Emma McGregor

Proteomics of the Heart Unraveling Disease

Heart diseases resulting in heart failure are among the leading causes of morbidity and mortality in developed countries. Underlying molecular causes of cardiac dysfunction in most heart diseases are still largely unknown but are expected to result from causal alterations in gene and protein expression. Proteomic technology now allows us to examine global alterations in protein expression in the diseased heart and can provide new insights into cellular mechanisms involved in cardiac dysfunction. The majority of proteomic investigations still use 2D gel electrophoresis (2-DE) with immobilized pH gradients to separate the proteins in a sample and combine this with mass spectrometry (MS) technologies to identify proteins. In spite of the development of novel gel-free technologies, 2-DE remains the only technique that can be routinely applied to parallel quantitative expression profiling of large sets of complex protein mixtures such as whole cell lysates. It can resolve >5000 proteins simultaneously (approximately 2000 proteins routinely) and can detect <1 ng of protein per spot. Furthermore, 2-DE delivers a map of intact proteins, which reflects changes in protein expression level, isoforms, or post-translational modifications. The use of proteomics to investigate heart disease should result in the generation of new diagnostic and therapeutic markers. In this article, we review the current status of proteomic technologies, describing the 2-DE proteomics workflow, with an overview of protein identification by MS and how these technologies are being applied to studies of human heart disease.

F-actin Capping (CapZ) and Other Contractile Saphenous Vein Smooth Muscle Proteins Are Altered by Hemodynamic Stress A PROTEOMIC APPROACH

Increased force generation and smooth muscle remodeling follow the implantation of saphenous vein as an arterial bypass graft. Previously, we characterized and mapped 129 proteins in human saphenous vein medial smooth muscle using two-dimensional (2-D) PAGE and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Here, we focus on actin filament remodeling in response to simulated arterial flow. Human saphenous vein was exposed to simulated venous or arterial flow for 90 min in vitro, and the contractile medial smooth muscle was dissected out and subjected to 2-D gel electrophoresis using a non-linear immobilized pH 3–10 gradient in the first dimension. Proteins were analyzed quantitatively using PDQuest 2-D software. The actin polymerization inhibitor cytochalasin B (1 μm) prevented increases in force generation after 90 min of simulated arterial flow. At this time point, there were several consistent changes in actin filament-associated protein expression (seven paired vein samples). The heat shock protein HSP27, identified as a three-spot charge train, showed a 1.6-fold increase in abundance (p = 0.01), but with reduced representation of the phosphorylated Ser82 and Ser15Ser82 isoforms (p = 0.018). The abundance of actin-capping protein α2 subunit CapZ had decreased 3-fold, p = 0.04. A 19-kDa proteolytic fragment of actin increased 2-fold, p = 0.04. For the four-spot charge train of gelsolin, there was reduced representation of the more acidic isoforms, p = 0.022. The abundance of other proteins associated with actin filaments, including cofilin and destrin, remained unchanged after arterial flow. Actin filament remodeling with differential expression and/or post-translational modification of proteins involved in capping the barbed end of actin filaments, HSP27 and CapZ, is an early response of contractile saphenous vein smooth muscle cells to hemodynamic stress. The observed changes would favor the generation of contractile stress fibers.

Identification and mapping of human saphenous vein medial smooth muscle proteins by two-dimensional polyacrylamide gel electrophoresis

Changing smooth muscle phenotype and abnormal cell proliferation are important features of vascular pathology, including the failure of saphenous vein bypass grafts. We have characterised and mapped protein expression in human saphenous vein medial smooth muscle, using two‐dimensional (2‐D) polyacrylamide gel electrophoresis. The 2‐D system comprised a nonlinear immobilised pH 3–10 gradient in the first dimension (separating proteins with isoelectric point values between pH 3–10), and 12%T total gel concentration sodium dodecyl sulphate polyacrylamide gel electrophoresis in the second dimension (separating proteins in the range 14 000–200 000 Daltons). Using a combination of peptide mass fingerprinting by matrix‐assisted laser desorption/ionisation‐time of flight mass spectrometry and partial amino acid sequencing by nanospray tandem mass spectrometry, a subset of 149 protein spots was analysed, with 129 protein spots being identified and mapped. The data presented here are an important addition to the limited knowledge of venous medial smooth muscle protein expression in vivo. Our protein map will facilitate the identification of proteins differentially expressed in human saphenous vein bypass grafts. In turn, this may lead to the elucidation of molecular events involved in saphenous vein bypass graft failure. The map should also provide a basis for comparative studies of protein expression in vascular smooth muscle of varying origins.

