Inhibiting SCAP/SREBP exacerbates liver injury and carcinogenesis in murine nonalcoholic steatohepatitis
Satoshi Kawamura, … , Kazuhiko Koike, Hayato Nakagawa
Satoshi Kawamura, … , Kazuhiko Koike, Hayato Nakagawa
Published April 5, 2022
Citation Information: J Clin Invest. 2022;132(11):e151895. https://doi.org/10.1172/JCI151895.
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Research Article Gastroenterology

Inhibiting SCAP/SREBP exacerbates liver injury and carcinogenesis in murine nonalcoholic steatohepatitis

Abstract

Enhanced de novo lipogenesis mediated by sterol regulatory element–binding proteins (SREBPs) is thought to be involved in nonalcoholic steatohepatitis (NASH) pathogenesis. In this study, we assessed the impact of SREBP inhibition on NASH and liver cancer development in murine models. Unexpectedly, SREBP inhibition via deletion of the SREBP cleavage–activating protein (SCAP) in the liver exacerbated liver injury, fibrosis, and carcinogenesis despite markedly reduced hepatic steatosis. These phenotypes were ameliorated by restoring SREBP function. Transcriptome and lipidome analyses revealed that SCAP/SREBP pathway inhibition altered the fatty acid (FA) composition of phosphatidylcholines due to both impaired FA synthesis and disorganized FA incorporation into phosphatidylcholine via lysophosphatidylcholine acyltransferase 3 (LPCAT3) downregulation, which led to endoplasmic reticulum (ER) stress and hepatocyte injury. Supplementation with phosphatidylcholines significantly improved liver injury and ER stress induced by SCAP deletion. The activity of the SCAP/SREBP/LPCAT3 axis was found to be inversely associated with liver fibrosis severity in human NASH. SREBP inhibition also cooperated with impaired autophagy to trigger liver injury. Thus, excessively strong and broad lipogenesis inhibition was counterproductive for NASH therapy; this will have important clinical implications in NASH treatment.

Authors

Satoshi Kawamura, Yuki Matsushita, Shigeyuki Kurosaki, Mizuki Tange, Naoto Fujiwara, Yuki Hayata, Yoku Hayakawa, Nobumi Suzuki, Masahiro Hata, Mayo Tsuboi, Takahiro Kishikawa, Hiroto Kinoshita, Takuma Nakatsuka, Masaya Sato, Yotaro Kudo, Yujin Hoshida, Atsushi Umemura, Akiko Eguchi, Tsuneo Ikenoue, Yoshihiro Hirata, Motonari Uesugi, Ryosuke Tateishi, Keisuke Tateishi, Mitsuhiro Fujishiro, Kazuhiko Koike, Hayato Nakagawa

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Figure 4

ER stress is involved in liver injury in PTEN/SCAPΔL mice.

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ER stress is involved in liver injury in PTEN/SCAPΔL mice. (A) Pathway a...
(A) Pathway analysis of RNA-Seq data. Pathways upregulated in 5-week-old PTEN/SCAPΔL mouse livers are shown. (B) Relative expression levels of ER stress–responsive genes involved in cell death determined by RNA-Seq. Data are expressed as log2 ratio compared with WT mice. (C) Relative expression levels of genes indicated in B were analyzed using real-time PCR (n = 6 per group). (D and E) WB analyses of ER stress markers (D) and IHC images of CHOP (E) for livers of 5-week-old WT, PTENΔL, SCAPΔL, and PTEN/SCAPΔL mice. Scale bars: 100 μm. (F) Primary hepatocytes isolated from Ptenfl/fl/Scapfl/fl mice were infected with Ad-Cont or Ad-Cre. The indicated proteins were assessed by WB 96 hours after infection. (G and H) At 24 hours after infection of Ptenfl/fl/Scapfl/fl hepatocytes with Ad-Cont or Ad-Cre, culture media were changed to normal FBS media, moderately delipidated FBS (30% lipid compared with normal FBS), or completely delipidated FBS (0% lipid). At 72 hours, expression levels of indicated proteins were determined by WB analyses (G). At 96 hours, cell death was assessed using the Cell Death Detection ELISA Kit (n = 4 per group) (H). (I–K) Effects of GRP78 overexpression in PTEN/SCAPΔL mouse livers. We intravenously injected 4-week-old PTEN/SCAPΔL mice with 1 × 109 PFU of Ad-Cont or Ad-GRP78. One week later, liver injury was assessed by H&E staining. (I) and serum ALT (Ad-Cont, n = 3; Ad-GRP78, n = 6) (J). Scale bars: 100 μm. Expression levels of GRP78 and CHOP in the liver were determined by WB analyses (K). Statistical data were assessed using 1-way ANOVA with Tukey’s multiple comparisons test (C) or Student’s t test (H and J). Data are presented as mean ± SEM. *P < 0.05.