Stagewise keratinocyte differentiation from human embryonic stem cells by defined signal transduction modulators

Small Molecules Promote the Rapid Generation of Dental Epithelial Cells from Human-Induced Pluripotent Stem Cells

Human-induced pluripotent stem cells (hiPSCs) offer a promising source for generating dental epithelial (DE) cells. Whereas the existing differentiation protocols were time-consuming and relied heavily on growth factors, herein, we developed a three-step protocol to convert hiPSCs into DE cells in 8 days. In the first phase, hiPSCs were differentiated into non-neural ectoderm using SU5402 (an FGF signaling inhibitor). The second phase involved differentiating non-neural ectoderm into pan-placodal ectoderm and simultaneously inducing the formation of oral ectoderm (OE) using LDN193189 (a BMP signaling inhibitor) and purmorphamine (a SHH signaling activator). In the final phase, OE cells were differentiated into DE through the application of Purmorphamine, XAV939 (a WNT signaling inhibitor), and BMP4. qRT-PCR and immunostaining were performed to examine the expression of lineage-specific markers. ARS staining was performed to evaluate the formation of the mineralization nodule. The expression of PITX2, SP6, and AMBN, the emergence of mineralization nodules, and the enhanced expression of AMBN and AMELX in spheroid culture implied the generation of DE cells. This study delineates the developmental signaling pathways and uses small molecules to streamline the induction of hiPSCs into DE cells. Our findings present a simplified and quicker method for generating DE cells, contributing valuable insights for dental regeneration and dental disease research.

Comprehensive transcriptional analysis of early dorsal skin development in pigs

Porcine skin is similar to human skin in physiology, anatomy and histology and is often used as a model animal for human skin research. There are few studies on the transcriptome aspects of pig skin during the embryonic period. In this study, RNA sequencing was performed on the dorsal skin of Chenghua sows at embryonic day 56 (E56), embryonic day 76 (E76), embryonic day 105 (E105), and 3 days after birth (D3) to explore RNA changes in pig dorsal skin at four ages. A number of skin-related differential genes were identified by intercomparison between RNAs at four time points, and KEGG functional analysis showed that these differential genes were mainly enriched in metabolic and developmental, immune, and disease pathways, and the pathways enriched in GO analysis were highly overlapping. Collagen is an important part of the skin, with type I collagen making up the largest portion. In this study, collagen type I alpha 1 (COL1A1) and collagen type I alpha 2 (COL1A2) were significantly upregulated at four time points. In addition, lncRNA-miRNA-mRNA and miRNA-circRNA coexpression networks were constructed. The data obtained may help to explain age-related changes in transcriptional patterns during skin development and provide further references for understanding human skin development at the molecular level.

Understanding the effects of per- and polyfluoroalkyl substances on early skin development: Role of ciliogenesis inhibition and altered microtubule dynamics

