LPS - Section on Liver Biology (LB)

Bin Gao MD., PhD, Section Chief
National Institute on Alcohol Abuse and Alcoholism
National Institutes of Health
5625 Fishers Lane, Room 2S-33:MSC 9413
Bethesda MD 20892-9412
telephone: +1 301.443.3998
fax: +1 301 480.0257
e-mail: bgao@mail.nih.gov

Hepatic Inflammation and Immunity

Alcohol consumption, nonalcoholic steatohepatitis, and viral hepatitis are three major causes of chronic liver injury leading to liver fibrosis, cirrhosis, and liver cancer. At present, the molecular and cellular mechanisms underlying liver injury and repair in these liver disorders are poorly understood. However, increasing evidence has suggested that immune cells play an important role in the pathogenesis of liver disease.
The hepatic immune system predominantly expresses innate immunity, whereby a large percentage of innate immune cells, including macrophages (i.e., Kupffer cells), natural killer (NK) cells, and natural killer T (NKT) cells are involved. These cells are important as the first line of defense against infection and are poised to quickly respond to potential attacks by any pathogen in the absence of antigen recognition via producing a variety of cytokines. Interestingly, in liver injury and repair, innate immunity is activated, followed by production of a wide variety of cytokines. Hence, our laboratory is investigating the immunologic mechanisms of liver injury and repair, focusing on innate immunity and cytokines in fatty liver, liver inflammation and fibrosis, as well as in liver regeneration.

Innate Immunity, Liver Injury, Fibrosis, and Repair

Jeong, Park, Wang, and Gao in collaboration with Tian, Kim, Lian, Gershwin

Our laboratory is actively studying: 1) the role of innate immune cells (NK/NKT cells) and cytokines [interferon (IFN)/ signal transducer and activator of transcription 1 (STAT 1)] in liver injury, fibrosis, and regeneration; 2) the effects of ethanol on innate immunity in the liver.

Regardless of etiology, all forms of chronic liver injury lead to liver fibrosis accompanied by an excessive accumulation of extracellular matrix proteins, including collagen. Recent evidence suggests that liver fibrosis, and even cirrhosis, can be reversible. While activation of hepatic stellate cells has been known to play a central role in the development and progression of liver fibrosis, the clearance of hepatic stellate cells by apoptosis has been suggested to be a key step involved in reversing liver fibrosis. However, the factors responsible for hepatic stellate cell apoptosis during liver fibrosis remain largely unknown. Our recent findings indicated that NK cells play an important role in inducing hepatic stellate cell apoptosis during liver fibrosis. Using an in vitro culture model, we demonstrated that NK cells kill early-activated hepatic stellate cells, but not quiescent or chronically activated stellate cells. Furthermore, this appeared to be due to the fact that early-activated hepatic stellate cells, but not quiescent or chronically-activated stellate cells, express high levels of the NK cell activating ligand, retinoic acid early inducible gene 1 (RAE1), which activates NK cell killing. RAE1 proteins were originally isolated from mouse embryonic carcinoma F9 cells treated with retinoic acid and later identified as the NKG2D ligand to activate NK cells (see Radaeva et al., 2006). Currently, we are exploring the roles of NKT cells in chronic liver injury and liver fibrosis. Our preliminary findings show that NKT cells play a diverse role in acute liver injury, but are depleted in chronic liver injury induced by carbon tetrachloride, suggesting that NKT cells may play a role in inhibiting the early stage of liver fibrosis but not the late stage of disease.

It is well documented that chronic alcohol consumption accelerates liver fibrosis in patients with hepatitis C virus (HCV) infection. Multiple mechanisms have been proposed to explore the underlying mechanisms mediating ethanol’s effects. Our laboratory has demonstrated that chronic alcohol consumption attenuates the anti-fibrotic effects of innate immune cells (NK/IFN-y), which could be an important mechanism contributing to alcohol acceleration of liver fibrosis in patients with chronic HCV infection (see Jeong et al., 2008).

