Lhx2 differentially regulates Sox9, Tcf4 and Lgr5 in hair follicle stem cells to promote epidermal regeneration after injury

Single-cell transcriptome profiling reveals cell type-specific variation and development in HLA expression of human skin

Skin, the largest organ of body, is a highly immunogenic tissue with a diverse collection of immune cells. Highly polymorphic human leukocyte antigen (HLA) molecules have a central role in coordinating immune responses as recognition molecules. Nevertheless, HLA gene expression patterns among diverse cell types within a specific organ, like the skin, have yet to be thoroughly investigated, with stromal cells attracting much less attention than immune cells. To illustrate HLA expression profiles across different cell types in the skin, we performed single-cell RNA sequencing (scRNA-seq) analyses on skin datasets, covering adult and fetal skin, and hair follicles as the skin appendages. We revealed the variation in HLA expression between different skin populations by examining normal adult skin datasets. Moreover, we evaluated the potential immunogenicity of multiple skin populations based on the expression of classical HLA class I genes, which were well represented in all cell types. Furthermore, we generated scRNA-seq data of developing skin from fetuses of 15 post conception weeks (PCW), 17 PCW, and 22 PCW, delineating the dynamic expression of HLA genes with cell type-dependent variation among various cell types during development. Notably, the pseudotime trajectory analysis unraveled the significant variance in HLA genes during the evolution of vascular endothelial cells. Moreover, we uncovered the immune-privileged properties of hair follicles at single-cell resolution. Our study presents a comprehensive single-cell transcriptomic landscape of HLA genes in the skin, which provides new insights into variation in HLA molecules and offers a clue for allogeneic skin transplantation.

Cellular plasticity in reprogramming, rejuvenation and tumorigenesis: a pioneer TF perspective

The multistep process of in vivo reprogramming, mediated by the transcription factors (TFs) Oct4, Sox2, Klf4, and c-Myc (OSKM), holds great promise for the development of rejuvenating and regenerative strategies. However, most of the approaches developed so far are accompanied by a persistent risk of tumorigenicity. Here, we review the groundbreaking effects of in vivo reprogramming with a particular focus on rejuvenation and regeneration. We discuss how the activity of pioneer TFs generates cellular plasticity that may be critical for inducing not only reprogramming and regeneration, but also cancer initiation. Finally, we highlight how a better understanding of the uncoupled control of cellular identity, plasticity, and aging during reprogramming might pave the way to the development of rejuvenating/regenerating strategies in a nontumorigenic manner.

Recent progress in hair follicle stem cell markers and their regulatory roles

Hair follicle stem cells (HFSCs) in the bulge are a multipotent adult stem cell population. They can periodically give rise to new HFs and even regenerate the epidermis and sebaceous glands during wound healing. An increasing number of biomarkers have been used to isolate, label, and trace HFSCs in recent years. Considering more detailed data from single-cell transcriptomics technology, we mainly focus on the important HFSC molecular markers and their regulatory roles in this review.

The Biology and Genomics of Human Hair Follicles: A Focus on Androgenetic Alopecia

Androgenetic alopecia is a highly prevalent condition mainly affecting men. This complex trait is related to aging and genetics; however, multiple other factors, for example, lifestyle, are also involved. Despite its prevalence, the underlying biology of androgenetic alopecia remains elusive, and thus advances in its treatment have been hindered. Herein, we review the functional anatomy of hair follicles and the cell signaling events that play a role in follicle cycling. We also discuss the pathology of androgenetic alopecia and the known molecular mechanisms underlying this condition. Additionally, we describe studies comparing the transcriptional differences in hair follicles between balding and non-balding scalp regions. Given the genetic contribution, we also discuss the most significant risk variants found to be associated with androgenetic alopecia. A more comprehensive understanding of this pathology may be generated through using multi-omics approaches.

Tenascin-C expressing touch dome keratinocytes exhibit characteristics of all epidermal lineages

The touch dome (TD) keratinocytes are specialized epidermal cells that intimately associate with the light touch sensing Merkel cells (MCs). The TD keratinocytes function as a niche for the MCs and can induce de novo hair follicles upon stimulation; however, how the TD keratinocytes are maintained during homeostasis remains unclear. scRNA-seq identified a specific TD keratinocyte marker, Tenascin-C (TNC). Lineage tracing of Tnc-expressing TD keratinocytes revealed that these cells maintain themselves as an autonomous epidermal compartment and give rise to MCs upon injury. Molecular characterization uncovered that, while the transcriptional and chromatin landscape of the TD keratinocytes is remarkably similar to that of the interfollicular epidermal keratinocytes, it also shares certain molecular signatures with the hair follicle keratinocytes. Our study highlights that the TD keratinocytes in the adult skin have molecular characteristics of keratinocytes of diverse epidermal lineages.

SOX family transcription factors as therapeutic targets in wound healing: A comprehensive review

The SOX family plays a vital role in determining the fate of cells and has garnered attention in the fields of cancer research and regenerative medicine. It also shows promise in the study of wound healing, as it actively participates in the healing processes of various tissues such as skin, fractures, tendons, and the cornea. However, our understanding of the mechanisms behind the SOX family's involvement in wound healing is limited compared to its role in cancer. Gaining insight into its role, distribution, interaction with other factors, and modifications in traumatized tissues could provide valuable new knowledge about wound healing. Based on current research, SOX2, SOX7, and SOX9 are the most promising members of the SOX family for future interventions in wound healing. SOX2 and SOX9 promote the renewal of cells, while SOX7 enhances the microvascular environment. The SOX family holds significant potential for advancing wound healing research. This article provides a comprehensive review of the latest research advancements and therapeutic tools related to the SOX family in wound healing, as well as the potential benefits and challenges of targeting the SOX family for wound treatment.

Biological and mechanical influence of three-dimensional microenvironment formed in microwell on multicellular spheroids composed of heterogeneous hair follicle stem cells

Hair loss caused by malfunction of the hair follicle stem cells (HFSCs) and physical damage to the skin is difficult to recover from naturally. To overcome these obstacles to hair follicle (HF) regeneration, it is essential to understand the three-dimensional (3D) microenvironment and interactions of various cells within the HFs. Therefore, 3D cell culture technology has been used in HF regeneration research; specifically, multicellular spheroids have been generally adapted to mimic the 3D volumetric structure of the HF. In this study, we culture HF-derived cells, which are mainly composed of HFSCs, in the form of 3D spheroids using a microwell array and discuss the effects of the 3D cellular environment on HF morphogenesis by expression measurements of Sonic hedgehog signaling and stem cell markers in the HF spheroids. Additionally, the influences of microwell depth on HF spheroid formation and biological conditions were investigated. The biomolecular diffusion and convective flow in the microwell were predicted using computational fluid dynamics, which allows analysis of the physical stimulations occurring on the spheroid at the micro-scale. Although a simple experimental method using the microwell array was adopted in this study, the results provide fundamental insights into the physiological phenomena of HFs in the 3D microenvironment, and the numerical analysis is expected to shed light on the investigation of the geometric parameters of the microwell system.

