Role of gelatinases in pathological and physiological processes involving the dystrophin-glycoprotein complex

Dystrophin is a cytosolic protein belonging to a membrane-spanning glycoprotein complex, called dystrophin-glycoprotein complex (DGC), that is expressed in many tissues, especially in skeletal muscle and in the nervous system. The DGC connects the cytoskeleton with the extracellular matrix and, although none of the protein of the DGC displays kinase or phosphatase activity, it is involved in many signal transduction pathways. Mutations in some components of the DGC are linked to many forms of inherited muscular dystrophies. In particular, a mutation hitting the dystrophin gene, leading to a complete loss of the protein, provokes one of the most prominent muscular dystrophy, the Duchenne muscular dystrophy, which affects 1 out of 3500 newborn males. In these circumstances, it can be observed a dramatic alteration of the expression levels of a multitude of metalloproteinases (MMPs), a family of extracellular Zn2+-dependent endopeptidases, especially MMP-2 and MMP-9, also called gelatinases. However, the enzymatic activity of MMP-2 and MMP-9 on dystroglycan, an important member of the DGC, plays an important role also in physiological processes taking place in the central and peripheral nervous system. This mini-review discusses the role of MMP-2 and MMP-9, in physiological as well as pathological processes involving members of the DGC

From adhesion complex to signaling hub:the dual role of dystroglycan

Dystroglycan (DG) is a transmembrane protein widely expressed in multiple cells and tissues. It is formed by two subunits, α- and β-DG, and represents a molecular bridge between the outside and the inside of the cell, which is essential for the mechanical and structural stability of the plasma membrane. The α-subunit is a cell-surface protein that binds to the extracellular matrix (ECM) and is tightly associated with the plasma membrane via a non-covalent interaction with the β-subunit, which, in turn, is a transmembrane protein that binds to the cytoskeletal actin. DG is a versatile molecule acting not only as a mechanical building block but also as a modulator of outside-inside signaling events. The cytoplasmic domain of β-DG interacts with different adaptor and cytoskeletal proteins that function as molecular switches for the transmission of ECM signals inside the cells. These interactions can modulate the involvement of DG in different biological processes, ranging from cell growth and survival to differentiation and proliferation/regeneration. Although the molecular events that characterize signaling through the ECM-DG-cytoskeleton axis are still largely unknown, in recent years, a growing list of evidence has started to fill the gaps in our understanding of the role of DG in signal transduction. This mini-review represents an update of recent developments, uncovering the dual role of DG as an adhesion and signaling molecule that might inspire new ideas for the design of novel therapeutic strategies for pathologies such as muscular dystrophy, cardiomyopathy, and cancer, where the DG signaling hub plays important roles.</p

The Structure of the N-terminal Region of Murine Skeletal Muscle α-Dystroglycan Discloses a Modular Architecture

Dystroglycan (DG) is a cell surface receptor consisting of two subunits: alpha-dystroglycan, extracellular and highly glycosylated, and beta-dystroglycan, spanning the cell membrane. It is a pivotal member of the dystrophin-glycoprotein complex and is involved in a wide variety of important cellular processes such as the stabilization of the muscle fiber sarcolemma or the clustering of acetylcholine receptors. We report the 2.3-A resolution crystal structure of the murine skeletal muscle N-terminal alpha-DG region, which confirms the presence of two autonomous domains; the first finally identified as an Ig-like and the second resembling ribosomal RNA-binding proteins. Solid-phase laminin binding assays show the occurrence of protein-protein type of interactions involving the Ig-like domain of alpha-DG

An Immunological Analysis of Dystroglycan Subunits: Lessons Learned from a Small Cohort of Non-Congenital Dystrophic Patients

The dystroglycan (DG) expression pattern can be altered in severe muscular dystrophies. In fact, some congenital muscular dystrophies (CMDs) and limb-girdle muscular dystrophies (LGMDs) are caused by point mutations identified in six glycosyltransferase genes which are likely to target different steps along the posttranslational “O-glycosylation route” leading to a fully decorated and functional α-DG subunit. Indeed, hypoglycosylation of α-DG is thought to represent a major pathological event, in that it could reduce the DG’s ability to bind the basement membrane components, thus leading to sarcolemmal instability and necrosis. In order to set up an efficient standard immunological protocol, taking advantage of a wide panel of antibodies, we have analyzed the two DG subunits in a small cohort of adult dystrophic patients, whom an extensive medical examination had already clinically classified as affected by LGMD (5), Miyoshi (1) or distal (1) myopathy. Immunofluorescence analysis of skeletal muscle tissue sections revealed a proper sarcolemmal localization of the DG subunits in all the patients analyzed. However, Western blot analysis of lectin enriched skeletal muscle samples revealed an abnormal glycosylation of α-DG in two patients. Our work reinforces the notion that a careful immunological and biochemical analysis of the two DG subunits should be always considered as a prerequisite for the identification of new putative cases of dystroglycanopathy

