Effect of the mitofusins knockout on the inheritance of deleterious mitochondrial DNA in mouse embryonic fibroblasts

Abstract

Diseases caused by mutations in the mitochondrial DNA (mtDNA) are among the most common genetic diseases in humans. These diseases result in symptoms that vary in severity between mild and lethal. However, there is no treatment option for treating mitochondrial diseases and their mechanisms of inheritance are unclear. Recently, some works have provided evidence based on in vitro models that the cells are capable of eliminating mutant mtDNAs through autophagy (e.g., mitophagy). Furthermore, several studies in mice and humans have found that deleterious mutations in mtDNA are selected against in the germline (e.g., oocytes and embryos). This mechanism seems to be associated with events of mitochondrial fusion and fission that segregate mutant and wild-type molecules of mtDNA, then exacerbating the effect of the mutation on the organelle. In spite of this, there is lack of evidence of this extension mechanism and of the molecular basis governing its occurrence. Thus, the aim of this project is to study mitochondrial inheritance in mouse embryonic fibroblasts (MEFs) with knockout of proteins responsible for mitochondrial fusion, Mfn1 and Mfn2. MEFs will be derived from heteroplasmic mice that harbor two distinct mtDNA haplotypes (C57BL/6 and NZB/BINJ), enabling to evaluate the effect of knockouts on mtDNA segregation. It is known that the NZB/BINJ haplotype results in mitochondrial dysfunction, which lead to its elimination in favor of the C57BL/6 haplotype, similar to that found for mutations causing mitochondrial disease. MEFs will be cultured under different conditions and treatments to evidence mitochondrial dysfunction caused by mtDNA NZB/BINJ and possibly mitophagy. If proved that these disturb mitochondrial segregation, the underlying mechanisms will be addressed. Among these, we will focus our studies on the role of mitophagy in the elimination of the deleterious mtDNA. It is expected that this work provide evidences of the role of mitophagy and the mitofusins (Mfn1 and Mfn2) on the inheritance of mtDNA. (AU)