Loss of NADPH Oxidase–Derived Superoxide Skews Macrophage Phenotypes to Delay Type 1 Diabetes

Abstract

Macrophages are early islet-infiltrating cells seen in type 1 diabetes (T1D). While proinflammatory M1 macrophages induce T1D, M2 macrophages have been shown to delay this autoimmune disease in nonobese diabetic (NOD) mice, but the environmental cues that govern macrophage polarization and differentiation remain unresolved. We previously demonstrated the importance of reactive oxygen species (ROS) in T1D, as NOD mice deficient in NADPH oxidase (NOX)-derived superoxide (Ncf1m1J) were protected against T1D partly because of blunted Toll-like receptor–dependent macrophage responses. We provide evidence that NOX-derived ROS contribute to macrophage differentiation in T1D. During spontaneous diabetes progression, T1D-resistant NOD.Ncf1m1J islet-resident macrophages displayed a dampened M1 and increased M2 phenotype. The transfer of diabetogenic T cells into NOX-deficient NOD.Rag.Ncf1m1J recipients resulted in decreased TNF-α+ and IL-1β+ islet-infiltrating M1 macrophages and a concomitant enhancement in arginase-1+ M2 macrophages. Mechanistic analysis of superoxide-deficient bone marrow–derived macrophages revealed a marked diminution in a proinflammatory M1 phenotype due to decreased P-STAT1 (Y701) and interferon regulatory factor 5 compared with NOD mice. We have therefore defined a novel mechanistic link between NOX-derived ROS and macrophage phenotypes, and implicated superoxide as an important factor in macrophage differentiation. Thus, targeting macrophage redox status may represent a promising therapy in halting human T1D.

Polarization of Macrophages toward M2 Phenotype Is Favored by Reduction in iPLA2β (Group VIA Phospholipase A2)

“…11B). These mice exhibit a marked delay in developing T1D relative to NOD mice (16). These findings suggest an additional component in the inflammatory process, wherein feedback regulation of iPLA 2 ␤ involves ROS.…”

“…For the purpose of identifying susceptibility of peritoneal macrophage polarization to iPLA 2 ␤ activation, we used various analyses to compare expression of multiple recognized markers of M1 (Arg2, CCL5, CD68, CXCL10, iNOS, NOX4, STAT1, and TNF␣ mRNA; TNF␣, IL-1␤, and IL-12 protein; nitrite accumulation) and M2 (Arg1, CCL2, RELA, STAT6, CHICL3, NF-B1, MRC1, and RETNLA mRNA; TGF␤ and IL-10 protein) macrophage phenotype (13,16).…”

“…Consistent with a link between ROS and iPLA 2 ␤ is our finding that, relative to diabetes-resistant mouse strains, an increased expression of iPLA 2 ␤ mRNA is evident in islets from diabetesprone NOD female mice, an autoimmune model of T1D, but not in islets from mice deficient in NOX-derived superoxide (NOD.Ncf1 m1J ). These mice exhibit a marked delay in T1D development (16).…”

“…The NOD mice were all generated as described (16,29). Before experimentation, the mice were genotyped as described (30,78).…”

“…Whereas M1 macrophages are recognized causative factors in T1D development (14), M2 macrophages appear to protect against T1D (15). Recent studies suggest that ROS can modulate macrophage polarization and that reduction in ROS generation promotes an M2 macrophage phenotype, blunts M1 macrophage phenotype, and dramatically delays T1D onset (16). Lipid signaling is increasingly recognized to modulate inflammation and immune responses (17).…”