Regulating dietary fat absorption may impact progression of nonalcoholic fatty liver disease (NAFLD). Here, we asked if inducible inhibition of chylomicron assembly, as observed in intestine-specific ...microsomal triglyceride (TG) transfer protein knockout mice (Mttp-IKO), could retard NAFLD progression and/or reverse established fibrosis in two dietary models. Mttp-IKO mice fed a methionine/choline-deficient (MCD) diet exhibited reduced hepatic TGs, inflammation, and fibrosis, associated with reduced oxidative stress and downstream activation of c-Jun N-terminal kinase and nuclear factor kappa B signaling pathways. However, when Mttpflox mice were fed an MCD for 5 weeks and then administered tamoxifen to induce Mttp-IKO, hepatic TG was reduced, but inflammation and fibrosis were increased after 10 days of reversal along with adaptive changes in hepatic lipogenic mRNAs. Extending the reversal time, following 5 weeks of MCD feeding to 30 days led to sustained reductions in hepatic TG, but neither inflammation nor fibrosis was decreased, and both intestinal permeability and hepatic lipogenesis were increased. In a second model, similar reductions in hepatic TG were observed when mice were fed a high-fat/high-fructose/high-cholesterol (HFFC) diet for 10 weeks, then switched to chow ± tamoxifen (HFFC → chow) or (HFFC → Mttp-IKO chow), but again neither inflammation nor fibrosis was affected. In conclusion, we found that blocking chylomicron assembly attenuates MCD-induced NAFLD progression by reducing steatosis, oxidative stress, and inflammation. In contrast, blocking chylomicron assembly in the setting of established hepatic steatosis and fibrosis caused increased intestinal permeability and compensatory shifts in hepatic lipogenesis that mitigate resolution of inflammation and fibrogenic signaling despite 50–90-fold reductions in hepatic TG.
Working toward reducing bias in peer review Rye, Kerry-Anne; Davidson, Nicholas O.; Burlingame, Alma L. ...
The Journal of biological chemistry,
10/2021, Letnik:
297, Številka:
4
Journal Article
Crohn's disease (CD) confers an increased risk of nonalcoholic fatty liver disease (NAFLD), but the pathogenesis remains poorly understood. We determined if active intestinal inflammation increases ...the risk of NAFLD in patients with CD.
Two cohorts (2017/2018 and 2020) with CD and no known liver disease were enrolled consecutively during staging magnetic resonance enterography. We quantified proton density fat fraction, MaRIA (Magnetic Resonance Index of Activity), and visceral adipose tissue. NAFLD was diagnosed when proton density fat fraction ≥5.5%. Synchronous endoscopy was graded by the Simple Endoscopic Score for CD and Rutgeerts score, while clinical activity was graded by the Harvey-Bradshaw index. Cytokine profiling was performed for the 2020 cohort. Transient elastography and liver biopsy were requested by standard of care.
NAFLD was diagnosed in 40% (n = 144 of 363), with higher prevalence during radiographically quiescent disease (odds ratio, 1.7; P = .01), independent of body mass index/visceral adipose tissue (adjusted odds ratio, 7.8; P = .03). These findings were corroborated by endoscopic disease activity, but not by aggregate clinical symptoms. Circulating interleukin-8 was independent of body mass index to predict NAFLD, but traditional proinflammatory cytokines were not. NAFLD subjects had similar liver stiffness estimates regardless of CD activity. Definitive or borderline steatohepatitis was present in most patients that underwent liver biopsy.
Quiescent CD is associated with risk of NAFLD. These findings suggest potentially distinct pathogenic mechanisms of NAFLD in patients with CD compared with the prevailing leaky gut hypothesis proposed for individuals without inflammatory bowel disease. Future validation and mechanistic studies are needed to dissect these distinct disease modifying factors.
