A Simple Method for Labeling Human Embryonic Stem Cells Destined to Lose Undifferentiated Potency

Titanium dioxide nanoparticles oral exposure induce osteoblast apoptosis, inhibit osteogenic ability and increase lipogenesis in mouse

Titanium dioxide nanoparticles (TiO2-NPs) are widely used in food, paint, coating, cosmetic, and composite orthodontic material. As a common food additive, TiO2-NPs can accumulate in various organs of human body, but the effect and underlying mechanism of bone remain unclear. Here mice were exposed to TiO2-NPs by oral gavage, and histological staining of femoral sections showed that TiO2-NPs reduced bone formation and enhanced osteoclast activity and lipogenesis, contributing to decreased trabecula bone. Transmission electron microscope (TEM) as well as biochemical and flow cytometry analysis of osteoblast exhibited that TiO2-NPs accumulated in osteoblast cytoplasm and impaired mitochondria ultrastructure with increased reactive oxygen species (ROS) and lipid hyperoxide, resulting in osteoblast apoptosis. In terms of mechanism, TiO2-NPs treatment inhibited expression of AKT and then increased pro-apoptotic protein Bax expression which was failure to form heterodimers with decreased anti-apoptotic Bcl-2, activating downstream Caspase-9 and Caspase-3 and inducing apoptosis. Additionally, TiO2-NPs suppressed Wnt3a level and then activated anti-Glycogen synthesis kinase (GSK-3β) phosphorylation, and ultimately resulted in degradation of β-catenin which down-regulated Runt-related transcription factor 2 (Runx2) and Osterix, inhibiting expression of osteogenic related proteins. Together, these results revealed that exposure of TiO2-NPs induced apoptosis and inhibited osteoblast differentiation through suppressing PI3K/AKT and Wnt/β-catenin signaling pathways, resulting in reduction of trabecula bone.

Quantitative analysis of mitochondrial membrane potential heterogeneity in unsynchronized and synchronized cancer cells

Mitochondrial membrane potential (ΔΨm) is a global indicator of mitochondrial function. Previous reports on heterogeneity of ΔΨm were qualitative or semiquantitative. Here, we quantified intercellular differences in ΔΨm in unsynchronized human cancer cells, cells synchronized in G1, S, and G2, and human fibroblasts. We assessed ΔΨm using a two-pronged microscopy approach to measure relative fluorescence of tetramethylrhodamine methyl ester (TMRM) and absolute values of ΔΨm. We showed that ΔΨm is more heterogeneous in cancer cells compared to fibroblasts, and it is maintained throughout the cell cycle. The effect of chemical inhibition of the respiratory chain and ATP synthesis differed between basal, low and high ΔΨm cells. Overall, our results showed that intercellular heterogeneity of ΔΨm is mainly modulated by intramitochondrial factors, it is independent of the ΔΨm indicator and it is not correlated with intercellular heterogeneity of plasma membrane potential or the phases of the cell cycle.

Inhibition of double-stranded RNA-dependent protein kinase prevents oxytosis and ferroptosis in mouse hippocampal HT22 cells

Double-stranded RNA-dependent protein kinase (PKR) is a component of signal transduction pathways mediating various stress signals including oxidative stress and endoplasmic reticulum (ER) stress and is suggested to be implicated in several neurodegenerative diseases. Cell death in neurodegenerative conditions has been linked to oxidative stress; however, the involvement of PKR in endogenous oxidative stress such as oxytosis and ferroptosis which is quite distinct from classical apoptosis remains unknown. We investigated here the effect of a PKR inhibitor C16 (an imidazole-oxindole derivative) on oxytosis and ferroptosis in cultured HT22 mouse hippocampal cells. C16 prevented glutamate- and erastin-induced cell death, reactive oxygen species accumulation, Ca²⁺ influx, phosphorylation of inositol-requiring enzyme 1 (IRE1), one of the three branches of ER stress signaling and its downstream signaling components. On the other hand, C16 did not prevent oxidative stress-induced heme oxygenase-1 expression; instead, C16 activated the extracellular signal-regulated kinase pathway. The protective effect of C16 is diminished in PKR knockout HT22 cells. Real time measurements of the oxygen consumption rate and extracellular acidification rate over a long period of time leading to cell death showed that C16 partially prevented erastin-induced mitochondrial and glycolytic dysfunction. These results suggest that PKR is an important component of oxytosis and ferroptosis and the inhibition of PKR is neuroprotective against endogenous oxidative stress-induced cell death and provide an effective strategy for neuroprotection.

Neural Crest Cell Models of Development and Toxicity: Cytotoxicity Assay Using Human Pluripotent Stem Cell-Derived Cranial Neural Crest Cell Model

Cranial neural crest cells (NCCs) migrate to the branchial arches and give rise to the majority of cranial mesenchyme that eventually differentiates into odontoblasts, cartilage, craniofacial bone, and connective tissue; a subset of these cells differentiate into cranial ganglia. Here we present a protocol that describes directed differentiation method of human pluripotent stem cells into cranial NCC-like cells and a cytotoxicity assay using hPSC-derived cranial NCC-like cells. This cell-based assay system allows for high-sensitive cytotoxicity detection of test chemicals. These methods can be applied to predict drug/chemical toxicity effect on early craniofacial development.

