Hair follicle aging is driven by transepidermal elimination of stem cells via COL17A1 proteolysis

Ribonucleotide Excision Repair Is Essential to Prevent Squamous Cell Carcinoma of the Skin

Because of imperfect discrimination against ribonucleoside triphosphates by the replicative DNA polymerases, large numbers of ribonucleotides are incorporated into the eukaryotic nuclear genome during S-phase. Ribonucleotides, by far the most common DNA lesion in replicating cells, destabilize the DNA, and an evolutionarily conserved DNA repair machinery, ribonucleotide excision repair (RER), ensures ribonucleotide removal. Whereas complete lack of RER is embryonically lethal, partial loss-of-function mutations in the genes encoding subunits of RNase H2, the enzyme essential for initiation of RER, cause the SLE-related type I interferonopathy Aicardi-Goutières syndrome. Here, we demonstrate that selective inactivation of RER in mouse epidermis results in spontaneous DNA damage and epidermal hyperproliferation associated with loss of hair follicle stem cells and hair follicle function. The animals developed keratinocyte intraepithelial neoplasia and invasive squamous cell carcinoma with complete penetrance, despite potent type I interferon production and skin inflammation. These results suggest that compromises to RER-mediated genome maintenance might represent an important tumor-promoting principle in human cancer.Significance: Selective inactivation of ribonucleotide excision repair by loss of RNase H2 in the murine epidermis results in spontaneous DNA damage, type I interferon response, skin inflammation, and development of squamous cell carcinoma. Cancer Res; 78(20); 5917-26. ©2018 AACR.

Interaction of Psoriasis and Bullous Diseases

Patients with psoriasis are frequently complicated with autoimmune bullous diseases, especially, pemphigoid diseases. It has been known that one-third cases of anti-laminin gamma1 pemphigoid, formerly anti-p200 pemphigoid, are associated with psoriasis whereas bullous pemphigoid is the most frequently associated bullous disease in psoriasis cases regardless of the lack of detectable levels of the accompanying anti-laminin gamma1 autoantibodies. Despite several suggestions, however, the definitive reason of the striking association of psoriasis and these autoimmune bullous diseases remains elusive. In this review, we look over the epidemiological evidence of the association of psoriasis and autoimmune bullous diseases and the information of genetic susceptibilities of each disease, and discuss the possible mechanisms of their complication with reference to the recent understandings of each pathogenesis.

Matrix molecules and skin biology

An extracellular matrix (ECM) is a prerequisite for multicellular life. It is adapted to tissues and constantly undergoes changes to preserve microenvironmental homeostasis. The ECM acts as a structural scaffold that establishes tissue architecture and provides tensile strength. It has cell-instructive functions by serving as a reservoir and presenter of soluble agents, being directly signaling, integrating transmission of mechanical and biological cues, or serving as a co-factor potentiating signaling. The skin contains a highly developed, mechanically tough, but yet flexible ECM. The tissue-specific features of this ECM are largely attributed by minor ECM components. A large number of genetic and acquired ECM diseases with skin manifestations, provide an illustrative testament to the importance of correct assembly of the ECM for dermal homeostasis. Here, we will present the composition and features of the skin ECM during homeostasis and regeneration. We will discuss genetic and acquired ECM diseases affecting skin, and provide a short outlook to therapeutic strategies for them.

Diverse mechanisms for endogenous regeneration and repair in mammalian organs

Mammalian organs comprise an extraordinary diversity of cell and tissue types. Regenerative organs, such as the skin and gastrointestinal tract, use resident stem cells to maintain tissue function. Organs with a lower cellular turnover, such as the liver and lungs, mostly rely on proliferation of committed progenitor cells. In many organs, injury reveals the plasticity of both resident stem cells and differentiated cells. The ability of resident cells to maintain and repair organs diminishes with age, whereas, paradoxically, the risk of cancer increases. New therapeutic approaches aim to harness cell plasticity for tissue repair and regeneration while avoiding the risk of malignant transformation of cells.

Age-Associated Differences in Infection of Human Skin in the SCID Mouse Model of Varicella-Zoster Virus Pathogenesis

Varicella-zoster virus (VZV) is the skin-tropic human alphaherpesvirus responsible for both varicella-zoster and herpes zoster. Varicella-zoster and herpes zoster skin lesions have similar morphologies, but herpes zoster occurs disproportionally in older individuals and is often associated with a more extensive local rash and severe zoster-related neuralgia. We hypothesized that skin aging could also influence the outcome of the anterograde axonal transport of VZV to skin. We utilized human skin xenografts maintained in immunodeficient (SCID) mice to study VZV-induced skin pathology in vivo in fetal and adult skin xenografts. Here we found that VZV replication is enhanced in skin from older compared to younger adults, correlating with clinical observations. In addition to measures of VZV infection, we examined the expression of type I interferon (IFN) pathway components in adult skin and investigated elements of the cutaneous proliferative and inflammatory response to VZV infection in vivo Our results demonstrated that VZV infection of adult skin triggers intrinsic IFN-mediated responses such as we have described in VZV-infected fetal skin xenografts, including MxA as well as promyelocytic leukemia protein (PML), in skin cells surrounding lesions. Further, we observed that VZV elicited altered cell signaling and proliferative and inflammatory responses that are involved in wound healing, driven by follicular stem cells. These cellular changes are consistent with VZV-induced activation of STAT3 and suggest that VZV exploits the wound healing process to ensure efficient delivery of the virus to keratinocytes. Adult skin xenografts offer an approach to further investigate VZV-induced skin pathologies in vivoIMPORTANCE Varicella-zoster virus (VZV) is the agent responsible for both varicella-zoster and herpes zoster. Herpes zoster occurs disproportionally in older individuals and is often associated with a more extensive local rash and severe zoster-related neuralgia. To examine the effect of skin aging on VZV skin lesions, we utilized fetal and adult human skin xenografts maintained in immunodeficient (SCID) mice. We measured VZV-induced skin pathology, examined the expression of type I interferon (IFN) pathway components in adult skin, and investigated elements of the cutaneous proliferative and inflammatory response to VZV infection in vivo Our results demonstrate that characteristics of aging skin are preserved in xenografts; that VZV replication is enhanced in skin from older compared to younger adults, correlating with clinical observations; and that VZV infection elicits altered cell signaling and inflammatory responses. Adult skin xenografts offer an approach to further investigate VZV-induced skin pathologies in vivo.

