Parkin overexpression and glucose deprivation induce selection against different types of pathological mitochondrial DNA mutations

Thursday, November 07, 2013 — Poster Session II
12:00 p.m. – 2:00 p.m.	FAES Academic Center (Upper-Level Terrace)	NINDS	CHEMCELL-17

Authors

C.L. Nezich
D.J. Ives
R.J. Youle
I.J. Holt

Abstract

Mitochondrial DNA (mtDNA) mutations cause severe metabolic diseases and are implicated in aging, cancer, and neurodegeneration. Mitochondria contain hundreds of mtDNA copies, permitting multiple genome variants per cell. Some cell types display a clear bias for or against mutated mtDNA, but the molecular basis of this preference is obscure. Overexpression of the mitophagy protein Parkin can enrich wild-type mtDNA by clearing mitochondria harbouring a deleterious protein-coding mutation, thus implicating the PINK1-Parkin pathway in biased mtDNA segregation. Therefore, we modulated the levels of Parkin and PINK1 in cells carrying the pathogenic A3243G tRNA point mutation. Interestingly, Parkin and PINK1 overexpression did not drive the selection of WT mtDNA in this system. Rationalizing that clearance of tRNA and protein-coding gene mutations may rely on different mechanisms, we increased demand on mitochondrial function via amino acid starvation or glycolysis inhibition. These treatments reduced mutation load in a subset of clones and, additionally, glucose deprivation promoted a reproducible reduction in the tRNA mutation load, regardless of Parkin and PINK1 overexpression. We conclude that the PINK1-Parkin pathway cannot effectively filter all types of mtDNA mutations and that glucose deprivation offers a viable alternative for reducing the level of mutant mtDNA in cells.