[P4-05] IGFI-induced UPR component gene XBP1s regulates the endoplasmic reticulum biogenesis of bovine mammary epithelial cell
Objective: To find out the role of IGFI induced XBP1s expression on endoplasmic reticulum (ER) biogenesis of bovine mammary epithelial cell. Methods: In vitro, MAC-T cells were treated with IGFI with or without 4μ8c (IRE1 inhibitor) to quantify the XBP1s and ER biogenesis related gene (EBG); CHKA, PCYT1A and SURF4 expressions and fluorescence intensity of ER tracker. In vivo, mammary XBP1s, EBG and IGFIR expressions, and plasma IGFI concentration were measured using mammary gland biopsy and blood samples respectively collected during late gestation to early lactation in dairy cows. Results: IGFI enhanced XBP1s and EBG expression, and fluorescence intensity of ER tracker, which were reduced by 4μ8c. Protein expressions of IRE1α and p-IRE1α (upstream of XBP1s) were increased by IGFI treated cell. In early lactation, XBP1s, CHKA, PCYT1A and SURF4 and IGFIR expression in mammary biopsy specimens and plasma IGFI concentration were higher compared with those during the precalving. Therefore, we suggest that IGFI mediated XBP1s expression contributes to ER expansion in the mammary gland during lactation.