Electrorotation Rates of K562 Cells Accompanied by Erythroid Differentiation Induced by Sodium Butyrate

Proliferation Inhibited by Genipin in Human Leukemia K562 Cells: Involvement of Uncoupling Protein 2 in Mitochondrial Damage

Background

Uncoupling protein 2 (UCP2) is essential for maintaining redox homeostasis and regulating energy metabolism. Abnormal expression of UCP2 has been associated with various tumors, including leukemia. Genipin (GEN), a specific inhibitor of UCP2, has a long history of use in traditional Chinese medicine. However, the precise role and underlying mechanisms of UCP2 in the inhibition of leukemia cells by GEN remain inadequately understood. This study focuses on the expression levels of UCP2 in myeloid leukemia (ML) and investigates the effects of GEN on the proliferation, mitochondrial function, and energy metabolism of the chronic myeloid leukemia (CML) cell line K562.

Methods

The expression of UCP2 in clinical samples and cell lines (HL-60, U937, and K562) was confirmed using real-time quantitative polymerase chain reaction (qPCR) and western blot. The effects of GEN on K562 cell viability, morphology, and apoptosis were assessed through a cell counting kit-8 (CCK-8), Wright-Giemsa staining, and an annexin V-fluorescein isothiocyanate/propidium iodide (FITC/PI) apoptosis detection kit. Additionally, the impact of GEN on mitochondrial function and energy metabolism, including reactive oxygen species (ROS), mitochondrial membrane permeability transition pore (MPTP), lactic acid (LA), oxygen consumption rate (OCR), and adenosine triphosphate (ATP) levels in K562 cells, was also examined.

Results

The results showed that UCP2 was differentially expressed in clinical samples from patients with ML. Among the three cell lines examined, K562 cells exhibited a significantly higher expression level of UCP2. Functionally, GEN markedly inhibited K562 cell viability while promoting K562 cell differentiation and apoptosis. Mechanistically, UCP2 mRNA and protein expression levels were inhibited by GEN in K562 cells in a concentration- and time-dependent manner. Additionally, GEN dramatically increased ROS generation and induced mitochondrial MPTP opening in K562 cells. Furthermore, GEN significantly reduced LA production in K562 cells and markedly increased OCR and ATP production.

Conclusion

The results suggest that UCP2 is differentially expressed in ML patients and cell lines; GEN, a UCP2 inhibitor, induces mitochondrial damage and metabolic remodeling, thereby inhibiting proliferation and promoting apoptosis in K562 cells, and thus could be suggested as an adjuvant of an antitumor metabolic therapy.

Fabrication of Two-Layer Microfluidic Devices with Porous Electrodes Using Printed Sacrificial Layers

Two-layer microfluidic devices with porous membranes have been widely used in bioapplications such as microphysiological systems (MPS). Porous electrodes, instead of membranes, have recently been incorporated into devices for electrochemical cell analysis. Generally, microfluidic channels are prepared using soft lithography and assembled into two-layer microfluidic devices. In addition to soft lithography, three-dimensional (3D) printing has been widely used for the direct fabrication of microfluidic devices because of its high flexibility. However, this technique has not yet been applied to the fabrication of two-layer microfluidic devices with porous electrodes. This paper proposes a novel fabrication process for this type of device. In brief, Pluronic F-127 ink was three-dimensionally printed in the form of sacrificial layers. A porous Au electrode, fabricated by sputtering Au on track-etched polyethylene terephthalate membranes, was placed between the top and bottom sacrificial layers. After covering with polydimethylsiloxane, the sacrificial layers were removed by flushing with a cold solution. To the best of our knowledge, this is the first report on the sacrificial approach-based fabrication of two-layer microfluidic devices with a porous electrode. Furthermore, the device was used for electrochemical assays of serotonin and could successfully measure concentrations up to 5 µM. In the future, this device can be used for MPS applications.

Development of a simultaneous electrorotation device with microwells for monitoring the rotation rates of multiple single cells upon chemical stimulation

Here, we described a unique simultaneous electrorotation (ROT) device for monitoring the rotation rate of Jurkat cells via chemical stimulation without fluorescent labeling and an algorithm for estimating cell rotation rates. The device comprised two pairs of interdigitated array electrodes that were stacked orthogonally through a 20 μm-thick insulating layer with rectangular microwells. Four microelectrodes (two were patterned on the bottom of the microwells and the other two on the insulating layer) were arranged on each side of the rectangular microwells. The cells, which were trapped in the microwells, underwent ROT when AC voltages were applied to the four microelectrodes to generate a rotating electric field. These microwells maintained the cells even in fluid flows. Thereafter, the ROT rates of the trapped cells were estimated and monitored during the stimulation. We demonstrated the feasibility of estimating the chemical efficiency of cells by monitoring the ROT rates of the cells. After introducing a Jurkat cell suspension into the device, the cells were subjected to ROT by applying an AC signal. Further, the rotating cells were chemically stimulated by adding an ionomycin (a calcium ionophore)-containing aliquot. The ROT rate of the ionomycin-stimulated cells decreased gradually to 90% of the initial rate after 30 s. The ROT rate was reduced by an increase in membrane capacitance. Thus, our device enabled the simultaneous chemical stimulation-induced monitoring of the alterations in the membrane capacitances of many cells without fluorescent labeling.

Selective Trapping and Retrieval of Single Cells Using Microwell Array Devices Combined with Dielectrophoresis

We proposed selective manipulation techniques for retrieving and retaining target cells arrayed in microwells based on dielectrophoresis (DEP). The upper substrate with microband electrodes was mounted on the lower substrate with microwells based on the same design of microband electrodes by 90 degree relative to the lower substrate. A repulsive force of negative dielectrophoresis (n-DEP) was employed to retrieve the target cells from the microwell array selectively. Furthermore, the target cells were retained in the microwells after other cells were removed by n-DEP. Thus, the system described in this study could make it possible to retrieve and recover single target cells from a microwell array after determining the function of cells trapped in each microwell.