TGF-beta and retinoic acid: regulators of growth and modifiers of differentiation in human epidermal cells

Contribution of GATA6 to homeostasis of the human upper pilosebaceous unit and acne pathogenesis

Although acne is the most common human inflammatory skin disease, its pathogenic mechanisms remain incompletely understood. Here we show that GATA6, which is expressed in the upper pilosebaceous unit of normal human skin, is down-regulated in acne. GATA6 controls keratinocyte proliferation and differentiation to prevent hyperkeratinisation of the infundibulum, which is the primary pathological event in acne. When overexpressed in immortalised human sebocytes, GATA6 triggers a junctional zone and sebaceous differentiation program whilst limiting lipid production and cell proliferation. It modulates the immunological repertoire of sebocytes, notably by upregulating PD-L1 and IL10. GATA6 expression contributes to the therapeutic effect of retinoic acid, the main treatment for acne. In a human sebaceous organoid model GATA6-mediated down-regulation of the infundibular differentiation program is mediated by induction of TGFβ signalling. We conclude that GATA6 is involved in regulation of the upper pilosebaceous unit and may be an actionable target in the treatment of acne.

New Insights Into the Roles of Retinoic Acid Signaling in Nervous System Development and the Establishment of Neurotransmitter Systems

Secreted chiefly from the underlying mesoderm, the morphogen retinoic acid (RA) is well known to contribute to the specification, patterning, and differentiation of neural progenitors in the developing vertebrate nervous system. Furthermore, RA influences the subtype identity and neurotransmitter phenotype of subsets of maturing neurons, although relatively little is known about how these functions are mediated. This review provides a comprehensive overview of the roles played by RA signaling during the formation of the central and peripheral nervous systems of vertebrates and highlights its effects on the differentiation of several neurotransmitter systems. In addition, the evolutionary history of the RA signaling system is discussed, revealing both conserved properties and alternate modes of RA action. It is proposed that comparative approaches should be employed systematically to expand our knowledge of the context-dependent cellular mechanisms controlled by the multifunctional signaling molecule RA.

Transcriptome Display During Testicular Differentiation of Channel Catfish (Ictalurus punctatus) as Revealed by RNA-Seq Analysis

Channel catfish (Ictalurus punctatus) has been recognized as a dominant freshwater aquaculture species in the United States. It is also a suitable model for studying the mechanisms of sex determination and differentiation because of its sexual plasticity and exhibition of both genetic and environmental sex determination. The testicular differentiation in male channel catfish normally starts between 90 and 102 days postfertilization (dpf), while the ovarian differentiation starts early from 19 dpf. As such, efforts to better understand the postponed testicular development at the molecular level are needed. Toward that end, we conducted transcriptomic comparison of gene expression of male and female gonads at 90, 100, and 110 dpf using high-throughput RNA-Seq. Transcriptomic profiles of male gonads on 90 and 100 dpf exhibited high similarities except for a small number of significantly up-regulated genes that were involved in development of germ cell-supporting somatic cells, while drastic changes were observed during 100-110 dpf, with a group of highly up-regulated genes that were involved in germ cells development, including nanog and pou5f1 Transcriptomic comparison between testes and ovaries identified male-preferential genes, such as gsdf, cxcl12, as well as other cytokines mediated the development of the gonad into a testis. Co-expression analysis revealed highly correlated genes and potential pathways underlying germ cell differentiation and spermatogonia stem cell development. The candidate genes and pathways identified in this study set the foundation for further studies on sex determination and differentiation in catfish as well as other teleosts.

Oxidative stress and dysfunctional NRF2 underlie pachyonychia congenita phenotypes

Palmoplantar keratoderma (PPK) are debilitating lesions that arise in individuals with pachyonychia congenita (PC) and feature upregulation of danger-associated molecular patterns and skin barrier regulators. The defining features of PC-associated PPK are reproduced in mice null for keratin 16 (Krt16), which is commonly mutated in PC patients. Here, we have shown that PPK onset is preceded by oxidative stress in footpad skin of Krt16-/- mice and correlates with an inability of keratinocytes to sustain nuclear factor erythroid-derived 2 related factor 2-dependent (NRF2-dependent) synthesis of the cellular antioxidant glutathione (GSH). Additionally, examination of plantar skin biopsies from individuals with PC confirmed the presence of high levels of hypophosphorylated NRF2 in lesional tissue. In Krt16-/- mice, genetic ablation of Nrf2 worsened spontaneous skin lesions and accelerated PPK development in footpad skin. Hypoactivity of NRF2 in Krt16-/- footpad skin correlated with decreased levels or activity of upstream NRF2 activators, including PKCδ, receptor for activated C kinase 1 (RACK1), and p21. Topical application of the NRF2 activator sulforaphane to the footpad of Krt16-/- mice prevented the development of PPK and normalized redox balance via regeneration of GSH from existing cellular pools. Together, these findings point to oxidative stress and dysfunctional NRF2 as contributors to PPK pathogenesis, identify K16 as a regulator of NRF2 activation, and suggest that pharmacological activation of NRF2 should be further explored for PC treatment.

The Aldo-Keto Reductase AKR1B10 Is Up-Regulated in Keloid Epidermis, Implicating Retinoic Acid Pathway Dysregulation in the Pathogenesis of Keloid Disease

Keloid disease is a recurrent fibroproliferative cutaneous tumor of unknown pathogenesis for which clinical management remains unsatisfactory. To obtain new insights into hitherto underappreciated aspects of keloid pathobiology, we took a laser capture microdissection-based, whole-genome microarray analysis approach to identify distinct keloid disease-associated gene expression patterns within defined keloid regions. Identification of the aldo-keto reductase enzyme AKR1B10 as highly up-regulated in keloid epidermis suggested that an imbalance of retinoic acid metabolism is likely associated with keloid disease. Here, we show that AKR1B10 transfection into normal human keratinocytes reproduced the abnormal retinoic acid pathway expression pattern we had identified in keloid epidermis. Cotransfection of AKR1B10 with a luciferase reporter plasmid showed reduced retinoic acid response element activity, supporting the hypothesis of retinoic acid synthesis deficiency in keloid epidermis. Paracrine signals released by AKR1B10-overexpressing keratinocytes into conditioned medium resulted in up-regulation of transforming growth factor-β1, transforming growth factor-β2, and collagens I and III in both keloid and normal skin fibroblasts, mimicking the typical profibrotic keloid profile. Our study results suggest that insufficient retinoic acid synthesis by keloid epidermal keratinocytes may contribute to the pathogenesis of keloid disease. We refocus attention on the role of injured epithelium in keloid disease and identify AKR1B10 as a potential new target in future management of keloid disease.

Safety and Efficacy of Growth Factor Concentrate in the Treatment of Nasolabial Fold Correction: Split Face Pilot Study

Background:

Growth factors have long been known as an effective treatment for facial wrinkles. We developed growth factor concentrate (GFC) from the platelets and evaluated their clinical outcome in nasolabial folds.

Aims and Objectives:

We evaluated safety and efficacy of autologous GFC on patients with nasolabial folds.

Materials and Methods:

Study was conducted on 80 patients for nasolabial folds in two groups. Group I (20) received bilateral single injection of GFC and group II (60) received single injection of GFC on the right side of the face and platelet-rich plasma (PRP) on the left side of the face. Severity of nasolabial folds was determined at the baseline and 3 months of follow-up visits based on wrinkle severity rating scale (WSRS), Global aesthetic improvement scale (GAIS) and atlas photographic grading at rest and at full smile. Objective clinical assessment and subjective satisfaction scale was determined for overall improvement at the end of the study.

