Molecular Biological Effects of Weightlessness and Hypergravity on Intervertebral Disc Degeneration

The rate of intervertebral disc degeneration (IVDD) is influenced by environmental factors. Extracellular matrix (ECM) destruction and apoptosis of intervertebral disc cells are major characteristics of IVDD. ECM degradation is closely linked to up-regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMP). This study aimed to elucidate the molecular biological changes during IVDD under conditions of weightlessness and hypergravity.

A total of 120 rabbits were divided randomly into four groups: control group, weightlessness group, hypergravity group, and mixed (hypergravity + weightlessness) group. Tail-suspension was used to simulate a weightless environment, and an animal centrifuge (+7 Gz three times for 60 s) was used to mimic hypergravity conditions. After exposure to the above conditions for 30, 60, and 90 d, respectively, 10 rabbits were selected from each group for immunohistochemical determination of MMP-1, MMP-3, and TIMP-1 expression. TUNEL staining was also carried out to detect apoptotic cells in each group at each time point.

MMP-1, MMP-3, and TIMP-1 were rarely expressed in the control group, but were positively expressed in the other three groups. The strongest expression was in the mixed group at every time point, followed by the hypergravity group, and then the weightlessness group. Cell apoptosis index followed a similar trend to MMPs and TIMP-1 expression.

The results suggested that weightlessness and hypergravity may both aggravate IVDD over time, with hypergravity having a particularly marked effect.Wu D, Zheng C, Wu J, Huang R, Chen X, Zhang T, Zhang L. Molecular biological effects of weightlessness and hypergravity on intervertebral disc degeneration. Aerosp Med Hum Perform. 2017; 88(12):1123-1128.