Three-dimensional correlative light and focused ion beam scanning electron microscopy reveals the distribution and ultrastructure of lanceolate nerve endings surrounding terminal hair follicles in human scalp skin.

Lanceolate nerve endings (LNEs) surrounding hair follicles (HFs) play an important role in detecting hair deflection. Complexes of the LNEs form a palisade-like structure along the longitudinal axis of hair roots in which axons are sandwiched between two processes of terminal Schwann cells (tSCs) at the isthmus of HFs. The structure and molecular mechanism of LNEs in animal sinus hair, pelage, and human vellus hairs have been investigated. Despite the high density of HFs in human scalp skin, the LNEs in human terminal HFs have not been investigated. In this study, we aimed to reveal the distribution and ultrastructure of LNEs in terminal HFs of human scalp skin. Using light-sheet microscopy and immunostaining, the LNEs were observed at one terminal HF but not at the other terminal HFs in the same follicular unit. The ultrastructure of the LNEs of terminal HFs in human scalp skin was characterized using correlated light and electron microscopy (CLEM). Confocal laser microscopy and transmission electron microscopy of serial transverse sections of HFs revealed that LNEs were aligned adjacent to the basal lamina outside the outer root sheath (ORS), at the isthmus of terminal HFs, and adjacent to CD200-positive ORS cells in the upper bulge region. Moreover, axons with abundant mitochondria were sandwiched between tSCs. Three-dimensional CLEM, specifically confocal laser microscopy and focused ion beam scanning electron microscopy, of stained serial transverse sections revealed that LNEs were wrapped with type I and type II tSCs, with the processes protruding from the space between the Schwann cells. Moreover, the ultrastructures of LNEs at miniaturized HFs were similar to those of LNEs at terminal HFs. Preembedding immunoelectron microscopy revealed that Piezo-type mechanosensitive ion channel component 2 (Piezo2), a gated ion channel, was in axons and tSCs and adjacent to the cell membrane of axons and tSCs, suggesting that LNEs function as mechanosensors. The number of LNEs increased as the diameter of the ORS decreased, suggesting that LNEs dynamically adapt to the HF environment as terminal HFs miniaturize into vellus-like hair. These findings will provide insights for investigations of mechanosensory organs, aging, and re-innervation during wound healing.

Human hair follicles operate an internal Cori cycle and modulate their growth via glycogen phosphorylase.

Hair follicles (HFs) are unique, multi-compartment, mini-organs that cycle through phases of active hair growth and pigmentation (anagen), apoptosis-driven regression (catagen) and relative quiescence (telogen). Anagen HFs have high demands for energy and biosynthesis precursors mainly fulfilled by aerobic glycolysis. Histochemistry reports the outer root sheath (ORS) contains high levels of glycogen. To investigate a functional role for glycogen in the HF we quantified glycogen by Periodic-Acid Schiff (PAS) histomorphometry and colorimetric quantitative assay showing ORS of anagen VI HFs contained high levels of glycogen that decreased in catagen. qPCR and immunofluorescence microscopy showed the ORS expressed all enzymes for glycogen synthesis and metabolism. Using human ORS keratinocytes (ORS-KC) and ex vivo human HF organ culture we showed active glycogen metabolism by nutrient starvation and use of a specific glycogen phosphorylase (PYGL) inhibitor. Glycogen in ORS-KC was significantly increased by incubation with lactate demonstrating a functional Cori cycle. Inhibition of PYGL significantly stimulated the ex vivo growth of HFs and delayed onset of catagen. This study defines translationally relevant and therapeutically targetable new features of HF metabolism showing that human scalp HFs operate an internal Cori cycle, synthesize glycogen in the presence of lactate and modulate their growth via PYGL activity.

Quantifying the impact of braiding and combing on the integrity of natural African hair.

