Loss of DLX3 tumor suppressive function promotes progression of SCC through EGFR-ERBB2 pathway

Cutaneous squamous cell carcinoma (cSCC) ranks second in the frequency of all skin cancers. The balance between keratinocyte proliferation and differentiation is disrupted in the pathological development of cSCC. DLX3 is a homeobox transcription factor which plays pivotal roles in embryonic development and epidermal homeostasis. To investigate the impact of DLX3 expression on cSCC prognosis, we carried out clinicopathologic analysis of DLX3 expression which showed statistical correlation between tumors of higher pathologic grade and levels of DLX3 protein expression. Further, Kaplan-Meier survival curve analysis demonstrated that low DLX3 expression correlated with poor patient survival. To model the function of Dlx3 in skin tumorigenesis, a two-stage dimethylbenzanthracene (DMBA)/12-O-tetradecanoylphorbol 13-acetate (TPA) study was performed on mice genetically depleted of Dlx3 in skin epithelium (Dlx3cKO). Dlx3cKO mice developed significantly more tumors, with more rapid tumorigenesis compared to control mice. In Dlx3cKO mice treated only with DMBA, tumors developed after ~16 weeks suggesting that loss of Dlx3 has a tumor promoting effect. Whole transcriptome analysis of tumor and skin tissue from our mouse model revealed spontaneous activation of the EGFR-ERBB2 pathway in the absence of Dlx3. Together, our findings from human and mouse model system support a tumor suppressive function for DLX3 in skin and underscore the efficacy of therapeutic approaches that target EGFR-ERBB2 pathway.

The effects of caffeine on wound healing

The purine alkaloid caffeine is a major component of many beverages such as coffee and tea. Caffeine and its metabolites theobromine and xanthine have been shown to have antioxidant properties. Caffeine can also act as adenosine-receptor antagonist. Although it has been shown that adenosine and antioxidants promote wound healing, the effect of caffeine on wound healing is currently unknown. To investigate the effects of caffeine on processes involved in epithelialisation, we used primary human keratinocytes, HaCaT cell line and ex vivo model of human skin. First, we tested the effects of caffeine on cell proliferation, differentiation, adhesion and migration, processes essential for normal wound epithelialisation and closure. We used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) proliferation assay to test the effects of seven different caffeine doses ranging from 0·1 to 5 mM. We found that caffeine restricted cell proliferation of keratinocytes in a dose-dependent manner. Furthermore, scratch wound assays performed on keratinocyte monolayers indicated dose-dependent delays in cell migration. Interestingly, adhesion and differentiation remained unaffected in monolayer cultures treated with various doses of caffeine. Using a human ex vivo wound healing model, we tested topical application of caffeine and found that it impedes epithelialisation, confirming in vitro data. We conclude that caffeine, which is known to have antioxidant properties, impedes keratinocyte proliferation and migration, suggesting that it may have an inhibitory effect on wound healing and epithelialisation. Therefore, our findings are more in support of a role for caffeine as adenosine-receptor antagonist that would negate the effect of adenosine in promoting wound healing.

Epithelialization in Wound Healing: A Comprehensive Review

Significance: Keratinocytes, a major cellular component of the epidermis, are responsible for restoring the epidermis after injury through a process termed epithelialization. This review will focus on the pivotal role of keratinocytes in epithelialization, including cellular processes and mechanisms of their regulation during re-epithelialization, and their cross talk with other cell types participating in wound healing. Recent Advances: Discoveries in epidermal stem cells, keratinocyte immune function, and the role of the epidermis as an independent neuroendocrine organ will be reviewed. Novel mechanisms of gene expression regulation important for re-epithelialization, including microRNAs and histone modifications, will also be discussed. Critical Issues: Epithelialization is an essential component of wound healing used as a defining parameter of a successful wound closure. A wound cannot be considered healed in the absence of re-epithelialization. The epithelialization process is impaired in all types of chronic wounds. Future Directions: A comprehensive understanding of the epithelialization process will ultimately lead to the development of novel therapeutic approaches to promote wound closure.

Deep tissue injury in development of pressure ulcers: a decrease of inflammasome activation and changes in human skin morphology in response to aging and mechanical load

Molecular mechanisms leading to pressure ulcer development are scarce in spite of high mortality of patients. Development of pressure ulcers that is initially observed as deep tissue injury is multifactorial. We postulate that biomechanical forces and inflammasome activation, together with ischemia and aging, may play a role in pressure ulcer development. To test this we used a newly-developed bio-mechanical model in which ischemic young and aged human skin was subjected to a constant physiological compressive stress (load) of 300 kPa (determined by pressure plate analyses of a person in a reclining position) for 0.5–4 hours. Collagen orientation was assessed using polarized light, whereas inflammasome proteins were quantified by immunoblotting. Loaded skin showed marked changes in morphology and NLRP3 inflammasome protein expression. Sub-epidermal separations and altered orientation of collagen fibers were observed in aged skin at earlier time points. Aged skin showed significant decreases in the levels of NLRP3 inflammasome proteins. Loading did not alter NLRP3 inflammasome proteins expression in aged skin, whereas it significantly increased their levels in young skin. We conclude that aging contributes to rapid morphological changes and decrease in inflammasome proteins in response to tissue damage, suggesting that a decline in the innate inflammatory response in elderly skin could contribute to pressure ulcer pathogenesis. Observed morphological changes suggest that tissue damage upon loading may not be entirely preventable. Furthermore, newly developed model described here may be very useful in understanding the mechanisms of deep tissue injury that may lead towards development of pressure ulcers.

