Hair Follicle Structures Research Articles

Timely Wound Healing Is Dependent on Endothelial but Not on Hair Follicle Stem Cell Toll-Like Receptor 2 Signaling

As a part of innate immunity, toll-like receptor 2 (TLR2) plays an important function in most defensive responses of the organism, including but not limited to infections. Cutaneous injury, one of the most common challenges for mammals, mobilizes a number of cell types, including epithelial, immune, and vascular cells, for timely tissue repair. However, in contrast to immune cells, little is known about TLR2 function on nonimmune cells during skin regeneration. In this study, we used two tissue-specific conditional Tlr2-knockout mouse lines to address the effects of TLR2 in endothelial and hair follicle stem cells (HFSCs) on cutaneous wound healing. The loss of TLR2 on endothelial cells diminishes their ability to migrate, sprout, and proliferate in response to specific TLR2 ligands and also reduces the secretion of key proangiogenic factors. Lack of TLR2 on endothelial cells prolongs wound healing owing to diminished angiogenesis. TLR2 is expressed in key structures of hair follicles, including HFSCs, secondary hair germ, and dermal papilla. Despite the prominent role of HFSCs in skin regeneration, excision of TLR2 from HFSCs has no effects on their proliferation or wound healing potential. Our study shows that timely tissue regeneration after skin injury is dependent on endothelial TLR2 for robust angiogenesis, whereas HFSC TLR2 is dispensable.

What's Race Got to Do With It? CRP Levels in Immune Mediated Skin Diseases: Considerations for Hidradenitis Suppurativa.

Currently, there is a lack of racial/ethnic heterogeneity in research databases, exposing a systematic issue in studies exploring inflammation-mediated diseases, such as hidradenitis suppurativa (HS). HS is a chronic inflammatory skin condition that disrupts normal structure and functioning of terminal hair follicles, resulting in the formation of recurrent abscesses, nodules, and sinus tracts within intertriginous regions. Studies have described higher serum levels of inflammation-mediated C-reactive protein (CRP) in patients with HS, a disease that predominantly affects skin of color (SOC) populations. Herein, we explore the role of CRP levels in the context of HS disease presentation, management, and psychosocial implications in SOC patients to determine existing disparities in research studies.

Sustained delivery of rhMG53 promotes diabetic wound healing and hair follicle development.

MG53 is an essential component of the cell membrane repair machinery, participating in the healing of dermal wounds. Here we develop a novel delivery system using recombinant human MG53 (rhMG53) protein and a reactive oxygen species (ROS)-scavenging gel to treat diabetic wounds. Mice with ablation of MG53 display defective hair follicle structure, and topical application of rhMG53 can promote hair growth in the mg53−/− mice. Cell lineage tracing studies reveal a physiological function of MG53 in modulating the proliferation of hair follicle stem cells (HFSCs). We find that rhMG53 protects HFSCs from oxidative stress-induced apoptosis and stimulates differentiation of HSFCs into keratinocytes. The cytoprotective function of MG53 is mediated by STATs and MAPK signaling in HFSCs. The thermosensitive ROS-scavenging gel encapsulated with rhMG53 allows for sustained release of rhMG53 and promotes healing of chronic cutaneous wounds and hair follicle development in the db/db mice. These findings support the potential therapeutic value of using rhMG53 in combination with ROS-scavenging gel to treat diabetic wounds.

Dendritic cells may help differentiate discoid lupus erythematosus alopecia from lichen planopilaris.

IntroductionPrimary cicatricial alopecia (PCA) encompasses a heterogeneous group of inflammatory diseases characterized by the replacement of hair follicle structures by fibrous tissue. Discoid lupus erythematosus (DLE) and lichen planopilaris (LPP) are the most common causes of scarring alopecia. The distinction between both entities is often challenging because of significant clinical and histopathological overlap.AimWe hypothesized that dendritic cells which are implicated in PCA pathogenesis can provide a reliable histopathological clue to distinguish between these two entities.Material and methodsIn a retrospective cohort study including 51 patients diagnosed with LPP and DLE we mapped and quantified the distribution of dendritic cells. Cell count in lesional skin was performed on immunohistochemistry by using characteristic monoclonal antibodies to specific subpopulations of dendritic cells.ResultsWe demonstrated that almost all subpopulations of dendritic cells were highly expressed in lesional skin of discoid lupus erythematosus patients in comparison with lichen planopilaris ones.ConclusionsIn the light of this observation, dendritic cells might be used as an additional clue in differential diagnosis of PCA.