Laminin-332 regulates differentiation of human interfollicular epidermal stem cells

Interfollicular epidermal stem cells (IFE-SCs) have self-renewal and differentiation potentials, and maintain epidermal homeostasis. Stem cells in vivo are regulated by the surrounding environment called niche to function properly, however, IFE-SC niche components are not fully understood. In order to elucidate the mechanisms of keeping epidermal homeostasis and of skin aging, and also to develop new therapeutic technologies for skin diseases, we searched for niche factors that regulate IFE-SCs. We found that laminin-332, a basement membrane component, was highly expressed at the tips of the dermal papillae, where IFE-SCs are localized, and that the stem cells by themselves expressed laminin-332. Knockdown of laminin-332 during the culture of IFE-SC-model cells to construct 3-dimensional epidermis in vitro resulted in failure to form proper structure, although no significant change was observed in either cell growth or apoptosis. Pre-coating of the culture insert with laminin-332 restored the normal formation of 3-dimensional epidermis. From these results, it was shown that laminin-332 is an essential niche component for the proper differentiation of IFE-SCs.

Extracellular Matrix as a Regulator of Epidermal Stem Cell Fate

Epidermal stem cells reside within the specific anatomic location, called niche, which is a microenvironment that interacts with stem cells to regulate their fate. Regulation of many important processes, including maintenance of stem cell quiescence, self-renewal, and homeostasis, as well as the regulation of division and differentiation, are common functions of the stem cell niche. As it was shown in multiple studies, extracellular matrix (ECM) contributes a lot to stem cell niches in various tissues, including that of skin. In epidermis, ECM is represented, primarily, by a highly specialized ECM structure, basement membrane (BM), which separates the epidermal and dermal compartments. Epidermal stem cells contact with BM, but when they lose the contact and migrate to the overlying layers, they undergo terminal differentiation. When considering all of these factors, ECM is of fundamental importance in regulating epidermal stem cells maintenance, proper mobilization, and differentiation. Here, we summarize the remarkable progress that has recently been made in the research of ECM role in regulating epidermal stem cell fate, paying special attention to the hair follicle stem cell niche. We show that the destruction of ECM components impairs epidermal stem cell morphogenesis and homeostasis. A deep understanding of ECM molecular structure as well as the development of in vitro system for stem cell maintaining by ECM proteins may bring us to developing new approaches for regenerative medicine.

Emerging nonmetabolic functions of skin fat

Although the major white adipose depots evolved primarily to store energy, secrete hormones and thermo-insulate the body, multiple secondary depots developed additional specialized and unconventional functions. Unlike any other fat tissue, dermal white adipose tissue (dWAT) evolved a large repertoire of novel features that are central to skin physiology, which we discuss in this Review. dWAT exists in close proximity to hair follicles, the principal appendages of the skin that periodically grow new hairs. Responding to multiple hair-derived signals, dWAT becomes closely connected to cycling hair follicles and periodically cycles itself. At the onset of new hair growth, hair follicles secrete activators of adipogenesis, while at the end of hair growth, a reduction in the secretion of activators or potentially, an increase in the secretion of inhibitors of adipogenesis, results in fat lipolysis. Hair-driven cycles of dWAT remodelling are uncoupled from size changes in other adipose depots that are controlled instead by systemic metabolic demands. Rich in growth factors, dWAT reciprocally signals to hair follicles, altering the activation state of their stem cells and modulating the pace of hair regrowth. dWAT cells also facilitate skin repair following injury and infection. In response to wounding, adipose progenitors secrete repair-inducing activators, while bacteria-sensing adipocytes produce antimicrobial peptides, thus aiding innate immune responses in the skin.

A matter of life and death: stem cell survival in tissue regeneration and tumour formation

In recent years, great strides have been made in our understanding of how stem cells (SCs) govern tissue homeostasis and regeneration. The inherent longevity of SCs raises the possibility that the unique protective mechanisms in these cells might also be involved in tumorigenesis. In this Opinion article, we discuss how SCs are protected throughout their lifespan, focusing on quiescent behaviour, DNA damage response and programmed cell death. We briefly examine the roles of adult SCs and progenitors in tissue repair and tumorigenesis and explore how signals released from dying or dormant cells influence the function of healthy or aberrant SCs. Important insight into the mechanisms that regulate SC death and survival, as well as the 'legacy' imparted by departing cells, may unlock novel avenues for regenerative medicine and cancer therapy.

