The avascular nature of approximately two-thirds of the meniscus means that damage to this tissue can be difficult to repair and outcomes of current surgical procedures are often unsatisfactory. In search of new treatment approaches Kawanishi et al. investigated the therapeutic potential of intra-articular injection of microRNA (miRNA)-210 in a rat model of medial meniscal injury; their findings have now been published in Arthritis Research & Therapy.

miRNA-210 in known to be involved in angiogenesis, DNA repair and cell survival, as well as having other roles. A previous study showed intra-articular injection of this miRNA could promote healing of the anterior cruciate ligament in rats. Yoshitaka Kawanishi and colleagues decided to apply this approach to meniscal damage, and as he says, “this is the first report of meniscal healing using miRNA.”

At 12 weeks all miRNA-210-treated rats had full tear repair and no signs of cartilage degeneration...

The middle segment of the medial meniscus of the right knees of Spraque Dawley rats were cut longitudinally with a scalpel, the capsule and skin were closed, and the joints were immediately injected intra-articularly with control double stranded RNA or synthetic miRNA-210. Histological, immunofluorescence and genetic analyses were performed on the menisci 4 weeks and 12 weeks later.

At 4 weeks, full meniscal repair was achieved in half of the miRNA-210-treated rats, with the other half achieving good or intermediate healing. No control-treated rats had achieved full repair and more than half had no healing at all at this stage. At 12 weeks all miRNA-210-treated rats had full tear repair and no signs of cartilage degeneration; in the control group signs of cartilage degeneration were evident and only two rats achieved tear repair.

The authors then performed immunohistochemical and genetic analyses of the menisci. Kawanishi explains their findings, “Intra-articular injection of miRNA-210 promoted the production of collagen type 2 from meniscus cells and upregulation of VEGF and FGF2 production from synovial cells.”

The authors conclude that intra-articular administration of synthetic miRNA-210 could be a new treatment option for meniscal tears, although at this stage the molecular mechanisms of the healing process have not been fully elucidated. Kawanishi adds that “For clinical application, large animal experiments, and a closer look at the mechanisms and safety of this procedure are necessary.”