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Lee SH, Platt S, Lim CH, Ito M, Myung P. The development of hair follicles and nail. Dev Biol 2024; 513:3-11. [PMID: 38759942 DOI: 10.1016/j.ydbio.2024.05.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 05/06/2024] [Accepted: 05/14/2024] [Indexed: 05/19/2024]
Abstract
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.
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Affiliation(s)
- Soung-Hoon Lee
- The Ronald O. Perelman Department of Dermatology and Department of Cell Biology, New York University School of Medicine, New York, NY, USA
| | - Sarah Platt
- Department of Dermatology, Yale School of Medicine, New Haven, CT, USA
| | - Chae Ho Lim
- The Ronald O. Perelman Department of Dermatology and Department of Cell Biology, New York University School of Medicine, New York, NY, USA
| | - Mayumi Ito
- The Ronald O. Perelman Department of Dermatology and Department of Cell Biology, New York University School of Medicine, New York, NY, USA
| | - Peggy Myung
- Department of Dermatology, Yale School of Medicine, New Haven, CT, USA; Department of Pathology, Yale School of Medicine, New Haven, CT, USA.
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2
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Prudkin L, Cedirian S, Santamaria J, Jourdan E, Piraccini BM. Exposome Impact on Nail Health. Skin Appendage Disord 2024; 10:186-198. [PMID: 38835707 PMCID: PMC11147530 DOI: 10.1159/000536573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2023] [Accepted: 01/25/2024] [Indexed: 06/06/2024] Open
Abstract
Background The nail unit is a complex system with various components, each serving distinct functions. The exposome, encompassing external and internal factors such as UV radiation, air pollution, dietary habits, and cosmetic product usage, substantially influences nail health and can lead to premature nail aging. Summary Internal and external exposomal factors can impact differently on nail health, inducing a variety of different clinical conditions. Effective therapeutic strategies exist, but a comprehensive understanding of how the exposome affects nails is lacking. This article aims to bridge this knowledge gap by exploring the relationship between the exposome and nail health, emphasizing it as a central focus of our analysis. Key Messages (1) The exposome, comprising various external and internal factors, may significantly influence nail health negatively, leading to premature nail aging. (2) Different nail conditions may arise due to the exposomal influence on nails. (3) Understanding the exposome's impact on nail health is crucial for developing solutions to mitigate negative effects and improve overall nail well-being.
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Affiliation(s)
| | - Stephano Cedirian
- Dermatology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Policlinico S. Orsola-Malpighi, Bologna, Italy
- Department of Medical and Surgical Sciences, Alma Mater Studiorum University of Bologna, Bologna, Italy
| | | | - Eric Jourdan
- Innovation and Development, ISDIN, Barcelona, Spain
| | - Bianca Maria Piraccini
- Dermatology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Policlinico S. Orsola-Malpighi, Bologna, Italy
- Department of Medical and Surgical Sciences, Alma Mater Studiorum University of Bologna, Bologna, Italy
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3
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A Kaleidoscope of Keratin Gene Expression and the Mosaic of Its Regulatory Mechanisms. Int J Mol Sci 2023; 24:ijms24065603. [PMID: 36982676 PMCID: PMC10052683 DOI: 10.3390/ijms24065603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 03/07/2023] [Accepted: 03/10/2023] [Indexed: 03/17/2023] Open
Abstract
Keratins are a family of intermediate filament-forming proteins highly specific to epithelial cells. A combination of expressed keratin genes is a defining property of the epithelium belonging to a certain type, organ/tissue, cell differentiation potential, and at normal or pathological conditions. In a variety of processes such as differentiation and maturation, as well as during acute or chronic injury and malignant transformation, keratin expression undergoes switching: an initial keratin profile changes accordingly to changed cell functions and location within a tissue as well as other parameters of cellular phenotype and physiology. Tight control of keratin expression implies the presence of complex regulatory landscapes within the keratin gene loci. Here, we highlight patterns of keratin expression in different biological conditions and summarize disparate data on mechanisms controlling keratin expression at the level of genomic regulatory elements, transcription factors (TFs), and chromatin spatial structure.
