Insulin-Like Growth Factor 2 Secreted from Mesenchymal Stem Cells with High Glutathione Levels Alleviates Osteoarthritis via Paracrine Rejuvenation of Senescent Chondrocytes.

Senescent chondrocytes, which are increased in osteoarthritic (OA) cartilage, promote cartilage defects and the senescent knee microenvironment by inducing senescence to surrounding normal chondrocytes by secreting senescence-associated secretory proteins. Many studies have used mesenchymal stem cells (MSCs) to treat OA, but MSC treatment remains challenging for clinical application owing to MSC quality control, engraftment, and fibrocartilage regeneration. Here, rather than relying on the direct regeneration of MSCs, we present a novel strategy to suppress OA by MSC-mediated senescent chondrocyte targeting via the paracrine activity of MSCs, thereby improving the knee microenvironment. First, to enable quality control of umbilical cord MSCs, priming MSCs by supplementing human platelet lysate (hPL) greatly enhanced MSC functions by increasing cellular glutathione levels throughout serial passaging. Intra-articular injection of primed MSCs successfully suppressed OA progression and senescent chondrocyte accumulation without direct regeneration. Indirect coculture with primed MSCs using transwell ameliorated the senescence phenotypes in OA chondrocytes, suggesting paracrine rejuvenation. Based on secretome analysis, we identified insulin-like growth factor 2 (IGF2) as a key component that induces paracrine rejuvenation by primed MSCs. The rejuvenation effects of IGF2 act through autophagy activation through the up-regulation of autophagy-related gene expression and autophagic flux. To cross-validate the effects of secreted IGF2 in vivo, knockdown of IGF2 in primed MSCs substantially abolished its therapeutic efficacy in a rabbit OA model. Collectively, these findings demonstrate that hPL supplementation enables MSC quality control by increasing MSC glutathione levels. The therapeutic mechanism of primed MSCs was secreted IGF2, which induces paracrine rejuvenation of senescent OA chondrocytes by activating autophagy.