Insights into Repeated Renal Injury Using RNA-Seq with Two New RPTEC Cell Lines

Renal proximal tubule epithelial cells (RPTECs) are a primary site for kidney injury. We created two RPTEC lines from CD-1 mice immortalized with hTERT (human telomerase reverse transcriptase) or SV40 LgT antigen (Simian Virus 40 Large T antigen). Our hypothesis was that low-level, repeated exposure to subcytotoxic levels of 0.25-2.5 μM cisplatin (CisPt) or 12.5-100 μM aflatoxin B1 (AFB1) would activate distinctive genes and pathways in these two differently immortalized cell lines. RNA-seq showed only LgT cells responded to AFB1 with 1139 differentially expressed genes (DEGs) at 72 h. The data suggested that AFB1 had direct nephrotoxic properties on the LgT cells. However, both the cell lines responded to 2.5 μM CisPt from 3 to 96 h expressing 2000-5000 total DEGs. For CisPt, the findings indicated a coordinated transcriptional program of injury signals and repair from the expression of immune receptors with cytokine and chemokine secretion for leukocyte recruitment; robust expression of synaptic and substrate adhesion molecules (SAMs) facilitating the expression of neural and hormonal receptors, ion channels/transporters, and trophic factors; and the expression of nephrogenesis transcription factors. Pathway analysis supported the concept of a renal repair transcriptome. In summary, these cell lines provide in vitro models for the improved understanding of repeated renal injury and repair mechanisms. High-throughput screening against toxicant libraries should provide a wider perspective of their capabilities in nephrotoxicity.

Wound-Induced Hair Neogenesis: A Portal to the Development of New Therapies for Hair Loss and Wound Regeneration

Adult mammals retain the remarkable ability to regenerate hair follicles after wounding. Wound-induced hair neogenesis (WIHN) in many ways recapitulates embryogenesis. The origin of the stem cells that give rise to a nascent hair follicle after wounding and the role of mesenchymal cells and signaling pathways responsible for this regenerative phenomenon are slowly being elucidated. WIHN provides a potential therapeutic window for manipulating cell fate by the introduction of factors during the wound healing process to enhance hair follicle formation.

DNA dioxygenases Tet2/3 regulate gene promoter accessibility and chromatin topology in lineage-specific loci to control epithelial differentiation

Execution of lineage-specific differentiation programs requires tight coordination between many regulators including Ten-eleven translocation (TET) family enzymes, catalyzing 5-methylcytosine oxidation in DNA. Here, by using Keratin 14-Cre-driven ablation of Tet genes in skin epithelial cells, we demonstrate that ablation of Tet2/Tet3 results in marked alterations of hair shape and length followed by hair loss. We show that, through DNA demethylation, Tet2/Tet3 control chromatin accessibility and Dlx3 binding and promoter activity of the Krt25 and Krt28 genes regulating hair shape, as well as regulate interactions between the Krt28 gene promoter and distal enhancer. Moreover, Tet2/Tet3 also control three-dimensional chromatin topology in Keratin type I/II gene loci via DNA methylation-independent mechanisms. These data demonstrate the essential roles for Tet2/3 in establishment of lineage-specific gene expression program and control of Dlx3/Krt25/Krt28 axis in hair follicle epithelial cells and implicate modulation of DNA methylation as a novel approach for hair growth control.

Downregulation of Lhx2 Markedly Impairs Wound Healing in Mouse Fetus

Multiple transitions occur in the healing ability of the skin during embryonic development in mice. Embryos up to embryonic day 13 (E13) regenerate completely without a scar after full-thickness wounding. Then, up to E16, dermal structures can be formed, including skin appendages such as hair follicles. However, after E17, wound healing becomes incomplete, and scar formation is triggered. Lhx2 regulates the switch between maintenance and activation of hair follicle stem cells, which are involved in wound healing. Therefore, we investigated the role of Lhx2 in fetal wound healing. Embryos of ICR mice were surgically wounded at E13, E15, and E17, and the expression of Lhx2 along with mitotic (Ki67 and p63) and epidermal differentiation (keratin-10 and loricrin) markers was analyzed. The effect of Lhx2 knockdown on wound healing was observed. Lhx2 expression was not noticed in E13 due to the absence of folliculogenesis but was evident in the epidermal basal layer of E15 and E17 and at the base of E17 wounds, along with Ki67 and p63 expression. Furthermore, Lhx2 knockdown in E15 markedly prolonged wound healing and promoted clear scar formation. Therefore, Lhx2 expression is involved in cell division associated with wound healing and may contribute to scar formation in late embryos.

LHX2 Enhances the Malignant Phenotype of Esophageal Squamous Cell Carcinoma by Upregulating the Expression of SERPINE2

LHX2 dysregulations have been found to present in cancers, but the function of LHX2 in esophageal squamous cell carcinoma (ESCC) remains unknown. Here, we report that LHX2 was upregulated in ESCC tissues in comparison to the LHX2 levels in adjacent normal tissues. Loss- and gain-of-function experiments demonstrated that the knockdown of LHX2 markedly inhibited ESCC cells’ proliferation, migration, invasion, tumor growth and metastasis, whereas the overexpression of LHX2 had the opposite effects. A mechanistic investigation revealed that LHX2 bound to the promoter of SERPINE2 gene and transcriptionally regulated the expression of SERPINE2. Collectively, LHX2 facilitates ESCC tumor progression, and it could be a potential therapeutic target for ESCC.

Differential distribution and genetic determination of eccrine sweat glands and hair follicles in the volar skin of C57BL/6 mice and SD rats

BACKGROUND

Eccrine sweat glands (ESGs) and hair follicles (HFs) are the prominent skin appendages regulating human body temperature. C57BL/6 mice and Sprague-Dawley (SD) rats are the most commonly used model animals for studying ESGs and HFs. Previous studies have shown the distribution of ESGs and HFs in volar hindfeet of C57BL/6 mice, but there are few or no reports on the distribution of ESGs and HFs in volar forefeet of C57BL/6 mice and volar feet of SD rats. Here, we investigated the differential distribution and genetic determination of ESGs and HFs in the volar skin of C57BL/6 mice and SD rats through gross observation, iodine-starch sweat test, double staining with Nile Blue A and Oil Red O, hematoxylin and eosin (HE) staining, double immunofluorescence staining of LIM Homeobox 2 (LHX2)/Na⁺-K⁺-ATPase α1(NKA) or LHX2/Na⁺-K⁺-2Cl^－ cotransporter 1 (NKCC1), and qRT-PCR detection of ESG-related gene Engrailed 1 (En1) and HF-related gene LHX2.

RESULTS

The results showed ESGs but no HFs in the footpads of C57BL/6 mice and SD rats, both ESGs and HFs in the inter-footpads (IFPs) of C57BL/6 mice, and neither ESGs nor HFs in the IFPs of SD rats. The relative quantitative change in En1 was consistent with the differential distribution of ESGs, and the relative quantitative change of LHX2 was consistent with the differential distribution of HFs.

CONCLUSION

C57BL/6 mice and SD rats had their own characteristics in the distribution of ESGs and HFs in the volar skin, and researchers should choose mice or rats, and even forefeet or hindfeet as their research object according to different purposes. The study provides a basis for selection of optimal animal models to study development, wound healing and regeneration of skin appendages.