Cytokines/STATs in Fatty Liver, Liver Inflammation, and Repair

Horiguchi, Miller, Lafdil, Wang, and Gao in collaboration with Kunos, Fu, Hennighausen, Pacher, Young.

Our laboratory has been also actively studying the roles of cytokines and their signaling pathways in liver diseases, focusing on the role of IL-6/STAT3 in fatty liver, liver inflammation and repair. We have previously demonstrated that IL-6 plays an important role in protecting against liver injury in several murine models of alcoholic liver injury, nonalcoholic fatty liver disease, fatty liver transplantation, and T cell hepatitis. It is believed that the action of IL-6 is mainly mediated via activation of signal transducer and activator of transcription 3 (STAT3).

By using immunohistochemistry analyses, we have demonstrated that phosphorylated STAT3 (STAT3 activation) are detected in hepatocytes, sinusoidal endothelial cells, bile duct-like cells, and inflammatory cells (macrophages, neutrophils, etc.) in human alcoholic cirrhotic livers (see Horiguchi et al., 2007). To understand the roles of STAT3 in alcoholic liver injury, we created liver-specific and macrophage/neutrophil-specific STAT3 knock out mice by crossing STAT3flox/flox mice with albumin-promoter Cre transgenic mice and lysozyme M-promoter Cre transgenic mice, respectively. Compared with wild-type mice, feeding hepatocyte-specific STAT3 knock out mice with an ethanol-containing diet induced greater hepatic steatosis, hypertriglyceridemia, and hepatic expression of lipogenic genes (sterol regulatory element- binding protein, fatty acid synthase, acetyl-CoA carboxylase-1, and stearoyl-CoA desaturase 1), but less inflammation and lower expression of hepatic proinflammatory cytokines. In contrast, ethanol-fed macrophage/neutrophil-specific STAT3 knock out mice showed more hepatic inflammation, worse injury, and increased hepatic expression of proinflammatory cytokines compared with wild-type mice. Kupffer cells isolated from ethanol-fed hepatocyte-specific STAT3 knock out mice produced similar amounts of reactive oxygen species and tumor necrosis factor alpha, whereas Kupffer cells from macrophage/neutrophil-specific STAT3 knock out mice produced more reactive oxygen species and tumor necrosis factor alpha compared with wild-type controls. Our findings suggest that STAT3 regulates hepatic inflammation in a cell type- dependent manner during alcoholic liver injury: STAT3 in hepatocytes promotes, whereas STAT3 in macrophages/Kupffer cells suppresses, inflammation. In addition, activation of hepatocellular STAT3 ameliorates alcoholic fatty liver via inhibition of sterol regulatory element-binding protein 1c expression (see Horiguchi et al., 2008). Currently, we are exploring the roles of endothelial cell- and macrophage/neutrophil-specific STAT3 in nonalcoholic fatty liver disease and liver regeneration.

In addition, we are also collaborating with Drs. George Kunos and Pal Pacher from NIAAA to investigate the role of the endocannabinoid system in alcoholic liver disease.

Selected Publications (over 110)

1. Gao, B., Radaeva, S., Park, O.: Liver NK/NKT cells: Immunobiology and emerging roles in liver diseases (Review).

J. Leukocyte Biology 2009

2. Park, O., Jeong, W., Wang, L., Wang, H., Lian, Z., Gershwin, E., and Gao, B: Diverse roles of invariant NKT cells in liver injury and fibrosis induced by carbon tetrachloride.

Hepatology 2009, 47:571-580

3. Horiguchi, N., Wang, L., Mukhopadhyay, P., Jeong, W., Lafdil, F., Osei-Hyiaman, D., Moh, A., Fu, X., Pacher, P., Kunos, G., Gao, B.: Cell-dependent pro- and anti-inflammatory role of STAT3 in alcoholic liver injury.

Gastroenterology 2008;134:1148-1158

4. Kunos, G., and Gao, B.: Endocannabinoids, CB1 receptors, and liver disease – hitting more than one bird with the same stone (Invited Editorial Comment).

