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Cellular, but Not Matrix, Immunolocalization of SPARC in the Human Intervertebral Disc: Decreasing Localization With Aging and Disc Degeneration

Gruber, Helen E., PhD; Ingram, Jane A., BS; Leslie, Kelly, MS; Hanley, Edward N. Jr, MD

doi: 10.1097/01.brs.0000142225.07927.29
Basic Science
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Study Design. 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.

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

Summary of the Background Data. 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.

SPARC (osteonectin) functions in cell-matrix interactions, matrix remodeling and cytokine expression, but its presence or role in the disc is unknown. Human disc tissue was examined with immunocytochemistry to determine SPARC localization. The percentage of cells with SPARC localization was significantly lower in anulus cells from study participants 4.7 to 76 years of age compared with that found in study participants newborn to 0.19 years (P = 0.04). Findings point to the importance of the unrecognized role of SPARC in disc remodeling, aging, and degeneration.

From the Department of Orthopaedic Surgery, Carolinas Medical Center, Charlotte, NC.

Acknowledgment date: July 22, 2003. First revision date: September 30, 2003. Second revision date: November 4, 2003. Acceptance date: November 6, 2003.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Helen E. Gruber, PhD, Orthopaedic Research Biology, Cannon Bldg., 3rd floor, Carolinas Medical Center, PO Box 32861, Charlotte, NC 28232; E-mail: helen.gruber@carolinashealthcare.org

© 2004 Lippincott Williams & Wilkins, Inc.