The Colonic Crypt Protects Stem Cells from Microbiota-Derived Metabolites.

In the mammalian intestine, crypts of Leiberkühn house intestinal epithelial stem/progenitor cells at their base. The mammalian intestine also harbors a diverse array of microbial metabolite compounds that potentially modulate stem/progenitor cell activity. Unbiased screening identified butyrate, a prominent bacterial metabolite, as a potent inhibitor of intestinal stem/progenitor proliferation at physiologic concentrations. During homeostasis, differentiated colonocytes metabolized butyrate likely preventing it from reaching proliferating epithelial stem/progenitor cells within the crypt. Exposure of stem/progenitor cells in vivo to butyrate through either mucosal injury or application to a naturally crypt-less host organism led to inhibition of proliferation and delayed wound repair. The mechanism of butyrate action depended on the transcription factor Foxo3. Our findings indicate that mammalian crypt architecture protects stem/progenitor cell proliferation in part through a metabolic barrier formed by differentiated colonocytes that consume butyrate and stimulate future studies on the interplay of host anatomy and microbiome metabolism.

Runx3 specifies lineage commitment of innate lymphoid cells.

Subsets of innate lymphoid cells (ILCs) reside in the mucosa and regulate immune responses to external pathogens. While ILCs can be phenotypically classified into ILC1, ILC2 and ILC3 subsets, the transcriptional control of commitment to each ILC lineage is incompletely understood. Here we report that the transcription factor Runx3 was essential for the normal development of ILC1 and ILC3 cells but not of ILC2 cells. Runx3 controlled the survival of ILC1 cells but not of ILC3 cells. Runx3 was required for expression of the transcription factor RORγt and its downstream target, the transcription factor AHR, in ILC3 cells. The absence of Runx3 in ILCs exacerbated infection with Citrobacter rodentium. Therefore, our data establish Runx3 as a key transcription factor in the lineage-specific differentiation of ILC1 and ILC3 cells.

Gut-Pancreatic Axis AMPlified in Islets of Langerhans.

Microbially derived metabolites in the intestine regulate host immunity and impact disease pathophysiology in various organs. Sun et al. (2015) suggest a direct effect of microbial metabolites on pancreatic endocrine cells in regulating type 1 diabetes pathophysiology.

Prostaglandin E2 promotes intestinal repair through an adaptive cellular response of the epithelium.

Adaptive cellular responses are often required during wound repair. Following disruption of the intestinal epithelium, wound-associated epithelial (WAE) cells form the initial barrier over the wound. Our goal was to determine the critical factor that promotes WAE cell differentiation. Using an adaptation of our in vitro primary epithelial cell culture system, we found that prostaglandin E2 (PGE2) signaling through one of its receptors, Ptger4, was sufficient to drive a differentiation state morphologically and transcriptionally similar to in vivo WAE cells. WAE cell differentiation was a permanent state and dominant over enterocyte differentiation in plasticity experiments. WAE cell differentiation was triggered by nuclear ß-catenin signaling independent of canonical Wnt signaling. Creation of WAE cells via the PGE2-Ptger4 pathway was required in vivo, as mice with loss of Ptger4 in the intestinal epithelium did not produce WAE cells and exhibited impaired wound repair. Our results demonstrate a mechanism by which WAE cells are formed by PGE2 and suggest a process of adaptive cellular reprogramming of the intestinal epithelium that occurs to ensure proper repair to injury.

Epithelial TNF Receptor Signaling Promotes Mucosal Repair in Inflammatory Bowel Disease.

