Figure 4. Strategy and cardiovascular phenotyping of Myoscape KO mice.

(a) Schematic representation of the knockout strategy resulting in a constitutive knockout after loxP-Cre-mediated deletion of exons 3–8. (b) Western blot analysis confirming that Myoscape −/− mice do not express detectable Myoscape protein at the expected size of 105kD. The mid-lane represents marker protein. (c) Representative echocardiographic recordings by a blinded observer from Myoscape +/+ mice at the age of 6–8 weeks and from Myoscape −/− mice at the age of 6–8 weeks. (d) Statistical evaluation of morphometric (HW/BW) and echocardiographic (LVEDD and FS in %) parameters from Myoscape −/− or +/+ mice at the age of approx. 8 weeks and (e) after one year revealing progressive heart failure in the absence of severe hypertrophy. *P<0.05; **P<0.01. (ANOVA) (f) After 4 weeks of pressure overload due to transverse aortic constriction (TAC), Myoscape knockouts showed a significant increase of heart weight to tibia length ratios compared with wild-type mice (136.6±24 versus 101.1±9; *P<0.05 (ANOVA)). (g) Myoscape-null mice show higher lung weight to tibia length ratios (110±15 versus 84±8.5; *P<0.05 (ANOVA)) than control littermates, indicating the presence of congestive heart failure. (h) In echocardiographic measurements of ventricular fractional shortening, Myoscape knockouts show significantly exacerbated contractile impairment (11.2±6.4 versus 25.6±4.4; *P<0.05 (ANOVA), further underlined by significant ventricular enlargement. (i) Absence of Myoscape leads to a nduction of the hypertrophy-associated fetal gene programme as assessed by qPCR analysis of significantly increasd ANF levels and a strong induction of Rcan 1.4 levels as compared with wild-type animals (j,k), and also leads to a more pronounced increase of cardiomyocyte cell size after transverse aortic constriction (l,m). (592 μm²± 6.3 s.e.m. versus 519 μm² ±5.1 SEM; *P<0.05 (ANOVA)). NS, not significant.