 2014; 53:393-403. [PMID: 25312970 DOI: 10.1530/jme-14-0127] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The prevalence of non-alcoholic fatty liver disease (NAFLD), a condition characterized by an excessive accumulation of triglycerides (TGs) in hepatocytes, has dramatically increased globally during recent decades. MicroRNAs (miRs) have been suggested to play crucial roles in many complex diseases and lipid metabolism. Our results indicated that miR199a-5p was remarkably upregulated in free fatty acid (FA)-treated hepatocytes. To investigate the role of miR199a-5p in the pathogenesis of fatty liver and the potential mechanism by which miR199a-5p regulates NAFLD, we first transfected two hepatocyte cell lines, HepG2 and AML12 cells, with agomiR199a-5p or antagomiR199a-5p. Our results indicated that miR199a-5p overexpression exacerbated deposition of FA and inhibited ATP levels and mitochondrial DNA (mtDNA) contents. Consistently, suppression of miR199a-5p partially alleviated deposition of FA and increased ATP levels and mtDNA contents. Moreover, miR199a-5p suppressed the expression of mitochondrial FA β-oxidation-related genes through inhibition of caveolin1 (CAV1) and the related peroxisome proliferator-activated receptor alpha (PPARα) pathway. Furthermore, suppression of CAV1 gene expression by CAV1 siRNA inhibited the PPARα signalling pathway. Finally, we examined the expression of miR199a-5p in liver samples derived from mice fed a high-fat diet, db/db mice, ob/ob mice and NAFLD patients, and found that miR199a-5p was upregulated while CAV1 and PPARA were downregulated in these systems, which was strongly indicative of the essential role of miR199a-5p in NAFLD. In summary, miR199a-5p plays a vital role in lipid metabolism, mitochondrial activity and mitochondrial β-oxidation in liver. Upregulated miR199a-5p in hepatocytes may contribute to impaired FA β-oxidation in mitochondria and aberrant lipid deposits, probably via CAV1 and the PPARα pathway.
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Affiliation(s)
- Bo Li
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Zhiguo Zhang
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Huizhi Zhang
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Kai Quan
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Yan Lu
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Dongsheng Cai
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Guang Ning
- Shanghai Institute of Endocrine and Metabolic DiseasesShanghai Clinical Center for Endocrine and Metabolic Diseases, RuiJin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Ruijin 2nd Road, Shanghai 200025, ChinaDepartment of NeurosurgeryHuashan Hospital of Fudan University, Shanghai 200040, ChinaDepartment of Molecular PharmacologyAlbert Einstein College of Medicine, Bronx, New York 10461, USA
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59
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Méndez-Giménez L, Rodríguez A, Balaguer I, Frühbeck G. Role of aquaglyceroporins and caveolins in energy and metabolic homeostasis. Mol Cell Endocrinol 2014; 397:78-92. [PMID: 25008241 DOI: 10.1016/j.mce.2014.06.017] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 06/25/2014] [Accepted: 06/26/2014] [Indexed: 12/23/2022]
Abstract
Aquaglyceroporins and caveolins are submicroscopic integral membrane proteins that are particularly abundant in many mammalian cells. Aquaglyceroporins (AQP3, AQP7, AQP9 and AQP10) encompass a subfamily of aquaporins that allow the movement of water, but also of small solutes, such as glycerol, across cell membranes. Glycerol constitutes an important metabolite as a substrate for de novo synthesis of triacylglycerols and glucose as well as an energy substrate to produce ATP via the mitochondrial oxidative phosphorylation. In this sense, the control of glycerol influx/efflux in metabolic organs by aquaglyceroporins plays a crucial role with the dysregulation of these glycerol channels being associated with metabolic diseases, such as obesity, insulin resistance, non-alcoholic fatty liver disease and cardiac hypertrophy. On the other hand, caveolae have emerged as relevant plasma membrane sensors implicated in a wide range of cellular functions, including endocytosis, apoptosis, cholesterol homeostasis, proliferation and signal transduction. Caveolae-coating proteins, namely caveolins and cavins, can act as scaffolding proteins within caveolae by concentrating signaling molecules involved in free fatty acid and cholesterol uptake, proliferation, insulin signaling or vasorelaxation, among others. The importance of caveolae in whole-body homeostasis is highlighted by the link between homozygous mutations in genes encoding caveolins and cavins with metabolic diseases, such as lipodystrophy, dyslipidemia, muscular dystrophy and insulin resistance in rodents and humans. The present review focuses on the role of aquaglyceroporins and caveolins on lipid and glucose metabolism, insulin secretion and signaling, energy production and cardiovascular homeostasis, outlining their potential relevance in the development and treatment of metabolic diseases.
