Notch1 is essential for postnatal hair follicle development and homeostasis

Progress on mitochondria and hair follicle development in androgenetic alopecia: relationships and therapeutic perspectives

Hair loss has long been a significant concern for many individuals. Recent studies have indicated that mitochondria play a more crucial role in hair loss than previously recognized. This review summarizes the connection between mitochondrial dysfunction and hair follicle development, outlines the links between diseases related to mitochondrial disorders and hair issues, and highlights the influence of mitochondrial dysfunction on androgenetic alopecia. We discuss the cellular and signaling mechanisms associated with hair loss and examine how mitochondrial dysfunction, such as insufficient energy supply, signaling irregularities, protein/gene abnormalities, and programmed cell death, can hinder the normal proliferation, differentiation, and growth of hair follicle cells. Furthermore, we discuss current treatment approaches and potential innovative therapies, including mitochondrion-targeting drugs and advanced techniques that directly target hair follicle cells, providing fresh insights into the crucial role of mitochondria in maintaining hair follicle health and managing hair disorders. Furthermore, this review explores future therapeutic strategies and proposes that mitochondrial research could lead to groundbreaking treatments for hair loss, thus providing optimism and new avenues for the treatment of individuals experiencing hair loss. This review not only underscores the central importance of mitochondria in hair health but also emphasizes the importance of advancing research and treatment in this field.

Unlocking the genetic secrets of Dorper sheep: insights into wool shedding and hair follicle development

Dorper sheep is popular among farming enterprises with strong adaptability, disease resistance, and roughage tolerance, and an unique characteristic of natural shedding of wool. In a large number of observations on experimental sheep farms, it was found that the wool of some sheep still had not shed after May, thus manual shearing was required. Therefore, understanding the molecular mechanisms of normal hair follicles (HFs) development is crucial to revealing the improvement of sheep wool-related traits and mammalian skin-related traits. In this study, transcriptome analysis was performed on skin tissues of adult Dorper ewes in the shedding (S) and non-shedding (N) groups in September 2019, January 2020, and March 2020, respectively. The results identified 3,278 differentially expressed transcripts (DETs) in the three comparison groups within the S group, 720 DETs in the three comparison groups within the N group, and 1,342 DETs in the three comparison groups between the S-vs-N groups. Time-series expression analysis revealed 2 unique expression patterns in HF development, namely, elevated expression in the anagen phase (A pattern) and the telogen phase (T pattern). DETs with stage-specific expression had a significant presence in processes related to the hair cycle and skin development, and several classic signaling pathways involved in sheep HF development, such as Rap1, estrogen, PI3K-Akt, and MAPK, were detected. Combined analysis of DETs, time-series expression data, and weighted gene co-expression network analysis identified core genes and their transcripts influencing HF development, such as DBI, FZD3, KRT17, ZDHHC21, TMEM79, and HOXC13. Additionally, alternative splicing analysis predicted that the isoforms XM_004004383.4 and XM_012125926.3 of ZDHHC21 might play a crucial role in sheep HF development. This study is a valuable resource for explaining the morphology of normal growth and development of sheep HFs and the genetic foundation of mammalian skin-related traits. It also offers potential insights into factors influencing human hair advancement.

ASH2L Mediates Epidermal Differentiation and Hair Follicle Morphogenesis through H3K4me3 Modification

The processes of epidermal development in mammals are regulated by complex molecular mechanisms, such as histone modifications. Histone H3 lysine K4 methylation mediated by COMPASS (complex of proteins associated with Set1) methyltransferase is associated with gene activation, but its effect on epidermal lineage development remains unclear. Therefore, we constructed a mouse model of specific ASH2L (COMPASS methyltransferase core subunit) deletion in epidermal progenitor cells and investigated its effect on the development of mouse epidermal lineage. Furthermore, downstream target genes regulated by H3K4me3 were screened using RNA sequencing combined with Cleavage Under Targets and Tagmentation sequencing. Deletion of ASH2L in epidermal progenitor cells caused thinning of the suprabasal layer of the epidermis and delayed hair follicle morphogenesis in newborn mice. These phenotypes may be related to the reduced proliferative capacity of epidermal and hair follicle progenitor cells. ASH2L depletion may also lead to depletion of the epidermal stem cell pools in late mouse development. Finally, genes related to hair follicle development (Shh, Edar, and Fzd6), Notch signaling pathway (Notch2, Notch3, Hes5, and Nrarp), and ΔNp63 were identified as downstream target genes regulated by H3K4me3. Collectively, ASH2L-dependent H3K4me3 modification served as an upstream epigenetic regulator in epidermal differentiation and hair follicle morphogenesis in mice.

Small molecule agents against alopecia: Potential targets and related pathways

Alopecia has emerged as a global concern, extending beyond the middle-aged and elderly population and increasingly affecting younger individuals. Despite its growing prevalence, the treatment options and effective drugs for alopecia remain limited due to the incomplete understanding of its underlying mechanisms. Therefore, it is urgent to explore the pathogenesis of alopecia and discover novel and safer therapeutic agents. This review provided an overview of the prevailing clinical disorders of alopecia, and the key pathways and targets involved in hair growth process. Additionally, it discusses FDA-approved drugs and clinical candidates for the treatment of alopecia, and explores small molecule compounds with anti-alopecia potential in the drug discovery phase. These endeavors are expected to provide researchers with valuable scientific insights and practical information for anti-alopecia drug discovery.

Dysbiosis-activated IL-17-producing T cells promote skin immunopathological progression in mice deficient of the Notch ligand Jag1 in keratinocytes

BACKGROUND

The Notch signaling pathway is an evolutionarily conserved regulatory cascade critical in skin development and homeostasis. Mice deficient of Notch signaling molecules have impaired skin and hair follicle development associated with local tissue inflammation. However, mechanisms underlying skin inflammation and pathology resulting from defective Notch signals are not well understood.

OBJECTIVE

To dissect molecular and cellular mechanisms underlying development of skin immunopathology in mice defective of the Notch ligand Jagged-1 (Jag1).

