Abstract 12702: The Eya4/six1 Signalling Cascade is Crucial in the Development of Heart Disease
Introduction: We identified a mutation in the human transcription cofactor Eya4 (E193) to cause terminal heart failure preceded by sensorineural hearing loss. Eya proteins lack DNA-binding and nuclear translocation sequences and therefore must interact with real transcription factors, including Six family members. The cyclin-dependent kinase inhibitor p27kip1 (p27), which inhibits hypertrophic growth in adult cardiomyocytes, is one of the few known Eya-Six targets expressed in the heart. We hypothesize that Eya4/Six1 regulates targets relevant to sustain normal cardiac function via p27.
Methods and results: We examined the correlation of Eya4 and the mutant E193 overexpression upon p27 in permanent mammalian cell lines and primary cardiac myocytes. Westernblot analysis demonstrated that an overexpression of Eya4 led to a significant suppression of p27, whereas E193 had no effect on p27 levels; knockdown of Eya4 via siRNA exerted opposing effects. Promoter studies using a p27 promoter fragment including Six1 consensus sites revealed that the constitutive suppression of p27 by Eya4 was released after targeting one of the Six1 consensus sites; E193 had no effect on p27 promoter activity. We constructed a transgenic mouse model with a constitutive myocardial overexpression of HA-tagged E193 to study the effect of a disturbed Eya4/Six1 complex upon cardiac physiology. Magnetic resonance imaging to visualize cardiac structures in detail along with hemodynamic measurements showed that an overexpression of E193 in mice leads to an age related onset of cardiomyopathy similar to patients carrying the E193 mutation. HE-stainings show dilation of the LV associated with a thinning of the myocardial wall. PSR-stainings show interstitial fibrosis of the myocardial tissue which is characteristic for cardiac disease.
Conclusion: In summary, we identified a mutation in Eya4 to cause DCM. Eya4/Six1 seems to suppress the expression of p27, an important inhibitor of the development of hypertrophy in postmitotic cardiomyocytes. Our transgenic mouse model with overexpression of the Eya4 mutant E193 supports our hypothesis whereas the dysfunctional E193 mutant could not suppress p27, finally leading to an age related onset of cardiomyopathy.
- © 2011 by American Heart Association, Inc.