Microenvironmental reprogramming by three-dimensional culture enables dermal papilla cells to induce de novo human hair-follicle growth. Proc Natl Acad Sci U S A. 2013;110:19679-19688. [PMID: 24145441 DOI: 10.1073/pnas.1309970110]

A Matrix-Derived Bioactive Peptide Enhances Epidermal Thickness and Hair Follicle Neogenesis in Grafted Dermal-Epidermal Composites

Cutaneous wounds can be treated using skin substitutes, but they heal with scarring and absence of skin adnexal structures. We previously demonstrated hair follicle neogenesis in dermal-epidermal composites made of neonatal foreskin human keratinocytes and human dermal papilla cells grafted onto nude mice. A challenge to adapting this approach to graft large areas in humans is that dermal papilla cells lose trichogenicity when expanded in vitro. Herein, a peptide derived from a coiled-coil domain of multimerin-1, TSN6, was evaluated for its effects on graft characteristics and hair follicle formation. In a hair follicle reconstitution assay, TSN6 increased the number of hair fibres by 1.8-fold (p value < 0.05). Dermal-epidermal composites, constructed using late-passage human dermal papilla cells and incubated with TSN6 prior to grafting, retained 14 of 14 grafts for 10-12 weeks, whereas scrambled and vehicle groups kept only 9 of 12 and 13 of 16 grafts, respectively. Histological evaluation of skin grafts showed the presence of human hair follicles in 12 of 14 dermal-epidermal composites in the TSN6 group, 3 of 9 in the scrambled group and 6 of 13 in the vehicle group. The median number and interquartile range of hair follicles was 4.5 (1.8, 10.3) for the TSN6 group, 0 (0, 3.5) for the scrambled group and 0 (0, 3.3) for the vehicle group. TSN6 also increased epidermal thickness, showing a thickness of 127 ± 18 μm for the TSN6 group and 70 ± 28 μm and 94 ± 18 μm for the scrambled and vehicle groups, respectively. In summary, TSN6 increases epidermal thickness and promotes hair follicle neogenesis in a skin substitute.

FGF20 Secreted From Dermal Papilla Cells Regulate the Proliferation and Differentiation of Hair Follicle Stem Cells in Fine-Wool Sheep

Wool traits determine the market value of fine-wool sheep, and wool fibre-breaking elongation (fibres can be stretched or elongated before they break) is one of the important wool traits. The interaction between hair follicle stem cells (HFSCs) and dermal papilla cells (DPCs) determines hair follicle development in fine wool sheep, thereby directly influencing wool traits. A genome-wide association study based on pre-sequencing data identified FGF20, which was significantly associated with wool fibre-breaking elongation. The study reveals that the regulatory mechanism of FGF20 secreted from DPCs affects the proliferation and differentiation of HFSCs through a co-culture system, to provide a new perspective for fine-wool sheep breeding. After knocking down FGF20 expression in DPCs, the results showed that the expression of fibroblast growth factor receptor 2 (FGFR2) and fibroblast growth factor receptor 3 (FGFR3) in DPCs and HFSCs was significantly decreased (p < 0.05), the number of EdU-positive cells and cell viability was significantly decreased (p < 0.01), and the apoptosis rate was significantly increased (p < 0.05). Meanwhile, the differentiation markers of SOX9, NOTCH1 and β-Catenin in HFSCs were also significantly reduced (p < 0.05). These findings indicate that FGF20-knockdown in DPCs of fine-wool sheep inhibits the proliferation and differentiation of HFSCs in the co-culture system, providing a theoretical basis for elucidating the regulatory mechanism of hair follicle self-renewal and differentiation of fine-wool sheep and providing a co-culture system for regenerative medicine.

CD133-positive dermal papilla cells are a major driver in promoting hair follicle formation

A major contributing factor to the failure of cell-based human hair follicle (HF) engineering is our inability to cultivate highly specialized, inductive mesenchymal fibroblasts, which reside in a unique niche at the HF base, called the dermal papilla (DP). We and other groups have discovered a unique DP fibroblast subpopulation that can be identified by the cell surface marker CD133. However, the biological difference between CD133-positive (CD133+) and CD133-negative (CD133-) DP cells remains unknown. Using a newly developed double fluorescent transgenic mouse strain, we isolated CD133 + and CD133- DP cells from mouse anagen HFs. In monolayer culture, both DP populations gradually lost expression of the anagen DP signature gene, versican. When maintained in three-dimensional spheroid culture, versican expression was restored in both CD133 + and CD133- DP cells. Importantly, CD133 + DP spheroids appeared more compact, showed stronger alkaline phosphatase staining (AP), and expressed higher levels of DP signature genes. In in vivo skin reconstitution assays, mice grafted with CD133 + DP spheroids grew more hairs in healed wounds than those grafted with CD133- DP spheroids. The data underscore the importance of CD133 + DP cells as a driver of HF formation, which may present a unique opportunity to improve the use of human DP cells in tissue-engineered skin substitutes (TESS).

Innovative strategies for the discovery of new drugs against androgenetic alopecia

INTRODUCTION

Androgenetic alopecia (AGA) is the most common cause of hair loss worldwide. The significant psychological and social impact of AGA continues to drive demand for more effective treatments beyond the limited options currently available.

AREAS COVERED

The authors review the key components of AGA pathogenesis, as well as current treatments, and therapeutic techniques under development. Innovative strategies for AGA drug discovery are still needed, given the significant unmet medical needs and the limited efficacy of both current and emerging treatments. The authors outline relevant preclinical models, such as hair follicle (HF) cell cultures, 3D spheroids, organoids, follicle explants, and animal models, highlighting their advantages and limitations in AGA research. Finally, they summarize the primary objectives in AGA treatment development, including direct hair growth promotion, interference with androgen signaling, and HF rejuvenation, identifying key pathogenesis intervention points for treatment development.

EXPERT OPINION

Developing better in vitro models, possibly using induced pluripotent stem cell (iPSC) systems, could greatly accelerate drug discovery. Similarly, a superior in vivo model could significantly expedite drug discovery. Near future development research should focus on drug delivery improvements. Longer term, treatments targeting AGA's underlying pathophysiology and promoting HF rejuvenation or true regeneration would provide the most benefit to prospective patients.

Anti-Hair Loss Effect of Veratric Acid on Dermal Papilla Cells

The activation of hair follicle dermal papilla cells (HFDPCs), a critical target of hair loss relief, can be achieved through the upregulation of proliferation, the stimulation of hair inducibility, and the inhibition of cellular senescence. Veratric acid (VA) is a major benzoic acid found in fruits and vegetables. The biological activity of VA on HFDPCs remains to be elucidated. In this study, we investigated the capacity of VA for hair loss mitigation. An MTT assay, Ki67 staining, quantitative RT-PCR (qRT-PCR), and a Western blot analysis were performed to confirm the proliferative effect of VA. Hair inductivity was determined through a cell aggregation assay and ALP staining. Annexin V/PI staining was performed to confirm the anti-apoptotic effect of VA. The inhibitory effect of VA on cellular senescence was confirmed by a β-galactosidase (β-gal) assay and qRT-PCR using replicative senescence and oxidative stress-induced senescence models. As a result, VA dose-dependently upregulated the proliferation of HFDPCs, the expression of growth factors, and β-catenin protein levels. VA also dose-dependently increased ALP activity and cell aggregation and decreased apoptotic cells through the regulation of BCL2 and BAX expression. Moreover, VA reduced β-gal activity and the senescence-associated secretory phenotype (SASP) in a dose-dependent manner in senescent HFDPCs. These findings suggest that VA may serve as a potential therapeutic agent for alleviating hair loss by targeting multiple pathways involved in HFDPC activation.

