Activation of ribosomal protein S6 kinase in psoriatic lesions and cultured human keratinocytes by epidermal growth factor receptor ligands

Adiponectin Prevents Skin Inflammation in Rosacea by Suppressing S6 Phosphorylation in Keratinocytes

Numerous recent evidence highlights epidemiological connections between rosacea and metabolic disorders. However, the precise path through which metabolic factors impact rosacea risk is still unclear. Therefore, this study aims to investigate the role of adiponectin, a crucial adipokine that regulates metabolic homeostasis, in the pathogenesis of rosacea. We elucidated a detrimental feedback loop between rosacea-like skin inflammation and decreased levels of skin adiponectin. To elaborate, rosacea lesional skin exhibits diminished adiponectin expression compared with nonlesional areas in the same patients. Induction of rosacea-like inflammation reduced adiponectin levels in the skin by generating inflammatory cytokines that suppress adiponectin production from subcutaneous adipocytes. Conversely, complete depletion of adiponectin exacerbated rosacea-like features in the mouse model. Mechanistically, adiponectin deficiency led to heightened S6 phosphorylation, a marker of the mTORC1 signaling pathway, in the epidermis. Adiponectin significantly inhibited S6 phosphorylation in cultured keratinocytes. Notably, replenishing adiponectin whole protein or topically applying an agonist for adiponectin receptor 1 successfully improved rosacea-like features in mice. This study contributes to understanding the role of adiponectin in skin inflammation associated with rosacea pathophysiology, suggesting that restoring adiponectin function in the skin could be a potential therapeutic strategy.

TNF stimulates IL-6, CXCL8 and VEGF secretion from human keratinocytes via activation of mTOR, inhibited by tetramethoxyluteolin

Psoriasis is an autoimmune skin disease characterized by keratinocyte hyperproliferation and chronic inflammation. The pathogenesis of psoriasis involves proinflammatory cytokines, such as tumor necrosis factor (TNF), but the mechanism of keratinocyte activation is not well understood. Here, we show that TNF (10 or 50 ng/mL) stimulates a significant (P < .0001) gene expression and secretion of proinflammatory IL-6, CXCL8 and VEGF from both cultured human HaCaT and normal epidermal human keratinocytes (NHEKs). This effect occurs via activation of the mammalian target of rapamycin (mTOR) signalling complex as shown by Western blot analysis and phospho-ELISAs. Pretreatment with the novel natural flavonoid tetramethoxyluteolin (10-100 μmol L^-1 ) significantly (P < .0001) inhibits gene expression and secretion (P < .0001) of all 3 mediators in a concentration-dependent manner. Moreover, tetramethoxyluteolin (50 μmol L^-1 ) appears to be a potent inhibitor of the phosphorylated mTOR substrates (pmTOR^Ser2448 , pp70S6K^Thr389 and p4EBP1^Thr37/46 ) as compared to known mTOR inhibitors in keratinocytes. The present findings indicate that TNF stimulates skin inflammation via mTOR signalling. Inhibition by tetramethoxyluteolin may be used in the treatment for psoriasis.

Treatment of psoriasis with topical sirolimus: preclinical development and a randomized, double-blind trial

BACKGROUND

Systemically administered sirolimus has demonstrated efficacy in psoriasis in a multicentre European study.

OBJECTIVES

To determine the efficacy and safety of topically applied sirolimus in treating psoriasis.

METHODS

In vitro studies were followed by a pilot study designed to determine if sirolimus penetrates human skin, and by a randomized, double-blind, left-right comparative, dose-ranging study consisting of treatment with 2.2% sirolimus for 6 weeks and 8% sirolimus for an additional 6 weeks in 24 patients with stable, chronic plaque psoriasis. The primary outcome measure was clinical score. Secondary measures were ultrasound plaque thickness, plaque erythema, and computerized image analysis of immunohistochemical stains for immunocytes and proliferating cells. Pharmacokinetics and blood chemistry monitoring for safety were also performed.

RESULTS

A significant reduction in the clinical score (P = 0.03) (mean score 9.1 following sirolimus vs. 11.2 in control) was achieved with topical sirolimus. Measurements of plaque thickness and erythema did not show significant improvement with treatment. Computerized image analysis of biopsies showed a significant reduction in CD4+ cells (P = 0.0054) and proliferating cells (stained by Ki-67) in the epidermis (P = 0.0153) with sirolimus treatment compared with control.

CONCLUSIONS

Topically applied sirolimus penetrates normal skin and may have some antipsoriatic and immunosuppressive activity.