Dysgenesis of Enteroendocrine Cells in Aristaless-Related Homeobox Polyalanine Expansion Mutations

OBJECTIVES: Severe congenital diarrhea occurs in approximately half of patients with Aristaless-Related Homeobox (ARX) null mutations. The cause of this diarrhea is unknown. In a mouse model of intestinal Arx deficiency, the prevalence of a subset of enteroendocrine cells is altered, leading to diarrhea. Because polyalanine expansions within the ARX protein are the most common mutations found in ARX-related disorders, we sought to characterize the enteroendocrine population in human tissue of an ARX((GGC)7) mutation and in a mouse model of the corresponding polyalanine expansion (Arx((GCG)7)). METHODS: Immunohistochemistry and quantitative real-time polymerase chain reaction were the primary modalities used to characterize the enteroendocrine populations. Daily weights were determined for the growth curves, and Oil-Red-O staining on stool and tissue identified neutral fats. RESULTS: An expansion of 7 alanines in the first polyalanine tract of both human ARX and mouse Arx altered enteroendocrine differentiation. In human tissue, cholecystokinin, glucagon-like peptide 1, and somatostatin populations were reduced, whereas the chromogranin A population was unchanged. In the mouse model, cholecystokinin and glucagon-like peptide 1 populations were also lost, although the somatostatin-expressing population was increased. The ARX((GGC)7) protein was present in human tissue, whereas the Arx((GCG)7) protein was degraded in the mouse intestine. CONCLUSIONS: ARX/Arx is required for the specification of a subset of enteroendocrine cells in both humans and mice. Owing to protein degradation, the Arx((GCG)7) mouse recapitulates findings of the intestinal Arx null model, but is not able to further the study of the differential effects of the ARX((GCG)7) protein on its transcriptional targets in the intestine.