Cardiac-specific deletion of protein phosphatase 1β promotes increased myofilament protein phosphorylation and contractile alterations.
There are 3 protein phosphatase 1 (PP1) catalytic isoforms (α, β and γ) encoded within the mammalian genome. These 3 gene products share ~90% amino acid homology within their catalytic domains but each has unique N- and C-termini that likely underlie distinctive subcellular localization or functionality. In this study, we assessed the effect associated with the loss of each PP1 isoform in the heart using a conditional Cre-loxP targeting approach in mice. Ppp1ca-loxP, Ppp1cb-loxP and Ppp1cc-loxP alleles were crossed with either an Nkx2.5-Cre knock-in containing allele for early embryonic deletion or a tamoxifen inducible α-myosin heavy chain (αMHC)-MerCreMer transgene for adult and cardiac-specific deletion. We determined that while deletion of Ppp1ca (PP1α) or Ppp1cc (PP1γ) had little effect on the whole heart, deletion of Ppp1cb (PP1β) resulted in concentric remodeling of the heart, interstitial fibrosis and contractile dysregulation, using either the embryonic or adult-specific Cre-expressing alleles. However, myocytes isolated from Ppp1cb deleted hearts surprisingly showed enhanced contractility. Mechanistically we found that deletion of any of the 3 PP1 gene-encoding isoforms had no effect on phosphorylation of phospholamban, nor were Ca(2+) handling dynamics altered in adult myocytes from Ppp1cb deleted hearts. However, the loss of Ppp1cb from the heart, but not Ppp1ca or Ppp1cc, resulted in elevated phosphorylation of myofilament proteins such as myosin light chain 2 and cardiac myosin binding protein C, consistent with an enriched localization profile of this isoform to the sarcomeres. These results suggest a unique functional role for the PP1β isoform in affecting cardiac contractile function.
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA.
Ruijie
R
Liu
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA.
Robert N
RN
Correll
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA.
Jennifer
J
Davis
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA.
Ronald J
RJ
Vagnozzi
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA.
Allen J
AJ
York
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA.
Michelle A
MA
Sargent
Department of Psychiatry, Yale University School of Medicine, New Haven, CT 06520 USA.
Angus C
AC
Nairn
Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Cincinnati, OH 45229, USA. Electronic address: jeff.molkentin@cchmc.org.
Jeffery D
JD
Molkentin
D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D055879:Gene Knock-In Techniques; D006321:Heart / Q000502:physiology*; D006801:Humans; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D009200:Myocardial Contraction / Q000235:genetics*; D009210:Myofibrils / Q000235:genetics / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000235:genetics*; D000071636:Protein Phosphatase 2C; D012518:Sarcomeres / Q000235:genetics / Q000378:metabolism; D024723:Ventricular Myosins / Q000235:genetics / Q000378:metabolism
D008840:Microfilament Proteins; D020033:Protein Isoforms; D010749:Phosphoprotein Phosphatases; C000607467:Ppm1b protein, mouse; D000071636:Protein Phosphatase 2C; D024723:Ventricular Myosins
Contractility; Heart failure; Myofilament protein; Protein phosphatase 1