Piezo1-Fstl1 Axis in Fracture Healing: Modulation of the Chondrocyte Inflammation-ROS-Mitochondrial Damage Cascade and Application of Smart Delivery System.

This study investigated the regulatory role of an intelligent drug delivery system in promoting fracture healing via Piezo1-Fstl1 signaling axis. It also verified its modulation of chondrocyte inflammatory response, mitochondrial oxidative stress, and osteoblast differentiation. Inflammation triggers the accumulation of pro-inflammatory factors, and reactive oxygen species (ROS) in chondrocytes. This leads to oxidative damage in mitochondria, a decrease in mitochondrial membrane potential (MMP), and the induction of mitochondrial permeability transition pore (mPTP) opening, thereby hindering fracture healing. Single-cell RNA sequencing revealed that Piezo1 deficiency markedly upregulated the expression of follistatin-like protein 1 (Fstl1) in chondrocytes. This upregulation exacerbated chondrocyte inflammation and impaired the chondrocyte-to-osteoblast differentiation. Inhibition of Fstl1 attenuated the inflammatory response and ROS accumulation associated with Piezo1 deficiency, alleviated mitochondrial oxidative stress, and improved mitochondrial function and homeostasis. It also restored mitochondrial cristae ultrastructure, thereby improving MMP and mitochondrial activity. This intervention concurrently upregulated osteogenic markers and accelerated endochondral ossification. Based on these, we developed a HA-PBA/TA self-healing hydrogel incorporating chondrocyte-targeting lipid nanoparticles (C-LNP(@Fstl1)) to suppress Fstl1 expression. Local injection of this hydrogel into murine femoral fracture sites significantly reduced inflammatory cytokines in callus tissue and promoted fracture healing, offering new insights and therapeutic strategies for fracture treatment.