Thalidomide induces apoptosis during early mesodermal differentiation of human induced pluripotent stem cells

Thalidomide was once administered to pregnant women as a mild sedative; however, it was subsequently shown to be strongly teratogenic. Recently, there has been renewed interest in thalidomide because of its curative effects against intractable diseases. However, the teratogenicity of thalidomide is manifested in various ways and is still not fully understood. In the present study, we evaluated the effects of thalidomide on early mesodermal differentiation by examining the differentiation of human induced pluripotent stem cells (hiPSCs). The most common symptom of thalidomide teratogenicity is limb abnormality, which led us to hypothesize that thalidomide prevents early mesodermal differentiation. Therefore, mesodermal differentiation of hiPSCs was induced over a 6-d period. To induce early mesoderm differentiation, 1 d after seeding, the cells were incubated with the small molecule compound CHIR99021 for 3 d. Thalidomide exposure was initiated at the same time as CHIR99021 treatment. After 5 d of thalidomide exposure, the hiPSCs began expressing a mesodermal marker; however, the number of viable cells decreased significantly as compared to that of control cells. We observed that the proportion of apoptotic and dead cells increased on day 2; however, the proportion of dead cells on day 5 had decreased, suggesting that the cells were damaged by thalidomide during early mesodermal differentiation (days 0-2). Our findings may help elucidate the mechanism underlying thalidomide teratogenicity and bring us closer to the safe use of this drug.

Thalidomide induces apoptosis in undifferentiated human induced pluripotent stem cells

Thalidomide, which was formerly available commercially to control the symptoms of morning sickness, is a strong teratogen that causes fetal abnormalities. However, the mechanism of thalidomide teratogenicity is not fully understood; thalidomide toxicity is not apparent in rodents, and the use of human embryos is ethically and technically untenable. In this study, we designed an experimental system featuring human-induced pluripotent stem cells (hiPSCs) to investigate the effects of thalidomide. These cells exhibit the same characteristics as those of epiblasts originating from implanted fertilized ova, which give rise to the fetus. Therefore, theoretically, thalidomide exposure during hiPSC differentiation is equivalent to that in the human fetus. We examined the effects of thalidomide on undifferentiated hiPSCs and early-differentiated hiPSCs cultured in media containing bone morphogenetic protein-4, which correspond, respectively, to epiblast (future fetus) and trophoblast (future extra-embryonic tissue). We found that only the number of undifferentiated cells was reduced. In undifferentiated cells, application of thalidomide increased the number of apoptotic and dead cells at day 2 but not day 4. Application of thalidomide did not affect the cell cycle. Furthermore, immunostaining and flow cytometric analysis revealed that thalidomide exposure had no effect on the expression of specific markers of undifferentiated and early trophectodermal differentiated cells. These results suggest that the effect of thalidomide was successfully detected in our experimental system and that thalidomide eliminated a subpopulation of undifferentiated hiPSCs. This study may help to elucidate the mechanisms underlying thalidomide teratogenicity and reveal potential strategies for safely prescribing this drug to pregnant women.

Mitochondrial Heterogeneity: Evaluating Mitochondrial Subpopulation Dynamics in Stem Cells

Although traditionally viewed as the “powerhouse” of the cell, an accruing body of evidence in the rapidly growing field of mitochondrial biology supports additional roles of mitochondria as key participants in a multitude of cellular functions. While it has been well established that mitochondria in different tissues have distinctive ultrastructural features consistent with differential bioenergetic demands, recent and emerging technical advances in flow cytometry, imaging, and “-omics”-based bioinformatics have only just begun to explore the complex and divergent properties of mitochondria within tissues and cell types. Moreover, contemporary studies evaluating the role of mitochondria in pluripotent stem cells, cellular reprogramming, and differentiation point to a potential importance of mitochondrial subpopulations and heterogeneity in the field of stem cell biology. This review assesses the current literature regarding mitochondrial subpopulations within cell and tissue types and evaluates the current understanding of how mitochondrial diversity and heterogeneity might impact cell fate specification in pluripotent stem cells.

Imaging-cytometry revealed spatial heterogeneities of marker expression in undifferentiated human pluripotent stem cells

Human pluripotent stem cells (hPSCs) provide a good model system for studying human development and are expected as a source for both cell-based medical and pharmaceutical research application. However, stable maintenance of undifferentiated hPSCs is yet challenging, and thus routine characterization is required. Flow-cytometry is one of the popular quantitative characterization tools for hPSCs, but it has drawback of spatial information loss of the cells in the culture. Here, we have applied a two-dimensional imaging cytometry that examines undifferentiated state of hPSCs to analyze localization and morphological information of immunopositive cells in the culture. The whole images of cells in a culture vessel were acquired and analyzed by an image analyzer, IN Cell Analyzer 2000, and determined staining intensity of the cells with their positional information. We have compared the expression of five hPSC-markers in four hPSC lines using the two-dimensional imaging cytometry and flow cytometry. The results showed that immunopositive ratios analyzed by the imaging cytometry had good correlation with those by the flow cytometry. Furthermore, the imaging cytometry revealed spatially heterogenic expression of hPSC-markers in undifferentiated hPSCs. Imaging cytometry is capable of reflecting minute aberrance without losing spatial and morphological information of the cells. It would be a powerful, useful, and time-efficient tool for characterizing hPSC colonies.