Rapid and scalable human stem cell differentiation: now in 3D

Optical and thermal fields induced in the bone marrow by external laser irradiation

In regenerative medicine, the problem of growing mesenchymal stem cells from the bone marrow often arises. In such cases is important that the number of initial cells was large enough and their proliferative activity was high. We believe that this problem can be solved by short-term heating of local areas of the bone marrow in vivo with laser radiation. In this regard, it is of interest to study the optical and temperature fields induced inside the tubular bone under external laser irradiation. In this work, we obtained experimental data on the spatial distribution of temperature in the bone marrow of the rat femur in vitro under external exposure to laser radiation with wavelengths of 970 and 1940 nm. Radiation delivery was carried out using an optical fiber which tip contacted the surface of the femur bone. A thin thermocouple was used to measure the temperature in a local area of the bone marrow. By moving the optical fiber tip discretely along the longitudinal axis of the bone, and the thermocouple in the perpendicular direction, the spatial temperature distributions in dynamics were measured. Similarly, the spatial distributions of the laser radiation intensity were measured by replacing thermocouple with optical fiber probe. A thermal camera was used to control the temperature of the bone surface near the tip of the fiber. It was shown that the marrow could be heated from the outside by about 5-10 °C during 10 s without significant overheating of the bone tissue. The data obtained make it possible to estimate the volume of the bone marrow heated by the laser to a predetermined temperature and to make a reasonable choice of laser exposure modes to stimulate the proliferative activity of bone marrow mesenchymal stem cells in vivo.

Hepatic population derived from human pluripotent stem cells is effectively increased by selective removal of undifferentiated stem cells using YM155

Background

Pluripotent stem cells (PSCs) such as embryonic stem cells and induced pluripotent stem cells are promising target cells for cell regenerative medicine together with recently advanced technology of in-vitro differentiation. However, residual undifferentiated stem cells (USCs) during in-vitro differentiation are considered a potential risk for development of cancer cells and nonspecific lineage cell types. In this study we observed that USCs still exist during hepatic differentiation, consequently resulting in poor quality of the hepatic population and forming teratoma in vivo. Therefore, we hypothesized that effectively removing USCs from in-vitro differentiation could improve the quality of the hepatic population and guarantee safety from risk of teratoma formation.

Methods

Human PSCs were differentiated to hepatocytes via four steps. YM155, a known BIRC5 inhibitor, was applied for removing the residual USCs on the hepatic differentiation. After YM155 treatment, hepatocyte development was evaluated by measuring gene expression, immunostaining and hepatic functions at each stage of differentiation, and forming teratomas were confirmed by cell transplantation with or without YM155.

Results

The selected concentrations of YM155 removed USCs (NANOG⁺ and OCT4⁺) in a dose-dependent manner. As a result, expression of endodermal markers (SOX17, FOXA2 and CXCR4) at stage II of differentiation and hepatic markers (ALB, AFP and HNF4A) at stage III was up-regulated by YM155 treatment as well as the hepatic population (ALB⁺), and functions (ALB/urea secretion and CYP450 enzyme activity) were enhanced at the final stage of differentiation (stage IV). Furthermore, we demonstrated that NANOG and OCT4 expression remaining until stage III (day 15 of differentiation) completely disappeared when treated with YM155 and teratoma formation was effectively prevented by YM155 pretreatment in the in-vitro study.

Conclusions

We suggest that the removal of USCs using YM155 could improve the quantity and quality of induced hepatocytes and eliminate the potential risk of teratoma formation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0517-2) contains supplementary material, which is available to authorized users.

