Recent progress in hair follicle stem cell markers and their regulatory roles

L-borneol regulates rno-miR-127/ PODXL2 to promote hair follicle stem cells to repair skin wounds

Hair follicle stem cells (HFSCs) can quickly activate and migrate to the wound site, differentiating into epidermal stem cells to facilitate early epithelialization. During the wound healing process, microRNAs (miRNAs) function coordinately. Chinese medicine borneol is derived from the Cinnamomum camphora plant, and its principal component, L-borneol, is renowned for its potential in facilitating skin wound healing. However, it remains unclear whether L-borneol can stimulate HFSCs to differentiate into epidermal cells or whether miRNAs are involved in this process. In the current study, HFSCs were isolated from the vibrissae of rats and identified based on the expression of CD34, Integrin-β1 and keratin type 1 cytoskeletal 15(CK15). We observed that stimulation with L-borneol significantly increased the differentiation marker K14 in HFSCs, suggesting that L-borneol could promote the differentiation of HFSCs into basal layer cells. On this basis, we transfected and confirmed that rno-miR-127 inhibitor could promote the differentiation of HFSCs. Furthermore, we demonstrated that PODXL2 is a target gene of rno-miR-127 through dual-luciferase reporter assays and confirmed that the rno-miR-127 mimic could inhibit the expression of PODXL2. To further elucidate the targeting relationship, we constructed the siPODXL2 fragment using siRNA technology, demonstrating that reducing PODXL2 expression can inhibit the differentiation of HFSCs into basal layer cells. Finally, a rat full-thickness skin defect model illustrated L-borneol-mediated negative regulation of PODXL2 by rno-miR-127, promoting skin injury repair through HFSCs.

[Hair transplantation in wound healing and scar repair in special areas]

Objective

To review recent advances in the application of hair transplantation in wound healing and scar repair in special areas.

Methods

An extensive review of the literature on the application of hair transplantation in wound healing and scar repair in special areas was conducted, focusing on cellular functions, molecular mechanisms, and clinical applications.

Results

Hair transplantation has been shown to effectively promote wound healing and scar repair in special areas. The underlying mechanisms are complex, but current understanding emphasizes a strong association with hair follicle-associated stem cells (including epidermal stem cells, dermal papilla cells, dermal sheath cells, etc).

Conclusion

The application of hair transplantation in wound healing and scar repair in special areas remains in its early stages. Further investigation into its mechanisms of action is essential, and randomized controlled trials are needed to establish its efficacy.

Generation of the Krt24-CreERT2 Mouse Line Targeting Outer Bulge Hair Follicle Cells

Outer bulge (OB) hair follicle stem cells (HFSCs) play a crucial role in maintaining hair follicle structural stability and regulating the hair follicle cycle. Previous studies demonstrated that keratin 24 (Krt24) exhibits spatiotemporally restricted expression in OB HFSCs. Here, we report the generation of the Krt24-CreERT2 mouse line. When crossed with Rosa26LSL-tdTomato or Rosa26LSL-DTR reporter lines, offspring exhibited specific labeling (Krt24-CreERT2;Rosa26LSL-tdTomato) or ablation (Krt24-CreERT2;Rosa26LSL-DTR) of Krt24+ cells. In Krt24-CreERT2;Rosa26LSL-tdTomato mice, phase-specific tamoxifen (TAM) administration demonstrated spatiotemporal fidelity of Cre activity to endogenous Krt24 expression patterns. Lineage tracing revealed that tdTomato-labeled Krt24+ cells differentiated into the outer root sheath (ORS) during the anagen phase and persisted when hair follicles reentered telogen. Ablation of Krt24+ cells via diphtheria toxin (DT) administration significantly delayed anagen initiation. Mice under continuous depletion of Krt24+ HFSCs experienced substantial mortality after ionizing irradiation. Notably, ionizing radiation triggered a marked expansion of tdTomato-labeled Krt24+ cells, accompanied by maintained hair follicle homeostasis. Taken together, this study established a Krt24-CreERT2 mouse line targeting OB HFSCs, which are essential for hair follicle development and damage repair.

