Hair Loss Phenotype Research Articles

Abstract 1244: Exploiting the pathogenesis of endogenous retrovirus to tackle squamous cancers

Abstract Retrotransposons are the evolution relic of ancestrally invaded retroviruses interspersed through our genome. Mostly domesticated as host regulome, retrotransposons shape lineage gene expressions or donate coding functions. A few rare evolutionarily young species remain virally active, leading to germline mutations and modulating immune functions. Aberrant retrotransposon activities have been widely observed in adult diseases, although the extent to which they ensue active viral form and function under those contexts is unclear. Their molecular trigger in adult pathophysiology is poorly defined. To address these questions, we use murine skin as our model, given its well-characterized, abundant and highly accessible adult stem cells, not only mediating postnatal remodeling and homeostatic regeneration, but also responding to stress by driving tissue repair and adaptations. By analyzing a genetic model lacking a known retrotransposon suppressor, histone methyltransferase Setdb1, which we found to be essential in the adult skin, we saw hair loss and hair follicle stem cell exhaustion phenotype, accompanied by a robust and selective surge of endogenous retroviruses (ERVs). When combined with squamous cell carcinoma drivers, Setdb1 loss significantly blocked tumor progression in vivo. Interestingly, compared to relatively mild or no induction of commonly observed evolutionarily young ERVs, the most induced species in our model is a class I ERV, murine leukemia virus (MuLV). We detected abundant retroviral peptides originated from its full-length copies through mass spectrometry and viral-like particles through transmission electron microscopy that are immunoreactive to a monoclonal MuLV env antibody. Similar viral-like particles were broadly evident across several epithelial tissues beyond skin, implicating its conserved function across squamous cancers. Epithelial originated ERVs elicit tissue wide inflammatory response, and can be ameliorated by pharmacological or genetic inhibition of retroviral activity. Physiologically, viral-coding ERVs arise as the epigenetic machinery declines in response to age-associated stress, and plummet when host safeguard prevails in UV induced skin hyperplasia. As an evolutionary conundrum, viral-coding ERVs pose a threat to host fitness and yet, they’ve resisted extinction persisting in the mammalian genome. Our findings suggest viral-coding ERVs wrestle with the host surveillance programs to regulate adult tissue physiology and pathology, thus providing a key target in eliciting innate immunity and tackling squamous cancers. Citation Format: Ying Lyu, Yejing Ge. Exploiting the pathogenesis of endogenous retrovirus to tackle squamous cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1244.

Abstract A132: Pathological analysis of a newly established immunocompetent mice with full Hpv16 genome integration

Abstract Human papillomaviruses (HPV) are associated with both benign and malignant epithelial lesions. High-risk HPV subtype HPV 16 is the causative agent of cervical and the majority of oropharyngeal squamous cell carcinomas. Despite the continuous increase in the disease burden, mechanisms and pathways of HPV16-induced cancer growth are not fully understood, thus leading to suboptimal treatment. In last decades, several transgenic mouse models were developed, helped tremendously to study HPV-induced carcinogenesis. However, all existent HPV transgenic mice were targeted early genes expression driven by an artificial promoter and did not encompass the functionality of the whole HPV genome, including the upstream regulatory region (URR) that contains HPV promoters, regulatory elements, and a replication origin, limited our ability to investigate HPV-associated malignant transformation and the role of host factors in this process. Therefore, we generated HPV16 transgenic mouse by using CRISPR/Cas9-mediated genome editing to insert the full-length HPV16 genome into the Rosa26 locus. Two founder mice, with single HPV copy and with tandem HPV integration, were used to establish mouse colonies. Interestingly, regardless of HPV copy number, ~50% of the HPV knock-in mice exhibited early death during the first 2 weeks after birth, while survived pups were significantly smaller than the same age wild-type mice, and had severe hair loss. Intriguingly, the growth retardant and hair loss phenotype in the HPV16 knock-in mice disappeared in ~4 weeks, most likely indicating that viral genes compromise specific stages of mouse development. We evaluated the expression of HPV genes during development, in different mouse organs, and in established fibroblasts and epithelial cell cultures. Our newly established HPV16 knock-in mouse model provides viral gene expression from natural viral promoters offering an essential basis to explore the role of cellular factors in HPV-driven pathologies. Citation Format: Xue Li, Aditi Kothari, Hina Rehmani, Wendell Yarbrough, Natalia Isaeva. Pathological analysis of a newly established immunocompetent mice with full Hpv16 genome integration [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A132.