BACKGROUND: Afro hair breakage is most commonly attributed to grooming practices such as braiding, hair extensions and weaves, both for chemically treated hair and natural Afro hair. These grooming practices are also frequently associated with traction alopecia in clinical studies. However, there is little to no quantitative scientific data on the surface and internal hair fibre damage caused by grooming, including combing, on Afro hair. METHODS: Qualitative and quantitative techniques such as scanning electron microscopy, cuticle cohesion and tensile testing were used to determine the effects of frequent braiding on the integrity of female Afro hair in 15 frequent braiders and 15 occasional braiders (control group) in Johannesburg, South Africa. Frequent braiders were women who braided more than 8 times per year, while occasional braiders typically limit braiding to only twice 2 per year. The severity of traction alopecia was quantified in both groups using the standard Marginal Traction Alopecia Scoring system. Surface damage on naturally curly Afro hair, that was combed but not braided, was assessed as another hairstyle option. RESULTS: All measurements showed a relationship between surface and internal hair fibre damage and braiding frequency. Frequent braiders had thinner hair, with more cuticle damage as shown by SEM and cuticle cohesion assessments. Their hair fibres were also significantly weaker (p < 0.05), as shown by the tensile testing. In addition, they also had higher traction alopecia severity scores. In the combing impact assessment, a linear trend was observed between surface hair fibre damage and the number of combing strokes. Cuticle damage from 480 combing strokes was more severe than that from frequent braiding. CONCLUSION: Frequent braiding and combing damage natural Afro hair. Quantification of damage caused by different grooming practices identifies a need to develop products that could help mitigate specific hair damage associated with grooming practices. The degree of damage and subsequent hair loss could also be minimized by education on best braiding practices to protect the hair fibre and avoid hair follicle miniaturization caused by high traction hairstyles.

CONTEXTE: La casse des cheveux d'origine Africaine est le plus souvent associées à des pratiques cosmétiques telles que le tressage et les extensions de cheveux, à la fois pour les cheveux traités chimiquement et les cheveux naturels. Ces pratiques cosmétiques sont également fréquemment associées à une alopécie de traction, comme le relatent les études cliniques. Cependant, il existe peu ou pas de données scientifiques quantitatives sur l'impact de ce type de pratiques, y compris le peignage, sur les dommages internes et de surface des cheveux d'origine africaine. MÉTHODES: Des techniques qualitatives et quantitatives, comme la microscopie électronique à balayage (MEB), la cohésion cuticulaire et des tests de traction, ont été utilisés pour déterminer les effets du tressage sur l'intégrité des cheveux de deux groupes de 15 femmes Africaines (à Johannesburg, Afrique du Sud) : un premier groupe de femmes pratiquant un tressage fréquent et un autre groupe un tressage occasionnel. Le groupe des tresseurs fréquents correspond à des femmes qui pratiquent le tressage plus de 8 fois par an, tandis que les tresseurs occasionnels limitent généralement le tressage à seulement deux fois par an. La gravité de l'alopécie de traction a été également quantifiée dans les deux groupes à l'aide du système standard de notation de l'alopécie tractionnelle. Parallèlement, à titre de comparaison, les dommages de surface ont été également évalués sur des cheveux d'origine Africaine naturellement bouclés, non tressés, mais qui ont subi un peignage répété. RÉSULTATS: Toutes les mesures ont montré une relation entre les dommages de surface et internes de la fibre et la fréquence de tressage. Les tresseurs fréquents ont des cheveux plus fins, avec un endommagement plus important de la cuticule, comme le montrent les évaluations MEB et la cohésion cuticulaire. Les cheveux sont également significativement plus fragiles (p <0,05), comme le montrent les tests de traction. De plus, ces femmes ont également des scores d'alopécie de traction plus élevés. Dans le cas spécifique du peignage répété, une tendance linéaire a été observée entre les dommages en surface de la fibre capillaire et le nombre de coups de peigne. On peut également noter que l'endommagement de la cuticule causé par 480 coups de peigne est plus important que celui causé par des tressages fréquents. CONCLUSION: Les tressages et peignages fréquents endommagent les cheveux naturels d'origine Africaine. La quantification des dommages causés par différentes pratiques cosmétiques met en évidence le besoin de développer des produits qui pourraient aider à atténuer les dommages liés à des pratiques spécifiques. Le niveau de dommage et la perte de cheveux pourraient également être minimisés par un apprentissage de meilleures pratiques de tressage pour protéger la fibre et éviter la diminution des follicules pileux causée par des coiffures qui entrainent un forte traction sur la fibre.

Hair follicle dystrophy in a litter of domestic cats resembling lanceolate hair mutant mice.

