Notch/RBP-J signaling regulates epidermis/hair fate determination of hair follicular stem cells

The Potential Reversible Transition between Stem Cells and Transient-Amplifying Cells: The Limbal Epithelial Stem Cell Perspective

Stem cells (SCs) undergo asymmetric division, producing transit-amplifying cells (TACs) with increased proliferative potential that move into tissues and ultimately differentiate into a specialized cell type. Thus, TACs represent an intermediary state between stem cells and differentiated cells. In the cornea, a population of stem cells resides in the limbal region, named the limbal epithelial stem cells (LESCs). As LESCs proliferate, they generate TACs that move centripetally into the cornea and differentiate into corneal epithelial cells. Upon limbal injury, research suggests a population of progenitor-like cells that exists within the cornea can move centrifugally into the limbus, where they dedifferentiate into LESCs. Herein, we summarize recent advances made in understanding the mechanism that governs the differentiation of LESCs into TACs, and thereafter, into corneal epithelial cells. We also outline the evidence in support of the existence of progenitor-like cells in the cornea and whether TACs could represent a population of cells with progenitor-like capabilities within the cornea. Furthermore, to gain further insights into the dynamics of TACs in the cornea, we outline the most recent findings in other organ systems that support the hypothesis that TACs can dedifferentiate into SCs.

Detection of native, activated Notch receptors in normal human apocrine-bearing skin and in hidradenitis suppurativa

Notch signalling has generated considerable interest as a pathogenetic factor and a drug target in a range of human diseases. The gamma-secretase complex is crucial in the activation of Notch receptors by cleaving the intracellular domain allowing nuclear translocation. In recent years several mutations in gamma-secretase components have been discovered in patients with familial hidradenitis suppurativa (HS). This has led to hypotheses that impaired Notch signalling could be an important driver for HS in general, not only in the monogenic variants. However, no study has examined in situ Notch activation per se in HS, and some reports with conflicting results have instead been based on expression of Notch receptors or indirect measures of Notch target gene expression. In this study we established immunostaining protocols to identify native, activated Notch receptors in human skin tissue. The ability to detect changes in Notch activation was confirmed with an ex vivo skin organ model in which signal was reduced or obliterated in tissue exposed to a gamma-secretase inhibitor. Using these methods on skin biopsies from healthy volunteers and a general HS cohort we demonstrated for the first time the distribution of active Notch signalling in human apocrine-bearing skin. Quantification of activated NOTCH1 & NOTCH2 revealed similar levels in non-lesional and peri-lesional HS to that of healthy controls, thus ruling out a general defect in Notch activation in HS patients. We did find a variable but significant reduction of activated Notch in epidermis of lesional HS with a distribution that appeared related to the extent of surrounding tissue inflammation.

Regulation of signaling pathways in hair follicle stem cells

Hair follicle stem cells (HFSCs) reside in the bulge region of the outer root sheath of the hair follicle. They are considered slow-cycling cells that are endowed with multilineage differentiation potential and superior proliferative capacity. The normal morphology and periodic growth of HFSCs play a significant role in normal skin functions, wound repair and skin regeneration. The HFSCs involved in these pathophysiological processes are regulated by a series of cell signal transduction pathways, such as lymphoid enhancer factor/T-cell factor, Wnt/β-catenin, transforming growth factor-β/bone morphogenetic protein, Notch and Hedgehog. The mechanisms of the interactions among these signaling pathways and their regulatory effects on HFSCs have been previously studied, but many mechanisms are still unclear. This article reviews the regulation of hair follicles, HFSCs and related signaling pathways, with the aims of summarizing previous research results, revealing the regulatory mechanisms of HFSC proliferation and differentiation and providing important references and new ideas for treating clinical diseases.

3D Spheroid Human Dermal Papilla Cell as an Effective Model for the Screening of Hair Growth Promoting Compounds: Examples of Minoxidil and 3,4,5-Tri-O-caffeoylquinic acid (TCQA)

Dermal papilla cells (DPCs) are an important element of the hair follicle (HF) niche, widely used as an in vitro model to study hair growth-related research. These cells are usually grown in 2D culture, but this system did not show efficient therapeutic effects on HF regeneration and growth, and key differences were observed between cell activity in vitro and in vivo. Recent studies have showed that DPCs grown in 3D hanging spheroids are more morphologically akin to an intact DP microenvironment. In this current study, global gene molecular analysis showed that the 3D model highly affected cell adhesion molecules and hair growth-related pathways. Furthermore, we compared the expression of signalling molecules and metabolism-associated proteins of DPCs treated with minoxidil (an FDA-approved drug for hair loss treatment) and 3,4,5-tri-O-caffeoylquinic acid (TCQA) (recently found to induce hair growth in vitro and in vivo) in 3D spheroid hanging drops and a 2D monolayer using DNA microarray analysis. Further validations by determining the gene and protein expressions of key signature molecules showed the suitability of this 3D system for enhancing the DPC activity of the hair growth-promoting agents minoxidil and TCQA.

RBP-J deficiency promoted the proliferation and differentiation of CD133-positive cells in vitro and in vivo studies

Although Notch signaling pathway could control the proliferation and differentiation of neural stem cells (NSCs), it is largely unknown about the effect of Notch signaling pathway on the neurogenesis of CD133-positive cells. By using the primary cultured ependymal cells and the transgenic mouse, we found that CD133 immunoreactivity was exclusively localized in the ependymal layer of ventricles, moreover, most CD133-positive cells were co-labeled with Nestin. In addition, recombination signal binding protein J (RBP-J), a key nuclear effector of Notch signaling pathway, was highly active in CD133-positive cells. CD133-positive cells can differentiate into the immature and mature neurons, in particular, the number of CD133-positive cells differentiating into the immature and mature neurons was significantly increased following the deficiency or interference of RBP-J in vivo or in vitro. By using real-time qPCR and western blot, we found that RBP-J and Hes1 were down-regulated while Notch1 was up-regulated in the expression levels of mRNAs and proteins following the deficiency or interference of RBP-J. These results demonstrated RBP-J deficiency promoted the proliferation and differentiation of CD133-positive cells. Therefore, we speculated that RBP-J could maintain CD133-positive cells in the characteristics of NSCs possibly by regulating Notch1/RBP-J/Hes1 pathway. It will provide a novel molecular insight into the function of RBP-J, as well as facilitate a future investigation of CD133-positive cells with respect to their potential application in neurodegenerative disorder.

