Improved capacity to evaluate changes in intestinal mucosal surface area using mathematical modeling

Jejunoileal mucosal growth in mice with a limited microbiome

Previous work demonstrated enhanced enterocyte proliferation and mucosal growth in gnotobiotic mice, suggesting that intestinal flora participate in mucosal homeostasis. Furthermore, broad-spectrum enteral antibiotics are known to induce near germ-free (GF) conditions in mice with conventional flora (CONV). We hypothesized that inducing near GF conditions with broad-spectrum enteral antibiotics would cause ordered small intestinal mucosal growth in CONV mice but would have no effect in GF mice with no inherent microbiome. C57BL/6J CONV and GF mice received either an antibiotic solution (Ampicillin, Ciprofloxacin, Metronidazole, Vancomycin, Meropenem) or a vehicle alone. After treatment, small intestinal villus height (VH), crypt depth (CD), mucosal surface area (MSA), crypt proliferation index (CPI), apoptosis, and villus and crypt cell types were assessed. Antibiotic-treated CONV (Abx-CONV) mice had taller villi, deeper crypts, increased CPI, increased apoptosis, and greater MSA compared to vehicle-treated CONV mice. Minor differences were noted in enterocyte and enterochromaffin cell proportions between groups, but goblet and Paneth cell proportions were unchanged in Abx-CONV mice compared to vehicle-treated CONV mice (p>0.05). Antibiotics caused no significant changes in VH or MSA in GF mice when compared to vehicle-treated GF mice (p>0.05). Enteral administration of broad-spectrum antibiotics to mice with a conventional microbiome stimulates ordered small intestinal mucosal growth. Mucosal growth was not seen in germ-free mice treated with antibiotics, implying that intestinal mucosal growth is associated with change in the microbiome in this model.

Potentiated serotonin signaling in serotonin re-uptake transporter knockout mice increases enterocyte mass and small intestinal absorptive function

Genetic knockout of the serotonin reuptake transporter (SERT) potentiates serotonin signaling and increases crypt‐cell proliferation, neuroplasticity, and mucosal surface area. However, it remains unknown whether these changes occur throughout the small intestine and whether they increase nutrient absorption. We hypothesized that serotonin‐mediated mucosal growth would occur throughout the intestine and would increase enterocyte mass and absorptive function. Following institutional approval, intestinal segments spanning the bowel were harvested from 10 to 12 week‐old SERT knockout (SERTKO) and wild‐type (WT) C57Bl/6 mice. Histologic sections were used to measure villus height (VH), crypt depth (CD), and crypt proliferation index (CPI). Plasma citrulline was measured colorimetrically. Glucose and peptide absorption in isolated segments of small bowel were calculated using a previously described method for quantification after luminal instillation of substrate. At baseline, morphometric (VH/CD) and proliferative (CPI) parameters varied from jejunum to ileum. Enhanced 5‐HT signaling significantly increased plasma citrulline levels and morphometric/proliferative parameters in all regions analyzed. Glucose absorption in WT mice varied throughout the small intestine, and SERTKO mice demonstrated significant increases in the middle and distal bowel. WT peptide absorption was similar throughout the small bowel, and SERTKO mice had significant increases in the proximal and distal bowel. Enhanced serotonin signaling results in increased morphometric and proliferative parameters throughout the small intestine, and results in increased enterocyte mass and intestinal absorptive function. These data further advance the concept that the serotonin system is an attractive therapeutic target for increasing functional intestinal mucosa.

The 5-HT4 Receptor Agonist Prucalopride Stimulates Mucosal Growth and Enhances Carbohydrate Absorption in the Ileum of the Mouse

BACKGROUND

Enteric serotonin may function as a mucosal growth factor. Previous work demonstrated increased crypt cell proliferation and intestinal mucosal surface area with potentiation of serotonin. While an indirect mechanism was postulated to explain these effects, the presence of 5-HT4 receptors on enterocytes raises the possibility of a direct action of serotonin. We hypothesized that a 5-HT4 specific agonist, prucalopride, would stimulate intestinal mucosal growth and enhance absorptive function in the murine small intestine.

METHODS

Adult wild-type mice were treated parenterally with prucalopride for 14 days via surgically implanted osmotic pumps. In vivo D-xylose absorption was assessed by oral gavage and serum D-xylose measurements. On day 14, glucose absorption was assessed by instilling a glucose solution into isolated segments of small intestine. The bowel was harvested and examined for morphologic parameters and crypt cell proliferation.

RESULTS

Villus height, crypt depth, and crypt proliferation were significantly increased in the distal small bowel of prucalopride-treated mice compared with control animals. Crypt depth was also increased in the proximal and middle small intestine in treated mice. There was no difference in D-xylose absorption throughout the study period; however, glucose absorption was significantly increased in the distal small intestine of prucalopride-treated mice.

CONCLUSION

Parenteral administration of the 5-HT4 receptor specific agonist, prucalopride, results in morphologic and functional changes in the murine small intestine that are most prominent in the distal small bowel. While further studies are necessary to delineate the mechanism, it is plausible that the effects are mediated by 5-HT4 receptors on enterocytes.