技术资料

The integration of microscale engineering,microfluidics,and AC electrokinetics such as dielectrophoresis has generated novel microsystems that enable quantitative analysis of cellular phenotype,function,and physiology. These systems are increasingly being used to assess diverse cell types,such as stem cells,so it becomes critical to thoroughly evaluate whether the systems themselves impact cell function. For example,engineered microsystems have been utilized to investigate neural stem/progenitor cells (NSPCs),which are of interest due to their potential to treat CNS disease and injury. Analysis by dielectrophoresis (DEP) microsystems determined that unlabeled NSPCs with distinct fate potential have previously unrecognized distinguishing electrophysiological characteristics,suggesting that NSPCs could be isolated by DEP microsystems without the use of cell type specific labels. To gauge the potential impact of DEP sorting on NSPCs,we investigated whether electric field exposure of varying times affected survival,proliferation,or fate potential of NSPCs in suspension. We found short-term DEP exposure (1 min or less) had no effect on NSPC survival,proliferation,or fate potential revealed by differentiation. Moreover,NSPC proliferation (measured by DNA synthesis and cell cycle kinetics) and fate potential were not altered by any length of DEP exposure (up to 30 min). However,lengthy exposure (textgreater5 min) to frequencies near the crossover frequency (50-100 kHz) led to decreased survival of NSPCs (maximum ∼30% cell loss after 30 min). Based on experimental observations and mathematical simulations of cells in suspension,we find that frequencies near the crossover frequency generate an induced transmembrane potential that results in cell swelling and rupture. This is in contrast to the case for adherent cells since negative DEP frequencies lower than the crossover frequency generate the highest induced transmembrane potential and damage for these cells. We clarify contrasting effects of DEP on adherent and suspended cells,which are related to the cell position within the electric field and the strength of the electric field at specific distances from the electrodes. Modeling of electrode configurations predicts optimal designs to induce cell movement by DEP while limiting the induced transmembrane potential. We find DEP electric fields are not harmful to stem cells in suspension at short exposure times,thus providing a basis for developing DEP-based applications for stem cells. View Publication

Although neural stem cells (NSCs) sustain continuous neurogenesis throughout the adult lifespan of mammals,they progressively exhibit proliferation defects that contribute to a sharp reduction in subventricular neurogenesis during aging. However,little is known regarding the early age-related events in neurogenic niches. Using a fluorescence-activated cell sorting technique that allows for the prospective purification of the main neurogenic populations from the subventricular zone (SVZ),we demonstrated an early decline in adult neurogenesis with a dramatic loss of progenitor cells in 4 month-old young adult mice. Whereas the activated and quiescent NSC pools remained stable up to 12 months,the proliferative status of activated NSCs was already altered by 6 months,with an overall extension of the cell cycle resulting from a specific lengthening of G1. Whole genome analysis of activated NSCs from 2- and 6-month-old mice further revealed distinct transcriptomic and molecular signatures,as well as a modulation of the TGFβ signalling pathway. Our microarray study constitutes a cogent identification of new molecular players and signalling pathways regulating adult neurogenesis and its early modifications. View Publication

Adverse effect of alcohol on neural function has been well documented. Especially,the teratogenic effect of alcohol on neurodevelopment during embryogenesis has been demonstrated in various models,which could be a pathologic basis for fetal alcohol spectrum disorders (FASDs). While the developmental defects from alcohol abuse during gestation have been described,the specific mechanisms by which alcohol mediates these injuries have yet to be determined. Recent studies have shown that alcohol has significant effect on molecular and cellular regulatory mechanisms in embryonic stem cell (ESC) differentiation including genes involved in neural development. To test our hypothesis that alcohol induces molecular alterations during neural differentiation we have derived neural precursor cells from pluripotent human ESCs in the presence or absence of ethanol treatment. Genome-wide transcriptomic profiling identified molecular alterations induced by ethanol exposure during neural differentiation of hESCs into neural rosettes and neural precursor cell populations. The Database for Annotation,Visualization and Integrated Discovery (DAVID) functional analysis on significantly altered genes showed potential ethanol's effect on JAK-STAT signaling pathway,neuroactive ligand-receptor interaction,Toll-like receptor (TLR) signaling pathway,cytokine-cytokine receptor interaction and regulation of autophagy. We have further quantitatively verified ethanol-induced alterations of selected candidate genes. Among verified genes we further examined the expression of P2RX3,which is associated with nociception,a peripheral pain response. We found ethanol significantly reduced the level of P2RX3 in undifferentiated hESCs,but induced the level of P2RX3 mRNA and protein in hESC-derived NPCs. Our result suggests ethanol-induced dysregulation of P2RX3 along with alterations in molecules involved in neural activity such as neuroactive ligand-receptor interaction may be a molecular event associated with alcohol-related peripheral neuropathy of an enhanced nociceptive response. View Publication