Uniaxial and Coaxial Vertical Embedded Extrusion Bioprinting.

The 3D bioprinting technologies have attracted increasing attention due to their flexibility in producing architecturally relevant tissue constructs. Here, a vertical embedded extrusion bioprinting strategy using uniaxial or coaxial nozzles is presented, which allows formation of vertical structures of homogeneous or heterogeneous properties. By adjusting the bioprinting parameters, the characteristics of the bioprinted vertical patterns can be precisely controlled. Using this strategy, two proof-of-concept applications in tissue biofabrication are demonstrated. Specifically, intestinal villi and hair follicles, two liner-shaped tissues in the human body, are successfully generated with the vertical embedded bioprinting method, reconstructing some of their key structures as well as restoring partial functions in vitro. Caco-2 cells in the bioprinted intestinal villus constructs proliferated and aggregated properly, also showing functional biomarker expressions such as ZO-1 and villin. Moreover, preliminary hair follicle structures featuring keratinized human keratinocytes and spheroid-shaped human dermal papilla cells are formed after vertical bioprinting and culturing. In summary, this vertical embedded extrusion bioprinting technique harnessing a uniaxial or coaxial format will likely bring further improvements in the reconstruction of certain human tissues and organs, especially those with a linear structure, potentially leading to wide utilities in tissue engineering, tissue model engineering, and drug discovery.

342 Human skin and its appendages regeneration in the large full-thickness xenografting model

Most of the skin biology data obtained from a mouse model. However, studies of human skin have shown differences in the cell molecular signatures, the processes of physiological regeneration, wound healing, the development of diseases, etc. Human skin xenografting to immunodeficiency mice allows the most complex experiments to study normal and pathological processes, the search for methods of therapy for various diseases of human skin. The main limitation of this approach is the graft size. Most studies use partial-thickness xenografts without terminal hairs with excision of the dermal part along with adipose tissue while small punch biopsies or follicular units of human scalp skin are used to study the structure of hair follicles. The purpose of the study was to develop a xenografting model of a reasonably large full-thickness skin flap containing terminal hair follicles. The graft size was 15×5 mm. The skin was successfully engrafted, all skin structures including epidermis, dermis, blood vessels, hair follicles, sebaceous and sweat glands were preserved. The xenografting procedure is traumatic and promotes catagen induction. On day 32, we observed active proliferation of the graft tissue, a network of small vessels in the dermis and epidermal ridges at the junction of the graft with the recipient’s skin. On day 78, the xenograft was at the late stages of regeneration, there was a general decrease in proliferation with reconstruction of papillary and reticular dermis, and hair follicles morphology corresponded to the anagen stage. On day 110, visible growth of hair shafts above the skin surface was observed. Our data indicate that the homeostasis establishment in a 15×5 mm full-thickness skin xenograft with terminal hair follicles is longer than that in a split-thickness skin graft and takes more than 12 weeks. The described humanized skin model is suitable for studying the regeneration of skin and its appendages with surrounding tissues.

Human iPS Cell-Derived Cell Aggregates Exhibited Dermal Papilla Cell Properties in in vitro Three-Dimensional Assemblage Mimicking Hair Follicle Structures.

