The hair follicle as a dynamic miniorgan

The development of hair follicles and nail

The hair follicle and nail unit develop and regenerate through epithelial-mesenchymal interactions. Here, we review some of the key signals and molecular interactions that regulate mammalian hair follicle and nail formation during embryonic development and how these interactions are reutilized to promote their regeneration during adult homeostasis and in response to skin wounding. Finally, we highlight the role of some of these signals in mediating human hair follicle and nail conditions.

1,25-(OH)2D3 promotes hair growth by inhibiting NLRP3/IL-1β and HIF-1α/IL-1β signaling pathways

Vitamin D is a crucial vitamin that participates in various biological processes through the Vitamin D Receptor (VDR). While there are studies suggesting that VDR might regulate hair growth through ligand-independent mechanisms, the efficacy of Vitamin D in treating hair loss disorders has also been reported. Here, through in vivo experiments in mice, in vitro organ culture of hair follicles, and cellular-level investigations, we demonstrate that 1,25-(OH)2D3 promotes mouse hair regeneration, prolongs the hair follicle anagen, and enhances the proliferation and migration capabilities of dermal papilla cells and outer root sheath keratinocytes in a VDR-dependent manner. Transcriptome analysis of VDR-knockout mouse skin reveals the involvement of HIF-1α, NLRP3, and IL-1β in these processes. Finally, we confirm that 1,25-(OH)2D3 can counteract the inhibitory effects of DHT on hair growth. These findings suggest that 1,25-(OH)2D3 has a positive impact on hair growth and may serve as a potential therapeutic agent for androgenetic alopecia (AGA).

Increasing GSH-Px Activity and Activating Wnt Pathway Promote Fine Wool Growth in FGF5-Edited Sheep

Fibroblast growth factor 5 (FGF5) plays key roles in promoting the transition from the anagen to catagen during the hair follicle cycle. The sheep serves as an excellent model for studying hair growth and is frequently utilized in various research processes related to human skin diseases. We used the CRISPR/Cas9 system to generate four FGF5-edited Dorper sheep and only low levels of FGF5 were detected in the edited sheep. The density of fine wool in GE sheep was markedly increased, and the proportion of fine wool with a diameter of 14.4-20.0 μm was significantly higher. The proliferation signal in the skin of gene-edited (GE) sheep was stronger than in wild-type (WT) sheep. FGF5 editing decreased cortisol concentration in the skin, further activated the activity of antioxidant enzymes such as Glutathione peroxidase (GSH-Px), and regulated the expression of Wnt signaling pathways containing Wnt agonists (Rspondins, Rspos) and antagonists (Notum) in hair regeneration. We suggest that FGF5 not only mediates the activation of antioxidant pathways by cortisol, which constitutes a highly coordinated microenvironment in hair follicle cells, but also influences key signals of the Wnt pathway to regulate secondary hair follicle (SHF) development. Overall, our findings here demonstrate that FGF5 plays a significant role in regulating SHF growth in sheep and potentially serves as a molecular marker of fine wool growth in sheep breeding.

Spatial Distribution and Functional Impact of Human Scalp Hair Follicle Microbiota

Human hair follicles (HFs) constitute a unique microbiota habitat that differs substantially from the skin surface. Traditional HF sampling methods fail to eliminate skin microbiota contaminants or assess the HF microbiota incompletely, and microbiota functions in human HF physiology remain ill explored. Therefore, we used laser-capture microdissection, metagenomic shotgun sequencing, and FISH to characterize the human scalp HF microbiota in defined anatomical compartments. This revealed significant compartment-, tissue lineage-, and donor age-dependent variations in microbiota composition. Greatest abundance variations between HF compartments were observed for viruses, archaea, Staphylococcus epidermidis, Cutibacterium acnes, and Malassezia restricta, with the latter 2 being the most abundant viable HF colonizers (as tested by propidium monoazide assay) and, surprisingly, most abundant in the HF mesenchyme. Transfection of organ-cultured human scalp HFs with S. epidermidis-specific lytic bacteriophages ex vivo downregulated transcription of genes known to regulate HF growth and development, metabolism, and melanogenesis, suggesting that selected microbial products may modulate HF functions. Indeed, HF treatment with butyrate, a metabolite of S. epidermidis and other HF microbiota, delayed catagen and promoted autophagy, mitochondrial activity, and gp100 and dermcidin expression ex vivo. Thus, human HF microbiota show spatial variations in abundance and modulate the physiology of their host, which invites therapeutic targeting.

Melatonin promotes hair regeneration by modulating the Wnt/β-catenin signalling pathway

Melatonin (MLT) is a circadian hormone that reportedly influences the development and cyclic growth of secondary hair follicles; however, the mechanism of regulation remains unknown. Here, we systematically investigated the role of MLT in hair regeneration using a hair depilation mouse model. We found that MLT supplementation significantly promoted hair regeneration in the hair depilation mouse model, whereas supplementation of MLT receptor antagonist luzindole significantly suppressed hair regeneration. By analysing gene expression dynamics between the MLT group and luzindole-treated groups, we revealed that MLT supplementation significantly up-regulated Wnt/β-catenin signalling pathway-related genes. In-depth analysis of the expression of key molecules in the Wnt/β-catenin signalling pathway revealed that MLT up-regulated the Wnt/β-catenin signalling pathway in dermal papillae (DP), whereas these effects were facilitated through mediating Wnt ligand expression levels in the hair follicle stem cells (HFSCs). Using a DP-HFSCs co-culture system, we verified that MLT activated Wnt/β-catenin signalling in DPs when co-cultured with HFSCs, whereas supplementation of DP cells with MLT alone failed to activate Wnt/β-catenin signalling. In summary, our work identified a critical role for MLT in promoting hair regeneration and will have potential implications for future hair loss treatment in humans.

Efficacy of probiotics in hair growth and dandruff control: A systematic review and meta-analysis

Background

Probiotics are intellectually rewarding for the discovery of their potential as a source of functional food. Investigating the economic and beauty sector dynamics, this study conducted a comprehensive review of scholarly articles to evaluate the capacity of probiotics to promote hair growth and manage dandruff.

Methods

We used the PRISMA 2020 with Embase, Pubmed, ClinicalTrials.gov, Scopus, and ICTRP databases to investigate studies till May 2023. Meta-analyses utilizing the random effects model were used with odds ratios (OR) and standardized mean differences (SMD).

Result

Meta-analysis comprised eight randomized clinical trials and preclinical studies. Hair growth analysis found a non-significant improvement in hair count (SMD = 0.32, 95 % CI -0.10 to 0.75) and a significant effect on thickness (SMD = 0.92, 95 % CI 0.47 to 1.36). In preclinical studies, probiotics significantly induced hair follicle count (SMD = 3.24, 95 % CI 0.65 to 5.82) and skin thickness (SMD = 2.32, 95 % CI 0.47 to 4.17). VEGF levels increased significantly (SMD = 2.97, 95 % CI 0.80 to 5.13), while IGF-1 showed a non-significant inducement (SMD = 0.53, 95 % CI -4.40 to 5.45). For dandruff control, two studies demonstrated non-significant improvement in adherent dandruff (OR = 1.31, 95 % CI 0.13-13.65) and a significant increase in free dandruff (OR = 5.39, 95 % CI 1.50-19.43). Hair follicle count, VEGF, IGF-1, and adherent dandruff parameters were recorded with high heterogeneity. For the systematic review, probiotics have shown potential in improving hair growth and controlling dandruff through modulation of the immune pathway and gut-hair axis. The Wnt/β-catenin pathway, IGF-1 pathway, and VEGF are key molecular pathways in regulating hair follicle growth and maintenance.

