[Show abstract][Hide abstract] ABSTRACT: We have recently proposed a new mechanism for explaining energy transfer in cancer metabolism. In this scenario, cancer cells behave as metabolic parasites, by extracting nutrients from normal host cells, such as fibroblasts, via the secretion of hydrogen peroxide as the initial trigger. Oxidative stress in the tumor microenvironment then leads to autophagy-driven catabolism, mitochondrial dys-function, and aerobic glycolysis. This, in turn, produces high-energy nutrients (such as L-lactate, ketones, and glutamine) that drive the anabolic growth of tumor cells, via oxidative mitochondrial metabolism. A logical prediction of this new "parasitic" cancer model is that tumor-associated fibroblasts should show evidence of mitochondrial dys-function (mitophagy and aerobic glycolysis). In contrast, epithelial cancer cells should increase their oxidative mitochondrial capacity. To further test this hypothesis, here we subjected frozen sections from human breast tumors to a staining procedure that only detects functional mitochondria. This method detects the in situ enzymatic activity of cytochrome C oxidase (COX), also known as Complex IV. Remarkably, cancer cells show an over-abundance of COX activity, while adjacent stromal cells remain essentially negative. Adjacent normal ductal epithelial cells also show little or no COX activity, relative to epithelial cancer cells. Thus, oxidative mitochondrial activity is selectively amplified in cancer cells. Although COX activity staining has never been applied to cancer tissues, it could now be used routinely to distinguish cancer cells from normal cells, and to establish negative margins during cancer surgery. Similar results were obtained with NADH activity staining, which measures Complex I activity, and succinate dehydrogenase (SDH) activity staining, which measures Complex II activity. COX and NADH activities were blocked by electron transport inhibitors, such as Metformin. This has mechanistic and clinical implications for using Metformin as an anti-cancer drug, both for cancer therapy and chemo-prevention. We also immuno-stained human breast cancers for a series of well-established protein biomarkers of metabolism. More specifically, we now show that cancer-associated fibroblasts over-express markers of autophagy (cathepsin B), mitophagy (BNIP3L), and aerobic glycolysis (MCT4). Conversely, epithelial cancer cells show the over-expression of a mitochondrial membrane marker (TOMM20), as well as key components of Complex IV (MT-CO1) and Complex II (SDH-B). We also validated our observations using a bioinformatics approach with data from > 2,000 breast cancer patients, which showed the transcriptional upregulation of mitochondrial oxidative phosphorylation (OXPHOS) in human breast tumors (p < 10(-20)), and a specific association with metastasis. Therefore, upregulation of OXPHOS in epithelial tumor cells is a common feature of human breast cancers. In summary, our data provide the first functional in vivo evidence that epithelial cancer cells perform enhanced mitochondrial oxidative phosphorylation, allowing them to produce high amounts of ATP. Thus, we believe that mitochondria are both the "powerhouse" and "Achilles' heel" of cancer cells.
[Show abstract][Hide abstract] ABSTRACT: Aquaporin-4 (AQP4) is the major water channel expressed in fast-twitch skeletal muscle fibers. AQP4 is reduced in Duchenne and Becker Muscular Dystrophies, but not in caveolinopathies, thus suggesting an interaction with dystrophin or with members of the dystrophin-glycoprotein complex (DGC) rather than a nonspecific effect due to muscle membrane damage. To establish the role of sarcoglycans in AQP4 decrease occurring in muscular dystrophy, AQP4 expression was analyzed in muscle biopsies from patients affected by Limb Girdle Muscular Dystrophies (LGMDs) 2C-F genetically confirmed. In all the LGMD 2C-F (2alpha-, 1beta-, 2gamma-, 1delta-deficiency), AQP4 was severely decreased. This effect was associated to a marked reduction in alpha1-syntrophin levels. In control muscle AQP4 did not show a direct interaction with any of the four sarcoglycans but, it co-immunoprecipitated with alpha1-syntrophin, indicating that this modular protein may link AQP4 levels with the DGC complex. To determine whether AQP4 expression could be affected in other LGMDs due to the defect of a membrane protein not associated to the dystrophin complex, we examined AQP4 expression in 6 patients affected by dysferlin deficiency genetically confirmed. All the patients displayed a reduction of the water channel, and AQP4 expression appeared to correlate with the severity of the muscle histopathological lesions. However, differently from what observed in the sarcoglycans, alpha1-syntrophin expression was normal or just slightly reduced. These results seem to indicate an additional mechanism of regulation of AQP4 levels in muscle cells. In accordance with a specific effect of membrane muscle disorders, AQP4 protein levels were not changed in 3 mitochondrial and 3 metabolic myopathies. In conclusion, AQP4 expression and membrane localization are markedly reduced in LGMD 2B-2F. The role of AQP4 in the degenerative mechanism occurring in these diseases will be the object of our future research.