Rho kinase inhibitor Y-27632 and dual media culture approach promote the construction and transplantation of rabbit limbal epithelial cell sheets via cell spheroid culture and auto-bioprinting

The shortage of corneal donors and the limitations in tissue engineering grafts, such as biocompatibility and mechanical properties, pose significant challenges in corneal transplantation. Here, for the first time, we investigate the effect of Rho kinase inhibitor Y-27632 and a dual media culture approach, including proliferative media (M1) and stabilizing media (M2), on rabbit limbal epithelial stem cells (LESCs), aiming to explore the feasibility of constructing corneal cell sheets in vitro through auto-bioprinting and assessing their corneal wound healing capacity in vivo. Y-27632 has primarily demonstrated significantly enhanced LESCs growth, proliferation, and reduced apoptosis. The dual media culture approach combined with Y-27632 improved LESCs proliferation while maintaining stemness. In spheroid culture, Y-27632 decreased cell death and promoted proliferation. Immunofluorescent staining and RNA sequencing revealed upregulation of genes related to tight junctions and cell adhesion and downregulation of genes associated with aging and cell cycle. Using a bioprinter, LESC spheroids were auto-bioprinted onto a custom-made curved collagen membrane, creating a bioactive, transplantable, tissue-engineered anterior corneal sheet. Anterior superficial corneal transplantation with these LESC sheets significantly accelerated epithelial wound healing in rabbit limbal stem cell deficiency (LSCD) models. Overall, the integration of Y-27632, dual-media culture, and spheroid cell culture led to the development of a highly bioactive and therapeutically promising bio-ink derived from LESCs. Auto-bioprinting these LESC spheroids produced a bioactive, transplantable corneal cell sheet, presenting a promising therapeutic option for LSCD. STATEMENT OF SIGNIFICANCE: The renewal and wound healing of the corneal epithelium are essential for maintaining normal vision and refractive function. Limbal stem cell deficiency (LSCD) is a major cause of blinding keratopathy, and current treatment options are limited. In this study, for the first time, we developed a highly bioactive and therapeutically potent bio-ink for ocular surface regeneration by integrating Y-27632, a dual-media culture approach, and spheroid cell culture. Additionally, using auto-bioprinting technology, the limbal epithelial stem cell (LESC) spheroid bio-ink was precisely auto-bioprinted onto the curved surface of the corneal membrane, significantly accelerating corneal epithelial healing in an LSCD rabbit model.

Direct reprogramming of human fibroblasts into hair-inducing dermal papilla cell-like cells by a single small molecule

Dermal papilla cells (DPCs) are a crucial subset of mesenchymal cells in the skin responsible for regulating hair follicle development and growth, making them invaluable for cell-based therapies targeting hair loss. However, obtaining sufficient DPCs with potent hair-inducing abilities remains a persistent challenge. In this study, the Food and Drug Administration (FDA)-approved drug library was utilized to screen small molecules capable of reprogramming readily accessible human skin fibroblasts into functional DPCs. In the initial screening, five candidate small molecules were identified from a pool of 1,817 compounds, and the small molecule peficitinib was further identified by the further hair follicle regeneration experiments. Following peficitinib treatment, fibroblasts derived from primary human foreskin and scalp exhibited the capability to induce hair growth and possessed a molecular profile highly similar to that of primary DPCs. We refer to these cells as dermal papilla cell-like cells (DPC-LCs). Furthermore, transcriptome analysis showed that the wingless/integrated (Wnt) signaling pathway and the transforming growth factor β (TGF-β) signaling pathway, both of which play crucial roles in hair follicle morphogenesis, are upregulated and enriched in these DPC-LCs. These functional DPC-LCs offer a promising avenue for obtaining a plentiful supply of hair-inducing cells, thereby advancing the development of therapeutic strategies for hair loss treatment.

A comparative proteomic-based study identifies essential factors involved in hair follicle growth in inner Mongolia cashmere goats

Renowned for its invaluable undercoat, the cashmere goat is well known. The growth of cashmere fibre initiates when the relatively inactive telogen stage transitions to the anagen stage, which involves active proliferation. However, the molecular mechanisms responsible for this process are still unclear. Here, SWATH mass spectrometry (MS), a comparative proteomic analysis, was conducted to examine the proteomic alterations in Inner Mongolia cashmere goat skin samples at two different developmental stages (anagen and telogen). In total, 2414 proteins were detected, with 631 proteins showing differential regulation (503 upregulated proteins and 128 downregulated proteins). Bioinformatic analysis revealed that these proteins, which are differentially regulated, play crucial roles in the pathways associated with metabolism and fatty acids according to the GO and KEGG analyses. Furthermore, interactome analysis revealed that differentially regulated keratins have a crucial impact. The localization of KRT25, KRT71, and KRT82 using immunohistochemistry revealed that these proteins were expressed in the secondary hair follicles of cashmere goat skin. The keratin family plays an irreplaceable and important role in the process of hair follicle growth.

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.

Bulge-Derived Epithelial Cells Isolated from Human Hair Follicles Using Enzymatic Digestion or Explants Result in Comparable Tissue-Engineered Skin

Hair follicle stem cells, located in the bulge region of the outer root sheath, are multipotent epithelial stem cells capable of differentiating into epidermal, sebaceous gland, and hair shaft cells. Efficient culturing of these cells is crucial for advancements in dermatology, regenerative medicine, and skin model development. This investigation aimed to develop a protocol for isolating enriched bulge-derived epithelial cells from scalp specimens to produce tissue-engineered substitutes. The epithelium, including hair follicles, was separated from the dermis using thermolysin, followed by microdissection of the bulge region. Epithelial stem cells were isolated using enzymatic dissociation to create a single-cell suspension and compared with the direct explant culture and a benchmark method which isolates cells from the epidermis and pilosebaceous units. After 8 days of culture, the enzymatic digestion of microdissected bulges yielded 5.3 times more epithelial cells compared to explant cultures and proliferated faster than the benchmark method. Cells cultured from all methods exhibited comparable morphology and growth rates. The fully stratified epidermis of tissue-engineered skin was similar, indicating comparable differentiation potential. This enzymatic digestion method improved early-stage cell recovery and expansion while maintaining keratinocyte functionality, offering an efficient hair bulge cell-extraction technique for tissue engineering and regenerative medicine applications.

Pathogenesis and regenerative therapy in vitiligo and alopecia areata: focus on hair follicle

Vitiligo is an autoimmune disease characterized by the loss of functional melanocytes in the hair follicles and epidermis, leading to white patches on the skin and mucous membranes. Alopecia areata (AA) is a common immune-mediated condition in which autoimmune attack on hair follicles cause non-scarring hair loss. Both diseases significantly impact patients's physical and mental health. Hair follicles, dynamic mini-organs, house diverse stem cell populations that form hair structures. Melanocyte stem cell (McSCs) and hair follicle stem cells (HFSC) located in the hair follicle bulge contribute to follicular structures during each anagen phase of the hair cycle, synchronizing periodic activities to impact color to the hair. Hair follicle dysfunction may contribute to hair loss and could potentially interfere with repigmentation efforts in vitiligo lesions. This article reviews the role of hair follicles in the pathogenesis, clinical manifestations, and therapeutic options for vitiligo and AA, aiming to deepen clinicians' understanding of follicular involvement in these diseases and explore potential treatment avenues.

Restoration of hair follicle inductive properties by depletion of senescent cells

Senescent cells secrete a senescence-associated secretory phenotype (SASP), which can induce senescence in neighboring cells. Human dermal papilla (DP) cells lose their original hair inductive properties when expanded in vitro, and rapidly accumulate senescent cells in culture. Protein and RNA-seq analysis revealed an accumulation of DP-specific SASP factors including IL-6, IL-8, MCP-1, and TIMP-2. We found that combined senolytic treatment of dasatinib and quercetin depleted senescent cells, and reversed SASP accumulation and SASP-mediated repressive interactions in human DP culture, resulting in an increased Wnt-active cell population. In hair reconstitution assays, senolytic-depleted DP cells exhibited restored hair inductive properties by regenerating de novo hair follicles (HFs) compared to untreated DP cells. In 3D skin constructs, senolytic-depleted DP cells enhanced inductive potential and hair lineage specific differentiation of keratinocytes. These data revealed that senolytic treatment of cultured human DP cells markedly increased their inductive potency in HF regeneration, providing a new rationale for clinical applications of senolytic treatment in combination with cell-based therapies.

