Self-organization process in newborn skin organoid formation inspires strategy to restore hair regeneration of adult cells

Skin Cyst: A Pathological Dead-End With a New Twist of Morphogenetic Potentials in Organoid Cultures

A cyst is a closed sac-like structure in which cyst walls wrap certain contents typically including air, fluid, lipid, mucous, or keratin. Cyst cells can retain multipotency to regenerate complex tissue architectures, or to differentiate. Cysts can form in and outside the skin due to genetic problems, errors in embryonic development, cellular defects, chronic inflammation, infections, blockages of ducts, parasites, and injuries. Multiple types of skin cysts have been identified with different cellular origins, with a common structure including the outside cyst wall engulfs differentiated suprabasal layers and keratins. The skin cyst is usually used as a sign in pathological diagnosis. Large or surfaced skin cysts affect patients' appearance and may cause the dysfunction or accompanying diseases of adjacent tissues. Skin cysts form as a result of the degradation of skin epithelium and appendages, retaining certain characteristics of multipotency. Surprisingly, recent organoid cultures show the formation of cyst configuration as a transient state toward more morphogenetic possibility. These results suggest, if we can learn more about the molecular circuits controlling upstream and downstream cellular events in cyst formation, we may be able to engineer stem cell cultures toward the phenotypes we wish to achieve. For pathological conditions in patients, we speculate it may also be possible to guide the cyst to differentiate or de-differentiate to generate structures more akin to normal architecture and compatible with skin homeostasis.

Implantable multifunctional black phosphorus nanoformulation-deposited biodegradable scaffold for combinational photothermal/ chemotherapy and wound healing

Surgery is the mainstream treatment for melanoma, but its clinical implementation suffers from some major drawbacks including residual infiltrating melanoma cells at resection margins and severe tissue injury. In this study, a nanocomposite scaffold is developed for in-situ therapy after melanoma surgery as well as wound healing, which is fabricated by embedding photothermal-capable black phosphorus nanosheets (BPNSs) into bioresorbable Gelatin-PCL (GP) nanofibrous scaffold. GP scaffold is a clinically-tested biomaterial with temperature sensitivity and tissue-healing effect, while the BPNSs are loaded with the anticancer antibiotic of doxorubicin (DOX) and conjugated with NH₂-PEG-FA for tumor-targeted delivery. The GP scaffold could undergo a sol-gel transition upon NIR irritation and release the BPNSs in situ. During this process, most of the BP-based nanoformulations were selectively internalized by the melanoma cells for the cooperative photothermal therapy and heat-triggerable DOX therapy, while some of the loaded DOX was released into the wound tissue to create a tumor-suppressive microenvironment. Moreover, BPNSs could be gradually degraded to phosphates/phosphonates and thus enhance tissue repair by activating the ERK1/2 and PI3K/Akt pathway. Meanwhile, the detached DOX molecules would also enter the wound tissues for continuous melanoma inhibition. Considering the anti-melanoma and wound healing effect of this composite scaffold, it may offer a facile strategy for the wound treatment after melanoma surgery.

"Two-Cell Assemblage" Assay: A Simple in vitro Method for Screening Hair Growth-Promoting Compounds

Alopecia arises due to inadequate hair follicle (HF) stem cell activation or proliferation, resulting in prolongation of the telogen phase of the hair cycle. Increasing therapeutic and cosmetic demand for alleviating alopecia has driven research toward the discovery or synthesis of novel compounds that can promote hair growth by inducing HF stem cell activation or proliferation and initiating the anagen phase. Although several methods for evaluating the hair growth-promoting effects of candidate compounds are being used, most of these methods are difficult to use for large scale simultaneous screening of various compounds. Herein, we introduce a simple and reliable in vitro assay for the simultaneous screening of the hair growth-promoting effects of candidate compounds on a large scale. In this study, we first established a 3D co-culture system of human dermal papilla (hDP) cells and human outer root sheath (hORS) cells in an ultra-low attachment 96-well plate, where the two cell types constituted a polar elongated structure, named "two-cell assemblage (TCA)." We observed that the long axis length of the TCA gradually increased for 5 days, maintaining biological functional integrity as reflected by the increased expression levels of hair growth-associated genes after treatment with hair growth-promoting molecules. Interestingly, the elongation of the TCA was more prominent following treatment with the hair growth-promoting molecules (which occurred in a dose-dependent manner), compared to the control group (p < 0.05). Accordingly, we set the long axis length of the TCA as an endpoint of this assay, using a micro confocal high-content imaging system to measure the length, which can provide reproducible and reliable results in an adequate timescale. The advantages of this assay are: (i) it is physiologically and practically advantageous as it uses 3D cultured two-type human cells which are easily available; (ii) it is simple as it uses length as the only endpoint; and (iii) it is a high throughput system, which screens various compounds simultaneously. In conclusion, the "TCA" assay could serve as an easy and reliable method to validate the hair growth-promoting effect of a large volume of library molecules.

Spheroid formation of human keratinocyte: Balancing between cell-substrate and cell-cell interaction

BACKGROUND

The formation of spheroids is tightly regulated by intrinsic cell-cell and cell-substrate interactions.

OBJECTIVE

The chitosan (CS)-coating was applied to investigate the driven force directed the spheroid formation.

METHODS

The effects of CS on cell functions were studied. Atomic force microscopy was employed to measure the cell- biomaterial interplay at single cell level.

