WD13-1
Diosgenin restores axonal degeneration and improves memory deficits in Alzheimer's disease via the reduction of HSC70
DiosgeninによるHSC70の減少はアルツハイマー病における軸索萎縮と記憶障害を改善する
Yang Ximeng（楊 熙蒙），東田 千尋
Division of Neuromedical Science, Institute of Natural Medicine, University of Toyama, Toyama, Japan
We previously found that diosgenin, a constituent of Dioscorea Rhizoma, restored Aβ-induced axonal degeneration and improved memory function in a mouse model of Alzheimer's disease (AD), 5XFAD. In this study, we aimed to investigate the downstream signaling of diosgenin which related to axonal regrowth and memory recovery. Vehicle solution or diosgenin was administered to wild-type or 5XFAD mice for 15 days. Protein expressions in cortical lysates were compared on 2D-PAGE. By MALDI-TOF/MS analysis, Heat shock cognate (HSC) 70 was identified as a drastically reduced protein by diosgenin administration in 5XFAD. By Aβ treatment, HSC70 was increased, and axonal length was decreased in primary cortical neurons. Post treatment of diosgenin significantly decreased HSC70 and increased axonal length. Next, we clarified the relationship between HSC70 and axonal degeneration by exploring binding partners of HSC70. By co-immunoprecipitation and nano-LC/MS analysis, α-tubulin was identified as a binding protein of HSC70. After Aβ treatment, α-tubulin was reduced in the degenerated axons, but diosgenin treatment significantly increased the α-tubulin level and promoted axonal regrowth. A specific inhibitor of HSC70, VER-155008, significantly restored Aβ-induced axonal atrophy in neurons. VER-155008 administration improved memory deficits in 5XFAD mice. Our study suggests that Aβ-induced increase in HSC70 may promote the degradation of α-tubulin and axonal degeneration. In contrast, diosgenin-elicited reduction of HSC70 may suppress the degradation of α-tubulin, and promote axonal regrowth. We also showed that specific inhibition of HSC70 promoted axonal regeneration and memory improvement in 5XFAD mice. This study indicates that inhibiting HSC70 is a new therapeutic target in AD. | | WD13-2
Toxic PR poly-dipeptides encoded by C9orf72 repeat expansion binds intermediate filaments and nuclear pores
C9orf72遺伝子の異常な繰返し配列から産生される毒性PRポリジペプチドは中間径フィラメントと核膜孔に結合する
Mori Eiichiro（森 英一朗）
Dept. of Future Basic Med., Nara Med. Univ.
A hexanucleotide repeat expansion in the first intron of the C9orf72 gene represents the most prominent form of heritable amyotrophic lateral sclerosis (ALS). Common among proline:arginine (PR) poly-dipeptide target proteins are low complexity (LC) domains shown herein to be both necessary and sufficient for PR poly-dipeptide binding. Two complementary proteomic approaches were used in search of the intracellular targets of the toxic PR poly-dipeptide. The top categories of PR poly-dipeptide-bound proteins include constituents of non-membrane invested cellular organelles, intermediate filaments, and nucleoporin proteins, including those composed of phenylalanine:glycine (FG) repeats. PR poly-dipeptide targets are enriched for the inclusion of LC sequences. The PR poly-dipeptide binds to polymeric forms of the LC domains located at the amino terminal ends of intermediate filament proteins and to polymeric forms of the FG repeat domain. A method of chemical footprinting was used to characterize labile, cross-beta polymers formed from the FG domain of the Nup54 protein. Mutations within the footprinted region of Nup54 polymers blocked both polymerization and binding by the PR poly-dipeptide. The aliphatic alcohol 1,6-hexanediol melted FG domain polymers in vitro and reversed PR-mediated enhancement of the nuclear pore permeability barrier. Evidence is presented indicating that LC sequences represent the direct target of PR poly-dipeptide binding and that interaction between the PR poly-dipeptide and LC domains is polymer-dependent. The study offers a mechanistic interpretation of PR poly-dipeptide toxicity in the context of a prominent form of ALS. |