High-Throughput Screening of 3-Dimensional Co-culture Hair Follicle Mimetic Tissue with an Enhanced Extracellular Matrix for the Screening of Hair Growth-Promoting Compounds

Hair follicle cells reside within a complex extracellular matrix (ECM) environment in vivo, where physical and chemical cues regulate their behavior. The ECM is crucial for hair follicle development and regeneration, particularly through epithelial-mesenchymal interactions. Current in vitro models often fail to replicate this complexity, leading to inconsistencies in evaluating hair loss treatments. Advanced 3-dimensional (3D) culture systems that better mimic in vivo ECM dynamics are needed for more effective therapeutic assessments. Here, we introduce a 3D co-culture system designed to replicate in vivo ECM dynamics. The system incorporates primary dermal papilla cells from human patients, co-cultured with neonatal keratinocytes. This platform facilitates uniform spheroid formation through cell sliding and aggregation, enabling the evaluation of approximately 60 spheroids per well. The model is optimized for high-throughput screening, allowing precise assessments of hair-loss-inducing compounds under consistent conditions. We successfully generated dermal papilla cell and keratinocyte spheroids that closely resemble the native ECM structure, providing an optimal microenvironment for studying hair follicle biology. The 3D co-culture model supported efficient spheroid formation with consistent cellular organization and polarization, along with enhanced ECM-related gene expression crucial for hair follicle regeneration. Uniform spheroid formation and reproducibility were demonstrated across experiments. Overall, the novel 3D co-culture system provides a robust platform for replicating in vivo-like ECM conditions, enabling effective assessment of potential hair loss treatments through epithelial-mesenchymal interactions. Its high-throughput capacity, combined with reproducibility and ease of use, makes it a valuable tool for screening therapeutic candidates and advancing hair loss treatment development.

Hair Regeneration Methods Using Cells Derived from Human Hair Follicles and Challenges to Overcome

The hair follicle is a complex of mesenchymal and epithelial cells acquiring different properties and characteristics responsible for fulfilling its inductive and regenerative role. The epidermal and dermal crosstalk induces morphogenesis and maintains hair follicle cycling properties. The hair follicle is enriched with pluripotent stem cells, where dermal papilla (DP) cells and dermal sheath (DS) cells constitute the dermal compartment and the epithelial stem cells existing in the bulge region exert their regenerative role by mediating the epithelial-mesenchymal interaction (EMI). Many studies have developed and focused on various methods to optimize the EMI through in vivo and in vitro approaches for hair regeneration. The culturing of human hair mesenchymal cells resulted in the loss of trichogenicity and inductive properties of DP cells, limiting their potential application in de novo hair follicle generation in vivo. Epithelial stem cells derived from human hair follicles are challenging to isolate and culture, making it difficult to obtain enough cells for hair regeneration purposes. Mesenchymal stem cells and epithelial stem cells derived from human hair follicles lose their ability to form hair follicles during culture, limiting the study of hair follicle formation in vivo. Therefore, many attempts and methods have been developed to overcome these limitations. Here, we review the possible and necessary cell methods and techniques used for human hair follicle regeneration and the restoration of hair follicle cell inductivity in culture.

Materials-based hair follicle engineering: Basic components and recent advances

The hair follicle (HF) is a significant skin appendage whose primary function is to produce the hair shaft. HFs are a non-renewable resource; skin damage or follicle closure may lead to permanent hair loss. Advances in biomaterials and biomedical engineering enable the feasibility of manipulating the HF-associated cell function for follicle reconstruction via rational design. The regeneration of bioengineered HF addresses the issue of limited resources and contributes to advancements in research and applications in hair loss treatment, HF development, and drug screening. Based on these requirements, this review summarizes the basic and recent advances in hair follicle regulation, including four components: acquisition of stem cells, signaling pathways, materials, and engineering methods. Recent studies have focused on efficiently combining these components and reproducing functionality, which would boost fabrication in HF rebuilding ex vivo, thereby eliminating the obstacles of transplantation into animals to promote mature development.

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.

Application of multi-omics techniques to androgenetic alopecia: Current status and perspectives

The rapid advancement of sequencing technologies has enabled the generation of vast datasets, allowing for the in-depth analysis of sequencing data. This analysis has facilitated the validation of novel pathogenesis hypotheses for understanding and treating diseases through ex vivo and in vivo experiments. Androgenetic alopecia (AGA), a common hair loss disorder, has been a key focus of investigators attempting to uncover its underlying mechanisms. Abnormal changes in mRNA, proteins, and metabolites have been identified in individuals with AGA, and future developments in sequencing technologies may reveal new biomarkers for AGA. By integrating multiple omics analysis datasets such as genomics, transcriptomics, proteomics, and metabolomics-along with clinical phenotype data-we can achieve a comprehensive understanding of the molecular underpinnings of AGA. This review summarizes the data-mining studies conducted on various omics analysis datasets as related to AGA that have been adopted to interpret the biological data obtained from different omics layers. We herein discuss the challenges of integrative omics analyses, and suggest that collaborative multi-omics studies can enhance the understanding of the complete pathomechanism(s) of AGA by focusing on the interaction networks comprising DNA, RNA, proteins, and metabolites.

Force-triggered density gradient sedimentation and cocktail enzyme digestion treatment for isolation of single dermal papilla cells from follicular unit extraction harvesting human hair follicles

BACKGROUND

Hair follicles (HFs) are dynamic structures which are readily accessible within the skin that contain various pools of stem cells with broad regenerative potential, such as dermal papilla cells (DPCs), dermal sheath cells, and epithelial HF stem cells. DPCs act as signalling centres for HF regeneration. The current method for isolating human DPCs are inefficient. These methods struggle to obtain freshly isolated original DPCs and do not maintain the characteristics of DPCs effectively.

METHODS

In this study, two simple but more efficient methods were explored. Force-triggered density gradient sedimentation (FDGS) and cocktail enzyme digestion treatment (CEDT) were used to isolate purified DP spheres from human HFs, obtaining purified freshly isolated original DPCs from DP spheres. The expression profiles of isolated DPCs were tested, and gene expression of DPC-specific markers were analyzed using immunofluorescence staining, RT-qPCR and western blot.

RESULTS

The 10% Ficoll PM400 was determined as the optimal concentration for FDGS method. Primary DPCs, DSCs and HFSCs were isolated simultaneously using the FDGS and CEDT method. The expression profiles of fresh DPCs isolated using the FDGS and CEDT methods were similar to those of traditionally isolated DPCs. DP-specific markers were expressed at significantly higher levels in freshly isolated DPCs than in traditionally isolated DPCs.

CONCLUSIONS

Compared to traditional methods, the presented laboratory protocols were able to isolate fresh DPCs with high efficiency, thereby improving their research potential.

Generating Skin-Derived Precursor-Like Cells From Human-Induced Pluripotent Stem Cell-Derived Skin Organoids

Skin-derived precursor (SKPs) cells are multipotent stem cells found in the dermis that contribute to wound healing and induce hair follicle neogenesis when transplanted. The clinical application of adult human SKPs, however, is hindered by their loss of potency after in vitro expansion. To overcome this challenge, we aimed to isolate SKPs from human-induced pluripotent stem cell-derived skin organoids (SKOs), to enable mass production of these cells for therapeutics. We developed a protocol to isolate skin-derived precursor-like cells (SKP-like cells) from human SKOs. SKP-like cells derived from SKOs exhibited characteristic spheroid morphology and were capable of self-renewal in defined SKP growth medium. Immunofluorescence analysis confirmed the expression of key markers, including SOX2, fibronectin and S100β, within the SKP-like cells. The findings of this pilot study shed light on the potential of SKO-derived SKP-like cells for future hair regenerative applications. Furthermore, this research highlights the application of human SKOs as a valuable source for isolating progenitor cells, aiming to advance hair regeneration and restore skin function.

