Elucidation of the liver pathophysiology of COVID-19 patients using liver-on-a-chips

SARS-CoV-2 induces severe organ damage not only in the lung but also in the liver, heart, kidney, and intestine. It is known that COVID-19 severity correlates with liver dysfunction, but few studies have investigated the liver pathophysiology in COVID-19 patients. Here, we elucidated liver pathophysiology in COVID-19 patients using organs-on-a-chip technology and clinical analyses. First, we developed liver-on-a-chip (LoC) which recapitulating hepatic functions around the intrahepatic bile duct and blood vessel. We found that hepatic dysfunctions, but not hepatobiliary diseases, were strongly induced by SARS-CoV-2 infection. Next, we evaluated the therapeutic effects of COVID-19 drugs to inhibit viral replication and recover hepatic dysfunctions, and found that the combination of anti-viral and immunosuppressive drugs (Remdesivir and Baricitinib) is effective to treat hepatic dysfunctions caused by SARS-CoV-2 infection. Finally, we analyzed the sera obtained from COVID-19 patients, and revealed that COVID-19 patients, who were positive for serum viral RNA, are likely to become severe and develop hepatic dysfunctions, as compared with COVID-19 patients who were negative for serum viral RNA. We succeeded in modeling the liver pathophysiology of COVID-19 patients using LoC technology and clinical samples.

Usability of Polydimethylsiloxane-Based Microfluidic Devices in Pharmaceutical Research Using Human Hepatocytes

A liver-on-a-chip (liver-chip) is a microfluidic device carrying liver cells such as human hepatocytes. It is used to reproduce a part of liver function. Many microfluidic devices are composed of polydimethylsiloxane (PDMS), which is a type of silicone elastomer. PDMS is easy to process and suitable for cell observation, but its high hydrophobicity carries the risk of drug absorption. In this study, we evaluated drug absorption to the PDMS device and investigated the drug responsiveness of human hepatocytes cultured in the PDMS device (hepatocyte-chips). First, the absorption rates of 12 compounds to the PDMS device were measured. The absorption rates of midazolam, bufuralol, cyclosporine A, and verapamil were 92.9, 71.7, 71.4, and 99.6%, respectively, but the other compounds were poorly absorbed. Importantly, the absorption rate of the compounds was correlated with their octanol/water distribution coefficient (log D) values (R² = 0.76). Next, hepatocyte-chips were used to examine the response to drugs, which are typically used to evaluate hepatic functions. Using the hepatocyte-chips, we could confirm the responsiveness of drugs including cytochrome P450 (CYP) inducers and farnesoid X receptor (FXR) ligands. We believe that our findings will contribute to drug discovery research using PDMS-based liver-chips.

Multicellular modeling of ciliopathy by combining iPS cells and microfluidic airway-on-a-chip technology

Mucociliary clearance is an essential lung function that facilitates the removal of inhaled pathogens and foreign matter unidirectionally from the airway tract and is innately achieved by coordinated ciliary beating of multiciliated cells. Should ciliary function become disturbed, mucus can accumulate in the airway causing subsequent obstruction and potentially recurrent pneumonia. However, it has been difficult to recapitulate unidirectional mucociliary flow using human-derived induced pluripotent stem cells (iPSCs) in vitro and the mechanism governing the flow has not yet been elucidated, hampering the proper humanized airway disease modeling. Here, we combine human iPSCs and airway-on-a-chip technology, to demonstrate the effectiveness of fluid shear stress (FSS) for regulating the global axis of multicellular planar cell polarity (PCP), as well as inducing ciliogenesis, thereby contributing to quantifiable unidirectional mucociliary flow. Furthermore, we applied the findings to disease modeling of primary ciliary dyskinesia (PCD), a genetic disease characterized by impaired mucociliary clearance. The application of an airway cell sheet derived from patient-derived iPSCs and their gene-edited counterparts, as well as genetic knockout iPSCs of PCD causative genes, made it possible to recapitulate the abnormal ciliary functions in organized PCP using the airway-on-a-chip. These findings suggest that the disease model of PCD developed here is a potential platform for making diagnoses and identifying therapeutic targets and that airway reconstruction therapy using mechanical stress to regulate PCP might have therapeutic value.

