title: Inhibiting p90 ribosomal S6 kinase prevents (Na+)-H+ exchanger-mediated cardiac ischemia-reperfusion injury.
abstract: BACKGROUND
  Pharmacological and genetic studies indicate that the (Na+)-H+ exchanger isoform 1 (NHE1) plays a critical role in myocardial ischemia and reperfusion (I/R) injury. We found that p90 ribosomal S6 kinase (RSK) phosphorylated serine 703 of NHE1, stimulating 14-3-3 binding and NHE1 activity. Therefore, we hypothesized that inhibiting RSK in cardiomyocytes would prevent NHE1 activation and decrease I/R-mediated injury.
  
  
  RESULTS
  To examine the role of RSK in vivo, we generated transgenic mice with cardiac-specific overexpression of dominant negative RSK (DN-RSK-TG). DN-RSK-TG hearts demonstrated normal basal cardiac function and morphology. However, myocardial infarction (left coronary artery occlusion for 45 minutes) in DN-RSK-TG hearts was significantly reduced at 24 hours of reperfusion from 46.9+/-5.6% area at risk in nontransgenic littermate controls to 26.0+/-4.2% in DN-RSK-TG (P<0.01). Cardiomyocyte apoptosis was significantly reduced after I/R in DN-RSK (0.9+/-0.2%) compared with nontransgenic littermate controls (6.2+/-2.6%). Importantly, activation of RSK and interaction of 14-3-3 with NHE1, necessary for agonist-stimulated NHE1 activity, were increased by I/R and inhibited by 70% in DN-RSK-TG (P<0.01). Next, we transduced rat neonatal cardiomyocytes with adenovirus-expressing DN-RSK (Ad.DN-RSK) and measured NHE1 activity. The baseline rate of pH recovery in acid-loaded cells was equal in cells expressing LacZ or DN-RSK. However, NHE1 activation by 100 micromol/L H2O2 was significantly inhibited in cells expressing DN-RSK (0.16+/-0.02 pH units/min) compared with Ad.LacZ (0.49+/-0.13 pH units/min). Apoptosis induced by 12 hours of anoxia followed by 24 hours' reoxygenation was significantly reduced in cells expressing Ad.DN-RSK (18.6+/-2.0%) compared with Ad.LacZ (29.3+/-5.4%).
  
  
  CONCLUSIONS
  In summary, RSK is a novel regulator of cardiac NHE1 activity by phosphorylating NHE1 serine 703 and a new pathological mediator of I/R injury in the heart.
authors.affiliation: Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, NY, USA.
authors.forename: Naoya
authors.initials: N
authors.lastname: Maekawa
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Abe
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shishido
authors.forename: Seigo
authors.initials: S
authors.lastname: Itoh
authors.forename: Bo
authors.initials: B
authors.lastname: Ding
authors.forename: Virendra K
authors.initials: VK
authors.lastname: Sharma
authors.forename: Shey-Shing
authors.initials: SS
authors.lastname: Sheu
authors.forename: Burns C
authors.initials: BC
authors.lastname: Blaxall
authors.forename: Bradford C
authors.initials: BC
authors.lastname: Berk
mesh_terms: D000818:Animals; D017209:Apoptosis; D027682:Cation Transport Proteins / Q000378:metabolism; D004791:Enzyme Inhibitors; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D015428:Myocardial Reperfusion Injury / Q000209:etiology / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000473:pathology; D010766:Phosphorylation; D051381:Rats; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors*; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism / Q000502:physiology*; D014161:Transduction, Genetic
chemical_list: D027682:Cation Transport Proteins; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; C490997:Slc9a1 protein, mouse; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D038744:Ribosomal Protein S6 Kinases, 90-kDa