Bile acids (BAs) are synthesized in the liver and secreted into the intestine. In the lumen, enteric bacteria metabolize BAs from conjugated, primary forms into more toxic unconjugated, secondary metabolites. Secondary BAs can be injurious to the intestine and may contribute to disease. The epidermal growth factor receptor (EGFR) and the nuclear farnesoid X receptor (FXR) are known to interact with BAs. In this study we examined the effects of BAs on intestinal epithelial cell proliferation and investigated the possible roles for EGFR and FXR in these effects. We report that taurine-conjugated cholic acid (TCA) induced proliferation, while its unconjugated secondary counterpart deoxycholic acid (DCA) inhibited proliferation. TCA stimulated phosphorylation of Src, EGFR, and ERK 1/2. Pharmacological blockade of any of these pathways or genetic ablation of EGFR abrogated TCA-stimulated proliferation. Interestingly, Src or EGFR inhibitors eliminated TCA-induced phosphorylation of both molecules, suggesting that their activation is interdependent. In contrast to TCA, DCA exposure diminished EGFR phosphorylation, and pharmacological or siRNA blockade of FXR abolished DCA-induced inhibition of proliferation. Taken together, these results suggest that TCA induces intestinal cell proliferation via Src, EGFR, and ERK activation. In contrast, DCA inhibits proliferation via an FXR-dependent mechanism that may include downstream inactivation of the EGFR/Src/ERK pathway. Since elevated secondary BA levels are the result of specific bacterial modification, this may provide a mechanism through which an altered microbiota contributes to normal or abnormal intestinal epithelial cell proliferation.

The intestinal barrier is often disrupted in disease states, and intestinal barrier failure leads to sepsis. Ursodeoxycholic acid (UDCA) is a bile acid that may protect the intestinal barrier. We hypothesized that UDCA would protect the intestinal epithelium in injury models. To test this hypothesis, we utilized an in vitro wound-healing assay and a mouse model of intestinal barrier injury. We found that UDCA stimulates intestinal epithelial cell migration in vitro, and this migration was blocked by inhibition of cyclooxygenase 2 (COX-2), epidermal growth factor receptor (EGFR), or ERK. Furthermore, UDCA stimulated both COX-2 induction and EGFR phosphorylation. In vivo UDCA protected the intestinal barrier from LPS-induced injury as measured by FITC dextran leakage into the serum. Using 5-bromo-2'-deoxyuridine and 5-ethynyl-2'-deoxyuridine injections, we found that UDCA stimulated intestinal epithelial cell migration in these animals. These effects were blocked with either administration of Rofecoxib, a COX-2 inhibitor, or in EGFR-dominant negative Velvet mice, wherein UDCA had no effect on LPS-induced injury. Finally, we found increased COX-2 and phosphorylated ERK levels in LPS animals also treated with UDCA. Taken together, these data suggest that UDCA can stimulate intestinal epithelial cell migration and protect against acute intestinal injury via an EGFR- and COX-2-dependent mechanism. UDCA may be an effective treatment to prevent the early onset of gut-origin sepsis. NEW & NOTEWORTHY In this study, we show that the secondary bile acid ursodeoxycholic acid stimulates intestinal epithelial cell migration after cellular injury and also protects the intestinal barrier in an acute rodent injury model, neither of which has been previously reported. These effects are dependent on epidermal growth factor receptor activation and downstream cyclooxygenase 2 upregulation in the small intestine. This provides a potential treatment for acute, gut-origin sepsis as seen in diseases such as necrotizing enterocolitis.

Background Airway secretions contain endogenous antimicrobial factors (AMFs) which contribute to the innate host defense of the respiratory tract. Antibacterial peptides as well as host-derived lipids including cholesteryl esters have been detected in maxillary lavage fluid. Sterol O-acyltransferase 1 (SOAT1) is a key enzyme in cholesteryl ester production. The purpose of this study is to determine if such intrinsic microbicidal molecules are acutely expressed within sinus tissue and to compare levels of expression between patients with and without chronic rhinosinusitis (CRS). Methods Sinus tissue was obtained from subjects with (24) and without (9) a history of CRS. Six CRS patients had nasal polyposis (CRSwNP). Immunofluorescence staining for human neutrophil peptide (HNP) was done as a marker for inflammation. RT-PCR following RNA extraction was used to quantify the expression of SOAT-1, the epithelial beta-defensins (HBD2,3), and the cathelicidin LL37 with ribosomal protein RPLP0 as the housekeeping gene. Results Immunofluorescence showed significant increase in HNP staining in CRS patients without nasal polyposis (CRSsNP) versus non-CRS specimens (p=0.010), in agreement with clinical inflammation status. SOAT1 mRNA expression was also upregulated in CRSsNP compared to non-CRS (p=0.041) and CRSwNP (p=0.005) patients; while increases for HBD2 and HBD3 were less prominent. LL37 was either absent or expressed at very low levels in all samples. Conclusions Increased biosynthesis of SOAT1, a key enzyme for antimicrobial cholesteryl ester production, was observed in the sinus tissue of CRSsNP but not in CRSwNP patients. This further supports the novel concept of lipid-mediated innate mucosal defense and delineates CRS with and without nasal polyposis as distinct subtypes.

High levels of PGE2 have been implicated in the pathogenesis of intestinal inflammatory disorders such as necrotizing enterocolitis (NEC) and peritonitis. However, PGE2 has a paradoxical effect: its low levels promote intestinal homeostasis, whereas high levels may contribute to pathology. These concentration-dependent effects are mediated by four receptors, EP1-EP4. In this study, we evaluate the effect of blockade of the low affinity pro-inflammatory receptors EP1 and EP2 on expression of COX-2, the rate-limiting enzyme in PGE2 biosynthesis, and on gut barrier permeability using cultured enterocytes and three different models of intestinal injury. PGE2 upregulated COX-2 in IEC-6 enterocytes, and this response was blocked by the EP2 antagonist PF-04418948, but not by the EP1 antagonist ONO-8711 or EP4 antagonist E7046. In the neonatal rat model of NEC, EP2 antagonist and low dose of COX-2 inhibitor Celecoxib, but not EP1 antagonist, reduced NEC pathology as well as COX-2 mRNA and protein expression. In the adult mouse endotoxemia and cecal ligation/puncture models, EP2, but not EP1 genetic deficiency decreased COX-2 expression in the intestine. Our results indicate that the EP2 receptor plays a critical role in the positive feedback regulation of intestinal COX-2 by its end-product PGE2 during inflammation and may be a novel therapeutic target in the treatment of NEC.

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