title: Nuclear miRNA regulates the mitochondrial genome in the heart.
abstract: BACKGROUND
  Mitochondria are semiautonomous cellular organelles with their own genome, which not only supply energy but also participate in cell death pathways. MicroRNAs (miRNAs) are usually 19 to 25 nt long, noncoding RNAs, involved in posttranscriptional gene regulation by binding to the 3'-untranslated regions of target mRNA, which impact on diverse cellular processes.
  
  
  OBJECTIVE
  To determine if nuclear miRNAs translocate into the mitochondria and regulate mitochondrial function with possible pathophysiological implications in cardiac myocytes.
  
  
  RESULTS
  We find that miR-181c is encoded in the nucleus, assembled in the cytoplasm, and finally translocated into the mitochondria of cardiac myocytes. Immunoprecipitation of Argonaute 2 from the mitochondrial fraction indicates binding of cytochrome c oxidase subunit 1 (mt-COX1) mRNA from the mitochondrial genome with miR-181c. Also, a luciferase reporter construct shows that mi-181c binds to the 3'UTR of mt-COX1. To study whether miR-181c regulates mt-COX1, we overexpressed precursor miR-181c (or a scrambled sequence) in primary cultures of neonatal rat ventricular myocytes. Overexpression of miR-181c did not change mt-COX1 mRNA but significantly decreased mt-COX1 protein, suggesting that miR-181c is primarily a translational regulator of mt-COX1. In addition to altering mt-COX1, overexpression of miR-181c results in increased mt-COX2 mRNA and protein content, with an increase in both mitochondrial respiration and reactive oxygen species generation in neonatal rat ventricular myocytes. Thus, our data show for the first time that miR-181c can enter and target the mitochondrial genome, ultimately causing electron transport chain complex IV remodeling and mitochondrial dysfunction.
  
  
  CONCLUSIONS
  Nuclear miR-181c translocates into the mitochondria and regulates mitochondrial genome expression. This unique observation may open a new dimension to our understanding of mitochondrial dynamics and the role of miRNA in mitochondrial dysfunction.
authors.affiliation: Department of Pathology, Cardiovascular Division, Johns Hopkins University, Baltimore, MD 21205.   csteenb1@jhmi.edu.
authors.forename: Samarjit
authors.initials: S
authors.lastname: Das
authors.forename: Marcella
authors.initials: M
authors.lastname: Ferlito
authors.forename: Oliver A
authors.initials: OA
authors.lastname: Kent
authors.forename: Karen
authors.initials: K
authors.lastname: Fox-Talbot
authors.forename: Richard
authors.initials: R
authors.lastname: Wang
authors.forename: Delong
authors.initials: D
authors.lastname: Liu
authors.forename: Nalini
authors.initials: N
authors.lastname: Raghavachari
authors.forename: Yanqin
authors.initials: Y
authors.lastname: Yang
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Wheelan
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Murphy
authors.forename: Charles
authors.initials: C
authors.lastname: Steenbergen
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D054629:Genome, Mitochondrial / Q000235:genetics*; D008297:Male; D035683:MicroRNAs / Q000502:physiology*; D008929:Mitochondria, Heart / Q000235:genetics* / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: C540193:MIrn181 microRNA, human; D035683:MicroRNAs