Cardiac defects and altered ryanodine receptor function in mice lacking FKBP12

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FKBP12, a cis–trans prolyl isomerase that binds the immunosuppressants FK506 and rapamycin, is ubiquitouslyexpressed and interacts with proteins in several intracellular signal transduction systems1.Although FKBP12 interacts with the cytoplasmic domains of type I receptors of the transforming growth factor-β(TGF-β) superfamily in vitro, the function of FKBP12 in TGF-β superfamily signalling iscontroversial2,3,4,5,6. FKBP12 also physicallyinteracts stoichiometrically with multiple intracellular calcium release channels including the tetrameric skeletal muscle ryanodine receptor(RyR1)7,8. In contrast, the cardiacryanodine receptor, RyR2, appears to bind selectively theFKBP12 homologue, FKBP12.6 (9, 10). To define the functions of FKBP12 in vivo, we generated mutantmice deficient in FKBP12 using embryonic stem (ES) cell technology. FKBP12-deficient mice have normal skeletal muscle buthave severe dilated cardiomyopathy and ventricular septal defects that mimic a human congenital heart disorder, noncompaction of leftventricular myocardium11,12. About 9% of themutants exhibit exencephaly secondary to a defect in neural tube closure. Physiological studies demonstrate that FKBP12 is dispensable forTGF-β-mediated signalling, but modulates the calcium release activity of both skeletal and cardiac ryanodinereceptors.

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Figure 1: Generation of FKBP12-deficient mice.
Figure 2: Cardiac and liver analysis of wild-type and FKBP12-deficient mutants.
Figure 3: Analysis of wild-type and FKBP12 exencephaly mutants.
Figure 4: Cardiac performance of adult mice.
Figure 5: FKBP12 is not essential for TGF-β-mediated signalling.
Figure 6: Single channel tracings of skeletal RyR1 (a, b) or cardiac RyR2 (c, d) reconstituted into planar lipid bilayers.


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We thank D. Kearney and M. Finegold for their expert opinions on the cardiac and liver pathology, J. Towbin for advice on congenital heart disease, K. Kurrelmeyer, T. Pham and G. Taffet for aid in echocardiographic analysis, J. Barrish for aid in electron microscopic analysis, S. Schreiber for the anti-FKBP12 antibody, J. Massagué for the p3TP-lux plasmid, J.-Z. Zhang for aid in sarcoplasmic reticulum membrane preparation, S. Li for statistical help, T. R. Kumar and J. Towbin for their critical reading of the manuscript and S. Baker for aid in manuscript preparation. These studies were supported in part by National Institutes of Health grants (to M.M.M., S.L.H., M.D.S. and L.S.M.) and a Muscular Dystrophy Association grant (to S.L.H.).

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Correspondence to Martin M. Matzuk.

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