Human Anulus Fibrosis and Nucleus Pulposus Cells of the Intervertebral Disc

Abstract

Human intervertebral disc cells were harvested from patients with adolescent idiopathic scoliosis (AIS) and from donors with degenerative disc disease. Anulus fibrosis (AF) was separated from nucleus pulposus (NP), and cells were cultured separately in two different cell culture models. To investigate changes in gene expression of human disc cells during in vitro expansion and to determine whether cells from adolescent idiopathic scoliosis donors show different gene expression profiles compared with cells from patients operated for degenerative disc disease. During in vitro expansion, cells undergo a dedifferentiation process, which is characterized by a switch in gene expression. Markers for the differentiation and dedifferentiation status of human disc cells are not yet known. Moreover, it is not known whether changes in the gene expression pattern occur during the degeneration process. Cells from AF and NP tissues were expanded in monolayer and alginate cultures under controlled and defined conditions. Cells were then harvested, and analysis of phenotype was performed using quantitative real-time polymerase chain reaction (PCR). The mRNA expression of Type I, II, and X collagen, aggrecan, and interleukin-1beta in scoliosis and degenerative human intervertebral disc cells was analyzed. The gene expression of Type II and X collagen and of aggrecan significantly decreased for both cell types during monolayer expansion. Reexpression of all genes was observed when cells were cultured in alginate. Additionally, NP cells from degenerative tissues displayed significant lower levels of Type II collagen compared with NP cells from scoliosis donors. These results provide a better understanding of how the phenotype of human healthy and degenerative disc cells is influenced by in vitro expansion. This may be useful for future tissue engineering purposes.