Per- and polyfluoroalkyl substances (PFAS) are a class of highly stable chemicals, widely used in everyday products, and widespread in the environment, even in pregnant women. While epidemiological studies have linked prenatal exposure to PFAS with atopic dermatitis in children, little is known about their toxic effects on skin development, especially during the embryonic stage. In this study, we utilized human embryonic stem cells to generate non-neural ectoderm (NNE) cells and exposed them to six PFAS (perfluorooctanoic acid (PFOA), undecafluorohexanoic acid (PFHxA), heptafluorobutyric acid (PFBA), perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS) and perfluorobutyric acid (PFBS)) during the differentiation process to assess their toxicity to early skin development. Our results showed that PFOS altered the spindle-like morphology of NNE cells to a pebble-like morphology, and disrupted several NNE markers, including KRT16, SMYD1, and WISP1. The six PFAS had a high potential to cause hypohidrotic ectodermal dysplasia (HED) by disrupting the expression levels of HED-relevant genes. Transcriptomic analysis revealed that PFOS treatment produced the highest number (1156) of differentially expressed genes (DEGs) among the six PFAS, including the keratinocyte-related genes KRT6A, KRT17, KRT18, KRT24, KRT40, and KRT81. Additionally, we found that PFOS treatment disturbed several signaling pathways that are involved in regulating skin cell fate decisions and differentiation, including TGF-β, NOTCH, Hedgehog, and Hippo signaling pathways. Interestingly, we discovered that PFOS inhibited, by partially interfering with the expression of cytoskeleton-related genes, the ciliogenesis of NNE cells, which is crucial for the intercellular transduction of the above-mentioned signaling pathways. Overall, our study suggests that PFAS can inhibit ciliogenesis and hamper the transduction of important signaling pathways, leading potential congenital skin diseases. It sheds light on the underlying mechanisms of early embryonic skin developmental toxicity and provides an explanation for the epidemiological data on PFAS. ENVIRONMENTAL IMPLICATION: We employed a model based on human embryonic stem cells to demonstrate that PFOS has the potential to elevate the risk of hypohidrotic ectodermal dysplasia. This is achieved by targeting cilia, inhibiting ciliogenesis, and subsequently disrupting crucial signaling pathways like TGF-β, NOTCH, Hedgehog, and Hippo, during the early phases of embryonic skin development. Our study highlights the dangers and potential impacts of six PFAS pollutants on human skin development. Additionally, we emphasize the importance of closely considering PFHxA, PFBA, PFHxS, and PFBS, as they have shown the capacity to modify gene expression levels, albeit to a lesser degree.

A Systematic Review of Stem Cell Differentiation into Keratinocytes for Regenerative Applications

To improve wound healing or treatment of other skin diseases, and provide model cells for skin biology studies, in vitro differentiation of stem cells into keratinocyte-like cells (KLCs) is very desirable in regenerative medicine. This study examined the most recent advancements in in vitro differentiation of stem cells into KLCs, the effect of biofactors, procedures, and preparation for upcoming clinical cases. A range of stem cells with different origins could be differentiated into KLCs under appropriate conditions. The most effective ways of stem cell differentiation into keratinocytes were found to include the co-culture with primary epithelial cells and keratinocytes, and a cocktail of growth factors, cytokines, and small molecules. KLCs should also be supported by biomaterials for the extracellular matrix (ECM), which replicate the composition and functionality of the in vivo extracellular matrix (ECM) and, thus, support their phenotypic and functional characteristics. The detailed efficient characterization of different factors, and their combinations, could make it possible to find the significant inducers for stem cell differentiation into epidermal lineage. Moreover, it allows the development of chemically known media for directing multi-step differentiation procedures.In conclusion, the differentiation of stem cells to KLCs is feasible and KLCs were used in experimental, preclinical, and clinical trials. However, the translation of KLCs from in vitro investigational system to clinically valuable cells is challenging and extremely slow.

Cooperation of TGF-β and FGF signalling pathways in skin development

The skin is a multi-layered structure composed of the epidermis, dermis and hypodermis. The epidermis originates entirely from the ectoderm, whereas the dermis originates from various germ layers depending on its anatomical location; thus, there are different developmental patterns of the skin. Although the regulatory mechanisms of epidermal formation are well understood, mechanisms regulating dermis development are not clear owing to the complex origin. It has been shown that several morphogenetic pathways regulate dermis development. Of these, transforming growth factor-β (TGF-β) and fibroblast growth factor (FGF) signalling pathways are the main modulators regulating skin cell induction, fate decision, migration and differentiation. Recently, the successful generation of human skin by modulating TGF-β and FGF signals further demonstrated the irreplaceable roles of these pathways in skin regeneration. This review provides evidence of the role of TGF-β and FGF signalling pathways in the development of different skin layers, especially the disparate dermis of different body regions. This review also provides new perspectives on the distinct developmental patterns of skin and explores new ideas for clinical applications in the future.

