Wnt-activating human skin organoid model of atopic dermatitis induced by Staphylococcus aureus and its protective effects by Cutibacterium acnes

Skin models for studying vector-borne kinetoplastid infections

Kinetoplastid infections, caused by Leishmania and Trypanosoma species, pose significant global health challenges, disproportionally affecting vulnerable populations in tropical regions. Despite the skin's pivotal role as both an entry point and a reservoir for these parasites, the mechanistic understanding of host-parasite interactions at this interface remains limited. Recent advancements in bioengineered skin models, such as full thickness skin equivalents and skin organoids, provide a promising complement to in vivo and ex vivo models. These in vitro systems address key challenges related to accessibility, reproducibility, and anatomical relevance, while potentially incorporating key tissue components, including immune cells and vascular structures. By replicating the complex structure of human skin at customizable levels of complexity, they offer powerful platforms for high-resolution studies of parasite-host interactions. Furthermore, by supporting natural vector transmission and enabling the simulation of diverse biological conditions, these systems open new avenues for investigating parasite development, tissue invasion, dissemination and immune dynamics.

Recent progress in the identification and in vitro culture of skin organoids

An organoid is a cell-based structure that shows organ-specific properties and shares a similar spatial organization as the corresponding organ. Organoids possess powerful capability to reproduce the key functions of the associated organ structures, and their similarity to the organs makes them physiologically relevant systems. The primary challenge associated with the development of skin organoids is the complexity of the human skin architecture, which encompasses the epidermis and the dermis as well as accessory structures, including hair follicles, sweat glands, and sebaceous glands, that perform various functions such as thermoregulation. The ultimate objectives of developing skin organoids are to regenerate the complete skin structure in vitro and reconstruct the skin in vivo. Consequently, safety, reliability, and the fidelity of the tissue interfaces are key considerations in this process. For this purpose, the present article reviews the most recent advances in this field, focusing on the cell sources, culture methods, culture conditions, and biomarkers for identifying the structure and function of skin organoids developed in vitro or in vivo. The subsequent sections summarize the recent applications of skin organoids in related disease diagnosis and treatments, and discuss the future prospects of these organoids in terms of clinical applications. This review of skin organoids can provide an important foundation for studies on human skin development, disease modeling, and reconstructive surgery, with broad utility for promising future opportunities in both biomedical research and clinical practice.

Engineered Tissue Models to Decode Host-Microbiota Interactions

A mutualistic co-evolution exists between the host and its associated microbiota in the human body. Bacteria establish ecological niches in various tissues of the body, locally influencing their physiology and functions, but also contributing to the well-being of the whole organism through systemic communication with other distant niches (axis). Emerging evidence indicates that when the composition of the microbiota inhabiting the niche changes toward a pathogenic state (dysbiosis) and interactions with the host become unbalanced, diseases may present. In addition, imbalances within a single niche can cause dysbiosis in distant organs. Current research efforts are focused on elucidating the mechanisms leading to dysbiosis, with the goal of restoring tissue homeostasis. In vitro models can provide critical experimental platforms to address this need, by reproducing the niche cyto-architecture and physiology with high fidelity. This review surveys current in in vitro host-microbiota research strategies and provides a roadmap that can guide the field in further developing physiologically relevant in vitro models of ecological niches, thus enabling investigation of the role of the microbiota in human health and diseases. Lastly, given the Food and Drug Administration Modernization Act 2.0, this review highlights emerging in vitro strategies to support the development and validation of new therapies on the market.

