TLR3: a receptor that recognizes cell injury is essential for permeability barrier homeostasis following UV irradiation

Polyinosinic:polycytidylic acid aggravates calcipotriol-induced atopic dermatitis-like skin lesions in mice by increasing the expression of thymic stromal lymphopoietin

Background

Polyinosinic:polycytidylic acid [poly (I:C)] is a synthetic viral double-stranded RNA analog that can activate Toll-like receptor 3 (TLR3) and induce the release of thymic stromal lymphopoietin (TSLP). TSLP has been shown to contribute to atopic dermatitis (AD). This study explored the effects of poly (I:C) in a calcipotriol-induced model of murine AD.

Methods

Calcipotriol (MC903) was used to establish AD-like mice model. Mice in the MC903 + poly (I:C) group were then treated with poly (I:C) in a concentration of 5 µg/g bodyweight. The impact of poly (I:C) treatment on these animals was assessed based upon changes in lesions, bodyweight, ear thickness, and histopathological findings. In addition, serum interleukin 4 (IL-4), interferon-γ (IFN-γ), immunoglobulin E (IgE), IL-13, and TSLP levels were measured using enzyme-linked immunosorbent assay (ELISA), while tissue IL-13 and TSLP levels were assessed using ELISA, Western blotting, and immunohistochemical staining, and mast cell infiltration was assessed through toluidine blue (TBO) staining.

Results

Relative to vehicle control treatment, poly (I:C) administration was associated with a significant exacerbation of calcipotriol-induced AD-like murine skin lesions. In animals treated with poly (I:C), the levels of serum IL-4, IL-13 and TSLP increased significantly, while the level of IFN-γ did not change. It also increased IL-13 and TSLP levels in skin lesions relative to the control-group mice and increased dermal mast cell infiltration and IgE production.

Conclusions

These data indicate that poly (I:C) treatment and exogenous activation of TLR3 exacerbate murine calcipotriol-induced AD-like skin lesions in part by increasing the production of TSLP and other T-helper 2 (Th2)-related cytokines.

Keywords

Atopic dermatitis (AD); polyinosinic:polycytidylic acid [poly (I:C)]; thymic stromal lymphopoietin (TSLP); Toll-like receptor 3 (TLR3)

Conjunctival Expression of Toll-Like Receptor 3 Plays a Pathogenic Role in the Formation of Ultraviolet Light-Induced Pterygium

Purpose

Toll-like receptor 3 (TLR3), as a damage-associated molecular pattern sensor, can detect self-RNA released from necrotic cells induced by ultraviolet B (UVB) radiation exposure. Pterygium formation is believed to be a tumorigenesis-like process induced by UVB exposure. In this study, we aimed to investigate the expression pattern of TLR3 in pterygium specimens and cultured pterygial epithelial cells (PECs).

Methods

Human pterygium and ipsilateral pterygium-free conjunctiva from the same patients were used in this study. The expression of TLR3 and nuclear factor-kappa B (NF-κB) was investigated in these specimens. PECs were exposed to UVB radiation to determine the effect of UVB on the expression of TLR3 and the activation of NF-κB.

Results

The immunofluorescence study showed stronger TLR3 expression in superficial epithelial cells in the pterygial epithelium in comparison with the normal conjunctival epithelium. The expression of TLR3 decreased in intensity from the superficial epithelium toward the basal cell layer, implying a correlation between UVB exposure and TLR3 expression. Differential TLR3 expression patterns in pterygial and conjunctival tissues were also found in quantitative PCR analyses. PECs after UVB irradiation had higher protein levels of TLR3 and phospho-NF-κB than those of the PECs without irradiation. Immunofluorescence studies showed that UVB irradiation induced the nuclear translocation of NF-κB in the PECs. In PECs with the targeted TLR3 gene silencing, the expression of phospho-NF-κB was not induced by UVB irradiation.

Conclusions

Our results indicate that UVB exposure, TLR3 expression, and NF-κB activation may be a critical sequence that leads to the formation of pterygium.

Up-regulation of hsa-miR-221-3p induced by UVB affects proliferation and apoptosis of keratinocytes via Bcl-xL/Bax pathway

BACKGROUND

Chronic actinic dermatitis (CAD) is a photoallergic skin disease with abnormal hyperplasia. At present, the mechanism of abnormal proliferation is not clear.

OBJECTIVE

To explore possible mechanism of CAD proliferative lesions.

METHODS

Immunohistochemistry (IHC) assay and small RNA sequencing were carried out. Quantitative real-time PCR (qRT-PCR) analysis was performed to evaluate expression levels of hsa-miR-221-3p and FOS. The interaction between hsa-miR-221-3p and FOS was identified by dual-luciferase reporter assay. Expression of hsa-miR-221-3p also was detected by qRT-PCR after UVB irradiation. Influences of hsa-miR-221-3p and FOS on cell viability and apoptosis were assessed through a series of functional experiments and rescue experiments. Western blot analysis was used to detect protein expression of fos, Bax, Bcl-xL, and caspase-3.

