ILEAL ENTEROCYTE BRUSH BORDER ABNORMALITIES ASSOCIATE WITH PROGRESSIVE DISEASE COURSE IN PEDIATRICS CROHN’S DISEASE

Biomarkers are needed to identify the subset of Crohn’s disease (CD) patients at-risk for severe, treatment-refractory disease. Short ileal microvillus length (MVL) is an epithelial biomarker that predicted non-response to treatment in adult CD. Here, we hypothesized that short MVL phenotype would occur in pediatric CD and associate with more severe disease. H&E-stained ileal tissue sections were obtained from 3 pediatric cohorts: WashU, CCHMC, and RISK (n=58 controls, n=377 CD). MVL was measured in regions not involved in acute inflammation. RISK had baseline “pre-treatment” and follow-up “post-treatment” sampling, clinical phenotyping, and transcriptomic data. Transmission electron microscopy (TEM) and immunofluorescence was performed on paired samples from 6 CD and 6 controls. Ileal MVL was shorter in pediatric CD (mean: 1.44 μm) vs. controls (mean: 1.64 μm; P<0.0001). MVL did not associate with body mass index, disease location, endoscopic deep ulcers, or disease activity index scores. Histological inflammation scores were greater in baseline CD vs. controls, but similar between CD with short (defined as <1.46 μm, 10th percentile of controls) or normal MVL. Progression from B1 inflammatory disease behavior to B2 stricturing or B3 internal penetrating disease behavior was more likely to occur in patients with shorter MVL (n=91 follow-up samples collected prior to disease progression event; B2: P=0.0077, B3: P=0.0186). Additionally, progression to B2 occurred sooner in those with short follow-up MVL (P=0.0206). In contrast, associations with disease behavior progression based on baseline MVL were not observed. RNA-seq analysis identified 92 genes differentially expressed between CD and controls and correlated with MVL. Gene function analysis showed enrichment (P<0.001) for actin cytoskeleton, transporter activity, and plasma membrane among the 43 genes positively associated with MVL, and enrichment for myeloid cell, response to bacterium, and extracellular matrix among the 49 genes negatively associated with MVL. TEM showed thinning of the terminal web in CD, with diminished microvillus rootlet length and organelle-free zones, features associated with shortened or disorganized microvilli in mouse models. We next assessed terminal web-associated proteins, PLS1 and MYH14, and found that both were altered in CD samples; PLS1 was abnormally enhanced at the brush border, and MYH14 was aberrantly localized in the cytoplasm. Misexpression of MYH14 was associated with terminal web thinning and shorter MVL. This study supports short ileal MVL phenotype in follow-up CD samples as an epithelial biomarker for more severe disease prognosis, particularly for progression to stricturing disease. Our data suggest that terminal web alterations underlie the short MVL phenotype.