Results:

In group I, 2 subjects showed improvement after GFC treatment with the score of 3.1–4 (76–100%), 3 subjects with the score of 2.1–3 (51–75%), 14 with the score of 1.1–2 (26–50%) and 1 subject with the score of 0–1 (<25%) at the end of study. In group II, 51 subjects were evaluated at the end of study where, 34 (66%) showed superior improvements after GFC, 6 (11%) patients showed similar improvement on both side of the face, 10 (19.6%) patients showed no noticeable improvement on the either side of the face and only 1 patient (1.96%) showed superior improvement for PRP at the end of the study. Overall improvement score analysis showed that GFC was significantly superior to PRP (P < 0.001).

Conclusion:

Present study is a strong evidence to support the use of GFC for nasolabial folds. The results showed that the single application of GFC is highly effective and safe.

Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro

Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.

Latent transforming growth factor-β binding proteins (LTBP-1 and LTBP-2) and gingiva keratinization

OBJECTIVE

Transforming growth factor-beta (TGF-β) proteins are involved in epithelial keratinization. The major function of latent TGF-β binding proteins (LTBPs) is modulating TGF-β activity. However, whether LTBP-1 and LTBP-2 play roles in gingiva keratinization remains unclear.

MATERIALS AND METHODS

Human keratinized gingiva and non-keratinized alveolar mucosa were processed for LTBP-1, LTBP-2, cytokeratin-1 (K1), cytokeratin-4 (K4), and TGF-β immunohistochemical (IHC) staining. Porcine heterotopically transplanted connective tissues and newly grown epithelia were harvested for IHC staining. The expression levels of LTBP-1 and LTBP-2 were compared between differentiated and undifferentiated human normal oral keratinocytes (hNOK). The expression of LTBP-1 and LTBP-2 was knocked down in a cell line (OEC-M1) to evaluate the effects on the expression of K1, K4, and involucrin (INV).

RESULTS

In human and porcine specimens, LTBP-2 expression patterns distinguished keratinized and non-keratinized oral epithelia. Western blotting results showed that K1, LTBP-1, and INV proteins were upregulated in differentiated hNOK. In OEC-M1 cells, LTBP-2 knockdown resulted in upregulated the expression of K1 and INV and downregulated the expression of K4. LTBP-1 knockdown resulted in opposite effects.

CONCLUSION

The expression patterns of LTBP-2 differ in keratinized gingiva and non-keratinized mucosa. LTBP-1 and LTBP-2 are involved in the keratinization of oral epithelium; however, the underlying mechanism remains to be elucidated.

Oral lining mucosa development depends on mesenchymal microRNAs

The oral mucosa plays critical roles in protection, sensation, and secretion and can be classified into masticatory, lining, and specialized mucosa that are known to be functionally, histologically, and clinically distinct. Each type of oral mucosa is believed to develop through discrete molecular mechanisms, which remain unclear. MicroRNAs (miRNAs) are 19 to 25nt non-coding small single-stranded RNAs that negatively regulate gene expression by binding target mRNAs. miRNAs are crucial for fine-tuning of molecular mechanisms. To investigate the role of miRNAs in oral mucosa development, we examined mice with mesenchymal (Wnt1Cre;Dicer(fl/fl)) conditional deletion of Dicer. Wnt1Cre;Dicer(fl/fl) mice showed trans-differentiation of lining mucosa into an epithelium with masticatory mucosa/ skin-specific characteristics. Up-regulation of Fgf signaling was found in mutant lining mucosal epithelium that was accompanied by an increase in Fgf7 expression in mutant mesenchyme. Mesenchyme miRNAs thus have an indirect effect on lining mucosal epithelial cell growth/differentiation.

Transforming growth factorbeta(1) transactivates EGFR via an H(2)O(2)-dependent mechanism in squamous carcinoma cell line

TGFbeta is known to transactivate EGFR. However, the signaling component involved in this crosstalk has yet to be revealed. Here, we found that TGFbeta(1) phosphorylated EGFR in a dose-dependent manner in SCC13 and A431 cells, and it was not blocked by EGF-neutralizing antibody. H(2)O(2) was increased by TGFbeta(1) treatment in the same time-kinetics as EGFR activation. Pretreatment of N-acetyl cysteine abolished TGFbeta(1)-induced H(2)O(2) induction and EGFR activation. Direct treatment of H(2)O(2) phosphorylated EGFR and catalase inhibitor prolonged TGFbeta(1)-induced EGFR activation. These results show that TGFbeta(1) activates EGFR via an H(2)O(2)-dependent mechanism, which subsequently leads to the activation of Erk(1/2).

The expression of SnoN in normal human skin and cutaneous keratinous neoplasms

BACKGROUND

SnoN is a member of the ski family of proto-oncogenes. It has been revealed that SnoN plays a role in the regulation of cell growth, vertebrate development, and tumorigenesis. This study investigated the expression and significance of SnoN protein in normal human skin and in the development of seborrheic keratosis (SK), basal cell carcinoma (BCC), and squamous cell carcinoma (SCC) of the skin.

METHODS

Six frozen sections of normal human skin, three of SK (acanthotic type), six of BCC, six of intraepidermal SCC (actinic keratosis, AK), and six each of poorly and well-differentiated SCC were immunohistochemically stained with a polyclonal antibody against SnoN.

RESULTS

In normal epidermis, strong positive staining was observed in the suprabasal layers, whereas the basal cell layer was entirely unstained. Expression was observed in tumor cells with a squamoid phenotype in SK, but not in BCC. In intraepidermal SCC, although a strong signal was seen in the well-differentiated keratinocytes of the superficial epidermal cell layers, no signal was seen in the poorly differentiated atypical cells situated in the lower epidermis. In invasive SCC, a few scattered cells were positive for SnoN in the well-differentiated sample, but much larger numbers of positive cells were observed in the poorly differentiated sample.

CONCLUSIONS

On the basis of our results, it is suggested that SnoN is involved in differentiation in normal skin and benign and nonmetastatic skin tumors, but plays a proto-oncogenic role in undifferentiated SCC.

Retinoid-responsive transcriptional changes in epidermal keratinocytes

Retinoids (RA) have been used as therapeutic agents for numerous skin diseases, from psoriasis to acne and wrinkles. While RA is known to inhibit keratinocyte differentiation, the molecular effects of RA in epidermis have not been comprehensively defined. To identify the transcriptional targets of RA in primary human epidermal keratinocytes, we compared the transcriptional profiles of cells grown in the presence or absence of all-trans retinoic acid for 1, 4, 24, 48, and 72 h, using large DNA microarrays. As expected, RA suppresses the protein markers of cornification; however the genes responsible for biosynthesis of epidermal lipids, long-chain fatty acids, cholesterol, and sphingolipids, are also suppressed. Importantly, the pathways of RA synthesis, esterification and metabolism are activated by RA; therefore, RA regulates its own bioavailability. Unexpectedly, RA regulates many genes associated with the cell cycle and programmed cell death. This led us to reveal novel effects of RA on keratinocyte proliferation and apoptosis. The response to RA is very fast: 315 genes were regulated already after 1 h. More than one-third of RA-regulated genes function in signal transduction and regulation of transcription. Using in silico analysis, we identified a set of over-represented transcription factor binding sites in the RA-regulated genes. Many psoriasis-related genes are regulated by RA, some induced, others suppressed. These results comprehensively document the transcriptional changes caused by RA in keratinocytes, add new insights into the molecular mechanism influenced by RA in the epidermis and demonstrate the hypothesis-generating power of DNA microarray analysis.

