UCH-L1 Affects The Formation Of Tau Protein Aggresome Mediated By HDAC6

The ubiquitin-proteasome system (UPS) and the autophagic-lysosomal pathway (ALP) are two major protein degradation pathways, which monitors and regulates the status of intracellular proteins and remove abnormal proteins timely. Tau-associate neurodegenerative diseases often show the abnormal modification of tau proteins and accumulation of intracellular aggregated tau, as well as UPS dysfunction, ubiquitin carboxy-terminal hydrolases L1 (UCH-L1) dysfunction and activated ALP. Not only HDAC6, p62 and dynein motors, but also deubiquitinating enzymes (DUBs) including ataxin3 and Pohl are required in autophagy. It was proved that HDAC6 could bind with UCH-L1, but how UCH-L1 works and the mechanism how they regulate protein degeneration are not clear.In the study, HEK 239/tau441 cells were transfection with UCH-L1 siRNA, then treatment cells with 2 μM MG132.24 hr later, we detected the levels of HDAC6 and total tau proteins by Western blot, as well as the tau ubiquitination changing and the interaction between HDAC6 and ubiquitin tau by immunoprecipitation. Finally, we observed the formation of tau aggresome by immunocytochemistry. The results showed: (1) compared with the controls, the levels HDAC6 were increased after MG132 treatment, which implied autophagy was activated and accompanied the increasement total tau proteins intracellular; (2) We also found transfection with UCH-L1 siRNA and MG132 treatment could decrease the levels of HDAC6 and increased the total tau expression compared with MG132 treatment; (3) As compared with controls, MG132 treatment could increase cellular total polyubiquitin and tau ubiquitination, as well as enhance the interaction of HDAC6 and ubiquitin; (4) As compared with MG132 group, meantime inhibition of UCH-L1 and proteasome could induce intracellular tau protein ubiquitination increased, while interaction of HDAC6 and ubiquitin was declined; (5) As compared with controls, MG132 treatment could enhance the interaction of HDAC6 and tau-5, while compared with MG132 group, meantime inhibition of UCH-L1 and proteasome could decrease the interaction of HDAC6 and tau-5; (6) We also observed the formation of tau aggresome in cells after MG132 treatment. Co-administration UCH-L1 siRNA and MG132 could cause aggregation of tau proteins, but not functional aggresome structures.The data above suggested that after proteasome inhibition by MG132, abnormal tau protein would form aggresome structures to remove intracellular abnormal protein aggregations, while attenuated UCH-L1 expression via UCH-L1 siRNA at the same time could prevent the formation of protein aggresome and disturb the autophagy pathway. Our study showed new evidence of UCH-L1 participating in the autophagic-lysosomal pathway and provide a new therapeutic target in the treatment of neurodegenerative diseases.