Epidermal aspects of type VII collagen: Implications for dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita

Type VII collagen (COL7), a major component of anchoring fibrils in the epidermal basement membrane zone, has been characterized as a defective protein in dystrophic epidermolysis bullosa and as an autoantigen in epidermolysis bullosa acquisita. Although COL7 is produced and secreted by both epidermal keratinocytes and dermal fibroblasts, the role of COL7 with regard to the epidermis is rarely discussed. This review focuses on COL7 physiology and pathology as it pertains to epidermal keratinocytes. We summarize the current knowledge of COL7 production and trafficking, its involvement in keratinocyte dynamics, and epidermal carcinogenesis in COL7 deficiency and propose possible solutions to unsolved issues in this field.

Hair Follicle Stem Cell Faith Is Dependent on Chromatin Remodeling Capacity Following Low-Dose Radiation

The main function of the skin, to protect against the environment, is supported by the activity of different stem cell populations. The main focus of this study was elucidating the coping mechanisms of stem cells against the stimulation of constant exposure to genotoxic stresses, both endogenous and exogenous, to ensure long-term function. Investigation of various mouse strains, differing in their DNA repair capacity, enables us to clarify fractionated low-dose irradiation (LDR)-induced consequences for different stem cell populations of the murine hair follicle (HF) in their physiological stem cell niche. Using microscopic techniques combined with flow cytometry, we could show that LDR induces accumulation of persisting; pKu70-independent 53BP1-foci ("chromatin-alterations") in heterochromatic regions of the HF stem cells (HFSCs). These remaining chromatin-alterations result in varying stem cell consequences. CD34-positive HFSCs react by ataxia telangiectasia mutated-dependent, premature senescence, which correlates with global chromatin compaction, whereby apoptosis is prevented by the activity of DNA-dependent protein kinase catalytic subunit. However, distinctively highly damaged HFSCs seem to be sorted out of the niche by differentiation, transferring their chromatin-alterations to more proliferative G protein-coupled receptor 5-positive stem cells. Consequentially, the loss of basal HFSCs is compensated by increased proliferation within the stem cell pool. Despite the initial success of these mechanisms in stem cell population maintenance, the combined effect of the chromatin-alterations and the modification in stem cell pool composition may lead to downstream long-term functional loss of tissue or organs. Stem Cells 2018;36:574-588.

Targeting of Cell Surface Proteolysis of Collagen XVII Impedes Squamous Cell Carcinoma Progression

Squamous cell carcinoma (SCC) is one of the most common skin cancers and causes significant morbidity. Although the expression of the epithelial adhesion molecule collagen XVII (ColXVII) has been linked to SCC invasion, only little is known about its mechanistic contribution. Here, we demonstrate that ColXVII expression is essential for SCC cell proliferation and motility. Moreover, it revealed that particularly the post-translational modification of ColXVII by ectodomain shedding is the major driver of SCC progression, because ectodomain-selective immunostaining was mainly localized at the invasive front of human cutaneous SCCs, and exclusive expression of a non-sheddable ColXVII mutant in SCC-25 cells inhibits their matrix-independent growth and invasiveness. This cell surface proteolysis, which is strongly elevated during SCC invasion and metastasis, releases soluble ectodomains and membrane-anchored endodomains. Both released ColXVII domains play distinct roles in tumor progression: the endodomain induces proliferation and survival, whereas the ectodomain accelerates invasiveness. Furthermore, specific blockage of shedding by monoclonal ColXVII antibodies repressed matrix-independent growth and invasion of SCC cells in organotypic co-cultures. Thus, selective inhibition of ColXVII shedding may offer a promising therapeutic strategy to prevent SCC progression.

Identification of tissue damage, extracellular matrix remodeling and bacterial challenge as common mechanisms associated with high-risk cutaneous squamous cell carcinomas

In this study we used a genetic extracellular matrix (ECM) disease to identify mechanisms associated with aggressive behavior of cutaneous squamous cell carcinoma (cSCC). cSCC is one of the most common malignancies and usually has a good prognosis. However, some cSCCs recur or metastasize and cause significant morbidity and mortality. Known factors that are associated with aggressiveness of cSCCs include tumor grading, size, localization and microinvasive behavior. To investigate molecular mechanisms that influence biologic behavior we used global proteomic and histologic analyses of formalin-fixed paraffin-embedded tissue of primary human cSCCs. We compared three groups: non-recurring, non-metastasizing low-risk sporadic cSCCs; metastasizing sporadic cSCCs; and cSCCs from patients with recessive dystrophic epidermolysis bullosa (RDEB). RDEB is a genetic skin blistering and ECM disease caused by collagen VII deficiency. Patients commonly suffer from high-risk early onset cSCCs that frequently metastasize. The results indicate that different processes are associated with formation of RDEB cSCCs compared to sporadic cSCCs. Sporadic cSCCs show signs of UV damage, whereas RDEB cSCCs have higher mutational rates and display tissue damage, inflammation and subsequent remodeling of the dermal ECM as tumor initiating factors. Interestingly the two high-risk groups - high-risk metastasizing sporadic cSCCs and RDEB cSCCs - are both associated with tissue damage and ECM remodeling in gene-ontology enrichment and Search Tool for the Retrieval of Interacting Genes/Proteins analyses. In situ histologic analyses validate these results. The high-risk cSCCs also show signatures of enhanced bacterial challenge. Histologic analyses confirm correlation of bacterial colonization with worse prognosis. Collectively, this unbiased study - performed directly on human patient material - reveals that common microenvironmental alterations linked to ECM remodeling and increased bacterial challenges are denominators of high-risk cSCCs. The proteins identified here could serve as potential diagnostic markers and therapeutic targets in high-risk cSCCs.

