title: The RSK Inhibitor BIX02565 Limits Cardiac Ischemia/Reperfusion Injury.
abstract: OBJECTIVE
  During ischemia/reperfusion (I/R), ribosomal S6 kinase (RSK) activates Na(+)/H(+) exchanger 1 (NHE1) by phosphorylating NHE1 at serine 703 (pS703-NHE1), which promotes cardiomyocyte death and injury. Pharmacologic inhibition of NHE1 effectively protects animal hearts from I/R. However, clinical trials using NHE1 inhibitors failed to show benefit in patients with acute myocardial infarction (MI). One possible explanation is those inhibitors block both agonist-stimulated activity (increasing I/R injury) and basal NHE1 activity (necessary for cell survival). We previously showed that dominant-negative RSK (DN-RSK) selectively blocked agonist-stimulated NHE1 activity. Therefore, we hypothesized that a novel RSK inhibitor (BIX02565) would blunt agonist-stimulated NHE1 and protect hearts from I/R.
  
  
  RESULTS
  Serum/angiotensin II-stimulated pS703-NHE1 was significantly decreased by BIX02565 in cultured cells. Intracellular pH recovery assay showed that BIX02565 selectively inhibited serum-stimulated NHE1 activity. Ischemia/reperfusion decreased left ventricular-developed pressure (LVDP; inhibited) to 8.7% of the basal level in non-transgenic littermate control (NLC) mouse hearts, which was significantly improved (44.6%) by BIX02565. Similar protection was observed in vehicle-treated, cardiac-specific DN-RSK-Tg mice (43%). No additional protective effect was seen in BIX02565-treated DN-RSK-Tg hearts. BIX02565 also improved LVDP in cardiac-specific wild-type (WT)-RSK-Tg mouse hearts (7.4%-40.9%, P < .01). Finally, Western Blotting results confirmed DN-RSK and BIX02565 significantly decreased I/R-induced pS703-NHE1.
  
  
  CONCLUSIONS
  The RSK plays a crucial role in I/R-induced activation of NHE1 and cardiac injury. The RSK inhibition may provide an alternative target for patients with MI.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.
authors.forename: Xi
authors.initials: X
authors.lastname: Shi
authors.affiliation: Department of CardioMetabolic Diseases Research, Boehringer-Ingelheim Pharmaceuticals, Inc, Ridgefield, CT, USA.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: O'Neill
authors.affiliation: Department of CardioMetabolic Diseases Research, Boehringer-Ingelheim Pharmaceuticals, Inc, Ridgefield, CT, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: MacDonnell
authors.affiliation: Department of Anesthesiology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Brookes
authors.affiliation: Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA.
authors.forename: Chen
authors.initials: C
authors.lastname: Yan
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA bradford_berk@urmc.rochester.edu.
authors.forename: Bradford C
authors.initials: BC
authors.lastname: Berk
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001381:Azepines / Q000494:pharmacology / Q000627:therapeutic use*; D001562:Benzimidazoles / Q000494:pharmacology / Q000627:therapeutic use*; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D015428:Myocardial Reperfusion Injury / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology*; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C571260:5-methyl-1-oxo-2,3,4,5-tetrahydro-1H-(1,4)diazepino(1,2-a)indole-8-carboxylic acid (1-(3-dimethylamino-propyl)-1H-benzoimidazol-2-yl)amide; D001381:Azepines; D001562:Benzimidazoles; D019893:Ribosomal Protein S6 Kinases
keywords: I/R; NHE1; RSK inhibitor; cardioprotection