FcgammaRIII expression on cultured human keratinocytes and upregulation by interferon-gamma

Melanin's Journey from Melanocytes to Keratinocytes: Uncovering the Molecular Mechanisms of Melanin Transfer and Processing

Skin pigmentation ensures efficient photoprotection and relies on the pigment melanin, which is produced by epidermal melanocytes and transferred to surrounding keratinocytes. While the molecular mechanisms of melanin synthesis and transport in melanocytes are now well characterized, much less is known about melanin transfer and processing within keratinocytes. Over the past few decades, distinct models have been proposed to explain how melanin transfer occurs at the cellular and molecular levels. However, this remains a debated topic, as up to four different models have been proposed, with evidence presented supporting each. Here, we review the current knowledge on the regulation of melanin exocytosis, internalization, processing, and polarization. Regarding the different transfer models, we discuss how these might co-exist to regulate skin pigmentation under different conditions, i.e., constitutive and facultative skin pigmentation or physiological and pathological conditions. Moreover, we discuss recent evidence that sheds light on the regulation of melanin exocytosis by melanocytes and internalization by keratinocytes, as well as how melanin is stored within these cells in a compartment that we propose be named the melanokerasome. Finally, we review the state of the art on the molecular mechanisms that lead to melanokerasome positioning above the nuclei of keratinocytes, forming supranuclear caps that shield the nuclear DNA from UV radiation. Thus, we provide a comprehensive overview of the current knowledge on the molecular mechanisms regulating skin pigmentation, from melanin exocytosis by melanocytes and internalization by keratinocytes to processing and polarization within keratinocytes. A better knowledge of these molecular mechanisms will clarify long-lasting questions in the field that are crucial for the understanding of skin pigmentation and can shed light on fundamental aspects of organelle biology. Ultimately, this knowledge can lead to novel therapeutic strategies to treat hypo- or hyper-pigmentation disorders, which have a high socio-economic burden on patients and healthcare systems worldwide, as well as cosmetic applications.

Pre-Existing Humoral Immunity Enhances Epicutaneously-Administered Allergen Capture by Skin DC and Their Migration to Local Lymph Nodes

Due to its richness in antigen presenting cells, e.g., dendritic cells (DC), the skin has been identified as a promising route for immunotherapy and vaccination. Several years ago, a skin delivery system was developed based on epicutaneous patches allowing the administration of antigen through intact skin. Using mouse models, we have shown that epicutaneous allergen application leads to a rapid uptake and transport of allergen-positive cells to skin-draining lymph nodes (LN). This occurred primarily in animals previously sensitized to the same allergen. In that context, we sought to better understand the role of the specific preexisting immunity in allergen capture by skin DC and their subsequent migration to LN. Specifically, we investigated the role of humoral immunity induced by sensitization and the involvement of IgG Fc receptors (FcγR). Epicutaneous patches containing fluorescently-labeled ovalbumin (OVA) were applied to naïve mice that had previously received either sera or purified IgG isolated from OVA-sensitized mice. To investigate the involvement of FcγR, animals received 2.4G2 (anti-FcγRII/RIII) blocking antibody, 24 hours before patch application. Mice that received sera or purified IgG originating from OVA-sensitized mice showed an increase in the quantity of OVA-positive DC in skin and LN. Moreover, the blockade of FcγR reduced the number of OVA-positive DC in LN to a level similar to that observed in naïve animals. Overall, these results demonstrate that preexisting specific-IgG antibodies are involved in allergen capture by skin DC following EPIT through the involvement of antigen-specific IgG-FcγR.

