Background: The blood-brain barrier (BBB) is a crucial interface between the central nervous system (CNS) and the circulatory system that maintains cerebral homeostasis by selectively allowing entry of blood solutes into the CNS. BBB dysfunction has been observed in cerebrovascular diseases and neurodegenerative disorders such as stroke. The BBB is opened during stroke, having negative impacts on stroke outcomes. Mitochondria are key players in this abnormal opening of the BBB, and decreased cytochrome c (CYC) levels have been shown in the mitochondrial fraction in stroke. We have recently demonstrated miR-34a regulates the BBB by targeting CYC in vitro.
Objective: To investigate the role of miR-34a in stroke and verify its target CYC in vivo.
Methods and Results: Using a murine transient middle cerebral artery occlusion (tMCAO) model, we demonstrate elevated miR-34a expression in serum and primary cerebral endothelial cells (CECs) from stroke mice. We report that deficiency of miR-34a significantly reduces BBB permeability and improves stroke outcomes. CYC is decreased in the ischemic hemisphere from wild-type (WT) but not miR-34a-/- mice following stroke reperfusion. Uncoupling of electron flow by a pharmacological inhibitor Carbonyl-cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) compromises mitochondrial oxidative phosphorylation (MOP) in cultured CECs and worsens infarction in stroke mice.
Conclusions: Our study provides the first description of miR-34a and electron flow affecting stroke outcomes, which could lead to a revision of current miR-34a targets and may lead to discovery of new mechanisms and treatments for cerebrovascular and neurodegenerative diseases such as stroke and Alzheimer’s disease.
Key words: Blood-brain barrier; Stroke; MiR-34a; Mitochondria; Cytochrome c.
Non-standard Abbreviations and Acronyms: CEC: cerebral endothelial cell CYC: cytochrome c FCCP: Carbonyl-cyanide-4-(trifluoromethoxy)phenylhydrazone MOP: mitochondrial oxidative phosphorylation tMCAO: transient middle cerebral artery occlusion