Tools have been developed to determine risk for nonalcoholic fatty liver disease (NAFLD) based on imaging, which does not always detect early-grade hepatic steatosis. We aimed to develop a tool to ...identify patients with NAFLD using
H MR spectroscopy (MRS).
We collected data from the Dallas Heart Study-a multiethnic, population-based, probability study of adults (18-65 y) that comprised an in-home medical survey; collection of fasting blood samples; MRS images to measure cardiac mass/function, abdominal subcutaneous/visceral adiposity; and quantification of hepatic triglyceride concentration, from 2000 through 2009. NAFLD were defined as 5.5% or more liver fat and we excluded patients with more than moderate alcohol use; 737 patients were included in the final analysis. We performed binary multivariable logistic regression analysis to develop a tool to identify patients with NAFLD and evaluate interactions among variables. We performed an internal validation analysis using 10-fold cross validation.
We developed the Dallas Steatosis Index (DSI) to identify patients with NAFLD based on level of alanine aminotransferase, body mass index, age, sex, levels of triglycerides and glucose, diabetes, hypertension, and ethnicity. The DSI discriminated between patients with vs without NAFLD with a C-statistic of 0.824. The DSI outperformed 4 risk analysis tools, based on net reclassification improvement and decision curve analysis.
We developed an index, called the DSI, which accurately identifies patients with NAFLD based on MRS data. The DSI requires external validation, but might be used in development NAFLD screening programs, in monitoring progression of hepatic steatosis, and in epidemiology studies.
Differentiated cells can re-enter the cell cycle to repair tissue damage via a series of discrete morphological and molecular stages coordinated by the cellular energetics regulator mTORC1. We ...previously proposed the term “paligenosis” to describe this conserved cellular regeneration program. Here, we detail a molecular network regulating mTORC1 during paligenosis in both mouse pancreatic acinar and gastric chief cells. DDIT4 initially suppresses mTORC1 to induce autodegradation of differentiated cell components and damaged organelles. Later in paligenosis, IFRD1 suppresses p53 accumulation. Ifrd1−/− cells do not complete paligenosis because persistent p53 prevents mTORC1 reactivation and cell proliferation. Ddit4−/− cells never suppress mTORC1 and bypass the IFRD1 checkpoint on proliferation. Previous reports and our current data implicate DDIT4/IFRD1 in governing paligenosis in multiple organs and species. Thus, we propose that an evolutionarily conserved, dedicated molecular network has evolved to allow differentiated cells to re-enter the cell cycle (i.e., undergo paligenosis) after tissue injury.
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•Dedicated genes govern paligenosis, a conserved cellular regeneration program•DDIT4 first blocks mTORC1, inducing massive autophagy to downscale the cell•p53 activation continues mTORC1 suppression to maintain cell quiescence•IFRD1 suppresses p53 to reinduce mTORC1 and license progression into the cell cycle
During regeneration or tumorigenesis, differentiated cells use an evolutionarily conserved program (paligenosis) to reprogram their metabolism and readopt a progenitor state. Miao et al. identify dedicated paligenosis genes: DDIT4 suppresses mTORC1 to induce massive autophagy that dismantles differentiated cell architecture, then IFRD1 derepresses mTORC1, licensing the dedifferentiated cell to proliferate.
Ethanol-mediated injury, combined with gut-derived lipopolysaccharide (LPS), provokes generation of proinflammatory cytokines in Kupffer cells, causing hepatic inflammation. Among the mediators of ...these effects, miR-217 aggravates ethanol-induced steatosis in hepatocytes. However, the role of miR-217 in ethanol-induced liver inflammation process is unknown. Here, we examined the role of miR-217 in the responses to ethanol, LPS, or a combination of ethanol and LPS in RAW 264.7 macrophages and in primary Kupffer cells. In macrophages, ethanol substantially exacerbated LPS-mediated induction of miR-217 and production of proinflammatory cytokines compared with LPS or ethanol alone. Consistently, ethanol administration to mice led to increases in miR-217 abundance and increased production of inflammatory cytokines in isolated primary Kupffer cells exposed to the combination of ethanol and LPS. miR-217 promoted combined ethanol and LPS-mediated inhibition of sirtuin 1 expression and activity in macrophages. Moreover, miR-217–mediated sirtuin 1 inhibition was accompanied by increased activities of two vital inflammatory regulators, NF-κB and the nuclear factor of activated T cells c4. Finally, adenovirus-mediated overexpression of miR-217 led to steatosis and inflammation in mice. These findings suggest that miR-217 is a pivotal regulator involved in ethanol-induced hepatic inflammation. Strategies to inhibit hepatic miR-217 could be a viable approach in attenuating alcoholic hepatitis.