RESULTS

Patients with CAD had marked epidermal hyperplasia. The expression of hsa-miR-221-3p was up-regulated in CAD while FOS was significantly down-regulated. Dual-luciferase reporter assay confirmed that hsa-miR-221-3p targeted FOS 3'UTR. Hsa-miR-221-3p induced by UVB ranged from 0 to 30 mJ. Moreover, hsa-miR-221-3p overexpression or FOS knockdown promoted cell proliferation and reduced cell apoptosis. Western blot showed that hsa-miR-221-3p negatively regulated fos, which regulated Bcl-xL/Bax. Cell proliferation caused by hsa-miR-221-3p overexpression or FOS knockdown could be reversed by Bcl-xL inhibitor.

CONCLUSION

Hsa-miR-221-3p induced by UVB targeted FOS 3'UTR, which played an important role in regulating proliferation and apoptosis of keratinocytes via Bcl-xL/Bax pathway; this may provide a new insight for CAD proliferative lesions.

Upregulation of hsa-miR-31-3p induced by ultraviolet affects keratinocytes permeability barrier by targeting CLDN1

Chronic actinic dermatitis (CAD) is a photoallergic skin disease with complicated pathogenesis. However, skin barrier dysfunction may be involved according to clinical manifestation. To investigate the mechanism of CAD barrier dysfunction, noninvasive detection of skin barrier and small RNA sequencing were carried out. Quantitative real-time PCR (qRT-PCR) was used to evaluate the expression levels of hsa-miR-31-3p and CLDN1. The correlation between hsa-miR-31-3p and CAD severity was explored. Further, dual-luciferase reporter assay was performed to identify the relationship between hsa-miR-31-3p and CLDN1. In addition, expression of hsa-miR-31-3p was detected after ultraviolet (UV) irradiation. Influences of hsa-miR-31-3p on primary human keratinocytes barrier were assessed by FITC-Dextran permeability assay. Moreover, western blot was used to detect the expression of claudin-1, filaggrin, loricrin and involucrin. Our results showed that transepidermal water loss (TEWL) significantly increased in CAD, while stratum corneum hydration (SCH) significantly decreased. The expression of hsa-miR-31-3p was up-regulated in CAD while CLDN1 was down-regulated. Hsa-miR-31-3p was correlated with TEWL, UV-MED (minimal erythema dose) and clinical severity scores of CAD (CSS-CAD). Dual-luciferase reporter assay confirmed that hsa-miR-31-3p targeted the 3'UTR region of CLDN1. Moreover, hsa-miR-31-3p was induced by UVB (0-30 mJ/cm²) and UVA (0-4 J/cm²). Furthermore, overexpression of hsa-miR-31-3p increased FITC-Dextran flux of primary human keratinocytes and reduced the expression of claudin-1, filaggrin, loricrin and involucrin. In conclusion, we demonstrated that hsa-miR-31-3p induced by UV was correlated with CAD severity, which played an important role in regulating keratinocytes permeability barrier through targeting CLDN1.

The role of toll-like receptor 3 in chronic contact hypersensitivity induced by repeated elicitation

BACKGROUND

Accumulating evidence suggests that Toll-like receptor (TLR)-3 signaling is involved in non-infectious immune and inflammatory reactions as well as in viral infections. The skin of patients with atopic dermatitis (AD) is often infected with virus and bacteria, leading to the aggravation of atopic symptoms. These findings suggest TLR3 signaling may be involved in the pathogenesis of AD, but the exact role of TLR3 in AD remains to be defined.

OBJECTIVE

The purpose of this study was to investigate the role of TLR3 in chronic contact hypersensitivity reactions induced by repeated elicitation, resembling the features of AD.

METHODS

Wild-type (WT) and Toll-like receptor 3 knockout (Tlr3 KO) mice were sensitized, and chronic contact hypersensitivity reactions were elicited in their ear skin via repeated application of a hapten, 2,4,6-trinitro-1-chlorobenzene (TNCB) or oxazolone.

RESULTS

The Tlr3 KO mice exhibited less ear swelling, less leukocyte infiltration into the skin, and lower serum total IgE levels than WT mice after hapten challenge. The Tlr3 KO mice also displayed lower expression levels of inflammatory cytokines (interleukin (IL)-33, IL-4, IL-10, and interferon-ɤ in their TNCB-treated ear skin than WT mice.

CONCLUSION

These results showed that TLR3 deficiency suppressed the development of chronic contact hypersensitivity reactions, suggesting that TLR3 signaling may participate in the pathogenesis of AD.