A miR-activated hydrogel for the delivery of a pro-chondrogenic microRNA-221 inhibitor as a minimally invasive therapeutic approach for articular cartilage repair

Articular cartilage has limited capacity for repair (or for regeneration) under pathological conditions, given its non-vascularized connective tissue structure and low cellular density. Our group has successfully developed an injectable hydrogel for cartilage repair, composed of collagen type I (Col I), collagen type II (Col II), and methacrylated-hyaluronic acid (MeHA), capable of supporting chondrogenic differentiation of mesenchymal stem cells (MSCs) towards articular cartilage-like phenotypes. Recent studies have demonstrated that silencing <i>miR-221</i> may be an effective approach in promoting improved MSC chondrogenesis. Thus, this study aimed to develop a <i>miR</i>-activated hydrogel capable of offering a more effective and less invasive therapeutic approach to articular cartilage repair by delivering a pro-chondrogenic <i>miR-221</i> inhibitor to MSCs using our MeHA-Col I/Col II hydrogel. The MeHA-Col I/Col II hydrogel was cast as previously shown and incorporated with cells transfected with <i>miR-221</i> inhibitor (using a non-viral peptide delivery vector) to produce the <i>miR</i>-activated hydrogel. Down-regulation of <i>miR-221</i> did not affect cell viability and enhanced MSCs-mediated chondrogenesis, as evidenced by significantly upregulated expression of key pro-chondrogenic articular cartilage genes (<i>COL2A1</i> and <i>ACAN</i>) without promoting hypertrophic events (<i>RUNX2</i> and <i>COL10A1</i>). Furthermore, <i>miR-221</i> down-regulation improved cartilage-like matrix formation in the MeHA-Col I/Col II hydrogel, with significantly higher levels of sulfated glycosaminoglycans (sGAG) and Col II produced by MSCs in the hydrogel. These results provide evidence of the potential of the <i>miR-</i>activated hydrogel as a minimally invasive therapeutic strategy for articular cartilage repair.