Gastroenterology, 2008;134:622-625

5. Jeong, W., Park, O., Gao, B.: Abrogation of anti-fibrotic effects of NK/IFN-g contributes to alcohol acceleration of liver fibrosis.

Gastroenterology 2008, 134:248-258

6. Hu, W., Ferris, S., Tweten, R., Wu, G., Radaeva, S., Gao, B., Bronson, R., Halperin, J., Qin, X.: Conditional, rapid and targeted ablation of cells expressing human CD59 in transgenic mice by intermedilysin.

Nature Medicine 2008;14, 98 – 103

7. Jeong, W., Osei-Hyiaman, D., Park, O., Liu, J., Bátkai, S., Mukhopadhyay, P., Horiguchi, N., Harvey-White, J., Marsicano, G., Lutz, B., Gao, B., Kunos, G.: Paracrine activation of hepatic CB1 receptors by stellate cell-derived endocannabinoids mediates alcoholic liver disease.

Cell Metabolism 2008; 7(3):227-35.

8. Chuang, Y., Lian, Z., Yang, G., Shu, S., Moritoki, Y., Ridgway, M., Kronenberg, M., Flavell, R., Gao, B., and Gershwin, E.: CD1d-restricted NKT cells exacerbate liver injury in a TGF-b receptor II dominant-negative mouse model of primary biliary cirrhosis.

Hepatology 2008;47:571-580

9. Gao, B., Jeong, W., and Tian, Z.: Liver: an organ with predominant innate immunity (Review).

Hepatology 2008; 47:729-736

10. Radaeva, S., Wang, L., Radaev, S., Jeong, W., Park, O., and Gao, B.: Retinoic acid signaling upregulates natural killer cell activating ligand RAE1 in hepatic stellate cells.

Am. J. Physiol (GI and Liver) 2007, 293:G809-816.

11. Gao, B., Radaeva, S., Jeong, W.: Activation of NK cells inhibits liver fibrosis: A novel strategy to treat liver fibrosis (Review).

Expert Review of Gastroenterology and Hepatology 2007, 1:173-180

12. Batkai, S., Osei-Hyiaman, D., Pan, H., El-Assal, O., Rajesh M., Mukhopadhyay, P., Hong, F., Harvey-White, J., Jafi, A., Hasko, G., Huffman, J., Gao, B., Kunos, G., Pacher, P.: Cannabinoid-2 receptor mediates protection against hepatic ischemia/reperfusion injury.

FASEB J 2007, 21:1788-800

13. Cui, Y., Hosui, A., Sun, R., Shen, K., Gavrilova, O., Chen, W., Cam, M., Gao, B., Robinson, G., Hennighausen, L.: Inactivation of hepatic Stat5a/b results in aberrant GH-induced activation of Stat1 and Stat3, hepatosteatosis, and diminished liver regeneration.

Hepatology 2007;46:504-513

14. Mohanraj, R., Pan, H., Mukhopadhyay, P., Bátkai, S., Osei-Hyiaman, D., Hasko, G., Liaudet, L., Gao, B., and Pacher, P.: Cannabinoid-2 receptor agonist HU-308 protects against hepatic ischemia/reperfusion injury by attenuating oxidative stress, inflammatory response and apoptosis.

J. Leuk. Biol. 2007, 82: 1382–1389

15. Sun R., Park, O., Horiguchi, N, Kulkarni, S., Jaruga, B., Jeong, W., Sun, H., Radaeva, S., and Gao, B:. STAT1 contributes to dsRNA inhibition of liver regeneration after partial hepatectomy in mice.

Hepatology 2006, 44:955-966

16. Jeong, W., Park, O., Radaeva, S., and Gao, B: STAT1 inhibits liver fibrosis through attenuating stellate cell activation and stimulating NK cell killing of activated stellate cells.