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4
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The Potential of Nail Mini-Organ Stem Cells in Skin, Nail and Digit Tips Regeneration. Int J Mol Sci 2021; 22:ijms22062864. [PMID: 33799809 PMCID: PMC7998429 DOI: 10.3390/ijms22062864] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Revised: 03/08/2021] [Accepted: 03/08/2021] [Indexed: 12/17/2022] Open
Abstract
Nails are highly keratinized skin appendages that exhibit continuous growth under physiological conditions and full regeneration upon removal. These mini-organs are maintained by two autonomous populations of skin stem cells. The fast-cycling, highly proliferative stem cells of the nail matrix (nail stem cells (NSCs)) predominantly replenish the nail plate. Furthermore, the slow-cycling population of the nail proximal fold (nail proximal fold stem cells (NPFSCs)) displays bifunctional properties by contributing to the peri-nail epidermis under the normal homeostasis and the nail structure upon injury. Here, we discuss nail mini-organ stem cells’ location and their role in skin and nail homeostasis and regeneration, emphasizing their importance to orchestrate the whole digit tip regeneration. Such endogenous regeneration capabilities are observed in rodents and primates. However, they are limited to the region adjacent to the nail’s proximal area, indicating the crucial role of nail mini-organ stem cells in digit restoration. Further, we explore the molecular characteristics of nail mini-organ stem cells and the critical role of the bone morphogenetic protein (BMP) and Wnt signaling pathways in homeostatic nail growth and digit restoration. Finally, we investigate the latest accomplishments in stimulating regenerative responses in regeneration-incompetent injuries. These pioneer results might open up new opportunities to overcome amputated mammalian digits and limbs’ regenerative failures in the future.
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5
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Nakatomi M, Ida-Yonemochi H, Nakatomi C, Saito K, Kenmotsu S, Maas RL, Ohshima H. Msx2 Prevents Stratified Squamous Epithelium Formation in the Enamel Organ. J Dent Res 2018; 97:1355-1364. [PMID: 29863959 DOI: 10.1177/0022034518777746] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Tooth enamel is manufactured by the inner enamel epithelium of the multilayered enamel organ. Msx2 loss-of-function mutation in a mouse model causes an abnormal accumulation of epithelial cells in the enamel organ, but the underlying mechanism by which Msx2 regulates amelogenesis is poorly understood. We therefore performed detailed histological and molecular analyses of Msx2 null mice. Msx2 null ameloblasts and stratum intermedium (SI) cells differentiated normally in the early stages of amelogenesis. However, during subsequent developmental stages, the outer enamel epithelium (OEE) became highly proliferative and transformed into a keratinized stratified squamous epithelium that ectopically expressed stratified squamous epithelium markers, including Heat shock protein 25, Loricrin, and Keratin 10. Moreover, expression of hair follicle-specific keratin genes such as Keratin 26 and Keratin 73 was upregulated in the enamel organ of Msx2 mutants. With the accumulation of keratin in the stellate reticulum (SR) region and subsequent odontogenic cyst formation, SI cells gradually lost the ability to differentiate, and the expression of Sox2 and Notch1 was downregulated, leading to ameloblast depolarization. As a consequence, the organization of the Msx2 mutant enamel organ became disturbed and enamel failed to form in the normal location. Instead, there was ectopic mineralization that likely occurred within the SR. In summary, we show that during amelogenesis, Msx2 executes a bipartite function, repressing the transformation of OEE into a keratinized stratified squamous epithelium while simultaneously promoting the development of a properly differentiated enamel organ competent for enamel formation.