Holding their own: the noncanonical roles of Smad proteins

The identification of Smads as protein transcription factors in 1995 led to elucidation of the canonical transforming growth factor-beta (TGF-beta) signaling pathway. In the years that have followed, nuances of the pathway have been realized, and the once-simple scheme of ligand to receptor to activated transcription factor is now understood to be highly regulated at each step and riddled with crosstalk from other pathways. The Smads are also recognized as important players outside of canonical TGF-beta-dependent signaling and are responsible for regulating diverse cellular processes. New evidence suggests that Smad7 plays an integral role in maintaining cell-cell adhesion through direct regulation of beta-catenin. Receptor-activated Smads regulate the processing of a subset of microRNAs, particularly miR-21. The number of reports demonstrating the interactions of Smads with proteins outside of canonical TGF-beta signaling is increasing, although the functional relevance of these interactions is not known. Investigating these interactions will likely yield more evidence that Smads serve important and diverse purposes beyond their original reported function as signal transducers in the TGF-beta pathway.

Transglutaminase inhibitors induce hyperproliferation and parakeratosis in tissue-engineered skin

BACKGROUND

The transglutaminase (TG) family consists of eight distinct isoforms. TG types 1, 3 and 5 play a major role in normal skin development, with TG2 also being elevated during dermal wounding. TG1, 3 and 5 are responsible for the cross-linking of keratin precursors and formation of the cornified envelope during keratinocyte differentiation. TG2 may play a role in keratinocyte basement membrane cross-linking. Abnormal TG expression has been demonstrated in Darier disease, Netherton syndrome, psoriasis and lamellar ichthyosis. During a recent investigation of skin contraction in tissue-engineered skin, transglutaminase inhibitors were found to produce hyperproliferation and parakeratosis.

OBJECTIVES

Accordingly, this study was designed to study the effect of pan-transglutaminase inhibition on morphology of tissue-engineered skin and expression of keratinocyte differentiation and proliferation-associated antigens.

METHODS

We used a tissue-engineered model of human skin, based on de-epidermized acellular human dermis, seeded with normal keratinocytes and dermal fibroblasts and cultured at an air-liquid interface. The pan-transglutaminase inhibitors putrescine, NTU283 (1-dimethyl,2-[(oxopropyl)thio]imidazolium) and NTU285 (N-benzyloxycarbonyl-l-glutaminyl-6-dimethylsulfonium-5-oxo-l-norleucine) were added to the culture medium. After 28 days, histology and immunohistochemistry for collagen IV, involucrin and cytokeratins 6, 10 and 16 were performed.

RESULTS

Keratinocyte hyperproliferation and parakeratosis were seen in response to transglutaminase inhibition. Inhibition of transglutaminase also resulted in loss of basement membrane collagen IV. Involucrin and cytokeratins 6 and 16 were confined to the basal layers in control composites but expressed throughout the epidermis in response to transglutaminase inhibition. A distinct band of expression of cytokeratin 10 was seen in the upper stratum granulosum of control composites but only patchy expression was seen after transglutaminase expression.

CONCLUSIONS

Pan-transglutaminase inhibition inhibits terminal differentiation of keratinocytes, leading to a hyperproliferative epidermis with parakeratosis and enhanced expression of involucrin and cytokeratins 6 and 16. Expression of the differentiation-associated cytokeratin, cytokeratin 10, is reduced. Basement membrane integrity is also lost as a result of transglutaminase inhibition.

Cytodifferentiation by retinoids, a novel therapeutic option in oncology: rational combinations with other therapeutic agents

Retinoic acid (RA) and derivatives are promising antineoplastic agents endowed with both therapeutic and chemopreventive potential. Although the treatment of acute promyelocytic leukemia with all-trans retinoic acid is an outstanding example, the full potential of retinoids in oncology has not yet been explored and a more generalized use of these compounds is not yet a reality. One way to enhance the therapeutic and chemopreventive activity of RA and derivatives is to identify rational combinations between these compounds and other pharmacological agents. This is now possible given the information available on the biochemical and molecular mechanisms underlying the biological activity of retinoids. At the cellular level, the antileukemia and anticancer activity of retinoids is the result of three main actions, cytodifferentiation, growth inhibition, and apoptosis. Cytodifferentiation is a particularly attractive modality of treatment and differentiating agents promise to be less toxic and more specific than conventional chemotherapy. This is the result of the fact that cytotoxicity is not the primary aim of differentiation therapy. At the molecular level, retinoids act through the activation of nuclear retinoic acid receptor-dependent and -independent pathways. The cellular pathways and molecular networks relevant for retinoid activity are modulated by a panoply of other intracellular and extracellular pathways that may be targeted by known drugs and other experimental therapeutics. This chapter aims to summarize and critically discuss the available knowledge in the field.

Differential transcriptional responses of keloid and normal keratinocytes to serum stimulation

BACKGROUND

Keloids are benign tumors that occur only in response to injury, for which there is no effective treatment. We demonstrated previously that keloid keratinocytes (KKs) promote fibroblast proliferation more than normal keratinocytes (NKs) and that transforming growth factor (TGF)-beta is a component of that signal. We used the transcriptional response to serum stimulation to examine how TGF-beta expression is stimulated in KKs.

MATERIALS AND METHODS

Quiescent KKs and NKs were stimulated using serum; harvested using RNA at 0, 1, 6, 12, and 24 h; and analyzed using quantitative real-time polymerase chain reaction. TGF-beta activity in the conditioned medium was measured with an MLEC/PAI-luciferase assay. Inhibition of ERK1/2, p38 kinase, and JNK pathways was performed with PD98059, SB203580, and SP600125, respectively.

RESULTS

Increased transcription of TGF-beta2 occurs within 1 h of serum stimulation in KKs but not in NKs. In contrast, TGF-beta3 transcription was suppressed in KKs compared with NKs. No significant differences were observed in the transcriptional response of TGF-beta1. Increased TGF-beta2 mRNA correlated with increased TGF-beta biological activity in the conditioned medium. Inhibition of the ERK, p38 kinase or JNK signal transduction pathways blocked the transcriptional up-regulation of TGF-beta2, TbetaR1, and TbetaR2 in KKs.

CONCLUSIONS

KKs produce more TGF-beta2 mRNA than NKs in response to serum stimulation, resulting in increased TGF-beta activity in conditioned medium. Combining these results with our previous data lead us to propose a model of keloid formation characterized by an exaggerated response to cellular stress and abnormal epithelial-mesenchymal signaling promoting keloid formation.

