Research has shown that mechanical loading affects matrix biosynthesis of intervertebral disc (IVD) cells; however the pathway(s) to this effect is currently unknown. Cellular matrix biosynthesis is an energy demanding process. The objective of this study was to investigate the effects of static and dynamic compressive loading on energy metabolism of IVD cells. Porcine annulus fibrosus (AF) and nucleus pulposus (NP) cells seeded in 2% agarose were used in this experiment. Experimental groups included 15% static compression and 0.1 and 1 Hz dynamic compression at 15% strain magnitude for 4 hours. ATP, lactate, glucose and nitric oxide (NO) contents in culture media, and ATP content in cell-agarose construct were measured using biochemical assays. While the total ATP content of AF cells was promoted by static and dynamic loading, only 1 Hz dynamic loading increased total ATP content of NP cells. Increases in lactate production and glucose consumption of AF cells suggest that ATP production via glycolysis is promoted by dynamic compression. ATP release and NO production of AF and NP cells were significantly increased by dynamic loading. Thus, this study clearly illustrates that static and dynamic compressive loading affect IVD cell energy production while cellular responses to mechanical loading were both cell type and compression type dependent.

Degeneration of the intervertebral disc (IVD) has been associated with low back pain, which is one of the major socio-economic problems in the United States. Since IVD is the largest avascular cartilaginous structure in the human body, poor nutrient supply has been suggested as a potential mechanism for IVD degeneration. Biosynthesis of extracellular matrix is an energy demanding process which is required to maintain tissue integrity [1]. Cells consume glucose and oxygen to produce adenosine triphosphate (ATP), the main energy form in cells. Glycolysis, the primary metabolic pathway for production of ATP in IVD cells, is strongly regulated by local oxygen concentration and pH (which is governed by lactate concentration) [2]. Therefore, energy metabolism may play an important role in the malnutrition pathway leading to IVD degeneration. The objective of this study was to investigate the effect of mechanical loading on cellular energy metabolism in whole disc and in agarose gels.