title: Annulus fibrosus cell characteristics are a potential source of intervertebral disc pathogenesis.
abstract: In the end stage of intervertebral disc degeneration, cartilage, bone, endothelial cells, and neurons appear in association with the worsening condition. The origin of the abnormal cells is not clear. This study investigated the properties of progenitor cells in the annulus fibrosus (AF) using one in vitro and two in vivo models. Cultivation of rabbit AF cells with chondrogenic media significantly increased expressions of collagen and aggrecan. Upon exposure to osteogenic conditions, the cultures showed increased mineralization and expression of osteopontin, runx2, and bmp2 genes. Two models were used in the in vivo subcutaneous implantation experiments: 1) rabbit AF tissue in a demineralized bone matrix (DBM) cylinder (DBM/AF), and, 2) rat intact and needle punctured lumbar discs. Bone formation in the AF tissue was detected and hypertrophic chondrocytes and osteoblasts were present 1 month after implantation of the DBM/AF to nude mice. In addition to collagen I and II, immunostaining shows collagen X and osteocalcin expression in DBM/AF specimens 4 months after implantation. Similar changes were detected in the injured discs. Almost the entire needle punctured disc had ossified at 6 months. The results suggest that AF cells have characteristics of progenitor cells and, under appropriate stimuli, are capable of differentiating into chondrocytes and osteoblasts in vitro as well as in vivo. Importantly, these cells may be a target for biological treatment of disc degeneration.
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Li
authors.initials: L
authors.lastname: Jin
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Qihai
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Phillip
authors.initials: P
authors.lastname: Scott
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Dawei
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Francis
authors.initials: F
authors.lastname: Shen
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Gary
authors.initials: G
authors.lastname: Balian
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Xudong
authors.initials: X
authors.lastname: Li
mesh_terms: D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism; D020219:Chondrogenesis; D003094:Collagen / Q000378:metabolism; D007403:Intervertebral Disc / Q000473:pathology*; D055959:Intervertebral Disc Degeneration / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000473:pathology; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis; D011817:Rabbits; D051381:Rats
chemical_list: D053674:Aggrecans; D015675:Osteocalcin; D003094:Collagen