Towards dissecting the pathogenesis of retinoid-induced hair loss: all-trans retinoic acid induces premature hair follicle regression (catagen) by upregulation of transforming growth factor-beta2 in the dermal papilla

Diffuse hair loss ranks among the most frequent and psychologically most distressing adverse effects of systemic therapy with retinoids, which severely limits their therapeutic use even where clinically desired. Since the underlying mechanisms of retinoid-induced effluvium are as yet unknown, we have investigated the influence of the prototypic retinoid all-trans retinoic acid (ATRA, tretinoin) on the growth of human scalp hair follicles (HF) in culture. HF in the anagen VI stage of the hair cycle were cultured in the presence of 10(-8) or 10(-10) M ATRA. Compared with controls, hair shaft elongation declined significantly already after 2 d in the ATRA-treated group, and approximately 80% of the ATRA-treated HF had prematurely entered catagen-like stage at day 6, compared with 30% in the control group. This corresponded to an upregulation of apoptotic and a downregulation of Ki67-positive cells in ATRA-treated HF. Since transforming growth factor (TGF)-beta has been implicated as a key inducer of catagen, we next studied whether ATRA treatment had any effect on follicular expression. TGF-beta2 immunoreactivity was detected in the outer root sheath of anagen VI scalp HF. In catagen follicles, TGF-beta2 was also expressed in the regressing epithelial strand. After 4 d of ATRA treatment, TGF-beta2 was significantly upregulated in anagen HF in the dermal papilla (DP) and the dermal sheath, 7, and TGF-beta neutralizing antibody partially abrogated at RA induced hair growth inhibition. Real-time PCR confirmed a significant upregulation of TGF-beta2 transcripts in ATRA-treated hair bulbs. This study is the first to provide direct evidence that ATRA can indeed induce a catagen-like stage in human HF and suggests that this occurs, at least in part, via upregulation of TGF-beta2 in the DP. Therefore, topical TGF-beta2/TGF-beta receptor II antagonists deserve to be explored for the prevention and management of retinoid-induced hair loss.

Accelerated wound healing by in vivo application of keratinocytes overexpressing KGF

Epidermal regeneration is a complex process, strongly influenced by growth factors, including keratinocyte growth factor (KGF). The objective of this study was to establish immortalized HaCaT keratinocytes and KMST-6-fibroblasts stably expressing KGF. Transfection efficiency, genomic integration, and functionality of the transgene were determined by ELISA and PCR, and KGF-expressing clones were selected using an air-liquid interface test system. HaCaT cells displayed stronger transgene expression compared to transfected fibroblasts, and the most effective HaCaT clone was incubated on a membrane carrier to form a "membrane cell graft." Twenty-one superficial second-degree burn wounds were created in each of three pigs, and wound healing capacity of the generated "polypeptide cell delivery system" after grafting was examined. Untransfected HaCaT keratinocytes and membrane-covered and untreated burn wounds served as controls. Histological and macroscopical follow-up revealed that grafting of transfected HaCaT cells resulted in complete reepithelialization within 5 days, while wounds covered with untransfected cells needed 2 days longer. At untreated sites, a thin epithelium was detectable after 10 days. The results indicate that wound healing processes can be stimulated distinctly by growth factors secreted from HaCaT cells, with a prominent role for transgenic KGF.

Wounds increase activin in skin and a vasoactive neuropeptide in sensory ganglia

Successful healing of skin wounds requires sensory innervation and the release of vasoactive neuropeptides that dilate blood vessels and deliver serum proteins to the wound, and that cause pain that protects from further injury. Activin has been proposed as a target-derived regulator of sensory neuropeptides during development, but its role in the mature nervous system is unknown. While adult skin contains a low level of activin, protein levels in skin adjacent to a wound increase rapidly after an excision. Neurons containing the neuropeptide calcitonin gene-related peptide (CGRP) increased in sensory ganglia that projected to the wounded skin, but not in ganglia that projected to unwounded skin, suggesting that neurons respond to a local skin signal. Indeed, many adult sensory neurons respond with increased CGRP expression to the application of activin in vitro and utilize a smad-mediated signal transduction pathway in this response. A second skin-derived factor nerve growth factor (NGF) also increased in wounded skin and increased CGRP in cultured adult dorsal root ganglia (DRG) neurons but with lower efficacy. Together, these data support the hypothesis that activin made by skin cells regulates changes in sensory neuropeptides following skin injury, thereby promoting vasodilation and wound healing.

Organotypic cocultures as skin equivalents: A complex and sophisticated in vitro system

To assess the role of genes required for skin organogenesis, tissue regeneration and homeostasis, we have established in vitro skin equivalents composed of primary cells or cell lines, respectively. In these organotypic cocultures keratinocytes generate a normal epidermis irrespective of the species and tissue origin of fibroblasts. The combination of cells derived from mouse and human tissues facilitates the identification of the origin of compounds involved in epidermal tissue reconstitution and thus the precise analysis of growth regulatory mechanisms.

Modeling tissue-specific signaling and organ function in three dimensions

In order to translate the findings from basic cellular research into clinical applications, cell-based models need to recapitulate both the 3D organization and multicellular complexity of an organ but at the same time accommodate systematic experimental intervention. Here we describe a hierarchy of tractable 3D models that range in complexity from organotypic 3D cultures (both monotypic and multicellular) to animal-based recombinations in vivo. Implementation of these physiologically relevant models, illustrated here in the context of human epithelial tissues, has enabled the study of intrinsic cell regulation pathways and also has provided compelling evidence for the role of the stromal compartment in directing epithelial cell function and dysfunction. Furthermore the experimental accessibility afforded by these tissue-specific 3D models has implications for the design and development of cancer therapies.

Platelet-rich plasma gel promotes differentiation and regeneration during equine wound healing

Nonhealing wounds of the lower equine limb represent a challenging model. The platelet is a natural source of a myriad of growth factors and cytokines that promote wound healing. This study evaluates the potential of platelet derived factors to enhance wound healing in the lower equine limb. Platelets were isolated from horse blood and activated with thrombin, a process known to induce growth factor release. This produced a platelet gel composed of platelet-rich plasma (PRP). To test this all-natural wound healant, 2.5-cm(2) full thickness cutaneous wounds were created below the knee and hock of a thoroughbred horse. Wounds were treated with PRP gel or left untreated. Sequential wound biopsies collected at Days 7, 36, and 79 postwounding permitted comparison of the temporal expression of differentiation markers and wound repair. To test the hypothesis that wounds treated with PRP gel exhibit more rapid epithelial differentiation and enhanced organization of dermal collagen compared to controls, tissues were stained for cytokeratin 10, a suprabasal differentiation marker, and the reestablishment of collagen was evaluated by trichrome staining. PRP gel-treated wounds at Day 7 expressed intense cytokeratin 10 staining near the wound junction in suprabasal epidermal layers, while staining in control tissues was less intense and restricted to apical epidermal layers distal to the wound junction. By Day 79, the staining was equal in both groups. However, PRP gel-treated wounds at Day 79 contained abundant, dense collagen bundles oriented parallel to each other and to the overlying epithelium, whereas control tissues contained fewer collagen fibers that were oriented randomly. Thus, treatment of wounds with PRP gel induced accelerated epithelial differentiation and produced tissue with organized, interlocking collagen bundles. This study reveals that this novel all-natural wound healant induced wound repair in injuries previously deemed untreatable.

Differential expression of a WD protein during squamous differentiation of tracheal epithelial cells

The lining of the trachea consists of a pseudostratified, mucociliary epithelium that under a variety of conditions, such as vitamin A deficiency, toxic and mechanical injury, becomes a stratified squamous epithelium. Several in vitro cell culture models have been established to study the process of differentiation of airway epithelium. Such studies have indicated that mucosecretory differentiation of tracheal epithelial cells can be modulated by substratum. This study was undertaken to understand molecular mechanisms of squamous differentiation in tracheal epithelia. Primary cultured tracheal cells grown on uncoated filters were differentiated to single layer of squamous cells, whereas cells were grown as stratified columnar cells on collagen-I coated filters. The responses to secretagogues were altered according to culture conditions. DD-PCR revealed that FAK and a WD protein expression was increased in squamous tracheal epithelia. Expression of a WD protein was changed by the treatment of retinoic acid in various epithelial cells. These results indicated that squamous differentiation of tracheal cells changes the expression of a variety of genes, and that the experimental model for this study can be employed to study molecular mechanisms of squamous differentiation in airway epithelial cells.