METHODS

We assessed involvement of microbiota and immune cell subsets in skin pathogenic symptoms in Foxn1CreJag1fl/fl mice that were deficient of Jag1 in keratinocytes. We also used RNA-seq and 16S rRNA gene-seq analyses to identify molecular factors and bacterial species contributing to skin pathologic symptoms in Foxn1CreJag1fl/fl mice.

RESULTS

Compared to Jag1-sufficient littermate control mice, Foxn1CreJag1fl/fl mice had specific expansion of IL-17a-producing T cells accompanying follicular and epidermal hyperkeratosis and cyst formation while antibody blockage of IL-17a reduced the skin pathology. RNA-sequencing and 16S rRNA gene-sequencing analyses revealed dysregulated immune responses and altered microbiota compositions in the skin of Foxn1CreJag1fl/fl mice. Antibiotic treatment completely prevented over-activation of IL-17a-producing T cells and alleviated skin pathology in Foxn1CreJag1fl/fl mice.

CONCLUSION

Dysbiosis-induced over-activation of IL-17a-producing T cells is critically involved in development of skin pathology in Foxn1CreJag1fl/fl mice, establishing Foxn1CreJag1fl/fl mice as a useful model to study pathogenesis and therapeutic targets in microbiota-IL-17-mediated skin inflammatory diseases such as hidradenitis suppurativa (HS) and psoriasis.

ADAM17 variant causes hair loss via ubiquitin ligase TRIM47-mediated degradation

Hypotrichosis is a genetic disorder characterized by a diffuse and progressive loss of scalp and/or body hair. Nonetheless, the causative genes for several affected individuals remain elusive, and the underlying mechanisms have yet to be fully elucidated. Here, we discovered a dominant variant in a disintegrin and a metalloproteinase domain 17 (ADAM17) gene caused hypotrichosis with woolly hair. Adam17 (p.D647N) knockin mice mimicked the hair abnormality in patients. ADAM17 (p.D647N) mutation led to hair follicle stem cell (HFSC) exhaustion and caused abnormal hair follicles, ultimately resulting in alopecia. Mechanistic studies revealed that ADAM17 binds directly to E3 ubiquitin ligase tripartite motif-containing protein 47 (TRIM47). ADAM17 variant enhanced the association between ADAM17 and TRIM47, leading to an increase in ubiquitination and subsequent degradation of ADAM17 protein. Furthermore, reduced ADAM17 protein expression affected the Notch signaling pathway, impairing the activation, proliferation, and differentiation of HFSCs during hair follicle regeneration. Overexpression of Notch intracellular domain rescued the reduced proliferation ability caused by Adam17 variant in primary fibroblast cells.

Epidermal retinol dehydrogenases cyclically regulate stem cell markers and clock genes and influence hair composition

The hair follicle (HF) is a self-renewing adult miniorgan that undergoes drastic metabolic and morphological changes during precisely timed cyclic organogenesis. The HF cycle is known to be regulated by steroid hormones, growth factors and circadian clock genes. Recent data also suggest a role for a vitamin A derivative, all-trans-retinoic acid (ATRA), the activating ligand of transcription factors, retinoic acid receptors, in the regulation of the HF cycle. Here we demonstrate that ATRA signaling cycles during HF regeneration and this pattern is disrupted by genetic deletion of epidermal retinol dehydrogenases 2 (RDHE2, SDR16C5) and RDHE2-similar (RDHE2S, SDR16C6) that catalyze the rate-limiting step in ATRA biosynthesis. Deletion of RDHEs results in accelerated anagen to catagen and telogen to anagen transitions, altered HF composition, reduced levels of HF stem cell markers, and dysregulated circadian clock gene expression, suggesting a broad role of RDHEs in coordinating multiple signaling pathways.

Keratin Microspheres as Promising Tool for Targeting Follicular Growth

Skin is the body barrier that constrains the infiltration of particles and exogenous aggression, in which the hair follicle plays an important role. Recent studies have shown that small particles can penetrate the skin barrier and reach the hair follicle, making them a potential avenue for delivering hair growth-related substances. Interestingly, keratin-based microspheres are widely used as drug delivery carriers in various fields. In this current study, we pursue the effect of newly synthesized 3D spherical keratin particles on inducing hair growth in C57BL/6 male mice and in human hair follicle dermal papilla cells. The microspheres were created from partially sulfonated, water-soluble keratin. The keratin microspheres swelled in water to form spherical gels, which were used for further experiments. Following topical application for a period of 20 days, we observed a regrowth of hair in the previously depleted area on the dorsal part of the mice in the keratin microsphere group. This observation was accompanied by the regulation of hair-growth-related pathways as well as changes in markers associated with epidermal cells, keratin, and collagen. Interestingly, microsphere keratin treatment enhanced the cell proliferation and the expression of hair growth markers in dermal papilla cells. Based on our data, we propose that 3D spherical keratin has the potential to specifically target hair follicle growth and can be employed as a carrier for promoting hair growth-related agents.

Preliminary study of melatonin in the proliferation and apoptosis of Hu sheep dermal papilla cells in vitro

Previous studies have shown that melatonin has a certain regulatory effect on the growth of sheep wool. However, the mechanism of melatonin action remains unknown. In the present study, we aimed to understand the role of exogenous melatonin in the dermal papilla cells of Hu sheep. To confirm the optimal melatonin treatment regimen for Hu sheep dermal papilla cells, we detected the cell viability by exposing them to different concentrations of melatonin and different treatment times. The results showed that cell viability was best when dermal papilla cells were treated with 1000 pg/ml of melatonin for 48 h. According to the results of qPCR, CCK-8, EDU, Western blot, and Flow cytometry analysis, we found that 1000 pg/ml melatonin promoted the proliferation and inhibited the apoptosis of dermal papilla cells compared with the exogenous melatonin blank group (control group). Furthermore, we also found that 1000 pg/ml of melatonin promoted the cell cycle progress of dermal papilla cells according to the results of qPCR and Flow cytometry analysis. Overall, our findings showed that melatonin plays an important role in the dermal papilla cells of Hu sheep.

