Stem Cells in Cartilage Regeneration

Cartilage is one of the chief structural tissues in the human body. Being resilient and smooth, it covers and protects the ends of long bones providing points of articulation at the joints and is a principal constituent of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components [1]. It is not as hard and rigid as bone, but it is stiffer and less flexible than muscle. Articular cartilage injuries in joints are frequently symptomatic and eventually lead to osteoarthritis, a disease reaching epidemic proportions within an increasingly aged population [2]. Osteoarthritis is a disease of the joint as an organ and is characterized by cartilage breakdown and alterations in the underlying subchondral bone [3]. It is estimated that about 27 million Americans aged 25 and older have osteoarthritis [4, 5]. Degeneration of the intervertebral disc, a fibrocartilaginous joint residing between adjacent vertebrae in the vertebral column, is the most frequent cause of low back pain and another significant cartilage-related disease [6]. The overall cost of chronic low back pain exceeds the combined costs of stroke, respiratory infection, diabetes, coronary artery disease, and rheumatoid disease [7]. Currently, a lack of understanding exists regarding the mechanisms that underly and connect the development of bone and cartilage diseases, resulting in few effective therapeutic options. For instance, there is poor angiogenic response of cartilage as a result of injury; therefore, damaged cartilage remains largely avascular and has poor regenerative potential [8]. Consequently, there is an urgent need to improve the understanding of the causes of bone and joint diseases and to identify new disease models to develop better treatments. Stem cells play a vital role in tissue repair and regeneration in response to injury. The aim of this special issue is to understand the relationship between the stem cells and cartilage regeneration. Within this issue, C. Sang and colleagues isolated two stem cell populations from the nucleus pulposus (NP) and annulus fibrosis (AF) of rabbit intervertebral disc (IVD) and studied the differential properties of these two kinds of stem cells. This study demonstrates for the first time that the stem cells in NP and AF of rabbit IVD exhibit differential properties, which may prove useful for devising new biological approaches for regenerating damaged IVD in affected patients. Mesenchymal stem cell-(MSC-) based therapy is regarded as a potential tissue engineering strategy to achieve nucleus pulposus (NP) …