Explore the protein misfolding and aggregation process in Huntington’s disease and amyotrophic lateral sclerosis

• Main Authors: Chia-Sui Sun, 孫嘉穗
• Other Authors: Joseph Jen-Tse Huang
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/3e6n5r

博士 === 國立陽明大學 === 生化暨分子生物研究所 === 103 === Protein misfolding and aggregation plays an important role in many neurodegenerative diseases such as Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). In this study, we show two cases of structural transformation in turning the amyloid-prone pathological proteins/peptides from filamentous to amorphous aggregates by either introducing isomerase in the protein system (Chapter 1), or substitution with de novo-designed proline mutations in peptide model (Chapter 2). Moreover, we have also disclosed that these conformational conversions reduced the proteinopathy of amyloidogenic proteins/peptides, which further elicit neuroprotective effect. The abundant accumulation of inclusion bodies containing polyglutamine-expanded mutant huntingtin (mHTT) aggregates is considered as the key pathological event in HD. In Chapter 1, we have disclosed that FK506 binding protein 12 (FKBP12), an peptidyl-prolyl cis-trans isomerase that exhibits reduced expression in HD, shows profound neuroprotection and motility improvement against polyglutamine (polyQ)-mediated neurotoxicity in Neuro2a cell and Caenorhabditis elegans. Instead of decreasing the aggregation level, FKBP12 structurally transforms mHTT and other disease-related (i.e. polyQ disease and ALS) peptides into benign amorphous aggregates as examined by multiple cell-biological, biochemical, and novel biophysical approaches. Besides, the oligomerization state of mHTT has also been remodeled by FKBP12. Our results suggest a novel function of FKBP12 in ameliorating the proteotoxicity of mHTT and its possible role in other neurodegenerative diseases. Besides HD, we have also focused our attention on TAR DNA-binding protein (TDP-43), the major ubiquitinated deposits in ALS patients in Chapter 2. Numerous ALS-related mutations have been identified at the C-terminal region of TDP-43, which implies the possible role of TDP-43 mutations during pathogenesis. Here, we synthesize various peptides harboring pathogenic or de novo-designed mutations and discover that peptides with pathological mutations are able to form twisted amyloid fibrils, cause liposome leakage, and mediate cellular toxicity. We also show that by replacing glycines with prolines, known to obstruct the -sheet formation, at the different positions in these peptides may influence their amyloidogenesis process and toxicity to the neuronal cell. Particularly, GGG308PPP mutant peptide could neither form beta-amyloid, cause the leakage of liposome, nor jeopardized cell survival, which implies the importance of the glycines residues at position 308-310 during amyloidogenesis. Collectively, our study provide insights into the field of protein folding/misfolding and shed light on the linkage between structural aberration and pathophysiological mechanism, which may benefit for future therapeutic development. By delineating the correlation between proteinopathy and neurotoxicity, we truly hope the derived results may benefit future therapeutic development against protein misfolding diseases.