The meniscus is a semi-lunar and wedge-shaped fibrocartilaginous structure between the distal femoral condyle and the proximal tibial plateaus in the knee joint. Meniscus plays indispensable roles in joint congruence, shock absorption, and stress transmission. Meniscus injuries do not heal spontaneously. Clinically, over one million patients undergo meniscectomy each year in the United States. Allograft transplantation from cadavers is the primary clinical substitute of resected meniscus, but suffers from donor shortage, pathogen transmission, immunorejection and tissue mis-match. Meniscectomy, with or without allograft transplantation, alleviates pain at best, but significantly increases the incidence of osteoarthritis later in life. By 2020, a total of 67 million Americans will suffer fro arthritis. Not surprisingly, regeneration of knee meniscus is an aspiring goal in orthopedic medicine, but has encountered multiple barriers. No regenerative therapies exist for meniscus injuries at this time. One of the critical barriers of meniscus regeneration is our insufficient knowledge of meniscus cells, known as fibrochondrocytes whose origin and lineage derivation are poorly understood. Our preliminary data demonstrate that 1) fibrochondrocytes were derived from adult stem/progenitor cells by step-wise induction with two recombinant human growth factors that are both necessary and sufficient for induction of fibrochondrocytes in vitro and in vivo;2) spatiotemporal release of these two growth factors induced de novo formation of multiphase fibrocartilage tissues in anatomically correct bioscaffolds that replaced partially resected knee meniscus in vivo in a preclinical model. Host endogenous cells were recruited into anatomically correct, microporous scaffolds and produced primarily type I collagen in the outer region, type II collagen in the inner region and blended type I and II collagens in the intermediate zone of the regenerated meniscus tissues. The overall objectives of this proposal are to optimize strategies for the recruitment of host endogenous cells and differentiation into fibrochondrocytes in our existing pre-clinical model of meniscus regeneration, without cell transplantation. Our overarching hypothesis is that spatiotemporal delivery of specific bioactive cues regulates the recruitment and fibrochondrogenic differentiation of endogenous cells, including stem/progenitor cells, towards meniscus regeneration. No regenerative therapies exist for fibrocartilage defects in intervertebral disks, tendon-bone junction and the temporomandibular joint. The planned studies will identify fibrochondrocyte populations that are pivotal for meniscus regeneration, and may have implications for the regeneration of other fibrocartilage structures. The planned cell recruitment strategies may be applicable in the regeneration of other tissues.
The meniscus is a wedge-shaped tissue in the knee between the thigh bone and leg bone, serving as an indispensable cushion without which the bones do not fit. Meniscus trauma is a common injury, and increases the risk of arthritis. We have discovered that two proteins can induce the regeneration of the knee meniscus by host endogenous stem cells, and plan to test the efficacy of this strategy in a preclinical model.