Ultrastructural changes of microvascular basement membrane and correlationship with MMP-9 expression in rat model with chronic cervical cord compression

English Keywords:Basement membrane  Chronic spinal cord compression  Ultrastructure  MMP-9  Rat

English Abstract:

  【Abstract】 Objectives: To investigate the temporal ultrastructural changes of microvascular basement membrane(BM) and basement membrane astrocyte contacts(BM-AC) in rat model with chronic cervical cord compression, and to explore their correlation with the expression of matrix metalloproteinase-9(MMP-9). Methods: 72 SD rats were randomly divided into the control group(n=36) and the experimental group(n=36). In the control group, C5 left semi-laminectomy was performed in each rat. In the experimental group, a water-absorbable polyurethane polymer was implanted into C6 left epidural space after C5 left semi-laminectomy. The Basso Beattie Bresnahan(BBB) score was used to evaluate the neurological function. HE staining, immumohistochemical staining and transmission electron microscopy(TEM) were performed at 1 day, 14 days, 21 days, 28 days, 42 days and 70 days after modeling to observe the changes of morphology, MMP-9 expression and ultrastructural changes of BM and BM-AC. Results: According to the BBB score, there was no significant difference between each time point in the control group and one day after modeling in the experimental group, neurological function in the experimental group showed an obvious decline from 14 days to 70 days after modeling(P<0.05). HE staining showed intact spinal cords at each time point in the control group. In the experimental group, a mild edema in white matter without spinal cord compression was shown at 1 day after modeling. The compressive deformation of spinal cord, vascular proliferation in grey matter, edema in white and grey matter and the fragmetation of nucleus in neurons were showen at 14 days after modeling. The damage was aggravated at 21 days and 28 days after modeling. At the 42th day after modeling, decreasing of edema in the spinal cord, intramedullary cavity, reducing number of motor neurons in the front foot of spinal cord, sparse cytoplasm, shrinking nucleus, reducing number of synapsis, sparse nerve fibers, the thinner layer of myelin were found. At the 70th day in the experimental group, edema in the white matter, the fragmetation of nucleus in neurons, focal hyperplasia of glial cells, increasing number of neurons were shown. The immunohistochemical staining displayed that MMP-9 was weakly expressed in the control group, and the same results were found at 1 day and 70 days after modeling in the experimental group. Strong expression of MMP-9 was found at 14 days and 28 days after modeling in the experimental group, strongest expression at 21 days after modeling, and moderate expression at 42 days after modeling in the experimental group. The proportion of BM-AC and electron density of BM in the experimental group decreased significantly at 14-28 days after modeling, and improved since the 42nd day after modeling(including the 70th day), but were still significantly lower than those in the control group(P<0.05). There was no significant difference between each time point in the control group and 1 day after modeling in the experimental group. MMP-9 expression was negatively correlated with the proportion of BM-astrocyte contacts(r=-0.664, P<0.001) and the BM density(r=-0.892, P<0.001). Conclusions: The BM and BM-AC are damaged after chronic cervical cord compression and rehabilitated incompletely at late stage. MMP-9 may affect the integrity of blood-spinal cord barrier by de?鄄grading the BM and BM-AC after spinal cord compression.