A chylous cyst at the right base of the neck

A case is presented of a cystic lesion, which presented at the base of the right side of the neck. The lesion was more obvious on forced expiration. Aspiration revealed chylous fluid and a Magnetic Resonance Imaging (M.R.I.) scan revealed a well-circumscribed cystic lesion with no deeper extension. So far, this chylous cyst has not required treatment, but is being kept under regular review.

c-kit is required for cardiomyocyte terminal differentiation

c-kit, the transmembrane tyrosine kinase receptor for stem cell factor, is required for melanocyte and mast cell development, hematopoiesis, and differentiation of spermatogonial stem cells. We show here that in the heart, c-kit is expressed not only by cardiac stem cells but also by cardiomyocytes, commencing immediately after birth and terminating a few days later, coincident with the onset of cardiomyocyte terminal differentiation. To examine the function of c-kit in cardiomyocyte terminal differentiation, we used compound heterozygous mice carrying the W (null) and W(v) (dominant negative) mutations of c-kit. In vivo, adult W/W(v) cardiomyocytes are phenotypically indistinguishable from their wild-type counterparts. After acute pressure overload adult W/W(v) cardiomyocytes reenter the cell cycle and proliferate, leading to left ventricular growth; furthermore in transgenic mice with cardiomyocyte-restricted overexpression of the dominant negative W(v) mutant, pressure overload causes cardiomyocytes to reenter the cell cycle. In contrast, in wild-type mice left ventricular growth after pressure overload results mainly from cardiomyocyte hypertrophy. Importantly, W/W(v) mice with pressure overload-induced cardiomyocyte hyperplasia had improved left ventricular function and survival. In W/W(v) mice, c-kit dysfunction also resulted in an approximately 14-fold decrease (P<0.01) in the number of c-kit(+)/GATA4(+) cardiac progenitors. These findings identify novel functions for c-kit: promotion of cardiac stem cell differentiation and regulation of cardiomyocyte terminal differentiation.

Cardiac alpha 1-adrenergic drive in pathological remodelling

The heart is richly innervated by sympathetic nerves, and both acute and chronic regulation of cardiac function via sympathetically released catecholamines acting on cardiomyocyte adrenergic receptors (ARs), is critical for circulatory homeostasis. Cardiomyocytes express alpha 1A- and alpha 1B-, and beta 1- and beta 2-AR subtypes, which are all members of the G-protein-coupled receptor superfamily that signal via interaction with heterotrimeric G-proteins. Cardiac function - both inotropy and chronotropy - is regulated predominantly by beta 1-AR. Activation of alpha 1-ARs also results in increased contractility, as well as changes in the electrophysiological properties and metabolic responses of the heart. Nonetheless, there is little evidence that cardiac alpha 1-ARs play a major functional role under normal physiological conditions. In pathological settings, alpha 1-ARs may function in a compensatory fashion to maintain cardiac inotropy when the beta-AR system is downregulated and uncoupled from G-proteins and effectors. In addition, as we consider here, recent evidence from clinical studies and from genetically engineered animal models indicates that alpha 1-ARs are importantly involved in both developmental cardiomyocyte growth, as well as pathological hypertrophy. In the presence of pressure overload or with myocardial infarction, activation of alpha 1-ARs, particularly the alpha 1A-subtype, also appears to produce important pro-survival effects at the level of the cardiomyocyte, and to protect against maladaptive cardiac remodelling and decompensation to heart failure.

Heightened alpha1A-adrenergic receptor activity suppresses ischaemia/reperfusion-induced Ins(1,4,5)P3 generation in the mouse heart: a comparison with ischaemic preconditioning