Familial 4p Interstitial Deletion Provides New Insights and Candidate Genes Underlying This Rare Condition

Chromosome 4p deletions can lead to two distinct phenotypic outcomes: Wolf-–Hirschhorn syndrome (a terminal deletion at 4p16.3) and less frequently reported proximal interstitial deletions (4p11-p16). Proximal 4p interstitial deletions can result in mild to moderate intellectual disability, facial dysmorphisms, and a tall thin body habitus. To date, only 35 cases of proximal 4p interstitial deletions have been reported, and only two of these cases have been familial. The critical region for this syndrome has been narrowed down to 4p15.33-15.2, but the underlying causative genes remain unclear. In this study, we report the case of a 3-year-old female with failure to thrive, developmental and motor delays, and morphological features. The mother also had a 4p15.2-p14 deletion, and the proband was found to have a 13.4-Mb 4p15.2-p14 deletion by chromosome microarray analysis. The deleted region encompasses 16 genes, five of which have a high likelihood of contributing to the phenotype: PPARGC1A, DHX15, RBPJ, STIM2, and PCDH7. These findings suggest that multiple genes are involved in this rare proximal 4p interstitial deletion syndrome. This case highlights the need for healthcare providers to be aware of proximal 4p interstitial deletions and the potential phenotypic manifestations.

An integrative analysis of the lncRNA-miRNA-mRNA competitive endogenous RNA network reveals potential mechanisms in the murine hair follicle cycle

Alopecia is a common progressive disorder associated with abnormalities of the hair follicle cycle. Hair follicles undergo cyclic phases of hair growth (anagen), regression (catagen), and rest (telogen), which are precisely regulated by various mechanisms. However, the specific mechanism associated with hair follicle cycling, which includes noncoding RNAs and regulation of competitive endogenous RNA (ceRNA) network, is still unclear. We obtained data from publicly available databases and performed real-time quantitative polymerase chain reaction validations. These analyses revealed an increase in the expression of miRNAs and a decrease in the expression of target mRNAs and lncRNAs from the anagen to telogen phase of the murine hair follicle cycle. Subsequently, we constructed the ceRNA networks and investigated their functions using enrichment analysis. Furthermore, the androgenetic alopecia (AGA) microarray data analysis revealed that several novel alopecia-related genes were identified in the ceRNA networks. Lastly, GSPT1 expression was detected using immunohistochemistry. Our analysis revealed 11 miRNAs (miR-148a-3p, miR-146a-5p, miR-200a-3p, miR-30e-5p, miR-30a-5p, miR-27a-3p, miR-143-3p, miR-27b-3p, miR-126a-3p, miR-378a-3p, and miR-22-3p), 9 target mRNAs (Atp6v1a, Cdkn1a, Gadd45a, Gspt1, Mafb, Mitf, Notch1, Plk2, and Slc7a5), and 2 target lncRNAs (Neat1 and Tug1) were differentially expressed in hair follicle cycling. The ceRNA networks were made of 12 interactive miRNA-mRNA pairs and 13 miRNA-lncRNA pairs. The functional enrichment analysis revealed the enrichment of hair growth–related signaling pathways. Additionally, GSPT1 was downregulated in androgenetic alopecia patients, possibly associated with alopecia progression. The ceRNA network identified by our analysis could be involved in regulating the hair follicle cycle.

Homeostases of epidermis and hair follicle, and development of basal cell carcinoma

Hedgehog signaling (Hh) plays a critical role in embryogenesis. On the other hand, its overactivity may cause basal cell carcinoma (BCC), the most common human cancer. Further, epidermal and hair follicle homeostases may have a key role in the development of BCC. This article describes the importance of different signaling pathways in the different stages of the two processes. The description of the homeostases brought up the importance of the Notch signaling along with the sonic hedgehog (Shh) and the Wnt pathways. Loss of the Notch signaling adversely affects the late stages of hair follicle formation and allows the bulge cells in the hair follicles to take the fate of the keratinocytes in the interfollicular epidermis. Further, the loss of Notch activity upregulates the Shh and Wnt activities, adversely affecting the homeostases. Notably, the Notch signaling is suppressed in BCC, and the peripheral BCC cells, which have low Notch activity, show drug resistance in comparison to the interior suprabasal BCC cells, which have high Notch activity.

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.

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.

Whole blood transcriptome profiling identifies candidate genes associated with alopecia in male giant pandas (Ailuropoda melanoleuca)

Background

The giant panda (Ailuropoda melanoleuca) is a threatened species endemic to China. Alopecia, characterized by thinning and broken hair, mostly occurs in breeding males. Alopecia significantly affects the health and public image of the giant panda and the cause of alopecia is unclear.

Results

Here, we researched gene expression profiles of four alopecia giant pandas and seven healthy giant pandas. All pandas were approximately ten years old and their blood samples collected during the breeding season. A total of 458 up-regulated DEGs and 211 down-regulated DEGs were identified. KEGG pathway enrichment identified that upregulated genes were enriched in the Notch signaling pathway and downregulated genes were enriched in ribosome, oxidative phosphorylation, and thermogenesis pathways. We obtained 28 hair growth-related DEGs, and identified three hub genes NOTCH1, SMAD3, and TGFB1 in PPI analysis. Five hair growth-related signaling pathways were identified with abnormal expression, these were Notch, Wnt, TGF-β, Mapk, and PI3K-Akt. The overexpression of NOTCH1 delays inner root sheath differentiation and results in hair shaft abnormalities. The delayed hair regression was associated with a significant decrease in the expression levels of TGFB1.

Conclusions

Our data confirmed the abnormal expression of several hair-related genes and pathways and identified alopecia candidate genes in the giant panda. Results of this study provide theoretical basis for the establishment of prevention and treatment strategies for giant pandas with alopecia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08501-z.

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.