Organoid-Guided Precision Medicine: From Bench to Bedside

Organoid technology, as an emerging field within biotechnology, has demonstrated transformative potential in advancing precision medicine. This review systematically outlines the translational trajectory of organoids from bench to bedside, emphasizing their construction methodologies, key regulatory factors, and multifaceted applications in personalized healthcare. By recapitulating physiological architectures and disease phenotypes through three-dimensional culture systems, organoids leverage natural and synthetic scaffolds, stem cell sources, and spatiotemporal cytokine regulation to model tissue-specific microenvironments. Diverse organoid types-including skin, intestinal, lung, and tumor organoids-have facilitated breakthroughs in modeling tissue development, drug efficacy and toxicity screening, disease pathogenesis studies, and patient-tailored diagnostics. For instance, patient-derived tumor organoids preserve tumor heterogeneity and genomic profiles, serving as predictive platforms for individualized chemotherapy responses. In precision medicine, organoid-guided multiomics analyses identify actionable biomarkers and resistance mechanisms, while clustered regularly interspaced short palindromic repeats-based functional screens optimize therapeutic targeting. Despite preclinical successes, challenges persist in standardization, vascularization, and ethical considerations. Future integration of artificial intelligence, microfluidics, and spatial transcriptomics will enhance organoid scalability, reproducibility, and clinical relevance. By bridging molecular insights with patient-specific therapies, organoids are poised to revolutionize precision medicine, offering dynamic platforms for drug development, regenerative strategies, and individualized treatment paradigms.

A skin organoid-based infection platform identifies an inhibitor specific for HFMD

The EV-A71 poses a serious threat to the health and lives of children. The EV-A71 can be transmitted by direct and indirect skin contact. Therefore, there is an urgent need to create novel skin models using human-derived cells to study the biology and pathogenesis of the virus and facilitate drug screening. Here, we use human induced pluripotent stem cells-derived skin organoids (hiPSC-SOs) as a model for EV-A71 infection and find that multiple cell types within the skin organoids, including epidermal cells, hair follicle cells, fibroblasts, and nerve cells, express EV-A71 receptors and are susceptible to EV-A71 infection. We elucidate the specific response of different cell types to EV-A71 and reveal that EV-A71 infection can degrade extracellular collagen and affect fibroblasts. We find that EV-A71 can mediate epidermal cell damage through autophagy and Integrin/Hippo-YAP/TAZ signaling pathways, thereby promoting hyperproliferation of progenitor cells. Based on this finding, we identify an autophagy-associated protein as a drug target of EV-A71 and discover an EV-A71 replication inhibitor. Altogether, these data suggest that hiPSC-SOs can be used as an infectious disease model to study skin infectious diseases, providing a valuable resource for drug screening to identify candidate virus therapeutics.

Functional regeneration strategies of hair follicles: advances and challenges

Hair follicles are essential appendages of human skin that function in protection, sensation, thermoregulation and social interactions. The multicellular components, particularly the dermal papilla, matrix and bulge housing stem cells, enable cyclic hair growth postnatally. However, miniaturization and loss of hair follicles can occur in the context of ageing, trauma and various alopecia-related diseases. Conventional treatments involve the redistribution of existing follicles, which may not be viable in patients lacking follicular resources. Recent progress in the comprehension of morphogenesis and the development of biomaterials has significantly advanced follicle reconstruction, incorporating organ germ assembling, stem cell induction and bioprinting techniques. Despite these advancements, fully restoring hair follicles remains challenging due to the complexities of replicating embryonic signals and sustaining growth cycles. Identifying suitable cell sources for clinical applications also presents a hurdle. Here, we retrospect the progress made in the field of hair follicle regeneration, aiming to offer an exhaustive analysis on the benefits and limitations of these methods, and to foster the development of innovative solutions.

The empowering influence of air-liquid interface culture on skin organoid hair follicle development

Background

Rodent models have been widely used to investigate skin development, but do not account for significant differences in composition compared to human skin. On the other hand, two-dimensional and three-dimensional engineered skin models still lack the complex features of human skin such as appendages and pigmentation. Recently, hair follicle containing skin organoids (SKOs) with a stratified epidermis, and dermis layer have been generated as floating spheres from human-induced pluripotent stem cells (hiPSCs).

Methods

The current study aims to investigate the generation of hiPSCs-derived SKOs using an air-liquid interface (ALI) model on transwell membranes (T-SKOs) and compares their development with conventional floating culture in low-attachment plates (F-SKOs).

