Proline-Rich Acidic Protein 1 (PRAP1) Protects the Gastrointestinal Epithelium From Irradiation-Induced Apoptosis

Background & aims: The intestinal epithelium must be resilient to physiochemical stress to uphold the physiological barrier separating the systemic compartment from the microbial and antigenic components of the gut lumen. Identifying proteins that mediate protection and enhancing their expression is therefore a clear approach to promote intestinal health. We previously reported that oral ingestion of the probiotic Lactobacillus rhamnosus GG not only induced the expression of several recognized cytoprotective factors in the murine colon, but also many genes with no previously described function, including the gene encoding proline-rich acidic protein 1 (PRAP1). PRAP1 is a highly expressed protein in the epithelium of the gastrointestinal tract and we sought to define its function in this tissue.

Methods: Purified preparations of recombinant PRAP1 were analyzed biochemically and PRAP1 antisera were used to visualize localization in tissues. Prap1^-/- mice were characterized at baseline and challenged with total body irradiation, then enteroids were generated to recapitulate the irradiation challenge ex vivo.

Results: PRAP1 is a 17-kilodalton intrinsically disordered protein with no recognizable sequence homology. PRAP1 expression levels were high in the epithelia of the small intestine. Although Prap1^-/- mice presented only mild phenotypes at baseline, they were highly susceptible to intestinal injury upon challenge. After irradiation, the Prap1^-/- mice showed accelerated death with a significant increase in apoptosis and p21 expression in the small intestinal epithelium.

Conclusions: PRAP1 is an intrinsically disordered protein highly expressed by the gastrointestinal epithelium and functions at exposed surfaces to protect the barrier from oxidative insult.