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Molecules and Cells Oct 2023The mammalian skin contains hair follicles, which are epidermal appendages that undergo periodic cycles and exhibit mini-organ features, such as discrete stem cell... (Review)
Review
The mammalian skin contains hair follicles, which are epidermal appendages that undergo periodic cycles and exhibit mini-organ features, such as discrete stem cell compartments and different cellular components. Wound-induced hair follicle neogenesis (WIHN) is the remarkable ability to regenerate hair follicles after large-scale wounding and occurs in several adult mammals. WIHN is comparable to embryonic hair follicle development in its processes. Researchers are beginning to identify the stem cells that, in response to wounding, develop into neogenic hair follicles, as well as to understand the functions of immune cells, mesenchymal cells, and several signaling pathways that are essential for this process. WIHN represents a promising therapeutic approach to the reprogramming of cellular states for promoting hair follicle regeneration and preventing scar formation. In the scope of this review, we investigate the contribution of several cell types and molecular mechanisms to WIHN.
Topics: Mice; Animals; Hair Follicle; Wound Healing; Mice, Inbred C57BL; Hair; Skin; Mammals
PubMed: 37650216
DOI: 10.14348/molcells.2023.0071 -
The Journal of Investigative Dermatology Jan 2005Hair shaft melanin components (eu- or/and pheomelanin) are a long-lived record of precise interactions in the hair follicle pigmentary unit, e.g., between follicular... (Review)
Review
Hair shaft melanin components (eu- or/and pheomelanin) are a long-lived record of precise interactions in the hair follicle pigmentary unit, e.g., between follicular melanocytes, keratinocytes, and dermal papilla fibroblasts. Follicular melanogenesis (FM) involves sequentially the melanogenic activity of follicular melanocytes, the transfer of melanin granules into cortical and medulla keratinocytes, and the formation of pigmented hair shafts. This activity is in turn regulated by an array of enzymes, structural and regulatory proteins, transporters, and receptors and their ligands, acting on the developmental stages, cellular, and hair follicle levels. FM is stringently coupled to the anagen stage of the hair cycle, being switched-off in catagen to remain absent through telogen. At the organ level FM is precisely coupled to the life cycle of melanocytes with changes in their compartmental distribution and accelerated melanoblast/melanocyte differentiation with enhanced secretory activity. The melanocyte compartments in the upper hair follicle also provides a reservoir for the repigmentation of epidermis and, for the cyclic formation of new anagen hair bulbs. Melanin synthesis and pigment transfer to bulb keratinocytes are dependent on the availability of melanin precursors, and regulation by signal transduction pathways intrinsic to skin and hair follicle, which are both receptor dependent and independent, act through auto-, para- or intracrine mechanisms and can be modified by hormonal signals. The important regulators are MC1 receptor its and adrenocorticotropic hormone, melanocyte stimulating hormone, agouti protein ligands (in rodents), c-Kit, and the endothelin receptors with their ligands. Melanin itself has a wide range of bioactivities that extend far beyond its determination of hair color.
Topics: Animals; Hair Color; Hair Follicle; Humans; Melanocytes
PubMed: 15654948
DOI: 10.1111/j.0022-202X.2004.23528.x -
Experimental Dermatology Jun 2017
Topics: Alopecia; Fungi; Hair Follicle; Humans; Microbiota; Tinea Capitis
PubMed: 28608517
DOI: 10.1111/exd.13384 -
Seminars in Cell & Developmental Biology Oct 2012Embryonic hair follicle induction and formation are regulated by mesenchymal-epithelial interactions between specialized dermal cells and epidermal stem cells that... (Review)
Review
Embryonic hair follicle induction and formation are regulated by mesenchymal-epithelial interactions between specialized dermal cells and epidermal stem cells that switch to a hair fate. Similarly, during postnatal hair growth, communication between mesenchymal dermal papilla cells and surrounding epithelial matrix cells coordinates hair shaft production. Adult hair follicle regeneration in the hair cycle again is thought to be controlled by activating signals originating from the mesenchymal compartment and acting on hair follicle stem cells. Although many signaling pathways are implicated in hair follicle formation and growth, the precise nature, timing, and intersection of these inductive and regulatory signals remains elusive. The goal of this review is to summarize our current understanding and to discuss recent new insights into mesenchymal-epithelial interactions during hair follicle morphogenesis and cycling.
