Titin isoform expression in aortic stenosis
Résumé
Background: Titin is a giant sarcomeric protein that plays a major role in determining passive myocardial stiffness. The shorter N2B isoform results in a higher passive myocardial stiffness than the longer N2BA isoform. We hypothesised that expression of the short N2B isoform would be increased in patients with aortic stenosis compared with healthy controls in response to pressure overload, in order to act as a modulator for the increased demand placed on the left ventricle during the early stages of the hypertrophic response. Methods: Myocardial biopsies were obtained from the left ventricle of 19 patients undergoing aortic valve replacement for aortic stenosis who had no significant co-existing coronary artery disease. Left ventricular biopsies were also obtained from thirteen donor hearts at the time of cardiac transplantation for comparison. Results: SDS-agarose gels revealed small N2B and large N2BA cardiac titin isoforms with a mean N2BA:N2B ratio that was significantly decreased in the 19 aortic stenotic patients compared with the 13 controls (0.66 ± 0.04 in the normal donor hearts versus 0.48 ± 0.03 in patients with aortic stenosis; p=0.02). However, total titin remained unchanged (0.28 ± 0.02 vs. 0.24 ± 0.02; p=0.29). Conclusion: Expression of less N2BA and more N2B titin in response to pressure overload will result in the generation of higher passive tension upon stretch at a given sarcomere length and thus affect cardiac performance.
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