Probing mechanical properties of cell as biomarkers of neurodegeneration

Abstract

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, drug induced neuropathy, etc., are main threat to affect millions of people worldwide, especially for the aged population. The neurons in patients suffering from neurodegenerative diseases are destined to death by neurodegeneration. Many indicators were developed based on the hypothetical reasons of neurodegenerative diseases including break of intracellular Ca2+ homeostasis, misfolded protein aggregation, genetic mutation, oxidative load and abnormal proteostasis. However, efficient biomarkers are still underdevelopment to indicate neurodegeneration, especially in the early stage. Previous studies demonstrated that cells under neurodegeneration were gradually degenerated accompanying by serial mechanical events including contraction of neurites and shrinkage of soma. In this thesis, the progressive states of neurodegeneration were evaluated based on the mechanical changes of neuronal cells under neurodegenerative loads. An atomic force microscope system was developed as a platform of cell characterization to collect sub-micrometer scale images and mechanical properties of cells under neurodegeneration. A coarse-gained molecular dynamics model of adherent cells was established to decipher the correlation between neurodegeneration and cell mechanical properties from molecular events in subcellular components. Pathogenesis of neurodegenerative diseases including Ca2+ influx, chemotherapy drug treatment and beta amyloid (Aβ) aggregation was applied to induce neurodegeneration and the mechanical changes of cells were monitored by the AFM. In order to quantify cell mechanical properties in the progressive states of neurodegeneration, Young's modulus of cell was calculated according to the modified Hertz model. The corresponding biological signaling pathway was also investigated to obtain the subcellular changes of cells in neurodegeneration. The Young's modulus of cells under N-methyl-D-aspartate (NMDA) treatment (inducing Ca2+ influx) presented time-dependent increase and it was discovered to involve activation of myosin IIb motor proteins mediating increase of cell prestress. The dosage-dependent changes of Young's modulus in chemotherapy drug (vincristine) treated cells were attributed to the changes of microtubules (depolymerized by vincristine). In the treatment of Aβ, the Young's modulus of cells was decreased. The experimental observations indicated that the monitored Young's modulus changes of neuronal cells were correlative and sensitive to neurodegenerative loads. The computational simulation of adherent cells was conducted by adjusting cell prestress (condition of NMDA treatment) and cytoskeletal components (condition of vincristine treatment). The corresponding mechanical changes of the cell model were well correlated with experimental observations and further provided spatio-temporal detail of subcellular reorganization and predicted trends of cell mechanical changes during neurodegeneration. The presented analysis of neurodegeneration and cell mechanical properties of neuronal cells based on the experimental and simulated approaches in this thesis demonstrated that the mechanical properties of cells are ideal as promising biomarkers to indicate the progressive states of neurodegeneration.

Date of Award	2 Oct 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Wai Chiu King LAI (Supervisor) & Ning XI (Supervisor)