Role of Endogenous HAP40 in Cellular Aggregate Formation and Biochemical Characterization of Transgenic HAP40 Mouse

Abstract

Huntington’s disease (HD) is a prevalent neurodegenerative disorder caused by the expansion of polyglutamine tract in the huntingtin (Htt) protein It is primarily characterized by progressive loss of brain and motor functions and the accumulation of aggregates constituted by mutant Htt Huntingtin associated protein 40 (HAP40) is discovered to interact and form a complex with Htt which regulates early endosomes To date however the function of HAP40 remains poorly understood This study attempted to investigate the role of HAP40 in cell culture and transgenic mouse models by the knockdown and overexpression approaches The results revealed that knockdown of endogenous HAP40 was able to increase cellular aggregates formation In conjunction with recent findings in the lab revealing an increase in cellular aggregates formation due to upregulation of HAP40 this study had shown that both downregulation and upregulation of HAP40 resulted in accumulation of aggregates in cells Downregulation of HAP40 resulted in a significant increment in the immunofluorescence intensity of UbG76V-GFP/mCherry and a decrease in ubiquitin-proteasome system (UPS)-associated proteins: PSMD4 and UCHL1 in the cells Likewise overexpression of HAP40 had increased the UbG76V-GFP/mCherry immunofluorescence intensity and decreased ADRM1 level Conversely knockdown and overexpression of HAP40 did not activate autophagic activity These results further imply that the induction of aggregates accumulation by HAP40 may be due to UPS impairment In the transgenic mouse model overexpression of HAP40 did not seem to affect the clasping phenotype of the FU-mCherry mHAP40 mice The biochemical analysis of the cortex and striatum mice brain lysates demonstrated no significant changes in the UPS-associated proteins across genotype or brain region differences However the UPS function in the mice brains remain inconclusive as a more in depth experimental approach is required to further confirm this This study has provided an insight of the role of HAP40 in cellular aggregates formation and UPS activity

Date of Award	2015 May 5
Original language	English
Supervisor	Lu-Shiun Her (Supervisor)