Molecular Mechanisms of Lipotoxicity in Nonalcoholic Fatty Liver Disease

ABSTRACT

Nonalcoholic fatty liver disease (NAFLD) is characterized by insulin resistance, which results in elevated serum concentration of free fatty acids (FFAs). Circulating FFAs provide the substrate for triacylglycerol formation in the liver, and may also be directly cytotoxic. Hepatocyte apoptosis is a key histologic feature of NAFLD, and correlates with progressive inflammation and fibrosis. The molecular pathways leading to hepatocyte apoptosis are not fully defined; however, recent studies suggest that FFA-induced apoptosis contributes to the pathogenesis of nonalcoholic steatohepatitis. FFAs directly engage the core apoptotic machinery by activating the proapoptotic protein Bax, in a c-jun N-terminal kinase-dependent manner. FFAs also activate the lysosomal pathway of cell death and regulate death receptor gene expression. The role of ER stress and oxidative stress in the pathogenesis of nonalcoholic steatohepatitis has also been described. Understanding the molecular mediators of liver injury should promote development of mechanism-based therapeutic interventions.

Bim - c-jun N-terminal kinase - oleic acid - palmitic acid - hepatocyte injury

REFERENCES

• 1 Unger R H. Minireview: weapons of lean body mass destruction—the role of ectopic lipids in the metabolic syndrome.  Endocrinology. 2003;  144(12) 5159-5165
• 2 Hotamisligil G S. Inflammation and metabolic disorders.  Nature. 2006;  444(7121) 860-867
• 3 Gregor M F, Hotamisligil G S. Thematic review series: adipocyte biology. adipocyte stress: the endoplasmic reticulum and metabolic disease.  J Lipid Res. 2007;  48(9) 1905-1914
• 4 Jaworski K, Sarkadi-Nagy E, Duncan R E, Ahmadian M, Sul H S. Regulation of triglyceride metabolism: IV. Hormonal regulation of lipolysis in adipose tissue.  Am J Physiol Gastrointest Liver Physiol. 2007;  293(1) G1-G4
• 5 Baranova A, Gowder S J, Schlauch K et al.. Gene expression of leptin, resistin, and adiponectin in the white adipose tissue of obese patients with non-alcoholic fatty liver disease and insulin resistance.  Obes Surg. 2006;  16(9) 1118-1125
• 6 Chitturi S, Farrell G, Frost L et al.. Serum leptin in NASH correlates with hepatic steatosis but not fibrosis: a manifestation of lipotoxicity?.  Hepatology. 2002;  36(2) 403-409
• 7 Hotamisligil G S, Arner P, Caro J F, Atkinson R L, Spiegelman B M. Increased adipose tissue expression of tumor necrosis factor-alpha in human obesity and insulin resistance.  J Clin Invest. 1995;  95(5) 2409-2415
• 8 Adams L A, Sanderson S, Lindor K D, Angulo P. The histological course of nonalcoholic fatty liver disease: a longitudinal study of 103 patients with sequential liver biopsies.  J Hepatol. 2005;  42(1) 132-138
• 9 Kohjima M, Enjoji M, Higuchi N et al.. Re-evaluation of fatty acid metabolism-related gene expression in nonalcoholic fatty liver disease.  Int J Mol Med. 2007;  20 351-358
• 10 Sanyal A J, Campbell-Sargent C, Mirshahi F et al.. Nonalcoholic steatohepatitis: association of insulin resistance and mitochondrial abnormalities.  Gastroenterology. 2001;  120(5) 1183-1192
• 11 Bakan E, Yildirim A, Kurtul N et al.. Effects of type 2 diabetes mellitus on plasma fatty acid composition and cholesterol content of erythrocyte and leukocyte membranes.  Acta Diabetol. 2006;  43(4) 109-113