Transcriptome Analysis Reveals an Inhibitory Effect of Dihydrotestosterone-Treated 2D- and 3D-Cultured Dermal Papilla Cells on Hair Follicle Growth

Dermal papillae are a target of androgen action in patients with androgenic alopecia, where androgen acts on the epidermis of hair follicles in a paracrine manner. To mimic the complexity of the dermal papilla microenvironment, a better culture model of human dermal papilla cells (DPCs) is needed. Therefore, we evaluated the inhibitory effect of dihydrotestosterone (DHT)-treated two-dimensional (2D)- and 3D-cultured DPCs on hair follicle growth. 2D- and 3D-cultured DPC proliferation was inhibited after co-culturing with outer root sheath (ORS) cells under DHT treatment. Moreover, gene expression levels of β-catenin and neural cell adhesion molecules were significantly decreased and those of cleaved caspase-3 significantly increased in 2D- and 3D-cultured DPCs with increasing DHT concentrations. ORS cell proliferation also significantly increased after co-culturing in the control-3D model compared with the control-2D model. Ki67 downregulation and cleaved caspase-3 upregulation in DHT-treated 2D and 3D groups significantly inhibited ORS cell proliferation. Sequencing showed an increase in the expression of genes related to extracellular matrix synthesis in the 3D model group. Additionally, the top 10 hub genes were identified, and the expression of nine chemokine-related genes in DHT-treated DPCs was found to be significantly increased. We also identified the interactions between transcription factor (TF) genes and microRNAs (miRNAs) with hub genes and the TF-miRNA coregulatory network. Overall, the findings indicate that 3D-cultured DPCs are more representative of in vivo conditions than 2D-cultured DPCs and contribute to our understanding of the molecular mechanisms underlying androgen-induced alopecia.

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.

The Act of Controlling Adult Stem Cell Dynamics: Insights from Animal Models

Adult stem cells (ASCs) are the undifferentiated cells that possess self-renewal and differentiation abilities. They are present in all major organ systems of the body and are uniquely reserved there during development for tissue maintenance during homeostasis, injury, and infection. They do so by promptly modulating the dynamics of proliferation, differentiation, survival, and migration. Any imbalance in these processes may result in regeneration failure or developing cancer. Hence, the dynamics of these various behaviors of ASCs need to always be precisely controlled. Several genetic and epigenetic factors have been demonstrated to be involved in tightly regulating the proliferation, differentiation, and self-renewal of ASCs. Understanding these mechanisms is of great importance, given the role of stem cells in regenerative medicine. Investigations on various animal models have played a significant part in enriching our knowledge and giving In Vivo in-sight into such ASCs regulatory mechanisms. In this review, we have discussed the recent In Vivo studies demonstrating the role of various genetic factors in regulating dynamics of different ASCs viz. intestinal stem cells (ISCs), neural stem cells (NSCs), hematopoietic stem cells (HSCs), and epidermal stem cells (Ep-SCs).

Back to the Future: From Appendage Development Toward Future Human Hair Follicle Neogenesis

Hair disorders such as alopecia and hirsutism often impact the social and psychological well-being of an individual. This also holds true for patients with severe burns who have lost their hair follicles (HFs). HFs stimulate proper wound healing and prevent scar formation; thus, HF research can benefit numerous patients. Although hair development and hair disorders are intensively studied, human HF development has not been fully elucidated. Research on human fetal material is often subject to restrictions, and thus development, disease, and wound healing studies remain largely dependent on time-consuming and costly animal studies. Although animal experiments have yielded considerable and useful information, it is increasingly recognized that significant differences exist between animal and human skin and that it is important to obtain meaningful human models. Human disease specific models could therefore play a key role in future therapy. To this end, hair organoids or hair-bearing skin-on-chip created from the patient’s own cells can be used. To create such a complex 3D structure, knowledge of hair genesis, i.e., the early developmental process, is indispensable. Thus, uncovering the mechanisms underlying how HF progenitor cells within human fetal skin form hair buds and subsequently HFs is of interest. Organoid studies have shown that nearly all organs can be recapitulated as mini-organs by mimicking embryonic conditions and utilizing the relevant morphogens and extracellular matrix (ECM) proteins. Therefore, knowledge of the cellular and ECM proteins in the skin of human fetuses is critical to understand the evolution of epithelial tissues, including skin appendages. This review aims to provide an overview of our current understanding of the cellular changes occurring during human skin and HF development. We further discuss the potential implementation of this knowledge in establishing a human in vitro model of a full skin substitute containing hair follicles and the subsequent translation to clinical use.

Pantothenic acid promotes dermal papilla cell proliferation in hair follicles of American minks via inhibitor of DNA Binding 3/Notch signaling pathway

AIMS

Pantothenic acid (PA) has been applied to treat alopecia, but the underlying mechanism is still unclear. Our study aims to explore the underlying mechanism of PA in regulating hair follicle (HF) growth.

MAIN METHODS

Mink HFs and dermal papilla (DP) cells were isolated and cultured in vitro. HFs and DP cells were treated with 0, 10, 20, 40 μg/ml PA. The effect of PA on HF growth, DP cell proliferation, cell cycle distribution, cell migration, and insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF) expressions in DP cells was measured. Moreover, the effect of PA on inhibitor of DNA binding 3 (ID3)/Notch signaling pathway was analyzed. Subsequently, ID3 was silenced to validate whether ID3/Notch signaling pathway was involved in regulating DP cell proliferation by PA.

KEY FINDINGS

Both 20 μg/ml and 40 μg/ml PA promoted HF growth, G1/S transition of DP cells and IGF-1 and VEGF expressions in DP cells, while only 20 μg/ml PA promoted cell viability and the migration of DP cells. Thus 20 μg/ml PA was chosen for the following experiments. PA treatment was found to up-regulate ID3 expression but down-regulate Notch receptor 1 (Notch1) and Notch signaling targets expressions. Furthermore, ID3 knockdown reversed PA-induced cell proliferation and inhibition of Notch1 and Notch signaling targets expressions, indicating that PA-induced DP cell proliferation and inhibition of Notch signaling were mediated via up-regulation of ID3.

SIGNIFICANCE

This study provides an underlying mechanism related to the effect of PA on stimulating DP cell proliferation.