RESULTS

HaCaT cells shifted from their flattened sheet to a compact 3D spheroidal morphology when increasing CS-coating concentration. The proliferative capacity of HaCaT was preserved in the spheroid. The expression and activation of integrin β1 (ITGB1) were enhanced on CS modified surfaces, while the active to total ratio of ITGB1 was decreased. The adhesive force of a single HaCaT cell to the tissue culture plate (TCP) was 4.84±0.72 nN. It decreased on CS-coated surfaces as CS concentration increased, from 2.16±0.26 nN to 0.96±0.17 nN. The adhesive force between the single HaCaT cell to its neighbor cell increased as CS concentration increased, from 1.15±0.09 nN to 2.60±0.51 nN.

CONCLUSIONS

Conclusively, the decreased cell- substrate adhesion was the main driven force in the spheroid formation. This finding might serve as a design criterion for biomaterials facilitating the formation of epithelial spheroids.

Human Fetal Scalp Dermal Papilla Enriched Genes and the Role of R-Spondin-1 in the Restoration of Hair Neogenesis in Adult Mouse Cells

Much remains unknown about the regulatory networks which govern the dermal papilla’s (DP) ability to induce hair follicle neogenesis, a capacity which decreases greatly with age. To further define the core genes which characterize the DP cell and to identify pathways prominent in DP cells with greater hair inductive capacity, comparative transcriptome analyses of human fetal and adult dermal follicular cells were performed. 121 genes were significantly upregulated in fetal DP cells in comparison to both fetal dermal sheath cup (DSC) cells and interfollicular dermal (IFD) populations. Comparison of the set of enriched human fetal DP genes with human adult DP, newborn mouse DP, and embryonic mouse dermal condensation (DC) cells revealed differences in the expression of Wnt/β-catenin, Shh, FGF, BMP, and Notch signaling pathways. We chose R-spondin-1, a Wnt agonist, for functional verification and show that exogenous administration restores hair follicle neogenesis from adult mouse cells in skin reconstitution assays. To explore upstream regulators of fetal DP gene expression, we identified twenty-nine transcription factors which are upregulated in human fetal DP cells compared to adult DP cells. Of these, seven transcription factor binding motifs were significantly enriched in the candidate promoter regions of genes differentially expressed between fetal and adult DP cells, suggesting a potential role in the regulatory network which confers the fetal DP phenotype and a possible relationship to the induction of follicle neogenesis.

Epidermal Stem Cells in Hair Follicle Cycling and Skin Regeneration: A View From the Perspective of Inflammation

There are many studies devoted to the role of hair follicle stem cells in wound healing as well as in follicle self-restoration. At the same time, the influence of the inflammatory cells on the hair follicle cycling in both injured and intact skin is well established. Immune cells of all wound healing stages, including macrophages, γδT cells, and T regs, may activate epidermal stem cells to provide re-epithelization and wound-induced hair follicle neogenesis. In addition to the ability of epidermal cells to maintain epidermal morphogenesis through differentiation program, they can undergo de-differentiation and acquire stem features under the influence of inflammatory milieu. Simultaneously, a stem cell compartment may undergo re-programming to adopt another fate. The proportion of skin resident immune cells and wound-attracted inflammatory cells (e.g., neutrophils and macrophages) in wound-induced hair follicle anagen and plucking-induced anagen is still under discussion to date. Experimental data suggesting the role of reactive oxygen species and prostaglandins, which are uncharacteristic of the intact skin, in the hair follicle cycling indicates the role of neutrophils in injury-induced conditions. In this review, we discuss some of the hair follicles stem cell activities, such as wound-induced hair follicle neogenesis, hair follicle cycling, and re-epithelization, through the prism of inflammation. The plasticity of epidermal stem cells under the influence of inflammatory microenvironment is considered. The relationship between inflammation, scarring, and follicle neogenesis as an indicator of complete wound healing is also highlighted. Taking into consideration the available data, we also conclude that there may exist a presumptive interlink between the stem cell activation, inflammation and the components of programmed cell death pathways.

Self-assembling 3D spheroid cultures of human neonatal keratinocytes have enhanced regenerative properties

Relative to conventional two-dimensional (2-D) culture, three-dimensional (3-D) suspension culture of epithelial cells more closely mimics the in vivo cell microenvironment regarding cell architecture, cell to matrix interaction, and osmosis exchange. However, primary normal human keratinocytes (NHKc) rapidly undergo terminal differentiation and detachment-induced cell death (anoikis) upon disconnection from the basement membrane, thus greatly constraining their use in 3-D suspension culture models. Here, we examined the 3-D anchorage-free growth potential of NHKc isolated from neonatal skin explants of 59 different individuals. We found that 40% of all isolates naturally self-assembled into multicellular spheroids within 24 h in anchorage-free culture, while 60% did not. Placing a single spheroid back into 2-D monolayer culture yielded proliferating cells that expressed elevated levels of nuclear P63 and basal cytokeratin 14. These cells also displayed prolonged keratinocyte renewal and a gene expression profile corresponding to cellular heterogeneity, quiescence, and de-differentiation. Notably, spheroid-derived (SD) NHKc were enriched for a P63/K14 double-positive population that formed holoclonal colonies and reassembled into multicellular spheroids during 3-D suspension subculture. This study reveals marked phenotypic differences in neonatal keratinocyte suspension cultures isolated from different individuals and present a model system that can be readily employed to study epithelial cell behavior, along with a variety of dermatological diseases.

Platelet factor 4 inhibits human hair follicle growth and promotes androgen receptor expression in human dermal papilla cells

Platelet-rich plasma (PRP) has been reported recently as a potential therapeutic approach for alopecia, such as androgenetic alopecia, but the exact mechanisms and effects of specific components of this recipe remain largely unknown. In this study, we identified that platelet factor 4 (PF4), a component of PRP, significantly suppressed human hair follicle growth and restrained the proliferation of human dermal papilla cells (hDPCs). Furthermore, our results showed that PF4 upregulated androgen receptor (AR) in human dermal papilla cells in vitro and via hair follicle organ culture. Among the hair growth-promoting and DP-signature genes investigated, PF4 decreased the expression of Wnt5a, Wnt10b, LEF1, HEY1 and IGF-1, and increased DKK1 expression, but did not affect BMP2 and BMP4 expression. Collectively, Our data demonstrate that PF4 suppresses human hair follicle growth possibly via upregulating androgen receptor signaling and modulating hair growth-associated genes, which provides thought-provoking insights into the application and optimization of PRP in treating hair loss.

