Dystrophin-glycoprotein complex and vinculin-talin-integrin system in human adult cardiac muscle.

Costameres were identified, for the first time, in skeletal and cardiac muscle, as regions associated with the sarcolemma, consisting of densely clustered patches of vinculin; they have many characteristics common to the cell-extracellular matrix-type of adherens junctions. Costameres are considered 'proteic machinery' and they appear to comprise two protein complexes, the dystrophin-glycoprotein complex (DGC) and the vinculin-talin-integrin system. In comparison to skeletal muscle, few studies have focused on cardiac muscle regarding these two complexes, and study is generally relative to dystrophin or to cardiac diseases, such as cardiomyopathies. However, insufficient data are available on these proteins in healthy human cardiomyocytes. For this reason, we performed an immunohistochemical study using human cardiac muscle fibers, in order to define the real distribution and the spatial relationship between the proteins in these two complexes. Our data showed a real costameric distribution of DGC and of the vinculin-talin-integrin system; all tested proteins were present in T-tubule and in intercalated disks. Moreover, our data demonstrated that all tested proteins of DGC colocalized with each other, as all tested components of the vinculin-talin-integrin system, and that all tested proteins of DGC colocalized with all tested proteins of the vinculin-talin-integrin system. Finally, all tested proteins of the two complexes were localized in the region of the sarcolemma over the I band, in 100% of our observations. The present study, for the first time, analyzed the majority of proteins of DGC and of the vinculin-talin-integrin system in cardiac muscle fibers, and it confirmed that DGC and the vinculin-talin-integrin system have a role in the transduction of mechanical force to the extracellular matrix. Finally it attributed a key role in the regulation of action potential duration to cardiac myocytes.

Sarcoglycan subcomplex expression in refluxing ureteral endings.

PURPOSE: Functional and structural lesions of ureteral endings seem to alter the active valve mechanism of the ureterovesical junction, causing vesicoureteral reflux. The interaction of the dystroglycan complex with components of the extracellular matrix may have an important role in force transmission and sarcolemma protection, and the sarcoglycan complex is an essential component of the muscle membrane located dystroglycan complex. We performed immunofluorescence and molecular analysis on the expression of sarcoglycan complex subunits. MATERIALS AND METHODS: A total of 21 specimens of refluxing ureteral endings were obtained during ureteral reimplantation. Six ureteral ends obtained during organ explantation were used as controls. Immunohistochemical analysis and reverse transcriptase polymerase chain reaction evaluation were performed for alpha, beta, gamma, delta and epsilon-sarcoglycan complex. RESULTS: The Spearman test revealed a significant positive correlation between alpha-sarcoglycan complex immunofluorescence intensity and grade of vesicoureteral reflux, while a negative correlation was recorded between epsilon-sarcoglycan complex immunofluorescence intensity and grade of vesicoureteral reflux. CONCLUSIONS: Semiquantitative analysis demonstrated a significant grade related impairment of epsilon-sarcoglycan complex coupled with an increased expression of alpha-sarcoglycan complex. This observation suggests that the structural deficiency of the trigonal ureterovesical junction could cause a passive stretching of refluxing urine on the ureter, deranging the multimodular tensegrity architecture of the sarcoglycan subcomplex, or that the sarcoglycan complex could have a key role in the physiopathology of vesicoureteral reflux. In fact, the defect in any of the sarcoglycan complexes results in degeneration of membrane integrity and muscle fiber. An altered configuration of the sarcoglycan complex could explain the structural and functional changes in refluxing ureteral endings. Our observations underline the assumption that primary vesicoureteral reflux might be regarded as a sarcoglycanopathy with marked quantitative deficiency of epsilon-sarcoglycan complex and over expression of alpha-sarcoglycan complex.