Increased expression of sterol regulatory element binding protein‑2 alleviates autophagic dysfunction in NAFLD

Cheng,Chunwei; Deng,Xiaoling; Xu,Keshu

doi:10.3892/ijmm.2018.3389

Increased expression of sterol regulatory element binding protein‑2 alleviates autophagic dysfunction in NAFLD

Authors:
- Chunwei Cheng
- Xiaoling Deng
- Keshu Xu
View Affiliations

Affiliations: Division of Gastroenterology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
Published online on: January 16, 2018 https://doi.org/10.3892/ijmm.2018.3389
Pages: 1877-1886
Copyright: © Cheng et al. This is an open access article distributed under the terms of Creative Commons Attribution License.

Metrics: Total Views: 0 (Spandidos Publications: | PMC Statistics: )

Metrics: Total PDF Downloads: 0 (Spandidos Publications: | PMC Statistics: )

Cited By (CrossRef): 0 citations Loading Articles...

Abstract

Sterol regulatory element binding protein‑2 (SREBP‑2) is an important transcription factor in lipid homeostasis. A previous study showed that SREBP‑2 also activated autophagic genes during cell‑sterol depletion. Alterations in autophagy are reported to be involved in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). However, whether the regulation of SREBP‑2 restores dysfunctional autophagy in hepatocytes during NAFLD remains to be elucidated. In the present study, a steatosis model was established with palmitic acid (PA) treatment at the indicated times and concentrations. Autophagosomes in hepatocytes were visualized by confocal microscopy after transfection with a tandem GFP‑mCherry‑LC3 construct. Autophagy‑associated protein levels were analyzed by western blot analysis. Loss‑ and gain‑of‑function studies were performed to examine the role of SREBP‑2 in the regulation of hepatocyte autophagy. It was demonstrated that PA induced autophagy and enhanced autophagic flux at the early stage, whereas prolonged treatment with PA resulted in dysfunction of autophagy in the PA‑induced steatotic hepatocytes. In addition, different cellular models presented with differing dysfunctional autophagy in response to fatty acid overload. It was also confirmed that SREBP‑2 regulated autophagy‑related gene expression in hepatocytes, and it was shown that the overexpression of SREBP‑2 increased the expression of autophagy‑related genes, but did not affect the inhibition of the autophagic flux in lipid‑overloaded HL‑7702 cells. By contrast, increased SREBP‑2 partly restored the inhibited autophagic activity in lipid‑overloaded hepatoma HepG2 cells. Taken together, the present study demonstrated that autophagic function was impaired in lipid‑overloaded human hepatocytes, and the differential effect of PA on autophagy was associated with the duration of PA and the cell type. Under these conditions, the overexpression of SREBP‑2 alleviated the inhibited autophagic activity rather than the inhibition of autophagic flux. Consequently, the results indicated that restoration of autophagy dysfunction via the regulation of SREBP‑2 may be a potential therapeutic target for the treatment of NAFLD.