Elucidation of the Potential Hair Growth-Promoting Effect of Botryococcus terribilis, Its Novel Compound Methylated-Meijicoccene, and C32 Botryococcene on Cultured Hair Follicle Dermal Papilla Cells Using DNA Microarray Gene Expression Analysis

A person’s quality of life can be adversely affected by hair loss. Microalgae are widely recognized for their abundance and rich functional components. Here, we evaluated the hair growth effect of a green alga, Botryococcus terribilis (B. terribilis), in vitro using hair follicle dermal papilla cells (HFDPCs). We isolated two types of cells from B. terribilis—green and orange cells, obtained from two different culture conditions. Microarray and real time-PCR results revealed that both cell types stimulated the expression of several pathways and genes associated with different aspect of the hair follicle cycle. Additionally, we demonstrated B. terribilis’ effect on collagen and keratin synthesis and inflammation reduction. We successfully isolated a novel compound, methylated-meijicoccene (me-meijicoccene), and C32 botryococcene from B. terribilis to validate their promising effects. Our study revealed that treatment with the two compounds had no cytotoxic effect on HFDPCs and significantly enhanced the gene expression levels of hair growth markers at low concentrations. Our study provides the first evidence of the underlying hair growth promoting effect of B. terribilis and its novel compound, me-meijicoccene, and C32 botryococcene.

Toward Elucidating Epigenetic and Metabolic Regulation of Stem Cell Lineage Plasticity in Skin Aging

Skin is the largest organ in human body, harboring a plethora of cell types and serving as the organismal barrier. Skin aging such as wrinkling and hair graying is graphically pronounced, and the molecular mechanisms behind these phenotypic manifestations are beginning to unfold. As in many other organs and tissues, epigenetic and metabolic deregulations have emerged as key aging drivers. Particularly in the context of the skin epithelium, the epigenome and metabolome coordinately shape lineage plasticity and orchestrate stem cell function during aging. Our review discusses recent studies that proposed molecular mechanisms that drive the degeneration of hair follicles, a major appendage of the skin. By focusing on skin while comparing it to model organisms and adult stem cells of other tissues, we summarize literature on genotoxic stress, nutritional sensing, metabolic rewiring, mitochondrial activity, and epigenetic regulations of stem cell plasticity. Finally, we speculate about the rejuvenation potential of rate-limiting upstream signals during aging and the dominant role of the tissue microenvironment in dictating aged epithelial stem cell function.

The Genomic Architecture of Hidradenitis Suppurativa-A Systematic Review

Hidradenitis suppurativa is a chronic, suppurative condition of the pilosebaceous unit manifesting as painful nodules, abscesses, and sinus tracts mostly in, but not limited to, intertriginous skin. Great strides have been made at elucidating the pathophysiology of hidradenitis suppurativa, which appears to be the product of hyperkeratinization and inflammation brought about by environmental factors and a genetic predisposition. The identification of familial hidradenitis suppurativa has sparked research aimed at identifying underlying pathogenic variants in patients who harbor them. The objective of this review is to provide a broad overview of the role of genetics in various aspects of hidradenitis suppurativa, specifically the pathophysiology, diagnosis, and clinical application.

Deletion of hypoxia-inducible factor prolyl 4-hydroxylase 2 in FoxD1-lineage mesenchymal cells leads to congenital truncal alopecia

Hypoxia-inducible factors (HIFs) induce numerous genes regulating oxygen homeostasis. As oxygen sensors of the cells, the HIF prolyl 4-hydroxylases (HIF-P4Hs) regulate the stability of HIFs in an oxygen-dependent manner. During hair follicle (HF) morphogenesis and cycling, the location of dermal papilla (DP) alternates between the dermis and hypodermis and results in varying oxygen levels for the DP cells. These cells are known to express hypoxia-inducible genes, but the role of the hypoxia response pathway in HF development and homeostasis has not been studied. Using conditional gene targeting and analysis of hair morphogenesis, we show here that lack of Hif-p4h-2 in Forkhead box D1 (FoxD1)-lineage mesodermal cells interferes with the normal HF development in mice. FoxD1-lineage cells were found to be mainly mesenchymal cells located in the dermis of truncal skin, including those cells composing the DP of HFs. We found that upon Hif-p4h-2 inactivation, HF development was disturbed during the first catagen leading to formation of epithelial-lined HF cysts filled by unorganized keratins, which eventually manifested as truncal alopecia. Furthermore, the depletion of Hif-p4h-2 led to HIF stabilization and dysregulation of multiple genes involved in keratin formation, HF differentiation, and HIF, transforming growth factor β (TGF-β), and Notch signaling. We hypothesize that the failure of HF cycling is likely to be mechanistically caused by disruption of the interplay of the HIF, TGF-β, and Notch pathways. In summary, we show here for the first time that HIF-P4H-2 function in FoxD1-lineage cells is essential for the normal development and homeostasis of HFs.

A systematic summary of survival and death signalling during the life of hair follicle stem cells

Hair follicle stem cells (HFSCs) are among the most widely available resources and most frequently approved model systems used for studying adult stem cells. HFSCs are particularly useful because of their self-renewal and differentiation properties. Additionally, the cyclic growth of hair follicles is driven by HFSCs. There are high expectations for the use of HFSCs as favourable systems for studying the molecular mechanisms that contribute to HFSC identification and can be applied to hair loss therapy, such as the activation or regeneration of hair follicles, and to the generation of hair using a tissue-engineering strategy. A variety of molecules are involved in the networks that critically regulate the fate of HFSCs, such as factors in hair follicle growth and development (in the Wnt pathway, Sonic hedgehog pathway, Notch pathway, and BMP pathway), and that suppress apoptotic cues (the apoptosis pathway). Here, we review the life cycle, biomarkers and functions of HFSCs, concluding with a summary of the signalling pathways involved in HFSC fate for promoting better understanding of the pathophysiological changes in the HFSC niche. Importantly, we highlight the potential mechanisms underlying the therapeutic targets involved in pathways associated with the treatment of hair loss and other disorders of skin and hair, including alopecia, skin cancer, skin inflammation, and skin wound healing.

Argan (Argania Spinosa) press cake extract enhances cell proliferation and prevents oxidative stress and inflammation of human dermal papilla cells

BACKGROUND

Hair follicle undergoes a growth cycle under the regulation of dermal papilla cells. Due to their enormous roles, these fibroblast cells have been used in various in vitro studies as a screening model to evaluate the effect of hair growth regulating agents.

OBJECTIVE

In the current study, we aim to check the hair growth potential effect of Argan press cake (APC) extracted using 50 or 80 % aqueous ethanol on human hair follicle dermal papilla cells (HFDPCs) and to determine the molecular mechanism.

METHODS

APC were applied to HFDPCs, then cell proliferation assays, mitochondrial biogenesis assay, and oxidative stress assay were assessed. DNA microarray was performed from the cells treated with our samples and minoxidil. Validation of the results was done using Quantitative Real-Time PCR with primers for hair-growth related genes. GC/MS analysis was used to determine the compounds contained in APC 50 and 80 %.

RESULTS

APC enhanced cell proliferation along with the stimulation of the ATP content. Additionally, APC had an anti-oxidant activity against H₂O₂ mediated oxidative stress preventing dermal papilla cell senescence. Consistent with this, global gene profiling analysis showed an activation of hair growth-related pathway, and a downregulation of inflammation- and oxidative stress-related genes by APC extracts. GC/MS analysis revealed that these extracts contained pure fatty acids, derived sugar chains, and pure compounds including tocopherols, squalene, and spinasterol.

CONCLUSION

Taken together, here we showed that APC extracts had an effect on stimulating hair growth while inhibiting the inflammation and the oxidative stress of HFDPCs and thus can potentially contribute to an anti-hair loss drug development.