167 Epidermal GRK2 knockout triggers a hair loss phenotype with features resembling immune-mediated alopecias

167 Epidermal GRK2 knockout triggers a hair loss phenotype with features resembling immune-mediated alopecias

Abstract LB350: Novel mouse model to study HPV associated pathologies

Abstract Papillomaviruses are species specific, non-enveloped, double-stranded DNA viruses that have an ~8kb circular genome enclosed by a 55 nm icosahedral capsid. Human papillomaviruses (HPV) are associated with both benign and malignant epithelial lesions. High-risk HPV subtypes are the causative agents of cervical and the majority of oropharyngeal squamous cell carcinomas. Persistent HPV infection is required for HPV-associated tumorigenesis; however, cellular factors needed to support the viral persistence and HPV genes expression are not completely understood. Several transgenic mouse models, developed in last decades, helped tremendously to study HPV-induced carcinogenesis. However, the absence of HPV non-coding upstream regulatory region and late coding region, as well as targeted early genes expression driven by an artificial promoter - features that are shared by all existent HPV transgenic mice - limit our ability to investigate HPV-associated malignant transformation and the role of host factors in this process. Therefore, we generated HPV16 transgenic mouse by using CRISPR/Cas9-mediated genome editing to insert the full-length HPV16 genome into the Rosa26 locus. Two founder mice, with single HPV copy and with tandem HPV integration, were used to establish mouse colonies. Interestingly, regardless of HPV copy number, ~30% of the HPV knock-in mice exhibited early death during the first 2 weeks after birth, while survived pups were significantly smaller than the same age wild-type mice, and had severe hair loss. Intriguingly, the growth retardant and hair loss phenotype in the HPV16 knock-in mice disappeared in ~4 weeks, most likely indicating that viral genes compromise specific stages of mouse development. We evaluated the expression of HPV genes during development, in different mouse organs, and in established fibroblasts and epithelial cell cultures. Our newly developed HPV16 knock-in mouse model provides viral gene expression from natural viral promoters offering an essential basis to explore the role of cellular factors in HPV-driven pathologies. Citation Format: Xue Li, Travis Schrank, Aditi Kothari, Hina Rehmani, Jason Tasoulas, Sulgi Kim, Wendell Yarbrough, Natalia Isaeva. Novel mouse model to study HPV associated pathologies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB350.

Consumption of fish oil high-fat diet induces murine hair loss via epidermal fatty acid binding protein in skin macrophages

Fats are essential in healthy diets, but how dietary fats affect immune cell function and overall health is not well understood. Mimicking human high-fat diets (HFDs), which are rich in different fatty acid (FA) components, we fed mice various HFDs from different fat sources, including fish oil and cocoa butter. Mice consuming the fish oil HFD exhibit a hair-loss phenotype. Further studies show that omega-3 (n-3) FAs in fish oil promote atypical infiltration of CD207- (langerin-) myeloid macrophages in skin dermis, which induce hair loss through elevated TNF-α signaling. Mechanistically, epidermal fatty acid binding protein (E-FABP) is demonstrated to play an essential role in inducing TNF-α-mediated hair loss by activating the n-3 FA/ROS/IL-36 signaling pathway in dermal resident macrophages. Absence of E-FABP abrogates fish oil HFD-induced murine hair loss. Altogether, these findings support a role for E-FABP as a lipid sensor mediating n-3 FA-regulated macrophage function and skin health.