Dermal Papilla Cells: From Basic Research to Translational Applications

As an appendage of the skin, hair protects against ultraviolet radiation and mechanical damage and regulates body temperature. It also reflects an individual's health status and serves as an important method of expressing personality. Hair loss and graying are significant psychosocial burdens for many people. Hair is produced from hair follicles, which are exclusively controlled by the dermal papilla (DP) at their base. The dermal papilla cells (DPCs) comprise a cluster of specialized mesenchymal cells that induce the formation of hair follicles during early embryonic development through interaction with epithelial precursor cells. They continue to regulate the growth cycle, color, size, and type of hair after the hair follicle matures by secreting various factors. DPCs possess stem cell characteristics and can be cultured and expanded in vitro. DPCs express numerous stemness-related factors, enabling them to be reprogrammed into induced pluripotent stem cells (iPSCs) using only two, or even one, Yamanaka factor. DPCs are an important source of skin-derived precursors (SKPs). When combined with epithelial stem cells, they can reconstitute skin and hair follicles, participating in the regeneration of the dermis, including the DP and dermal sheath. When implanted between the epidermis and dermis, DPCs can induce the formation of new hair follicles on hairless skin. Subcutaneous injection of DPCs and their exosomes can promote hair growth. This review summarizes the in vivo functions of the DP; highlights the potential of DPCs in cell therapy, particularly for the treatment of hair loss; and discusses the challenges and recent advances in the field, from basic research to translational applications.

Identification of Key Proteins Related to Cashmere Fiber Diameter by Integrated Proteomics and Bioinformatic Analyses in the Alpas and Alxa Goat Breeds

BACKGROUND

Goats (Capra hircus) have always been a source of fiber for human use and hold an important place in international high-end textiles. Fiber diameter is the most concerning economic indicator for producers. Understanding the formation mechanism of fiber diameter and its related key proteins can help optimize and control the production of cashmere.

METHODS

Cashmere goats (n = 36) of the Alpas (n = 18) and Alxa (n = 18) breeds, with a similar age (2 years old) and live weight (25-26 kg), were selected from the Yiwei White Cashmere Goat Breeding Farm, Erdos, Inner Mongolia. Using phenotypic indicators, we evaluated the diameter of the cashmere fibers in Alxa and Alpas goats. We also used electron microscopy to examine the cashmere fiber's structure and label-free liquid chromatography-tandem mass spectrometry to determine the protein content of the two cashmere fibers. The proteins affecting fiber diameter were identified and analyzed by Western blot, Co-Immunoprecipitation, and bioinformatics analysis.

RESULTS

The average diameter of the Alxa breed was smaller (p < 0.05) than that of the Alpas breed (Alxa's cashmere vs. Alpas' cashmere). Proteomics technology enabled the highly confident detection of 171 proteins. A total of 68 differentially expressed proteins were identified in the two types of cashmere; 131 proteins were specifically expressed in Alpas goats, and 40 proteins were specifically expressed in Alxa goats. A key protein group that could cause variations in fiber diameter was found using the protein-protein interaction network. To ascertain the reason for the variation in fiber diameter, a structural study of the major protein groups was carried out.

CONCLUSIONS

KRT10, KRT14, KRT17, and KRT82 are the main proteins impacting the diameter difference, and they have a substantial effect on the average fiber diameter.

The efficacy of adipose stem cell-derived exosomes in hair regeneration based on a preclinical and clinical study

BACKGROUND

Androgenetic alopecia (AGA) is a prevalent hair loss disorder with psychological repercussions. Traditional treatments have limitations, leading to the exploration of regenerative therapies such as exosomes derived from adipose tissue stem cells (ASC-Exosomes).

METHODS

First, using human hair follicle (HF) dermal papilla cells (hDPCs) treated with ASC-Exosomes, ALP, VCAN, β-catenin, and LEF-1 levels with RT-PCR and p-GSK3β, GSK3β, β-catenin, ALP, and β-actin levels with western blot analysis were assessed. Hair shaft elongation test and assay for ALP, Ki-67, and β-catenin were done using human HF organ culture. Patients with AGA had ASC-Exosomes treatment and were evaluated for hair counts, photographic assessments, subjective satisfaction, and safety profiles.

RESULTS

ASC-Exosomes impact hDPCs, increasing proliferation and the upregulation of hair growth-related genes, including ALP, VCAN, β-catenin, and LEF-1. The Wnt/β-catenin pathway was activated, indicating their role in promoting hair growth. ASC-Exosomes also promoted hair shaft elongation and ALP activity, suggesting a potential for hair regeneration. Thirty participants with AGA enrolled and treated over 24 weeks. The subjects experienced a significant increase in total hair density, improved global photographic assessments, and reported higher subjective satisfaction without severe adverse reactions.

CONCLUSION

This research contributes to the growing body of evidence supporting the use of exosomes in hair loss treatment, offering a safe and effective alternative for individuals with AGA.

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.

FGF7 and FGF10 Promote Fate Transition of Human Epidermal Cell-derived Organoids to an Eccrine Gland Phenotype

Rationale: Reconstruction of hair follicles (HFs) and eccrine sweat glands (ESGs) is essential for functional skin regeneration. In skin reconstruction research, we found that foreskin-derived epidermal cells reconstructed HF organoids unidirectionally, but not ESG organoids. Methods: To investigate key genes and pathways influencing the fate of ESG and HF, a transcriptome profiling of ESG placode-containing skin and HF placode-containing skin was employed, and key DEGs were identified and validated by RT-qPCR and immunofluorescence staining in mice and rats. Subsequently, adult human epidermal cell-derived organoids were reconstructed to probe functional roles and mechanisms of FGF7 and FGF10 by series of approaches integrating RT-qPCR, immunofluorescence-staining, WB, apoptosis assay, and pathway interference assay. Results: All members of FGF7 subfamily were among the key DEGs screened, the differential expression of FGF7 and FGF10 and their receptors FGFR1/FGFR2 was verified between ESG placode-containing skin and HF placode-containing skin. In vivo and in vitro Matrigel plug models showed that both FGF7 and FGF10 promoted fate transition of human epidermal cell-derived organoids to ESG phenotype organoids, FGF7 and FGF10 had a synergistic effect, and mainly function through the FGFR1/2-MEK1/2-ERK1/2 pathway. Conclusions: Adult epidermal cells can be manipulated to reconstruct personalized HF and ESG to meet different needs.

A biopsy-sized 3D skin model with a perifollicular vascular plexus enables studying immune cell trafficking in the skin

Human skin vasculature features a unique anatomy in close proximity to the skin appendages and acts as a gatekeeper for constitutive lymphocyte trafficking to the skin. Approximating such structural complexity and functionality in 3D skin models is an outstanding tissue engineering challenge. In this study, we leverage the capabilities of the digital-light-processing bioprinting to generate an anatomically-relevant and miniaturized 3D skin-on-a-chip (3D-SoC) model in the size of a 6 mm punch biopsy. The 3D-SoC contains a perfusable vascular network resembling the superficial vascular plexus of the skin and closely surrounding bioengineered hair follicles. The perfusion capabilities of the 3D-SoC enables the circulation of immune cells, and high-resolution imaging of the immune cell-endothelial cell interactions, namely tethering, rolling, and extravasation in real-time. Moreover, the vascular pattern in 3D-SoC captures the physiological range of shear rates found in cutaneous blood vessels and allows for studying the effect of shear rate on T cell trafficking. In 3D-SoC, as expected,in vitro-polarized T helper 1 (Th1) cells show a stronger attachment on the vasculature compared to naïve T cells. Both naïve and T cells exhibit higher retention in the low-shear zones in the early stages (<5 min) of T cell attachment. Interestingly, at later stages T cell retention rate becomes independent of the shear rate. The attached Th1 cells further transmigrate from the vessel walls to the extracellular space and migrate toward the bioengineered hair follicles and interfollicular epidermis. When the epidermis is not present, Th1 cell migration toward the epidermis is significantly hindered, underscoring the role of epidermal signals on T cell infiltration. Our data validates the capabilities of 3D-SoC model to study the interactions between immune cells and skin vasculature in the context of epidermal signals. The biopsy-sized 3D-SoC model in this study represents a new level of anatomical and cellular complexity, and brings us a step closer to generating a truly functional human skin with its tissue-specific vasculature and appendages in the presence of circulating immune cells.

