USP5-induced deubiquitination of P4HB alleviates ER stress-mediated apoptosis in intestinal ischemia/reperfusion

Intestinal ischemia/reperfusion (I/R) is a severe pathophysiological process that occurs in a variety of clinical conditions and can trigger multiple life-threatening syndromes. Intestinal I/R is associated endoplasmic reticulum (ER) stress. Prolyl 4-hydroxylase subunit beta (P4HB) contributes significantly to maintaining ER redox homeostasis, which is affected by I/R injury. Nevertheless, the molecular mechanism of P4HB expression and function in intestinal I/R is still unknown. In our study, we discovered that the expression of P4HB was clearly downregulated in the intestine of mice at the reperfusion stage and in Caco2 cells at the reoxygenation stage. In addition, P4HB-knockdown mice exhibited clearly enhanced ER stress-mediated apoptosis of intestinal tissue under intestinal I/R, whereas P4HB overexpression in Caco2 cells alleviated ER stress-mediated apoptosis under HR. Furthermore, via bioinformatics screening of proteins that interact with P4HB, ubiquitin-specific protease 5 (USP5) was identified as a critical factor in the abnormal expression of P4HB. USP5 interacts with P4HB and remains stable by removing ubiquitin. In vivo, P4HB knockdown counteracted the effect of USP5 overexpression on alleviating ER stress-mediated apoptosis in response to intestinal I/R. In summary, this study revealed that P4HB plays a crucial role in regulating ER stress-mediated apoptosis and identified USP5, which is a novel mediator of P4HB, as a prospective target for the treatment of intestinal I/R.