Protein Kinase C Downregulation upon Rapamycin Treatment Attenuates Neuroinflammation and Mitochondrial Disease

Mitochondrial dysfunction causes many poorly understood diseases, such as Leigh Syndrome, that are often caused by dysfunctions in proteins involved in the electron transport chain. My lab previously reported mTOR is pathologically involved in the neurodegenerative phenotype and premature death of mice missing the Complex I subunit Ndufs4 (Ndufs4-/- mice). We discovered treatment with rapamycin extends lifespan, reduces neuroinflammation, and attenuates the neurodegenerative phenotype in these mice, although the mechanisms remain unclear. Rapamycin-treated Ndufs4-/- mice exhibited decreased activation of the mTORC1 pathway. It also deactivated the mTORC2 pathway. We observed that phosphorylation of the canonical protein kinase C (PKC) isoforms (PKC-α, -β, and -γ) decreased more than any other kinases, leading us to hypothesize its deactivation contributes to the observed lifespan extension. To test this, we treated Ndufs4-/- mice with three different PKC inhibitors: the pan-PKC inhibitors GO6983 and GF109203X, and the PKC-β specific inhibitor ruboxistaurin. Similar to rapamycin, all three drugs were able to significantly delay the onset of neurological symptoms (i.e. clasping) and increase survival. We also observed that PKC-β inhibition reduced skin inflammation to suppress the hair loss phenotype displayed by Ndufs4-/- mice at weaning. We further discovered PKC-β inhibition reduces neuroinflammation by deactivating the NF-kB inflammatory pathway. These results suggest that mTORC2 may play a critical role in the etiology of mitochondrial diseases such as Leigh Syndrome.

Alopecia areata susceptibility variant in MHC region impacts expressions of genes contributing to hair keratinization and is involved in hair loss.

BackgroundAlopecia areata (AA) is considered a highly heritable, T-cell-mediated autoimmune disease of the hair follicle. However, no convincing susceptibility gene has yet been pinpointed in the major histocompatibility complex (MHC), a genome region known to be associated with AA as compared to other regions.MethodsWe engineered mice carrying AA risk allele identified by haplotype sequencing for the MHC region using allele-specific genome editing with the CRISPR/Cas9 system. Finally, we performed functional evaluations in the mice and AA patients with and without the risk allele.FindingsWe identified a variant (rs142986308, p.Arg587Trp) in the coiled-coil alpha-helical rod protein 1 (CCHCR1) gene as the only non-synonymous variant in the AA risk haplotype. Furthermore, mice engineered to carry the risk allele displayed a hair loss phenotype. Transcriptomics further identified CCHCR1 as a novel component interacting with hair cortex keratin in hair shafts. Both, these alopecic mice and AA patients with the risk allele displayed morphologically impaired hair and comparable differential expression of hair-related genes, including hair keratin and keratin-associated proteins (KRTAPs).InterpretationOur results implicate CCHCR1 with the risk allele in a previously unidentified subtype of AA based on aberrant keratinization in addition to autoimmune events.FundingThis work was supported by JSPS KAKENHI (JP16K10177) and the NIHR UCLH Biomedical Research center (BRC84/CN/SB/5984).

ROBO4 deletion ameliorates PAF-mediated skin inflammation via regulating the mRNA translation efficiency of LPCAT1/LPCAT2 and the expression of PAF receptor.

