Loss of epigenetic information as a cause of mammalian aging.

All living things experience an increase in entropy, manifested as a loss of genetic and epigenetic information. In yeast, epigenetic information is lost over time due to the relocalization of chromatin-modifying proteins to DNA breaks, causing cells to lose their identity, a hallmark of yeast aging. Using a system called "ICE" (inducible changes to the epigenome), we find that the act of faithful DNA repair advances aging at physiological, cognitive, and molecular levels, including erosion of the epigenetic landscape, cellular exdifferentiation, senescence, and advancement of the DNA methylation clock, which can be reversed by OSK-mediated rejuvenation. These data are consistent with the information theory of aging, which states that a loss of epigenetic information is a reversible cause of aging.

Dynamic stem cell selection safeguards the genomic integrity of the epidermis.

Maintaining genomic integrity and stability is crucial for life; yet, no tissue-driven mechanism that robustly safeguards the epithelial genome has been discovered. Epidermal stem cells (EpiSCs) continuously replenish the stratified layers of keratinocytes that protect organisms against various environmental stresses. To study the dynamics of DNA-damaged cells in tissues, we devised an in vivo fate tracing system for EpiSCs with DNA double-strand breaks (DSBs) and demonstrated that those cells exit from their niches. The clearance of EpiSCs with DSBs is caused by selective differentiation and delamination through the DNA damage response (DDR)-p53-Notch/p21 axis, with the downregulation of ITGB1. Moreover, concomitant enhancement of symmetric cell divisions of surrounding stem cells indicates that the selective elimination of cells with DSBs is coupled with the augmented clonal expansion of intact stem cells. These data collectively demonstrate that tissue autonomy through the dynamic coupling of cell-autonomous and non-cell-autonomous mechanisms coordinately maintains the genomic quality of the epidermis.

Stem cell spreading dynamics intrinsically differentiate acral melanomas from nevi.

Early differential diagnosis between malignant and benign tumors and their underlying intrinsic differences are the most critical issues for life-threatening cancers. To study whether human acral melanomas, deadly cancers that occur on non-hair-bearing skin, have distinct origins that underlie their invasive capability, we develop fate-tracing technologies of melanocyte stem cells in sweat glands (glandular McSCs) and in melanoma models in mice and compare the cellular dynamics with human melanoma. Herein, we report that glandular McSCs self-renew to expand their migratory progeny in response to genotoxic stress and trauma to generate invasive melanomas in mice that mimic human acral melanomas. The analysis of melanocytic lesions in human volar skin reveals that genetically unstable McSCs expand in sweat glands and in the surrounding epidermis in melanomas but not in nevi. The detection of such cell spreading dynamics provides an innovative method for an early differential diagnosis of acral melanomas from nevi.

Obesity accelerates hair thinning by stem cell-centric converging mechanisms.

Obesity is a worldwide epidemic that predisposes individuals to many age-associated diseases, but its exact effects on organ dysfunction are largely unknown1. Hair follicles-mini-epithelial organs that grow hair-are miniaturized by ageing to cause hair loss through the depletion of hair follicle stem cells (HFSCs)2. Here we report that obesity-induced stress, such as that induced by a high-fat diet (HFD), targets HFSCs to accelerate hair thinning. Chronological gene expression analysis revealed that HFD feeding for four consecutive days in young mice directed activated HFSCs towards epidermal keratinization by generating excess reactive oxygen species, but did not reduce the pool of HFSCs. Integrative analysis using stem cell fate tracing, epigenetics and reverse genetics showed that further feeding with an HFD subsequently induced lipid droplets and NF-κB activation within HFSCs via autocrine and/or paracrine IL-1R signalling. These integrated factors converge on the marked inhibition of Sonic hedgehog (SHH) signal transduction in HFSCs, thereby further depleting lipid-laden HFSCs through their aberrant differentiation and inducing hair follicle miniaturization and eventual hair loss. Conversely, transgenic or pharmacological activation of SHH rescued HFD-induced hair loss. These data collectively demonstrate that stem cell inflammatory signals induced by obesity robustly represses organ regeneration signals to accelerate the miniaturization of mini-organs, and suggests the importance of daily prevention of organ dysfunction.

Distinct types of stem cell divisions determine organ regeneration and aging in hair follicles.

Hair follicles, mammalian mini-organs that grow hair, miniaturize during aging, leading to hair thinning and loss. Here we report that hair follicle stem cells (HFSCs) lose their regenerative capabilities during aging owing to the adoption of an atypical cell division program. Cell fate tracing and cell division axis analyses revealed that while HFSCs in young mice undergo typical symmetric and asymmetric cell divisions to regenerate hair follicles, upon aging or stress, they adopt an atypical 'stress-responsive' type of asymmetric cell division. This type of division is accompanied by the destabilization of hemidesmosomal protein COL17A1 and cell polarity protein aPKCλ and generates terminally differentiating epidermal cells instead of regenerating the hair follicle niche. With the repetition of these atypical divisions, HFSCs detach from the basal membrane causing their exhaustion, elimination and organ aging. The experimentally induced stabilization of COL17A1 rescued organ homeostasis through aPKCλ stabilization. These results demonstrate that distinct stem cell division programs may govern tissue and organ aging.

