Generation of transmitochondrial cybrids using a microfluidic device.

Mitochondrial cloning is a promising approach to achieve homoplasmic mitochondrial DNA (mtDNA) mutations. We previously developed a microfluidic device that performs single mitochondrion transfer from a mtDNA-intact cell to a mtDNA-less (ρ0) cell by promoting cytoplasmic connection through a microtunnel between them. In the present study, we described a method for generating transmitochondrial cybrids using the microfluidic device. After achieving mitochondrial transfer between HeLa cells and thymidine kinase-deficient ρ0143B cells using the microfluidic device, selective culture was carried out using a pyruvate and uridine (PU)-absent and 5-bromo-2'-deoxyuridine-supplemented culture medium. The resulting cells contained HeLa mtDNA and 143B nuclei, but both 143B mtDNA and HeLa nuclei were absent in these cells. Additionally, these cells showed lower lactate production than parent ρ0143B cells and disappearance of PU auxotrophy for cell growth. These results suggest successful generation of transmitochondrial cybrids using the microfluidic device. Furthermore, we succeeded in selective harvest of generated transmitochondrial cybrids under a PU-supplemented condition by removing unfused ρ0 cells with puromycin-based selection in the microfluidic device.

Cytoplasmic fusion between an enlarged embryonic stem cell and a somatic cell using a microtunnel device.

Based on a previous finding that fusion of a somatic cell with an embryonic stem (ES) cell reprogrammed the somatic cell, genes for reprogramming transcription factors were selected and induced pluripotent stem (iPS) cell technology was developed. The cell fusion itself produced a tetraploid cell. To avoid nuclear fusion, a method for cytoplasmic fusion using a microtunnel device was developed. However, the ES cell was too small for cell pairing at the device. Therefore, in the present study, ES cell enlargement was carried out with the colchicine derivative demecolcine (DC). DC induced enlargement of ES cells without loss of their stemness. When an enlarged ES cell was paired with a somatic cell in the microtunnel device, cytoplasmic fusion was observed. The present method may be useful for further development of reprogramming techniques for iPS cell preparation without gene transfection.

Cryopreservation of adhered mammalian cells on a microfluidic device: Toward ready-to-use cell-based experimental platforms.

In this paper, we describe cryopreservation of mammalian cells in the adhered state on a microfluidic device (microdevice) for the first time. HeLa, NIH3T3, MCF-7, and PC12 cells were cultured on a microdevice in which a commercial polystyrene dish surface was used as the cell adhesion surface. Without cell-detaching treatment, the microdevice was stored in a freezer at -80°C. After thawing, we observed a greater number of live cells on the microdevice than those on a control culture dish. Although the effectiveness of the microdevice varied depending on the cell type and surface coating, the trend was consistent. We confirmed that the phenotype of the PC12 cells to differentiate into neuron-like cells was kept after the on-chip cryopreservation, and that the results of cytotoxicity test of cisplatin against the HeLa cells were essentially unchanged by the on-chip cryopreservation. These findings will open up a new possibility of ready-to-use cell-based experimental platforms.

Modulating F-actin organization induces organ growth by affecting the Hippo pathway.

The Hippo tumour suppressor pathway is a conserved signalling pathway that controls organ size. The core of the Hpo pathway is a kinase cascade, which in Drosophila involves the Hpo and Warts kinases that negatively regulate the activity of the transcriptional coactivator Yorkie. Although several additional components of the Hippo pathway have been discovered, the inputs that regulate Hippo signalling are not fully understood. Here, we report that induction of extra F-actin formation, by loss of Capping proteins A or B, or caused by overexpression of an activated version of the formin Diaphanous, induced strong overgrowth in Drosophila imaginal discs through modulating the activity of the Hippo pathway. Importantly, loss of Capping proteins and Diaphanous overexpression did not significantly affect cell polarity and other signalling pathways, including Hedgehog and Decapentaplegic signalling. The interaction between F-actin and Hpo signalling is evolutionarily conserved, as the activity of the mammalian Yorkie-orthologue Yap is modulated by changes in F-actin. Thus, regulators of F-actin, and in particular Capping proteins, are essential for proper growth control by affecting Hippo signalling.