The diminished level of platelet-activating factor acetylhydrolase (PAFAH) in milk causes an enhanced level of platelet activating factor (PAF) in the skin, leading to a severe hair loss phenotype during neonatal pup's lactation. The deletion of very-low-density-lipoprotein receptor (VLDLR) prevents the expression and secretion of PAFAH. Here we revealed that deletion of Roundabout 4 (ROBO4) in mice ameliorated hair loss phenotype via reducing PAF concentration in skin. As a consequence, the neonatal pups with ROBO4 deletion lactated by mother with VLDLR deletion showed normal hair phenotype during lactation. In details,ROBO4 deletion reduced the protein but not mRNA expression of two PAF synthetic enzymes LPCAT1/LPCAT2 in macrophage as well as the expression of PAF receptor in both macrophage and ocular tissue, but increased PAFAH protein in serum. On the other hand, RNA expression profile analysis in macrophages revealed that the genes involving in oxidative phosphorylation and ribosome obviously decreased their expression in response to ROBO4 deletion. Moreover, through High Performance Liquid Chromatography (HPLC) analysis, we found that ATP concentration also reduced in ROBO4 deletion macrophages. Because ribosome and energy are very important factors for the mRNA translation, we then tested whether ROBO4 deletion affects LPCAT1/LPCAT2 mRNA translation using polyribosome assay. As expected, the mRNA level of LPCAT1/LPCAT2 significantly decreased in polyribosome in ROBO4 deletion macrophage comparing to that of wild type. Additionally, mice with ROBO4 deletion suppressed LPS-induced IL-6 expression as well as the phosphorylation of p44/42 and p65, but enhanced the AKT phosphorylation. Collectively, ROBO4 deletion alleviates PAF- and LPS-mediated inflammation. And above results also indicate PAF signal might be a crosstalk point of ROBO4- and VLDLR-activated pathways.

How chemotherapy and radiotherapy damage the tissue: Comparative biology lessons from feather and hair models.

Chemotherapy and radiotherapy are common modalities for cancer treatment. While targeting rapidly growing cancer cells, they also damage normal tissues and cause adverse effects. From the initial insult such as DNA double-strand break, production of reactive oxygen species (ROS) and a general stress response, there are complex regulatory mechanisms that control the actual tissue damage process. Besides apoptosis, a range of outcomes for the damaged cells are possible including cell cycle arrest, senescence, mitotic catastrophe, and inflammatory responses and fibrosis at the tissue level. Feather and hair are among the most actively proliferating (mini-)organs and are highly susceptible to both chemotherapy and radiotherapy damage, thus provide excellent, experimentally tractable model systems for dissecting how normal tissues respond to such injuries. Taking a comparative biology approach to investigate this has turned out to be particularly productive. Started in chicken feather and then extended to murine hair follicles, it was revealed that in addition to p53-mediated apoptosis, several other previously overlooked mechanisms are involved. Specifically, Shh, Wnt, mTOR, cytokine signalling and ROS-mediated degradation of adherens junctions have been implicated in the damage and/or reparative regeneration process. Moreover, we show here that inflammatory responses, which can be prominent upon histological examination of chemo- or radiotherapy-damaged hair follicle, may not be essential for the hair loss phenotype. These studies point to fundamental, evolutionarily conserved mechanisms in controlling tissue responses in vivo, and suggest novel strategies for the prevention and management of adverse effects that arise from chemo- or radiotherapy.

Reversal of the hair loss phenotype by modulating the estradiol-ANGPT2 axis in the mouse model of female pattern hair loss

BackgroundDespite high demand for a remedy, the treatment options for female pattern hair loss (FPHL) are limited. FPHL is frequent in postmenopausal women. In ovariectomized (OVX) mice, which lack β-estradiol (E2) and manifest hair loss mimicking FPHL, E2 supplementation has been shown to increase hair density. However, the mechanism by which E2 exhibits its biological activity remains elusive. ObjectiveTo identify the downstream targets of E2 in the context of FPHL pathophysiology and discover a potential therapeutic agent for the E2-dependent subtype of FPHL. MethodsHuman dermal papilla cells (hDPCs) were cultured with E2, and a microarray analysis was performed to identify the genes regulated by E2. Using OVX mice, the identified gene product was intradermally administered and then quantitative image analysis of hair density was conducted. In silico analysis to link E2 and the identified gene was performed. ResultsGlobal gene expression and bioinformatics analyses revealed that the genes associated with the angiopoietin-2 (ANGPT2) pathway were upregulated by E2 in hDPCs. ANGPT2 was significantly downregulated in OVX mice than in sham-operated mice (P < 0.01). Importantly, hair density was higher in OVX mice treated with ANGPT2 than in control mice (P < 0.05). In silico analysis showed DNA sequences with high possibility of estrogen receptor binding in the promoter region of ANGPT2. ConclusionThe E2-ANGPT2 axis is present in hair follicles. ANGPT2 provides a strategy for the management of E2-dependent and postmenopausal subsets of FPHL.