Effect of fibroblasts on epidermal regeneration

BACKGROUND

There is little information on specific interactions between dermal fibroblasts and epidermal keratinocytes. The use of engineered skin equivalents consisting of organotypic cocultures of keratinocytes and fibroblasts offers an attractive approach for such studies.

OBJECTIVES

To examine the role fibroblasts play in generation and maintenance of reconstructed epidermis.

METHODS

Human keratinocytes were seeded on collagen matrices populated with increasing numbers of fibroblasts and cultured for 2 weeks at the air-liquid interface.

RESULTS

In the absence of fibroblasts, stratified epidermis with only three or four viable cell layers was formed. In the presence of fibroblasts, keratinocyte proliferation was stimulated and epidermal morphology was improved. Epidermal morphogenesis was also markedly improved in epidermis generated in organotypic keratinocyte monocultures grown in medium derived from dermal equivalents or from organotypic keratinocyte-fibroblast cocultures. These observations clearly indicate the proliferation-stimulating activity of soluble factors released from fibroblasts. Under all experimental conditions, onset of keratinocyte differentiation was shown by the expression of keratin 10 in all suprabasal cell layers. With increasing numbers of fibroblasts incorporated into the collagen matrix, the expression of markers associated with keratinocyte activation, e.g. keratins 6, 16 and 17 and the cornified envelope precursor SKALP decreased, and involucrin localization shifted toward the granulosum layer. This fibroblast-mediated effect was even more pronounced when the fibroblasts were precultured in the collagen matrices for 1 week instead of overnight. The basement membrane proteins collagen VII and laminin 5 were present at the epithelial-matrix border. The expression of integrin alpha 6 beta 4 and of E-cadherin was comparable with that seen in native skin and was not significantly modulated by fibroblasts. Under all experimental conditions the expression of integrin subunits alpha 2, alpha 3 and beta 1 was upregulated, indicating keratinocyte activation.

CONCLUSIONS

Our results illustrate that numbers of fibroblasts in the collagen matrix and their functional state is a critical factor for establishment of normal epidermal morphogenesis.

Epidermis proliferative effect of the Panax ginseng ginsenoside Rb2

Ginseng has been used as a traditional medicine with various therapeutic effects. However, it is still unknown which component of this plant is effective at promoting wound healing. Recently, ginsenoside Rb2 has been reported to improve wound healing. In this study, to investigate the reported wound healing effect of the ginsenoside Rb2, cell morphology and protein factors involved in epidermal formation were evaluated by immunochemical and immunoblotting analysis. Rb2 stimulated epidermal cell proliferation, and the cell showed a 1.5-fold increase in thymidine uptake compared to the control (p<0.05, n=3). Furtheremore, Rb2 was found to stimulate epidermis formation in a dose-dependent manner in raft culture, and to dose dependently enhance the expressions of protein factors related to cell proliferation, namely, epidermal growth factor and its receptor, fibronectin and its receptor, keratin 5/14, and collagenase I (p<0.05, n=3-9). It is believed that ginsenoside Rb2 enhances epidermal cell proliferation by upregulating the expressions of these proliferation-related factors.

The wound-healing effect of a glycoprotein fraction isolated from aloe vera

BACKGROUND

Aloe vera has been used as a family medicine for promoting wound healing, but it is not known which component of the plant is effective for this purpose.

OBJECTIVES

To isolate and characterize the component effective in wound healing.

METHODS

Chromatography, electrophoresis and spectroscopic methods were used. The cell-proliferation activity of each component isolated was measured by a [3H]thymidine uptake assay. The cell-proliferation activity of the effective component was tested on a three-dimensional raft culture (cell culture technique by which artificial epidermis is made from keratinocytes). The effect of the active component on cell migration and wound healing was observed on a monolayer of human keratinocytes and in hairless mice.

RESULTS

A glycoprotein fraction was isolated and named G1G1M1DI2. It showed a single band on sodium dodecyl sulphate-polyacrylamide gel electrophoresis, with an apparent molecular weight of about 5.5 kDa. It exhibited significant [3H]thymidine uptake in squamous cell carcinoma cells. The effect of G1G1M1DI2 on cell migration was confirmed by accelerated wound healing on a monolayer of human keratinocytes. When this fraction was tested on a raft culture, it stimulated the formation of epidermal tissue. Furthermore, proliferation markers (epidermal growth factor receptor, fibronectin receptor, fibronectin, keratin 5/14 and keratin 1/10) were markedly expressed at the immunohistochemical level. The glycoprotein fraction enhanced wound healing in hairless mice by day 8 after injury, with significant cell proliferation.

CONCLUSIONS

It is considered that this glycoprotein fraction is involved in the wound-healing effect of aloe vera via cell proliferation and migration.

Collagen matrix in development and progression of experimentally induced respiratory neoplasms in the hamster

Intratracheal instillations of 7H-dibenzo(c, g)carbazole (DBC), a tobacco smoke component, into Syrian golden hamsters, resulted in preneoplastic lesions and benign and malignant respiratory neoplasms. Neoplastic progression was associated with specific changes in the extracellular matrix (ECM), dependent on the stage of tumor development. DBC-induced tracheobronchial squamous metaplasia was associated with an increase in collagen type I and type III deposition in the subepithelial ECM, as observed by computer-assisted image analysis of immunohistochemical staining for the aminoterminal propeptides of collagen type I (PINP) and collagen type III (PIIINP). Increased collagen matrix synthesis was detected in dysplasia by in situ hybridization of alpha1(I) mRNA for collagen I and alpha1(III) mRNA for collagen type III after continued exposure to DBC. In well-differentiated squamous cell carcinomas with an expansive growth pattern, collagen deposition increased, as did fiber size. In moderately differentiated neoplasms, basement membrane (BM) destruction and invasion was associated with a destructive growth pattern and decreases in collagen synthesis and the deposition of new collagen. Preserved deposition of mature collagen was detected by staining for the telopeptide of collagen type I propeptide. In less differentiated tumors, ECM development was minimal, with few and small fibers, possibly explaining the rapid development of these neoplasms. Transforming growth factor beta (TGFbeta1) immunoreactivity was increased in hyperplastic epithelium and well differentiated neoplasms and decreased in dysplasia and less differentiated squamous cell carcinomas, while TGFbeta2 and TGFbeta3 expression was also distinct in neoplastic cells. Collagen synthesis and epithelial differentiation were associated with an increased number of myofibroblasts in the ECM and with increased TGFbeta3 immunoreactivity in differentiated cells and in the matrix. The nature of the composition of the ECM was related to neoplastic growth and progression when analyzed by computer-associated image analysis, revealing alterations in collagen structure, size, and shape.