Glucocorticoid receptor localizes to adherens junctions at the plasma membrane of keratinocytes

Glucocorticoids are important regulators of epidermal tissue homeostasis. As such, their clinical applications are widespread, ranging from inflammatory skin disorders to keloids and cancer. Glucocorticoids exert their effect by binding to glucocorticoid receptor (GR) which translocates to the nucleus and regulates gene expression (genomic effect). In addition, GR has rapid non- genomic effects that are mediated by cell signaling proteins and do not involve gene transcription. Although genomic effects of GR in the epidermis are well documented, the non-genomic effects are not completely understood. Therefore, we utilized immunostaining and immunoprecipitations to determine specific localization of the GR in human keratinocytes that may contribute to non-genomic effects of glucocorticoid action. Here we describe a novel finding of GR localization to the plasma membrane of keratinocytes. Immunocytochemistry showed co-localization of GR with α-catenin. Immunoprecipitation of the membranous fraction revealed an association of GR with α-catenin, confirming its localization to adherens junctions. We conclude that GR localization to adherens junctions of keratinocytes provides a new mechanism of non-genomic signaling by glucocorticoids which may have significant biological and clinical impact.

Ion-exchange albumin microcapsules of doxorubicin: an in vitro release kinetic evaluation

Cross-linked albumin microcapsules were prepared, using a polycondensation interfacial process. Doxorubicin was incorporated in these microcapsules by simple adsorption from aqueous solution. Increasing the extent of cross-linkage of the microcapsule walls by either increasing the cross-linking agent concentration or the time of reaction significantly reduced the absorption ability of these microcapsules. Doxorubicin release kinetic evaluation revealed that the presence of a salt in the release medium was needed to enable much of the drug to be released. Furthermore, the doxorubicin displacement intensity from the microcapsules was dependent on the nature and concentration of the cations used, indicating that an ion-exchange process was involved. Analysis of the various doxorubicin release profiles, using ion-exchange kinetic equation, showed that the release kinetic process is governed by a film diffusion process at low and moderate Na+ ion concentrations in the exchanging solution, and by a particle diffusion process at high Na+ ion concentrations, sufficient to drive the doxorubicin exchange to completion.

Binding mechanism of doxorubicin in ion-exchange albumin microcapsules

The absorption efficiency of cross-linked albumin microcapsules was evaluated as a function of various experimental conditions in an attempt to elucidate the doxorubicin binding mechanism of these microcapsules. The amount of drug absorbed augmented with increasing doxorubicin concentration until saturation was reached. Neither a Langmuir nor a Freundlich isotherm relationship was observed, indicating that the fixation of doxorubicin on the microcapsule walls did not follow a common physical adsorption process. Decreasing the mean particle diameter of the microcapsules increased the absorption rate and the total amount of doxorubicin absorbed, as expected. The absorption rate was enhanced by the elevation of the stirring rate of the aqueous drug solution. Furthermore, the presence of electrolytes in this aqueous solution profoundly altered the absorption profile of doxorubicin. Increasing the NaCl concentration in the solution reduced the total amount of drug absorbed. Moreover, the nature of the cation used also affected the absorption profile. These results suggested that there is a competitive fixation of the cation on the binding sites (identified as R-COO groups) available to the drug molecules. The weakly cross-linked microcapsules acted as cation-exchange resins which can exchange their labile sodium with the protonated drug present in the solution. This was also confirmed by the results of the titrimetric assay of the acidic microcapsules with NaOH.

Calcium and thiocyanate interactions with crosslinked albumin microcapsules: influence of the reticulation rate

Ca2+ and SCN- interactions with strongly or lightly crosslinked albumin microcapsules were studied, using 45Ca2+ for a pH range varying from 5.5 to 7.8 and 14SCN- ions for the range 2.15 to 3.0. With strongly crosslinked albumin, the Scatchard plots of equilibrium isotherms indicate a maximum number of binding sites for Ca2+ ions, when N is equal to 12 and an apparent association constant, K' is equal to 7.8 X 10(3) l/mol. For the weakly crosslinked albumin, this constant is equal to 11 X 10(3) l/mol and the variation of calcium absorption with pH has an unusual shape, with a maximum at pH 6.5. The measurement of SCN- ion absorption by lightly crosslinked microcapsules indicates a K' value of 5.4 X 10(3) l/mol and an N value of 7 for pH 2.15. These values are, respectively, 8.3 X 10(3) l/mol and 2 for pH 2.15 when using strongly crosslinked microcapsules.