Age-dependent effects of fibroblast-derived exosomes on keratinocyte differentiation.

Skin aging is driven by both extrinsic factors, such as ultraviolet exposure, and intrinsic, chronological processes that lead to progressive deterioration in skin homeostasis and structure. Chronological aging is associated with replicative senescence and a range of molecular and cellular alterations, including genomic instability, mitochondrial dysfunction, and impaired intercellular communication. The dynamic cross-talk between dermal fibroblasts and epidermal keratinocytes is crucial for maintaining skin integrity throughout aging, with extracellular vesicles (EVs) emerging as key mediators of this intercellular communication. While the impact of keratinocyte-derived EVs in modulating dermal fibroblast function is increasingly recognized, the reciprocal influence of fibroblast-derived EVs on keratinocytes remains largely unexplored, particularly in the context of aging. In this study, we isolated and characterized small EVs, mainly exosomes, from primary human dermal fibroblasts derived from young and aged donors. We analyzed their size, molecular composition, and age-related differences, and assessed their effects on keratinocyte function. While small EVs treatment had limited impact on keratinocyte proliferation, migration, or inflammatory response, it modestly supported the survival of aged keratinocytes and it significantly modulated their differentiation in a manner that varied with both the age of the small EVs donor and the recipient keratinocytes. Notably, aging modified the microRNA cargo of fibroblast-derived EVs, which in turn influences keratinocyte behavior. These findings highlight that dermal EV-mediated signaling is modulated by the aging status of both sender and target cells, providing novel insights into the molecular mechanisms underlying dermis-to-epidermis communication during aging.