Noncanonical role for Caspase-5 in the human intestinal epithelium

Introduction/Rationale: Caspase-5 (CASP5) is a member of the inflammatory caspase family of cysteine proteases involved in inflammation and cell death. CASP5 shares highest homology with inflammatory caspase-4, but while caspase-4 is essential for noncanonical inflammasome activation, CASP5 is generally dispensable. This conundrum has left a knowledge gap in understanding CASP5 function.

Methods: We mapped CASP5 expression across human tissues and epithelial cell types, then used proteomics and molecular biology to define interacting partners and pathways. We validated function in human intestinal organoids, and localized isoforms in human tissues by immunohistochemistry and RNAscope.

Results: CASP5 expression was largely restricted to human intestinal epithelium and resolved into three isoforms. Proteomics and interaction mapping suggested that CASP5 interacts with an important developmental signaling scaffold in epithelial cells. Strikingly, during human tissue analysis and organoid differentiation, we noted differential expression of CASP5 isoforms along the crypt-to-lumen axis with specific enrichment of the developmental isoform in crypt regions. Functional studies demonstrated that the developmental isoform augmented the growth of colonic and small-intestinal organoids, which together with supporting data from biochemical studies provided robust evidence for a novel function for CASP5 in sustaining proliferative programs and epithelial renewal.

Conclusion: Our findings reveal that a select developmental isoform of CASP5 amplifies a key epithelial growth program, peaking in specific cell subsets in the intestinal epithelium to sustain their proliferation during stages critical of intestinal epithelial differentiation and regeneration. Our work broadens the role of inflammatory caspases beyond innate immunity, highlighting their contribution to tissue homeostasis.