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Affiliation(s)
- Leire Méndez-Giménez
- Metabolic Research Laboratory, Clínica Universidad de Navarra, Pamplona, Spain; CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Pamplona, Spain
| | - Amaia Rodríguez
- Metabolic Research Laboratory, Clínica Universidad de Navarra, Pamplona, Spain; CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Pamplona, Spain.
| | - Inmaculada Balaguer
- Metabolic Research Laboratory, Clínica Universidad de Navarra, Pamplona, Spain
| | - Gema Frühbeck
- Metabolic Research Laboratory, Clínica Universidad de Navarra, Pamplona, Spain; CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, Pamplona, Spain; Department of Endocrinology and Nutrition, Clínica Universidad de Navarra, Pamplona, Spain.
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60
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Caveolin-1 is required for TGF-β-induced transactivation of the EGF receptor pathway in hepatocytes through the activation of the metalloprotease TACE/ADAM17. Cell Death Dis 2014; 5:e1326. [PMID: 25032849 PMCID: PMC4123087 DOI: 10.1038/cddis.2014.294] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Revised: 05/14/2014] [Accepted: 06/05/2014] [Indexed: 12/28/2022]
Abstract
Transforming growth factor-beta (TGF-β) plays a dual role in hepatocytes, inducing both pro- and anti-apoptotic responses, whose balance decides cell fate. Survival signals are mediated by the epidermal growth factor receptor (EGFR) pathway, which is activated by TGF-β in these cells. Caveolin-1 (Cav1) is a structural protein of caveolae linked to TGF-β receptors trafficking and signaling. Previous results have indicated that in hepatocytes, Cav1 is required for TGF-β-induced anti-apoptotic signals, but the molecular mechanism is not fully understood yet. In this work, we show that immortalized Cav1(-/-) hepatocytes were more sensitive to the pro-apoptotic effects induced by TGF-β, showing a higher activation of caspase-3, higher decrease in cell viability and prolonged increase through time of intracellular reactive oxygen species (ROS). These results were coincident with attenuation of TGF-β-induced survival signals in Cav1(-/-) hepatocytes, such as AKT and ERK1/2 phosphorylation and NFκ-B activation. Transactivation of the EGFR pathway by TGF-β was impaired in Cav1(-/-) hepatocytes, which correlated with lack of activation of TACE/ADAM17, the metalloprotease responsible for the shedding of EGFR ligands. Reconstitution of Cav1 in Cav1(-/-) hepatocytes rescued wild-type phenotype features, both in terms of EGFR transactivation and TACE/ADAM17 activation. TACE/ADAM17 was localized in detergent-resistant membrane (DRM) fractions in Cav1(+/+) cells, which was not the case in Cav1(-/-) cells. Disorganization of lipid rafts after treatment with cholesterol-binding agents caused loss of TACE/ADAM17 activation after TGF-β treatment. In conclusion, in hepatocytes, Cav1 is required for TGF-β-mediated activation of the metalloprotease TACE/ADAM17 that is responsible for shedding of EGFR ligands and activation of the EGFR pathway, which counteracts the TGF-β pro-apoptotic effects. Therefore, Cav1 contributes to the pro-tumorigenic effects of TGF-β in liver cancer cells.