Current approaches for human hair follicle (HF) regeneration mostly adopt cell-autonomous tissue reassembly in a permissive murine intracorporeal environment. This, together with the limitation in human-derived trichogenic starting materials, potentially hinders the bioengineering of human HF structures, especially for the drug discovery and treatment of hair loss disorders. In this study, we attempted to reproduce the anatomical relationship between an epithelial main body and the dermal papilla (DP) within HF in vitro by three-dimensionally assembling columnarly molded human keratinocytes (KCs) and the aggregates of DP cells and evaluated how HF characteristics were reproduced in the constructs. The replaceability of human-induced pluripotent stem cell (hiPSC)-derived DP substitutes was assessed using the aforementioned reconstruction assay. Human DP cell aggregates were embedded into Matrigel as a cluster. Subsequently, highly condensed human KCs were cylindrically injected onto DP spheroids. After 2-week culture, the structures visually mimicking HFs were obtained. KC-DP constructs partially reproduced HF microanatomy and demonstrated differential keratin (KRT) expression pattern in HFs: KRT14 in the outermost part and KRT13, KRT17, and KRT40, respectively, in the inner portion of the main body. KC-DP constructs tended to upregulate HF-related genes, KRT25, KRT33A, KRT82, WNT5A, and LEF1. Next, DP substitutes were prepared by exposing hiPSC-derived mesenchymal cells to retinoic acid and subsequently to WNT, BMP, and FGF signal activators, followed by cell aggregation. The resultant hiPSC-derived DP substitutes (iDPs) were combined with KCs in the invented assay. KC-iDP constructs morphologically resemble KC-DP constructs and analogously mimicked KRT expression pattern in HF. iDP in the constructs expressed DP-related markers, such as vimentin and versican. Intriguingly, KC-iDP constructs more intensely expressed KRT33A, KRT82, and LEF1, which were stepwisely upregulated by the addition of WNT ligand and the mixture of WNT, SHH, and EDA signaling activators, supporting the idea that iDP exhibited biological properties analogous to DP cell aggregates in the constructs in vitro. These preliminary findings suggested the possibility of regenerating DP equivalents with in vitro hair-inductive capacity using hiPSC-derived cell composites, which potentially reduce the necessity of human tissue-derived trichogenic cell subset and eventually allow xeno-free bioengineering of human HFs.

Mesenchymal Stem Cells Antagonize IFN-Induced Proinflammatory Changes and Growth Inhibition Effects via Wnt/β-Catenin and JAK/STAT Pathway in Human Outer Root Sheath Cells and Hair Follicles.

Mesenchymal stem cell therapy (MSCT) has been shown to be a new therapeutic option for treating alopecia areata (AA). Outer root sheath cells (ORSCs) play key roles in maintaining the hair follicle structure and supporting the bulge area. In human ORSCs (hORSCs), the mechanism for this process has not been extensively studied. In this study, we aimed to examine the influence of human hematopoietic mesenchymal stem cells (hHMSCs) in the hORSCs in vitro model of AA and determine the mechanisms controlling efficacy. Interferon-gamma (IFN-γ) pretreatment was used to induce an in vitro model of AA in hORSCs. The effect of MSCT on the viability and migration of hORSCs was examined using co-cultures, the MTT assay, and migration assays. We investigated the expression of molecules related to the Wnt/β-catenin pathway, JAK/STAT pathway, and growth factors in hHMSC-treated hORSCs by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses. hHMSCs increased hORSC viability and migration when they were co-cultured. hHMSCs reverted IFN-γ-induced expression—including NLRP3, ASC, caspase-1, CXCL-9 through 11, IL-1β, and IL-15—and upregulated several growth factors and hair stem cell markers. hHMSCs activated several molecules in the Wnt/β-catenin signaling pathway, such as in the Wnt families, β-catenin, phosphorylated GSK-3β and cyclin D1, and suppressed the expression of DKK1 induced by IFN-γ in hORSCs. hHMSCs suppressed the phosphorylation of JAK1 to 3, STAT1, and STAT3 compared to the controls and IFN-γ-pretreated hORSCs. These results demonstrate that hHMSCs increased hORSC viability and migration in the in vitro AA model. Additionally, MSCT definitely stimulated anagen survival and hair growth in an HF organ culture model. MSCT appeared to be associated with the Wnt/β-catenin and JAK/STAT pathways in hORSCs.

Histology of Hair Follicles in Different Breeds of Rabbits

Background: Rabbit farming provides a valuable additional source of income in the rural areas of the county. Skin is the largest organ in the body and the hair coat forms the first line of defense against the invading pathogenic organisms as well as the physical environment. So far, no detailed comparative study has been conducted on the skin of various breeds of rabbits. Hence, the present work was undertaken to compare the structure and distribution of hair follicles in different breeds of rabbits commonly reared in Kerala.Methods: The study was conducted on the skin of six breeds of rabbits namely, Soviet Chinchilla, New Zealand White, Grey Giant, White Giant, Angora and crossbred. In total, 36 animals were used for the study. From each animal, skin samples were collected from eight representative areas of the body viz., dorsal nasal region, pinna, dorsal neck, dorsal thorax, dorsal abdomen, ventral abdomen, perineal and carpal regions. Standard procedures were adopted for histological studies.Result: All the six breeds of rabbits showed compound hair follicles with primary and secondary follicles with associated sebaceous glands. Arrangement of hair follicles showed differences among the breeds. There was no difference in the histology of hair/hair follicle among the breeds. This work will form a basis for further breed specific research in the area of fur and leather industry and skin penetration studies.

