BASIC SCIENCE SPINE Volume 37, Number 1, pp 18–25 ©2012, Lippincott Williams & Wilkins 18 www.spinejournal.com January 2012 Mechanical Destabilization Induced by Controlled Annular Incision of the Intervertebral Disc Dysregulates Metalloproteinase Expression and Induces Disc Degeneration James Melrose, PhD,* Cindy Shu, PhD,* Cara Young, PhD,† Ronald Ho, BSc,† Margaret M. Smith, PhD,* Allan A. Young, PhD,* Susan S. Smith, MedVet BVSc,* Ben Gooden, PhD,* Andrew Dart, Dip ACVS, Dip ECVS,‡ Juan Podadera, MedVet BVSc,‡ Richard C. Appleyard, PhD,† and Christopher B. Little, PhD, Dip ACVS* Study Design. An investigation of mechanical destabilization of the lumbar ovine intervertebral disc (IVD) inducing IVD degeneration (IVDD) as determined by multiparameter outcome measures (magnetic resonance imaging [MRI], IVD composition, biomechanical testing, gene profiling, immunohistochemistry, and immunoblotting). Objective. To assess the effect of IVD mechanical destabilization on matrix protein and metalloproteinase gene expression to investigate the pathophysiological mechanisms of lumbar IVDD. Summary of Background Data. Several earlier studies have used annular transection to induce IVDD in sheep, but none have optimized or validated the most appropriate lesion size. Methods. The annulus fibrosus (AF) incision inducing maximal change in IVD biomechanics was applied to L1-L2, L3-L4, and L5- L6 discs in vivo to compare with a sham procedure at 3 months post operation. IVDs were evaluated by MRI, biomechanics, histopathology, proteoglycan and collagen content, gene expression, and aggrecan proteolysis by Western blotting. Results. Significant changes were observed in lesion (6 × 20 mm 2 ) compared with sham IVDs at 3 months post operation: reduced disc height on MRI; increased neutral zone in biomechanical testing; depleted proteoglycan and collagen content in the nucleus pulposus T he intervertebral disc (IVD) provides weight-bearing properties, mechanical stability, and spinal flexibility 1 ,2 by the interplay of different tissue types with variable mechanical properties. 3 The outermost region of the IVD, the annulus fibrosus (AF), is composed of collagenous lamellae, which, along with the superior and inferior cartilaginous end- plates, enclose the aggrecan-rich nucleus pulposus (NP). Ag- grecan forms entrap macromolecular hydrophilic aggregates with hyaluronan 4 ,5 within the NP, generating internal hydro- static pressure and hydrodynamic weight-bearing properties. In human beings, the IVD undergoes age-related cellular and matrix changes leading to degeneration and a diminution in its functional capability 6 including loss of aggrecan and IVD height, rim lesions arising from discontinuities in the vertebral attachment to the outer AF, and radiating and concentric an- nular tears. 7 Although there is clearly a central role for loss of NP aggrecan in IVD degeneration (IVDD), the molecular mechanisms underlying this loss remain to be elucidated. 5 ,8 ,9 Lumbar IVDD represents a significant socioeconomic dis- ease and is implicated in approximately 40% of all cases of low-back pain 10 ,11 ; 80% of the population will experience at From the *Raymond Purves Bone and Joint Research Laboratories and †Murray Maxwell Biomechanics Laboratory, Kolling Institute of Medical Research, Institute of Bone and Joint Research, University of Sydney, The Royal North Shore Hospital of Sydney, St Leonards, New South Wales, Australia; and ‡Faculty of Veterinary Science, University of Sydney, Camden, Australia. Acknowledgment date: April 28, 2010. First revision date: October 20, 2010. Acceptance date: December 22, 2010. The manuscript submitted does not contain information about medical device(s)/drug(s). Corporate/industry and institutional funds were received to support 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 James Melrose, PhD, Raymond Purves Bone and Joint Research Laboratories, Institute of Bone and Joint Research, Kolling Institute of Medical Research, Level 10, Kolling Bldg B6, University of Sydney at Royal North Shore Hospital, St Leonards, NSW 2065, Australia; E-mail: jmelrose@med.usyd.edu.au (NP) and lesion half of the AF but not in the contralateral AF; increased messenger RNA for collagen I and II, aggrecan, versican, perlecan, matrix metalloproteinase (MMP)-1 & 13, and ADAMTS-5, in the lesion-site AF and NP but not in the contralateral AF. ADAMTS-4 messenger RNA was increased in the lesion-site AF but decreased in the NP. Despite an upregulation in MMPs, there was no change in MMP- or ADAMTS-generated aggrecan neoepitopes in any region of the IVD in lesion or sham discs. Conclusion. Lumbar IVDD was reproducibly induced with a 6 × 20 mm 2 annular lesion, with focal dysregulation of MMP gene expression, cell cloning in the inner AF, loss of NP aggrecan, and disc height. Loss of aggrecan from the NP was not attributable to increased proteolysis in the interglobular domain by MMPs or ADAMTS. Key words: intervertebral disc degeneration, lumbar interver- tebral disc mechanical destabilization, matrix metalloproteinase dysregulation. Spine 2012;37:18–25 DOI: 10.1097/BRS.0b013e31820cd8d5 Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.