Biology of the hair follicle: the basics

Functional fibrillar interfaces: Biological hair as inspiration across scales

Hair, or hair-like fibrillar structures, are ubiquitous in biology, from fur on the bodies of mammals, over trichomes of plants, to the mastigonemes on the flagella of single-celled organisms. While these long and slender protuberances are passive, they are multifunctional and help to mediate interactions with the environment. They provide thermal insulation, sensory information, reversible adhesion, and surface modulation (e.g., superhydrophobicity). This review will present various functions that biological hairs have been discovered to carry out, with the hairs spanning across six orders of magnitude in size, from the millimeter-thick fur of mammals down to the nanometer-thick fibrillar ultrastructures on bateriophages. The hairs are categorized according to their functions, including protection (e.g., thermal regulation and defense), locomotion, feeding, and sensing. By understanding the versatile functions of biological hairs, bio-inspired solutions may be developed across length scales.

Thyroid receptor β: A promising target for developing novel anti-androgenetic alopecia drugs

Androgenetic alopecia (AGA) significantly impacts the self-confidence and mental well-being of people. Recent research has revealed that thyroid receptor β (TRβ) agonists can activate hair follicles and effectively stimulate hair growth. This review aims to comprehensively elucidate the specific mechanism of action of TRβ in treating AGA from various perspectives, highlighting its potential as a drug target for combating AGA. Moreover, this review provides a thorough summary of the research advances in TRβ agonist candidates with anti-AGA efficacy and outlines the structure-activity relationships (SARs) of TRβ agonists. We hope that this review will provide practical information for the development of effective anti-alopecia drugs.

Promotion of hair growth by a conditioned medium from human umbilical cord mesenchymal stem cells cultivated in a 3D scaffold of gelatin sponge

BACKGROUND

This study aims to investigate the effects of a conditioned medium (CM) from human umbilical cord mesenchymal stem cells (HuMSCs) cultivated in gelatin sponge (GS-HuMSCs-CM) on hair growth in a mouse model.

METHODS

CM was collected from the HuMSCs cultivated in a monolayer or in a gelatin sponge. Vascular endothelial growth factor (VEGF), insulin-like growth factor-1 (IGF-1), keratinocyte growth factor (KGF), and hepatocyte growth factor (HGF) levels in CMs were measured by enzyme-linked immunosorbent assays (ELISAs). A hair loss model by a C57 BL/6J mouse was prepared. The effects of GS-HuMSCs-CM and HuMSCs on hair regrowth in mice were investigated by intradermal injection in the depilated back skin with normal saline (NS) as the control. The time for hair regrowth and full covering in depilated areas was observed, and the hair growth was evaluated histologically and by grossly measuring hair length and diameter.

RESULTS

Compared with monolayer cultured cells, the three-dimensional (3D) culture of HuMSCs in gelatin sponge drastically increased VEGF, IGF-1, KGF, and HGF production. GS-HuMSCs-CM and HuMSCs injection both promoted hair regeneration in mice, while GS-HuMSCs-CM presented more enhanced effects in hair length, hair diameter, and growth rate. GS-HuMSCs-CM significantly promoted angiogenesis in injected skin areas, which might also contribute to faster hair regrowth.

CONCLUSION

GS-HuMSCs-CM exerted significant effects on inducing hair growth and promoted skin angiogenesis in C57BL/6J mice.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Enhancing the contemporary human and water isotope reference database for the Netherlands: New insights from Sr-O-C-N-H isotope data

The determination of an individual's geographic origin is an essential aspect of forensic investigations. When primary identifiers cannot be used to make a positive identification, isotope analysis can be utilized to provide new leads. Modern reference data are essential for accurate interpretation of human isotopic data in terms of diet and origin. This article presents Sr-O-C-N-H isotope data of modern individuals (hair, dental enamel, and dentine collagen) and drinking water from the Netherlands. The δ15N values of human hair fall within the range of values observed worldwide and cannot be utilized to differentiate from other countries. Distinct disparities in the hair δ13C are evident between European countries and other regions, making it possible to exclude the Netherlands as a region of origin. Comparing Dutch dental isotope data to those of other nations has proven difficult due to the limited availability of reference data. The same limitation applies to tap water δ2H data.

The Biology and Genomics of Human Hair Follicles: A Focus on Androgenetic Alopecia

Androgenetic alopecia is a highly prevalent condition mainly affecting men. This complex trait is related to aging and genetics; however, multiple other factors, for example, lifestyle, are also involved. Despite its prevalence, the underlying biology of androgenetic alopecia remains elusive, and thus advances in its treatment have been hindered. Herein, we review the functional anatomy of hair follicles and the cell signaling events that play a role in follicle cycling. We also discuss the pathology of androgenetic alopecia and the known molecular mechanisms underlying this condition. Additionally, we describe studies comparing the transcriptional differences in hair follicles between balding and non-balding scalp regions. Given the genetic contribution, we also discuss the most significant risk variants found to be associated with androgenetic alopecia. A more comprehensive understanding of this pathology may be generated through using multi-omics approaches.

ChIP-Seq analysis reveals PRKACB as a target gene of HOXC13 involved in rabbit hair follicle development

Dermal papilla cells (DPCs) are key regulators of hair follicle (HF) development and growth, which not only regulate HF growth and cycling but play a role in the pathogenesis of hair loss. The transcription factor Homeobox C13 (HOXC13) can modulate the growth and development of HFs. Nevertheless, the specific genes and pathways regulated by HOXC13 in DPCs have yet to be determined. Thus, to gain a better understanding of genomic binding sites involved in HOXC13-regulated HF development, chromatin immunoprecipitation followed by high throughput sequencing (ChIP-Seq) was performed on rabbit DPCs with pcDNA3.1-3 × Flag-HOXC13 overexpression. A complete set of 9670 enrichment peaks was acquired by applying HOXC13-Flag ChIP. Subsequently, the peak sequence was annotated to the rabbit genome, revealing that 6.1 % of the peaks were identified within in the promoter region. Thereafter, five annotated genes were verified using RT-qPCR. The peak-associated genes were mainly enriched in signaling pathways related to HF development, such as MAPK and PI3K-Akt. Furthermore, by using a dual-luciferase reporter assay, we found that HOXC13 can target the protein kinase cAMP‑dependent catalytic β (PRKACB) promoter region (-1596 ∼ -1107 bp) and inhibit its transcription, which was consistent with data obtained from ChIP-seq analysis. Overexpression of PRKACB gene significantly modulated the expression of BCL2, WNT2, LEF1, and SFRP2 genes related to HF development as determined by RT-qPCR (P < 0.01, P < 0.05). The CCK-8 and flow cytometry assays showed that PRKACB significantly inhibited the proliferation of DPCs and promoted apoptosis (P < 0.01). In conclusion, our research revealed that PRKACB has the potential to serve as a novel target gene of HOXC13, contributing to the regulation of the proliferation and apoptosis of DPCs. The process of identifying global target genes can contribute to the understanding of the intricate pathways that HOXC13 regulates in the growth of HFs.