[Show abstract][Hide abstract] ABSTRACT: Defects in glycosylation of alpha-dystroglycan are associated with several forms of muscular dystrophies. Mutations in POMT2 gene have been identified in patients with congenital muscular dystrophy and brain involvement, either characterized by a Walker-Warburg/muscle-eye-brain phenotype, or by microcephaly, mental retardation, and cerebellar hypoplasia. We identified a POMT2 homozygous missense mutation in a girl with a mild limb-girdle muscular dystrophy (LGMD) phenotype, marked elevated serum creatine kinase levels, and absence of brain involvement. Muscle biopsy revealed myopathic and inflammatory changes and severe alpha-dystroglycan reduction. In view of the remarkable mild clinical picture, we propose to designate this phenotype as LGMD2N.
Biochemical and Biophysical Research Communications 12/2007; 363(4):1033-7. DOI:10.1016/j.bbrc.2007.09.066 · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Muscle-eye-brain disease is a congenital muscular dystrophy with eye and brain involvement due to POMGnT1 mutations.
To describe the clinical and molecular features of 3 Italian patients with POMGnT1 mutations.
One patient had muscle and brain abnormalities without eye involvement. Two patients had a classic muscle-eye-brain disease phenotype with different levels of clinical severity.
Brain magnetic resonance imaging showed cortical malformation and posterior fossa involvement. Immunofluorescence for glycosylated alpha-dystroglycan performed on muscle biopsy specimens demonstrated an absent signal in 1 patient and reduced staining in 2 patients. Molecular analysis identified 5 mutations, 2 of which are novel.
This article adds to what is known about the genotype-phenotype correlation and expands our awareness of the clinical spectrum associated with POMGnT1 mutations.
[Show abstract][Hide abstract] ABSTRACT: Danon disease, an X-linked cardioskeletal myopathy caused by primary deficiency of lysosome-associated membrane protein-2 (LAMP-2), is clinically characterized by cardiomyopathy, myopathy, and variable mental retardation. The pathological hallmark of the disease is the absence of LAMP-2 immunohistochemical staining in muscle. The LAMP-2 gene mutations reported thus far are generally private mutations. We describe two cases of Danon disease with different clinical presentation, in whom we identified the same exon skipping mutation c.928G>A in the LAMP-2 gene. The first patient was affected by an early onset myopathy and hypertrophic cardiomyopathy (HCM) that partially improved with drug treatment. A first muscle biopsy at age 4 months showed markedly increased glycogen, and acid maltase deficiency was ruled out biochemically. A second muscle biopsy, performed at age 3(1/2) years, showed very mild abnormalities. The second child at age 15 years had mild, diffuse muscle weakness and wasting, moderate mental deficiency, and HCM. Two serial biopsies performed at age 8 and 15 years showed similar findings of multiple esterase-positive vacuoles in type I myofibers. In both patients the immunohistochemical study demonstrated the absence of LAMP-2 in skeletal muscle.
