Liver fatty acid binding protein (L‐Fabp) modulates lipid trafficking in enterocytes, hepatocytes, and hepatic stellate cells (HSCs). We examined hepatocyte vs. HSC L‐Fabp deletion in hepatic metabolic adaptation and fibrotic injury. Floxed L‐Fabp mice were bred to different transgenic Cre mice or injected with adeno‐associated virus type 8 (AAV8) Cre and fed diets to promote steatosis and fibrosis or were subjected to either bile duct ligation or CCl4 injury. Albumin‐Cre‐mediated L‐Fabp deletion revealed recombination in hepatocytes and HSCs; these findings were confirmed with 2 other floxed alleles. Glial fibrillary acid protein‐Cre and platelet‐derived growth factor receptor β‐Cre‐mediated L‐Fabp deletion demonstrated recombination only in HSCs. Mice with albumin promoter‐driven Cre recombinase (Alb‐Cre)‐mediated or AAV8‐mediated L‐Fabp deletion were protected against food withdrawal‐induced steatosis. Mice with Alb‐Cre‐mediated L‐Fabp deletion were protected against high saturated fat‐induced steatosis and fibrosis, phenocopying germline L‐Fabp−/− mice. Mice with HSC‐specific L‐Fabp deletion exhibited retinyl ester depletion yet demonstrated no alterations in fibrosis. On the other hand, fibrogenic resolution after CCl4 administration was impaired in mice with Alb‐Cre‐mediated L‐Fabp deletion. These findings suggest cell type‐specific roles for L‐Fabp in mitigating hepatic steatosis and in modulating fibrogenic injury and reversal.—Newberry, E. P., Xie, Y., Lodeiro, C., Solis, R., Moritz, W., Kennedy, S., Barron, L., Onufer, E., Alpini, G., Zhou, T., Blaner, W. S., Chen, A., Davidson, N. O. Hepatocyte and stellate cell deletion of liver fatty acid binding protein reveal distinct roles in fibrogenic injury. FASEB J. 33, 4610–4625 (2019). http://www.fasebj.org

Background & AimsIntestinal adaptation is a compensatory response to the massive loss of small intestine after surgical resection. We investigated the role of intestinal epithelial cell–specific mammalian target of rapamycin complex 1 (i-mTORC1) in intestinal adaptation after massive small bowel resection (SBR).MethodsWe performed 50% proximal SBR on mice to study adaptation. To manipulate i-mTORC1 activity, Villin-CreER transgenic mice were crossed with tuberous sclerosis complex (TSC)1flox/flox or Raptorflox/flox mice to inducibly activate or inactivate i-mTORC1 activity with tamoxifen. Western blot was used to confirm the activity of mTORC1. Crypt depth and villus height were measured to score adaptation. Immunohistochemistry was used to investigate differentiation and rates of crypt proliferation.ResultsAfter SBR, mice treated with systemic rapamycin showed diminished structural adaptation, blunted crypt cell proliferation, and significant body weight loss. Activating i-mTORC1 via TSC1 deletion induced larger hyperproliferative crypts and disorganized Paneth cells without a significant change in villus height. After SBR, ablating TSC1 in intestinal epithelium induced a robust villus growth with much stronger crypt cell proliferation, but similar body weight recovery. Acute inactivation of i-mTORC1 through deletion of Raptor did not change crypt cell proliferation or mucosa structure, but significantly reduced lysozyme/matrix metalloproteinase-7–positive Paneth cell and goblet cell numbers, with increased enteroendocrine cells. Surprisingly, ablation of intestinal epithelial cell–specific Raptor after SBR did not affect adaptation or crypt proliferation, but dramatically reduced body weight recovery after surgery.ConclusionsSystemic, but not intestinal-specific, mTORC1 is important for normal adaptation responses to SBR. Although not required, forced enterocyte mTORC1 signaling after resection causes an enhanced adaptive response.

Remnant small bowel length appears to be a predictor of stunting with diminished linear growth, parenteral nutrition dependency, and a greater relative abundance of Proteobacteria in the gut. These findings suggest an integrated adaptive response predicted by remnant intestinal length. Further research is necessary to examine the effects of intestinal dysbiosis on clinical outcomes.

Background Intestinal failure-associated liver disease (IFALD) causes significant mortality in patients with short bowel syndrome (SBS). Steatosis, a major component of IFALD has been shown to persist even after weaning from parenteral nutrition. We sought to determine whether steatosis occurs in our murine model of SBS, and more importantly, whether steatosis was affected by manipulation of the intestinal microbiome. Methods Male C57BL6 mice underwent 50% small bowel resection (SBR) and orogastric gavage with vancomycin or vehicle for 10 weeks. DNA was extracted from stool samples then sequenced using 16s rRNA. Liver lipid content was analyzed. Bile acids were measured in liver and stool. Results Compared with unoperated mice, SBR resulted in significant changes in the fecal microbiome and was associated with > 25-fold increase in steatosis. Oral vancomycin profoundly altered the gut microbiome and was associated with a 15-fold reduction in hepatic lipid content after resection. There was a 17-fold reduction in fecal secondary bile acids after vancomycin treatment. Conclusion Massive SBR in mice is associated with development of steatosis, and prevented by oral vancomycin. These findings implicate a critical role for gut bacteria in IFALD pathogenesis and illuminate a novel surgical model for future investigation into this important morbidity.

Intestinal tuft cells are one of 4 secretory cell linages in the small intestine and the source of IL-25, a critical initiator of the type 2 immune response to parasite infection. When Raptor, a critical scaffold protein for mammalian target of rapamycin complex 1 (mTORC1), was acutely deleted in intestinal epithelium via Tamoxifen injection in Tritrichomonas muris (Tm) infected mice, tuft cells, IL-25 in epithelium and IL-13 in the mesenchyme were significantly reduced, but Tm burden was not affected. When Tm infected mice were treated with rapamycin, DCLK1 and IL-25 expression in enterocytes and IL-13 expression in mesenchyme were diminished. After massive small bowel resection, tuft cells and Tm were diminished due to the diet used postoperatively. The elimination of Tm and subsequent re-infection of mice with Tm led to type 2 immune response only in WT, but Tm colonization in both WT and Raptor deficient mice. When intestinal organoids were stimulated with IL-4, tuft cells and IL-25 were induced in both WT and Raptor deficient organoids. In summary, our study reveals that enterocyte specific Raptor is required for initiating a type 2 immune response which appears to function through the regulation of mTORC1 activity.

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Introduction Necrotizing enterocolitis (NEC) is a common and devastating gastrointestinal disease of premature infants. NEC severity varies widely. Recent data have demonstrated a strong link between gut microbial dysbiosis and development of NEC. We tested the hypothesis that alterations in the gut microbiome at the time of diagnosis predict the severity of NEC. Methods We used prospectively collected fecal samples from very low birth weight infants who developed NEC, stratifying by NEC severity. Fecal bacterial DNA was sequenced using 16S rRNA pyrosequencing. A generalized Wald-type test based on the Dirichlet multinomial distribution was used to test for differences in microbial communities. Results Of 489 infants at risk, 30 NEC cases had 410 fecal samples collected in the 28 days prior to the onset of NEC available for analysis. There were no differences the pre NEC gut microbial community between infants treated medically vs. surgically, or those with NEC totalis. Furthermore, neither treatment of NEC significantly changed the gut microbiome post NEC among the survivors. Conclusion We found no evidence that the gut microbiome, prior to the onset of disease, differentiates the clinical course of NEC. These data suggest that factors other than the gut microbiome may dictate disease severity.

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