Comparative genomics analyses of alpha-keratins reveal insights into evolutionary adaptation of marine mammals

BackgroundDiversity of hair in marine mammals was suggested as an evolutionary innovation to adapt aquatic environment, yet its genetic basis remained poorly explored. We scanned α-keratin genes, one major structural components of hair, in 16 genomes of mammalian species, including seven cetaceans, two pinnipeds, polar bear, manatee and five terrestrial species.ResultsExtensive gene loss and high pseudogenization rate of α-keratin genes were identified in cetaceans when compared to terrestrial artiodactylans (average number of α-keratins 37.29 vs. 58.33; pseudogenization rate 29.89% vs. 8.00%), especially of hair follicle-specific keratin genes (average pseudogenization rate in cetaceans of 43.88% relative to 3.80% artiodactylian average). Compared to toothed whale, the much more number of intact functional α-keratin genes was examined in the baleen whale that had specific keratinized baleen. In contrast, the number of keratin genes in pinnipeds, polar bear and manatee were comparable to those of their respective terrestrial relatives. Additionally, four keratin genes (K39, K9, K42, and K74) were found to be pseudogenes or lost uniquely in cetaceans and manatees.ConclusionsSpecies-specific evolution of α-keratin gene family identified in the marine mammals might be responsible for their different hair characteristics. Increased gene loss and pseudogenization rate identified in cetacean lineages was likely to contribute to hair-less phenotype to adaptation for complete aquatic environment. However, the fully aquatic manatee still remained the comparable number of intact genes to its terrestrial relative, probably due to its perioral bristles and bristle-like hairs on the oral disk. By contrast, similar evolution pattern of α-keratin gene repertoire in the pinnipeds, polar bear and their terrestrial relatives was likely due to abundant hair to keep warm when they went ashore. Interestingly, some keratin genes were exclusively lost in cetaceans and manatees, likely as a result of convergent hair-loss phenotype to inhabit completely aquatic environment in both groups.

Simple generation of hairless mice for in vivo imaging.

The in vivo imaging of mice makes it possible to analyze disease progress non-invasively through reporter gene expression. As the removal of hair improves the accuracy of in vivo imaging, gene-modified mice with a reporter gene are often crossed with Hos:HR-1 mutant mice homozygous for the spontaneous Hrhr mutation that exhibit a hair loss phenotype. However, it is time consuming to produce mice carrying both the reporter gene and mutant Hrhr gene by mating. In addition, there is a risk that genetic background of the gene-modified mice would be altered by mating. To resolve these issues, we established a simple method to generate hairless mice maintaining the original genetic background by CRISPR technology. First, we constructed the pX330 vector, which targets exon 3 of Hr. This DNA vector (5 ng/µl) was microinjected into the pronuclei of C57BL/6J mice. Induced Hr gene mutations were found in many founders (76.1%) and these mutations were heritable. Next, we performed in vivo imaging using these gene-modified hairless mice. As expected, luminescent objects in their body were detected by in vivo imaging. This study clearly showed that hairless mice could be simply generated by the CRISPR/Cas9 system, and this method may be useful for in vivo imaging studies with various gene-modified mice.

