A study of mitochondrial protein import in the aging brain using Nothobranchius furzeri as a model

Details

Supervisors

Page, Melissa ; Rees, Jean-François

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

Aging is a process that affects every living organism and that has an impact on the metabolism at the molecular, cellular and tissue level. One hallmark of aging is mitochondrial dysfunction. Indeed, mitochondria become less efficient to produce energy, and are more subject to oxidative stress with age. Mitochondrial dysfunction has been associated with various age-related disease, including neurodegenerative pathologies such as Alzheimer’s disease or Parkinson’s disease. One particularity of mitochondria is the requirement to import nuclear encoded protein because mitochondrial DNA only encode 13 proteins out of the more than 1000 proteins needed to function properly. Therefore, mitochondrial protein import pathways exist to enable proteins to reach the organelle after synthesis in the cytosol. Heat-shock proteins CytHsp70 and Hsp90 are the cytosolic chaperones responsible for transporting preproteins to the mitochondrial outer membrane. The translocase of the outer membrane (TOM) is responsible for transporting the preprotein to the intermembrane space via the channel formed by the subunit Tom40 protein. The inner membrane translocase (TIM23) then moves the preprotein into the mitochondrial matrix through the channel formed by Tim23. TIM23 is also a complex of several subunits, including the Tim17 protein, which plays a crucial role in the structure of the channel. These different components have been poorly studied in relation to aging in the brain. Our aim was therefore to determine whether gene expression and protein levels of these components are reduced during aging in the brain of Nothobranchius furzeri. Rt-qPCR and Western Blot were used to compare brain tissue from 6-, 14-, 20- and 26-weeks of age. Gene expression of the cytosolic chaperone CytHsp70 and the Hsp90β isoform, as well as the translocase components Tom40, Tim23 and Tim17, did not change with age. Only the expression of the Hsp90α isoform increased significantly after 26 weeks of age. Analysis of Tim23 protein levels showed a non-significant tendency to decrease with age. At the gene level, there does not appear to be an impairment in the components of import. However, this does not mean that import itself is not impacted. A study of the rate of protein import within the mitochondria is needed to determine whether import efficiency changes during aging.