Transient prenatal expression of NPY-Y1 receptor in trigeminal axons innervating the mystacial vibrissae.

Using immunohistochemistry in combination with confocal laser scanning microscopy, we studied the ontogeny of neuropeptide Y-Y1 receptor (Y1-R) expression in the trigeminal system of the rat. The study was limited to the nerve fibers innervating the mystacial pad and the trigeminal ganglia. In the trigeminal ganglia, Y1-R-immunoreactive (IR) neurons were first observed at E16.5. At this same stage some nerve fibers in the trigeminal ganglia also exhibited Y1-R-like immunoreactivity (LI). Strongly Y1-R-IR nerve fibers innervating the follicles of the mystacial vibrissae were first observed at E18. After double labeling, the Y1-R-LI was found to be colocalized with the neuronal marker protein gene product 9.5. At P1 only weak labeling for the Y1-R was found around the vibrissae follicles, whereas the neurons in the trigeminal ganglia were intensely labeled. The same was true for the adult rat, but at this stage no Y1-R labeling at all was observed in nerve fibers around the vibrissal follicles. These results strongly support an axonal localization of the Y1-R at this developmental stage. The transient expression of the Y1-R during prenatal mystacial pad development suggests a role for the Y1-R in the functional development of the vibrissae.

Coat color dilution in mice because of inactivation of the melanoma antigen MART-1.

Melanoma antigen recognized by T cells 1 (MART-1) is a melanoma-specific antigen, which has been thoroughly studied in the context of immunotherapy against malignant melanoma and which is found only in the pigment cell lineage. However, its exact function and involvement in pigmentation is not clearly understood. Melanoma antigen recognized by T cells 1 has been shown to interact with the melanosomal proteins Pmel17 and OA1. To understand the function of MART-1 in pigmentation, we developed a new knockout mouse model. Mice deficient in MART-1 are viable, but loss of MART-1 leads to a coat color phenotype, with a reduction in total melanin content of the skin and hair. Lack of MART-1 did not affect localization of melanocyte-specific proteins nor maturation of Pmel17. Melanosomes of hair follicle melanocytes in MART-1 knockout mice displayed morphological abnormalities, which were exclusive to stage III and IV melanosomes. In conclusion, our results suggest that MART-1 is a pigmentation gene that is required for melanosome biogenesis and/or maintenance.

Androgenetic alopecia: identification of four genetic risk loci and evidence for the contribution of WNT signaling to its etiology.

The pathogenesis of androgenetic alopecia (AGA, male-pattern baldness) is driven by androgens, and genetic predisposition is the major prerequisite. Candidate gene and genome-wide association studies have reported that single-nucleotide polymorphisms (SNPs) at eight different genomic loci are associated with AGA development. However, a significant fraction of the overall heritable risk still awaits identification. Furthermore, the understanding of the pathophysiology of AGA is incomplete, and each newly associated locus may provide novel insights into contributing biological pathways. The aim of this study was to identify unknown AGA risk loci by replicating SNPs at the 12 genomic loci that showed suggestive association (5 × 10(-8)<P<10(-5)) with AGA in a recent meta-analysis. We analyzed a replication set comprising 2,759 cases and 2,661 controls of European descent to confirm the association with AGA at these loci. Combined analysis of the replication and the meta-analysis data identified four genome-wide significant risk loci for AGA on chromosomes 2q35, 3q25.1, 5q33.3, and 12p12.1. The strongest association signal was obtained for rs7349332 (P=3.55 × 10(-15)) on chr2q35, which is located intronically in WNT10A. Expression studies in human hair follicle tissue suggest that WNT10A has a functional role in AGA etiology. Thus, our study provides genetic evidence supporting an involvement of WNT signaling in AGA development.

Lineage potential, plasticity and environmental reprogramming of epithelial stem/progenitor cells.