Divergent proliferation patterns of distinct human hair follicle epithelial progenitor niches in situ and their differential responsiveness to prostaglandin D2

Human scalp hair follicles (hHF) harbour several epithelial stem (eHFSC) and progenitor cell sub-populations organised into spatially distinct niches. However, the constitutive cell cycle activity of these niches remains to be characterized in situ. Therefore, the current study has studied these characteristics of keratin 15+ (K15), CD200+ or CD34+ cells within anagen VI hHFs by immunohistomorphometry, using Ki-67 and 5-ethynyl-2'-deoxyuridine (EdU). We quantitatively demonstrate in situ the relative cell cycle inactivity of the CD200+/K15+ bulge compared to other non-bulge CD34+ and K15+ progenitor compartments and found that in each recognized eHFSC/progenitor niche, proliferation associates negatively with eHFSC-marker expression. Furthermore, we also show how prostaglandin D2 (PGD2), which is upregulated in balding scalp, differentially impacts on the proliferation of distinct eHFSC populations. Namely, 24 h organ-cultured hHFs treated with PGD2 displayed reduced Ki-67 expression and EdU incorporation in bulge resident K15+ cells, but not in supra/proximal bulb outer root sheath K15+ progenitors. This study emphasises clear differences between the cell cycle behaviour of spatially distinct stem/progenitor cell niches in the hHF, and demonstrates a possible link between PGD2 and perturbed proliferation dynamics in epithelial stem cells.

Stem cells: Aging and transcriptional fingerprints

Keyes and Fuchs discuss the decline in stem cell renewal and function with aging and the ensuing consequences on tissue homeostasis and regeneration.

Stem cells are imbued with unique qualities. They have the capacity to propagate themselves through symmetric divisions and to divide asymmetrically to engender new cells that can progress to differentiate into tissue-specific, terminal cell types. Armed with these qualities, stem cells in adult tissues are tasked with replacing decaying cells and regenerating tissue after injury to maintain optimal tissue function. With increasing age, stem cell functional abilities decline, resulting in reduced organ function and delays in tissue repair. Here, we review the effect of aging in five well-studied adult murine stem cell populations and explore age-related declines in stem cell function and their consequences for stem cell self-renewal, tissue homeostasis, and regeneration. Finally, we examine transcriptional changes that have been documented in aged stem cell populations and discuss new questions and future directions that this collection of data has uncovered.

Covering the Stem Cell Explosion at the 2017 ISSCR Conference in Boston

The meeting covered a plethora of rapidly evolving approaches and areas, such as organoid cultures modeling tissues and organs; stem cell-specific metabolites revealing new signaling pathways; single-cell technologies discovering new cell types and exploring stem cell niche interactions; novel methods studying stem cells in aging and cancer; lineage-tracing experiments exploring cell plasticity of tissues before and after injury; epigenetic studies illuminating cell reprogramming; new protocols improving cells for regenerative purposes; and several other timely and exciting topics.

Wnt/β-catenin signaling promotes aging-associated hair graying in mice

Canities is an obvious sign of aging in mouse and human, shown as hair graying. Melanocytes in the hair follicle show cyclic activity with hair cycling, which transitions from anagen, catagen to telogen. How the hairs turn gray during aging is not completely uncovered. Here, by using immunostaining and LacZ staining in Dct-LacZ mice, we show that β-catenin is expressed in melanocytes during hair cycling. RT-PCR, western blot and immunostaining show that β-catenin expression is significantly increased in both anagen and telogen skin of aged mice, when compared to the anagen and telogen skin of young mice, respectively. Overexpression of Wnt10b not only accelerates hair follicle to enter anagen phase, but also promotes melanocytes differentiation in young adult mice (2-month old), with increased β-catenin expression in melanocytes at the secondary hair germ and matrix region of regenerated hair follicles. Overexpression of Wnt10b also promotes melanocyte progenitor cells differentiation in vitro. Our data suggest that increased Wnt signaling promotes excessive differentiation of melanocytes, leading to exhaustion of melanocyte stem cells and eventually canities in aged mice.

Rejuvenating Strategies for Stem Cell-Based Therapies in Aging

Recent advances in our understanding of tissue regeneration and the development of efficient approaches to induce and differentiate pluripotent stem cells for cell replacement therapies promise exciting avenues for treating degenerative age-related diseases. However, clinical studies and insights from model organisms have identified major roadblocks that normal aging processes impose on tissue regeneration. These new insights suggest that specific targeting of environmental niche components, including growth factors, ECM, and immune cells, and intrinsic stem cell properties that are affected by aging will be critical for the development of new strategies to improve stem cell function and optimize tissue repair processes.

Type XVII collagen coordinates proliferation in the interfollicular epidermis

Type XVII collagen (COL17) is a transmembrane protein located at the epidermal basement membrane zone. COL17 deficiency results in premature hair aging phenotypes and in junctional epidermolysis bullosa. Here, we show that COL17 plays a central role in regulating interfollicular epidermis (IFE) proliferation. Loss of COL17 leads to transient IFE hypertrophy in neonatal mice owing to aberrant Wnt signaling. The replenishment of COL17 in the neonatal epidermis of COL17-null mice reverses the proliferative IFE phenotype and the altered Wnt signaling. Physical aging abolishes membranous COL17 in IFE basal cells because of inactive atypical protein kinase C signaling and also induces epidermal hyperproliferation. The overexpression of human COL17 in aged mouse epidermis suppresses IFE hypertrophy. These findings demonstrate that COL17 governs IFE proliferation of neonatal and aged skin in distinct ways. Our study indicates that COL17 could be an important target of anti-aging strategies in the skin.