A novel mouse model demonstrates that oncogenic melanocyte stem cells engender melanoma resembling human disease.

Melanoma, the deadliest skin cancer, remains largely incurable at advanced stages. Currently, there is a lack of animal models that resemble human melanoma initiation and progression. Recent studies using a Tyr-CreER driven mouse model have drawn contradictory conclusions about the potential of melanocyte stem cells (McSCs) to form melanoma. Here, we employ a c-Kit-CreER-driven model that specifically targets McSCs to show that oncogenic McSCs are a bona fide source of melanoma that expand in the niche, and then establish epidermal melanomas that invade into the underlying dermis. Further, normal Wnt and Endothelin niche signals during hair anagen onset are hijacked to promote McSC malignant transformation during melanoma induction. Finally, molecular profiling reveals strong resemblance of murine McSC-derived melanoma to human melanoma in heterogeneity and gene signatures. These findings provide experimental validation of the human melanoma progression model and key insights into the transformation and heterogeneity of McSC-derived melanoma.

Stem cell competition orchestrates skin homeostasis and ageing.

Stem cells underlie tissue homeostasis, but their dynamics during ageing-and the relevance of these dynamics to organ ageing-remain unknown. Here we report that the expression of the hemidesmosome component collagen XVII (COL17A1) by epidermal stem cells fluctuates physiologically through genomic/oxidative stress-induced proteolysis, and that the resulting differential expression of COL17A1 in individual stem cells generates a driving force for cell competition. In vivo clonal analysis in mice and in vitro 3D modelling show that clones that express high levels of COL17A1, which divide symmetrically, outcompete and eliminate adjacent stressed clones that express low levels of COL17A1, which divide asymmetrically. Stem cells with higher potential or quality are thus selected for homeostasis, but their eventual loss of COL17A1 limits their competition, thereby causing ageing. The resultant hemidesmosome fragility and stem cell delamination deplete adjacent melanocytes and fibroblasts to promote skin ageing. Conversely, the forced maintenance of COL17A1 rescues skin organ ageing, thereby indicating potential angles for anti-ageing therapeutic intervention.

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

Hair thinning and loss are prominent aging phenotypes but have an unknown mechanism. We show that hair follicle stem cell (HFSC) aging causes the stepwise miniaturization of hair follicles and eventual hair loss in wild-type mice and in humans. In vivo fate analysis of HFSCs revealed that the DNA damage response in HFSCs causes proteolysis of type XVII collagen (COL17A1/BP180), a critical molecule for HFSC maintenance, to trigger HFSC aging, characterized by the loss of stemness signatures and by epidermal commitment. Aged HFSCs are cyclically eliminated from the skin through terminal epidermal differentiation, thereby causing hair follicle miniaturization. The aging process can be recapitulated by Col17a1 deficiency and prevented by the forced maintenance of COL17A1 in HFSCs, demonstrating that COL17A1 in HFSCs orchestrates the stem cell-centric aging program of the epithelial mini-organ.

LGR4 is required for sequential molar development.

Tooth development requires proliferation, differentiation, and specific migration of dental epithelial cells, through well-organized signaling interactions with mesenchymal cells. Recently, it has been reported that leucine-rich repeat-containing G protein coupled receptor 4 (LGR4), the receptor of R-spondins, is expressed in many epithelial cells in various organs and tissues and is essential for organ development and stem cell maintenance. Here, we report that LGR4 contributes to the sequential development of molars in mice. LGR4 expression in dental epithelium was detected in SOX2+ cells in the posterior end of the second molar (M2) and the early tooth germ of the third molar (M3). In keratinocyte-specific Lgr4-deficient mice (Lgr4K5 KO ), the developmental defect became obvious by postnatal day 14 (P14) in M3. Lgr4K5 KO adult mice showed complete absence or the dwarfed form of M3. In M3 development in Lgr4K5 KO mice, at Wnt/ß-catenin signal activity was down-regulated in the dental epithelium at P3, as indicated by lymphoid enhancer-binding factor-1 (LEF1) expression. We also confirmed the decrease, in dental epithelium of Lgr4K5 KO mice, of the number of SOX2+ cells and the arrest of cell proliferation at P7, and observed abnormal differentiation at P14. Our data demonstrated that LGR4 controls the sequential development of molars by maintaining SOX2+ cells in the dental epithelium, which have the ability to form normal molars.