Effects of age-dependent changes in cell size on endothelial cell proliferation and senescence through YAP1

Angiogenesis - the growth of new blood capillaries- is impaired in aging animals. Biophysical factors such as changes in cell size control endothelial cell (EC) proliferation and differentiation. However, the effects of aging on EC size and the mechanism by which changes in cell size control age-dependent decline in EC proliferation are largely unknown. Here, we have demonstrated that aged ECs are larger than young ECs and that age-dependent increases in EC size control EC proliferation and senescence through CDC42-Yes-associated protein (YAP1) signaling. Reduction of aged EC size by culturing on single-cell sized fibronectin-coated smaller islands decreases CDC42 activity, stimulates YAP1 nuclear translocation and attenuates EC senescence. Stimulation of YAP1 or inhibition of CDC42 activity in aged ECs also restores blood vessel formation. Age-dependent changes in EC size and/or CDC42 and YAP1 activity may be the key control point of age-related decline in angiogenesis.

Modeling Hematopoiesis and Responses to Radiation Countermeasures in a Bone Marrow-on-a-Chip

Studies on hematopoiesis currently rely on animal models because in vitro culture methods do not accurately recapitulate complex bone marrow physiology. We recently described a bone marrow-on-a-chip microfluidic device that enables the culture of living hematopoietic bone marrow and mimics radiation toxicity in vitro. In the present study, we used this microdevice to demonstrate continuous blood cell production in vitro and model bone marrow responses to potential radiation countermeasure drugs. The device maintained mouse hematopoietic stem and progenitor cells in normal proportions for at least 2 weeks in culture. Increases in the number of leukocytes and red blood cells into the microfluidic circulation also could be detected over time, and addition of erythropoietin induced a significant increase in erythrocyte production. Exposure of the bone marrow chip to gamma radiation resulted in reduction of leukocyte production, and treatment of the chips with two potential therapeutics, granulocyte-colony stimulating factor or bactericidal/permeability-increasing protein (BPI), induced significant increases in the number of hematopoietic stem cells and myeloid cells in the fluidic outflow. In contrast, BPI was not found to have any effect when analyzed using static marrow cultures, even though it has been previously shown to accelerate recovery from radiation-induced toxicity in vivo. These findings demonstrate the potential value of the bone marrow-on-a-chip for modeling blood cell production, monitoring responses to hematopoiesis-modulating drugs, and testing radiation countermeasures in vitro.

Biomechanical forces promote blood development through prostaglandin E2 and the cAMP-PKA signaling axis

Blood flow promotes emergence of definitive hematopoietic stem cells (HSCs) in the developing embryo, yet the signals generated by hemodynamic forces that influence hematopoietic potential remain poorly defined. Here we show that fluid shear stress endows long-term multilineage engraftment potential upon early hematopoietic tissues at embryonic day 9.5, an embryonic stage not previously described to harbor HSCs. Effects on hematopoiesis are mediated in part by a cascade downstream of wall shear stress that involves calcium efflux and stimulation of the prostaglandin E2 (PGE2)-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling axis. Blockade of the PGE2-cAMP-PKA pathway in the aorta-gonad-mesonephros (AGM) abolished enhancement in hematopoietic activity. Furthermore, Ncx1 heartbeat mutants, as well as static cultures of AGM, exhibit lower levels of expression of prostaglandin synthases and reduced phosphorylation of the cAMP response element-binding protein (CREB). Similar to flow-exposed cultures, transient treatment of AGM with the synthetic analogue 16,16-dimethyl-PGE2 stimulates more robust engraftment of adult recipients and greater lymphoid reconstitution. These data provide one mechanism by which biomechanical forces induced by blood flow modulate hematopoietic potential.

