Local delivery of TGF-β1-mRNA decreases fibrosis in osteochondral defects

Osteoarthritis (OA) is a condition that affects the quality of life of millions of patients worldwide. Current clinical treatments, in most cases, lead to cartilage repair with deposition of fibrocartilage tissue, which is mechanically inferior and not as durable as hyaline cartilage tissue. We designed an mRNA delivery strategy to enhance the natural healing potential of autologous bone marrow aspirate concentrate (BMAC) for articular cartilage repair. We used mineral-coated microparticles to deliver TGF-β1 mRNA to autologous BMAC. mRNA-activated BMAC was suspended in peripheral blood to generate therapeutic BMAC clots, which were then implanted in rabbit osteochondral defects. Tracking studies revealed that the clots were reliably maintained in the defects for at least 2 weeks. TGF-β1 mRNA delivery significantly increased TGF-β1 production in BMAC clots and increased early expression of articular chondrocyte markers within osteochondral defects. At 9 weeks post-surgery, the mRNA-treated defects had a superior macroscopic cartilage appearance, decreased type I collagen deposition, increased stain intensity for type II collagen and increased glycosaminoglycan deposition area when compared to the controls. Despite the transient expression of therapeutic mRNA we have detected lasting effects, such as a decrease in fibrocartilage formation demonstrated by the decrease in type I collagen deposition and the improvement in macroscopic appearance in the treatment group.