An in vitro study of dynamic cyclic compressive stress on human inner annulus fibrosus and nucleus pulposus cells

Abstract

Background context Intervertebral disc (IVD) cells exhibit diverse biologic responses to compressive stress depending on the compressive stress type, magnitude, duration, and anatomic zone of IVD cell origin. The previous studies mainly focused on the effects of compressive stress on animal IVD tissue. Few studies have investigated the response of human IVD tissue to compressive stress. Purpose To assess the effect of dynamic cyclic compressive stress on biosynthesis of collagen and glycosaminoglycan of human inner annulus fibrosus (AF) and nucleus pulposus (NP) cells. Study design/setting Observation of moderate and high magnitudes of compressive stress on human IVD cell biosynthesis. Patient sample Human IVD of adolescent idiopathic scoliosis case undergoing thoracoscopic discectomy and fusion was collected. Outcome measures Cell morphology, cell proliferation assay, as well as collagen and glycosaminoglycan content were examined in vitro. Methods Intervertebral discs were cultured under 0.2 or 0.4 MPa of compressive stress at 1 Hz for 2 hours twice a day up to 7 days. These were compared with samples unloaded. The analysis was done via electron microscopy examination, cell proliferation assay, as well as collagen and glycosaminoglycan content analysis. Results Collagen and glycosaminoglycan content in the inner AF and NP cells cultured under 0.2 MPa of compressive stress was significantly higher than that in the control cells but was significantly lower than that in the control cells under 0.4 MPa of compressive stress. The number of endoplasmic reticulum in the inner AF and NP cells cultured under 0.2 MPa of compressive stress was significantly higher than that in the control cells but was significantly lower than that in the control cells under 0.4 MPa of compressive stress. Conclusion These findings imply that biosynthetic characteristics of human inner AF and NP cells may vary under varying degrees of compressive stresses, which may result in varying amounts of extracellular matrix being secreted.