Contractile properties,structure and fiber phenotype of intact and regenerating slow-twitch muscles of mice treated with cyclosporin A

We have studied the contractile properties, structure, fiber-type composition, and myosin heavy chain (MyHC) expression pattern of regenerating and intact soleus muscles of adult CBA/J mice treated with cyclosporin A (CsA) or vehicle solutions (Cremophor, saline). A comparison of muscles after 4-7 weeks drug application with those receiving vehicle showed that the isometric contractile force of intact drug-treated muscles was reduced (tetanus, -21%; twitch, -34%) despite normal mass and muscle cross-sectional area. The frequency of fast-twitch fibers was increased, whereas no innervation deficits, histopathological alterations, or changes in fiber numbers were observed. Regeneration after cryolesion of the contralateral soleus proceeded more slowly in CsA-treated than in vehicle-treated animals. Despite this, when muscle properties reached mature levels (4-7 weeks), muscle mass recovery was better in CsA-treated animals (30% higher weight, 50% more fiber profiles in cross-sections). The force production per unit cross-sectional area was deficient, but not the maximum tension. Twitch time-to-peak and half-relaxation time were shorter than controls correlating with a predominance of fast-twitch fibers (98% Type II fibers versus 16%-18% in control muscles) and fast MyHC isoforms. Partial reversal of this fast phenotype and an increase in muscle force were observed when the animals were left to recover without treatment for 5-8 weeks after CsA application over 7 weeks. The high numbers of fiber profiles in CsA-treated regenerated muscles and increased mass remained unchanged after withdrawal. Thus, CsA treatment has a hyperplastic effect on regenerating muscles, and drug-induced phenotype alterations are much more prominent in regenerated muscles.     

Detection and quantification of mitochondrial DNA deletions in individual cells by real-time PCR

Defects of mitochondrial DNA (mtDNA) are an important cause of disease and play a role in the ageing process. There are multiple copies of the mitochondrial genome in a single cell. In many patients with acquired or inherited mtDNA mutations, there exists a mixture of mutated and wild type genomes (termed heteroplasmy) within individual cells. As a biochemical and clinical defect is only observed when there are high levels of mutated mtDNA, a crucial investigation is to determine the level of heteroplasmic mutations within tissues and individual cells. We have developed an assay to determine the relative amount of deleted mtDNA using real-time fluorescence PCR. This assay detects the vast majority of deleted molecules, thus eliminating the need to develop specific probes. We have demonstrated an excellent correlation with other techniques (Southern blotting and three- primer competitive PCR), and have shown this technique to be sensitive to quantify the level of deleted mtDNA molecules in individual cells. Finally, we have used this assay to investigate patients with mitochondrial disease and shown in individual skeletal muscle fibres that there exist different patterns of abnormalities between patients with single or multiple mtDNA deletions. We believe that this technique has significant advantages over other methods to quantify deleted mtDNA and, employed alongside our method to sequence the mitochondrial genome from single cells, will further our understanding of the role of mtDNA mutations in human disease and ageing.     

Microtubule-dependent transport of secretory vesicles in RBL-2H3 cells

Antigen-mediated activation of mast cells results in Ca²⁺-dependent exocytosis of preformed mediators of the inflammatory response. To investigate the role of secretory vesicle motility in this response, we have performed time-lapse confocal microscopy on RBL-2H3 cells transfected with a green fluorescent protein-Fas ligand fusion protein (GFP-FasL). Green fluorescent protein-labeled vesicles exhibit rapid, bidirectional movement in both resting and activated cells and can be localized adjacent to microtubules. Colchicine treatment inhibits the motility of secretory vesicles as measured by fluorescence recovery after photobleaching (FRAP). Colchicine also inhibits both the extent and the rate of exocytosis triggered by receptor activation or by Ca²⁺ ionophore, demonstrating that microtubule-dependent movement of secretory vesicles plays an important role in the exocytic response .     

