Gastroenterology

Gastroenterology

Volume 134, Issue 2, February 2008, Pages 568-576
Gastroenterology

Basic–Liver, Pancreas, and Biliary Tract
Activation and Dysregulation of the Unfolded Protein Response in Nonalcoholic Fatty Liver Disease

This work has been presented, in partial form, at the annual meeting of the American Association for Study of Liver Diseases in Boston, October 2006.
https://doi.org/10.1053/j.gastro.2007.10.039Get rights and content

Background & Aims: Nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) are associated with known triggers of the unfolded protein response (UPR). The aims were to (1) evaluate the activity of UPR in NAFL and NASH and (2) correlate expression of UPR pathways with liver histology. Methods: Messenger RNA (mRNA) and protein expression were measured by quantitative real-time PCR and Western blot, respectively. Apoptosis was assessed by TUNEL assay. Liver histology was scored using the NASH clinical research network criteria. Results: Compared with subjects with the metabolic syndrome and normal liver histology (n = 17), both NAFL (n = 21) and NASH (n = 21) were associated with increased eukaryotic initiation factor-2α (eIF-2α) phosphorylation. Activating transcription factor 4 (ATF4) mRNA and protein, C/EBP homologous protein (CHOP), and growth arrest, DNA damage-34 (GADD34) mRNA were not increased in NAFL or NASH. Whereas immunoglobulin heavy chain binding protein mRNA was significantly increased in NASH, unspliced X-box protein-1 (XBP-1) protein did not increase. Also, endoplasmic reticulum degradation-enhancing α-mannosidase-like protein mRNA levels were inversely related to spliced XBP-1 mRNA in NASH. NASH was specifically associated with low sXBP-1 protein and increased JNK phosphorylation. This correlated with increased TUNEL activity in NASH. The histologic severity correlated with sXBP-1 mRNA and JNK phosphorylation. Conclusions: There is a variable degree of UPR activation in NAFL and NASH. Although both NAFL and NASH are associated with eIF-2α phosphorylation, there is a failure to activate downstream recovery pathways, ie, ATF4-CHOP-GADD34. NASH is specifically associated with (1) failure to generate sXBP-1 protein and (2) activation of JNK.

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Study Cohort

Consecutive subjects who were referred for either obesity management or suspected NAFLD were screened for this study. All subjects underwent routine clinical assessment and radiologic, hematologic, biochemical, and serologic testing. The metabolic syndrome was diagnosed using the Adult Treatment Panel III criteria.19 Alcohol consumption was assessed clinically and considered to be significant when >20 g/day for females and >30 g/day for males. All subjects were tested for hepatitis B and C,

Results

A total of 89 subjects were screened: 59 subjects were enrolled (controls [normal histology + normal ALT] = 17, NAFL = 21, and NASH = 21). The reasons for exclusion included refusal to consent (n = 17), insufficient amount of tissue for experimental studies (n = 9), and alanine aminotransferse (ALT) elevation in those with normal histology (n = 4). The baseline characteristics of the study population are shown in Table 2. The 3 groups were comparable with respect to gender, ethnicity, and

Discussion

The delicate balance between a cell’s synthetic needs and the ability of the ER to meet these demands is an important determinant of whether a given cell lives or dies. Perturbation of this balance triggers the UPR, which can either correct the imbalance and help the cell adapt or condemns the cell to death.6 In this study, we demonstrate that there is activation of the UPR in both NAFL and NASH. However, NASH is distinguished from NAFL subjects and controls with the metabolic syndrome and

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    Supported in part by grants K24 DK 02755-07, T32 DK 007150-32, and RO1 56331 (to A.J.S.) from the National Institutes of Health.

    This work was fully approved by the IRB of the VCU Medical Center (IRB No. 04286).

    No conflicts of interest exist.

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