View Figures

View References

1	Brunt EM, Wong VW, Nobili V, Day CP, Sookoian S, Maher JJ, Bugianesi E, Sirlin CB, Neuschwander-Tetri BA and Rinella ME: Nonalcoholic fatty liver disease. Nat Rev Dis Primers. 1:150802015. View Article : Google Scholar : PubMed/NCBI
2	Wang FS, Fan JG, Zhang Z, Gao B and Wang HY: The global burden of liver disease: The major impact of China. Hepatology. 60:2099–2108. 2014. View Article : Google Scholar : PubMed/NCBI
3	Cheung O and Sanyal AJ: Recent advances in nonalcoholic fatty liver disease. Curr Opin Gastroenterol. 26:202–208. 2010. View Article : Google Scholar : PubMed/NCBI
4	Neuschwander-Tetri BA: Hepatic lipotoxicity and the pathogenesis of nonalcoholic steatohepatitis: The central role of nontriglyceride fatty acid metabolites. Hepatology. 52:774–788. 2010. View Article : Google Scholar : PubMed/NCBI
5	Li S, Li J, Shen C, Zhang X, Sun S, Cho M, Sun C and Song Z: Tert-Butylhydroquinone (tBHQ) protects hepatocytes against lipotoxicity via inducing autophagy independently of Nrf2 activation. Biochim Biophys Acta. 1841:22–33. 2014. View Article : Google Scholar
6	Wu J, Wu JJ, Yang LJ, Wei LX and Zou DJ: Rosiglitazone protects against palmitate-induced pancreatic beta-cell death by activation of autophagy via 5′-AMP-activated protein kinase modulation. Endocrine. 44:87–98. 2013. View Article : Google Scholar
7	Ryter SW, Cloonan SM and Choi AM: Autophagy: A critical regulator of cellular metabolism and homeostasis. Mol Cells. 36:7–16. 2013. View Article : Google Scholar : PubMed/NCBI
8	Singh R, Kaushik S, Wang Y, Xiang Y, Novak I, Komatsu M, Tanaka K, Cuervo AM and Czaja MJ: Autophagy regulates lipid metabolism. Nature. 458:1131–1135. 2009. View Article : Google Scholar : PubMed/NCBI
9	Fukuo Y, Yamashina S, Sonoue H, Arakawa A, Nakadera E, Aoyama T, Uchiyama A, Kon K, Ikejima K and Watanabe S: Abnormality of autophagic function and cathepsin expression in the liver from patients with non-alcoholic fatty liver disease. Hepatol Res. 44:1026–1036. 2014. View Article : Google Scholar
10	González-Rodríguez Á, Mayoral R, Agra N, Valdecantos MP, Pardo V, Miquilena-Colina ME, Vargas-Castrillón J, Lo Iacono O, Corazzari M, Fimia GM, et al: Impaired autophagic flux is associated with increased endoplasmic reticulum stress during the development of NAFLD. Cell Death Dis. 5:e11792014. View Article : Google Scholar : PubMed/NCBI
11	Yang L, Li P, Fu S, Calay ES and Hotamisligil GS: Defective hepatic autophagy in obesity promotes ER stress and causes insulin resistance. Cell Metab. 11:467–478. 2010. View Article : Google Scholar : PubMed/NCBI
12	Liu HY, Han J, Cao SY, Hong T, Zhuo D, Shi J, Liu Z and Cao W: Hepatic autophagy is suppressed in the presence of insulin resistance and hyperinsulinemia: Inhibition of FoxO1-dependent expression of key autophagy genes by insulin. J Biol Chem. 284:31484–31492. 2009. View Article : Google Scholar : PubMed/NCBI
13	Czaja MJ: Functions of autophagy in hepatic and pancreatic physiology and disease. Gastroenterology. 140:1895–1908. 2011. View Article : Google Scholar : PubMed/NCBI
14	Koga H, Kaushik S and Cuervo AM: Altered lipid content inhibits autophagic vesicular fusion. FASEB J. 24:3052–3065. 2010. View Article : Google Scholar : PubMed/NCBI
15	Inami Y, Yamashina S, Izumi K, Ueno T, Tanida I, Ikejima K and Watanabe S: Hepatic steatosis inhibits autophagic proteolysis via impairment of autophagosomal acidification and cathepsin expression. Biochem Biophys Res Commun. 412:618–625. 2011. View Article : Google Scholar : PubMed/NCBI
16	Park HW, Park H, Semple IA, Jang I, Ro SH, Kim M, Cazares VA, Stuenkel EL, Kim JJ, Kim JS and Lee JH: Pharmacological correction of obesity-induced autophagy arrest using calcium channel blockers. Nat Commun. 5:48342014. View Article : Google Scholar : PubMed/NCBI
17	Seo YK, Jeon TI, Chong HK, Biesinger J, Xie X and Osborne TF: Genome-wide localization of SREBP-2 in hepatic chromatin predicts a role in autophagy. Cell Metab. 13:367–375. 2011. View Article : Google Scholar : PubMed/NCBI
18	Livak KJ and Schmittgen TD: Analysis of relative gene expression data using real-time quantitative PCR and the 2^−ΔΔ^C T method. Methods. 25:402–408. 2001. View Article : Google Scholar