Sr-Pb isotope differences in pre- and post-burial human bone, teeth, and hair keratin: implications for isotope forensics

The isotopic signatures of human tissues can provide valuable information on geographic origin for medicolegal investigations involving unidentified persons. It is important to understand the impact of diagenetic processes on isotopic signatures, as alterations could result in incorrect estimation of geographic origin. This study examines alterations in isotope signatures of different tissues of five human body donors studied throughout decomposition at the Forensic Anthropology Research Facility (FARF), San Marcos, TX. Two body donors were buried, two were placed in open pits, and one was first allowed to naturally mummify and then buried. Remains were recovered after a period of 7-34 months. The preplacement and post-recovery Sr-Pb isotope data of scalp hair, bone (iliac and tibia), and tooth enamel and dentine were compared. The hair samples record significant shifts in Sr-Pb isotope compositions, with hair keratin Pb isotope composition shifting towards the Pb signature of local soil samples. Hair keratin Sr isotope compositions were altered by the burial environment and possibly also by the lab sample cleaning method. The spongy iliac bone samples show inconsistencies in the recoverability of the preplacement Sr-Pb isotope signatures. The post-placement signatures of the buried donors show slight elevation over preplacement signatures. The post-placement signatures of donors placed in open pits are significantly elevated. The tibia and dental samples record the most consistent isotopic data with the least alteration. These more densely mineralised elements show good recoverability of the preplacement isotope signatures in burials and open pits and are thus deemed better targets for forensic investigative purposes.

Cannabinoids and Their Receptors in Skin Diseases

The therapeutic application of cannabinoids has gained traction in recent years. Cannabinoids interact with the human endocannabinoid system in the skin. A large body of research indicates that cannabinoids could hold promise for the treatment of eczema, psoriasis, acne, pruritus, hair disorders, and skin cancer. However, most of the available data are at the preclinical stage. Comprehensive, large-scale, randomized, controlled clinical trials have not yet been fully conducted. In this article, we describe new findings in cannabinoid research and point out promising future research areas.

Astragalus membranaceus and Cinnamomum cassia Stimulate the Hair Follicle Differentiation-Related Growth Factor by the Wnt/β-Catenin Signaling Pathway

Astragalus membranaceus and Cinnamomum cassia are used as spices and flavorful ingredients, or medicinal herbs with pharmacological effects. In this study, the hair-growth-promoting effects of the YH complex, a newly developed formula consisting of membranaceus and C. cassia, are investigated with the prediction of its molecular mechanism. The target gene of the YH complex was about 74.8% overlapped with the gene set of 'Hair growth' on the GO Biological Process database. The oral administration of the YH complex promoted hair regrowth and increased hair-shaft thickness in depilated hair loss mice. In addition, the anagen/telogen hair follicle ratio was significantly increased by the YH complex. The growth factors affecting the growth of hair follicles were dose-dependently increased by treatment with the YH complex. The Wnt/β-catenin signaling pathway expressions in skin tissues were apparently increased by the administration of the YH complex. In conclusion, the YH complex consisting of A. membranaceus and C. cassia induced hair follicle differentiation and preserved the growing-anagen phase by increasing growth factors and the Wnt/β-catenin signaling pathway, leading to the restoration of hair loss. The YH complex can be a remedy for hair loss diseases, such as alopecia areata, androgenetic alopecia, telogen effluvium, and chemotherapy-induced alopecia.

Impact of Thyroid Dysfunction on Hair Disorders

Hair loss is a problem for everyone, regardless of their age or sex. The three most prevalent types of hair loss, telogen effluvium, alopecia areata, and androgenetic alopecia, have been associated with a variety of risk factors. Strong evidence links thyroid hormones (THs) to hair loss. THs control the growth, differentiation, metabolism, and thermogenesis of body cells. The skin is a significant target organ for THs; however, the cellular and molecular causes of thyroid dysfunction-related skin diseases remain unknown. Hyperthyroidism, hypothyroidism, and drug-induced hypothyroidism can induce widespread hair shedding. Little information is available regarding the incidence and effects of thyroid dysfunction on hair problems. This study aimed to review the impact and prevalence of thyroid disorders on hair loss. The conclusions drawn from this study highlight the underestimated prevalence and impact of thyroid disorders on hair loss. The review of scientific articles, including original research, review articles, and a case report, provides a comprehensive understanding of the topic. This research adds to the existing literature by enhancing our understanding of the relationship between thyroid dysfunction and hair disorders. It contributes to the body of evidence by reviewing relevant studies and summarizing the impact of thyroid disorders on hair loss. The study also highlights the gaps in knowledge and the need for more research in this area to improve the diagnosis and management of hair disorders associated with thyroid dysfunction.

Exploring the Effects of Wetting and Free Fatty Acid Deposition on an Atomistic Hair Fiber Surface Model Incorporating Keratin-Associated Protein 5-1

The complex development of cosmetic and medical formulations relies on an ever-growing accuracy of predictive models of hair surfaces. Hitherto, modeling efforts have focused on the description of 18-methyl eicosanoic acid (18-MEA), the primary fatty acid covalently attached to the hair surface, without explicit modeling of the protein layer. Herein, the molecular details of the outermost surface of the human hair fiber surface, also called the F-layer, were studied using molecular dynamics (MD) simulations. The F-layer is composed primarily of keratin-associated proteins KAP5 and KAP10, which are decorated with 18-MEA on the outer surface of a hair fiber. In our molecular model, we incorporated KAP5-1 and evaluated the surface properties of 18-MEA through MD simulations, resulting in 18-MEA surface density, layer thickness, and tilt angles in agreement with previous experimental and computational studies. Subsequent models with reduced 18-MEA surface density were also generated to mimic damaged hair surfaces. Response to wetting of virgin and damaged hair showed rearrangement of 18-MEA on the surface, allowing for water penetration into the protein layer. To demonstrate a potential use case for these atomistic models, we deposited naturally occurring fatty acids and measured 18-MEA's response in both dry and wet conditions. As fatty acids are often incorporated in shampoo formulations, this work demonstrates the ability to model the adsorption of ingredients on hair surfaces. This study illustrates, for the first time, the complex behavior of a realistic F-layer at the molecular level and opens up the possibility of studying the adsorption behavior of larger, more complex molecules and formulations.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Regulation of secondary hair follicle cycle in cashmere goats by miR-877-3p targeting IGFBP5 gene

Cashmere, a highly valuable animal product derived from cashmere goats, holds significant economic importance. MiRNAs serve as crucial regulators in the developmental processes of mammalian hair follicles. Understanding the regulation of miRNAs during the hair follicle cycle is essential for enhancing cashmere quality. In this investigation, we employed high-throughput sequencing technology to analyze the expression profiles of miRNAs in the secondary hair follicles of Jiangnan cashmere goats at different stages. Through bioinformatics analysis, we identified differentially expressed miRNAs (DE miRNAs). The regulatory relationships between miRNAs and their target genes were verified using multiple techniques, including RT-qPCR, western blot, Dual-Luciferase Reporter, and CKK-8 assays. Our findings revealed the presence of 193 DE miRNAs during various stages of the hair follicle cycle in Jiangnan cashmere goats. Based on the previously obtained mRNA data, the target genes of DE miRNA were predicted, and 1,472 negative regulatory relationships between DE miRNAs and target genes were obtained. Notably, the expression of chi-miR-877-3p was down-regulated during the telogen (Tn) phase compared to the anagen (An) and catagen (Cn) phases, while the IGFBP5 gene exhibited up-regulation. Further validation experiments confirmed that overexpression of chi-miR-877-3p in dermal papilla cells suppressed IGFBP5 gene expression and facilitated cell proliferation. The results of this study provide novel insights for analyzing the hair follicle cycle.

