Protein oxidation and degradation during postmitotic senescence

Area of Science:

• Cellular senescence
• Molecular biology of aging
• Protein degradation pathways

Background:

• Oxidized protein aggregates accumulate with age and in age-related diseases.
• Proteasome and lysosomal protease inhibition may contribute to this accumulation.
• Most aging studies use dividing cells, yet protein aggregates are prominent in non-dividing tissues.

Purpose of the Study:

• To investigate oxidized protein accumulation in non-dividing human fibroblasts (IMR-90 and MRC-5).
• To determine if this accumulation correlates with reduced proteolytic activity.
• To model age-related oxidative senescence in postmitotic cells.

Main Methods:

• Cultured confluent, postmitotic IMR-90 and MRC-5 fibroblasts at various population doubling levels.
• Induced age-related oxidative senescence using hyperoxic conditions.
• Assessed protein carbonyl formation, proteasomal activities, and lysosomal cathepsin activities.

Main Results:

• Significant decreases in both proteasomal and lysosomal protease activities were observed during fibroblast senescence.
• Peptidyl-glutamyl-hydrolyzing activity of the proteasome showed particular inhibition.
• An increase in oxidized protein accumulation was associated with the decline in proteolytic capacity.

Conclusions:

• Proteolytic capacity, including proteasomal and lysosomal systems, diminishes in senescent non-dividing fibroblasts.
• Reduced protein degradation contributes to the age-dependent accumulation of oxidized proteins in postmitotic cells.
• This finding highlights the importance of studying non-dividing cells in aging research.