Pre-aggregation of scalp progenitor dermal and epidermal stem cells activates the WNT pathway and promotes hair follicle formation in in vitro and in vivo systems

Characterization of heterogeneous skin constructs for full thickness skin regeneration in murine wound models

An autologous heterogeneous skin construct (AHSC) has been developed and used clinically as an alternative to traditional skin grafting techniques for treatment of cutaneous defects. AHSC is manufactured from a small piece of healthy skin in a manner that preserves endogenous regenerative cellular populations. To date however, specific cellular and non-cellular contributions of AHSC to the epidermal and dermal layers of closed wounds have not been well characterized given limited clinical opportunity for graft biopsy following wound closure. To address this limitation, a three-part mouse full-thickness excisional wound model was developed for histologic and macroscopic graft tracing. First, fluorescent mouse-derived AHSC (mHSC) was allografted onto non-fluorescent recipient mice to enable macroscopic and histologic time course evaluation of wound closure. Next, mHSC-derived from haired pigmented mice was allografted onto gender- and major histocompatibility complex (MHC)-mismatched athymic nude mouse recipients. Resulting grafts were distinguished from recipient murine skin via immunohistochemistry. Finally, human-derived AHSC (hHSC) was xenografted onto athymic nude mice to evaluate engraftment and hHSC contribution to wound closure. Experiments demonstrated that mHSC and hHSC facilitated wound closure through production of viable, proliferative cellular material and promoted full-thickness skin regeneration, including hair follicles and glands in dermal compartments. This combined macroscopic and histologic approach to tracing AHSC-treated wounds from engraftment to closure enabled robust profiling of regenerated architecture and further understanding of processes underlying AHSC mechanism of action. These models may be applied to a variety of wound care investigations, including those requiring longitudinal assessments of healing and targeted identification of donor and recipient tissue contributions.

Cocktail Cell-Reprogrammed Hydrogel Microspheres Achieving Scarless Hair Follicle Regeneration

The scar repair inevitably causes damage of skin function and loss of skin appendages such as hair follicles (HF). It is of great challenge in wound repair that how to intervene in scar formation while simultaneously remodeling HF niche and inducing in situ HF regeneration. Here, chemical reprogramming techniques are used to identify a clinically chemical cocktail (Tideglusib and Tamibarotene) that can drive fibroblasts toward dermal papilla cell (DPC) fate. Considering the advantage of biomaterials in tissue repair and their regulation in cell behavior that may contributes to cellular reprogramming, the artificial HF seeding (AHFS) hydrogel microspheres, inspired by the natural processes of "seeding and harvest", are constructed via using a combination of liposome nanoparticle drug delivery system, photoresponsive hydrogel shell, positively charged polyamide modification, microfluidic and photocrosslinking techniques. The identified chemical cocktail is as the core nucleus of AHFS. In vitro and in vivo studies show that AHFS can regulate fibroblast fate, induce fibroblast-to-DPC reprogramming by activating the PI3K/AKT pathway, finally promoting wound healing and in situ HF regeneration while inhibiting scar formation in a two-pronged translational approach. In conclusion, AHFS provides a new and effective strategy for functional repair of skin wounds.

The Role of Mesenchymal Stem Cells in Hair Regeneration and Hair Cycle

The health of hair is directly related to people's health and appearance. Hair has key physiological functions, including skin protection and temperature regulation. Hair follicle (HF) is a vital mini-organ that directly impacts hair growth. Besides, various signaling pathways and molecules regulate the growth cycle transition of HFs. Hair and its regeneration studies have attracted much interest in recent years with the increasing rate of alopecia. Mesenchymal stem cells (MSCs), as pluripotent stem cells, can differentiate into fat, bone, and cartilage and stimulate regeneration and immunological regulation. MSCs have been widely employed to treat various clinical diseases, such as bone and cartilage injury, nerve injury, and lung injury. Besides, MSCs can be used for treatment of hair diseases due to their regenerative and immunomodulatory abilities. This review aimed to assess MSCs' treatment for alopecia, pertinent signaling pathways, and new material for hair regeneration in the last 5 years.

