Lower expression of catalytic and structural subunits of the proteasome contributes to decreased proteolysis in peripheral blood T lymphocytes during aging.
Aging, in the immune system, is characterized by a decreased ability to respond to exogenous insults, resulting in increased susceptibility to infections and blunted response to vaccination. While significant age-associated deficits in immune function have been documented, the underlying molecular mechanisms are still being investigated. A consistent decline in the proteolytic activity of the proteasome has been demonstrated with advancing age, implicating an important role for the proteasome in immune senescence, by studies that largely employed proteasome-enriched preparations from cell lysates. With the availability of novel cell permeable active site probes designed specifically for assaying proteasomal activity in live cells, we now confirm our earlier data demonstrating lower catalytic activity of the proteasome in primary human T cells obtained from the elderly when compared to those from young donors. Loss in proteasomal catalytic activity translated into a loss in functional activity, as was observed in a degradation assay employing an ubiquitinated protein substrate, Ub-IkappaBalpha. Unlike fluorogenic peptide substrates, use of ubiquitinated protein substrates not only confer greater stringency in terms of proteasomal hydrolysis, but also involve the participation of the 19S regulatory component. This age-associated loss in proteasomal activity is accompanied by alteration in the levels of catalytic, structural and regulatory subunits, with no change in that of the 11S activator or the inhibitor PAAF1. Oxidative modification, such as carbonylation and lipid-peroxidation, of proteasomal subunits was also detected in T cells from the elderly. Thus, oxidative modification and lower levels of proteasomal subunits contribute to decreased proteolytic activity during immune-senescence.
Ponnappan
Subramaniam
S
Department of Geriatrics, University of Arkansas for Medical Sciences, and Central Arkansas VA Health Care System, Little Rock, AR 72205, United States. uponnappan@uams.edu
Ovaa
Huib
H
Ponnappan
Usha
U
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002384:Catalysis; D020134:Catalytic Domain / Q000235:genetics; D002478:Cells, Cultured; D015180:Electrophoresis, Gel, Two-Dimensional; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D019169:Jurkat Cells; D015227:Lipid Peroxidation; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D050050:Protein Carbonylation; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C501074:PAAF1 protein, human; D021122:Protein Subunits; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease