Effects Of Simulated Microgravity On Tissue Structure And Matrix Metalloproteinase Expression In Lungs Of Rhesus Macaques

Objective To investigate the effects of simulated weightlessness on the tissue structure and the m RNA and protein expression of MMP-1, 2, 3, 7, 8, 9, 11, 12 and 13 in lung of rhesus macaque.Methods Using the common ground model of simulated microgravity,-10 degree head-down-tilt was used to simulated weightlessness in a special device. Fifteen healthy young male rhesus monkeys were randomly divided into three groups, five in each group, which are the control group: 6 weeks of free activities in the cage; the simulated microgravity group:- 10 degrees head-down-tilt in the special simulated microgravity device for six weeks; the recovery group: in the same device living for 6 weeks, followed by 4 weeks of free activities in the cage. HE staining and transmission electron microscopy(TEM) were used to observe the histopathological and ultra-structure changes of pulmonary tissues. The m RNA expression of MMP-1, 2, 3, 7, 8, 9, 11, 12 and 13 in lung tissues were detected by real–time fluorescence quantitative PCR(FQ-PCR). According to the changes of m RNA expression, immunoblotting(Western blotting, WB) was used to examine the expression of MMP2, MMP7 and MMP9 protein in lung tissue. And immunohistochemical staining was used to observation the location of MMP2, MMP7 and MMP9 in lung tissue.Results HE staining results showed that the lung tissue structure of control group rhesus monkeys were integrated, and there were no pathological changes. While, the histopathological changes, alveolar septal thickening, alveolar fusion, alveolar and interstitial lymphocytic infiltration, were observed in simulated microgravity group and recovery group. Besides, the recovery group’s histopathological changes were lighter than the simulated microgravity group’s. The ultrastructure examination showed that there were smaller and irregular nucleus of alveolar epithelial cells, increased number and volume of the lamellar bodies, enhanced evacuation, part of vacuolar degeneration and mitochondrial swelling in the simulated microgravity group and the recovery group. FQ-PCR revealed that there were no m RNA expression of MMP-1, 3, 8, 11, 12 and 13 in the lung tissues of each group, but it can express the MMP-2, 7 and 9. In addition, the test results also showed that simulated microgravity can induce the increased expression of MMP2 m RNA in lung tissue of rhesus monkey, but between each group, there were no statistical significance differences(F =2.56, P > 0.05); can cause the decreased expression of MMP7 m RNA, the difference between the simulated microgravity group and the control group is statistical significance(F=4.33, P < 0.05), there were no statistical significance differences between other groups((F=4.33, P < 0.05)); can cause the decreased expression of MMP9 m RNA, but between each group, there were no statistical significance differences(F=0.85, P > 0.05). Immunohistochemical staining results showed that the lung tissues of each group can express MMP-2, 7 and 9. Positive cells mainly distributed across the bronchial epithelial cells, vascular endothelial cells, alveolar epithelial cells, cytoplasm and nucleus, either in cytoplasm or in nucleus, mainly in cytoplasm. Western blotting results showed that rhesus lung tissue can express or weakly express MMP2, MMP7 and MMP9 protein, semi quantitative analysis showed that the expression of MMP2 and MMP7 protein in the lung tissue of rhesus monkeys induced by simulated microgravity were increased, the expression of MMP9 protein was decreased.Conclusion Simulated microgravity can cause the monkey lung tissue pathology and ultrastructural changes. And also, simulated microgravity can induce enhanced expression of MMP2, MMP7 protein in rhesus lung tissue, decreased the expression of MMP9 protein, which may participate in the pathology and ultrastructural injury process under simulated microgravity conditions.