Keratins and the keratinocyte activation cycle

In wound healing and many pathologic conditions, keratinocytes become activated: they turn into migratory, hyperproliferative cells that produce and secrete extracellular matrix components and signaling polypeptides. At the same time, their cytoskeleton is also altered by the production of specific keratin proteins. These changes are orchestrated by growth factors, chemokines, and cytokines produced by keratinocytes and other cutaneous cell types. The responding intracellular signaling pathways activate transcription factors that regulate expression of keratin genes. Analysis of these processes led us to propose the existence of a keratinocyte activation cycle, in which the cells first become activated by the release of IL-1. Subsequently, they maintain the activated state by autocrine production of proinflammatory and proliferative signals. Keratins K6 and K16 are markers of the active state. Signals from the lymphocytes, in the form of Interferon-gamma, induce the expression of K17 and make keratinocytes contractile. This enables the keratinocytes to shrink the provisional fibronectin-rich basement membrane. Signals from the fibroblasts, in the form of TGF-beta, induce the expression of K5 and K14, revert the keratinocytes to the healthy basal phenotype, and thus complete the activation cycle.

Function and regulation of AP-1 subunits in skin physiology and pathology

The mouse skin has become the model of choice to study the regulation and function of AP-1 subunits in many physiological and pathological processes in vivo and in vitro. Genetically modified mice, in vitro reconstituted skin equivalents and epidermal cell lines were established, in which AP-1-regulated genetic programs of cell proliferation, differentiation and tumorigenesis can be analysed. Since the epidermis, as our interface with the environment, is subjected to radiation and injury, signal transduction pathways and critical AP-1 members regulating the mammalian stress response could be identified. Regulated expression of important components of the cytokine network, cell surface receptors and proteases, which orchestrate the process of wound healing has been found to rely on AP-1 activity. Here we review our current knowledge on the function of AP-1 subunits and AP-1 target genes in these fascinating fields of skin physiology and pathology.

c-Jun and JunB antagonistically control cytokine-regulated mesenchymal-epidermal interaction in skin

Interactions between mesenchymal and epithelial cells are responsible for organogenesis and tissue homeostasis. This mutual cross-talk involves cell surface proteins and soluble factors, which are mostly the result of regulated transcription. To elucidate dimer-specific functions of the AP-1 family of transcription factors, we reconstituted skin by combining primary human keratinocytes and mouse wild-type, c-jun(-/-), and junB(-/-) fibroblasts. We have discovered an antagonistic function of these AP-1 subunits in the fibroblast-mediated paracrine control of keratinocyte proliferation and differentiation, and traced this effect to the IL-1-dependent regulation of KGF and GM-CSF. These data suggest that the relative activation state of these AP-1 subunits in a non-cell-autonomous, transregulatory fashion directs regeneration of the epidermis and maintenance of tissue homeostasis in skin.

Forced expression of keratin 16 alters the adhesion, differentiation, and migration of mouse skin keratinocytes

Injury to the skin results in an induction of keratins K6, K16, and K17 concomitant with activation of keratinocytes for reepithelialization. Forced expression of human K16 in skin epithelia of transgenic mice causes a phenotype that mimics several aspects of keratinocyte activation. Two types of transgenic keratinocytes, with forced expression of either human K16 or a K16-C14 chimeric cDNA, were analyzed in primary culture to assess the impact of K16 expression at a cellular level. High K16-C14-expressing and low K16-expressing transgenic keratinocytes behave similar to wild type in all aspects tested. In contrast, high K16-expressing transgenic keratinocytes show alterations in plating efficiency and calcium-induced differentiation, but proliferate normally. Migration of keratinocytes is reduced in K16 transgenic skin explants compared with controls. Finally, a subset of high K16-expressing transgenic keratinocytes develops major changes in the organization of keratin filaments in a time- and calcium concentration-dependent manner. These changes coincide with alterations in keratin content while the steady-state levels of K16 protein remain stable. We conclude that forced expression of K16 in progenitor skin keratinocytes directly impacts properties such as adhesion, differentiation, and migration, and that these effects depend upon determinants contained within its carboxy terminus.

Treatment with all-trans-retinoic acid decreases levels of endogenous TGF-beta(1) in the mesenchyme of the developing mouse inner ear

BACKGROUND

Previous studies have shown that in utero exposure of the mouse embryo to high doses of all-trans-retinoic acid (atRA) produces defects of the developing inner ear and its surrounding cartilaginous capsule, while exposure of cultured periotic mesenchyme plus otic epithelium to high doses of exogenous atRA results in an inhibition of otic capsule chondrogenesis.

METHODS

In this study, we examine the effects of atRA exposure on the endogenous expression of transforming growth factor-beta(1) (TGF-beta(1)), a signaling molecule that mediates the epithelial-mesenchymal interactions that guide the development of the capsule of the inner ear.

RESULTS

Our results demonstrate a marked reduction in immunostaining for TGF-beta(1) in the periotic mesenchyme of atRA-exposed embryos of age E10.5 and E12 days in comparison with control specimens. Consistent with these in vivo findings, high-density cultures of E10.5 periotic mesenchyme plus otic epithelium, treated with doses of atRA that suppress chondrogenesis, showed significantly decreased levels of TGF-beta(1), as compared with TGF-beta(1) levels in untreated control cultures. Furthermore, we demonstrate a rescue of cultured periotic mesenchyme plus otic epithelium from atRA-induced chondrogenic suppression by supplementation of cultures with excess TGF-beta(1).

CONCLUSIONS

Our results support the hypothesis that TGF-beta(1) plays a role in mechanisms of atRA teratogenicity during inner ear development.

Multistep production of bioengineered skin substitutes: sequential modulation of culture conditions

Many studies are being conducted to define the role of growth factors in cutaneous physiology in order to add cytokines in a timely fashion for optimal tissue engineering of skin. This study is aimed at developing a multistep approach for the production of bioengineered skin substitutes, taking into account the effects of various growth factors according to the culture time. The use of a serum-supplemented medium throughout the whole culture period of skin substitutes was compared to the sequential use of specific additives at defined culture steps. Histological analysis revealed that serum was necessary for keratinocyte proliferation and migration on dermal substitutes during the first 2 d after their seeding. However, the serum-free medium presented some advantages when supplemented with different additives at specific culture steps. Interestingly, ascorbic acid added to the dermal substitutes before and after keratinocyte seeding maintained their cuboidal morphology in the basal epidermal layer. In the absence of serum, collagen matrix degradation slowed down, and a better multilayered epidermal organization was obtained, notably with retinoic acid. Stratum corneum formation was also enhanced by fatty acids. Thus, sequential addition of exogenous factors to the medium used to produce skin substitutes can improve their structural features and functional properties in vitro.

Organotypic keratinocyte cocultures in defined medium with regular epidermal morphogenesis and differentiation

Skin equivalents formed by keratinocytes cocultured with fibroblasts embedded in collagen lattices represent promising tools for mechanistic studies of skin physiology, for pharmacotoxicologic testing, and for the use as skin substitutes in wound treatment. Such cultures would be superior in defined media to avoid interference with components of serum or tissue extracts. Here we demonstrate that a defined medium (supplemented keratinocyte defined medium) supports epidermal morphogenesis in organotypic cocultures equally well as serum-containing medium (mixture of Ham's F12 and Dulbecco's modified Eagle's medium), as documented by hallmarks of the epidermal phenotype studied by immunofluorescence and electron microscopy. In both cases regularly structured, orthokeratinized epithelia evolved with similar kinetics. Morphology in mixture of Ham's F12 and Dulbecco's modified Eagle's medium was slightly hyperplastic, and keratins 1 and 10 synthesis less co-ordinated than in supplemented keratinocyte defined medium, but a consistently inverted sequence of expression of keratins 1 and 10 was found in either medium. The late differentiation markers filaggrin, involucrin, keratin 2e, and transglutaminase 1 corresponded in their typical distribution in upper suprabasal layers. Keratin 16 persisted under both conditions indicating the activated epidermal state. Keratinocyte proliferation was comparable in both media, whereas fibroblast multiplication and proliferation was delayed and reduced in supplemented keratinocyte defined medium. In both media, ultrastructural features of epidermal differentiation as well as reconstitution of a basement membrane occurred similarly. Immature lamellar bodies and cytoplasmatic vacuoles, however, indicated an impaired lipid metabolism in supplemented keratinocyte defined medium. Nevertheless, these defined organotypic cocultures provide a suitable basis for in vitro skin models to study molecular mechanisms of tissue homeostasis and for use in pharmacotoxicologic testing.