Effects of gamma rays on the regeneration of murine hair follicles in the natural hair cycle

PURPOSE

This review evaluates the effects of γ-rays on the regeneration of murine hair follicles in the natural hair cycle. A series of studies were performed to investigate this issue, in which the whole bodies of C57BL/10JHir mice in the 1st telogen phase of the hair cycle were irradiated with γ-rays.

RESULTS

The dermis of the irradiated skin showed a decrease in hair follicle density and induction of curved hair follicles along with the presence of white hairs and hypopigmented hair bulbs in the 2nd and 3rd anagen phases. An increased frequency of hypopigmented hair bulbs was still observed in the later hair cycle at postnatal day 200. There was no significant difference in the number of stem cells in the hair bulge region between control and irradiated skin.

CONCLUSIONS

These results show that the effects of γ-rays on the pigmentation of murine hair follicles are persistently carried over to later hair cycles, although those on the number and structure of hair follicles appear to be hidden by the effects of aging. Our findings may be important for understanding the mechanisms of the actions of stem cells on hair regeneration in connection with age-related phenotypes.

Aging in hair follicle stem cells and niche microenvironment

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

WNT10A mutation causes ectodermal dysplasia by impairing progenitor cell proliferation and KLF4-mediated differentiation

Human WNT10A mutations are associated with developmental tooth abnormalities and adolescent onset of a broad range of ectodermal defects. Here we show that β-catenin pathway activity and adult epithelial progenitor proliferation are reduced in the absence of WNT10A, and identify Wnt-active self-renewing stem cells in affected tissues including hair follicles, sebaceous glands, taste buds, nails and sweat ducts. Human and mouse WNT10A mutant palmoplantar and tongue epithelia also display specific differentiation defects that are mimicked by loss of the transcription factor KLF4. We find that β-catenin interacts directly with region-specific LEF/TCF factors, and with KLF4 in differentiating, but not proliferating, cells to promote expression of specialized keratins required for normal tissue structure and integrity. Our data identify WNT10A as a critical ligand controlling adult epithelial proliferation and region-specific differentiation, and suggest downstream β-catenin pathway activation as a potential approach to ameliorate regenerative defects in WNT10A patients.

Human WNT10A mutations are associated with dental defects and adult onset ectodermal dysplasia. Xu et al. show that WNT10A-activated ß-catenin plays dual roles in adult epithelial progenitor proliferation and differentiation by complexing with KLF4 in differentiating, but not proliferating, cells.

The role of matrix metalloproteinases in aging: Tissue remodeling and beyond

Proteases are a set of enzymes that have been involved in multiple biological processes throughout evolution. Among them, extracellular matrix (ECM) remodeling has emerged as one of the most relevant functions exerted by these proteins, being essential in the regulation of critical events such as embryonic development or tissue homeostasis. Hence, it is not surprising that dysregulation in any protease function that affects ECM homeostasis may contribute to the aging process. Matrix metalloproteinases (MMPs) are one of the most important families of proteases involved in the tight control of ECM remodeling over time. In this review, we will discuss how MMPs and other proteases alter ECM composition and mechanical properties in aging, thereby affecting stem cell niches and the development of senescent phenotypes. Finally, we will summarize recent findings that associate MMPs with the development of age-related diseases, such as neurodegenerative disorders.

A Holistic Approach to Antiaging as an Adjunct to Antiaging Procedures: A Review of the Literature

BACKGROUND

Aging is a multifactorial process and depends on both intrinsic and extrinsic factors. Procedural options for diminishing signs of intrinsic aging and cosmetic rejuvenation have expanded dramatically. However, less attention is paid to counseling patients on options for mitigating extrinsic factors related to aging.

OBJECTIVE

The objective of this study was to review changes that occur with intrinsic and extrinsic aging, and provide evidence-based holistic counseling recommendations that can be used synergistically with aesthetic procedures to maximize antiaging interventions.

MATERIALS AND METHODS

A PubMed search was conducted for articles on intrinsic and extrinsic aging as it relates to skin, fat, muscle, and bone. Key clinical trials and studies on the effect of diet, hormones, exercise, sleep, stress, dental hygiene, smoking, pollution, and oxidative stress on the aging process are reviewed, and treatment recommendations are summarized based on available evidence.

RESULTS

Conventional cosmetic procedures and cosmeceuticals work together with nutritious diet, exercise, dental hygiene, hormonal balance, stress reduction, smoking and pollution avoidance, and healthy sleep patterns for a better effect on antiaging.

CONCLUSION

A combination approach of multiple nonsurgical modalities along with healthy lifestyle recommendations to minimize intrinsic and extrinsic aging factors allows cosmetic practitioners to target multiple facets of aging concurrently and maximize the aesthetic interventions cosmetic dermatologists/practitioners provide.