Enhancement of lipid content and inflammatory cytokine secretion in SZ95 sebocytes by palmitic acid suggests a potential link between free fatty acids and acne aggravation

A relationship between acne and free fatty acids (FFAs) has been suggested recently. However, the effects of FFAs on sebaceous glands are still largely unknown. At the same time, the role of FFAs during chronic inflammation is well established. Considering that FFAs are also a major component of sebum, it is likely that changes in FFA affect both the synthesis of sebum and the inflammatory response in sebaceous glands. In this study, we examined a hypothesis that FFAs increase the production of sebum and induce inflammation in the sebaceous glands. We found that treatment of SZ95 sebocytes with exogenously applied palmitic acid (PA), a major saturated FFA, induced a significant increase in intracellular lipid levels. Moreover, PA treatment also increased the expression and secretion of the proinflammatory cytokines in SZ95 sebocytes. We also found that Toll-like receptors were required for the inflammatory response triggered by PA. The results of our study strengthen the notion about the link between acne and FFAs and suggest the mechanism underlying this relationship. Our results serve as a foundation for future work that will explore the association between FFA and acne and pave way to the development of novel treatment options for acne.

Simplified low-cost methodology to establish, histologically process and analyze three-dimensional cancer cell spheroid arrays

Differently of two-dimensional cell culture, three-dimensional (3D) multicellular spheroid model allows cells to establish cell-cell/cell-matrix interactions over the entire cell surface, more closely mimicking tumor microenvironments and cellular subpopulations with specific standards of morphology, differentiation and gene expression. Thenceforth several methodologies involving or the 3D cell aggregates generation or its histological processing and analysis have emerged, but in general they are laborious, expensive and complex to set up as a routine technique. Thus, we developed a complete methodology, detailing a simple, accessible and low-cost step by step, including 1) the 3D cell aggregate generation using hanging drop technique; 2) providing a simple way to assess morphological parameters of generated spheroids; followed by 3) a multiple and organized histological processing, keeping several individual spheroids inside an agarose apparatus, maintaining a known order and position of each ones, similar to tissue microarray principle; 4) until the last step, where it is allowed a simultaneous histological composition analysis of several spheroid slices, organized side by side, in a same block section, through conventional stainings or 5) immunostaining against different molecular markers. Therefore, the present methodology aims to popularize 3D cell culture, allowing to make this a regular technique in basic cell biology research, once all steps are performed without using onerous reagents, materials or equipment. In addition to bring the agarose apparatus as a simple low cost novelty, allowing high-throughput analysis of several spheroids simultaneously in an organized manner.

Hair-bearing human skin generated entirely from pluripotent stem cells

The skin is a multi-layered organ equipped with appendages (i.e. follicles and glands) critical for regulating bodily fluid retention and temperature, guarding against external stresses, and mediating touch and pain sensation^1,2. Reconstruction of appendage-bearing skin in cultures and in bioengineered grafts remains an unmet biomedical challenge^3–9. Here, we report an organoid culture system that generates complex skin from human pluripotent stem cells. We use step-wise modulation of the TGFβ and FGF signalling pathways to co-induce cranial epithelial cells and neural crest cells within a spherical cell aggregate. During 4–5 months incubation, we observe the emergence of a cyst-like skin organoid composed of stratified epidermis, fat-rich dermis, and pigmented hair follicles equipped with sebaceous glands. A network of sensory neurons and Schwann cells form nerve-like bundles that target Merkel cells in organoid hair follicles, mimicking human touch circuitry. Single-cell RNA-sequencing and direct comparison to foetal specimens suggest that skin organoids are equivalent to human facial skin in the second-trimester of development. Moreover, we show that skin organoids form planar hair-bearing skin when grafted on nude mice. Together, our results demonstrate that nearly complete skin can self-assemble in vitro and be used to reconstitute skin in vivo. We anticipate skin organoids will be foundational to future studies of human skin development, disease modelling, or reconstructive surgery.

PCL-Blended Chitosan Substrates for Patterning the Heterotypic Cell Distribution in an Epithelial and Mesenchymal Coculture System

Cell-cell and cell-substrate interactions in coculture systems are very important to the context of biomaterial scaffolds for tissue engineering applications. Understanding the cellular interactions and distribution of epithelial-mesenchymal microtissues on the controllable biomaterial surfaces is useful to study the organoid applications. The aim of the present study is to investigate the effects of chitosan/poly(ε-caprolactone) (PCL)-blended biomaterials on the distribution and spheroid formation of HaCaT and Hs68 cells in a coculture system. In this study, we demonstrated that the cocultured cells gradually changed their pattern from core/shell spheroid to monolayered morphology as the PCL content increased in the blended substrates. This indicates that the chitosan/PCL-blended substrates are able to regulate cell-substrate and cell-cell interactions to modify the distribution of HaCaT and Hs68 cells similar to various mesenchymal-epithelial organizations in biological tissues. Moreover, we also developed a two-dimension lattice model to elaborate the dependence of cell spheroid development on complex cell-cell interactions. This information may be helpful to develop appropriate biomaterials with appropriate properties to the applications of engineered epithelial-mesenchymal organoids.

