Ultrastructural and temporal changes of the microvascular basement membrane and astrocyte interface following focal cerebral ischemia

Abstract

Microvascular integrity is lost during cerebral ischemia. Detachment of the microvascular basement membrane (BM) from the astrocyte, as well as degradation of the BM, is responsible for the loss of microvascular integrity. However, their ultrastructural and temporal changes during cerebral ischemia are not well known. Male Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO) for 1, 4, 8, 12, 16, 20, and 48 hr. By using transmission electron microscopy, the proportion of intact BM-astrocyte contacts and electron densities of the BM were measured from five randomly selected microvessels in the ischemic basal ganglia. Their temporal changes and associations with activities of the matrix metalloproteinases (MMPs) were investigated. The intact portion of the BM-astrocyte contacts was decreased significantly within 4 hr and was rarely observed at 48 hr after MCAO. Decreases in the electron density and degradation of the BM were significant 12 hr after MCAO. The intact BM-astrocyte contacts and the mean BM density showed a significant positive correlation (r = 0.784, P < 0.001). MMP-9 activity was correlated negatively with the intact BM-astrocyte contacts (r = -0.711, P < 0.001) and with the BM density (r = -0.538, P = 0.0016). The increase in MMP-9 coincided temporally with the loss of the BM-astrocyte contacts and a decrease in the BM density. Ultrastructural alterations occurring in the microvascular BM and its contacts with astrocyte endfeet were temporally associated in cerebral ischemia. Time courses of their alterations should be considered in the treatment targeted to the microvascular BM and its contact with astrocytes.