Molecular Mechanisms Underlying Pluripotency and Self-Renewal of Embryonic Stem Cells

Embryonic stem cells (ESCs) are derived from the inner cell mass (ICM) of the blastocyst. ESCs have two distinctive properties: ability to proliferate indefinitely, a feature referred as "self-renewal", and to differentiate into different cell types, a peculiar characteristic known as "pluripotency". Self-renewal and pluripotency of ESCs are finely orchestrated by precise external and internal networks including epigenetic modifications, transcription factors, signaling pathways, and histone modifications. In this systematic review, we examine the main molecular mechanisms that sustain self-renewal and pluripotency in both murine and human ESCs. Moreover, we discuss the latest literature on human naïve pluripotency.

Clever Experimental Designs: Shortcuts for Better iPSC Differentiation

For practical use of pluripotent stem cells (PSCs) for disease modelling, drug screening, and regenerative medicine, the cell differentiation process needs to be properly refined to generate end products with consistent and high quality. To construct and optimize a robust cell-induction process, a myriad of cell culture conditions should be considered. In contrast to inefficient brute-force screening, statistical design of experiments (DOE) approaches, such as factorial design, orthogonal array design, response surface methodology (RSM), definitive screening design (DSD), and mixture design, enable efficient and strategic screening of conditions in smaller experimental runs through multifactorial screening and/or quantitative modeling. Although DOE has become routinely utilized in the bioengineering and pharmaceutical fields, the imminent need of more detailed cell-lineage specification, complex organoid construction, and a stable supply of qualified cell-derived material requires expedition of DOE utilization in stem cell bioprocessing. This review summarizes DOE-based cell culture optimizations of PSCs, mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), and Chinese hamster ovary (CHO) cells, which guide effective research and development of PSC-derived materials for academic and industrial applications.

Pluripotent stem cell therapy for retinal diseases

Pluripotent stem cells (PSCs), which include human embryonic stem cells (hESCs) and induced pluripotent stem cell (iPSC), have been used to study development of disease processes, and as potential therapies in multiple organ systems. In recent years, there has been increasing interest in the use of PSC-based transplantation to treat disorders of the retina in which retinal cells have been functionally damaged or lost through degeneration. The retina, which consists of neuronal tissue, provides an excellent system to test the therapeutic utility of PSC-based transplantation due to its accessibility and the availability of high-resolution imaging technology to evaluate effects. Preclinical trials in animal models of retinal diseases have shown improvement in visual outcomes following subretinal transplantation of PSC-derived photoreceptors or retinal pigment epithelium (RPE) cells. This review focuses on preclinical studies and clinical trials exploring the use of PSCs for retinal diseases. To date, several phase I/II clinical trials in patients with age-related macular degeneration (AMD) and Stargardt disease (STGD1) have demonstrated the safety and feasibility of PSC-derived RPE transplantation. Additional phase I/II clinical trials using PSC-derived RPE or photoreceptor cells for the treatment of AMD, STGD1, and also retinitis pigmentosa (RP) are currently in the pipeline. As this field continues to evolve, additional technologies may enhance PSC-derived cell transplantation through gene-editing of autologous cells, transplantation of more complex cellular structures such as organoids, and monitoring of transplanted cells through novel imaging technologies.

Anti-Inflammatory Effects of M-MSCs in DNCB-Induced Atopic Dermatitis Mice

Atopic dermatitis (AD) is an inflammatory skin disease caused by an imbalance between Th1 and Th2 cells. AD patients suffer from pruritus, excessive dryness, red or inflamed skin, and complications such as sleep disturbances and depression. Although there are currently many AD treatments available there are insufficient data on their long-term stability and comparative effects. Moreover, they have limitations due to various side effects. Multipotent mesenchymal stem cells (M-MSCs) might have potential for next-generation AD therapies. MSCs are capable of immune function regulation and local inflammatory response inhibition. M-MSCs, derived from human embryonic stem cells (hESC), additionally have a stable supply. In L507 antibody array, M-MSCs generally showed similar tendencies to bone marrow-derived mesenchymal stem cells (BM-MSCs), although the immunoregulatory function of M-MSCs seemed to be superior to BM-MSCs. Based on the characteristics of M-MSCs on immunoregulatory functions, we tested a M-MSC conditioned media concentrate (MCMC) in mice with AD lesions on their dorsal skin. MCMC significantly decreased RNA expression levels of inflammatory cytokines in the mouse dorsal skin. It also suppressed serum IgE levels. In addition, significant histopathologic alleviation was identified. In conclusion, secretions of M-MSCs have the potential to effectively improve AD-related inflammatory lesions. M-MSCs showed potential for use in next-generation AD treatment.