The Retinoic-Acid-Related Orphan Receptor Alpha May Be Highly Involved in the Regulation of Seasonal Hair Molting

Seasonal molting in mammals is a crucial survival strategy, yet the underlying molecular mechanisms have not been fully characterized. Melatonin, serving as a bridge for the transmission of photoperiod signals, plays a significant regulatory role in animals' seasonal molting, and the physiological regulatory effects of melatonin signaling are highly dependent on the retinoic-acid-related orphan receptor alpha (Rorα). Hair follicle stem cells (HFSCs) are the most essential cell type in the process of hair follicle regeneration and seasonal replacement. Therefore, this study aims to discuss the regulatory effects of melatonin and its nuclear receptor RORA on HFSCs. This research found that RORA can downregulate cellular proliferation levels by inhibiting the cell cycle of HFSCs, while simultaneously promoting apoptosis in HFSCs and affecting the expression of some genes involved in ferroptosis. RORA can directly bind to the promoter regions of the cyclin genes Ccna2 and Ccne1 to regulate their transcription. Melatonin may enhance the viability of HFSCs by downregulating RORA levels. In this study, the impact of melatonin and its nuclear receptor RORA on the viability of HFSCs, along with some of the underlying molecular mechanisms, is characterized. These findings provide a theoretical foundation for research on the regulation of animal hair follicle development.

In vitro hair growth-promoting effects of araliadiol via the p38/PPAR-γ signaling pathway in human hair follicle stem cells and dermal papilla cells

Background

Scalp hair plays a crucial role in social communication by expressing personal appearance and self-identity. Consequently, hair loss often leads to a perception of unattractiveness, negatively impacting an individual's life and mental health. Currently, the use of Food and Drug Administration (FDA)-approved drugs for hair loss is associated with several side effects, highlighting the need for identifying new drug candidates, such as plant-derived phytochemicals, to overcome these issues.

Objective

This study investigated the hair growth-promoting effects of araliadiol, a polyacetylene compound found in plants such as Centella asiatica.

Methods

We employed an in vitro model comprising human hair follicle stem cells (HHFSCs) and human dermal papilla cells (HDPCs) to evaluate the hair growth-promoting effects of araliadiol. The proliferation-stimulating effects of araliadiol were assessed using water-soluble tetrazolium salt assay, adenosine triphosphate content assay, and crystal violet staining assay. In addition, we performed luciferase reporter assay, polymerase chain reaction analysis, cell fractionation, Western blot analysis, and enzyme-linked immunosorbent assay (ELISA) to elucidate the mechanism underlying the hair growth-inductive effects of araliadiol.

Results

Araliadiol exhibited both proliferation- and hair growth-promoting effects in HHFSCs and HDPCs. Specifically, it increased the protein expression of cyclin B1 and Ki67. In HHFSCs, it elevated the expression of hair growth-promoting factors, including CD34, vascular endothelial growth factor (VEGF), and angiopoietin-like 4. Similarly, araliadiol increased the expression of hair growth-inductive proteins such as fibroblast growth factor 7, VEGF, noggin, and insulin-like growth factor 1 in HDPCs. Subsequent Western blot analysis and ELISA using inhibitors such as GW9662 and SB202190 confirmed that these hair growth-promoting effects were dependent on the p38/PPAR-γ signaling in both HHFSCs and HDPCs.

Conclusion

Araliadiol promotes hair growth through the p38/PPAR-γ signaling pathway in human hair follicle cells. Therefore, araliadiol can be considered a novel drug candidate for the treatment of alopecia.