Hepatology 2006, 44:1441-1451

17. Radaeva, S., Sun, R., Jaruga, B., Nguyen, V., Tian, Z., Gao B.: Natural killer cells ameliorate liver fibrosis through killing activated stellate cells in RAE1/NKG2D- and TRAIL-dependent manners.

Gastroenterology 2006, 130: 435-452.

18. Li, B., Sun, R., Wei, H., Gao, B., and Tian, Z.: Interleukin-15 prevents Con-A induced liver injury via NKT-dependent mechanism.

Hepatology 2006, 43:1211-1219

19. Xu, X., Kobayashi, S., Qiao, W., Li, C., Xiao, C., Radaeva, S., Stiles, B., Wang, R., Ohara, N., Yoshino, T., LeRoith, D., Torbenson, M., Gores, G., Wu, H., Gao, B., and Deng, C. Induction of cholangiocellular carcinoma by liver specific disruption of Smad4 and Pten in mice.

J. Clin. Invest. 2006, 116(7):1843-1852

20. Kunos, G., Osei-Hyiaman, D., Bátkai, S., and Gao, B.: Cannabinoids hurt, heal in cirrhosis (News and Views).

Nature Medicine 2006, 12:608-610

21. Kim, W., Lee, J., Suh, Y., Hong, S., Choi, J., Lim, J., Song, J., Gao, B., and Jung, M.: Exposure to chronic high glucose induces b-cell apoptosis through decreased interaction of GCK with mitochondria: downregulation of GCK in pancreatic b cells.

Diabetes 2005,54:2602-11

22. Sun R., and Gao, B.: Negative regulation of liver regeneration by innate immunity (NK/IFN-g).

Gastroenterology 2004, 127, 1525-1539

23. Sun R., Tian, Z., Kulkarni, S., and Gao, B.: Interleukin-6 (IL-6) prevents T cell-mediated hepatitis: IL-6 inhibits NKT cells by CD4+ cells- and STAT3-dependent mechanisms.

J. Immunol. 2004 172:5648-5655

24. Radaeva, R., Sun, R., Pan, H., Hong, F., and Gao, B.: Interleukin-22 (IL-22) plays a protective role in T cell hepatitis: IL-22 is a survival factor for hepatocytes via activation of STAT3.

Hepatology 2004, 39(5):1332-1342.

25. Hong, F., Radaeva, S., Pan, H., Tian, Z., Veech, R., and Gao, B.: Interleukin-6 treatment alleviates steatosis and ischemia/reperfusion injury in mice with fatty liver disease.

Hepatology 2004, 40: 933-941.

26. Gao, B., Hong, F., and Radaeva, S: Host factors and interferon-a treatment failure in hepatitis C: molecular mechanisms and potential therapeutic improvement (Review).

Hepatology 2004, 39:880-890.

27. Radaeva, S., Jaruga, B., Kim, W., Heller, T., Liang, T., and Gao, B.: IFN-g treatment inhibits IFN-α-activated signaling in hepatic cells: Evidence for the involvement of STAT1 induction and hyperexpression of STAT1 in chronic hepatitis C.

Biochem. J. 2004 379: 199-208

28. Jaruga, B., Hong F., Kim, E., Sun, R., and Gao, B.: Chronic ethanol consumption potentiates liver injury in T-cell mediated hepatitis: Disregulation of STAT3 and NF-kB signals.

Am. J. Physiol (GI and Liver) 2004, 287:G471-G479

29. Jaruga, B., Kim, W., Hong, F., and Gao, B.: IFN-g/STAT1 acts as a pro-inflammatory signal in T cell-mediated hepatitis via induction of multiple chemokines/adhesion molecules: A central role of IRF-1.

Am. J. Physiol (GI and Liver) 2004, 287:G1044-G1052

30. Jaruga, B., Hong, F., Sun, R., Radaeva, S., and Gao, B.: Crucial Role of IL-4/STAT6 in T cell-mediated hepatitis: Upregulating eotaxins and IL-5, and recruiting leukocytes.

