Cell-based assay for the detection of chemically induced cellular stress by immortalized untransformed transgenic hepatocytes

YAP integrates the regulatory Snail/HNF4α circuitry controlling epithelial/hepatocyte differentiation

Yes-associated protein (YAP) is a transcriptional co-factor involved in many cell processes, including development, proliferation, stemness, differentiation, and tumorigenesis. It has been described as a sensor of mechanical and biochemical stimuli that enables cells to integrate environmental signals. Although in the liver the correlation between extracellular matrix elasticity (greatly increased in the most of chronic hepatic diseases), differentiation/functional state of parenchymal cells and subcellular localization/activation of YAP has been previously reported, its role as regulator of the hepatocyte differentiation remains to be clarified. The aim of this study was to evaluate the role of YAP in the regulation of epithelial/hepatocyte differentiation and to clarify how a transducer of general stimuli can integrate tissue-specific molecular mechanisms determining specific cell outcomes. By means of YAP silencing and overexpression we demonstrated that YAP has a functional role in the repression of epithelial/hepatocyte differentiation by inversely modulating the expression of Snail (master regulator of the epithelial-to-mesenchymal transition and liver stemness) and HNF4α (master regulator of hepatocyte differentiation) at transcriptional level, through the direct occupancy of their promoters. Furthermore, we found that Snail, in turn, is able to positively control YAP expression influencing protein level and subcellular localization and that HNF4α stably represses YAP transcription in differentiated hepatocytes both in cell culture and in adult liver. Overall, our data indicate YAP as a new member of the HNF4/Snail epistatic molecular circuitry previously demonstrated to control liver cell state. In this model, the dynamic balance between three main transcriptional regulators, that are able to control reciprocally their expression/activity, is responsible for the induction/maintenance of different liver cell differentiation states and its modulation could be the aim of therapeutic protocols for several chronic liver diseases.

Brain organoids as a model system for human neurodevelopment and disease

The ability to reproduce early stages of human neurodevelopment in the laboratory is one of the most exciting fields in modern neuroscience. The inaccessibility of the healthy human brain developing in utero has delayed our understanding of the initial steps in the formation of one of the most complex tissues in the body. Animal models, postmortem human tissues and cellular systems have been instrumental in contributing to our understanding of the human brain. However, all model systems have intrinsic limitations. The emerging field of brain organoids, which are three-dimensional self-assembled multicellular structures derived from human pluripotent stem cells, offers a promising complementary cellular model for the study of the human brain. Here, we will discuss the initial experiments that were the foundation for this emerging field, highlight recent uses of the technology and offer our perspective on future directions that might guide further exploratory experimentation to improve the human brain organoid model system.

TGFbeta Induces Binucleation/Polyploidization in Hepatocytes through a Src-Dependent Cytokinesis Failure

In all mammals, the adult liver shows binucleated as well as mononucleated polyploid hepatocytes. The hepatic polyploidization starts after birth with an extensive hepatocyte binucleation and generates hepatocytes of several ploidy classes. While the functional significance of hepatocyte polyploidy is becoming clearer, how it is triggered and maintained needs to be clarified. Aim of this study was to identify a major inducer of hepatocyte binucleation/polyploidization and the cellular and molecular mechanisms involved. We found that, among several cytokines analyzed, known to be involved in early liver development and/or mass control, TGFbeta1 was capable to induce, together with the expected morphological changes, binucleation in hepatocytes in culture. Most importantly, the pharmacological inhibition of TGFbeta signaling in healthy mice during weaning, when the physiological binucleation occurs, induced a significant decrease of hepatocyte binucleation rate, without affecting cell proliferation and hepatic index. The TGFbeta-induced hepatocyte binucleation resulted from a cytokinesis failure, as assessed by video microscopy, and is associated with a delocalization of the cytokinesis regulator RhoA-GTPase from the mid-body of dividing cells. The use of specific chemical inhibitors demonstrated that the observed events are Src-dependent. Finally, the restoration of a fully epithelial phenotype by TGFbeta withdrawal gave rise to a cell progeny capable to maintain the polyploid state. In conclusion, we identified TGFbeta as a major inducer of hepatocyte binucleation both in vitro and in vivo, thus ascribing a novel role to this pleiotropic cytokine. The production of binucleated/tetraploid hepatocytes is due to a cytokinesis failure controlled by the molecular axis TGFbeta/Src/RhoA.

