Gary A. Rosenberg

National Institute of Neurological Disorders and Stroke–Canadian Stroke Network Vascular Cognitive Impairment Harmonization Standards

Background and Purpose— One in 3 individuals will experience a stroke, dementia or both. Moreover, twice as many individuals will have cognitive impairment short of dementia as either stroke or dementia. The commonly used stroke scales do not measure cognition, while dementia criteria focus on the late stages of cognitive impairment, and are heavily biased toward the diagnosis of Alzheimer disease. No commonly agreed standards exist for identifying and describing individuals with cognitive impairment, particularly in the early stages, and especially with cognitive impairment related to vascular factors, or vascular cognitive impairment. Methods— The National Institute for Neurological Disorders and Stroke (NINDS) and the Canadian Stroke Network (CSN) convened researchers in clinical diagnosis, epidemiology, neuropsychology, brain imaging, neuropathology, experimental models, biomarkers, genetics, and clinical trials to recommend minimum, common, clinical and research standards for the description and study of vascular cognitive impairment. Results— The results of these discussions are reported herein. Conclusions— The development of common standards represents a first step in a process of use, validation and refinement. Using the same standards will help identify individuals in the early stages of cognitive impairment, will make studies comparable, and by integrating knowledge, will accelerate the pace of progress.

Matrix Metalloproteinases and TIMPs Are Associated With Blood-Brain Barrier Opening After Reperfusion in Rat Brain

BACKGROUND AND PURPOSE Reperfusion disrupts cerebral capillaries, causing cerebral edema and hemorrhage. Middle cerebral artery occlusion (MCAO) induces the matrix-degrading metalloproteinases, but their role in capillary injury after reperfusion is unknown. Matrix metalloproteinases (MMPs) and tissue inhibitors to metalloproteinases (TIMPs) modulate capillary permeability. Therefore, we measured blood-brain barrier (BBB) permeability, brain water and electrolytes, MMPs, and TIMPs at multiple times after reperfusion. METHODS Adult rats underwent MCAO for 2 hours by the suture method. Brain uptake of 14C-sucrose was measured from 3 hours to 14 days after reperfusion. Levels of MMPs and TIMPs were measured by zymography and reverse zymography, respectively, in contiguous tissues. Other rats had water and electrolytes measured at 3, 24, or 48 hours after reperfusion. Treatment with a synthetic MMP inhibitor, BB-1101, on BBB permeability and cerebral edema was studied. RESULTS Brain sucrose uptake increased after 3 and 48 hours of reperfusion, with maximal opening at 48 hours and return to normal by 14 days. There was a correlation between the levels of gelatinase A at 3 hours and the sucrose uptake (P<0.05). Gelatinase A (MMP-2) was maximally increased at 5 days, and TIMP-2 was highest at 5 days. Gelatinase B and TIMP-1 were maximally elevated at 48 hours. The inhibitor of gelatinase B, TIMP-1, was also increased at 48 hours. Treatment with BB-1101 reduced BBB opening at 3 hours and brain edema at 24 hours, but neither was affected at 48 hours. CONCLUSIONS The initial opening at 3 hours correlated with gelatinase A levels and was blocked by a synthetic MMP inhibitor. The delayed opening, which was associated with elevated levels of gelatinase B, failed to respond to the MMP inhibitor, suggesting different mechanisms of injury for the biphasic BBB injury.

Matrix metalloproteinases in neuroinflammation

Matrix metalloproteinases (MMPs) are a gene family of neutral proteases that are important in normal development, wound healing, and a wide variety of pathological processes, including the spread of metastatic cancer cells, arthritic destruction of joints, atherosclerosis, and neuroinflammation. In the central nervous system (CNS), MMPs have been shown to degrade components of the basal lamina, leading to disruption of the blood‐brain barrier (BBB), and to contribute to the neuroinflammatory response in many neurological diseases. Brain cells express both constitutive and inducible MMPs in response to cellular stress. MMPs are tightly regulated to avoid unwanted proteolysis. Secreted as inactive enzymes, the MMPs require activation by other proteases and free radicals. The MMPs are part of a larger class of metalloproteinases (MPs), which includes the recently discovered ADAMs (a disintegrin and metalloproteinase domain) and ADAMTS (a disintegrin and metalloproteinase thrombospondin) families. MPs have complex roles at the cell surface and within the extracellular matrix. At the cell surface, they act as sheddases, releasing growth factors, death receptors, and death‐inducing ligands, making them important in cell survival and death. Tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors that regulate the activity of the MMPs. Synthetic inhibitors have been developed for the treatment of arthritis and cancer. These hydroxymate‐based compounds have been shown to reduce injury in experimental allergic encephalomyelitis (EAE), experimental allergic neuritis (EAN), cerebral ischemia, intracerebral hemorrhage, and viral and bacterial infections. MPs have both beneficial and detrimental roles; understanding their expression in various CNS insults will allow for the use of MMP inhibitors in the treatment of neurological disorders. GLIA 39:279–291, 2002.