Results

Mature SKOs containing an epidermis, dermis, and appendages are created in both T-SKO and F-SKO conditions. It was found that the hair follicles are smaller and shorter in the F-SKO compared with T-SKOs. Additionally, the ALI conditions contribute to enhanced hair follicle numbers than conventional floating culture.

Conclusions

Together, this study demonstrates the significant influence of transwell culture on the morphogenesis of hair follicles within SKOs and highlights the potential for refinement of skin model engineering for advancing dermatology and skin research.

Organoids in skin wound healing

Stem cells (SCs) can self-replicate and differentiate into multiple lineages. Organoids, 3D cultures derived from SCs, can replicate the spatial structure and physiological characteristics of organs in vitro. Skin organoids can effectively simulate the physiological structure and function of skin tissue, reliably restoring the natural skin ecology in various in vitro environments. Skin organoids have been employed extensively in skin development and pathology research, offering valuable insights for drug screening. Moreover, they play crucial roles in skin regeneration and tissue repair. This in-depth review explores the construction and applications of skin organoids in wound healing, with a focus on their construction process, including skin appendage integration, and significant advancements in wound-healing research.

Diversity of human skin three-dimensional organotypic cultures

Recently, significant strides have been made in the development of high-fidelity skin organoids, encompassing techniques such as 3D bioprinting, skin-on-a-chip systems, and models derived from pluripotent stem cells (PSCs), replicating appendage structures and diverse skin cell types. Despite the emergence of these state-of-the-art skin engineering models, human organotypic cultures (OTCs), initially proposed in the 1970s, continue to reign as the predominant in vitro cultured three-dimensional skin model in the field of tissue engineering. This enduring prevalence is owed to their cost-effectiveness, straight forward setup, time efficiency, and faithful representation of native human skin. In this review, we systematically delineate recent advances in skin OTC models, aiming to inform future efforts to enhance in vitro skin model fidelity and reproducibility.

Advances in, and prospects of, 3D preclinical models for skin drug discovery

The skin has an important role in regulating homeostasis and protecting the body from endogenous and exogenous microenvironments. Although 3D models for drug discovery have been extensively studied, there is a growing demand for more advanced 3D skin models to enhance skin research. The use of these advanced skin models holds promise across domains such as cosmetics, skin disease treatments, and toxicity testing of new therapeutics. Recent advances include the development of skin-on-a-chip, spheroids, reconstructed skin, organoids, and computational approaches, including quantitative structure-activity relationship (QSAR) and quantitative structure-property relationship (QSPR) research. These innovations are bridging the gap between traditional 2D and advanced 3D models, moving progress from research to clinical applications. In this review, we highlight in vitro and computational skin models with advanced drug discovery for skin-related applications.

Beyond skin deep: Revealing the essence of iPS cell-generated skin organoids in regeneration

Various methods have been used for in vivo and in vitro skin regeneration, including stem cell therapy, tissue engineering, 3D printing, and platelet-rich plasma (PRP) injection therapy. However, these approaches are rooted in the existing knowledge of skin structures, which overlook the normal physiological processes of skin development and fall short of replicating the skin's regenerative processes outside the body. This comprehensive review primarily focuses on skin organoids derived from human pluripotent stem cells, which have the capacity to regenerate human skin tissue by restoring the embryonic skin structure, thus offering a novel avenue for producing in vitro skin substitutes. Furthermore, they contribute to the repair of damaged skin lesions in patients with systemic sclerosis or severe burns. Particular emphasis will be placed on the origins, generations, and applications of skin organoids, especially in dermatology, and the challenges that must be addressed before clinical implementation.

Targeting the Complexity of In Vitro Skin Models: A Review of Cutting-Edge Developments

Skin in vitro models offer much promise for research, testing drugs, cosmetics, and medical devices, reducing animal testing and extensive clinical trials. There are several in vitro approaches to mimicking human skin behavior, ranging from simple cell monolayer to complex organotypic and bioengineered 3-dimensional models. Some have been approved for preclinical studies in cosmetics, pharmaceuticals, and chemicals. However, development of physiologically reliable in vitro human skin models remains in its infancy. This review reports on advances in in vitro complex skin models to study skin homeostasis, aging, and skin disease.

