Rejuvenation of tendon stem/progenitor cells for functional tendon regeneration through platelet-derived exosomes loaded with recombinant Yap1

The regenerative capabilities including self-renewal, migration and differentiation potentials shift from the embryonic phase to the mature period of endogenous tendon stem/progenitor cells (TSPCs) char-acterize restricted functions and disabilities following tendon injuries. Recent studies have shown that tendon regeneration and repair rely on multiple specific transcription factors to maintain TSPCs charac-teristics and functions. Here, we demonstrate Yap, a Hippo pathway downstream effector, is associated with TSPCs phenotype and regenerative potentials through gene expression analysis of tendon develop-ment and repair process. Exosomes have been proven an efficient transport platform for drug delivery. In this study, purified exosomes derived from donor platelets are loaded with recombinant Yap1 pro-tein (PLT-Exo-Yap1) via electroporation to promote the stemness and differentiation potentials of TSPCs in vitro . Programmed TSPCs with Yap1 import maintain stemness and functions after long-term passage in vitro . The increased oxidative stress levels of TSPCs are related to the phenotype changes in duplica-tive senescent processes. The results show that treatment with PLT-Exo-Yap1 significantly protects TSPCs against oxidative stressor-induced stemness loss and senescence-associated secretory phenotype (SASP) through the NF-kappa B signaling pathway. In addition, we fabricate an Exos-Yap1-functioned GelMA hydrogel with a parallel-aligned substrate structure to enhance TSPCs adhesion, promote cell stemness and force regenerative cells toward the tendon lineage for in vitro and in vivo tendon regeneration. The application of Exos-Yap1 functioned implant assists new tendon-like tissue formation with good mechanical proper-ties and locomotor functions in a full-cut Achilles tendon defect model. Thus, PLT-Exo-Yap1-functionalized GelMA promotes the rejuvenation of TSPCs to facilitate functional tendon regeneration.Statement of significanceThis is the first study to explore that the hippo pathway downstream effector Yap is involved in tendon aging and repair processes, and is associated with the regenerative capabilities of TSPCs.In this syudy, Platelet-derived exosomes (PLT-Exos) act as an appropriate carrier platform for the de-livery of recombinant Yap1 into TSPCs to regulate Yap activity.Effective Yap1 delivery inhibit oxidative stress-induced senescence associated phenotype of TSPCs by blocking ROS-mediated NF-kappa b signaling pathway activation.

Automated summary

This study reveals that the downstream effector of the Hippo pathway, Yap, is involved in tendon aging and repair processes and is associated with the regenerative capabilities of TSPCs. Platelet-derived exosomes loaded with recombinant Yap1 effectively inhibit oxidative stress-induced senescence and promote tendon regeneration. Additionally, the functionalized GelMA hydrogel with parallel-aligned substrate structure enhances TSPCs adhesion and stemness for tendon rejuvenation.