396 Induced expression of gasdermin A3 in the skin caused keratinocyte necrosis and anagen delay in the hair cycle

The epidermis forms a critical physical and immune barrier. Dysregulation of keratinocyte to cell death upon external stimuli could compromise the epidermal barrier immunity and cause skin inflammation. Gasdermin A was involved in gastric epithelial apoptosis; its function in the skin was hinted by the skin inflammation and hair loss phenotype in mice with dominant mutations in gasdermin A3 (Gsdma3). The mode of GSDMA3’s action and pathogenesis are in dispute. We and other group have demonstrated that N-terminal portion of Gsdma3 (N-Gsdma3) contains the functional domain, which is auto-regulated by its C-terminal domain. However, overexpression of N-Gsdma3 has been shown to induce autophagy or pyroptosis in some cell culture models. To study the biological function of GSDMA3 in vivo, we generated a doxycycline-inducible double transgenic (DTg) mouse model to express GSDMA3 in the epidermis using K14-rtTA mouse. We found that GSDMA3 overexpression caused epidermal hyperplasia and inflammatory infiltrations, which were associated with increased TNF-α and IL-1α expression. In addition, hair plucking was employed to induce hair cycle reentry at telogen phase. We found a significant delay in anagen initiation in DTg mice but their catagen phase seemed normal. We also observed increased macrophages around and in the bulge region of DTg hair follicles compared with control hair follicles, suggesting that bulge immune privilege was compromised. Regarding the underlying pathogenesis mechanism, we found increased TUNEL-positive staining and spontaneous necrotic-like keratinocytes in DTg mice. In primary keratinocytes isolated from the DTg mice, induced expression of Gsdma3 caused increased mitochondria ROS production, leakage of intracellular components, and spontaneous necrosis. Our data indicated that an innate immune-mediated mechanism could underlie the Gsdma3-mediated skin inflammation phenotype.

Betaine supplementation is less effective than methionine restriction in correcting phenotypes of CBS deficient mice.

Cystathionine beta synthase (CBS) deficiency is a recessive inborn error of metabolism characterized by elevated serum total homocysteine (tHcy). Betaine supplementation, which can lower tHcy by stimulating homocysteine remethylation to methionine, is often given to CBS deficient patients in combination with other treatments such as methionine restriction and supplemental B-vitamins. However, the effectiveness of betaine supplementation by itself in the treatment of CBS deficiency has not been well explored. Here, we have examined the effect of a betaine supplemented diet on the Tg-I278T Cbs (-/-) mouse model of CBS deficiency and compared its effectiveness to our previously published data using a methionine restricted diet. Tg-I278T Cbs (-/-) mice on betaine, from the time of weaning until for 240days of age, had a 40% decrease in mean tHcy level and a 137% increase in serum methionine levels. Betaine-treated Tg-I278T Cbs (-/-) mice also exhibited increased levels of betaine-dependent homocysteine methyl transferase (BHMT), increased levels of the lipogenic enzyme stearoyl-coenzyme A desaturase (SCD-1), and increased lipid droplet accumulation in the liver. Betaine supplementation largely reversed the hair loss phenotype in Tg-I278T Cbs (-/-) animals, but was far less effective than methionine restriction in reversing the weight-loss, fat-loss, and osteoporosis phenotypes. Surprisingly, betaine supplementation had several negative effects in control Tg-I278T Cbs (+/-) mice including decreased weight gain, lean mass, and bone mineral density. Our findings indicate that while betaine supplementation does have some beneficial effects, it is not as effective as methionine restriction for reversing the phenotypes associated with severe CBS deficiency in mice.

Loss of conserved Gsdma3 self-regulation causes autophagy and cell death.

Gasdermin A3 (Gsdma3) was originally identified in association with hair-loss phenotype in mouse mutants. Our previous study found that AE mutant mice, with a Y344H substitution at the C-terminal domain of Gsdma3, display inflammation-dependent alopecia and excoriation [Zhou et al. (2012) Am. J. Pathol. 180, 763-774]. Interestingly, we found that the newly-generated null mutant of Gsdma3 mice did not display the skin dysmorphology, indicating that Gsdma3 is not essential for differentiation of epidermal cells and maintenance of the hair cycle in normal physiological conditions. Consistently, human embryonic kidney (HEK)293 and HaCaT cells transfected with wild-type (WT) Gsdma3 did not show abnormal morphology. However, Gsdma3 Y344H mutation induced autophagy. Gsdma3 N-terminal domain, but not the C-terminal domain, also displayed the similar pro-autophagic activity. The Gsdma3 Y344H mutant protein and N-terminal domain-induced autophagy was associated with mitochondria and ROS generation. Co-expression of C-terminal domain reversed the cell autophagy induced by N-terminal domain. Moreover, C-terminal domain could be co-precipitated with N-terminal domain. These data indicated that the potential pro-autophagic activity of WT Gsdma3 protein is suppressed through an intramolecular inhibition mechanism. Studies on other members of the GSDM family suggested this mechanism is conserved in several sub-families.

