Nonalcoholic steatohepatitis (NASH) is characterized by hepatic steatosis and inflammation. The mechanism by which simple steatosis progresses to NASH is elusive. Farnesoid X receptor (FXR), the central regulator of bile acid homeostasis, has emerged as a key regulator of glucose and lipid metabolism, and protection against hepatic inflammation, making it currently a key pharmacological target to combat NASH. FXR agonists are reported to be protective against NASH development, but no clear mechanism has been defined to fully understand whole-body effects of agonism. Our laboratory has identified hepatic FXR as a key regulator of the acute phase response (APR), which can contribute to the chronic inflammatory state of the disease. Specifically, we have focused on the exacerbated NASH phenotype in liver-specific FXR knock-out (KO) mice, and the dysregulated profile compared to intestine-specific FXR KO. The proposal aims to characterize hepatic- but not intestine-FXR-dependent regulation of a family of proteins, lipocalins, to determine a direct tissue (liver)-specific mechanism in the regulation of inflammation in the disease-state. Long-term time-course studies will specifically be used to assess key changes during the progression of NAFLD in tissue-specific (e.g. liver and intestine) FXR KO mice. Overexpression of a specific FXR-regulated lipocalin will be achieved via adeno-associated virus, and identify a protective role of the lipocalin against inflammation.
Aim 1 will determine the effect of Lcn13 on the hepatic APR following an acute infection. Liver-specific FXR KO mice are more susceptible to acute infection, but the effects of Lcn13 on the APR following LPS or E.coli infection are unknown.
Aim 2 tests the hypothesis that differential regulation of lipocalin expression by hepatic FXR protects NASH development. Lcn2 and Lcn13 are differentially regulated in liver-specific FXR KO mice on a high-fat diet, therefore the mechanism by which Lcn13 may be protective of the transition from simple steatosis to NASH will be assessed.
Aim 3 will determine FXR- and Lcn13-mediated effects on white adipose tissue (WAT) that contribute to overall systemic inflammation associated with NASH development.
This aim will address whole-body benefits of hepatic Lcn13 overexpression by determining if secreted Lcn13 acts on WAT to maintain glucose, insulin, and lipid homeostasis that is dysregulated in models of NASH. The completion of these studies and training will greatly benefit NASH research in understanding FXR role in preventing inflammation through the early stage APR in the liver, and addresses whole-organism effects of a liver-specific Lcn13 overexpression to fully describe the benefits of developing tissue-specific pharmacological drug therapy for NASH. Identifying in vivo mechanisms of inflammation related to the disease-state of NASH, and protective mechanism of FXR and FXR-dependent genes against inflammation can provide essential data to contribute to the development of tissue-specific FXR agonists to combat NASH. .
Farnesoid X receptor (FXR) has emerged as a key regulator in the protection against hepatic inflammation, making it currently a key pharmacological target in the pipeline to combat nonalcoholic steatohepatitis (NASH). The identification of liver FXR as a key regulator of the acute phase response (APR), and further characterizing FXR-dependent regulation of key proteins of the APR, specifically lipocalins, will define a direct tissue-specific mechanism in the regulation of inflammation during the transition from simple steatosis to NASH, identifying a protective mechanism of FXR and FXR-dependent genes against inflammation. These studies will directly contribute to understanding the elusive mechanism of NASH development and future development of effective tissue-specific FXR agonists to combat NASH.