MAP Kinase Phosphatase (Mkp)-1 Controls Type I Interferon (IFN) and PD-L1 Expression during Sepsis

Abstract

Abstract Mkp-1 is a critical negative regulator of the inflammatory response and plays a crucial role for bacterial clearance in an animal model of sepsis. Mkp-1−/− mice exhibit augmented inflammation, increased bacterial burden, elevated organ damage, and increased mortality relative to Mkp-1+/+ mice following systemic E. coli infection. To understand the immunological functions of Mkp-1, we performed RNA-seq analysis with mouse livers. Under normal conditions, 357 genes were differentially expressed between Mkp-1+/+ and Mkp-1−/− mice. However, following E. coli infection > 5,400 genes displayed differential expression between the two groups. Among genes upregulated by E. coli infection and exacerbated by Mkp-1 knockout are IL-6, IL-10, as well as a large number of IFN-inducible genes including Mx1/2, Gbp2/3, Isg15, Usp18, Ifitm1-3, STAT3, and immune checkpoint protein PD-L1. qRT-PCR and Western blot analyses verified E. coli infection-induced PD-L1 expression and further exacerbation in Mkp-1−/− mice. Examination of the RNA-seq dataset also revealed a clear interferon signature. ELISA analyses on the serum revealed low IFN-β levels in uninfected Mkp-1+/+ and Mkp-1−/− mice, increased IFN-β levels in E. coli-infected Mkp-1+/+ mice, and further augmented IFN-β levels in E. coli-infected Mkp-1−/− mice. Similarly, Mkp-1−/− bone marrow-derived macrophages also produced more IFN-β than Mkp-1+/+ macrophages following stimulation with either LPS or heat-killed E. coli. Analysis of the signaling pathways critical for IFN-β expression indicates a marked increase in TBK1 activity. Our studies suggest that exaggerated expression of type I interferons and PD-L1 contribute to the phenotypes of Mkp-1−/− mice in the model of sepsis.