Transwells with microstamped membranes produce micropatterned two-dimensional and three-dimensional co-cultures

This article describes a simple and rapid cell patterning method to form co-culture microarrays in commercially available Transwells. A thin poly(dimethylsiloxane) (PDMS) layer is printed on the underside of a Transwell using a PDMS stamp. Arbitrary cellular patterns are generated according to the geometric features of the thin PDMS layer through hydrodynamic forces that guide cells onto the membrane only over the PDMS-uncoated regions. Micropatterns of surface-adhered cells (we refer to this as two-dimensional) or non-surface-adhered clusters of cells (we refer to this as three-dimensional) can be generated depending on the surface treatment of the filter membrane. Additionally, co-cultures can be established by introducing different types of cells on the membrane or in the bottom chamber of the Transwell. We show that this co-culture method can evaluate mouse embryonic stem (mES) cell differentiation based on heterogeneous cell-cell interactions. Co-culture of mES cells and HepG2 cells decreased SOX17 expression of mES cells, and direct cell-cell contact further decreased SOX17 expression, indicating that co-culture with HepG2 cells inhibits endoderm differentiation through soluble factors and cell-cell contact. This method is simple and user-friendly and should be broadly useful to study cell shapes and cell-cell interactions.

Measurement of gene expression from single adherent cells and spheroids collected using fast electrical lysis

The cytosol of a single adherent cell was collected by the electrical cell lysis method with a Pt-ring capillary probe, and the cellular messenger RNA (mRNA) was analyzed at a single-cell level. The ring electrode probe was positioned 20 microm above the cultured cells that formed a monolayer on an indium-tin oxide (ITO) electrode, and an electric pulse with a magnitude of 40 V was applied for 10 micros between the probe and the ITO electrodes in an isotonic sucrose solution. Immediately after the electric pulse, less than 1 microL of the lysed solution was collected using a micro-injector followed by RNA purification and first strand cDNA synthesis. Real-time PCR was performed to quantify the copy numbers of mRNA encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression inside the single cell. The average copy numbers of GAPDH mRNA collected by the electrical cell lysis method were found to be comparable to those obtained by a simple capillary suction method. Although single-cell analysis has already been demonstrated, we have shown for the first time that the fast electrical cell lysis can be used for quantitative mRNA analysis at the single-cell level. This electrical cell lysis method was further applied for the analysis of mRNA obtained from single spheroids-the aggregated cellular masses formed during the three-dimensional culture -- as a model system to isolate small cellular clusters from tissues and organs.

Regulation and characterization of the polarity of cells embedded in a reconstructed basement matrix using a three-dimensional micro-culture system

Three cell lines, that is, the human breast cancer cell line (MCF-7) and the human mammary epithelial cell line (S-1) and its malignant form (T4-2) were embedded in a reconstituted basement membrane (Matrigel) that had 20-nL pyramid-shaped silicon microstructures. The proliferative behavior of the MCF-7 cells was dependent on the surrounding conditions (2-D, collagen gel, or Matrigel), whereas the respiratory activity of a single cell (F(c)) was almost identical under different culture conditions. The F(c) value changed with cellular polarity. The F(c) value for the S-1 cells was observed to decrease slightly, whereas that of the T4-2 cells increased 2 days after cultivation in the microstructures within the Matrigel. However, when the T4-2 cells were cultured in the presence of tyrphostin AG 1478 (T4-2 tyr) to inhibit epidermal growth factor (EGF) signaling, the F(c) value decreased slightly and remained almost constant for an additional 1 week; this was similar to the behavior of the S-1 cells. Further, fluorescence images showed that the T4-2 tyr cells formed polar structures that were similar to those formed by the S-1 cells whereas the T4-2 cells did not form such structures. These results indicate that cellular polarity can be assessed by measuring cellular respiratory activity.