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61
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Mundy DI, Lopez AM, Posey KS, Chuang JC, Ramirez CM, Scherer PE, Turley SD. Impact of the loss of caveolin-1 on lung mass and cholesterol metabolism in mice with and without the lysosomal cholesterol transporter, Niemann-Pick type C1. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1841:995-1002. [PMID: 24747682 DOI: 10.1016/j.bbalip.2014.04.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Revised: 04/08/2014] [Accepted: 04/11/2014] [Indexed: 11/17/2022]
Abstract
Caveolin-1 (Cav-1) is a major structural protein in caveolae in the plasma membranes of many cell types, particularly endothelial cells and adipocytes. Loss of Cav-1 function has been implicated in multiple diseases affecting the cardiopulmonary and central nervous systems, as well as in specific aspects of sterol and lipid metabolism in the liver and intestine. Lungs contain an exceptionally high level of Cav-1. Parameters of cholesterol metabolism in the lung were measured, initially in Cav-1-deficient mice (Cav-1(-/-)), and subsequently in Cav-1(-/-) mice that also lacked the lysosomal cholesterol transporter Niemann-Pick C1 (Npc1) (Cav-1(-/-):Npc1(-/-)). In 50-day-old Cav-1(-/-) mice fed a low- or high-cholesterol chow diet, the total cholesterol concentration (mg/g) in the lungs was marginally lower than in the Cav-1(+/+) controls, but due to an expansion in their lung mass exceeding 30%, whole-lung cholesterol content (mg/organ) was moderately elevated. Lung mass (g) in the Cav-1(-/-):Npc1(-/-) mice (0.356±0.022) markedly exceeded that in their Cav-1(+/+):Npc1(+/+) controls (0.137±0.009), as well as in their Cav-1(-/-):Npc1(+/+) (0.191±0.013) and Cav-1(+/+):Npc1(-/-) (0.213±0.022) littermates. The corresponding lung total cholesterol contents (mg/organ) in mice of these genotypes were 6.74±0.17, 0.71±0.05, 0.96±0.05 and 3.12±0.43, respectively, with the extra cholesterol in the Cav-1(-/-):Npc1(-/-) and Cav-1(+/+):Npc1(-/-) mice being nearly all unesterified (UC). The exacerbation of the Npc1 lung phenotype and increase in the UC level in the Cav-1(-/-):Npc1(-/-) mice imply a regulatory role of Cav-1 in pulmonary cholesterol metabolism when lysosomal sterol transport is disrupted.
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Affiliation(s)
- Dorothy I Mundy
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
| | - Adam M Lopez
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
| | - Kenneth S Posey
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
| | - Jen-Chieh Chuang
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
| | - Charina M Ramirez
- Department of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
| | - Philipp E Scherer
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
| | - Stephen D Turley
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA.
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Kassan A, Herms A, Fernández-Vidal A, Bosch M, Schieber NL, Reddy BJN, Fajardo A, Gelabert-Baldrich M, Tebar F, Enrich C, Gross SP, Parton RG, Pol A. Acyl-CoA synthetase 3 promotes lipid droplet biogenesis in ER microdomains. ACTA ACUST UNITED AC 2014; 203:985-1001. [PMID: 24368806 PMCID: PMC3871434 DOI: 10.1083/jcb.201305142] [Citation(s) in RCA: 218] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Acyl-CoA synthetase 3 is recruited early to lipid droplet assembly sites on the ER, where it is required for efficient lipid droplet nucleation and lipid storage. Control of lipid droplet (LD) nucleation and copy number are critical, yet poorly understood, processes. We use model peptides that shift from the endoplasmic reticulum (ER) to LDs in response to fatty acids to characterize the initial steps of LD formation occurring in lipid-starved cells. Initially, arriving lipids are rapidly packed in LDs that are resistant to starvation (pre-LDs). Pre-LDs are restricted ER microdomains with a stable core of neutral lipids. Subsequently, a first round of “emerging” LDs is nucleated, providing additional lipid storage capacity. Finally, in proportion to lipid concentration, new rounds of LDs progressively assemble. Confocal microscopy and electron tomography suggest that emerging LDs are nucleated in a limited number of ER microdomains after a synchronized stepwise process of protein gathering, lipid packaging, and recognition by Plin3 and Plin2. A comparative analysis demonstrates that the acyl-CoA synthetase 3 is recruited early to the assembly sites, where it is required for efficient LD nucleation and lipid storage.