Dutasteride nanoemulsion preparation to inhibit 5-alpha-hair follicle reductase enzymes in the hair follicle; an ex vivo study

Alopecia is a treatable disorder that usually occurs due to high levels of 5-alpha dihydrotestosterone in hair follicles. To enhance the storage capacity of hair follicles and alleviate the inherent characteristics of dutasteride, 5-alpha reductase inhibitor, a prolonged-release nanocarrier was synthesised, and its influence on rat abdomen's skin was investigated. Results showed the lower ratio of S/Co (higher ethanol concentration) increased the hydrodynamic nanocarriers' particle size due to thermodynamic disturbance and Ostwald ripening. In contrast, an increase in surfactant through a decrease in interfacial tension resulted in smaller nanocarriers of 32.4 nm. Moreover, an increase in viscosity had an inverse correlation with the nanoemulsions' particle size. Nanocarriers containing ethanol showed less entrapment efficacy, perhaps due to the rapid dissolution of dutasteride into ethanol during nanoemulsification, while, based on Stokes' equation, the addition of ethanol resulted in smaller particle size and stability of the system. Skin permeation analysis using Franz diffusion cells showed nanocarriers could pass through the skin and release dutasteride for 6 days. In conclusion, the optimum concentration of ingredients is decisive in guaranteeing the ideal particle size, stability, and skin permeation of nanocarriers. The Present dutasteride nanocarrier would promise a prolonged and sustained-release drug delivery system for Alopecia therapy.

In ovo injection of CHIR-99021 promotes feather follicles development via activating Wnt/β-catenin signaling pathway during chick embryonic period

The Wingless-types/beta-catenin (Wnt/β-catenin) signaling pathway plays an important role in embryonic development and affects the physiological development processes of feather follicles. To investigate the role of Wnt/β-catenin pathway in regulating feather follicles morphogenesis, in ovo injection of CHIR-99021, an activator of the Wnt/β-catenin signaling pathway, was conducted in chick embryo model. Initially, a total of 40 embryos were used to assess feather follicles morphogenesis and the expression of β-catenin (E9–E17). The histological results showed that feather follicle morphogenesis was mainly completed from E9 to E17. β-catenin was involved in the processing of the appearance of dermal cell condensation (E9) and the completion of the feather follicles morphogenesis (E17). Next, a total of 160 fertilized eggs were randomly divided into 8 groups for in ovo injection at E9, including a Normal Saline injected group (CON) and the 500, 1,000, 2,000, 5,000, 10,000, 50,000, and 100,000 ng CHIR-99021 groups. Dorsal skin tissue samples were collected at E17 for investigating feather follicles morphology and expressions of β-catenin and lymphoid enhancerbinding factor-1 (LEF1) at gene and protein levels. The results showed that feather follicle diameter in the injected groups were significantly (P < 0.05) increased with limit dose-independence compared to the CON group. CHIR-99021 significantly (P < 0.05) influenced the mRNA expressions of catenin beta-1 (CTNNB1) and downstream target LEF1. In ovo injection of CHIR-99021 caused that β-catenin and LEF1 were significantly (P < 0.05) increased followed the increased doses as determined by western blotting. The immunochemical results showed that β-catenin was detected in the dermal papilla of feather follicles. Given these results, this study suggests to developmental biology that in ovo injection of CHIR-99021 promoted feather follicles morphogenesis and development via activating Wnt/β-catenin signaling pathway and upregulating downstream target LEF1 during embryonic period in chick embryo model. Moreover, CHIR-99021 may be a strong candidate to promote the animal feather/hair industry, especially as a reference for bird feather production.

3D bioprinting of a gelatin-alginate hydrogel for tissue-engineered hair follicle regeneration

Hair follicle (HF) regeneration remains challenging, principally due to the absence of a platform that can successfully generate the microenvironmental cues of hair neogenesis. Here, we demonstrate a 3D bioprinting technique based on a gelatin/alginate hydrogel (GAH) to construct a multilayer composite scaffold simulating the HF microenvironment in vivo. Fibroblasts (FBs), human umbilical vein endothelial cells (HUVECs), dermal papilla cells (DPCs), and epidermal cells (EPCs) were encapsulated in GAH (prepared from a mixture of gelatin and alginate) and respectively 3D-bioprinted into the different layers of a composite scaffold. The bioprinted scaffold with epidermis- and dermis-like structure was subsequently transplanted into full-thickness wounds in nude mice. The multilayer scaffold demonstrated suitable cytocompatibility and increased the proliferation ability of DPCs (1.2-fold; P < 0.05). It also facilitated the formation of self-aggregating DPC spheroids and restored DPC genes associated with hair induction (ALP, β-catenin, and α-SMA). The dermal and epidermal cells self-assembled successfully into immature HFs in vitro. HFs were regenerated in the appropriate orientation in vivo, which can mainly be attributed to the hierarchical grid structure of the scaffold and the dot bioprinting of DPCs. Our 3D printed scaffolds provide a suitable microenvironment for DPCs to regenerate entire HFs and could make a significant contribution in the medical management of hair loss. This method may also have broader applications in skin tissue (and appendage) engineering. STATEMENT OF SIGNIFICANCE: Hair loss remains a challenging clinical problem that influences quality of life. Three-dimensional (3D) bioprinting has become a useful tool for the fabrication of tissue constructs for transplantation and other biomedical applications. In this study, we used a 3D bioprinting technique based on a gelatin/alginate hydrogel to construct a multi-layer composite scaffold with cuticular and corium layers to simulate the microenvironment of dermal papilla cells (DPCs) in the human body. This new approach permits the controllable formation of self-aggregating spheroids of DPCs in a physiologically relevant extracellular matrix and the initiation of epidermal-mesenchymal interactions, which results in HF formation in vivo. The ability to regenerate entire HFs should have a significant impact on the medical management of hair loss.