The Wnt/β-catenin signaling pathway is involved in regulating feather growth of embryonic chicks

Avian feathers have robust growth and regeneration capability and serve as a useful model for decoding hair morphogenesis and other developmental studies. However, the molecular signaling involved in regulating the development of feather follicles is unclear. The purpose of this study was to investigate the role of the Wnt/β-catenin pathway in regulating feather morphogenesis in embryonic chicks through in ovo injection of different doses of Dickkopf-1 (DKK1, a specific inhibitor of the target of the Wnt/β-catenin pathway). A total of 120 fertilized embryo eggs were randomly divided into 4 treatments, including a noninjection group (control group) and groups injected with 100 μL of phosphate-buffered saline (PBS)/egg (PBS control group), 100 μL of PBS/egg containing 600-ng DKK1/egg (600-ng DKK1 group), and 100-μL PBS/egg containing 1,200-ng DKK1/egg (1,200-ng DKK1 group). Feathers and skin tissues were sampled on embryonic (E) day 15 and the day of hatching to examine the feather mass, diameter and density of feather follicles, and the protein expression of the Wnt/β-catenin pathway. The results showed that, compared with CON and PBS treatment, the injection of DKK1 into the yolk sac of chick embryos had no significant effect on the hatching rate and embryo weight (P > 0.05), while it significantly decreased the relative mass of feathers in the whole body (P < 0.05). The high dose of DKK1 (1,200-ng DKK1/egg) decreased the relative mass of feathers on the back, chest, belly, neck, wings, head, and legs, which was more obvious than that in the 600-ng DKK1 group, which presented a dose-dependent effect. In addition, DKK1 injection significantly downregulated the protein expression levels of β-catenin, transcription factor 4, Cyclin D1, and c-Myc (P < 0.05). The immunofluorescence result of β-catenin was consistent with the Western blotting assay results. Altogether, these observations suggested that the Wnt/β-catenin signaling pathway is involved in regulating feather follicle development and feather growth during the embryonic development of chicks.

The aging skin microenvironment dictates stem cell behavior

Aging manifests with architectural alteration and functional decline of multiple organs throughout an organism. In mammals, aged skin is accompanied by a marked reduction in hair cycling and appearance of bald patches, leading researchers to propose that hair follicle stem cells (HFSCs) are either lost, differentiate, or change to an epidermal fate during aging. Here, we employed single-cell RNA-sequencing to interrogate aging-related changes in the HFSCs. Surprisingly, although numbers declined, aging HFSCs were present, maintained their identity, and showed no overt signs of shifting to an epidermal fate. However, they did exhibit prevalent transcriptional changes particularly in extracellular matrix genes, and this was accompanied by profound structural perturbations in the aging SC niche. Moreover, marked age-related changes occurred in many nonepithelial cell types, including resident immune cells, sensory neurons, and arrector pili muscles. Each of these SC niche components has been shown to influence HF regeneration. When we performed skin injuries that are known to mobilize young HFSCs to exit their niche and regenerate HFs, we discovered that aged skin is defective at doing so. Interestingly, however, in transplantation assays in vivo, aged HFSCs regenerated HFs when supported with young dermis, while young HFSCs failed to regenerate HFs when combined with aged dermis. Together, our findings highlight the importance of SC:niche interactions and favor a model where youthfulness of the niche microenvironment plays a dominant role in dictating the properties of its SCs and tissue health and fitness.

Tissue engineering strategies for human hair follicle regeneration: How far from a hairy goal?

The demand for an efficient therapy for alopecia disease has fueled the hair research field in recent decades. However, despite significant improvements in the knowledge of key processes of hair follicle biology such as genesis and cycling, translation into hair follicle replacement therapies has not occurred. Great expectation has been recently put on hair follicle bioengineering, which is based on the development of fully functional hair follicles with cycling activity from an expanded population of hair‐inductive (trichogenic) cells. Most bioengineering approaches focus on in vitro reconstruction of folliculogenesis by manipulating key regulatory molecular/physical features of hair follicle growth/cycling in vivo. Despite their great potential, no cell‐based product is clinically available for hair regeneration therapy to date. This is mainly due to demanding issues that still hinder the functionality of cultured human hair cells. The present review comprehensively compares emergent strategies using different cell sources and tissue engineering approaches, aiming to successfully achieve a clinical cure for hair loss. The hurdles of these strategies are discussed, as well as the future directions to overcome the obstacles and fulfill the promise of a “hairy” feat.

Stimulating hair growth via hormesis: Experimental foundations and clinical implications

Numerous agents (approximately 90) are shown to stimulate hair growth in cellular and animal models in a hormetic-like biphasic dose response manner. These hormetic dose responses occur within the framework of direct stimulatory responses as well as in preconditioning experimental protocols. These findings have important implications for experimental and clinical investigations with respect to study design strategies, dose selection and dose spacing along with sample size and statistical power issues. These findings further reflect the general occurrence of hormetic dose responses within the biological and biomedical literature that consistently appear to be independent of biological model, level of biological organization (i.e., cell, organ, and organism), endpoint, inducing agent, potency of the inducing agent, and mechanism.

Building Complex Life Through Self-Organization

Cells are inherently conferred with the ability to self-organize into the tissues and organs comprising the human body. Self-organization can be recapitulated in vitro and recent advances in the organoid field are just one example of how we can generate small functioning elements of organs. Tissue engineers can benefit from the power of self-organization and should consider how they can harness and enhance the process with their constructs. For example, aggregates of stem cells and tissue-specific cells benefit from the input of carefully selected biomolecules to guide their differentiation toward a mature phenotype. This can be further enhanced by the use of technologies to provide a physiological microenvironment for self-organization, enhance the size of the constructs, and enable the long-term culture of self-organized structures. Of importance, conducting self-organization should be limited to fine-tuning and should avoid over-engineering that could counteract the power of inherent cellular self-organization. Impact Statement Self-organization is a powerful innate feature of cells that can be fine-tuned but not over-engineered to create new tissues and organs.