Electrochemical Monitoring of Cellular Signal Transduction with a Secreted Alkaline Phosphatase Reporter System

Electrochemical monitoring of cellular signal transduction under three-dimensional (3-D) cell culture conditions has been demonstrated by combining cell-based microarrays with a secreted alkaline phosphatase (SEAP) reporter system. The cells were genetically engineered to produce SEAP under the control of nuclear factor kappaB (NFkappaB) enhancer elements, and they were embedded with a small volume of a collagen gel matrix on a pyramidal-shaped silicon microstructure. Cellular SEAP expression triggered by NFkappaB activation was assessed by two types of electrochemical systems. First, SEAP expression of a 3-D cell array on a chip was continuously monitored in situ for 2 days by scanning electrochemical microscopy (SECM). Since the SECM-based assay enables the evaluation of cellular respiratory activity, simultaneous measurements of cellular viability and signal transduction were possible. Further, we have developed an electrode-integrated cell culture device for parallel evaluation of cellular SEAP expression. The detector electrode was integrated around the silicon microhole. Two kinds of cells were immobilized on the array of microholes on the same chip for comparative characterization of their SEAP activity. This electrochemical microdevice can be applied to evaluate the SEAP expression activity in multiple cellular microarrays by a high-throughput method.

A multicellular spheroid-based drug sensitivity test by scanning electrochemical microscopy

The respiratory activity of a multicellular spheroid was non-invasively monitored by scanning electrochemical microscopy (SECM) to investigate the anticancer drug sensitivity. The effects of the three anticancer drugs, cisplatin (CDDP), 5-fluorouracil (5-FU), and paclitaxel (TXL), were continuously evaluated based on respiratory activity for 5 days. The drug sensitivities obtained by SECM were higher compared to those evaluated by the spheroid volume and conformed to those evaluated by a conventional colorimetric assay. Our results show that the SECM-based assay directly correlates with the number of viable cells within the spheroid, whereas the spheroid volume does not necessarily correlate with the number of viable cells. Furthermore, the results obtained by spheroid culture (3-D) were compared to those of cells cultured in a flask (2-D) and within a collagen gel (3-D). The drug sensitivity of cells cultured in 2-D is more pronounced than that of the cells cultured in 3-D. Since the cellular proliferation status in a 3-D culture is similar to that in vivo, the drug sensitivity test performed in the spheroid culture will give meaningful results that can be extended to an in vivo application. A SECM-based assay is perfectly suitable to directly evaluate the drug sensitivity of the spheroid.

On-Chip Transformation of Bacteria

On-chip transformation of Escherichia coli cells was accomplished for the first time using a microbial array chip. The continuous E. coli transformation procedures were performed on a chip in which the microcompartment was composed of PDMS microfluidic channels and a silicon substrate predeposited with different plasmid DNAs. The PDMS microfluidic device enabled the parallel transformation of E. coli cells with various plasmid DNAs by separating each transformation area. The phenotypic differences reflecting different plasmid DNAs were identified by various approaches such as colorimetry, fluorometry, and electrochemical methods. This microbial array chip could become a versatile tool for many cell biological applications.

Scanning electrochemical microscopy-based drug sensitivity test for a cell culture integrated in silicon microstructures

The respiratory activity of collagen-embedded living cells was imaged by scanning electrochemical microscopy (SECM) with the objective to study anticancer drug sensitivity. Two kinds of cancer cells, the human erythroleukemia cell line (K562) and its adriamycin-resistant subline (K562/ADM), were immobilized at the array of microholes micromachined on a silicon wafer for comparative characterization of their sensitivity to the anticancer drug, ADM. The results obtained by the SECM method showed correspondence to a conventional colorimetric assay (SDI assay). Furthermore, since the SECM assay is based on the noninvasive measurement of the respiration activity, continuous monitoring of a dose response was possible.