Drugs from bugs: YopM - a bacteria-derived anti-inflammatory cell-penetrating peptide for the topical treatment of psoriasis

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During Yersinia enterocolitica infection bacteria translocate different Yersinia outer proteins (Yops) into the host cell cytoplasm through a type III secretion system. YopM, in contrast to other Yops, does not possess any enzymatic activity and it has been shown that after translocation into the host cell, YopM traffics to the nucleus via a vesicle-associated pathway. In the nucleus YopM inhibits the transcription of genes encoding pro-inflammatory cytokines such as TNF-alpha, IL 1beta, IFN-gamma, IL-12, or IL-18. Accordingly, in a mouse model of Y. pestis infection YopM reduced the expression of these pro-inflammatory cytokines in macrophages leading to an increased virulence of bacteria as well as a down-regulated anti-bacterial immunity in the host. However, thus far it is not known how a locally translocated effector protein might be responsible for systemic effects on anti-bacterial immune responses. Interestingly, in previous studies we identified YopM as a cell-penetrating peptide and demonstrated its ability to autonomously enter various mammalian cells including immune and epithelial cells via caveolin-dependent endocytosis followed by endosomal escape and without the help of additional factors. In support of this, treatment of activated primary immune cells with recombinant YopM (rYopM) led to the down-regulation of TNF-alpha, IL-1beta and IFN-gamma indicating that rYopM acts as a self-delivering anti-inflammatory drug and therefore, might be of interest for the treatment of inflammatory disorders. To investigate the anti-inflammatory and therapeutic potential of rYopM in vivo we used the mouse model of imiquimod-induced psoriasis. Usually, immunomodulators, corticosteroids or biologics are used for the treatment of psoriasis. However, many of these drugs are ineffective when applied locally because of their inability to penetrate the epidermal barrier. As rYopM breaches barriers and enters host cells without the requirement of additional factors we topically treated psoriatic mice with a rYopM-containing cream and surprisingly, could show that epicutaneous application of rYopM markedly reduced all characteristic hallmarks of psoriasis like acanthosis or papillomatosis. Now, we intend to analyze the cellular and molecular mechanisms underlying the amelioration of psoriasis by topical rYopM treatment in mouse as well as human skin. With the help of tissue culture models the effect of rYopM on signaling networks will be analyzed, including the skin barrier function and the innate as well as adaptive immune response. Furthermore, we will generate truncated rYopM proteins by site-directed mutagenesis to identify domains required for the penetration of epithelial barriers as well as the anti-inflammatory activity. Thereby, rYopM variants with improved immunomodulatory capacities and increased stability will be determined, which might represent the basis for the development of a novel therapeutic alternative for local immunotherapy.