Impaired differentiation potential of CD34-positive cells derived from mouse hair follicles after long-term culture

Hair follicle epithelial stem cells (HFSCs), which exist in the bulge region, have important functions for homeostasis of skin as well as hair follicle morphogenesis. Although several methods for isolation of HFSCs using a variety of stem cell markers have been reported, few investigations regarding culture methods or techniques to yield long-term maintenance of HFSCs in vitro have been conducted. In the present study, we screened different types of commercially available culture medium for culturing HFSCs. Among those tested, one type was shown capable of supporting the expression of stem cell markers in cultured HFSCs. However, both the differentiation potential and in vivo hair follicle-inducing ability of HFSCs serially passaged using that optimal medium were found to be impaired, probably because of altered responsiveness to Wnt signaling. The changes noted in HFSCs subjected to a long-term culture suggested that the Wnt signaling-related environment must be finely controlled for maintenance of the cells.

LGR5 is a conserved marker of hair follicle stem cells in multiple species and is present early and throughout follicle morphogenesis

Hair follicle stem cells are key for driving growth and homeostasis of the hair follicle niche, have remarkable regenerative capacity throughout hair cycling, and display fate plasticity during cutaneous wound healing. Due to the need for a transgenic reporter, essentially all observations related to LGR5-expressing hair follicle stem cells have been generated using transgenic mice, which have significant differences in anatomy and physiology from the human. Using a transgenic pig model, a widely accepted model for human skin and human skin repair, we demonstrate that LGR5 is a marker of hair follicle stem cells across species in homeostasis and development. We also report the strong similarities and important differences in expression patterns, gene expression profiles, and developmental processes between species. This information is important for understanding the fundamental differences and similarities across species, and ultimately improving human hair follicle regeneration, cutaneous wound healing, and skin cancer treatment.

The stem cell quiescence and niche signaling is disturbed in the hair follicle of the hairpoor mouse, an MUHH model mouse

BACKGROUND

Hair follicle stem cells (HFSC) play an essential role in the maintenance of hair homeostasis; during the hair cycle, HFSC remain quiescent for most of its duration. The hairpoor mouse (+ /Hr^Hp), an animal model of Marie-Unna hypotrichosis (MUHH), overexpresses hairless in the bulge, inner root sheath, and outer root sheath of HF and shows the same phenotype as in MUHH patients manifesting sparse hair with progression to alopecia with age. The aim of this study was to gain an understanding of the hair cycle and the status of HFSC during the hair cycle of the hairpoor mouse in order to delineate the pathogenesis of MUHH.

METHODS

H&E staining was performed in order to define the state of the hair follicle. FACS analysis and immunostaining were performed at the 1st and 2nd telogen stages for observation of the HFSC. A label retaining assay was performed to determine the quiescent state of hair follicles. qRT-PCR was performed to determine expression of factors involved in niche signaling and Wnt signaling.

RESULTS

We observed a drastic decrease in the number of hair follicles after the 1st telogen, followed by an intensified disturbance in the hair cycle with shorter anagen as well as 2nd telogen in the hairpoor mouse. A dramatic reduction in the number of CD34 expressing bulges as well as cells was observed at the telogen of the HFs, with prominent high proliferation of bulge cells, suggesting the loss of HFSC quiescence in the hairpoor mouse. The increased cell proliferation in HF was reiterated following the synchronization of the hair cycle, leading to acceleration of HF cycling. Reduced expression of Fgf18 and Bmp6, the factors involved in HFSC quiescence, was observed in the HFSC niche of the hairpoor mouse. In addition, disturbed expression of Wnt signaling molecules including Wnt7b, Wnt10b, and Sfrp1 was observed, which induced the telogen-to-anagen transition of HFs in the hairpoor mouse.

CONCLUSIONS

These results indicate that the quiescent state of HFSC is not properly maintained in the hairpoor mouse, consequently leading HFs to the completely disarrayed hair cycle. These findings may provide an understanding of an underlying mechanism for development of alopecia with age in MUHH patients.

Ptch2 is a Potential Regulator of Mesenchymal Stem Cells

Ptch receptors 1 and 2 mediate Hedgehog signaling pivotal for organ development and homeostasis. In contrast to embryonic lethal Ptch1^−/− phenotype, Ptch2^−/− mice display no effect on gross phenotype. In this brief report, we provide evidence of changes in the putative incisor mesenchymal stem cell (MSC) niches that contribute to accelerated incisor growth, as well as intriguing changes in the bones and skin which suggest a role for Ptch2 in the regulation of MSCs and their regenerative potential. We employed histological, immunostaining, and computed tomography (µCT) analyses to analyze morphological differences between Ptch2^−/− and wild-type incisors, long bones, and skins. In vitro CFU and differentiation assays were used to demonstrate the MSC content and differentiation potential of Ptch2^−/− bone marrow stromal cells. Wound healing assay was performed in vivo and in vitro on 8-week-old mice to assess the effect of Ptch2 on the wound closure. Loss of Ptch2 causes increases in the number of putative MSCs in the continuously growing incisor, associated with increased vascularization observed in the tooth mesenchyme and the neurovascular bundle. Increased length and volume of Ptch2^−/− bones is linked with the increased number and augmented in vitro differentiation potential of MSCs in the bone marrow. Dynamic changes in the Ptch2^−/− skin thickness relate to changes in the mesenchymal compartment and impact the wound closure potential. The effects of Ptch2 abrogation on the postnatal MSCs suggest a crucial role for Ptch2 in Hedgehog signaling regulation of the organ regenerative potential.

Bioactive Small Molecule Enhances Skin Burn Wound Healing and Hair Follicle Regeneration by Activating PI3K/AKT Signaling Pathway: A Preclinical Evaluation in Animal Model

Rational: A bioactive small molecule of precision medicine involves targeted therapies. Shikonin, a herbal extract, is an active small molecule that is traditionally used in wound healing for its anti-tumor and anti-inflammatory properties. Therefore, the present study aims to evaluate the anti-inflammatory role of shikonin in skin burn wound healing and hair follicle regeneration and to identify molecular signaling pathways that promote the regeneration. Method: A secondary skin burn model of mice was established by conventional method. The burn wound was externally treated with shikonin ointment and excipient treated mice were used as controls. Skin samples were taken on the day 3 and 7 after drug treatment and the dosage was unified in the experiments. The wound healing process was observed by histopathological and immunofluorescence (IF) staining. The proliferation of hair follicle cells in wound skin was tracked by 5-Ethynyl-2'-deoxyuridne (EdU) staining. The inflammatory factors at the wound healing site were quantified by polymerase chain reaction (qPCR). The PI3K/Akt, P65, Ki67 signaling proteins and Bax/BCL2 apoptosis proteins were studied by western blot analysis. The functionality of PI3K/Akt signaling pathway was tested using LY294002, an inhibitor of PI3K. Result: Shikonin treated mice group exhibited better and faster skin burn wound healing in comparison with the controls. The proliferation of new skin cells and hair follicle regeneration in the wound site of the shikonin treated group was more active. The recruitment of macrophages in shikonin treated group was inhibited inturn decreased the expression of inflammatory factors. However, LY294002 inhibited the shikonin-mediated PI3K/Akt signaling pathway and affected the wound healing process. Conclusion: In conclusion, this study strengthens the hypothesis that bioactive small molecule, shikonin, inhibits inflammation, promotes wound healing and has a significant protective effect on the deep hair follicles against burn skin injury by activating the PI3K/Akt signaling pathway.

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.