Delineating the early transcriptional specification of the mammalian trachea and esophagus

The genome-scale transcriptional programs that specify the mammalian trachea and esophagus are unknown. Though NKX2-1 and SOX2 are hypothesized to be co-repressive master regulators of tracheoesophageal fates, this is untested at a whole transcriptomic scale and their downstream networks remain unidentified. By combining single-cell RNA-sequencing with bulk RNA-sequencing of Nkx2-1 mutants and NKX2-1 ChIP-sequencing in mouse embryos, we delineate the NKX2-1 transcriptional program in tracheoesophageal specification, and discover that the majority of the tracheal and esophageal transcriptome is NKX2-1 independent. To decouple the NKX2-1 transcriptional program from regulation by SOX2, we interrogate the expression of newly-identified tracheal and esophageal markers in Sox2/Nkx2-1 compound mutants. Finally, we discover that NKX2-1 binds directly to Shh and Wnt7b and regulates their expression to control mesenchymal specification to cartilage and smooth muscle, coupling epithelial identity with mesenchymal specification. These findings create a new framework for understanding early tracheoesophageal fate specification at the genome-wide level.

Platform Effects on Regeneration by Pulmonary Basal Cells as Evaluated by Single-Cell RNA Sequencing

Cell-based therapies have shown promise for treating myriad chronic pulmonary diseases through direct application of epithelial progenitors or by way of engineered tissue grafts or whole organs. To elucidate environmental effects on epithelial regenerative outcomes in vitro, here, we isolate and culture a population of pharmacologically expanded basal cells (peBCs) from rat tracheas. At peak basal marker expression, we simultaneously split peBCs into four in vitro platforms: organoid, air-liquid interface (ALI), engineered trachea, and engineered lung. Following differentiation, these samples are evaluated using single-cell RNA sequencing (scRNA-seq) and computational pipelines are developed to compare samples both globally and at the population level. A sample of native rat tracheal epithelium is also evaluated by scRNA-seq as a control for engineered epithelium. Overall, this work identifies platform-specific effects that support the use of engineered models to achieve the most physiologic differential outcomes in pulmonary epithelial regenerative applications.

Hes1 regulates anagen initiation and hair follicle regeneration through modulation of hedgehog signaling

Adult hair follicles undergo repeated cycling of regression (catagen), resting (telogen), and growth (anagen), which is maintained by hair follicle stem cells (HFSCs). The mechanism underlying hair growth initiation and HFSC maintenance is not fully understood. Here, by epithelial deletion of Hes1, a major Notch downstream transcriptional repressor, we found that hair growth is retarded, but the hair cycle progresses normally. Hes1 is specifically upregulated in the lower bulge/HG during anagen initiation. Accordingly, loss of Hes1 results in delayed activation of the secondary hair germ (HG) and shortened anagen phase. This developmental delay causes reduced hair shaft length but not identity changes in follicular lineages. Remarkably, Hes1 ablation results in impaired hair regeneration upon repetitive depilation. Microarray gene profiling on HFSCs indicates that Hes1 modulates Shh responsiveness in anagen initiation. Using primary keratinocyte cultures, we demonstrated that Hes1 deletion negatively influences ciliogenesis and Smoothened ciliary accumulation upon Shh treatment. Furthermore, transient application of Smoothened agonist during repetitive depilation can rescue anagen initiation and HFSC self-renewal in Hes1-deficient hair follicles. We reveal a critical function of Hes1 in potentiating Shh signaling in anagen initiation, which allows sufficient signaling strength to expand the HG and replenish HFSCs to maintain the hair cycle homeostasis.

Mice lacking the epidermal retinol dehydrogenases SDR16C5 and SDR16C6 display accelerated hair growth and enlarged meibomian glands

Retinol dehydrogenases catalyze the rate-limiting step in the biosynthesis of retinoic acid, a bioactive lipid molecule that regulates the expression of hundreds of genes by binding to nuclear transcription factors, the retinoic acid receptors. Several enzymes exhibit retinol dehydrogenase activities in vitro; however, their physiological relevance for retinoic acid biosynthesis in vivo remains unclear. Here, we present evidence that two murine epidermal retinol dehydrogenases, short-chain dehydrogenase/reductase family 16C member 5 (SDR16C5) and SDR16C6, contribute to retinoic acid biosynthesis in living cells and are also essential for the oxidation of retinol to retinaldehyde in vivo Mice with targeted knockout of the more catalytically active SDR16C6 enzyme have no obvious phenotype, possibly due to functional redundancy, because Sdr16c5 and Sdr16c6 exhibit an overlapping expression pattern during later developmental stages and in adulthood. Mice that lack both enzymes are viable and fertile but display accelerated hair growth after shaving and also enlarged meibomian glands, consistent with a nearly 80% reduction in the retinol dehydrogenase activities of skin membrane fractions from the Sdr16c5/Sdr16c6 double-knockout mice. The up-regulation of hair-follicle stem cell genes is consistent with reduced retinoic acid signaling in the skin of the double-knockout mice. These results indicate that the retinol dehydrogenase activities of murine SDR16C5 and SDR16C6 enzymes are not critical for survival but are responsible for most of the retinol dehydrogenase activity in skin, essential for the regulation of the hair-follicle cycle, and required for the maintenance of both sebaceous and meibomian glands.

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.

CD49fhigh Defines a Distinct Skin Mesenchymal Stem Cell Population Capable of Hair Follicle Epithelial Cell Maintenance

The dermis harbors distinct mesenchymal stem cell (MSC) populations, which play equally important roles as epidermal stem cells in skin homeostasis and regeneration. However, to reliably identify and directly isolate the in vivo counterpart of these cells is still challenging. Using the epidermal stem cell marker CD49f, we defined a CD49f^high distinct mesenchymal subpopulation in the dermis. In vitro and in vivo differentiation assays, and transcriptome analysis demonstrated that CD49f^high cells possess neural crest-like cell characteristics. Our results showed that the formation of hair follicle-like budding structure and the expressions of key genes regulating hair follicle development were induced when hair follicle epithelial cells were co-cultured with CD49f^high cells. We also found that CD49f^high cells activated Notch signaling in co-cultured hair follicle epithelial cells, whereas the inhibition of Notch signaling resulted in epidermal cyst-like spheres and loss of maintenance of hair follicle epithelial cell characteristics. Furthermore, we identified Itga7 and CD49f as an efficient biomarker panel for direct selection of CD49f^high skin MSCs. Our results lead to a deeper understanding of heterogeneity and the function of MSCs in the skin and may facilitate potential translational applications of these cells.