The Impact of Notch Signaling for Carcinogenesis and Progression of Nonmelanoma Skin Cancer: Lessons Learned from Cancer Stem Cells, Tumor Angiogenesis, and Beyond

Since many decades, nonmelanoma skin cancer (NMSCs) is the most common malignancy worldwide. Basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) are the major types of NMSCs, representing approximately 70% and 25% of these neoplasias, respectively. Because of their continuously rising incidence rates, NMSCs represent a constantly increasing global challenge for healthcare, although they are in most cases nonlethal and curable (e.g., by surgery). While at present, carcinogenesis of NMSC is still not fully understood, the relevance of genetic and molecular alterations in several pathways, including evolutionary highly conserved Notch signaling, has now been shown convincingly. The Notch pathway, which was first developed during evolution in metazoans and that was first discovered in fruit flies (Drosophila melanogaster), governs cell fate decisions and many other fundamental processes that are of high relevance not only for embryonic development, but also for initiation, promotion, and progression of cancer. Choosing NMSC as a model, we give in this review a brief overview on the interaction of Notch signaling with important oncogenic and tumor suppressor pathways and on its role for several hallmarks of carcinogenesis and cancer progression, including the regulation of cancer stem cells, tumor angiogenesis, and senescence.

Genome-wide detection and sequence conservation analysis of long non-coding RNA during hair follicle cycle of yak

BACKGROUND

Long non-coding RNA (lncRNA) as an important regulator has been demonstrated playing an indispensable role in the biological process of hair follicles (HFs) growth. However, their function and expression profile in the HFs cycle of yak are yet unknown. Only a few functional lncRNAs have been identified, partly due to the low sequence conservation and lack of identified conserved properties in lncRNAs. Here, lncRNA-seq was employed to detect the expression profile of lncRNAs during the HFs cycle of yak, and the sequence conservation of two datasets between yak and cashmere goat during the HFs cycle was analyzed.

RESULTS

A total of 2884 lncRNAs were identified in 5 phases (Jan., Mar., Jun., Aug., and Oct.) during the HFs cycle of yak. Then, differential expression analysis between 3 phases (Jan., Mar., and Oct.) was performed, revealing that 198 differentially expressed lncRNAs (DELs) were obtained in the Oct.-vs-Jan. group, 280 DELs were obtained in the Jan.-vs-Mar. group, and 340 DELs were obtained in the Mar.-vs-Oct. group. Subsequently, the nearest genes of lncRNAs were searched as the potential target genes and used to explore the function of DELs by GO and KEGG enrichment analysis. Several critical pathways involved in HFs development such as Wnt signaling pathway, VEGF signaling pathway, and signaling pathways regulating pluripotency of stem cells, were enriched. To further screen key lncRNAs influencing the HFs cycle, 24 DELs with differ degree of sequence conservation were obtained via a comparative analysis of partial DELs with previously published lncRNA-seq data of cashmere goat in the HFs cycle using NCBI BLAST-2.9.0+, and 3 DELs of them were randomly selected for further detailed analysis of the sequence conservation properties.

CONCLUSIONS

This study revealed the expression pattern and potential function of lncRNAs during HFs cycle of yak, which would expand the knowledge about the role of lncRNAs in the HFs cycle. The findings related to sequence conservation properties of lncRNAs in the HFs cycle between the two species may provide valuable insights into the study of lncRNA functionality and mechanism.

β-catenin-mediated hair growth induction effect of 3,4,5-tri-O-caffeoylquinic acid

The hair follicle is a complex structure that goes through a cyclic period of growth (anagen), regression (catagen), and rest (telogen) under the regulation of several signaling pathways, including Wnt/ β-catenin, FGF, Shh, and Notch. The Wnt/β-catenin signaling is specifically involved in hair follicle morphogenesis, regeneration, and growth. β-catenin is expressed in the dermal papilla and promotes anagen induction and duration, as well as keratinocyte regulation and differentiation. In this study, we demonstrated the activation of β-catenin by a polyphenolic compound 3,4,5-tri-O-caffeoylquinic acid (TCQA) in mice model and in human dermal papilla cells to promote hair growth cycle. A complete regrowth of the shaved area of C3H mice was observed upon treatment with TCQA. Global gene expression analysis using microarray showed an upregulation in hair growth-associated genes. Moreover, the expression of β-catenin was remarkably upregulated in vivo and in vitro. These findings suggest that β-catenin activation by TCQA promoted the initiation of the anagen phase of the hair cycle.

The Role of microRNAs in Organismal and Skin Aging

The aging process starts directly after birth and lasts for the entire lifespan; it manifests itself with a decline in an organism’s ability to adapt and is linked to the development of age-related diseases that eventually lead to premature death. This review aims to explore how microRNAs (miRNAs) are involved in skin functioning and aging. Recent evidence has suggested that miRNAs regulate all aspects of cutaneous biogenesis, functionality, and aging. It has been noted that some miRNAs were down-regulated in long-lived individuals, such as let-7, miR-17, and miR-34 (known as longevity-related miRNAs). They are conserved in humans and presumably promote lifespan prolongation; conversely, they are up-regulated in age-related diseases, like cancers. The analysis of the age-associated cutaneous miRNAs revealed the increased expression of miR-130, miR-138, and miR-181a/b in keratinocytes during replicative senescence. These miRNAs affected cell proliferation pathways via targeting the p63 and Sirtuin 1 mRNAs. Notably, miR-181a was also implicated in skin immunosenescence, represented by the Langerhans cells. Dermal fibroblasts also expressed increased the levels of the biomarkers of aging that affect telomere maintenance and all phases of the cellular life cycle, such as let-7, miR-23a-3p, 34a-5p, miR-125a, miR-181a-5p, and miR-221/222-3p. Among them, the miR-34 family, stimulated by ultraviolet B irradiation, deteriorates collagen in the extracellular matrix due to the activation of the matrix metalloproteinases and thereby potentiates wrinkle formation. In addition to the pro-aging effects of miRNAs, the plausible antiaging activity of miR-146a that antagonized the UVA-induced inhibition of proliferation and suppressed aging-related genes (e.g., p21WAF-1, p16, and p53) through targeting Smad4 has also been noticed. Nevertheless, the role of miRNAs in skin aging is still not fully elucidated and needs to be further discovered and explained.

Novel Mutation of the NCSTN Gene Identified in a Chinese Acne Inversa Family

Acne inversa is a chronic inflammatory follicular disease with autosomal dominant inheritance. In recent years, many functional mutations in the NCSTN genes have been identified as the cause of familial acne inversa. Herein, we recruited four patients and seven unaffected individuals from a Chinese family and performed Sanger sequencing of the NCSTN gene. One novel frameshift mutation, c.450_459del (p.Ser 151GlnfsX48), was identified in exon 5 of the NCSTN gene. Three normal-looking children carrying the mutation were proven to be patients. We also presented a literature review from previous studies of acne inversa, suggesting that NCSTN is a hotspot gene for acne inversa. Most affected individuals experienced onset in adolescence. We confirmed the diagnosis in this family based on the mutation. This finding will help expound the relationship between the NCSTN gene and the pathogenesis of acne inversa and emphasize the value of genetic diagnosis in monogenic disorder.