MOB1-YAP1/TAZ-NKX2.1 axis controls bronchioalveolar cell differentiation, adhesion and tumour formation

Mps One Binder Kinase Activator (MOB)1A/1B are core components of the Hippo pathway. These proteins, which coactivate LArge Tumour Suppressor homologue kinases, are also tumour suppressors. To investigate MOB1A/B's roles in normal physiology and lung cancer, we generated doxycycline (Dox)-inducible, bronchioalveolar epithelium-specific, null mutations of MOB1A/B in mice (SPC-rtTA/(tetO)₇-Cre/Mob1a^flox/flox/Mob1b^-/-; termed luMob1DKO mice). Most mutants (70%) receiving Dox in utero (luMob1DKO (E6.5-18.5) mice) died of hypoxia within 1 h post-birth. Their alveolar epithelial cells showed increased proliferation, impaired YAP1/TAZ-dependent differentiation and decreased surfactant protein production, all features characteristic of human respiratory distress syndrome. Intriguingly, mutant mice that received Dox postnatally (luMob1DKO (P21-41) mice) did not develop spontaneous lung adenocarcinomas, and urethane treatment-induced lung tumour formation was decreased (rather than increased). Lungs of luMob1DKO (P21-41) mice exhibited increased detachment of bronchiolar epithelial cells and decreased numbers of the bronchioalveolar stem cells thought to initiate lung adenocarcinomas. YAP1/TAZ-NKX2.1-dependent expression of collagen XVII, a key hemidesmosome component, was also reduced. Thus, a MOB1-YAP1/TAZ-NKX2.1 axis is essential for normal lung homeostasis and expression of the collagen XVII protein necessary for alveolar stem cell maintenance in the lung niche.

Significant Role of Collagen XVII And Integrin β4 in Migration and Invasion of The Less Aggressive Squamous Cell Carcinoma Cells

Collagen XVII and integrin α6β4 have well-established roles as epithelial adhesion molecules. Their binding partner laminin 332 as well as integrin α6β4 are largely recognized to promote invasion and metastasis in various cancers, and collagen XVII is essential for the survival of colon and lung cancer stem cells. We have studied the expression of laminin γ2, collagen XVII and integrin β4 in tissue microarray samples of squamous cell carcinoma (SCC) and its precursors, actinic keratosis and Bowen's disease. The expression of laminin γ2 was highest in SCC samples, whereas the expression of collagen XVII and integrin β4 varied greatly in SCC and its precursors. Collagen XVII and integrin β4 were also expressed in SCC cell lines. Virus-mediated RNAi knockdown of collagen XVII and integrin β4 reduced the migration of less aggressive SCC-25 cells in horizontal scratch wound healing assay. Additionally, in a 3D organotypic myoma invasion assay the loss of collagen XVII or integrin β4 suppressed equally the migration and invasion of SCC-25 cells whereas there was no effect on the most aggressive HSC-3 cells. Variable expression patterns and results in migration and invasion assays suggest that collagen XVII and integrin β4 contribute to SCC tumorigenesis.

Expression profiling and bioinformatic analyses suggest new target genes and pathways for human hair follicle related microRNAs

BACKGROUND

Human hair follicle (HF) cycling is characterised by the tight orchestration and regulation of signalling cascades. Research shows that micro(mi)RNAs are potent regulators of these pathways. However, knowledge of the expression of miRNAs and their target genes and pathways in the human HF is limited. The objective of this study was to improve understanding of the role of miRNAs and their regulatory interactions in the human HF.

METHODS

Expression levels of ten candidate miRNAs with reported functions in hair biology were assessed in HFs from 25 healthy male donors. MiRNA expression levels were correlated with mRNA-expression levels from the same samples. Identified target genes were tested for enrichment in biological pathways and accumulation in protein-protein interaction (PPI) networks.

RESULTS

Expression in the human HF was confirmed for seven of the ten candidate miRNAs, and numerous target genes for miR-24, miR-31, and miR-106a were identified. While the latter include several genes with known functions in hair biology (e.g., ITGB1, SOX9), the majority have not been previously implicated (e.g., PHF1). Target genes were enriched in pathways of interest to hair biology, such as integrin and GnRH signalling, and the respective gene products showed accumulation in PPIs.

CONCLUSIONS

Further investigation of miRNA expression in the human HF, and the identification of novel miRNA target genes and pathways via the systematic integration of miRNA and mRNA expression data, may facilitate the delineation of tissue-specific regulatory interactions, and improve our understanding of both normal hair growth and the pathobiology of hair loss disorders.

Minor collagens of the skin with not so minor functions

The structure and function of the skin relies on the complex expression pattern and organisation of extracellular matrix macromolecules, of which collagens are a principal component. The fibrillar collagens, types I and III, constitute over 90% of the collagen content within the skin and are the major determinants of the strength and stiffness of the tissue. However, the minor collagens also play a crucial regulatory role in a variety of processes, including cell anchorage, matrix assembly, and growth factor signalling. In this article, we review the expression patterns, key functions and involvement in disease pathogenesis of the minor collagens found in the skin. While it is clear that the minor collagens are important mediators of normal tissue function, homeostasis and repair, further insight into the molecular level structure and activity of these proteins is required for translation into clinical therapies.

Amino acid duplication in the coiled-coil structure of collagen XVII alters its maturation and trimerization causing mild junctional epidermolysis bullosa

The function and stability of collagens depend on the accurate triple helix formation of three distinct polypeptide chains. Disruption of this triple-helical structure can result in connective-tissue disorders. Triple helix formation is thought to depend on three-stranded coiled-coil oligomerization sites within non-collagenous domains. However, only little is known about the physiological relevance of these coiled-coil structures. Transmembrane collagen XVII, also known as 180 kDa bullous pemphigoid antigen provides mechanical stability through the anchorage of epithelial cells to the basement membrane. Mutations in the collagen XVII gene, COL17A1, cause junctional epidermolysis bullosa (JEB), characterized by chronic trauma-induced skin blistering. Here we exploited a novel naturally occurring COL17A1 mutation, leading to an in-frame lysine duplication within the coiled-coil structure of the juxtamembranous NC16A domain of collagen XVII, which resulted in a mild phenotype of JEB due to reduced membrane-anchored collagen XVII molecules. This mutation causes structural changes in the mutant molecule and interferes with its maturation. The destabilized coiled-coil structure of the mutant collagen XVII unmasks a furin cleavage site that results in excessive and non-physiological ectodomain shedding during its maturation. Furthermore, it decreases its triple-helical stability due to defective coiled-coil oligomerization, which makes it highly susceptible to proteolytic degradation. As a consequence of altered maturation and decreased stability of collagen XVII trimers, reduced collagen XVII is incorporated into the cell membrane, resulting in compromised dermal-epidermal adhesion. Taken together, using this genetic model, we provide the first proof that alteration of the coiled-coil structure destabilizes oligomerization and impairs physiological shedding of collagen XVII in vivo.

