Dimethyl Fumarate Inhibits Keratinocyte Hyperproliferation and Ameliorates Psoriasis via Directly Targeting Ribosomal Protein S6 Kinase A1

Background: Dimethyl fumarate (DMF) is a widely used first-line treatment for psoriasis due to its proven efficacy and irreplaceable therapeutic effects. Keratinocyte (KC) hyperproliferation is a central pathogenic feature of psoriasis. However, the precise mechanisms by which DMF regulates KC hyperproliferation remain poorly understood.Methods: We employed an imiquimod (IMQ)-induced mouse model of psoriasis to evaluate the in vivo efficacy of DMF, alongside multiple inflammatory factors-induced HaCaT cells to assess the effect of DMF on KC proliferation in vitro. Using streamlined cysteine activity-based protein profiling (SLC-ABPP), surface plasmon resonance (SPR), molecular docking, and active-site mutation analysis, we aimed to to clarify the specific target of DMF and its key binding site. Immunoprecipitation (IP) coupled with mass spectrometry (MS)/Western blot (WB), and kinase activity assay were employed to identify and evaluate the effect of DMF on the interacting protein of its target. Flow cytometry technology, WB, immunofluorescence staining, and transmission electron microscopy (TEM) were employed to assess the effect of DMF on mitophagy.Findings: Through a series of in vitro and in vivo experiments, we demonstrated that DMF feectively suppressed KC hyperproliferation in psoriasis both in vivo and in vitro. We identified that DMF exerts its effects by directly targeting the Cys432 site of Ribosomal Protein S6 Kinase A1 (RSK1). DMF suppresses RSK1 kinase activity, leading to the dephosphorylation of its downstream substrate protein-ATP/ADP translocase 1 (ANT1), This, in turn, diminishes ANT1-PTEN induced putative kinase 1 (PINK1)-Parkin axis-mediated mitophagy. Importantly, epidermis-specific RSK1 knockdown in mice results in the inhibition of KC hyperproliferation in psoriasis, an effect that could not be further influenced by DMF treatment.Interpretation: Our study reveals a novel mechanism by which DMF targets RSK1 to suppress KC hyperproliferation in psoriasis, offering new insights into its therapeutic efficacy. Furthermore, our results establish RSK1 as a potential therapeutic target for psoriasis treatment.