Aquatic Adaptation and Depleted Diversity: A Deep Dive into the Genomes of the Sea Otter and Giant Otter

Despite its recent invasion into the marine realm, the sea otter (Enhydra lutris) has evolved a suite of adaptations for life in cold coastal waters, including limb modifications and dense insulating fur. This uniquely dense coat led to the near-extinction of sea otters during the 18th-20th century fur trade and an extreme population bottleneck. We used the de novo genome of the southern sea otter (E. l. nereis) to reconstruct its evolutionary history, identify genes influencing aquatic adaptation, and detect signals of population bottlenecks. We compared the genome of the southern sea otter with the tropical freshwater-living giant otter (Pteronura brasiliensis) to assess common and divergent genomic trends between otter species, and with the closely related northern sea otter (E. l. kenyoni) to uncover population-level trends. We found signals of positive selection in genes related to aquatic adaptations, particularly limb development and polygenic selection on genes related to hair follicle development. We found extensive pseudogenization of olfactory receptor genes in both the sea otter and giant otter lineages, consistent with patterns of sensory gene loss in other aquatic mammals. At the population level, the southern sea otter and the northern sea otter showed extremely low genomic diversity, signals of recent inbreeding, and demographic histories marked by population declines. These declines may predate the fur trade and appear to have resulted in an increase in putatively deleterious variants that could impact the future recovery of the sea otter.

Niche-Specific Factors Dynamically Regulate Sebaceous Gland Stem Cells in the Skin

Oil-secreting sebaceous glands (SGs) are critical for proper skin function; however, it remains unclear how different factors act together to modulate SG stem cells. Here, we provide functional evidence that each SG lobe is serviced by its own dedicated stem cell population. Upon ablating Notch signaling in different skin subcompartments, we find that this pathway exerts dual counteracting effects on SGs. Suppressing Notch in SG progenitors traps them in a hybrid state where stem and differentiation features become intermingled. In contrast, ablating Notch outside of the SG stem cell compartment indirectly drives SG expansion. Finally, we report that a K14:K5→K14:K79 keratin shift occurs during SG differentiation. Deleting K79 destabilizes K14 in sebocytes, and attenuates SGs and eyelid meibomian glands, leading to corneal ulceration. Altogether, our findings demonstrate that SGs integrate diverse signals from different niches and suggest that mutations incurred within one stem cell compartment can indirectly influence another.

Leukemia development initiated by deletion of RBP-J: mouse strain, deletion efficiency and cell of origin

Conditional deletion of RBP-J, the major transcriptional effector of Notch signaling, specifically within renin-expressing cells leads to the development of B-cell leukemia. However, the influence of contributing factors such as mouse strain, cell of origin and Cre recombinase copy number are unknown. In this study, we compared RBP-J deletion efficiency using one versus two copies of Cre recombinase. Further, we compared the incidence and timing of leukemia development in two unique strains of mice, C57BL/6 and 129/SV, as well as at different B-cell developmental stages. We found that animals expressing two copies of Cre recombinase developed B-cell leukemia at an earlier age and with more fulminant disease, compared with control animals and animals expressing one copy of Cre recombinase. In addition, we found a difference in leukemia incidence between C57BL/6 and 129/SV mouse strains. Whereas deletion of RBP-J in renin-expressing cells of C57BL/6 mice leads to the development of B-cell leukemia, 129/SV mice develop dermatitis with a reactive, myeloproliferative phenotype. The difference in phenotypes is explained, in part, by the differential expression of extra-renal renin; C57BL/6 mice have more renin-expressing cells within hematopoietic tissues. Finally, we found that deletion of RBP-J in Mb1- or CD19-expressing B lymphocytes does not result in leukemia development. Together, these studies establish that renin progenitors are vulnerable cells for neoplastic transformation and emphasize the importance of genetic background on the development of inflammatory and malignant conditions.This article has an associated First Person interview with the first author of the paper.

Tumor Architecture and Notch Signaling Modulate Drug Response in Basal Cell Carcinoma

Hedgehog (Hh) pathway inhibitors such as vismodegib are highly effective for treating basal cell carcinoma (BCC); however, residual tumor cells frequently persist and regenerate the primary tumor upon drug discontinuation. Here, we show that BCCs are organized into two molecularly and functionally distinct compartments. Whereas interior Hh⁺/Notch⁺ suprabasal cells undergo apoptosis in response to vismodegib, peripheral Hh⁺⁺⁺/Notch^- basal cells survive throughout treatment. Inhibiting Notch specifically promotes tumor persistence without causing drug resistance, while activating Notch is sufficient to regress already established lesions. Altogether, these findings suggest that the three-dimensional architecture of BCCs establishes a natural hierarchy of drug response in the tumor and that this hierarchy can be overcome, for better or worse, by modulating Notch.

Association of papillomavirus E6 proteins with either MAML1 or E6AP clusters E6 proteins by structure, function, and evolutionary relatedness

Papillomavirus E6 proteins bind to LXXLL peptide motifs displayed on targeted cellular proteins. Alpha genus HPV E6 proteins associate with the cellular ubiquitin ligase E6AP (UBE3A), by binding to an LXXLL peptide (ELTLQELLGEE) displayed by E6AP, thereby stimulating E6AP ubiquitin ligase activity. Beta, Gamma, and Delta genera E6 proteins bind a similar LXXLL peptide (WMSDLDDLLGS) on the cellular transcriptional co-activator MAML1 and thereby repress Notch signaling. We expressed 45 different animal and human E6 proteins from diverse papillomavirus genera to ascertain the overall preference of E6 proteins for E6AP or MAML1. E6 proteins from all HPV genera except Alpha preferentially interacted with MAML1 over E6AP. Among animal papillomaviruses, E6 proteins from certain ungulate (SsPV1 from pigs) and cetacean (porpoises and dolphins) hosts functionally resembled Alpha genus HPV by binding and targeting the degradation of E6AP. Beta genus HPV E6 proteins functionally clustered with Delta, Pi, Tau, Gamma, Chi, Mu, Lambda, Iota, Dyokappa, Rho, and Dyolambda E6 proteins to bind and repress MAML1. None of the tested E6 proteins physically and functionally interacted with both MAML1 and E6AP, indicating an evolutionary split. Further, interaction of an E6 protein was insufficient to activate degradation of E6AP, indicating that E6 proteins that target E6AP co-evolved to separately acquire both binding and triggering of ubiquitin ligase activation. E6 proteins with similar biological function clustered together in phylogenetic trees and shared structural features. This suggests that the divergence of E6 proteins from either MAML1 or E6AP binding preference is a major event in papillomavirus evolution.

