Intradiscal transplantation of synovial mesenchymal stem cells prevents intervertebral disc degeneration through suppression of matrix metalloproteinase-related genes in nucleus pulposus cells in rabbits

The nucleus pulposus tissues of rabbit's intervertebral discs were aspirated to induce disc degeneration, and allogenic synovial MSCs were transplanted. At 2, 4, 6, 8, 16, 24 weeks postoperatively, we evaluated with imaging analyses such as X-ray and magnetic resonance imaging (MRI), and histological analysis. To investigate interaction between synovial MSCs and nucleus pulposus cells, human synovial MSCs and rat nucleus pulposus cells were co-cultured, and species specific microarray were performed.The existence of transplanted cells labeled with DiI or derived from green fluorescent protein (GFP)-expressing transgenic rabbits was confirmed up until 24 weeks. X-ray analyses demonstrated that intervertebral disc height in the MSC group remained higher than that in the degeneration group. T2 weighted MR imaging showed higher signal intensity of nucleus pulposus in the MSC group. Immunohistological analyses revealed higher expression of type II collagen around nucleus pulposus cells in the MSC group compared with even that of the normal group. In co-culture of rat nucleus pulposus cells and human synovial MSCs, species specific microarray revealed that gene profiles of nucleus pulposus were altered markedly with suppression of genes relating matrix degradative enzymes and inflammatory cytokines.Synovial MSCs injected into the nucleus pulposus space promoted synthesis of the remaining nucleus pulposus cells to type II collagen and inhibition of expressions of degradative enzymes and inflammatory cytokines, resulting in maintaining the structure of the intervertebral disc being maintained.Intervertebral discs lie between adjacent vertebrae in the spine and are composed of three major structures called nucleus pulposus, annulus fibrosus, and cartilage end plates [1]. The nucleus pulposus of normal disc includes sparse chondrocytes surrounded by extracellular matrix which mainly consist of type II collagen and proteoglycan. It functions as a shock absorber against mechani