Chemically induced hepatotoxicity in human stem cell-induced hepatocytes compared with primary hepatocytes and HepG2

Stem cell-induced hepatocytes (SC-iHeps) have been suggested as a valuable model for evaluating drug toxicology. Here, human-induced pluripotent stem cells (QIA7) and embryonic stem cells (WA01) were differentiated into hepatocytes, and the hepatotoxic effects of acetaminophen (AAP) and aflatoxin B1 (AFB1) were compared with primary hepatocytes (p-Heps) and HepG2. In a cytotoxicity assay, the IC50 of SC-iHeps was similar to that in p-Heps and HepG2 in the AAP groups but different from that in p-Heps of the AFB1 groups. In a multi-parameter assay, phenotypic changes in mitochondrial membrane potential, calcium influx and oxidative stress were similar between QIA7-iHeps and p-Heps following AAP and AFB1 treatment but relatively low in WA01-iHeps and HepG2. Most hepatic functional markers (hepatocyte-specific genes, albumin/urea secretion, and the CYP450 enzyme activity) were decreased in a dose-dependent manner following AAP and AFB1 treatment in SC-iHeps and p-Heps but not in HepG2. Regarding CYP450 inhibition, the cell viability of SC-iHeps and p-Heps was increased by ketoconazole, a CYP3A4 inhibitor. Collectively, SC-iHeps and p-Heps showed similar cytotoxicity and hepatocyte functional effects for AAP and AFB1 compared with HepG2. Therefore, SC-iHeps have phenotypic characteristics and sensitivity to cytotoxic chemicals that are more similar to p-Heps than to HepG2 cells.

Modulating innate immunity improves hepatitis C virus infection and replication in stem cell-derived hepatocytes

In this study, human embryonic stem cell-derived hepatocytes (hESC-Heps) were investigated for their ability to support hepatitis C virus (HCV) infection and replication. hESC-Heps were capable of supporting the full viral life cycle, including the release of infectious virions. Although supportive, hESC-Hep viral infection levels were not as great as those observed in Huh7 cells. We reasoned that innate immune responses in hESC-Heps may lead to the low level of infection and replication. Upon further investigation, we identified a strong type III interferon response in hESC-Heps that was triggered by HCV. Interestingly, specific inhibition of the JAK/STAT signaling pathway led to an increase in HCV infection and replication in hESC-Heps. Of note, the interferon response was not evident in Huh7 cells. In summary, we have established a robust cell-based system that allows the in-depth study of virus-host interactions in vitro.

Stem cells in a three-dimensional scaffold environment

Stem cells have emerged as important players in the generation and maintenance of many tissues. However, the accurate in vitro simulation of the native stem cell niche remains difficult due at least in part to the lack of a comprehensive definition of the critical factors of the stem cell niche based on in vivo models. Three-dimensional (3D) cell culture systems have allowed the development of useful models for investigating stem cell physiology particularly with respect to their ability to sense and generate mechanical force in response to their surrounding environment. We review the use of 3D culture systems for stem cell culture and discuss the relationship between stem cells and 3D growth matrices including the roles of the extracellular matrix, scaffolds, soluble factors, cell-cell interactions and shear stress effects within this environment. We also discuss the potential for novel methods that mimic the native stem cell niche in vitro as well as the current associated challenges.

Accurate prediction of drug-induced liver injury using stem cell-derived populations

Despite major progress in the knowledge and management of human liver injury, there are millions of people suffering from chronic liver disease. Currently, the only cure for end-stage liver disease is orthotopic liver transplantation; however, this approach is severely limited by organ donation. Alternative approaches to restoring liver function have therefore been pursued, including the use of somatic and stem cell populations. Although such approaches are essential in developing scalable treatments, there is also an imperative to develop predictive human systems that more effectively study and/or prevent the onset of liver disease and decompensated organ function. We used a renewable human stem cell resource, from defined genetic backgrounds, and drove them through developmental intermediates to yield highly active, drug-inducible, and predictive human hepatocyte populations. Most importantly, stem cell-derived hepatocytes displayed equivalence to primary adult hepatocytes, following incubation with known hepatotoxins. In summary, we have developed a serum-free, scalable, and shippable cell-based model that faithfully predicts the potential for human liver injury. Such a resource has direct application in human modeling and, in the future, could play an important role in developing renewable cell-based therapies.

Modeling human liver biology using stem cell-derived hepatocytes

Stem cell-derived hepatocytes represent promising models to study human liver biology and disease. This concise review discusses the recent progresses in the field, with a focus on human liver disease, drug metabolism and virus infection.