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Affiliation(s)
- M Nakatomi
- 1 Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.,2 Division of Anatomy, Department of Health Promotion, Kyushu Dental University, Kitakyushu, Japan
| | - H Ida-Yonemochi
- 1 Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - C Nakatomi
- 3 General Dentistry and Clinical Education Unit, Niigata University Medical and Dental Hospital, Niigata, Japan.,4 Division of Molecular Signaling and Biochemistry, Department of Health Promotion, Kyushu Dental University, Kitakyushu, Japan
| | - K Saito
- 1 Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - S Kenmotsu
- 1 Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - R L Maas
- 5 Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - H Ohshima
- 1 Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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6
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Kahata K, Dadras MS, Moustakas A. TGF-β Family Signaling in Epithelial Differentiation and Epithelial-Mesenchymal Transition. Cold Spring Harb Perspect Biol 2018; 10:cshperspect.a022194. [PMID: 28246184 DOI: 10.1101/cshperspect.a022194] [Citation(s) in RCA: 84] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Epithelia exist in the animal body since the onset of embryonic development; they generate tissue barriers and specify organs and glands. Through epithelial-mesenchymal transitions (EMTs), epithelia generate mesenchymal cells that form new tissues and promote healing or disease manifestation when epithelial homeostasis is challenged physiologically or pathologically. Transforming growth factor-βs (TGF-βs), activins, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs) have been implicated in the regulation of epithelial differentiation. These TGF-β family ligands are expressed and secreted at sites where the epithelium interacts with the mesenchyme and provide paracrine queues from the mesenchyme to the neighboring epithelium, helping the specification of differentiated epithelial cell types within an organ. TGF-β ligands signal via Smads and cooperating kinase pathways and control the expression or activities of key transcription factors that promote either epithelial differentiation or mesenchymal transitions. In this review, we discuss evidence that illustrates how TGF-β family ligands contribute to epithelial differentiation and induce mesenchymal transitions, by focusing on the embryonic ectoderm and tissues that form the external mammalian body lining.
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Affiliation(s)
- Kaoru Kahata
- Ludwig Institute for Cancer Research, Science for Life Laboratory, Uppsala University, SE-751 24 Uppsala, Sweden
| | - Mahsa Shahidi Dadras
- Ludwig Institute for Cancer Research, Science for Life Laboratory, Uppsala University, SE-751 24 Uppsala, Sweden.,Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University, SE-751 23 Uppsala, Sweden
| | - Aristidis Moustakas
- Ludwig Institute for Cancer Research, Science for Life Laboratory, Uppsala University, SE-751 24 Uppsala, Sweden.,Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University, SE-751 23 Uppsala, Sweden
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7
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Bergqvist C, Ramia P, Abbas O, Kurban M. Genetics of syndromic and non-syndromic hereditary nail disorders. Clin Genet 2016; 91:813-823. [PMID: 27613389 DOI: 10.1111/cge.12852] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 08/22/2016] [Accepted: 08/22/2016] [Indexed: 01/18/2023]
Abstract
The nail is a unique epithelial skin appendage made up of a fully keratinized nail plate. The nail can be affected in several systemic illnesses, dermatological diseases, and inherited nail disorders. Nail dystrophies can present as isolated disorders or as a part of syndromes. Substantial progress has been achieved in the management and diagnosis of nail diseases; however, not much is known about the underlying molecular controls of nail growth. The homeostasis and development of the nail appendage depend on the intricate interactions between the epidermis and underlying mesenchyme, and comprise different signaling pathways such as the WNT signaling pathway. Digit-tip regeneration in mice and humans has been a known fact for the past six decades; however, only recently the underlying biological mechanisms by which the nail organ achieves digit regeneration have been elucidated. Moreover, significant progress has been made in identifying nail stem cells and localizing stem cell niches in the nail unit. More fascinating, however, is the role they play in orchestrating the processes that lead to the regeneration of the digit. Further elucidating the role of nail stem cells and the signaling pathways driving epithelial-mesenchymal interactions in the nail unit might contribute to the development of novel therapeutic tools for amputees.
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Affiliation(s)
- C Bergqvist
- Department of Dermatology, American University of Beirut, Beirut, Lebanon
| | - P Ramia
- Department of Internal Medicine, American University of Beirut, Beirut, Lebanon
| | - O Abbas
- Department of Dermatology, American University of Beirut, Beirut, Lebanon
| | - M Kurban
- Department of Dermatology, American University of Beirut, Beirut, Lebanon.,Department of Biochemistry and Molecular Genetics, American University of Beirut, Beirut, Lebanon.,Department of Dermatology, Columbia University Medical Center, New York, NY, USA
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8
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Lanzini J, Dargère D, Regazzetti A, Tebani A, Laprévote O, Auzeil N. Changing in lipid profile induced by the mutation of Foxn1 gene: A lipidomic analysis of Nude mice skin. Biochimie 2015; 118:234-43. [PMID: 26427556 DOI: 10.1016/j.biochi.2015.09.029] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 09/23/2015] [Indexed: 10/23/2022]
Abstract
Nude mice carry a spontaneous mutation affecting the gene Foxn1 mainly expressed in the epidermis. This gene is involved in several skin functions, especially in the proliferation and the differentiation of keratinocytes which are key cells of epithelial barrier. The skin, a protective barrier for the body, is essentially composed of lipids. Taking into account these factors, we conducted a lipidomic study to search for any changes in lipid composition of skin possibly related to Foxn1 mutation. Lipids were extracted from skin biopsies of Nude and BALB/c mice to be analyzed by liquid chromatography coupled to a high resolution mass spectrometer (HRMS). Multivariate and univariate data analyses were carried out to compare lipid extracts. Identification was performed using HRMS data, retention time and mass spectrometry fragmentation study. These results indicate that mutation of Foxn1 leads to significant modifications in the lipidome in Nude mice skin. An increase in cholesterol sulfate, phospholipids, sphingolipids and fatty acids associated with a decrease in glycerolipids suggest that the lipidome in mice skin is regulated by the Foxn1 gene.
