Adenosine A2A and A2B Receptors Differentially Modulate Keratinocyte Proliferation: Possible Deregulation in Psoriatic Epidermis.

Adenosine is a potent regulator of inflammation and immunity, but the role of adenosine receptors in keratinocytes remains controversial. We determined that in addition to A2B receptors, human epidermal keratinocytes also express A2A receptors, although to a lower extent. Through the use of selective adenosine receptor agonists and antagonists, we showed that physiological concentrations of adenosine activate A2B receptors in normal human keratinocytes, inducing cell cycle arrest through the increase of intracellular calcium but not through cAMP signaling. In contrast, the selective activation of A2A receptors by CGS-21680 induces keratinocyte proliferation via p38-mitogen-activated protein kinase activation. Adenosine and selective A2A and A2B agonists presented anti-inflammatory profiles independent of adenosine receptors but mediated by membrane phosphatase activation. Finally, keratinocyte exposure to diverse inflammatory cytokines altered adenosine receptor expression by reducing A2B and increasing A2A, a pattern also observed in psoriatic epidermis. Because increased epidermal turnover and inflammatory response are characteristics of psoriatic disease, further studies are needed to assess the role and consequences of the altered adenosine receptor expression in lesional and nonlesional psoriatic keratinocytes.

NF-κB and STAT3 inhibition as a therapeutic strategy in psoriasis: in vitro and in vivo effects of BTH.

Benzo[b]thiophen-2-yl-3-bromo-5-hydroxy-5H-furan-2-one (BTH) is a simple and interesting synthetic derivative of petrosaspongiolide M, a natural compound isolated from a sea sponge with demonstrated potent anti-inflammatory activity through inhibition of the NF-κB signaling pathway. In the present study, we report the in vitro and in vivo pharmacological effect of BTH on some parameters related to the innate and adaptive response in the pathogenesis of psoriasis. BTH inhibited the release of some of the key psoriatic cytokines such as tumor necrosis factor α, IL-8, IL-6, and CCL27 through the downregulation of NF-κB in normal human keratinocytes. Moreover, it impaired signal transducers and activators of transcription 3 (STAT3) phosphorylation and translocation to the nucleus, which resulted in decreased keratinocyte proliferation. These results were confirmed in vivo in two murine models of psoriasis: the epidermal hyperplasia induced by 12-O-tetradecanoylphorbol-13-acetate and the imiquimod-induced skin inflammation model. In both cases, topical administration of BTH prevented skin infiltration and hyperplasia through suppression of NF-κB and STAT3 phosphorylation. Our results confirm the pivotal role of both transcriptional factors in skin inflammation, as occurs in psoriasis, and highlight the potential of small molecules as therapeutic agents for the treatment of this skin disease, with BTH being a potential candidate for future drug research.

Studies of Jak/STAT3 expression and signalling in psoriasis identifies STAT3-Ser727 phosphorylation as a modulator of transcriptional activity.

Jak/Tyk proteins have recently aroused as possible therapeutic targets for the treatment of psoriasis. In psoriasis, these proteins signal through STAT molecules including STAT3, and STAT3 expression and activation has been shown augmented in psoriatic lesions. Here, we characterized the expression of Jak/Tyk proteins in lesional compared with non-lesional psoriatic skin. Jak1, Jak2 mRNA and protein and Tyk2 mRNA appeared to be downregulated, whereas Jak3 mRNA expression was increased. Moreover, STAT3 expression and activation was examined in psoriasis. STAT3 is activated at two phosphorylation sites: Tyr705 and Ser727. Both phosphorylation sites were phosphorylated in lesional psoriatic skin. The activation of STAT3 by Jak/Tyk proteins was studied in cultured normal human keratinocytes. Tyr705 phosphorylation was induced by IL-6 and IL-20 in a Jak2-dependent manner, and moreover, phosphorylation of Tyr705 produced a strong increase in STAT3 transcriptional activity. TNFα, 12-O-Tetradecanoylphorbol 13-acetate (TPA) and UVB irradiation induced Ser727 phosphorylation of STAT3 in an ERK1/2- and p38 MAPK-dependent manner, which resulted in a modulatory effect on STAT3 transcriptional activity. Our results demonstrate how different signalling pathways can integrate and lead to regulation of STAT3 transcriptional activity.

Potential antipsoriatic effect of chondroitin sulfate through inhibition of NF-κB and STAT3 in human keratinocytes.

Chondroitin sulfate (CS) is a natural glycosaminoglycan, formed by the 1-3 linkage of d-glucuronic acid to N-acetylgalactosamine, present in the extracellular matrix. It is used as a slow acting disease modifying agent in the treatment of osteoarthritis, and part of its beneficial effects are due to its antiinflammatory properties that result from an inhibitory effect on NF-κB signaling pathway. This ability raises the hypothesis that CS might be effective in other chronic inflammatory processes such as psoriasis, in which a deregulation of NF-κB is a key feature. In addition, psoriasis is characterized by an upregulation of STAT3 signaling pathway that is related to the epidermal hyperplasia. In the present study we report the pharmacological modulation of the NF-κB and STAT3 signaling pathways by CS in normal human keratinocytes. CS inhibited NF-κB activation and the release of some of the key psoriatic cytokines such as TNFα, IL-8, IL-6 and CCL27. Moreover, it impaired STAT3 translocation to the nucleus and significantly reduced STAT3 transcriptional activity by a mechanism that was independent from STAT3 phosphorylation. Our results confirm the interest of CS as a candidate for future drug research in the therapeutics of psoriasis given the need of more effective and safer oral medications for these patients.

Toward the discovery of new agents able to inhibit the expression of microsomal prostaglandin E synthase-1 enzyme as promising tools in drug development.

In our recent studies, we focused our attention on the synthesis of several gamma-hydroxybutenolides designed on the basis of petrosaspongiolide M 1 (PM) structure that has been recognized to potently inhibit the inflammatory process through the selective PLA(2) enzyme inhibition. By means of a combination of computational methods and efficient synthetic strategies, we generated small collections of PM modified analogs to identify new potent PLA(2) inhibitors, suitable for clinical development. In the course of the biological screening of our compounds, we discovered a potent and selective inhibitor of mPGES-1 expression, the benzothiophene gamma-hydroxybutenolide 2, which so far represents the only product, together with resveratrol, able to reduce PGE(2) production through the selective downregulation of mPGES-1 enzyme. In consideration that microsomal prostaglandin E synthase 1 (mPGES-1) is one of the most strategic target involved both in inflammation and in carcinogenesis processes, we decided to explore the biological effects of some structural changes of the gamma-hydroxybutenolide 2, hoping to improve its biological profile. This optimization process led to the identification of three strictly correlated compounds 14g, 16g, and 18 with higher inhibitory potency on PGE(2) production on mouse macrophage cell line RAW264.7 through the selective modulation of mPGES-1 enzyme expression.