Identification and modelling of a GT-A fold in the α-dystroglycan glycosylating enzyme LARGE1

LARGE xylosyl- and glucuronyltransferase 1 (LARGE1)is an enzyme responsible for the final steps of the post-translational modifications of dystroglycan (DG), a membrane receptor that links the cytoskeleton with the extracellular matrix in skeletal muscle and in a variety of other tissues. LARGE1 acts by adding the repeating disaccharide unit [-3Xyl-\u3b11,3GlcA\u3b21-] to the extracellular portion of the DG complex (\u3b1-DG); defects in the LARGE1 gene result in an aberrant glycosylation of \u3b1-DG and consequent impairment of its binding to laminin, eventually affecting the connection between the cell and the extracellular environment. In skeletal muscle, this leads to degeneration of the muscular tissue and muscular dystrophy. So far, a few missense mutations have been identified within the LARGE1 protein and linked to congenital muscular dystrophy and, since no structural information is available on this enzyme, our understanding of the molecular mechanisms underlying these pathologies is still very limited. Here, we generated a 3D model structure of the two catalytic domains of LARGE1, combining different molecular modelling approaches. Furthermore, by using molecular dynamics simulations we analyzed the effect on the structure and stability of the first catalytic domain of the pathological missense mutation S331F that gives rise to a severe form of muscle-eye-brain disease

The Structure of the T190M Mutant of Murine α-Dystroglycan at High Resolution: Insight into the Molecular Basis of a Primary Dystroglycanopathy

Bozzi M, Cassetta A, Covaceuszach S, et al. The Structure of the T190M Mutant of Murine α-Dystroglycan at High Resolution: Insight into the Molecular Basis of a Primary Dystroglycanopathy. PLOS ONE. 2015;10(5): e0124277

Seroprevalence of group B Coxsackieviruses: retrospective study in an Italian population

Purpose Group B Coxsackieviruses (CVB) include 6 serotypes (B1‐6) responsible for a wide range of clinical diseases. Since no recent seroepidemiologic data are available in Italy, the study aim was to investigate CVB seroprevalence in a wide Italian population. Methods The study retrospectively included 2,459 subjects referring to a large academic hospital in Rome (Italy) in the period 2004‐2016. Seroprevalence rates and neutralizing antibodies (nAb) titers were evaluated in relation to years of observation and subjects’ characteristics. Results Positivity for at least one serotype was detected in 69.1% of individuals. Overall, the prevalent serotype was B4, followed by B3 (33.3%), B5 (26.2%), B1 (12.7%), B2 (11.0%), and B6 (1.7%). For B2, a significant decrease in seroprevalence over years was observed. Positivity to at least one virus was 25.2% in children aged 0‐2 years, but significantly increased in pre‐school (3‐5 yr) (50.3%) and school (6‐10 yr) children (70.4%). Higher nAb responses for B3 and B4 were observed in children aged 3‐5 years. Conclusion A high overall CVB prevalence was found. Type‐specific variations in prevalence over time probably reflect the fluctuations in circulation typical of Enteroviruses. Children are at greater risk for CVB infection given the high number of seronegative subjects aged 0‐10 years

From adhesion complex to signaling hub: the dual role of dystroglycan

Dystroglycan (DG) is a transmembrane protein widely expressed in multiple cells and tissues. It is formed by two subunits, α− and β-DG, and represents a molecular bridge between the outside and the inside of the cell, which is essential for the mechanical and structural stability of the plasma membrane. The α-subunit is a cell-surface protein that binds to the extracellular matrix (ECM) and is tightly associated with the plasma membrane via a non-covalent interaction with the β-subunit, which, in turn, is a transmembrane protein that binds to the cytoskeletal actin. DG is a versatile molecule acting not only as a mechanical building block but also as a modulator of outside–inside signaling events. The cytoplasmic domain of β-DG interacts with different adaptor and cytoskeletal proteins that function as molecular switches for the transmission of ECM signals inside the cells. These interactions can modulate the involvement of DG in different biological processes, ranging from cell growth and survival to differentiation and proliferation/regeneration. Although the molecular events that characterize signaling through the ECM-DG-cytoskeleton axis are still largely unknown, in recent years, a growing list of evidence has started to fill the gaps in our understanding of the role of DG in signal transduction. This mini-review represents an update of recent developments, uncovering the dual role of DG as an adhesion and signaling molecule that might inspire new ideas for the design of novel therapeutic strategies for pathologies such as muscular dystrophy, cardiomyopathy, and cancer, where the DG signaling hub plays important roles