Oxidative stress in myocardial ischaemia reperfusion injury: a renewed focus on a long-standing area of heart research

Advances in the treatment of coronary artery disease have seen a significant drop in mortality and morbidity particularly amongst patients with acute myocardial infarction (MI). In particular, percutaneous trans-luminal balloon angioplasty (PTCA) with stenting to re-open atherosclerotic coronary arteries has yielded marked improvement in clinical outcome for patients with acute MI. Furthermore, with the advent of drug-eluting stents occurrence rates for coronary artery restenosis, one common clinical problem associated with angioplasty and stent deployment, have declined markedly. However, coronary restenosis in diabetic patients remains an on-going problem. The success of drug-eluting stents has seen a renewed focus on myocardial ischaemia reperfusion (IR) injury as this represents one area of research where many questions remain unanswered. In particular, the relationship between myocardial IR injury and decreased myocardial micro-vasculature re-flow post PTCA (that ultimately leads to poor clinical outcome and myocardial damage/dysfunction) is one area of research with the potential to decrease current complication rates further in patients suffering myocardial IR injury sustained during MI. This review discusses the role for oxidative stress, oxidant source(s) and both gene regulation and stem-cell therapy as potential strategic targets in the ischaemic myocardium, with the ultimate aim of providing significant cardioprotection in the setting of acute MI.     

Phylogeographic patterns in the Philippine archipelago influence symbiont diversity in the bobtail squid–Vibrio mutualism

Marine microbes encounter a myriad of biotic and abiotic factors that can impact fitness by limiting their range and capacity to move between habitats. This is especially true for environmentally transmitted bacteria that cycle between their hosts and the surrounding habitat. As geologic history, biogeography, and other factors such as water temperature, salinity, and physical barriers can inhibit bacterial movement to novel environments, we chose to examine the genetic architecture of Euprymna albatrossae (Mollusca: Cephalopoda) and their Vibrio fischeri symbionts in the Philippine archipelago using a combined phylogeographic approach. Eleven separate sites in the Philippine islands were examined using haplotype estimates that were examined via nested clade analysis to determine the relationship between E. albatrossae and V. fischeri populations and their geographic location. Identical analyses of molecular variance (AMOVA) were used to estimate variation within and between populations for host and symbiont genetic data. Host animals demonstrated a significant amount of variation within island groups, while symbiont variation was found within individual populations. Nested clade phylogenetic analysis revealed that hosts and symbionts may have colonized this area at different times, with a sudden change in habitat. Additionally, host data indicate restricted gene flow, whereas symbionts show range expansion, followed by periodic restriction to genetic flow. These differences between host and symbiont networks indicate that factors “outside the squid” influence distribution of Philippine V. fischeri. Our results shed light on how geography and changing environmental factors can impact marine symbiotic associations at both local and global scales.     

Macronutrient composition and availability affects repeatability of fly activity through changes in among- and within-individual (residual) variation

Evolutionary Ecology - Understanding how environmental conditions affect trait expression in animals is important for estimating the evolutionary potential of that trait. Two different mechanisms...     

Phosphatidylinositol-5-phosphate activation and conserved substrate specificity of the myotubularin phosphatidylinositol 3-phosphatases

Phosphoinositides control many different processes required for normal cellular function. Myotubularins are a family of Phosphatidylinositol 3-phosphate (PtdIns3P) phosphatases identified by the positional cloning of the MTM1 gene in patients suffering from X-linked myotubular myopathy and the MTMR2 gene in patients suffering from the demyelinating neuropathy Charcot-Marie-Tooth disease type 4B. MTM1 is a phosphatidylinositol phosphatase with reported specificity toward PtdIns3P, while the related proteins MTMR2 and MTMR3 hydrolyze both PtdIns3P and PtdIns(3,5)P2. We have investigated MTM1 and MTMR6 and find that they use PtdIns(3,5)P2 in addition to PtdIns3P as a substrate in vitro. The product of PtdIns(3,5)P2 hydrolysis, PtdIns5P, causes MTM1 to form a heptameric ring that is 12.5 nm in diameter, and it is a specific allosteric activator of MTM1, MTMR3, and MTMR6. A disease-causing mutation at arginine 69 of MTM1 falling within a putative pleckstrin homology domain reduces the ability of the enzyme to respond to PtdIns5P. We propose that the myotubularin family of enzymes utilize both PtdIns3P and PtdIns(3,5)P2 as substrates, and that PtdIns5P functions in a positive feedback loop controlling their activity. These findings highlight the importance of regulated phosphatase activity for the control of phosphoinositide metabolism.     

The platelet microparticle proteome

Platelet-derived microparticles are the most abundant type of microparticle in human blood and contribute to many biologically significant processes. Here, we report the first proteomic analysis of microparticles generated from activated platelets. Using 1D SDS-PAGE and liquid chromatography coupled to a linear ion trap mass spectrometer, the identification of 578 proteins was accomplished using a minimum of 5 MS/MS detections of at least two different peptides for each protein. These microparticles displayed many proteins intrinsic to and well-characterized on platelets. For example, microparticles in these experiments were found to contain membrane surface proteins including GPIIIa, GPIIb, and P-selectin, as well other platelet proteins such as the chemokines CXCL4, CXCL7, and CCL5. In addition, approximately 380 of the proteins identified were not found in two previous studies of the platelet proteome. Since several of the proteins detected here have been previously implicated in microparticle formation and/or pathological function, it is hoped that this study will help fuel future work concerning the possible role of microparticles in various disease states.     

Soluble Oligomers of the Pore-forming Toxin Cytolysin A from Escherichia coli Are Off-pathway Products of Pore Assembly

The α-pore-forming toxin Cytolysin A (ClyA) is responsible for the hemolytic activity of various Escherichia coli and Salmonella enterica strains. Soluble ClyA monomers spontaneously assemble into annular dodecameric pore complexes upon contact with membranes or detergent. At ClyA monomer concentrations above ∼100 nm, the rate-limiting step in detergent- or membrane- induced pore assembly is the unimolecular reaction from the monomer to the assembly-competent protomer, which then oligomerizes rapidly to active pore complexes. In the absence of detergent, ClyA slowly forms soluble oligomers. Here we show that soluble ClyA oligomers cannot form dodecameric pore complexes after the addition of detergent and are hemolytically inactive. In addition, we demonstrate that the natural cysteine pair Cys-87/Cys-285 of ClyA forms a disulfide bond under oxidizing conditions and that both the oxidized and reduced ClyA monomers assemble to active pores via the same pathway in the presence of detergent, in which an unstructured, monomeric intermediate is transiently populated. The results show that the oxidized ClyA monomer assembles to pore complexes about one order of magnitude faster than the reduced monomer because the unstructured intermediate of oxidized ClyA is less stable and dissolves more rapidly than the reduced intermediate. Moreover, we show that oxidized ClyA forms soluble, inactive oligomers in the absence of detergent much faster than the reduced monomer, providing an explanation for several contradictory reports in which oxidized ClyA had been described as inactive.