19	Pan X, Wang P, Luo J, Wang Z, Song Y, Ye J and Hou X: Adipogenic changes of hepatocytes in a high-fat diet-induced fatty liver mice model and non-alcoholic fatty liver disease patients. Endocrine. 48:834–847. 2015. View Article : Google Scholar
20	Choi SE, Lee SM, Lee YJ, Li LJ, Lee SJ, Lee JH, Kim Y, Jun HS, Lee KW and Kang Y: Protective role of autophagy in palmitate-induced INS-1 beta-cell death. Endocrinology. 150:126–134. 2009. View Article : Google Scholar
21	Mei S, Ni HM, Manley S, Bockus A, Kassel KM, Luyendyk JP, Copple BL and Ding WX: Differential roles of unsaturated and saturated fatty acids on autophagy and apoptosis in hepatocytes. J Pharmacol Exp Ther. 339:487–498. 2011. View Article : Google Scholar : PubMed/NCBI
22	Mizushima N, Yoshimori T and Levine B: Methods in mammalian autophagy research. Cell. 140:313–326. 2010. View Article : Google Scholar : PubMed/NCBI
23	Klionsky DJ, Abdelmohsen K, Abe A, Abedin MJ, Abeliovich H, Acevedo Arozena A, Adachi H, Adams CM, Adams PD, Adeli K, et al: Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition). Autophagy. 12:1–222. 2016. View Article : Google Scholar : PubMed/NCBI
24	Jaishy B, Zhang Q, Chung HS, Riehle C, Soto J, Jenkins S, Abel P, Cowart LA, Van Eyk JE and Abel ED: Lipid-induced NOX2 activation inhibits autophagic flux by impairing lysosomal enzyme activity. J Lipid Res. 56:546–561. 2015. View Article : Google Scholar :
25	Osborne TF and Espenshade PJ: Evolutionary conservation and adaptation in the mechanism that regulates SREBP action: What a long, strange tRIP it's been. Genes Dev. 23:2578–2591. 2009. View Article : Google Scholar : PubMed/NCBI
26	Shao W and Espenshade PJ: Expanding roles for SREBP in metabolism. Cell Metab. 16:414–419. 2012. View Article : Google Scholar : PubMed/NCBI
27	Wong TY, Lin SM and Leung LK: The flavone luteolin suppresses SREBP-2 expression and Post-translational activation in hepatic cells. PLoS One. 10:e01356372015. View Article : Google Scholar : PubMed/NCBI
28	Levine B and Kroemer G: Autophagy in the pathogenesis of disease. Cell. 132:27–42. 2008. View Article : Google Scholar : PubMed/NCBI
29	Wang K: Autophagy and apoptosis in liver injury. Cell Cycle. 14:1631–1642. 2015. View Article : Google Scholar : PubMed/NCBI
30	Lavallard VJ and Gual P: Autophagy and non-alcoholic fatty liver disease. Biomed Res Int. 2014:1201792014. View Article : Google Scholar : PubMed/NCBI
31	Mizushima N and Levine B: Autophagy in mammalian development and differentiation. Nat Cell Biol. 12:823–830. 2010. View Article : Google Scholar : PubMed/NCBI
32	Codogno P and Meijer AJ: Autophagy: A potential link between obesity and insulin resistance. Cell Metab. 11:449–451. 2010. View Article : Google Scholar : PubMed/NCBI
33	Tan SH, Shui G, Zhou J, Li JJ, Bay BH, Wenk MR and Shen HM: Induction of autophagy by palmitic acid via protein kinase C-mediated signaling pathway independent of mTOR (mammalian target of rapamycin). J Biol Chem. 287:14364–14376. 2012. View Article : Google Scholar : PubMed/NCBI
34	Ogata M, Hino S, Saito A, Morikawa K, Kondo S, Kanemoto S, Murakami T, Taniguchi M, Tanii I, Yoshinaga K, et al: Autophagy is activated for cell survival after endoplasmic reticulum stress. Mol Cell Biol. 26:9220–9231. 2006. View Article : Google Scholar : PubMed/NCBI
35	Yorimitsu T and Klionsky DJ: Endoplasmic reticulum stress: A new pathway to induce autophagy. Autophagy. 3:160–162. 2007. View Article : Google Scholar : PubMed/NCBI
36	Park M, Sabetski A, Kwan Chan Y, Turdi S and Sweeney G: Palmitate induces ER stress and autophagy in H9c2 cells: Implications for apoptosis and adiponectin resistance. J Cell Physiol. 230:630–639. 2015. View Article : Google Scholar
37	Cai N, Zhao X, Jing Y, Sun K, Jiao S, Chen X, Yang H, Zhou Y and Wei L: Autophagy protects against palmitate-induced apoptosis in hepatocytes. Cell Biosci. 4:282014. View Article : Google Scholar : PubMed/NCBI
38	Liu J, Chang F, Li F, Fu H, Wang J, Zhang S, Zhao J and Yin D: Palmitate promotes autophagy and apoptosis through ROS-dependent JNK and p38 MAPK. Biochem Biophys Res Commun. 463:262–267. 2015. View Article : Google Scholar : PubMed/NCBI
39	Kim KY, Jang HJ, Yang YR, Park KI, Seo J, Shin IW, Jeon TI, Ahn SC, Suh PG, Osborne TF and Seo YK: Corrigendum: SREBP-2/PNPLA8 axis improves non-alcoholic fatty liver disease through activation of autophagy. Sci Rep. 6:357322016. View Article : Google Scholar