Effects of ROCK inhibitor Y-27632 on cell fusion through a microslit.

We previously reported a direct cytoplasmic transfer method using a microfluidic device, in which cell fusion was induced through a microslit (slit-through-fusion) by the Sendai virus envelope (HVJ-E) to prevent nuclear mixing. However, the method was impractical due to low efficiency of slit-through-fusion formation and insufficient prevention of nuclear mixing. The purpose of this study was to establish an efficient method for inducing slit-through-fusion without nuclear mixing. We hypothesized that modulation of cytoskeletal component can decrease nuclear migration through the microslit considering its functions. Here we report that supplementation with Y-27632, a specific ROCK inhibitor, significantly enhances cell fusion induction and prevention of nuclear mixing. Supplementation with Y-27632 increased the formation of slit-through-fusion efficiency by more than twofold. Disruption of F-actin by Y-27632 prevented nuclear migration between fused cells through the microslit. These two effects of Y-27632 led to promotion of the slit-through-fusion without nuclear mixing with a 16.5-fold higher frequency compared to our previous method (i.e., cell fusion induction by HVJ-E without supplementation with Y-27632). We also confirmed that mitochondria were successfully transferred to the fusion partner under conditions of Y-27632 supplementation. These findings demonstrate the practicality of our cell fusion system in producing direct cytoplasmic transfer between live cells.

Hippo pathway regulation by cell morphology and stress fibers.

The Hippo signaling pathway plays an important role in regulation of cell proliferation. Cell density regulates the Hippo pathway in cultured cells; however, the mechanism by which cells detect density remains unclear. In this study, we demonstrated that changes in cell morphology are a key factor. Morphological manipulation of single cells without cell-cell contact resulted in flat spread or round compact cells with nuclear or cytoplasmic Yap, respectively. Stress fibers increased in response to expanded cell areas, and F-actin regulated Yap downstream of cell morphology. Cell morphology- and F-actin-regulated phosphorylation of Yap, and the effects of F-actin were suppressed by modulation of Lats. Our results suggest that cell morphology is an important factor in the regulation of the Hippo pathway, which is mediated by stress fibers consisting of F-actin acting upstream of, or on Lats, and that cells can detect density through their resulting morphology. This cell morphology (stress-fiber)-mediated mechanism probably cooperates with a cell-cell contact (adhesion)-mediated mechanism involving the Hippo pathway to achieve density-dependent control of cell proliferation.

Cell fusion through a microslit between adhered cells and observation of their nuclear behavior.

This paper describes a novel cell fusion method which induces cell fusion between adhered cells through a microslit for preventing nuclear mixing. For this purpose, a microfluidic device which had ∼ 100 cell pairing structures (CPSs) making cell pairs through microslits with 2.1 ± 0.3 µm width was fabricated. After trapping NIH3T3 cells with hydrodynamic forces at the CPSs, the cells were fused through the microslit by the Sendai virus envelope method. With following timelapse observation, we discovered that the spread cells were much less susceptible to nuclear migration passing through the microslit compared with round cells, and that cytoplasmic fraction containing mitochondria was transferred through the microslit without nuclear mixing. These findings will provide an effective method for cell fusion without nuclear mixing, and will lead to an efficient method for reprograming and transdifferentiation of target cells toward regenerative medicine.

A Microfluidic Device for Modulation of Organellar Heterogeneity in Live Single Cells.

The quantitatively controlled organellar transfer between living single cells provides a unique experimental platform to analyze the contribution of organellar heterogeneity on cellular phenotypes. We previously developed a microfluidic device which can perform quantitatively controlled mitochondrial transfer between live single cells by promoting strictured cytoplasmic connections between live single cells, but its application to other organelles is unclear. In this study, we investigated the quantitative properties of peroxisome transfer in our microfluidic device. When cells were fused through a 10 or 4 µm long microtunnel by a Sendai virus envelope-based method, a strictured cytoplasmic connection was achieved with a length corresponding to that of the microtunnel, and a subsequent recovery culture disconnected the fused cells. The peroxisome number being transferred through a 10 µm length of the microtunnel was smaller than that of 4 µm. These data suggest that our microfuidic device can perform a quantitative control of peroxisome transfer.