Organoids: development and applications in disease models, drug discovery, precision medicine, and regenerative medicine

Organoids are miniature, highly accurate representations of organs that capture the structure and unique functions of specific organs. Although the field of organoids has experienced exponential growth, driven by advances in artificial intelligence, gene editing, and bioinstrumentation, a comprehensive and accurate overview of organoid applications remains necessary. This review offers a detailed exploration of the historical origins and characteristics of various organoid types, their applications-including disease modeling, drug toxicity and efficacy assessments, precision medicine, and regenerative medicine-as well as the current challenges and future directions of organoid research. Organoids have proven instrumental in elucidating genetic cell fate in hereditary diseases, infectious diseases, metabolic disorders, and malignancies, as well as in the study of processes such as embryonic development, molecular mechanisms, and host-microbe interactions. Furthermore, the integration of organoid technology with artificial intelligence and microfluidics has significantly advanced large-scale, rapid, and cost-effective drug toxicity and efficacy assessments, thereby propelling progress in precision medicine. Finally, with the advent of high-performance materials, three-dimensional printing technology, and gene editing, organoids are also gaining prominence in the field of regenerative medicine. Our insights and predictions aim to provide valuable guidance to current researchers and to support the continued advancement of this rapidly developing field.

Ideal Living Skin Equivalents, From Old Technologies and Models to Advanced Ones: The Prospects for an Integrated Approach

The development of technologies for the generation and transplantation of living skin equivalents (LSEs) is a significant area of translational medicine. Such functional equivalents can be used to model and study the morphogenesis of the skin and its derivatives, to test drugs, and to improve the healing of chronic wounds, burns, and other skin injuries. The evolution of LSEs over the past 50 years has demonstrated the leap in technology and quality and the shift from classical full-thickness LSEs to principled new models, including modification of classical models and skin organoids with skin derived from human-induced pluripotent stem cells (iPSCs) (hiPSCs). Modern methods and approaches make it possible to create LSEs that successfully mimic native skin, including derivatives such as hair follicles (HFs), sebaceous and sweat glands, blood vessels, melanocytes, and nerve cells. New technologies such as 3D and 4D bioprinting, microfluidic systems, and genetic modification enable achievement of new goals, cost reductions, and the scaled-up production of LSEs.

Replacing Animal Testing with Stem Cell-Organoids : Advantages and Limitations

Various groups including animal protection organizations, medical organizations, research centers, and even federal agencies such as the U.S. Food and Drug Administration, are working to minimize animal use in scientific experiments. This movement primarily stems from animal welfare and ethical concerns. However, recent advances in technology and new studies in medicine have contributed to an increase in animal experiments throughout the years. With the rapid increase in animal testing, concerns arise including ethical issues, high cost, complex procedures, and potential inaccuracies.Alternative solutions have recently been investigated to address the problems of animal testing. Some of these technologies are related to stem cell technologies, such as organ-on-a-chip, organoids, and induced pluripotent stem cell models. The aim of the review is to focus on stem cell related methodologies, such as organoids, that can serve as an alternative to animal testing and discuss its advantages and limitations, alongside regulatory considerations.Although stem cell related methodologies has shortcomings, it has potential to replace animal testing. Achieving this requires further research on stem cells, with potential societal and technological benefits.

Efficient Generation of Skin Organoids from Pluripotent Cells via Defined Extracellular Matrix Cues and Morphogen Gradients in a Spindle-Shaped Microfluidic Device

