339 Senescent human fibroblasts selectively secrete miRNAs in extracellular vesicles and modulate keratinocyte functionality during skin aging

The presence of up to 60% of senescent cells in aged skin and their accumulation with age contribute to the development of systemic tissue dysfunctions. A major culprit for the skin derogatory effects of aged cells is the acquiring of a senescence-associated secretory phenotype (SASP) that alters the tissue environment. In the present study, we identified human dermal fibroblast (HDF) derived miRNAs, enclosed in extracellular vesicles (EV-miRNAs) as novel factors of the SASP. Correlation of miRNA-Seq and qPCR identified a selective packaging of EV-miRNAs in response to dermal aging. The most highly secreted miRNAs target five pro-apoptotic mediators, suggesting a protective activity of the miR-SASP that was further substantiated in vitro. In addition, we confirmed a paracrine EV-miRNA crosstalk between dermal and epidermal cells in monolayers as well as in human skin equivalents and identified EVs in human skin sections. Finally, we evaluated how EVs derived from senescent HDF influence the differentiation potential and wound healing capacity of keratinocytes (NHEK) and identified miR-23a-3p as a crucial ‘miRdiator’ of the miR-SASP. To summarize, our data indicate that EV-miRNAs of senescent HDF are bona fide members of the SASP ('the miR-SASP'). The selective sorting of senescence-associated EV-miRNAs contribute to the communication between HDF and NHEK and impair epidermal homeostasis. The biological role of other abundantly and selectively secreted miRNAs and their implications in vivo and in age-associated diseases remain to be determined.