Investigating mito-nuclear interactions in human admixed populations

To function properly, mitochondria utilize products of 37 mitochondrial and >1,000 nuclear genes, which should be compatible with each other. Discordance between mitochondrial and nuclear genetic ancestry could contribute to phenotypic variation in admixed populations. Here we explored potential mito-nuclear incompatibility in six admixed human populations from the Americas: African Americans, African Caribbeans, Colombians, Mexicans, Peruvians, and Puerto Ricans. By comparing nuclear vs. mitochondrial ancestry in these populations, we first show that mtDNA copy number decreases with increasing discordance between nuclear and mitochondrial DNA ancestry. The direction of this effect is consistent across mtDNA haplogroups of different geographic origins. This observation suggests suboptimal regulation of mtDNA replication when its components are encoded by nuclear and mtDNA genes with different ancestry. Second, while most populations analyzed exhibit no such trend, in African Americans and Puerto Ricans, we find a significant enrichment of ancestry at nuclear-encoded mitochondrial genes towards the source populations contributing the most prevalent mtDNA haplogroups (African and Native American, respectively). This possibly reflects compensatory effects of selection in recovering mito-nuclear interactions optimized in the source populations. Our results provide evidence of mito-nuclear interactions in human admixed populations and we discuss their implications for human health and disease.