Pluripotent stem cell-derived skin organoids (PSOs) emerge as a developmental skin model that is self-organized into multiple components, such as hair follicles. Despite their impressive complexity, PSOs are currently generated in the absence of 3D extracellular matrix (ECM) signals and have several major limitations, including an inverted anatomy (e.g., epidermis inside/dermis outside). In this work, a method is established to generate PSOs effectively in a chemically-defined 3D ECM environment. After examining various dermal ECM molecules, it is found that PSOs generated in collagen -type I (COLI) supplemented with laminin 511 (LAM511) exhibit increased growth compared to conventional free-floating conditions, but fail to induce complete skin differentiation due in part to necrosis. This problem is addressed by generating the PSOs in a 3D bioprinted spindle-shaped hydrogel device, which constrains organoid growth longitudinally. This culture system significantly reduces organoid necrosis and leads to a twofold increase in keratinocyte differentiation and an eightfold increase in hair follicle formation. Finally, the system is adapted as a microfluidic device to create asymmetrical gradients of differentiation factors and improves the spatial organization of dermal and epidermal cells. This study highlights the pivotal role of ECM and morphogen gradients in promoting and spatially-controlling skin differentiation in the PSO framework.

Guidelines for Manufacturing and Application of Organoids: Skin

To address the limitations of animal testing, scientific research is increasingly focused on developing alternative testing methods. These alternative tests utilize cells or tissues derived from animals or humans for in vitro testing, as well as artificial tissues and organoids. In western countries, animal testing for cosmetics has been banned, leading to the adoption of artificial skin for toxicity evaluation, such as skin corrosion and irritation assessments. Standard guidelines for skin organoid technology becomes necessary to ensure consistent data and evaluation in replacing animal testing with in vitro methods. These guidelines encompass aspects such as cell sourcing, culture techniques, quality requirements and assessment, storage and preservation, and organoid-based assays.

Modelling Human Hair Follicles-Lessons from Animal Models and Beyond

The hair follicle is a specialized appendage of the skin that is critical for multiple functions, including thermoregulation, immune surveillance, and sebum production. Mammals are born with a fixed number of hair follicles that develop embryonically. Postnatally, these hair follicles undergo regenerative cycles of regression and growth that recapitulate many of the embryonic signaling pathways. Furthermore, hair cycles have a direct impact on skin regeneration in homeostasis, cutaneous wound healing, and disease conditions such as alopecia. Here, we review the current knowledge of hair follicle formation during embryonic development and the post-natal hair cycle, with an emphasis on the molecular signaling pathways underlying these processes. We then discuss efforts to capitalize on the field's understanding of in vivo mechanisms to bioengineer hair follicles or hair-bearing skin in vitro and how such models may be further improved to develop strategies for hair regeneration.

Recreating Human Skin In Vitro: Should the Microbiota Be Taken into Account?

Skin plays crucial roles in the human body: besides protecting the organism from external threats, it acts as a thermal regulator, is responsible for the sense of touch, hosts microbial communities (the skin microbiota) involved in preventing the invasion of foreign pathogens, contains immunocompetent cells that maintain a healthy immunogenic/tolerogenic balance, and is a suitable route for drug administration. In the skin, four defense levels can be identified: besides the physical, chemical, and immune barriers that are inherent to the tissue, the skin microbiota (i.e., the numerous microorganisms living on the skin surface) provides an additional barrier. Studying the skin barrier function or the effects of drugs or cosmetic agents on human skin is a difficult task since snapshot evidence can only be obtained using bioptic samples where dynamic processes cannot properly be followed. To overcome these limitations, many different in vitro models of human skin have been developed that are characterized by diverse levels of complexity in terms of chemical, structural, and cellular composition. The aim of this review is to summarize and discuss the advantages and disadvantages of the different human skin models so far available and to underline how the insertion of a proper microbiota would positively impact an in vitro human skin model in an attempt to better mimic conditions in vivo.

Modeling of solar UV-induced photodamage on the hair follicles in human skin organoids

Solar ultraviolet (sUV) exposure is known to cause skin damage. However, the pathological mechanisms of sUV on hair follicles have not been extensively explored. Here, we established a model of sUV-exposed skin and its appendages using human induced pluripotent stem cell-derived skin organoids with planar morphology containing hair follicles. Our model closely recapitulated several symptoms of photodamage, including skin barrier disruption, extracellular matrix degradation, and inflammatory response. Specifically, sUV induced structural damage and catagenic transition in hair follicles. As a potential therapeutic agent for hair follicles, we applied exosomes isolated from human umbilical cord blood-derived mesenchymal stem cells to sUV-exposed organoids. As a result, exosomes effectively alleviated inflammatory responses by inhibiting NF-κB activation, thereby suppressing structural damage and promoting hair follicle regeneration. Ultimately, our model provided a valuable platform to mimic skin diseases, particularly those involving hair follicles, and to evaluate the efficacy and underlying mechanisms of potential therapeutics.