Bay11-7082 facilitates wound healing by antagonizing mechanical injury- and TNF-α-induced expression of MMPs in posterior cruciate ligament

Purposes: To investigate the ability of synoviocytes (SCs) in regulating MMPs expression in the posterior cruciate ligament fibroblasts (PCLfs) after TNF-α treatment, to test whether a specific inflammation inhibitor Bay11-7082 can antagonize the expression of MMPs in PCLfs after injury. Methods: The microenvironment of knee joint cavity after PCL injury was mimicked in an in vitro co-culture system. The effects of TNF-α treatment on the expression of MMPs in PCL fibroblasts (PCLfs) were studied. The expression of MMPs mRNA and protein was detected by qRT-PCR and western blot. For the in vivo study, the Bay11-7082 inhibitor was injected into the knee joint cavity after injury, and then were performed on histological analysis. Results: In the mono-culture conditions, 6% mechanical injury upregulated the expression of MMP-2, whereas downregulated MMP-1 and -3, additionally 12% mechanical injury were upregulated all. However, in co-culture conditions, 6% and 12% both significantly increased MMPs expressions. Stretch injury and TNF-α treatment significantly upregulated expression of MMPs mRNA and protein levels in mono-cultured PCLfs. This effect was more significant in PCLfs Plus SCs co-culture system, in which the cells were treated by combination of stretch injury and TNF-α. In addition, Bay11-7082, a specific inflammation inhibitor, could significantly decrease the expression of MMPs induced by stretch injury and/or TNF-α treatment. Less infiltrated inflammatory cells and more integrated tissues were detected in injury PCL 2 weeks after Bay11-7082 treatment, compared to injury group. Immunofluorescent staining showed very low expression levels of MMPs in PCL of Bay11-7082-treated group, compared to the injury groups. Conclusions: SCs sever as the supporting cells that aggravate the TNF-α-induced MMPs accumulation in PCLfs. Inhibition of the expression of MMPs by Bay11-7082 is a promising way to facilitate the self-healing of PCL.

Long-term expansion and differentiation of adult murine epidermal stem cells in 3D organoid cultures

Mammalian epidermal stem cells maintain homeostasis of the skin epidermis and contribute to its regeneration throughout adult life. While 2D mouse epidermal stem cell cultures have been established decades ago, a long-term, feeder cell- and serum-free culture system recapitulating murine epidermal architecture has not been available. Here we describe an epidermal organoid culture system that allows long-term, genetically stable expansion of adult epidermal stem cells. Our epidermal expansion media combines atypically high calcium concentrations, activation of cAMP, FGF, and R-spondin signaling with inhibition of bone morphogenetic protein (BMP) signaling. Organoids are established robustly from adult mouse skin and expand over at least 6 mo, while maintaining the basal-apical organization of the mouse interfollicular epidermis. The system represents a powerful tool to study epidermal homeostasis and disease in vitro.

What gastroenterologists and hepatologists should know about organoids in 2019

Most of the research behind new medical advances is carried out using either animal models or cancer cells, which both have their disadvantage in particular with regard to medical applications such as personalized medicine and novel therapeutic approaches. However, recent advances in stem cell biology have enabled long-term culturing of organotypic intestinal or hepatic tissues derived from tissue resident or pluripotent stem cells. These 3D structures, denoted as organoids, represent a substantial advance in structural and functional complexity over traditional in vitro cell culture models that are often non-physiological and transformed. They can recapitulate the in vivo architecture, functionality and genetic signature of the corresponding tissue. The opportunity to model epithelial cell biology, epithelial turnover, barrier dynamics, immune-epithelial communication and host-microbe interaction more efficiently than previous culture systems, greatly enhance the translational potential of organotypic hepato-gastrointestinal culture systems. Thus there is increasing interest in using such cultured cells as a source for tissue engineering, regenerative medicine and personalized medicine. This review will highlight some of the established and also some exciting novel perspectives on organoids in the fields of gastroenterology and hepatology.

Biomaterials to Mimic and Heal Connective Tissues

Connective tissue is one of the four major types of animal tissue and plays essential roles throughout the human body. Genetic factors, aging, and trauma all contribute to connective tissue dysfunction and motivate the need for strategies to promote healing and regeneration. The goal here is to link a fundamental understanding of connective tissues and their multiscale properties to better inform the design and translation of novel biomaterials to promote their regeneration. Major clinical problems in adipose tissue, cartilage, dermis, and tendon are discussed that inspire the need to replace native connective tissue with biomaterials. Then, multiscale structure-function relationships in native soft connective tissues that may be used to guide material design are detailed. Several biomaterials strategies to improve healing of these tissues that incorporate biologics and are biologic-free are reviewed. Finally, important guidance documents and standards (ASTM, FDA, and EMA) that are important to consider for translating new biomaterials into clinical practice are highligted.

Current Biomedical Applications of 3D Printing and Additive Manufacturing

Additive manufacturing (AM) has emerged over the past four decades as a cost-effective, on-demand modality for fabrication of geometrically complex objects. The ability to design and print virtually any object shape using a diverse array of materials, such as metals, polymers, ceramics and bioinks, has allowed for the adoption of this technology for biomedical applications in both research and clinical settings. Current advancements in tissue engineering and regeneration, therapeutic delivery, medical device fabrication and operative management planning ensure that AM will continue to play an increasingly important role in the future of healthcare. In this review, we outline current biomedical applications of common AM techniques and materials.