Coupling of the radiosensitivity of melanocyte stem cells to their dormancy during the hair cycle.

Current studies have revealed that stem cells are more radiosensitive than mature cells. As somatic stem cells are mostly kept in a quiescent state, this conflicts with Bergonié and Tribondeau's law that actively mitotic cells are the most radiosensitive. In this study, we focused on hair graying to understand the stress-resistance of melanocyte stem cells (McSCs). We used Dct-H2B-GFP transgenic mice which enables the stable visualization of McSCs and an anti-Kit monoclonal antibody which selectively eradicates amplifying McSCs. The results demonstrate that quiescent McSCs are rather radiosensitive, but the coexistence of non-quiescent McSCs provides the stem cell pool with radioresistance. The irradiated quiescent McSCs prematurely differentiate in the niche upon their activation without sufficiently renewing themselves for cyclic hair pigmentation. These data indicate that tissue radiosensitivity is largely dependent on the state of somatic stem cells under their local microenvironment.

LGR4 expressed in uterine epithelium is necessary for uterine gland development and contributes to decidualization in mice.

In previous work we generated mice with a tissue specific ablation of a leucine-rich repeat containing G-protein-coupled receptor 4 (Lgr4) using the Keratin-5 (K5) Cre transgenic mouse strain (Lgr4(K5 KO)). Interestingly, the Lgr4(K5 KO) female mice were subfertile, and their embryos had impaired development. Notably, the contributions of uterine development to the subfertility phenotype were not elucidated in the previous report. In a readdress, the following study explores uterine aberration in Lgr4(K5 KO) female mice. Histological analysis revealed that the uteri of Lgr4(K5 KO) mice displayed altered epithelial differentiation characterized by a reduction in the number of uterine glands. Furthermore, Lgr4 deletion led to the reduced expression of morphoregulatory genes related to the Wnt signaling pathway. Additionally, the uteri of the Lgr4(K5 KO) mice lost the ability to undergo induced decidualization. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis and administration of recombinant leukemia inhibitory factor (LIF) demonstrated that the impaired decidualization in Lgr4(K5 KO) mice resulted from the decreased secretion of LIF concurrent with a reduction in uterine gland count. Thus, we propose that LGR4 contributes to uterine gland development, which supports decidualization during pregnancy.

LGR4 is required for the cell survival of the peripheral mesenchyme at the embryonic stages of nephrogenesis.

In mice, homozygous Lgr4 inactivation results in hypoplastic kidneys. To understand better the role of LGR4 in kidney development, we performed an analysis of kidneys in Lgr4-/- embryos. We stained Lgr4-/- kidneys with anti-WT1 and anti-Cleaved Caspase3 antibodies at E16.5, and observed that the structures of the cap mesenchyme were disrupted and that apoptosis increased. In addition, the expression of PAX2, an anti-apoptotic factor in kidney development, was also significantly decreased at E16.5. We found that the LGR4 defect caused an increase in apoptosis in the peripheral mesenchyme during kidney development.

Immunological characteristics and response to lipopolysaccharide of mouse lines selectively bred with natural and acquired immunities.

Genetic improvement of resistance to infectious diseases is a challenging goal in animal breeding. Infection resistance involves multiple immunological characteristics, including natural and acquired immunity. In the present study, we developed an experimental model based on genetic selection, to improve immunological phenotypes. We selectively established three mouse lines based on phagocytic activity, antibody production and the combination of these two phenotypes. We analyzed the immunological characteristics of these lines using a lipopolysaccharide (LPS), which is one of the main components of Gram-negative bacteria. An intense immunological reaction was induced in each of the three mouse lines. Severe loss of body weight and liver damage were observed, and a high level of cytokine messenger RNA was detected in the liver tissue. The mouse line established using a combination of the two selection standards showed unique characteristics relative to the mouse lines selected on the basis of a single phenotype. Our results indicate that genetic selection and breeding is effective, even for immunological phenotypes with a relatively low heritability. Thus, it may be possible to improve resistance to infectious diseases by means of genetic selection.

Lgr5 homologues associate with Wnt receptors and mediate R-spondin signalling.

The adult stem cell marker Lgr5 and its relative Lgr4 are often co-expressed in Wnt-driven proliferative compartments. We find that conditional deletion of both genes in the mouse gut impairs Wnt target gene expression and results in the rapid demise of intestinal crypts, thus phenocopying Wnt pathway inhibition. Mass spectrometry demonstrates that Lgr4 and Lgr5 associate with the Frizzled/Lrp Wnt receptor complex. Each of the four R-spondins, secreted Wnt pathway agonists, can bind to Lgr4, -5 and -6. In HEK293 cells, RSPO1 enhances canonical WNT signals initiated by WNT3A. Removal of LGR4 does not affect WNT3A signalling, but abrogates the RSPO1-mediated signal enhancement, a phenomenon rescued by re-expression of LGR4, -5 or -6. Genetic deletion of Lgr4/5 in mouse intestinal crypt cultures phenocopies withdrawal of Rspo1 and can be rescued by Wnt pathway activation. Lgr5 homologues are facultative Wnt receptor components that mediate Wnt signal enhancement by soluble R-spondin proteins. These results will guide future studies towards the application of R-spondins for regenerative purposes of tissues expressing Lgr5 homologues.