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Affiliation(s)
- Adam Kassan
- Equip de Senyalització i Proliferació Cellular, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain
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63
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Sahini N, Borlak J. Recent insights into the molecular pathophysiology of lipid droplet formation in hepatocytes. Prog Lipid Res 2014; 54:86-112. [PMID: 24607340 DOI: 10.1016/j.plipres.2014.02.002] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Revised: 02/17/2014] [Accepted: 02/21/2014] [Indexed: 12/11/2022]
Abstract
Triacyglycerols are a major energy reserve of the body and are normally stored in adipose tissue as lipid droplets (LDs). The liver, however, stores energy as glycogen and digested triglycerides in the form of fatty acids. In stressed condition such as obesity, imbalanced nutrition and drug induced liver injury hepatocytes accumulate excess lipids in the form of LDs whose prolonged storage leads to disease conditions most notably non-alcoholic fatty liver disease (NAFLD). Fatty liver disease has become a major health burden with more than 90% of obese, nearly 70% of overweight and about 25% of normal weight patients being affected. Notably, research in recent years has shown LD as highly dynamic organelles for maintaining lipid homeostasis through fat storage, protein sorting and other molecular events studied in adipocytes and other cells of living organisms. This review focuses on the molecular events of LD formation in hepatocytes and the importance of cross talk between different cell types and their signalling in NAFLD as to provide a perspective on molecular mechanisms as well as possibilities for different therapeutic intervention strategies.
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Affiliation(s)
- Nishika Sahini
- Centre for Pharmacology and Toxicology, Hannover Medical School, 30625 Hannover, Germany
| | - Jürgen Borlak
- Centre for Pharmacology and Toxicology, Hannover Medical School, 30625 Hannover, Germany.
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64
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Ghiraldini FG, Silveira AB, Kleinjan DA, Gilbert N, Mello MLS. Genomic profiling of type-1 adult diabetic and aged normoglycemic mouse liver. BMC Endocr Disord 2014; 14:19. [PMID: 24581510 PMCID: PMC4016577 DOI: 10.1186/1472-6823-14-19] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Accepted: 02/25/2014] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Hyperglycemia induces chromatin remodeling with consequences on differential gene expression in mouse hepatocytes, similar to what occurs during aging. The liver is the central organ for the regulation of glucose homeostasis and xenobiotic and lipid metabolism and is affected by insulin signaling. The precise transcriptional profiling of the type-1 diabetic liver and its comparison to aging have not been elucidated yet. METHODS Here, we studied the differential genomic expression of mouse liver cells under adult hyperglycemic and aged normoglycemic conditions using expression arrays. RESULTS Differential gene expression involved in an increase in glucose and impaired lipid metabolism were detected in the type-1 diabetic liver. In this regard, Ppargc1a presents an increased expression and is a key gene that might be regulating both processes. The differential gene expression observed may also be associated with hepatic steatosis in diabetic mouse liver, as a secondary disease. Similarly, middle-aged mice presented differential expression of genes involved in glucose, lipid and xenobiotic metabolism. These genes could be associated with an increase in polyploidy, but the consequences of differential expression were not as drastic as those observed in diabetic animals. CONCLUSIONS Taken together, these findings provide new insights into gene expression profile changes in type-1 diabetic liver. Ppargc1a was found to be the key-gene that increases glucose metabolism and impairs lipid metabolism impairment. The novel results reported here open new areas of investigation in diabetic research and facilitate the development of new strategies for gene therapy.