Self-organizing hair peg-like structures from dissociated skin progenitor cells: New insights for human hair follicle organoid engineering and Turing patterning in an asymmetric morphogenetic field

Human skin progenitor cells will form new hair follicles, although at a low efficiency, when injected into nude mouse skin. To better study and improve upon this regenerative process, we developed an in vitro system to analyse the morphogenetic cell behaviour in detail and modulate physical-chemical parameters to more effectively generate hair primordia. In this three-dimensional culture, dissociated human neonatal foreskin keratinocytes self-assembled into a planar epidermal layer while fetal scalp dermal cells coalesced into stripes, then large clusters, and finally small clusters resembling dermal condensations. At sites of dermal clustering, subjacent epidermal cells protruded to form hair peg-like structures, molecularly resembling hair pegs within the sequence of follicular development. The hair peg-like structures emerged in a coordinated, formative wave, moving from periphery to centre, suggesting that the droplet culture constitutes a microcosm with an asymmetric morphogenetic field. In vivo, hair follicle populations also form in a progressive wave, implying the summation of local periodic patterning events with an asymmetric global influence. To further understand this global patterning process, we developed a mathematical simulation using Turing activator-inhibitor principles in an asymmetric morphogenetic field. Together, our culture system provides a suitable platform to (a) analyse the self-assembly behaviour of hair progenitor cells into periodically arranged hair primordia and (b) identify parameters that impact the formation of hair primordia in an asymmetric morphogenetic field. This understanding will enhance our future ability to successfully engineer human hair follicle organoids.

Sweat gland organoids contribute to cutaneous wound healing and sweat gland regeneration

Sweat glands perform a vital thermoregulatory function in mammals. Like other skin components, they originate from epidermal progenitors. However, they have low regenerative potential in response to injury. We have established a sweat gland culture and expansion method using 3D organoids cultures. The epithelial cells derived from sweat glands in dermis of adult mouse paw pads were embedded into Matrigel and formed sweat gland organoids (SGOs). These organoids maintained remarkable stem cell features and demonstrated differentiation capacity to give rise to either sweat gland cells (SGCs) or epidermal cells. Moreover, the bipotent SGO-derived cells could be induced into stratified epidermis structures at the air−liquid interface culture in a medium tailored for skin epidermal cells in vitro. The SGCs embedded in Matrigel tailored for sweat glands formed epithelial organoids, which expressed sweat-gland-specific markers, such as cytokeratin (CK) 18 and CK19, aquaporin (AQP) 5 and αATP. More importantly, they had potential of regeneration of epidermis and sweat gland when they were transplanted into the mouse back wound and claw pad with sweat gland injury, respectively. In summary, we established and optimized culture conditions for effective generation of mouse SGOs. These cells are candidates to restore impaired sweat gland tissue as well as to improve cutaneous skin regeneration.

Tissue engineering of human hair follicles using a biomimetic developmental approach

Human skin constructs (HSCs) have the potential to provide an effective therapy for patients with significant skin injuries and to enable human-relevant drug screening for skin diseases; however, the incorporation of engineered skin appendages, such as hair follicles (HFs), into HSCs remains a major challenge. Here, we demonstrate a biomimetic approach for generation of human HFs within HSCs by recapitulating the physiological 3D organization of cells in the HF microenvironment using 3D-printed molds. Overexpression of Lef-1 in dermal papilla cells (DPC) restores the intact DPC transcriptional signature and significantly enhances the efficiency of HF differentiation in HSCs. Furthermore, vascularization of hair-bearing HSCs prior to engraftment allows for efficient human hair growth in immunodeficient mice. The ability to regenerate an entire HF from cultured human cells will have a transformative impact on the medical management of different types of alopecia, as well as chronic wounds, which represent major unmet medical needs.

Human skin constructs hold potential for regenerative medicine, but the incorporation of hair follicles into such constructs is a challenge. Here, the authors use 3D printed molds to pattern hair follicle cell types in a physiological organization, and achieve human hair growth on the back of a mouse.

From single cells to tissue self-organization

Self-organization is a process by which interacting cells organize and arrange themselves in higher order structures and patterns. To achieve this, cells must have molecular mechanisms to sense their complex local environment and interpret it to respond accordingly. A combination of cell-intrinsic and cell-extrinsic cues are decoded by the single cells dictating their behaviour, their differentiation and symmetry-breaking potential driving development, tissue remodeling and regenerative processes. A unifying property of these self-organized pattern-forming systems is the importance of fluctuations, cell-to-cell variability, or noise. Cell-to-cell variability is an inherent and emergent property of populations of cells that maximize the population performance instead of the individual cell, providing tissues the flexibility to develop and maintain homeostasis in diverse environments. In this review, we will explore the role of self-organization and cell-to-cell variability as fundamental properties of multicellularity-and the requisite of single-cell resolution for its understanding. Moreover, we will analyze how single cells generate emergent multicellular dynamics observed at the tissue level 'travelling' across different scales: spatial, temporal and functional.

Suppression of IGF1R in Melanoma Cells by an Adenovirus-Mediated One-Step Knockdown System

Abnormal activation of the IGF1R signaling pathway accelerates melanoma development and metastases. RNAi systems with complex cloning procedures and unsatisfactory efficiency in suppressing gene expression have become the technical difficulties that hinder their utility when studying gene knockdown. Here we established a simplified adenovirus-mediated gene knockdown system by which a single adenoviral vector carries multiple siRNA fragments that can effectively suppress IGF1R expression in melanoma cells. We first generated the adenovirus that simultaneously expresses three human or mouse siRNAs targeting IGF1R (AdRIGF1R-OK). qRT-PCR and immunofluorescence staining revealed that IGF1R expression was significantly decreased in the melanoma cells that were infected with AdRIGF1R-OK. Bioluminescence imaging showed that the size of the tumor formed by the xenografts infected with AdRIGF1R-OK was significantly smaller than that of the controls. Annexin V-FITC flow cytometry assay, immunofluorescence staining for cleaved caspase-3, and Hoechst staining showed that more cells underwent apoptosis after infection with AdRIGF1R-OK. Luciferase reporter assay, crystal violet cell viability assay, and cell-cycle analysis showed that the proliferation of melanoma cells infected with AdRIGF1R-OK was significantly decreased compared to the controls. This study demonstrates that the OK system is effective in silencing gene expression, with promising potential to treat melanoma and other diseases.

