Localization of sarcoglycan, neuronal nitric oxide synthase, beta-dystroglycan, and dystrophin molecules in normal skeletal myofiber: triple immunogold labeling electron microscopy

Downregulating SynCAM and MPP6 expression is associated with ovarian cancer progression

Synaptic cell adhesion molecules (SynCAMs) are single transmembrane proteins that belong to the immunoglobulin superfamily of cell adhesion molecules. In the present study, a decrease in SynCAM levels in ovarian tumor tissues compared with normal tissues is reported; the downregulation was accompanied by the grade malignancy. The observations suggested that SynCAM may be essential for important novel functions in ovarian cancer. Further experiments showed that low SynCAM expression inhibited membrane palmitoylated protein 6 (MPP6) expression, a member of the palmitoylated membrane protein subfamily of peripheral membrane-associated guanylate kinases. In addition, low levels of MPP6 in ovarian tumor tissues correlated with shorter patient survival. A SynCAM-regulated pathway may provide molecular targets for the treatment of ovarian cancer and novel biomarkers to be used in clinical diagnosis.

Biophysical Stimulation for Engineering Functional Skeletal Muscle

Tissue engineering is a promising therapeutic strategy to regenerate skeletal muscle. However, ex vivo cultivation methods typically result in a low differentiation efficiency of stem cells as well as grafts that resemble the native tissues morphologically, but lack contractile function. The application of biomimetic tensile strain provides a potent stimulus for enhancing myogenic differentiation and engineering functional skeletal muscle grafts. We reviewed integrin-dependent mechanisms that potentially link mechanotransduction pathways to the upregulation of myogenic genes. Yet, gaps in our understanding make it challenging to use these pathways to theoretically determine optimal ex vivo strain regimens. A multitude of strain protocols have been applied to in vitro cultures for the cultivation of myogenic progenitors (adipose- and bone marrow-derived stem cells and satellite cells) and transformed murine myoblasts, C2C12s. Strain regimens are characterized by orientation, amplitude, and time-dependent factors (effective frequency, duration, and the rest period between successive strain cycles). Analysis of published data has identified possible minimum/maximum values for these parameters and suggests that uniaxial strains may be more potent than biaxial strains, possibly because they more closely mimic physiologic strain profiles. The application of these biophysical stimuli for engineering 3D skeletal muscle grafts is nontrivial and typically requires custom-designed bioreactors used in combination with biomaterial scaffolds. Consideration of the physical properties of these scaffolds is critical for effective transmission of the applied strains to encapsulated cells. Taken together, these studies demonstrate that biomimetic tensile strain generally results in improved myogenic outcomes in myogenic progenitors and differentiated myoblasts. However, for 3D systems, the optimization of the strain regimen may require the entire system including cells, biomaterials, and bioreactor, to be considered in tandem.

SynCAM, a novel putative tumor suppressor, suppresses growth and invasiveness of glioblastoma

SynCAM, also named by TSLC1, SgIGSF and IGSF4, was identified as a neural tissue-specific immunoglobulin-like cell-cell adhesion molecule. However, the role of SynCAM in tumorigenesis remains elusive. We aimed to clarify its epigenetic regulation and biological functions in glioblastoma. SynCAM was silenced in 72 % (5/7) glioblastoma cell lines. A significant downregulation was also detected in paired glioblastoma tumors compared with adjacent non-cancerous tissues. In contrast, SynCAM was readily expressed in various normal adult brain tissues. Ectopic expression of SynCAM in the silenced cancer cell line T98G significantly reduced colony formation and cell proliferation, induced cell cycle arrests and repressed cell invasive ability. Nude mice were subcutaneously injected into the flank with T98G cells and treated with normal saline, pcDNA3.1 (vector) or pcDNA3.1-SynCAM, respectively. Treatment with pcDNA3.1-SynCAM retarded growth in the xenografts, which contributed to a 58 % decrease in tumor volume compared to controls. In conclusion, our results suggest that SynCAM suppressions growth of glioblastoma and may serve as a novel functional tumor-suppressor gene.

