Conditional FKBP12.6 overexpression in mouse cardiac myocytes prevents triggered ventricular tachycardia through specific alterations in excitation-contraction coupling.
BACKGROUND
Ca(2+) release from the sarcoplasmic reticulum via the ryanodine receptor (RyR2) activates cardiac myocyte contraction. An important regulator of RyR2 function is FKBP12.6, which stabilizes RyR2 in the closed state during diastole. Beta-adrenergic stimulation has been suggested to dissociate FKBP12.6 from RyR2, leading to diastolic sarcoplasmic reticulum Ca(2+) leakage and ventricular tachycardia (VT). We tested the hypothesis that FKBP12.6 overexpression in cardiac myocytes can reduce susceptibility to VT in stress conditions.


RESULTS
We developed a mouse model with conditional cardiac-specific overexpression of FKBP12.6. Transgenic mouse hearts showed a marked increase in FKBP12.6 binding to RyR2 compared with controls both at baseline and on isoproterenol stimulation (0.2 mg/kg i.p.). After pretreatment with isoproterenol, burst pacing induced VT in 10 of 23 control mice but in only 1 of 14 transgenic mice (P<0.05). In isolated transgenic myocytes, Ca(2+) spark frequency was reduced by 50% (P<0.01), a reduction that persisted under isoproterenol stimulation, whereas the sarcoplasmic reticulum Ca(2+) load remained unchanged. In parallel, peak I(Ca,L) density decreased by 15% (P<0.01), and the Ca(2+) transient peak amplitude decreased by 30% (P<0.001). A 33.5% prolongation of the caffeine-evoked Ca(2+) transient decay was associated with an 18% reduction in the Na(+)-Ca(2+) exchanger protein level (P<0.05).


CONCLUSIONS
Increased FKBP12.6 binding to RyR2 prevents triggered VT in normal hearts in stress conditions, probably by reducing diastolic sarcoplasmic reticulum Ca(2+) leak. This indicates that the FKBP12.6-RyR2 complex is an important candidate target for pharmacological prevention of VT.
Gellen
Barnabas
B
Inserm, U698, Paris, France.
Fernández-Velasco
María
M
Briec
François
F
Vinet
Laurent
L
LeQuang
Khai
K
Rouet-Benzineb
Patricia
P
Bénitah
Jean-Pierre
JP
Pezet
Mylène
M
Palais
Gael
G
Pellegrin
Noémie
N
Zhang
Andy
A
Perrier
Romain
R
Escoubet
Brigitte
B
Marniquet
Xavier
X
Richard
Sylvain
S
Jaisser
Fréderic
F
Gómez
Ana María
AM
Charpentier
Flavien
F
Mercadier
Jean-Jacques
JJ
D000200:Action Potentials; D000318:Adrenergic beta-Agonists / Q000633:toxicity; D000818:Animals; D020013:Calcium Signaling; D002304:Cardiac Pacing, Artificial; D002395:Catecholamines / Q000502:physiology; D004318:Doxycycline / Q000494:pharmacology; D007545:Isoproterenol / Q000633:toxicity; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000517:prevention & control*; D022021:Tacrolimus Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects
D000318:Adrenergic beta-Agonists; D002395:Catecholamines; D004318:Doxycycline; D007545:Isoproterenol; D011993:Recombinant Fusion Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D022021:Tacrolimus Binding Proteins; C509259:FKBP1B protein, mouse