Zinc Supplementation, via GPR39, Upregulates PKCζ to Protect Intestinal Barrier Integrity in Caco-2 Cells Challenged bySalmonella entericaSerovar Typhimurium

Background: Zinc has been shown to improve intestinal barrier function against Salmonella enterica serovar Typhimurium (S. typhimurium) infection, but the mechanisms involved in this process remain undefined. Objective: We aimed to explore the roles of G protein–coupled receptor (GPR)39 and protein kinase Cζ (PKCζ) in the regulation by zinc of intestinal barrier function. Methods: A Transwell Caco-2 monolayer was pretreated with 0, 50, or 100 μM Zn and then incubated with S. typhimurium for 0–6 h. Afterward, cells silenced by the small interfering RNA for GPR39 or PKCζ were pretreated with 100 μM Zn and incubated with S. typhimurium for 3 h. Finally, transepithelial electrical resistance (TEER), permeability, tight junction (TJ) proteins, and signaling molecules GPR39 and PKCζ were measured. Results: Compared with controls, S. typhimurium decreased TEER by 62.3–96.2% at 4–6 h (P < 0.001), increased (P < 0.001) permeability at 6 h, and downregulated (P < 0.05) TJ protein zonula occludens (ZO)-1 and occludin by 104–123%, as well as Toll-like receptor 2 and PKCζ by 35.1% and 75.2%, respectively. Compared with S. typhimurium–challenged cells, 50 and 100 μM Zn improved TEER by 26.3–60.9% at 4–6 h (P < 0.001) and decreased (P < 0.001) permeability and bacterial invasion at 6 h. A total of 100 μM Zn increased ZO-1, occludin, GPR39, and PKCζ 0.72- to 1.34-fold (P < 0.05); however, 50 μM Zn did not affect ZO-1 or occludin (P > 0.1). Silencing GPR39 decreased (P < 0.05) zinc-activated PKCζ and blocked (P < 0.05) the promotion of zinc on epithelial integrity. Furthermore, silencing PKCζ counteracted the protective effect of zinc on epithelial integrity but did not inhibit GPR39 (P = 0.138). Conclusion: We demonstrated that zinc upregulates PKCζ by activating GPR39 to enhance the abundance of ZO-1, thereby improving epithelial integrity in S. typhimurium–infected Caco-2 cells.