MAP kinase phosphatase (Mkp)-1 Controls Program Death-Ligand (PD-L)1 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 increase mortality relative to Mkp-1+/+ mice following E. coli infection. To understand the functions of Mkp-1, we performed RNA-seq 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−/− are PD-L1 and CTLA-4, two key immune checkpoint proteins. Interestingly, the expression of PD-L1 and CTLA-4 were highly correlated with the expression of IL-6, IL-10, and STAT3. 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 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 following stimulation with either LPS or heat-killed E. coli than Mkp-1+/+ macrophages. Our studies indicate that expression of immune check point proteins, PD-L1 and CTLA-4, are controlled by Mkp-1 during microbial infection. Our studies also suggest that exaggerated expression of type I interferons and PD-L1 contribute to the phenotypes of Mkp-1−/− mice in the model of sepsis.