Conclusions

This review found significant aspects exemplified by the properties of probiotics related to promoting hair growth and anti-dandruff effect, which serve as a roadmap for further in-depth studies to make it into pilot scales.

Can Plant Extracts Help Prevent Hair Loss or Promote Hair Growth? A Review Comparing Their Therapeutic Efficacies, Phytochemical Components, and Modulatory Targets

This narrative review aims to examine the therapeutic potential and mechanism of action of plant extracts in preventing and treating alopecia (baldness). We searched and selected research papers on plant extracts related to hair loss, hair growth, or hair regrowth, and comprehensively compared the therapeutic efficacies, phytochemical components, and modulatory targets of plant extracts. These studies showed that various plant extracts increased the survival and proliferation of dermal papilla cells in vitro, enhanced cell proliferation and hair growth in hair follicles ex vivo, and promoted hair growth or regrowth in animal models in vivo. The hair growth-promoting efficacy of several plant extracts was verified in clinical trials. Some phenolic compounds, terpenes and terpenoids, sulfur-containing compounds, and fatty acids were identified as active compounds contained in plant extracts. The pharmacological effects of plant extracts and their active compounds were associated with the promotion of cell survival, cell proliferation, or cell cycle progression, and the upregulation of several growth factors, such as IGF-1, VEGF, HGF, and KGF (FGF-7), leading to the induction and extension of the anagen phase in the hair cycle. Those effects were also associated with the alleviation of oxidative stress, inflammatory response, cellular senescence, or apoptosis, and the downregulation of male hormones and their receptors, preventing the entry into the telogen phase in the hair cycle. Several active plant extracts and phytochemicals stimulated the signaling pathways mediated by protein kinase B (PKB, also called AKT), extracellular signal-regulated kinases (ERK), Wingless and Int-1 (WNT), or sonic hedgehog (SHH), while suppressing other cell signaling pathways mediated by transforming growth factor (TGF)-β or bone morphogenetic protein (BMP). Thus, well-selected plant extracts and their active compounds can have beneficial effects on hair health. It is proposed that the discovery of phytochemicals targeting the aforementioned cellular events and cell signaling pathways will facilitate the development of new targeted therapies for alopecia.

Dab2 (Disabled-2), an adaptor protein, regulates self-renewal of hair follicle stem cells

Disabled 2 (Dab2), an adaptor protein, is up regulated in the hair follicle stem cells (HFSCs); however, its role in any tissue stem cells has not been studied. In the present study, we have reported that Dab2 conditional knockout (Dab2-cKO) mice exhibited a delay in the HF cycle due to perturbed activation of HFSCs. Further, Dab2-cKO mice showed a reduction in the number of HFSCs and reduced colony forming ability of HFSCs. Dab2-cKO mice showed extended quiescence of HFSCs concomitant with an increased expression of Nfatc1. Dab2-cKO mice showed a decreased expression of anti-aging genes such as Col17a1, decorin, Sirt2 and Sirt7. Dab2-cKO mice did not show full hair coat recovery in aged mice thereby suggesting an accelerated aging process. Overall, we unveil for the first time, the role of Dab2 that regulate activation and self-renewal of HFSCs.

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.

Integrating Single-Cell and Spatial Transcriptomics Reveals Heterogeneity of Early Pig Skin Development and a Subpopulation with Hair Placode Formation

The dermis and epidermis, crucial structural layers of the skin, encompass appendages, hair follicles (HFs), and intricate cellular heterogeneity. However, an integrated spatiotemporal transcriptomic atlas of embryonic skin has not yet been described and would be invaluable for studying skin-related diseases in humans. Here, single-cell and spatial transcriptomic analyses are performed on skin samples of normal and hairless fetal pigs across four developmental periods. The cross-species comparison of skin cells illustrated that the pig epidermis is more representative of the human epidermis than mice epidermis. Moreover, Phenome-wide association study analysis revealed that the conserved genes between pigs and humans are strongly associated with human skin-related diseases. In the epidermis, two lineage differentiation trajectories describe hair follicle (HF) morphogenesis and epidermal development. By comparing normal and hairless fetal pigs, it is found that the hair placode (Pc), the most characteristic initial structure in HFs, arises from progenitor-like OGN+/UCHL1+ cells. These progenitors appear earlier in development than the previously described early Pc cells and exhibit abnormal proliferation and migration during differentiation in hairless pigs. The study provides a valuable resource for in-depth insights into HF development, which may serve as a key reference atlas for studying human skin disease etiology using porcine models.

Modelling Human Hair Follicles-Lessons from Animal Models and Beyond

The hair follicle is a specialized appendage of the skin that is critical for multiple functions, including thermoregulation, immune surveillance, and sebum production. Mammals are born with a fixed number of hair follicles that develop embryonically. Postnatally, these hair follicles undergo regenerative cycles of regression and growth that recapitulate many of the embryonic signaling pathways. Furthermore, hair cycles have a direct impact on skin regeneration in homeostasis, cutaneous wound healing, and disease conditions such as alopecia. Here, we review the current knowledge of hair follicle formation during embryonic development and the post-natal hair cycle, with an emphasis on the molecular signaling pathways underlying these processes. We then discuss efforts to capitalize on the field's understanding of in vivo mechanisms to bioengineer hair follicles or hair-bearing skin in vitro and how such models may be further improved to develop strategies for hair regeneration.

Immune niches for hair follicle development and homeostasis

The hair follicle is a dynamic mini-organ that has specialized cycles and architectures with diverse cell types to form hairs. Previous studies for several decades have investigated morphogenesis and signaling pathways during embryonic development and adult hair cycles in both mouse and human skin. In particular, hair follicle stem cells and mesenchymal niches received major attention as key players, and their roles and interactions were heavily revealed. Although resident and circulating immune cells affect cellular function and interactions in the skin, research on immune cells has mainly received attention on diseases rather than development or homeostasis. Recently, many studies have suggested the functional roles of diverse immune cells as a niche for hair follicles. Here, we will review recent findings about immune niches for hair follicles and provide insight into mechanisms of hair growth and diseases.

