Oxidized and Original article degraded mitochondrial polynucleotides (DeMPs), especially RNA, are potent immunogenic regulators in primary mouse macrophages

Abstract

Certain mitochondrial components can act as damage-associated molecular patterns (DAMPs) or danger signals, triggering a proinflammatory response in target (usually immune) cells. We previously reported the selective degradation of mitochondrial DNA and RNA in response to cellular oxidative stress, and the immunogenic effect of this DNA in primary mouse astrocytes. Here, we extend these studies to assess the immunogenic role of both mitochondrial DNA and RNA isolated from hydrogen peroxide (HP) treated HA1 cells (designated "DeMPs" for degraded mitochondrial polynucleotides) using mouse bone marrow derived macrophages (BMDMs), a conventional immune cell type. DeMPs and control mitochondrial DNA (cont mtDNA) and RNA (cont mtRNA) were transfected into BMDMs and cell-free media analyzed for the presence of proinflammatory cytokines (IL-6, MCP-1, and TNFα) and Type I interferon (IFN-α and IFN-β). Cont mtDNA induced IL-6 and MCP-1 production, and this effect was even greater with DeMP DNA. A similar response was observed for Type I interferons. An even stronger induction of proinflammatory cytokine and type 1 interferons was observed for cont mtRNA. However, contrary to DeMP DNA, DeMP RNA attenuated rather than potentiated the cont mtRNA cytokine inductions. This attenuation effect was not accompanied by an IL-10 or TGFβ anti-inflammatory response. All DeMP effects were observed at multiple oxidant concentrations. Finally, DeMP production and immunogenicity overlaps with cellular adaptive response and so may contribute to cellular oxidant protection. These results provide new insight into the immunogenicity of mitochondrial polynucleotides, and identify new roles and selective consequences of cellular oxidation.

Keywords: DAMPs; DeMPs; Degraded mitochondrial polynucleotides; Hydrogen peroxide; Macrophages; Mitochondria; Oxidative stress; Proinflammatory cytokine.