Monocyte-derived macrophages are the most abundant innate immune cells in the gut and are essential for host defense and homeostasis. Resident intestinal macrophages are anti-inflammatory in nature and regulate epithelial integrity. However, in an inflammatory state, classically activated macrophages are recruited into the gut. These macrophages are a substantial source of pro-inflammatory agents and contribute to chronic intestinal inflammation. The transcriptional events governing macrophage activation and gene expression in the context of chronic inflammation such as Inflammatory bowel disease (IBD) remain incompletely understood. Recently, we identified Kruppel-like transcription factor 6 (KLF6) as a critical regulator of pathogenic myeloid cell activation in human and experimental IBD.Methods:
Colonic biopsies and blood samples were obtained from healthy adult volunteers or patients with diagnosed Crohn's colitis or UC during endoscopy following informed consent. Total RNA derived from monocyte-derived macrophages and tissue samples were evaluated for inflammatory gene expression by quantitative PCR analysis. Myeloid-specific KLF6 null mice were generated by crossing Klf6 floxed mice with Lyz2cre mice expressing the lysozyme M promoter-driven Cre recombinase. Primary macrophages derived from these mice were stimulated pro- or anti-inflammatory agents and analyzed for alteration in inflammatory gene expression program. Further, control and myeloid KLF6-null mice were challenged to DSS-induced colitis and were assessed for body weight change, intestinal bleeding, colonic endoscopy and euthanized for collection of colon tissues following the procedure.Results:
We observed that KLF6 was significantly upregulated in myeloid cells and intestinal tissue from IBD patients and experimental models of IBD, particularly in actively inflamed regions of the colon. Using complementary gain- and loss-of-function studies, we observed that KLF6 promotes pro-inflammatory gene expression, while suppressing anti-inflammatory gene expression in myeloid cells. At the molecular level, KLF6 suppresses BCL6 expression to promote pro-inflammatory gene expression in macrophages. Interestingly, KLF6 suppressed anti-inflammatory gene expression through repression of signal transducer and activator of transcription 3 (STAT3) signaling. Importantly, myeloid-specific KLF6-knockout mice were protected against DSS-induced. Further, loss of myeloid KLF6 significantly attenuated prothrombotic gene expression and reduced systemic vascular inflammation.Conclusions:
Collectively, our observations reveal that myeloid-KLF6 is a novel transcriptional regulator that enhances pro-inflammatory macrophage activation in the setting of chronic intestinal inflammation and associated vascular complications such as thrombosis.