Retinoic Acid-Related Orphan Receptor Alpha May Regulate the State of Hair Follicle Stem Cells by Upregulating the Expression of BNIP3

The hair, an exclusive keratinized dermal appendage in mammals, stands as a quintessential outcome of adaptive evolution, conferring resilience against adverse environmental conditions. The ontogenesis of the coat displays a pronounced rhythmic pattern, with hair follicle stem cells (HFSCs) emerging as pivotal facilitators of hair follicle reconstitution. The retinoic acid-related orphan receptor alpha, a nuclear receptor with extensive involvement in the regulation of cellular physiological states, exerts its functions predominantly through the modulation of downstream target gene transcription. The Bnip3 gene exhibits a robust correlation with cellular apoptosis and autophagy, which are indispensable physiological mechanisms underlying the maintenance of HFSC homeostasis. Consequently, the expression level of Bnip3 may be intimately linked to the status of HFSCs. In this investigative endeavor, we employed rat HFSCs as a model system to validate the regulatory impact of RORA on Bnip3 gene expression. Our findings unequivocally demonstrate that Bnip3 serves as a direct downstream target of RORA. Specifically, RORA binds to the motif within the Bnip3 promoter region, thereby upregulating Bnip3 expression levels. In light of our research findings, we propose that RORA holds potential as a target for modulating the status of HFSCs.

Molecular Mechanisms of Hair Follicle Development

Hair is an intricate biological structure that originates from hair follicles (HFs), which are complex mini-organs embedded in the skin. Each HF undergoes continuous cycles of growth (anagen), regression (catagen), and rest (telogen), driven by intricate signaling pathways and interactions between epithelial and mesodermal cells. The development of HFs requires the interplay of several key signaling pathways, including Wnt, Shh, Notch, and BMP. The Wnt pathway is primarily involved in induction, Shh is essential for early organogenesis and later stages of cytodifferentiation, Notch signaling governs the fate of HF stem cells, and BMP plays a role in cytodifferentiation. Hair health is closely associated with psychological well-being and personal distress. While hair loss (alopecia) does not impact biological health, it significantly affects social well-being. Therefore, a deep understanding of the molecular mechanisms underlying HF development is crucial for developing treatments for hair-related problems and improving hair health. This knowledge has led to significant advancements in therapeutic applications, particularly in treating hair loss disorders, enhancing wound healing, and developing cosmetic treatments. This paper aims to review the molecular mechanisms involved in HF development, with an emphasis on their potential impact on human health and well-being.

Pilose antler extract promotes hair growth in androgenic alopecia mice by promoting the initial anagen phase

Androgenetic alopecia (AGA) is a prevalent disease in worldwide, local application or oral are often used to treat AGA, however, effective treatments for AGA are currently limited. In this work, we observed the promoting the initial anagen phase effect of pilose antler extract (PAE) on hair regeneration in AGA mice. We found that PAE accelerated hair growth and increased the degree of skin blackness by non-invasive in vivo methods including camera, optical coherence tomography and dermoscopy. Meanwhile, HE staining of sagittal and coronal skin sections revealed that PAE augmented the quantity and length of hair follicles, while also enhancing skin thickness and hair papilla diameter. Furthermore, PAE facilitated the shift of the growth cycle from the telogen to the anagen phase and expedited the proliferation of hair follicle stem cells and matrix cells in mice with AGA. This acceleration enabled the hair follicles to enter the growth phase at an earlier stage. PAE upregulated the expression of the sonic hedgehog (SHH), smoothened receptor, glioma-associated hemolog1 (GLI1), and downregulated the expression of bone morphogenetic protein 4 (BMP4), recombinant mothers against decapentaplegic homolog (Smad) 1 and 5 phosphorylation. This evidence suggests that PAE fosters hair growth and facilitates the transition of the growth cycle from the telogen to the anagen phase in AGA mice. This effect is achieved by enhancing the proliferation of follicle stem cells and matrix cells through the activation of the SHH/GLI pathway and suppression of the BMP/Smad pathway.