Biophysical Characteristics of Cell Migration Mediated by Subcellular Cytoskeletal Arrangements

Abstract

Cell migration is essential in morphogenesis, involving processes such as embryonic gastrulation, organ and tissue formations, and the corresponding function developments. However, abnormal cell migration including immobilization and uncontrolled/non-synchronized movement directions can cause defects or even severe fatal malfunction of the developed tissues and organs. For instance, migration of fibroblast cells and differentiated myofibroblast cells can mediate the skin wound healing process by expressing different levels of stress fibers, which are stimulated by the chemoattractant such as growth factors and cytokines released in wounds. Indeed, cell migration regulate by both biochemical and biomechanical cues in the surrounding microenvironment including soluble factors, cell-cell signaling molecules, and extracellular matrix (ECM) proteins and substrates structures/topography in micro-/nano-scales. Detailed analysis of cell migration behaviors in different combinations of biochemical and biophysical conditions will help to explain and further predict the cell migration behaviors. Pervious work demonstrated that cell migration regulated by Rho GTPase (ROCK) and myosin light-chain kinase (MLCK) could regulate the actin organizations. We further demonstrated that both actin and microtubule distributions were highly involved in single fibroblast cell migration. We categorized actin stress fibers into 'peripheral actin' near cell edges and 'central actin' in the inner parts of cell bodies, which could be illustrated by the ratios of P-actin/C-actin. We demonstrated that inhibiting ROCK activities significantly increased the ratio of P-actin/C-actin and stimulated cell migration, whereas the ratios greatly decreased by applying MLCK inhibitors as well as cell locomotion. Importantly, we further showed that control cells exhibited a positive correlation between ratios of P-actin/C-actin and migration velocities. In addition, microtubules were also involved in this process as our results demonstrated that inhibiting microtubule dynamics significantly reduced the cell migration even if with higher ratios of P-actin/C-actin. Furthermore, these were consistent with the studies of cell population migration by applying the polydimethylsiloxane (PDMS) stamp-based wound-healing assay. Hence, it is conceivable that subcellular arrangements of cytoskeleton should be involved in the intricate mechanism of fibroblasts migration. We further demonstrated the possible involvements of intracellular characteristics in contractile force distributions and cell migration behaviors by investigating the correlations among them. Strong correlations among stress fiber, nucleus and cell body orientations exhibited for cells with relative low ratios of P-actin/C-actin. Our results further revealed that most of aligning cells with relative low orientation deviations (< 10°) of cell bodies and nucleus exhibited slow cell migration (< 1 μm/min) for control cells, which might provide an alternative and non-invasive method to predict cell migration behaviors by analyzing intracellular characteristics. In particular, we also found the consistent subcellular contractile force distributions for the aligning cells by applying the micropost array detectors (mPADs). This relation implicated the effects of actin distributions in regulating intracellular contractile force profiles, which might be also involved in mediating cell migration behaviors as central stress fibers were the critical components of myosin-based contractile systems in the mechanotransduction sense. Altogether, this research not only revealed the important roles and interrelations of the subcellular cytoskeleton arrangements and fibroblast cell migration, but also provided important insights for deepening our understanding on the key cell migration mechanisms involved in organ and tissue developments.

Date of Award	2 Nov 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hiu Wai Raymond LAM (Supervisor) & Dong SUN (Supervisor)