Epidermal retinol dehydrogenases cyclically regulate stem cell markers and clock genes and influence hair composition

The hair follicle (HF) is a self-renewing adult miniorgan that undergoes drastic metabolic and morphological changes during precisely timed cyclic organogenesis. The HF cycle is known to be regulated by steroid hormones, growth factors and circadian clock genes. Recent data also suggest a role for a vitamin A derivative, all-trans-retinoic acid (ATRA), the activating ligand of transcription factors, retinoic acid receptors, in the regulation of the HF cycle. Here we demonstrate that ATRA signaling cycles during HF regeneration and this pattern is disrupted by genetic deletion of epidermal retinol dehydrogenases 2 (RDHE2, SDR16C5) and RDHE2-similar (RDHE2S, SDR16C6) that catalyze the rate-limiting step in ATRA biosynthesis. Deletion of RDHEs results in accelerated anagen to catagen and telogen to anagen transitions, altered HF composition, reduced levels of HF stem cell markers, and dysregulated circadian clock gene expression, suggesting a broad role of RDHEs in coordinating multiple signaling pathways.

miR-133a-3p and miR-145-5p co-promote goat hair follicle stem cell differentiation by regulating NANOG and SOX9 expression

OBJECTIVE

Hair follicle stem cells (HFSCs) differentiation is a critical physiological progress in skin hair follicle (HF) formation. Goat HFSCs differentiation is one of the essential processes of superior-quality brush hair (SQBH) synthesis. However, knowledge regarding the functions and roles of miR-133a-3p and miR-145-5p in differentiated goat HFSCs is limited.

METHODS

To examine the significance of chi-miR-133a-3p and chi-miR-145-5p in differentiated HFSCs, overexpression and knockdown experiments of miR-133a-3p and miR-145-5p (Mimics and Inhibitors) separately or combined were performed. NANOG, SOX9, and stem cell differentiated markers (β-catenin, C-myc, Keratin 6 [KRT6]) expression levels were detected and analyzed by using real-time quantitative polymerase chain reaction, western blotting, and immunofluorescence assays in differentiated goat HFSCs.

RESULTS

miR-133a-3p and miR-145-5p inhibit NANOG (a gene recognized in keeping and maintaining the totipotency of embryonic stem cells) expression and promote SOX9 (an important stem cell transcription factor) expression in differentiated stem cells. Functional studies showed that miR-133a-3p and miR-145-5p individually or together overexpression can facilitate goat HFSCs differentiation, whereas suppressing miR-133a-3p and miR-145-5p or both inhibiting can inhibit goat HFSCs differentiation.

CONCLUSION

These findings could more completely explain the modulatory function of miR-133a-3p and miR-145-5p in goat HFSCs growth, which also provide more understandings for further investigating goat hair follicle development.

Aged polystyrene microplastics exacerbate alopecia associated with tight junction injuries and apoptosis via oxidative stress pathway in skin

Microplastics (MPs) are pervasive pollutants in the natural environment and contribute to increased levels of illness in both animals and humans. However, thespecific impacts of MPs on skin damage and alopeciaare not yet well understood. In this study, we have examined the effects of two types of polystyrene MPs (pristine and aged) on skin and hair follicle damage in mice. UV irradiation changed the chemical and physical properties of the aged MPs, including functional groups, surface roughness, and contact angles. In both in vivo and in vitro experiments, skin and cell injuries related to oxidative stress, apoptosis, tight junctions (TJs), alopecia, mitochondrial dysfunction, and other damages were observed. Mechanistically, MPs and aged MPs can induce TJs damage via the oxidative stress pathway and inhibition of antioxidant-related proteins, and this can lead to alopecia. The regulation of cell apoptosis was also observed, and this is involved in the ROS-mediated mitochondrial signaling pathway. Importantly, aged MPs showed exacerbated toxicity, which may be due to their elevated surface irregularities and altered chemical compositions. Collectively, this study suggests a potential therapeutic approach for alopecia and hair follicle damage caused by MPs pollution.

The promising prospect of human hair follicle regeneration in the shadow of new tissue engineering strategies

Hair loss disorder (alopecia) affects numerous people around the world. The low effectiveness and numerous side effects of common treatments have prompted researchers to investigate alternative and effective solutions. Hair follicle (HF) bioengineering is the knowledge of using hair-inductive (trichogenic) cells. Most bioengineering-based approaches focus on regenerating folliculogenesis through manipulation of regulators of physical/molecular properties in the HF niche. Despite the high potential of cell therapy, no cell product has been produced for effective treatment in the field of hair regeneration. This problem shows the challenges in the functionality of cultured human hair cells. To achieve this goal, research and development of new and practical approaches, technologies and biomaterials are needed. Based on recent advances in the field, this review evaluates emerging HF bioengineering strategies and the future prospects for the field of tissue engineering and successful HF regeneration.

Optimal microneedle length for hair regrowth in hair cycle arrest (alopecia X) in six dogs

BACKGROUND

Hair cycle arrest (HCA) is a chronic alopecic disorder in dogs. Clinical responses vary and are often insufficient. Microneedling (MN) has been used as a successful treatment for HCA in dogs; ideal protocols have not yet been established.

OBJECTIVES

The objective of the study was to compare the efficacy and safety of three needle lengths for MN in dogs with HCA.

ANIMALS

Six unrelated client-owned dogs, including five Pomeranians and one mixed-breed dog, diagnosed with HCA.

MATERIALS AND METHODS

Individual alopecic sites were divided into three sections. For each section, different lengths of needles (1, 2 and 3 mm) were used. Efficacy and safety were evaluated at 1, 3 and 6 months. Treated sections were monitored for 20 months.

RESULTS

Three months after treatment with 3 mm needles, all sections showed hair regrowth. There was no hair regrowth in two of six sections treated with 2 mm needles, and four of six sections did not show a response to treatment with 1 mm needles. Two dogs developed transient pruritus. Five of six dogs had recurrent hair loss between 5 and 16 months of follow-up.

CONCLUSION AND CLINICAL RELEVANCE

Microneedling using longer needles stimulated better hair regrowth in dogs with HCA. Alopecia relapsed in most dogs and minor pruritus occurred in some dogs.

In vitro hair growth-promoting effect of Lgr5-binding octapeptide in human primary hair cells

BACKGROUND

Hair loss occurs due to various biological and environmental causes, which can have psychosocial consequences. The Wnt/β-catenin signaling is well-known for its role in hair growth and regeneration, as it induces the proliferation and differentiation of hair cells. When the leucine-rich G protein-coupled receptor 5 (Lgr5) interacts with the R-spondins, the frizzled receptor (FZD), a Wnt receptor, becomes stabilized, resulting in an increased β-catenin activity.

AIM

We investigated whether the octapeptide that binds to Lgr5 enhances proliferation and differentiation of human primary hair cells through the activation of Wnt/β-catenin signaling.

METHODS

The binding affinity of the octapeptide to Lgr5 was evaluated using surface plasmon resonance (SPR). We confirmed changes in proliferation and related factors like β-catenin activation and growth factors (GFs) expression in human hair follicle dermal papilla cells (HHFDPCs). Additionally, we observed the proliferation and the expression of differentiation markers in human hair follicle outer root sheath cells (HHFORSCs), human hair follicle germinal matrix cells (HHFGMCs), and human hair follicle stem cells (HHFSCs). We used three-dimensional HHFDPC spheroid culture treated with dihydrotestosterone (DHT) to create in vitro conditions that mimic androgenetic alopecia, and we studied the effects of octapeptide on Wnt expression and HHFSC differentiation.

