Essential Roles of an Intercalated Disc Protein, mXinβ, in Postnatal Heart Growth and Survival

Abstract

Rationale: The Xin repeat-containing proteins mXin␣ and mXin␤ localize to the intercalated disc of mouse heart and are implicated in cardiac development and function. The mXin␣ directly interacts with ␤-catenin, p120-catenin, and actin filaments. Ablation of mXin␣ results in adult late-onset cardiomyopathy with conduction defects. An upregulation of the mXin␤ in mXin␣-deficient hearts suggests a partial compensation. Objective: The essential roles of mXin␤ in cardiac development and intercalated disc maturation were investigated. Methods and Results: Ablation of mXin␤ led to abnormal heart shape, ventricular septal defects, severe growth retardation, and postnatal lethality with no upregulation of the mXin␣. Postnatal upregulation of mXin␤ in wild-type hearts, as well as altered apoptosis and proliferation in mXin␤-null hearts, suggests that mXin␤ is required for postnatal heart remodeling. The mXin␤-null hearts exhibited a misorganized myocardium as detected by histological and electron microscopic studies and an impaired diastolic function, as suggested by echocardiography and a delay in switching off the slow skeletal troponin I. Loss of mXin␤ resulted in the failure of forming mature intercalated discs and the mislocalization of mXin␣ and N-cadherin. The mXin␤-null hearts showed upregulation of active Stat3 (signal transducer and activator of transcription 3) and downregulation of the activities of Rac1, insulin-like growth factor 1 receptor, protein kinase B, and extracellular signal-regulated kinases 1 and 2. Conclusions: These findings identify not only an essential role of mXin␤ in the intercalated disc maturation but also mechanisms of mXin␤ modulating N-cadherin-mediated adhesion signaling and its crosstalk signaling for postnatal heart growth and animal survival. (Circ Res. 2010;106:1468-1478.)Key Words: N-cadherin-mediated adhesion signaling Ⅲ Xin repeat-containing protein Ⅲ intercalated disc maturation Ⅲ diastolic dysfunction Ⅲ postnatal heart growth A regulatory network of transcription factors is known to control cardiac morphogenesis. Although the core players in this network are highly conserved, from organisms with simple heart-like cells to those with complex four-chambered hearts, it has been theorized and proven that expansion of this regulatory network by adding new transcription factors is a major force for the heart to evolve new structures. 1,2 However, the addition of new transcription factors can only be a part of the mechanism underlying the formation of complex hearts. The transcription factors must act through their downstream targets, which are directly involved in cardiac morphogenesis, growth and function. However, our inventory of such downstream targets remains incomplete.The Xin repeat-containing proteins from chicken and mouse hearts (cXin and mXin␣, respectively) were first identified as a target of the Nkx2.5-Mef2C pathway. 3,4 Another mouse Xin protein, mXin␤ (or myomaxin), has been subsequently identified as a Mef2A downstream target. 5 Evolutionary studies suggest t...

Localization and function of Xinα in mouse skeletal muscle

“…The evolutionarily more conserved mXin␤ is essential for initiating the formation and maturation of intercalated discs (19, 60 -62). mXin␤-null mice die postnatally with cardiac chamber defects (61). During the second Fig.…”

“…Several rabbit polyclonal antibodies against mXin isoforms were used: U1013 recognizing both mXin␣ and mXin␤ (49), U1697 recognizing only mXin␣, U1741 recognizing only mXin␤, and U1040 recognizing only mXin␤ (20,61). The specificities of the anti-Xin antibodies have been characterized in details in the cited publications.…”

“…19). Through alternative splicing, each gene is capable of producing several protein variants (20,43,57,61).…”

“…Therefore, mXin␣ may play an important role in the Ncadherin-mediated adhesion and signaling between cardiomyocytes (10,20,43). Mouse hearts without mXin␤ had mislocalization of mXin␣ and N-cadherin and severe growth retardation, diastolic dysfunction, and postnatal lethality (61).…”

Promoter analysis of bovine cardiomyopathy-associated protein 1 gene

“…A homozygous CMYA1 deletion mouse model was found to have disordered myocardium, abnormally sized heart, lack of ventricular septum, and diastolic dysfunction (Otten et al, 2010). The mouse CMYA1 plays an important role in the control of postnatal heart growth and, thus, in animal survival, by regulating N-cadherin (Wang et al, 2010). When CMYA1 expression was reduced, skeletal muscle regeneration was delayed (Nissar et al, 2012).…”