Differential effect of three-repeat and four-repeat tau on mitochondrial axonal transport

Tau protein is present in six different splice forms in the human brain and interacts with microtubules via either 3 or 4 microtubule binding repeats. An increased ratio of 3 repeat to 4 repeat isoforms is associated with neurodegeneration in inherited forms of frontotemporal dementia. Tau over-expression diminishes axonal transport in several systems, but differential effects of 3 repeat and 4 repeat isoforms have not been studied. We examined the effects of tau on mitochondrial transport and found that both 3 repeat and 4 repeat tau change normal mitochondrial distribution within the cell body and reduce mitochondrial localization to axons; 4 repeat tau has a greater effect than 3 repeat tau. Further, we observed that the 3 repeat and 4 repeat tau cause different alterations in retrograde and anterograde transport dynamics with 3 repeat tau having a slightly stronger effect on axon transport dynamics. Our results indicate that tau-induced changes in axonal transport may be an underlying theme in neurodegenerative diseases associated with isoform specific changes in tau's interaction with microtubules.

Clusters of Circulating Tumor Cells: a Biophysical and Technological Perspective

The vast majority of cancer associated deaths result from metastasis, yet the behaviors of its most potent cellular driver, circulating tumor cell clusters, are only beginning to be revealed. This review highlights recent advances to our understanding of tumor cell clusters with emphasis on enabling technologies. The importance of intercellular adhesions among cells in clusters have begun to be unraveled with the aid of promising microfluidic strategies for isolating clusters from patient blood. Due to their metastatic potency, the utility of circulating tumor cell clusters for cancer diagnosis, drug screening, precision oncology and as targets of antimetastatic therapeutics are being explored. The continued development of tools for exploring circulating tumor cell clusters will enhance our fundamental understanding of the metastatic process and may be instrumental in devising new strategies to suppress and eliminate metastasis.

A highly-occupied, single-cell trapping microarray for determination of cell membrane permeability

Semi- and selective permeability is a fundamentally important characteristic of the cell membrane. Membrane permeability can be determined by monitoring the volumetric change of cells following exposure to a non-isotonic environment. For this purpose, several microfluidic perfusion chambers have been developed recently. However, these devices only allow the observation of one single cell or a group of cells that may interact with one another in an uncontrolled way. Some of these devices have integrated on-chip temperature control to investigate the temperature-dependence of membrane permeability, but they inevitably require sophisticated fabrication and assembly, and delicate temperature and pressure calibration. Therefore, it is highly desirable to design a simple single-cell trapping device that allows parallel monitoring of multiple separate, individual cells subjected to non-isotonic exposure at various temperatures. In this study, we developed a pumpless, single-layer microarray with high trap occupancy of single cells. The benchmark performance of the device was conducted by targeting spherical particles of 18.8 μm in diameter as a model, yielding trap occupancy of up to 86.8% with a row-to-row shift of 10-30 μm. It was also revealed that in each array the particles larger than a corresponding critical size would be excluded by the traps in a deterministic lateral displacement mode. Demonstrating the utility of this approach, we used the single-cell trapping device to determine the membrane permeability of rat hepatocytes and patient-derived circulating tumor cells (Brx-142) at 4, 22 and 37 °C. The membrane of rat hepatocytes was found to be highly permeable to water and small molecules such as DMSO and glycerol, via both lipid- and aquaporin-mediated pathways. Brx-142 cells, however, displayed lower membrane permeability than rat hepatocytes, which was associated with strong coupling of water and DMSO transport but less interaction between water and glycerol. The membrane permeability data reported here provide new insights into the biophysics of membrane transport such as aquaporin expression and coupling transport of water and solutes, as well as providing essential data for the ultimate goal of biobanking rare cells and precious tissues.

Assessment of the Viability of Transplant Organs with 3D Electrical Impedance Tomography

Methods that can determine the extent of tissue damage in transplant organs, before the decision to transplant has been made, have the potential to improve the outcome of the procedure by preventing unfit organs from being transplanted into the patient. The raised confidence in the organ state with such a technique would also increase availability. Now restricted due to the fear of introducing a failed organ resulting from the relative lack of viability data during transport, stringent criteria for donation would relax. Electrical impedance tomography is an imaging modality that recovers the spatial variation of the complex impedivity in the body from electrical measurements made on the periphery. In this study, we apply 3D EIT with the complete electrode model to a sample conductivity distribution that might result from an organ that is losing its viability due to prolonged ischemia. The reconstructed images show that EIT has the potential to become an adjuvant method for the field of organ transplantation.

Label-Free Microfluidic Apheresis of Circulating Tumor Cell Clusters

Screening liters of blood (i.e., apheresis) represents a generalized approach to promote the reliable access to circulating tumor cell clusters (CTCCs), which are known to be highly metastasis-competent, yet ultrarare. However, no existing CTCC sorting technology has demonstrated high throughput, high yield, low shear stress, and minimal blood dilution simultaneously as required in apheresis. Here, a label-free method is introduced termed Precision Apheresis for Non-invasive Debulking of cell Aggregates (PANDA) to continuously isolate CTCCs from undiluted blood to clean buffer through size sorting, processing 1.4 billion cells per second. The cell focusing is optimized within whole blood leveraging secondary transverse flow and margination. The PANDA chip recovers >90% of spiked ≈24 rare HeLa cell clusters from 100 mL undiluted blood samples (equivalent to ≈500 billion blood cells) at 1 L h-1 throughput, with ≤20s device residence time, ≤15 Pa shear stress, and >99.9% return of blood components. The technology lays the groundwork for future routine isolation to increase the recovery of these ultrarare yet clinically significant tumor cell populations from large volumes of blood to advance cancer research, early detection, and treatment.