Topics: Animals; Cell Communication; Cell Cycle; Epithelial-Mesenchymal Transition; Hair Follicle; Humans; Morphogenesis; Signal Transduction
PubMed: 22960356
DOI: 10.1016/j.semcdb.2012.08.011 -
The International Journal of... 2004Ten years ago, Hardy (1992) wrote a timely review on the major features of hair follicle development and hair growth which she referred to as a secret life. Many of... (Review)
Review
Ten years ago, Hardy (1992) wrote a timely review on the major features of hair follicle development and hair growth which she referred to as a secret life. Many of these secrets are now being revealed. The information discussed in this brief review comprises the structure of the hair and hair follicle, the continuing characterisation of the genes for keratin and keratin associated proteins, the determination of the location of their expression in the different cell layers of the hair follicle, molecular signals which control keratin gene expression and post-translational events in the terminal stages of hair formation.
Topics: Animals; Cell Differentiation; Gene Expression Regulation, Developmental; Hair; Hair Follicle; Humans; Intermediate Filaments; Keratinocytes; Keratins; Models, Biological; Protein Processing, Post-Translational; Proteins; RNA, Messenger; Signal Transduction
PubMed: 15272381
DOI: 10.1387/ijdb.15272381 -
Indian Journal of Dermatology,... 2021
Topics: Adult; Hair Diseases; Hair Follicle; Humans; Male
PubMed: 31857519
DOI: 10.4103/ijdvl.IJDVL_139_19 -
Experimental Dermatology Apr 2021Adult hair follicle stem cells (HFSCs) undergo dynamic and periodic molecular changes in their cellular states throughout the hair homeostatic cycle. These states are... (Review)
Review
Adult hair follicle stem cells (HFSCs) undergo dynamic and periodic molecular changes in their cellular states throughout the hair homeostatic cycle. These states are tightly regulated by cell-intrinsic mechanisms and by extrinsic signals from the microenvironment. HFSCs are essential not only for fuelling hair growth, but also for skin wound healing. Increasing evidence suggests an important role of HFSCs in organizing multiple skin components around the hair follicle, thus functioning as an organizing centre during adult skin homeostasis. Here, we focus on recent findings on cell-intrinsic mechanisms of HFSC homeostasis, which include transcription factors, histone modifications, DNA regulatory elements, non-coding RNAs, cell metabolism, cell polarity and post-transcriptional mRNA processing. Several transcription factors are now known to participate in well-known signalling pathways that control hair follicle homeostasis, as well as in super-enhancer activities to modulate HFSC and progenitor lineage progression. Interestingly, HFSCs have been shown to secrete molecules that are important in guiding the organization of several skin components around the hair follicle, including nerves, arrector pili muscle and vasculature. Finally, we discuss recent technological advances in the field such as single-cell RNA sequencing and live imaging, which revealed HFSC and progenitor heterogeneity and brought new light to understanding crosstalking between HFSCs and the microenvironment. The field is well on its way to generate a comprehensive map of molecular interactions that should serve as a solid theoretical platform for application in hair and skin disease and ageing.