Maintaining Inducibility of Dermal Follicle Cells on Silk Fibroin/Sodium Alginate Scaffold for Enhanced Hair Follicle Regeneration.

Simple SummaryPatients with severe skin damage need to transplant artificial skin substitutes to achieve repair, and often the repaired part cannot achieve the regeneration of accessory organs such as hair follicles. It is very important to study artificial skin substitutes that can promote the regeneration of hair follicles. Dermal papilla cells in hair follicles can express a variety of growth factors, which play an important role in the growth of hair follicles. Dermal papilla cells were used as seed cells and cultured with a biomimetic silk fibroin/sodium alginate scaffold similar to the extracellular matrix around the dermal papilla to explore cell-compatibility on the scaffold. Our research found that a silk fibroin/sodium alginate scaffold is a good biomimetic of the extracellular matrix structure, and that the dermal papilla cells could maintain normal morphology and aggregate growth characteristics on the scaffold. We then proved through animal experiments that this scaffold can promote skin repair and induce hair follicle regeneration.The extracellular matrix (ECM) is important for maintaining cell phenotype and promoting cell proliferation and differentiation. In order to better solve the problem of skin appendage regeneration, a combination of mechanical/enzymatic digestion methods was used to self-extract dermal papilla cells (DPCs), which were seeded on silk fibroin/sodium alginate scaffolds as seed cells to evaluate the possibility of skin regeneration/regeneration of accessory organs. Scanning electron microscopy (SEM) graphs showed that the interconnected pores inside the scaffold had a pore diameter in the range of 153–311 μm and a porosity of 41–82%. Immunofluorescence (IF) staining and cell morphological staining proved that the extracted cells were DPCs. The results of a Cell Counting Kit-8 (CCK-8) and Calcein-AM/PI live-dead cell staining showed that the DPCs grew well in the composite scaffold extract. Normal cell morphology and characteristics of aggregation growth were maintained during the 3-day culture, which showed that the silk fibroin/sodium alginate (SF/SA) composite scaffold had good cell-compatibility. Hematoxylin-eosin (H&E) staining of tissue sections further proved that the cells adhered closely and aggregated to the pore wall of the scaffold, and retained the ability to induce differentiation of hair follicles. All these results indicate that, compared with a pure scaffold, the composite scaffold promotes the adhesion and growth of DPCs. We transplanted the SF/SA scaffolds into the back wounds of SD rats, and evaluated the damage model constructed in vivo. The results showed that the scaffold inoculated with DPCs could accelerate the repair of the skin and promote the regeneration of the hair follicle structure.

HaCaT‑conditioned medium supplemented with the small molecule inhibitors SB431542 and CHIR99021 and the growth factor PDGF‑AA prevents the dedifferentiation of dermal papilla cells in vitro

Hair loss, including alopecia, is a common and distressing problem for men and women, and as a result, there is considerable interest in developing treatments that can prevent or reverse hair loss. Dermal papillae closely interact with epidermal cells and play a key role during hair follicle induction and hair morphogenesis. As dermal papilla cells (DPCs) lose their hair-inducing ability in monolayer cultures in vitro, it is difficult to obtain de novo hair follicle structures following DPC transplantation in vivo. The present study aimed to explore culture conditions to maintain DPC characteristics using conditioned media (CM) from the supernatant of cultured HaCaT keratinocyte cells supplemented with other components. Initially, it was observed that during passaging of in vitro monolayer DPC cultures, the Wnt/β-catenin pathway was repressed, while the TGF-β/Smad pathway was activated, and that HaCaT cells cultivated in 1% fetal bovine serum had higher levels of expression of Wnt3a and Wnt10b compared with normal keratinocytes. Culturing of high-passage (P7) DPCs in CM from HaCaT cells (HaCaT-CM) actively stimulated cell proliferation and maintained Sox2 and Versican expression levels. Supplementation of HaCaT-CM with SB431542 (SB, a TGF-β receptor inhibitor), CHIR99021, (CHIR, a GSK3α/β inhibitor and activator of Wnt signaling) and platelet-derived growth factor (PDGF)-AA further increased the expression levels of Sox2, Versican and alkaline phosphatase (ALP) in P7 DPCs. Three-dimensional culture of P7 DPCs using hanging drop cultures in HaCaT-CM supplemented with SB, CHIR and PDGF-AA resulted in larger cell aggregates and a further significant upregulation of Sox2, ALP and Versican expression levels. Taken together, these findings demonstrated that HaCaT-CM supplemented with SB, CHIR and PDGF-AA may preserve the hair-inducing ability of high-passage DPCs and may therefore be useful in reconstructing new hair follicles in vivo.