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Affiliation(s)
- Flávia G Ghiraldini
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas (Unicamp), 13083-862 Campinas, SP, Brazil
| | - André B Silveira
- Laboratory of Molecular Biology, Centro Infantil Boldrini, Campinas, SP, Brazil
| | - Dirk A Kleinjan
- Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, UK
| | - Nick Gilbert
- Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, UK
| | - Maria Luiza S Mello
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas (Unicamp), 13083-862 Campinas, SP, Brazil
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65
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Madaro L, Antonangeli F, Favia A, Esposito B, Biamonte F, Bouché M, Ziparo E, Sica G, Filippini A, D'Alessio A. Knock down of caveolin-1 affects morphological and functional hallmarks of human endothelial cells. J Cell Biochem 2013; 114:1843-51. [PMID: 23463606 DOI: 10.1002/jcb.24526] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Accepted: 02/21/2013] [Indexed: 12/20/2022]
Abstract
Caveolin-1 (CAV1) is the principal structural component of caveolae which functions as scaffolding protein for the integration of a variety of signaling pathways. In this study, we investigated the involvement of CAV1 in endothelial cell (EC) functions and show that siRNA-induced CAV1 silencing in the human EC line EA.hy926 induces distinctive morphological changes, such as a marked increase in cell size and formation of stress fibers. Design-based stereology was employed in this work to make unbiased quantification of morphometric properties such as volume, length, and surface of CAV1 silenced versus control cells. In addition, we showed that downregulation of CAV1 affects cell cycle progression at G1/S phase transition most likely by perturbation of AKT signaling. With the aim to assess the contribution of CAV1 to typical biological processes of EC, we report here that CAV1 targeting affects cell migration and matrix metalloproteinases (MMPs) activity, and reduces angiogenesis in response to VEGF, in vitro. Taken together our data suggest that the proper expression of CAV1 is important not only for maintaining the appropriate morphology and size of ECs but it might represent a prospective molecular target for studying key biological mechanisms such as senescence and tumorigenesis.
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Affiliation(s)
- Luca Madaro
- Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy
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66
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Mitochondrial dysfunction induces formation of lipid droplets as a generalized response to stress. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013; 2013:327167. [PMID: 24175011 PMCID: PMC3794647 DOI: 10.1155/2013/327167] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 08/20/2013] [Indexed: 01/05/2023]
Abstract
Lipid droplet (LD) formation is a hallmark of cellular stress. Cells attempt to combat noxious stimuli by switching their metabolism from oxidative phosphorylation to glycolysis, sparing resources in LDs for generating cellular reducing power and for anabolic biosynthesis. Membrane phospholipids are also a source of LDs. To elucidate the formation of LDs, we exposed mice to hyperoxia, hypoxia, myocardial ischemia, and sepsis induced by cecal ligation and puncture (CLP). All the above-mentioned stressors enhanced the formation of LDs, as assessed by transmission electron microscopy, with severe mitochondrial swelling. Disruption of mitochondria by depleting mitochondrial DNA ( ρ 0 cells) significantly augmented the formation of LDs, causing transcriptional activation of fatty acid biosynthesis and metabolic reprogramming to glycolysis. Heme oxygenase (HO)-1 counteracts CLP-mediated septic shock in mouse models. In HO-1-deficient mice, LD formation was not observed upon CLP, but a concomitant decrease in "LD-decorating proteins" was observed, implying a link between LDs and cytoprotective activity. Collectively, LD biogenesis during stress can trigger adaptive LD formation, which is dependent on mitochondrial integrity and HO-1 activity; this may be a cellular survival strategy, apportioning energy-generating substrates to cellular defense.
