Background and Objectives Little is known about the cell metabolism of the acetabular labrum, a horseshoe-shaped structure sealing the hip joint. It performs similar functions as the menisci in the knee though the metabolic aspects of labrum cells show fibrochondrocyte characteristics, different from menisci and cartilage. The goal of this study was to investigate whether labrum cells derived from osteoarthritic tissue have different cell metabolic characteristics compared with labrum cells derived from healthy tissue. Furthermore this study aimed to investigate specific processes of functional importance in the pathology of osteoarthritis.

Materials and Methods Labrum cells from 5 OA patients en 3 healthy control patients were isolated and cultured in the 3-Dimensional alginate culture system. A genome wide gene expression analysis was performed using the Affymetrix microarray technology. Differential gene expression levels were confirmed on additional patient samples by quantitative PCR (qPCR), western blot and immunohistochemistry.

Results Gene expression analysis showed, as expected, downregulation of aggrecan and several matrix degrading enzymes such as (MMP’s) and (ADAMTS’s) were up regulated in OA. qPCR confirmation occurred for 20 of the most pronounced differences between normal and OA labrum. Of these 20 genes the Short leucine-rich repeat proteins (SLRP’s) asporin (ASPN) and osteomodulin (OMD) were of special interest, both showed a reduced expression level and protein presence in OA labrum cells. More over stimulation in vitro of labrum cell with IL1β down regulated the expression of both proteins.

Conclusions Labrum cells derived from OA patients show a consistent altered metabolism compared to cells isolated from healthy controls. The reduced expression of ECM genes in OA labrum point towards a distorted ECM synthesis. Together with the observed increase in ECM degradation by MMP’s, our data indicate that both distorted anabolism and catabolism contribute to degeneration of labrum tissue in OA. The short leucine-rich proteins (SLPR’s) ASPN and OMD were of special interest as these exhibited the most pronounced expression differences. In conclusion this study clearly indicates that similar events occur during OA development in labrum and cartilage. Though labrum specific expression differences are observed that merit further investigation.