BACKGROUND: A new congenital hair-shaft abnormality resembling the lanceolate hair phenotype of rodents is described in a litter of four domestic short hair (DSH) cats. Data relating to hair shaft and follicle disorders remain scarce in veterinary medicine. OBJECTIVES: To describe and compare structural abnormalities in these cats with other hair dystrophies in cats and other mammals. ANIMALS: A DSH cat litter with progressive noninflammatory alopecia. METHODS AND MATERIALS: Histopathological evaluation, scanning and transmission electron microscopy, and X-ray based element analysis defined the hair and skin changes in cats born with alopecia. Findings were compared to archival data from normal cats and lanceolate hair (Dsg4lahJ ) and Keratin 75 (Krt75tm1Der ) mutant mice. RESULTS: Light and scanning electron microscopy of the hairs revealed lance- or spear-head shaped defects of the hair tip. Histological findings were swollen hair shafts, initially above the hair bulb matrix and later found in the distal parts of the telogen hair follicles, similar to those observed in Dsg4lahJ Krt75tm1Der mutant mice. Transmission electron microscopy of the hair shaft and hair follicles showed a loss in the normal structure of the guard hairs in the alopecic cats. There was a statistically significant decrease in sulfur content just below the defects in the hair shafts (trichothiodystrophy). CONCLUSION AND CLINICAL IMPORTANCE: A rare form of congenital alopecia resulting in follicular dystrophy is described in cats which is similar to hair follicle and hair-shaft changes reported in several mutant mouse strains with single gene mutations in adhesion molecules or keratin genes.

The microfollicle: a model of the human hair follicle for in vitro studies.

Access to complex in vitro models that recapitulate the unique markers and cell-cell interactions of the hair follicle is rather limited. Creation of scalable, affordable, and relevant in vitro systems which can provide predictive screens of cosmetic ingredients and therapeutic actives for hair health would be highly valued. In this study, we explore the features of the microfollicle, a human hair follicle organoid model based on the spatio-temporally defined co-culture of primary cells. The microfollicle provides a 3D differentiation platform for outer root sheath keratinocytes, dermal papilla fibroblasts, and melanocytes, via epidermal-mesenchymal-neuroectodermal cross-talk. For assay applications, microfollicle cultures were adapted to 96-well plates suitable for medium-throughput testing up to 21 days, and characterized for their spatial and lineage markers. The microfollicles showed hair-specific keratin expression in both early and late stages of cultivation. The gene expression profile of microfollicles was also compared with human clinical biopsy samples in response to the benchmark hair-growth compound, minoxidil. The gene expression changes in microfollicles showed up to 75% overlap with the corresponding gene expression signature observed in the clinical study. Based on our results, the cultivation of the microfollicle appears to be a practical tool for generating testable insights for hair follicle development and offers a complex model for pre-clinical substance testing.

High-pressure freezing followed by freeze substitution of a complex and variable density miniorgan: the wool follicle.

Cryofixation by high-pressure freezing (HPF) followed by freeze substitution (FS) is a preferred method to prepare biological specimens for ultrastructural studies. It has been shown to achieve uniform vitrification and ultrastructure preservation of complex structures in different cell types. One limitation of HPF is the small sample volume of <200 µm thickness and about 2000 µm across. A wool follicle is a rare intact organ in a single sample about 200 µm thick. Within each follicle, specialized cells derived from multiple cell lineages assemble, mature and cornify to make a wool fibre, which contains 95% keratin and associated proteins. In addition to their complex structure, large density changes occur during wool fibre development. Limited water movement and accessibility of fixatives are some issues that negatively affect the preservation of the follicle ultrastructure via conventional chemical processing. Here, we show that HPF-FS of wool follicles can yield high-quality tissue preservation for ultrastructural studies using transmission electron microscopy.

Scanning electron microscopy approach for evaluation of hair dyed with Lawsonia inermis powder: in vitro Study / Método de microscopía electrónica de barrido para la evaluación de cabello teñido con extracto de Lawsonia inermis: estudio in vitro

During aging, usually graying of the hair occurs as a result of oxidative stress. Driven by social acceptance and self-perception of the exterior appearance, both men and women rely on hair dyeing products, in order to mask the graying hair. At the same time, a frequent use of synthetic products and treatment can damage the hair shaft; for this reason, this study aimed to evaluate the morphological effect of the herbal dye derived from Lawsonia inermis (henna), on hair. Dyed hairs were evaluated by means of SEM. Subsequently, they were compared, qualitatively and quantitatively, with undyed hairs. Results showed a positive impact on the cuticula pattern and on the diameters of the examined samples, after henna application. Different results, about the degree and the type of morphological changes occurring on pigmented hairs, may depend on the phenotype and on the health condition of hair, before dye treatment.