Modulating the Substrate Stiffness to Manipulate Differentiation of Resident Liver Stem Cells and to Improve the Differentiation State of Hepatocytes

In many cell types, several cellular processes, such as differentiation of stem/precursor cells, maintenance of differentiated phenotype, motility, adhesion, growth, and survival, strictly depend on the stiffness of extracellular matrix that, in vivo, characterizes their correspondent organ and tissue. In the liver, the stromal rigidity is essential to obtain the correct organ physiology whereas any alteration causes liver cell dysfunctions. The rigidity of the substrate is an element no longer negligible for the cultivation of several cell types, so that many data so far obtained, where cells have been cultured on plastic, could be revised. Regarding liver cells, standard culture conditions lead to the dedifferentiation of primary hepatocytes, transdifferentiation of stellate cells into myofibroblasts, and loss of fenestration of sinusoidal endothelium. Furthermore, standard cultivation of liver stem/precursor cells impedes an efficient execution of the epithelial/hepatocyte differentiation program, leading to the expansion of a cell population expressing only partially liver functions and products. Overcoming these limitations is mandatory for any approach of liver tissue engineering. Here we propose cell lines as in vitro models of liver stem cells and hepatocytes and an innovative culture method that takes into account the substrate stiffness to obtain, respectively, a rapid and efficient differentiation process and the maintenance of the fully differentiated phenotype.

Stem cells, immortalized cells and primary cells in ADMET assays

Cell-based assays are beginning to replace traditional absorption, distribution, metabolism, elimination and toxicology (ADMET) models employing subcellular fractions in high throughput drug discovery screening and drug development where drugs are characterized and predictions are formulated to forecast in vivo biological outcomes. Significant and continuing advances in stem cell research, new immortalized cell lines and our enhanced ability to predict outcomes from primary cells have increased the ability to employ cell-based assays to study ADMET properties of new drugs.:

Glutathione-S-transferase enhances proliferation-migration and protects against shikonin-induced cell death in breast cancer cells

Glutathione-S-transferase (GST) is a cytoplasmic protein responsible for detoxification, but the effect of the enzyme on cell biological events, including proliferation and migration, has never been reported. Thus, we evaluated the detoxification effect of in vitro-applied GST on cancer cell proliferation and migration. Assays for proliferation and migration of human breast cancer cells in the presence of GST were carried out. Binding of GST on the surface of the cancer cells was studied by flow cytometry. Detoxification through GST pathway was studied in the presence of shikonin. The effective dosage of GST in enhancement of cell proliferation was 10-50 nM, and the cell migration could be significantly enhanced after 6 hours in the presence of 2-50 nM GST. Therefore, overall cell proliferation and migration could be enhanced in the presence of 10nM or greater concentration of GST, and 15 μM shikonin-induced toxification of the cancer cells could be neutralized by 1.0 μM GST. Flow cytometry showed that GST directly bound to the surface of the cancer cells, and this was confirmed by fluorescence confocal microscopic observation. It is concluded that human class π-GST enhances proliferation and migration of human breast cancer cells by means of direct binding to the cell surface and maintaining cell viability by detoxification.

Mammalian cell-based sensor system

Use of living cells or cellular components in biosensors is receiving increased attention and opens a whole new area of functional diagnostics. The term "mammalian cell-based biosensor" is designated to biosensors utilizing mammalian cells as the biorecognition element. Cell-based assays, such as high-throughput screening (HTS) or cytotoxicity testing, have already emerged as dependable and promising approaches to measure the functionality or toxicity of a compound (in case of HTS); or to probe the presence of pathogenic or toxigenic entities in clinical, environmental, or food samples. External stimuli or changes in cellular microenvironment sometimes perturb the "normal" physiological activities of mammalian cells, thus allowing CBBs to screen, monitor, and measure the analyte-induced changes. The advantage of CBBs is that they can report the presence or absence of active components, such as live pathogens or active toxins. In some cases, mammalian cells or plasma membranes are used as electrical capacitors and cell-cell and cell-substrate contact is measured via conductivity or electrical impedance. In addition, cytopathogenicity or cytotoxicity induced by pathogens or toxins resulting in apoptosis or necrosis could be measured via optical devices using fluorescence or luminescence. This chapter focuses mainly on the type and applications of different mammalian cell-based sensor systems.