The stressful condition as a nutritionally dependent adaptive dichotomy

The injured body manifests a cascade of cytokine-induced metabolic events aimed at developing defense mechanisms and tissue repair. Rising concentrations of counterregulatory hormones work in concert with cytokines to generate overall insulin and insulin-like growth factor 1 (IGF-1), postreceptor resistance and energy requirements grounded on lipid dependency. Salient features are self-sustained hypercortisolemia persisting as long as cytokines are oversecreted and down-regulation of the hypothalamo-pituitary-thyroid axis stabilized at low basal levels. Inhibition of thyroxine 5'-deiodinating activity (5'-DA) accounts for the depressed T3 values associated with the sparing of both N and energy-consuming processes. Both the liver and damaged territories adapt to stressful signals along up-regulated pathways disconnected from the central and peripheral control systems. Cytokines stimulate liver 5'-DA and suppress the synthesis of transthyretin (TTR), causing the drop of retinol-binding protein (RBP) and the leakage of increased amounts of T4 and retinol in free form. TTR and RBP thus work as prohormonal reservoirs of precursor molecules which need to be converted into bioactive derivatives (T3 and retinoic acids) to reach transcriptional efficiency. The converting steps (5'-DA and cellular retinol-binding protein-I) are activated by T4 and retinol, themselves operating as limiting factors of positive feedback loops. Healthy adults with normal macrophage functioning and liver parenchymal integrity, who submitted to a stress of medium severity, are characterized by TTR-RBP plasma levels reduced by half and an estimated ten-fold increase in free ligand disposal to target cells during the days ensuing injury. This transient hyperthyroid and hyperretinoid climate creates a second defense line strengthening and fine-tuning the effects primarily initiated by cytokines. The suicidal behavior of thyroxine-binding globulin (TBG), corticosteroid-binding globulin (CBG), and IGFBP-3 allows the occurrence of peak endocrine and mitogenic influences at the site of inflammation. The production rate of TTR by the liver is the main determinant of both the hepatic release and blood transport of holoRBP, which explains why poor nutritional status concomitantly impairs thyroid- and retinoid-dependent acute-phase responses, hindering the stressed body to appropriately face the survival crisis. The prognostic significance of low TT4 blood levels may be assigned to the exhaustion of extrathyroidal hormonal pools normally stored in liver and plasma but markedly shrunken in protein-depleted states. These data offer new insights into the mechanisms whereby preexisting malnutrition and stressful complications are interrelated, emphasizing the pivotal role played by TTR in that context.

Tissue-engineered human skin substitutes developed from collagen-populated hydrated gels: clinical and fundamental applications

The field of tissue engineering has opened several avenues in biomedical sciences, through ongoing progress. Skin substitutes are currently optimised for clinical as well as fundamental applications. The paper reviews the development of collagen-populated hydrated gels for their eventual use as a therapeutic option for the treatment of burn patients or chronic wounds: tools for pharmacological and toxicological studies, and cutaneous models for in vitro studies. These skin substitutes are produced by culturing keratinocytes on a matured dermal equivalent composed of fibroblasts included in a collagen gel. New biotechnological approaches have been developed to prevent contraction (anchoring devices) and promote epithelial cell differentiation. The impact of dermo-epidermal interactions on the differentiation and organisation of bio-engineered skin tissues has been demonstrated with human skin cells. Human skin substitutes have been adapted for percutaneous absorption studies and toxicity assessment. The evolution of these human skin substitutes has been monitored in vivo in preclinical studies showing promising results. These substitutes could also serve as in vitro models for better understanding of the immunological response and healing mechanism in human skin. Thus, such human skin substitutes present various advantages and are leading to the development of other bio-engineered tissues, such as blood vessels, ligaments and bronchi.

Cellular characterization and successful transfection of serially subcultured normal human esophageal keratinocytes

BACKGROUND

In vitro cell culture models can provide unique insights into squamous epithelial proliferation, differentiation, and neoplastic transformation. Cultures of human esophageal keratinocytes could be advantageous for the study of these processes.

METHODS

Normal human esophageal keratinocytes were cultivated on 3T3 fibroblast feeder layers in vitro and expanded through four serial subcultivations. Confluent tertiary cultures were analyzed by morphological and immunohistochemical techniques to define their basic properties. The ability to transiently transfect cultured esophageal epithelium was tested using a Rous sarcoma virus-luciferase reporter gene by the calcium phosphate and lipofection methods.

RESULTS

Postconfluent cultures displayed a predominantly basal cell phenotype with limited stratification, widespread expression of keratins 5 and 14, and production of attachment specialization proteins such as alpha6beta4 integrin and collagen VII. Terminal differentiation markers (involucrin and transglutaminase) were prematurely expressed. The cells expressed growth factors important in proliferation and differentiation, such as transforming growth factor-beta and interleukin-1beta. Tertiary cultures were successfully transiently transfected with a Rous sarcoma virus-luciferase reporter gene construct.

CONCLUSION

Normal human esophageal cells can be serially passaged through extended numbers of cell generations and transfected by standard methods. This in vitro system may be useful in the study of fundamental cellular processes governing proliferation and differentiation in the esophageal epithelium.

Galectin-7, a marker of all types of stratified epithelia

Galectin-7 is a 14-kDA member of the lectin family we have previously cloned in the human. Its expression was found at all stages of differentiation of the human epidermis and was reduced but not suppressed when oral metaplasia of reconstructed epidermis was induced by retinoic acid. This suggested that galectin-7 could be a marker of both keratinized and non-keratinized stratified epithelia. To ascertain this hypothesis, we cloned the rat and the mouse cDNAs and produced a specific antiserum raised against a synthetic peptide. The distribution of galectin-7 mRNAs and protein was studied by in situ hybridization and immunolabelling of various human, rat and mouse epithelia. Galectin-7 was found to be expressed in interfollicular epidermis and in the outer root sheath of the hair follicle, but not in the hair matrix, nor in the sebaceous glands. It was present in esophagus and oral epithelia, cornea, Hassal's corpuscles of the thymus, but not in simple and transitional epithelia. Galectin-7 can thus be considered as a marker of all subtypes of keratinocytes. In that respect it differs from both "basal-specific" keratins K5-K14 and from "suprabasal-specific" markers such as keratins K1-K10 and involucrin. Galectin-7 also differs from some desmosomal proteins, which are present in all types of epithelia and in myocardium. Galectin-7 was absent from cultured carcinoma cell lines and was reduced both in human carcinomas and in murine tumors produced with the two-stage carcinogenesis protocol.