Single cell transcriptional zonation of human psoriasis skin identifies an alternative immunoregulatory axis conducted by skin resident cells

Psoriasis is the most common skin disease in adults. Current experimental and clinical evidences suggested the infiltrating immune cells could target local skin cells and thus induce psoriatic phenotype. However, recent studies indicated the existence of a potential feedback signaling loop from local resident skin cells to infiltrating immune cells. Here, we deconstructed the full-thickness human skins of both healthy donors and patients with psoriasis vulgaris at single cell transcriptional level, and further built a neural-network classifier to evaluate the evolutional conservation of skin cell types between mouse and human. Last, we systematically evaluated the intrinsic and intercellular molecular alterations of each cell type between healthy and psoriatic skin. Cross-checking with psoriasis susceptibility gene loci, cell-type based differential expression, and ligand-receptor communication revealed that the resident psoriatic skin cells including mesenchymal and epidermis cell types, which specifically harbored the target genes of psoriasis susceptibility loci, intensively evoked the expression of major histocompatibility complex (MHC) genes, upregulated interferon (INF), tumor necrosis factor (TNF) signalling and increased cytokine gene expression for primarily aiming the neighboring dendritic cells in psoriasis. The comprehensive exploration and pathological observation of psoriasis patient biopsies proposed an uncovered immunoregulatory axis from skin local resident cells to immune cells, thus provided a novel insight for psoriasis treatment. In addition, we published a user-friendly website to exhibit the transcriptional change of each cell type between healthy and psoriatic human skin.

REGγ regulates hair cycle by activating Lgr5 positive hair follicle stem cells

BACKGROUND

REGγ acts as a proteasome activating factor mediating proteasome degradation of substrate proteins in an ATP and ubiquitination independent manner and also as an important regulator of cell cycle, proliferation and apoptosis. Hair cycle involves dynamic, continuous morphological changes of three stages (anagen, catagen and telogen).

OBJECTIVE

The function of REGγ in hair cycling is still unclear.

METHODS

Here, we used REGγ knockout 293 T cells, inducible 293WT and 293N151Y cell, REGγ knockout mice to identify the novel molecular mechanism of REGγ in regulating hair follicle stem cells.

RESULTS

In the present study, we found that REGγ deletion markedly delayed the transition of hair follicles from telogen to anagen and hair regeneration in mice. We also observed significant decrease of hair follicle stem cell number, stem-like property and proliferation ability. Interestingly, the results from real-time PCR, FACS, Western Blot and immunofluorescent analysis showed that REGγ deletion could greatly downregulate Lgr5 expression in the hair follicles. Meanwhile, REGγ was demonstrated to directly interact with LHX2 and promotes its degradation. Importantly, REGγ specific deletion in Lgr5⁺ stem cells induced the marked delay of hair regeneration after depilation.

CONCLUSION

These data together indicate that REGγ was a new mediator of Lgr5 expression in hair follicle at least partly by promoting the degradation of its suppressive transcription factor LHX2. It seemed that REGγ regulated hair anagen entry and hair regrowth by activating Lgr5 positive hair follicle stem cells.

Stem cell-intrinsic mechanisms regulating adult hair follicle homeostasis

Adult hair follicle stem cells (HFSCs) undergo dynamic and periodic molecular changes in their cellular states throughout the hair homeostatic cycle. These states are tightly regulated by cell-intrinsic mechanisms and by extrinsic signals from the microenvironment. HFSCs are essential not only for fuelling hair growth, but also for skin wound healing. Increasing evidence suggests an important role of HFSCs in organizing multiple skin components around the hair follicle, thus functioning as an organizing centre during adult skin homeostasis. Here, we focus on recent findings on cell-intrinsic mechanisms of HFSC homeostasis, which include transcription factors, histone modifications, DNA regulatory elements, non-coding RNAs, cell metabolism, cell polarity and post-transcriptional mRNA processing. Several transcription factors are now known to participate in well-known signalling pathways that control hair follicle homeostasis, as well as in super-enhancer activities to modulate HFSC and progenitor lineage progression. Interestingly, HFSCs have been shown to secrete molecules that are important in guiding the organization of several skin components around the hair follicle, including nerves, arrector pili muscle and vasculature. Finally, we discuss recent technological advances in the field such as single-cell RNA sequencing and live imaging, which revealed HFSC and progenitor heterogeneity and brought new light to understanding crosstalking between HFSCs and the microenvironment. The field is well on its way to generate a comprehensive map of molecular interactions that should serve as a solid theoretical platform for application in hair and skin disease and ageing.

Long-term expansion of directly reprogrammed keratinocyte-like cells and in vitro reconstitution of human skin

Background

Human keratinocytes and derived products are crucial for skin repair and regeneration. Despite substantial advances in engineered skin equivalents, their poor availability and immunorejection remain major challenges in skin grafting.

Methods

Induced keratinocyte-like cells (iKCs) were directly reprogrammed from human urine cells by retroviral transduction of two lineage-specific transcription factors BMI1 and △NP63α (BN). Expression of keratinocyte stem cell or their differentiation markers were assessed by PCR, immunofluorescence and RNA-Sequencing. Regeneration capacity of iKCs were assessed by reconstitution of a human skin equivalent under air-interface condition.

Results

BN-driven iKCs were similar to primary keratinocytes (pKCs) in terms of their morphology, protein expression, differentiation potential, and global gene expression. Moreover, BN-iKCs self-assembled to form stratified skin equivalents in vitro.

Conclusions

This study demonstrated an approach to generate human iKCs that could be directly reprogrammed from human somatic cells and extensively expanded in serum- and feeder cell-free systems, which will facilitate their broad applicability in an efficient and patient-specific manner.

Exploring differentially expressed genes between anagen and telogen secondary hair follicle stem cells from the Cashmere goat (Capra hircus) by RNA-Seq

Hair follicle stem cells (HFSCs) have been shown to be essential in the development and regeneration of hair follicles (HFs). The Inner Mongolia Cashmere goat (Capra hircus) has two types of HFs, primary and secondary, with cashmere being produced from the secondary hair follicle. To identify the genes associated with cashmere growth, transcriptome profiling of anagen and telogen secondary HFSCs was performed by RNA-Seq. The RNA-Seq analysis generated over 58 million clean reads from each group, with 2717 differentially expressed genes (DEGs) detected between anagen and telogen, including 1500 upregulated and 1217 downregulated DEGs. A large number of DEGs were predominantly associated with cell part, cellular process, binding, biological regulation and organelle. In addition, the PI3K-Akt, MAPK, Ras and Rap1 signaling pathways may be involved in the growth of HFSCs cultured in vitro. The RNA-Seq results showed that the well-defined HFSC signature genes and cell cycle-associated genes showed no significant differences between anagen and telogen HFSCs, indicating a relatively quiescent cellular state of the HFSCs cultured in vitro. These results are useful for future studies of complex molecular mechanisms of hair follicle cycling in cashmere goats.

Epidermal stem cells in wound healing and their clinical applications

The skin has important barrier, sensory, and immune functions, contributing to the health and integrity of the organism. Extensive skin injuries that threaten the entire organism require immediate and effective treatment. Wound healing is a natural response, but in severe conditions, such as burns and diabetes, this process is insufficient to achieve effective treatment. Epidermal stem cells (EPSCs) are a multipotent cell type and are committed to the formation and differentiation of the functional epidermis. As the contributions of EPSCs in wound healing and tissue regeneration have been increasingly attracting the attention of researchers, a rising number of therapies based on EPSCs are currently under development. In this paper, we review the characteristics of EPSCs and the mechanisms underlying their functions during wound healing. Applications of EPSCs are also discussed to determine the potential and feasibility of using EPSCs clinically in wound healing.