Topics: Animals; Hair Follicle; Homeostasis; Humans; Mice; Skin Physiological Phenomena; Stem Cells
PubMed: 33278851
DOI: 10.1111/exd.14251 -
Autoimmunity Reviews May 2022Alopecia areata (AA) is an autoimmune disease that affects approximately 2% of the general population. Patients with AA most commonly present with one or more patches of... (Review)
Review
Alopecia areata (AA) is an autoimmune disease that affects approximately 2% of the general population. Patients with AA most commonly present with one or more patches of hair loss on the scalp in defined circular areas. A fraction of patients progress to more severe forms of the disease, in some cases with involvement of all body surfaces. The healthy anagen stage hair follicle is considered an immune privileged site, described as an environment that suppresses inflammatory immune responses. However, in AA, this immune privileged state collapses and marks the hair follicle as a target for the immune system, resulting in peri- and intrafollicular infiltration by lymphocytes. The complexity of the inflammatory ecosystem of the immune response to the hair follicle, and the relationships between the cellular and soluble participants, in AA remains incompletely understood. Many studies have demonstrated the presence of various immune cells around diseased hair follicles; however, often little is known about their respective contributions to AA pathogenesis. Furthering our understanding of the mechanisms of disease in AA is essential for the novel identification of targeted therapeutics that are efficacious and have few unintended effects.
Topics: Alopecia Areata; Autoimmune Diseases; Ecosystem; Hair Follicle; Humans
PubMed: 35151885
DOI: 10.1016/j.autrev.2022.103061 -
Journal of Optometry 2018The primary role of eyelashes is to protect and maintain the health of the lid margin. However, the mechanisms to fulfill this role are not fully understood. Unraveling... (Review)
Review
The primary role of eyelashes is to protect and maintain the health of the lid margin. However, the mechanisms to fulfill this role are not fully understood. Unraveling these mechanisms will stand to greatly improve the efficiency of eye care professionals' interventions in anomalies of the eyelashes. The aim of this article is to provide a review on eyelashes including highlights and new avenues for research; the biology of both the lash and its follicle; the pathophysiology and management of lash anomalies by eye care professionals; and the effect of iatrogenic factors on lashes. Using the database of Ovid MEDLINE, we reviewed studies specifically directed on human/mammalian eyelashes and key articles on current trends in scalp hair methodologies that can be applicable to lash research. The eyelash morphology, pigmentation and growth rate have been documented using techniques ranging from lash imaging to follicle immunohistochemistry. Furthermore, studies have demonstrated that the lash follicle is sensitive to many factors of the external environment, a variety of systemic/topical medications and cosmetics. Recently, aerodynamic studies using a mammalian eye model confirmed that an optimal lash length was needed so that eyelashes serve a protective role in reducing the number of particles that can reach the eye. Despite recent advances in lash research, studies are still scarce, due to the limited availability of the human lid for sampling. This review brings awareness that further research is needed with respect to eyelashes and will hopefully reduce the gap with scalp hair research.
Topics: Aging; Eyelashes; Eyelid Diseases; Hair Diseases; Hair Follicle; Humans; Iatrogenic Disease
PubMed: 30017866
DOI: 10.1016/j.optom.2018.05.003 -
The Journal of Investigative... Jun 2003The workshop on Hair Follicle Stem Cells brought together investigators who have used a variety of approaches to try to understand the biology of follicular epithelial... (Review)
Review
The workshop on Hair Follicle Stem Cells brought together investigators who have used a variety of approaches to try to understand the biology of follicular epithelial stem cells, and the role that these cells play in regulating the hair cycle. One of the main concepts to emerge from this workshop is that follicular epithelial stem cells are multipotent, capable of giving rise not only to all the cell types of the hair, but also to the epidermis and the sebaceous gland. Furthermore, such multipotent stem cells may represent the ultimate epidermal stem cell. Another example of epithelial stem cell and transit amplifying cell plasticity, was the demonstration that adult corneal epithelium, under the influence of embryonic skin dermis could form an epidermis as well as hair follicles. With regards to the location of follicular epithelial stem cells, immunohistochemical and ultrastructural data was presented, indicating that cells with stem cell attributes were localized to the prominent bulge region of developing human fetal hair follicles. Finally, a new notion was put forth concerning the roles that the bulge-located stem cells and the hair germ cells played with respect to the hair cycle.
Topics: Animals; Embryo, Mammalian; Epidermis; Epithelium, Corneal; Hair Follicle; Humans; Models, Biological; Skin; Stem Cells
PubMed: 12894992
DOI: 10.1046/j.1523-1747.2003.12169.x