Reperfusion of ischaemic rat or mouse hearts causes NE [noradrenaline ('norepinephrine')] release, stimulation of alpha(1)-ARs (alpha(1)-adrenergic receptors), PLC (phospholipase C) activation, Ins(1,4,5)P(3) generation and the development of arrhythmias. In the present study, we examined the effect of increased alpha(1A)-AR drive on these responses. In hearts from non-transgenic mice (alpha(1A)-WT), Ins(1,4,5)P(3) generation was observed after 2 min of reperfusion following 30 min of zero-flow ischaemia. No Ins(1,4,5)P(3) response was observed in hearts from transgenic mice with 66-fold overexpression of alpha(1A)-AR (alpha(1A)-TG). This was despite the fact that alpha(1A)-TG hearts had 8-10-fold higher PLC responses to NE than alpha(1A)-WT under normoxic conditions. The immediate phospholipid precursor of Ins(1,4,5)P(3), PtdIns(4,5)P(2), responded to ischaemia and reperfusion similarly in alpha(1A)-WT and alpha(1A)-TG mice. Thus the lack of Ins(1,4,5)P(3) generation in alpha(1A)-TG mice is not caused by limited availability of PtdIns(4,5)P(2). Overall, alpha(1)-AR-mediated PLC activity was markedly enhanced in alpha(1A)-WT mice under reperfusion conditions, but responses in alpha(1A)-TG mice were not significantly different in normoxia and post-ischaemic reperfusion. Ischaemic preconditioning prevented Ins(1,4,5)P(3) generation after 30 min of ischaemic insult in alpha(1A)-WT mice. However, the precursor lipid PtdIns(4,5)P(2) was also reduced by preconditioning, whereas heightened alpha(1A)-AR activity did not influence PtdIns(4,5)P(2) responses in reperfusion. Thus preconditioning and alpha(1A)-AR overexpression have different effects on early signalling responses, even though both prevented Ins(1,4,5)P(3) generation. These studies demonstrate a selective inhibitory action of heightened alpha(1A)-AR activity on immediate post-receptor signalling responses in early post-ischaemic reperfusion.

Store-Operated Ca 2+ Influx and Expression of TRPC Genes in Mouse Sinoatrial Node

Store-operated Ca 2+ entry was investigated in isolated mouse sinoatrial nodes (SAN) dissected from right atria and loaded with Ca 2+ indicators. Incubation of the SAN in Ca 2+ -free solution caused a substantial decrease in resting intracellular Ca 2+ concentration ([Ca 2+ ] i ) and stopped pacemaker activity. Reintroduction of Ca 2+ in the presence of cyclopiazonic acid (CPA), a sarcoplasmic reticulum Ca 2+ pump inhibitor, led to sustained elevation of [Ca 2+ ] i , a characteristic of store-operated Ca 2+ channel (SOCC) activity. Two SOCC antagonists, Gd 3+ and SKF-96365, inhibited 72±8% and 65±8% of this Ca 2+ influx, respectively. SKF-96365 also reduced the spontaneous pacemaker rate to 27±4% of control in the presence of CPA. Because members of the transient receptor potential canonical (TRPC) gene family may encode SOCCs, we used RT-PCR to examine mRNA expression of the 7 known mammalian TRPC isoforms. Transcripts for TRPC1, 2, 3, 4, 6, and 7, but not TRPC5, were detected. Immunohistochemistry using anti-TRPC1, 3, 4, and 6 antibodies revealed positive labeling in the SAN region and single pacemaker cells. These results indicate that mouse SAN exhibits store-operated Ca 2+ activity which may be attributable to TRPC expression, and suggest that SOCCs may be involved in regulating pacemaker firing rate.

Bacterially derived 400 nm particles for encapsulation and cancer cell targeting of chemotherapeutics

Systemic administration of chemotherapeutic agents results in indiscriminate drug distribution and severe toxicity. Here we report a technology potentially overcoming these shortcomings through encapsulation and cancer cell-specific targeting of chemotherapeutics in bacterially derived 400 nm minicells. We discovered that minicells can be packaged with therapeutically significant concentrations of chemotherapeutics of differing charge, hydrophobicity, and solubility. Targeting of minicells via bispecific antibodies to receptors on cancer cell membranes results in endocytosis, intracellular degradation, and drug release. This affects highly significant tumor growth inhibition and regression in mouse xenografts and case studies of lymphoma in dogs despite administration of minute amounts of drug and antibody; a factor critical for limiting systemic toxicity that should allow the use of complex regimens of combination chemotherapy.

