Frontiers Media SA
Matrix Metalloproteinases and Blood-Brain Barrier Disruption in Acute Ischemic Stroke
Shaheen E. Lakhan, Annette Kirchgessner, [...], and Aidan Leonard
Abstract
Ischemic
stroke continues to be one of the most challenging diseases in
translational neurology. Tissue plasminogen activator (tPA) remains the
only approved treatment for acute ischemic stroke, but its use is
limited to the first hours after stroke onset due to an increased risk
of hemorrhagic transformation over time resulting in enhanced brain
injury.
In this review we discuss the role of matrix metalloproteinases
(MMPs) in blood-brain barrier (BBB) disruption as a consequence of
ischemic stroke.
MMP-9 in particular appears to play an important role
in tPA-associated hemorrhagic complications. Reactive oxygen species (ROS) can
enhance the effects of tPA on MMP activation through the loss of
caveolin-1 (cav-1), a protein encoded in the cav-1 gene that serves as a
critical determinant of BBB permeability.
This review provides an
overview of MMPs’ role in BBB breakdown during acute ischemic stroke.
The possible role of MMPs in combination treatment of acute ischemic
stroke is also examined.
Keywords: '
MMPs matrix metalloproteinases,
BBB blood-brain barrier,
stroke,
caveolin-1,
ROS reactive oxygen species
Introduction
Stroke is the third leading cause of death in industrialized countries (Lo et al., 2003) and the most frequent cause of permanent disability in adults worldwide (Donnan et al., 2008).
Acute ischemic stroke is the most common form of stroke and results
from sudden blood vessel occlusion by a thrombus or embolism, resulting
in an almost immediate loss of oxygen and glucose to the cerebral
tissue. Although different mechanisms are involved in the pathogenesis
of stroke, increasing evidence shows that ischemic injury and
inflammation account for its pathogenic progression (Muir et al., 2007).
Cerebral ischemia initiates cascades of pathological events, including
vasogenic edema, disruption of the blood-brain barrier (BBB),
intracranial hemorrhage (ICH), astroglial activation, and neuronal
death. This ultimately causes irreversible neuronal injury in the
ischemic core within minutes of the onset (Dimagl et al., 1999).
Despite
advances in understanding the pathophysiology of cerebral ischemia,
treatment options for acute ischemic stroke remain very limited (Donnan
et al., 2008).
Intravenous recombinant tissue plasminogen activator (tPA) remains the
only FDA-approved thrombolytic therapy for reestablishing blood flow and
salvaging brain tissue after acute ischemic stroke (Lijnen and Collen, 1987; National Institute of Neurological Disorders and Stroke rt-PA Stroke Study Group, 1995). By degrading fibrin clots, tPA acts as a thrombolytic agent through the activation of plasminogen to plasmin (Lijnen and Collen, 1987).Although tPA administered within 4.5
h or less of symptom onset improves the functional outcome in patients (Miller et al., 2012; Wardlaw et al., 2012),
it induces a 10-fold increase of symptomatic intracranial hemorrhage
(ICH) (National Institute of Neurological Disorders and Stroke rt-PA
Stroke Study Group, 1995).Furthermore, delayed reperfusion with tPA beyond 3
h is associated with an increased risk of hemorrhagic transformation (HT) with enhanced brain injury (Clark et al., 1999).Moreover, tPA may cause injury to the BBB by activating matrix metalloproteinases (MMPs) (Wang et al., 2003).
Thus, the therapeutic application of tPA is limited to specific clinical settings (National Institute of Neurological Disorders and Stroke t-PA Stroke Study Group, 1997). There is a pressing need to identify new combination therapies that can prevent tPA-associated ICH as well as extend the time window for thrombolysis without reducing its benefits.
Recent
studies suggest that tPA adverse effects are mediated through MMPs, a
family of >20 zinc-dependent enzymes that increase BBB permeability
by degrading components of the extracellular matrix (ECM) and tight
junctions (TJ) in endothelial cells (ECs) (Lapchak et al., 2000; Lijnen, 2001; Briasoulis et al., 2012).
Increased expression and activation of MMPs plays a pivotal role in
thrombolysis-mediated BBB leakage and edema, resulting in intracranial
hemorrhage (Lapchak et al., 2000; Sumii and Lo, 2002). Reactive oxygen species (ROS) and its signaling pathways can enhance the effects of tPA on MMP activation (Harada et al., 2012).
- In this review we provide an overview of the role of MMPs in BBB breakdown during acute ischemic stroke and the potential for MMP inhibition in the treatment of stroke.
