463 research outputs found
Autophagy in Skeletal Muscle Homeostasis and in Muscular Dystrophies
No full textSkeletal muscles are the agent of motion and one of the most important tissues responsible for the control of metabolism. The maintenance of muscle homeostasis is finely regulated by the balance between catabolic and anabolic process. Macroautophagy (or autophagy) is a catabolic process that provides the degradation of protein aggregation and damaged organelles through the fusion between autophagosomes and lysosomes. Proper regulation of the autophagy flux is fundamental for the homeostasis of skeletal muscles during physiological situations and in response to stress. Defective as well as excessive autophagy is harmful for muscle health and has a pathogenic role in several forms of muscle diseases. This review will focus on the role of autophagy in muscle homeostasis and diseases
Dysfunction of mitochondria and sarcoplasmic reticulum in the pathogenesis of collagen VI muscular dystrophies.
No full textUllrich Congenital Muscular Dystrophy (UCMD) and Bethlem Myopathy (BM) are muscle diseases due to mutations in the genes encoding the extracellular matrix protein collagen VI. Generation of a dystrophic mouse model where collagen VI synthesis was prevented by genetic ablation of the Col6a1 gene allowed an investigation of pathogenesis, which revealed the existence of a Ca2+-mediated dysfunction of mitochondria and the sarcoplasmic reticulum. A key event appears to be inappropriate opening of the mitochondrial permeability transition pore, an inner membrane high-conductance channel. Consistently, the Col6a1−/− myopathic mice could be cured with cyclosporin A through inhibition of cyclophilin D, a matrix protein that sensitizes the pore to opening.
Studies of myoblasts from UCMD and BM patients demonstrated the existence of a latent mitochondrial dysfunction irrespective of the genetic lesion responsible for the lack or the alteration of collagen VI. These studies suggest that PTP opening may represent
the final common pathway for skeletal muscle fiber death; and provided a rationale for a pilot clinical trial with cyclosporin A in patients affected by UCMD and BM, a study that holds great promise for the future treatment of collagen VI myopathies
Mitochondrial dysfunction and defective autophagy in the pathogenesis of collagen VI muscular dystrophies.
No full textUllrich Congenital Muscular Dystrophy (UCMD), Bethlem Myopathy (BM) and Congenital Myosclerosis are diseases due to mutations in the genes encoding the extracellular matrix protein collagen VI. A dystrophic mouse model where collagen VI synthesis was prevented by targeted inactivation of the Col6a1 gene allowed the investigation of pathogenesis, which revealed the existence of a Ca2+-mediated dysfunction of mitochondria and sarcoplasmic reticulum, and of defective autophagy. Key events are dysregulation of the mitochondrial permeability transition pore, an inner membrane high-conductance channel that for prolonged open times causes mitochondrial dysfunction; and inadequate removal of defective mitochondria, which amplifies the damage. Consistently, the Col6a1-/- myopathic mice could be cured with through inhibition of cyclophilin D, a matrix protein that sensitizes the pore to opening, and through stimulation of autophagy. Similar defects contribute to disease pathogenesis in patients irrespective of the genetic lesion causing the collagen VI defect. These studies indicate that PTP opening and defective autophagy represent key elements for skeletal muscle fiber death, and provide a rationale for the use of cyclosporin A and its non immunosuppressive derivatives in patients affected by collagen VI myopathies, a strategy that holds great promise for treatment
Ruolo dell'autofagia nella patogenesi delle miopatie legate al collagene VI
No full textCollagen VI is a large protein forming a microfilamentous network in the extracellular matrix of muscles and other tissues. Inherited mutations of genes encoding for collagen VI chains in humans cause three skeletal muscle diseases: Bethlem Myopathy, Ullrich Congenital Muscular Dystrophy and Myosclerosis Myopathy.
Previous work, performed in mice with genetic inactivation of Col6a1 gene and in patients, showed that complete or partial deficiency of collagen VI cause spontaneous apoptosis of muscle fibers. Myofibers death is due to sarcoplasmic reticulum alterations and mitochondrial dysfunction.