Triethylene Glycol Squalene Improves Hair Regeneration by Maintaining the Inductive Capacity of Human Dermal Papilla Cells and Preventing Premature Aging

De novo hair follicle (HF) regeneration, achieved through the replenishment of the dermal papilla (DP), acknowledged as the principal orchestrator of the hair growth cycle, is emerging as a prospective therapeutic intervention for alopecia. Nonetheless, multiple attempts have shown that these cells lose key inductive properties when cultured in a two-dimensional (2D) monolayer, leading to precocious senescence engendered by oxidative stress and inflammatory processes. Consequently, the three-dimensional (3D) spheroid technique is presently widely employed for DP cell culture. Nevertheless, substantiating the regenerative potential of these cells within the hair follicle (HF) milieu remains a challenge. In this current study, we aim to find a new approach to activate the inductive properties of DP cells. This involves the application of hair-growth-stimulating agents that not only exhibit concurrent protective efficacy against the aging process but also induce HF regeneration. To achieve this objective, we initially synthesized a novel highly amphiphilic derivative derived from squalene (SQ), named triethylene glycol squalene (Tri-SQ). Squalene itself is a potent antioxidant and anti-inflammatory compound traditionally employed as a drug carrier for alopecia treatment. However, its application is limited due to its low solubility. Subsequently, we applied this newly synthesized derivative to DP cells. The data obtained demonstrated that the derivative exhibits robust antioxidant and anti-inflammatory activities while concurrently promoting the expression of genes associated with hair growth. Moreover, to further assess the hair regrowth inductive properties of DP cells, we cultured the cells and treated them with Tri-SQ within a 3D spheroid system. Subsequently, these treated cells were injected into the previously depilated dorsal area of six-week-old male C57BL/6 mice. Results revealed that 20 days postinjection, a complete regrowth of hair in the previously hairless area, particularly evident in the case of 3D spheroids treated with the derivative, was observed. Additionally, histological and molecular analyses demonstrated an upregulation of markers associated with hair growth and a concurrent decrease in aging hallmarks, specifically in the 3D spheroids treated with the compound. In summary, our approach, which involves the treatment of Tri-SQ combined with a 3D spheroid system, exhibited a notably robust stimulating effect. This effect was observed in the induction of inductive properties in DP cells, leading to HF regeneration, and concurrently, it demonstrated an inhibitory effect on cellular and follicular aging.

Single-Cell and Spatial Transcriptome Analysis of Dermal Fibroblast Development in Perinatal Mouse Skin: Dynamic Lineage Differentiation and Key Driver Genes

Several single-cell RNA studies of developing mouse skin have elucidated the molecular and cellular processes involved in skin development. However, they have primarily focused on either the fetal or early postnatal period, leaving a gap in our understanding of skin development. In this study, we conducted a comprehensive time-series analysis by combining single-cell RNA-sequencing datasets collected at different stages of development (embryonic days 13.5, 14.5, and 16.5 and postnatal days 0, 2, and 4) and validated our findings through multipanel in situ spatial transcriptomics. Our analysis indicated that embryonic fibroblasts exhibit heterogeneity from a very early stage and that the rapid determination of each lineage occurs within days after birth. The expression of putative key driver genes, including Hey1, Ebf1, Runx3, and Sox11 for the dermal papilla trajectory; Lrrc15 for the dermal sheath trajectory; Zfp536 and Nrn1 for the papillary fibroblast trajectory; and Lrrn4cl and Mfap5 for the fascia fibroblast trajectory, was detected in the corresponding, spatially identified cell types. Finally, cell-to-cell interaction analysis indicated that the dermal papilla lineage is the primary source of the noncanonical Wnt pathway during skin development. Together, our study provides a transcriptomic reference for future research in the field of skin development and regeneration.

Materiobiomodulated ROS Therapy for De Novo Hair Growth

Hair loss is characterized by the inability of hair follicles (HFs) to enter the telogen-anagen transition (TAT) and lack of de novo HFs. Current pharmaceutical therapies and surgical modalities have been largely limited to regulating hair regrowth efficiently without side effects and lacking treatment compliance. Here, this work proposes a materiobiomodulation therapy (MBMT), wherein polydopamine (PDA) nanoparticles with redox activity can be modulated to have a stoichiometric ROS (H2O2) donating ability. These nanoparticles can intracellularly deliver ROS with high-efficiency via the clathrin-dependent endocytosis process. Utilizing homozygote transgenic HyPerion (a genetically-encoded H2O2 biosensor) mice, this work also achieves in vivo dynamic monitoring of intracellular H2O2 elevation induced by ROS donators. Subcutaneous administration with ROS donators results in rapid onset of TAT and subsequent hair regrowth with a specific ROS "hormesis effect." Mechanistically, ROS activate β-catenin-dependent Wnt signaling, upregulating hair follicle stem cell expression. This work further develops a microneedles patch for transdermal ROS delivery, demonstrating long-term, low-dose ROS release. Unlike photobiomodulation therapy (PBMT), MBMT requires no external stimuli, providing a convenient and efficient approach for clinical hair loss treatment. This material-HF communication implicates new avenues in HF-related diseases, achieving targeted ROS delivery with minimal side effects.

Three-dimensional bioprinting of tissue-engineered skin: Biomaterials, fabrication techniques, challenging difficulties, and future directions: A review

As an emerging new manufacturing technology, Three-dimensional (3D) bioprinting provides the potential for the biomimetic construction of multifaceted and intricate architectures of functional integument, particularly functional biomimetic dermal structures inclusive of cutaneous appendages. Although the tissue-engineered skin with complete biological activity and physiological functions is still cannot be manufactured, it is believed that with the advances in matrix materials, molding process, and biotechnology, a new generation of physiologically active skin will be born in the future. In pursuit of furnishing readers and researchers involved in relevant research to have a systematic and comprehensive understanding of 3D printed tissue-engineered skin, this paper furnishes an exegesis on the prevailing research landscape, formidable obstacles, and forthcoming trajectories within the sphere of tissue-engineered skin, including: (1) the prevalent biomaterials (collagen, chitosan, agarose, alginate, etc.) routinely employed in tissue-engineered skin, and a discerning analysis and comparison of their respective merits, demerits, and inherent characteristics; (2) the underlying principles and distinguishing attributes of various current printing methodologies utilized in tissue-engineered skin fabrication; (3) the present research status and progression in the realm of tissue-engineered biomimetic skin; (4) meticulous scrutiny and summation of the extant research underpinning tissue-engineered skin inform the identification of prevailing challenges and issues.

Chromatin accessibility profiling reveals that human fibroblasts respond to mechanical stimulation in a cell-specific manner

Fibroblasts in the skin are highly heterogeneous, both in vivo and in vitro. One difference between follicular (dermal papilla fibroblasts [DP]) and interfollicular fibroblasts (papillary fibroblasts [PFi]) in vitro is their ability to differentiate in response to osteogenic media (OM), or mechanical stimulation. Here, we asked whether differences in the ability of DP and PFi to respond to differentiation stimuli are due to differences in chromatin accessibility. We performed chromatin accessibility and transcriptional profiling of DP and PFi in human skin, which arise from a common progenitor during development, yet display distinct characteristics in adult tissue and in vitro. We found that cells cultured in growth media had unique chromatin accessibility profiles; however, these profiles control similar functional networks. Upon introduction of a chemical perturbation (OM) to promote differentiation, we observed a divergence not only in the accessible chromatin signatures but also in the functional networks controlled by these signatures. The biggest divergence between DP and PFi was observed when we applied 2 perturbations to cells: growth in OM and mechanical stimulation (a shock wave [OMSW]). DP readily differentiate into bone in OMSW conditions, while PFi lack differentiation capability in vitro. In the DP we found a number of uniquely accessible promoters that controlled osteogenic interaction networks associated with bone and differentiation functions. Using ATAC-seq and RNA-seq we found that the combination of 2 stimuli (OMSW) could result in significant changes in chromatin accessibility associated with osteogenic differentiation, but only within the DP (capable of osteogenic differentiation). De novo motif analysis identified enrichment of motifs bound by the TEA domain (TEAD) family of transcription factors, and inter-cell comparisons (UpSet analysis) displayed large groups of genes to be unique to single cell types and conditions. Our results suggest that these 2 stimuli (OMSW) elicit cell-specific responses by modifying chromatin accessibility of osteogenic-related gene promoters.