• 12 Puri P, Baillie R A, Wiest M M et al.. A lipidomic analysis of nonalcoholic fatty liver disease.  Hepatology. 2007;  46(4) 1081-1090
• 13 Mari M, Fernandez-Checa J C. Sphingolipid signalling and liver diseases.  Liver Int. 2007;  27(4) 440-450
• 14 Malhi H, Bronk S F, Werneburg N W, Gores G J. Free fatty acids induce JNK-dependent hepatocyte lipoapoptosis.  J Biol Chem. 2006;  281(17) 12093-12101
• 15 Donnelly K L, Smith C I, Schwarzenberg S J et al.. Sources of fatty acids stored in liver and secreted via lipoproteins in patients with nonalcoholic fatty liver disease.  J Clin Invest. 2005;  115(5) 1343-1351
• 16 Nehra V, Angulo P, Buchman A L, Lindor K D. Nutritional and metabolic considerations in the etiology of nonalcoholic steatohepatitis.  Dig Dis Sci. 2001;  46(11) 2347-2352
• 17 Bradbury M W. Lipid metabolism and liver inflammation: I. Hepatic fatty acid uptake—possible role in steatosis.  Am J Physiol Gastrointest Liver Physiol. 2006;  290(2) G194-G198
• 18 Pohl J, Ring A, Hermann T, Stremmel W. Role of FATP in parenchymal cell fatty acid uptake.  Biochim Biophys Acta. 2004;  1686(1–2) 1-6
• 19 Pohl J, Ring A, Korkmaz U, Ehehalt R, Stremmel W. FAT/CD36-mediated long-chain fatty acid uptake in adipocytes requires plasma membrane rafts.  Mol Biol Cell. 2005;  16(1) 24-31
• 20 Doege H, Baillie R A, Ortegon A M et al.. Targeted deletion of FATP5 reveals multiple functions in liver metabolism: alterations in hepatic lipid homeostasis.  Gastroenterology. 2006;  130(4) 1245-1258
• 21 Newberry E P, Xie Y, Kennedy S et al.. Decreased hepatic triglyceride accumulation and altered fatty acid uptake in mice with deletion of the liver fatty acid-binding protein gene.  J Biol Chem. 2003;  278(51) 51664-51672
• 22 de Almeida I T, Cortez-Pinto H, Fidalgo G, Rodrigues D, Camilo M E. Plasma total and free fatty acids composition in human non-alcoholic steatohepatitis.  Clin Nutr. 2002;  21(3) 219-223
• 23 Allard J P, Aghdassi E, Mohammed S et al.. Nutritional assessment and hepatic fatty acid composition in non-alcoholic fatty liver disease (NAFLD): a cross-sectional study.  J Hepatol. 2008;  48(2) 300-307
• 24 Wei Y, Wang D, Pagliassotti M J. Saturated fatty acid-mediated endoplasmic reticulum stress and apoptosis are augmented by trans-10, cis-12-conjugated linoleic acid in liver cells.  Mol Cell Biochem. 2007;  303(1–2) 105-113
• 25 Listenberger L L, Han X, Lewis S E et al.. Triglyceride accumulation protects against fatty acid-induced lipotoxicity.  Proc Natl Acad Sci U S A. 2003;  100(6) 3077-3082
• 26 Yamaguchi K, Yang L, McCall S et al.. Inhibiting triglyceride synthesis improves hepatic steatosis but exacerbates liver damage and fibrosis in obese mice with nonalcoholic steatohepatitis.  Hepatology. 2007;  45(6) 1366-1374
• 27 Feldstein A E, Canbay A, Angulo P et al.. Hepatocyte apoptosis and fas expression are prominent features of human nonalcoholic steatohepatitis.  Gastroenterology. 2003;  125(2) 437-443
• 28 Susca M, Grassi A, Zauli D et al.. Liver inflammatory cells, apoptosis, regeneration and stellate cell activation in non-alcoholic steatohepatitis.  Dig Liver Dis. 2001;  33(9) 768-777
• 29 Ribeiro P S, Cortez-Pinto H, Sola S et al.. Hepatocyte apoptosis, expression of death receptors, and activation of NF-kappaB in the liver of nonalcoholic and alcoholic steatohepatitis patients.  Am J Gastroenterol. 2004;  99(9) 1708-1717
