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 5 0.0016). The increase in MMP-9 coincided temporally with the loss of the BMastrocyte 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.Keywords cerebral ischemia; astrocytes; basement membrane; electron microscopy Brain edema and hemorrhagic transformation are major consequences of cerebral ischemic injury. Brain edema is the leading cause of death during the first week after cerebral infarction (Vahedi et al., 2007), and hemorrhagic transformation is a major obstacle of thrombolytic treatment, diminishing its efficacy. Both pathologic conditions are associated with damage to the cerebral microvessels. In addition, microvascular damage may contribute to cell death (Heo et al., 1999). In this regard, protection of the microvessels from ischemic injury could be a major target for specific treatments in acute stroke patients. The cerebral microvessels are a constituent of the blood-brain barrier (BBB), which is composed of microvascular endothelial cells, the basement membrane (BM), astrocyte endfeet, and pericytes (Ballabh et al., 2004). The BM attaches endothelial cells to one side and astrocyte endfeet to the other side. The astrocyte endfeet form an envelope around the blood vessels and are attached to the BM tightly by their adhesion molecules. The BM is composed of extracellular matrix (ECM) molecules such as type IV collagen, laminins, fibronectin, heparan sulfates, and proteoglycans. The integrity of the microvessels is maintained by the presence of an intact BM that provides stru...

Extracellular matrix and matrix receptors in blood–brain barrier formation and stroke

“…In addition, reperfusion results in a fresh supply of leukocytes, which translocate in the CNS triggering a cascade of cytokine release (Wang et al, 2007). This wide variety of oxidative and inflammatory responses results in a multitude of effects, including loss of microvascular integrity, loss of TJ regulation, multi-phasic changes in permeability, proteolytic degradation of BMs, loss of integrins, loss of cell adhesion, edema, extracellular deposition of plasma proteins, and further inflammation (Figure 1) (Hamann et al, 1995; Wang and Lo, 2003; Wang et al, 2007; Sandoval and Witt, 2008; Baumann et al, 2009; Kwon et al, 2009). Notably, these processes all contribute to BBB disruption, and although the exact cause-and-effect relationships of the different pathological changes are hard to establish, they are likely to be interdependent (Sandoval and Witt, 2008).…”

“…However, astrocytes are clearly affected by hypoxia over time. Transmission electron microscopy (TEM) of middle cerebral artery occlusion (MCAO) in rats showed that astrocytic endfeet swell due to osmosis and obstruct the vessel lumen or lose contact with the vessels (Figure 1) (Melgar et al, 2005; Kwon et al, 2009). The percentage of microvascular surface that was covered by astrocytic endfeet reduced gradually from 94% in sham-operated animals to 74% after 4 hours and 16% after 16 hours, to almost non-existent after 48 hours (Kwon et al, 2009).…”

Interendothelial Claudin-5 Expression Depends on Cerebral Endothelial Cell–Matrix Adhesion by β1-Integrins

“…However, during focal ischemia endothelial cell demise is infrequent, suggesting the stability of endothelial cell-matrix adhesion (Tagaya et al, 1997). In contrast, focal ischemia induces detachment of astrocyte end-feet from the basal lamina (Garcia et al, 1971;Milner et al, 2008b;Kwon et al, 2009).…”

Toward the Neurovascular Unit A Journey in Clinical Translation

“…28 Other groups have described the generation of pro-MMP-9 in rodent models of ischemic injury. [29][30][31][32] Heo et al [33][34][35] recently showed graphically the very similar phenomenon of MMP-9 appearance and the loss of basal lamina electron density in rodents.…”