REG3α is a Predictive Biomarker of Complicated Disease from Preclinical Through Established Crohn’s Disease

BACKGROUND:Regenerating islet-derived 3-alpha (REG3α) is a serum biomarker in patients with graft-versus-host disease (GVHD) linked to 6-month mortality. REG3α is produced by intestinal Paneth cells, which are implicated in Crohn's disease (CD) pathophysiology. OBJECTIVE:To assess associations between serum REG3α and progressive CD DESIGN: Serum REG3α was measured in two cross-sectional (M: Mount Sinai, L: Leuven) and a pre-diagnostic cohort (P: PREDICTS) with serial samples up to 10 years before CD diagnosis. Tissue REG3α expression was assessed via bulk RNA sequencing from paired ileal and colonic biopsies. Serum REG3α and tissue REG3α were associated with CD progression (hospitalization, surgery, steroid course, or new advanced therapy). Single-cell RNA sequencing data explored associations between REG3α expression, Paneth cell phenotypes, and CD. RESULTS:In 394 patients, high serum REG3α associated with CD progression, independent of C-reactive protein and endoscopic activity (M: HR 1.9 (95%CI 1.3-2.8); L: HR 2.9 (95%CI 1.9-4.6), both p<0.001). The association persisted in patients with mild or inactive CD. In the pre-diagnostic cohort, high serum REG3α predicted the development of CD, particularly complicated (B2/3) and surgical presentations, up to 10 years before diagnosis (P). Analysis of REG3α expression and Paneth cell transcriptomes suggested that CD is associated with loss of regenerative Paneth cell populations and enrichment in REG3α-expressing populations, suggesting a mechanism through which changes in serum REG3α associate with complicated CD. CONCLUSION:Serum REG3α holds potential as a non-invasive, prognostic biomarker in CD, independent of disease activity. High serum REG3α, even years before diagnosis, is linked to a complicated disease course.