Although these studies have provided key information on the pathophysiological defects of collagen VI disorders, it is still unclear which molecular mechanisms are responsible for myopatic phenotype and, in particular, what is the link between collagen VI, organelle alterations and muscle fiber death. Therefore, for this thesis work, I focused on studies aimed at elucidating the molecular mechanisms affected by collagen VI deficiency in muscle, using Col6a1–/– mice as an experimental model. Initially, I searched for possible differences between knockout and wild-type muscles on proteins and pathways regulating cell death. Analysis of Bcl2 family members and of AKT kinase did not reveal any obvious alteration in Col6a1–/– muscles. However, the AMPK kinase was markedly activated, indicating an energetic unbalance, and this finding drove me to investigate autophagy, another mechanism of cell death. Macroautophagy (often simply called ‘autophagy’) is a self-degradative process involved both in basal turnover of cellular components and in their removal in response to nutrient starvation or organelle damage.Il collagene VI è una proteina ampiamente diffusa nella matrice extracellulare dei muscoli scheletrici e di altri organi. Mutazioni a carico dei geni codificanti le catene ?1, ?2 e ?3 della proteina causano nell’uomo tre patologie muscolari: la miopatia di Bethlem, la distrofia congenita di Ullrich e la miosclerosi.
Gli studi eseguiti in precedenza, prima sui topi con inattivazione mirata del gene Col6a1 e poi confermate sui pazienti, hanno dimostrato come la mancanza totale o parziale del collagene VI porti all’apoptosi nelle fibre muscolari. La morte delle miofibre è causata dalle alterazioni del reticolo sarcoplasmatico e dei mitocondri, ai quali è associata una disfunzione latente.
Nonostante questi studi abbiano fornito informazioni cruciali sui difetti patofisiologici nelle malattie legate al collagene VI, rimane ancora poco chiaro quale sia il meccanismo molecolare responsabile del fenotipo miopatico, ed in particolar modo quale sia il legame tra il collagene VI, le alterazioni agli organelli e la morte delle fibre muscolari. In questo lavoro di tesi mi sono quindi dedicato allo studio dei meccanismi molecolari affetti dalla carenza di collagene VI nel muscolo, utilizzando i topi Col6a1–/– come modello sperimentale. Ho ricercato, inizialmente, se vi fossero delle differenze tra topi knockout e topi selvatici nei principali fattori che regolano la morte cellulare. L’analisi delle proteine della famiglia Bcl2 e della chinasi AKT non hanno evidenziato alterazioni di rilievo nei muscoli Col6a1–/–. Tuttavia, la chinasi AMPK è risultata significativamente alterata nei muscoli Col6a1–/–, suggerendo una condizione di deficit energetico che mi ha indotto ad indagare un altro meccanismo di morte cellulare: l’autofagia. La macroautofagia o autofagia è un processo autodegradativo coinvolto sia nella normale sostituzione dei componenti cellulari, sia nella loro rimozione in risposta a situazioni di mancanza di nutrimento o di organelli danneggiati
Cellular and molecular mechanisms of muscle atrophy
No full textSkeletal muscle is a plastic organ that is maintained by multiple pathways regulating cell and protein turnover. During muscle atrophy, proteolytic systems are activated, and contractile proteins and organelles are removed, resulting in the shrinkage of muscle fibers. Excessive loss of muscle mass is associated with poor prognosis in several diseases, including myopathies and muscular dystrophies, as well as in systemic disorders such as cancer, diabetes, sepsis and heart failure. Muscle loss also occurs during aging. In this paper, we review the key mechanisms that regulate the turnover of contractile proteins and organelles in muscle tissue, and discuss how impairments in these mechanisms can contribute to muscle atrophy. We also discuss how protein synthesis and degradation are coordinately regulated by signaling pathways that are influenced by mechanical stress, physical activity, and the availability of nutrients and growth factors. Understanding how these pathways regulate muscle mass will provide new therapeutic targets for the prevention and treatment of muscle atrophy in metabolic and neuromuscular diseases
Role of macrophage polarization in tumor angiogenesis and vessel normalization: implications for new anticancer therapies.