RESULTS

The binding of the octapeptide to Lgr5 was confirmed using SPR analysis. In HHFDPCs, treatment with octapeptide resulted in a concentration-dependent increase in proliferation. We also observed increased nuclear translocation of β-catenin and increased expression of its downstream targets. HHFDPCs treated with octapeptide exhibited increased expression of growth factors and phosphorylation of Akt and ERK. In addition, we confirmed that octapeptide increased proliferation and induced differentiation in HHFORSCs, HHFGMCs, and HHFSCs. Under the HHFDPC spheroid culture conditions, we found that octapeptide restored the inhibition of Wnt-5a and Wnt-10b expressions by DHT. In HHFSCs treated with HHFDPC spheroid culture media, we observed that octapeptide recovered the inhibition of differentiation by DHT.

CONCLUSION

We found that octapeptides activated the Wnt/β-catenin signaling and induced the proliferation and differentiation of human primary hair cells by acting as an exogenous ligand for Lgr5. In addition, octapeptides recovered inhibited hair regeneration characters by DHT in androgenetic alopecia-mimic in vitro model. These findings suggest that octapeptides may be a promising therapeutic option for treating hair loss.

Human Hair Graying Revisited: Principles, Misconceptions, and Key Research Frontiers

Hair graying holds psychosocial importance and serves as an excellent model for studying human pigmentation and aging in an accessible miniorgan. Current evidence suggests that graying results from an interindividually varying mixture of cumulative oxidative and DNA damage, excessive mTORC1 activity, melanocyte senescence, and inadequate production of pigmentation-promoting factors in the hair matrix. Various regulators modulate this process, including genetic factors (DNA repair defects and IRF4 sequence variation, peripheral clock genes, P-cadherin signaling, neuromediators, HGF, KIT ligand secretion, and autophagic flux. This leads to reduced MITF- and tyrosinase-controlled melanogenesis, defective melanosome transfer to precortical matrix keratinocytes, and eventual depletion of hair follicle (HF) pigmentary unit (HFPU) melanocytes and their local progenitors. Graying becomes irreversible only when bulge melanocyte stem cells are also depleted, occurring later in this process. Distinct pigmentary microenvironments are created as the HF cycles: early anagen is the most conducive phase for melanocytic reintegration and activation, and only during anagen can the phenotype of hair graying and repigmentation manifest, whereas the HFPU disassembles during catagen. The temporary reversibility of graying is highlighted by several drugs and hormones that induce repigmentation, indicating potential target pathways. We advise caution in directly applying mouse model concepts, define major open questions, and discuss future human antigraying strategies.

Screening of hair follicle telogen-associated circRNAs in sheep and construction of their ceRNA network

Sheep breeds with hair-shedding traits have many advantages over non-shedding sheep breeds, not only because of reduced shearing labor and feeding management costs but also because it reduces in vitro parasites and improves adaptability to summer heat stress. The wool of Dorper sheep naturally sheds in spring due to the periodic growth of hair follicles. CircRNAs primarily regulate the morphogenesis of hair follicles through the ceRNA mechanism. In this study, five 2-year-old Dorper ewes with extreme hair-shedding phenotype (S) and three Dorper ewes with non-shedding (N) phenotype were selected for subsequent analyses. For RNA extraction, skin tissues were collected on 27th September 2019 (S1, N1), 3rd January 2020 (S2, N2), and 17th March 2020 (S3, N3), which were then subjected to RNA-seq. RNA-seq technology revealed 20,185 novel circRNAs in the hair follicles of Dorper sheep. Among them, 1450 circRNAs were differentially expressed (DE). Clustering heatmap and expression pattern analyses were performed on DE circRNAs, which indicated 78 circRNAs with T pattern (Telogen, highly expressed in telogen), and the source genes for candidate circRNAs were further screened by functional enrichment analysis, which identified 13 crucial genes enriched in pathways associated with hair follicle development. Additionally, a ceRNA regulatory network comprising 4 circRNAs, 11 miRNAs, and 13 target genes was constructed. Overall, this study screened circRNAs that may be associated with the telogen phase of hair follicles in sheep, providing a relevant theoretical basis for wool shedding in sheep and for breeding Dorper sheep with automatic wool shedding.

The development of anin vitrohuman hair follicle organoid with a complexity similar to thatin vivo

In vitrohair follicle (HF) models are currently limited toex vivoHF organ cultures (HFOCs) or 2D models that are of low availability and do not reproduce the architecture or behavior of the hair, leading to poor screening systems. To resolve this issue, we developed a technology for the construction of a humanin vitrohair construct based on the assemblage of different types of cells present in the hair organ. First, we demonstrated that epithelial cells, when isolatedin vitro, have similar genetic signatures regardless of their dissection site, and their trichogenic potential is dependent on the culture conditions. Then, using cell aggregation techniques, 3D spheres of dermal papilla (DP) were constructed, and subsequently, epithelial cells were added, enabling the production and organization of keratins in hair, similar to what is seenin vivo. These reconstructed tissues resulted in the following hair compartments: K71 (inner root-sheath), K85 (matrix region), K75 (companion layer), and vimentin (DP). Furthermore, the new hair model was able to elongate similarly toex vivoHFOC, resulting in a shaft-like shape several hundred micrometers in length. As expected, when the model was exposed to hair growth enhancers, such as ginseng extract, or inhibitors, such as TGF-B-1, significant effects similar to thosein vivowere observed. Moreover, when transplanted into skin biopsies, the new constructs showed signs of integration and hair bud generation. Owing to its simplicity and scalability, this model fully enables high throughput screening of molecules, which allows understanding of the mechanism by which new actives treat hair loss, finding optimal concentrations, and determining the synergy and antagonism among different raw materials. Therefore, this model could be a starting point for applying regenerative medicine approaches to treat hair loss.

Analysis of bioprinting strategies for skin diseases and injuries through structural and temporal dynamics: historical perspectives, research hotspots, and emerging trends

This study endeavors to investigate the progression, research focal points, and budding trends in the realm of skin bioprinting over the past decade from a structural and temporal dynamics standpoint. Scholarly articles on skin bioprinting were obtained from WoSCC. A series of bibliometric tools comprising R software, CiteSpace, HistCite, and an alluvial generator were employed to discern historical characteristics, evolution of active topics, and upcoming tendencies in the area of skin bioprinting. Over the past decade, there has been a consistent rise in research interest in skin bioprinting, accompanied by an extensive array of meaningful scientific collaborations. Concurrently, diverse dynamic topics have emerged during various periods, as substantiated by an aggregate of 22 disciplines, 74 keywords, and 187 references demonstrating citation bursts. Four burgeoning research subfields were discerned through keyword clustering-namely, #3 'in situbioprinting', #6 'vascular', #7 'xanthan gum', and #8 'collagen hydrogels'. The keyword alluvial map reveals that Module 1, including 'transplantation' etc, has primarily dominated the research module over the previous decade, maintaining enduring relevance despite annual shifts in keyword focus. Additionally, we mapped out the top six key modules from 2023 being 'silk fibroin nanofiber', 'system', 'ionic liquid', 'mechanism', and 'foot ulcer'. Three recent research subdivisions were identified via timeline visualization of references, particularly Clusters #0 'wound healing', #4 'situ mineralization', and #5 '3D bioprinter'. Insights derived from bibliometric analyses illustrate present conditions and trends in skin bioprinting research, potentially aiding researchers in pinpointing central themes and pioneering novel investigative approaches in this field.

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.

