Neurofibromatosis type 1 tumour suppressor gene expression is deficient in psoriatic skin in vivo and in vitro: a potential link to increased Ras activity

RAS-activated PI3K/AKT signaling sustains cellular senescence via P53/P21 axis in experimental models of psoriasis

BACKGROUND

Psoriasis is a chronic immune-mediated skin disease in which upper epidermal keratinocytes exhibit a senescent-like phenotype. In psoriatic skin, a variety of inflammatory cytokines can activate intracellular pathways including phosphatidylinositol 3-kinase (PI3K)/AKT signaling and RAS effectors. AKT and RAS participate to cellular senescence, but currently their role in senescence responses occurring in psoriasis have not yet been investigated.

OBJECTIVE

The role of AKT molecular axis and RAS activation was evaluated in the context of cellular senescence in psoriasis disease.

METHODS

RAS/AKT involvement in senescence was analyzed in psoriatic keratinocytes cultures subjected to multiple passages to promote senescence in vitro, as well as in skin lesions of patients affected by psoriasis. The impact of pharmacological inhibition of PI3K/AKT pathway on senescence and inflammation responses was tested in senescent psoriatic keratinocytes and in a psoriasiform dermatitis murine model induced by RAS overexpression in the upper epidermis of mice.

RESULTS

We found AKT hyperactivation associated to the upregulation of senescence markers, in senescent psoriatic keratinocyte cultures, as well as in skin lesions of psoriatic patients. AKT-induced senescence was sustained by constitutive RAS activation, and down-stream responses were mediated by P53/P21 axis. PI3K/AKT inhibition contrasted senescence processes induced by cytokines in psoriatic keratinocytes. Additionally, RAS-induced psoriasis-like dermatitis in mice was accompanied by AKT upregulation, increase of senescence marker expression and by skin inflammation. In this model, both senescence and inflammation were significantly reduced by selective AKT inhibition.

CONCLUSION

Therefore, targeting RAS-AKT pathway could be a promising novel strategy to counteract multiple psoriasis symptoms.

Recurrent spontaneous clearance of psoriasis during exacerbations of concomitant chronic spontaneous urticaria

In this case report, we describe a patient with a chronological relationship between exacerbations of chronic spontaneous urticaria and remissions of concomitant generalized plaque psoriasis.

Diversity of actin architecture in human osteoclasts: network of curved and branched actin supporting cell shape and intercellular micrometer-level tubes

Osteoclasts are multinucleated bone-resorbing cells with a dynamic actin cytoskeleton. Osteoclasts are derived from circulating mononuclear precursors. Confocal and stimulated emission depletion (STED) super-resolution microscopy was used to investigate peripheral blood-derived human osteoclasts cultured on glass surfaces. STED and confocal microscopy demonstrated that the actin was curved and branched, for instance, in the vicinity of membrane ruffles. The overall architecture of the curved actin network extended from the podosomes to the top of the cell. The other novel finding was that a micrometer-level tube containing actin bridged the osteoclasts well above the level of the culture glass. The actin filaments of the tubes originated from the network of curved actin often surrounding a group of nuclei. Furthermore, nuclei were occasionally located inside the tubes. Our findings demonstrated the accumulation of c-Src, cortactin, cofilin, and actin around nuclei suggesting their role in nuclear processes such as the locomotion of nuclei. ARP2/3 labeling was abundant at the substratum level of osteoclasts and in the branched actin network, where it localized to the branching points. We speculate that the actin-containing tubes of osteoclasts may provide a means of transportation of nuclei, e.g., during the fusion of osteoclasts. These novel findings can pave the way for future studies aiming at the elucidation of the differentiation of multinucleated osteoclasts.

CD8(+) T cells mediate RAS-induced psoriasis-like skin inflammation through IFN-γ

The RAS signaling pathway is constitutively activated in psoriatic keratinocytes. We expressed activated H-RAS^V12G in suprabasal keratinocytes of adult mice and observed rapid development of a psoriasis-like skin phenotype characterized by basal keratinocyte hyperproliferation, acanthosis, hyperkeratosis, intraepidermal neutrophil microabscesses and increased Th1/Th17 and Tc1/Tc17 skin infiltration. The majority of skin infiltrating CD8⁺ T cells co-expressed IFN-γ and IL-17A. When RAS was expressed on a Rag1−/− background, microabscess formation, iNOS expression and keratinocyte hyperproliferation were suppressed. Depletion of CD8⁺ but not CD4⁺ T cells reduced cutaneous and systemic inflammation, the RAS-induced increase in cutaneous Th17 and IL-17⁺ γΔ T cells, and epidermal hyperproliferation to levels similar to a Rag1−/− background. Reconstitution of Rag1−/− inducible RAS mice with purified CD8⁺ T cells restored microabscess formation and epidermal hyperproliferation. Neutralization of IFN-γ but not IL-17A in CD8⁺ T cell reconstituted Rag1−/− mice expressing RAS blocked CD8-mediated skin inflammation, iNOS expression and keratinocyte hyperproliferation. These results show for that CD8⁺ T cells can orchestrate skin inflammation with psoriasis-like pathology in response to constitutive RAS activation in keratinocytes, and this is primarily mediated through IFN-γ.

Psoriatic skin expresses the transcription factor Gli1: possible contribution of decreased neurofibromin expression

BACKGROUND

Psoriasis is a chronic inflammatory disorder of skin characterized by hyperproliferation of keratinocytes. Intracellular signalling pathways inducing the hyperproliferation of keratinocytes remain to be elucidated. An inhibitor of Hedgehog (Hh) signalling, cyclopamine, was recently reported to clear psoriatic skin lesions, suggesting involvement of the Hh signalling pathway in the hyperproliferation of lesional keratinocytes. We have previously observed activation of the Hh signalling pathway in Schwann cells of plexiform neurofibroma in neurofibromatosis type 1 (NF1), which results from functional loss of the NF1 encoding protein, neurofibromin. In psoriasis, deficiency of neurofibromin expression has been observed in lesional keratinocytes.

OBJECTIVES

To investigate whether the Hh signalling pathway would be activated in psoriasis and whether inhibition of neurofibromin expression would enhance the activation of the Hh signalling pathway.

METHODS

Activation of the Hh signalling pathway was examined by protein expression of one of the target genes, GLI1, coding for the transcription factor Gli1. Immunohistochemical studies were performed on seven psoriatic skin samples and seven control normal skin samples with a standard immunoperoxidase technique. mRNA expression of GLI1 was analysed by reverse transcriptase-polymerase chain reaction in HaCaT cells transfected with double-strand small interfering RNA for NF1.

RESULTS

Our results showed Gli1 expression in psoriatic skin but not in control normal skin. Inhibition of neurofibromin expression in HaCaT cells upregulated mRNA expression of GLI1.

CONCLUSIONS

Our findings indicate that the Hh signalling pathway is activated in psoriasis and that neurofibromin deficiency may upregulate the pathway.