Skin Stem Cells, Their Niche and Tissue Engineering Approach for Skin Regeneration

Skin is the main organ that covers the human body and acts as a protective barrier between the human body and the environment. Skin tissue as a stem cell source can be used for transplantation in therapeutic application in terms of its properties such as abundant, easy to access, high plasticity and high ability to regenerate. The immunological profile of these cells makes it a suitable resource for autologous and allogeneic applications. The lack of major histo-compatibility complex 1 is also advantageous in its use. Epidermal stem cells are the main stem cells in the skin and are suitable cells in tissue engineering studies for their important role in wound repair. In the last 30 years, many studies have been conducted to develop substitutions that mimic human skin. Stem cell-based skin substitutions have been developed to be used in clinical applications, to support the healing of acute and chronic wounds and as test systems for dermatological and pharmacological applications. In this chapter, tissue specific properties of epidermal stem cells, composition of their niche, regenerative approaches and repair of tissue degeneration have been examined.

JunB defines functional and structural integrity of the epidermo-pilosebaceous unit in the skin

Transcription factors ensure skin homeostasis via tight regulation of distinct resident stem cells. Here we report that JunB, a member of the AP-1 transcription factor family, regulates epidermal stem cells and sebaceous glands through balancing proliferation and differentiation of progenitors and by suppressing lineage infidelity. JunB deficiency in basal progenitors results in a dermatitis-like syndrome resembling seborrheic dermatitis harboring structurally and functionally impaired sebaceous glands with a globally altered lipid profile. A fate switch occurs in a subset of JunB deficient epidermal progenitors during wound healing resulting in de novo formation of sebaceous glands. Dysregulated Notch signaling is identified to be causal for this phenotype. In fact, pharmacological inhibition of Notch signaling can efficiently restore the lineage drift, impaired epidermal differentiation and disrupted barrier function in JunB conditional knockout mice. These findings define an unprecedented role for JunB in epidermal-pilosebaceous stem cell homeostasis and its pathology.

Epidermal homeostasis is maintained by the activity of stem cells. Here, the authors show that deficiency of the transcription factor JunB leads to altered Notch signaling in stem cells, resulting in a cell fate switch and de novo formation of aberrant sebaceous glands, altered epidermal differentiation and impaired barrier function.

A boy with 13.34-Mb interstitial deletion of chromosome 4p15: A new case report and review of the literature

RATIONALE

To date, >40 cases have been described with interstitial deletions involving the 4p15 region.

PATIENT CONCERNS AND DIAGNOSIS

We report a case of a 3-year-old boy with an interstitial de novo deletion of approximately 13.34 Mb in 4p15.1-15.31 having mild developmental delay and multiple minor congenital abnormalities.

LESSONS

This case presents a clinical manifestation that is similar but not identical to other reported cases. In this report, we have provided a detailed description of a 3-year-old patient with an interstitial 4p deletion and mildly affected phenotype. We discuss the possible involvement of SLIT2, KCNIP4, and LGI2 in cortical development and RBPJ in skeletal abnormalities.

Regulatory T Cells in Skin Facilitate Epithelial Stem Cell Differentiation

The maintenance of tissue homeostasis is critically dependent on the function of tissue-resident immune cells and the differentiation capacity of tissue-resident stem cells (SCs). How immune cells influence the function of SCs is largely unknown. Regulatory T cells (Tregs) in skin preferentially localize to hair follicles (HFs), which house a major subset of skin SCs (HFSCs). Here, we mechanistically dissect the role of Tregs in HF and HFSC biology. Lineage-specific cell depletion revealed that Tregs promote HF regeneration by augmenting HFSC proliferation and differentiation. Transcriptional and phenotypic profiling of T_regs and HFSCs revealed that skin-resident Tregs preferentially express high levels of the Notch ligand family member, Jagged 1 (Jag1). Expression of Jag1 on Tregs facilitated HFSC function and efficient HF regeneration. Taken together, our work demonstrates that Tregs in skin play a major role in HF biology by promoting the function of HFSCs.

Down-regulation of E-cadherin enhances prostate cancer chemoresistance via Notch signaling

Background

The chemoresistance of prostate cancer (PCa) is invariably associated with the aggressiveness and metastasis of this disease. New emerging evidence indicates that the epithelial-to-mesenchymal transition (EMT) may play pivotal roles in the development of chemoresistance and metastasis. As a hallmark of EMT, E-cadherin is suggested to be a key marker in the development of chemoresistance. However, the molecular mechanisms underlying PCa chemoresistance remain unclear. The current study aimed to explore the association between EMT and chemoresistance in PCa as well as whether changing the expression of E-cadherin would affect PCa chemoresistance.

Methods

Parental PC3 and DU145 cells and their chemoresistant PC3-TxR and DU145-TxR cells were analyzed. PC3-TxR and DU145-TxR cells were transfected with E-cadherin-expressing lentivirus to overexpress E-cadherin; PC3 and DU145 cells were transfected with small interfering RNA to silence E-cadherin. Changes of EMT phenotype-related markers and signaling pathways were assessed by Western blotting and quantitative real-time polymerase chain reaction. Tumor cell migration, invasion, and colony formation were then evaluated by wound healing, transwell, and colony formation assays, respectively. The drug sensitivity was evaluated using MTS assay.

