Somatic mutations in mitochondrial DNA (mtDNA) are hypothesized to play a role in Parkinson disease (PD), but large increases in mtDNA mutations have not previously been found in PD, potentially because neurons with high mutation levels degenerate and thus are absent in late-stage tissue. To address this issue, we studied early stage PD cases and cases of incidental Lewy body disease (ILBD), which is thought to represent presymptomatic PD. We show for the first time that mtDNA mutation levels in substantia nigra (SN) neurons are significantly elevated in this group of early PD and ILBD cases.

Lung ischemia-reperfusion (IR) injury contributes to post-transplant complications, including primary graft dysfunction. Decades of reports show that reactive oxygen species generated during lung IR contribute to pulmonary vascular endothelial barrier disruption and edema formation, but the specific target molecule(s) that "sense" injury-inducing oxidant stress to activate signaling pathways culminating in pathophysiologic changes have not been established. This review discusses evidence that mitochondrial DNA (mtDNA) may serve as a molecular sentinel wherein oxidative mtDNA damage functions as an upstream trigger for lung IR injury. First, the mitochondrial genome is considerably more sensitive than nuclear DNA to oxidant stress. Multiple studies suggest that oxidative mtDNA damage could be transduced to physiologic dysfunction by pathways that are either a direct consequence of mtDNA damage per se or involve formation of proinflammatory mtDNA damage-associated molecular patterns. Second, transgenic animals or cells overexpressing components of the base excision DNA repair pathway in mitochondria are resistant to oxidant stress-mediated pathophysiologic effects. Finally, published and preliminary studies show that pharmacologic enhancement of mtDNA repair or mtDNA damage-associated molecular pattern degradation suppresses reactive oxygen species-induced or IR injury in multiple organs, including preclinical models of lung procurement for transplant. Collectively, these findings point to the interesting prospect that pharmacologic enhancement of DNA repair during procurement or ex vivo lung perfusion may increase the availability of lungs for transplant and reduce the IR injury contributing to primary graft dysfunction.

Lung IR injury mtDNA damage Lung transplant mtDNA DAMPs a b s t r a c t Background: Transplantation of lungs procured after donation after circulatory death (DCD)is challenging because postmortem metabolic degradation may engender susceptibility to ischemiaereperfusion (IR) injury. Because oxidative mitochondrial DNA (mtDNA) damage has been linked to endothelial barrier disruption in other models of IR injury, here we used a fusion protein construct targeting the DNA repair 8-oxoguanine DNA glycosylase-1 (OGG1) to mitochondria (mtOGG1) to determine if enhanced repair of mtDNA damage attenuates endothelial barrier dysfunction after IR injury in a rat model of lung procurement after DCD.Materials and methods: Lungs excised from donor rats 1 h after cardiac death were cold stored for 2 h after which they were perfused ex vivo in the absence and presence of mt-OGG1 or an inactive mt-OGG1 mutant. Lung endothelial barrier function and mtDNA integrity were determined during and at the end of perfusion, respectively. Results and Conclusions:Mitochondria-targeted OGG1 attenuated indices of lung endothelial dysfunction incurred after a 1h post-mortem period. Oxidative lung tissue mtDNA damage as well as accumulation of proinflammatory mtDNA fragments in lung perfusate, but not nuclear DNA fragments, also were reduced by mitochondria-targeted OGG1. A repairdeficient mt-OGG1 mutant failed to protect lungs from the adverse effects of DCD procurement.Conclusions: These findings suggest that endothelial barrier dysfunction in lungs procured after DCD is driven by mtDNA damage and point to strategies to enhance mtDNA repair in concert with EVLP as a means of alleviating DCD-related lung IR injury. ª

Dear Editor, Plasma mitochondrial DNA (mtDNA) fragment abundance has emerged as a biomarker in multiple human disorders, thus pointing to the prospect that mtDNA, like F I G U R E 1 RNA target bait-capture and bioinformatics protocol and nuclear mitochondrial (NUMT) identification. (A) DNA is isolated from plasma or tissue. In the figure, nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) are denoted by colour. DNA isolation and library preparation are applied to all sample DNA, regardless of nuclear or mitochondrial origin. A target bait-capture kit consists of biotinylated RNA probes complementary to the mitochondrial genome. The probes efficiently bind mtDNA but can also bind homologous NUMT, as illustrated by the DNA fragment half coloured as mitochondrial and half coloured as nuclear. Once enriched, samples are pooled and sequenced on a standard Illumina instrument. From there, a Workflow Description Language pipeline aligns the reads to the whole genome -nuclear and mitochondrial. Three custom C/C++ programs built on the htslib library then call mitochondrial and nuclear coverage, insert (the size of a fragment after end repair and sequencing adapter ligation), and variant calling. (B) Schematic depiction of how target-bait capture also leads to the sequencing of flanking regions of polymorphic NUMTs. (C) Integrated Genome Viewer (IGV) histograms depicting a specific polymorphic NUMT in a nontransfused patient whereas the second patient lacks this insertion at either t0 or t72 post-admittance. Subfigures (A) and (B) were prepared in Inkscape.