Background and Aims
Human transmembrane 6 superfamily 2 (TM6SF2) variant rs58542926 is associated with NAFLD and HCC. However, conflicting reports in germline Tm6sf2 knockout mice suggest no change ...or decreased very low density lipoprotein (VLDL) secretion and either unchanged or increased hepatic steatosis, with no increased fibrosis. We generated liver‐specific Tm6Sf2 knockout mice (Tm6 LKO) to study VLDL secretion and the impact on development and progression of NAFLD.
Approach and Results
Two independent lines of Tm6 LKO mice exhibited spontaneous hepatic steatosis. Targeted lipidomic analyses showed increased triglyceride species whose distribution and abundance phenocopied findings in mice with liver‐specific deletion of microsomal triglyceride transfer protein. The VLDL triglyceride secretion was reduced with small, underlipidated particles and unchanged or increased apolipoprotein B. Liver‐specific adeno‐associated viral, serotype 8 (AAV8) rescue using either wild‐type or mutant E167K‐Tm6 reduced hepatic steatosis and improved VLDL secretion. The Tm6 LKO mice fed a high milk‐fat diet for 3 weeks exhibited increased steatosis and fibrosis, and those phenotypes were further exacerbated when mice were fed fibrogenic, high fat/fructose diets for 20 weeks. In two models of HCC, either neonatal mice injected with streptozotocin (NASH/STAM) and high‐fat fed or with diethylnitrosamine injection plus fibrogenic diet feeding, Tm6 LKO mice exhibited increased steatosis, greater tumor burden, and increased tumor area versus Tm6 flox controls. Additionally, diethylnitrosamine‐injected and fibrogenic diet–fed Tm6 LKO mice administered wild‐type Tm6 or E167K‐mutant Tm6 AAV8 revealed significant tumor attenuation, with tumor burden inversely correlated with Tm6 protein levels.
Conclusions
Liver‐specific Tm6sf2 deletion impairs VLDL secretion, promoting hepatic steatosis, fibrosis, and accelerated development of HCC, which was mitigated with AAV8‐ mediated rescue.
The mechanisms by which mucosal homeostasis is maintained are of central importance to inflammatory bowel disease. Critical to these processes is the intestinal epithelial cell (IEC), which regulates ...immune responses at the interface between the commensal microbiota and the host. CD1d presents self and microbial lipid antigens to natural killer T (NKT) cells, which are involved in the pathogenesis of colitis in animal models and human inflammatory bowel disease. As CD1d crosslinking on model IECs results in the production of the important regulatory cytokine interleukin (IL)-10 (ref. 9), decreased epithelial CD1d expression--as observed in inflammatory bowel disease--may contribute substantially to intestinal inflammation. Here we show in mice that whereas bone-marrow-derived CD1d signals contribute to NKT-cell-mediated intestinal inflammation, engagement of epithelial CD1d elicits protective effects through the activation of STAT3 and STAT3-dependent transcription of IL-10, heat shock protein 110 (HSP110; also known as HSP105), and CD1d itself. All of these epithelial elements are critically involved in controlling CD1d-mediated intestinal inflammation. This is demonstrated by severe NKT-cell-mediated colitis upon IEC-specific deletion of IL-10, CD1d, and its critical regulator microsomal triglyceride transfer protein (MTP), as well as deletion of HSP110 in the radioresistant compartment. Our studies thus uncover a novel pathway of IEC-dependent regulation of mucosal homeostasis and highlight a critical role of IL-10 in the intestinal epithelium, with broad implications for diseases such as inflammatory bowel disease.
Human and animal model data show that maternal obesity promotes nonalcoholic fatty liver disease in offspring and alters bile acid (BA) homeostasis. Here we investigated whether offspring exposed to ...maternal obesogenic diets exhibited greater cholestatic injury. We fed female C57Bl6 mice conventional chow (CON) or high fat/high sucrose (HF/HS) diet and then bred them with lean males. Offspring were fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) for 2 weeks to induce cholestasis, and a subgroup was then fed CON for an additional 10 days. Additionally, to evaluate the role of the gut microbiome, we fed antibiotic-treated mice cecal contents from CON or HF/HS offspring, followed by DDC for 2 weeks. We found that HF/HS offspring fed DDC exhibited increased fine branching of the bile duct (ductular reaction) and fibrosis but did not differ in BA pool size or intrahepatic BA profile compared to offspring of mice fed CON. We also found that after 10 days recovery, HF/HS offspring exhibited sustained ductular reaction and periportal fibrosis, while lesions in CON offspring were resolved. In addition, cecal microbiome transplant from HF/HS offspring donors worsened ductular reaction, inflammation, and fibrosis in mice fed DDC. Finally, transfer of the microbiome from HF/HS offspring replicated the cholestatic liver injury phenotype. Taken together, we conclude that maternal HF/HS diet predisposes offspring to increased cholestatic injury after DDC feeding and delays recovery after returning to CON diets. These findings highlight the impact of maternal obesogenic diet on hepatobiliary injury and repair pathways during experimental cholestasis.
