Abstract
Mitochondria and mitochondrial debris are found in the brain’s extracellular space, and extracellular mitochondrial components can act as damage associated molecular pattern (DAMP) molecules. To characterize the effects of potential mitochondrial DAMP molecules on neuroinflammation, we injected either isolated mitochondria or mitochondrial DNA (mtDNA) into hippocampi of C57BL/6 mice and seven days later measured markers of inflammation. Brains injected with whole mitochondria showed increased Tnfα and decreased Trem2 mRNA, increased GFAP protein, and increased NFκB phosphorylation. Some of these effects were also observed in brains injected with mtDNA (decreased Trem2 mRNA, increased GFAP protein, and increased NFκB phosphorylation), and mtDNA injection also caused several unique changes including increased CSF1R protein and AKT phosphorylation. To further establish the potential relevance of this response to Alzheimer’s disease (AD), a brain disorder characterized by neurodegeneration, mitochondrial dysfunction, and neuroinflammation we also measured App mRNA, APP protein, and Aβ1–42 levels. We found mitochondria (but not mtDNA) injections increased these parameters. Our data show that in the mouse brain extracellular mitochondria and its components can induce neuroinflammation, extracellular mtDNA or mtDNA-associated proteins can contribute to this effect, and mitochondria derived-DAMP molecules can influence AD-associated biomarkers.
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Acknowledgments
This project was supported by the University of Kansas Alzheimer’s Disease Center (P30 AG035982), the Frank and Evangeline Thompson Alzheimer’s Treatment Program fund, the Kansas IDeA Network for Biomedical Research Excellence (KINBRE, P20GM103418), the University of Kansas Medical Center Biomedical Research Training Program, and a Mabel Woodyard Fellowship award. No conflicts of interest, financial or otherwise, are declared by the authors.
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Supplemental Figure 1
Enrichment of mitochondria and mtDNA. A. Western blot quantification of TATA BP (nuclear marker), GAPDH (cytosolic marker), and Cox4I (mitochondrial marker) in mitochondrial lysates. B. qPCR verification of mtDNA enrichment. (GIF 40 kb)
Supplemental Figure 2
Representative Immunoblots. A. p-NFĸB (p65, Ser536), NFĸB, and actin. B. p-AKT (Ser473), AKT, and actin. C. p-AKT (Thr308), AKT, and actin. D. CSF1R and HDAC1. (GIF 113 kb)
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Wilkins, H.M., Koppel, S.J., Weidling, I.W. et al. Extracellular Mitochondria and Mitochondrial Components Act as Damage-Associated Molecular Pattern Molecules in the Mouse Brain. J Neuroimmune Pharmacol 11, 622–628 (2016). https://doi.org/10.1007/s11481-016-9704-7
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DOI: https://doi.org/10.1007/s11481-016-9704-7