J. Immunol. 2003, 171: 3233-3244

31. Kim, W., Hong, F., Radaeva, S., Jaruga, B., and Gao, B.: STAT1 plays an essential role in LPS/D-galactosamine-induced liver injury.

Am. J. Physiol (GI and Liver) 2003, 285:G761-768.

32. Liu, J., Batkai, S., Pacher, P., Harvey-White, J., Wagner, J.A., Cravatt, B.F., Gao, B., and Kunos, G.: LPS Induces anandamide synthesis in macrophages via CD14/MAPK/PI3K/ NF-kB independently of platelet activating factor.

J. Biol. Chem 2003, 278:45034-45039.

33. Sun, Z., Klein, A. S., Radaeva, S., Hong, F., El-Assal, O., Jaruga, B., Pan, H., Batkai, S., Tian, Z., Hoshino, S., Kunos, G., Diehl, A., and Gao, B.: In vitro interleukin-6 treatment prevents mortality associated with fatty liver transplants in rats.

Gastroenterology 2003, 125:202-215.

34. Radaeva, S., Jaruga, B., Hong, F., Kim, W. H., Fan, S., Cai, H., Strom S., Liu, Y., El-Assal, O., and Gao, B.: Interferon-a activates multiple STAT signals and downregulates c-Met in primary human hepatocytes.

Gastroenterology 2002, 122:1020-1034.

35. Nguyen, V. N., and Gao, B.: Expression of interferon-a signaling components in human alcoholic liver disease.

Hepatology 2002, 35:425-432.

36. Hong, F., Kim, W. H., Tian, Z., Jaruga, B., Ishac, E., Shen, X., and Gao, B.: Elevated interleukin-6 during ethanol consumption acts as a potential endogenous protective cytokine against ethanol-induced apoptosis in the liver: involvement of Bcl-2 and Bcl-x(L) proteins.

Oncogene 2002, 21:32-43.

37. Hong, F., Jaruga, B., Kim, W. H., Radaeva, S., Tian, Z., El-Assal, O., Nguyen, V., and Gao, B.: Opposing roles of STAT1 and STAT3 in T cell-mediated hepatitis: regulation by SOCS.

J. Clin. Invest. 2002, 110 (10): 1503-1513.

38. Liu, J., Tian, Z., Gao, B., and Kunos G.: Dose-dependent activation of antiapoptotic and proapoptotic pathways by ethanol treatment in human vascular endothelial cells: differential involvement of adenosine.

J. Biol. Chem. 2002, 277:20927-20933.

39. Kim, W. H., Hong, F., Jaruga, B., Hu, Z., Fan, S., Liang, J., and Gao, B.: Additive activation of nuclear factor-kB by ethanol, hepatitis B protein X and HCV core protein: Involvement of TNFa receptor 1-independent and –dependent mechanisms.

FASEB J. 2001, 15:2551-2553.

40. Hong, F., Nguyen, V. N., and Gao, B.: Tumor necrosis factor a attenuates interferon a/b signaling in the liver: involvement of SOCS3 and SHP2 and implication in resistance to interferon therapy.

FASEB J. 2001, 15:1595-1597

41. Tian, Z. G., Shen, X. N., Hong, F., and Gao, B.: IL-1 b attenuates interferon a/b-induced antiviral activity and STAT1 activation in the liver: involvement of proteasome-dependent mechanism.

J. Immunol. 2000, 165:3959-3965

42. Nguyen, V. A., Hong, F., Ishac, E., Chen, J., and Gao, B.: Interferons activate MAP kinase and STAT1 in freshly isolated rat liver cells: differential regulation by acute ethanol.

Biochem. J. 2000, 349:427-435

43. Shen, X. N., Tian, Z. G., Holtzman, M. J., and Gao, B.: Cross-talk between interleukin 1b (IL-1b) and IL-6 signaling pathways: IL-1b inhibits IL-6-activated STAT1 by a ubiquitin-proteasome dependent mechanism.

Biochem. J. 2000, 352:913-919

Updated: May 2009