Harnessing Endogenous Neuroprotection Following ICH

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 DESCRIPTION (provided by applicant): At present, there are no consistently effective treatments available for intracerebral hemorrhage (ICH), a common and often fatal stroke subtype. Secondary brain injury after ICH is known to involve disruption of the blood-brain barrier (BBB), followed by formation of brain edema, which is indicative of a poor clinical prognosis. Interestingly, pathological processes, such as ICH, also elicit endogenous defense mechanisms that antagonize the damaging events and mediate repair. We propose to investigate how the brain protects itself from ICH-induced neurovascular injury, and subsequently, augment these protective mechanisms as an innovative and specific treatment strategy. Based on our preliminary observations, we suggest that dopamine-induced stimulation of the dopamine receptor D2 (DRD2) may confer such endogenous protection following ICH. We found increased dopamine levels in the brain of mice subjected to experimental ICH. Furthermore, pharmacological stimulation of the DRD2 attenuated BBB disruption, brain edema, and neurological deficits following ICH. The Gβγ subunit of the DRD2 has been shown to activate extracellular-signal-regulated kinase1/2 (ERK1/2), which in turn activate αB-crystallin (CRYAB), a widely expressed small heat shock protein. CRYAB functions as a molecular chaperone, preventing vital cellular proteins from stress-induced degradation. We believe that CRYAB can protect endothelial barrier-forming tight junction and adherens junction proteins, thus preserving BBB integrity following ICH. We hypothesize that DRD2 stimulation will attenuate BBB disruption, and consequent brain edema formation through Gβγ/ERK-induced activation of CRYAB, thereby improving short- and long-term neurological outcomes after ICH. We will utilize intrastriatal injections of either collagenase (causing spontaneous vessel rupture) or autologous whole blood to induce ICH in rodents. We will measure the concentrations of dopamine and its receptors in the brain of ICH animals. Following that, we will establish the role of DRD2 and its downstream targets in providing neurovascular protection following ICH. Our specific Aim 1 will investigate the role of endogenous and pharmacological DRD2 stimulation in reducing BBB disruption, brain edema formation, and neurological deficits following ICH. Specific Aim 2 will investigate the proposed mechanism of DRD2-induced Gβγ/ERK/CRYAB signaling following ICH. The long-term goals of this proposal are to establish DRD2 agonism as a novel treatment strategy for ICH, demonstrate its underlying protective mechanism, and provide a basis for clinical translation and implementation of DRD2 agonists in patients suffering from ICH.