Quantitatively Controlled Intercellular Mitochondrial Transfer by Cell Fusion-Based Method Using a Microfluidic Device.

Quantitative control of mitochondrial transfer is a promising approach for genetic manipulation of mitochondrial DNA (mtDNA) because it enables precise modulation of heteroplasmy. Furthermore, single mitochondrion transfer from a mtDNA mutation-accumulated cell to a mtDNA-less (ρ0) cell potentially achieves homoplasmy of mutated mtDNA. Here we describe the method for quantitative control of mitochondrial transfer including achieving single mitochondrion transfer between live single cells using a microfluidic device.

EMF 35 JMIP study for Japan's long-term climate and energy policy: scenario designs and key findings.

In June, 2019, Japan submitted its mid-century strategy to the United Nations Framework Convention on Climate Change and pledged 80% emissions cuts by 2050. The strategy has not gone through a systematic analysis, however. The present study, Stanford Energy Modeling Forum (EMF) 35 Japan Model Intercomparison project (JMIP), employs five energy-economic and integrated assessment models to evaluate the nationally determined contribution and mid-century strategy of Japan. EMF 35 JMIP conducts a suite of sensitivity analyses on dimensions including emissions constraints, technology availability, and demand projections. The results confirm that Japan needs to deploy all of its mitigation strategies at a substantial scale, including energy efficiency, electricity decarbonization, and end-use electrification. Moreover, they suggest that with the absence of structural changes in the economy, heavy industries will be one of the hardest to decarbonize. Partitioning of the sum of squares based on a two-way analysis of variance (ANOVA) reconfirms that mitigation strategies, such as energy efficiency and electrification, are fairly robust across models and scenarios, but that the cost metrics are uncertain. There is a wide gap of policy strength and breadth between the current policy instruments and those suggested by the models. Japan should strengthen its climate action in all aspects of society and economy to achieve its long-term target. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11625-021-00913-2.

Reproducible fashion of the HSP70B' promoter-induced cytotoxic response on a live cell-based biosensor by cell cycle synchronization.

Live cell-based sensors potentially provide functional information about the cytotoxic effect of reagents on various signaling cascades. Cells transfected with a reporter vector derived from a cytotoxic response promoter can be used as intelligent cytotoxicity sensors (i.e., sensor cells). We have combined sensor cells and a microfluidic cell culture system that can achieve several laminar flows, resulting in a reliable high-throughput cytotoxicity detection system. These sensor cells can also be applied to single cell arrays. However, it is difficult to detect a cellular response in a single cell array, due to the heterogeneous response of sensor cells. The objective of this study was cell homogenization with cell cycle synchronization to enhance the response of cell-based biosensors. Our previously established stable sensor cells were brought into cell cycle synchronization under serum-starved conditions and we then investigated the cadmium chloride-induced cytotoxic response at the single cell level. The GFP positive rate of synchronized cells was approximately twice as high as that of the control cells, suggesting that cell homogenization is an important step when using cell-based biosensors with microdevices, such as a single cell array.

[Development of novel culture system using nano-biotechnology].

We have developed two cell culture systems for use in pharmaceutical research using nano-biotechnology. First, we developed a double layered co-culture system using cell sheet technology, and showed that in a layered co-culture system with HepG2 and bovine endothelial cells, the expression levels of various cytochrome P450 (CYP) genes were significantly increased compared to monolayer cultured HepG2 cells. In the layered HepG2 co-culture, expression of the CYP2C and CYP3A family genes was induced by phenobarbital treatment. We also detected CYP3A4 enzyme induction using this co-culture system. Next, we developed sensor cells. Living cells maintain homeostasis by responding quickly and with great sensitivity to changes in the external environment. Consequently, sensors using cells as active elements are thought to be able to perform analyses faster and with more sensitivity than previous methods. We have modified mammalian cells using genetic engineering techniques to develop next-generation cell sensors that can visually represent specific reactions. We successfully produced devices using sensor cells that can process a variety of specimens using Micro-Electro-Mechanical System (MEMS), Nano-Electro-Mechanical System (NEMS), and other nano/micro processing technologies. These systems may serve as a useful model for in vitro pharmacological studies on the coordinated regulation of metabolism and cytotoxicity. In this review, we introduce our research and describe recent trends in this field.