Activation of hepatic stellate cells (HSCs) is crucial to the development of fibrosis in nonalcoholic fatty liver disease. Quiescent HSCs contain lipid droplets (LDs), whose depletion upon activation ...induces a fibrogenic gene program. Here we show that liver fatty acid‐binding protein (L‐Fabp), an abundant cytosolic protein that modulates fatty acid (FA) metabolism in enterocytes and hepatocytes, also modulates HSC FA utilization and in turn regulates the fibrogenic program. L‐Fabp expression decreased 10‐fold following HSC activation, concomitant with depletion of LDs. Primary HSCs isolated from L‐FABP−/− mice contain fewer LDs than wild‐type (WT) HSCs, and exhibit up‐regulated expression of genes involved in HSC activation. Adenoviral L‐Fabp transduction inhibited activation of passaged WT HSCs and increased both the expression of prolipogenic genes and also augmented intracellular lipid accumulation, including triglyceride and FA, predominantly palmitate. Freshly isolated HSCs from L‐FABP−/− mice correspondingly exhibited decreased palmitate in the free FA pool. To investigate whether L‐FABP deletion promotes HSC activation in vivo, we fed L‐FABP−/− and WT mice a high‐fat diet supplemented with trans‐fatty acids and fructose (TFF). TFF‐fed L‐FABP−/− mice exhibited reduced hepatic steatosis along with decreased LD abundance and size compared to WT mice. In addition, TFF‐fed L‐FABP−/− mice exhibited decreased hepatic fibrosis, with reduced expression of fibrogenic genes, compared to WT mice. Conclusion: L‐FABP deletion attenuates both diet‐induced hepatic steatosis and fibrogenesis, despite the observation that L‐Fabp paradoxically promotes FA and LD accumulation and inhibits HSC activation in vitro. These findings highlight the importance of cell‐specific modulation of hepatic lipid metabolism in promoting fibrogenesis in nonalcoholic fatty liver disease. (Hepatology 2013)
Liver fatty acid–binding protein (L‐Fabp) regulates murine hepatic fatty acid trafficking in response to fasting. In this study, we show that L‐Fabp−/− mice fed a high‐fat Western diet for up to 18 ...weeks are less obese and accumulate less hepatic triglyceride than C57BL/6J controls. Paradoxically, both control and L‐Fabp−/− mice manifested comparable glucose intolerance and insulin resistance when fed a Western diet. Protection against obesity in Western diet–fed L‐Fabp−/− mice was not due to discernable changes in food intake, fat malabsorption, or heat production, although intestinal lipid secretion kinetics were significantly slower in both chow‐fed and Western diet–fed L‐Fabp−/− mice. By contrast, there was a significant increase in the respiratory exchange ratio in L‐Fabp−/− mice, suggesting a shift in energy substrate use from fat to carbohydrate, findings supported by an approximately threefold increase in serum lactate. Microarray analysis revealed increased expression of genes involved in lipid synthesis (fatty acid synthase, squalene epoxidase, hydroxy‐methylglutaryl coenzyme A reductase), while genes involved in glycolysis (glucokinase and glycerol kinase) were decreased in L‐Fabp−/− mice. Fatty acid synthase expression was also increased in the skeletal muscle of L‐Fabp−/− mice. In conclusion, L‐Fabp may function as a metabolic sensor in regulating lipid homeostasis. We suggest that L‐Fabp−/− mice are protected against Western diet–induced obesity and hepatic steatosis through a series of adaptations in both hepatic and extrahepatic energy substrate use. (HEPATOLOGY 2006;44:1191–1205.)