Matrix metalloproteinase-mediated disruption of tight junction proteins in cerebral vessels is reversed by synthetic matrix metalloproteinase inhibitor in focal ischemia in rat.

Matrix metalloproteinases (MMPs) disrupt the blood—brain barrier (BBB) during reperfusion. Occludin and claudins are recently described tight junction proteins (TJPs) that form the BBB. We hypothesized that the opening of the BBB was because of the degradation of TJPs by the MMPs. Spontaneously hypertensive rats had a 90 mins middle cerebral artery occlusion with reperfusion for 2, 3, or 24 h. Matrix metalloproteinases were measured by immunohistochemistry and in situ and gel zymography. Real-time polymerase chain reaction (PCR) measured mRNAs of MMP-2 and −9, furin, membrane-type MMP (MT1-MMP), occludin, and claudin-5. There was opening of the BBB in the piriform cortex after 3 h of reperfusion, and an MMP inhibitor, BB-1101 (30 mg/kg), prevented the opening. At 3 h, in situ zymograms showed gelatinase activity. Zymography and PCR showed greater increases in MMP-2 than in MMP-9. There were increased mRNA and immunohistochemistry for MT1-MMP and furin, which activate MMP-2. Claudin-5 and occludin mRNA expression decreased at 2 h in both hemispheres with fragments of both proteins seen on Western blot by 3 h on the ischemic side; treatment with BB-1101 reversed the degradation of the TJPs. Immunohistochemistry at 3 h showed fragmented TJPs within the endothelial cell clefts. By 24 h, in situ zymography showed gelatinase activity and gel zymography showed elevated levels of MMP-9. Disrupted TJPs previously seen in endothelial cells appeared in the surrounding astrocytes. Our results provide direct evidence that MMPs open the BBB by degrading TJPs and that an MMP inhibitor prevents degradation of the TJPs by MMPs.

Collagenase-induced intracerebral hemorrhage in rats.

Intracranial bleeding is an important cause of brain masses and edema. To study the pathophysiology of intracerebral hemorrhage, we produced experimental hemorrhages in 53 rats and characterized the lesion by histology, brain water content, and behavior. Adult rats had 2 microliters saline containing 0.5 unit bacterial collagenase infused into the left caudate nucleus. Histologically, erythrocytes were seen around blood vessels at the needle puncture site within the first hour. By 4 hours there were hematomas, the size of which depended on the amount of collagenase injected. Necrotic masses containing fluid, blood cells, and fibrin were seen at 24 hours. Lipid-filled macrophages were observed at 7 days and cysts at 3 weeks. Water content was significantly increased 4, 24, and 48 hours after infusion at the needle puncture site and for 24 hours in posterior brain sections. Behavioral abnormalities were present for 48 hours, with recovery of function occurring during the first week. Brain tissue contains Type IV collagen in the basal lamina. Collagenase, which occurs in an inactive form in cells, is released and activated during injury, leading to disruption of the extracellular matrix. Collagenase-induced intracerebral hemorrhage is a reproducible animal model for the study of the effects of the hematoma and brain edema.

Matrix metalloproteinases and their multiple roles in neurodegenerative diseases

Matrix metalloproteinases (MMPs) and proteins containing a disintegrin and metalloproteinase domain (ADAM) are important in neuroinflammation, and recent studies have linked their actions to neurodegenerative disorders. MMPs act as cell-surface sheddases and can affect cell signalling initiated by growth factors or death receptors. Four tissue inhibitors of metalloproteinases (TIMPs) regulate metalloproteinase activity. These proteases increase the permeability of the blood-brain barrier, which can cause oedema, haemorrhage, and cell death. MMPs also participate in tissue repair by promoting angiogenesis and neurogenesis. In vascular cognitive impairment, MMPs change permeability of the blood-brain barrier and might contribute to white matter damage. MMPs and ADAMs might contribute to the formation and degradation of amyloid proteins in Alzheimers disease and cause death of dopaminergic neurons in Parkinsons disease. In this Review, by examining the effects of neuroinflammation, we try to understand the role that MMPs might have in neurodegenerative diseases. Therapeutic strategies that use inhibitors of MMPs could represent potential novel treatments for neurological diseases.

Diverse roles of matrix metalloproteinases and tissue inhibitors of metalloproteinases in neuroinflammation and cerebral ischemia.

Regulation of the extracellular matrix by proteases and protease inhibitors is a fundamental biological process for normal growth, development and repair in the CNS. Matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs) are the major extracellular-degrading enzymes. Two other enzyme families, a disintegrin and metalloproteinase (ADAM), and the serine proteases, plasminogen/plasminogen activator (P/PA) system, are also involved in extracellular matrix degradation. Normally, the highly integrated action of these enzyme families remodels all of the components of the matrix and performs essential functions at the cell surface involved in signaling, cell survival, and cell death. During the inflammatory response induced in infection, autoimmune reactions and hypoxia/ischemia, abnormal expression and activation of these proteases lead to breakdown of the extracellular matrix, resulting in the opening of the blood-brain barrier (BBB), preventing normal cell signaling, and eventually leading to cell death. There are several key MMPs and ADAMs that have been implicated in neuroinflammation: gelatinases A and B (MMP-2 and -9), stromelysin-1 (MMP-3), membrane-type MMP (MT1-MMP or MMP-14), and tumor necrosis factor-alpha converting enzyme (TACE). In addition, TIMP-3, which is bound to the cell surface, promotes cell death and impedes angiogenesis. Inhibitors of metalloproteinases are available, but balancing the beneficial and detrimental effects of these agents remains a challenge.

