Age-related protein and mRNA expression of glutathione peroxidases (GPx) and Hsp-70 in different regions of rat kidney with and without stressor

Abstract

Small molecular weight oxygen free radical species (ROS) involved in oxidative stress can cause damage to cellular macromolecules including proteins, DNA and lipids. One of the most important enzymes involved in ROS detoxification is glutathione peroxidase (GPx). Here we study the age-related expression of GPx isoenzymes in various parts of the rat kidney with and without exposure to external oxidative stress. These results are correlated to the age dependent changes in the expression of the chaperone, 'Hsp-70'. Protein and mRNA expression of GPx1 and GPx4 was studied in different regions of the kidney in ageing rats in the presence and absence of the external stressor 0.2 mM H₂O₂. Protein levels were examined by Western blot analysis following detection with appropriate antibodies and mRNA levels were analysed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) using appropriate primer sequences. mRNA expression for the chaperone 'Hsp70' was investigated in parallel. After reaching a peak at maturity (12 weeks), GPx1 protein and mRNA levels decreased with age under both control and stress conditions, and were higher in the cortex than in the outer and inner medulla. GPx4 protein and mRNA levels showed few comparable age-related changes. By contrast with the observed age-related decrease in GPx1 expression, chaperone 'Hsp-70' mRNA expression greatly increased with age. These findings suggest that the age-related decline in GPx1 expression in the cortex may be partly offset by a reciprocal change in 'Hsp-70' expression. These results are consistent with the oxidative stress theory of ageing.