Wharton’s jelly-derived mesenchymal stem cells in the treatment of four patients with alopecia areata

Alopecia areata (AA) is the second most common cause of non-scarring alopecia. Little is known on the etiopathogenesis of AA. It is considered an autoimmune disease, with T lymphocytes and antibodies directed against hair follicle structures. Topical and systemic therapies are used for the treatment of AA, but none of the therapies used to date have a permanent therapeutic effect. To evaluate the efficacy and safety of AA treatment through a single intradermal injection of a suspension of allogeneic MSCs extracted from Wharton's jelly (WJ-MSCs) into the alopecia foci. The study involved 4 AA patients who underwent experimental therapy with a suspension of WJ-MSCs. The AA intensity was measured using the SALT score. This measure was performed 3 times during treatment: 1st measure (SALT0) prior to treatment; 2nd measure (SALT12) 12 weeks after the treatment; and 3rd measure (SALT24) 24 weeks after the treatment. Furthermore, during each follow-up visit (6, 12, 18, and 24 weeks after the administration of WJ-MSCs) the patient's general condition (physical examination) and local condition were assessed, their mood was evaluated, and a photo of the scalp was taken. Hair regrowth was observed in all patients by an average of 67% at the sites where the cell suspension was administered. In all cases, we observed greater dynamics of hair regrowth in the first 3 months after the treatment, with an average increase of 52.2%, compared to the following 3 months, with an average of 32%. The results of the applied intradermal injections of an allogeneic WJ-MSC suspension were positive with hair growth observed in all participants and the therapy was found to be safe, with no side effects.

Transcriptome Profiling of Human Follicle Dermal Papilla Cells in response to Porphyra-334 Treatment by RNA-Seq.

Porphyra-334 is a kind of mycosporine-like amino acid absorbing ultraviolet-A. Here, we characterized porphyra-334 as a potential antiaging agent. An in vitro assay revealed that porphyra-334 dramatically promoted collagen synthesis in fibroblast cells. The effect of porphyra-334 on cell proliferation was dependent on the cell type, and the increase of cell viability by porphyra-334 was the highest in keratinocyte cells among the three tested cell types. An in vivo clinical test with 22 participants demonstrated the possible role of porphyra-334 in the improvement of periorbital wrinkles. RNA-sequencing using human follicle dermal papilla (HFDP) cells upon porphyra-334 treatment identified the upregulation of metallothionein- (MT-) associated genes, confirming the antioxidant role of porphyra-334 with MT. Moreover, the expression of genes involved in nuclear chromosome segregation and the encoding of components of kinetochores was upregulated by porphyra-334 treatment. Furthermore, we found that several genes associated with the hair follicle cycle, the hair follicle structure, the epidermal structure, and stem cells were upregulated by porphyra-334 treatment, suggesting the potential role of porphyra-334 in hair follicle growth and maintenance. In summary, we provided several new pieces of evidence of porphyra-334 as a potential antiaging cosmetic agent and elucidated the expression network in HFDP cells upon porphyra-334.

Using WGCNA (weighted gene co-expression network analysis) to identify the hub genes of skin hair follicle development in fetus stage of Inner Mongolia cashmere goat.

Mature hair follicles represent an important stage of hair follicle development, which determines the stability of hair follicle structure and its ability to enter the hair cycle. Here, we used weighted gene co-expression network analysis (WGCNA) to identify hub genes of mature skin and hair follicles in Inner Mongolian cashmere goats. We used transcriptome sequencing data for the skin of Inner Mongolian cashmere goats from fetal days 45-135 days, and divided the co expressed genes into different modules by WGCNA. Characteristic values were used to screen out modules that were highly expressed in mature skin follicles. Module hub genes were then selected based on the correlation coefficients between the gene and module eigenvalue, gene connectivity, and Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The results were confirmed by quantitative polymerase chain reaction (qPCR). Ten modules were successfully defined, of which one, with a total of 3166 genes, was selected as a specific module through sample and gene expression pattern analyses. A total of 584 candidate hub genes in the module were screened by the correlation coefficients between the genes and module eigenvalue and gene connectivity. Finally, GO/KEGG functional enrichment analyses detected WNT10A as a key gene in the development and maturation of skin hair follicles in fetal Inner Mongolian cashmere goats. qPCR showed that the expression trends of 13 genes from seven fetal skin samples were consistent with the sequencing results, indicating that the sequencing results were reliable.n.