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.

The promising prospect of human hair follicle regeneration in the shadow of new tissue engineering strategies

Hair loss disorder (alopecia) affects numerous people around the world. The low effectiveness and numerous side effects of common treatments have prompted researchers to investigate alternative and effective solutions. Hair follicle (HF) bioengineering is the knowledge of using hair-inductive (trichogenic) cells. Most bioengineering-based approaches focus on regenerating folliculogenesis through manipulation of regulators of physical/molecular properties in the HF niche. Despite the high potential of cell therapy, no cell product has been produced for effective treatment in the field of hair regeneration. This problem shows the challenges in the functionality of cultured human hair cells. To achieve this goal, research and development of new and practical approaches, technologies and biomaterials are needed. Based on recent advances in the field, this review evaluates emerging HF bioengineering strategies and the future prospects for the field of tissue engineering and successful HF regeneration.

Optimization of hair follicle spheroids for hair-on-a-chip

Currently, most models for hair follicle research have the limitation of not replicating some key features of the hair follicle microenvironment. To complement this, we transfected various factors for hair growth into dermal papilla cells (DPCs) by electroporation and cultured the spheroids with keratinocytes (KCs). We optimized the cell number and culture period for applying spheroids to hair-on-a-chip. Furthermore, we investigated the expression of hair growth factors in spheroids depending on the presence or absence of human umbilical vein endothelial cells (HUVECs) and transfection. In spheroids in which DPCs, KCs, and HUVECs were co-cultured for 21 days, the expression of lymphoid enhancer factor 1 (LEF1), T-cell factor 1 (TCF1), and keratin 25 (K25) in the center of the spheroid, the expression of keratin 17 (K17) on the outer surface of the spheroid, and the shape of hair extending outward from the spheroid surface were observed. From these results, it is expected that a hair-on-a-chip experiment in which short-term cultured TKH spheroids are injected into the dermis and co-cultured with KC will enable the production of full-thickness skin equivalents containing hair in vitro without transplantation into animals.

Keratin Microspheres as Promising Tool for Targeting Follicular Growth

Skin is the body barrier that constrains the infiltration of particles and exogenous aggression, in which the hair follicle plays an important role. Recent studies have shown that small particles can penetrate the skin barrier and reach the hair follicle, making them a potential avenue for delivering hair growth-related substances. Interestingly, keratin-based microspheres are widely used as drug delivery carriers in various fields. In this current study, we pursue the effect of newly synthesized 3D spherical keratin particles on inducing hair growth in C57BL/6 male mice and in human hair follicle dermal papilla cells. The microspheres were created from partially sulfonated, water-soluble keratin. The keratin microspheres swelled in water to form spherical gels, which were used for further experiments. Following topical application for a period of 20 days, we observed a regrowth of hair in the previously depleted area on the dorsal part of the mice in the keratin microsphere group. This observation was accompanied by the regulation of hair-growth-related pathways as well as changes in markers associated with epidermal cells, keratin, and collagen. Interestingly, microsphere keratin treatment enhanced the cell proliferation and the expression of hair growth markers in dermal papilla cells. Based on our data, we propose that 3D spherical keratin has the potential to specifically target hair follicle growth and can be employed as a carrier for promoting hair growth-related agents.

Applications, advancements, and challenges of 3D bioprinting in organ transplantation

To date, organ transplantation remains an effective method for treating end-stage diseases of various organs. In recent years, despite the continuous development of organ transplantation technology, a variety of problems restricting its progress have emerged one after another, and the shortage of donors is at the top of the list. Bioprinting is a very useful tool that has huge application potential in many fields of life science and biotechnology, among which its use in medicine occupies a large area. With the development of bioprinting, advances in medicine have focused on printing cells and tissues for tissue regeneration and reconstruction of viable human organs, such as the heart, kidneys, and bones. In recent years, with the development of organ transplantation, three-dimensional (3D) bioprinting has played an increasingly important role in this field, giving rise to many unsolved problems, including a shortage of organ donors. This review respectively introduces the development of 3D bioprinting as well as its working principles and main applications in the medical field, especially in the applications, and advancements and challenges of 3D bioprinting in organ transplantation. With the continuous update and progress of printing technology and its deeper integration with the medical field, many obstacles will have new solutions, including tissue repair and regeneration, organ reconstruction, etc., especially in the field of organ transplantation. 3D printing technology will provide a better solution to the problem of donor shortage.

In vitro hair growth-promoting effect of Lgr5-binding octapeptide in human primary hair cells

BACKGROUND

Hair loss occurs due to various biological and environmental causes, which can have psychosocial consequences. The Wnt/β-catenin signaling is well-known for its role in hair growth and regeneration, as it induces the proliferation and differentiation of hair cells. When the leucine-rich G protein-coupled receptor 5 (Lgr5) interacts with the R-spondins, the frizzled receptor (FZD), a Wnt receptor, becomes stabilized, resulting in an increased β-catenin activity.

AIM

We investigated whether the octapeptide that binds to Lgr5 enhances proliferation and differentiation of human primary hair cells through the activation of Wnt/β-catenin signaling.

METHODS

The binding affinity of the octapeptide to Lgr5 was evaluated using surface plasmon resonance (SPR). We confirmed changes in proliferation and related factors like β-catenin activation and growth factors (GFs) expression in human hair follicle dermal papilla cells (HHFDPCs). Additionally, we observed the proliferation and the expression of differentiation markers in human hair follicle outer root sheath cells (HHFORSCs), human hair follicle germinal matrix cells (HHFGMCs), and human hair follicle stem cells (HHFSCs). We used three-dimensional HHFDPC spheroid culture treated with dihydrotestosterone (DHT) to create in vitro conditions that mimic androgenetic alopecia, and we studied the effects of octapeptide on Wnt expression and HHFSC differentiation.

RESULTS

The binding of the octapeptide to Lgr5 was confirmed using SPR analysis. In HHFDPCs, treatment with octapeptide resulted in a concentration-dependent increase in proliferation. We also observed increased nuclear translocation of β-catenin and increased expression of its downstream targets. HHFDPCs treated with octapeptide exhibited increased expression of growth factors and phosphorylation of Akt and ERK. In addition, we confirmed that octapeptide increased proliferation and induced differentiation in HHFORSCs, HHFGMCs, and HHFSCs. Under the HHFDPC spheroid culture conditions, we found that octapeptide restored the inhibition of Wnt-5a and Wnt-10b expressions by DHT. In HHFSCs treated with HHFDPC spheroid culture media, we observed that octapeptide recovered the inhibition of differentiation by DHT.

CONCLUSION

We found that octapeptides activated the Wnt/β-catenin signaling and induced the proliferation and differentiation of human primary hair cells by acting as an exogenous ligand for Lgr5. In addition, octapeptides recovered inhibited hair regeneration characters by DHT in androgenetic alopecia-mimic in vitro model. These findings suggest that octapeptides may be a promising therapeutic option for treating hair loss.

Dermal papilla cells cultured as spheres improve angiogenesis

Tissue-engineered skin represents a helpful strategy for the treatment of deep skin injuries. Nevertheless, these skin substitutes must promote and encourage proper vascularization for a successful graft take. Previous work showed that dermal papilla cells (DPC) favour an earlier neovascularization process of grafted skin substitute contributing to the rapid maturation of the neovascular network, reducing inflammation and favouring extracellular matrix remodelling in nude mice. Based on these results, we studied the influence of DPC and its culture conditions on the different stages of angiogenesis in in vitro models. Here, we showed that DPC cultured as spheres favour the expression of angiogenic factors such as VEGF, FGF2 and angiogenin compared to their monolayer culture. To study the effects of DPC on the different stages of angiogenesis, an in vitro model has been adapted. DPC cultured as spheres significantly enhanced HUVEC migration and tubule formation, indicating the importance of employing physiological culture systems that provide a closer representation of cell behaviour and interactions occurring in vivo. Overall, these results allow us to speculate that the use of DPC spheres in skin substitutes could promote its grafting, vascularization and vascular network maturation through the secretion of angiogenic factors. This approach has great potential to improve clinical outcomes in regenerative medicine and skin wound repair.