Reversible Cysteine-Targeted Oxidation of Proteins during Renal Oxidative Stress

Biotin-cysteine was used to study protein S-thiolation in isolated rat kidneys subjected to ischemia and reperfusion. After 40 min of ischemia, total protein S-thiolation increased significantly (P < 0.05), by 311%, and remained significantly elevated (P < 0.05), 221% above control, after 5 min of postischemic reperfusion. Treatment of protein samples with 2-mercaptoethanol abolished the S-thiolation signals detected, consistent with the dependence of the signal on the presence of a disulfide bond. With the use of gel filtration chromatography followed by affinity purification with streptavidin-agarose, S-thiolated proteins were purified from CHAPS-soluble kidney homogenate. The proteins were then separated by SDS-PAGE and stained with Coomassie blue. With a combination of matrix-assisted laser desorption ionization time of flight mass spectrometry and LC/MS/MS analysis of protein bands digested with trypsin, a number of S-thiolation substrates were identified. These included the LDL receptor-related protein 2, ATP synthase alpha chain, heat shock protein 90 beta, hydroxyacid oxidase 3, serum albumin precursor, triose phosphate isomerase, and lamin. These represent proteins that may be functionally regulated by S-thiolation and thus could undergo a change in activity or function after renal ischemia and reperfusion.

Circumferential stretching of saphenous vein smooth muscle enhances vasoconstrictor responses by Rho kinase-dependent pathways

OBJECTIVE Surgical preparation and/or pulsatile arterial perfusion of saphenous vein increases the sensitivity of vein rings to calcium mobilising agonists such as phenylephrine. We have investigated the mechanism(s) underlying this effect. METHODS We have used an ex vivo flow circuit, with simulated arterial or venous flows (mean pressure 100 and 20 mmHg, respectively), to investigate the sensitivity of human saphenous vein to phenylephrine, 5-hydroxytryptamine (5-HT) and KCl, using organ chamber pharmacology. RESULTS After 90 min of pulsatile arterial perfusion the mean maximum tension induced by KCl had increased from 4.7 to 11.1 g (n=5), by phenylephrine had increased from 4.4 to 10.2 g (n=8) and by 5-HT had increased from 4.4 to 6.7 g (n=10), all P<0.01. Phenylephrine did not augment the tension in vein rings maximally precontracted with KCl (n=4). The EC(50) for KCl was unchanged after pulsatile arterial perfusion (n=5), but for phenylephrine and 5-HT there were significant reductions from 14+/-5 to 2+/-1 microM (n=8) and from 1.0+/-0.4 to 0.20+/-0.06 microM (n=10), respectively. The rate of contraction (in response to 3 microM phenylephrine) increased from 0.11 g/min to 0.37 g/min, P<0.02, after arterial perfusion (n=4). These changes in contractile properties (to phenylephrine) were endothelium-independent, evident within 5 min of simulated arterial perfusion. The changes in contractile properties could be abrogated by external stenting of the vein (to attenuate circumferential deformation) or inclusion in the perfusate of a vasodilator, e.g., cromakalim (5 microM) or the selective Rho kinase inhibitor Y-27632 (20 microM). The heightened sensitivity and contractility to phenylephrine was maintained after inclusion of adenosine (100 microM), gadolinium (10 microM) or cycloheximide (10 microM) in the vein perfusate. CONCLUSIONS The circumferential deformations imposed by simulated arterial perfusion alter the vasomotor responses of saphenous vein smooth muscle. These effects are independent of new protein synthesis or the activation of stretch activated cation channels. The Rho kinase pathway appears to mediate the signalling mechanisms leading to increased agonist-induced tension and the increased sensitivity to vasoconstrictors.

Proteomics and Laser Microdissection

Two-dimensional gel electrophoresis (2-DE) combined with protein identification by mass spectrometry (MS) is currently the method of choice in the majority of proteomic projects. Novel gel-free technologies have been developed but 2-DE remains the technique of choice for quantitative expression profiling of large sets of complex protein mixtures such as whole cell/tissue lysates. Solubilized proteins are separated in the first dimension according to their charge properties (isoelectric point, pI) by isoelectric focusing (IEF) under denaturing conditions, followed by their separation in the second dimension by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), according to their relative molecular mass (Mr). 2-DE can resolve more than 5000 proteins simultaneously (approximately 2000 proteins routinely) and can detect less than 1 ng of protein per spot. Furthermore, it delivers a map of intact proteins, which reflects changes in protein expression level, isoforms or posttranslational modifications. In this chapter we describe the various steps in the 2-DE proteomics workflow, namely sample preparation, solubilization, 2-D gel electrophoresis, protein detection and visualization, and protein identification by mass spectrometry. The use of 2-DE in conjunction with laser microdissection microscopy is presented and discussed.