Regulation by Jun N-terminal kinase/stress activated protein kinase of cytokine expression in Mycobacterium avium subsp paratuberculosis-infected bovine monocytes

Abstract

Objective - To evaluate activation of Jun N-terminal kinase/ stress-activated protein kinase (JNK/SAPK) pathway in bovine monocytes after incubation with Mycobacterium avium subsp paratuberculosis (Mptb) organisms. Sample Population - Bovine monocytes obtained from 4 healthy adult Holstein dairy cows. Procedures - Bovine monocytes were incubated with Mptb organisms with or without a specific inhibitor of the JNK/SAPK pathway (SP600125) for 2, 6, 24, or 72 hours. Expression of interleukin (IL)-1β, IL-10, IL-12, IL-18; transforming growth factor-β (TGF-β); and tumor necrosis factor-α (TNF-α) and the capacity of Mptb-infected monocytes to acidify phagosomes and kill Mptb organisms were evaluated. Phosphorylation status of JNK/SAPK was evaluated at 10, 30, and 60 minutes after Mptb incubation. Results - Compared with uninfected control monocytes, Mptb-infected monocytes had increased expression of IL-10 at 2 and 6 hours after incubation and had increased expression of TNF-α, IL-1β, IL-18, and TGF-β at 2, 4, and 6 hours. Additionally, Mptb-infected monocytes had increased expression of IL-12 at 6 and 24 hours. Addition of SP600125 (specific chemical inhibitor of JNK/SAPK) resulted in a decrease in TNF-α expression at 2, 6, and 24 hours, compared with untreated Mptb-infected cells. Addition of SP600125 resulted in a decrease in TGF-β expression at 24 hours and an increase in IL-18 expression at 6 hours. Addition of SP600125 failed to alter phagosome acidification but did enhance the capacity of monocytes to kill Mptb organisms. Conclusions and Clinical Relevance - Activation of JNK/SAPK may be an important mechanism used by Mptb to regulate cytokine expression in bovine monocytes for survival and to alter inflammatory and immune responses.