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67
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Obayashi Y, Campbell JS, Fausto N, Yeung RS. Impaired lipid accumulation in the liver of Tsc2-heterozygous mice during liver regeneration. Biochem Biophys Res Commun 2013; 437:146-50. [DOI: 10.1016/j.bbrc.2013.06.056] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Accepted: 06/14/2013] [Indexed: 01/20/2023]
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68
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Caveolin-1 Is Necessary for Hepatic Oxidative Lipid Metabolism: Evidence for Crosstalk between Caveolin-1 and Bile Acid Signaling. Cell Rep 2013; 4:238-47. [DOI: 10.1016/j.celrep.2013.06.017] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2012] [Revised: 03/04/2013] [Accepted: 06/14/2013] [Indexed: 12/14/2022] Open
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69
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Yao Z, Zhou H, Figeys D, Wang Y, Sundaram M. Microsome-associated lumenal lipid droplets in the regulation of lipoprotein secretion. Curr Opin Lipidol 2013; 24:160-70. [PMID: 23123764 DOI: 10.1097/mol.0b013e32835aebe7] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
PURPOSE OF REVIEW Liver is the major organ in mammals that possesses the capacity to release triglyceride within VLDL. VLDL assembly requires apolipoprotein (apo) B-100 with the assistance of microsomal triglyceride transfer protein (MTP), which facilitates the mobilization of triglyceride into the microsomal lumen. Recent experimental evidence has suggested that the lumenal triglyceride associated with endoplasmic reticulum (ER)/Golgi may represent an entity serving as precursors for large VLDL1. RECENT FINDINGS Under lipid-rich conditions, discrete triglyceride-rich lipidic bodies, termed lumenal lipid droplets, are accumulated in association with ER/Golgi microsomes. Formation of the microsome-associated lumenal lipid droplets (MALD) is dependent on the activity of MTP, and the resulting apoB-free lipidic body is associated with a variety of proteins including apolipoproteins that are components of VLDL. Formation and utilization of MALD during the assembly and secretion of VLDL1 have a profound influence on hepatic cell physiology, such as ER stress responses. SUMMARY This review summarizes current understanding of hepatic triglyceride homeostasis in general, and highlights the functional significance of triglyceride compartmentalization between cytosol and microsomes in particular. Understanding of MALD metabolism may shed new light on the prevention and treatment of liver diseases associated with abnormally elevated intracellular triglycerides.
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Affiliation(s)
- Zemin Yao
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Ontario, Canada.
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70
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Parton RG, del Pozo MA. Caveolae as plasma membrane sensors, protectors and organizers. Nat Rev Mol Cell Biol 2013; 14:98-112. [PMID: 23340574 DOI: 10.1038/nrm3512] [Citation(s) in RCA: 648] [Impact Index Per Article: 58.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Caveolae are submicroscopic, plasma membrane pits that are abundant in many mammalian cell types. The past few years have seen a quantum leap in our understanding of the formation, dynamics and functions of these enigmatic structures. Caveolae have now emerged as vital plasma membrane sensors that can respond to plasma membrane stresses and remodel the extracellular environment. Caveolae at the plasma membrane can be removed by endocytosis to regulate their surface density or can be disassembled and their structural components degraded. Coat proteins, called cavins, work together with caveolins to regulate the formation of caveolae but also have the potential to dynamically transmit signals that originate in caveolae to various cellular destinations. The importance of caveolae as protective elements in the plasma membrane, and as membrane organizers and sensors, is highlighted by links between caveolae dysfunction and human diseases, including muscular dystrophies and cancer.
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Affiliation(s)
- Robert G Parton
- Institute for Molecular Bioscience and Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, QLD 4072, Australia.
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71
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Current world literature. Curr Opin Organ Transplant 2013; 18:241-50. [PMID: 23486386 DOI: 10.1097/mot.0b013e32835f5709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
Genetically modified mouse models have unparalleled power to determine the mechanisms behind different processes involved in the molecular and physiologic etiology of various classes of human pulmonary hypertension (PH). Processes known to be involved in PH for which there are extensive mouse models available include the following: (1) Regulation of vascular tone through secreted vasoactive factors; (2) regulation of vascular tone through potassium and calcium channels; (3) regulation of vascular remodeling through alteration in metabolic processes, either through alteration in substrate usage or through circulating factors; (4) spontaneous vascular remodeling either before or after development of elevated pulmonary pressures; and (5) models in which changes in tone and remodeling are primarily driven by inflammation. PH development in mice is of necessity faster and with different physiologic ramifications than found in human disease, and so mice make poor models of natural history of PH. However, transgenic mouse models are a perfect tool for studying the processes involved in pulmonary vascular function and disease, and can effectively be used to test interventions designed against particular molecular pathways and processes involved in disease.