Dendritic cells as predictive markers of responsiveness to hydroxychloroquine treatment in primary cicatricial alopecia patients

Primary cicatricial alopecia (PCA) encompasses a diverse group of inflammatory diseases characterized by the irreversible replacement of hair follicle structures by fibrous tissue. Although the pathogenesis of PCA remains not fully understood, the key to its understanding might be the location of dendritic cells (DCs) inflammatory infiltrate. One of the systemic therapy of choice in PCA patients is hydroxychloroquine (HCQ). We hypothesized that DCs are implicated in PCA pathogenesis and that they might constitute the biological target of HCQ treatment. For these reasons, we investigated whether DCs could affect the antimalarial responsiveness, and if DCs might be used as predictive factor of responsiveness to HCQ. In this retrospective cohort study, 65 patients diagnosed with PCA were grouped accordingly to their response to HCQ therapy. Skin biopsies had been taken before the treatment was started. Cell count was performed on immunohistochemistry by using characteristic monoclonal antibodies to specific subpopulations of DCs. In almost every second patient (47.7%), we observed remission of the disease during HCQ treatment. The number of plasmacytoid and myeloid DCs as well as Langerhans cells in lesional skin of HCQ responders was higher in comparison with HCQ nonresponders. Moreover, in a predictive model receiver operating characteristic (ROC curve) we showed that plasmacytoid DCs might be used as a predictive factor of responsiveness to HCQ. The results of this study are important as identifying biomarkers for responsiveness to a HCQ therapy will be helpful to individualize treatment and make it more effective.

Expression of Protein Kinases RIPK-1 and RIPK-3 in Mouse and Human Hair Follicle.

Expression of cell death regulators RIPK-1 and RIPK-3 in mouse and human hair follicle structures was studied by immunohistochemistry. At anagen and catagen stages of mouse hair follicle, RIPK-1+ cells were located in the inner root sheath, whereas RIPK-3+ cells were found in the inner and outer root sheath, dermal papilla, and interfollicular epidermis. RIPK-1 expression intensity was low in the early anagen and increased as mature anagen and catagen approached. RIPK-1+ and RIPK-3+ cells were also found in human hair follicle. It is assumed that the role of necroptosis markers in hair follicle life activity is independent of programmed cell death and that they may have yet unknown functions and take part in noncanonical signal cascades.

Transcriptome Profiling and Differential Gene Expression in Canine Microdissected Anagen and Telogen Hair Follicles and Interfollicular Epidermis.

The transcriptome profile and differential gene expression in telogen and late anagen microdissected hair follicles and the interfollicular epidermis of healthy dogs was investigated by using RNAseq. The genes with the highest expression levels in each group were identified and genes known from studies in other species to be associated with structure and function of hair follicles and epidermis were evaluated. Transcriptome profiling revealed that late anagen follicles expressed mainly keratins and telogen follicles expressed GSN and KRT15. The interfollicular epidermis expressed predominately genes encoding for proteins associated with differentiation. All sample groups express genes encoding for proteins involved in cellular growth and signal transduction. The expression pattern of skin-associated genes in dogs is similar to humans. Differences in expression compared to mice and humans include BMP2 expression mainly in telogen and high KRT17 expression in the interfollicular epidermis of dogs. Our data provide the basis for the investigation of the structure and function of canine skin or skin disease and support the use of dogs as a model for human cutaneous disease by assigning gene expression to specific tissue states.

Hormonal Effects on Hair Follicles.

The hair cycle and hair follicle structure are highly affected by various hormones. Androgens—such as testosterone (T); dihydrotestosterone (DHT); and their prohormones, dehydroepiandrosterone sulfate (DHEAS) and androstendione (A)—are the key factors in terminal hair growth. They act on sex-specific areas of the body, converting small, straight, fair vellus hairs into larger darker terminal hairs. They bind to intracellular androgen receptors in the dermal papilla cells of the hair follicle. The majority of hair follicles also require the intracellular enzyme 5-alpha reductase to convert testosterone into DHT. Apart from androgens, the role of other hormones is also currently being researched—e.g., estradiol can significantly alter the hair follicle growth and cycle by binding to estrogen receptors and influencing aromatase activity, which is responsible for converting androgen into estrogen (E2). Progesterone, at the level of the hair follicle, decreases the conversion of testosterone into DHT. The influence of prolactin (PRL) on hair growth has also been intensively investigated, and PRL and PRL receptors were detected in human scalp skin. Our review includes results from many analyses and provides a comprehensive up-to-date understanding of the subject of the effects of hormonal changes on the hair follicle.