Up-regulated lncRNA5322 elevates MAPK1 to enhance proliferation of hair follicle stem cells as a ceRNA of microRNA-19b-3p

Hair follicle stem cells (HFSCs), located in the bulge region of the follicle, maintain hair follicle growth and cycling. Long non-coding RNAs (lncRNAs), non-protein coding transcripts, are widely known to play critical roles in differentiation and proliferation of stem cells. Therefore, the current study aimed to explore the regulatory roles of lncRNA5322 in HFSCs proliferation and the underlying regulatory mechanisms. Initially, the expression patterns of lncRNA5322 and microRNA-19b-3p (miR-19b-3p) in HFSCs were detected. Subsequently, gain-and loss-of-functions analyses were conducted to explore the roles of lncRNA5322, miR-19b-3p and mitogen-activated protein kinase 1 (MAPK1) in cell proliferation, colony formation and apoptosis of HFSCs, with the expression of cyclin-dependent kinase (CDK)1 and CDK2 examined. Also, the interaction relationships among lncRNA5322, miR-19b-3p and MAPK1 were explored. Furthermore, a mouse model was established to detect the roles of lncRNA5322, miR-19b-3p, and MAPK1 in wound contraction and epidermal regeneration. Over-expressed lncRNA5322 was found to promote proliferation, colony formation ability but inhibit apoptosis of HFSCs, in addition to up-regulation of the expression of CDK1 and CDK2. LncRNA5322 was found to act as a ceRNA of miR-19b-3p which directly targeted MAPK1. Furthermore, up-regulation of lncRNA5322 enhanced wound contraction and epidermal regeneration in vivo by increasing the expression of MAPK1 through functioning as a ceRNA of miR-19b-3p. In summary, the results in this study suggested that lncRNA5322 serves as a ceRNA of miR-19b-3p to elevate the expression of MAPK1, ultimately promoting HFSCs proliferation, wound contraction and epidermal regeneration of mouse model.

Functional anatomy of the hair follicle: The Secondary Hair Germ

The secondary hair germ (SHG)-a transitory structure in the lower portion of the mouse telogen hair follicle (HF)-is directly involved in anagen induction and eventual HF regrowth. Some crucial aspects of SHG functioning and ontogenetic relations with other HF parts, however, remain undefined. According to recent evidence (in contrast to previous bulge-centric views), the SHG is the primary target of anagen-inducing signalling and a source of both the outer root sheath (ORS) and ascending HF layers during the initial (morphogenetic) anagen subphase. The SHG is comprised of two functionally distinct cell populations. Its lower portion (originating from lower HF cells that survived catagen) forms all ascending HF layers, while the upper SHG (formed by bulge-derived cells) builds up the ORS. The predetermination of SHG cells to a specific morphogenetic fate contradicts their attribution to the "stem cell" category and supports SHG designation as a "germinative" or a "founder" cell population. The mechanisms of this predetermination driving transition of the SHG from "refractory" to the "competent" state during the telogen remain unknown. Functionally, the SHG serves as a barrier, protecting the quiescent bulge stem cell niche from the extensive follicular papilla/SHG signalling milieu. The formation of the SHG is a prerequisite for efficient "precommitment" of these cells and provides for easier sensing and a faster response to anagen-inducing signals. In general, the formation of the SHG is an evolutionary adaptation, which allowed the ancestors of modern Muridae to acquire a specific, highly synchronized pattern of hair cycling.

MicroRNA-506 inhibits tumor growth and metastasis in nasopharyngeal carcinoma through the inactivation of the Wnt/β-catenin signaling pathway by down-regulating LHX2

Background

Epithelial-mesenchymal transition (EMT)-associated proteins play key roles in cancer progression and metastasis with the involvement of microRNAs (miRNAs). This study aims to assess the role of miR-506 working in tandem with LIM Homeobox 2 (LHX2) in EMT and metastasis through the Wnt/β-catenin signaling pathway in nasopharyngeal carcinoma (NPC).

Methods

Differentially expressed genes associated with NPC were screened using microarray analyses, from which LHX2 was identified. Next, the potential relationship between miR-506 and LHX2 was analyzed. In order to explore the effect of miR-506 or LHX2 on NPC cell proliferation, migration, invasion and apoptosis, serials of mimics, inhibitors or siRNA against LHX2 were transfected into NPC cells. Then, the expression patterns of LHX2, Wnt1, β-catenin, E-cadherin, Vimentin, TCF4 and Twist were determined to assess the influence of miR-506 or LHX2 on EMT as well as the relationship between the Wnt/β-catenin signaling pathway and TCF4. The tumorigenicity and lymph node metastasis (LNM) in xenograft tumors of nude mice were observed.

Results

The has-miR-506-3p was identified as the down-regulated gene in NPC based on the microarray data while LHX2 was negatively regulated by miR-506. Over-expression of miR-506 or silencing of LHK2 inhibited NPC cell proliferation, migration, invasion, tumorigenicity and LNM but promoted apoptosis indicated by decreased Wnt1, β-catenin, Vimentin, TCF4 and Twist expressions along with increased E-cadherin expressions.

Conclusions

miR-506 inhibits tumor growth and metastasis in NPC via inhibition of Wnt/β-catenin signaling by down-regulating LHX2, accompanied by decreased TCF4. Taken together, miR-506 targeted-inhibition LHX2 presents a promising therapeutic strategy for the treatment of NPC.

Trial registration

ChiCTR1800018889. Registered 15 October 2018.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1023-4) contains supplementary material, which is available to authorized users.

LIM homeobox 2 promotes interaction between human iPS-derived hepatic progenitors and iPS-derived hepatic stellate-like cells

Human induced pluripotent stem (iPS) cells can differentiate into hepatocyte lineages, although the phenotype of the differentiated cells is immature compared to adult hepatocytes. Improvement of cell-cell interactions between epithelium and mesenchyme is a potential approach to address this phenotype issue. In this study, we developed a model system for improving interactions between human iPS-derived hepatic progenitor cells (iPS-HPCs) and human iPS-derived hepatic stellate cell-like cells (iPS-HSCs). The phenotype of iPS-HSCs, including gene and protein expression profiles and vitamin A storage, resembled that of hepatic stellate cells. Direct co-culture of iPS-HSCs with iPS-HPCs significantly improved hepatocytic maturation in iPS-HPCs, such as their capacity for albumin production. Next, we generated iPS cell lines overexpressing LIM homeobox 2 (LHX2), which suppresses myofibroblastic changes in HSCs in mice. Hepatocytic maturation in iPS-HPCs was significantly increased in direct co-culture with iPS-HSCs overexpressing LHX2, but not in co-culture with a human hepatic stellate cell line (LX-2) overexpressing LHX2. LHX2 regulated the expression of extracellular matrices, such as laminin and collagen, in iPS-HSCs. In conclusion, this study provides an evidence that LHX2 upregulation in iPS-HSCs promotes hepatocytic maturation of iPS-HPCs, and indicates that genetically modified iPS-HSCs will be of value for research into cell-cell interactions.

