Molecular Pathological Studies On Carotid Atherosclerotic Stenosis (CASS)

Background: Carotid atherosclerotic stenosis is one major reason for brain ischemic stroke. It is the basis for curing this disease to probe the aspects of molecular pathogenesis. Previous pathological studies on atherosclerosis showed that there existed large amount of apoptosis and lysis of extracelluar matrix (ECM), in addition to intima hyperplasia, lipid accumulation and infiltration of inflammation cells in atherosclerotic plaque. Apoptosis in vascular smooth muscle cells(VSMC) results in reduction of the synthesis of ECM and thinning of the fibrous cap, while the lysis of ECM by MMPs renders plaque to vulnerability and rupture. The instability of carotid plaque is the main cause of clinical events such as TIA. It is of important value to probe the molecular pathogenesis on atherosclerosis in prevention and treatment for ischemic brain vascular diseases from the investigation in apoptosis and the degradation of ECM .Objectives: To investigate (1) BAX gene expression, (2) Bcl-2 gene expression, (3) MMP-8 expression in different types of carotid plaque, and examine the relationship between gene expression and atherosclerotic plaque instability, which was the main cause of clinical ischemic events. Materials and Methods: 42 human carotid plaque specimens obtained during carotid endarterectomy were divided into stable/fibrous(n=19) and unstable/vulnerable (n=23) groups based on histopathological studies(HE staining), 8 aortic arteries with their branches from hepatic transplantation donors were taken as control group. BAX was detected by TUNEL, immunohistochemistry(IHC)stainning and in situ hybridization(ISH) (n=25, statble 13/unstable 12) , while Bcl-2 gene and MMP-8 expression were detected through IHC and ISH.Results: There were 20 cases of TUNEL (+) cells in unstable plaque and 10 cases of TUNEL (+) cells in stable plaque, which was seen in neclus of smooth muscle cells and macrophages. There were 20 and 11 cases of BAX(+) cells in vulnerable plaque while 8 and 5 cases in fibrous plaque through IHC and ISH, respectively. Bcl-2 gene expression, which was expressed in smooth muscle cells(VSMC) and endothelial cells(EC) and macrophages(MP) as well as foam cells, was detected in 20 and 9 cases of unstable plaque while 11 and 6 cases in stable plaque by IHC and ISH, correspondingly. Finally, MMP-8 expression with IHC and ISH, which was expressed in SMCs and macrophages and also foam cells, wasdetected in 19 and 12 cases in vulnerable plaques while 7and 5 cases in fibrous plaques, respectively. The expression intensity of all the three parameters was up-regulated in vulnerable than in fibrous groups (p<0.01), and no expression was found in control group. Conclusions: (1) The expression of BAX, Bcl-2 and MMP-8 was up-regulated in vulnerable carotid plaques than in fibrous ones, especially in shoulder region where rupture was incline to happen. (2) The expression rate of Bcl-2, which was one of the elements for maintaining plaque stability, was higher than papers reported abroad in the same period. It may be related to ethnic race difference in genotypes. (3)Apoptosis in VSMC and lysis of ECM by MMP-8, which may result in ECM reduction and ECM degradation working together, renders carotid plaque to fragility and rupture. (4)Apoptosis of smooth muscle cells may facilitate the infiltration of the macrophages and lymphocytes from the circulation and worsen the inflammation reaction in atherosclerosis through releasing inflammation cytokines. (5) The lysis function of MMP-8 to ECM may modulate the primary stenosis in atherosclerosis and restenosis after carotid endarterectomy or angioplasty through overexpression of ECM by VSMC. It may provide the targets for future studies and gene therapy by controlling the function in different stage of atherosclerosis and restenosis.