Potential application of PBM use in hair follicle organoid culture for the treatment of androgenic alopecia

Androgenic alopecia is a hereditary condition of pattern hair loss in genetically susceptible individuals. The condition has a significant impact on an individual's quality of life, with decreased self-esteem, body image issues and depression being the main effects. Various conventional treatment options, such as minoxidil, finasteride and herbal supplements, aim to slow down hair loss and promote hair growth. However, due to the chronic nature of the condition the financial cost of treatment for androgenic alopecia is very high and conventional treatment options are not universally effective and come with a host of side effects. Therefore, to address the limitations of current treatment options a novel regenerative treatment option is required. One promising approach is organoids, organoids are 3D cell aggregates with similar structures and functions to a target organ. Hair follicle organoids can be developed in vitro. However, the main challenges are to maintain the cell populations within the organoid in a proliferative and inductive state, as well as to promote the maturation of organoids. Photobiomodulation is a form of light therapy that stimulates endogenous chromophores. PBM has been shown to improve cell viability, proliferation, migration, differentiation and gene expression in dermal papilla cells and hair follicle stem cells. Therefore, photobiomodulation is a potential adjunct to hair follicle organoid culture to improve the proliferation and inductive capacity of cells.

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.

In vitro hair follicle growth model for drug testing

In vitro models of human hair follicle-like tissue could be fundamental tools to better understand hair follicle morphogenesis and hair drug screening. During prenatal development and postnatal cyclic hair regeneration, hair follicle morphogenesis is triggered by reciprocal interactions and the organization of the epithelial and mesenchymal cell populations. Given this mechanism, we developed an approach to induce hair peg-like sprouting in organoid cultures composed of epithelial and mesenchymal cells. Human fetal/adult epithelial and mesenchymal cells were cultured in a medium supplemented with a low concentration of either Matrigel or collagen I. These extracellular matrices significantly enhanced the self-organization capabilities of the epithelial and mesenchymal cells, resulting in spherical aggregation and subsequent hair peg-like sprouting. The length of the hair peg sprouting and associated gene expression significantly increased in the presence of a well-known hair drug, minoxidil. This approach may be beneficial for testing hair growth-promoting drug candidates.

A Kaleidoscope of Keratin Gene Expression and the Mosaic of Its Regulatory Mechanisms

Keratins are a family of intermediate filament-forming proteins highly specific to epithelial cells. A combination of expressed keratin genes is a defining property of the epithelium belonging to a certain type, organ/tissue, cell differentiation potential, and at normal or pathological conditions. In a variety of processes such as differentiation and maturation, as well as during acute or chronic injury and malignant transformation, keratin expression undergoes switching: an initial keratin profile changes accordingly to changed cell functions and location within a tissue as well as other parameters of cellular phenotype and physiology. Tight control of keratin expression implies the presence of complex regulatory landscapes within the keratin gene loci. Here, we highlight patterns of keratin expression in different biological conditions and summarize disparate data on mechanisms controlling keratin expression at the level of genomic regulatory elements, transcription factors (TFs), and chromatin spatial structure.

The dermal papilla dilemma and potential breakthroughs in bioengineering hair follicles

The generation and growing of de novo hair follicles is the most daring hair replacement approach to treat alopecia. This approach has been explored at least since the 1960s without major success. Latest in the 1980s, the realization that the mesenchymal compartment of hair follicles, the dermal papilla (DP), is the crucial signaling center and element required for fulfilling this vision of hair follicle engineering, propelled research into the fibroblasts that occupy the DP. However, working with DP fibroblasts has been stubbornly frustrating. Decades of work in understanding the nature of DP fibroblasts in vitro and in vivo have led to the appreciation that hair follicle biology is complex, and the dermal papilla is an enigma. Functional DP fibroblasts tend to aggregate in 2D culture, while impaired DP cells do not. This fact has stimulated recent approaches to overcome the hurdles to DP cell culture by mimicking their natural habitat, such as growing DP fibroblasts in three dimensions (3D) by their self-aggregation, adopting 3D matrix scaffold, or bioprinting 3D microstructures. Furthermore, including keratinocytes in the mix to form hair follicle-like composite structures has been explored but remains a far cry from a useful and affordable method to generate human hair follicles in sufficient quantity and quality in a practical time frame for patients. This suggests that the current strategies may have reached their limitations in achieving successful hair follicle bioengineering for clinical applications. Novel approaches are required to overcome these barriers, such as focusing on embryonic cell types and processes in combination with emerging techniques.