Structural Components of the BBB/Neurovascular Unit
The
BBB is a dynamic interface between the peripheral circulation and the
CNS. It controls the influx and efflux of biological substances needed
for the brain metabolic processes, as well as for neuronal function.
Thus, the functional and structural integrity of the BBB is vital in
maintaining brain homeostasis.
The structure of the BBB has been discussed in reviews elsewhere (Sandoval and Witt, 2008; Abbott et al., 2010).
Briefly, the anatomical substrate of the BBB is the cerebral
microvascular endothelium, which together with the closely associated
astrocytes, pericytes, neurons, and the ECM, constitute a “neurovascular
unit” that is essential for the health and function of the CNS (del
Zoppo, 2009).
Cell–cell interactions in the neurovascular unit form the basis for
brain function. Dysfunctional signaling in the neurovascular unit
underlies the basis for disease. Alterations in microvessel integrity
may have other effects within the neurovascular unit that affect
neuronal function. The mechanisms of neurovascular unit response to
stroke are not fully understood. However, any fully effective stroke
therapy must include both prevention of cell death as well as repair of
integrated neurovascular function.
The microcapillary endothelium is composed of TJs and follow a
biphasic time course. Morphologically, BBB opening correlates with a
redistribution of the TJ and AJ proteins from the plasma membrane to the
cytoplasm as well as reorganization of the endothelial actin
cytoskeleton.The extent of BBB disruption is associated with the type, severity, and duration of ischemic insults.
The molecular mechanisms underlying BBB opening are not fully understood, although several MMPs are believed to regulate BBB permeability and function during ischemic stroke (Mun-Bryce and Rosenberg, 1998).
The
expression of MMPs in the adult brain is very low to undetectable, but
clinical and experimental studies have shown that several MMPs are
upregulated and activated after ischemic stroke (Lee et al., 2007; McColl et al., 2008).
MMPs disrupt the BBB by degrading the TJ proteins and basal lamina
proteins, thereby leading to BBB leakage, leukocyte infiltration, brain
edema, and hemorrhage.
Evidence suggests that MMP-2 and MMP-9 play
different roles in BBB disruption during ischemic stroke.
- MMP-2 KO( knock out) does not provide neuroprotection in mouse models of permanent and transient MCAO (Asahi et al., 2001b). Consistently, in vitro data show that MMP-2 is not toxic to neurons in hippocampal slice preparations (Cunningham, 2005).
- In contrast, MMP-9 KO (knock out) provides strong neuroprotection in the same animal models, and in vitro MMP-9 is toxic to neurons in hippocampal slice preparations and in cultured primary cortical neurons (Asahi et al., 2000b).
In support of these data, a clinical study (Lucivero et al., 2007) reported an increase in plasma MMP-2 only in patients with lacunar (mild) stroke early (within 12h)
and this was related to better outcome. In contrast, an increase in
plasma MMP-9 was observed later (at day 7) and related to more severe
stroke.
h)
and this was related to better outcome. In contrast, an increase in
plasma MMP-9 was observed later (at day 7) and related to more severe
stroke.
Matrix metalloproteinases are
thought to have beneficial roles in stroke recovery.
Shortly after an
ischemic insult, a cascade of events is initiated in an attempt to
repair the damage, a process similar to that found in wound healing
(National Institute of Neurological Disorders and Stroke rt-PA Stroke
Study Group, 1995; Wardlaw et al., 2012).
Following injury, blood vessels are dependent on the plasminogen
activator system and
on MMPs for their regeneration (Suzuki et al., 2009).
It may be that a balanced level of MMP activity is important for
vascular remodeling after ischemic brain injury (Yang and Rosenberg, 2011).
Therefore, extended inhibition of MMPs, especially through the use of
broad-spectrum inhibitors, might prove deleterious (National Institute
of Neurological Disorders and Stroke rt-PA Stroke Study Group, 1995; Donnan et al., 2008).
MMP-2 (gelatinase A)
Matrix
metalloproteinase-2 is one of the two described human gelatinases in
the MMP family, named for their ability to proteolytically degrade
gelatine (denatured collagen) (see Table Table11
for a list of MMPs and their putative roles in acute ischemic stroke).
MMP-2 is ubiquitously expressed as a 72-kDa proenzyme and subject to
extensive glycosylation (Klein and Bischoff, 2011).
