Title : Characterization of circulating monocytes in atopic dermatitis through Single-Cell RNA sequencing
Abstract:
Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by Th2-driven immune responses, impaired skin barrier function, and immune dysregulation. Circulating monocytes (cMono), which migrate to inflammatory sites and produce cytokines, play a pivotal role in inflammation; however, their specific contribution to AD pathogenesis remains poorly understood. In this study, we utilized multiplexed single-cell RNA sequencing (scRNA-seq) to investigate the transcriptional and functional profiles of cMono in AD. Peripheral blood mononuclear cells (PBMCs) were obtained from healthy controls (HC, N=16) and AD patients (N=16), with approximately 56,000 monocytes analyzed. AD-specific monocyte subsets were identified, along with key upregulated genes, including CXCL3, SEMA6B, LRG1, CD141, PHLDA1, and PRDM1. Compared to HC, monocyte clusters in AD displayed heightened expression of Th2-related, inflammatory, migratory, and differentiation-associated transcription factors. Pathways related to angiogenesis and Th17 responses were also enriched. Additionally, migration-associated genes GPR183 and CCR1 and neutrophil activation markers were significantly upregulated in AD monocytes. Strikingly, AD-specific cMono biomarkers identified in PBMCs (PBMC_AD_cMono) were also upregulated in skin-derived monocytes (skin_cMono), reflecting shared transcriptional profiles. Correlation heatmap analysis confirmed a strong relationship between PBMC_AD_cMono and skin_cMono clusters. Differentially expressed gene (DEG) analysis further revealed 109 commonly upregulated genes between these two monocyte populations, implicating pathways such as LPS response, MAPK signaling, NF-kB activation, and wound healing, all of which are central to AD pathogenesis. To explore monocyte-keratinocyte interactions, keratinocytes (KC) were classified into seven distinct clusters. Among these, a cluster of KRT15-expressing basal keratinocytes with high CCL2 expression was identified as inflammatory keratinocytes (Inf_KC). Inf_KC were significantly enriched in AD skin compared to HC and are hypothesized to recruit monocytes via CCL2-mediated signaling. Importantly, PBMC_AD_cMono was shown to interact with KC, promoting both the proliferation and inflammatory activity of Inf_KC, thereby contributing to the pathogenesis of AD. In conclusion, this study provides a comprehensive characterization of cMono in AD, highlighting their role in disease-specific inflammation and their interaction with keratinocytes to drive chronic skin inflammation. These findings uncover potential therapeutic targets for modulating monocyte function and disrupting monocyte-keratinocyte interactions in AD.