Papillomaviruses are a large family of viruses with great medical and veterinary importance. This study explores the viral E6 oncoproteins from diverse papillomavirus genera to determine how E6 distinguishes in interaction between cellular proteins. E6 proteins have been previously found to interact with a ubiquitin ligase called E6AP and thereby target particular cellular proteins for degradation, or to interact with MAML family proteins to repress Notch signaling and thereby alter cellular differentiation. It has been unclear if diverse families of papillomavirus E6 proteins interact with only E6AP or MAML (or possibly both), how E6 distinguishes between these interactions, and if interaction of E6 with E6AP is coupled to ubiquitin ligase activation. We find here that none of the tested E6 proteins physically and functionally interacted with both E6AP and MAML1, indicating an evolutionary split that clustered E6 proteins by sequence similarity analysis. Currently, the categorization of papillomaviruses is complex, with thirty-eight genera so far described. This study establishes an early evolutionary split among most papillomavirus genera between those viruses that encode E6 proteins that physically and functionally associate with MAML compared to E6AP. This provides a structural and functional basis for categorizing most currently described papillomaviruses into two major functional groups.

Roles of the Hedgehog Signaling Pathway in Epidermal and Hair Follicle Development, Homeostasis, and Cancer

The epidermis is the outermost layer of the skin and provides a protective barrier against environmental insults. It is a rapidly-renewing tissue undergoing constant regeneration, maintained by several types of stem cells. The Hedgehog (HH) signaling pathway is one of the fundamental signaling pathways that contributes to epidermal development, homeostasis, and repair, as well as to hair follicle development and follicle bulge stem cell maintenance. The HH pathway interacts with other signal transduction pathways, including those activated by Wnt, bone morphogenetic protein, platelet-derived growth factor, Notch, and ectodysplasin. Furthermore, aberrant activation of HH signaling is associated with various tumors, including basal cell carcinoma. Therefore, an understanding of the regulatory mechanisms of the HH signaling pathway is important for elucidating fundamental mechanisms underlying both organogenesis and carcinogenesis. In this review, we discuss the role of the HH signaling pathway in the development and homeostasis epidermis and hair follicles, and in basal cell carcinoma formation, providing an update of current knowledge in this field.

Aging in hair follicle stem cells and niche microenvironment

Hair graying and hair loss are prominent and common characteristics of the elderly population. In some individuals these processes can significantly impact their quality of life, leading to depression, anxiety and other serious mental health problems. Accordingly, there has been much interest in understanding the complex physiological changes within the hair follicle in the aging individual. It is now known that hair follicles represent a prototypical stem cell niche, where both micro- and macroenvironmental influences are integrated alongside stem cell-stem cell and stem cell-stem niche interactions to determine hair growth or hair follicle senescence. Recent studies have identified imbalanced stem cell differentiation and altered stem cell activity as important factors during hair loss, indicating new avenues for the development of therapeutic agents to stimulate hair growth. Here, we pull together the latest findings on the hair follicle stem cell niche and the multifactorial interactions underlying the various forms of hair loss.

Notch1 Signaling Contributes to Hypoxia-induced High Expression of Integrin β1 in Keratinocyte Migration

Oxygen tension is an important micro-environmental factor that affects epidermal development and function. After injury, high oxygen consumption and vascular injury result in partial hypoxia. However, whether hypoxia benefits or hurts wound healing remains controversial. In this study, a tissue oxygen tension monitor was used to detect the spatial and temporal distribution of oxygen in burn wounds. In vitro, we demonstrate that hypoxia promoted the expression of integrin β1 and the migration of keratinocytes. Furthermore, hypoxia-induced migration was slowed by Notch1 ligands and a siRNA against ITGB1 (integrin β1). Our findings suggest that integrin β1 may be an oxygen-sensitive molecule that promotes keratinocyte migration during wound healing and that Notch1 signaling is involved in this process.

Notch signaling is significantly suppressed in basal cell carcinomas and activation induces basal cell carcinoma cell apoptosis

A subset of basal cell carcinomas (BCCs) are directly derived from hair follicles (HFs). In some respects, HFs can be defined as 'ordered' skin appendage growths, while BCCs can be regarded as 'disordered' skin appendage growths. The aim of the present study was to examine HFs and BCCs to define the expression of common and unique signaling pathways in each skin appendage. Human nodular BCCs, along with HFs and non‑follicular skin epithelium from normal individuals, were examined using microarrays, qPCR, and immunohistochemistry. Subsequently, BCC cells and root sheath keratinocyte cells from HFs were cultured and treated with Notch signaling peptide Jagged1 (JAG1). Gene expression, protein levels, and cell apoptosis susceptibility were assessed using qPCR, immunoblotting, and flow cytometry, respectively. Specific molecular mechanisms were found to be involved in the process of cell self‑renewal in the HFs and BCCs, including Notch and Hedgehog signaling pathways. However, several key Notch signaling factors showed significant differential expression in BCCs compared with HFs. Stimulating Notch signaling with JAG1 induced apoptosis of BCC cells by increasing Fas ligand expression and downstream caspase-8 activation. The present study showed that Notch signaling pathway activity is suppressed in BCCs, and is highly expressed in HFs. Elements of the Notch pathway could, therefore, represent targets for the treatment of BCCs and potentially in hair follicle engineering.

Nicastrin mutations in familial acne inversa impact keratinocyte proliferation and differentiation through the Notch and phosphoinositide 3-kinase/AKT signalling pathways

BACKGROUND

Acne inversa (AI) is a chronic inflammatory skin disease with an autosomal dominant inheritance pattern. Mutations of the gene encoding nicastrin (NCSTN), a cofactor subunit of γ-secretase, are responsible for familial AI. However, whether deficiency of nicastrin is functionally implicated in the biological behaviours of human keratinocytes and related molecular mechanisms remains unknown.

OBJECTIVES

To study alterations of biological traits and related signalling pathways modulated by nicastrin knockdown in keratinocytes.

METHODS

A human immortalized keratinocyte cell line (HaCaT) was treated with efficient small interfering (si)RNA-targeted NCSTN. Cell proliferation was measured by CCK-8 assay; cell-cycle and cell apoptosis analyses were detected by flow cytometry. Microarray analysis was applied to uncover impacts of NCSTN silencing on whole-genome expression of HaCaT cells. Altered signalling pathways were further confirmed by real-time polymerase chain reaction, Western blotting and immunohistochemistry in both HaCaT cells and lesions of a patient with AI with NCSTN mutation.

RESULTS

NCSTN knockdown in HaCaT cells impaired γ-secretase activity, leading to increased cell proliferation and S-phase population. Microarray data also showed that numerous genes and pathways implicated in proliferation and differentiation of keratinocytes were statistically changed. Among these genes, expression levels of several Notch pathway molecules, known as γ-secretase substrates, were validated to be significantly attenuated in both nicastrin-silencing HaCaT cells and the lesion of the patient. Furthermore, a remarkable elevation of expression of phosphoinositide 3-kinase (PI3K), AKT and its activated form pAKT was illustrated in siRNA-treated HaCaT cells.

