Role of defective ERK phosphorylation in the impaired GM-CSF-induced oxidative response of neutrophils in elderly humans.

GM-CSF-induced oxidative responses are defective in neutrophils of elderly humans. In the present study we evaluated whether this phenomenon might be related to alterations in cytokine-dependent MAPK signalling. Neutrophils obtained from elderly humans and stimulated with GM-CSF showed a significant reduction in phosphorylated ERK1/2 levels and an even higher decrease in ERK1/2 activation with respect to baseline. No changes in GM-CSF-induced p38 MAPK phosphorylation were observed. Cell pretreatment with the MEK inhibitor PD98059 determined a marked suppression of GM-CSF-induced O2- release. Interestingly, under the above experimental condition, there was no longer any difference in O2- production observed between elderly and young subjects. Furthermore, despite the fact that the p38 MAPK pathway was activated less strongly by GM-CSF, the p38 MAPK inhibitor SB203580 reduced GM-CSF-induced O2- production in the neutrophils of the elderly to levels similar to those obtained with PD98059. TNF-alpha-triggered O2- production was not altered by ageing and in fact, a similar ERK1/2 or p38 MAPK activation was found in TNF-alpha-stimulated neutrophils from elderly and young individuals. In accordance with the different potency of TNF-alpha in activating ERK1/2 and p38 MAPK, the TNF-alpha-induced oxidative responses were more sensitive to the inhibitory effects of SB203580 than to those of PD98059 in young as well as elderly subjects. These results suggest that, along the GM-CSF-dependent ERK signalling pathway, a step proximal to MEK1/2 but distal to the connection with the p38 MAPK module likely becomes defective as a feature of age. The consequent decline in ERK1/2 activation could potentially account for the GM-CSF-dependent impairment of the neutrophil respiratory burst that occurs with ageing.