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 5

Comprehensive lipidomic analyses identified altered phospholipid composition in PTEN/SCAPΔL mice.

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Comprehensive lipidomic analyses identified altered phospholipid composi...
(A) Liver FA contents of 5-week-old WT, PTENΔL, SCAPΔL, and PTEN/SCAPΔL mice analyzed by GC-MS. Data are expressed as fold changes relative to the average in WT mice (n = 3 per group). *P < 0.05, WT versus PTENΔL; †P < 0.05, PTENΔL versus PTEN/SCAPΔL; ‡P < 0.05, SCAPΔL versus PTEN/SCAPΔL. Right panel shows enlargement of the lower range of the data. (B) Relative expression levels of lipogenesis genes determined by RNA-Seq. (C) Hierarchical clustering analyses of LC-MS results for liver tissues from 5-week-old WT, PTENΔL, SCAPΔL, and PTEN/SCAPΔL mice. Bar graph shows relative amounts of PC species (n = 3 per group). *P < 0.05 compared with WT mice. (D) ER fractions extracted from 3 livers of 5-week-old WT or PTEN/SCAPΔL mice were pooled and analyzed for FA composition of PCs using LC-MS. (E) Model of membrane fluidity. A double bond in the unsaturated FA results in a bend in the string of carbon that gives the ER membrane a fluid character. (F) Primary hepatocytes isolated from Ptenfl/fl/Scapfl/fl mice were infected with Ad-Cont or Ad-Cre, and PTEN/SCAPΔ/Δ hepatocytes were treated with ER-targeting liposomes enriched for PC(16:0_20:4) and PC(18:0_20:4) or saline (control). At 96 hours, the indicated proteins were assessed by WB. (G–I) We orally administered a PC cocktail or vehicle to 4-week-old PTEN/SCAPΔL mice once daily; liver injury was assessed 1 week later. (G) H&E images of livers. Scale bars: 100 μm. (H) ALT and ALP serum levels (means ± SEM, n = 7 per group). *P < 0.05. (I) WB analysis of CHOP protein in the liver. Statistical data were assessed using 1-way ANOVA with Tukey’s multiple comparison test (A), Dunnett’s test (C), and Student’s t test (H).