PDGFA in Cashmere Goat: A Motivation for the Hair Follicle Stem Cells to Activate

The cashmere hair follicle (HF) perpetually goes through cycles of growth, involution and rest. The photoperiod is the main factor in the control of seasonal coat change in cashmere goats while stem cells play a crucial role in the HF growth. Several factors, including Platelet-Derived Growth Factor A (PDGFA), Bone Morphogenetic Protein 2 (BMP2) and Lim-Homeobox gene 2 (LHX2) are implicated in HF morphogenesis and cycle. In this work, the mentioned molecules were investigated to evaluate their role in follicular cycle activation. The study was performed on skin samples collected at different periods of HF cycle and the molecular expression of PDGFA, BMP2 and LHX2 was evaluated by Real-Time PCR (qPCR) at each time point. Since PDGFA showed the most variation, the goat PDGFA gene was sequenced and the protein localization was investigated by immunohistochemistry together with PDGF receptor α (PDGFRα). PDGFA immunostaining was observed in the basal layer of the HF outer root sheath and the immunoreaction appeared stronger in the regressive HFs compared to those in the anagen phase according to qPCR analysis. PDGFRα was observed in the HF epithelium, proving the effect of PDGFA on the follicular structure. The data obtained suggest that PDGFA and BMP2 are both implicated in HF cycle in goat. In particular, PDGFA secreted by the HF is involved in the anagen activation.

Are hair follicle stem cells promising candidates for wound healing?

INTRODUCTION

With the continued focus on in-depth investigations of hair follicle stem cells (HFSCs), the role of HFSCs in wound healing has attracted increasing attention from researchers. This review may afford meaningful implications for HFSC treatment of wounds.

AREAS COVERED

We present the properties of HFSCs, analyze the possibility of HFSCs in wound healing, and sum up the recent studies into wound repair with HFSCs. The details of HFSCs in wound healing have been discussed. The possible mechanisms of wound healing with HFSCs have been elaborated. Additionally, the factors that influence HFSCs in wound healing are also summarized.

EXPERT OPINION

Hair follicle stem cells are promising sources for wound healing. However, a further understanding of human HFSCs and the safety use of HFSCs in clinical practice still remain in relative infancy.

Ultimate Precision: Targeting Cancer but Not Normal Self-replication

Self-replication is the engine that drives all biologic evolution, including neoplastic evolution. A key oncotherapy challenge is to target this, the heart of malignancy, while sparing the normal self-replication mandatory for health and life. Self-replication can be demystified: it is activation of replication, the most ancient of cell programs, uncoupled from activation of lineage-differentiation, metazoan programs more recent in origin. The uncoupling can be physiologic, as in normal tissue stem cells, or pathologic, as in cancer. Neoplastic evolution selects to disengage replication from forward-differentiation where intrinsic replication rates are the highest, in committed progenitors that have division times measured in hours versus weeks for tissue stem cells, via partial loss of function in master transcription factors that activate terminal-differentiation programs (e.g., GATA4) or in the coactivators they use for this purpose (e.g., ARID1A). These loss-of-function mutations bias master transcription factor circuits, which normally regulate corepressor versus coactivator recruitment, toward corepressors (e.g., DNMT1) that repress rather than activate terminal-differentiation genes. Pharmacologic inhibition of the corepressors rebalances to coactivator function, activating lineage-differentiation genes that dominantly antagonize MYC (the master transcription factor coordinator of replication) to terminate malignant self-replication. Physiologic self-replication continues, because the master transcription factors in tissue stem cells activate stem cell, not terminal-differentiation, programs. Druggable corepressor proteins are thus the barriers between self-replicating cancer cells and the terminal-differentiation fates intended by their master transcription factor content. This final common pathway to oncogenic self-replication, being separate and distinct from the normal, offers the favorable therapeutic indices needed for clinical progress.

De novo transcriptome analysis to search for sex-differentiation genes in the Siberian sturgeon

The sturgeon family includes many species that are lucrative for commercial caviar production, some of which face critical conservation problems. The purpose of this study was to identify genes involved in gonadal sex differentiation in sturgeons, contributing to our understanding of the biological cycle of this valuable species. A high-quality de novo Siberian sturgeon gonadal transcriptome was built for this study using gonadal samples from undifferentiated fish at 3, 5, and 6 months of age; recently sex-differentiated fish at 9 months of age; and immature males and females at 14-17 months of age. Undifferentiated fish were sexed after validation of forkhead box L2 (foxl2) and cytochrome P450, family 19, subfamily A, and polypeptide 1a (cyp19a1a) as sex markers, and the transcriptomes of the 3-month-old undifferentiated fish, 5-6-month-old future females, and 5-6-month-old putative males were compared. The ovarian program was associated with strong activation of genes involved in estrogen synthesis (cyp19a1, foxl2, and estradiol 17-beta-dehydrogenase 1), stem-cell niche building and regulation, and sex-specific nerve cell development. The genes related to the stem-cell niche were: (1) the family of iroquois-class homeodomain proteins 3, 4, and 5 (irx3, irx4, irx5-1, irx5-2, and irx5-3), which are essential for somatic-germ cell interaction; (2) extracellular matrix remodeling genes, such as collagen type XXVIII alpha 1 chain and collagen type II alpha 1 chain, matrix metalloproteinases 24-1 and 24-2, and NADPH oxidase organizer 1, which, along with the somatic cells, provide architectural support for the stem-cell niche; and (3) mitogenic factors, such as lim homeobox 2, amphiregulin, G2/M phase-specific E3 ubiquitin-protein ligase, and connector enhancer of kinase suppressor of ras 2, which are up regulated in conjunction with the anti-apoptotic gene G2/M phase-specific E3 ubiquitin-protein ligase suggesting a potential involvement in regulating the number of germ cells. Genes related to sex-specific nerve cell developments were: the neurofilament medium polypeptides, the gene coding for serotonin receptor 7, 5-hydroxytryptamine receptor 7; neurotensin, isoform CRA-a, the neuron-specific transmembrane protein Delta/Notch-like epidermal growth factor-related receptor; and insulinoma-associated protein 1. The putative testicular program was poorly characterized by elements of the immune response. The classic markers of maleness were not specifically activated, indicating that testicular differentiation occurs at a later stage. In sum, the ovarian program, but not the testicular program, is in place by 5-6 months of age in the Siberian sturgeon. The female program is characterized by estrogen-related genes with well-established roles in gonadal differentiation, but also by several genes with no previously-described function in the ovarian development of fish. These newly-reported genes are involved in stem-cell niche building and regulation as well as sex-specific nerve development.

Embryonic-like regenerative phenomenon: wound-induced hair follicle neogenesis

Wound-induced hair follicle neogenesis (WIHN) is a regenerative phenomenon that occurs widely in the skin of adult mammalians. A fully functional follicle can regenerate in the center of a full-thickness wound with a large enough size. The cellular origin of this process is similar to embryonic process. Many growth and development-related pathways are involved in WIHN. Studying WIHN can deeply explore the mechanism of biological growth, development and regeneration, and can identify new treatments for hair-related disorders. Our review aims to enlighten future study by summarizing the clinical manifestation of WIHN, as well as the cellular and molecular mechanism of WIHN in recent studies.

