Ischemic injury to the deep white matter is frequently seen in patients with vascular cognitive impairment (VCI). Brain tissue from patients with VCI has matrix metalloproteinases (MMPs) in regions of myelin loss. VCI patients have increased MMPs in the cerebrospinal fluid. The MMPs may be important factors in the white matter injury. Bilateral carotid artery occlusion (BCAO) leads to opening of the blood-brain barrier (BBB), death of oligodendrocytes (OL), and breakdown of myelin, simulating the pathology of VCI. During the prior grant, we showed that MMPs disrupt tight junction proteins and that tissue inhibitor of metallorproteinases-3 (TIMP-3) induces apoptosis in neurons and oligodendrocytes (OL) in focal ischemia induced by middle cerebral artery occlusion. This suggested that MMPs and TIMP-3 might be important in global ischemia from BCAO. In preliminary studies with the BCAO model in WKY rats, we found that MRI identifies the site of the BBB damage by an increase in apparent diffusion coefficients (ADC). Furthermore, the regions with increased ADC showed extravasation of Evans blue (EB), and vessels with leakage of EB had increased MMP activity related to MMP-2 and MMP-9. Spontaneously hypertensive rats that are stroke prone (SHR/SP) and are fed a hypertensive diet have greater damage to the white matter than WKY, making them a better model to study the pathophysiology of VCI. We hypothesize: 1) that BBB opening by MMPs occurs in SHR/SP during hypoxic/hypoperfusion from BCAO, and 2) that TIMP-3 expression in hypoxic white matter contributes to OL death.
Specific Aim 1 is to characterize the time course and spatial location of the BBB damage induced by hypoxic hypoperfusion after permanent BCAO in SHR/SP. MRI will be used to identify the sites of increased ADC from 3 days to one month, and to correlate the regions with increased BBB permeability to Gadolinium- DTPA as measured with the multiple time graphical method (Patlak plots).
Specific Aim 2 is to determine the factors related to white matter damage, using immunohistochemistry to identify MMPs, TIMP-3 and factors involved in tumor necrosis factor-a (TNF-a death receptor family, such as p55TNFR1. The MRI will be used to guide the tissue studies to measure myelin breakdown by western blot and OL death by stereology of CC-1 immunostained cell. Specfic Aim 3 is to use broad-spectrum MMP inhibitors (MMPIs), BB-94 and BB-1101, to reduce the opening of the BBB, the breakdown of myelin, and OL death. Inflammation plays an important role in VCI and may be the key factor in the slowly progressive forms, such as Binswanger's disease. MMPIs are potential agents to use to reduce the on-going tissue damage.
Vascular cognitive impairment (VCI) is a major problem in the elderly. Disease of the blood vessels from hypertension and diabetes causes inflammation that damages the white matter. This proposal will use animal models of chronic hypoxia to determine the role of matrix metalloproteinases and tissue inhibitors of metalloproteinases in loss of cells in the white matter. Matrix metalloproteinase inhibitors will be studied that have the potential to be used to prevent the death of vulnerable cells in the white matter.
Showing the most recent 10 out of 47 publications
