Complex loading affects intervertebral disc mechanics and biology

• Published in: Osteoarthritis and cartilage Vol. 19; no. 8; pp. 1011 - 1018
• Main Authors: Walter, B.A, Korecki, C.L, Purmessur, D, Roughley, P.J, Michalek, A.J, Iatridis, J.C
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.08.2011
• Subjects: ADAM Proteins - metabolism; ADAMTS4 Protein; Aggrecans - metabolism; Animals; Apoptosis; Apoptosis - physiology; Blotting, Western; Case-Control Studies; Caspase 3 - metabolism; Catabolism; Cattle; Cell Death - physiology; Disease Models, Animal; Interleukin-1beta - metabolism; Interleukin-6 - metabolism; Intervertebral disc; Intervertebral Disc - injuries; Intervertebral Disc - metabolism; Intervertebral Disc - physiopathology; Matrix Metalloproteinase 1 - metabolism; Mechanical loading; Organ culture; Procollagen N-Endopeptidase - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Rheumatology; Spinal Diseases - metabolism; Spinal Diseases - physiopathology; Weight-Bearing - physiology; Catabolism; Mechanical loading; Intervertebral disc; Organ culture; Apoptosis
• ISSN: 1063-4584; 1522-9653
• DOI: 10.1016/j.joca.2011.04.005

Summary Background Complex loading develops in multiple spinal motions and in the case of hyperflexion is known to cause intervertebral disc (IVD) injury. Few studies have examined the interacting biologic and structural alterations associated with potentially injurious complex loading, which may be an important contributor to chronic progressive degeneration. Objective This study tested the hypothesis that low magnitudes of axial compression loading applied asymmetrically can induce IVD injury affecting cellular and structural responses in a large animal IVD ex-vivo model. Methods Bovine caudal IVDs were assigned to either a control or wedge group (15°) and placed in organ culture for 7 days under static 0.2 MPa load. IVD tissue and cellular responses were assessed through confined compression, qRT-PCR, histology and structural and compositional measurements, including Western blot for aggrecan degradation products. Results Complex loading via asymmetric compression induced cell death, an increase in caspase-3 staining (apoptosis), a loss of aggrecan and an increase in aggregate modulus in the concave annulus fibrosis. While an up-regulation of MMP-1, ADAMTS4, IL-1β, and IL-6 mRNA, and a reduced aggregate modulus were induced in the convex annulus. Conclusion Asymmetric compression had direct deleterious effects on both tissue and cells, suggesting an injurious loading regime that could lead to a degenerative cascade, including cell death, the production of inflammatory mediators, and a shift towards catabolism. This explant model is useful to assess how injurious mechanical loading affects the cellular response which may contribute to the progression of degenerative changes in large animal IVDs, and results suggest that interventions should address inflammation, apoptosis, and lamellar integrity.