Adipose TG lipase (ATGL) catalyzes the rate-limiting step in TG hydrolysis in most tissues. We have shown that hepatic ATGL preferentially channels hydrolyzed FAs to β-oxidation and induces PPAR-α ...signaling. Previous studies have suggested that liver FA binding protein (L-FABP) transports FAs from lipid droplets to the nucleus for ligand delivery and to the mitochondria for β-oxidation. To determine if L-FABP is involved in ATGL-mediated FA channeling, we used adenovirus-mediated suppression or overexpression of hepatic ATGL in either WT or L-FABP KO mice. Hepatic ATGL knockdown increased liver weight and TG content of overnight fasted mice regardless of genotype. L-FABP deletion did not impair the effects of ATGL overexpression on the oxidation of hydrolyzed FAs in primary hepatocyte cultures or on serum β-hydroxybutyrate concentrations in vivo. Moreover, L-FABP deletion did not influence the effects of ATGL knockdown or overexpression on PPAR-α target gene expression. Taken together, we conclude that L-FABP is not required to channel ATGL-hydrolyzed FAs to mitochondria for β-oxidation or the nucleus for PPAR-α regulation.
ANGPTL3 (angiopoietin-like 3) is a therapeutic target for reducing plasma levels of triglycerides and low-density lipoprotein cholesterol. A recent trial with vupanorsen, an antisense oligonucleotide ...targeting hepatic production of ANGPTL3, reported a dose-dependent increase in hepatic fat. It is unclear whether this adverse effect is due to an on-target effect of inhibiting hepatic ANGPTL3.
We recruited participants with ANGPTL3 deficiency related to
loss-of-function (LoF) mutations, along with wild-type (WT) participants from 2 previously characterized cohorts located in Campodimele, Italy, and St. Louis, MO. Magnetic resonance spectroscopy and magnetic resonance proton density fat fraction were performed to measure hepatic fat fraction and the distribution of extrahepatic fat. To estimate the causal relationship between ANGPTL3 and hepatic fat, we generated a genetic instrument of plasma ANGPTL3 levels as a surrogate for hepatic protein synthesis and performed Mendelian randomization analyses with hepatic fat in the UK Biobank study.
We recruited participants with complete (n=6) or partial (n=32) ANGPTL3 deficiency related to
LoF mutations, as well as WT participants (n=92) without LoF mutations. Participants with ANGPTL3 deficiency exhibited significantly lower total cholesterol (complete deficiency, 78.5 mg/dL; partial deficiency, 172 mg/dL; WT, 188 mg/dL;
<0.05 for both deficiency groups compared with WT), along with plasma triglycerides (complete deficiency, 26 mg/dL; partial deficiency, 79 mg/dL; WT, 88 mg/dL;
<0.05 for both deficiency groups compared with WT) without any significant difference in hepatic fat (complete deficiency, 9.8%; partial deficiency, 10.1%; WT, 9.9%;
>0.05 for both deficiency groups compared with WT) or severity of hepatic steatosis as assessed by magnetic resonance imaging. In addition, ANGPTL3 deficiency did not alter the distribution of extrahepatic fat. Results from Mendelian randomization analyses in 36 703 participants from the UK Biobank demonstrated that genetically determined ANGPTL3 plasma protein levels were causally associated with low-density lipoprotein cholesterol (
=1.7×10
) and triglycerides (
=3.2×10
) but not with hepatic fat (
=0.22).
ANGPTL3 deficiency related to LoF mutations in
, as well as genetically determined reduction of plasma ANGPTL3 levels, is not associated with hepatic steatosis. Therapeutic approaches to inhibit ANGPTL3 production in hepatocytes are not necessarily expected to result in the increased risk for hepatic steatosis that was observed with vupanorsen.