Construction and identification of mouse model with conditional knockout of p75 neurotrophin receptor gene in epidermal cells by Cre-loxP system

Objective: To construct and identify a mouse model with conditional knockout (cKO) of p75 neurotrophin receptor (p75NTR-cKO) gene in epidermis cells by Cre-loxP system. Methods: Five p75NTR(flox/flox) transgenic C57BL/6J mice (aged 6-8 weeks, male and female unlimited, the age and sex of mice used for reproduction were the same below) and five keratin 14 promotor-driven (KRT14-) Cre(+ /-) transgenic C57BL/6J mice were bred and hybridized via Cre-loxP system. Five p75NTR(flox/+) ·KRT14-Cre(+ /-) mice selected from the first generation of mice were mated with five p75NTR(flox/flox) mice to obtain the second generation hybrids. After the second generation mice were born 20-25 days, the parts of the mice tail were cut off to identify the genotype by polymerase chain reaction method. Four p75NTR gene complete cKO mice (6 weeks old) and 4 wild-type mice (6 weeks old) were selected and sacrificed respectively. The abdominal skin tissue and brain tissue were excised to observe the expression of p75NTR in the two tissue of two types of mice by immunohistochemical staining. The abdominal skin tissue of two types of mice was obtained to observe the histomorphological changes by hematoxylin and eosin staining. Results: (1) Twenty second generation mice were bred. The genotype of 4 mice was p75NTR(flox/flox)·KRT14-Cre(+ /-)(p75NTR(-/-)), i. e. p75NTR gene complete cKO mice; the genotype of 5 mice was p75NTR(flox/+) ·KRT14-Cre(+ /-), i. e. p75NTR gene partial cKO mice; the genotype of 5 mice was p75NTR(flox/flox)·KRT14-Cre(-/-), and that of 6 mice was p75NTR(flox/+) ·KRT14-Cre(-/-), all of which were wild-type mice. (2) The expression of p75NTR was negative in skin epidermis tissue of p75NTR gene complete cKO mice, while numerous p75NTR positive expression was observed in skin epidermis tissue of wild-type mice. Abundant p75NTR positive expression was observed in brain tissue of both wild-type mice and p75NTR gene complete cKO mice. (3) There was no abnormal growth of skin epidermis tissue in both wild-type mice and p75NTR gene complete cKO mice, with intact hair follicle structure. Conclusions: Applying Cre-loxP system can successfully construct a p75NTR-cKO mice model in epidermis cells without obvious changes in skin histomorphology.

Morphological Characterization and Gene Expression Patterns for Melanin Pigmentation in Rex Rabbit.

Animal melanin has an important role in the formation of animal fur and skin, which is determined by its quantities, character, and distribution. To identify the effect of melanin on the formation of multi-colored Rex rabbits (Black, Chinchilla, Beaver, Protein cyan, Protein yellow, White), the structure of hair follicles and melanin content in multi-colored Rex rabbit skins were observed by Hematoxylin and Eosin (H&E) staining and melanin staining, respectively. The melanin granules were primarily found in the epidermis and hair follicle roots. The melanin content of skin was measured by extracting melanin from skin tissue. The results demonstrated that the melanin content was the highest in the skin of black Rex rabbit. Additionally, we measured the mRNA and protein expression levels of melanin-related key genes (MITF and TYR) in the skin of different hair color by quantitative real-time PCR and Wes assay, respectively. The results revealed that the mRNA expression levels in the skin of black Rex rabbit was highly expressed when as compared with other Rex rabbit skin (P < 0.01), and they were the lowest in the skin of white Rex rabbit. Finally, correlation analysis was conducted between melanin content and the expression levels of mRNA and protein. The results indicated a significant correlation between melanin content and the mRNA expression of MITF (P < 0.05), but it was not correlated with the mRNA expression of TYR (P > 0.05). In summary, melanin deposition has important economic value, and the coat color of fur-bearing animals is partly determined by the melanin-related genes.