Comparisons of mouse models for hair follicle reconstitution

Phenotyping mice with skin, hair, or nail abnormalities: A systematic approach and methodologies from simple to complex

The skin and adnexa can be difficult to interpret because they change dramatically with the hair cycle throughout life. However, a variety of methods are commonly available to collect skin and perform assays that can be useful for figuring out morphological and molecular changes. This overview provides information on basic approaches to evaluate skin and its molecular phenotype, with references for more detail, and interpretation of results on the skin and adnexa in the mouse. These approaches range from mouse genetic nomenclature, setting up a cutaneous phenotyping study, skin grafts, hair follicle reconstitution, wax stripping, electron microscopy, and Köbner reaction to very specific approaches such as lipid and protein analyses on a large scale.

Twist2-driven chromatin remodeling governs the postnatal maturation of dermal fibroblasts

Dermal fibroblasts lose stem cell potency after birth, which prevents regenerative healing. However, the underlying intracellular mechanisms are largely unknown. We uncover the postnatal maturation of papillary fibroblasts (PFs) driven by the extensive Twist2-mediated remodeling of chromatin accessibility. A loss of the regenerative ability of postnatal PFs occurs with decreased H3K27ac levels. Single-cell transcriptomics, assay for transposase-accessible chromatin sequencing (ATAC-seq), and chromatin immunoprecipitation sequencing (ChIP-seq) reveal the postnatal maturation trajectory associated with the loss of the regenerative trajectory in PFs, which is characterized by a marked decrease in chromatin accessibility and H3K27ac modifications. Histone deacetylase inhibition delays spontaneous chromatin remodeling, thus maintaining the regenerative ability of postnatal PFs. Genomic analysis identifies Twist2 as a major regulator within chromatin regions with decreased accessibility during the postnatal period. When Twist2 is genetically deleted in dermal fibroblasts, the intracellular cascade of postnatal maturation is significantly delayed. Our findings reveal the comprehensive intracellular mechanisms underlying intrinsic postnatal changes in dermal fibroblasts.

Adaptive multi‐degree‐of‐freedom in situ bioprinting robot for hair‐follicle‐inclusive skin repair: A preliminary study conducted in mice

Skin acts as an essential barrier, protecting organisms from their environment. For skin trauma caused by accidental injuries, rapid healing, personalization, and functionality are vital requirements in clinical, which are the bottlenecks hindering the translation of skin repair from benchside to bedside. Herein, we described a novel design and a proof‐of‐concept demonstration of an adaptive bioprinting robot to proceed rapid in situ bioprinting on a full‐thickness excisional wound in mice. The three‐dimensional (3D) scanning and closed‐loop visual system integrated in the robot and the multi‐degree‐of‐freedom mechanism provide immediate, precise, and complete wound coverage through stereotactic bioprinting, which hits the key requirements of rapid‐healing and personalization in skin repair. Combined with the robot, epidermal stem cells and skin‐derived precursors isolated from neonatal mice mixed with Matrigel were directly printed into the injured area to replicate the skin structure. Excisional wounds after bioprinting showed complete wound healing and functional skin tissue regeneration that closely resembling native skin, including epidermis, dermis, blood vessels, hair follicles and sebaceous glands etc. This study provides an effective strategy for skin repair through the combination of the novel robot and a bioactive bioink, and has a promising clinical translational potential for further applications.

Cellular Nanofiber Structure with Secretory Activity-Promoting Characteristics for Multicellular Spheroid Formation and Hair Follicle Regeneration

Multicellular spheroids can mimic the in vivo microenvironment and maintain the unique functions of tissues, which has attracted great attention in tissue engineering. However, the traditional culture microenvironment with structural deficiencies complicates the culture and collection process and tends to lose the function of multicellular spheroids with the increase of cell passage. In order to construct efficient and functional multicellular spheroids, in this study, a chitosan/polyvinyl alcohol nanofiber sponge which has an open-cell cellular structure is obtained. The hair follicle (HF) regeneration model was employed to evaluate HF-inducing ability of dermal papilla (DP) multicellular spheroids which formed on the cellular structure nanofiber sponge. Through structural fine-tuning, the nanofiber sponge has appropriate elasticity for the creation of a three-dimensional dynamic microenvironment to regulate cellular behavior. The cellular structure nanofiber sponge tilts the balance of cell-substratum and cell-cell interactions to a state which is more conducive to the formation of controllable multicellular spheroids in a short time. More importantly, it improves the secretory activity of high-passaged dermal papilla cells and restores their intrinsic properties. Experiments using BALB/c nude mice show that cultured DP multicellular spheroids could effectively enhance HF-inducing ability. This novel system provides a simple and efficient strategy for multicellular spheroid formation and HF regeneration.