Deletion of hypoxia-inducible factor prolyl 4-hydroxylase 2 in FoxD1-lineage mesenchymal cells leads to congenital truncal alopecia

Hypoxia-inducible factors (HIFs) induce numerous genes regulating oxygen homeostasis. As oxygen sensors of the cells, the HIF prolyl 4-hydroxylases (HIF-P4Hs) regulate the stability of HIFs in an oxygen-dependent manner. During hair follicle (HF) morphogenesis and cycling, the location of dermal papilla (DP) alternates between the dermis and hypodermis and results in varying oxygen levels for the DP cells. These cells are known to express hypoxia-inducible genes, but the role of the hypoxia response pathway in HF development and homeostasis has not been studied. Using conditional gene targeting and analysis of hair morphogenesis, we show here that lack of Hif-p4h-2 in Forkhead box D1 (FoxD1)-lineage mesodermal cells interferes with the normal HF development in mice. FoxD1-lineage cells were found to be mainly mesenchymal cells located in the dermis of truncal skin, including those cells composing the DP of HFs. We found that upon Hif-p4h-2 inactivation, HF development was disturbed during the first catagen leading to formation of epithelial-lined HF cysts filled by unorganized keratins, which eventually manifested as truncal alopecia. Furthermore, the depletion of Hif-p4h-2 led to HIF stabilization and dysregulation of multiple genes involved in keratin formation, HF differentiation, and HIF, transforming growth factor β (TGF-β), and Notch signaling. We hypothesize that the failure of HF cycling is likely to be mechanistically caused by disruption of the interplay of the HIF, TGF-β, and Notch pathways. In summary, we show here for the first time that HIF-P4H-2 function in FoxD1-lineage cells is essential for the normal development and homeostasis of HFs.

Stimulatory Effects of Extracellular Vesicles Derived from Leuconostoc holzapfelii That Exists in Human Scalp on Hair Growth in Human Follicle Dermal Papilla Cells

Human hair follicle dermal papilla cells (HFDPCs) located in hair follicles (HFs) play a pivotal role in hair follicle morphogenesis, hair cycling, and hair growth. Over the past few decades, probiotic bacteria (PB) have been reported to have beneficial effects such as improved skin health, anti-obesity, and immuno-modulation for conditions including atopic dermatitis and inflammatory bowel disease (IBD). PB can secrete 50~150 nm sized extracellular vesicles (EVs) containing microbial DNA, miRNA, proteins, lipids, and cell wall components. These EVs can regulate communication between bacteria or between bacteria and their host. Although numerous biological effects of PB-EVs have been reported, the physiological roles of Leuconostoc holzapfelii (hs-Lh), which is isolated from human scalp tissue, and the extracellular vesicles derived from them (hs-LhEVs) are largely unknown. Herein, we investigated the effects of hs-LhEVs on hair growth in HFDPCs. We show that hs-LhEVs increase cell proliferation, migration, and regulate the cell cycle. Furthermore, hs-LhEVs were found to modulate the mRNA expression of hair-growth-related genes in vitro. These data demonstrate that hs-LhEVs can reduce apoptosis by modulating the cell cycle and promote hair growth by regulation via the Wnt/β-catenin signal transduction pathway.

Tissue Engineering and Regeneration of the Human Hair Follicle in Androgenetic Alopecia: Literature Review

Androgenetic alopecia (AGA) is an androgen-dependent process and represents the most frequent non-scarring alopecia. Treatments for AGA do not always achieve a satisfactory result for the patient, and sometimes cause side effects that lead to discontinuation of treatment. AGA therapeutics currently includes topical and oral drugs, as well as follicular unit micro-transplantation techniques. Tissue engineering (TE) is postulated as one of the possible future solutions to the problem and aims to develop fully functional hair follicles that maintain their cyclic rhythm in a physiological manner. However, despite its great potential, reconstitution of fully functional hair follicles is still a challenge to overcome and the knowledge gained of the key processes in hair follicle morphogenesis and biology has not yet been translated into effective replacement therapies in clinical practice. To achieve this, it is necessary to research and develop new approaches, techniques and biomaterials. In this review, present and emerging hair follicle bioengineering strategies are evaluated. The current problems of these bioengineering techniques are discussed, as well as the advantages and disadvantages, and the future prospects for the field of TE and successful hair follicle regeneration.

The Effect of Botulinum Toxin on Hair Follicle Cell Regeneration Under Continuous Stress Conditions: a Pilot Animal Study

We analyzed the effect of botulinum toxin (BTX) type A on the regeneration of hair follicle cells under continuous stress conditions. Thirty 6-week-old C57BL/6 mice were used, and hair loss was induced on their backs (10 control (CTL) mice, reared under normal conditions without stress; 10 mice, exposed to continuous stress (STRESS) by fixing in an enclosed space; 10 BTX + STRESS mice, injected subcutaneously with 1 IU of BTX (0.1 cc) where the hair follicles were removed under the same stress conditions). There was less hair growth in the STRESS and BTX + STRESS groups compared to that in the CTL group at 2 weeks. At 3 weeks, the telogen stage was mainly observed in the STRESS group whereas the anagen stage was observed in the CTL and BTX + STRESS groups. A substantial increase in terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells was observed in the STRESS group compared to that in the CTL and BTX + STRESS groups. Substance P (SP) immunoreactivity cell levels increased in the STRESS group at 2 and 3 weeks compared to those in the BTX + STRESS group. SP expression increased at 2 and 3 weeks in the STRESS group compared to that in the CTL and BTX + STRESS groups. A delay in the regeneration cycle of the hair follicle cells occurred when stress was applied, and an almost normal regeneration cycle occurred when BTX was injected subcutaneously. Therefore, BTX may be a positive indicator for hair loss treatment.

Stem Cells from Human Exfoliated Deciduous teeth Promote Hair Regeneration in Mouse

Stem cells in different types may interact with each other to maintain homeostasis or growth and the interactions are complicated and extensive. There is increasing evidence that mesenchymal-epithelial interactions in early morphogenesis stages of both tooth and hair follicles show many similarities. In order to explore whether stem cells from one tissue could interact with cells from another tissue, a series of experiments were carried out. Here we successfully extracted and identified stem cells from human exfoliated deciduous teeth (SHED) of 8–12 years old kids, and then found that SHED could promote hair regeneration in a mouse model. In vitro, SHED shortened the hair regeneration cycle and promoted the proliferation and aggregation of dermal cells. In vivo, when SHED and skin cells of C57 mice were subcutaneously co-transplanted to nude mice, more hair was formed than skin cells without SHED. To further explore the molecular mechanism, epidermal and dermal cells were freshly extracted and co-cultured with SHED. Then several signaling molecules in hair follicle regeneration were detected and we found that the expression of Sonic Hedgehog (Shh) and Glioma-associated oncogene 1 (Gli1) was up-regulated. It seems that SHED may boost the prosperity of hairs by increase Shh/Gli1 pathway, which brings new perspectives in tissue engineering and damaged tissue repairing.