A TP63 mutation identified in a Han Chinese family with ectodermal dysplasia

OBJECTIVE

The purpose of this study was to identify a pathogenic mutation located in TP63 in a nuclear Han Chinese family.

DESIGN

Whole-exome sequencing and Sanger sequencing were performed to identify candidate variants. The AlphaFold and PyMOL predicted the three-dimensional structure of the protein. Single-cell RNA-sequencing data and spatiotemporal transcriptomic atlas were used to generate the dissection of candidate gene expression at single-cell resolution. Significant genes (Pearson's coefficient ≥0.8 and P < 0.05) were identified for Gene Ontology (GO) analysis and Kyoto encyclopedia of genes and genomes (KEGG) pathways analysis.

RESULTS

A heterozygous missense variant at TP63 exon 8 (c.1010 G>A:p.Arg337Gln) was identified in the proband. This variant was predicted deleterious and likely to impair the local stability of the protein. In addition, single-cell RNA-sequencing indicated that TP63 was highly expressed in skin tissues. Furthermore, spatial transcriptome data of mice embryos showed TP63 was mainly enriched in the mucosal epithelium, thymus, epidermis, mesenchyme, and surface ectoderm. GO and KEGG pathway annotation analysis revealed that TP63 played a positive role in the process of ectoderm via the TGF-beta signaling pathway.

CONCLUSIONS

The missense variant of TP63 (c.1010 G>A:p.Arg337Gln) was associated with ectodermal dysplasia.

Differentiation of pluripotent stem cells for modeling human skin development and potential applications

The skin of mammals is a multilayered and multicellular tissue that forms an environmental barrier with key functions in protection, regulation, and sensation. While animal models have long served to study the basic functions of the skin in vivo, new insights are expected from in vitro models of human skin development. Human pluripotent stem cells (PSCs) have proven to be invaluable tools for studying human development in vitro. To understand the mechanisms regulating human skin homeostasis and injury repair at the molecular level, recent efforts aim to differentiate PSCs towards skin epidermal keratinocytes, dermal fibroblasts, and skin appendages such as hair follicles and sebaceous glands. Here, we present an overview of the literature describing strategies for human PSC differentiation towards the components of skin, with a particular focus on keratinocytes. We highlight fundamental advances in the field employing patient-derived human induced PSCs (iPSCs) and skin organoid generation. Importantly, PSCs allow researchers to model inherited skin diseases in the search for potential treatments. Skin differentiation from human PSCs holds the potential to clarify human skin biology.

miR-203 represses keratinocyte stemness by targeting survivin

OBJECTIVE

The epidermis possesses the capacity to replace dying cells and to heal wounds, thanks to resident stem cells, which have self-renewal properties. In skin physiology, miRNAs have been shown to be involved in many processes, including skin and hair morphogenesis. Recently, differentiation of epidermal stem cells was shown to be promoted by the miR-203. The miR-203 is upregulated during epidermal differentiation and is of interest because of significant targets.

METHODS

By utilizing a bioinformatic tool, we identified a target site for miR-203 in the survivin mRNA. Silencing miR-203 was managed with the use of antagomir; the silencing of survivin was performed with a siRNA. Survivin expression was determined by qPCR or immunofluorescence in cultured cells, and by immunohistochemistry in skin sections. Involucrin expression was used as marker of keratinocyte differentiation. A rice extract with previously demonstrated anti-aging properties was evaluated on miR-203 modulation.

RESULTS

In this study, we identified a miR-203/survivin axis, important for epidermal homeostasis. We report that differentiation of keratinocyte is dependent on the level of miR-203 expression and that inhibition of miR-203 can increase the expression of survivin, an epidermal marker of stemness.

CONCLUSION

In summary, our findings suggest that miR-203 target 3'UTR region of survivin mRNA and directly represses survivin expression in the epidermis. The rice extract was identified as modulator of miR-203 and pointed out as a promising microRNA-based strategy in treating skin changes occurring with aging.