• 30 Malhi H, Gores G J, Lemasters J J. Apoptosis and necrosis in the liver: a tale of two deaths?.  Hepatology. 2006;  43(suppl 1) S31-S44
• 31 Grassi A, Susca M, Ferri S et al.. Detection of the M30 neoepitope as a new tool to quantify liver apoptosis: timing and patterns of positivity on frozen and paraffin-embedded sections.  Am J Clin Pathol. 2004;  121(2) 211-219
• 32 Wieckowska A, Zein N N, Yerian L M et al.. In vivo assessment of liver cell apoptosis as a novel biomarker of disease severity in nonalcoholic fatty liver disease.  Hepatology. 2006;  44(1) 27-33
• 33 Green D R. Apoptotic pathways: ten minutes to dead.  Cell. 2005;  121(5) 671-674
• 34 Green D R, Kroemer G. The pathophysiology of mitochondrial cell death.  Science. 2004;  305(5684) 626-629
• 35 Wang D, Wei Y, Pagliassotti M J. Saturated fatty acids promote endoplasmic reticulum stress and liver injury in rats with hepatic steatosis.  Endocrinology. 2006;  147(2) 943-951
• 36 Shimabukuro M, Zhou Y T, Levi M, Unger R H. Fatty acid-induced beta cell apoptosis: a link between obesity and diabetes.  Proc Natl Acad Sci U S A. 1998;  95(5) 2498-2502
• 37 Karaskov E, Scott C, Zhang L et al.. Chronic palmitate but not oleate exposure induces endoplasmic reticulum stress, which may contribute to INS-1 pancreatic beta-cell apoptosis.  Endocrinology. 2006;  147(7) 3398-3407
• 38 Kong J Y, Rabkin S W. Palmitate-induced apoptosis in cardiomyocytes is mediated through alterations in mitochondria: prevention by cyclosporin A.  Biochim Biophys Acta. 2000;  1485(1) 45-55
• 39 Chai W, Liu Z. p38 mitogen-activated protein kinase mediates palmitate-induced apoptosis but not inhibitor of nuclear factor-kappaB degradation in human coronary artery endothelial cells.  Endocrinology. 2007;  148(4) 1622-1628
• 40 Miller T A, LeBrasseur N K, Cote G M et al.. Oleate prevents palmitate-induced cytotoxic stress in cardiac myocytes.  Biochem Biophys Res Commun. 2005;  336(1) 309-315
• 41 Epand R F, Martinou J C, Montessuit S, Epand R M. Fatty acids enhance membrane permeabilization by pro-apoptotic Bax.  Biochem J. 2004;  377(Pt 2) 509-516
• 42 Barreyro F J, Kobayashi S, Bronk S F et al.. Transcriptional regulation of Bim by FoxO3A mediates hepatocyte lipoapoptosis.  J Biol Chem. 2007;  282(37) 27141-27154
• 43 Zhu Y, Schwarz S, Ahlemeyer B et al.. Oleic acid causes apoptosis and dephosphorylates Bad.  Neurochem Int. 2005;  46(2) 127-135
• 44 Christen V, Treves S, Duong F H, Heim M H. Activation of endoplasmic reticulum stress response by hepatitis viruses up-regulates protein phosphatase 2A.  Hepatology. 2007;  46(2) 558-565
• 45 Feldstein A E, Werneburg N W, Li Z, Bronk S F, Gores G J. Bax inhibition protects against free fatty acid-induced lysosomal permeabilization.  Am J Physiol Gastrointest Liver Physiol. 2006;  290(6) G1339-G1346
• 46 Feldstein A E, Werneburg N W, Canbay A et al.. Free fatty acids promote hepatic lipotoxicity by stimulating TNF-alpha expression via a lysosomal pathway.  Hepatology. 2004;  40(1) 185-194
• 47 Guicciardi M E, Leist M, Gores G J. Lysosomes in cell death.  Oncogene. 2004;  23(16) 2881-2890
• 48 Ron D, Walter P. Signal integration in the endoplasmic reticulum unfolded protein response.  Nat Rev Mol Cell Biol. 2007;  8(7) 519-529
• 49 Ji C, Kaplowitz N. ER stress: can the liver cope?.  J Hepatol. 2006;  45(2) 321-333
• 50 Ozcan U, Cao Q, Yilmaz E et al.. Endoplasmic reticulum stress links obesity, insulin action, and type 2 diabetes.  Science. 2004;  306(5695) 457-461