Results

Chemoresistant PC3-TxR and DU145-TxR cells exhibited an invasive and metastatic phenotype that associated with EMT, including the down-regulation of E-cadherin and up-regulation of Vimentin, Snail, and N-cadherin, comparing with that of parental PC3 and DU145 cells. When E-cadherin was overexpressed in PC3-TxR and DU145-TxR cells, the expression of Vimentin and Claudin-1 was down-regulated, and tumor cell migration and invasion were inhibited. In particular, the sensitivity to paclitaxel was reactivated in E-cadherin-overexpressing PC3-TxR and DU145-TxR cells. When E-cadherin expression was silenced in parental PC3 and DU145 cells, the expression of Vimentin and Snail was up-regulated, and, particularly, the sensitivity to paclitaxel was decreased. Interestingly, Notch-1 expression was up-regulated in PC3-TxR and DU145-TxR cells, whereas the E-cadherin expression was down-regulated in these cells comparing with their parental cells. The use of γ-secretase inhibitor, a Notch signaling pathway inhibitor, significantly increased the sensitivity of chemoresistant cells to paclitaxel.

Conclusion

The down-regulation of E-cadherin enhances PCa chemoresistance via Notch signaling, and inhibiting the Notch signaling pathway may reverse PCa chemoresistance.

Regeneration of hair and other skin appendages: A microenvironment-centric view

Advances in skin regeneration have resulted in techniques and products that have allowed regeneration of both the dermis and epidermis. Yet complete skin regeneration requires the adnexal skin structures. Thus it is crucial to understand the regenerative potential of hair follicles where genetic, nutritional, and hormonal influences have important effects and are critical for skin regeneration. The follicular stem cell niche serves as an anatomical compartment, a structural unit, a functional integrator, and a dynamic regulator necessary to sustain internal homeostasis and respond to outside stimuli. In particular, mechanics such as pressure, compression, friction, traction, stretch, shear, and mechanical wounding can influence hair loss or growth. Relevant niche signaling pathways such as Wnt, bone morphogenetic protein, fibroblast growth factor, Shh, and Notch may yield potential targets for therapeutic interventions.

The Notch Intracellular Domain Has an RBPj-Independent Role during Mouse Hair Follicular Development

Ligand-dependent activation, γ-secretase-processed cleavage, and recombining binding protein Jk (RBPj)-mediated downstream transcriptional activities of Notch receptors constitute the "canonical" Notch signaling pathway, which is essential for skin organogenesis. However, in Msx2-Cre mice, keratinocyte-specific deletion of the Rbpj gene in utero produced a significantly milder phenotype than either global Notch or γ-secretase loss. Herein, we investigated the underlying mechanisms for this apparent noncanonical signal using mouse genetics. We found no evidence that ligand back-signaling contributed to skin organogenesis. The perdurance of RBPj protein did not establish an epigenetic memory of a canonical signal in the youngest epidermal stem cells, and Notch targets were not derepressed. We provide evidence that γ-secretase-dependent but RBPj-independent Notch intracellular domain activity operating in the first hair follicles is responsible for a delay in follicular destruction, which results in lower serum thymic stromal lymphopoietin levels, milder B-cell lymphoproliferative disease, and improved survival in Msx2-Cre(+/tg);Rbpj(f/f) mice. Minimal amounts of the Notch intracellular domain were sufficient for rescue, which was not mediated by transcription, suggesting that the Notch intracellular domain is acting through a novel mechanism.

A facile one-step strategy for the generation of conditional knockout mice to explore the role of Notch1 in oroesophageal tumorigenesis

NOTCH1 plays an important role in epithelial differentiation and carcinogenesis. To investigate the impact of Notch1 inactivation in oroesophageal epithelium, we generated conditional knockout (cKO) mice, using a combined construct which induces the expression of single guide RNA targeting Notch1 and Cas9 by the KRT14 promoter. The cKO mice exhibited patchy hair loss and multiple NOTCH1-negative areas in the tongue epithelium, indicative of heterogeneous knockout. The cKO mice showed susceptibility to esophageal tumorigenesis, underscoring Notch1 as a tumor suppressor. Our one-step strategy for generation of cKO mice provides a versatile method to examine a gene function in vivo.

Crosstalk between Nrf2 and Notch signaling

The transcription factor Nrf2 (nuclear factor, erythroid derived 2, like 2) belongs to the CNC-bZip protein family, forming a transcriptosome with its direct heterodimer partner, sMaf, and co-factors such as CBP/p300. Nrf2 binds to one or more AREs (antioxidant response elements) that are located in the gene regulatory regions of the hundreds of Nrf2 target genes. The AREs are key enhancers that are activated in response to endogenous or exogenous stresses to maintain cellular and tissue homeostasis. Data emanating from gene expression microarray analyses comparing Nrf2-disrupted and wild-type mouse embryonic fibroblasts (MEF) showed that expression of Notch1 and Notch-signaling-related genes were decreased in Nrf2-disrupted cells. This observation triggered our research on Nrf2-Notch crosstalk. A functional ARE has been identified upstream of the Notch1 major transcription start site. Furthermore, an Rbpjκ binding site is conserved on the promoters of Nrf2 among animal species. Notch1 is one of the transmembrane Notch family receptors that drive Notch signaling, together with the Rbpjκ transcription factor. After canonically accepting ligands such as Jags and Deltas, the receptor undergoes cleavage to yield the Notch intracellular domain, which translocates to the nucleus. Recent studies using conditional knockout mice indicate that Notch1 as well as Notch2 plays an important role postnatally in liver development and in maintenance of hepatic function. In this review, we summarize current understanding of the role of reciprocal transcriptional regulation between Nrf2 and Notch in adult liver from studies using Nrf2, Keap1, and Notch1 genetically engineered mice.

