Robert Lloyd Binder

Evidence that initiated keratinocytes clonally expand into multiple existing hair follicles during papilloma histogenesis in SENCAR mouse skin

We have previously shown that the precursors of cutaneous papillomas in SENCAR mice initiated with 7,12‐dimethylbenz[a]anthracene and promoted with 12‐O‐tetradecanoylphorbol‐13‐acetate are focal hyperplastic lesions that we refer to as squamous cell hyperplastic foci (SCHF). Ha‐ras gene codon 61 mutations were frequently found in SCHF, providing evidence that these lesions represent clones of initiated cells. We report here the pathogenesis of multiple hair follicle involvement in more advanced SCHF and describe the role of the hair follicle in papilloma histogenesis. Detailed histological evaluation of 83 SCHF and 25 early papillomas revealed a morphological continuum from the least developed SCHF, involving only one hair follicle, to advanced SCHF and early papillomas, which involved more than 10 hair follicles. These results provide evidence of the recruitment of additional hair follicles as SCHF progress. In advanced SCHF and early papillomas the bulk of the epithelial component in all cases consisted of several markedly hyperplastic adjacent hair follicles, whereas the involved interfollicular epidermis (IFE) was generally less hyperplastic. All of the hair follicles involved in SCHF appeared to have been preexisting, based on their pattern of spacing, that they were consistently normal appearing below the level of the sebaceous glands, and that they were in the same phase of the hair cycle as surrounding, uninvolved hair follicles. Also, no evidence of follicular neogenesis was observed in serially sectioned SCHF, and coalescence of smaller lesions was rare. To investigate whether the involvement of multiple hair follicles in SCHF was due to expansion of initiated cells into existing hair follicles or, possibly, to a paracrine mechanism, we analyzed different levels of three serially sectioned SCHF and one early papilloma for Ha‐ras mutations. These analyses revealed cells with Ha‐ras gene codon 61 mutations at multiple levels that involved different hair follicles. Overall, our results provide evidence that as initiated cells clonally expand, they spread across the IFE and populate the upper permanent portions of existing hair follicles. The abnormal proliferation of the infundibula of the hair follicles involved in SCHF appears to give rise to most of the epithelial component of papillomas. Mol. Carcinog. 20:151–158, 1997.

Ultraviolet B-induced squamous epithelial and melanocytic cell changes in a xenograft model of cancer development in human skin

We previously demonstrated that precancers (actinic keratoses and dysplasias) and squamous cell carcinomas (SCCs) develop in one quarter of human neonatal foreskins grafted onto recombinase‐activating gene‐1–knockout mice treated once with 7,12‐dimethylbenz[a]anthracene (DMBA) followed by chronic intermediate‐range ultraviolet (UV) B light irradiation. The goals of this study were to determine if a longer UVB exposure followed by further observation would increase the number of precancers and invasive cancers and to evaluate whether this model results in changes in p53 expression and cell proliferation similar to those seen in sun‐damaged normal skin, actinic keratoses, and SCCs. The treatment consisted of a single dose of DMBA followed by 500 J/m2 UVB radiation administered three times weekly for at least 5 mo. Histologic changes (cysts, hyperplasias, precancers, and/or invasive cancers) were seen in 24 of 25 treated xenografts but not in controls. Ten of 25 grafts (40%) had two or more histological changes, and two human SCCs developed. After seven or more months of UV exposure and a total time from DMBA treatment to killing of 12–18 mo, 83% (15 of 18) of specimens developed squamous precancer or SCC of human origin, and 44% (eight of 18) developed melanocytic hyperplasia or melanoma. The change from moderate dysplasias to SCC required longer UV exposure (median, 11 mo), and 5 mo more observation than did the development of mild dysplasias (median UV exposure, 7 mo; median DMBA to death time, 12 mo). There was a direct correlation between both p53 expression and cell proliferation and the degree of histologic alteration both in squamous epithelial and melanocytic cells. Mol. Carcinog. 23:168–174, 1998.

Transcriptional profiling of epidermal barrier formation in vitro

BACKGROUND Barrier function is integral to the health of epithelial tissues. Currently, there is a broad need to develop and improve our knowledge with regard to barrier function for reversal of mild skin irritation and dryness. However, there are few in vitro models that incorporate modulations of both lipids and epidermal differentiation programs for pre-clinical testing to aid in the understanding of barrier health. OBJECTIVE We have generated a reconstituted epidermis on a decellularized dermis (DED) and characterized its barrier properties relative to human epidermis in order to determine its utility for modeling barrier formation and repair. METHODS We followed the process of epidermal differentiation and barrier formation through immunocytochemistry and transcriptional profiling. We examined barrier functionality through measurements of surface pH, lipid composition, stratum corneum water content, and the ability to demonstrate topical dose-dependent exclusion of surfactant. RESULTS Transcriptional profiling of the epidermal model during its formation reveals temporal patterns of gene expression associated with processes regulating barrier function. The profiling is supported by gradual formation and maturation of a stratum corneum and expression of appropriate markers of epidermis development. The model displays a functional barrier and a water gradient between the stratum corneum and viable layers, as determined by confocal Raman spectroscopy. The stratum corneum layer displays a normal acidic pH and an appropriate composition of barrier lipids. CONCLUSION The epidermal model demonstrates its utility as an investigative tool for barrier health and provides a window into the transcriptional regulation of multiple aspects of barrier formation.

Age-induced and photoinduced changes in gene expression profiles in facial skin of Caucasian females across 6 decades of age

Background: Intrinsic and extrinsic factors, including ultraviolet irradiation, lead to visible signs of skin aging. Objective: We evaluated molecular changes occurring in photoexposed and photoprotected skin of white women 20 to 74 years of age, some of whom appeared substantially younger than their chronologic age. Methods: Histologic and transcriptomics profiling were conducted on skin biopsy samples of photoexposed (face and dorsal forearm) or photoprotected (buttocks) body sites from 158 women. 23andMe genotyping determined genetic ancestry. Results: Gene expression and ontologic analysis revealed progressive changes from the 20s to the 70s in pathways related to oxidative stress, energy metabolism, senescence, and epidermal barrier; these changes were accelerated in the 60s and 70s. The gene expression patterns from the subset of women who were younger‐appearing were similar to those in women who were actually younger. Limitations: Broader application of these findings (eg, across races and Fitzpatrick skin types) will require further studies. Conclusions: This study demonstrates a wide range of molecular processes in skin affected by aging, providing relevant targets for improving the condition of aging skin at different life stages and defining a molecular pattern of epidermal gene expression in women who appear younger than their chronologic age.