Abstract 19446: Role of miR-181 Family in the Heart: A Tale of Two Intracellular Compartments

Abstract

Recent reports suggest that mi(cro)RNAs, non-coding RNAs, can regulate numerous human genes. miRNAs play an important role in physiologic and pathologic processes of cardiovascular health. We identified a nuclear encoded miRNA (miR-181c) that translocates into mitochondria to regulate a mitochondrial gene, and ultimately affects mitochondrial function. To investigate how miR-181c leads to cardiac injury, we designed miR-181-sponges, RNA molecules with ten repeated complimentary miR-181 “seed” sequences, and generated a set of stable-H9c2 cells by transfecting either a scrambled- or the miR-181-sponge-sequences. Sponge-H9c2 showed a significant decrease in ROS production and reduced basal mitochondrial respiration, and significant protection against Doxorubicin-induced oxidative stress. However, chronic down-regulation of the entire miR-181 family also stimulates PTEN expression, and thus the sponge decreased PI3K signaling. Thus, protection against Doxorubicin is enhanced when we treated sponge-H9c2 with siRNA against PTEN. We hypothesize that miR-181a/b targets PTEN in the cytosol and miR-181c targets mt-COX1 in the mitochondria. To extend this finding, miR-181a/b-/- and miR-181c/d-/- mice were used. miR-181a/b-/- shows a significant decrease in cardiac function at baseline compared to both miR-181c/d-/- and WT groups. Basal mitochondrial ROS production was significantly decreased in miR-181c/d-/- compare to WT or miR-181a/b-/-. Using both Electron Microscopy and light-scattering at 540 nm by isolated heart mitochondria, we found that the mitochondria are smaller in the miR-181c/d-/- , and genomic DNA-qPCR showed the number of mitochondria was markedly higher in the miR-181c/d-/- heart compared to the WT or 181a/b-/- groups. miR-181c/d-/- showed a significant decrease, while miR-181a/b-/- showed a significant increase in infarct size compared to WT, when the hearts were challenged with ischemia-reperfusion injury. Taken together, the miR-181 family regulates important signaling pathways in oxidative stress, notably with detrimental results by targeting mt-COX1 (miR-181c), or with protection by targeting PTEN (miR-181a/b).