Skin-on-a-chip strategies for human hair follicle regeneration

The number of hair loss patients increases every year, and hair loss treatment has several limitations, so research on hair is attracting attention recently. However, most current hair follicle research models are limited by their inability to replicate several key functions of the hair follicle microenvironment. To complement this, an in vitro culture system similar to the in vivo environment must be constructed. It is necessary to develop a hair-on-a-chip that implements a fully functional hair follicle model by reproducing the main characteristics of hair follicle morphogenesis and cycle. In this review, we summarize the gradation of hair follicle morphogenesis and the roles and mechanisms of molecular signals involved in the hair follicle cycle. In addition, we discuss research results of various in vitro organoid products and organ-on-a-chip-based hair follicle tissue chips for the treatment of alopecia and present future research and development directions.

Biofabrication of Human Skin with Its Appendages

Much effort has been made to generate human skin organ in the laboratory. Yet, the current models are limited due to the lack of many critical biological and structural features of the skin. Importantly, these in vitro models lack appendages and fail to recapitulate the whole human skin construction. Thus, engineering a human skin with the capacity to generate all components, including appendages, is a major challenge. This review intends to provide an update on the recent efforts underway to regenerate appendage-bearing skin organs based on scaffold-free and scaffold-based bioengineering approaches. Although the mouse skin equivalents containing hair follicles, sebaceous glands, and sweat glands have been established in vitro, there has been limited success in humans. A combination of biofabricated matrices and cell aggregates, such as organoids, can pave the way for generating skin substitutes with human-like biological, structural, and physical features. Accordingly, the formation of human skin organoids and reconstruction of vascularized skin equipped with immune cells prompt calls for more scientific research. The generation of appendage-bearing skin substitutes can be applied in practice for wound healing, hair restoration, and scar treatment.

Self-assembled complete hair follicle organoids by coculture of neonatal mouse epidermal cells and dermal cells in Matrigel

BACKGROUND

3D organoid cultures of hair follicles (HFs) are powerful models that mimic native HF for both in-depth study of HF disease and precision therapy. However, few studies have investigated the complete structure and properties of HF organoids. To investigate and characterize the complete HF organoids self-assembled by coculture of neonatal mouse epidermal cells (MECs) and dermal cells in Matrigel.

METHODS

Fresh epidermal and dermal cells from newborn mice (n=4) were isolated, and cocultured (1:1 ratio) in Matrigel using DMEM/F12 medium for 1 week. During the culture, an inverted microscope was used to observe the morphology of the 3D constructs. After 1 week, hematoxylin-eosin (HE) and immunofluorescence (IF) staining of HF-related markers (K5, K73, AE13, and K10), HF stem cell markers (K15, CD34, CD49f), skin-derived precursor-related marker (Nestin), and dermal papillae (DP)-specific markers (SOX2 and ALP) was performed in the harvested constructs to identify the HF organoids.

RESULTS

Epidermal and dermal cells self-assembled into HF organoids comprising an infundibular cyst-like structure, a lower segment-like structure, and a bulb-like structure from tail to root. The HF organoid had multiple, well-defined compartments similar to native anagen HF. Of the three segments, K73 was expressed in the inner root sheath-like layer, AE13 was localized in the hair shaft-like structure, K5, K15, CD34, and CD49f were present in the outer root sheath-like layer, Nestin labeled the connective tissue sheath-like layer, and SOX2 and ALP were expressed in the DP-like structure. Furthermore, K10 and K73 were expressed in the infundibular cyst-like structure. The expression of these molecular proteins was consistent with native anagen HF.

CONCLUSIONS

The complete HF organoid regenerated in Matrigel has specific compartments and is an excellent model to study HF disease and precision therapy.