Mpox virus infection and drug treatment modelled in human skin organoids

Mpox virus (MPXV) primarily infects human skin to cause lesions. Currently, robust models that recapitulate skin infection by MPXV are lacking. Here we demonstrate that human induced pluripotent stem cell-derived skin organoids are susceptible to MPXV infection and support infectious virus production. Keratinocytes, the predominant cell type of the skin epithelium, effectively support MPXV infection. Using transmission electron microscopy, we visualized the four stages of intracellular virus particle assembly: crescent formation, immature virions, mature virions and wrapped virions. Transcriptional analysis showed that MPXV infection rewires the host transcriptome and triggers abundant expression of viral transcripts. Early treatment with the antiviral drug tecovirimat effectively inhibits infectious virus production and prevents host transcriptome rewiring. Delayed treatment with tecovirimat also inhibits infectious MPXV particle production, albeit to a lesser extent. This study establishes human skin organoids as a robust experimental model for studying MPXV infection, mapping virus-host interactions and testing therapeutics.

Applications of Human Pluripotent Stem Cell-Derived Skin Organoids in Dermatology

Pluripotent stem cells have the potential to become any cell type, and recently, they have been used to create organoids that can recapitulate several pertinent features of human organs. Skin organoids have been developed that possess many of the crucial accessory organs, including hair follicles, sebaceous glands, nerves, fat, and melanocytes. These skin organoids present the opportunity to study skin development and disease as well as perform screens to identify new drug candidates. In the future, skin organoids might augment clinical practice by serving as source material for transplantation to treat wounds or other conditions. Nevertheless, several limitations, such as the lengthy differentiation protocol, which can result in heterogeneous products, must first be addressed before the full potential of skin organoids can be realized. The purpose of this article is to provide a broad overview of skin organoids so that a broader audience can become familiar with this technology, which has important implications for dermatologic research and medicine.

Bioengineered skin organoids: from development to applications

Significant advancements have been made in recent years in the development of highly sophisticated skin organoids. Serving as three-dimensional models that mimic human skin, these organoids have evolved into complex structures and are increasingly recognized as effective alternatives to traditional culture models and human skin due to their ability to overcome the limitations of two-dimensional systems and ethical concerns. The inherent plasticity of skin organoids allows for their construction into physiological and pathological models, enabling the study of skin development and dynamic changes. This review provides an overview of the pivotal work in the progression from 3D layered epidermis to cyst-like skin organoids with appendages. Furthermore, it highlights the latest advancements in organoid construction facilitated by state-of-the-art engineering techniques, such as 3D printing and microfluidic devices. The review also summarizes and discusses the diverse applications of skin organoids in developmental biology, disease modelling, regenerative medicine, and personalized medicine, while considering their prospects and limitations.

Advanced In Vitro Three-Dimensional Skin Models of Atopic Dermatitis

Atopic dermatitis (AD) is one of the most prevalent inflammatory skin diseases that is characterized by eczematous rashes, intense itching, dry skin, and sensitive skin. Although AD significantly impacts the quality of life and the number of patients keeps increasing, its pathological mechanism is still unknown because of its complexity. The importance of developing new in vitro three-dimensional (3D) models has been underlined in order to understand the mechanisms for the development of therapeutics since the limitations of 2D models or animal models have been repeatedly reported. Thus, the new in vitro AD models should not only be created in 3D structure, but also reflect the pathological characteristics of AD, which are known to be associated with Th2-mediated inflammatory responses, epidermal barrier disruption, increased dermal T-cell infiltration, filaggrin down-regulation, or microbial imbalance. In this review, we introduce various types of in vitro skin models including 3D culture methods, skin-on-a-chips, and skin organoids, as well as their applications to AD modeling for drug screening and mechanistic studies.