In several important lung diseases, including emphysema, vascular remodeling after ARDS, andpossibly primary pulmonary hypertension, there is a prominent cytotoxic response of pulmonarymicrovascular endothelial cells (MV ECs) leading to a diminution in capillary density. While there is no doubtthat reactive oxygen species play an important role in this response, the specific target(s) of ROS that serveas a sentinel molecule - triggering cell death when the oxidant stress is so severe as to preclude effectiverecovery or threaten the organism with mutation - is not known. In this regard, an intriguing target of ROS ismitochondrial (mt) DNA. The mitochondrial genome is at least 30-fold more sensitive to oxidative damagethan nuclear DNA, and our work during the initial funding period supports the hypothesis that oxidativemtDNA damage is a proximate trigger for lung EC death. If this hypothesis is valid, then mtDNA repairpathways could emerge as a new target for intervention in oxidant-induced MV EC death and capillaryrarefaction. However, there is a stark lack of the information about the details of mtDNA repair in MV ECsand other cells. For example, while it is suspected that the base excision repair mechanism is the dominantpathway defending the mitochondrial genome from oxidative damage, the presence of other DNA repairpathway components suggests that a more complicated repair paradigm could be operative. In addition,neither the identities of the enzymes participating in mitochondrial base excision repair nor the rate limitingdeterminants are known. Against this background, the Aims of this proposal are to: (1) Identify the dominantpathway repairing oxidative damage to the mitochondrial genome in MV ECs; (2) Determine the rate-limitingfunctional steps in mtDNA repair; and, (3) Establish the critical operational enzymes repairing mtDNA in MVECs. Collectively, these studies will provide the first detailed understanding of pathways defending themitochondrial genome in this important lung cell population and determine the suitability of mtDNA repairenzymes to serve as isolated targets for intervention. Importantly, the outcome of these studies also will setthe stage for pre-clinical, translational experiments on the ability of augmented mtDNA repair to suppresscapillary rarefaction in relevant animal models.
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