Treated dentin matrix induces odontogenic differentiation of dental pulp stem cells via regulation of Wnt/β-catenin signaling

Treated dentin matrix (TDM) is an ideal scaffold material containing multiple extracellular matrix factors. The canonical Wnt signaling pathway is necessary for tooth regeneration. Thus, this study investigated whether the TDM can promote the odontogenic differentiation of human dental pulp stem cells (hDPSCs) and determined the potential role of Wnt/β-catenin signaling in this process. Different concentrations of TDM promoted the dental differentiation of the hDPSCs and meanwhile, the expression of GSK3β was decreased. Of note, the expression of the Wnt/β-catenin pathway-related genes changed significantly in the context of TDM induction, as per RNA sequencing (RNA seq) data. In addition, the experiment showed that new dentin was visible in rat mandible cultured with TDM, and the thickness was significantly thicker than that of the control group. In addition, immunohistochemical staining showed lower GSK3β expression in new dentin. Consistently, the GSK3β knockdown hDPSCs performed enhanced odotogenesis compared with the control groups. However, GSK3β overexpressing could decrease odotogenesis of TDM-induced hDPSCs. These results were confirmed in immunodeficient mice and Wistar rats. These suggest that TDM promotes odontogenic differentiation of hDPSCs by directly targeting GSK3β and activating the canonical Wnt/β-catenin signaling pathway and provide a theoretical basis for tooth regeneration engineering.

The potential role of hsa_circ_0001079 in androgenetic alopecia via sponging hsa-miR-136-5p

Background

Androgenetic alopecia (AGA) is an androgen‐dependent polygenic hereditary disease.

Methods

Diseased hair follicles from 5 AGA patients and normal hair follicles from 5 healthy individuals were selected as specimens to carry out whole transcriptome sequencing. Multiple high‐expression circular RNAs (circRNAs) were screened from the diseased group. We further verified the presence of the circRNAs in the clinical specimens by real‐time fluorescence quantitative PCR (qRT‐PCR).

Results

In total, 100 circRNAs were significantly upregulated, and 184 circRNAs were significantly downregulated. The top 10 upregulated circRNAs were hsa_circ_0101041, hsa_circ_0001578, hsa_circ_0135062, hsa_circ_0002980, hsa_circ_0005062, hsa_circ_0072688, hsa_circ_0133954, hsa_circ_0001079, hsa_circ_0005974, hsa_circ_0000489. The top 10 downregulated circRNAs were hsa_circ_0001278, hsa_circ_0031482, hsa_circ_0008285, hsa_circ_0003784, hsa_circ_0077096, hsa_circ_0001148, hsa_circ_0006886, hsa_circ_0000638, hsa_circ_0084521, and hsa_circ_0101074. Among top 10 upregulated circRNAs, hsa_circ_0001079 showed significantly high expression via large‐sample verification and clinical application potential. Based on a database comparison and base pairing analysis, we found that has‐miR‐136‐5p bound to hsa_circ_0001079 and that hsa‐miR‐136‐5p had potential binding sites with Wnt5A.

Conclusion

In summary, through high‐throughput sequencing and bioinformatic analysis, a potential diagnostic marker for alopecia and a key circRNA that might adsorb microRNA (miRNA) through a sponging mechanism, thus mediating alopecia, were discovered in this study.

A systematic summary of survival and death signalling during the life of hair follicle stem cells

Hair follicle stem cells (HFSCs) are among the most widely available resources and most frequently approved model systems used for studying adult stem cells. HFSCs are particularly useful because of their self-renewal and differentiation properties. Additionally, the cyclic growth of hair follicles is driven by HFSCs. There are high expectations for the use of HFSCs as favourable systems for studying the molecular mechanisms that contribute to HFSC identification and can be applied to hair loss therapy, such as the activation or regeneration of hair follicles, and to the generation of hair using a tissue-engineering strategy. A variety of molecules are involved in the networks that critically regulate the fate of HFSCs, such as factors in hair follicle growth and development (in the Wnt pathway, Sonic hedgehog pathway, Notch pathway, and BMP pathway), and that suppress apoptotic cues (the apoptosis pathway). Here, we review the life cycle, biomarkers and functions of HFSCs, concluding with a summary of the signalling pathways involved in HFSC fate for promoting better understanding of the pathophysiological changes in the HFSC niche. Importantly, we highlight the potential mechanisms underlying the therapeutic targets involved in pathways associated with the treatment of hair loss and other disorders of skin and hair, including alopecia, skin cancer, skin inflammation, and skin wound healing.