Epidermal signal transduction and transcription factor activation in activated keratinocytes

In the area of biology, many laboratories around the world are dissecting and characterizing signal transduction mechanisms and transcription factors responsive to various growth factors and cytokines, in various cell types. However, because of the differences in systems used, it is not clear whether these systems coexist, whether they interact meaningfully, and what their relative roles are. Epidermal keratinocytes are the perfect cell type in which to integrate this knowledge, because in these cells these mechanisms are known to be relevant. Keratinocytes both produce and respond to growth factors and cytokines, especially in pathological conditions and during wound healing, when the physiology of keratinocytes is altered in a way specified by the presence of a subset growth factors and cytokines. In fact, growth factors and cytokines cause the major changes in gene expression and keratinocyte behavior in various cutaneous diseases. In some cases, such as in wound healing, these responses are highly beneficial; in others, such as in psoriasis, they are pathological. It is not clear at present which are operating in which conditions, which are important for the healing process and which are harmful. Growth factors and cytokines affect keratinocytes sometimes simultaneously, at other times individually. In this manuscript we describe the signal transduction pathways responsible for the effects of interferons, the EGF/TGF alpha family and the TNF alpha/IL-1 family of signaling molecules. We also describe the important transcription factors known to be functional in epidermis, with particular emphasis on those factors that are activated by growth factors and cytokines. Finally, we describe what is known about transcriptional regulation of keratin genes, especially those specifically expressed in pathological processes in the epidermis. We expect that the enhanced understanding of the pathways regulating gene expression in keratinocytes will identify the pharmacological targets, the signal transducing proteins and the corresponding transcription factors, used by growth factors and cytokines. This research will led to development of compounds precisely aimed at those targets, allowing us to isolate and inhibit the harmful side effects of growth factors and cytokines. Such compounds should lead to highly specific and therefore more effective treatments of the cutaneous disorders in which these pathways play significant roles.

Identification of receptors and Smad proteins involved in activin signalling in a human epidermal keratinocyte cell line

BACKGROUND

Activin A is a multifunctional protein, which is a member of the transforming growth factor-beta (TGF-beta) superfamily. Smad proteins have recently been shown to transduce signals for the TGF-beta superfamily of proteins, and Smad2 was implicated in activin signalling in Xenopus embryos.

RESULTS

We identified the receptors and Smad proteins activated by activin A in a human epidermal keratinocyte cell line, HaCaT. The major activin receptors expressed on HaCaT cells were activin type II receptor (ActR-II) and activin type IB receptor (ActR-IB). We have also shown that in HaCaT cells, activin A induced the phosphorylation of Smad3 and, to a lesser extent, of Smad2. On the other hand, TGF-beta induced an efficient phosphorylation of both Smad2 and Smad3. Activin A preferentially induced the nuclear translocation of Smad3 in HaCaT cells, whereas TGF-beta strongly induced the nuclear translocation of Smad2, as well as other Smads. Moreover, a constitutively active form of ActR-IB efficiently stimulated the formation of a heteromeric complex between Smad3 and Smad4 in COS cells transfected with Smad cDNAs.

CONCLUSIONS

These results suggest that activin A binds to a receptor complex of ActR-II and ActR-IB, and preferentially activates Smad3 in HaCaT human keratinocytes.

Defining a region of the human keratin 6a gene that confers inducible expression in stratified epithelia of transgenic mice

Injury to the epidermis and other stratified epithelia triggers a repair response involving the rapid induction of several genes, including keratin 6 (K6). The signaling pathways and mechanisms presiding over this induction in keratinocytes at the wound edge remain to be defined. We reported previously that of the multiple genes encoding K6 isoforms in human, K6a is dominant in skin epithelia (Takahashi, K., Paladini, R., Coulombe, P. A. (1995) J. Biol. Chem. 270, 18581-18592). Using bacterial LacZ as a reporter gene in transgenic mice, we show that the proximal 5.2 kilobases of 5'-upstream sequence from the K6a gene fails to direct sustained expression in any adult tissue, including those where K6 is constitutively expressed (e.g. hair follicle, nail, oral mucosa, tongue, esophagus, forestomach). In contrast, the proximal 960 base pairs of 5'-upstream sequence suffice to mediate an induction of beta-galactosidase expression in a near-correct spatial and temporal fashion after injury to epidermis and other stratified epithelia. Transgene expression also occurs following topical application of phorbol esters, all-trans-retinoic acid, or 2-4-dinitro-1-fluorobenzene, all known to induce K6 expression in skin. Our data show that critical regulatory sequences for this inducibility are located between -960 and -550 bp in the 5'-upstream sequence of K6a and that their activity is influenced by enhancer element(s) located between -2500 and -5200 base pairs. These findings have important implications for the control of gene expression after injury to stratified epithelia.

Retinoic acid stimulates essential fatty acid-supplemented human keratinocytes in culture

The effect of all-trans retinoic acid on the proliferation of essential fatty acid (EFA)-deficient and of EFA-supplemented adult human keratinocytes was investigated. EFA-deficient cell strains were supplied with one of four different fatty acid-supplemented media at the P0 to P1 passage. All-trans retinoic acid at 0.5 or 1.0 microM was added to the cultures at the P1 to P2 passage. At passage P3, and 3 and 7 d thereafter, the cell growth rate was determined. The fatty acid content of cultures grown in each medium was measured using gas chromatography. All the EFA media "normalized" the cellular fatty acid composition and drastically decreased the cell number and total DNA and protein of the cultures. All-trans retinoic acid at 1 microM prevented the loss of cell viability and growth usually associated with EFA supplementation but did not affect the control (EFA deficient) or 18:1 fatty acid-supplemented cultures. All-trans retinoic acid at 1 microM altered the fatty acid content of the EFA-supplemented cultures. A statistically significant increase in 14:0, 14:1, 16:1, 18:1, and 20:4 fatty acids occurred, whereas the amounts of 18:0 and 18:2 fatty acids decreased. The largest changes were in 16:1 fatty acid (8-14%) and 18:2 fatty acid (12-5%). All-trans retinoic acid at 0.5 microM also affected both cell growth and fatty acid composition without induction of the CRABP II message. These studies demonstrate that all-trans retinoic acid stimulates the growth of EFA-supplemented keratinocyte cultures while also altering the fatty acid composition of the cells.

JSID Tanioku Memorial Lecture 1996. Genetic disorders of keratins and their associated proteins

It has recently been demonstrated that genetic defects in keratin genes cause a number of different skin disorders, including epidermolysis bullosa simplex (EBS), epidermolytic hyperkeratosis (EH), the EH form of epidermal nevi, epidermolytic and non-epidermolytic forms of palmoplantar keratoderma (EPPK and PPK) and pachyonychia congenita (PC). In this review, I describe the research that led to this discovery.

The cytoskeleton and disease: genetic disorders of intermediate filaments

Specialized cytoskeletons play many fascinating roles, including mechanical integrity and wound-healing in epidermal cells, cell polarity in simple epithelia, contraction in muscle cells, hearing and balance in the inner ear cells, axonal transport in neurons, and neuromuscular junction formation between muscle cells and motor neurons. These varied functions are dependent upon cytoplasmic networks of actin microfilaments (6 nm), intermediate filaments (10 nm) and microtubules (23 nm), and their many associated proteins. In this chapter, I review what is known about the cytoskeletons of intermediate filaments and their associated proteins. I focus largely on epidermal cells, which devote most of their protein-synthesizing machinery to producing an extensive intermediate filament network composed of keratin. Recent studies have shown that many of the devastating human disorders that arise from degeneration of this cell type have as their underlying basis either defects in the genes encoding keratins or abnormalities in keratin IF networks. I discuss what we know about the functions of IFs, and how the link to genetic disease has enhanced this understanding.