Abstract Background Recent advances in immunology revealed causal roles of self-derived DNA fragments in the pathogenesis of lifestyle-associated diseases. DNase II (DN2) is an essential enzyme digesting DNA fragments, particularly in macrophages. Previous studies have demonstrated that DN2 deficiency provokes innate immunity, leading to the development of inflammatory diseases. However, its role in metabolic disorders remains unknown. This study investigated the role of DN2 in obesity-induced adipose tissue inflammation and metabolic disorder. Methods and results Macrophage-specific DN2 knockout (DN2-KO) mice were generated through crossbreeding of DN2-flox mice with LysM/Cre mice. DN2-KO mice and DN2-flox mice were fed a high-fat diet (HFD) for 12 weeks, then inflammation and metabolic status were assessed. High-fat feeding increased body weight in both strains, although the weight of visceral fat was lighter (P 0.001), and the weight of the liver was heavier (P 0.001) in DN2-KO mice compared with DN2-flox mice. DN2-KO mice showed impaired insulin resistance as determined by GTT (P 0.001) and ITT (P 0.05). In fact, insulin-stimulated Akt phosphorylation in the adipose tissue (P 0.05) as well as in the liver and muscle (P 0.05) were reduced in DN2-KO mice. Macrophage-specific DN2 deletion accumulated DNA fragments in the cytosol of adipose tissue macrophages. Macrophage-specific DN2 deletion promoted macrophage infiltration (P 0.001) and skewed macrophage polarization towards M1 phenotype in the adipose tissue. Expectedly, in the white adipose tissue of DN2-KO mice, the expression of inflammatory molecules (e.g., TNF-α and IL-12b) was significantly higher, while the expression of insulin sensitivity-related genes such as PPARγ (P 0.01) and adiponectin (P 0.05), and angiogenic markers (P 0.05) was lower. In in vitro experiments using murine macrophages, stimulation with TLR9 agonist, CpG1826, increased TNF-α and IL-12b expression (P 0.05) in DN2-deficient macrophages, accompanied by the activation of NF-κB and MAPK pathways. On the other hand, overexpression of DN2 in macrophages by transfection of coding plasmid significantly suppressed CpG1826-induced inflammatory responses. Conclusion The lack of digestion ability of DNA fragments regulated by DN2 plays a crucial role in pro-inflammatory activation of macrophages and development of insulin resistance in obese mice. Our results also suggested that DN2 can be a potential therapeutic target against inflammatory disorders associated with cell-free DNA fragments.
Bavuu et al. (Sat,) studied this question.