TNF plays an integral role in inflammatory bowel disease (IBD), as evidenced by the dramatic therapeutic responses in Crohn's disease (CD) patients induced by chimeric anti-TNF mAbs. However, treatment of CD patients with etanercept, a decoy receptor that binds soluble TNF, fails to improve disease. To explore this discrepancy, we investigated the role of TNF signaling in Wnt/ß-catenin-mediated intestinal stem cell and progenitor cell expansion in CD patients, human cells, and preclinical mouse models. We hypothesized that TNF exerts beneficial effects on intestinal epithelial cell (IEC) responses to injury. In CD patients, intestinal stem cell and progenitor cell Wnt/ß-catenin signaling correlates with inflammation status. TNF-deficient (Tnf-/-) mice exhibited increased apoptosis, less IEC proliferation, and less Wnt signaling when stimulated with anti-CD3 mAb. Bone marrow (BM) chimera mice revealed that mucosal repair depended on TNF production by BM-derived cells and TNFR expression by radioresistant IECs. Wild-type→Tnfr1/2-/- BM chimera mice with chronic dextran sodium sulfate colitis exhibited delayed ulcer healing, more mucosal inflammation, and impaired Wnt/ß-catenin signaling, consistent with the hypothesis that epithelial TNFR signaling participates in mucosal healing. The direct effect of TNF on stem cells was demonstrated by studies of TNF-induced Wnt/ß-catenin target gene expression in murine enteroids and colonoid cultures and TNF-induced ß-catenin activation in nontransformed human NCM460 cells (TOPFlash) and mice (TOP-GAL). Together, these data support the hypothesis that TNF plays a beneficial role in enhancing Wnt/ß-catenin signaling during ulcer healing in IBD. These novel findings will inform clinicians and therapeutic chemists alike as they strive to develop novel therapies for IBD patients.

Correction: Validation of near infrared fluorescence (NIRF) probes in vivo with dual laser NIRF endoscope.

[This corrects the article DOI: 10.1371/journal.pone.0206568.].

Cellular differentiation: Potential insight into butyrate paradox?

We recently demonstrated that cellular responses to butyrate depend on the differentiation status of the colonic epithelium. Here, we apply the implications of these findings to cancer biology and discuss discrepancies in the effects of butyrate on cancer progression.

A Common Mechanism Links Activities of Butyrate in the Colon.

Two biological activities of butyrate in the colon (suppression of proliferation of colonic epithelial stem cells and inflammation) correlate with inhibition of the activity of histone deacetylases. Cellular and biochemical studies of molecules similar in structure to butyrate, but different in molecular details (functional groups, chain-length, deuteration, oxidation level, fluorination, or degree of unsaturation), demonstrated that these activities were sensitive to molecular structure, and were compatible with the hypothesis that butyrate acts by binding to the Zn2+ in the catalytic site of histone deacetylases. Structure-activity relationships drawn from a set of 36 compounds offer a starting point for the design of new compounds targeting the inhibition of histone deacetylases. The observation that butyrate was more potent than other short-chain fatty acids is compatible with the hypothesis that crypts evolved (at least in part), to separate stem cells at the base of crypts from butyrate produced by commensal bacteria.

Validation of near infrared fluorescence (NIRF) probes in vivo with dual laser NIRF endoscope.

PURPOSE: The development of NIRF cathepsin activity probes offered the ability to visualize tumor associated tumor reaction and act as a surrogate marker to delineate the dysplastic lesions. One major type is a NIRF substrate of cathepsins (SBP), which is involved in catalytic way to produce high levels of fluorescence emission. The other major type (ABP) reacts with active cathepsins in stoichiometric manner since they bind covalently with their active center. Little is known about the sensitivity and the specificity of the NIRF probes to detect autochthonous developed dysplastic lesions. Dual laser NIRF endoscope provides a good tool to determine the efficiency of various NIRF probes in vivo in the same lesions. EXPERIMENTAL DESIGN: In the current study, we validated both types of NIRF probes by using the dual laser NIRF endoscope to detect lesions colon cancer mouse model (TS4Cre/cAPC +/lox). RESULTS: The dual laser NIRF endoscope is emitting equal power with both lasers. It can detect with the same efficiency in 680 mode, as well as, 750 mode when NIFR probes of the same scaffold in vivo. When SBP and ABP were used, our results showed both probes are efficient enough to detect large polyps but small dysplastic lesions could not efficiently imaged with the ABP. CONCLUSIONS: The dual laser NIRF endoscope is a powerful tool to validate probes. The probes that react catalytically with the active center of cathepsins are more efficient than the ones that react stoichiometrically in detecting small lesions.