Effect of Adalimumab on Gene Expression Profiles of Psoriatic Skin and Blood

BACKGROUND

Adalimumab is an anti-TNF biologic drug that is efficacious in the treatment of psoriasis. However, the effect of adalimumab on genome-wide gene expression changes in skin and peripheral blood is not well characterized.<BR />

METHODS

Thirty adult subjects with &gt; 10% body surface area of chronic plaque psoriasis were recruited for the study. Lesional skin and peripheral blood mononuclear cell samples prior to and one month following treatment with adalimumab were collected. The skin samples were analyzed using genome-wide RNAseq, and the blood samples were analyzed using genome-wide Affymetrix microarrays. Data preprocessing and analysis were conducted using the EdgeR and Affy packages in R/Bioconductor.<BR />

RESULTS

In the skin, paired analysis before and after treatment revealed changes in pathways important to epidermal development and keratinocyte differentiation. Such important genes as keratin 6A and 6B, tubulin B6, desmocollin, and desmoglein 3 were among the top differentially expressed genes. In peripheral blood, pathways involved in hematopoetic cell lineage and immune response were found to be differentially expressed, including genes such as the Fc receptor-like A and 5, as well as immunoglobulin heavy chains. Using a principal components approach, we show that expression of genes in post-treatment skin more closely resembles that of healthy controls.<BR />

CONCLUSION

Treatment of psoriasis with adalimumab appears to be associated with modulation of keratinocyte and epidermal proliferation in the skin and with immunologic changes in the blood. We discuss the ramifications of these findings for the treatment for psoriasis.<BR /><BR /> <em>J Drugs Dermatol</em>. 2016;15(8):988-994.

Accumulation of C-reactive protein in basal keratinocytes of normal skins

BACKGROUND

C-reactive protein (CRP) is a prototypic acute phase protein which increases dramatically in the blood during the first 48h of tissue inflammation and has been recognized as a risk factor for atherosclerosis. CRP interacts with a variety of proteins.

OBJECTIVE

To know the role of accumulated CRP in the skin.

METHODS

Interaction of CRP with basal keratinocytes was studied using immunohistochemical method and keratinocyte culture system.

RESULTS

We found an immunohistochemical deposition of CRP on the basal keratinocyte membrane in some normal human skins (23 out of 46 skins). When added to cultured keratinocytes, heat-denatured but not native CRP was found to adhere to keratinocyte cell membrane after 1h, then internalized into cytoplasm after 24h. The heat-denatured CRP recognized at least four keratinocyte polypeptides with the molecular weights of 56, 42, 32 and 24kDa. Ligand binding assays suggested that multiple populations of receptor-ligand interactions were involved in the binding between CRP and keratinocyte. Cultured dermal microvascular endothelial cells were found to express CRP of which expression was greatly induced by interleukin-1β (IL-1β) treatment, suggesting that the deposited CRP in the basal keratinocytes can be derived from local dermal microvasculatures as well as from systemic circulation (serum). Treatment of cultured keratinocytes with heat-denatured CRP induced interleukin-8 (IL-8) expression, a potent leukocyte chemotactic cytokine. CRP in the medium (liquid phase) and CRP-coated dishes (solid phase) both inhibited the adhesion of keratinocytes in culture.

CONCLUSION

Accumulation of CRP may regulate the skin inflammation and keratinocyte proliferation by modulating keratinocyte cytokine expression and adhesion to substrate.

Surface assembly of poly(I:C) on PEGylated microspheres to shield from adverse interactions with fibroblasts