FGF signalling controls the specification of hair placode-derived SOX9 positive progenitors to Merkel cells

Merkel cells are innervated mechanosensory cells responsible for light-touch sensations. In murine dorsal skin, Merkel cells are located in touch domes and found in the epidermis around primary hairs. While it has been shown that Merkel cells are skin epithelial cells, the progenitor cell population that gives rise to these cells is unknown. Here, we show that during embryogenesis, SOX9-positive (+) cells inside hair follicles, which were previously known to give rise to hair follicle stem cells (HFSCs) and cells of the hair follicle lineage, can also give rise to Merkel Cells. Interestingly, while SOX9 is critical for HFSC specification, it is dispensable for Merkel cell formation. Conversely, FGFR2 is required for Merkel cell formation but is dispensable for HFSCs. Together, our studies uncover SOX9(+) cells as precursors of Merkel cells and show the requirement for FGFR2-mediated epithelial signalling in Merkel cell specification.

Merkel cells are mechanoreceptors located in the epidermis whose developmental origin is unclear. Here the authors show that Merkel cells originate from SOX9 positive cells inside hair follicles and that FGFR2-mediated epithelial signalling is required for their specification.

An epistatic effect of KRT25 on SP6 is involved in curly coat in horses

Curly coat represents an extraordinary type of coat in horses, particularly seen in American Bashkir Curly Horses and Missouri Foxtrotters. In some horses with curly coat, a hypotrichosis of variable extent was observed, making the phenotype appear more complex. In our study, we aimed at investigating the genetic background of curly coat with and without hypotrichosis using high density bead chip genotype and next generation sequencing data. Genome-wide association analysis detected significant signals (p = 1.412 × 10⁻⁰⁵–1.102 × 10⁻⁰⁸) on horse chromosome 11 at 22–35 Mb. In this significantly associated region, six missense variants were filtered out from whole-genome sequencing data of three curly coated horses of which two variants within KRT25 and SP6 could explain all hair phenotypes. Horses heterozygous or homozygous only for KRT25 variant showed curly coat and hypotrichosis, whereas horses with SP6 variant only, exhibited curly coat without hypotrichosis. Horses with mutant alleles in both variants developed curly hair and hypotrichosis. Thus, mutant KRT25 allele is masking SP6 allele effect, indicative for epistasis of KRT25 variant over SP6 variant. In summary, genetic variants in two different genes, KRT25 and SP6, are responsible for curly hair. All horses with KRT25 variant are additionally hypotrichotic due to the KRT25 epistatic effect on SP6.

Lhx2, an evolutionarily conserved, multifunctional regulator of forebrain development

A hundred years after Lhx2 ortholog apterous was identified as a critical regulator of wing development in Drosophila, LIM-HD gene family members have proved to be versatile and powerful components of the molecular machinery that executes the blueprint of embryogenesis across vertebrate and invertebrate species. Here, we focus on the spatio-temporally varied functions of LIM-homeodomain transcription factor LHX2 in the developing mouse forebrain. Right from its earliest known role in telencephalic and eye field patterning, to the control of the neuron-glia cell fate switch, and the regulation of axon pathfinding and dendritic arborization in late embryonic stages, LHX2 has been identified as a fundamental, temporally dynamic, always necessary, and often sufficient factor in a range of critical developmental phenomena. While Lhx2 mutant phenotypes have been characterized in detail in multiple brain structures, only recently have we advanced in our understanding of the molecular mechanisms by which this factor acts. Common themes emerge from how this multifunctional molecule controls a range of developmental steps in distinct forebrain structures. Examining these shared features, and noting unique aspects of LHX2 function is likely to inform our understanding of how a single factor can bring about a diversity of effects and play central and critical roles across systems and stages. The parallels in LHX2 and APTEROUS functions, and the protein complexes they participate in, offer insights into evolutionary strategies that conserve tool kits and deploy them to play new, yet familiar roles in species separated by hundreds of millions of years.

Co-expression of Lgr5 and CXCR4 characterizes cancer stem-like cells of colorectal cancer

Therapies designed to target cancer stem cells (CSCs) in colorectal cancer (CRC) may improve treatment outcomes. Different markers have been used to identify CSCs or CSC-like cells in CRC, but the enrichment of CSCs using these markers has yet to be optimized. We recently reported the importance of Lgr5-positive CRC cells in cancer growth. Here, we studied the possibility of using Lgr5 and CXCR4 as CSC markers for CRC. We detected high Lgr5 and CXCR4 levels in stage IV CRC specimens. Both high Lgr5 and CXCR4 levels were associated with poor prognosis in stage IV CRC patients. In vitro, Lgr5+CXCR4-, CXCR4+Lgr5- and Lgr5+CXCR4+ cells were purified in human CRC cell lines and examined for their CSC properties. We found that compared to the unsorted cells, CXCR4+Lgr5-, Lgr5+CXCR4-, and Lgr5+/CXCR4+ cells showed significantly greater cancer mass after subcutaneous transplantation, greater tumor sphere formation, higher resistance to chemotherapy, and higher incidence of tumor formation after serial adoptive transplantation into NOD/SCID mice. Taken together, our data suggest that the combined use of Lgr5 and CXCR4 may facilitate the enrichment of CSCs in CRC, and that treating Lgr5+/CXCR4+ CRC cells may improve the outcome of CRC therapy.

Alkaline Ceramidase 1 Protects Mice from Premature Hair Loss by Maintaining the Homeostasis of Hair Follicle Stem Cells

Ceramides and their metabolites are important for the homeostasis of the epidermis, but much remains unknown about the roles of specific pathways of ceramide metabolism in skin biology. With a mouse model deficient in the alkaline ceramidase (Acer1) gene, we demonstrate that ACER1 plays a key role in the homeostasis of the epidermis and its appendages by controlling the metabolism of ceramides. Loss of Acer1 elevated the levels of various ceramides and sphingoid bases in the skin and caused progressive hair loss in mice. Mechanistic studies revealed that loss of Acer1 widened follicular infundibulum and caused progressive loss of hair follicle stem cells (HFSCs) due to reduced survival and stemness. These results suggest that ACER1 plays a key role in maintaining the homeostasis of HFSCs, and thereby the hair follicle structure and function, by regulating the metabolism of ceramides in the epidermis.

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Acer1 is a skin-specific ceramidase that controls the catabolism of ceramides

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Acer1 plays a key role in the homeostasis of the epidermis and its appendages

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Acer1^−/− mice suffer from progressive alopecia

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Loss of Acer1 progressively depletes the population of hair follicle stem cells

p63 Transcription Factor Regulates Nuclear Shape and Expression of Nuclear Envelope-Associated Genes in Epidermal Keratinocytes

The maintenance of a proper nuclear architecture and three-dimensional organization of the genes, enhancer elements, and transcription machinery plays an essential role in tissue development and regeneration. Here we show that in the developing skin, epidermal progenitor cells of mice lacking p63 transcription factor display alterations in the nuclear shape accompanied by a marked decrease in expression of several nuclear envelope-associated components (Lamin B1, Lamin A/C, Sun1, Nesprin-3, Plectin) compared with controls. Furthermore, chromatin immunoprecipitation-quantitative PCR assay showed enrichment of p63 on Sun1, Syne3, and Plec promoters, suggesting them as p63 targets. Alterations in the nuclei shape and expression of nuclear envelope-associated proteins were accompanied by altered distribution patterns of the repressive histone marks trimethylation on lysine 27 of histone H3, trimethylation on lysine 9 of histone H3, and heterochromatin protein 1-alpha in p63-null keratinocytes. These changes were also accompanied by downregulation of the transcriptional activity and relocation of the keratinocyte-specific gene loci away from the sites of active transcription toward the heterochromatin-enriched repressive nuclear compartments in p63-null cells. These data demonstrate functional links between the nuclear envelope organization, chromatin architecture, and gene expression in keratinocytes and suggest nuclear envelope-associated genes as important targets mediating p63-regulated gene expression program in the epidermis.

