Abstract 19758: The mXinβ Initiates the Formation of Intercalated Discs in the Developing Postnatal Hearts, while the mXinα Further Stabilizes their Integrity in the Adult Mouse Heart
About 200 known proteins are associated with intercalated disc (ICD), 40% of which change in human cardiomyopathy, arrhythmias, and failing heart. The molecular mechanisms by which these proteins promote normal cardiac function remain unclear. The mouse orthologs (mXinα and mXinβ) of human cardiomyopathy-associated genes (CMYA1 and CMYA3, respectively) encode proteins localized to ICDs. Ablation of mXinα results in adult late-onset cardiomyopathy with conduction defects and up-regulation of mXinβ. Despite a normal appearance of ICD in the juvenile mutant hearts, the ICD structural defects can be detected at young adult and progressively worsen with aging. On the other hand, complete loss of mXinβ leads to failure of forming ICD and early postnatal lethality. A significant up-regulation of mXinβ during the first two weeks of postnatal life parallels the initial clustering of ICD components to the cell termini. Thus, we hypothesize that ICDs form in two phases, the initiation phase requiring mXinβ and the maturation phase involving mXinα. Analyzing the spatiotemporal distributions of known ICD components by quantitative confocal microscopy and biochemical fractionation of developing wild type and mXinβ-null hearts, we found a critical role for mXinβ in clustering these molecules into large punctae to the terminals and a functional hierarchy among mXinβ, mXinα and ICD components in their terminally localized actions. Using co-transfection and co-immunoprecipitation to further study the role of mXinα in the stability of ICD components, we found that mXinα not only interacted with β-catenin and p-120-catenin but also stabilized them. We have also shown that mXinα-null cardiomyocytes had significantly reduced transient outward K+ (Ito) current density. Using yeast two hybrid assay, we found that similar to Kv4.2 (a channel-forming subunit of Ito), mXinα also interacted with both kv channel interacting protein 2 (an auxiliary subunit of Ito) and filamin. Through these interactions, mXinα likely promotes the surface expression of a portion of the Ito channel to the ICD. In conclusion, our findings suggest for the first time that a family of mXin proteins plays essential roles in the ICD formation and integrity for normal cardiac function.
- © 2010 by American Heart Association, Inc.