Identification of novel sarcomeric modifiers of hypertrophy in hypertrophic cardiomyopathy using the yeast two-hybrid system

[摘要] ENGLISH ABSTRACT: Left ventricular hypertrophy (LVH) occurs when the cardiomyocytes in the left ventricle become enlarged by increasing in mass in response to haemodynamic pressure overload. This can either be attributed to a normal physiological response to exercise or can be the result of a maladaptive process or disease state, such as chronic hypertension. Hypertrophic cardiomyopathy (HCM) is the most common form of Mendelian-inherited cardiac disease. A defining characteristic thereof is primary LVH that occurs when there are no other hypertrophy-predisposing conditions present. Therefore, HCM provides a unique opportunity to study the molecular determinants of LVH in the context of a Mendelian disorder, instead of in more complex disorders such as hypertension. Over 1000 HCM-causing mutations in 19 genes have been identified thus far, most of them encoding sarcomeric proteins residing in the sarcomeric C-zone. However, for many HCM patients no disease-causing genes have been identified. Moreover, studies have shown phenotypic variation in presentation of disease in, as well as between, families in which the same HCM-causing mutation segregates. This has led many investigators to conclude that genetic modifiers of hypertrophy exist.The aim of the study was to identify novel plausible HCM-causing or modifier genes by searching for interactors of a known HCM-causing protein, namely titin. The hypothesis was that genes encoding proteins, which interact with proteins that are encoded by known HCM-causative genes, may also be considered HCM-causing or may modify the HCM phenotype. To this end, the aim was to identify novel interactors of the 11-domain super-repeat region of titin, which resides within the sarcomeric C-zone, using yeast two-hybrid analysis. Five putative interactors of the 11-domain super-repeat region of titin were identified in this study. These interactions were subsequently verified by colocalisation in H9C2 rat cardiomyocytes, providing further evidence for possible interactions between titin and these proteins.The putative interactor proteins of titin determined from the Y2H library screen were: filamin C (FLNC), phosphatidylethanolamine-binding protein 4 (PEBP4), heart-type fatty acid binding protein 3 (H-FABP3), myomesin 2 (MYOM2) and myomesin 1 (MYOM1).The FLNC gene could be a candidate for cardiac diseases, especially cardiomyopathies that are associated with hypertrophy or developmental defects. The putative interaction of titin and PEBP4 is speculated to be indicative of the formation of the interstitial fibrosis and myocyte disarray seen in HCM. Heart-type fatty acid-binding protein 3 has prognostic value to predict recurrent cardiac events. Its suggested interaction with titin is speculated to play a role in inhibiting its functional abilities. Myomesin 2 is jointly responsible, with MYOM1, for the formation of a head structure on one end of the titin string that connects the Z and M bands of the sarcomere. This is speculated to be linked to a developmental error with the result being a defect in sarcomeric structure formation, which could result in pathologies such as HCM.Therefore, these identified proteins could likely play a functional role in HCM due to their interactions with titin. This research could thus help with new insights into the further understanding of HCM patho-aetiology.

[发布机构] Stellenbosch University