Advancing insights into stem cell niche complexities with next-generation technologies

Adult tissue-specific stem cells are essential for homeostatic tissue maintenance and key to regeneration during injury repair or disease. Many critical stem cell functions rely on the presence of well-timed cues from the microenvironment or niche, which includes a diverse range of components, including neuronal, circulating and extracellular matrix inputs as well as an array of neighboring niche cells directly interacting with the stem cells. However, studies of stem cells and their niche have been challenging due to the complexity of adult stem cell functions, their intrinsic controls and the multiple regulatory niche components. Here, we review recent major advances in our understanding of the complex interplay between stem cells and their niche that were enabled by the tremendous technological leaps in single-cell transcriptome analyses, 3D in vitro cultures and 4D in vivo microscopy of stem cell niches.

Establishment and characterization of a canine keratinocyte organoid culture system

BACKGROUND

Perturbations of epidermal and follicular homeostasis have been attributed to a variety of skin diseases affecting dogs. The availability of an in vitro system to investigate these diseases is important to understand underlying pathomechanisms.

OBJECTIVES

To establish an accurate and reliable in vitro 3D system of canine keratinocyte organoids to lay the basis for studying functional defects in interfollicular epidermis (IFE) and hair follicle (HF) morphogenesis, reconstitution and differentiation that lead to alopecic and epidermal diseases.

ANIMALS

Skin biopsies were obtained from freshly euthanized dogs of different breeds with no skin abnormalities.

METHODS

Cells derived from microdissected IFE and HFs were seeded in Matrigel and keratinocyte organoids were grown and characterized using immunohistochemistry, RT-qPCR and RNA sequencing.

RESULTS

Both organoid lines develop into a basal IFE-like cell type. Gene and protein expression analysis revealed high mRNA and protein levels of keratins 5 and 14, IFE differentiation markers and intercellular molecules. Key markers of HF stem cells were lacking. Withdrawal of growth factors resulted in upregulation of markers such as KRT16, Involucrin, KRT17 and SOX9, showing the potential of the organoids to develop towards more differentiated tissue.

CONCLUSION AND CLINICAL IMPORTANCE

Our 3D in vitro culture system provides the basis to explore epidermal function, to investigate the culture conditions necessary for the development of organoids with a HF signature and to address cutaneous disorders in dogs. However, for induction of HF signatures or hair growth, addition of different growth factors or co-culture with dermal papilla will be required.

Inducing hair follicle neogenesis with secreted proteins enriched in embryonic skin

Organ development is a sophisticated process of self-organization. However, despite growing understanding of the developmental mechanisms, little is known about how to reactivate them postnatally for regeneration. We found that treatment of adult non-hair fibroblasts with cell-free extract from embryonic skin conferred upon them the competency to regenerate hair follicles. Proteomics analysis identified three secreted proteins enriched in the embryonic skin, apolipoprotein-A1, galectin-1 and lumican that together were essential and sufficient to induce new hair follicles. These 3 proteins show a stage-specific co-enrichment in the perifolliculogenetic embryonic dermis. Mechanistically, exposure to embryonic skin extract or to the combination of the 3 proteins altered the gene expression to an inductive hair follicle dermal papilla fibroblast-like profile and activated Igf and Wnt signaling, which are crucial for the regeneration process. Therefore, a cocktail of organ-specific extracellular proteins from the embryonic environment can render adult cells competent to re-engage in developmental interactions for organ neogenesis. Identification of factors that recreate the extracellular context of respective developing tissues can become an important strategy to promote regeneration in adult organs.

Nature-derived lignan compound VB-1 exerts hair growth-promoting effects by augmenting Wnt/β-catenin signaling in human dermal papilla cells

Background

Vitexin is a kind of lignan compound which has been shown to possess a variety of pharmacological effects, such as anti-inflammatory, anti-oxidative and anti-cancer activities. However the effect of vitexin on hair regeneration has not been elaborated.

Methods

The proliferation of human dermal papilla cells (hDPCs) was examined by cell counting and continuous cell culture after vitexin compound 1 (VB-1) was treated. The expression of lef1, wnt5a, bmp2, bmp4, alpl and vcan was examined by RT-PCR. The expression of dkk1, tgf-β1, active-β-Catenin, and AXIN2 was examined by RT-PCR or immunoblotting. Hair shaft growth was measured in the absence or presence of VB-1.

Results

We demonstrated that VB-1 significantly promotes the proliferation of hDPCs in a concentration-dependent manner within a certain concentration range. Among the hair growth-related genes investigated, dkk1 was clearly down-regulated in hDPCs treated with VB-1. The increased active β-Catenin and decreased AXIN2 protein levels suggest that VB-1 facilitates Wnt/β-catenin signaling in hDPCs in vitro. The expression of DP signature genes was also upregulated after VB-1 treatment. Our study further indicated that VB-1 promotes human hair follicle (HF) growth by HF organ culture assay.

Discussion

VB-1 may exert hair growth-promoting effects via augmenting Wnt/β-catenin signaling in hDPCs.