By expressing an array of pattern recognition receptors (PRRs), fibroblasts play an important role in stimulating and modulating the response of the innate immune system. The TLR3 ligand polyriboinosinic acid-polyribocytidylic acid, poly(I:C), a mimic of viral dsRNA, is a vaccine adjuvant candidate to activate professional antigen presenting cells (APCs). However, owing to its ligation with extracellular TLR3 on fibroblasts, subcutaneously administered poly(I:C) bears danger towards autoimmunity. It is thus in the interest of its clinical safety to deliver poly(I:C) in such a way that its activation of professional APCs is as efficacious as possible, whereas its interference with non-immune cells such as fibroblasts is controlled or even avoided. Complementary to our previous work with monocyte-derived dendritic cells (MoDCs), here we sought to control the delivery of poly(I:C) surface-assembled on microspheres to human foreskin fibroblasts (HFFs). Negatively charged polystyrene (PS) microspheres were equipped with a poly(ethylene glycol) (PEG) corona through electrostatically driven coatings with a series of polycationic poly(L-lysine)-graft-poly(ethylene glycol) copolymers, PLL-g-PEG, of varying grafting ratios g from 2.2 up to 22.7. Stable surface assembly of poly(I:C) was achieved by incubation of polymer-coated microspheres with aqueous poly(I:C) solutions. Notably, recognition of both surface-assembled and free poly(I:C) by extracellular TLR3 on HFFs halted their phagocytic activity. Ligation of surface-assembled poly(I:C) with extracellular TLR3 on HFFs could be controlled by tuning the grafting ratio g and thus the chain density of the PEG corona. When assembled on PLL-5.7-PEG-coated microspheres, poly(I:C) was blocked from triggering class I MHC molecule expression on HFFs. Secretion of interleukin (IL)-6 by HFFs after exposure to surface-assembled poly(I:C) was distinctly lower as compared to free poly(I:C). Overall, surface assembly of poly(I:C) may have potential to contribute to the clinical safety of this vaccine adjuvant candidate.

The epidermis as an adjuvant

It is now clear that the epidermis has an active role in local immune responses in the skin. Keratinocytes are involved early in inflammation by providing first-line innate mechanisms and, in addition, can contribute to adaptive immune responses that may be associated with clinical disease. Moreover, keratinocytes are capable of enhancing and shaping the outcome of inflammation in response to stimuli and promoting particular types of immune bias. Through understanding the underlying mechanisms, the role of keratinocytes in disease pathogenesis will be further defined, which is likely to lead to the identification of potential targets for prophylactic or therapeutic intervention.

Modulation of the Fcgamma receptors induced by anti-Ro and anti-La autoantibodies: observations in salivary gland cells

Only few reports have shown protein expression of the Fcgamma receptors (FcgammaRs) molecules on human salivary gland cells. In this study we investigate a possible upregulation of FcgammaRs following anti-Ro and anti-La autoantibodies treatment. Anti-Ro and anti-La autoantibodies were purified from IgG fractions obtained from 14 patients with primary Sjögren's syndrome (SS), using Sepharose 4B-Ro and Sepharose 4B-La affinity columns. Flow cytometry and RT-PCR were used to study the FCgammaRI, FCgammaRII and FCgammaRIII receptors expression and upregulation by anti-Ro and anti-La on a salivary gland cell line. The present data document that the anti-Ro and anti-La autoantibodies determine an increase of the FcgammaRs expression on salivary gland cells, and provide evidence that both the high affinity FcgammaRI and the low affinity FcgammaRII and FcgammaRIII are overexpressed. Treatment with IgG isolated from healthy donors had no effect on the basal FCgammaRs expression.

The constitutive capacity of human keratinocytes to kill Staphylococcus aureus is dependent on beta-defensin 3

Normal skin is often exposed to bacteria, including potent pathogens such as E. coli, Staphylococcus aureus, and Streptococcus sp., but these microbes usually do not cause skin inflammation or infection in healthy individuals. Therefore, we hypothesized that there must be a constitutive mechanism for rapid destruction and elimination of small numbers of bacteria which penetrate the stratum corneum from everyday activities. This study found that exposure of keratinocytes cultured from a number of individuals to S. aureus resulted in approximately 2-3 log better killing than by HaCaT cells within 1 hour. Killing required contact between the keratinocytes and the bacteria, but was not dependent on internalization. Contact between the bacteria and the keratinocytes resulted in rapid deposition of several antimicrobial peptides onto the bacteria, but only human beta-defensin (HBD) 3 accumulated at levels sufficient to account for killing when S. aureus were exposed to human skin explants. Blocking peptide binding of HBD3 inhibited killing of the bacteria, indicating an essential role for beta-defensin 3 in the constitutive killing of bacteria by normal keratinocytes.

