Research Article: PLAU promotes fibroblast activation and keloid fibrogenesis through PLAUR–Dependent TGF–?/Smad signaling

Abstract:
Keloids are fibroproliferative disorders conditions of the dermis with dysregulated immune responses contributing to disease progression. However, the causal inflammatory mediators and their pathogenic mechanisms remain undefined. This study aims to identify causal inflammatory mediators for keloids and their pathogenic mechanisms. Two–sample Mendelian randomization (MR) analyses were performed using genetic instruments for 91 inflammatory proteins as exposures and genome–wide association study (GWAS) summary statistics for keloid susceptibility as the outcome. Sensitivity analyses were conducted to assess the robustness of MR findings. Single–cell RNA sequencing (scRNA–seq) datasets from keloid tissues were analyzed to identify the cellular distribution of prioritized candidates. Functional validation was performed using immunohistochemistry (IHC), immunofluorescence staining, qRT–PCR, western blotting, siRNA–mediated knockdown, recombinant protein stimulation, and transcriptome sequencing. Pharmacological inhibition and rescue experiments were further performed to investigate the downstream signaling pathway. MR analysis identified five inflammatory proteins with potential causal associations with keloid susceptibility, among which urokinase–type plasminogen activator (PLAU) was the only one consistently enriched in fibroblasts across two independent scRNA–seq datasets. PLAU expression was significantly elevated at both the mRNA and protein levels in keloid tissues and primary fibroblasts. PLAU knockdown in keloid fibroblasts reduced collagen I/III expression, proliferation, and migration, whereas recombinant PLAU stimulation enhanced these profibrotic phenotypes in normal dermal fibroblasts. Mechanistically, RNA–sequencing implicated activation of the TGF–? signaling pathway. Furthermore, inhibition of TGF–? receptor signaling attenuated PLAU–induced profibrotic responses, while exogenous TGF–?1 rescued the effects of PLAU depletion. Importantly, PLAUR knockdown attenuated PLAU–induced TGF–?/Smad activation and reduced PLAU–mediated enhancement of fibroblast activation. This integrative study identifies PLAU as a genetically supported and biologically relevant mediator of keloid fibrosis. PLAU promotes fibroblast activation through PLAUR–dependent regulation of the TGF–?/Smad signaling pathway, leading to enhanced collagen production, proliferation, and migration. These findings provide new insights into inflammatory regulation in keloid pathogenesis and highlight PLAU as a potential therapeutic target for keloid intervention.

Introduction:
Keloids are fibroproliferative disorders conditions of the dermis with dysregulated immune responses contributing to disease progression. However, the causal inflammatory mediators and their pathogenic mechanisms remain undefined.

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