Identification of a novel PPARβ/δ/miR-21-3p axis in UV-induced skin inflammation.

Although excessive exposure to UV is widely recognized as a major factor leading to skin perturbations and cancer, the complex mechanisms underlying inflammatory skin disorders resulting from UV exposure remain incompletely characterized. The nuclear hormone receptor PPARβ/δ is known to control mouse cutaneous repair and UV-induced skin cancer development. Here, we describe a novel PPARβ/δ-dependent molecular cascade involving TGFβ1 and miR-21-3p, which is activated in the epidermis in response to UV exposure. We establish that the passenger miRNA miR-21-3p, that we identify as a novel UV-induced miRNA in the epidermis, plays a pro-inflammatory function in keratinocytes and that its high level of expression in human skin is associated with psoriasis and squamous cell carcinomas. Finally, we provide evidence that inhibition of miR-21-3p reduces UV-induced cutaneous inflammation in ex vivo human skin biopsies, thereby underlining the clinical relevance of miRNA-based topical therapies for cutaneous disorders

In Vivo Dioxin Favors Interleukin-22 Production by Human CD4+ T Cells in an Aryl Hydrocarbon Receptor (AhR)-Dependent Manner

The transcription factor aryl hydrocarbon receptor (AhR) mediates the effects of a group of chemicals known as dioxins, ubiquitously present in our environment. However, it is poorly known how the in vivo exposure to these chemicals affects in humans the adaptive immune response. We therefore assessed the functional phenotype of T cells from an individual who developed a severe cutaneous and systemic syndrome after having been exposed to an extremely high dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).T cells of the TCDD-exposed individual were studied for their capacity to produce cytokines in response to polyclonal and superantigenic stimulation, and for the expression of chemokine receptors involved in skin homing. The supernatants from T cells of the exposed individual contained a substantially increased amount of interleukin (IL)-22 but not of IL-17A, interferon (IFN)-γ or IL-10 when compared to nine healthy controls. In vitro experiments confirmed a direct, AhR-dependent, enhancing effect of TCDD on IL-22 production by CD4+ T cells. The increased production of IL-22 was not dependent on AhR occupancy by residual TCDD molecules, as demonstrated in competition experiments with the specific AhR antagonist CH-223191. In contrast, it was due to an increased frequency of IL-22 single producing cells accompanied by an increased percentage of cells expressing the skin-homing chemokine receptors CCR6 and CCR4, identified through a multiparameter flow cytometry approach. Of interest, the frequency of CD4+CD25(hi)FoxP3+ T regulatory cells was similar in the TCDD-exposed and healthy individuals.This case strongly supports the contention that human exposure to persistent AhR ligands in vivo induce a long-lasting effect on the human adaptive immune system and specifically polarizes CD4+ T cells to produce IL-22 and not other T cell cytokines with no effect on T regulatory cells

IL-17A Dissociates Inflammation from Fibrogenesis in Systemic Sclerosis

IL-17A is abundant in scleroderma but its role in fibrogenesis is controversial. We interrogated the role of IL-17A in extracellular matrix deposition and inflammation by investigating its effects on keratinocytes and fibroblasts cross-talk and in organotypic skin cultures. Keratinocyte-conditioned media of resting, IL-17A-, and/or transforming growth factor-β-primed primary keratinocytes were used to stimulate healthy donors and scleroderma fibroblasts. Alternatively, organotypic cultures of full human skin were challenged with these cytokines. Keratinocyte-conditioned media tilted the balance of col-I to matrix metalloproteinase-1 production by fibroblasts in favor of matrix metalloproteinase-1, significantly more so in healthy donors than in scleroderma, resulting in enhanced extracellular matrix turnover, further increased by IL-17A. In organotypic skin, transforming growth factor-β induced an extensive pro-fibrotic gene signature, including the enhanced expression of several collagen genes associated with Wnt signaling. IL-17A strongly promoted the expression of pro-inflammatory genes, with no direct effects on collagen genes, and attenuated Wnt signaling induced by transforming growth factor-β. In this model, at the protein level, IL-17A significantly decreased col-I production. Our data strongly support a pro-inflammatory and antifibrogenic activity of IL-17A in the context of keratinocyte-fibroblast interaction and in full skin. These data help in directing and interpreting targeted therapeutic approaches in scleroderma

<i>In vitro</i> TCDD enhances IL-22 and down-regulates IL-17A production by PBMC in an AhR dependent manner.

<p>(<b>A</b>) PBMC were activated by CD3-crosslinking in the presence or absence of TCDD and the specific AhR inhibitor CH-223191. Cytokine levels were assessed in the supernatants harvested at d 7. Dose-dependent responses to TCDD in a single TCDD-exposed individual (full symbols) and one healthy individual (empty symbols). (<b>B</b>) Culture conditions as in A. Cytokine determination in a single TCDD-exposed individual (full symbols) and 2 healthy individuals (empty symbols) (<b>C</b>) mRNA levels of <i>CYP1A1</i> quantified by real-time PCR of resting PBMC from a single TCDD-exposed (full symbols) and five healthy individual (empty symbols). Expression levels have been normalized against the geometric mean of two house-keeping genes (EEF1A1 and TBP).</p

Increased frequency of CD4+ memory T cells expressing the skin-homing receptors CCR6+ and CCR4+ in an individual exposed <i>in vivo</i> to high levels of TCDD.

<p>Surface chemokine receptor expression on CD4+CD45RA- memory T cells from <i>ex-vivo</i> isolated PBMC in a TCDD-exposed (full symbols) or 5 healthy individuals (empty symbols). (<b>A</b>) Mean ± SD of cells expressing CCR6, CCR4, CXCR3 and CCR10. (<b>B</b>) Percentage of cells expressing various combinations of CCR6, CCR4, CXCR3 and CCR10. Data from the 5 healthy individuals are expressed as box plots. Box plots were automatically generated using GraphPad Prism version 4.00 for Windows (GraphPad Software). The box represents values between 25th and 75th percentile with a line at the median (50th percentile). The whiskers extend above and below the box to show the highest and the lowest values. 6, 4, 3 and 10 in panel B denote CCR6, CCR4, CXCR3 and CCR10, respectively.</p

<i>In vivo</i> TCDD-exposure favors the expansion of Th22 cells.

<p>(<b>A</b>) Intracellular staining of <i>ex-vivo</i> isolated PBMC from a TCDD-exposed (full symbols) and healthy individuals (empty symbols) upon activation by PMA/Ionomycin for 4.5 h (n = 5) or CD3/CD28 crosslinking for 24 h (n = 9). (<b>B, C, D</b>) Representative FACS plots of cells activated by PMA/Ionomycin from the TCDD-exposed and a control individual (upper right panel in B) after gating on the forward and side scatter of viable PBMC (<b>B, C</b>) or on CD4+ cells (<b>D</b>). Numbers in plots indicate the percentage of cells in each quadrant.</p