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Affiliation(s)
- Justine Lanzini
- UMR CNRS 8638, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de L'Observatoire, 75006 Paris, France
| | - Delphine Dargère
- UMR CNRS 8638, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de L'Observatoire, 75006 Paris, France
| | - Anne Regazzetti
- UMR CNRS 8638, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de L'Observatoire, 75006 Paris, France
| | - Abdellah Tebani
- UMR CNRS 8638, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de L'Observatoire, 75006 Paris, France
| | - Olivier Laprévote
- UMR CNRS 8638, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de L'Observatoire, 75006 Paris, France; AP-HP, Service de Toxicologie Biologique, Hôpital Lariboisière, 4 Rue Ambroise Paré, 75475 Paris Cedex 10, France
| | - Nicolas Auzeil
- UMR CNRS 8638, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de L'Observatoire, 75006 Paris, France.
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9
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Khan S, Basit S, Habib R, Kamal A, Muhammad N, Ahmad W. Genetics of human isolated hereditary nail disorders. Br J Dermatol 2015; 173:922-9. [PMID: 26149975 DOI: 10.1111/bjd.14023] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/02/2015] [Indexed: 12/17/2022]
Abstract
Human hereditary nail disorders constitute a rare and heterogeneous group of ectodermal dysplasias. They occur as isolated and/or syndromic ectodermal conditions where other ectodermal appendages are also involved, and can occur associated with skeletal dysplasia. 'Nail disorder, nonsyndromic congenital' (OMIM; Online Mendelian Inheritance in Man) is subclassified into 10 different types. The underlying genes identified thus far are expressed in the nail bed and play important roles in nail development and morphogenesis. Here, we review the current literature on nail disorders and present a coherent review on the genetics of nail disorders. This review will pave the way to identifying putative genes and pathways involved in nail development and morphogenesis.
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Affiliation(s)
- S Khan
- Department of Biotechnology and Genetic Engineering, Kohat University of Science and Technology (KUST), Kohat 26000, Khyber Pakhtunkhwa, Pakistan.,Genomic Core Facility, interim Translational Research Institute (iTRI), Academic Health System, Hamad Medical Corporation, 3050 Doha, Qatar
| | - S Basit
- Center for Genetics and Inherited Diseases, Taibah University Almadinah Almunawarah, 30001 Almadinah Almunawarah, Saudi Arabia
| | - R Habib
- Department of Biosciences, COMSATS Institute of Information Technology, Park Road, Islamabad, 45600, Pakistan
| | - A Kamal
- Department of Biotechnology and Genetic Engineering, Kohat University of Science and Technology (KUST), Kohat 26000, Khyber Pakhtunkhwa, Pakistan
| | - N Muhammad
- Department of Biotechnology and Genetic Engineering, Kohat University of Science and Technology (KUST), Kohat 26000, Khyber Pakhtunkhwa, Pakistan
| | - W Ahmad
- Department of Biochemistry, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad 45320, Pakistan
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10
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Yin Y, Lin C, Zhang I, Fisher AV, Dhandha M, Ma L. Homeodomain Transcription Factor Msx-2 Regulates Uterine Progenitor Cell Response to Diethylstilbestrol. ACTA ACUST UNITED AC 2015; 1. [PMID: 26457333 DOI: 10.19104/jstb.2015.105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
The fate of mouse uterine epithelial progenitor cells is determined between postnatal days 5 to 7. Around this critical time window, exposure to an endocrine disruptor, diethylstilbestrol (DES), can profoundly alter uterine cytodifferentiation. We have shown previously that a homeo domain transcription factor MSX-2 plays an important role in DES-responsiveness in the female reproductive tract (FRT). Mutant FRTs exhibited a much more severe phenotype when treated with DES, accompanied by gene expression changes that are dependent on Msx2. To better understand the role that MSX-2 plays in uterine response to DES, we performed global gene expression profiling experiment in mice lacking Msx2 By comparing this result to our previously published microarray data performed on wild-type mice, we extracted common and differentially regulated genes in the two genotypes. In so doing, we identified potential downstream targets of MSX-2, as well as genes whose regulation by DES is modulated through MSX-2. Discovery of these genes will lead to a better understanding of how DES, and possibly other endocrine disruptors, affects reproductive organ development.