Recent evidence supports and reinforces the concept that environmental cues may reprogramme somatic cells and change their natural fate. In the present review, we concentrate on environmental reprogramming and fate potency of different epithelial cells. These include stratified epithelia, such as the epidermis, hair follicle, cornea and oesophagus, as well as the thymic epithelium, which stands alone among simple and stratified epithelia, and has been shown recently to contain stem cells. In addition, we briefly discuss the pancreas as an example of plasticity of intrinsic progenitors and even differentiated cells. Of relevance, examples of plasticity and fate change characterize pathologies such as oesophageal metaplasia, whose possible cell origin is still debated, but has important implications as a pre-neoplastic event. Although much work remains to be done in order to unravel the full potential and plasticity of epithelial cells, exploitation of this phenomenon has already entered the clinical arena, and might provide new avenues for future cell therapy of these tissues.

Functions of peroxisome proliferator-activated receptors (PPAR) in skin homeostasis.

The peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors that belong to the nuclear hormone receptor family. Three isotypes (PPAR alpha, PPAR beta or delta, and PPAR gamma) with distinct tissue distributions and cellular functions have been found in vertebrates. All three PPAR isotypes are expressed in rodent and human skin. They were initially investigated for a possible function in the establishment of the permeability barrier in skin because of their known function in lipid metabolism in other cell types. In vitro studies using specific PPAR agonists and in vivo gene disruption approaches in mice indeed suggest an important contribution of PPAR alpha in the formation of the epidermal barrier and in sebocyte differentiation. The PPAR gamma isotype plays a role in stimulating sebocyte development and lipogenesis, but does not appear to contribute to epidermal tissue differentiation. The third isotype, PPAR beta, regulates the late stages of sebaceous cell differentiation, and is the most effective isotype in stimulating lipid production in these cells, both in rodents and in humans. In addition, PPAR beta activation has pro-differentiating effects in keratinocytes under normal and inflammatory conditions. Finally, preliminary studies also point to a potential role of PPAR in hair follicle growth and in melanocyte differentiation. By their diverse biological effects on cell proliferation and differentiation in the skin, PPAR agonists or antagonists may offer interesting opportunities for the treatment of various skin disorders characterized by inflammation, cell hyperproliferation, and aberrant differentiation.

Microenvironmental reprogramming of thymic epithelial cells to skin multipotent stem cells.

The thymus develops from the third pharyngeal pouch of the anterior gut and provides the necessary environment for thymopoiesis (the process by which thymocytes differentiate into mature T lymphocytes) and the establishment and maintenance of self-tolerance. It contains thymic epithelial cells (TECs) that form a complex three-dimensional network organized in cortical and medullary compartments, the organization of which is notably different from simple or stratified epithelia. TECs have an essential role in the generation of self-tolerant thymocytes through expression of the autoimmune regulator Aire, but the mechanisms involved in the specification and maintenance of TECs remain unclear. Despite the different embryological origins of thymus and skin (endodermal and ectodermal, respectively), some cells of the thymic medulla express stratified-epithelium markers, interpreted as promiscuous gene expression. Here we show that the thymus of the rat contains a population of clonogenic TECs that can be extensively cultured while conserving the capacity to integrate in a thymic epithelial network and to express major histocompatibility complex class II (MHC II) molecules and Aire. These cells can irreversibly adopt the fate of hair follicle multipotent stem cells when exposed to an inductive skin microenvironment; this change in fate is correlated with robust changes in gene expression. Hence, microenvironmental cues are sufficient here to re-direct epithelial cell fate, allowing crossing of primitive germ layer boundaries and an increase in potency.

