title: AMP-activated protein kinase phosphorylates cardiac troponin I at Ser-150 to increase myofilament calcium sensitivity and blunt PKA-dependent function.
abstract: AMP-activated protein kinase (AMPK) is an energy-sensing enzyme central to the regulation of metabolic homeostasis. In the heart AMPK is activated during cardiac stress-induced ATP depletion and functions to stimulate metabolic pathways that restore the AMP/ATP balance. Recently it was demonstrated that AMPK phosphorylates cardiac troponin I (cTnI) at Ser-150 in vitro. We sought to determine if the metabolic regulatory kinase AMPK phosphorylates cTnI at Ser-150 in vivo to alter cardiac contractile function directly at the level of the myofilament. Rabbit cardiac myofibrils separated by two-dimensional isoelectric focusing subjected to a Western blot with a cTnI phosphorylation-specific antibody demonstrates that cTnI is endogenously phosphorylated at Ser-150 in the heart. Treatment of myofibrils with the AMPK holoenzyme increased cTnI Ser-150 phosphorylation within the constraints of the muscle lattice. Compared with controls, cardiac fiber bundles exchanged with troponin containing cTnI pseudo-phosphorylated at Ser-150 demonstrate increased sensitivity of calcium-dependent force development, blunting of both PKA-dependent calcium desensitization, and PKA-dependent increases in length dependent activation. Thus, in addition to the defined role of AMPK as a cardiac metabolic energy gauge, these data demonstrate AMPK Ser-150 phosphorylation of cTnI directly links the regulation of cardiac metabolic demand to myofilament contractile energetics. Furthermore, the blunting effect of cTnI Ser-150 phosphorylation cross-talk can uncouple the effects of myofilament PKA-dependent phosphorylation from β-adrenergic signaling as a novel thin filament contractile regulatory signaling mechanism.
authors.affiliation: Department of Physiology and Cell Biology and The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Nixon
authors.forename: Ariyoporn
authors.initials: A
authors.lastname: Thawornkaiwong
authors.forename: Janel
authors.initials: J
authors.lastname: Jin
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Brundage
authors.forename: Sean C
authors.initials: SC
authors.lastname: Little
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Davis
authors.forename: R John
authors.initials: RJ
authors.lastname: Solaro
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Biesiadecki
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D006801:Humans; D009200:Myocardial Contraction / Q000502:physiology; D009210:Myofibrils / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D011817:Rabbits; D051381:Rats; D012694:Serine / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D019210:Troponin I / Q000235:genetics / Q000378:metabolism*
chemical_list: D019210:Troponin I; D012694:Serine; D055372:AMP-Activated Protein Kinases; D002118:Calcium