Changes in circulating lymphocyte subpopulations following administration of the leucocyte function-associated antigen-3 (LFA-3)/IgG1 fusion protein alefacept

Alefacept, a recombinant leucocyte function-associated antigen-3 (LFA-3)/IgG1 fusion protein approved for the treatment of psoriasis, is reported to reduce selectively the numbers of circulating CD4(+) CD45RO(+) and CD8(+) CD45RO(+) T cells, while sparing the naive cells. The purpose of the present study was to elucidate further the effect of alefacept on various circulating lymphocyte subsets. Sixteen patients, 12 with chronic plaque psoriasis and four with pustular psoriasis, received alefacept 7.5 mg once weekly for 12 weeks. Blood samples collected at study entry and after 12 weeks of treatment were analysed by four-colour flow cytometry. There were statistically significant reductions in the total number of conventional memory (CD45RA(-) CD27(+)) and effector (CD45RA(-) CD27(-) or CD45RA(+) CD27(-)) T cells, including CD4(+) and CD8(+) T cells expressing CD161 and CD8(+) T cells expressing cutaneous lymphocyte-associated antigen (CLA). Natural killer (NK) T cells were also reduced significantly, while no statistically significant changes were seen in NK cells and CD4(+) CD25(high) cells. The affected subpopulations were all characterized by a high expression of CD2. However, CD4(+) CD25(low), and CD4(+) CLA(+) cells, which also expressed relative high levels of CD2, were not reduced significantly. Our results suggest a heterogeneous effect of alefacept on the circulating memory T cell population, indicating that high expression of CD2 may not, by itself, be sufficient to explain the reduction in cell count for a specific subpopulation.

Identification of a novel FcγRIII receptor that is up-regulated in fetal wound healing

The mid-gestation fetus is able to heal skin wounds rapidly and without scarring, an ability that is lost as development proceeds. The aim of this study was to identify novel genes involved in this process. We established an ex vivo wound model from embryonic rats and showed that over 72 hours, embryonic day 17 wounds reepithelialized and closed whereas day 19 wounds did not. To investigate the molecular basis of this phenomenon we analyzed changes in gene expression using differential display polymerase chain reaction. We characterized one transcript that was strongly up-regulated in the healing response of wounded, day 17 skin. It encodes a protein of 249 amino acids with striking similarity to the human low-affinity receptor for the Fc portion of IgG (FcgammaRIII), suggesting that it is a novel member of the FcgammaR family, which we named FcgammaRIII-X. A wound-healing timecourse shows that FcgammaRIII-X was up-regulated in healing, wounded day 17 skin but not in nonhealing, wounded day 19 skin and that its up-regulation was accelerated in skin with multiple wounds. We suggest that up-regulation of FcgammaRIII-X may contribute to scarless healing of fetal skin.

Expression of FcRn, the MHC class I-related receptor for IgG, in human keratinocytes

The neonatal Fc receptor (FcRn) for IgG has been shown to be responsible for IgG transport and to be involved in IgG catabolism. In this study, we show expression of FcRn in normal human epidermal keratinocytes. By RT-PCR, we demonstrate the FcRn alpha-chain mRNA obtained from cultured keratinocytes creating a 457 bp product as confirmed by sequence analysis. Northern blot analysis shows a 1.5 kb transcript. Real-time PCR reveals consistent expression of FcRn alpha-chain mRNA in human keratinocytes from different donors. Anti-FcRn alpha2-extracellular domain and anti-FcRn cytoplasmic tail antibody (Ab) directed against defined antigenic targets were generated and used for immunoblotting and immunoprecipitation revealing protein expression of the 46 kDa FcRn alpha-chain. By immunofluorescence microscopy, we find granular-vesicular staining for FcRn alpha-chain in keratinocytes. Fluorescence-activated cell sorting analysis gives predominantly an intracellular distribution of FcRn in keratinocytes. Biochemically, we demonstrate Fc-dependent binding of human IgG at acidic pH. In normal human epidermis, we find a cytoplasmic vesicular staining of predominantly basal and suprabasal keratinocytes. In summary, we demonstrate expression of a functional FcRn in normal human epidermal keratinocytes. These findings further emphasize the role of keratinocytes as immunomodulating cells in inflammatory and immunologic processes of the skin.

