Changes in 20S subunit composition are largely responsible for altered proteasomal activities in experimental autoimmune encephalomyelitis

摘要

We recently reported that the proteasomal peptidase activities are altered in the cerebellum of mice with MOG peptide-induced experimental autoimmune encephalomyelitis (EAE). To determine whether these fluctuations are caused by proteasome activation/inactivation and/or changes in the levels of individual β subunits, we characterized the proteasome subunit composition by western blotting. The results show that the rise in proteasomal peptidase activity in acute EAE correlates with an augmented expression of inducible β subunits whereas the decline in activity in chronic EAE correlates with a reduction in the amount of standard β subunits. Using pure standard (s) and immuno (i) 20S particles for calibration, we determined that the changes in the levels of catalytic subunits account for all of the fluctuations in peptidase activities in EAE. The i-20S and s-20S proteasome were found to degrade carbonylated β-actin with similar efficiency, suggesting that the amount of protein carbonyls in EAE may be controlled by the activity of both core particles. We also found an increase in proteasome activator PA28 and a decrease in inhibitor PI31 levels in acute EAE, reflecting a response to inflammation. Elevated levels of PA700 and PA28 in chronic EAE, on the other hand, may occur in response to diminished proteasomal activity in this phase. These findings are central towards understanding the altered proteasomal physiology in inflammatory demyelinating disorders.