Isolated hypoglossal nerve palsy due to a vascular anomaly

The case of a patient with an unusual cause of an isolated hypoglossal nerve palsy is presented. Magnetic resonance (MR) imaging demonstrated marked dilatation and ectasia of the right vertebral artery and basilar artery, thereby causing compression of the brainstem. It is therefore proposed that a dilated vascular loop compression of the nerve rootlets, as they exit the medulla, has caused the hypoglossal nerve palsy. This case demonstrates that excellent images can be obtained from MR imaging, and also emphasises that other pathologies must be considered in the differential diagnosis of hypoglossal nerve palsy.

Transglutaminase 2 regulates mallory body inclusion formation and injury-associated liver enlargement

BACKGROUND & AIMS

Mallory body (MB) inclusions are a characteristic feature of several liver disorders and share similarities with cytoplasmic inclusions observed in neural diseases and myopathies. MBs consist primarily of keratins 8 and 18 (K8/K18), require a K8-greater-than-K18 ratio for their formation, and contain glutamine-lysine cross-links generated by transglutaminase (TG). We hypothesized that protein transamidation is essential for MB formation.

METHODS

Because TG2 is the most abundant hepatocyte TG, we tested our hypothesis using TG2(-/-) and their wild-type counterpart mice fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), an established MB inducer. Keratin cross-linking was further examined using recombinant proteins or transgenic mice that overexpress K8 or K18.

RESULTS

TG2(-/-) livers have markedly reduced TG2 activity as compared with TG2(+/+) livers. The DDC-fed TG2(-/-) mice have dramatic decreases in MB formation and liver hypertrophy response as contrasted with DDC-fed TG2(+/+) mice. Despite similar hepatocellular damage, TG2(-/-) mice had more gallstones, jaundice, and ductal proliferation than wild-type mice. Inhibition of MB formation in TG2(-/-) mice was associated with marked attenuation of ubiquitination and K8-containing protein cross-linking. MB formation and resolution paralleled the generation then disappearance of cross-linked K8, respectively. K8 is a preferential TG2 substrate when compared to K18, as examined in vitro or in DDC-fed transgenic mice that overexpress K8 or K18.

CONCLUSIONS

We demonstrate an essential role for TG2 in determining injury-mediated liver enlargement and the necessity of K8 and TG2 for generating cross-linked keratins and MBs. The role of TG in inclusion formation might extend to nonkeratin intermediate filament protein-related diseases.

Profound thrombocytopenia related to G-CSF

Severe thrombocytopenia in association with G-CSF therapy is extremely rare. Here we report a case of profound thrombocytopenia in a 57-year-old male with refractory cardiac ischemia, who received G-CSF during an angiogenesis trial. After 5 days of G-CSF therapy (10 microg/kg/day) the platelet count fell progressively to a nadir of 5x10(9)/L. The patient received steroid, immunoglobulin and platelet support and recovered without sequelae. Subsequent investigations suggested an underlying immune-mediated thrombocytopenia, which we hypothesize was exacerbated by G-CSF therapy.

Iron absorption and hepatic iron uptake are increased in a transferrin receptor 2 (Y245X) mutant mouse model of hemochromatosis type 3

Hereditary hemochromatosis type 3 is an iron (Fe)-overload disorder caused by mutations in transferrin receptor 2 (TfR2). TfR2 is expressed highly in the liver and regulates Fe metabolism. The aim of this study was to investigate duodenal Fe absorption and hepatic Fe uptake in a TfR2 (Y245X) mutant mouse model of hereditary hemochromatosis type 3. Duodenal Fe absorption and hepatic Fe uptake were measured in vivo by 59Fe-labeled ascorbate in TfR2 mutant mice, wild-type mice, and Fe-loaded wild-type mice (2% dietary carbonyl Fe). Gene expression was measured by real-time RT-PCR. Liver nonheme Fe concentration increased progressively with age in TfR2 mutant mice compared with wild-type mice. Fe absorption (both duodenal Fe uptake and transfer) was increased in TfR2 mutant mice compared with wild-type mice. Likewise, expression of genes participating in duodenal Fe uptake (Dcytb, DMT1) and transfer (ferroportin) were increased in TfR2 mutant mice. Nearly all of the absorbed Fe was taken up rapidly by the liver. Despite hepatic Fe loading, hepcidin expression was decreased in TfR2 mutant mice compared with wild-type mice. Even when compared with Fe-loaded wild-type mice, TfR2 mutant mice had increased Fe absorption, increased duodenal Fe transport gene expression, increased liver Fe uptake, and decreased liver hepcidin expression. In conclusion, despite systemic Fe loading, Fe absorption and liver Fe uptake were increased in TfR2 mutant mice in association with decreased expression of hepcidin. These findings support a model in which TfR2 is a sensor of Fe status and regulates duodenal Fe absorption and liver Fe uptake.