CONCLUSIONS

Deficiency of the NCSTN in familial AI may regulate proliferation and differentiation of keratinocytes mainly through the Notch and PI3K/AKT signalling pathways.

c-Myc and Epidermal Stem Cell Fate Determination

The epidermis is sustained by a multipotent stem cell population that gives rise to cells of different fates including those forming hair follicles, interfollicular epidermis and associated glands such as sebaceous glands. The most intriguing evidence comes from using a variety of mouse models with which studies have found the WNT pathway to be involved in regulating stem cell fate decisions. These mouse models have been used to analyze different members of the WNT pathway in the epidermis and altogether suggest that different levels of beta-catenin correlate with the adoption of different epidermal stem cell fates. Recent data specifically analyzing c-Myc, a downstream target of the WNT pathway, has found that c-Myc can divert epidermal stem cells to a sebaceous gland fate at the expense of hair follicles. Also, newly emerging data using gene expression profiling techniques have uncovered a more direct role of c-Myc in stem cell fate determination.

Therapeutic potential of a gamma-secretase inhibitor for hearing restoration in a guinea pig model with noise-induced hearing loss

Background

Notch signaling plays a crucial role in the fate determination of cochlear progenitor cells, hair cells, and supporting cells in the developing cochlea. Recent studies have demonstrated the temporal activation of Notch signaling in damaged mature cochleae, and have demonstrated the induction of new hair cells by pharmacologically inhibiting Notch signaling. The present study aimed to illustrate the feasibility of pharmacologically inhibiting Notch signaling by using a gamma-secretase inhibitor for treating sensorineural hearing loss.

Results

The effect of the sustained local delivery of MDL28170, a gamma-secretase inhibitor, on hearing and hair cell induction was tested in a guinea pig model with noise-induced hearing loss. MDL28170 was directly delivered into the cochlear fluids via a micro-osmotic pump. Drug application was initiated 7 days after noise exposure. Measurements of auditory brainstem responses revealed better hearing in the MDL28170-treated animals than in the vehicle controls. Histological analysis demonstrated a higher number of outer hair cells in the MDL28170-treated cochleae than the vehicle-treated cochleae.

Conclusion

These findings strongly suggest that local sustained delivery of a gamma-secretase inhibitor into the cochlea could be a novel strategy for treating acute hearing loss that is refractory to conventional treatment.

Cutaneous Notch signaling in health and disease

The development and maintenance of the skin are dependent on myriad signaling pathways that regulate a variety of cellular processes. In cutaneous epithelial cells, the Notch cascade plays a central role in ensuring that proliferation and differentiation are coordinated appropriately, a function that it imparts during both ontogeny and homeostasis. Aberrations of the Notch signaling pathway result in severe abnormalities in the epidermis and its appendages and cause functional defects such as perturbed barrier function. In addition, impaired Notch signaling is associated with diseases of the skin such as atopy and cancer. The pathology associated with aberrant cutaneous Notch signaling reflects the complex mechanisms underpinning its function in this tissue and involves both cell-autonomous and nonautonomous mechanisms. This review summarizes our current knowledge of the role of Notch signaling in the skin during health and disease.

Keratin 79 identifies a novel population of migratory epithelial cells that initiates hair canal morphogenesis and regeneration

The formation of epithelial tubes underlies the development of diverse organs. In the skin, hair follicles resemble tube-like structures with lumens that are generated through poorly understood cellular rearrangements. Here, we show that creation of the hair follicle lumen is mediated by early outward movement of keratinocytes from within the cores of developing hair buds. These migratory keratinocytes express keratin 79 (K79) and stream out of the hair germ and into the epidermis prior to lumen formation in the embryo. Remarkably, this process is recapitulated during hair regeneration in the adult mouse, when K79(+) cells migrate out of the reactivated secondary hair germ prior to formation of a new hair canal. During homeostasis, K79(+) cells line the hair follicle infundibulum, a domain we show to be multilayered, biochemically distinct and maintained by Lrig1(+) stem cell-derived progeny. Upward movement of these cells sustains the infundibulum, while perturbation of this domain during acne progression is often accompanied by loss of K79. Our findings uncover previously unappreciated long-distance cell movements throughout the life cycle of the hair follicle, and suggest a novel mechanism by which the follicle generates its hollow core through outward cell migration.

A novel splice site mutation in NCSTN underlies a Japanese family with hidradenitis suppurativa

BACKGROUND

 Hidradenitis suppurativa (HS) is a chronic follicular occlusive disease with characteristic recurrent draining sinuses, skin abscesses and disfiguring scars, mainly involving the axilla, groin, perianal and perineal regions. While most HS cases are nonfamilial, familial cases showing autosomal dominant inheritance have been reported. Recently, loss-of-function mutations in the genes encoding γ-secretase have been identified as a cause of familial HS in the Chinese and British populations.

OBJECTIVES

 To identify mutations in the genes encoding γ-secretase in Japanese patients with familial and nonfamilial HS.

METHODS

 Two affected and three unaffected individuals from a Japanese family with familial HS and nine patients with nonfamilial HS were recruited. We conducted mutation analysis of the γ-secretase genes in Japanese patients with familial and nonfamilial HS.

RESULTS

  A novel splice site mutation in the nicastrin gene NCSTN, one of the six key component genes encoding γ-secretase, was identified in the patients with familial HS. Neither unaffected individuals in the family nor 100 ethnically matched control alleles carry this mutation. None of the nine patients with nonfamilial HS carry nonsense, frameshift or splice site mutations in this gene.

CONCLUSIONS

  A novel splice site mutation, c.582+1delG, in NCSTN was identified in the familial patients with HS. We also reveal for the first time that a γ-secretase gene mutation is not linked to the development of nonfamilial HS. These results would further pave the way to a better understanding of the contribution of γ-secretase and other genes to the pathogenesis of HS and to the development of a new therapeutic strategy for HS.

Hairy tale of signaling in hair follicle development and cycling

Hair follicles (HFs) is an appendage from the vertebrate skin epithelium, and is critical for environmental sensing, animal appearance, and body heat maintenance. HFs arise from the embryonic ectoderm and regenerate cyclically during adult life. Distinct morphological and functional stages from development through homeostasis have been extensively studied for the past decades to dissect the critical molecular mechanisms. Accumulating work suggests that different signaling cascades, such as Wnt, Bmp, Shh, and Notch, together with specific combinations of transcription factors are at work at different stages. Here we provide a comprehensive review of mouse genetics studies, which include lineage tracing along with knockout and over-expression of core genes from key signaling pathways, to paint an updated view of the molecular regulatory network that govern each stage of hair follicle development and adult cycling.