NK3 and NK4 of HGF enhance filamin production via STAT pathway, but not NK1 and NK2 in human breast cancer cells

AIM

The purpose of this study was to reveal the effects of hepatocyte growth factor (HGF) variants on human breast cancer cells and the differential signaling pathways of the variants in controlling cell proliferation and invasion.

METHODS

Four HGF variants (NK1, NK2, NK3, and NK4) were created by gene engineering, and the variant DNA fragments were cloned into pGEM-T for DNA sequencing and then transferred to a pTrcHis-A plasmid for expression. Recombinant proteins were purified from Escherichia coli, and a series of assays, including cell proliferation and invasion were carried out. Phosphorylated components in the HGF-c-Met and STAT (signal transducers and activators of transcription) pathways were detected by immunoprecipitation-Western blots.

RESULTS

All the HGF variants inhibited the vigorous growth of the cancer cells differently and dose-dependently, but the effect of NK3 or NK4 was 7.5-fold higher than NK1 or NK2. In addition, the assays for the phosphorylation of the components in the HGF-c-Met pathway showed that NK3 and NK4 inhibited invasion via the STAT pathway, whereas NK1 and NK2 were via the HGF-c-Met pathway.

CONCLUSION

The engineered HGF variants inhibited the proliferation of human breast cancer cells via different signaling pathways, NK1 and NK2 via the HGF-c-Met pathways, and NK3 and NK4 via the STAT pathway, the latter being a possible key route for the inhibition of cell invasion. All of the HGF variants have the potential to become pharmaceutical drugs in the treatment of human cancer.

Plasticity of hepatic cell differentiation: bipotential adult mouse liver clonal cell lines competent to differentiate in vitro and in vivo

In fetal liver, bipotential hepatoblasts differentiate into hepatocytes and bile duct cells (cholangiocytes). The persistence of such progenitor cells in adult mouse liver is still debated. In damaged liver of adult murine animals, when hepatocyte proliferation is compromised, bipotential oval cells emerge, probably from bile ducts, proliferate, and differentiate to regenerate the liver. However, treatment to elicit oval cell proliferation is not necessary to obtain bipotential stem cells from adult mouse liver. Here, we have isolated bipotential clonal cell lines from healthy liver of 8-10-week-old C57BL/6 mice. Primary cultures established from hepatocyte-enriched suspensions were characterized by time-lapse image acquisition, immunocytology, and RNA transcript analysis. Although hepatocytes dedifferentiated with loss of apical polarity and other hepatocyte markers, they rapidly activated expression of bile duct/oval cell markers. Reversibility of these processes was achieved in part by culture under dilute Matrigel or by aging of confluent cultures. Cell lines were obtained at high frequency from mass cultures, from isolated colonies, and by primary cloning of the hepatocyte-enriched suspension. Cells of the clonal cell lines do not grow in soft agar and are nontumorigenic, and they express cytokeratin 19, A6 antigen, and alpha6 integrin, as well as a large panel of hepatocyte functions. Furthermore, they can participate in liver regeneration in albumin-urokinase-type plasminogen activator/severe combined immune-deficient mice, where they differentiate in clusters of hepatocytes and occasionally bile ducts. These results demonstrate the existence, in normal adult mouse liver, of a significant pool of clonogenic cells that are (or can become) bipotential.

New hepatocytes for toxicology?

In a recent article M.G. Sacco and co-workers described the establishment of immortalized untransformed transgenic hepatocyte (MMH-GH) cell lines, obtained from a cross between the AT/cytoMet and Hsp70/hGH transgenic mice. This strategy proved to be successful because the MMH-GH showed stability in culture and sensitivity to chemical exposure. Based on these results, the MMH-GH cell lines could prove to be a valid alternative cell-based assay for use in toxicological studies.