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Affiliation(s)
- Mita Das
- Department of Internal Medicine, University of Arkansas Medical Sciences, Little Rock, Arkansas, USA
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Meyer C, Liu Y, Kaul A, Peipe I, Dooley S. Caveolin-1 abrogates TGF-β mediated hepatocyte apoptosis. Cell Death Dis 2013; 4:e466. [PMID: 23328673 PMCID: PMC3563992 DOI: 10.1038/cddis.2012.204] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Transforming growth factor (TGF)-β has a dual role in liver, providing cytostatic effects during liver damage and regeneration, as well as carcinogenic functions in malignant transformation and hepatocellular cancer. In cultured hepatocytes, TGF-β can trigger apoptosis and epithelial-mesenchymal transition (EMT). Caveolin-1 is associated with progression of hepatocellular cancer and has been linked to TGF-β signaling. This study aimed at elucidating whether Caveolin-1 regulates TGF-β mediated hepatocyte fate. Knockdown of Caveolin-1 strongly reduced TGF-β mediated AKT phosphorylation, thus sensitized primary murine hepatocytes for proapoptotic TGF-β signaling. Restoration of AKT activity in Caveolin-1 knockdown cells via expression of a constitutive active AKT mutant did not completely blunt the apoptotic response to TGF-β, indicating an additional mechanism how Caveolin-1 primes hepatocytes for resistance to TGF-β triggered apoptosis. On the molecular level, Caveolin-1 interfered with TGF-β initiated expression of the proapoptotic mediator BIM. Additionally, RNAi for Caveolin-1 reduced (and its overexpression increased) expression of antiapoptotic mediators BCL-2 and BCL-xl. Noteworthy, reduced Caveolin-1 protein levels had no effect on collagen 1α1, E- and N-cadherin expression upon TGF-β challenge and thus no effect on hepatocyte EMT. Hence, via affecting TGF-β mediated non-Smad AKT signaling and regulation of pro- and antiapoptotic factors, Caveolin-1 is a crucial hepatocyte fate determinant for TGF-β effects.
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Affiliation(s)
- C Meyer
- Department of Medicine II, Section Molecular Hepatology, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
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Al-Daghri NM, Cagliani R, Forni D, Alokail MS, Pozzoli U, Alkharfy KM, Sabico S, Clerici M, Sironi M. Mammalian NPC1 genes may undergo positive selection and human polymorphisms associate with type 2 diabetes. BMC Med 2012; 10:140. [PMID: 23153210 PMCID: PMC3520752 DOI: 10.1186/1741-7015-10-140] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Accepted: 11/15/2012] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND The NPC1 gene encodes a protein involved in intracellular lipid trafficking; its second endosomal loop (loop 2) is a receptor for filoviruses. A polymorphism (His215Arg) in NPC1 was associated with obesity in Europeans. Adaptations to diet and pathogens represented powerful selective forces; thus, we analyzed the evolutionary history of the gene and exploited this information for the identification of variants/residues of functional importance in human disease. METHODS We performed phylogenetic analysis, population genetic tests, and genotype-phenotype analysis in a population from Saudi Arabia. RESULTS Maximum-likelihood ratio tests indicated the action of positive selection on loop 2 and identified three residues as selection targets; these were confirmed by an independent random effects likelihood (REL) analysis. No selection signature was detected in present-day human populations, but analysis of nonsynonymous polymorphisms showed that a variant (Ile642Met, rs1788799) in the sterol sensing domain affects a highly conserved position. This variant and the previously described His215Arg polymorphism were tested for association with obesity and type 2 diabetes (T2D) in a cohort from Saudi Arabia. Whereas no association with obesity was detected, 642Met allele was found to predispose to T2D. A significant interaction was noted with sex (P = 0.041), and stratification on the basis of gender indicated that the association is driven by men (P = 0.0021, OR = 1.5). Notably, two NPC1 haplotypes were also associated with T2D in men (rs1805081-rs1788799, His-Met: P = 0.0012, OR = 1.54; His-Ile: P = 0.0004, OR = 0.63). CONCLUSIONS Our data indicate a sex-specific effect of NPC1 variants on T2D risk and describe putative binding sites for filoviruses entry.