Topical drug delivery: History, percutaneous absorption, and product development

Topical products, widely used to manage skin conditions, have evolved from simple potions to sophisticated delivery systems. Their development has been facilitated by advances in percutaneous absorption and product design based on an increasingly mechanistic understanding of drug-product-skin interactions, associated experiments, and a quality-by-design framework. Topical drug delivery involves drug transport from a product on the skin to a local target site and then clearance by diffusion, metabolism, and the dermal circulation to the rest of the body and deeper tissues. Insights have been provided by Quantitative Structure Permeability Relationships (QSPR), molecular dynamics simulations, and dermal Physiologically Based PharmacoKinetics (PBPK). Currently, generic product equivalents of reference-listed products dominate the topical delivery market. There is an increasing regulatory interest in understanding topical product delivery behavior under 'in use' conditions and predicting in vivo response for population variations in skin barrier function and response using in silico and in vitro findings.

A three-dimensional bioprinting technique, based on a gelatin/alginate hydrogel, for the tissue engineering of hair follicle reconstruction

Hair loss remains a challenging clinical problem that influences the quality of life. Three-dimensional (3D) bioprinting has become a valuable tool for fabricating tissue constructs for transplantation and other biomedical applications. Although some simple organs, such as skin and cartilage, have been successfully simulated, it remains challenging to make hair follicles (HFs), which are highly complex organs. The tissue engineering of human HFs has been a long-standing challenge, and progress with this has lagged behind that with other lab-grown tissues. This is principally due to a lack of availability of a platform that can successfully recapitulate the microenvironmental cues required to maintain the requisite cellular interactions for hair neogenesis. In this study, we used a 3D bioprinting technique based on a gelatin/alginate hydrogel to construct a multilayer composite scaffold with cuticular and corium layers to simulate the microenvironment of dermal papilla cells (DPCs) in the human body. This new approach permits the controllable formation of self-aggregating spheroids of DPCs in a physiologically relevant extracellular matrix and the initiation of epidermal-mesenchymal interactions, which results in HF formation in vivo. In conclusion, our 3D-bioprinted multilayer composite scaffold prepared using a gelatin/alginate hydrogel provides a suitable 3D microenvironment for DPCs to induce HF formation. The ability to regenerate entire HFs should have a significant impact on the medical management of hair loss. This method may also have critical applications for skin tissue engineering, with its appendages, for other purposes.

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

OBJECTIVE

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.

METHODS

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).

RESULTS

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.

Therapeutic Potential of Cannabidiol (CBD) for Skin Health and Disorders

Though there is limited research confirming the purported topical benefits of cannabinoids, it is certain that cutaneous biology is modulated by the human endocannabinoid system (ECS). Receptors from the ECS have been identified in the skin and systemic abuse of synthetic cannabinoids, and their analogs, have also been associated with the manifestation of dermatological disorders, indicating the effects of the ECS on cutaneous biology. In particular, cannabidiol (CBD), a non-psychoactive compound from the cannabis plant, has garnered significant attention in recent years for its anecdotal therapeutic potential for various pathologies, including skin and cosmetic disorders. Though a body of preclinical evidence suggests topical application of CBD may be efficacious for some skin disorders, such as eczema, psoriasis, pruritis, and inflammatory conditions, confirmed clinical efficacy and elucidation of underlying molecular mechanisms have yet to be fully identified. This article provides an update on the advances in CBD research to date and the potential areas of future exploration.

Hair growth potential of Salvia plebeia extract and its associated mechanisms

Context: Although Salvia plebeia (SP) R. Brown (Labiatae) is known to possess various biological activities, the effects of SP on hair growth have not been elucidated.Objective: To investigate the hair growth potential of SP extract by using human dermal papilla cells (hDPCs) and C57BL/6 mice.Materials and methods: The entire SP plant sample was ground into powder and extracted with 99.9% methyl alcohol. Various concentrations of SP extract were added to hDPCs to evaluate the proliferation, migration, and factors related to hair growth and cycling. Effect of topical SP administration on hair regrowth was tested in vivo in male C57BL/6 mice for 21 days.Results: SP extract significantly increased the proliferation of cultured hDPCs at doses of 15.6 and 31.3 μg/mL compared to control group by 123% and 132%, respectively. Expression of hepatocyte growth factor increased while the level of TGF-β1 and SMAD2/3 decreased when treated with SP extract. At the molecular level, the extract activated Wnt/β-catenin signalling by raising β-catenin and phospho-GSK3β expression. SP extract also exerted anti-apoptotic and proliferative effects in hDPCs by increasing the Bcl-2/Bax ratio and activating cell proliferation-related proteins, ERK and Akt. Finally, the extract caused an induction of the anagen phase leading to significantly enhanced hair growth in treated male mice.Discussion and conclusion: Our results indicate that SP extract has the capacity to activate hDPCs into a proliferative state to promote hair growth. Further research is necessary to determine the bioactive components and their mechanisms of action responsible for SP-related hair growth effect.

Epidermal Stem Cells in Hair Follicle Cycling and Skin Regeneration: A View From the Perspective of Inflammation

There are many studies devoted to the role of hair follicle stem cells in wound healing as well as in follicle self-restoration. At the same time, the influence of the inflammatory cells on the hair follicle cycling in both injured and intact skin is well established. Immune cells of all wound healing stages, including macrophages, γδT cells, and T regs, may activate epidermal stem cells to provide re-epithelization and wound-induced hair follicle neogenesis. In addition to the ability of epidermal cells to maintain epidermal morphogenesis through differentiation program, they can undergo de-differentiation and acquire stem features under the influence of inflammatory milieu. Simultaneously, a stem cell compartment may undergo re-programming to adopt another fate. The proportion of skin resident immune cells and wound-attracted inflammatory cells (e.g., neutrophils and macrophages) in wound-induced hair follicle anagen and plucking-induced anagen is still under discussion to date. Experimental data suggesting the role of reactive oxygen species and prostaglandins, which are uncharacteristic of the intact skin, in the hair follicle cycling indicates the role of neutrophils in injury-induced conditions. In this review, we discuss some of the hair follicles stem cell activities, such as wound-induced hair follicle neogenesis, hair follicle cycling, and re-epithelization, through the prism of inflammation. The plasticity of epidermal stem cells under the influence of inflammatory microenvironment is considered. The relationship between inflammation, scarring, and follicle neogenesis as an indicator of complete wound healing is also highlighted. Taking into consideration the available data, we also conclude that there may exist a presumptive interlink between the stem cell activation, inflammation and the components of programmed cell death pathways.

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.

Effect of Chrysanthemum zawadskii Extract on Dermal Papilla Cell Proliferation and Hair Growth

Background

Chrysanthemum zawadskii (CZ) belongs to the genus Chrysanthemum, also known as ‘Gu-Jeol-Cho’ in Korea. CZ has been used as herbal remedy to manage cough, hypertensive disorders, pharyngitis, bronchitis, gastroenteritis, pneumonia, bladder diseases and common cold. However, its effect on hair growth has not been documented.

Objective

The aim of present study was to elucidate the beneficial effects of CZ on hair growth.

Methods

Proliferation of follicular dermal papilla (DP) cells from human scalp skin was evaluated by MTT assay. The expression of various molecules in DP cells was checked by western blot assay. Effect of CZ extract on the hair growth was evaluated by hair organ culture and C57BL/6 mice model.