Cortical spreading depression activates and upregulates MMP-9

Cortical spreading depression (CSD) is a propagating wave of neuronal and glial depolarization and has been implicated in disorders of neurovascular regulation such as stroke, head trauma, and migraine. In this study, we found that CSD alters blood-brain barrier (BBB) permeability by activating brain MMPs. Beginning at 3-6 hours, MMP-9 levels increased within cortex ipsilateral to the CSD, reaching a maximum at 24 hours and persisting for at least 48 hours. Gelatinolytic activity was detected earliest within the matrix of cortical blood vessels and later within neurons and pia arachnoid (> or =3 hours), particularly within piriform cortex; this activity was suppressed by injection of the metalloprotease inhibitor GM6001 or in vitro by the addition of a zinc chelator (1,10-phenanthroline). At 3-24 hours, immunoreactive laminin, endothelial barrier antigen, and zona occludens-1 diminished in the ipsilateral cortex, suggesting that CSD altered proteins critical to the integrity of the BBB. At 3 hours after CSD, plasma protein leakage and brain edema developed contemporaneously. Albumin leakage was suppressed by the administration of GM6001. Protein leakage was not detected in MMP-9-null mice, implicating the MMP-9 isoform in barrier disruption. We conclude that intense neuronal and glial depolarization initiates a cascade that disrupts the BBB via an MMP-9-dependent mechanism.

Immunohistochemistry of matrix metalloproteinases in reperfusion injury to rat brain: activation of MMP-9 linked to stromelysin-1 and microglia in cell cultures

Reperfusion damages the blood-brain barrier (BBB). Matrix metalloproteinases (MMPs) are associated with the opening of the BBB, but their cellular localization and activation mechanisms are uncertain. We used immunohistochemistry to determine the cellular localization of the MMPs in reperfused rat brain, and cell cultures to study their activation. Spontaneously hypertensive rats (SHR) had a 90 min middle cerebral artery occlusion (MCAO) followed by reperfusion for times from 3 h to 21 days. Frozen sections were immunostained with antibodies to gelatinase A (MMP-2), stromelysin-1 (MMP-3), and gelatinase B (MMP-9). Sham-operated control rats showed MMP-2 immunostaining in astrocytic processes next to blood vessels. After 3 h of the onset of reperfusion MMP-2 immunostaining increased in astrocytes. At 24 h immunoreactivity for MMP-3 and MMP-9 appeared. MMP-3 co-localized with activated microglia (Ox-42+) and ischemic neurons (NeuN+). MMP-9 immunostaining was seen at 48 h in endothelial cells, neutrophils, and neurons. At 5 and 21 days intense MMP-2 staining was seen in reactive astrocytes around the ischemic core. Studies of activation of the MMP were done in lipopolysaccharide (LPS)-stimulated astrocyte and microglia cultures. Stimulated astrocytes produced an activated form of MMP-2. When microglia were stimulated, they activated MMP-9. Immunostaining showed MMP-3 in cultures of enriched microglial cells. The hydroxymate-type, MMP inhibitor, BB-1101, blocked the activation of MMP-2 and MMP-9 by LPS in mixed glial cultures. We propose that MMP-2 is normally present in astrocytic end feet, and that during ischemia MMP-9 and MMP-3 are produced. MMP-3 in microglia/macrophages may be activating proMMP-9. Our results show that a differential expression of MMPs by astrocytes, microglia, and endothelial cells at the blood vessels is involved in the proteolytic disruption of the BBB.

Matrix Metalloproteinases in Cerebrovascular Disease

Cerebral ischemia and intracerebral hemorrhage cause extensive damage to neurons, disrupt the extracellular matrix, and increase capillary permeability. Multiple substrates participate in the cellular damage, including free radicals and proteases. Matrix metalloproteinases and serine proteases are two classes of proteases that are normally present in brain in latent forms, but once activated, contribute to the injury process. These enzymes have a unique role in the remodeling of the extracellular matrix and in the modulation of the capillary permeability. Intracerebral injection of the matrix metalloproteinase, type IV collagenase, attacks the basal lamina around the capillary and opens the blood—brain barrier, Extracellular matrix-degrading proteases are induced by immediate early genes and cytokines, and regulated by growth factors. Activity of the matrix metalloproteinases is tightly controlled by activation mechanisms and tissue inhibitors of metalloproteinases. During ischemia and hemorrhage, multiple matrix metalloproteinases and serine proteases are produced along with their inhibitors. These proteolytic enzymes are involved in the delayed injury that accompanies the neuroinflammatory response. Synthetic inhibitors to metalloproteinases reduce proteolytic tissue damage, and may limit secondary neuroinflammation.