CtBP1 Overexpression in Keratinocytes Perturbs Skin Homeostasis

Carboxyl-terminal binding protein-1 (CtBP1) is a transcriptional co-repressor with multiple in vitro targets, but its in vivo functions are largely unknown. We generated keratinocyte-specific CtBP1 transgenic mice with a keratin 5 promoter (K5.CtBP1) to probe the pathological roles of CtBP1. At transgene expression levels comparable with endogenous CtBP1 in acute skin wounds, K5.CtBP1 epidermis displayed hyperproliferation, loss of E-cadherin, and failed terminal differentiation. Known CtBP1 target genes associated with these processes, e.g., p21, Brca1, and E-cadherin were down-regulated in K5.CtBP1 skin. Surprisingly, K5.CtBP1 pups also exhibited a hair loss phenotype. We found that expression of the Distal-less 3 (Dlx3), a critical regulator of hair follicle differentiation and cycling, was decreased in K5.CtBP1 mice. Molecular studies revealed that CtBP1 directly suppressed Dlx3 transcription. Consistently, K5.CtBP1 mice displayed abnormal hair follicles with decreased expression of Dlx3 downstream targets Gata3, Hoxc13, and hair keratins. In sum, this first CtBP1 transgenic model provides in vivo evidence for certain CtBP1 functions predicted from in vitro studies, reveals to our knowledge previously unreported functions and transcriptional activities of CtBP1 in the context of epithelial-mesenchymal interplay, and suggest CtBP1 has a pathogenesis role in hair follicle morphogenesis and differentiation.

Iron deficient toxic milk leads to the mask phenotype in hephaestin knockout mice (907.4)

Iron is an essential element that is required for many cellular functions. Multiple symptoms of iron deficiency have been reported in humans, including anemia, hair loss, stunted growth, and reduced oxygen transport. Mammalian iron intake is mediated in two different ways, across the placenta during fetal growth, and through the intestine during postnatal growth and development. We previously identified hephaestin (Hp), a copper‐iron ferroxidase, which plays a key role in intestinal iron transport. Hephaestin oxidizes iron and works in conjunction with ferroportin to facilitate iron export from enterocytes and its efficient binding to plasma transferrin. Null mutations in the Hp gene cause an accumulation of intracellular iron, specifically in the intestine. During analysis of the Hp null mice, we discovered that neonates born to Hp knockout (Hp KO) dams developed truncal hair loss (the “mask” hair loss phenotype) that resolved after weaning. The same phenotype was also observed in pups born to mothers with intestine‐specific knockout of Hp (even WT (floxed) pups born to these mothers), suggesting that lack of maternal Hp in the intestine alone is responsible for the mask phenotype. In order to determine the stage (ante and/or post natal) at which lack of maternal Hp leads to pup hair loss, we performed cross‐fostering studies. Wild‐type pups fed by Hp KO dams presented with the “mask” phenotype, whereas, all pups fed by the WT dams had normal hair growth. Histology of the affected skin of pups fed by Hp KO dams showed disorientation and keratinization of the follicles, follicular infundibular plugging and some tortuosity to the hair canals. Our findings suggest the involvement of a “toxic milk” phenotype involving low iron levels in the milk causing this phenotype.Grant Funding Source: R01 GM083198‐01A1

Deletion of Cysteine Cathepsins B or L Yields Differential Impacts on Murine Skin Proteome and Degradome

