STAT3 regulates pathogen control and clearance in macrophages by reprogramming inflammation-induced microbial defense response
STAT3 is pivotal in controlling hyperinflammation and governing effector macrophage responses to inflammation, yet the precise mechanisms by which STAT3 mediates pathogen control and clearance remain unclear. Herein, we performed RNA sequencing in bone marrow derived macrophages (BMDMs) to investigate STAT3-mediated transcriptional regulation of LPS-induced inflammation. Genome-wide profiling revealed significant enrichment of type-I interferon (IFN-I) associated genes and the IFN Gamma response pathway in Stat3-deficient BMDMs in homeostasis. We observed significant reduction in the expression of pathogen response genes and secretion of cytokines and chemokines associated with pathogen clearance in Stat3-deficient BMDMs upon LPS stimulation. Using BM chimeric mice with 20% Stat3-deficient hematopoietic cells infected with Citrobacter rodentium, we show that STAT3 is essential for preventing bacterial dissemination to tissues and regulating production of cytokines and chemokines related to immune cell recruitment and bacterial control. Stat3-deficient BMDMs infected with C. rodentium showed impaired ability to kill intracellular bacteria and demonstrated dampened expression of pathogen response genes. Further, IL-6 blockade subdued the  intrinsic IFN signature in Stat3-deficient macrophages and rescued aberrant expression of  pathogen response genes upon LPS stimulation, suggesting STAT3 restrains an aberrant autocrine IL-6 signal that deregulates macrophage-mediated pathogen control. Our data identifies novel functions for STAT3 in orchestrating an optimal microbial defense response, by promoting bacterial control and clearance in macrophages. Overall design: To investigate the roles for STAT3 in regulation of macrophages in homeostasis and infection, we performed RNA-sequencing (RNA-seq) analyses of bone marrow-derived marophages (BMDMs) derived from CreER (wild-type controls) and CreER Stat3f/f (Stat3-deficient) bone marrow cells. BMDMs were treated with PBS or lipopolysaccharide (LPS) at two timepoints and three biologically independent samples for each treatment group and genotype were processed for RNA-seq.