Lgr4-deficient mice showed premature differentiation of ureteric bud with reduced expression of Wnt effector Lef1 and Gata3.

We previously reported that Lgr4 has a critical role in the morphogenesis of kidney, but the detailed functions of Lgr4 in kidney development have not been elucidated. In contrast to Lgr4 null mice with 129Ola × C57BL/6J mixed background, C57BL/6J-backcrossed Lgr4 null mice (Lgr4(-/-)) showed the severe phenotype of embryonic lethality and also had dilated tubules in kidneys at E16.5. Based on quantitative RT-PCR and in situ hybridization, branching morphogenesis at E15.5 in the Lgr4(-/-) was arrested earlier, and both DBA-lectin staining and immunohistochemical analysis using Aqp3 antibodies showed that the ureteric bud (UB) of Lgr4(-/-) kidneys underwent premature differentiation. Furthermore, quantitative RT-PCR and histological analysis suggested that the impaired UB differentiation was caused by down-regulation of the Wnt pathway and Gata3 in the Lgr4(-/-) kidneys. We demonstrate here that Lgr4 has a novel function for maintaining the UB in an undifferentiated state.

Reduced fertility with impairment of early-stage embryos observed in mice lacking Lgr4 in epithelial tissues.

Lgr4 is one of the genes identified as novel G protein-coupled receptor genes designated Lgr4-Lgr8, with high homology with FSH receptor, LH receptor, and TSH receptor genes, but studies of Lgr4-mutant mice have suggested that Lgr4 has essential functions in development. This is the first report describing the relationship between the functions of Lgr4 and female reproductive systems.

Impaired hair placode formation with reduced expression of hair follicle-related genes in mice lacking Lgr4.

We observed that Lgr4K5 KO mice had sparse head hair and focal alopecia behind their ears, as observed in tabby (Eda) and downless (Edar) mice, which are models of the human genetic disorder hypohidrotic (anhidrotic) ectodermal dysplasia (HED). Lgr4-deficient mice showed partial impairment in hair follicle development with reduced expression of Edar, Lef1, and Shh, which were essential for hair follicle morphogenesis, in the epidermis. Immunohistochemical analysis of Lgr4-/- mice epidermis using shh antibody showed reduced numbers of hair placodes, and we also detected higher phosphorylation of Smad1/5/8, which is required to suppress normal hair follicle induction. We suspected that Lgr4 might be a novel gene class regulating the development of hair follicles.

Eye-open at birth phenotype with reduced keratinocyte motility in LGR4 null mice.

We observed a consistent eye-open at birth (EOB) phenotype in mouse pups homozygous for a leucine-rich repeat containing G-protein coupled receptor 4 (Lgr4) allele deleting the whole transmembrane domain coding region. An in vitro wound-healing scratch assay showed notably reduced keratinocyte motility in the null mice. Phalloidin staining of F-actin in the eyelid epidermis was also reduced. We also generated keratinocyte-specific Lgr4 deficient mice, circumventing the embryonic/neonatal lethality and kidney abnormalities. Most of the conditional Lgr4 knockout mice showed the EOB phenotype. Thus, Lgr4 might be a novel gene class regulating cell motility.

Leucine-rich repeat-containing G protein-coupled receptor-4 (LGR4, Gpr48) is essential for renal development in mice.

Leucine-rich repeat-containing G protein-coupled receptor (LGR)-4 is a G protein-coupled receptor (GPCR) with a seven-transmembrane domain structure. LGRs are evolutionally and structurally phylogenetic, classified into three subgroups and are members of the so-called orphan receptors whose ligands have yet to be identified. We generated knockout mice lacking Lgr4(Gpr48) by targeted deletion of part of exon 18, which codes for the transmembrane and signal-transducing domains of the receptor. Lgr4 null mice were born at much less than the 25% expected frequency from crosses of Lgr4 heterozygous mice (Lgr4+/-). Lgr4 null mice that survived in utero died shortly after birth in almost all cases. We observed striking renal hypoplasia in the null mice, accompanied by elevated concentration of plasma creatinine. Histological analysis of the P0 null mouse kidney showed a notable decrease in the total number and density of the glomerulus. Thus, the function of Lgr4 is essential to regulate renal development in the mouse. This study suggests that the Lgr4 gene is a new and important member of LGRs involved in a group of genes responsible for hereditary disease in the kidney.