Keratin 17 enhances the chemotaxis of neutrophils through regulating CXCL1 secretion in keratinocytes via PI3K/AKT/NF-κB pathway in psoriasis

To the Editor: Psoriasis is a chronic inflammatory skin disease characterized by epidermal keratinocyte (KC) hyperproliferation and immune dysregulation. KCs drive pathological cell expansion and inflammation through cytokine/chemokine production, which activates dendritic cells, T cells, and neutrophils to sustain inflammatory cascades.[1] Keratin 17 (K17), a type I epithelial keratin critical for epidermal homeostasis, shows marked upregulation in psoriatic lesions under cytokine induction such as vascular endothelial growth factor (VEGF), interleukin (IL)-17A , interferon-gamma (IFN-γ), and IL-22.[2,3] Beyond its structural role, K17 promotes disease progression through a K17/T-cell/cytokine autoimmune loop.[4,5] This study demonstrated that K17 triggered neutrophil chemotaxis via C-X-C motif chemokine ligand 1 (CXCL1) upregulation, fostering neutrophil microabscess formation and inflammatory amplification. These findings provide new evidence that K17 is a key molecule regulating immune responses in KCs. Methods and data availability can be found in the Supplementary Text, https://links.lww.com/CM9/C733. To address the role of K17 in psoriasis pathogenesis, we first established K17-deficient (K17−/−) mice for imiquimod (IMQ)-induced psoriasis-like modelling. Compared to wild type (WT) controls, K17−/− mice exhibited attenuated psoriatic pathology with reduced erythema, scaling, and epidermis thickness [Figure 1A and Supplementary Figure 1A, https://links.lww.com/CM9/C733]. Flow cytometry of skin lesions revealed diminished neutrophil infiltration in K17−/− mice vs. WT mice [Figure 1B and Supplementary Figure 1B, https://links.lww.com/CM9/C733], corroborated by suppressed inflammatory cytokine messenger RNA (mRNA) levels [Supplementary Figure 1C, https://links.lww.com/CM9/C733]. These findings confirm the dual role of K17 in epidermal hyperplasia and immune activation.Figure 1: K17-mediated CXCL1 secretion in psoriatic keratinocytes: PI3K/AKT/NF-κB-dependent neutrophil chemotaxis. (A) Phenotype and representative hematoxylin and eosin staining staining of control and IMQ-treated mice in indicated groups on day 5. Images are representative of three individual mice per group. Scale bar = 50 µm. (B) Flow cytometry analysis of Ly6G-positive cells in dorsal skin lesions of mice (n = 3). (C) Gene Ontology analysis showing the pathways enriched in K17-sufficient KCs compared with K17-deficient KCs. (D) mRNA expression of the genes associated with chemotaxis in K17-sufficient and K17-deficient KCs (n = 3). (E) mRNA expression of CXCL1 in K17-sufficient and K17-deficient KCs stimulated with TNF-α and IL-17A (n = 3). (F) Immunofluorescence staining of K17 and CXCL1 in the lesional skin of psoriasis patients (n = 3) and skin of healthy controls (n = 3). Scale bar = 100 µm. (G) Protein expression levels of K17 and CXCL1 in the lesional skin of psoriasis patients and skin of healthy controls. (H) Flow cytometry analysis of neutrophils in dorsal skin lesions of mice (n = 3). (I) Transwell assays of neutrophil trafficking induced by KCs with or without TNF-α and IL17-A stimulation. Scale bar = 100 µm. (J) Transwell assays of neutrophil trafficking induced by KCs with or without CXCL1 neutralizing antibody. Scale bar = 100 µm. (K) Protein levels of phosphorylated AKT and AKT in KCs treated with LY-294002. (L) Protein levels of phosphorylated AKT and AKT in KCs treated with PDTC. (M) Protein levels of CXCL1 in KCs in K17-sufficient and K17-deficient KCs treated with LY-294002 and PDTC. (N) Protein levels of phosphorylated AKT, AKT, phosphorylated p65, and p65 in K17-sufficient and K17-deficient KCs. (O) Phenotype and representative hematoxylin and eosin staining of control and IMQ-treated with or without siK17-treated mice in indicated groups. Images are representative of three individual mice per group. Scale bar = 50 µm. (P) Flow cytometry analysis of Ly6G-positive cells in dorsal skin lesions of mice (n = 3). Abs: Antibodies; AKT: Protein kinase B; CCL: C-C motif chemokine ligand;CXCL: C-X-C motif chemokine ligand ; DAPI: 4′,6-diamidino-2-phenylindole; DEG: differentially expressed gene; DMSO: Dimethyl sulfoxide; IMQ: Imiquimod; IL-17A: Interleukin-17A; K17: Keratin 17; KC: Keratinocyte; KD: Knockdown; mRNA: Messenger RNA; OE: Overexpression; p-AKT: Phosphorylated AKT; PBS: Phosphate-buffered saline; PDTC: Pyrrolidinedithiocarbamate ammonium; p-p65: Phosphorylated p65; siK17: small interfering RNA of K17; TNF-α: Tumor necrosis factor-alpha; WT: Wild type.Transcriptomic profiling of lentivirus-transduced human primary KCs with K17 overexpressed (K17OE) or K17 knockdown (K17KD) identified 287 upregulated and 128 downregulated differentially expressed genes (DEGs) in K17OE KCs and 355 upregulated and 400 downregulated DEGs (false discovery rate [FDR] 3) in K17KD KCs vs. controls [Supplementary Figure 2A, https://links.lww.com/CM9/C733]. Functional pathway analysis showed upregulated DEG enrichment in leukocyte chemotaxis, cell differentiation, and inflammatory cell migration [Figure 1C]. To validate this chemotactic signature, we selected a panel of significantly upregulated chemokines for quantitative reverse transcription polymerase chain reaction (qRT-PCR) confirmation, which were chosen for their established and diverse roles in recruiting key immune cells in psoriasis, such as neutrophils and T lymphocytes. The validation confirmed a broad upregulation of these chemokines, among which CXCL1 emerged as the top upregulated chemokine in K17OE KCs, with reciprocal suppression following K17 knockdown. [Figure 1D]. We found that tumour necrosis factor-alpha (TNF-α) and IL-17A together could synergistically increase the expression and secretion of CXCL1 in KCs [Supplementary Figures 2B, C, https://links.lww.com/CM9/C733]. Notably, K17 knockdown abolished cytokine-induced CXCL1 expression [Figure 1E and Supplementary Figure 2D, https://links.lww.com/CM9/C733], confirming its necessity for chemokine production. Therefore, K17 orchestrates CXCL1-driven chemotaxis in psoriasis pathogenesis through transcriptional control in KCs. Immunofluorescence analysis revealed CXCL1 enrichment in the epidermis of psoriatic lesions, with spatially overlapping areas of K17-positive staining [Figure 1F]. qRT-PCR and Western blotting confirmed elevated K17 and CXCL1 levels in lesional skin of psoriasis patients [Figure 1G and Supplementary Figure 3A, https://links.lww.com/CM9/C733]. In a psoriasis cohort (GSE13355), lesional skin exhibited significantly elevated K17 and CXCL1 mRNA [Supplementary Figure 3B, https://links.lww.com/CM9/C733], and their positive correlation was further validated by regression analysis (R2 = 0.385, P