Abstract 329: δ-Opioid Receptor Mediated Regulation of Cortical MicroRNAs in the Rat Under Hypoxia

Cardiovascular disorders may reduce blood/oxygen supply to the brain, causing serious neurological disabilities. Activation of the delta-opioid receptor (DOR) induces cortical protection against hypoxic/ischemic insults. However, the mechanism underlying DOR protection is largely unclear yet. We have recently found that DOR activation modulates microRNA expression in the kidney exposed to hypoxic stress, suggesting that DOR protection may involve a microRNA mechanism. To determine if the microRNAs expressed in the cortex mediate DOR neuroprotection, we examined nineteen microRNAs, that are previously identified as hypoxia- and DOR-regulated microRNAs in the kidney, in the cortex treated with DOR activation in hypoxic condition. Total RNA for qPCR was isolated from the cortex of control or hypoxic rats as well as those animals treated with UFP-512, a potent and specific DOR agonist. Of the 19 microRNAs tested, 17 were significantly altered by hypoxia and/or DOR activation with the direction and amplitude dependent on hypoxic duration and times of DOR treatment. Several microRNAs such as miR-29b, 101b, -298, 324-3p, -347 and 466b were significantly depressed by hypoxia for 24 hours. The similar changes were seen in normoxic condition 24 hours after DOR activation with one time treatment of UFP-512. In contrast, some miRNAs were more tolerant to hypoxic stress and did not show any significant reduction until 5-days (e.g., miR-31 and -186) or 10-days (e.g., miR-29a, let-7f and -511), while DOR activation had differential effects on these miRNAs. Moreover, some miRNAs like miRs-363* and -370 were affected only by the combination of hypoxia and DOR treatment, with reductions greater than 70% in 5-day group. These data suggest that cortical microRNAs are significantly altered in response to hypoxia with differential hypoxia sensitivity among them and that DOR activation is able to modify, enhance or resolve the changes in microRNAs that are predicted to target ion transport, HIF, axonal guidance, free radical signaling, apoptosis and many other functions.