Sarcoglycan subcomplex and Alpha-Dystroglycan in human digestive tract: immunofluorescence analysis

Abstract

The sarcoglycan complex (SGC) is a multimember transmembrane complex consisting of six glycosylated transmembrane proteins (α,β,δ,γ,ε,ζ). These proteins, primarily expressed in skele- tal muscle fibers, interact with other member of dystrophin-glycoprotein complex (DGC), dytro- phin, dystroglycans and syntrophins, in order to provide a mechano-signaling connection from the cytoskeleton to the extracellular matrix in myocytes and to stabilize the sarcolemma dur- ing contraction and release cycles in the muscle tissue. Our previous investigations have shown that sarcoglycans are not only muscle-specific but they are also present in the epithelial tissues, such as gingival, prostatic, respiratory and digestive, and also in the adipose tissue, demon- strating that these proteins are involved in cell-cell and cell-matrix interactions [1]. In order to verify the presence of sarcoglycans in the digestive epithelium and their interaction between α-dystroglycan, we performed immunofluorescence reactions on biopsies of normal sigmoid colon obtained from 10 subjects who underwent for other pathological reasons. Moreover, in the same samples, also we carried-out immunofluorescence reactions testing mucins. Mucins are a superfamily of highly glycosylated protein, they are part of mucus. The main roles of mucus are to protect and lubricate the underlying epithelia by injuries like enzymes, pH, bacte- ria and viruses. Mucins, also, lead to coordinate the apoptosis among cellular responses playing a key role as biomarkers for cancer and inflammatory diseases [2]. For the first time, our results show that: (i) sarcoglycans are expressed in the basal, lateral and apical cell’s sides; (ii) sarco- glycans colocalize in the apical region with mucins and α-dystroglycan; (iii) α-dystroglycan colocalizes with mucin in the cellular apical region. Our results suggest that a interactions between these sarcoglycans and mucus exists and, in our opinion, α-dystroglycan can play a key role in this interaction. On the basis of our results, we hypothesize that α-dystroglycan and sarcoglycans may have a role in the determination of the cell’s polarity, supported by the colo- calization of mucins and dystroglycans in the apical area.