Therapeutic Efficacy of Targeting CTLA-4-PKC-η Signaling Pathway for Modulating Inflammatory Skin Disease by Inducing Regulatory T Cells

Abstract

Psoriasis is a representative inflammatory skin disease belonging to autoimmune diseases. The representative features of psoriasis include hyperplasia of keratinocytes and infiltration of immune cells. As an immunopathological mechanism, it is well known that various immune cells such as Th17 are activated through the IL-23/IL-17A axis to induce psoriatic skin inflammation. It is known that the balance between Th17 and Tregs is important in autoimmune diseases, and Tregs play an important role in immune homeostasis and immune tolerance. In clinical psoriasis patients, unstable features, such as conversion of Treg to cells secreting IL-17A, which play a pathogenic role, have been reported, and in animal models, there have been reports that the skin inflammation appeared more severe when Treg was depleted. Despite the importance of Tregs in psoriasis as described above, most of psoriasis drugs are targeting Th17, and little is known about studies on drugs targeting Tregs. Therefore, this study was conducted to explore the efficacy of therapeutic strategy for psoriasis through inducing Treg cells. We used CTLA-4 signaling peptide, which was effective in inhibiting EAE progression through Treg increase in a previous report, to verify whether it would have therapeutic efficacy through Treg induction in a psoriasis mouse model. CTLA-4 signaling peptide (dNP2-ctCTLA4) increased Tregs and alleviated psoriasis progression in an IMQ-induced psoriasis-like mouse model. CTLA4-Ig, a drug made using the extracellular domain of CTLA-4, showed a tendency to decrease Treg and did not inhibit psoriasis, whereas dNP2-ctCTLA4 using the cytoplasmic domain increased Tregs and suppressed psoriasis well. In addition, the optimized form (AP-K2) made by using a lysine motif which was known to be important for increasing Treg within ctCTLA-4 increased Tregs to a level similar to that of the original form (dNP2-ctCTLA4), and increased Treg cells in psoriasis-induced mice, whereas the lysine mutant form (AP-KA) failed to increase Treg and showed no inhibitory effect. A PKC-η inhibitory peptide was synthesized by targeting PKC-η, known as the binding partner of the lysine motif, and it was found that it could increase Tregs and have therapeutic efficacy in inhibiting psoriasis. To confirm the efficacy of CTLA-4 signaling peptide and PKC-η inhibitory peptide through transcutaneous administration as well as systemic administration, a transdermal delivery strategy through CPP (Cell-penetrating peptide) was used. The efficacy of transdermal application of PKC-η inhibitory peptide was verified using AP, which showed high delivery efficiency into various primary cells in vitro and in vivo skin tissue. However, in an IMQ-induced psoriasis mouse model in which IL-17A-producing γδ T cells are dominant, the therapeutic efficacy of the PKC-η inhibitory peptide could not be confirmed through transdermal application, and it did not affect immune cells in lymphoid tissue. In this study, we found that CTLA-4 signaling peptide and PKC-η inhibitory peptide had systemic effects in psoriasis-induced mice, increasing Tregs and regulating disease severity. Collectively, this study revealed that CTLA-4 signaling peptide could be a potential therapeutic agent and PKC-η could be a novel target molecule as a strategy of psoriasis treatment by increasing regulatory T cells.