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Rationale Activation of NLRP3 inflammasome mediating IL-1β secretion has emerged as an important component of inflammatory processes in atherosclerosis. Mitochondrial DNA (mtDNA) damage is detrimental in atherosclerosis and mitochondria are central regulators of the NLRP3 inflammasome. Human atherosclerotic plaques express increased mtDNA damage. The major DNA glycosylase OGG1, is responsible for removing the most abundant form of oxidative DNA damage. Objective To test the role of OGG1 in development of atherosclerosis in mouse. Methods and Results We observed that Ogg1 expression decreases over time in atherosclerotic lesion macrophages of Ldlr KO mice fed a western diet. Ogg1−/−Ldlr−/− mice fed a western diet resulted in an increase in plaque size and lipid content. We found increased oxidized mtDNA, inflammasome activation, and apoptosis in atherosclerotic lesions and also higher serum IL-1β and IL-18 in Ogg1−/−Ldlr−/− mice compared with Ldlr−/−. Transplantation with Ogg1−/− bone marrow (BM) into Ldlr−/− mice led to larger atherosclerotic lesions and increased IL-1β production. However, transplantation of Ogg1−/−Nlrp3−/− BM reversed the Ogg1−/− phenotype of increased plaque size. Ogg1−/− macrophages showed increased oxidized mtDNA and had greater amounts of cytosolic mtDNA and cytochrome c, increased apoptosis, and more IL-1β secretion. Finally, we found that proatherogenic miR-33 can directly inhibit human OGG1 expression and indirectly suppress both mouse and human OGG1 via AMPK. Conclusions OGG1 plays a protective role in atherogenesis by preventing excessive inflammasome activation. Our study provides insight into a new target for therapeutic intervention based on a link between oxidative mtDNA damage, OGG1, and atherosclerosis via NLRP3 inflammasome.

SUMMARY Acute lung injury (ALI) remains a serious health issue with little improvement in our understanding of the pathophysiology and therapeutic approaches. We investigated the mechanism that lipopolysaccharide (LPS) induces early neutrophil recruitment to lungs and increases pulmonary vascular permeability during ALI. Intratracheal LPS induced release of pro-interleukin-1α (IL-1α) from necrotic alveolar macrophages (AM), which activated endothelial cells (EC) to induce vascular leakage via loss of vascular endothelial (VE)-cadherin. LPS triggered the AM purinergic receptor P2X7(R) to induce Ca2+ influx and ATP depletion, which led to necrosis. P2X7R deficiency significantly reduced necrotic death of AM and release of pro-IL-1α into the lung. CD14 was required for LPS binding to P2X7R, as CD14 neutralization significantly diminished LPS induced necrotic death of AM and pro-IL-1α release. These results demonstrate a key role for pro-IL-1α from necrotic alveolar macrophages in LPS-mediated ALI, as a critical initiator of increased vascular permeability and early neutrophil infiltration.

Pathogen burden accelerates atherosclerosis, but the mechanisms remain unresolved. Activation of the NLRP3 inflammasome is linked to atherogenesis. Here we investigated whether Chlamydia pneumoniae (C.pn) infection engages NLRP3 in promoting atherosclerosis. C.pn potentiated hyperlipidemia-induced inflammasome activity in cultured macrophages and in foam cells in atherosclerotic lesions of Ldlr mice. C.pn-induced acceleration of atherosclerosis was significantly dependent on NLRP3 and caspase-1. We discovered that C.pn-induced extracellular IL-1β triggers a negative feedback loop to inhibit GPR109a and ABCA1 expression and cholesterol efflux, leading to accumulation of intracellular cholesterol and foam cell formation. Gpr109a and Abca1 were both upregulated in plaque lesions in Nlrp3 mice in both hyperlipidemic and C.pn infection models. Mature IL-1β and cholesterol may compete for access to the ABCA1 transporter to be exported from macrophages. C.pn exploits this metabolic-immune crosstalk, which can be modulated by NLRP3 inhibitors to alleviate atherosclerosis.

The effect of a-galactosylceramide (a-GalCer) on lipopolysaccharide (LPS)-mediated lethality was examined. Administration of LPS killed all mice pretreated with a-GalCer, but not untreated control mice. The lethal shock in a-GalCer-sensitized mice was accompanied by severe pulmonary lesions with marked infiltration of inflammatory cells and massive cell death. On the other hand, hepatic lesions were focal and mild. A number of cells in pulmonary and hepatic lesions underwent apoptotic cell death. a-GalCer sensitization was ineffective for the development of the systemic lethal shock in Va14-positive natural killer T cell-deficient mice. Sensitization with a-GalCer led to the circulation of a high level of interferon (IFN)-c and further augmented the production of tumor necrosis factor (TNF)-a in response to LPS. The lethal shock was abolished by the administration of anti-IFN-c or TNF-a antibody. Further, the lethal shock did not occur in TNF-a-deficient mice. Taken together, a-GalCer sensitization rendered mice very susceptible to LPS-mediated lethal shock, and IFN-c and TNF-a were found to play a critical role in the preparation and execution of the systemic lethal shock, respectively. The LPS-mediated lethal shock using a-GalCer sensitization might be useful for researchers employing experimental models of sepsis and septic shock.