A unifying feature of many neurodegenerative disorders is the accumulation of polyubiquitinated protein inclusions in dystrophic neurons, e.g. containing ␣-synuclein, which is suggestive of an insufficient proteasomal activity. We demonstrate that ␣-synuclein and 20 S proteasome components co-localize in Lewy bodies and show that subunits from 20 S proteasome particles, in contrast to subunits of the 19 S regulatory complex, bind efficiently to aggregated filamentous but not monomeric ␣-synuclein. Proteasome binding to insoluble ␣-synuclein filaments and soluble ␣-synuclein oligomers results in marked inhibition of its chymotrypsin-like hydrolytic activity through a non-competitive mechanism that is mimicked by model amyloid-A␤ peptide aggregates. Endogenous ligands of aggregated ␣-synuclein like heat shock protein 70 and glyceraldehyde-6-phosphate dehydrogenase bind filaments and inhibit their anti-proteasomal activity. The inhibitory effect of amyloid aggregates may thus be amenable to modulation by endogenous chaperones and possibly accessible for therapeutic intervention.

No abstract

Repeated mild heat shock (RMHS) has been shown to have several beneficial hormetic effects on human skin fibroblast undergoing aging in vitro. Because an age-related decline in proteasome activity is 1 of the reasons for the accumulation of abnormal proteins during aging, we have investigated the effects of RMHS on the 20S proteasome, which is the major proteolytic system involved in the removal of abnormal and oxidatively damaged proteins. Serially passaged human skin fibroblasts exposed to RMHS at 41°C for 60 minutes twice a week had increased 3 proteasomal activities by 40% to 95% in early- and midpassage cultures. RMHS-treated cells also contained a 2-fold higher amount of the proteasome activator 11S, and the extent of the bound activator was double in early- and midpassage cells only. Furthermore, there was no difference in the content of the 19S proteasome regulator in the stressed and the unstressed cells. Therefore, RMHS-induced proteasome stimulation in early- and midpassage fibroblasts appears to be due to an induction and enhanced binding of 11S proteasome activators. In contrast to this, the proteasomal system in late-passage senescent cells appears to be less responsive to the stimulatory effects of mild heat shock

Repeated mild heat shock (RMHS) has been shown to have several beneficial hormetic effects on human skin fibroblast undergoing aging in vitro. Because an age-related decline in proteasome activity is 1 of the reasons for the accumulation of abnormal proteins during aging, we have investigated the effects of RMHS on the 20S proteasome, which is the major proteolytic system involved in the removal of abnormal and oxidatively damaged proteins. Serially passaged human skin fibroblasts exposed to RMHS at 41 degrees C for 60 minutes twice a week had increased 3 proteasomal activities by 40% to 95% in early- and midpassage cultures. RMHS-treated cells also contained a 2-fold higher amount of the proteasome activator 11S, and the extent of the bound activator was double in early- and midpassage cells only. Furthermore, there was no difference in the content of the 19S proteasome regulator in the stressed and the unstressed cells. Therefore, RMHS-induced proteasome stimulation in early- and midpassage fibroblasts appears to be due to an induction and enhanced binding of 11S proteasome activators. In contrast to this, the proteasomal system in late-passage senescent cells appears to be less responsive to the stimulatory effects of mild heat shock.

No abstract