Chitosan Hydrogel-loaded MSC-derived Extracellular Vesicles Promote Skin Rejuvenation by Ameliorating the Senescence of Dermal Fibroblasts

Background: The senescence of dermal fibroblasts (DFLs) leads to an imbalance in the synthesis and degradation of extracellular matrix (ECM) proteins, presenting so-called senescence-associated secretory phenotype (SASP), which ultimately leads to skin aging. Recently increasing evidence has supported the idea that mesenchymal stem cells (MSCs) derived extracellular vesicles (MSC-EVs) opened a new avenue for treating skin aging.Methods: In this study, we utilized chitosan (CS) hydrogel for effective loading and sustained release of EVs. In vitro, we explored the rejuvenation effects of CS hydrogel-incorporated EVs (CS-EVs) on replicative senescence DFLs through a series of experiments such as senescence-associated β-galactosidase (SA-β-gal) staining, RT-PCR, and western blots. Besides, we employed local multi-site subcutaneous injection to treat the back skin of naturally aging mice with CS-EVs and used DiI fluorescent dye to label EVs to achieve in vivo real-time tracking.Results: CS-EVs can significantly improve the biological functions of senescent fibroblasts, including promoting their proliferation, enhancing the synthesis of ECM proteins, and inhibiting the overexpression of matrix metalloproteinases (MMPs). Moreover, CS hydrogel could prolong the release of EVs and significantly increase the retention rate of EVs in vivo. After CS-EVs subcutaneous injection treatment, the aging skin tissues showed a state of rejuvenation, which was specifically manifested as enhanced expression of collagen, decreased expression of SASP-related factors, and restoration of tissue structures.Conclusions: CS hydrogel-encapsulated EVs could delay the skin aging process by ameliorating the function of aging DFLs. Our results also highlight the potential of CS hydrogel-encapsulated EVs as a novel therapeutic strategy for ameliorating aging skin to rejuvenation.