The development of anin vitrohuman hair follicle organoid with a complexity similar to thatin vivo

In vitrohair follicle (HF) models are currently limited toex vivoHF organ cultures (HFOCs) or 2D models that are of low availability and do not reproduce the architecture or behavior of the hair, leading to poor screening systems. To resolve this issue, we developed a technology for the construction of a humanin vitrohair construct based on the assemblage of different types of cells present in the hair organ. First, we demonstrated that epithelial cells, when isolatedin vitro, have similar genetic signatures regardless of their dissection site, and their trichogenic potential is dependent on the culture conditions. Then, using cell aggregation techniques, 3D spheres of dermal papilla (DP) were constructed, and subsequently, epithelial cells were added, enabling the production and organization of keratins in hair, similar to what is seenin vivo. These reconstructed tissues resulted in the following hair compartments: K71 (inner root-sheath), K85 (matrix region), K75 (companion layer), and vimentin (DP). Furthermore, the new hair model was able to elongate similarly toex vivoHFOC, resulting in a shaft-like shape several hundred micrometers in length. As expected, when the model was exposed to hair growth enhancers, such as ginseng extract, or inhibitors, such as TGF-B-1, significant effects similar to thosein vivowere observed. Moreover, when transplanted into skin biopsies, the new constructs showed signs of integration and hair bud generation. Owing to its simplicity and scalability, this model fully enables high throughput screening of molecules, which allows understanding of the mechanism by which new actives treat hair loss, finding optimal concentrations, and determining the synergy and antagonism among different raw materials. Therefore, this model could be a starting point for applying regenerative medicine approaches to treat hair loss.

Large-Scale Preparation of Hair Follicle Germs Using a Microfluidic Device

Hair follicle morphogenesis during embryonic development is driven by the formation of hair follicle germs (HFGs) via interactions between epithelial and mesenchymal cells. Bioengineered HFGs are potential tissue grafts for hair regenerative medicine because they can replicate interactions and hair follicle morphogenesis after transplantation. However, a mass preparation approach for HFGs is necessary for clinical applications, given that thousands of de novo hair follicles are required to improve the appearance of a single patient with alopecia. In this study, we developed a microfluidics-based approach for the large-scale preparation of HFGs. A simple flow-focusing microfluidic device allowed collagen solutions containing epithelial and mesenchymal cells to flow and generate collagen microbeads with distinct Janus structures. During the 3 days of culture, the collagen beads contracted owing to cellular traction forces, resulting in collagen- and cell-dense HFGs. The transplantation of HFGs into nude mice resulted in highly efficient de novo hair follicle regeneration. This method provides a scalable and robust tissue graft preparation approach for hair regeneration.

Expansion of Human Dermal Papilla Cells for Clinical Applications Using Human Platelet-rich Plasma as a Substitute for Fetal Bovine Serum

Context

Cell expansion for clinical cell culture often involves the use of fetal bovine serum (FBS). Recently, human platelet-rich plasma (hPRP) was suggested as an FBS substitute, to minimize the risk of transmission of various pathogens and immunogenic reactions. However, whether hPRP can replace FBS for the expansion of human dermal papilla cells (hDPCs) remains controversial.

Aims

To assess the potential of hPRP as a substitute for FBS in hDPC expansion, we investigated the effect of hPRP on hDPC expansion.

Materials and Methods

We first standardized the method of hPRP preparation, and then investigated the effect of hPRP on the proliferation and hair-inductive capacity of cultured hDPCs by comparing with that of FBS. To prepare hPRP, we used heparin as the anticoagulant, with purification by single-spin centrifugation, and freeze-thaw hPRP activation.

Results

Compared with an FBS-supplemented medium, hPRP supplementation significantly shortened the population doubling time of cultured hDPCs, and increased the ratio of bromodeoxyuridine-labeled proliferating cells. Expression of the alkaline phosphatase gene related to hair-inductive capacity was enhanced in hDPCs cultured in an hPRP-supplemented medium. In vivo hair follicle reconstitution assay confirmed that hPRP supplementation enhanced the hair-inductive capacity of hDPCs compared with an FBS-supplemented medium, based on the increased number of regenerated hair follicles and their maturity. Overall, compared with FBS, hPRP enhanced the proliferation of hDPCs, while preserving their hair-inductive capacity.

Conclusions

The results show that hPRP can be used to replace FBS for hDPC expansion. These findings inform the development of an effective clinically applicable hair regeneration therapy.

In vitro induction of hair follicle signatures using human dermal papilla cells encapsulated in fibrin microgels

Cellular spheroids have been described as an appropriate culture system to restore human follicle dermal papilla cells (hFDPc) intrinsic properties; however, they show a low and variable efficiency to promote complete hair follicle formation in in vivo experiments. In this work, a conscientious analysis revealed a 25% cell viability in the surface of the dermal papilla spheroid (DPS) for all culture conditions, questioning whether it is an appropriate culture system for hFDPc. To overcome this problem, we propose the use of human blood plasma for the generation of fibrin microgels (FM) with encapsulated hFDPc to restore its inductive signature, either in the presence or in the absence of blood platelets. FM showed a morphology and extracellular matrix composition similar to the native dermal papilla, including Versican and Collagen IV and increasing cell viability up to 85%. While both systems induce epidermal invaginations expressing hair-specific keratins K14, K15, K71, and K75 in in vitro skin cultures, the number of generated structures increases from 17% to 49% when DPS and FM were used, respectively. These data show the potential of our experimental setting for in vitro hair follicle neogenesis with wild adult hFDPc using FM, being a crucial step in the pursuit of human hair follicle regeneration therapies.

In Vitro Three-Dimensional (3D) Models for Melanoma Immunotherapy

Melanoma is responsible for the majority of skin cancer-related fatalities. Immune checkpoint inhibitor (ICI) treatments have revolutionized the management of the disease by significantly increasing patient survival rates. However, a considerable number of tumors treated with these drugs fail to respond or may develop resistance over time. Tumor growth and its response to therapies are critically influenced by the tumor microenvironment (TME); it directly supports cancer cell growth and influences the behavior of surrounding immune cells, which can become tumor-permissive, thereby rendering immunotherapies ineffective. Ex vivo modeling of melanomas and their response to treatment could significantly advance our understanding and predictions of therapy outcomes. Efforts have been directed toward developing reliable models that accurately mimic melanoma in its appropriate tissue environment, including tumor organoids, bioprinted tissue constructs, and microfluidic devices. However, incorporating and modeling the melanoma TME and immune component remains a significant challenge. Here, we review recent literature regarding the generation of in vitro 3D models of normal skin and melanoma and the approaches used to incorporate the immune compartment in such models. We discuss how these constructs could be combined and used to test immunotherapies and elucidate treatment resistance mechanisms. The development of 3D in vitro melanoma models that faithfully replicate the complexity of the TME and its interaction with the immune system will provide us with the technical tools to better understand ICI resistance and increase its efficacy, thereby improving personalized melanoma therapy.

