Effects of Aging on the Heat Shock Response and Autophagy in Human Peripheral Blood Mononuclear Cells

Abstract

INTRODUCTIONAging is associated with an accumulation of damaged aberrant macromolecules. Autophagy is the process that contributes to the maintenance of cellular homeostasis through degradation and subsequent recycling of damaged proteins and organelles and may be coordinated by the heat shock response. In this pilot study, we tested the hypothesis that aging reduces the heat shock and autophagy responses to heat shock in human peripheral blood mononuclear cells (PBMC).METHODSFour young control (21.25 ± 1.5 years, 3 male, 1 female) and four older subjects (63 ± 2.9 years, 2 male, 2 female) participated in this study. PBMCs were isolated from whole blood and cells were analyzed for baseline levels of LC3‐II and HSP70 proteins. In subsequent studies, PBMCs collected from young and older subjects were exposed to 1 h heat incubation at 42°C, and HSP70 and LC3‐II expression were measured by Western blot analysis and normalized to β‐actin. Densitometric values (mean ± standard deviation) for baseline and heat shock studies are reported.RESULTSSurprisingly, the PBMCs from older subjects had a higher (p < .01) baseline level, 0.64 ± 0.14, of LC3‐II than the younger subjects, 0.07 ± 0.14. An increase (p < .05) in heat shock protein (HSP70) from baseline levels of 0.03 ± 0.07 to 1.77 ± 1.32 following heat shock was found in young subjects, but not older subjects. No within or between group differences were found in LC3‐II following heat shock.CONCLUSIONSContrary to findings in animals, our results suggest that autophagy is increased, not decreased with aging in humans. This increased baseline level may partially compensate for the compromised ability to upregulate HSP70 and stimulate autophagy after a heat stress exposure.