Transcription Factor CTIP2 Maintains Hair Follicle Stem Cell Pool and Contributes to Altered Expression of LHX2 and NFATC1

Transcription factor CTIP2 (COUP-TF-interacting protein 2), also known as BCL11B, is expressed in hair follicles of embryonic and adult skin. Ctip2-null mice exhibit reduced hair follicle density during embryonic development. In contrast, conditional inactivation of Ctip2 in epidermis (Ctip2^ep−/− mice) leads to a shorter telogen and premature entry into anagen during the second phase of hair cycling without a detectable change in the number of hair follicles. Keratinocytes of the bulge stem cells niche of Ctip2^ep−/− mice proliferate more and undergo reduced apoptosis than the corresponding cells of wild-type mice. However, premature activation of follicular stem cells in mice lacking CTIP2 leads to the exhaustion of this stem cell compartment in comparison to Ctip2^L2/L2 mice, which retained quiescent follicle stem cells. CTIP2 modulates expression of genes encoding EGFR and NOTCH1 during formation of hair follicles, and those encoding NFATC1 and LHX2 during normal hair cycling in adult skin. The expression of most of these genes is disrupted in mice lacking CTIP2 and these alterations may underlie the phenotype of Ctip2-null and Ctip2^ep−/− mice. CTIP2 appears to serve as a transcriptional organizer that integrates input from multiple signaling cues during hair follicle morphogenesis and hair cycling.

Wnt/β-Catenin Signaling Pathway in Skin Carcinogenesis and Therapy

Cooperating with other signaling pathways, Wnt signaling controls cell proliferation, morphology, motility, and embryonic development destination and maintains the homeostasis of tissues including skin, blood, intestine, and brain by regulating somatic stem cells and their niches throughout adult life. Abnormal regulation of Wnt pathways leads to neoplastic proliferation in these tissues. Recent research shows that Wnt signaling is also associated with the regulation of cancer stem cells (CSCs) through a similar mechanism to that observed in normal adult stem cells. Thus, the Wnt/β-catenin signaling pathway has been intensively studied and characterized. For this review, we will focus on the regulation of the Wnt/β-catenin signaling pathway in skin cancer. With the important role in stemness and skin CSC proliferation, the Wnt/β-catenin signaling pathway and its elements have the potential to be targets for skin cancer therapy.

Skin manifestations in CDG

The group of congenital disorders of glycosylation (CDG) has expanded tremendously since its first description in 1980, with around 70 distinct disorders described to date. A great phenotypic variability exists, ranging from multisystem disease to single organ involvement. Skin manifestations, although inconsistently present, are part of this broad clinical spectrum. Indeed, the presence of inverted nipples, fat pads and orange peel skin in a patient with developmental delay are considered as a hallmark of CDG, particularly seen in PMM2 deficiency. However, over the years many more dermatological findings have been observed (e.g., ichthyosis, cutis laxa, tumoral calcinosis…). In this review we will discuss the variety of skin manifestations reported in CDG. Moreover, we will explore the possible mechanisms that link a certain glycosylation deficiency to its skin phenotype.

Heterogeneity and plasticity of epidermal stem cells

The epidermis is an integral part of our largest organ, the skin, and protects us against the hostile environment. It is a highly dynamic tissue that, during normal steady-state conditions, undergoes constant turnover. Multiple stem cell populations residing in autonomously maintained compartments facilitate this task. In this Review, we discuss stem cell behaviour during normal tissue homeostasis, regeneration and disease within the pilosebaceous unit, an integral structure of the epidermis that is responsible for hair growth and lubrication of the epithelium. We provide an up-to-date view of the pilosebaceous unit, encompassing the heterogeneity and plasticity of multiple discrete stem cell populations that are strongly influenced by external cues to maintain their identity and function.

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.

De Novo Transcriptome Assembly and Differential Gene Expression Profiling of Three Capra hircus Skin Types during Anagen of the Hair Growth Cycle

Despite that goat is one of the best nonmodel systems for villus growth studies and hair biology, limited gene resources associated with skin or hair follicles are available. In the present study, using Illumina/Solexa sequencing technology, we de novo assembled 130 million mRNA-Seq reads into a total of 49,115 contigs. Searching public databases revealed that about 45% of the total contigs can be annotated as known proteins, indicating that some of the assembled contigs may have previously uncharacterized functions. Functional classification by KOG and GO showed that activities associated with metabolism are predominant in goat skin during anagen phase. Many signaling pathways was also created based on the mapping of assembled contigs to the KEGG pathway database, some of which have been previously demonstrated to have diverse roles in hair follicle and hair shaft formation. Furthermore, gene expression profiling of three skin types identified ~6,300 transcript-derived contigs that are differentially expressed. These genes mainly enriched in the functional cluster associated with cell cycle and cell division. The large contig catalogue as well as the genes which were differentially expressed in different skin types provide valuable candidates for further characterization of gene functions.

Mastermind-like transcriptional co-activator-mediated Notch signaling is indispensable for maintaining conjunctival epithelial identity

Conjunctival goblet cells primarily synthesize mucins to lubricate the ocular surface, which is essential for normal vision. Notch signaling has been known to associate with goblet cell differentiation in intestinal and respiratory tracts, but its function in ocular surface has yet to be fully characterized. Herein, we demonstrate that conditional inhibition of canonical Notch signaling by expressing dominant negative mastermind-like 1 (dnMaml1) in ocular surface epithelia resulted in complete suppression of goblet cell differentiation during and subsequent to development. When compared with the ocular surface of wild-type mice (OS(Wt)), expression of dnMaml1 at the ocular surface (OS(dnMaml1)) caused conjunctival epithelial hyperplasia, aberrant desquamation, failure of Mucin 5ac (Muc5ac) synthesis, subconjunctival inflammation and epidermal metaplasia in cornea. In addition, conditional deletion of Notch1 from the ocular surface epithelia partially recapitulated OS(dnMaml1) phenotypes. We have demonstrated that N1-ICD (Notch1 intracellular domain) transactivated the mouse Krüppel-like factor 4 (Klf) promoter and that Klf4 directly bound to and significantly potentiated the Muc5ac promoter. By contrast, OS(dnMaml1) dampened Klf4 and Klf5 expression, and diminished Muc5ac synthesis. Collectively, these findings indicated that Maml-mediated Notch signaling plays a pivotal role in the initiation and maintenance of goblet cell differentiation for normal ocular surface morphogenesis and homeostasis through regulation of Klf4 and Klf5.