Role of Notch signaling in epidermis and appendages

Résumé Dans la peau, il a été montré que Notch1 induit l'arrêt de la prolifération et la différentiation des keratinocytes. L'inactivation de Notch1 cause une hyperplasie de l'épiderme et la formation de carcinomes basaux cellulaires. Notre groupe a principalement identifié deux voies de signalisations, la voie Shh et la voie Wnt, qui sont dérégulées en conséquence de l'inactivation de Notch1 dans la peau. Nous avons démontré l'habilité de Notch1 à réprimer la voie Wnt induite par ß-catenin dans les keratinocytes primaires ainsi que dans d'autres types de cellules épithéliales humaines. De plus, nous avons pu déterminer que Notch1 régule cette voie, probablement en favorisant la phosphorylation de ß-catenin par le complexe axin/APC/GSK-3ß. La protéine faisant partie de la voie Wnt, ou la protéine affectant la voie Wnt, qui est régulée par Notch1 est sujette à de plus amples investigations. Un autre but de cette étude a été l'identification de potentiels gènes cibles de Notch1 autres que ceux faisant partie des voies de signalisation Shh et Wnt précédemment évoquées. Ce projet fut abordé par l'analyse de puces à ADN (ISREC et Affymetrix) qui ont été utilisées pour des expériences de gain et de perte de fonction de Notch1 dans des keratinocytes prúmaires. En plus de l'hyperplasie épidermale, les souris Notch1 déficiente ont une perte importante de poils. Nous avons montré que Notch1 est nécessaire pour le développement et l'homéostasie des follicules pileux. En effet, l'inactivation du gène Notch1 mediée par l'activation des kératines 5 ou 14 dans l'épiderme, cause des défauts du cycle ainsi que de la structure des poils. De plus, d'autres appendices de la peau, comme les glandes sudoripares et de Meibomius, ont une structure anormale et sont non fonctionnelles dans les souris Notch1 déficiente. Finalement, nous avons observé que la déficience de Notch1 dans l'épithélium cornéen mène à la formation d'une plaque épidermale opaque sur la cornée. Basé sur l'hypothèse que le défaut des glandes de Meibomius des souris Notch1 déficientes cause des lésions de la surface oculaire, nous avons montré que Notch1 est essentiel pour la cicatrisation de la cornée. Lorsque Notch1 est absent, les cellules souches de l'épithélium cornéen ne sont plus capables de se différentier en cellules cornéennes, mais réparent la blessure en se différentiant en épiderme. Ce résultat indique que Notch1 est essentiel pour la différentiation de cellules souches de la cornée qui sont spécifiquement impliquées dans la réparation de la cornée. De plus, nous avons montré que l'expression de CRBP1 dans l'épithélium cornéen est diminuée en l'absence de Notch1, ceci étant possiblement à l'origine de la formation de la plaque épidermale. Abstract: In the skin, Notch1 has been shown to trigger cell growth arrest and differentiation of keratinocytes. Notch1 inactivation results in epidermal hyperplasia and subsequent formation of basal cell carcinoma-like (BCC-like) tumors. So far our group has identified two main pathways, the Shh and the Wnt pathway, that are deregulated as a consequence of Notch1 inactivation in the skin. We showed the ability of Notch1 to represses ß-catenin-mediated Wnt signaling in primary keratinocytes as well as in other types of human epithelial cells. In addition we were able to determine that Notch1 regulates this pathway possibly by enhancing ß-catenin phosphorylation by the axin/APC/GSK-3ß complex. The exact target protein of the Wnt pathway or target protein that affects the Wnt pathway, and that is regulated by Notch1, is subject of current investigation. Another aim of this study was the identification of possible Notch1 target genes in addition to those of the Shh and Wnt signaling pathways. This was addressed by gene chip analysis using ISREC as well as Affymetrix microarrays for gain and loss of function of Notch1 in mouse primary keratinocytes. In addition to epidermal hyperplasia, Notch1 deficient mice show an important hair loss. We showed that Notch1 is required for postnatal development and homeostasis of hair follicles. Indeed, keratin5 or keratinl4-driven Cre recombinase-mediated inactivation of the Notch1 gene in the epidermis causes perturbations of the hair cycle and structural defects of the hair follicle. Moreover, other skin appendages, like the sweat and Meibomian glands show abnormal morphology and are not functional in the Notch 1 deficient mice. Finally, we observed that Notch1 deficiency in the corneal epithelium leads to the formation of an epidermal corneal plaque. Based on the hypothesis that the Meiboinian gland defect in the Notch1 deficient mice results in lesions of the eye surface, we showed that Notch1 is essential for wound-healing of the cornea. In absence of Notch1 the stem cells of the corneal epithelium are no longer able to differentiate in the corneal fate but instead repair the wound by differentiating into skin-like epidermis. This result indicated that Notch1 is essential for the differentiation of corneal stem cells specifically implicated in corneal wound-healing. Moreover, we showed that CRBP1 expression in the corneal epithelium was lost in the absence of Notch1, possibly being at the origin of plaque formation.

