ABSTRACT: Epidermal pigmentation has been implicated in skin barrier function, yet its role in modulating inflammatory barrier responses remains incompletely understood. We investigated how pigmentation influences epidermal barrier integrity in a murine model of acute skin inflammation. Wildtype (black, highly pigmented) and Mc1r-mutant (yellow, lowly pigmented) C57BL/6 mice were challenged via intradermal injection into shaved dorsal skin using pooled serum from human atopic dermatitis (AD) patients. Twenty-four hours following the inflammatory challenge, the injected skin sites were excised and profiled molecularly and biochemically. Epidermal injury and inflammation were assessed using histological H&E scoring, while global transcriptional remodeling was evaluated through bulk skin RNA sequencing, differential gene expression profiling, and pathway analyses. Highly pigmented (Mc1r⁺/⁺) mice exhibited more severe epidermal injury, ulceration, and dermal edema compared with low-pigmented Mc1r-mutant or counterparts. Bulk skin RNA sequencing revealed extensive pigmentation-dependent transcriptional remodeling, with pigmentation status emerging as the dominant source of variance. Gene set enrichment analysis demonstrated a coordinated downregulation of pathways associated with the establishment of the skin barrier (GO:0061436) in highly pigmented mice following the inflammatory challenge. At the gene level, pigmented skin demonstrated marked downregulation of epidermal structural proteins, including filaggrin, loricrin, claudin-1, and Spink5, alongside suppression of lipid-metabolic enzymes critical for stratum corneum organization, such as Elovl3 and Fads2b. Key transcriptional regulators of keratinocyte differentiation and barrier maintenance, including Ovol1, Nrf2, ΔNp63, Grhl3, Klf4, Sp1, and the aryl hydrocarbon receptor (Ahr), were also coordinately downregulated. In parallel, stress-associated signaling pathways were upregulated. Together these findings identify pigmentation-linked suppression of epidermal differentiation and lipid programs as a potential molecular basis for increased barrier fragility under inflammatory stress, with implications for atopic dermatitis in highly pigmented skin.