Functional hair follicle regeneration: an updated review

The hair follicle (HF) is a highly conserved sensory organ associated with the immune response against pathogens, thermoregulation, sebum production, angiogenesis, neurogenesis and wound healing. Although recent advances in lineage-tracing techniques and the ability to profile gene expression in small populations of cells have increased the understanding of how stem cells operate during hair growth and regeneration, the construction of functional follicles with cycling activity is still a great challenge for the hair research field and for translational and clinical applications. Given that hair formation and cycling rely on tightly coordinated epithelial-mesenchymal interactions, we thus review potential cell sources with HF-inducive capacities and summarize current bioengineering strategies for HF regeneration with functional restoration.

Early-stage bilayer tissue-engineered skin substitute formed by adult skin progenitor cells produces an improved skin structure in vivo

BACKGROUND

In recent years, significant progress has been made in developing highly complex tissue-engineered skin substitutes (TESSs) for wound healing. However, the lack of skin appendages, such as hair follicles and sweat glands, and the time required, are two major limitations that hinder its broad application in the clinic. Therefore, it is necessary to develop a competent TESS in a short time to meet the needs for clinical applications.

METHODS

Adult scalp dermal progenitor cells and epidermal stem cells together with type I collagen as a scaffold material were used to reconstitute bilayer TESSs in vitro. TESSs at 4 different culture times (5, 9, 14, and 21 days) were collected and then grafted onto full-thickness wounds created in the dorsal skin of athymic nude/nude mice. The skin specimens formed from grafted TESSs were collected 4 and 8 weeks later and then evaluated for their structure, cell organization, differentiation status, vascularization, and formation of appendages by histological analysis, immunohistochemistry, and immunofluorescent staining.

RESULTS

Early-stage bilayer TESSs after transplantation had a better efficiency of grafting. A normal structure of stratified epidermis containing multiple differentiated layers of keratinocytes was formed in all grafts from both early-stage and late-stage TESSs, but higher levels of the proliferation marker Ki-67 and the epidermal progenitor marker p63 were found in the epidermis formed from early-stage TESSs. Interestingly, the transplantation of early-stage TESSs produced a thicker dermis that contained more vimentin- and CD31-positive cells, and importantly, hair follicle formation was only observed in the skin grafted from early-stage TESSs. Finally, early-stage TESSs expressed high levels of p63 but had low expression levels of genes involved in the activation of the apoptotic pathway compared to the late-stage TESSs in vitro.

CONCLUSIONS

Early-stage bilayer TESSs reconstituted from skin progenitor cells contained more competent cells with less activation of the apoptotic pathway and produced a better skin structure, including hair follicles associated with sebaceous glands, after transplantation, which should potentially provide better wound healing when applied in the clinic in the future.

Sustained release of inhibitor from bionic scaffolds for wound healing and functional regeneration

Small molecules play remarkable roles in promoting tissue regeneration, but are limited by their burst release. Small molecules such as deferoxamine (DFO) have been released slowly from silk hydrogels and stimulated angiogenesis and wound healing, but failed to achieve functional recovery of skin. Various bioactive molecules are required to create a suitable niche for better skin regeneration by controlling their release behaviors. Herein, a small molecule SB216763, a GSK-3 inhibitor, was loaded on silk fibroin nanofibers (SNF), and then mixed with chitosan (CS) to prepare the small molecule-loaded composite bionic scaffolds (CSNF-SB). Given the interaction of SNF and SB216763, the sustained release of SB216763 for more than 21 days was achieved for SNF and CSNF-SB composite scaffolds. Compared to drug-free CSNF scaffolds, CSNF-SB showed better cell adhesion and proliferation capacity, suggesting bioactivity. The upregulated expression of β-catenin in fibroblasts in vitro revealed that the released small molecules maintained their function in composite scaffolds. Quicker and better wound healing was realized with the drug-loaded scaffolds, which was significantly superior to that treated with drug-free scaffolds. Unlike the DFO-loaded silk hydrogel system, hair follicle neogenesis was also found in the drug-loaded-scaffold treatment wounds, demonstrating functional recovery. Therefore, silk nanofibers as versatile carriers for different small bioactive molecules could be used to fabricate scaffolds with optimized niches and then achieve functional recovery of tissues. The small molecule-loaded bionic scaffolds have a promising future in skin tissue regeneration.