title: Limitations of FKBP12.6-directed treatment strategies for maladaptive cardiac remodeling and heart failure.
abstract: Sarcoplasmic reticulum (SR) calcium (Ca) leak can be reduced by enhancing FKBP12.6 binding to SR Ca release channels (RyR2) and expression of a "sticky" FKBP12.6(D37S) mutant may correct reduced binding stoichiometry in RyR2 from failing hearts. Both calcium/calmodulin-dependent protein kinase IIδc (CaMKIIδc) and protein kinase A (PKA) are activated in heart failure and promote SR Ca leak at RyR2. It is possible that FKBP12.6 dissociation from RyR2 may promote remodeling and that interventions to reassociate FKBP12.6 with RyR2 reflect a future therapeutic strategy. We created transgenic (TG) mice expressing FKBP12.6(D37S) and tested their capacity to improve intracellular Ca handling and pathological remodeling in vivo. FKBP12.6(D37S) TG mice were cross-bred with CaMKIIδc TG mice, which are known to exhibit pronounced RyR2 dysfunction and heart failure. We observed a significant improvement of post-rest Ca transients and a higher SR Ca content in FKBP12.6(D37S) TG mice. In double-TG mice, a marked reduction of SR Ca spark frequency indicated reduced SR Ca leak but neither SR Ca transient amplitude, SR Ca content nor morphological or functional parameters improved in vivo. Likewise, FKBP12.6(D37S) TG mice subjected to increased afterload after aortic banding exhibited higher SR Ca load but did not exhibit any improvement in hypertrophic growth or functional decline. Enhancement of FKBP12.6-RyR2 binding markedly reduced RyR2 Ca leak in CaMKIIδc-induced heart failure and in pressure overload. Our data suggest that activation of CaMKIIδc and pressure overload confer significant resistance towards approaches aiming at FKBP12.6-RyR2 reconstitution in heart failure and maladaptive remodeling, although RyR2 Ca leak can be reduced.
authors.affiliation: Department of Cardiology and Pneumology, Heart Center, University of Göttingen, Germany. tseidle@gwdg.de
authors.forename: Tim
authors.initials: T
authors.lastname: Seidler
authors.forename: Nils
authors.initials: N
authors.lastname: Teucher
authors.forename: Kristian
authors.initials: K
authors.lastname: Hellenkamp
authors.forename: Bernhard
authors.initials: B
authors.lastname: Unsöld
authors.forename: Cornelia
authors.initials: C
authors.lastname: Grebe
authors.forename: Petra
authors.initials: P
authors.lastname: Kramps
authors.forename: Hanna
authors.initials: H
authors.lastname: Schotola
authors.forename: Stefan
authors.initials: S
authors.lastname: Wagner
authors.forename: Friedrich A
authors.initials: FA
authors.lastname: Schöndube
authors.forename: Gerd
authors.initials: G
authors.lastname: Hasenfuss
authors.forename: Lars S
authors.initials: LS
authors.lastname: Maier
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D006333:Heart Failure / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D022021:Tacrolimus Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020257:Ventricular Remodeling / Q000235:genetics / Q000502:physiology
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D022021:Tacrolimus Binding Proteins; C403484:tacrolimus binding protein 1B; D002118:Calcium