008 Smad7 dampened IL22 signaling-induced inflammation through IL22RA2 upregulation

Abstract

IL22 signaling plays a critical role in the pathogenesis of skin inflammatory diseases such as psoriasis and atopic dermatitis. Smad7 is a transforming growth factor β (TGFβ) inhibitor consisting of an N-terminal domain, a C-terminal domain, and a linker region harboring a PY motif. Smad7 transgene expression in Keratin 5 (K5)+ keratinocytes attenuated K5.TGFβ1 transgene-induced psoriatic inflammation. The downstream mechanistic players and functional domains of Smad7 that mediates its anti-inflammatory properties and whether the anti-inflammatory function of Smad7 applies to other skin conditions remain to be determined. Here, we showed that mice expressing K5.Smad7, but not the N-terminal domain of Smad7, caused resistance to imiquimod (IMQ)-induced dermatitis compared to their wildtype littermates. Further, we generated a truncated Smad7 protein with C-terminal Smad7 and PY motif (PYC-Smad7) fused with the cell-penetrating Tat peptide (Tat-PYC-Smad7). Topical application of Tat-PYC-Smad7 significantly attenuated IMQ-induced psoriatic inflammation, 2,4-dinitrofluorobenzene-induced atopic dermatitis, and tape-stripping-induced skin inflammation. RNA sequencing analysis and spatial phenotyping with multiplex immunofluorescence identified that Tat-PYC-Smad7 not only mitigated TGFβ and NFκβ signaling but alleviated inflammation-induced epidermal hyperproliferation, neutrophil, macrophage and T-cell infiltration, angiogenesis, and STAT3 activation. These anti-inflammatory effects of Tat-PYC-Smad7 were mediated by Tat-PYC-Smad7 upregulation of IL22RA2, a negative regulator of IL22/STAT3 signaling. Upregulation of IL22RA2 by Tat-PYC-Smad7 was dependent upon transcriptional factor C/EBP-β, which binds to IL22RA2 promotor in cells expressing PYC-Smad7. Thus, PYC-Smad7 contains the functional domain of Smad7 to dampen multiple IL-22-dependent pro-inflammatory signaling pathways and Smad7-based Tat protein is a potential therapeutic agent for treating skin inflammatory diseases.