Skin wound healing in humans and mice: Challenges in translational research

Despite the great progress in translational research concerning skin wound healing in the last few decades, no animal model fully predicts all clinical outcomes. The mouse is the most commonly used model, as it is easy to maintain and standardize, and is economically accessible. However, differences between murine and human skin repair, such as the contraction promoted by panniculus carnosus and the role of specific niches of skin stem cells, make it difficult to bridge the gap between preclinical and clinical studies. Therefore, this review highlights the particularities of each species concerning skin morphophysiology, immunology, and genetics, which is essential to properly interpret findings and translate them to medicine.

The patch assay reconstitutes mature hair follicles by culture-expanded human cells

AIM

We tested whether the a simple injection known as the patch assay could reconstitute mature hair follicles by culture-expanded human cells and explored whether the assay could reflect the trichogenicity of cultured cells.

MATERIALS & METHODS

Dissociated culture-expanded fetal or adult scalp dermal cells combined with foreskin keratinocytes were subcutaneously injected into the back skin of immunosuppressive mice to form the patch skin. The patches were collected and characterized and were analyzed for hair formation efficiency.

RESULTS

Using culture-expanded human fetal cells, the patch assay can efficiently reconstitute mature hair follicles and the efficiency of hair formation in the patch assay correlates with cell trichogenicity.

CONCLUSION

The patch assay has the potential for testing the trichogenicity of human cells.

Basement Membrane Matrix Promotes the Efficiency of Hair Follicle Reconstruction In Vivo and Is a Cell Delivery Vehicle for Follicle Regeneration

BACKGROUND

The efficiency of hair follicle (HF) reconstruction is decreased by extensive apoptotic remodeling that occurs soon after grafting.

OBJECTIVE

To evaluate a basement membrane matrix (matrix) to improve the efficiency of HF reconstruction and serve as a cell delivery vehicle.

MATERIALS AND METHODS

Newborn mouse skin cells were suspended in a matrix and transplanted in a chamber assay. The viability and proliferation of mouse dermal papilla cells seeded in the matrix were tested. Dermal papilla cells and epidermal cells seeded in matrix sheets were grafted into nude mice to observe hair formation.

RESULTS

The matrix significantly shortened the time to hair formation. The first hair shafts appeared within the matrix at 17.67 ± 1.21 days versus 23.00 ± 1.41 days for Dulbecco's modified Eagle medium controls. There was a significant difference (p < .05) in the number of newly formed hairs in areas of reconstructed skin with the matrix (100 μL) grafts (323 ± 12) versus controls (276 ± 11). Dermal papilla cells were successfully cultured in the matrix, and hair formation was dense when the matrix was used as a cell delivery vehicle for follicle reconstruction.

CONCLUSION

The matrix improved the efficiency of HF reconstruction and was a suitable delivery vehicle of cells for HF engineering.

Norepinephrine Regulates Keratinocyte Proliferation to Promote the Growth of Hair Follicles

Psychological factors and stress can cause hair loss. The sympathetic-adrenal-medullary (SAM) axis has been reported to regulate the growth of hair follicles (HF). The sympathetic nerve is a component of the SAM axis, but it has not been sufficiently or convincingly linked to hair growth. In this study, we demonstrate that chemical sympathectomy via administration of the neurotoxin 6-hydroxydopamine (6-OHDA) to mice inhibited HF growth, but treatment with the β-adrenoceptor antagonist propranolol (PR) had no effect. HF length and skin thickness were greater in PR-treated and control mice than in 6-OHDA-treated mice, as evidenced by hematoxylin and eosin staining. Furthermore, we found that the reduced HF growth in sympathectomized animals was accompanied by a decreased keratinocyte proliferation. Moreover, the neurotransmitter norepinephrine (NE) was found to efficiently promote HF growth in an organotypic skin culture model. Together, these findings suggest that sympathetic nerves regulate keratinocyte behaviors to promote hair growth, providing novel insights into stress-related, chemotherapy-, and radiotherapy-induced alopecia.

Isolation of Mouse Hair Follicle Bulge Stem Cells and Their Functional Analysis in a Reconstitution Assay

The hair follicle (HF) is a dynamic structure readily accessible within the skin, and contains various pools of stem cells that have a broad regenerative potential during normal homeostasis and in response to injury. Recent discoveries demonstrating the multipotent capabilities of hair follicle stem cells and the easy access to skin tissue make the HF an attractive source for isolating stem cells and their subsequent application in tissue engineering and regenerative medicine. Here, we describe the isolation and purification of hair follicle bulge stem cells from mouse skin, and hair reconstitution assays that allows the functional analysis of multipotent stem cells.

Skin Diseases in Laboratory Mice: Approaches to Drug Target Identification and Efficacy Screening

A large variety of mouse models for human skin, hair, and nail diseases are readily available from investigators and vendors worldwide. Mouse skin is a simple organ to observe lesions and their response to therapy, but identifying and monitoring the progress of treatments of mouse skin diseases can still be challenging. This chapter provides an overview on how to use the laboratory mouse as a preclinical tool to evaluate efficacy of new compounds or test potential new uses for compounds approved for use for treating an unrelated disease. Basic approaches to handling mice, applying compounds, and quantifying effects of the treatment are presented.