Stem cells of the human epidermis and their niche: composition and function in epidermal regeneration and carcinogenesis

Skin, as the largest organ, has long been subject of excellent and pioneering studies on stem cells and their role in tissue regulation and tumor formation. In particular, intensive research on mouse skin, and here especially the hair follicle, has largely extended our knowledge. Surprisingly, human skin, although the most easily accessible tissue in man, is far less conceived with regard to its stem cells and their specific environment (the niche). In consequence, these features are as yet only insufficiently defined and it still has to be elucidated how insights in cutaneous stem cell biology gained in mice can be extrapolated to humans. In the last few years, human model systems such as humanized mice or in vitro organotypic cultures that support maintenance or reconstruction of human skin and long-term epidermal regeneration have been developed. These models allow lineage tracing experiments and can be modified by adopting genetically manipulated cell types. Accordingly, they represent proper tools for human stem cell research and will clearly help to improve our still incomplete understanding. Like normal skin, the non-melanoma skin cancers and their respective tumors have gained considerable interest in basic as well as in clinical research. Being the most frequent human tumors globally, basal cell carcinomas and cutaneous squamous cell carcinomas (SCCs) continue to increase in incidence and specifically SCCs predominate in immunosuppressed transplant recipients. This review intends to compile the present knowledge on keratinocyte stem cells and their niches in normal skin and skin carcinomas with a special focus on the human situation. In particular, the role of the microenvironment, the niche, is emphasized, promoting our view of the decisive importance of the niche as a key regulatory element for controlling position, fate and regenerative potential of the stem cell population both in healthy skin and in carcinomas.

25 years of epidermal stem cell research

This is a chronicle of concepts in the field of epidermal stem cell biology and a historic look at their development over time. The past 25 years have seen the evolution of epidermal stem cell science, from first fundamental studies to a sophisticated science. The study of epithelial stem cell biology was aided by the ability to visualize the distribution of stem cells and their progeny through lineage analysis studies. The excellent progress we have made in understanding epidermal stem cell biology is discussed in this article. The challenges we still face in understanding epidermal stem cells include defining molecular markers for stem and progenitor sub-populations, determining the locations and contributions of the different stem cell niches, and mapping regulatory pathways of epidermal stem cell proliferation and differentiation. However, our rapidly evolving understanding of epidermal stem cells has many potential uses that promise to translate into improved patient therapy.

Hematopoietic stem cells: to be or Notch to be

Notch is a well-conserved signaling pathway and its function in cell fate determination is crucial in embryonic development and in the maintenance of tissue homeostasis during adult life. Notch activation depends on cell-cell interactions that are essential for the generation of cell diversity from initially equivalent cell populations. In the adult hematopoiesis, Notch is undoubtedly a very efficient promoter of T-cell differentiation, and this has masked for a long time the effects of Notch on other blood lineages, which are gradually being identified. However, the adult hematopoietic stem cell (HSC) remains mostly refractory to Notch intervention in experimental systems. In contrast, Notch is essential for the generation of the HSCs, which takes place during embryonic development. This review summarizes the knowledge accumulated in recent years regarding the role of the Notch pathway in the different stages of HSC ontology from embryonic life to fetal and adult bone marrow stem cells. In addition, we briefly examine other systems where Notch regulates specific stem cell capacities, in an attempt to understand how Notch functions in stem cell biology.

Cutaneous papillomavirus E6 oncoproteins associate with MAML1 to repress transactivation and NOTCH signaling

Papillomavirus E6 oncoproteins associate with LXXLL motifs on target cellular proteins to alter their function. Using a proteomic approach, we found the E6 oncoproteins of cutaneous papillomaviruses Bovine Papillomavirus Type 1 (BE6) and HPV types 1 and 8 (1E6 and 8E6) associated with the MAML1 transcriptional co-activator. All three E6 proteins bind to an acidic LXXLL motif at the carboxy-terminus of MAML1 and repress transactivation by MAML1. MAML1 is best known as the co-activator and effector of NOTCH induced transcription, and BPV-1 E6 represses synthetic NOTCH responsive promoters, endogenous NOTCH responsive promoters, and is found in a complex with MAML1 in stably transformed cells. BPV-1 induced papillomas show characteristics of repressed NOTCH signal transduction, including suprabasal expression of integrins, talin, and basal type keratins, and delayed expression of the NOTCH dependent HES1 transcription factor. These observations give rise to a model whereby papillomavirus oncoproteins including BPV-1 E6 and the cancer associated HPV-8 E6 repress Notch induced transcription, thereby delaying keratinocyte differentiation.

Role of adrenomedullin in the growth and differentiation of stem and progenitor cells

Stem cells have captured the imagination of the general public by their potential as new therapeutic tools in the fight against degenerative diseases. This potential is based on their capability for self-renewal and at the same time for producing progenitor cells that will eventually provide the building blocks for tissue and organ regeneration. These processes are carefully orchestrated in the organism by means of a series of molecular cues. An emerging molecule which is responsible for some of these physiological responses is adrenomedullin, a 52-amino acid regulatory peptide which increases proliferation and regulates cell fate of stem cells of different origins. Adrenomedullin binds to specific membrane receptors in stem cells and induces several intracellular pathways such as those involving cAMP, Akt, or MAPK. Regulation of adrenomedullin levels may help in directing the growth and differentiation of stem cells for applications (e.g., cell therapy) both in vitro and in vivo.

Notch signaling and the developing hair follicle

Notch function in the hair follicle has been mainly studied by use of transgenic mice carrying either loss or gain of function mutations in various members of the pathway. These studies revealed that whereas embryonic development of the hair follicle can be achieved without Notch, its postnatal development requires an intact Notch signaling in the hair bulb and the outer root sheath. Among the many roles played by Notch in the hair follicle, two can be highlighted: in the bulge, Notch controls a cell fate switch in hair follicle stem cells or their progenitors, preventing them from adopting an epidermal fate. In the hair bulb, Notch controls cell differentiation, ensuring the proper development of every layer of the hair shaft and inner root sheath. Notch function in the hair follicle is both cell autonomous and cell non autonomous and involves intercellular communication between adjacent layers.

IRF6 is a mediator of Notch pro-differentiation and tumour suppressive function in keratinocytes

While the pro-differentiation and tumour suppressive functions of Notch signalling in keratinocytes are well established, the underlying mechanisms remain poorly understood. We report here that interferon regulatory factor 6 (IRF6), an IRF family member with an essential role in epidermal development, is induced in differentiation through a Notch-dependent mechanism and is a primary Notch target in keratinocytes and keratinocyte-derived SCC cells. Increased IRF6 expression contributes to the impact of Notch activation on growth/differentiation-related genes, while it is not required for induction of 'canonical' Notch targets like p21(WAF1/Cip1), Hes1 and Hey1. Down-modulation of IRF6 counteracts differentiation of primary human keratinocytes in vitro and in vivo, promoting ras-induced tumour formation. The clinical relevance of these findings is illustrated by the strikingly opposite pattern of expression of Notch1 and IRF6 versus epidermal growth factor receptor in a cohort of clinical SCCs, as a function of their grade of differentiation. Thus, IRF6 is a primary Notch target in keratinocytes, which contributes to the role of this pathway in differentiation and tumour suppression.

IKK1 control of epidermal differentiation is modulated by notch signaling

The molecular mechanism by which IκB kinase 1 (IKK1) regulates epidermal differentiation and tumor suppression in the skin is not well understood. As two major regulatory signaling pathways that regulate epidermal homeostasis and differentiation, the p63 and Notch pathways were examined in Ikk1 mutant epidermis and keratinocytes. Ikk1 inactivation in keratinocytes resulted in increased p63 expression and repression of Notch signaling. The impaired differentiation of Ikk1(-/-) keratinocytes was partially rescued by overexpression of the active form of the Notch1 receptor, the Notch intracellular domain (NICD). In contrast, knockdown of p63 expression by RNA interference was unable to rescue the defect. These results suggest that, in the mammalian skin, IKK1 functions as a differentiation regulator and tumor suppressor through the Notch signaling pathway.