Results

Cultivation of DP cells with CZ extract increased cellular proliferation, increased expression of phosphorylated protein kinase B (p-Akt), p-ERK, B-cell lymphoma 2, and decreased expression of Bax. Treatment of human hair follicles with CZ extract significantly enhanced hair growth. Additionally, CZ markedly shortened telogen period, increased anagen transformation and stimulated hair growth in the animal study.

Conclusion

These results suggest that CZ extract has an effect of promoting hair growth and may therefore be a useful a therapeutic remedy for preventing hair loss.

Socioeconomic and geographic implications from carbon, nitrogen, and sulfur isotope ratios in human hair from Mexico

This article presents data on carbon (C), nitrogen (N), and sulfur (S) isotopic composition of human hair collected throughout Mexico. The recorded values ranged from -18.3‰ to -12.8‰ for δ¹³C, 6.8‰ to 10.8‰ for δ¹⁵N and from 2.7‰ to 8.0‰ for δ³⁴S. The socioeconomic covariates explored in this study showed, in part strong correlations with the recorded isotope values. Furthermore, these three isotope systems provide records of the dietary preferences and practices and also showed some spatial variation. This study detected geospatial patterning in the δ¹³C values of hair samples from Mexico as well as significant correlations with socioeconomic factors. No geospatial variation was detected in the δ¹⁵N and δ³⁴S values, however, socioeconomic correlations were found. A δ¹³C isoscape was generated using a GIS approach, which provides a tool to narrow down region-of-origin predictions (in combination with other isotope systems) and to document the travel history of unidentified individuals.

Comparison of strontium isotope ratios in Mexican human hair and tap water as provenance indicators

Deceased undocumented border crossers are some of the most difficult individuals to identify due to the inability to narrow down the region of origin and therefore to obtain family reference samples for DNA comparison. The isotopic compositions of various body tissues have been demonstrated to be useful biomarkers for tracking locations and movements to aid in the identification of human remains. This study closes the large spatial gap of available ⁸⁷Sr/⁸⁶Sr ratios from North America in tap water and presents the first ⁸⁷Sr/⁸⁶Sr human tissue-based ratios from Mexico. The 101 hair samples from 32 locations in Mexico range in ⁸⁷Sr/⁸⁶Sr ratios from 0.70424 to 0.71613 (ΔSr_max-min=0.01189). Furthermore, 151 tap water samples from 51 locations range between 0.70404 to 0.71385 (ΔSr_max-min=0.00981). Overall, small variations in the hair and tap water samples collected from individual locations were recorded (ΔSr_max-min=0.00041 and 0.00034 respectively). Despite the fact that Mexico is one of the largest bottled water consumers in the world, the ⁸⁷Sr/⁸⁶Sr ratios of human hair and tap water correlated strongly (R²=0.87 for location averages and R²=0.80 when using individual data points). These data represent a valuable resource for identifying the provenance of human remains.

Crosstalk between androgen and Wnt/β-catenin leads to changes of wool density in FGF5-knockout sheep

Fibroblast growth factor 5 (FGF5) is a famous dominant inhibitor of anagen phase of hair cycle. Mutations of FGF5 gene result in a longer wool in mice, donkeys, dogs, cats, and even in human eyelashes. Sheep is an important source of wool production. How to improve the production of wool quickly and effectively is an urgent problem to be solved. In this study, we generated five FGF5-knockout Dorper sheep by the CRISPR/Cas9 system. The expression level of FGF5 mRNA in knockout (KO) sheep decreased significantly, and all FGF5 proteins were dysfunctional. The KO sheep displayed a significant increase in fine-wool and active hair-follicle density. The crosstalk between androgen and Wnt/β-catenin signaling downstream of FGF5 gene plays a key role. We established downstream signaling cascades for the first time, including FGF5, FGFR1, androgen, AR, Wnt/β-catenin, Shh/Gli2, c-MYC, and KRTs. These findings further improved the function of FGF5 gene, and provided therapeutic ideas for androgen alopecia.

Integral Roles of Specific Proteoglycans in Hair Growth and Hair Loss: Mechanisms behind the Bioactivity of Proteoglycan Replacement Therapy with Nourkrin® with Marilex® in Pattern Hair Loss and Telogen Effluvium

Follicular proteoglycans are key players with structural, functional, and regulatory roles in the growth and cycling behaviour of the hair follicles. The expression pattern of specific proteoglycans is strongly correlated with follicular phase transitions, which further affirms their functional involvement. Research shows that bioactive proteoglycans, e.g., versican and decorin, can actively trigger follicular phase shift by their anagen-inducing, anagen-maintaining, and immunoregulatory properties. This emerging insight has led to the recognition of “dysregulated proteoglycan metabolism” as a plausible causal or mediating pathology in hair growth disorders in both men and women. In support of this, declined expression of proteoglycans has been reported in cases of anagen shortening and follicular miniaturisation. To facilitate scientific communication, we propose designating this pathology “follicular hypoglycania (FHG),” which results from an impaired ability of follicular cells to replenish and maintain a minimum relative concentration of key proteoglycans during anagen. Lasting FHG may advance to structural decay, called proteoglycan follicular atrophy (PFA). This process is suggested to be an integral pathogenetic factor in pattern hair loss (PHL) and telogen effluvium (TE). To address FHG and PFA, a proteoglycan replacement therapy (PRT) program using oral administration of a marine-derived extract (Nourkrin® with Marilex®, produced by Pharma Medico Aps, Aarhus, Denmark) containing specific proteoglycans has been developed. In clinical studies, this treatment significantly reduced hair fall, promoted hair growth, and improved quality of life in patients with male- and female-pattern hair loss. Accordingly, PRT (using Nourkrin® with Marilex®) can be recommended as an add-on treatment or monotherapy in patients with PHL and TE.

The Wnt/β-catenin signaling pathway is involved in regulating feather growth of embryonic chicks

Avian feathers have robust growth and regeneration capability and serve as a useful model for decoding hair morphogenesis and other developmental studies. However, the molecular signaling involved in regulating the development of feather follicles is unclear. The purpose of this study was to investigate the role of the Wnt/β-catenin pathway in regulating feather morphogenesis in embryonic chicks through in ovo injection of different doses of Dickkopf-1 (DKK1, a specific inhibitor of the target of the Wnt/β-catenin pathway). A total of 120 fertilized embryo eggs were randomly divided into 4 treatments, including a noninjection group (control group) and groups injected with 100 μL of phosphate-buffered saline (PBS)/egg (PBS control group), 100 μL of PBS/egg containing 600-ng DKK1/egg (600-ng DKK1 group), and 100-μL PBS/egg containing 1,200-ng DKK1/egg (1,200-ng DKK1 group). Feathers and skin tissues were sampled on embryonic (E) day 15 and the day of hatching to examine the feather mass, diameter and density of feather follicles, and the protein expression of the Wnt/β-catenin pathway. The results showed that, compared with CON and PBS treatment, the injection of DKK1 into the yolk sac of chick embryos had no significant effect on the hatching rate and embryo weight (P > 0.05), while it significantly decreased the relative mass of feathers in the whole body (P < 0.05). The high dose of DKK1 (1,200-ng DKK1/egg) decreased the relative mass of feathers on the back, chest, belly, neck, wings, head, and legs, which was more obvious than that in the 600-ng DKK1 group, which presented a dose-dependent effect. In addition, DKK1 injection significantly downregulated the protein expression levels of β-catenin, transcription factor 4, Cyclin D1, and c-Myc (P < 0.05). The immunofluorescence result of β-catenin was consistent with the Western blotting assay results. Altogether, these observations suggested that the Wnt/β-catenin signaling pathway is involved in regulating feather follicle development and feather growth during the embryonic development of chicks.