DNA damage sensible engineered promoter for cellular biosensing of cytotoxicity.

We have established a cytotoxic sensor cell line by transfecting HepG2 cells with a luciferase protein plasmid derived from the heat shock protein 70B' (HSP70B') promoter, which is induced by cytotoxic reagents. HSP70B genes are up-regulated by a wide-range of cytotoxic stimulators, in particular, those that denature proteins. However, the HSP70B genes do not respond to DNA damage. We used a PCR array to detect marker genes of DNA damage-related cytotoxic stimulation and found the BTG2 gene to be one such gene. Analysis of the BTG2 gene functional promoter region by transfection of various deletion constructs into HepG2 cells indicated that the p53 and NFY biding sites on BTG2 are important for the response to DNA damage. We then constructed HepG2 sensor cells using the functional BTG2 promoter, and found that these sensor cells can specifically detect the cytotoxicity accompanied by DNA strand breaks with high sensitivity.

Live cells-based cytotoxic sensorchip fabricated in a microfluidic system.

We report here a live cells-based sensorchip fabricated in microfluidic channels in which several laminar flows were achieved. In addition, we established a cytotoxic sensor cell line, which was transfected with a green fluorescence protein (GFP) plasmid derived from the heat shock protein 70B' (HSP70B') promoter, which is induced by cytotoxic reagents. The fluorescence in the sensor cells increased in a CdCl(2) dose-dependent manner in the microfluidic channels. In this system, cytotoxic reagents can be quantitatively detected in a quick, sensitive and high-throughput manner. The combination of sensor cells and microfluidic systems will provide an important basis for the development of micro-total analysis systems (micro-TAS) technology, and can be applied to toxicology, environmental assessment and drug screening.

Quantitative control of mitochondria transfer between live single cells using a microfluidic device.

Quantitative control of mitochondria transfer between live cells is a promising approach for genetic manipulation of mitochondrial DNA (mtDNA) because single mitochondrion transfer to a mtDNA-less (ρ0) cell potentially leads to homoplasmy of mtDNA. In this paper, we describe a method for quantitative control of mitochondria transfer between live single cells. For this purpose, we fabricated novel microfluidic devices having cell paring structures with a 4.1, 5.6 or 10.0 µm-length microtunnel. When cells were fused through a microtunnel using the Sendai virus envelope-based method, a strictured cytoplasmic connection was achieved with a length corresponding to that of the microtunnel. Elongation of the cytoplasmic connection led to a decrease in mitochondria transfer to the fusion partner. Moreover, some cell pairs that fused through a 10.0 µm-length microtunnel showed single mitochondrion transfer. Fused cells were spontaneously disconnected from each other when they were recovered in a normal culture medium. These results suggest that our cell fusion method can perform quantitative control of mitochondria transfer that includes a single mitochondrion transfer.

The significance of membrane fluidity of feeder cell-derived substrates for maintenance of iPS cell stemness.

The biological activity of cell-derived substrates to maintain undifferentiated murine-induced pluripotent stem (iPS) cells was correlated to membrane fluidity as a new parameter of cell culture substrates. Murine embryonic fibroblasts (MEFs) were employed as feeder cells and their membrane fluidity was tuned by chemical fixation using formaldehyde (FA). Membrane fluidity was evaluated by real-time single-molecule observations of green fluorescent protein-labeled epidermal growth factor receptors on chemically fixed MEFs. Biological activity was monitored by colony formation of iPS cells. Treatment with a low concentration of FA sustained the membrane fluidity and biological activity, which were comparable to those of mitomycin C-treated MEFs. The biological activity was further confirmed by sustained expression of alkaline phosphatase, SSEA-1, and other pluripotency markers in iPS cells after 3-5 days of culture on FA-fixed MEFs. Chemical fixation of feeder cells has several advantages such as providing ready-to-use culture substrates without contamination by proliferating feeder cells. Therefore, our results provide an important basis for the development of chemically fixed culture substrates for pluripotent stem cell culture as an alternative to conventional treatment by mitomycin C or x-ray irradiation.