Numerous studies highlight the fact that concerted proteolysis is essential for skin morphology and function. The cysteine protease cathepsin L (Ctsl) has been implicated in epidermal proliferation and desquamation, as well as in hair cycle regulation. In stark contrast, mice deficient in cathepsin B (Ctsb) do not display an overt skin phenotype. To understand the systematic consequences of deleting Ctsb or Ctsl, we determined the protein abundances of >1300 proteins and proteolytic cleavage events in skin samples of wild-type, Ctsb(-/-), and Ctsl(-/-) mice via mass-spectrometry-based proteomics. Both protease deficiencies revealed distinct quantitative changes in proteome composition. Ctsl(-/-) skin revealed increased levels of the cysteine protease inhibitors cystatin B and cystatin M/E, increased cathepsin D, and an accumulation of the extracellular glycoprotein periostin. Immunohistochemistry located periostin predominantly in the hypodermal connective tissue of Ctsl(-/-) skin. The proteomic identification of proteolytic cleavage sites within skin proteins revealed numerous processing sites that are underrepresented in Ctsl(-/-) or Ctsb(-/-) samples. Notably, few of the affected cleavage sites shared the canonical Ctsl or Ctsb specificity, providing further evidence of a complex proteolytic network in the skin. Novel processing sites in proteins such as dermokine and Notch-1 were detected. Simultaneous analysis of acetylated protein N termini showed prototypical mammalian N-alpha acetylation. These results illustrate an influence of both Ctsb and Ctsl on the murine skin proteome and degradome, with the phenotypic consequences of the absence of either protease differing considerably.

The Hairless Gene: A Putative Navigator of Hair Follicle Development

Abstract The Hairless (HR) gene regulates the expression of sev-eral target genes as a transcriptional corepressor of nu-clear receptors. The hair follicle (HF), a small independ-ent organ of the skin, resides in the epidermis and un-dergoes regenerative cycling for normal hair formation. HF development requires many genes and signaling pathways to function properly in time and space, one of them being the HR gene. Various mutations of the HR gene have been reported to cause the hair loss pheno-type in rodents and humans. In recent studies, it has been suggested that the HR gene is a critical player in the regulation of the hair cycle and, thus, HF develop-ment. Furthermore, the HR gene is associated with the Wnt signaling pathway, which regulates proliferation and differentiation of cells and plays an essential role in hair and skin development. In this review, we summarize the mutations responsible for human hair disorders and dis-cuss the roles of the HR gene in HF development. Keywords: hairless, corepressor, hair follicle, hair cycle, hair loss

Delineating Immune-Mediated Mechanisms Underlying Hair Follicle Destruction in the Mouse Mutant Defolliculated

Defolliculated (Gsdma3(Dfl)/+) mice have a hair loss phenotype that involves an aberrant hair cycle, altered sebaceous gland differentiation with reduced sebum production, chronic inflammation, and ultimately the loss of the hair follicle. Hair loss in these mice is similar to that seen in primary cicatricial, or scarring alopecias in which immune targeting of hair follicle stem cells has been proposed as a key factor resulting in permanent hair follicle destruction. In this study we examine the mechanism of hair loss in GsdmA3(Dfl)/+ mice. Aberrant expression patterns of stem cell markers during the hair cycle, in addition to aberrant behavior of the melanocytes leading to ectopic pigmentation of the hair follicle and epidermis, indicated the stem cell niche was not maintained. An autoimmune mechanism was excluded by crossing the mice with rag1-/- mice. However, large numbers of macrophages and increased expression of ICAM-1 were still present and may be involved either directly or indirectly in the hair loss. Reverse transcriptase-PCR (RT-PCR) and immunohistochemistry of sebaceous gland differentiation markers revealed reduced peroxisome proliferator-activated receptor-γ (PPARγ), a potential cause of reduced sebum production, as well as the potential involvement of the innate immune system in the hair loss. As reduced PPARγ expression has recently been implicated as a cause for lichen planopilaris, these mice may be useful for testing therapies.