Small molecules facilitate single factor-mediated sweat gland cell reprogramming

BACKGROUND

Large skin defects severely disrupt the overall skin structure and can irreversibly damage sweat glands (SG), thus impairing the skin's physiological function. This study aims to develop a stepwise reprogramming strategy to convert fibroblasts into SG lineages, which may provide a promising method to obtain desirable cell types for the functional repair and regeneration of damaged skin.

METHODS

The expression of the SG markers cytokeratin 5 (CK5), cytokeratin 10 (CK10), cytokeratin 18 (CK18), carcino-embryonic antigen (CEA), aquaporin 5 (AQP5) and α-smooth muscle actin (α-SMA) was assessed with quantitative PCR (qPCR), immunofluorescence and flow cytometry. Calcium activity analysis was conducted to test the function of induced SG-like cells (iSGCs). Mouse xenograft models were also used to evaluate the in vivo regeneration of iSGCs. BALB/c nude mice were randomly divided into a normal group, SGM treatment group and iSGC transplantation group. Immunocytochemical analyses and starch-iodine sweat tests were used to confirm the in vivo regeneration of iSGCs.

RESULTS

EDA overexpression drove HDF conversion into iSGCs in SG culture medium (SGM). qPCR indicated significantly increased mRNA levels of the SG markers CK5, CK18 and CEA in iSGCs, and flow cytometry data demonstrated (4.18 ± 0.04)% of iSGCs were CK5 positive and (4.36 ± 0.25)% of iSGCs were CK18 positive. The addition of chemical cocktails greatly accelerated the SG fate program. qPCR results revealed significantly increased mRNA expression of CK5, CK18 and CEA in iSGCs, as well as activation of the duct marker CK10 and luminal functional marker AQP5. Flow cytometry indicated, after the treatment of chemical cocktails, (23.05 ± 2.49)% of iSGCs expressed CK5⁺ and (55.79 ± 3.18)% of iSGCs expressed CK18⁺, respectively. Calcium activity analysis indicated that the reactivity of iSGCs to acetylcholine was close to that of primary SG cells [(60.79 ± 7.71)% vs. (70.59 ± 0.34)%, ns]. In vivo transplantation experiments showed approximately (5.2 ± 1.1)% of the mice were sweat test positive, and the histological analysis results indicated that regenerated SG structures were present in iSGCs-treated mice.

CONCLUSION

We developed a SG reprogramming strategy to generate functional iSGCs from HDFs by using the single factor EDA in combination with SGM and small molecules. The generation of iSGCs has important implications for future in situ skin regeneration with SG restoration.

Regulation of energy metabolism in human pluripotent stem cells

All living organisms need energy to carry out their essential functions. The importance of energy metabolism is increasingly recognized in human pluripotent stem cells. Energy production is not only essential for cell survival and proliferation, but also critical for pluripotency and cell fate determination. Thus, energy metabolism is an important target in cellular regulation and stem cell applications. In this review, we will discuss key factors that influence energy metabolism and their association with stem cell functions.

Human pluripotent stem cells: An alternative for 3D in vitro modelling of skin disease

To effectively study the skin and its pathology, various platforms have been used to date, with in vitro 3D skin models being considered the future gold standard. These models have generally been engineered from primary cell lines. However, their short life span leading to the use of various donors, imposes issues with genetic variation. Human pluripotent stem cell (hPSC)-technology holds great prospects as an alternative to the use of primary cell lines to study the pathophysiology of human skin diseases. This is due to their potential to generate an unlimited number of genetically identical skin models that closely mimic the complexity of in vivo human skin. During the past decade, researchers have therefore started to use human embryonic and induced pluripotent stem cells (hESC/iPSC) to derive skin resident-like cells and components. These have subsequently been used to engineer hPSC-derived 3D skin models. In this review, we focus on the advantages, recent developments, and future perspectives in using hPSCs as an alternative cell source for modelling human skin diseases in vitro.