Multimodal single cell analyses reveal mechanisms of perianal fistula in diverse Crohn’s disease [Multiome]

Crohn’s disease (CD) is a chronic inflammatory condition that can affect any part of the gastrointestinal tract. African ancestry (AA) populations have been substantially under-represented in genome-wide association studies (GWAS) of CD and inflammatory bowel disease (IBD), reflecting in part the lower prevalence of CD in AA compared to European ancestry (EA) populations. Importantly, CD complicated by perianal fistulae has been found to be more prevalent and severe in African-ancestry patients. Perianal fistulae arise from the distal rectal mucosa and can course to a cutaneous surface, resulting in highly morbid complications. Monoclonal antibodies against anti-TNF are the mainstay of treatment, but recurrence and secondary loss-of-response is common. In severe, uncontrolled cases, complete proctectomy is required. The intestine is unique among adult tissues in that under homeostasis, residential macrophages are continually replenished from recruited blood monocytes. In EA cohorts, we established that chronic monocyte cultures stimulated with NOD2 agonists result in aberrant myeloid-stromal differentiation stratified by risk allele carrier status. NOD2 risk alleles are not associated with perianal fistulae; African-American patients with CD do not carry them (except via recent European ancestry admixture). There is no direct association between known CD GWAS risk loci and the risk of developing perianal fistula. Here, we present direct ex-vivo, single cell multiomic analyses of colorectal tissues and perianal fistulous tracts in AA and EA cases to define mechanisms of perianal fistula development. We implicate myeloid-stromal crosstalk and define cell subtypes using single cell RNA (scRNASeq), ATAC sequencing, and chronic, unstimulated monocyte cultures. Transcription factor motifs and ATAC signals co-localized with fine-mapped GWAS loci provide insight to cell-specific and transcriptional network regulation.