RPE65 of Retinal Pigment Epithelium, A Putative Receptor Molecule for Plasma Retinol-Binding Protein, is Expressed in Human Keratinocytes

Retinoids are important modulators for cell growth and differentiation of normal skin. In plasma, retinol is transported coupled to plasma retinol-binding protein. In this study, we investigated gene and protein expression of RPE65, a putative receptor for plasma retinol-binding protein in human epidermal keratinocytes. We performed real-time PCR analysis to evaluate expression of RPE65 mRNA in proliferating and differentiating keratinocytes. Immunoblotting with anti-RPE65 antibody shows distinct reactivity to a 61-kDa protein. Indirect immunofluorescence on normal human epidermis reveals cell surface labeling of keratinocytes. Laser scan microscopy exhibits colocalization of plasma retinol-binding protein and RPE65 on cultured keratinocytes. Internalization experiments with [3H]retinoic acid-retinol-binding protein complex in the presence and absence of excess of retinol-binding protein indicates receptor-dependent uptake of retinoids. We further show isolation of RPE65 protein by affinity chromatography from lysates of keratinocytes using a retinol-binding protein-matrix gel column. In summary, we demonstrate mRNA and protein expression of RPE65 in epidermal keratinocytes. Colocalization of plasma retinol-binding protein with RPE65 and affinity binding suggest a direct interaction of RPE65 with plasma retinol-binding protein in cultured human keratinocytes that might be involved in retinoid uptake of keratinocytes.

Proliferation of peripheral blood mononuclear cells is suppressed by the indoleamine 2,3-dioxygenase expression of interferon-gamma-treated skin cells in a co-culture system

Indoleamine 2,3-dioxygenase (IDO) is an intracellular tryptophan-oxidizing enzyme possessing various immunosuppressive characteristics. In this study, we report the possible use of this enzyme in an allogenic skin substitute to suppress the proliferation of immune cells. Human fetal skin fibroblasts and keratinocytes were treated with the cytokine interferon-gamma to induce expression of IDO mRNA and protein. IDO enzyme activity was evaluated by measurement of kynurenine levels in the interferon-gamma-treated and -untreated cells. Results of Northern analysis showed a dose-dependent response in expression of IDO mRNA to the various concentrations of interferon-gamma used. Northern blot analysis also showed a time-dependent expression of IDO in response to different durations of interferon-gamma treatment. The level of kynurenine measured, as the bioactivity of IDO enzyme, was significantly higher in the interferon-gamma-treated fibroblasts and keratinocytes compared to those of controls (p < 0.001). To illustrate the immunosuppressive effects of IDO on immune cell proliferation, IDO-expressing fibroblasts were cocultured with human peripheral blood mononuclear cells for a period of 5 days. Results of 3H-thymidine incorporation assays showed a significant reduction in proliferation of the mononuclear cells cocultured with IDO-expressing skin cells compared to monocytes cocultured with control (non-IDO-expressing) skin cells (p < 0.001). Furthermore, addition of the IDO-inhibitor (1-methyl-D-tryptophan) significantly reversed the immunosuppressive effects of IDO on monocyte proliferation (p < 0.001). In conclusion, suppression of peripheral blood mononuclear cell proliferation due to interferon-gamma-induced IDO-expression in allogenic human skin cells might shed new light on developing a nonrejectable allogenic skin substitute.