Mechanism of allosteric regulation of transglutaminase 2 by GTP

Allosteric regulation is a fundamental mechanism of biological control. Here, we investigated the allosteric mechanism by which GTP inhibits cross-linking activity of transglutaminase 2 (TG2), a multifunctional protein, with postulated roles in receptor signaling, extracellular matrix assembly, and apoptosis. Our findings indicate that at least two components are involved in functionally coupling the allosteric site and active center of TG2, namely (i) GTP binding to mask a conformationally destabilizing switch residue, Arg-579, and to facilitate interdomain interactions that promote adoption of a compact, catalytically inactive conformation and (ii) stabilization of the inactive conformation by an uncommon H bond between a cysteine (Cys-277, an active center residue) and a tyrosine (Tyr-516, a residue located on a loop of the beta-barrel 1 domain that harbors the GTP-binding site). Although not essential for GTP-mediated inhibition of cross-linking, this H bond enhances the rate of formation of the inactive conformer.

Actions and therapeutic potential of G-CSF and GM-CSF in cardiovascular disease

Despite their names, the cytokines granulocyte- and granulocyte-macrophage-colony stimulating factor (G-CSF and GM-CSF respectively) have actions far beyond simply stimulating the proliferation of neutrophil and monocyte lineage cells. A comprehensive body of evidence now exists demonstrating that G-CSF and GM-CSF effectively mobilize bone-marrow-derived progenitor cells into the peripheral circulation. These mobilized progenitor cells can be conveniently harvested for use in reconstituting bone marrow by transplantation after myelo-ablative treatment of hematological malignancies. In addition, much evidence has recently emerged to suggest that these cytokines may have multiple direct and indirect beneficial cardiovascular effects--including neovascularization of ischemic myocardium and reducing the extent of myocardial damage after infarction. Based on this knowledge and a strong safety record in hematological applications, a number of early clinical trials have evaluated the use of G-CSF or GM-CSF in patients with both acute and chronic myocardial ischemia. Although the interpretation of these trials is complicated by heterogeneity in study design, small patient numbers and methodological concerns related to appropriate selection and blinding of patients, the results of ongoing larger phase II/III trials should soon be available to determine if these agents will be useful additions to the cardiovascular armamentarium.

Cross-linking transglutaminases with G protein-coupled receptor signaling

Transglutaminases are a family of calcium- and thiol-dependent acyl transferases that catalyze the formation of an amide bond between the gamma-carboxamide groups of peptide-bound glutamine residues and the primary amino groups in various compounds, including the epsilon-amino group of lysines in certain proteins. As a result, these enzymes effect posttranslational modification of proteins by amine incorporation, or stabilization of protein assemblies by their cross-linking; such actions profoundly influence critical biological processes such as blood clotting and protection from infection and dehydration by establishing the barrier function of skin. In addition, transglutaminases have other more diverse actions, including involvement in signaling by the superfamily of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) in one of three ways: (i) through actions as guanosine triphosphate-binding proteins that activate intracellular effectors, such as phospholipase C; (ii) by cross-linking GPCR monomers to enhance signaling as a result of covalent dimer formation; or (iii) by interacting with an apparent growth inhibitory orphan GPCR, GPR56, to limit metastatic spread of melanoma cells. The implications of these receptor-coupled actions of transglutaminases are discussed.

Neuregulin-1/erbB-activation improves cardiac function and survival in models of ischemic, dilated, and viral cardiomyopathy

OBJECTIVES

We evaluated the therapeutic potential of a recombinant 61-residue neuregulin-1 (beta2a isoform) receptor-active peptide (rhNRG-1) in multiple animal models of heart disease.