• 51 Wei Y, Wang D, Topczewski F, Pagliassotti M J. Saturated fatty acids induce endoplasmic reticulum stress and apoptosis independently of ceramide in liver cells.  Am J Physiol Endocrinol Metab. 2006;  291(2) E275-E281
• 52 Puri P, Mirshahi F, Cheung O et al.. Activation and dysregulation of the unfolded protein response in nonalcoholic fatty liver disease.  Gastroenterology. 2008;  134 568-576
• 53 Johnson G L, Nakamura K. The c-jun kinase/stress-activated pathway: regulation, function and role in human disease.  Biochim Biophys Acta. 2007;  1773(8) 1341-1348
• 54 Yamamoto K, Ichijo H, Korsmeyer S J. BCL-2 is phosphorylated and inactivated by an ASK1/Jun N-terminal protein kinase pathway normally activated at G(2)/M.  Mol Cell Biol. 1999;  19(12) 8469-8478
• 55 Kim B J, Ryu S W, Song B J. JNK- and p38 kinase-mediated phosphorylation of Bax leads to its activation and mitochondrial translocation and to apoptosis of human hepatoma HepG2 cells.  J Biol Chem. 2006;  281(30) 21256-21265
• 56 Hirosumi J, Tuncman G, Chang L et al.. A central role for JNK in obesity and insulin resistance.  Nature. 2002;  420(6913) 333-336
• 57 Schattenberg J M, Singh R, Wang Y et al.. JNK1 but not JNK2 promotes the development of steatohepatitis in mice.  Hepatology. 2006;  43(1) 163-172
• 58 Tuncman G, Hirosumi J, Solinas G et al.. Functional in vivo interactions between JNK1 and JNK2 isoforms in obesity and insulin resistance.  Proc Natl Acad Sci U S A. 2006;  103(28) 10741-10746
• 59 Weisberg S P, McCann D, Desai M et al.. Obesity is associated with macrophage accumulation in adipose tissue.  J Clin Invest. 2003;  112(12) 1796-1808
• 60 Solomon S S, Usdan L S, Palazzolo M R. Mechanisms involved in tumor necrosis factor-alpha induction of insulin resistance and its reversal by thiazolidinedione(s).  Am J Med Sci. 2001;  322(2) 75-78
• 61 Li Z, Yang S, Lin H et al.. Probiotics and antibodies to TNF inhibit inflammatory activity and improve nonalcoholic fatty liver disease.  Hepatology. 2003;  37(2) 343-350
• 62 Barbuio R, Milanski M, Bertolo M B, Saad M J, Velloso L A. Infliximab reverses steatosis and improves insulin signal transduction in liver of rats fed a high-fat diet.  J Endocrinol. 2007;  194(3) 539-550
• 63 Feldstein A E, Canbay A, Guicciardi M E et al.. Diet associated hepatic steatosis sensitizes to Fas mediated liver injury in mice.  J Hepatol. 2003;  39(6) 978-983
• 64 Inoue Y, Asanuma T, Smith N et al.. Modulation of Fas-FasL related apoptosis by PBN in the early phases of choline deficient diet-mediated hepatocarcinogenesis in rats.  Free Radic Res. 2007;  41(9) 972-980
• 65 Siebler J, Schuchmann M, Strand S et al.. Enhanced sensitivity to CD95-induced apoptosis in ob/ob mice.  Dig Dis Sci. 2007;  52(9) 2396-2402
• 66 Malhi H, Barreyro F J, Isomoto H, Bronk S F, Gores G J. Free fatty acids sensitise hepatocytes to TRAIL mediated cytotoxicity.  Gut. 2007;  56(8) 1124-1131
• 67 Volkmann X, Fischer U, Bahr M J et al.. Increased hepatotoxicity of tumor necrosis factor-related apoptosis-inducing ligand in diseased human liver.  Hepatology. 2007;  46(5) 1498-1508
• 68 Summers S A. Ceramides in insulin resistance and lipotoxicity.  Prog Lipid Res. 2006;  45(1) 42-72
• 69 Paumen M B, Ishida Y, Muramatsu M, Yamamoto M, Honjo T. Inhibition of carnitine palmitoyltransferase I augments sphingolipid synthesis and palmitate-induced apoptosis.  J Biol Chem. 1997;  272(6) 3324-3329
