Static and dynamic compression application and removal on the intervertebral discs of growing rats

The Influence of Axial Compression on the Cellular and Mechanical Function of Spinal Tissues; Emphasis on the Nucleus Pulposus and Annulus Fibrosus: A Review

In light of the correlation between chronic back pain and intervertebral disc (IVD) degeneration, this literature review seeks to illustrate the importance of the hydraulic response across the nucleus pulposus (NP)-annulus fibrosus (AF) interface, by synthesizing current information regarding injurious biomechanics of the spine, stemming from axial compression. Damage to vertebrae, endplates (EPs), the NP, and the AF, can all arise from axial compression, depending on the segment's posture, the manner in which it is loaded, and the physiological state of tissue. Therefore, this movement pattern was selected to illustrate the importance of the bracing effect of a pressurized NP on the AF, and how injuries interrupting support to the AF may contribute to IVD degeneration.

Hyaluronic Acid Microgels Modulate Inflammation and Key Matrix Molecules toward a Regenerative Signature in the Injured Annulus Fibrosus

Low back pain results from disc degeneration, which is a chronic inflammatory disease characterized by an imbalance between anabolic and catabolic factors. Today, regenerative medicine is focused on identifying inflammatory markers to target disc disease. Hyaluronan is used as a scaffold for cell delivery in disc degeneration; however, to date high molecular weight hyaluronan (HMW HA) is evaluated for its anti-inflammatory and matrix modulatory properties in an in vivo disc injury model. Ex vivo bovine organ culture studies demonstrate the anti-inflammatory and matrix modulatory effects of HMW HA on the IFNα2β signaling pathway that provides the motivation for evaluating its efficacy in regenerating the annulus fibrosus in an in vivo disc injury model. It is demonstrated that the HMW HA microgel acts as an anti-inflammatory molecule in the annulus fibrosus, by downregulating the expression of the pro-inflammatory interferon gamma (IFNα) and pro-apoptotic insulin-like growth factor-binding protein 3 (IGFBP3) and the apoptosis marker caspase 3. Mass spectrometry studies demonstrate that the HMW HA microgel modulates the matrix modulatory effect by upregulating hyaluronic acid link protein (HAPLN1) and aggrecan, which are further confirmed by immunostaining. The microgel's regenerative capacity is illustrated by the increase in the disc height index.

Biological Responses of the Immature Annulus Fibrosus to Dynamic Compression in a Disc Perfusion Culture

Mechanical stimuli participate in disc development and remodelling. However, the effects of mechanical load on the immature annulus fibrosus (AF) are largely unclear. This study aimed to investigate how the immature AF responded to dynamic compressive magnitude and duration. Immature porcine discs were bioreactor-cultured for 7 days and then dynamically compressed at various magnitudes (0.1, 0.2, 0.4, 0.8 and 1.3 MPa at a frequency of 1.0 Hz for 2 h/day) and durations (1, 2, 4 and 8 h/day at a magnitude of 0.4 MPa and a frequency of 1.0 Hz). Non-compressed discs were used as controls. The immature AF tissue was analysed for histology, gene expression (aggrecan, collagen I, ADAMTS-4, MMP-3, TIMP-1 and TIMP-3), biochemical content of glycosaminoglycans (GAG) and hydroxyproline (HYP) and aggrecan immunohistochemical staining. In the lower-compressive-magnitude groups (0.1, 0.2 and 0.4 MPa), the immature AF showed an up-regulation in the expression of matrix genes, GAG and HYP content and aggrecan deposition. In the compression duration groups, the GAG and HYP content and aggrecan deposition declined to a minimum in the 8-hour group, in which a catabolic gene expression profile was found. In conclusion, this study indicated that the effects of dynamic compression on the immature AF are magnitude and duration dependent and that catabolic remodelling within the immature AF can be induced by high compressive magnitudes and long compressive durations.

Genetic Factors in Intervertebral Disc Degeneration

Low back pain (LBP) is a major cause of disability and imposes huge economic burdens on human society worldwide. Among many factors responsible for LBP, intervertebral disc degeneration (IDD) is the most common disorder and is a target for intervention. The etiology of IDD is complex and its mechanism is still not completely understood. Many factors such as aging, spine deformities and diseases, spine injuries, and genetic factors are involved in the pathogenesis of IDD. In this review, we will focus on the recent advances in studies on the most promising and extensively examined genetic factors associated with IDD in humans. A number of genetic defects have been correlated with structural and functional changes within the intervertebral disc (IVD), which may compromise the disc's mechanical properties and metabolic activities. These genetic and proteomic studies have begun to shed light on the molecular basis of IDD, suggesting that genetic factors are important contributors to the onset and progression of IDD. By continuing to improve our understanding of the molecular mechanisms of IDD, specific early diagnosis and more effective treatments for this disabling disease will be possible in the future.