Synergistic effect of PDGF and FGF2 for cell proliferation and hair inductive activity in murine vibrissal dermal papilla in vitro

BACKGROUND

The dermal papilla is composed of a small clump of mesenchymal cells, called dermal papilla cells (DPCs). DPCs closely interact with epidermal cells to give rise to hair follicles and shafts during hair follicle development and the hair cycle. DPCs are promising cell sources for hair regeneration therapy for alopecia patients. However, once DPCs are put into conventional two-dimensional culture conditions, they quickly lose their capability to produce hair follicles.

OBJECTIVE

We aimed to expand a sufficiently large population of DPCs that retain their hair inductive activity.

METHODS

Murine DPCs were cultured in the presence of platelet-derived growth factor-AA (PDGF-AA) and fibroblast growth factor 2 (FGF2). Expressions of follicular-related genes were analyzed by real time PCR and hair inductive activity was determined by patch assay and chamber assay in vivo.

RESULTS

FGF2 significantly increased the expression of platelet-derived growth factor receptor alpha (PDGFRα) in cultured vibrissal DPCs. PDGF-AA, a ligand of PDGFRα, promoted proliferation of DPCs synergistically when utilized with FGF2 and enhanced the expression of several follicular-related genes in DPCs. Hair reconstitution assays revealed that DPCs treated with both PDGF-AA and FGF-2 were able to maintain their hair inductive activity better than those treated with FGF2 alone.

CONCLUSION

Both cell proliferation and hair inductive activity in murine DPCs are maintained by the synergistic effect of FGF2 and PDGF-AA.

A simple and rapid model for hair-follicle regeneration in the nude mouse

BACKGROUND

Methods for hair-follicle regeneration are important tools for investigating signalling and cytokines during hair-follicle morphogenesis and cycling. Several animal models for hair reconstitution have been established; however, these models have several shortcomings.

AIM

To develop a simple and rapid model for hair induction in nude mouse.

METHODS

We designed an improved flap model (IFM) for hair regeneration based on the existing flap assay. Histological sections and scanning electron microscopy were used to evaluate the regenerated hair. The fates of grafted cells were traced by fluorescence. The time required for hair induction was analysed and compared.

RESULTS

IFM produced a large number of normal hairs, and the time required for hair induction using IFM was 20.67 ± 0.67 days, compared with 29.33 ± 0.67 days for the traditional flap assay.

CONCLUSIONS

The time required for hair regeneration is considerably shortened with IFM. We speculate that this is due to increased blood supply at the transplantation sites.

Neonatal murine skin-derived cells transplanted using a mini-chamber model produce robust and normal hair

Hair follicle reconstitution models are useful tools for investigating signalling and cytokines during hair follicle morphogenesis and cycling. The chamber model is one of the most established methods available for the study of hair follicle reconstitution and appears to be the most reproducible. However, the chamber model has several deficiencies: infection of skin wounds and subsequent animal death commonly occur, a large number of cells are required and only one chamber can be transplanted onto each animal. We modified these deficiencies by using a mini-chamber method, which has the advantages of having a high graft take rate, requiring fewer cells and allowing several mini-chambers to be transplanted onto each animal. In our study, cultured dermal cells at different passages (0 to high) lost the ability to reconstruct hair follicles, but dermal cells cultured overnight (12 h) retained this ability. Using the assay, newborn mice dermal cells that were freshly isolated and cultured overnight (12 h), as well as cultured dermal papilla cells from mice vibrissa follicles, all reconstructed hair follicles. However, cultured dermal papilla cells from human scalp follicles could not reconstruct hair follicles. Copyright © 2013 John Wiley & Sons, Ltd.

Rapid genetic analysis of epithelial-mesenchymal signaling during hair regeneration

Hair follicle morphogenesis, a complex process requiring interaction between epithelia-derived keratinocytes and the underlying mesenchyme, is an attractive model system to study organ development and tissue-specific signaling. Although hair follicle development is genetically tractable, fast and reproducible analysis of factors essential for this process remains a challenge. Here we describe a procedure to generate targeted overexpression or shRNA-mediated knockdown of factors using lentivirus in a tissue-specific manner. Using a modified version of a hair regeneration model ^{5, 6, 11}, we can achieve robust gain- or loss-of-function analysis in primary mouse keratinocytes or dermal cells to facilitate study of epithelial-mesenchymal signaling pathways that lead to hair follicle morphogenesis. We describe how to isolate fresh primary mouse keratinocytes and dermal cells, which contain dermal papilla cells and their precursors, deliver lentivirus containing either shRNA or cDNA to one of the cell populations, and combine the cells to generate fully formed hair follicles on the backs of nude mice. This approach allows analysis of tissue-specific factors required to generate hair follicles within three weeks and provides a fast and convenient companion to existing genetic models.