• 70 Tepper A D, Cock J G, de Vries E, Borst J, van Blitterswijk W J. CD95/Fas-induced ceramide formation proceeds with slow kinetics and is not blocked by caspase-3/CPP32 inhibition.  J Biol Chem. 1997;  272(39) 24308-24312
• 71 Mari M, Caballero F, Colell A et al.. Mitochondrial free cholesterol loading sensitizes to TNF- and Fas-mediated steatohepatitis.  Cell Metab. 2006;  4(3) 185-198
• 72 Feng B, Yao P M, Li Y et al.. The endoplasmic reticulum is the site of cholesterol-induced cytotoxicity in macrophages.  Nat Cell Biol. 2003;  5(9) 781-792
• 73 Devries-Seimon T, Li Y, Yao P M et al.. Cholesterol-induced macrophage apoptosis requires ER stress pathways and engagement of the type A scavenger receptor.  J Cell Biol. 2005;  171(1) 61-73
• 74 Chalasani N, Deeg M A, Crabb D W. Systemic levels of lipid peroxidation and its metabolic and dietary correlates in patients with nonalcoholic steatohepatitis.  Am J Gastroenterol. 2004;  99(8) 1497-1502
• 75 Seki S, Kitada T, Sakaguchi H. Clinicopathological significance of oxidative cellular damage in non-alcoholic fatty liver diseases.  Hepatol Res. 2005;  33(2) 132-134
• 76 Madan K, Bhardwaj P, Thareja S, Gupta S D, Saraya A. Oxidant stress and antioxidant status among patients with nonalcoholic fatty liver disease (NAFLD).  J Clin Gastroenterol. 2006;  40(10) 930-935
• 77 Yesilova Z, Yaman H, Oktenli C et al.. Systemic markers of lipid peroxidation and antioxidants in patients with nonalcoholic fatty liver disease.  Am J Gastroenterol. 2005;  100(4) 850-855
• 78 Bonnefont-Rousselot D, Ratziu V, Giral P et al.. Blood oxidative stress markers are unreliable markers of hepatic steatosis.  Aliment Pharmacol Ther. 2006;  23(1) 91-98
• 79 Chalasani N, Gorski J C, Asghar M S et al.. Hepatic cytochrome P450 2E1 activity in nondiabetic patients with nonalcoholic steatohepatitis.  Hepatology. 2003;  37(3) 544-550
• 80 Weltman M D, Farrell G C, Hall P, Ingelman-Sundberg M, Liddle C. Hepatic cytochrome P450 2E1 is increased in patients with nonalcoholic steatohepatitis.  Hepatology. 1998;  27(1) 128-133
• 81 Chtioui H, Semela D, Ledermann M, Zimmermann A, Dufour J F. Expression and activity of the cytochrome P450 2E1 in patients with nonalcoholic steatosis and steatohepatitis.  Liver Int. 2007;  27(6) 764-771
• 82 Albano E, Mottaran E, Vidali M et al.. Immune response towards lipid peroxidation products as a predictor of progression of non-alcoholic fatty liver disease to advanced fibrosis.  Gut. 2005;  54(7) 987-993
• 83 Lee J Y, Zhao L, Youn H S et al.. Saturated fatty acid activates but polyunsaturated fatty acid inhibits Toll-like receptor 2 dimerized with Toll-like receptor 6 or 1.  J Biol Chem. 2004;  279(17) 16971-16979
• 84 Suganami T, Nishida J, Ogawa Y. A paracrine loop between adipocytes and macrophages aggravates inflammatory changes: role of free fatty acids and tumor necrosis factor alpha.  Arterioscler Thromb Vasc Biol. 2005;  25(10) 2062-2068
• 85 Shi H, Kokoeva M V, Inouye K et al.. TLR4 links innate immunity and fatty acid-induced insulin resistance.  J Clin Invest. 2006;  116(11) 3015-3025
• 86 Szabo G, Velayudham A, Romics Jr L, Mandrekar P. Modulation of non-alcoholic steatohepatitis by pattern recognition receptors in mice: the role of toll-like receptors 2 and 4.  Alcohol Clin Exp Res. 2005;  29(suppl) 140S-145S