The response of the mitochondrial proteome and ROS production to ageing and dietary restriction

Abstract

The free radical theory of ageing proposes ageing is the result of macromolecules, damaged by free radicals, accumulating in cells over time. Mitochondria are critical to this theory as they are the primary source of the free radical superoxide. This thesis aims to understand the effect of age and dietary restriction (DR) with regard to mitochondrial protein abundance and superoxide generation. Superoxide production and protein composition was studied from multiple ages in isolated mitochondria from both ad libitum (AL) and DR mice. Superoxide production was assessed by measuring hydrogen peroxide release from multiple electron transport chain (ETC) sites. Mass spectrometry was used to determine the mitochondrial protein composition from mouse liver tissue. Older mice have increased hydrogen peroxide release from ETC complexes I and III. DR has decreased complex I hydrogen peroxide release in brain, skeletal muscle and liver mitochondria analysed at 15 and 24 months old. DR doesn’t prevent but delays the age associated hydrogen peroxide release. Hydrogen peroxide release at the same survival point is not significantly different between AL and DR mice. The liver mitochondrial proteome is affected by age and DR. Fatty acid metabolism protein abundance increases with age whereas amino acid metabolism protein abundance decreased. Superoxide clearance protein abundance is increased in older and DR liver mitochondria. Catalase had increased abundance in DR mitochondria at 15 and 24 months than at 3 or 36 months old. In conclusion hydrogen peroxide release, superoxide clearance protein abundance and fatty acid metabolism protein abundance are increased with ageing. The age associated increase in hydrogen peroxide release is delayed in DR mitochondria possibly due to increased abundance of catalase.