Hair-cycle dependent differential expression of ADAM 10 and ADAM 12: An immunohistochemical analysis in human hair follicles in situ

BACKGROUND

ADAM proteases play important roles in processes of development and differentiation. However, no report has been found in the literature addressing the expression and function of ADAM proteases during hair cycling.

RESULTS

Cytoplasmic expression pattern of ADAM 10, 12 was similar between normal epidermis and hair infundibulum. In addition, cytoplasmic expression of ADAM 10 was observed in the hair bulb keratinocytes and fibroblasts of dermal papilla in anagen I-III hair follicles. In contrast, decreased ADAM 10 expression was observed in the hair matrix keratinocytes as compared to the hair bulb keratinocytes in anagen I-III hair follicles. Interestingly, ADAM 10 immunoreactivity was expressed weakly in the lower portion of outer root sheath (ORS) of anagen VI hair follicles, and strong ADAM 10 expression was detected in the ORS of catagen and telogen hair follicles. By contrast, ADAM 12 expression was not detected in the hair bulb keratinocytes of anagen I-III hair follicles. ADAM 12 immunoreactivity firstly appeared in the inner root sheath ( IRS ) of anagen IV-V hair follicles and was down-regulated in the IRS and hair cortex and medulla of catagen hair follicles, Strong ADAM 12 immunoreactivity was observed in the ORS of catagen and telogen hair follicles.

MATERIAL AND METHODS

Samples of normal human skin (n = 30) were used. Immunohistochemical analysis was performed using ADAM 10, 12 specific polyclonal antibodies and a sensitive streptavidin-peroxidase technique.

CONCLUSION

Our study demonstrates a comparable staining pattern of decreased ADAM 10 immunoreactivity in hair matrix keratinocytes and the basal cell layer of normal epidermis and hair infundibulum. Expression of ADAM 10 in dermal papilla cells may imply a role in the induction and development of anagen hair follicles. In addition, expression of ADAM 10 in the ORS and hair bulb assume the involvment of ADAM 10 in the downward migration of anagen hair follicles. Furthermore ADAM 12 expression in the IRS may indicate a role in the differentiation of anagen hair follicles. Downregulation of ADAM 12 upon the onset of catagen hair stage suggests that ADAM 12 may play an important role of ADAM 12 in the apoptosis of hair follicle keratinocytes. In summary our findings suggest that ADAM 10 and 12 may be of importance for the regulation of hair cycling.

The disintegrin/metalloproteinase Adam10 is essential for epidermal integrity and Notch-mediated signaling

The disintegrin and metalloproteinase Adam10 has been implicated in the regulation of key signaling pathways that determine skin morphogenesis and homeostasis. To address the in vivo relevance of Adam10 in the epidermis, we have selectively disrupted Adam10 during skin morphogenesis and in adult skin. K14-Cre driven epidermal Adam10 deletion leads to perinatal lethality, barrier impairment and absence of sebaceous glands. A reduction of spinous layers, not associated with differences in either proliferation or apoptosis, indicates that loss of Adam10 triggers a premature differentiation of spinous keratinocytes. The few surviving K14-Adam10-deleted mice and mice in which Adam10 was deleted postnatally showed loss of hair, malformed vibrissae, epidermal hyperproliferation, cyst formation, thymic atrophy and upregulation of the cytokine thymic stromal lymphopoetin (TSLP), thus indicating non cell-autonomous multi-organ disease resulting from a compromised barrier. Together, these phenotypes closely resemble skin specific Notch pathway loss-of-function phenotypes. Notch processing is indeed strongly reduced resulting in decreased levels of Notch intracellular domain fragment and functional Notch signaling. The data identify Adam10 as the major Site-2 processing enzyme for Notch in the epidermis in vivo, and thus as a central regulator of skin development and maintenance.

RBPJkappa-dependent signaling is essential for long-term maintenance of neural stem cells in the adult hippocampus

The generation of new neurons from neural stem cells in the adult hippocampal dentate gyrus contributes to learning and mood regulation. To sustain hippocampal neurogenesis throughout life, maintenance of the neural stem cell pool has to be tightly controlled. We found that the Notch/RBPJκ-signaling pathway is highly active in neural stem cells of the adult mouse hippocampus. Conditional inactivation of RBPJκ in neural stem cells in vivo resulted in increased neuronal differentiation of neural stem cells in the adult hippocampus at an early time point and depletion of the Sox2-positive neural stem cell pool and suppression of hippocampal neurogenesis at a later time point. Moreover, RBPJκ-deficient neural stem cells displayed impaired self-renewal in vitro and loss of expression of the transcription factor Sox2. Interestingly, we found that Notch signaling increases Sox2 promoter activity and Sox2 expression in adult neural stem cells. In addition, activated Notch and RBPJκ were highly enriched on the Sox2 promoter in adult hippocampal neural stem cells, thus identifying Sox2 as a direct target of Notch/RBPJκ signaling. Finally, we found that overexpression of Sox2 can rescue the self-renewal defect in RBPJκ-deficient neural stem cells. These results identify RBPJκ-dependent pathways as essential regulators of adult neural stem cell maintenance and suggest that the actions of RBPJκ are, at least in part, mediated by control of Sox2 expression.

Non-canonical activation of Notch signaling/target genes in vertebrates

Evolutionarily conserved Notch signaling orchestrates diverse physiological mechanisms during metazoan development and homeostasis. Classically, ligand-activated Notch receptors transduce the signaling cascade through the interaction of DNA-bound CBF1-co-repressor complex. However, recent reports have demonstrated execution of a CBF1-independent Notch pathway through signaling cross-talks in various cells/tissues. Here, we have tried to congregate the reports that describe the non-canonical/CBF1-independent Notch signaling and target gene activation in vertebrates with specific emphasis on their functional relevance.

Control of hair follicle cell fate by underlying mesenchyme through a CSL-Wnt5a-FoxN1 regulatory axis

Epithelial-mesenchymal interactions are key to skin morphogenesis and homeostasis. We report that maintenance of the hair follicle keratinocyte cell fate is defective in mice with mesenchymal deletion of the CSL/RBP-Jkappa gene, the effector of "canonical" Notch signaling. Hair follicle reconstitution assays demonstrate that this can be attributed to an intrinsic defect of dermal papilla cells. Similar consequences on hair follicle differentiation result from deletion of Wnt5a, a specific dermal papilla signature gene that we found to be under direct Notch/CSL control in these cells. Functional rescue experiments establish Wnt5a as an essential downstream mediator of Notch-CSL signaling, impinging on expression in the keratinocyte compartment of FoxN1, a gene with a key hair follicle regulatory function. Thus, Notch/CSL signaling plays a unique function in control of hair follicle differentiation by the underlying mesenchyme, with Wnt5a signaling and FoxN1 as mediators.