Fukutin-related protein resides in the Golgi cisternae of skeletal muscle fibres and forms disulfide-linked homodimers via an N-terminal interaction

Limb-Girdle Muscular Dystrophy type 2I (LGMD2I) is an inheritable autosomal, recessive disorder caused by mutations in the FuKutin-Related Protein (FKRP) gene (FKRP) located on chromosome 19 (19q13.3). Mutations in FKRP are also associated with Congenital Muscular Dystrophy (MDC1C), Walker-Warburg Syndrome (WWS) and Muscle Eye Brain disease (MEB). These four disorders share in common an incomplete/aberrant O-glycosylation of the membrane/extracellular matrix (ECM) protein α-dystroglycan. However, further knowledge on the FKRP structure and biological function is lacking, and its intracellular location is controversial. Based on immunogold electron microscopy of human skeletal muscle sections we demonstrate that FKRP co-localises with the middle-to-trans-Golgi marker MG160, between the myofibrils in human rectus femoris muscle fibres. Chemical cross-linking experiments followed by pairwise yeast 2-hybrid experiments, and co-immune precipitation, demonstrate that FKRP can exist as homodimers as well as in large multimeric protein complexes when expressed in cell culture. The FKRP homodimer is kept together by a disulfide bridge provided by the most N-terminal cysteine, Cys6. FKRP contains N-glycan of high mannose and/or hybrid type; however, FKRP N-glycosylation is not required for FKRP homodimer or multimer formation. We propose a model for FKRP which is consistent with that of a Golgi resident type II transmembrane protein.

δ-Sarcoglycan-deficient muscular dystrophy: from discovery to therapeutic approaches

Mutations in the δ-sarcoglycan gene cause limb-girdle muscular dystrophy 2F (LGMD2F), an autosomal recessive disease that causes progressive weakness and wasting of the proximal limb muscles and often has cardiac involvement. Here we review the clinical implications of LGMD2F and discuss the current understanding of the putative mechanisms underlying its pathogenesis. Preclinical research has benefited enormously from various animal models of δ-sarcoglycan deficiency, which have helped researchers to explore therapeutic approaches for both muscular dystrophy and cardiomyopathy.

Sarcospan: ultrastructural localization and its relation to the sarcoglycan subcomplex

Sarcospan is a 25 kDa transmembrane component of dystrophin-associated glycoprotein. We generated a rabbit polyclonal antibody against synthetic peptide of the N-terminal domain of human sarcospan. Using this antibody we investigated the localization of sarcospan and its spacial relation to the components of sarcoglycan subcomplex in normal human skeletal myofibers by immunofluorescent microscopy and immunogold electron microscopy. In immunofluorescence the reaction was observed continuously at the myofiber surface. Ultrastructurally the gold signals of rabbit anti sarcospan antibody were present along the muscle plasma membrane, mainly at its inside surface. The triple immunogold labeled muscle samples showed that the signals of rabbit or sheep polyclonal anti alpha-, beta-, gamma- and delta-sarcoglycan antibodies and/or mouse monoclonal anti beta-, gamma- and delta-sarcoglycan antibodies were located along the muscle plasma membrane, and the cluster formation of different two or three sarcoglycan molecules was observed. The triple immunogold labeling also revealed that the signal of sarcospan molecules are present frequently in doublets and/or triplets with the components of sarcoglycan subcomplex, resulting in the cluster formation of signals of sarcoglycan and sarcospan molecules. The result of this study showed that sarcospan was expressed at the myofiber surface and that sarcospan was present in close association with alpha-, beta-, gamma- and delta-sarcoglycans and formed a functional unit with sarcoglycan subcomplex.

New aspects of the location of neuronal nitric oxide synthase in the skeletal muscle: A light and electron microscopic study

The action of nitric oxide (NO) synthesized by NO synthases (NOS) is spatially restricted. Hence, the intracellular location of NOS might play an important role for the functional interactions of NO with its target molecules. In the skeletal muscle the neuronal NOS (nNOS) is considered to be the predominant isoform expressed as a muscle specific elongated splice variant. There are only a few and highly discrepant reports of the subcellular distribution of nNOS, which prompted us to re-examine the distribution of nNOS in the skeletal muscle of rat and mouse applying immunocytochemistry and NADPH-diaphorase (NADPH-d) histochemistry. Light microscopically, the sarcolemma, areas beneath the sarcolemma, areas around the nuclei, and the cross striation were labeled by antibodies and by the NADPH-d reaction as well. Ultrastructurally, nNOS visualized immunocytochemically or by the histochemical BSPT-reaction, was associated discretely with extrajunctional portions of the sarcolemma. Both reaction products were additionally observed in the vicinity of endoplasmic reticulum and mitochondria, or associated with their outer membranes. In the neuromuscular junction (NMJ)-region NOS was localized to the cytoplasm of nerve terminals and terminal Schwann cells. In contrast to the commonly accepted assumption, the enzyme was found in association with the presynaptic, and not with the postsynaptic membrane. Cytosolic NADPH-d was exhibited especially between mitochondria accumulated in the postsynaptic region of the NMJ. Surprisingly, in nNOS-/--mice the skeletal muscle showed patterns of significant nNOS-immunoreactivity and NADPH-d activity possibly due to alternative nNOS-splice isoforms, which might be up-regulated to compensate for decreased NO formation.