Aberrant Epithelial Differentiation Contributes to Pathogenesis in a Murine Model of Congenital Tufting Enteropathy

Abstract

Background & Aims: Congenital Tufting Enteropathy (CTE) is an intractable diarrheal disease of infancy caused by mutation of Epithelial Cell Adhesion Molecule (EpCAM). The cellular and molecular basis of CTE pathology has been elusive. We hypothesized that the loss of EpCAM in CTE results in altered lineage differentiation and defects in absorptive enterocytes thereby contributing to CTE pathogenesis. Methods: Intestine from CTE mice was evaluated for specific markers by RT-qPCR, western blotting and immunostaining. Body weight, blood glucose and intestinal enzyme activity were also investigated. A CTE enteroid model was used to assess whether the decreased census of secretory cells could be rescued. Results: CTE mice exhibited alterations in brush-border function, disaccharidase activity and glucose absorption, potentially contributing to nutrient malabsorption and impaired weight gain. Altered cell differentiation in CTE mice led to decreased secretory cells and increased numbers of absorptive cells, though the absorptive enterocytes lacked key features, causing brush border malfunction. Further, treatment with Notch signaling inhibitor, DAPT, increased the numbers of major secretory cell types in CTE enteroids. Conclusions: Alterations in intestinal epithelial cell differentiation in CTE mice favor an increase in absorptive cells at the expense of secretory cells. Although the proportion of absorptive enterocytes is increased, they lack key functional properties. We conclude that these effects underlie pathogenic features of CTE such as malabsorption and diarrhea, and ultimately the failure to thrive seen in patients. The ability of DAPT to reverse aberrant differentiation suggests a possible therapeutic strategy.

Congenital Tufting Enteropathy: Biology, Pathogenesis and Mechanisms

“…Altered localization and decreased expression of ion transporters NKCC1, but unchanged CFTR, has been reported in CTE mice and an EpCAM knockout model indicating some ion transporters are compromised in CTE [37]. This observation is further supported in the most recent report demonstrating key transporters such as NHE3 and glucose transporters, SGLT1 and GLUT2, are affected in a CTE murine model [41]. Alteration in expression and localization of ion transporters and tight junction proteins explains the secretory nature of diarrhea found in CTE, whereas changes in glucose transporters explain osmotic diarrhea seen in these patients [3,18].…”

“…Epithelial homeostasis is maintained through a dynamic equilibrium between intestinal epithelial cells (IECs) and the gut mucosal barrier (both physical and chemical). CTE disrupts various aspects of this homeostasis: cell differentiation [39,41], barrier [37], cell-cell junction [10,42] and structural composition [43]. The present review will discuss each aspect in the context of CTE to understand the pathogenesis of this disease.…”

“…The explanation may lay in regulatory molecules or the trafficking of the ion transporters [47]. Moreover, apart from ion/glucose transporters, other key components of the brush border machinery, glycoside hydrolases (maltase, sucrase and lactase), that help in digestion of disaccharides are also found to be disrupted in CTE biopsies [43] and CTE mice [41], indicating involvement of malabsorption in this disease. These findings provide a rationale as to why parenteral nutrition is often the only reliable source of nutrients in these patients and the clinical observation that enteral feeding has been shown to worsen CTE [3].…”

“…Studies in CTE murine intestinal tissue showed increased proliferation index when compared to its normal counterparts, and it was proposed that intestinal tissue compensates for epithelial dysfunction leading to enhanced proliferation with crowding of enterocytes [38]. Secretory cell differentiation is found to be impaired in both CTE enteroids [39] and CTE murine intestines [41], leading to decreased goblet cell and Paneth cell populations in CTE enteroids, patients, and murine intestines [39]. Data suggests that in CTE, intestinal cell differentiation is biased toward absorptive lineage differentiation through Notch signaling at the expense of Atoh1-mediated secretory lineage differentiation.…”

“…Data suggests that in CTE, intestinal cell differentiation is biased toward absorptive lineage differentiation through Notch signaling at the expense of Atoh1-mediated secretory lineage differentiation. Further, it was shown that Notch signal γ-secretase inhibitor treatment (DAPT) could rescue key secretory cell marker expression in a CTE enteroid model [41]. The causal mechanism behind altered cell differentiation cascade and how abnormal cell differentiation impacts CTE disease outcomes is still not known.…”