Upregulation of the mitochondrial Lon Protease allows adaptation to acute oxidative stress but dysregulation is associated with chronic stress, disease, and aging

Abstract

The elimination of oxidatively modified proteins is a crucial process in maintaining cellular homeostasis, especially during stress. Mitochondria are protein-dense, high traffic compartments, whose polypeptides are constantly exposed to superoxide, hydrogen peroxide, and other reactive species, generated by 'electron leakage' from the respiratory chain. The level of oxidative stress to mitochondrial proteins is not constant, but instead varies greatly with numerous metabolic and environmental factors. Oxidized mitochondrial proteins must be removed rapidly (by proteolytic degradation) or they will aggregate, cross-link, and cause toxicity. The Lon Protease is a key enzyme in the degradation of oxidized proteins within the mitochondrial matrix. Under conditions of acute stress Lon is highly inducible, possibly with the oxidant acting as the signal inducer, thereby providing increased protection. It seems that under chronic stress conditions, however, Lon levels actually decline. Lon levels also decline with age and with senescence, and senescent cells even lose the ability to induce Lon during acute stress. We propose that the regulation of Lon is biphasic, in that it is up-regulated during transient stress and down-regulated during chronic stress and aging, and we suggest that the loss of Lon responsiveness may be a significant factor in aging, and in age-related diseases.

Keywords: 2D-PAGE, two-dimensional polyacrylamide gel electrophoresis; AAA, ATPases associated with diverse cellular activities; Aco1, Aconitase 1; Adaptation; CDDO, 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid; CDDO-Me, methyl-2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oate; COX, cytochrome c oxidase; COX4-1, cytochrome c oxidase subunit IV isoform 1; COX4-2, cytochrome c oxidase subunit IV isoform 2; Ccp1, mitochondrial cytochrome-c peroxidase; Clp, caseinolytic protease; ClpP, core catalytic protease unit; ERAD, endoplasmic reticulum-associated degradation; FRDA, Friedreich's ataxia; Fe/S, iron/SULFUR; HAART, highly active antiretroviral therapy; HIF-1, hypoxia inducible factor-1; HSP104, heat shock protein 104; HSP60, heat shock protein 60; Hormesis; HsIVU, bacterial ATP-dependent protease; Lon Protease; MELAS, mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes; MPPβ, mitochondrial processing peptidase beta subunit; Mitochondria; NRF-2, nuclear factor (erythroid-derived 2)-like 2; Nfκb, nuclear factor kappa-light-chain-enhancer of activated B csells; Oxidative stress; PRSS15, LON gene; Pim1, ATP-dependent Lon protease from yeast; Protease La, ATP-dependent protease; Protein degradation and oxidation; Prx1, mitochondrial peroxiredoxin 1; SLLVY-AMC, N-succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin; SOD, cytosolic superoxide dismutase; SOD2, mitochondrial superoxide dismutase 2; SPG13, hereditary spastic paraplegia; WI-38, human lung fibroblast; Yjl200c, mitochondrial aconitase isozyme.