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Affiliation(s)
- Yan Yin
- Division of Dermatology, Washington University School of Medicine, St. Louis, MO
| | - Congxing Lin
- Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | - Ivy Zhang
- Department of Dermatology, Saint Louis University School of Medicine, St. Louis, MO
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Exploring the biology of the nail: An intriguing but less-investigated skin appendage. J Dermatol Sci 2015; 79:187-93. [PMID: 25999148 DOI: 10.1016/j.jdermsci.2015.04.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Revised: 04/25/2015] [Accepted: 04/28/2015] [Indexed: 02/04/2023]
Abstract
The nail is a highly keratinized structure covering the tip of the digit, and considered to have several important functions in our daily life. In recent years, as biological aspects of the nail organ have been characterized, we realize that the nail unit and the hair follicle share various biological and immunological features. In particular, development and homeostasis of the nail unit also requires intimate epithelial-mesenchymal interactions that involve signaling pathways such as Wnt. There is also a striking immunological resemblance between both appendages, since the nail matrix, like the anagen hair bulb and the bulge, was shown to present unique characteristics of an immune privileged site. On the other hand, considerable progress in identifying nail stem cells has succeeded in locating putative stem cell niches in the nail unit. In this context, it is intriguing that nail stem cells residing in the nail matrix were recently shown to possess the ability to organize the process leading to digit regeneration. Further elucidation of signaling pathways governing epithelial-mesenchymal interactions in the nail unit seems to be a key to develop a novel therapeutic tool to treat amputees using nail epithelium. However, it is at least certain that the nail unit has a promising potential for the future of regenerative medicine. This review explores the biology of the nail organ by focusing on intriguing knowledge gained from recent studies.
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12
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Bifunctional ectodermal stem cells around the nail display dual fate homeostasis and adaptive wounding response toward nail regeneration. Proc Natl Acad Sci U S A 2014; 111:15114-9. [PMID: 25277970 DOI: 10.1073/pnas.1318848111] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Regulation of adult stem cells (SCs) is fundamental for organ maintenance and tissue regeneration. On the body surface, different ectodermal organs exhibit distinctive modes of regeneration and the dynamics of their SC homeostasis remain to be unraveled. A slow cycling characteristic has been used to identify SCs in hair follicles and sweat glands; however, whether a quiescent population exists in continuously growing nails remains unknown. Using an in vivo label retaining cells (LRCs) system, we detected an unreported population of quiescent cells within the basal layer of the nail proximal fold, organized in a ring-like configuration around the nail root. These nail LRCs express the hair stem cell marker, keratin 15 (K15), and lineage tracing show that these K15-derived cells can contribute to both the nail structure and peri-nail epidermis, and more toward the latter. Thus, this stem cell population is bifunctional. Upon nail plucking injury, the homeostasis is tilted with these SCs dominantly delivering progeny to the nail matrix and differentiated nail plate, demonstrating their plasticity to adapt to wounding stimuli. Moreover, in vivo engraftment experiments established that transplanted nail LRCs can actively participate in functional nail regeneration. Transcriptional profiling of isolated nail LRCs revealed bone morphogenetic protein signaling favors nail differentiation over epidermal fate. Taken together, we have found a previously unidentified ring-configured population of bifunctional SCs, located at the interface between the nail appendage organ and adjacent epidermis, which physiologically display coordinated homeostatic dynamics but are capable of rediverting stem cell flow in response to injury.
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