No full textThe carboxyl terminus of the chicken alpha3 chain of collagen VI is a unique mosaic structure with glycoprotein Ib-like, fibronectin type III, and Kunitz modules.
No full textThe primary amino acid sequence of the carboxyl-terminal portion of the alpha 3 chain of chick type VI collagen as deduced from the nucleotide sequence is reported. This carboxyl-terminal segment is not present in the alpha 1 and alpha 2 chains of chick type VI collagen and is specific for a mosaic region with extensive similarities to several other proteins. This unique segment, beginning with a stretch (73 residues) very rich in serine and threonine, is preceded by sequences analogous to the platelet glycoprotein Ib. This region is followed by one segment that closely resembles the type III domains of fibronectin. At the end of the sequence, there is a 58-residue motif very similar to sequences characteristic of the Kunitz-type proteinase inhibitors. The present findings and our recent observation that the alpha 3(VI) chain contains 11 repeats similar to type A repeats of von Willebrand factor raise interesting questions about the peculiar mosaic structure and the multiple functions that this unique collagen might play in growth and remodeling of connective tissues
Biosynthesis of chick type VI collagen. II: Processing and secretion in fibroblasts and smooth muscle cells.
No full textThe biosynthesis of type VI collagen was studied in "matrix-free" chick embryo smooth muscle cells and fibroblasts. Omission of ascorbate from the culture affected to a great extent the secretion in fibroblasts but had a very minor effect on smooth muscle cells. Quantitative analysis of the secretion process in continuous time course and in pulse-chase experiments confirmed that fibroblasts and smooth muscle cells secreted type VI collagen with the same chain composition but with different kinetics: after 4 h of chase more than 60% of the labeled type VI collagen was present in the culture medium of fibroblasts, whereas at the same time interval less than 25% was secreted by smooth muscle cells. The different kinetics depends on intrinsic properties of the cells, since it was detected also in adherent cells. However, even in fibroblasts, secretion of type VI collagen was much slower than secretion of fibronectin, of which more than 50% was already in the cell medium after 1 h of chase. Treatment of the cells with inhibitors of hydroxylation and glycosylation caused a shift in mobility that revealed a size heterogeneity in the Mr = 260,000 subunit. No evidence of processing was observed in chick cells for any of the subunits that were synthesized and secreted uncleaved. In addition, after several days of chase the Mr of the subunits of type VI collagen isolated from the matrix remained unchanged, thus excluding that in the chick even a partial or incomplete processing takes place
The superfamily of proteins with von Willebrand Factor type A-like domains: one theme common to components of extracellular matrix, hemostasis, cellular adhesion, and defense mechanisms.
No full textAltered Threshold of the Mitochondrial Permeability Transition Pore in Ullrich Congenital Muscular Dystrophy
No full textWe have studied the effects of rotenone in myoblasts from healthy donors and from patients with Ullrich congenital muscular dystrophy (UCMD), a severe muscle disease due to mutations in the genes encoding the extracellular matrix protein collagen VI. Addition of rotenone to normal myoblasts caused a very limited
mitochondrial depolarization because the membrane potential was maintained by the F1FO synthase, as indicated by full depolarization following the subsequent addition of oligomycin. In UCMD myoblasts rotenone instead caused complete mitochondrial depolarization, which was followed by faster ATP depletion than in healthy myoblasts. Mitochondrial depolarization could be prevented by treatment with cyclosporin A and intracellular Ca2+ chelators, while it was worsened by depleting Ca2+ stores with thapsigargin. Thus, in UCMD myoblasts rotenone-induced depolarization is due to opening of the permeability transition pore rather than to inhibition of electron flux as such. These findings indicate that in UCMD myoblasts the threshold for pore opening is very close to the resting membrane potential, so that even a small depolarization causes permeability transition pore opening and precipitates ATP depletion
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