(KUVA)
h
after reperfusion and increased activation of MMP-2 correlated with the
early opening of the BBB and the degradation of the TJ proteins
claudin-5 and occludin in both cerebral hemispheres (Rosenberg et al., 1992; Yang et al., 2007). Experimental data clearly demonstrated an increase in MMP-2 at 3h,
along with increased expression of the MMP-2 activators, MT1-MMP and
furin.
A synthetic MMP inhibitor (BB-1101) blocked the increase in brain MMP-2 levels, but it did not have any effect on stroke lesion size at 48h after MCAO and had significant adverse effects on neurologic function in rats at 3 and 4weeks after MCAO (Rosenberg et al., 1992, 1998; Yang et al., 2007).
In contrast, direct injection of MMP-2 into the rat brain resulted in the disruption of the BBB with subsequent hemorrhage, and this effect was inhibited by co-administration of TIMP-2 (Rosenberg et al., 1992). Thus, the early degradation of TJ proteins seems to be associated with a marked increase in MMP-2 in the early phase of ischemia.
(KUVA)
- 3 tuntia halvauksesta NNP-2:n aiheuttama BBB läpivuoto
h
after reperfusion and increased activation of MMP-2 correlated with the
early opening of the BBB and the degradation of the TJ proteins
claudin-5 and occludin in both cerebral hemispheres (Rosenberg et al., 1992; Yang et al., 2007). Experimental data clearly demonstrated an increase in MMP-2 at 3h,
along with increased expression of the MMP-2 activators, MT1-MMP and
furin.A synthetic MMP inhibitor (BB-1101) blocked the increase in brain MMP-2 levels, but it did not have any effect on stroke lesion size at 48
h after MCAO and had significant adverse effects on neurologic function in rats at 3 and 4weeks after MCAO (Rosenberg et al., 1992, 1998; Yang et al., 2007).In contrast, direct injection of MMP-2 into the rat brain resulted in the disruption of the BBB with subsequent hemorrhage, and this effect was inhibited by co-administration of TIMP-2 (Rosenberg et al., 1992). Thus, the early degradation of TJ proteins seems to be associated with a marked increase in MMP-2 in the early phase of ischemia.
Suofu et al. (2012)
recently assessed the effects of MMP-2 KO, MMP-9 KO, and MMP-2/9 double
KO (dKO) in protecting against mechanical reperfusion-induced HT and
other brain injuries after the early stages of cerebral ischemia in mice
of the same genetic background.
Both MMP-2 and MMP-9 specifically
attack the type IV collagen, laminin, and fibronectin, which are the
major components of the basal lamina around the cerebral blood vessels.
MCAO was performed and reperfusion was started at 1 or 1.5h after onset of MCAO. Mice were sacrificed 8h
later. Both pro- and active-MMP-2 and MMP-9 levels were significantly
elevated in the early ischemic brain. After the early stages of ischemia
and reperfusion, the hemorrhagic incidence was reduced in the cortex of
MMP-2 KO mice. The hemorrhagic volume was also significantly decreased
in the cortexes of MMP-2 and/or -9 KO mice. In the basal ganglia, MMP-2
KO and MMP-2/9 dKO mice displayed a remarkable decrease in hemorrhagic
volume, but MMP-9 deletion did not protect against hemorrhage. MMP-2
and/or -9 KO mice displayed significantly decreased infarction volume in
both the cortex and striatum, in addition to improved neurological
function. The results suggested that MMP-2 deficiency as well as MMP-2
and MMP-9 double deficiency were more protective than MMP-9 deficiency
alone against HT after the early stages of ischemia and reperfusion.
h after onset of MCAO. Mice were sacrificed 8h
later. Both pro- and active-MMP-2 and MMP-9 levels were significantly
elevated in the early ischemic brain. After the early stages of ischemia
and reperfusion, the hemorrhagic incidence was reduced in the cortex of
MMP-2 KO mice. The hemorrhagic volume was also significantly decreased
in the cortexes of MMP-2 and/or -9 KO mice. In the basal ganglia, MMP-2
KO and MMP-2/9 dKO mice displayed a remarkable decrease in hemorrhagic
volume, but MMP-9 deletion did not protect against hemorrhage. MMP-2
and/or -9 KO mice displayed significantly decreased infarction volume in
both the cortex and striatum, in addition to improved neurological
function. The results suggested that MMP-2 deficiency as well as MMP-2
and MMP-9 double deficiency were more protective than MMP-9 deficiency
alone against HT after the early stages of ischemia and reperfusion.MMP-3 (stromelysin-1)
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