Laurent Barnes

Synergistic Effect of Hyaluronate Fragments in Retinaldehyde-Induced Skin Hyperplasia Which Is a Cd44-Dependent Phenomenon

Background CD44 is a polymorphic proteoglycan and functions as the principal cell-surface receptor for hyaluronate (HA). Heparin-binding epidermal growth factor (HB-EGF) activation of keratinocyte erbB receptors has been proposed to mediate retinoid-induced epidermal hyperplasia. We have recently shown that intermediate size HA fragments (HAFi) reverse skin atrophy by a CD44-dependent mechanism. Methodology and Principal Findings Treatment of primary mouse keratinocyte cultures with retinaldehyde (RAL) resulted in the most significant increase in keratinocyte proliferation when compared with other retinoids, retinoic acid, retinol or retinoyl palmitate. RAL and HAFi showed a more significant increase in keratinocyte proliferation than RAL or HAFi alone. No proliferation with RAL was observed in CD44−/− keratinocytes. HA synthesis inhibitor, 4-methylumbelliferone inhibited the proliferative effect of RAL. HB-EGF, erbB1, and tissue inhibitor of MMP-3 blocking antibodies abrogated the RAL- or RAL- and HAFi-induced keratinocyte proliferation. Topical application of RAL or RAL and HAFi for 3 days caused a significant epidermal hyperplasia in the back skin of wild-type mice but not in CD44−/− mice. Topical RAL and HAFi increased epidermal CD44 expression, and the epidermal and dermal HA. RAL induced the expression of active HB-EGF and erbB1. However, treatment with RAL and HAFi showed a more significant increase in pro-HB-EGF when compared to RAL or HAFi treatments alone. We then topically applied RAL and HAFi twice a day to the forearm skin of elderly dermatoporosis patients. After 1 month of treatment, we observed a significant clinical improvement. Conclusions and Significance Our results indicate that (i) RAL-induced in vitro and in vivo keratinocyte proliferation is a CD44-dependent phenomenon and requires the presence of HA, HB-EGF, erbB1 and MMPs, (ii) RAL and HAFi show a synergy in vitro and in vivo in mouse skin, and (iii) the combination of RAL and HAFi seems to have an important therapeutic effect in dermatoporosis.

Topical Corticosteroid-Induced Skin Atrophy: A Comprehensive Review

Skin atrophy is an adverse effect of topical corticosteroids (TCs) which, as an established non-life-threatening effect, has been poorly reported by trials involving these drugs. Atopic dermatitis and psoriasis are example of disorders that require repeated therapies with TCs; however, assessing the atrophogenic activity of TCs is still an issue. This study aims to review clinical data on skin atrophy induced by TCs. Searches of the PubMed, EMBASE, and Cochrane (Central) databases from 1965 to May 2013 were undertaken using the keywords ‘corticosteroid’, ‘skin’, and ‘atrophy’. Skin and epidermal thickness values were retrieved from trials on healthy skin, and studies including skin atrophy as a safety endpoint in trials testing the efficacy of TCs were analyzed. Overall, 60 articles were retrieved. Whole skin and epidermal thickness were relevant parameters to measure early skin atrophy on healthy skin before it becomes clinically obvious. Epidermis thickness also seems to be more sensitive than whole skin thickness in detecting early atrophy; however, measuring skin atrophy still requires standardization. Further clinical trials on the atrophic effects of each TC are required to better evaluate their respective atrophic risks and their risk/benefit ratios. However, measuring epidermal or whole skin thickness will not be relevant in acute phases of inflammatory skin disorders treated with TCs because of the thickening induced by inflammation. In addition, skin atrophy seems to be induced by chronic TC use rather than by acute treatments. Long-term safety studies may be more relevant to evaluate atrophic activity.

Inhibition of Putative Hyalurosome Platform in Keratinocytes as a Mechanism for Corticosteroid-Induced Epidermal Atrophy

The main limitation of using topical corticosteroids in dermatology is their atrophic effects on the skin. We have previously proposed a molecular platform composed of CD44, EGFR, and hyaluronate synthase (HAS) that is functionally defective in dermatoporosis, a chronic cutaneous insufficiency/fragility syndrome. In this study, we explored the molecular mechanisms of the skin atrophy induced by corticosteroids. We observed an important skin atrophy and a significant decrease of hyaluronic acid (HA), its main cell surface receptor CD44, and F-actin in mouse skin treated with topical clobetasol propionate (CP). Human keratinocytes exposed to CP showed an impaired HA secretion and diminished expression of CD44 and HAS3. CP also abolished filopodia of keratinocytes exposed to CP together with a redistribution of CD44 and F-actin depolymerization. We also show that HA fragments of intermediary size (HAFi) induced keratinocyte filopodia and protected them against CP. Topical HAFi induced hyperplasia in mouse epidermis and prevented CP-induced atrophy. Our results suggest that a CD44/EGFR/HAS platform associated with F-actin and filopodia of keratinocytes is the target of corticosteroids for their atrophogenic effects. These observations may lead to the development of new treatment and prevention strategies for corticosteroid-induced skin atrophy.

