The SOX9 transcription factor in the human disc: decreased immunolocalization with age and disc degeneration

Human intervertebral disc anulus tissue was obtained in a prospective study of immunolocalization of SOX9, a protein that plays a role in chondrogenesis and Type II collagen expression. The Human Subjects Institutional Review Board approved experimental studies. Discs were obtained from surgical specimens and from control donors.

To determine whether SOX9 could be detected in discs of Thompson Grades I-IV using immunohistochemistry and to quantify the percentage of cells with SOX9 expression.

SOX9 is involved with cell-specific activation of COL2A1 in chondrocytes. Recent studies have used adenoviral delivery vectors expressing SOX9 to infect a chondroblastic cell line and human disc cells; SOX9 and Type II collagen production increased. The AdSOX9 virus has also been injected directly into rabbit discs in which disc architecture was preserved for 5 weeks. Despite current interest in SOX9 for gene therapy, there have been few studies of SOX9 in normal or degenerated discs.

Discs from 12 normal donors and 25 surgical subjects 15-76 years old were examined for SOX9 immunolocalization. Eight Thompson Grade I discs, 7 Grade II discs, 10 Grade III discs, and 12 Grade IV discs were studied.

In Thompson Grade I discs, SOX9 was uniformly localized throughout the anulus and in some cells of the nucleus. However, in discs from adult donors, anulus cells were present that showed no SOX9 localization, although neighboring cells might be positive. Mean percent localization was 74% for Grade II discs, 69% for Grade III, and 71.6% for Grade IV. Cervical sites showed significantly greater localization than lumbar sites.

Findings showed a uniform expression of SOX9 in the newborn healthy anulus. With aging and disc degeneration, some anulus cells no longer express this transcription product. These observations suggest that the loss of expression of SOX9 in some disc cells may play a role indisc aging and disc degeneration by resulting in decreased expression and production of Type II collagen.