The role of microRNA-802 regulated by the nuclear receptor FXR-SHP cascade in obesity and non-alcoholic fatty liver disease

Sun, Hao

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https://hdl.handle.net/2142/117669 Copy

Description

Title

The role of microRNA-802 regulated by the nuclear receptor FXR-SHP cascade in obesity and non-alcoholic fatty liver disease

Author(s)

Sun, Hao

Issue Date

2022-12-02

Director of Research (if dissertation) or Advisor (if thesis)

Kemper, K. Jongsook

Doctoral Committee Chair(s)

Kemper, K. Jongsook

Committee Member(s)

• Chen, Lin-Feng
• Nelson, Eric R
• Raetzman, Lori T

Department of Study

Molecular & Integrative Physl

Discipline

Molecular & Integrative Physi

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

obesity, fatty liver, AMPK, microRNA, nuclear receptor

Abstract

The prevalence of obesity has increased dramatically worldwide, becoming a global epidemic. Obesity substantially increases risks for many human diseases, ranging from metabolic disorders, including type 2 diabetes, non-alcoholic fatty liver disease (NAFLD), and cardiovascular disease, to infertility, depression, and even, certain types of cancer. The urgent need for effective drugs for the treatment of obesity-related metabolic diseases has greatly increased research interest in Farnesoid X Receptor (FXR/NR1H4), a key metabolic regulator. FXR is a member of the nuclear receptor superfamily and is the primary biosensor for bile acids. After a meal, FXR is activated by its physiological ligands, bile acids, and regulates transcription of numerous genes involved in bile acid, cholesterol, lipid and glucose metabolic pathways. The orphan nuclear receptor, small heterodimer partner (SHP, NR0B2), and fed-state gut hormones, fibroblast growth factor 15/19 (FGF19 in human, FGF15 in mouse), are two well-known direct FXR targets that play a critical role in metabolic regulation and energy balance. MicroRNAs (miRs) have also emerged as promising targets for treatment of obesity-related diseases. MiRs are small non-coding RNAs that negatively regulate target genes by binding to the 3’-untranslated regions of mRNAs and inhibiting their translation and/or stability. MiRs play important roles in numerous biological pathways and the aberrant expression of miRs has been reported in many diseases, including metabolic disorders. For example, hepatic miR-802 levels are highly elevated in overweight patients and obese mice. Furthermore, miR-802 promotes insulin resistance and glucose intolerance by directly targeting Hnf1b, an important regulator of glucose metabolism. However, it remained unknown whether the miR-802 inhibits other targets besides Hnf1b to promote obesity-associated metabolic problems and why miR-802 levels are abnormally elevated in obesity. Initially, I worked with Dr. Sunmi Seok, a research scientist in the Kemper lab, and investigated the role of the nuclear receptor FXR/SHP cascade in miR-802 expression in physiology and obesity. In this study, we found that hepatic expression of miR-802 is negatively regulated by the FXR-induced SHP under physiological conditions and is aberrantly elevated in obesity due to defective FXR-SHP function. This study was published (Diabetes, 2020), with me as the second author, and is included in the Appendix of my thesis. In the first part of my thesis study, based on microRNA bioinformatics analyses, I tested the hypothesis that obesity-induced miR-802 promotes NAFLD and a severe form, nonalcoholic steatohepatitis (NASH), by directly targeting AMP-activated protein kinase (AMPK), a key energy sensor. I found that hepatic miR-802 and AMPK levels were inversely correlated in both NAFLD patients and obese mice. MicroRNA in silico analysis and biochemical studies suggested that miR-802 inhibits hepatic expression of AMPK by binding to the 3’ untranslated regions of the mRNAs of subunits of AMPK. In diet-induced NASH mice, treatment with obeticholic acid (OCA), a specific FXR agonist currently being tested in clinical trials for NASH patients, reduced hepatic miR-802 levels and improved AMPK activity, ameliorating NASH pathologies like hepatic inflammation and apoptosis. However, these OCA effects were reversed by overexpression of miR-802 or downregulation of AMPK. These results suggest that miR-802 directly targets AMPK, promoting NASH in mice. The miR-802-AMPK axis that modulates OCA-mediated beneficial effects on NASH may represent a new therapeutic target. This miR-802/AMPK study was published in Molecular Metabolism with me as the first author. In published studies, our lab showed that the orphan nuclear receptor SHP is an important physiological regulator of lipid metabolism and that its function is enhanced by phosphorylation at Thr-58 mediated by FGF15/19 signaling. Remarkably, protein levels of phosphorylated SHP at Thr-55 (human T55, mouse T58) were substantially reduced in NAFLD patients. To investigate the long-term in vivo role of FGF15/19-SHP function in whole-body energy metabolism, Dr. Young Kim, a research scientist in the lab, generated phosphorylation-defective SHP-T58A knock-in (SHP-KI) mice. In the second part of my thesis, to broaden my view of nuclear receptor regulation of metabolism, I collaborated with Dr. Kim to examine the role of FGF15/19-mediated SHP phosphorylation in energy metabolism by performing metabolic cage and histological studies. Because SHP inhibits expression of miR-802 (Diabetes, 2020), I also examined whether the miR-802 expression is altered in these mice. Compared with WT mice, SHP-KI mice gained weight more rapidly under normal chow and developed NAFLD more prominently upon feeding a high fat diet. These obesity/NAFLD-prone phenotypes were associated with altered bile acid composition and gut bacteria and expression of lipid metabolic genes, as well as increased miR-802 levels. My metabolic cage studies and histological analyses are included in a manuscript, “Impaired phosphorylation of SHP by FGF15/19 alters bile acids and gut bacteria, promoting NAFLD,” which has been submitted, with me as a coauthor. In summary, in this thesis, I studied the role of the miR-802-AMPK axis in NAFLD as a mediator of nuclear receptor FXR-SHP metabolic function (Molecular Metabolism, 2022). In collaborations with other members of the lab, we found that miR-802 levels are aberrantly elevated in obesity by defective FXR/SHP function (Diabetes, 2020), and further investigated the role of FGF15/19-mediated SHP phosphorylation in development of NAFLD (PNAS, under review). My most significant finding was showing that miR-802 regulates AMPK levels, which provided a mechanistic explanation for the known low AMPK activity in obesity and NAFLD. I hope these findings on the miR-802/AMPK axis and on the SHP-KI mice will help to develop novel potential targets for treating NAFLD/NASH and other obesity-associated diseases.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Hao Sun

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