Modulation of Notch Processing by γ-Secretase Inhibitors Causes Intestinal Goblet Cell Metaplasia and Induction of Genes Known to Specify Gut Secretory Lineage Differentiation

Abstract

It is anticipated that gamma-secretase inhibitors (gamma-Sec-I) that modulate Notch processing will alter differentiation in tissues whose architecture is governed by Notch signaling. To explore this hypothesis, Han Wistar rats were dosed for up to 5 days with 10-100 micromol/kg b.i.d. gamma-Sec-I from three chemical series that inhibit Notch processing in vitro at various potencies (Notch IC(50)). These included an arylsulfonamide (AS) (142 nM), a dibenzazepine (DBZ) (1.7 nM), and a benzodiazepine (BZ) (2.2 nM). The DBZ and BZ caused dose-dependent intestinal goblet cell metaplasia. In contrast, the AS produced no detectable in vivo toxicity, despite higher exposure to free drug. In a time course using BZ, small intestinal crypt cell and large intestinal glandular cell epithelial apoptosis was observed on days 1-5, followed by goblet cell metaplasia on days 2-5 and crypt epithelial and glandular epithelial regenerative hyperplasia on days 4-5. Gene expression profiling of duodenal samples from BZ-dosed animals revealed significant time-dependent deregulation of mRNAs for various panendocrine, hormonal, and transcription factor genes. Somatostatin, secretin, mucin, CCK, and gastrin mRNAs were elevated twofold or more by day 2, and a number of candidate "early-predictive" genes were altered on days 1-2, remaining changed for 4-5 days; these included Delta1, NeuroD, Hes1-regulated adipsin, and the Hes-regulated transcriptional activator of gut secretory lineage differentiation, the rat homolog of Drosophila atonal, Rath1. Western blotting of fecal protein from BZ-and DBZ-dosed animals exhibited increased levels of both anti-Rath1 reactive protein and anti-adipsin reactive proteins, confirming their potential value as noninvasive biomarkers of intestinal goblet metaplasia.