Cellular, but not matrix, immunolocalization of SPARC in the human intervertebral disc: decreasing localization with aging and disc degeneration.
METHODS
Human intervertebral disc anulus tissue was obtained in a prospective study of immunolocalization of SPARC (secreted protein, acidic and rich in cysteine) (osteonectin). Experimental studies were approved by the authors' Human Subjects Institutional Review Board. Discs were obtained from surgical specimens and from control donors.


OBJECTIVE
To determine whether SPARC could be detected in the disc with immunohistochemistry and to determine the incidence of SPARC-positive cells.


BACKGROUND
SPARC is a glycoprotein that has an important role in modulating interactions between cells and matrix. It influences remodeling, collagen fibrillogenesis, metalloproteinase expression, and cytokine expression. Little is known about SPARC in the disc, and one previous study reported the absence of its immunolocalization in fetal and adult disc tissue.


METHODS
Eight normal human discs from subjects aged newborn to 10 years, and 11 disc specimens from control donors or surgical patients aged 15to 76 years were examined for immunolocalization of SPARC. Anulus cells were also tested for the presence of SPARC in vitro in monolayer or three-dimensional agarose culture.


RESULTS
In discs of subjects aged newborn to 0.19 years, SPARC was present in all cells in the outer anulus, in 76.4% of inner anulus cells, and 76.0% of nucleus cells. Localization was significantly lower in anulus cells of study participants aged 4.7 to 76 years (66.7%, P = 0.04). Anulus cells cultured in agarose or monolayer showed positive localization in all cells.


CONCLUSIONS
Findings show decreased presence of SPARC in disc cells of older subjects with disc degeneration and point to the importance of future studies designed to elucidate the unrecognized role of SPARC in disc remodeling, aging, and degeneration.
Department of Orthopaedic Surgery, Carolinas Medical Center, Charlotte, NC 28232, USA. helen.gruber@carolinashealthcare.org
Helen E
HE
Gruber
Jane A
JA
Ingram
Kelly
K
Leslie
Edward N
EN
Hanley
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002478:Cells, Cultured / Q000737:chemistry; D002648:Child; D002675:Child, Preschool; D015299:Discitis / Q000378:metabolism / Q000473:pathology / Q000601:surgery; D017586:Diskectomy; D005109:Extracellular Matrix / Q000737:chemistry; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D007223:Infant; D007231:Infant, Newborn; D007403:Intervertebral Disc / Q000737:chemistry* / Q000166:cytology / Q000254:growth & development; D008297:Male; D008875:Middle Aged; D015676:Osteonectin / Q000032:analysis* / Q000502:physiology; D011446:Prospective Studies
D015676:Osteonectin