Mice exposed in gestation to maternal high-fat/high-sucrose (HF/HS) diet develop altered bile acid (BA) homeostasis. We hypothesized that these reflect an altered microbiome and asked if microbiota ...transplanted from HF/HS offspring change hepatic BA and lipid metabolism to determine the directionality of effect. Female mice were fed HF/HS or chow (CON) for 6 wk and bred with lean males. 16S sequencing was performed to compare taxa in offspring. Cecal microbiome transplantation (CMT) was performed from HF/HS or CON offspring into antibiotic-treated mice fed chow or high fructose. BA, lipid metabolic, and gene expression analyses were performed in recipient mice. Gut microbiomes from HF/HS offspring segregated from CON offspring, with increased Firmicutes to Bacteriodetes ratios and Verrucomicrobial abundance. After CMT was performed, HF/HS-recipient mice had larger BA pools, increased intrahepatic muricholic acid, and decreased deoxycholic acid species. HF/HS-recipient mice exhibited downregulated hepatic
, increased hepatic
and decreased ileal
mRNA expression. HF/HS-recipient mice exhibited decreased cecal butyrate and increased hepatic expression of
. HF/HS-recipient mice had larger livers and increased intrahepatic triglyceride versus CON-recipient mice after fructose feeding, with increased hepatic mRNA expression of lipogenic genes including
and
CMT from HF/HS offspring increased BA pool and shifted the composition of the intrahepatic BA pool. CMT from HF/HS donor offspring increased fructose-induced liver triglyceride accumulation. These findings support a causal role for vertical transfer of an altered microbiome in hepatic BA and lipid metabolism in HF/HS offspring.
We utilized a mouse model of maternal obesogenic diet exposure to evaluate the effect on offspring microbiome and bile acid homeostasis. We identified shifts in the offspring microbiome associated with changes in cecal bile acid levels. Transfer of the microbiome from maternal obesogenic diet-exposed offspring to microbiome-depleted mice altered bile acid homeostasis and increased fructose-induced hepatic steatosis.
The unfolded protein response (UPR) is a complex adaptive signaling pathway activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). ER stress (ERS) triggers a cascade ...of responses that converge upon C/EBP homologous protein (CHOP) to drive inflammation and apoptosis. Herein, we sought to determine whether liver injury and fibrosis after small bowel resection (SBR) were mediated by a maladaptive hepatic ERS/UPR. C57BL/6 mice underwent 50% proximal SBR or sham operation. Markers of liver injury and UPR/ERS pathways were analyzed. These were compared with experimental groups including dietary fat manipulation, tauroursodeoxycholic acid (TUDCA) treatment, distal SBR, and global CHOP knockout (KO). At 10 wk, proximal SBR had elevated alanine aminotransferase/aspartate aminotransferase (ALT/AST) (
< 0.005) and greater hepatic tumor necrosis factor-α (TNFα) (
= 0.001) and collagen type 1 α1 (COL1A1) (
= 0.02) than shams. SBR livers had increased CHOP and p-eIF2α, but were absent in activating transcription factor 4 (ATF4) protein expression. Low-fat diet (LFD), TUDCA, and distal SBR groups had decreased liver enzymes, inflammation, and fibrosis (
< 0.05). Importantly, they demonstrated reversal of hepatic UPR with diminished CHOP and robust ATF4 signal. CHOP KO-SBR had decreased ALT but not AST compared with wild-type (WT)-SBR (
= 0.01,
= 0.12). There were no differences in TNFα and COL1A1 (
= 0.09,
= 0.50). SBR-induced liver injury, fibrosis is associated with a novel hepatic UPR/ERS response characterized by increased CHOP and decreased ATF4. LFD, TUDCA, and ileocecal resection rescued the hepatic phenotype and reversed the UPR pattern. Global CHOP KO only partially attenuated liver injury. This underscores the significance of disruptions to the gut/liver axis after SBR and potentiates targets to mitigate the progression of intestinal failure-associated liver disease.
The unfolded protein response (UPR) is a complex signaling cascade that converges upon C/EBP-homologous protein (CHOP). Under conditions of chronic cellular stress, the UPR shifts from homeostatic to proapoptotic leading to inflammation and cell death. Here, we provide evidence that small bowel resection-induced liver injury and fibrosis are mediated by a maladaptive hepatic UPR. Low-fat diet, TUDCA treatment, and ileocecal resection rescued the hepatic phenotype and reversed the UPR pattern.
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