The Xin repeat-containing protein, mXinβ, initiates the maturation of the intercalated discs during postnatal heart development

Abstract

The intercalated disc (ICD) is a unique structure to the heart and plays vital roles in communication and signaling among cardiomyocytes. ICDs are formed and matured during postnatal development through a profound redistribution of the intercellular junctions, as well as recruitment and assembly of more than 200 proteins at the termini of cardiomyocytes. The molecular mechanism underlying this process is not completely understood. The mouse orthologs (mXinα and mXinβ) of human cardiomyopathy-associated (CMYA)/Xin actin-binding repeat-containing protein (XIRP) genes (CMYA1/XIRP1 and CMYA3/XIRP2, respectively) encode proteins localized to ICDs. Ablation of mXinα results in adult late-onset cardiomyopathy with conduction defects and up-regulation of mXinβ. ICD structural defects are found in adult but not juvenile mXinα-null hearts. On the other hand, loss of mXinβ leads to ICD defects at postnatal day 16.5, a developmental stage when the heart is forming ICDs, suggesting mXinβ is required for ICD formation. Using quantitative Western blot, we showed in this study that mXinβ but not mXinα was uniquely up-regulated during the redistribution of intercellular junction from the lateral membrane of cardiomyocytes to their termini. In the absence of mXinβ, the intercellular junctions failed to be restricted to the termini of the cells, and the onset of such defect correlated with the peak expression of mXinβ. Immunofluorescence staining and subcellular fractionation showed that mXinβ preferentially associated with the forming ICDs, further suggesting that mXinβ functioned locally to promote ICD maturation. In contrast, the spatiotemporal expression profile of mXinα and the lack of more severe ICD defects in mXinα−/−;mXinβ−/− double knockout hearts than in mXinβ−/− hearts suggested that mXinα was not essential for the postnatal formation of ICDs. A two-step model for the development of ICD is proposed where mXinβ is essential for the redistribution of intercellular junction components from the lateral puncta to the cell termini.

Localization and function of Xinα in mouse skeletal muscle

“…week postnatal, upregulated mXin␤ colocalized with N-cadherin puncta to form bigger aggregates along the developing intercalated discs between cardiomyocytes (60). In this regard, we also observed similar mXin␤ aggregates along the MTJ of mXin␣-null muscles (data not shown), suggesting an analogous mechanism for the MTJ formation.…”

Global phosphoproteomic profiling reveals perturbed signaling in a mouse model of dilated cardiomyopathy

“…XIRPs interact with catenins and ion channels in mature cardiac muscle and, although the significance of phosphorylation is unclear, gene knockout mice display early-onset cardiomyopathy (18).…”

A Short Splice Form of Xin-Actin Binding Repeat Containing 2 (XIRP2) Lacking the Xin Repeats Is Required for Maintenance of Stereocilia Morphology and Hearing Function

“…Because previous studies have reported that XIRP2 is specific for cardiac and skeletal muscle (Huang et al, 2006; Q. Wang et al, 2012), our discovery of XIRP2 in sensory hair cells came as a surprise. The genetic locus of the Xirp2 gene overlaps with two unresolved human deafness loci (DFNB27 and DFNA16;Fukushima et al, 1999;Pulleyn et al, 2000), making its study significant for deafness research.…”

“…Complete loss of XIRP2 causes diastolic dysfunction and early postnatal mortality in mice (Q. Wang et al, 2010), suggesting that it might play a role in the development and maturation of the intercalated disks (Q. Wang et al, 2010Wang et al, , 2013.…”

“…Wang et al, 2010), suggesting that it might play a role in the development and maturation of the intercalated disks (Q. Wang et al, 2010Wang et al, , 2013. Because previous studies have reported that XIRP2 is specific for cardiac and skeletal muscle (Huang et al, 2006; Q.…”