MicroRNA-223 is neuroprotective by targeting glutamate receptors

Stroke is a major cause of mortality and morbidity worldwide. Extracellular glutamate accumulation leading to overstimulation of the ionotropic glutamate receptors mediates neuronal injury in stroke and in neurodegenerative disorders. Here we show that miR-223 controls the response to neuronal injury by regulating the functional expression of the glutamate receptor subunits GluR2 and NR2B in brain. Overexpression of miR-223 lowers the levels of GluR2 and NR2B by targeting 3′-UTR target sites (TSs) in GluR2 and NR2B, inhibits NMDA-induced calcium influx in hippocampal neurons, and protects the brain from neuronal cell death following transient global ischemia and excitotoxic injury. MiR-223 deficiency results in higher levels of NR2B and GluR2, enhanced NMDA-induced calcium influx, and increased miniature excitatory postsynaptic currents in hippocampal neurons. In addition, the absence of MiR-223 leads to contextual, but not cued memory deficits and increased neuronal cell death following transient global ischemia and excitotoxicity. These data identify miR-223 as a major regulator of the expression of GluR2 and NR2B, and suggest a therapeutic role for miR-223 in stroke and other excitotoxic neuronal disorders.MicroRNAs (miRNAs) are small noncoding endogenous RNA molecules that repress their target mRNA through complementary binding in the message 3′-UTR (1). MiRNAs play important roles in multiple physiological processes such as cell death and survival, cellular response to stress, stem cell division, and pluripotency (2). MiRNAs also play important roles in disease processes including cancer (3), cardiovascular disease (4), and neurodegenerative diseases (5). Due to their small size, relative ease of delivery, and sequence specificity in recognizing their targets, miRNAs are promising therapeutic targets (6).Stroke is the second major killer and the leading cause of disability worldwide (7). Overstimulation of the glutamate receptor (glutamate excitotoxicity) is a major mechanism for neuronal cell death during stroke, central nervous system (CNS) trauma, and chronic neurodegenerative disorders. Excessive calcium influx through the N-methyl-d-aspartate receptors (NMDARs) results in abnormally high intracellular calcium concentrations leading to lethal consequences. This calcium influx through the NMDAR requires membrane depolarization induced by sodium influx through 2-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) (8). Whereas accumulating evidence indicates that phosphorylation and trafficking play important roles in regulation of glutamate receptor signaling, the molecular mechanisms regulating glutamate receptor expression levels remain unexplored. Recent work suggests that the miRNA pathway regulates the AMPAR subunit GluR2 expression (9, 10). In hippocampal neurons, MiR-125b has been shown to regulate the NMDAR subunit NR2A (11). However, miRNA regulation of glutamate receptor expression remains poorly characterized. Identifying miRNAs that could regulate the glutamate receptor provide the opportunity for treating stroke and chronic neurodegenerative diseases. Recent success in therapeutic targeting of small RNAs in animal models and in humans emphasizes such treatment strategies (6).MiR-223 is highly expressed in bone marrow and neutrophils where it plays an important role in regulating granulopoeisis and neutrophil function (12, 13). MiR-223 is deregulated in acute myeloid leukemia (14, 15). We find that miR-223 is also expressed in the nervous system and we demonstrate that miR-223 controls the expression and function of GluR2 and NR2B subunits of the glutamate receptor. Using in vitro and in vivo models of ischemic reperfusion brain injury and excitotoxic neuronal death we show that miR-223 is a neuroprotective microRNA.