Runx Family Genes in Tissue Stem Cell Dynamics

The Runx family genes play important roles in development and cancer, largely via their regulation of tissue stem cell behavior. Their involvement in two organs, blood and skin, is well documented. This review summarizes currently known Runx functions in the stem cells of these tissues. The fundamental core mechanism(s) mediated by Runx proteins has been sought; however, it appears that there does not exist one single common machinery that governs both tissue stem cells. Instead, Runx family genes employ multiple spatiotemporal mechanisms in regulating individual tissue stem cell populations. Such specific Runx requirements have been unveiled by a series of cell type-, developmental stage- or age-specific gene targeting studies in mice. Observations from these experiments revealed that the regulation of stem cells by Runx family genes turned out to be far more complex than previously thought. For instance, although it has been reported that Runx1 is required for the endothelial-to-hematopoietic cell transition (EHT) but not thereafter, recent studies clearly demonstrated that Runx1 is also needed during the period subsequent to EHT, namely at perinatal stage. In addition, Runx1 ablation in the embryonic skin mesenchyme eventually leads to complete loss of hair follicle stem cells (HFSCs) in the adult epithelium, suggesting that Runx1 facilitates the specification of skin epithelial stem cells in a cell extrinsic manner. Further in-depth investigation into how Runx family genes are involved in stem cell regulation is warranted.

Pterostilbene and Its Glucoside Induce Type XVII Collagen Expression

The glycosylation of pterostilbene by cultured plant cells of Phytolacca americana gave pterostilbene 4′- O-β-D-glucoside. Both pterostilbene and its 4- O-β-D-glucoside induced type XVII collagen expression in the EpiDermFT EFT-400 human skin cell model. Pterostilbene 4′- O-β-D-glucoside strongly induced type XVII collagen expression rather than pterostilbene.

A multi-scale model for hair follicles reveals heterogeneous domains driving rapid spatiotemporal hair growth patterning

The control principles behind robust cyclic regeneration of hair follicles (HFs) remain unclear. Using multi-scale modeling, we show that coupling inhibitors and activators with physical growth of HFs is sufficient to drive periodicity and excitability of hair regeneration. Model simulations and experimental data reveal that mouse skin behaves as a heterogeneous regenerative field, composed of anatomical domains where HFs have distinct cycling dynamics. Interactions between fast-cycling chin and ventral HFs and slow-cycling dorsal HFs produce bilaterally symmetric patterns. Ear skin behaves as a hyper-refractory domain with HFs in extended rest phase. Such hyper-refractivity relates to high levels of BMP ligands and WNT antagonists, in part expressed by ear-specific cartilage and muscle. Hair growth stops at the boundaries with hyper-refractory ears and anatomically discontinuous eyelids, generating wave-breaking effects. We posit that similar mechanisms for coupled regeneration with dominant activator, hyper-refractory, and wave-breaker regions can operate in other actively renewing organs.

Biology of Hsp47 (Serpin H1), a collagen-specific molecular chaperone

Hsp47, a collagen-specific molecular chaperone that localizes in the endoplasmic reticulum (ER), is indispensable for molecular maturation of collagen. Hsp47, which is encoded by the SERPINH1 gene, belongs to the serpin family and has the serpin fold; however, it has no serine protease inhibitory activity. Hsp47 transiently binds to procollagen in the ER, dissociates in the cis-Golgi or ER-Golgi intermediate compartment (ERGIC) in a pH-dependent manner, and is then transported back to the ER via its RDEL retention sequence. Hsp47 recognizes collagenous (Gly-Xaa-Arg) repeats on triple-helical procollagen and can prevent local unfolding and/or aggregate formation of procollagen. Gene disruption of Hsp47 in mice causes embryonic lethality due to impairments in basement membrane and collagen fibril formation. In Hsp47-knockout cells, the type I collagen triple helix forms abnormally, resulting in thin and frequently branched fibrils. Secretion of type I collagens is slow and plausible in making aggregates of procollagens in the ER of hsp47-knocked out fibroblasts, which are ultimately degraded by autophagy. Mutations in Hsp47 are causally associated with osteogenesis imperfecta. Expression of Hsp47 is strongly correlated with expression of collagens in multiple types of cells and tissues. Therefore, Hsp47 represents a promising target for treatment of collagen-related disorders, including fibrosis of the liver, lung, and other organs.

Quorum sensing and other collective regenerative behavior in organ populations

Stem cell and microenvironment molecular interactions have been studied in detail but regenerative behavior at the organ population level has remained unexplored. Organ renewal can occur continuously or in cyclic episodes. Progenitors may be distributed as one entity or compartmentalized into multiple units. Multiple units offer advantages as each unit can be regulated differently in different body regions or physiological stages, adapting animals to their niche with flexible functional forms. Using the hair paradigm, we show how periodic patterning can convert one morphogenetic field into many hair germs, how follicles can be renewed with different cycle times and phenotypes in a region-specific manner, and how new properties, such as regenerative waves and quorum sensing, emerge to coordinate collective regenerative behavior.

