Cystic fibrosis (CF) is a common and deadly inherited disease, caused by mutations in the CFTR gene that encodes a cAMP-activated chloride channel. One outstanding manifestation of the disease is the persistent bacterial infection and inflammation in the lung, which claims over 90% of CF mortality. It has been debated whether neutrophil-mediated phagocytic innate immunity has any intrinsic defect that contributes to the host lung defense failure. Here we compared phagosomal CFTR targeting, hypochlorous acid (HOCl) production, and microbial killing of the neutrophils from myeloid Cftr-inactivated (Myeloid-Cftr−/−) mice and the non-inactivated control (Cftrfl10) mice. We found that the mutant CFTR that lacked Exon-10 failed to target to the neutrophil phagosomes. This dysfunction resulted in impaired intraphagosomal HOCl production and neutrophil microbial killing. In vivo lung infection with a lethal dose of Pseudomonas aeruginosa caused significantly higher mortality in the myeloid CF mice than in the controls. The myeloid-Cftr−/− lungs were deficient in bacterial clearance, and had sustained neutrophilic inflammation and stalled transition from early to late immunity. These manifestations recapitulated the symptoms of human CF lungs. The data altogether suggest that myeloid CFTR expression is critical to normal host lung defense. CFTR dysfunction in neutrophils compromises the phagocytic innate immunity, which may predispose CF lungs to infection.

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Though the presence of anti-oxLDL IgG is well documented in clinical and animal studies, the role for FcγRs to the progression of atherosclerosis has not been studied in detail. In the present study, we investigated the role for activating FcγR in the progression of atherosclerosis using apoE-Fcγ chain double knockout (DKO) mice. Relative to apoE KO mice, arterial lesion formation was significantly decreased in apoE-Fcγ chain DKO mice. Bone marrow chimera studies showed reduced lesions in apoE KO mice receiving the bone marrow of apoE-Fcγ chain DKO mice. Compared to apoE KO mice, anti-oxLDL IgG1 (Th2) and IgG2a (Th1), IL-10, and IFN-γ secretion by activated T cells were increased in apoE-Fc γ chain DKO mice. These findings suggest that reduced atherosclerotic lesion in apoE-Fcγ chain DKO mice is not due to Th1/Th2 imbalance. Interestingly, number of Th17 cells and the secretion of IL-17 by activated CD4+ cells were decreased in apoE-Fcγ chain DKO mice. Notably, the number of T-regulatory cells, expression of mRNA, and secretion of TGF-β and IL-10 were increased in apoE-Fcγ chain DKO mice. Furthermore, secretions of IL-6 and STAT-3 phosphorylation essential for Th17 cell genesis were reduced in apoE-Fcγ chain DKO mice. Importantly, decrease in Th17 cells in apoE-Fcγ chain DKO mice was due to reduced IL-6 release by antigen presenting cells of apoE-Fcγ chain DKO mice. Collectively, our data suggest that activating FcγR promotes atherosclerosis by inducing Th17 response in the hyperlipidemic apoE KO mouse model.

Macrophage‐mediated inflammation is an explicitly robust biologic response that plays a critical role in maintaining tissue homeostasis by eliminating deleterious agents. These tissue macrophages tailor appropriate responses to external cues by altering inflammatory gene expression. Therefore, transcription factors and regulators that modulate inflammatory gene expression play an essential role in shaping the macrophage inflammatory response. Here, we identify that Kruppel‐like factor (KLF)6 promotes inflammation by restraining microRNA‐223 (miR‐223) expression in macrophages. We uncovered that pro‐ and anti‐inflammatory agents oppositely regulate KLF6 and miR‐223 expression in macrophages. Using complementary gain‐ and loss‐of‐function studies, we observed that overexpression of KLF6 attenuates and deficiency of KLF6 elevates miR‐223 expression in macrophages. Furthermore, heightened miR‐223 expression in KLF6‐deficient macrophages significantly attenuates inducible proinflammatory gene expression. Concordantly, myeloid‐KZ/6 deficiency significantly curbs diet‐induced adipose tissue inflammation, obesity, glucose intolerance, and insulin resistance. At the molecular level, KLF6 directly represses miR‐223 expression by occupying its promoter region. More importantly, genetic inhibition of miR‐223‐3P in KLF6‐deficient macrophages completely reversed attenuated proinflammatory gene expression in macrophages. Collectively, our studies reveal that KLF6 promotes proinflammatory gene expression and functions by repressing miR‐223 expression in macrophages.—Kim, G.‐D., Ng, H. P., Patel, N., Mahabeleshwar, G. H. Kruppel‐like factor 6 and miR‐223 signaling axis regulates macrophage‐mediated inflammation. FASEB J. 33, 10902–10915 (2019). http://www.fasebj.org