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Affiliation(s)
- Nasser M Al-Daghri
- Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, King Abdullah road, Riyadh 11451, Kingdom of Saudi Arabia.
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Caveolin-1 deficiency leads to increased susceptibility to cell death and fibrosis in white adipose tissue: characterization of a lipodystrophic model. PLoS One 2012. [PMID: 23049990 DOI: 10.1371/journal.pone0046242] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Caveolin-1 (CAV1) is an important regulator of adipose tissue homeostasis. In the present study we examined the impact of CAV1 deficiency on the properties of mouse adipose tissue both in vivo and in explant cultures during conditions of metabolic stress. In CAV1(-/-) mice fasting caused loss of adipose tissue mass despite a lack of hormone-sensitive lipase (HSL) phosphorylation. In addition, fasting resulted in increased macrophage infiltration, enhanced deposition of collagen, and a reduction in the level of the lipid droplet protein perilipin A (PLIN1a). Explant cultures of CAV1(-/-) adipose tissue also showed a loss of PLIN1a during culture, enhanced secretion of IL-6, increased release of lactate dehydrogenase, and demonstrated increased susceptibility to cell death upon collagenase treatment. Attenuated PKA-mediated signaling to HSL, loss of PLIN1a and increased secretion of IL-6 were also observed in adipose tissue explants of CAV1(+/+) mice with diet-induced obesity. Together these results suggest that while alterations in adipocyte lipid droplet biology support adipose tissue metabolism in the absence of PKA-mediated pro-lipolytic signaling in CAV1(-/-) mice, the tissue is intrinsically unstable resulting in increased susceptibility to cell death, which we suggest underlies the development of fibrosis and inflammation during periods of metabolic stress.
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Caveolin-1 deficiency leads to increased susceptibility to cell death and fibrosis in white adipose tissue: characterization of a lipodystrophic model. PLoS One 2012; 7:e46242. [PMID: 23049990 PMCID: PMC3458842 DOI: 10.1371/journal.pone.0046242] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Accepted: 08/28/2012] [Indexed: 12/31/2022] Open
Abstract
Caveolin-1 (CAV1) is an important regulator of adipose tissue homeostasis. In the present study we examined the impact of CAV1 deficiency on the properties of mouse adipose tissue both in vivo and in explant cultures during conditions of metabolic stress. In CAV1−/− mice fasting caused loss of adipose tissue mass despite a lack of hormone-sensitive lipase (HSL) phosphorylation. In addition, fasting resulted in increased macrophage infiltration, enhanced deposition of collagen, and a reduction in the level of the lipid droplet protein perilipin A (PLIN1a). Explant cultures of CAV1−/− adipose tissue also showed a loss of PLIN1a during culture, enhanced secretion of IL-6, increased release of lactate dehydrogenase, and demonstrated increased susceptibility to cell death upon collagenase treatment. Attenuated PKA-mediated signaling to HSL, loss of PLIN1a and increased secretion of IL-6 were also observed in adipose tissue explants of CAV1+/+ mice with diet-induced obesity. Together these results suggest that while alterations in adipocyte lipid droplet biology support adipose tissue metabolism in the absence of PKA-mediated pro-lipolytic signaling in CAV1−/− mice, the tissue is intrinsically unstable resulting in increased susceptibility to cell death, which we suggest underlies the development of fibrosis and inflammation during periods of metabolic stress.
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