Establishment and characterization of matched immortalized human frontal and occipital scalp dermal papilla cell lines from androgenetic alopecia

Androgenetic alopecia (AGA), also known as male pattern baldness, is a common hair loss condition influenced by genetic and hormonal factors. Variations in gene expression and androgen responsiveness have been observed between the frontal and occipital regions of AGA patients. However, obtaining and cultivating frontal hair follicles is challenging. Therefore, no matched frontal and occipital dermal papilla (DP) cell lines have been reported yet. This study aimed to establish matched immortalized human frontal and occipital scalp DP cell lines from AGA patients. Simian virus 40 large T antigen (SV40T-Ag) and human telomerase reverse transcriptase (hTERT) were introduced into primary human DP cells. The obtained cell lines were characterized by assessing their gene expression patterns, androgen receptor (AR) levels, and the presence of 5-alpha reductase (5αR). Additionally, we examined their response to dihydrotestosterone (DHT) and evaluated cell viability. The conditioned medium from the frontal DP cell line inhibited human hair follicle growth, leading to reduced keratinocyte proliferation and increased apoptosis. Furthermore, when the cells were cultured in a 3D environment mimicking in vivo conditions, the 3D cultured frontal DP cell line exhibited weaker sphere aggregation than the occipital DP cell line due to the increased expression of matrix metalloproteinase 1 (MMP1), MMP3, and MMP9. Additionally, the expression of DP signature genes was inhibited in the 3D cultured frontal DP cell line. These matched frontal and occipital DP cell lines hold significant potential as valuable resources for research on hair loss. Their establishment allows us to investigate the differences between frontal and occipital DP cells, contributing to a better understanding of the molecular mechanisms underlying AGA. Furthermore, these cell lines may be valuable for developing targeted therapeutic approaches for hair loss conditions.

The frontline of alternatives to animal testing: novel in vitro skin model application in drug development and evaluation

The FDA Modernization Act 2.0 has brought nonclinical drug evaluation into a new era. In vitro models are widely used and play an important role in modern drug development and evaluation, including early candidate drug screening and preclinical drug efficacy and toxicity assessment. Driven by regulatory steering and facilitated by well-defined physiology, novel in vitro skin models are emerging rapidly, becoming the most advanced area in alternative testing research. The revolutionary technologies bring us many in vitro skin models, either laboratory-developed or commercially available, which were all built to emulate the structure of the natural skin to recapitulate the skin's physiological function and particular skin pathology. During the model development, how to achieve balance among complexity, accessibility, capability, and cost-effectiveness remains the core challenge for researchers. This review attempts to introduce the existing in vitro skin models, align them on different dimensions, such as structural complexity, functional maturity, and screening throughput, and provide an update on their current application in various scenarios within the scope of chemical testing and drug development, including testing in genotoxicity, phototoxicity, skin sensitization, corrosion/irritation. Overall, the review will summarize a general strategy for in vitro skin model to enhance future model invention, application, and translation in drug development and evaluation.

Epidermal-dermal coupled spheroids are important for tissue pattern regeneration in reconstituted skin explant cultures

Tissue patterning is critical for the development and regeneration of organs. To advance the use of engineered reconstituted skin organs, we study cardinal features important for tissue patterning and hair regeneration. We find they spontaneously form spheroid configurations, with polarized epidermal cells coupled with dermal cells through a newly formed basement membrane. Functionally, the spheroid becomes competent morphogenetic units (CMU) that promote regeneration of tissue patterns. The emergence of new cell types and molecular interactions during CMU formation was analyzed using scRNA-sequencing. Surprisingly, in newborn skin explants, IFNr signaling can induce apical-basal polarity in epidermal cell aggregates. Dermal-Tgfb induces basement membrane formation. Meanwhile, VEGF signaling mediates dermal cell attachment to the epidermal cyst shell, thus forming a CMU. Adult mouse and human fetal scalp cells fail to form a CMU but can be restored by adding IFNr or VEGF to achieve hair regeneration. We find different multi-cellular configurations and molecular pathways are used to achieve morphogenetic competence in developing skin, wound-induced hair neogenesis, and reconstituted explant cultures. Thus, multiple paths can be used to achieve tissue patterning. These insights encourage more studies of "in vitro morphogenesis" which may provide novel strategies to enhance regeneration.

Histological characteristics of hair follicles at different hair cycle and in vitro modeling of hair follicle-associated cells of yak (Bos grunniens)

To adapt to the extreme conditions of plateau environments, yaks have evolved thick hair, making them an ideal model for investigating the mechanisms involved in hair growth. We can gain valuable insights into how hair follicles develop and their cyclic growth in challenging environments by studying yaks. However, the lack of essential data on yak hair follicle histology and the absence of in vitro cell models for hair follicles serve as a limitation to such research objectives. In this study, we investigated the structure of skin tissue during different hair follicle cycles using the yak model. Additionally, we successfully established in vitro models of hair follicle-associated cells derived from yak skin, including dermal papilla cells (DPCs), preadipocytes, and fibroblasts. We optimized the microdissection technique for DPCs culture by simplifying the procedure and reducing the time required. Furthermore, we improved the methodology used to differentiate yak preadipocytes into mature adipocytes, thus increasing the differentiation efficiency. The introduction of yak as a natural model provides valuable research resources for exploring the mechanisms of hair growth and contributes to a deeper understanding of hair follicle biology and the development of regenerative medicine strategies.

Mesenchyme governs hair follicle induction

Tissue interactions are essential for guiding organ development and regeneration. Hair follicle formation relies on inductive signalling between two tissues, the embryonic surface epithelium and the adjacent mesenchyme. Although previous research has highlighted the hair-inducing potential of the mesenchymal component of the hair follicle - the dermal papilla and its precursor, the dermal condensate - the source and nature of the primary inductive signal before dermal condensate formation have remained elusive. Here, we performed epithelial-mesenchymal tissue recombination experiments using hair-forming back skin and glabrous plantar skin from mouse embryos to unveil that the back skin mesenchyme is inductive even before dermal condensate formation. Moreover, the naïve, unpatterned mesenchyme was sufficient to trigger hair follicle formation even in the oral epithelium. Building on previous knowledge, we explored the hair-inductive ability of the Wnt agonist R-spondin 1 and a Bmp receptor inhibitor in embryonic skin explants. Although R-spondin 1 instigated precocious placode-specific transcriptional responses, it was insufficient for hair follicle induction, either alone or in combination with Bmp receptor inhibition. Our findings pave the way for identifying the hair follicle-inducing cue.

Recent omics advances in hair aging biology and hair biomarkers analysis

Aging is a complex natural process that leads to a decline in physiological functions, which is visible in signs such as hair graying, thinning, and loss. Although hair graying is characterized by a loss of pigment in the hair shaft, the underlying mechanism of age-associated hair graying is not fully understood. Hair graying and loss can have a significant impact on an individual's self-esteem and self-confidence, potentially leading to mental health problems such as depression and anxiety. Omics technologies, which have applications beyond clinical medicine, have led to the discovery of candidate hair biomarkers and may provide insight into the complex biology of hair aging and identify targets for effective therapies. This review provides an up-to-date overview of recent omics discoveries, including age-associated alterations of proteins and metabolites in the hair shaft and follicle, and highlights the significance of hair aging and graying biomarker discoveries. The decline in hair follicle stem cell activity with aging decreased the regeneration capacity of hair follicles. Cellular senescence, oxidative damage and altered extracellular matrix of hair follicle constituents characterized hair follicle and hair shaft aging and graying. The review attempts to correlate the impact of endogenous and exogenous factors on hair aging. We close by discussing the main challenges and limitations of the field, defining major open questions and offering an outlook for future research.

Nanotechnology-based techniques for hair follicle regeneration

The hair follicle (HF) is a multicellular complex structure of the skin that contains a reservoir of multipotent stem cells. Traditional hair repair methods such as drug therapies, hair transplantation, and stem cell therapy have limitations. Advances in nanotechnology offer new approaches for HF regeneration, including controlled drug release and HF-specific targeting. Until recently, embryogenesis was thought to be the only mechanism for forming hair follicles. However, in recent years, the phenomenon of wound-induced hair neogenesis (WIHN) or de novo HF regeneration has gained attention as it can occur under certain conditions in wound beds. This review covers HF-specific targeting strategies, with particular emphasis on currently used nanotechnology-based strategies for both hair loss-related diseases and HF regeneration. HF regeneration is discussed in several modalities: modulation of the hair cycle, stimulation of progenitor cells and signaling pathways, tissue engineering, WIHN, and gene therapy. The HF has been identified as an ideal target for nanotechnology-based strategies for hair regeneration. However, some regulatory challenges may delay the development of HF regeneration nanotechnology based-strategies, which will be lastly discussed.