My long term career objective is to define the mechanisms of liver inflammation in nonalcoholic steatohepatitis (NASH), the most-prevalent chronic liver disease in the United States of America. NASH is characterized by endoplasmic reticulum (ER) stress, which results in activation of the ER stress sensor Inositol Requiring Enzyme-1 alpha (IRE1?), due to the accumulation of toxic lipids within hepatocytes. Macrophage- mediated liver inflammation associated with recruitment of circulating myeloid cells into the liver is also pivotal in NASH. The current proposal links hepatocyte-derived lipid mediators to macrophage-mediated inflammation by proposing that extracellular vesicles (EVs) from lipotoxic hepatocytes recruit macrophages to the liver, resulting in liver injury and inflammation. In preliminary experiments we have observed that lipotoxic hepatocytes (treated with the free fatty acid palmitate) release ceramide-enriched proinflammatory EVs in an IRE1?-dependent manner. Sphingosine 1-phosphate (S1P), derived from ceramide, on these EVs activates its receptor S1P1 on macrophages, which may promote macrophage chemotaxis into the liver. This has led to the central hypothesis that hepatocyte IRE1? regulates PA-induced EV biogenesis, release and lipid cargo (ceramide and ceramide-derived S1P) accumulation, which in turn attracts macrophages into the liver promoting NASH pathogenesis. Therefore, the goals of this proposal are to understand: i) how IRE1? mediates release of ceramide-enriched EVs; ii) how the ceramide-derived lipid mediator, S1P, on PA- stimulated EVs recruits macrophages to the liver; and iii) can lipotoxic EV production and signaling be targeted in vivo to decrease liver inflammation? The proposed experiments will employ complementary in vitro and in vivo models of lipotoxicity and NASH, respectively; and pharmacological, molecular and genetic approaches to address three integrated hypotheses. First we will directly test the hypothesis that palmitate-induced ER stress drives ceramide biosynthesis leading to EV release by a) the IRE1?-activated transcription factor, X-box binding protein-1 (XBP1) upregulation of the ceramide biosynthesis regulating enzyme serine palmitoyltransferase 1 (SPT1), and b) the transfer of ceramide to multivesicular bodies via the ceramide transport protein STARD11. Second we will directly test the hypothesis that S1P on lipotoxic EVs activates macrophage chemotaxis by a) compartmental generation of S1P by sphingosine kinase 2 forming S1P on PA- induced EVs, and b) S1P on EVs activates macrophage chemotaxis via S1P1 receptor. Third we will directly test the hypothesis that interrupting EV release or signaling is salutary in vivo in a NASH mouse model by a) reduction of EV release by IRE1? hepatocyte-specific knockout mice, and b) genetic and pharmacologic inhibition of S1P signaling on macrophages. This R01 grant application by a current K08 awarded early stage investigator will yield mechanistic insights into the processes of macrophage recruitment in NASH, thus identifying potentially druggable targets, e.g., inhibitors of IRE1?, SPT or S1P1 receptor.

Public Health Relevance

This grant examines how fatty liver cells release extracellular vesicles to communicate with white blood cells termed macrophages. These macrophages, in turn cause liver damage. This research is important because increasing obesity has resulted in large numbers of people with fatty liver disease, for which there are no proven treatments. With the proposed research we will identify the cellular machinery liver cells utilize to release lipid mediator-enriched extracellular vesicles, and determine how these vesicles recruit macrophages into the liver, and, thus, identify pathways that can potentially be targeted therapeutically to treat fatty liver disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK111378-03
Application #
9532833
Study Section
Hepatobiliary Pathophysiology Study Section (HBPP)
Program Officer
Burgess-Beusse, Bonnie L
Project Start
2016-09-23
Project End
2021-08-31
Budget Start
2018-09-01
Budget End
2019-08-31
Support Year
3
Fiscal Year
2018
Total Cost
Indirect Cost
Name
Mayo Clinic, Rochester
Department
Type
DUNS #
006471700
City
Rochester
State
MN
Country
United States
Zip Code
55905
Yang, Ju Dong; Malhi, Harmeet (2018) Green tea consumption: A potential chemopreventive measure for hepatocellular carcinoma? Hepatology 67:10-12
Fukushima, Masanori; Dasgupta, Debanjali; Mauer, Amy S et al. (2018) StAR-related lipid transfer domain 11 (STARD11)-mediated ceramide transport mediates extracellular vesicle biogenesis. J Biol Chem 293:15277-15289
Bandla, Harikrishna; Dasgupta, Debanjali; Mauer, Amy S et al. (2018) Deletion of endoplasmic reticulum stress-responsive co-chaperone p58IPK protects mice from diet-induced steatohepatitis. Hepatol Res 48:479-494
Malhi, Harmeet; Camilleri, Michael (2017) Modulating bile acid pathways and TGR5 receptors for treating liver and GI diseases. Curr Opin Pharmacol 37:80-86
Greuter, Thomas; Malhi, Harmeet; Gores, Gregory J et al. (2017) Therapeutic opportunities for alcoholic steatohepatitis and nonalcoholic steatohepatitis: exploiting similarities and differences in pathogenesis. JCI Insight 2:
Camilleri, Michael; Malhi, Harmeet; Acosta, Andres (2017) Gastrointestinal Complications of Obesity. Gastroenterology 152:1656-1670
Mauer, Amy S; Hirsova, Petra; Maiers, Jessica L et al. (2017) Inhibition of sphingosine 1-phosphate signaling ameliorates murine nonalcoholic steatohepatitis. Am J Physiol Gastrointest Liver Physiol 312:G300-G313