Dynamic and static overloading induce early degenerative processes in caprine lumbar intervertebral discs.

Cornelis P L Paul,Marco N Helder,Peter M Van De Ven,Hendrik A Zuiderbaan,Barend J Van Royen,Behrouz Zandieh Doulabi,Margriet G Mullender,Albert J Van Der Veen,Theo H Smit,Tom Schoorl

doi:10.1371/journal.pone.0062411

Cornelis P L Paul, Marco N Helder + Show 8 more

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https://doi.org/10.1371/journal.pone.0062411

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Abstract

Mechanical overloading of the spine is associated with low back pain and intervertebral disc (IVD) degeneration. How excessive loading elicits degenerative changes in the IVD is poorly understood. Comprehensive knowledge of the interaction between mechanical loading, cell responses and changes in the extracellular matrix of the disc is needed in order to successfully intervene in this process. The purpose of the current study was to investigate whether dynamic and static overloading affect caprine lumbar discs differently and what mechanisms lead to mechanically induced IVD degeneration. Lumbar caprine IVDs (n = 175) were cultured 7, 14 and 21 days under simulated-physiological loading (control), high dynamic or high static loading. Axial deformation and stiffness were continuously measured. Cell viability, cell density, and gene expression were assessed in the nucleus, inner- and outer annulus. The extracellular matrix (ECM) was analyzed for water, glycosaminoglycan and collagen content. IVD height loss and changes in axial deformation were gradual with dynamic and acute with static overloading. Dynamic overloading caused cell death in all IVD regions, whereas static overloading mostly affected the outer annulus. IVDs expression of catabolic and inflammation-related genes was up-regulated directly, whereas loss of water and glycosaminoglycan were significant only after 21 days. Static and dynamic overloading both induced pathological changes to caprine lumbar IVDs within 21 days. The mechanism by which they inflict biomechanical, cellular, and extracellular changes to the nucleus and annulus differed. The described cascades provide leads for the development of new pharmacological and rehabilitative therapies to halt the progression of DDD.

Highlights

Lumbar intervertebral disc (IVD) degeneration is a dominant factor in the etiology of low back pain (LBP) [1]
Total axial deformation during the loading phase was highest in the high static, intermediate in the high dynamic, and smallest in the simulated physiological loading (SPL) regime
We investigated the effects of high dynamic and static loading on large species IVDs in an ex-vivo culture model

Summary

Introduction

Lumbar intervertebral disc (IVD) degeneration is a dominant factor in the etiology of low back pain (LBP) [1]. Disc degeneration is an age-related process [2], and may arise from any of several pathological conditions, such as trauma to the spine [3] or an inflammatory response. It is influenced by many factors, such as genetics [4,5], systemic disorders (atherosclerosis, high cholesterol and diabetes) [6] and nutrient supply to the disc [7,8,9]. Mechanical (over)loading has been identified as a major extrinsic component in the onset and progression of IVD degeneration [10,11]. Whether mechanical loading is a positive stimulus or induces damage to the IVD, is dependent on the type of load applied, its magnitude, duration and frequency [14,15]

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