Sarcoglycans in Human Skeletal Muscle and Human Cardiac Muscle: A Confocal Laser Scanning Microscope Study

Abstract

Sarcoglycans are a subcomplex of transmembrane proteins which are part of the dystrophin-glycoprotein complex. They are expressed in the skeletal, cardiac and smooth muscle. Although numerous studies have been conducted on the sarcoglycan subcomplex in skeletal and cardiac muscle, the manner of the distribution and localization of these proteins along the nonjunctional sarcolemma is not clear. We therefore carried out an indirect immunofluorescence study on surgical biopsies of normal human skeletal muscle and of healthy human atrial myocardium biopsies of patients affected by valvulopathy. Our results indicate that, in skeletal muscle, sarcoglycans have a costameric distribution and all colocalize with each other. Only in a few cases did the α-sarcoglycan not colocalize with other sarcoglycans. In addition, these glycoproteins can be localized in different fibers either in the regions of the sarcolemma over band I or band A. In cardiac muscle, our results show a costameric distribution of all proteins examined and, unlike in skeletal muscle, they show a constant colocalization of all sarcoglycans with each other, along with a consistent localization of these proteins in the region of the sarcolemma over band I. In our opinion, this situation seems to confirm the hypothesis of a correlation between the region of the sarcolemma occupied by costameric proteins and the metabolic type, fast or slow, of the muscular fibers. These data, besides opening a new line of research in understanding interactions between the sarcoglycans and other transmembrane proteins, could also be extended to skeletal and cardiac muscles affected by neuromuscular and cardiovascular pathologies to understand possible structural alterations.

Expression of muscle-specific integrins in masseter muscle fibers during malocclusion disease

“…In agreement with several reports (21-23), we offered support for the hypothesis that integrins have a role in the function of human adult skeletal muscle (24) and demonstrated a bidirectional signaling between sarcoglycans and integrins (25). This reciprocal control may determine the prevalence of one system over another with a consequent transmission of different messages to the sarcolemma-associated cytoskeleton (24,25).…”

“…This reciprocal control may determine the prevalence of one system over another with a consequent transmission of different messages to the sarcolemma-associated cytoskeleton (24,25).…”

Alpha sarcoglycan is required for FGF-dependent myogenic progenitor cell proliferation in vitro and in vivo

“…We propose that SGCA modulates FGFR1 activity via the formation of a complex, and that the absence of SGCA destabilizes FGFR1, leading to the proliferative impairment of MPCs. This phenomenon, together with the enhanced apoptosis previously reported (Allikian et al, 2004;Anastasi et al, 2004;Yoshida et al, 1998), might explain the severity of this form of muscular dystrophy in mice and the success of previous cell transplantation experiments (Sampaolesi et al, 2003).…”

“…It has been reported that the absence of SGCA can alter integrindependent adhesion and motility pathways, causing enhanced apoptosis (Allikian et al, 2004;Anastasi et al, 2004;Yoshida et al, 1998). To test this possibility, active caspase 9 (Casp9) levels 4527 RESEARCH ARTICLE Novel role of alpha sarcoglycan in myogenesis (F)Human myoblasts isolated from healthy (30XY, left graph) or LGMD2D (32XY, right graph) patients were stimulated with bFGF (gray lines) or HGF (dashed lines) and the total number of cells was counted (n5).…”

“…Interestingly, an association of SGCA with integrins has been reported (Allikian et al, 2004;Anastasi et al, 2004;Yoshida et al, 1998), and thus the absence of SGCA might also contribute to impaired migration through inadequate integrindependent adhesion and motility. This might also explain, at in least in part, the enhanced apoptosis observed in Sgca-null MPCs in vitro and in vivo.…”