Evaluation of efficacy of Silybum marianum flower extract on the mitigating hair loss in vitro and in vivo

BACKGROUND

Natural components that can exert a wide range of anti-hair loss activity with fewer side effects are in high demand. The objective of this study was to investigate the anti-hair loss potential of Silybum marianum flower extract (SMFE) in vitro and in vivo.

METHODS

The effect of SMFE on dermal papilla cells was evaluated by measuring cell proliferation and VEGF production in hair follicle dermal papilla cells (HFDPCs). In addition, to confirm the effect of SMFE on dermal papilla senescence, SA-β-gal staining and senescence associated secretory phenotype (SASP) production such as IL-6 was observed in both replicative and hydrogen peroxide (H2 O2 )-induced senescence models. In a clinical study, hair growth was determined by reconstitution analysis after shaving the hair of the clinical subject's scalp and hair area.

RESULTS

SMFE increased the proliferation and VEGF production of HFDPCs. It also suppressed cellular senescence of HFDPCs and IL-6 production in replicative senescence and oxidative stress-induced senescence models. The hair density and total hair count at 16 and 24 weeks after using hair shampoo containing SMFE were significantly increased compared with those of the placebo group.

CONCLUSION

SMFE has the potential to be used as a natural ingredient for alleviating hair loss.

Deciphering the molecular mechanisms of stem cell dynamics in hair follicle regeneration

Hair follicles, which are connected to sebaceous glands in the skin, undergo cyclic periods of regeneration, degeneration, and rest throughout adult life in mammals. The crucial function of hair follicle stem cells is to maintain these hair growth cycles. Another vital aspect is the activity of melanocyte stem cells, which differentiate into melanin-producing melanocytes, contributing to skin and hair pigmentation. Sebaceous gland stem cells also have a pivotal role in maintaining the skin barrier by regenerating mature sebocytes. These stem cells are maintained in a specialized microenvironment or niche and are regulated by internal and external signals, determining their dynamic behaviors in homeostasis and hair follicle regeneration. The activity of these stem cells is tightly controlled by various factors secreted by the niche components around the hair follicles, as well as immune-mediated damage signals, aging, metabolic status, and stress. In this study, we review these diverse stem cell regulatory and related molecular mechanisms of hair regeneration and disease conditions. Molecular insights would provide new perspectives on the disease mechanisms as well as hair and skin disorder treatment.

The formulation and in vitro evaluation of WS Biotin, a novel encapsulated form of D-Biotin with improved water solubility for hair and skin treatment applications

OBJECTIVE

To develop and evaluate the efficacy of WS Biotin, a novel water-soluble form of D-Biotin, for cosmetic use.

METHODS

A new encapsulated form of D-Biotin was developed with the purpose of improving the water solubility of biotin. This novel form of encapsulated biotin was characterized by its physicochemical properties: particle size, D-Biotin content and solubility in water. Also, proliferation and gene expression in vitro tests in cell culture were performed to evaluate its effectiveness in promoting hair growth, an ELISA test was conducted for hair keratinization and skin lightening property was tested by analysing the intracellular melanin content.

RESULTS

The developed WS Biotin microcapsules exhibit a particle size range of 2-30 μm with D-Biotin content of ~50% (w/w). The water solubility of WS Biotin was found to be 20-fold greater than free biotin. The obtained in vitro results indicated that WS Biotin enhances the expression of hair-related keratins in hair follicle keratinocytes, as well as the expression of hair growth-promoting genes in dermal papilla cells. Moreover, the melanin content in UVA-exposed epidermal melanocytes was reduced upon exposure to WS Biotin.

CONCLUSION

In this work, a novel form of encapsulated biotin, WS Biotin, was developed in order to improve the water solubility of free biotin and was found to be effective for cosmetic use in both hair and skin applications.

Association of different cell types and inflammation in early acne vulgaris

Acne vulgaris, one of the most common skin diseases, is a chronic cutaneous inflammation of the upper pilosebaceous unit (PSU) with complex pathogenesis. Inflammation plays a central role in the pathogenesis of acne vulgaris. During the inflammatory process, the innate and adaptive immune systems are coordinately activated to induce immune responses. Understanding the infiltration and cytokine secretion of differential cells in acne lesions, especially in the early stages of inflammation, will provide an insight into the pathogenesis of acne. The purpose of this review is to synthesize the association of different cell types with inflammation in early acne vulgaris and provide a comprehensive understanding of skin inflammation and immune responses.

SP1 and KROX20 Regulate the Proliferation of Dermal Papilla Cells and Target the CUX1 Gene

Previous studies have demonstrated that CUX1 could contribute to the proliferation of DPCs in vitro, but the upstream transcriptional regulatory mechanisms of CUX1 remain largely unknown. This study aimed to investigate the upstream transcriptional regulators of CUX1 to enhance our comprehension of the mechanism of action of the CUX1 gene in ovine DPCs. Initially, the JASPAR (2024) software was used to predict the upstream target transcription factors for the CUX1 gene. Subsequently, through RT-qPCR and a double luciferase reporter assay, the interaction between SP1, KROX20, and CUX1 was established, respectively. The results indicated that SP1 and KROX20 were two highly reliable upstream transcription regulators for the CUX1 gene. Additionally, we found that SP1 promoted the proliferation of DPCs by overexpressing SP1 in DPCs, and KROX20 inhibited the proliferation of DPCs by overexpressing KROX20 in DPCs. These findings are also consistent with the transcriptional regulation of CUX1 by SP1 and KROX20, respectively. This study suggests that the effect of DPC proliferation in vitro by CUX1 may regulated by the transcription factors SP1 and KROX20.

Whole-Genome Resequencing Reveals Genetic Diversity and Wool Trait-Related Genes in Liangshan Semi-Fine-Wool Sheep

Understanding the genetic makeup of local sheep breeds is essential for their scientific conservation and sustainable utilization. The Liangshan semi-fine-wool sheep (LSS), a Chinese semi-fine-wool breed renowned for its soft wool, was analyzed using whole-genome sequencing data including 35 LSS, 84 sheep from other domestic breeds, and 20 Asiatic mouflons. We investigated the genetic composition of LSS by conducting analyses of the population structure, runs of homozygosity, genomic inbreeding coefficients, and selection signature. Our findings indicated that LSS shares greater genetic similarity with Border Leicester and Romney sheep than with Tibetan (TIB), Yunnan (YNS), and Chinese Merino sheep. Genomic analysis indicated low to moderate inbreeding coefficients, ranging from 0.014 to 0.154. In identifying selection signals across the LSS genome, we pinpointed 195 candidate regions housing 74 annotated genes (e.g., IRF2BP2, BVES, and ALOX5). We also found the overlaps between the candidate regions and several known quantitative trait loci related to wool traits, such as the wool staple length and wool fiber diameter. A selective sweep region, marked by the highest value of cross-population extended haplotype homozygosity, encompassed IRF2BP2-an influential candidate gene affecting fleece fiber traits. Furthermore, notable differences in genotype frequency at a mutation site (c.1051 + 46T > C, Chr25: 6,784,190 bp) within IRF2BP2 were observed between LSS and TIB and YNS sheep (Fisher's exact test, p < 2.2 × 10-16). Taken together, these findings offer insights crucial for the conservation and breeding enhancement of LSS.