Immunoexpression of adhesion molecules during human fetal hair development

INTRODUCTION

Hair follicles are produced in a cyclical manner and the machinery involved in the reproduction of these follicles is present since the fetal stage. Although extensive research has been done on the human hair follicle, very little is known about the importance of adhesion molecules in its development.

MATERIAL AND METHODS

We analyzed here, the immunoexpression of beta-1 integrin, p-cadherin, e-cadherin, and beta-catenin in hair follicles from 26 formalin-fixed and paraffin-embedded skin samples from human embryos and fetus between 12-23 weeks of gestational age.

RESULTS

The adhesion molecules beta-1 integrin and e-cadherin/p-cadherin were expressed from 12 weeks and seemed to play a role in regulating epidermis invagination. Beta-catenin immunostaining was negative in all cases; down regulation of this protein may be necessary for fetal hair development and thus facilitating hair follicle down growth.

DISCUSSION/CONCLUSION

Adhesion molecules are essential for hair follicle down growth and proliferation; integrins and cadherins play a major role in this process. More studies are needed to describe hair follicle development.

A study on clinical effectiveness of cosmetics containing human stem cell conditioned media

Background

With the steadily increasing trend of functional cosmetics consumption, the public is increasingly expecting the efficacy of cosmetics, and in order to meet these consumer needs, the development of various effective raw materials, as well as products through technical convergence research, has been activating focusing on dermatology. In the Republic of Korea, much attention was paid to cosmetic raw materials using human stem cells as a new growth engine at the end of the 2000s. Accordingly, the Ministry of Food and Drug Safety implemented the Regulations on Cosmetic Safety Standards, etc., which contains the safety standards of human-derived cell and tissue culture as raw materials for cosmetics.

Methods

Twice a day, morning and evening, for 28 days, 3 mL of the sample provided for each subject was applied onto the entire face using an airbrush. The subjects were divided into a control group (C), an experimental group 1 (ADSC-CM 5% group, E1) and an experimental group 2 (polymersome-containing of ADSC-CM 5% group, E2), and there were 20 subjects in each group.

Results

Moisture content on the U-zone, melanin and erythema of lid-cheek, overall size and depth of eye wrinkles, and skin roughness of the items showed significant differences among all three groups. More specifically, E1 had a higher rate of skin improvement than C, and E2 had the highest skin improvement rate in all items: skin moisture content, transepidermal water loss (TEWL), melanin and erythema of lid-cheek, eye wrinkles, and skin roughness of lid-cheek.

Conclusions

The effectiveness of ADSC-CM was verified in all items: increases in moisture content, decrease in TEWL, and improvements of whitening and wrinkles. Moreover, the effectiveness of ADSC-CM was observed as higher in samples of polymersome-containing ADSC-CM than those of raw material ADSC-CM. Furthermore, percutaneous absorption was improved compared with previous studies on formulations in relation to polymersome at the same concentration of ADSC-CM, thereby resulting in higher effectiveness.

Trial registration

Korea National Institute for Bioethics Policy, P01–201809–13-001, Registered 06 September 2018, http://public.irb.or.kr/.

Recent advances in follicular drug delivery of nanoparticles

Introduction: The improvement of percutaneous absorption represents a clear dermatopharmaceutical aim. Recently, the hair follicle was recognized to be an important penetration pathway. Especially nanoparticles show an enhanced intrafollicular penetration and can be utilized to target specific cell populations within the hair follicle.Areas covered: The present review briefly summarizes the recent advances in follicular drug delivery of nanoparticles. Moreover, the particularities of the hair follicle as a penetration pathway are summarized which include its structure and specific barrier properties. Recently, the mechanism of the follicular penetration process has been clarified.In the meantime, different strategies have been developed to successfully improve follicular drug delivery of nanoparticles. One approach is to equip the nanocarriers with a triggered release system enabling them to release their drug load at the right time and place.Expert opinion: Follicular drug delivery with smart nanocarrier-based drug delivery systems represents a promising approach to increase the percutaneous absorption of topically applied substances. Although technical achievements and efficacy proofs concerning an increased penetration of substances are already available, the practical implementation into clinical application still represents an additional challenge and should be in the focus of interest in future research.

Methionine promotes the development of hair follicles via the Wnt/β-catenin signalling pathway in Rex rabbits

To investigate the effect and molecular mechanism of methionine (Met) on the growth of hair follicles (HFs) in Rex rabbits. A total of 200 weaning Rex rabbits were divided into four groups and fed varying levels of Met-supplemented diets. We measured the HF density on dorsal skin and the Wnt/β-catenin pathway protein expression level. Meanwhile, whole HFs were isolated from Rex rabbit skins and cultured with Met in vitro to measure hair shaft growth. The relationship between Met and the Wnt/β-catenin signalling pathway was also characterized by using the Wnt/β-catenin signalling inhibitor, XAV-939. The results showed that the addition of dietary Met could significantly increase the HF density on dorsal skin (p < .05) and enhance the protein expression level of Wnt10b (p < .05), β-catenin (p < .05) and DSH (p < .05). Methionine stimulation could also prolong the hair shafts growth in vitro (p < .05). And inhibition of Wnt/β-catenin signalling using XAV-939 could eliminate this phenomenon. In summary, Met can increase the density of HFs on dorsal skin in vitro and prolong the hair shaft growth of HFs in vivo via the Wnt/β-catenin signalling pathway.

Monofilament threads in treatment of female hair loss

BACKGROUND

Recently, thread treatment has been commonly used in Korean medicine for cosmetic reasons such as decreasing skin wrinkles. It was noted that an inserted thread caused constant stimulation, followed by assistance for connective tissue regeneration. However, its role in hair development has not yet been revealed.

OBJECTIVE

To perform a pilot study on the effect of monofilament threads scalp injections in women with female androgenetic alopecia.

MATERIALS AND METHODS

This double-blind, multicenter, placebo-controlled study compared the effect of monofilament threads with that of saline as placebo. The endpoints were hair count and hair mass index (HMI), along with patient-opinion survey responses.

RESULTS

HMI or hair count has statistically significantly differed between the study and placebo groups. However, 73.3% of the treatment subjects (vs. 0% of the placebo subjects) experienced substantial improvement in hair loss, rate of hair loss, hair thickness, and ease of managing/styling hair, and 76.8% (vs. 18.4% of the placebo group) reported that their hair felt coarser or heavier after the treatment.

