Genetic Control of Mitochondrial DNA content with Aging
Our long-term goal is to access innate mechanisms to elevate mtDNA levels as a strategy to resist cardiac stress. Toward that goal, the application’s overall objective is to identify and understand mechanisms that elevate heart mtDNA levels and protect cardiomyocytes. To address this gap in a translational and mechanistic manner, we propose the following specific aims:
Aim 1: Identify genetic regulators of mouse strain-specific heart mtDNA content. Our preliminary data in mice show that heart mtDNA levels are tightly regulated, and are strain specific. We find that mtDNA abundance spans a nearly 6-fold range among eight tested strains, with tight distributions within each strain. We therefore hypothesize that mtDNA levels are genetically controlled. In this aim, we will quantitate heart mtDNA levels from 600 mice from the Diversity Outbred (DO) collection, a new high-resolution genetic mapping resource. In collaboration with Ron Korstanje and Gary Churchill at The Jackson Laboratory, we will develop multi-probe datasets for mtDNA content to determine candidate loci through Quantitative Trait Locus (QTL) mapping. We will also determine whether specific QTL differentially alter mtDNA copy number in combination with factors such as age, gender, and mtDNA sequences in the DO collection. Additional studies will utilize forthcoming proteomic and gene expression data to further elaborate the mtDNA regulatory network. The ultimate goal is to demonstrate via gene editing that the genetic variants identified are necessary and sufficient for the observed mtDNA alteration, and determine the pathways involved in mtDNA content control.
Aim 2: Test whether parental mouse lines with different mtDNA levels show correlated sensitivity to cardiac stress. Our preliminary data show a range of mtDNA levels in whole heart; however, the relativemtDNA abundance among the chambers of the heart is unknown. We hypothesize that heart chambers with higher mtDNA content are protected against cardiac stress. In this aim, we will quantitate mtDNA abundance in left and right atria, as well as left and right ventricle free wall. We expect that left ventricle, which has higher mitochondrial respiratory activity than the right ventricle or atria, will show higher levels of mtDNA than other chambers. We also expect that the left ventricle will show a larger range of differences in mtDNA levels among the founder lines than in whole heart. Knowing which chambers are genetically regulated for mtDNA abundance in these lines, we will surgically induce hemodynamic stress in that specific compartment, such as traverse aortic banding for left ventricle or fibrillation in atria, to assess how differing mtDNA levels alter vulnerability to heart failure.