Concise Review: Mechanisms of Quiescent Hair Follicle Stem Cell Regulation

Maintaining a pool of adult stem cells is essential for tissue homeostasis and wound repair. In mammalian tissues, notably hair follicles, blood, and muscle, stem cells acquire quiescence and infrequently divide for self-renewal. Mechanistic understanding of stem cell quiescence is critical for applying these multipotent cells in regenerative medicine and interrogating their roles in human diseases such as cancer. Quiescent and dividing epithelial stem cells located in hair follicle are conspicuously organized in a spatiotemporally specific manner, allowing them to be studied at a considerable depth. Recent advancements in mouse genetics, genomics, and imaging have revealed unprecedented insights into establishment, maintenance, and regulation of quiescent hair follicle stem cells. This concise review summarizes the progress with a focus on mechanisms mediated by signaling pathways and transcription factors and discusses their implications in the understanding of stem cell biology. Stem Cells 2017;35:2323-2330.

Hair follicle specific ACVR1/ALK2 critically affects skin morphogenesis and attenuates wound healing

The bone morphogenic protein signaling (BMP) is intricately involved in the quiescence and regulation of stem cells through activation of BMP receptors. Hair follicle stem cells play a critical role in cutaneous homeostasis and regeneration. Here, we utilize a novel mouse model with targeted overexpression of the BMP receptor ALK2/ACVR1 in hair follicle stem cells, to characterize its role in skin development and postnatal wound healing. Initial histologic evaluation demonstrated significant dysregulation in hair follicle morphogenesis in mutant mice. These demonstrated increased numbers of individual hair follicles with altered morphology and localization. Mutant follicles were found to exhibit elevated proliferative activity as well as increased prevalence of CD34 and ITGA6 positive follicle stem cells. Interestingly, constitutive overexpression of ALK2 resulted in attenuation of cutaneous wound healing. These findings demonstrate that hair follicle specific ALK2 is intricately involved in maintenance of the stem cell niche and wound healing.

Exploring a Role for Regulatory miRNAs In Wound Healing during Ageing:Involvement of miR-200c in wound repair

Multiple factors and conditions can lead to impaired wound healing. Chronic non-healing wounds are a common problem among the elderly. To identify microRNAs negatively impacting the wound repair, global miRNA profiling of wounds collected from young and old mice was performed. A subset of miRNAs that exhibited an age-dependent expression pattern during wound closure was identified, including miR-31 and miR-200c. The expression of miR-200 family members was markedly downregulated upon wounding in both young and aged mice, with an exception of acute upregulation of miR-200c at the early phase of wound healing in aged skin. In unwounded aged skin (versus unwounded younger skin), the level of miR-200c was also found elevated in both human and mice. Overexpression of miR-200c in human ex vivo wounds delayed re-epithelialisation and inhibited cell proliferation in the wound epithelium. Modulation of miR-200c expression in both human and mouse keratinocytes in vitro revealed inhibitory effects of miR-200c on migration, but not proliferation. Accelerated wound closure in vitro induced by anti-miR-200c was associated with upregulation of genes controlling cell migration. Thus, our study identified miR-200c as a critical determinant that inhibits cell migration during skin repair after injury and may contribute to age-associated alterations in wound repair.

Msi2 Maintains Quiescent State of Hair Follicle Stem Cells by Directly Repressing the Hh Signaling Pathway

Hair follicles (HFs) undergo precisely regulated cycles of active regeneration (anagen), involution (catagen), and relative quiescence (telogen). Hair follicle stem cells (HFSCs) play important roles in regenerative cycling. Elucidating mechanisms that govern HFSC behavior can help uncover the underlying principles of hair development, hair growth disorders, and skin cancers. RNA-binding proteins of the Musashi (Msi) have been implicated in the biology of different stem cell types, yet they have not been studied in HFSCs. Here we utilized gain- and loss-of-function mouse models to demonstrate that forced MSI2 expression retards anagen entry and consequently delays hair growth, whereas loss of Msi2 enhances hair regrowth. Furthermore, our findings show that Msi2 maintains quiescent state of HFSCs in the process of the telogen-to-anagen transition. At the molecular level, our unbiased transcriptome profiling shows that Msi2 represses Hedgehog signaling activity and that Shh is its direct target in the hair follicle. Taken together, our findings reveal the importance of Msi2 in suppressing hair regeneration and maintaining HFSC quiescence. The previously unreported Msi2-Shh-Gli1 pathway adds to the growing understanding of the complex network governing cyclic hair growth.

RNA-Seq analysis of Gtf2ird1 knockout epidermal tissue provides potential insights into molecular mechanisms underpinning Williams-Beuren syndrome

BACKGROUND

Williams-Beuren Syndrome (WBS) is a genetic disorder associated with multisystemic abnormalities, including craniofacial dysmorphology and cognitive defects. It is caused by a hemizygous microdeletion involving up to 28 genes in chromosome 7q11.23. Genotype/phenotype analysis of atypical microdeletions implicates two evolutionary-related transcription factors, GTF2I and GTF2IRD1, as prime candidates for the cause of the facial dysmorphology.

RESULTS

Using a targeted Gtf2ird1 knockout mouse, we employed massively-parallel sequencing of mRNA (RNA-Seq) to understand changes in the transcriptional landscape associated with inactivation of Gtf2ird1 in lip tissue. We found widespread dysregulation of genes including differential expression of 78 transcription factors or coactivators, several involved in organ development including Hey1, Myf6, Myog, Dlx2, Gli1, Gli2, Lhx2, Pou3f3, Sox2, Foxp3. We also found that the absence of GTF2IRD1 is associated with increased expression of genes involved in cellular proliferation, including growth factors consistent with the observed phenotype of extreme thickening of the epidermis. At the same time, there was a decrease in the expression of genes involved in other signalling mechanisms, including the Wnt pathway, indicating dysregulation in the complex networks necessary for epidermal differentiation and facial skin patterning. Several of the differentially expressed genes have known roles in both tissue development and neurological function, such as the transcription factor Lhx2 which regulates several genes involved in both skin and brain development.

CONCLUSIONS

Gtf2ird1 inactivation results in widespread gene dysregulation, some of which may be due to the secondary consequences of gene regulatory network disruptions involving several transcription factors and signalling molecules. Genes involved in growth factor signalling and cell cycle progression were identified as particularly important for explaining the skin dysmorphology observed in this mouse model. We have noted that a number of the dysregulated genes have known roles in brain development as well as epidermal differentiation and maintenance. Therefore, this study provides clues as to the underlying mechanisms that may be involved in the broader profile of WBS.