Selective expression of a dominant-negative form of peroxisome proliferator-activated receptor in keratinocytes leads to impaired epidermal healing.

Many nuclear hormone receptors are involved in the regulation of skin homeostasis. However, their role in the epithelial compartment of the skin in stress situations, such as skin healing, has not been addressed yet. The healing of a skin wound after an injury involves three major cell types: immune cells, which are recruited to the wound bed; dermal fibroblasts; and epidermal and hair follicle keratinocytes. Our previous studies have revealed important but nonredundant roles of PPARalpha and beta/delta in the reparation of the skin after a mechanical injury in the adult mouse. However, the mesenchymal or epithelial cellular compartment in which PPARalpha and beta/delta play a role could not be determined in the null mice used, which have a germ line PPAR gene invalidation. In the present work, the role of PPARalpha was studied in keratinocytes, using transgenic mice that express a PPARalpha mutant with dominant-negative (dn) activity specifically in keratinocytes. This dn PPARalpha lacks the last 13 C terminus amino acids, binds to a PPARalpha agonist, but is unable to release the nuclear receptor corepressor and to recruit the coactivator p300. When selectively expressed in keratinocytes of transgenic mice, dn PPARalphaDelta13 causes a delay in the healing of skin wounds, accompanied by an exacerbated inflammation. This phenotype, which is similar to that observed in PPARalpha null mice, strongly suggests that during skin healing, PPARalpha is required in keratinocytes rather than in other cell types.

Cutaneous benign mixed tumor (chondroid syringoma) of the eyelid: clinical presentation and management.

PURPOSE: To describe the clinical presentation of cutaneous benign mixed tumor of the eyelid and its management options. METHODS: Periocular cases of cutaneous benign mixed tumor were gathered from members of an oculoplastics specialty Internet discussion group. A total of 9 patients are described in this retrospective, interventional case series. The clinical presentation, histopathology, and management of these lesions is reviewed. RESULTS: Patients were typically asymptomatic, presenting with a slowly enlarging, nontender nodule of 2 to 8 years' duration. The lesions ranged from 4 mm to 17 mm in greatest dimension. Four of the lesions were on the eyelid margin, three in the sub-brow area of the upper eyelid, and two in the central lids. All six cases not involving the brow were fixed to the tarsus; one brow lesion was believed to be adherent to the skin. None of the lesions was associated with significant changes of the overlying epidermis, although one lesion showed overlying pigmentation. All patients underwent excisional biopsy for diagnostic or cosmetic reasons. On histopathologic examination, the tumors were biphasic, with an epithelial component exhibiting apocrine or hair follicle differentiation and a myxoid, adipocytic, chondroid, and/or fibrous stroma. The pathologic diagnoses were all consistent with cutaneous benign mixed tumor (chondroid syringoma, pleomorphic adenoma). Follow-up ranged from 2 weeks to 12 months, although several patients failed to keep scheduled follow-up appointments. No clinical recurrences were identified. CONCLUSIONS: Cutaneous benign mixed tumor may occur in the eyelid, and, although uncommon, should be included in the differential diagnosis of firm, nodular eyelid tumors. The histopathologic features are similar to those seen in this tumor type arising in other areas of the body. Preoperative consideration of this diagnostic possibility may allow the surgeon to plan for complete excision, thereby reducing the possibility of recurrence or malignant transformation.

Syndrome of birt-hogg-dubé, a histopathological pitfall with similarities to tuberous sclerosis: a report of three cases.