Role of TIMPs (tissue inhibitors of metalloproteinases) in pericellular proteolysis: the specificity is in the detail

Pericellular proteolysis represents one of the key modes by which the cell can modulate its environment, involving not only turnover of the extracellular matrix but also the regulation of cell membrane proteins, such as growth factors and their receptors. The metzincins are active players in such proteolytic events, and their mode of regulation is therefore of particular interest and importance. The TIMPs (tissue inhibitors of metalloproteinases) are established endogenous inhibitors of the matrix metalloproteinases (MMPs), and some have intriguing abilities to associate with the pericellular environment. It has been shown that TIMP-2 can bind to cell surface MT1-MMP (membrane-type 1 MMP) to act as a 'receptor' for proMMP-2 (progelatinase A), such that the latter can be activated efficiently in a localized fashion. We have examined the key structural features of TIMP-2 that determine this unique function, showing that Tyr36 and Glu192-Asp193 are vital for specific interactions with MT1-MMP and proMMP-2 respectively, and hence activation of proMMP-2. TIMP-3 is sequestered at the cell surface by association with the glycosaminoglycan chains of proteoglycans, especially heparan sulphate, and we have shown that it may play a role in the regulation of some ADAMs (a disintegrin and metalloproteinases), including tumour necrosis factor alpha-converting enzyme (TACE; ADAM17). We have established that key residues in TIMP-3 determine its interaction with TACE. Further studies of the features of TIMP-3 that determine specific binding to both ADAM and glycosaminoglycan are required in order to understand these unique properties.     

Validation of liquid chromatography assay for the quantitation of (Z)-3-[2,4-dimethyl-5-(2-oxo-1,2-dihydro-indol-3-ylidenemethyl)-1H-pyrrol-3-yl]propionic acid (SU006668) in human plasma and its application to a phase I clinical trial

The validation of an analytical method to quantify the antiangiogenic, (Z)-3-[2,4-dimethyl-5-(2-oxo-1,2-dihydro-indol-3-ylidenemethyl)-1H-pyrrol-3-yl]propionic acid (SU006668) for pharmacokinetic determination in a phase I clinical trial, is described. HPLC, with a gradient mobile phase and UV detection at 440 nm, was used. SU006668 was extracted from plasma by precipitation of proteins with acetonitrile. The assay was linear from 25 to 2000 ng/ml (r(2)=0.997); sensitive (limit of quantification 25 ng/ml), accurate (RE 2.6-11.9%) and reproducible (inter-batch precision C.V. 3.2%). Pharmacokinetic data for six patients are presented. They show linear pharmacokinetics with a low volume of distribution and induction at doses of 50, 100 and 200 mg/m(2).     

A novel function for tissue inhibitor of metalloproteinases-3 (TIMP3): inhibition of angiogenesis by blockage of VEGF binding to VEGF receptor-2

Tissue inhibitor of metalloproteinases-3 (TIMP3) is one of four members of a family of proteins that were originally classified according to their ability to inhibit matrix metalloproteinases (MMP). TIMP3, which encodes a potent angiogenesis inhibitor, is mutated in Sorsby fundus dystrophy, a macular degenerative disease with submacular choroidal neovascularization. In this study we demonstrate the ability of TIMP3 to inhibit vascular endothelial factor (VEGF)-mediated angiogenesis and identify the potential mechanism by which this occurs: TIMP3 blocks the binding of VEGF to VEGF receptor-2 and inhibits downstream signaling and angiogenesis. This property seems to be independent of its MMP-inhibitory activity, indicating a new function for this molecule.     

A complete inventory of fungal kinesins in representative filamentous ascomycetes

Complete inventories of kinesins from three pathogenic filamentous ascomycetes, Botryotinia fuckeliana, Cochliobolus heterostrophus, and Gibberella moniliformis, are described. These protein sequences were compared with those of the filamentous saprophyte, Neurospora crassa and the two yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. Data mining and phylogenetic analysis of the motor domain yielded a constant set of 10 kinesins in the filamentous fungal species, compared with a smaller set in S. cerevisiae and S. pombe. The filamentous fungal kinesins fell into nine subfamilies when compared with well-characterized kinesins from other eukaryotes. A few putative kinesins (one in B. fuckeliana and two in C. heterostrophus) could not be defined as functional, due to unorthodox organization and lack of experimental data. The broad representation of filamentous fungal kinesins across most of the known subfamilies and the ease of gene manipulation make fungi ideal models for functional and evolutionary investigation of these proteins.