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Open Access Research article

Aggrecanolysis and in vitro matrix degradation in the immature bovine meniscus: mechanisms and functional implications

Christopher G Wilson1, Eric J Vanderploeg2, Fengrong Zuo3, John D Sandy4 and Marc E Levenston12*

Author Affiliations

1 Wallace H Coulter Department of Biomedical Engineering, 313 Ferst Drive, Georgia Institute of Technology, Atlanta, GA 30332, USA

2 George W Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332, USA

3 Roche-Palo Alto, 3431 Hillview Avenue, Palo Alto, CA 94304, USA

4 Department of Biochemistry, Rush University Medical Center, 1735 West Harrison Street, 5th Floor Cohn Building, Chicago, IL 60612, USA

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Arthritis Research & Therapy 2009, 11:R173  doi:10.1186/ar2862

Published: 17 November 2009

Abstract

Introduction

Little is known about endogenous or cytokine-stimulated aggrecan catabolism in the meniscal fibrocartilage of the knee. The objectives of this study were to characterize the structure, distribution, and processing of aggrecan in menisci from immature bovines, and to identify mechanisms of extracellular matrix degradation that lead to changes in the mechanical properties of meniscal fibrocartilage.

Methods

Aggrecanase activity in the native immature bovine meniscus was examined by immunolocalization of the aggrecan NITEGE neoepitope. To investigate mechanisms of cytokine-induced aggrecan catabolism in this tissue, explants were treated with interleukin-1α (IL-1) in the absence or presence of selective or broad spectrum metalloproteinase inhibitors. The sulfated glycosaminoglycan (sGAG) and collagen contents of explants and culture media were quantified by biochemical methods, and aggrecan catabolism was examined by Western analysis of aggrecan fragments. The mechanical properties of explants were determined by dynamic compression and shear tests.

Results

The aggrecanase-generated NITEGE neoepitope was preferentially localized in the middle and outer regions of freshly isolated immature bovine menisci, where sGAG density was lowest and blood vessels were present. In vitro treatment of explants with IL-1 triggered the accumulation of NITEGE in the inner and middle regions. Middle region explants stimulated with IL-1 exhibited substantial decreases in sGAG content, collagen content, and mechanical properties. A broad spectrum metalloproteinase inhibitor significantly reduced sGAG loss, abrogated collagen degradation, and preserved tissue mechanical properties. In contrast, an inhibitor selective for ADAMTS-4 and ADAMTS-5 was least effective at blocking IL-1-induced matrix catabolism and loss of mechanical properties.

Conclusions

Aggrecanase-mediated aggrecanolysis, typical of degenerative articular cartilage, may play a physiologic role in the development of the immature bovine meniscus. IL-1-induced release of sGAG and loss of mechanical properties can be ascribed primarily to the activity of MMPs or aggrecanases other than ADAMTS-4 and ADAMTS-5. These results may have implications for the clinical management of osteoarthritis.