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Free radicals produced by chronic inflammation cause cumulative damage to cellular macromolecules and appear to contribute to senescence/aging, age-related disorders, and neuromuscular degenerative diseases such as inclusion-body myositis. Proteins are major targets for oxidative damage (in addition to DNA and lipids) and the accumulation of oxidized proteins has been reported in many aging and disease models. In young and healthy individuals, moderately oxidized soluble cell proteins are selectively and rapidly degraded by the 20S proteasome. The mechanism of selective proteolysis appears to depend upon oxidation-induced protein unfolding, with increasing surface hydrophobicity as (previously shielded) hydrophobic residues are exposed from the interior. The 20S proteasome can preferentially bind to and degrade such mildly oxidized, hydrophobic proteins without a need for ubiquitin targeting or ATP activation. Severely oxidized, aggregated, and crosslinked proteins, however, are poor substrates for degradation and actually inhibit the proteasome. During aging, and in many age-related diseases/disorders, the proteasome is progressively inhibited by binding to increasing levels of oxidized and cross-linked protein aggregates. Cellular aging and inflammatory neuromuscular degenerative diseases probably include both an increase in the generation of reactive oxygen species as well as a decline in proteasome activity, resulting in the progressive accumulation of oxidatively damaged protein aggregates that eventually contribute to cellular dysfunction and senescence.

This study examined the hypothesis that postischemic levels of oxidized and/or ubiquitinated proteins may be predictive of functional recovery as they may be indicative of activity of the 20S and/or 26S proteasomes, respectively. Subjecting isolated rat hearts to 15 min of ischemia had no effect on 20S- and 26S-proteasome activities; however, both were significantly (p < 0.05) decreased by 70% and 54%, respectively, following 30 min of ischemia and 60 min of reperfusion, changes associated with increased levels of protein carbonyls and ubiquitinated proteins. Preischemic treatment of hearts with the proteasome inhibitor, MG132, resulted in dose-dependent decreases (p < 0.05) in recovery of postischemic function [MG132 (microM), heart rate x pressure product: 0, 11,158 +/- 2,423; 6, 11,400 +/- 3,009; 12, 5,513 +/- 2,225; 25, 2,325 +/- 992] and increased accumulation of ubiquitinated proteins. Preconditioning with repetitive ischemia (IP) or preischemic treatment with nicorandil (Nic) resulted in a significant increase in postischemic 20S-proteasome activity after 60 min of reperfusion (control, 95 +/- 4; IP, 301 +/- 65; Nic, 242 +/- 61 fluorescence units). Only Nic had similar effects on 26S-proteasome activity. These results support the conclusion that a correlation exists between eventual recovery of postischemic function and levels of oxidized and/or ubiquitinated proteins, a phenomenon that may be dependent on activity of the 20S and 26S proteasomes.

A significant body of evidence supports a key role for free radicals in causing cumulative damage to cellular macromolecules, thereby contributing to senescence/aging, and a number of age-related disorders. Proteins are recognized as major targets for oxidative damage (in addition to DNA and lipids) and the accumulation of oxidized proteins has been reported for many experimental aging models, as measured by several markers for protein oxidation. In young and healthy individuals, moderately oxidized soluble cell proteins are selectively and rapidly degraded by the proteasome. However, severely oxidized, cross-linked proteins are poor substrates for degradation and actually inhibit the proteasome. Considerable evidence now indicates that proteasome activity declines during aging, as the protease is progressively inhibited by binding to ever increasing levels of oxidized and cross-linked protein aggregates. Cellular aging probably involves both an increase in the generation of reactive oxygen species and a progressive decline in proteasome activity, resulting in the progressive accumulation of oxidatively damaged protein aggregates that eventually contribute to cellular dysfunction and senescence.

Determines whether ubiquitin conjugation is necessary for the degradation of oxidized proteins in intact cells. Inhibition of degradation by proteasome inhibitors; Rates of oxidized protein degradation by cell lysates; Presence of adenosine triphosphate; Tendency of a protein to be ubiquitinylated.

A significant body of evidence supports a key role for free radicals in causing cumulative damage to cellular macromolecules, thereby contributing to senescence/aging, and a number of age-related disorders. Proteins are recognized as major targets for oxidative damage (in addition to DNA and lipids) and the accumulation of oxidized proteins has been reported for many experimental aging models, as measured by several markers for protein oxidation. In young and healthy individuals, moderately oxidized soluble cell proteins are selectively and rapidly degraded by the proteasome. However, severely oxidized, cross-linked proteins are poor substrates for degradation and actually inhibit the proteasome. Considerable evidence now indicates that proteasome activity declines during aging, as the protease is progressively inhibited by binding to ever increasing levels of oxidized and cross-linked protein aggregates. Cellular aging probably involves both an increase in the generation of reactive oxygen species and a progressive decline in proteasome activity, resulting in the progressive accumulation of oxidatively damaged protein aggregates that eventually contribute to cellular dysfunction and senescence. [Copyright &y& Elsevier]

Reactive oxygen species generated as by-products of oxidative metabolism, or from environmental sources, frequently damage cellular macromolecules. Proteins are recognized as major targets of oxidative modification, and the accumulation of oxidized proteins is a characteristic feature of aging cells. An increase in the amount of oxidized proteins has been reported in many experimental aging models, as measured by the level of intracellular protein carbonyls or dityrosine, or by the accumulation of protein-containing pigments such as lipofuscin and ceroid bodies. In younger individuals, moderately oxidized soluble cell proteins appear to be selectively recognized and rapidly degraded by the proteasome. An age-related accumulation of oxidized proteins could, therefore, be a result of declining activity of the proteasome. Previous research to investigate the notion of an age-related decline in the content and/or activity of the proteasome has generated contradictory results. The latest evidence, including our own recent findings, indicates that proteasome activity does, indeed, decline during aging as the enzyme complex is progressively inhibited by oxidized and cross-linked protein aggregates. We propose that cellular aging involves both an increase in (mitochondrial) oxidant production and a progressive decline in proteasome activity. Eventually so much proteasome is inactivated that oxidized proteins begin to accumulate rapidly and contribute to cellular dysfunction and senescence. [ABSTRACT FROM AUTHOR]