The Mechanism Of White Matter Injury In Spontaneously Hypertensive Rat

Spontaneously hypertensive rat (SHR) is the ideal animal model for the study of primary hypertension and the cognitive impairment caused by hypertension. Little research has been done on the white matter changes in SHR. White matter changes were seen in a variety of CNS disorders. In clinic cases, some white matter pathological changes, such as reduced axonal, demyelization, gliosis, can easily be seen in the majority of patients with hypertension. The myelin basic protein (MBP), neurofilament (NF) and glial fibrillary acidic protein (GFAP) are stained to show their expressions in white matter of SHR. At the same time, as the inflammatory is involved in the occurrence of many CNS lesions, this study also detected the expressions of Toll-like receptor4(TLR-4), monocyte chemotactic protein-1(MCP-1) and vascular cell adhesion molecule-1(VCAM-1) in the white matter of SHR in order to investigate the role of inflammatory in the changes of white matter of SHR. Analyzing of the mRNA expression of matrix metalloproteinases(MMPs) and their inhibitors(TIMPs) in their white matter, we investigated the mechanism of the leukoaraiosis caused by blood-brain barrier damage.Experimental animals are male SHR and Wistar-Kyoto rat (WKY),14weeks old, in standard animal husbandry conditions until40-week of age.18male SHR were treated as the experimental group, the same age seven male WKY rats as a control group. We took the animal brain tissue for HE staining and immunohistochemical staining to observe the pathological changes and MBP, NF and GFAP changes. We detected mRNA expression levels of MMP-9, MMP-2and TIMP-1in the white matter. We also took the fresh white matte at the same time to detect the mRNA expression levels of TLR-4, MCP-1and VCAM-1by using real-time PCR. Independent samples t-test was used for statistical analysis.There is obvious injury in the white matter of40-week-old SHR. The HE staining shows that the white matter of SHR, especially around the ventricular, has a change usually called leukoaraiosis. Compared to WKY rats, the immunohistochemical staining results of GFAP, NF, MBP show that GFAP content in SHR white matter increase, while the other two indicators decrease, suggesting that, in the SHR white matter, there is significantly reduce in the number of nerve fibers, but a proliferation of astrocytes. In SHR white matter regions, the mRNA expression levels of TLR-4, MCP-1, VCAM-1are3.35,3.82and3.46times compared to WKY rat, indicating that their expressions in the SHR white matter are significantly increased (P<0.05). According to the HE staining,18SHR are divided into mild group (n=12) and severe group (n=6) by the degree of leukoaraiosis. To compare the2-ΔΔCt value of TLR-4, MCP-1of VCAM-1between two groups, the expressions of TLR-4, MCP-1, VCAM-1in severe group are higher (P<0.05). In the white matter regions of SHR, the mRNA expression levels of TIMP-1, MMP-9, and MMP-2increased. TIMP-1and MMP-2increased significantly (P<0.05), the expression of MMP-9was no significant difference (P>0.05).The inflammatory response is also involved in the pathogenesis of chronic CNS diseases. The increase of TLR-4, MCP-1, and VCAM-1mRNA expression in SHR white matter associate with the severity of white matter damage. The long-term hypertension status causes the atherosclerosis in the small brain vascular of SHR, followed by chronic diffuse hypoxic ischemic of brain tissue. White matter of the relatively poor blood supply is the first to be affected and changed. Innate immune involved in SHR white matter injury occurred. In this study, we found that, relative to WKY, leukoaraiosis is common in the white matter (periventricular and corpus callosum, internal/external capsule) of40-week-old SHR. However, our results also reflect the severity of the white matter change in the same-age SHR is not consistent. We found that inflammatory involve in the pathophysiological process of SHR white matter damage, and the expression levels of inflammation related factors are related with the severity of SHR white matter damage. Therefore the detection of inflammatory markers (such as MCP-1, sVCAM-1) is a more viable method to asses the degree of white matter damage of SHR. The BBB damage caused by MMPs involved in the SHR white matter lesions in the pathophysiological process.