Impact of Stem Cells on Reparative Regeneration in Abdominal and Dorsal Skin in the Rat

A characteristic feature of repair processes in mammals is the formation of scar tissue at the site of injury, which is designed to quickly prevent contact between the internal environment of the organism and the external environment. Despite this general pattern, different organs differ in the degree of severity of scar changes in response to injury. One of the areas in which regeneration after wounding leads to the formation of a structure close to the original one is the abdominal skin of laboratory rats. Finding out the reasons for such a phenomenon is essential for the development of ways to stimulate full regeneration. The model of skin wound healing in the abdominal region of laboratory animals was reproduced in this work. It was found that the wound surface is completely epithelialized on the abdomen by 20 days, while on the back-by 30 days. The qPCR method revealed higher expression of marker genes of skin stem cells (Sox9, Lgr6, Gli1, Lrig1) in the intact skin of the abdomen compared to the back, which corresponded to a greater number of hairs with which stem cells are associated on the abdomen compared to the back. Considering that some stem cell populations are associated with hair, it can be suggested that one of the factors in faster regeneration of abdominal skin in the rat is the greater number of stem cells in this area.

Pan-Omics in Sheep: Unveiling Genetic Landscapes

Multi-omics-integrated analysis, known as panomics, represents an advanced methodology that harnesses various high-throughput technologies encompassing genomics, epigenomics, transcriptomics, proteomics, and metabolomics. Sheep, playing a pivotal role in agricultural sectors due to their substantial economic importance, have witnessed remarkable advancements in genetic breeding through the amalgamation of multiomics analyses, particularly with the evolution of high-throughput technologies. This integrative approach has established a robust theoretical foundation, enabling a deeper understanding of sheep genetics and fostering improvements in breeding strategies. The comprehensive insights obtained through this approach shed light on diverse facets of sheep development, including growth, reproduction, disease resistance, and the quality of livestock products. This review primarily focuses on the application of principal omics analysis technologies in sheep, emphasizing correlation studies between multiomics data and specific traits such as meat quality, wool characteristics, and reproductive features. Additionally, this paper anticipates forthcoming trends and potential developments in this field.

Th22 is the effector cell of thymosin β15-induced hair regeneration in mice

BACKGROUND

Thymosin beta family has a significant role in promoting hair regeneration, but which type of T cells play a key role in this process has not been deeply studied. This research aimed to find out the subtypes of T cell that play key role in hair regeneration mediated by thymosin beta 15 (Tβ15).

METHODS

Ready-to-use adenovirus expressing mouse Tmsb15b (thymosin beta 15 overexpression, Tβ15 OX) and lentivirus-Tβ15 short hairpin RNA (Tβ15 sh) were used to evaluate the role of Tβ15 in hair regeneration and development. The effect of Th22 cells on hair regeneration was further studied by optimized Th22-skewing condition medium and IL-22 binding protein (IL-22BP, an endogenous antagonist of IL-22, also known as IL-22RA2) in both ex vivo culture C57BL/6J mouse skin and BALB/c nude mice transplanted with thymus organoid model.

RESULTS

The results show that Tβ15, the homologous of Tβ4, can promote hair regeneration by increasing the proliferation activity of hair follicle cells. In addition, high-level expression of Tβ15 can not only increase the number of Th22 cells around hair follicles but also accelerate the transformation of hair follicles to maturity. Consistent with the expected results, when the IL-22BP inhibitor was used to interfere with Th22, the process of hair regeneration was blocked.

CONCLUSIONS

In conclusion, Th22 is the key effector cell of Tβ15 inducing hair regeneration. Both Tβ15 and Th22 may be the potential drug targets for hair regeneration.

Neurotensin counteracts hair growth inhibition induced by chronic restraint stress

Stress has been considered as a potential trigger for hair loss through the neuroendocrine-hair follicle (HF) axis. Neurotensin (NTS), a neuropeptide, is known to be dysregulated in the inflammatory-associated skin diseases. However, the precise role of NTS in stress-induced hair loss is unclear. To investigate the function and potential mechanisms of NTS in stress-induced hair growth inhibition, we initially detected the expression of neurotensin receptor (Ntsr) and NTS in the skin tissues of stressed mice by RNA-sequencing and ELISA. We found chronic restraint stress (CRS) significantly decreased the expression of both NTS and Ntsr in the skin tissues of mice. Intracutaneous injection of NTS effectively counteracted CRS-induced inhibition of hair growth in mice. Furthermore, NTS regulated a total of 1093 genes expression in human dermal papilla cells (HDPC), with 591 genes being up-regulated and 502 genes being down-regulated. GO analysis showed DNA replication, cell cycle, integral component of plasma membrane and angiogenesis-associated genes were significantly regulated by NTS. KEGG enrichment demonstrated that NTS also regulated genes related to the Hippo signalling pathway, axon guidance, cytokine-cytokine receptor interaction and Wnt signalling pathway in HDPC. Our results not only uncovered the potential effects of NTS on stress-induced hair growth inhibition but also provided an understanding of the mechanisms at the gene transcriptional level.

In vitro induction of hair follicle signatures using human dermal papilla cells encapsulated in fibrin microgels

Cellular spheroids have been described as an appropriate culture system to restore human follicle dermal papilla cells (hFDPc) intrinsic properties; however, they show a low and variable efficiency to promote complete hair follicle formation in in vivo experiments. In this work, a conscientious analysis revealed a 25% cell viability in the surface of the dermal papilla spheroid (DPS) for all culture conditions, questioning whether it is an appropriate culture system for hFDPc. To overcome this problem, we propose the use of human blood plasma for the generation of fibrin microgels (FM) with encapsulated hFDPc to restore its inductive signature, either in the presence or in the absence of blood platelets. FM showed a morphology and extracellular matrix composition similar to the native dermal papilla, including Versican and Collagen IV and increasing cell viability up to 85%. While both systems induce epidermal invaginations expressing hair-specific keratins K14, K15, K71, and K75 in in vitro skin cultures, the number of generated structures increases from 17% to 49% when DPS and FM were used, respectively. These data show the potential of our experimental setting for in vitro hair follicle neogenesis with wild adult hFDPc using FM, being a crucial step in the pursuit of human hair follicle regeneration therapies.

Hair Growth-Promoting Effects of Rosehip (Rosa canina L.) Seed Oil in C57BL/6 Mice

Rosehip (Rosa canina L.) seeds, a by-product of the food processing industry, contain various bioactive compounds that have potential cosmetic and pharmacological applications. Rosehip seed oil (RHSO) has been shown to exert therapeutic effects in skin disorders, but its role in promoting hair growth remains unknown. In this study, we aimed to elucidate the hair growth-promoting activity of RHSO and the related mechanisms of action. The depleted dorsal skin of telogenic C57BL/6 mice was topically treated with RHSO for 21 days, and the extent of hair regrowth was assessed. The results indicated that RHSO stimulated hair growth by inducing the early transition of hair follicles from telogen to anagen phase. Histological analysis revealed significant increases in hair follicle density, hair bulb size, and skin thickness. RHSO treatment also upregulated the expression of hair growth-associated genes, including β-catenin, phospho-glycogen synthase kinase-3 beta, Sonic hedgehog, smoothened, cyclin D1, cyclin E, and insulin like growth factor 1. These findings suggest that RHSO stimulates hair growth and may show promise as a preventive and/or therapeutic agent for hair loss.