Regenerating human epithelia with cultured stem cells: feeder cells, organoids and beyond

More than 40 years ago, Howard Green's laboratory developed a method for long-term expansion of primary human epidermal keratinocytes by co-culture with 3T3 mouse embryonic fibroblasts. This was a breakthrough for in vitro cultivation of cells from human skin and later for other epithelia: it led to the first stem cell therapy using cultured cells and has vastly increased our understanding of epithelial stem cell biology. In recent years, new methods to expand epithelial cells as three-dimensional organoids have provided novel means to investigate the functions of these cells in health and disease. Here, we outline the history of stratified epithelial stem cell culture and the application of cultured epithelial cells in clinical therapies. We further discuss the derivation of organoids from other types of epithelia and the challenges that remain for the translation of novel stem cell therapies toward clinical use.

RANKL Reduces Body Weight and Food Intake via the Modulation of Hypothalamic NPY/CART Expression

The receptor activator of nuclear factor-κB ligand (RANKL) modulates energy metabolism. However, how RANKL regulates energy homeostasis is still not clear. This study aims to investigate the central mechanisms by which central administration of RANKL inhibits food intake and causes weight loss in mice. We carried out a systematic and in-depth analysis of the neuronal pathways by which RANKL mediates catabolic effects. After intracerebroventricle (i.c.v.) injection of RANKL, the expression of neuropeptide Y (NPY) mRNA in the Arc was significantly decreased, while the CART mRNA expression dramatically increased in the Arc and DMH. However, the agouti-related protein (AgRP) and pro-opiomelanocortin (POMC) mRNA had no significant changes compared with control groups. Together, the results suggest that central administration of RANKL reduces food intake and causes weight loss via modulating the hypothalamic NPY/CART pathways.

Regeneration of Mouse Skin Melanocyte Stem Cells In Vivo and In Vitro

Coordinated regeneration of melanocyte stem cells (McSCs) and hair follicle stem cells (HSCs) contributes to generation of pigmented hairs. Synchronous regeneration of McSCs with activation of HSCs occurs not only during initiation of a new hair cycle in vivo but also during reconstitution of hair follicles in vitro. The duration of the quiescent state of these stem cells becomes longer and longer in lifespan of mammals, leading to a decreased regenerative ability to form hair follicles. Here, we describe methods to activate McSCs during hair follicle regeneration in vivo, and isolate melanocytes from neonatal mouse skin to generate an immortalized cell line of melanocyte progenitors in vitro, aiming to use them for studying melanogenesis and future clinical application.

Reverse-engineering organogenesis through feedback loops between model systems

Biological complexity and ethical limitations necessitate models of human development. Traditionally, genetic model systems have provided inexpensive routes to define mechanisms governing organ development. Recent progress has led to 3D human organoid models of development and disease. However, robust methods to control the size and morphology of organoids for high throughput studies need to be developed. Additionally, insights from multiple developmental contexts are required to reveal conserved genes and processes regulating organ growth and development. Positive feedback between quantitative studies using mammalian organoids and insect micro-organs enable identification of underlying principles for organ size and shape control. Advances in the field of multicellular systems engineering are enabling unprecedented high-content studies in developmental biology and disease modeling. These will lead to fundamental advances in regenerative medicine and tissue-engineered soft robotics.

Gsdma3 regulates hair follicle differentiation via Wnt5a-mediated non-canonical Wnt signaling pathway

Hair follicle is a mini-organ that consists of complex but well-organized structures, which are differentiated from hair follicle progenitor or stem cells. How non-canonical Wnt signaling pathway is involved in regulating hair follicle differentiation remains elusive. Here we showed that Wnt5a regulates hair follicle differentiation through an epithelial-mesenchymal interaction mechanism in mice. We first observed that Wnt5a is expressed in the epithelial and dermal papilla cells during hair follicle development and growth. For the upstream of Wnt5a, RT-PCR and immunohistochemistry staining showed that Wnt5a expression is significantly decreased in the Gsdma3-mutant mice in vivo. Overexpression of Gsdma3 results in a significantly increased expression of Wnt5a in the cultured epidermal cells in vitro. We also checked the downstream factors of Wnt5a by adenovirus-mediated overexpression of Wnt5a to the dermal papilla cells isolated from the mouse whisker. We found that overexpression of Wnt5a suppresses canonical Wnt signaling pathway effectors such as β-catenin and Lef1. In addition, genes involved in maintaining cell quiescent state are also significantly decreased in their expression to the DP cells which were treated by Wnt5a. Our study indicates that Wnt5a mediates epithelia-expressed Gsdma3 to influence DP cell behaviors, which in turn regulate hair follicle epithelia differentiation in mice.

Wnt/β-catenin signaling promotes aging-associated hair graying in mice

Canities is an obvious sign of aging in mouse and human, shown as hair graying. Melanocytes in the hair follicle show cyclic activity with hair cycling, which transitions from anagen, catagen to telogen. How the hairs turn gray during aging is not completely uncovered. Here, by using immunostaining and LacZ staining in Dct-LacZ mice, we show that β-catenin is expressed in melanocytes during hair cycling. RT-PCR, western blot and immunostaining show that β-catenin expression is significantly increased in both anagen and telogen skin of aged mice, when compared to the anagen and telogen skin of young mice, respectively. Overexpression of Wnt10b not only accelerates hair follicle to enter anagen phase, but also promotes melanocytes differentiation in young adult mice (2-month old), with increased β-catenin expression in melanocytes at the secondary hair germ and matrix region of regenerated hair follicles. Overexpression of Wnt10b also promotes melanocyte progenitor cells differentiation in vitro. Our data suggest that increased Wnt signaling promotes excessive differentiation of melanocytes, leading to exhaustion of melanocyte stem cells and eventually canities in aged mice.