: Birt-Hogg-Dubé Syndrome (BHD) is a rare condition, transmitted as an autosomal-dominant trait. The etiology is due to a mutation in the BHD gene, which encodes folliculin (FLCN), located on chromosome 17p. The skin changes observed are benign skin tumors consisting of hamartomas of the hair follicle with dermal changes. Patients with BHD have an increased risk of spontaneous pneumothorax due to rupture of lung cysts and an increased risk of kidney tumors. We report 3 new cases of BHD and discuss their clinical features, histopathological findings, and molecular diagnostics. We highlight the importance of genetic analysis to confirm the diagnosis because of the clinical pitfalls involved in establishing a diagnosis. Finally, we discuss the histopathological features in BHD and tuberous sclerosis complex and focus on their overlapping criterias. A correct diagnosis is essential as it can be life saving for patients.

Transcriptional repression of peroxisome proliferator-activated receptor beta/delta in murine keratinocytes by CCAAT/enhancer-binding proteins.

The roles of peroxisome proliferator-activated receptors (PPARs) and CCAAT/enhancer-binding proteins (C/EBPs) in keratinocyte and sebocyte differentiation suggest that both families of transcription factors closely interact in the skin. Initial characterization of the mouse PPARbeta promoter revealed an AP-1 site that is crucial for the regulation of PPARbeta expression in response to inflammatory cytokines in the skin. We now present evidence for a novel regulatory mechanism of the expression of the PPARbeta gene by which two members of the C/EBP family of transcription factors inhibit its basal promoter activity in mouse keratinocytes. We first demonstrate that C/EBPalpha and C/EBPbeta, but not C/EBPdelta, inhibit the expression of PPARbeta through the recruitment of a transcriptional repressor complex containing HDAC-1 to a specific C/EBP binding site on the PPARbeta promoter. Consistent with this repression, the expression patterns of PPARbeta and C/EBPs are mutually exclusive in keratinocytes of the interfollicular epidermis and hair follicles in mouse developing skin. This work reveals the importance of the regulatory interplay between PPARbeta and C/EBP transcription factors in the control of proliferation and differentiation in this organ. Such insights are crucial for the understanding of the molecular control regulating the balance between proliferation and differentiation in many cell types including keratinocytes.

Recent advances in the epidermal growth factor receptor/ligand system biology on skin homeostasis and keratinocyte stem cell regulation.

The epidermal growth factor (EGF) receptor/ligand system stimulates multiple pathways of signal transduction, and is activated by various extracellular stimuli and inter-receptor crosstalk signaling. Aberrant activation of EGF receptor (EGFR) signaling is found in many tumor cells, and humanized neutralizing antibodies and synthetic small compounds against EGFR are in clinical use today. However, these drugs are known to cause a variety of skin toxicities such as inflammatory rash, skin dryness, and hair abnormalities. These side effects demonstrate the multiple EGFR-dependent homeostatic functions in human skin. The epidermis and hair follicles are self-renewing tissues, and keratinocyte stem cells are crucial for maintaining these homeostasis. A variety of molecules associated with the EGF receptor/ligand system are involved in epidermal homeostasis and hair follicle development, and the modulation of EGFR signaling impacts the behavior of keratinocyte stem cells. Understanding the roles of the EGF receptor/ligand system in skin homeostasis is an emerging issue in dermatology to improve the current therapy for skin disorders, and the EGFR inhibitor-associated skin toxicities. Besides, controlling of keratinocyte stem cells by modulating the EGF receptor/ligand system assures advances in regenerative medicine of the skin. We present an overview of the recent progress in the field of the EGF receptor/ligand system on skin homeostasis and regulation of keratinocyte stem cells.

Integration of Notch 1 and calcineurin/NFAT signaling pathways in keratinocyte growth and differentiation control.

