Cerebrovascular sequelae comprise a critical part of traumatic brain injury (TBI). In the acute phase, damage to the blood-brain barrier (BBB) leads to cerebral edema. In the delayed phase, persisting dysfunction in microvessels impair angiogenesis and neurogenesis. Hence, any attempt to treat TBI must take into account these evolving cerebrovascular mechanisms over time. Our overall hypothesis states that (i) in the acute phase, recombinant annexin A2 binds endothelial cell membrane F-actin that preserves endothelial integrity thus protecting against TBI-induced BBB disruption; and (ii) in the delayed phase, annexin A2 promotes remodeling with enhanced angiogenesis, and concurrently increases vascular-derived trophic factor secretion for promoting endogenous neurogenesis and neurorepair.
Aim 1 : Investigate mechanisms of annexin A2 in early cerebrovascular protection after TBI. We will test temporal profile of BBB permeability and correlate with junction protein expression, and brain edema in vivo TBI model and in vitro endothelial/astrocytes co-cultures. Denatured rA2 or pharmacological inhibitors will be applied to test specific roles of rA2 in binding to F-actin, F-actin stress fiber formation, and permeability modulated signaling pathways.
Aim 2 : Investigate mechanisms of annexin A2 in cerebrovascular remodeling after TBI. We will test temporal profile of angiogenesis by immunohistochemistry. In situ plasmin activity assay will examine vascular fibrinolytic activity; mRNA microarrays will examine expression profiles of vascular endothelium derived angiogenic/anti-angiogenic, and trophic factors in isolated cerebral microvascular fragments. Long-term neurological function will be examined for up to three months post-TBI. In endothelial cultures, we will test rA2 effects and mechanisms in angiogenesis with in vitro angiogenic assays.
Aim 3 : Investigate mechanisms of annexin A2 in promoting vascular-derived trophic factor expression for enhancing endogenous neurogenesis and neurorepair. mRNA microarray will examine expression of neuronal trophic factors in isolated microvascular fragments, immunohistochemistry, RT-PCR and western blots will investigate hippocampus neuron degeneration, neurogenesis in different brain areas, and white matter injury and repair over time after TBI.
After TBI, early BBB disruption and late neurovascular remodeling are two key cerebrovascular therapeutic targets. Endothelial cell membrane protein annexin A2 functions a regulator of endothelial barrier integrity for BBB stabilization, and a pro-angiogenic factor for neurovascular remodeling. By testing our hypotheses, we may be able to develop a novel cerebrovascular targeting therapy to improve clinical outcomes of TBI patients.