P030 Distinct molecular profiles between idiopathic cryptoglandular and Crohn-related perianal fistulas

Abstract

Abstract Background Perianal fistula can originate idiopathically (cryptoglandular fistula) or can be a representation of underlying Crohn’s disease (CD). In case of idiopathic fistula, the cryptoglandular theory suggests their development from the anal glands. In contrast, the pathophysiology of CD-related fistula is very poorly understood. Hence, we molecularly characterised and compared the fistula tract in both conditions. Methods We collected surgical biopsies from the fistula tract in 70 CD patients with active draining perianal fistula and in 12 patients with cryptoglandular non-CD related, active draining fistula, all requiring surgical examination under anaesthesia. RNA was sequenced using Illumina HiSeq4000, and these data were analysed through differential gene expression analysis (DESeq2). A false discovery rate (FDR) of 0.05 and a |log 2-fold change (log2FC)| >1 was considered significant. Pathway analysis was performed using IPA (Qiagen). In addition, cellular deconvolution methods (xCell) were applied to study the cellular composition. Results Gene expression analysis identified 1087 genes being differentially expressed between CD-related and cryptoglandular fistula (716 up, 371 down). Top differentially expressed genes encode proteins implicated in IBD pathogenesis including CARD18 (log2FC= 23.2, p=3.9E-21), BATF2 (log2FC=2.8, p=1.8E-8), ETV7 (log2FC=2.1, p=2.0E-7), DSG1 (log2FC=7.8, p=2.7E-6) and IL22RA1 (log2FC=5.3, p=4.6E-6). Additional pathway analysis highlighted various proinflammatory processes in CD fistula (as compared to cryptoglandular fistula), including upregulation of antigen presentation and Th1/Th2 activation (p<1.0E-9). Intriguingly, CD fistula showed a significant downregulation of wound healing signaling pathways (p=6.5E-6), emphasising the refractory character of this debilitating condition. Upstream analyses showed an increased activation of top regulators IFNγ, TNF, LPS and STAT1 (p<1.0E-24). Cellular deconvolution identified significant differences between both fistula types, with a predominance of inflammatory cells in CD including Th1 cells, dendritic cells, naïve CD4 T cells, memory B cells and central memory CD8 and CD4 T cells (p<5.0E-2). In contrast, cryptoglandular fistula were characterised by a significant enrichment of myocytes, smooth muscle cells and neurons (p<3.0E-3). Presence of neutrophils, wound healing and pro-inflammatory macrophages did not differ between both fistula types. Conclusion CD fistulas have a strong proinflammatory fingerprint, but seem to have lower wound healing capacity as compared to cryptoglandular fistula. An aggressive medical and surgical treatment is therefore required, including the search for novel, powerful anti-inflammatory and wound healing compounds.