Spatiotemporal response of living cell structures in Dictyostelium discoideum with semiconductor quantum dots

Development of an in vitro model to study the biological effects of blinking

PURPOSE

To develop a mechanical model in which a contact lens is swept over ocular surface cells under conditions that mimic the force and speed of the blink, and to investigate the resulting biological changes.

METHODS

A computer controlled mechanical instrument was developed to hold a dish containing 3D cultured stratified human ocular surface epithelial cells, across which an arm bearing a contact lens was swept back and forth repeatedly at a speed and force mimicking the human blink. Cells were subjected to repeated sweep cycles for up to 1 h at a speed of 120 mm/s with or without an applied force of 19.6 mN (to mimic pressure exerted by upper eyelid), after which the cell layer thickness was measured, the cell layer integrity was investigated using fluorescent quantum dots (6 and 13 nm) and the phosphorylation levels of various protein kinases were analyzed by human phospho-kinase arrays. Data for selected kinases were further quantitated by enzyme immunoassays.

RESULTS

The thickness of the cell layers did not change after exposure to sweep cycles with or without applied force. Quantum dots (6 and 13 nm) were able to penetrate the layers of cells exposed to sweep cycles but not layers of untreated control cells. The phosphorylation levels of HSP27 and JNK1/2/3 increased for cells exposed to sweep cycles with applied force compared to untreated control cells.

CONCLUSIONS

The in vitro mechanical instrument is a useful tool to investigate the effects of blinking on the ocular surface.

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Colourful cells and tissues: semiconductor quantum dots and their versatile applications in multiplexed bioimaging research.

Influence of electrotaxis on cell behaviour

Understanding the mechanism of cell migration and interaction with the microenvironment is not only of critical significance to the function and biology of cells, but also has extreme relevance and impact on physiological processes and diseases such as morphogenesis, wound healing, neuron guidance, and cancer metastasis.

How do control-based approaches enter into biology?

Control is intrinsic to biological organisms, whose cells are in a constant state of sensing and response to numerous external and self-generated stimuli. Diverse means are used to study the complexity through control-based approaches in these cellular systems, including through chemical and genetic manipulations, input-output methodologies, feedback approaches, and feed-forward approaches. We first discuss what happens in control-based approaches when we are not actively examining or manipulating cells. We then present potential methods to determine what the cell is doing during these times and to reverse-engineer the cellular system. Finally, we discuss how we can control the cell's extracellular and intracellular environments, both to probe the response of the cells using defined experimental engineering-based technologies and to anticipate what might be achieved by applying control-based approaches to affect cellular processes. Much work remains to apply simplified control models and develop new technologies to aid researchers in studying and utilizing cellular and molecular processes.

An intein-mediated site-specific click conjugation strategy for improved tumor targeting of nanoparticle systems

The ability to modify and directly target nanoparticulate carriers has greatly increased their applicability in diagnostic and therapeutic studies. Generally essential to the targeting of nanoparticles is the bioconjugation of targeting ligands to the agent's surface. While bioconjugation techniques have steadily improved in recent years, the field is still plagued with inefficient conjugations reactions and/or the lack of site-specific coupling. To overcome these limitations, click chemistry and expressed protein ligation (EPL) are combined to produce a highly efficient, site-specific reaction. This new EPL-click conjugation strategy is applied to create superparamagnetic iron oxide nanoparticles (SPIO) labeled with HER2/neu affibodies. These HER2-SPIO nanoparticles prove to be highly potent and receptor-specific in both in vitro cell studies and murine tumor models. Moreover, when EPL-click-derived HER2-SPIO are compared with SPIO that had been labeled with HER2 affibodies using other popular bioconjugation methods, they produce a statistically significant improvement in contrast enhancement upon cell binding. The EPL-click system is also successfully extended to other nanoparticle platforms (i.e., liposomes and dendrimers) highlighting the versatility of the approach.

Spatiotemporal control of apical and basal living subcellular chemical environments through vertical phase separation

Molecular distribution within living cells is organized through multiscaled compartmentalization that enables specialized processes to occur with high efficiency. The ability to control the chemical environment at a subcellular level is limited due to deficient positional control over the aqueous stimulant. Here, a multilayered microfluidic system built from polydimethylsiloxane to separate chemical stimulants over single living cells vertically through aqueous-phase separation under laminar flow is demonstrated. Cells are cultured on top of single micrometer-scale channels inside a larger channel, allowing labeling of the apical domain of single cells through the main channel with simultaneous and distinct labeling of the basal domain via the lower microchannels. The system is transparent, which allows the use of optical microscopy to investigate the spatiotemporal response of labeled components. By employing this technique, the examination of localized subcellular domain responses in polarization, lipid bilayer mobility, and apical-to-basal signal transduction can be explored.

Semiconductor nanocrystals in autophagy research: methodology improvement at nanosized scale

Our recent findings establish a functional link between foreign nanosized bodies and autophagy. We find that nanoparticles (NP) within a certain size range act as potent autophagy activators, and that autophagic flux is an underlying physiological process of the cellular clearance of the NP. Therefore, NP may be used to study and to monitor autophagy. We provide a detailed description of laboratory protocols designed for studying NP-mediated autophagy. In addition, we review available methods of nanotechnology, which may benefit autophagy research.

Delivering quantum dots into cells: strategies, progress and remaining issues

The use of semiconductor quantum dots (QDs) in biological sensing and labeling continues to grow with each year. Current and projected applications include use as fluorescent labels for cellular labeling, intracellular sensors, deep-tissue and tumor imaging agents, sensitizers for photodynamic therapy, and more recently interest has been sparked in using them as vectors for studying nanoparticle-mediated drug delivery. Many of these applications will ultimately require the QDs to undergo targeted intracellular delivery, not only to specific cells, but also to a variety of subcellular compartments and organelles. It is apparent that this issue will be critical in determining the efficacy of using QDs, and indeed a variety of other nanoparticles, for these types of applications. In this review, we provide an overview of the current methods for delivering QDs into cells. Methods that are covered include facilitated techniques such as those that utilize specific peptide sequences or polymer delivery reagents and active methods such as electroporation and microinjection. We critically examine the benefits and liabilities of each strategy and illustrate them with selected examples from the literature. Several important related issues such as QD size and surface coating, methods for QD biofunctionalization, cellular physiology and toxicity are also discussed. Finally, we conclude by providing a perspective of how this field can be expected to develop in the future.