RNA editing encompasses a post-transcriptional process in which the genomically templated sequence is enzymatically altered and introduces a modified base into the edited transcript. Mammalian C-to-U ...RNA editing represents a distinct subtype of base modification, whose prototype is intestinal apolipoprotein B mRNA, mediated by the catalytic deaminase Apobec-1. However, the genome-wide identification, tissue-specificity and functional implications of Apobec-1-mediated C-to-U RNA editing remain incompletely explored.
Deep sequencing, data filtering and Sanger-sequence validation of intestinal and hepatic RNA from wild-type and Apobec-1-deficient mice revealed 56 novel editing sites in 54 intestinal mRNAs and 22 novel sites in 17 liver mRNAs, all within 3' untranslated regions. Eleven of 17 liver RNAs shared editing sites with intestinal RNAs, while 6 sites are unique to liver. Changes in RNA editing lead to corresponding changes in intestinal mRNA and protein levels for 11 genes. Analysis of RNA editing in vivo following tissue-specific Apobec-1 adenoviral or transgenic Apobec-1 overexpression reveals that a subset of targets identified in wild-type mice are restored in Apobec-1-deficient mouse intestine and liver following Apobec-1 rescue. We find distinctive polysome profiles for several RNA editing targets and demonstrate novel exonic editing sites in nuclear preparations from intestine but not hepatic apolipoprotein B RNA. RNA editing is validated using cell-free extracts from wild-type but not Apobec-1-deficient mice, demonstrating that Apobec-1 is required.
These studies define selective, tissue-specific targets of Apobec-1-dependent RNA editing and show the functional consequences of editing are both transcript- and tissue-specific.
Mammalian C to U RNA is mediated by APOBEC1, the catalytic deaminase, together with RNA binding cofactors (including A1CF and RBM47) whose relative physiological requirements are unresolved. Although ...A1CF complements APOBEC1 for in vitro RNA editing,
mice exhibited no change in apolipoproteinB (apoB) RNA editing, while
mutant mice exhibited impaired intestinal RNA editing of apoB as well as other targets. Here we examined the role of A1CF and RBM47 in adult mouse liver and intestine, following deletion of either one or both gene products and also following forced (liver or intestinal) transgenic A1CF expression. There were minimal changes in hepatic and intestinal apoB RNA editing in
mice and no changes in either liver- or intestine-specific A1CF transgenic mice.
liver-specific knockout (
) mice demonstrated reduced editing in a subset (11 of 20) of RNA targets, including apoB. By contrast, apoB RNA editing was virtually eliminated (<6% activity) in intestine-specific (
) mice with only five of 53 targets exhibiting C-to-U RNA editing. Double knockout of
and
in liver (
) eliminated apoB RNA editing and reduced editing in the majority of other targets, with no changes following adenoviral APOBEC1 administration. Intestinal double knockout mice (
) demonstrated further reduced editing (<10% activity) in four of five of the residual APOBEC1 targets identified in
mice. These data suggest that A1CF and RBM47 each function independently, yet interact in a tissue-specific manner, to regulate the activity and site selection of APOBEC1 dependent C-to-U RNA editing.
Background
Genetic mutations causing defective VLDL secretion and low LDL cholesterol are associated with hepatic steatosis and nonalcoholic fatty liver disease (NAFLD).
Aims
Determine if low LDL ...cholesterol (< 5th percentile) was an independent predictor of hepatic steatosis.
Methods
Secondary data analysis of the Dallas Heart study (an urban, multiethnic, probability-based sample), we defined hepatic steatosis utilizing intrahepatic triglyceride (IHTG) analyzed using magnetic resonance spectroscopy in conjunction and available demographic, serological and genetic information. We exclude patients on lipid lowering medications.
Results
Of the 2094 subjects that met our exclusion criteria, 86 had a low LDL cholesterol, of whom 19 (22%) exhibited hepatic steatosis. After matching for age, sex, BMI, and alcohol consumption, low LDL cholesterol was not a risk factor for hepatic steatosis compared to those with normal (50–180 mg/dL) or high (> 180 mg/dL) LDL. When analyzed as a continuous variable, we observed lower IHTG in the low LDL group compared to the normal or high LDL groups (2.2%, 3.5%, 4.6%; all pairwise comparisons p < 0.001). Subjects with both hepatic steatosis and low LDL cholesterol exhibited a more favorable lipid profile but similar insulin resistance and hepatic fibrosis risk compared to other subjects with hepatic steatosis. The distribution of variant alleles associated with NAFLD, including PNPLA3, GCKR, and MTTP was indistinguishable between subjects with hepatic steatosis and low versus high LDL cholesterol.
Conclusion
These findings suggest that low serum LDL levels are not a useful predictor of hepatic steatosis and NAFLD. Moreover, subjects with low LDL exhibit a more favorable lipid profile and lower IHTG.
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