Controlling Hair Loss by Regulating Apoptosis in Hair Follicles: A Comprehensive Overview

Apoptosis is a physiological process that occurs in all cell types of the human body, and it profoundly changes the fate of hair by affecting hair follicle cells. This review outlines the cellular changes, intrinsic biochemical characteristics, and mechanisms underlying apoptosis and summarizes the hair follicle life cycle, including development, cycle stages, and corresponding cellular changes. Finally, the relationship between apoptosis and the hair cycle is discussed and the significance of apoptosis in hair loss conditions and drug treatments is highlighted. Apoptosis induces cellular changes and exhibits distinctive properties through intricate signaling pathways. Hair follicles undergo cyclic periods of growth, regression, and dormancy. Apoptosis is closely correlated with the regression phase by triggering hair follicle cell death and shedding. Regulation of apoptosis in hair follicles plays an essential role in hair loss due to maladies and drug treatments. Mitigating apoptosis can enhance hair growth and minimize hair loss. A comprehensive understanding of the correlation between apoptosis and the hair cycle can facilitate the development of novel treatments to prevent hair loss and stimulate hair regeneration.

Interpretation of the Yak Skin Single-Cell Transcriptome Landscape

The morphogenesis of hair follicle structure is accompanied by the differentiation of skin tissue. Mammalian coats are produced by hair follicles. The formation of hair follicles requires signal transmission between the epidermis and dermis. However, knowledge of the transcriptional regulatory mechanism is still lacking. We used single-cell RNA sequencing to obtain 26,573 single cells from the scapular skin of yaks at hair follicle telogen and anagen stages. With the help of known reference marker genes, 11 main cell types were identified. In addition, we further analyzed the DP cell and dermal fibroblast lineages, drew a single-cell map of the DP cell and dermal fibroblast lineages, and elaborated the key genes, signals, and functions involved in cell fate decision making. The results of this study provide a very valuable resource for the analysis of the heterogeneity of DP cells and dermal fibroblasts in the skin and provide a powerful theoretical reference for further exploring the diversity of hair follicle cell types and hair follicle morphogenesis.

miR-133a-3p regulates the growth of hair follicle stem cells in white goats from the Yangtze River Delta

The Yangtze River Delta white goats are the sole goat breed producing brush hair of high quality. Owing to the particularities of its wool production, a higher demand is placed on breeding efforts for this animal. Studies on the developmental mechanisms of the aligned hair follicle stem cells (HFSCs) provide a theoretical basis for molecular breeding. In the present study, HFSCs were isolated using the technique of immunohistochemistry from the cervical spinal skin tissue samples from the fetal sheep, and the miR-133a-3p expression was confirmed using quantitative reverse-transcription PCR (RT-qPCR) and western blotting experiments from the isolated HFSCs. Additionally, the effects on the proliferation and apoptosis of HFSCs were detected using flow cytometry and 5-ethynyl-2'-deoxyuridine assays, along with other methods, following the overexpression of miR-133a-3p or its inhibition. The experimental results revealed that miR-133a-3p overexpressed could inhibit the proliferation of HFSCs and promote apoptosis by specifically targeting DUSP6. While the miR-133a-3p knockdown could promote the proliferation but inhibit the apoptosis of the HFSCs. Meanwhile, the miR-133a-3p knockdown experiments showed opposite outcomes. These results illustrate the presence of a relevant network between DUSP6 and miR-133a-3p, which regulates the production of superior-quality brush hair.

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

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

Strain and Strain Recovery of Human Hair from the Nano- to the Macroscale

In this study, in operandi SAXS experiments were conducted on samples of human hair with a varying degree of strain (2% within the elastic region and 10% beyond). Four different features in the SAXS patterns were evaluated: The intermediate filament distance perpendicular to and the distance from the meridional arc in the load direction, as well as the distances of the lipid bilayer peak in and perpendicular to the load direction. From the literature, one concludes that polar lipids in the cuticle are the origin of the lipid peak in the SAXS pattern, and this study shows that the observed strain in the lipids is much lower than in the intermediate filaments. We support these findings with SEM micrographs, which show that the scales in the cuticle deform much less than the cortex. The observed deformation of the intermediate filaments is very high, about 70% of the macrostrain, and the ratio of the transverse strain to the longitudinal strain at the nanoscale gives a Poisson ratio of νnano = 0.44, which is typical for soft matter. This work also finds that by varying the time period between two strain cycles, the typical strain recovery time is about 1000 min, i.e., one day. After this period, the structure is nearly identical to the initial structure, which suggests an interpretation that this is the typical time for the self-healing of hair after mechanical treatment.

Histological characteristics of hair follicles at different hair cycle and in vitro modeling of hair follicle-associated cells of yak (Bos grunniens)

To adapt to the extreme conditions of plateau environments, yaks have evolved thick hair, making them an ideal model for investigating the mechanisms involved in hair growth. We can gain valuable insights into how hair follicles develop and their cyclic growth in challenging environments by studying yaks. However, the lack of essential data on yak hair follicle histology and the absence of in vitro cell models for hair follicles serve as a limitation to such research objectives. In this study, we investigated the structure of skin tissue during different hair follicle cycles using the yak model. Additionally, we successfully established in vitro models of hair follicle-associated cells derived from yak skin, including dermal papilla cells (DPCs), preadipocytes, and fibroblasts. We optimized the microdissection technique for DPCs culture by simplifying the procedure and reducing the time required. Furthermore, we improved the methodology used to differentiate yak preadipocytes into mature adipocytes, thus increasing the differentiation efficiency. The introduction of yak as a natural model provides valuable research resources for exploring the mechanisms of hair growth and contributes to a deeper understanding of hair follicle biology and the development of regenerative medicine strategies.

Recent omics advances in hair aging biology and hair biomarkers analysis

Aging is a complex natural process that leads to a decline in physiological functions, which is visible in signs such as hair graying, thinning, and loss. Although hair graying is characterized by a loss of pigment in the hair shaft, the underlying mechanism of age-associated hair graying is not fully understood. Hair graying and loss can have a significant impact on an individual's self-esteem and self-confidence, potentially leading to mental health problems such as depression and anxiety. Omics technologies, which have applications beyond clinical medicine, have led to the discovery of candidate hair biomarkers and may provide insight into the complex biology of hair aging and identify targets for effective therapies. This review provides an up-to-date overview of recent omics discoveries, including age-associated alterations of proteins and metabolites in the hair shaft and follicle, and highlights the significance of hair aging and graying biomarker discoveries. The decline in hair follicle stem cell activity with aging decreased the regeneration capacity of hair follicles. Cellular senescence, oxidative damage and altered extracellular matrix of hair follicle constituents characterized hair follicle and hair shaft aging and graying. The review attempts to correlate the impact of endogenous and exogenous factors on hair aging. We close by discussing the main challenges and limitations of the field, defining major open questions and offering an outlook for future research.