From the Cover: High Susceptibility of Lrig1 Sebaceous Stem Cells to TCDD in Mice

We have previously shown that cytochrome P450 1A1 (CYP1A1) was highly induced for a long period of time in a patient who had been poisoned by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a compound known to activate the aryl hydrocarbon receptor (AhR). During that period of time, no sebaceous glands could be observed in the skin of this patient. In this study, starting from observations in the patient exposed to TCDD, we analyzed the seboatrophy induced by dioxins in mice. We observed a very different pattern of AhR and CYP1A1 immunostaining in skin biopsies of the patient. When applying TCDD and beta-naphthoflavone, another AhR agonist, on the ears of C57BL/6J mice, we reproduced (1) an atrophy of sebaceous glands, (2) a strong induction of CYP1A1 within the glands, and (3) a dramatic repression of the genes encoding the sebogenic enzymes AWAT1, ELOVL3, and SCD1. These effects were reversible. Leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) expressing progenitor cells, found in the vicinity of sebaceous glands, were shown to be the initial skin cellular targets of AhR agonists. These cells retained the DNA label BrdU and colocalized with the CYP1A1 protein for at least 30 days. A downregulation of LRIG1 by siRNA in cultured sebocytes significantly decreased the CYP1A1 response to TCDD, indicating that LRIG1 contributes to a higher susceptibility of AhR agonists. In conclusion, these observations provide for the first time a strong experimental support to the concept that dioxin-induced skin pathology may be driven by a molecular switch in progenitor cells involved in the physiological turnover of sebaceous glands.

Senescent Atrophic Epidermis Retains Lrig1+ Stem Cells and Loses Wnt Signaling, a Phenotype Shared with CD44KO Mice

Lrig1 is known to repress the epidermal growth through its inhibitory activity on EGFR, while CD44 promotes it. We analyzed the expression of these molecules in senescent atrophic human epidermis and in the epidermis of CD44KO mice. In normal human epidermis, Lrig1+ cells form clusters located in the basal layer in which CD44 expression is downregulated and Lef1 expression reflects an active Wnt signaling. In senescent atrophic human epidermis, we found retention of Lrig1high+ cells all along the basal layer, forming no clusters, with decrease of CD44 and lef1 expression. In vitro silencing of CD44 indicated that CD44 may be required for Wnt signaling. However, if looking at the ear epidermis of CD44KO mice, we only found a limited interfollicular epidermal atrophy and unchanged Lrig1high+ cells in the hair follicle. Cell lineage tracing further revealed that interfollicular epidermis did lost its self-renewing capacity but that its homeostasis relied on Lrig1-derived keratinocytes migrating from the hair follicle. Therefore, we conclude that CD44 downregulation is part of the phenotype of senescent atrophic human epidermis, and contributes to reduce Wnt signaling and to alter Lrig1high+ stem cell distribution.

Primordial germ cells as a potential shared cell of origin for mucinous cystic neoplasms of the pancreas and mucinous ovarian tumors: PGCs as cell of origin for mucinous ovarian and pancreatic tumors

Mucinous ovarian tumors (MOTs) morphologically and epidemiologically resemble mucinous cystic neoplasms (MCNs) of the pancreas, sharing a similar stroma and both occurring disproportionately among young females. Additionally, MOTs and MCNs share similar clinical characteristics and immunohistochemical phenotypes. Exome sequencing has revealed frequent recurrent mutations in KRAS and RNF43 in both MOTs and MCNs. The cell of origin for these tumors remains unclear, but MOTs sometimes arise in the context of mature cystic teratomas and other primordial germ cell (PGC) tumors. We undertook the present study to investigate whether non‐teratoma‐associated MOTs and MCNs share a common cell of origin. Comparisons of the gene expression profiles of MOTs [including both the mucinous borderline ovarian tumors (MBOTs) and invasive mucinous ovarian carcinomas (MOCs)], high‐grade serous ovarian carcinomas, ovarian surface epithelium, Fallopian tube epithelium, normal pancreatic tissue, pancreatic duct adenocarcinomas, MCNs, and single‐cell RNA‐sequencing of PGCs revealed that both MOTs and MCNs are more closely related to PGCs than to either eutopic epithelial tumors or normal epithelia. We hypothesize that MCNs may arise from PGCs that stopped in the dorsal pancreas during their descent to the gonads during early human embryogenesis, while MOTs arise from PGCs in the ovary. Together, these data suggest a common pathway for the development of MCNs and MOTs, and suggest that these tumors may be more properly classified as germ cell tumor variants. Copyright

Lrig1 Expression in Human Sebaceous Gland Tumors.

Background: Sebaceous glands contribute significantly to the barrier functions of the skin. However, little is known about their homeostasis and tumorigenesis. Recently, increased expression of stem cell marker Lrig1 has been reported in sebaceous carcinoma-like tumors of K14ΔNLef1 transgenic mice. In this study, we analyzed the Lrig1 expression in human sebaceous tumors. Methods: Twenty-eight formalin-fixed paraffin-embedded sebaceous tumor specimens (7 sebaceous hyperplasias, 7 sebaceous adenomas, 10 sebaceomas and 4 sebaceous carcinomas) were stained with anti-Lrig1, anti-CD44v3 and anti-Ki67 antibody. Results: Four (100%) sebaceous carcinomas, 8 (80%) sebaceomas, 3 (43%) sebaceous adenomas and no sebaceous hyperplasia showed Lrig1 overexpression. Discussion and Conclusion: Lrig1 is a known tumor suppressor gene and is usually considered to be an indicator of poorly aggressive tumors. In human sebaceous tumors, the stronger Lrig1 staining in sebaceous carcinoma compared to other sebaceous tumors might be a feature of an advanced stage in tumorigenesis and a bad prognosis. In our study, 100% of sebaceous carcinomas revealed Lrig1 overexpression. We propose that Lrig1 may be used as a possible new marker of poorly differentiated sebaceous carcinoma.