Abstract
IntroductionAsporin, also known as periodontal ligament-associated protein 1 (PLAP1), is a member of the family of small leucine-rich proteoglycan (SLRP) family. It is present within the cartilage extracellular matrix (ECM), and is reported to have a genetic association with osteoarthritis. Its D14 allele has recently been found to be associated with lumbar disc degeneration in Asian subjects. There have been no studies, however, of this gene's normal immunohistochemical localization within the human intervertebral disc, or of expression levels in Caucasian individuals with disc degeneration.MethodsStudies were approved by our human subjects Institutional Review Board. Methods included immunohistochemical localization of asporin in the disc of humans and the sand rat (a small rodent with spontaneous age-related disc degeneration), and Affymetrix microarray analysis of asporin gene expression in vivo and in vitro.ResultsImmunohistochemical studies of human discs revealed that some, but not all, cells of the outer annulus expressed asporin. Fewer cells in the inner annulus contained asporin, and it was rarely present in cells in the nucleus pulposus. Similar patterns were found for the presence of asporin in lumbar discs of sand rats. Substantial relative gene expression levels were seen for asporin in both disc tissue and in annulus cells grown in three-dimensional culture. More degenerate human discs (Thompson grade 4) showed higher expression levels of asporin than did less degenerate (grade 1, 2 and 3) discs, P = 0.004.ConclusionsIn the discs of Caucasian subjects studied here, and in the sand rat, greater immunolocalization levels were found in the outer compared to inner annulus. Localization was rare in the nucleus. Gene expression studies showed greatest expression of asporin in the more degenerate human discs in vivo.
Highlights
Asporin, known as periodontal ligamentassociated protein 1 (PLAP1), is a member of the family of small leucine-rich proteoglycan (SLRP) family
Similar patterns were found for the presence of asporin in lumbar discs of sand rats
Substantial relative gene expression levels were seen for asporin in both disc tissue and in annulus cells grown in three-dimensional culture
Summary
Known as periodontal ligamentassociated protein 1 (PLAP1), is a member of the family of small leucine-rich proteoglycan (SLRP) family. It is present within the cartilage extracellular matrix (ECM), and is reported to have a genetic association with osteoarthritis. Known as periodontal ligament-associated protein 1 (PLAP1), is an interesting, recently discovered leucinerich protein that is a member of the family of small leucine-rich proteoglycan (SLRP) family and is associated with the extracellular matrix (ECM) in cartilage, meniscus and several other tissues [1,2]. Recent studies have identified populations of individuals with osteoarthritis of the knee and asporin alleles with 14 aspartic acid repeats in the N-terminal region of the protein (designated D14). Associations of the ASPN SNPs with OA have been studied by Shi et al [6] and by Nakamura et al [7]
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