Nanotechnology-based techniques for hair follicle regeneration

The hair follicle (HF) is a multicellular complex structure of the skin that contains a reservoir of multipotent stem cells. Traditional hair repair methods such as drug therapies, hair transplantation, and stem cell therapy have limitations. Advances in nanotechnology offer new approaches for HF regeneration, including controlled drug release and HF-specific targeting. Until recently, embryogenesis was thought to be the only mechanism for forming hair follicles. However, in recent years, the phenomenon of wound-induced hair neogenesis (WIHN) or de novo HF regeneration has gained attention as it can occur under certain conditions in wound beds. This review covers HF-specific targeting strategies, with particular emphasis on currently used nanotechnology-based strategies for both hair loss-related diseases and HF regeneration. HF regeneration is discussed in several modalities: modulation of the hair cycle, stimulation of progenitor cells and signaling pathways, tissue engineering, WIHN, and gene therapy. The HF has been identified as an ideal target for nanotechnology-based strategies for hair regeneration. However, some regulatory challenges may delay the development of HF regeneration nanotechnology based-strategies, which will be lastly discussed.

The role of telomerase in hair growth and relevant disorders: A review

BACKGROUND

Hair diseases may present with hair loss, hirsutism, hair melanin abnormalities and other manifestations. Hair follicles are known as mini-organs that undergo periodic remodeling, and their constant regeneration in vivo reflects interesting anti-aging functions. Telomerase prevents cellular senescence by maintaining telomere length, but its excessive proliferation in cancer cells may also induce cancer. However, the effects of telomerase in hair growth have rarely been reported.

METHODS

In this study, we reviewed the role of telomerase in hair growth and the effects of hair disorders through literature search and analysis.

RESULTS

There is growing evidence that telomerase plays an important role in maintaining hair follicle function and proliferation. Changes in telomerase levels in hair follicles have also been found in a variety of hair disorders.

CONCLUSION

Telomerase plays a positive role in hair growth and is expected to become a new target for the treatment of alopecia or other hair diseases in the future.

VDR is an essential regulator of hair follicle regression through the progression of cell death

Vitamin D receptor (VDR) is essential for hair follicle homeostasis as its deficiency induces hair loss, although the mechanism involved remains unknown. Our research shows that, in Vdr-knockout mice, the hair cycle is halted during the catagen stage, preceding alopecia. In addition, in Vdr-knockout hair follicles, epithelial strands that normally regress during the catagen phase persist as "surviving epithelial strands." Single-cell RNA sequencing analysis suggests that these surviving epithelial strands are formed by cells in the lower part of the hair follicle. These findings emphasize the importance of the regression phase in hair follicle regeneration and establish VDR as a regulator of the catagen stage.

Basic principles of hair follicle structure, morphogenesis, and regeneration

Diseases affecting the hair follicle are common in domestic animals, but despite the importance of an intact skin barrier and a fully functional hair coat, knowledge about the detailed morphological features and the diversity of these complex mini-organs are often limited, although mandatory to evaluate skin biopsies with a history of alopecia. The factors that regulate the innate hair follicle formation and the postnatal hair cycle are still not completely understood in rodents, only rudimentarily known in humans, and are poorly understood in our companion animals. This review aims to summarize the current knowledge about hair follicle and hair shaft anatomy, the arrangement of hair follicles, hair follicle morphogenesis in the embryo, and the lifelong regeneration during the postnatal hair cycle in domestic animals. The role of follicular stem cells and the need for a multitude of interacting signaling events during hair follicle morphogenesis and regeneration is unquestioned. Because of the lack of state of the art methods that can be applied in rodents but are not feasible in companion animals, most of the information in this review is based on rodent studies. However, the few data from domestic animals that are available will be discussed, and it can be assumed that at least the principal molecular mechanisms are similar in rodents and other species.

Non-invasive assessment of hair regeneration in androgenetic alopecia mice in vivo using two-photon and second harmonic generation imaging

The identification of crucial targets for hair regrowth in androgenetic alopecia (AGA) involves determining important characteristics and different stages during the process of hair follicle regeneration. Traditional methods for assessing key features and different stages of hair follicle primarily involve taking skin tissue samples and determining them through various staining or other methods. However, non-invasive assessment methods have been long sought. Therefore, in this study, endogenous fluorescence signals from skin keratin and second harmonic signals from skin collagen fibers were utilized as probes, two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging techniques were employed to non-invasively assess hair shafts and collagen fibers in AGA mice in vivo. The TPEF imaging technique revealed that the alternation of new and old hair shafts and the different stages of the growth period in AGA mice were delayed. In addition, SHG imaging found testosterone reduced hair follicle area and miniaturized hair follicles. The non-invasive TPEF and SHG imaging techniques provided important methodologies for determining significant characteristics and different stages of the growth cycle in AGA mice, which will facilitate future non-invasive assessments on human scalps in vivo and reduce the use of animal testing.

Expression of miRNA-1-3p and its target gene in hair follicle cycle development of Liaoning Cashmere goat

MicroRNA exerts an important regulatory role in almost all the biological process, including hair follicle development in Liaoning Cashmere goat. In order to improve the Cashmere performance of goat, the regulatory role of microRNA in hair follicle cycle has drawn hotspot attention. However, the molecular mechanisms of miRNA-1-3p involved in hair follicle development are poorly understood. In this study, we found that miRNA-1-3p was less expressed in anagen stage of hair follicle cycle of Cashmere goat than that in telogen stage by using RT-qPCR and immunoblotting analysis, in contrast to the expression pattern of FGF14. The Dual-Luciferase reporter assay was employed to verify the relationship between miRNA-1-3p and FGF14. The results showed that miRNA-1-3p specifically binds to the 3'UTR of FGF14 mRNA, and FGF14 is the target gene of miR-1-3p. In conclusion, this study shows that miRNA-1-3p may regulate hair follicle development in Liaoning Cashmere goats by targeting FGF14.

Canine noninflammatory alopecia: An approach to its classification and a diagnostic aid

Noninflammatory alopecia is common in dogs and is a frequent cause to consult a veterinarian. It is also a common reason to take biopsies. Noninflammatory alopecia can be attributed to a decreased formation or cytodifferentiation of the hair follicle or the hair shaft in utero, resulting in congenital alopecia. Congenital alopecia often has a hereditary cause, and examples of such disorders are ectodermal dysplasias associated with gene variants of the ectodysplasin A gene. Noninflammatory alopecia may also be caused by impaired postnatal regeneration of hair follicles or shafts. Such disorders may have a clear breed predilection, and alopecia starts early in life. A hereditary background is suspected in those cases but has not been proven. They are referred to as follicular dysplasia although some of these disorders present histologically like a hair cycle disturbance. Late-onset alopecia is usually acquired and may be associated with endocrinopathies. Other possible causes are impaired vascular perfusion or stress. As the hair follicle has limited possible responses to altered regulation, and histopathology may change during the course of a disease, a detailed clinical history, thorough clinical examination including blood work, appropriate biopsy site selection, and detailed histological findings need to be combined to achieve a final diagnosis. This review aims to provide an overview about the known noninflammatory alopecic disorders in dogs. As the pathogenesis of most disorders is unknown, some statements are based on comparative aspects or reflect the authors' opinion.