P351 The Histo-endoscopic Spectrum in Ulcerative Colitis reveals a Distinct Mucosal Transcriptome for Histo-endoscopic Remission

Abstract

Abstract Background Aiming for histological remission on top of endoscopic remission, is an aspiring target in ulcerative colitis [UC]. We investigated the mucosal transcriptional profiles in UC patients with varying depths of histologic activity as compared to healthy controls. Methods UC patients with endoscopic improvement (Mayo endoscopic score [MES] 0 or 1) were recruited. Endoscopies were video-recorded and biopsies from the most affected segment were collected for histological assessment and bulk RNAseq (Illumina HiSeq 4000, single read). Geboes Score [GS] was determined by two pathologists blinded for endoscopic scores. The included patients were divided into endoscopic improvement with histologic activity [EIHA] (MES ≤1, GS ≥2B.1) and histo-endoscopic mucosal remission [HEMR] (MES ≤1, GS <2B.1). We distinguished a subpopulation within the HEMR group that we labelled as histo-endoscopic mucosal normalization [HEMN] (MES ≤1, GS ≤0.1). As comparators, 50 healthy individuals [HV] and 50 UC patients with active disease (MES 2-3, independent, matched by treatment) [AD] were included. Normalised RNA counts were analysed by principal component analysis [PCA] and differential expression analysis. Genes with a |log2 FC|>1 and a FDR <0.05 were considered as differentially expressed [DEG], and were selected for pathway analysis (R 4.3.2, DEseq2; QIAGEN IPA). Results In this study cohort 172 patients were included (Table). PCA analysis showed clustering patterns for each study group (Figure). In particular, separation along the PC1 axis tended to follow the different degrees of histo-endoscopic activity. Interestingly, besides inflammatory and tissue remodeling markers (e.g., DUOX2, MMP 3, CHI3L1) for PC1 and epithelial and metabolic markers (e.g., SLC9A3, LPIN3) for PC2, the gene with the highest variance for both PC1 and PC2 was Aquaporin-8 (AQP8). This gene encodes for a water transporter at the apical surface of the colon, and its mucosal expression level indeed follows a spectrum of histo-endoscopic activity (Figure). Differential expression analyses identified 1261 DEG in HEMN, 1684 DEG in HEMR (not HEMN), 2178 DEG in EIHA, all compared to HV. A total of 1014 overlapping DEG were identified for all these comparisons, being enriched for pathways related to inflammation, metabolic epithelial functions (lipid metabolism, bile acid regulation) and wound healing. Conclusion UC patients with histo-endoscopic remission have a mucosal transcriptional profile which significantly differs from that of healthy individuals, even in UC patients whose biopsies appear normal upon histological evaluation. The histo-endoscopic spectrum of the mucosal transcriptome in UC is nicely illustrated by the gene expression of Aquaporin-8 (AQP8).