Durante el envejecimiento, generalmente se produce el envejecimiento del cabello como resultado del estrés oxidativo. Motivados por la aceptación social y la autopercepción de la apariencia, tanto hombres como mujeres confían en productos para teñir el cabello para enmascarar las canas. Al mismo tiempo, el uso frecuente de productos y tratamientos sintéticos puede dañar el tallo del cabello. Por esta razón, este estudio tuvo como objetivo evaluar el efecto morfológico del tinte derivado de Lawsonia inermis (henna) en el cabello. Los cabellos teñidos se evaluaron mediante SEM. Posteriormente, se compararon, cualitativa y cuantitativamente, con cabellos sin teñir. Los resultados mostraron un impacto positivo en el patrón de la cutícula y en los diámetros de las muestras examinadas, después de la aplicación de henna. Los diferentes resultados, sobre el grado y el tipo de cambios morfológicos que ocurren en los cabellos pigmentados, pueden depender del fenotipo y del estado de salud del cabello, antes del tratamiento con tinte.

Protective effects of human umbilical cord blood­derived mesenchymal stem cells against dexamethasone­induced apoptotic cell death in hair follicles.

Alopecia is a common and distressing condition, and developing new therapeutic agents to prevent hair loss is important. Human umbilical cord blood­derived mesenchymal stem cells (hUCB­MSCs) have been studied intensively in regenerative medicine. However, the therapeutic potential of these cells against hair loss and hair organ damage remains unclear, and the effects of hUCB­MSC transplantation on hair loss require evaluation. The current study aimed to investigate the effects of hUCB­MSCs on hair regression in vivo and restoration of anagen conduction on hair growth in vitro. The effects of hUCB­MSCs were explored in mouse catagen induction models using a topical treatment of 0.1% dexamethasone to induce hair regression. Dexamethasone was also used to simulate a stress environment in vitro. The results demonstrated that hUCB­MSCs significantly prevented hair regression induced by dexamethasone topical stimulation in vivo. Additionally, hUCB­MSCs significantly increased the proliferation of human dermal papilla cells (hDPCs) and HaCaT cells, which are key constituent cells of the hair follicle. Stimulation of vascular endothelial growth factor secretion and decreased expression of DKK­1 by hUCB­MSCs were also observed in hDPCs. Restoration of cell viability by hUCB­MSCs suggested that these cells exerted a protective effect on glucocorticoid stress­associated hair loss. In addition, anti­apoptotic effects and regulation of the autophagic flux recovery were observed in HaCaT cells. The results of the present study indicated that hUCB­MSCs may have the capacity to protect hair follicular dermal papilla cells and keratinocytes, thus preventing hair loss. Additionally, the protective effects of hUCB­MSCs may be resistant to dysregulation of autophagy under harmful stress.

Histological and functional comparisons of four anatomical regions of porcine skin with human abdominal skin.

Because of the shortage of human skin for research purposes, porcine skin has been used as a model of human skin. The aim of this study was to identify the region of German Landrace pig skin that could be used as the best possible substitute for human abdominal skin. Porcine samples were collected from the ear, flank, back and caudal abdomen; human abdominal skin samples were excised during plastic surgery. Histological and ultrastructural assessments were carried out on the epidermis and dermis, with emphasis on the dermo-epidermal interface length, dermo-epidermal thickness ratio as well as densities of; hair follicles, arrector pili muscles, blood vessels and sweat glands. In the pig, the barrier function of the four anatomical regions was assessed. Results showed that both histologically and ultrastructurally, all four regions of porcine skin were similar to human skin. These include the shapes of keratinocytes, structure of cell contacts and presence of Weibel Palade bodies in endothelial cells. Other parameters such as the thickness of epidermis, the thickness of stratum basale, spinosum and granulosum and the number of cell layers in the stratum corneum were similar in human abdominal and in all four regions of porcine skin. However, there were also significant differences especially in the thickness of the stratum corneum, the dermo-epidermal interface length and the blood vessel density.

Regional Control of Hairless versus Hair-Bearing Skin by Dkk2.