The Notch and Calcineurin/NFAT pathways have both been implicated in control of keratinocyte differentiation. Induction of the p21(WAF1/Cip1) gene by Notch 1 activation in differentiating keratinocytes is associated with direct targeting of the RBP-Jkappa protein to the p21 promoter. We show here that Notch 1 activation functions also through a second Calcineurin-dependent mechanism acting on the p21 TATA box-proximal region. Increased Calcineurin/NFAT activity by Notch signaling involves downregulation of Calcipressin, an endogenous Calcineurin inhibitor, through a HES-1-dependent mechanism. Besides control of the p21 gene, Calcineurin contributes significantly to the transcriptional response of keratinocytes to Notch 1 activation, both in vitro and in vivo. In fact, deletion of the Calcineurin B1 gene in the skin results in a cyclic alopecia phenotype, associated with altered expression of Notch-responsive genes involved in hair follicle structure and/or adhesion to the surrounding mesenchyme. Thus, an important interconnection exists between Notch 1 and Calcineurin-NFAT pathways in keratinocyte growth/differentiation control.

The 5alpha-reductase type 1, but not type 2, gene is expressed in anagen hairs plucked from the vertex area of the scalp of hirsute women and normal individuals

The aim of the present study was to determine the expression of the genes for type 1 (SDR5A1) and type 2 (SDR5A2) 5alpha-reductase isoenzymes in scalp hairs plucked from 33 hirsute patients (20 with polycystic ovary syndrome and 13 with idiopathic hirsutism) and compare it with that of 10 men and 15 normal women. SDR5A1 and SDR5A2 expression was estimated by RT-PCR using the gene of the ubiquitously expressed protein ß2-microglobulin as an internal control. The results are expressed as arbitrary units in relation to ß2-microglobulin absorbance (mean ± SEM). SDR5A2 expression was not detected in any hair samples analyzed in this study. No differences were found in SDR5A1 mRNA levels between men and normal women (0.78 ± 0.05 vs 0.74 ± 0.06, respectively). SDR5A1 gene expression in the cells of hair plucked from the scalp of normal women (0.85 ± 0.04) and of women with polycystic ovary syndrome (0.78 ± 0.05) and idiopathic hirsutism (0.80 ± 0.06) was also similar. These results indicate that SDR5A1 gene expression in the follicular keratinocytes from the vertex area of the scalp seems not to be related to the differences in hair growth observed between normal men and women and hirsute patients. Further studies are needed to investigate the expression of the 5alpha-reductase genes in other scalp follicular compartments such as dermal papillae, and also in hair follicles from other body sites, in order to elucidate the mechanism of androgen action on the hair growth process and related diseases.

Evaluación a largo plazo en mujeres tratadas con laser para depilación facial en uniláser medica

El vello facial no deseado es un problema común en las mujeres, los tratamientos láser han mostrado efectividad para su manejo. Objetivo: Evaluar los resultados de la depilación láser en cara de las pacientes tratadas a largo plazo (20 sesiones o más ) luego de un seguimiento de 6 meses durante los años 1997 y 2012. Metodología: 55 mujeres que con tipo de piel II a V recibieron 20 o más sesiones de láser con seguimiento mayor a 6 meses posterior al la última sesión. Resultados: la edad promedio fue (32 ± 9,3 años), el 18,2 % presentaban SOP o Hiperandrogenismo el número de sesiones en cara fue de (30,84 ± 12,132), un promedio de disparos de (6,330 ± 7,804), los Kilojulios acumulados tuvieron un promedio de (126,5 ± 161,4) la fluencia promedio fue (18,5 ± 3,2 Julios/cm2), el láser de Alexandrita fue utilizado en el 98% de las pacientes. Se encontró cambios significativos entre el conteo inicial y el final de vello facial (484,9 ± 568.9 (med=300) vs. 103,33± 138,63 (med=60), p<0.001, Test de Wilcoxon). El 32.7% mostraron reducción > 90% (5,5% reducción del 100%). Conclusión : El tratamiento con de depilación con láser mostro una reducción significativa del vello facial, en mujeres mayores de 14 años con un tratamiento a largo plazo (20 sesiones o más), con una tasa de reducción mayor del 90% en 32.7% de las pacientes y un promedio de reducción del grupo de 79,36 ±15,51 %, similar a lo reportado en los diferentes estudios (77%).