Microfluidic perfusion cell culture system confined in 35 mm culture dish for standard biological laboratories.

An extremely simple, self-standing microfluidic cell culture system is reported. The whole system is confined in a 35 mm culture dish, and requires only a standard CO2 incubator. The culture medium is perfused by gravity. We successfully cultured NIH3T3-derived cells up to 10 days with a viability of ∼90%.

Formation process and fate of the nuclear chain after injury in regenerated myofiber.

Although it is well known that regenerated myofibers contain nuclear chains (arrayed nuclear clusters), details of its process of formation and fate are still remained unclear. In the present study, we isolated single myofibers from injured ICR mouse tibialis anterior muscles by the alkali maceration-based method, and carried out histological observation and bromodeoxyuridine (BrdU) pulse-chase analysis on the nuclear chains. The nuclear chains were formed after injury and remained stable for at least 6 months after injury. When BrdU was administered during the first 4 days after injury, up to 56% of nuclei in the nuclear chains were labeled with BrdU, whereas when BrdU was administered 5 days or later after injury, less than 3% of myonuclei were labeled with BrdU. Among BrdU-positive nuclei in the nuclear chains, the nuclei showing attenuated and strong BrdU signal were dominant when BrdU was administered at the time points of 0-2 and 3-4 days after injury, respectively. These results suggest that successive nuclear divisions occur during the first 4 days after injury and might be involved in the appearance of the stable nuclear chains in regenerated myofibers.

Highly sensitive detection of cytotoxicity using a modified HSP70B' promoter.

We have previously found that the DNA fragment from nucleotides (nts) -287 to +110 in the HSP70B' gene is a functional promoter responding to Cadmium Chloride-induced cytotoxicity (Wada et al., Biotechnol Bioeng, 92, 410-415, 2005). In order to increase the cytotoxic response of this promoter, we first determined the location of the cytotoxic responding element (CRE) and then constructed tandem repeats of the CRE in front of the HSP70B' promoter. 5'- and 3'-deletion analysis revealed that the DNA fragment from nts -192 to -56 in the HSP70B' gene induces a significant response to cytotoxicity. When the AP-1 binding site in this region was mutated, the basal activity of HSP70B' gene promoter decreased but the cytotoxic response was unchanged. Thus, the CRE is located in nts -192 to -56 in the HSP70B' promoter, and the AP-1 binding site is not essential for the cytotoxic response. In addition, cells transfected with a luciferase construct carrying three tandem repeats of the CRE upstream of the HSP70B' promoter and containing AP-1 binding site mutation, showed a 2.28-fold higher response than that of no repeats. Moreover, the detection limit of Cadmium Chloride in the cells was 382 pmol/mL. Thus, highly sensitive sensor cells for Cadmium Chloride can be constructed using a HSP70B' promoter construct containing upstream tandem repeats of the CRE and mutation of the AP-1 binding site.

Rapid and highly sensitive detection of cadmium chloride induced cytotoxicity using the HSP70B' promoter in live cells.

One unique to detect cytotoxicity is to utilize reporter gene assays for promoters that respond to stress-induced effects. In the present study, we discovered that the DNA sequence from nt -287 to +110 of the heat shock protein 70B' (HSP70B') gene could be used as a functional promoter to detect cytotoxicity of cadmium chloride. We thus detected cytotoxicity induced by cadmium chloride with the luciferase assay using this functional HSP70B' promoter, as well as the cell viability test based on the quantification of intracellular ATP. The luciferase assay using the functional HSP70B' promoter resulted in nearly maximal luciferase activity after only 12 h of exposure to cadmium chloride, however, with intracellular ATP quantification, the decrease in cell viability only reached a plateau after 24 h of exposure. Cytotoxicity detection limits for cadmium chloride with the functional HSP70B' promoter assay or cell viability based on ATP quantification were 130 ng/mL and 530 ng/mL, respectively. Our results therefore suggest that the novel reporter gene assay using a functional region of the HSP70B' promoter has significant advantages for the detection of cytotoxicity in terms of both speed and sensitivity, when compared to the cell viability test based on ATP quantification.