Calreticulin regulates a switch between osteoblast and chondrocyte lineages derived from murine embryonic stem cells

Calreticulin is a highly conserved, ubiquitous Ca²⁺-buffering protein in the endoplasmic reticulum that controls transcriptional activity of various developmental programs and also of embryonic stem cell (ESC) differentiation. Calreticulin activates calcineurin, which dephosphorylates and induces the nuclear import of the osteogenic transcription regulator nuclear factor of activated T cells 1 (NFATC1). We investigated whether calreticulin controls a switch between osteogenesis and chondrogenesis in mouse ESCs through NFATC1. We found that in the absence of calreticulin, intranuclear transport of NFATC1 is blocked and that differentiation switches from osteogenic to chondrogenic, a process that could be mimicked by chemical inhibition of NFAT translocation. Glycogen synthase kinase 3β (GSK3β) deactivation and nuclear localization of β-catenin critical to osteogenesis were abrogated by calreticulin deficiency or NFAT blockade. Chemically induced GSK3β inhibition bypassed the calreticulin/calcineurin axis and increased osteoblast output from both control and calreticulin-deficient ESCs, while suppressing chondrogenesis. Calreticulin-deficient ESCs or cells treated with an NFAT blocker had enhanced expression of dickkopf WNT-signaling pathway inhibitor 1 (Dkk1), a canonical Wnt pathway antagonist that blocks GSK3β deactivation. The addition of recombinant mDKK1 switched osteogenic ESC differentiation toward chondrogenic differentiation. The results of our study indicate a role for endoplasmic reticulum calcium signaling via calreticulin in the differentiation of ESCs to closely associated osteoblast or chondrocyte lineages.

Generation of Mouse Parthenogenetic Epiblast Stem Cells and Their Imprinting Patterns

Pluripotent stem cells can be established from parthenogenetic embryos, which only possess maternal alleles with maternal-specific imprinting patterns. Previously, we and others showed that parthenogenetic embryonic stem cells (pESCs) and parthenogenetic induced pluripotent stem cells (piPSCs) progressively lose the bimaternal imprinting patterns. As ESCs and iPSCs are naïve pluripotent stem cells, parthenogenetic primed pluripotent stem cells have not yet been established, and thus, their imprinting patterns have not been studied. Here, we first established parthenogenetic epiblast stem cells (pEpiSCs) from 7.5 dpc parthenogenetic implantation embryos and compared the expression patterns and DNA methylation status of the representative imprinted genes with biparental EpiSCs. We found that there were no striking differences between pEpiSCs and biparental EpiSCs with respect to morphology, pluripotency gene expression, and differentiation potential, but there were differences in the expression and DNA methylation status of imprinted genes (H19, Igf2, Peg1, and Peg3). Moreover, pEpiSCs displayed a different DNA methylation pattern compared with that of parthenogenetic neural stem cells (pNSCs), which showed a typical bimaternal imprinting pattern. These results suggest that both naïve pluripotent stem cells and primed pluripotent stem cells have an unstable imprinting status.

The paradox of Foxd3: how does it function in pluripotency and differentiation of embryonic stem cells?

Uncommitted cells of the early mammalian embryo transition through distinct stages of pluripotency, including establishment of ground state "naïve" pluripotency in the early epiblast, transition to a post-implantation "primed" state, and subsequent lineage commitment of the gastrulating epiblast. Previous transcriptional profiling of in vitro models to recapitulate early to late epiblast transition and differentiation suggest that distinct gene regulatory networks are likely to function in each of these states. While the mechanisms underlying transition between pluripotent states are poorly understood, the forkhead family transcription factor Foxd3 has emerged as a key regulatory factor. Foxd3 is required to maintain pluripotent cells of the murine epiblast and for survival, self-renewal and pluripotency of embryonic stem cells (ESCs). Two recent, simultaneous studies have shed light on how Foxd3 regulates gene expression in early cell fate transitions of progenitor cells. While the two publications shared some common findings, they also presented some conflicting results and suggest different models for the mechanisms underlying Foxd3 function. Here, we discuss the key similarities and differences between the publications, highlight data from the literature relevant to their findings, and hypothesize a potential mechanism of Foxd3 action.