The age- and sex-specific decline of the 20s proteasome and the Nrf2/CncC signal transduction pathway in adaption and resistance to oxidative stress in Drosophila melanogaster.

Laura C D Pomatto,Caroline Carney,Kelvin J A Davies,Brenda Shen,Sarah Wong,John Tower

doi:10.18632/aging.101218

Abstract

Hallmarks of aging include loss of protein homeostasis and dysregulation of stress-adaptive pathways. Loss of adaptive homeostasis, increases accumulation of DNA, protein, and lipid damage. During acute stress, the Cnc-C (Drosophila Nrf2 orthologue) transcriptionally-regulated 20S proteasome degrades damaged proteins in an ATP-independent manner. Exposure to very low, non-toxic, signaling concentrations of the redox-signaling agent hydrogen peroxide (H2O2) cause adaptive increases in the de novo expression and proteolytic activity/capacity of the 20S proteasome in female D. melanogaster (fruit-flies). Female 20S proteasome induction was accompanied by increased tolerance to a subsequent normally toxic but sub-lethal amount of H2O2, and blocking adaptive increases in proteasome expression also prevented full adaptation. We find, however, that this adaptive response is both sex- and age-dependent. Both increased proteasome expression and activity, and increased oxidative-stress resistance, in female flies, were lost with age. In contrast, male flies exhibited no H2O2 adaptation, irrespective of age. Furthermore, aging caused a generalized increase in basal 20S proteasome expression, but proteolytic activity and adaptation were both compromised. Finally, continual knockdown of Keep1 (the cytosolic inhibitor of Cnc-C) in adults resulted in older flies with greater stress resistance than their age-matched controls, but who still exhibited an age-associated loss of adaptive homeostasis.

Highlights

Multiple byproducts of cellular metabolism, with which aerobic organisms must cope, include numerous free radicals and reactive oxygen/nitrogen species, which can damage lipids, proteins, and DNA [1]
Prior studies suggest an age-related decline in stress resistance of D. melanogaster to stresses such as starvation [45] and the redox-cycling agent paraquat [46], resulting in increased mortality
A prior study found an increase in hydrogen peroxide (H2O2) sensitivity within 35 day old flies [47], arguably ‘middle-age’ in typical control strains of D. melanogaster [48]

Summary

Introduction

Multiple byproducts of cellular metabolism, with which aerobic organisms must cope, include numerous free radicals and reactive oxygen/nitrogen species, which can damage lipids, proteins, and DNA [1]. If damaged proteins are not immediately removed, hydrophobic protein aggregates can accumulate, cross-link, and accelerate cellular senescence [2, 3] To cope with these insults, cells rely upon an array of stress responsive enzymes, including the well-characterized 20S proteasome, which can rapidly degrade oxidized proteins in the cytoplasm, nucleus and endoplasmic reticulum, preventing proteins from forming toxic cross-linked aggregates [4,5,6]. The adaptive homeostasis process describes the ability of cells, tissues, or organisms, to activate various stressresponsive pathways, including de novo synthesis of the 20S proteasome, in response to exposure to very low www.aging‐us.com and non-toxic levels of a stimulating agent or condition. The response is not binary, but rather exhibits a dynamic range, that enables the fine-tuning in its activation. The ability to adapt to varying levels of oxidative stress declines

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