Genetic dissection of mitonuclear interactions in aging and neurodegenerative disease

ABSTRACT Mitochondria are ancient cellular “powerhouses” critical to energy metabolism. They contain their own, maternally transmitted genome (mtDNA) that encodes 13 components required for oxidative phosphorylation, but the remaining >99% (~1100 proteins) of its proteome, including all proteins required for mtDNA replication and maintenance, is encoded by the nuclear genome. mtDNA is a high copy number genome, and when a cell contains a mixture of wild-type and mutant mtDNA molecules, a state of “heteroplasmy” results. It has long been known that as we age, our mtDNA copy number declines and mtDNA mutational heteroplasmy accumulates. A decline in mtDNA copy number has also been documented in the blood and brains of patients with Alzheimer’s disease, while an accumulation of mtDNA heteroplasmy has been documented in Parkinson’s disease and Lewy body dementia. At present we do not know the origins of these mtDNA alterations and whether they contribute in a causal way to Alzheimer’s disease and related dementias (ADRD), but certainly, mitochondrial interactions are key. Understanding mitonuclear interactions has historically been challenging due to a lack of key technologies. During the past four years our lab has contributed to two technological advances that will now transform our approach to mitonuclear genetic interactions: (i) mtDNA editing using ddCBE base editors (as CRISPR doesn’t work in mitochondria) and (ii) biobank-scale analysis of mtDNA copy number and heteroplasmy across hundreds of thousands of humans. In this grant we propose to leverage these two new technologies to systematically investigate how mitonuclear interactions contribute to aging and age-associated neurodegenerative diseases such as Alzheimer’s disease. We anticipate generating an experimentally validated inventory of nuclear genes and proteins that control mtDNA copy number. Importantly, we will also better understand if and how mutations in the nuclear genome interact with mutations in the mtDNA to contribute to ADRD.