Glioblastoma (GBM) is the most aggressive primary brain tumor and is resistant to all therapeutic regimens. Relapse occurs regularly and might be caused by a poorly characterized tumor stem cell (TSC) subpopulation escaping therapy. We suggest aldehyde dehydrogenase 1 (ALDH1) as a novel stem cell marker in human GBM. Using the neurosphere formation assay as a functional method to identify brain TSCs,we show that high protein levels of ALDH1 facilitate neurosphere formation in established GBM cell lines. Even single ALDH1 positive cells give rise to colonies and neurospheres. Consequently,the inhibition of ALDH1 in vitro decreases both the number of neurospheres and their size. Cell lines without expression of ALDH1 do not form tumor spheroids under the same culturing conditions. High levels of ALDH1 seem to keep tumor cells in an undifferentiated,stem cell-like state indicated by the low expression of beta-III-tubulin. In contrast,ALDH1 inhibition induces premature cellular differentiation and reduces clonogenic capacity. Primary cell cultures obtained from fresh tumor samples approve the established GBM cell line results. View Publication

Human embryonic stem cells (hESCs) are emerging as an attractive alternative source for cell replacement therapy since the cells can be expanded in culture indefinitely and differentiated into any cell types in the body. In order to optimize cell-to-cell interaction,cell proliferation and differentiation into specific lineages as well as tissue organization,it is important to provide a microenvironment for the hESCs which mimics the stem cell niche. One approach is to provide a three-dimensional (3D) environment such as encapsulation. We present an approach to culture and differentiate hESCs into midbrain dopamine (mdDA) neurons in a 3D microenvironment using alginate microcapsules for the first time. A detailed gene and protein expression analysis during neuronal differentiation showed an increased gene and protein expression of various specific DA neuronal markers,particularly tyrosine hydroxylase (TH) by textgreater100 folds after 2weeks and at least 50% higher expression after 4weeks respectively,compared to cells differentiated under conventional two-dimensional (2D) platform. The encapsulated TH+ cells co-expressed mdDA neuronal markers,forkhead box protein A-2 (FOXA2) and pituitary homeobox-3 (PITX3) after 4weeks and secreted approximately 60pg/ml/106 cells higher DA level when induced. We propose that the 3D platform facilitated an early onset of DA neuronal generation compared to that with conventional 2D system which also secretes more DA under potassium-induction. It is a very useful model to study the proliferation and directed differentiation of hESCs to various lineages,particularly to mdDA neurons. This 3D system also allows the separation of feeder cells from hESCs during the process of differentiation and also has potential for immune-isolation during transplantation studies. ?? 2013 Elsevier B.V. View Publication

Glioblastoma multiforme (GBM) is an aggressive,Grade IV astrocytoma with a poor survival rate,primarily due to the GBM tumor cells migrating away from the primary tumor site along the nanotopography of white matter tracts and blood vessels. It is unclear whether this nanotopography influences the biomechanical properties (i.e. cytoskeletal stiffness) of GBM tumor cells. Although GBM tumor cells have an innate propensity to migrate,we believe this capability is enhanced due to the influence of nanotopography on the tumor cells' biomechanical properties. In this study,we used an aligned nanofiber film that mimics the nanotopography in the tumor microenvironment to investigate the mechanical properties of GBM tumor cells in vitro. The data demonstrate that the cytoskeletal stiffness,cell traction stress,and focal adhesion area were significantly lower in the GBM tumor cells compared to healthy astrocytes. Moreover,the cytoskeletal stiffness was significantly reduced when cultured on aligned nanofiber films compared to smooth and randomly aligned nanofiber films. Gene expression analysis showed that tumor cells cultured on the aligned nanotopography upregulated key migratory genes and downregulated key proliferative genes. Therefore,our data suggest that the migratory potential is elevated when GBM tumor cells are migrating along aligned nanotopographical substrates. View Publication

We introduce a novel all-optical assay for functional studies of biological neural networks in vitro. We created a novel optogenetic construct named OptoCaMP which is a combination of a channelrhodopsin variant (CheRiff) and a red genetically encoded calcium indicator (GECI) (jRCaMP1b). It enables simultaneous optical stimulation and recording from large population of neurons with single-cell readout. Additionally,we have developed a spatio-temporal all-optical assay to simultaneously stimulate a sub-section of a neural network and record evoked calcium activity,in both stimulated and non-stimulated neurons,thus allowing the investigation of the spread of excitation through an interconnected network. Finally,we demonstrate the sensitivity of this assay to the change of neural network connectivity. View Publication