Single-Cell Transcriptomics Reveals that Differentiation and Spatial Signatures Shape Epidermal and Hair Follicle Heterogeneity

The murine epidermis with its hair follicles represents an invaluable model system for tissue regeneration and stem cell research. Here we used single-cell RNA-sequencing to reveal how cellular heterogeneity of murine telogen epidermis is tuned at the transcriptional level. Unbiased clustering of 1,422 single-cell transcriptomes revealed 25 distinct populations of interfollicular and follicular epidermal cells. Our data allowed the reconstruction of gene expression programs during epidermal differentiation and along the proximal-distal axis of the hair follicle at unprecedented resolution. Moreover, transcriptional heterogeneity of the epidermis can essentially be explained along these two axes, and we show that heterogeneity in stem cell compartments generally reflects this model: stem cell populations are segregated by spatial signatures but share a common basal-epidermal gene module. This study provides an unbiased and systematic view of transcriptional organization of adult epidermis and highlights how cellular heterogeneity can be orchestrated in vivo to assure tissue homeostasis.

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Single-cell RNA-seq analysis identifies 25 populations of epidermal cells

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Differentiation and spatial gene expression signatures can be defined

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Interplay of differentiation and spatial signatures explains most heterogeneity

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Stem cell populations are divided by spatial signatures and only share basal identity

Cell therapy for basement membrane-linked diseases

For most disorders caused by mutations in genes encoding basement membrane (BM) proteins, there are at present only limited treatment options available. Genetic BM-linked disorders can be viewed as especially suited for treatment with cell-based therapy approaches because the proteins that need to be restored are located in the extracellular space. In consequence, complete and permanent engraftment of cells does not necessarily have to occur to achieve substantial causal therapeutic effects. For these disorders cells can be used as transient vehicles for protein replacement. In addition, it is becoming evident that BM-linked genetic disorders are modified by secondary diseases mechanisms. Cell-based therapies have also the ability to target such disease modifying mechanisms. Thus, cell therapies can simultaneously provide causal treatment and symptomatic relief, and accordingly hold great potential for treatment of BM-linked disorders. However, this potential has for most applications and diseases so far not been realized. Here, we will present the state of cell therapies for BM-linked diseases. We will discuss use of both pluripotent and differentiated cells, the limitation of the approaches, their challenges, and the way forward to potential wider implementation of cell therapies in the clinics.

Essential Role of Polarity Protein Par3 for Epidermal Homeostasis through Regulation of Barrier Function, Keratinocyte Differentiation, and Stem Cell Maintenance

Partitioning-defective (Par) proteins contribute to multiprotein complexes that drive cell polarity and fate in invertebrates. Of these, the ternary Par3-atypical protein kinase C-Par6 polarity complex mediates asymmetry in various systems, whereas Par3 and aPKC/Par6 can also act independently. aPKC-λ has recently been implicated in epidermal differentiation and stem cell fate; however, whether Par3 contributes to the homeostasis of adult stratified epithelia is currently unknown. Here, we provide functional evidence that epidermal Par3 loss disturbed the inside-out skin barrier, coinciding with altered expression and localization of principle tight junction components, and that epidermal differentiation and thickness were increased. Moreover, Par3 inactivation caused an initial expansion and later decline of hair follicle bulge stem cells, accompanied by an enrichment of committed progenitors, formation of hypertrophic sebaceous glands, and increased epidermal differentiation, suggesting aberrant cell fate decisions. Importantly, and opposite to aPKCλ deletion, Par3 loss did not enhance perpendicular cell divisions. Instead, in Par3-deficient hair follicles, spindles were shifted toward planar orientation, indicating that abnormal differentiation after Par3 inactivation is unlikely to be attributed to increased perpendicular spindle orientation. Collectively, mammalian Par3 controls the epidermal barrier, differentiation, and stem cell maintenance in the pilosebaceous unit, which are all essential for the homeostasis of an important barrier-forming epithelium.

Extracellular Matrix Regulation of Stem Cell Behavior

Stem cells hold great promise in treating many diseases either through promoting endogenous cell repair or through direct cell transplants. In order to maximize their potential, understanding the fundamental signals and mechanisms that regulate their behavior is essential. The extracellular matrix (ECM) is one such component involved in mediating stem cell fate. Recent studies have made significant progress in understanding stem cell-ECM interactions. Technological developments have provided greater clarity in how cells may sense and respond to the ECM, in particular the physical properties of the matrix. This review summarizes recent developments, providing illustrative examples of the different modes with which the ECM controls both embryonic and adult stem cell behavior.

Cellular mechanisms of skin repair in humans and other mammals

The increased incidence of non-healing skin wounds in developed societies has prompted tremendous research efforts on the complex process known as "wound healing". Unfortunately, the weak relevance of modern wound healing research to human health continues to be a matter of concern. This review summarizes the current knowledge of the cellular mechanisms that mediate wound closure in the skin of humans and laboratory animals. The author highlights the anatomical singularities of human skin vs. the skin of other mammals commonly used for wound healing research (i.e. as mice, rats, rabbits, and pigs), and discusses the roles of stem cells, myofibroblasts, and the matrix environment in the repair process. The majority of this review focuses on reepithelialization and wound closure. Other aspects of wound healing (e.g. inflammation, fibrous healing) are referred to when relevant to the main topic. This review aims at providing the reader with a clear understanding of the similarities and differences that have been reported over the past 100 years between the healing of human wounds and that of other mammals.