Fibroblast State Remodelling and Stromal Depletion Shape the Ageing Microenvironment of Human Penile Skin

Disentangling intrinsic (chronological) skin ageing from ultraviolet-driven photoaging remains challenging because most human skin single-cell studies are biassed towards sun-exposed sites and non-genital anatomy. Here, we profiled histologically normal human penile skin, a typically UV-shielded mucocutaneous niche, to characterise ageing-associated remodelling in a specialised cutaneous microenvironment. We analysed 137 880 cells from 13 healthy male donors (13-63 years) and identified 12 major cell types. Donor-aware compositional profiling revealed pronounced age-associated stromal depletion, driven by progressive loss of fibroblasts and pericyte/vascular smooth muscle cells. Whole-skin pseudo-bulk modelling across continuous age captured broad transcriptional drift towards senescence- and inflammation-related programmes alongside reduced extracellular matrix organisation and Wnt-associated maintenance pathways. Cell type-resolved pseudo-bulk analyses localised the strongest age-associated changes to stromal lineages. In fibroblasts, unsupervised temporal module analysis indicated a shift from matrix-supportive/regenerative programmes towards a pro-inflammatory, senescence-associated secretory phenotype-like state. Cross-compartment overlap further identified a 21-gene core module shared across epidermal, stromal, and immune compartments in older donors, consistent with coordinated tissue-wide remodelling. Together, these findings nominate stromal attrition and inflammatory fibroblast reprogramming as central features of ageing in human penile skin and provide a site-specific framework for distinguishing conserved intrinsic ageing modules from niche-shaped execution mechanisms. This UV-shielded genital reference offers a complementary baseline for interpreting intrinsic ageing signals across anatomically diverse skin sites.