[Show abstract][Hide abstract] ABSTRACT: Caveolin-3, a muscle specific caveolin-related protein, is the principal structural protein of caveolar membranes. We have recently identified an autosomal dominant form of limb girdle muscular dystrophy (LGMD-1C) that is due to caveolin-3 deficiency and caveolin-3 gene mutations. Here, we studied by electron microscopy, including freeze-fracture and lanthanum staining, the distribution of caveolae and the organization of the T-tubule system in caveolin-3 deficient human muscle fibers. We found a severe impairment of caveolae formation at the muscle cell surface, demonstrating that caveolin-3 is essential for the formation and organization of caveolae in muscle fibers. In addition, we also detected a striking disorganization of the T-system openings at the sub-sarcolemmal level in LGMD-1C muscle fibers. These observations provide new perspectives in our understanding of the role of caveolin-3 in muscle and of the pathogenesis of muscle weakness in caveolin-3 deficient muscle.
American Journal Of Pathology 02/2002; 160(1):265-70. DOI:10.1016/S0002-9440(10)64370-2 · 4.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mutations in the caveolin-3 (CAV3) gene are associated with autosomal dominant limb-girdle muscular dystrophy (LGMD1C). The authors report a novel sporadic mutation in the CAV3 gene in two unrelated children with persistent elevated levels of serum creatine kinase (hyperCKemia) without muscle weakness. Immunohistochemistry and quantitative immunoblot analysis of caveolin-3 showed reduced expression of the protein in muscle fibers. Our data indicate that a partial caveolin-3 deficiency should be considered in the differential diagnosis of idiopathic hyperCKemia.
[Show abstract][Hide abstract] ABSTRACT: Caveolae are small pockets or invaginations localized at the plasma membrane. Caveolins are the principal protein components of caveolae and play an important structural role in the formation of caveolae membranes. Here, we studied by freeze fracture and immunological techniques the spatial organization of caveolae at the muscle cell plasma membrane and the expression of caveolin-3 in Duchenne muscular dystrophy (DMD) muscle fibers. In DMD muscle, we found an increased number of caveolae at the sarcolemma that corresponds to an overexpression of caveolin-3 by immunohistochemistry and by Western blot analysis. These findings suggest a possible role for caveolae and caveolin-3 in the pathogenesis of DMD.
Biochemical and Biophysical Research Communications 09/1999; 261(3):547-50. DOI:10.1006/bbrc.1999.1055 · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Limb-girdle muscular dystrophy (LGMD) is a clinically and genetically heterogeneous group of myopathies, including autosomal dominant and recessive forms. To date, two autosomal dominant forms have been recognized: LGMD1A, linked to chromosome 5q, and LGMD1B, associated with cardiac defects and linked to chromosome 1q11-21. Here we describe eight patients from two different families with a new form of autosomal dominant LGMD, which we propose to call LGMD1C, associated with a severe deficiency of caveolin-3 in muscle fibres. Caveolin-3 (or M-caveolin) is the muscle-specific form of the caveolin protein family, which also includes caveolin-1 and -2. Caveolins are the principal protein components of caveolae (50-100 nm invaginations found in most cell types) which represent appendages or sub-compartments of plasma membranes. We localized the human caveolin-3 gene (CAV3) to chromosome 3p25 and identified two mutations in the gene: a missense mutation in the membrane-spanning region and a micro-deletion in the scaffolding domain. These mutations may interfere with caveolin-3 oligomerization and disrupt caveolae formation at the muscle cell plasma membrane.
[Show abstract][Hide abstract] ABSTRACT: Myophosphorylase deficiency or McArdle's disease is rarely recognized in childhood. The onset is generally in adolescence or in adult age with exercise intolerance, muscle cramps and myoglobinuria. Two siblings of 6 and 2 years of age are described. The first patient showed early fatigue and both had elevated CK levels. Morphological and biochemical studies of muscle biopsies revealed a defect of myophosphorylase.