CONCLUSION

Monofilament threads demonstrate highly statistically significant improvement in HMI or hair count in women female pattern hair loss. The patient survey results suggest a therapeutic advantage of monofilament threads as perceived by patients and according to hair count or HMI.

Cholesterol homeostasis: Links to hair follicle biology and hair disorders

Lipids and lipid metabolism are critical factors in hair follicle (HF) biology, and cholesterol has long been suspected of influencing hair growth. Altered cholesterol homeostasis is involved in the pathogenesis of primary cicatricial alopecia, mutations in a cholesterol transporter are associated with congenital hypertrichosis, and dyslipidaemia has been linked to androgenic alopecia. The underlying molecular mechanisms by which cholesterol influences pathways involved in proliferation and differentiation within HF cell populations remain largely unknown. As such, expanding our knowledge of the role for cholesterol in regulating these processes is likely to provide new leads in the development of treatments for disorders of hair growth and cycling. This review describes the current state of knowledge with respect to cholesterol homeostasis in the HF along with known and putative links to hair pathologies.

Hairless-knockout piglets generated using the clustered regularly interspaced short palindromic repeat/CRISPR-associated-9 exhibit abnormalities in the skin and thymus

The nuclear receptor corepressor Hairless (HR) interacts with nuclear receptors and controls expression of specific target genes involved in hair morphogenesis and hair follicle cycling. Patients with HR gene mutations exhibit atrichia, and in rare cases, immunodeficiency. Pigs with HR gene mutations may provide a useful model for developing therapeutic strategies because pigs are highly similar to humans in terms of anatomy, genetics, and physiology. The present study aimed to knockout the HR gene in pigs using the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated-9 (Cas9) system and to investigate the molecular and structural alterations in the skin and thymus. We introduced a biallelic mutation into the HR gene in porcine fetal fibroblasts and generated nine piglets via somatic cell nuclear transfer. These piglets exhibited a lack of hair on the eyelids, abnormalities in the thymus and peripheral blood, and altered expression of several signaling factors regulated by HR. Our results indicate that introduction of the biallelic mutation successfully knocked out the HR gene, resulting in several molecular and structural changes in the skin and thymus. These pigs will provide a useful model for studying human hair disorders associated with HR gene mutations and the underlying molecular mechanisms.

Bioinformatics analysis of evolutionary characteristics and biochemical structure of FGF5 Gene in sheep

Fibroblast growth factor (FGF) 5 regulates the development and periodicity of hair follicles, which can affect hair traits. Loss-of-function mutations associated with long-hair phenotypes have been described in several mammalian species. Sheep is an important economic animal, however, the evolution characterizations and biological mechanism of oFGF5 (Ovis aries FGF5) gene are still poorly understood. In this study, oFGF5 gene was obtained by resequencing the whole genome of three Dorper sheep and RACE of two Kazakh sheep FGF5. We proposed FGF5 was phylogenetically related to FGF4 family and oFGF5 clearly orthologed to goat FGF5. Six loci were found from the positive selection results of FGF5 and half of them located on signal peptide. The basically similar rates of function-altering substitutions in sheep and goat lineage and the rest of the mammalian lineage of 365 SNPs indicated that the FGF5 gene was quite conservative during evolution. Homology modeling of the oFGF5 suggested that it has a highly conserved FGF superfamily domain containing 10 β-strands. Furthermore, the protein-protein docking analysis revealed that oFGF5 have the potential to form heterodimers with oFGFR1, the predicted interaction interface of FGF5-FGFR1 heterodimer was formed mainly by residues from FGF superfamily domain. Our observations suggested the evolutionary and structural biology features of oFGF5 might be relevant to its function about hair follicle development and modulating hair growth, and we confirmed our speculation by using the FGF5 gene editing sheep produced by CRISPR/Cas9 technology.

Exposure to 50 Hz electromagnetic fields enhances hair follicle regrowth in C57BL/6 mice

IMPACT STATEMENT

In this study, our experiments confirmed that 50 Hz EMF affected hair follicle regrowth, and 50 Hz EMF enhanced K15⁺ stem cells proliferation in the hair bulb and follicular outer root sheath of hair follicles. Those results indicated that 50 Hz EMF may be beneficial for functional healing of hair loss.

Activin B Stimulates Mouse Vibrissae Growth and Regulates Cell Proliferation and Cell Cycle Progression of Hair Matrix Cells through ERK Signaling

Activins and their receptors play important roles in the control of hair follicle morphogenesis, but their role in vibrissae follicle growth remains unclear. To investigate the effect of Activin B on vibrissae follicles, the anagen induction assay and an in vitro vibrissae culture system were constructed. Hematoxylin and eosin staining were performed to determine the hair cycle stages. The 5-ethynyl-2′-deoxyuridine (EdU) and Cell Counting Kit-8 (CCK-8) assays were used to examine the cell proliferation. Flow cytometry was used to detect the cell cycle phase. Inhibitors and Western blot analysis were used to investigate the signaling pathway induced by Activin B. As a result, we found that the vibrissae follicle growth was accelerated by 10 ng/mL Activin B in the anagen induction assay and in an organ culture model. 10 ng/mL Activin B promoted hair matrix cell proliferation in vivo and in vitro. Moreover, Activin B modulates hair matrix cell growth through the ERK–Elk1 signaling pathway, and Activin B accelerates hair matrix cell transition from the G1/G0 phase to the S phase through the ERK–Cyclin D1 signaling pathway. Taken together, these results demonstrated that Activin B may promote mouse vibrissae growth by stimulating hair matrix cell proliferation and cell cycle progression through ERK signaling.

PDGFA in Cashmere Goat: A Motivation for the Hair Follicle Stem Cells to Activate

The cashmere hair follicle (HF) perpetually goes through cycles of growth, involution and rest. The photoperiod is the main factor in the control of seasonal coat change in cashmere goats while stem cells play a crucial role in the HF growth. Several factors, including Platelet-Derived Growth Factor A (PDGFA), Bone Morphogenetic Protein 2 (BMP2) and Lim-Homeobox gene 2 (LHX2) are implicated in HF morphogenesis and cycle. In this work, the mentioned molecules were investigated to evaluate their role in follicular cycle activation. The study was performed on skin samples collected at different periods of HF cycle and the molecular expression of PDGFA, BMP2 and LHX2 was evaluated by Real-Time PCR (qPCR) at each time point. Since PDGFA showed the most variation, the goat PDGFA gene was sequenced and the protein localization was investigated by immunohistochemistry together with PDGF receptor α (PDGFRα). PDGFA immunostaining was observed in the basal layer of the HF outer root sheath and the immunoreaction appeared stronger in the regressive HFs compared to those in the anagen phase according to qPCR analysis. PDGFRα was observed in the HF epithelium, proving the effect of PDGFA on the follicular structure. The data obtained suggest that PDGFA and BMP2 are both implicated in HF cycle in goat. In particular, PDGFA secreted by the HF is involved in the anagen activation.