Haired skin is a defining characteristic of mammals. However, some specialized skin regions, such as human palms, soles and ventral wrist, and mouse plantar foot, are entirely hairless. Using mouse plantar skin as a model system, we show that the endogenous secreted Wnt inhibitor DKK2 suppresses plantar hair follicle development and permits the formation of hairless skin. Plantar skin retains all of the mechanistic components needed for hair follicle development, as genetic deletion of Dkk2 permits formation of fully functional plantar hair follicles that give rise to external hair, contain sebaceous glands and a stem cell compartment, and undergo regenerative growth. In the absence of Dkk2, Wnt/ß-catenin signaling activity is initially broadly elevated in embryonic plantar skin and gradually becomes patterned, mimicking follicular development in normally haired areas. These data provide a paradigm in which regionally restricted expression of a Wnt inhibitor underlies specification of hairless versus hairy skin.

Stem cells repurpose proliferation to contain a breach in their niche barrier.

Adult stem cells are responsible for life-long tissue maintenance. They reside in and interact with specialized tissue microenvironments (niches). Using murine hair follicle as a model, we show that when junctional perturbations in the niche disrupt barrier function, adjacent stem cells dramatically change their transcriptome independent of bacterial invasion and become capable of directly signaling to and recruiting immune cells. Additionally, these stem cells elevate cell cycle transcripts which reduce their quiescence threshold, enabling them to selectively proliferate within this microenvironment of immune distress cues. However, rather than mobilizing to fuel new tissue regeneration, these ectopically proliferative stem cells remain within their niche to contain the breach. Together, our findings expose a potential communication relay system that operates from the niche to the stem cells to the immune system and back. The repurposing of proliferation by these stem cells patch the breached barrier, stoke the immune response and restore niche integrity.

Transmission electron microscopic and immunohistochemical observations of resting follicles of feathers in chicken show massive cell degeneration.

The molting cycle of feathers includes an anagen (growth) stage, a likely catagen stage where the feather follicles degenerate, and a resting stage where fully grown feathers remain in their follicles and are functional before molting. However, the cytological changes involved in the resting and molting stages are poorly known, so the results of an ultrastructural analysis of these processes in adult chick feathers are presented here. The study showed that the dermal papilla shrinks, and numerous cells present increased heterochromatin and free collagen fibrils in the extracellular matrix. Degeneration of the germinal epithelium of the follicle-the papillary collar-occurs with an initial substantial contraction of cells followed by an increase in heterochromatin, vesicle and lipid accumulation, and membrane and organelle degeneration. Desmosomes are still present between degenerating epithelial cells, but ribosomes and tonofilaments disappear. This suggests that cell necrosis initially proceeds as a major contraction resembling apoptosis-a process termed necroptosis, which was previously also shown to occur during the formation of barbs and barbules in mature down and pennaceous feathers. This study suggests that, aside from apoptosis, the collar epithelium degenerates due to external factors, in particular the retraction of blood vessels supplying the dermal papilla. In contrast, revascularization of the dermal papilla triggers a new phase of feather growth (anagen).

Melatonin promotes Cashmere goat (Capra hircus) secondary hair follicle growth: a view from integrated analysis of long non-coding and coding RNAs.

The role of melatonin in promoting the yield of Cashmere goat wool has been demonstrated for decades though there remains a lack of knowledge regarding melatonin mediated hair follicle growth. Recent studies have demonstrated that long non-coding RNAs (lncRNAs) are widely transcribed in the genome and play ubiquitous roles in regulating biological processes. However, the role of lncRNAs in regulating melatonin mediated hair follicle growth remains unclear. In this study, we established an in vitro Cashmere goat secondary hair follicle culture system, and demonstrated that 500 ng/L melatonin exposure promoted hair follicle fiber growth. Based on long intergenic RNA sequencing, we demonstrated that melatonin promoted hair follicle elongation via regulating genes involved in focal adhesion and extracellular matrix receptor pathways and further cis predicting of lncRNAs targeted genes indicated that melatonin mediated lncRNAs mainly targeted vascular smooth muscle contraction and signaling pathways regulating the pluripotency of stem cells. We proposed that melatonin exposure not only perturbed key signals secreted from hair follicle stem cells to regulate hair follicle development, but also mediated lncRNAs mainly targeted to pathways involved in the microvascular system and extracellular matrix, which constitute the highly orchestrated microenvironment for hair follicle stem cell. Taken together, our findings here provide a profound view of lncRNAs in regulating Cashmere goat hair follicle circadian rhythms and broaden our knowledge on melatonin mediated hair follicle morphological changes.