BACKGROUND

Activation of the erbB family of receptor tyrosine kinases by rhNRG-1 could provide a treatment option for heart failure, because neuregulin-stimulated erbB2/erbB4 heterodimerization is not only critical for myocardium formation in early heart development but prevents severe dysfunction of the adult heart and premature death. Disabled erbB-signaling is also implicated in the transition from compensatory hypertrophy to failure, whereas erbB receptor-activation promotes myocardial cell growth and survival and protects against anthracycline-induced cardiomyopathy.

METHODS

rhNRG-1 was administered IV to animal models of ischemic, dilated, and viral cardiomyopathy, and cardiac function and survival were evaluated.

RESULTS

Short-term intravenous administration of rhNRG-1 to normal dogs and rats did not alter hemodynamics or cardiac contractility. In contrast, rhNRG-1 improved cardiac performance, attenuated pathological changes, and prolonged survival in rodent models of ischemic, dilated, and viral cardiomyopathy, with the survival benefits in the ischemic model being additive to those of angiotensin-converting enzyme inhibitor therapy. In addition, despite continued pacing, rhNRG-1 produced global improvements in cardiac function in a canine model of pacing-induced heart failure.

CONCLUSIONS

These beneficial effects make rhNRG-1 promising as a broad-spectrum therapeutic for the treatment of heart failure due to a variety of common cardiac diseases.

Transgenic α1A-adrenergic activation limits post-infarct ventricular remodeling and dysfunction and improves survival

OBJECTIVE

Myocardial contractility is enhanced in transgenic (TG) mice with cardiac-restricted overexpression of the alpha1A-adrenergic receptors (alpha1A-AR). We tested the hypothesis that this enhanced inotropy protects against dysfunction and remodeling after myocardial infarction (MI).

METHODS

We subjected alpha1A-TG and non-TG mice (NTG) to MI and determined changes in left ventricular (LV) function and diastolic dimension (LVDd) by echocardiography prior to and at 1, 3, 7, 12 and 15 weeks thereafter.

RESULTS

Although infarct size was similar in the NTG and alpha1A-TG groups (32+/-2 vs. 29+/-2% of LV, P=NS), mortality due to heart failure was lower after MI in the alpha1A-TG (37%, n=39) than that in the NTG animals (63%, n=56, P=0.026). NTG and alpha1A-TG mice showed similar reductions in LV fractional shortening (FS) and increases in LVDd at week-1 after MI. However, whereas NTG mice showed continuous deterioration over a 15-week period after MI in FS (fell by 40%, from 30+/-2 to 18+/-1%, P<0.01) and LVDd (increased by 24%, from 4.2+/-0.1 to 5.2+/-0.1 mm, P<0.01), the changes in both FS (fell by 14%, from 42+/-2 to 36+/-2%) and LVDd (increased by 8%, from 3.8+/-0.1 to 4.1+/-0.1 mm, both changes P<0.01 vs. NTG) were significantly less severe in the alpha1A-TG mice and did not progress after 3 weeks. At 15 weeks after MI, LV catheterization revealed better preservation of dP/dtmax in the alpha1A-TG vs. NTG mice (7270+/-324, vs. 5938+/-372 mmHg/s, P<0.05).

CONCLUSION

Enhanced inotropy resulting from transgenic overexpression of alpha1A-AR is well maintained chronically after MI and limits echocardiography-determined LV remodeling, preserves function, and reduces acute heart failure death.

Mutation of a critical arginine in the GTP-binding site of transglutaminase 2 disinhibits intracellular cross-linking activity

Transglutaminase type 2 (TG2; also known as G(h)) is a multifunctional protein involved in diverse cellular processes. It has two well characterized enzyme activities: receptor-stimulated signaling that requires GTP binding and calcium-activated transamidation or cross-linking that is inhibited by GTP. In addition to the GDP binding residues identified from the human TG2 crystal structure (Liu, S., Cerione, R. A., and Clardy, J. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 2743-2747), we have previously implicated Ser171 in GTP binding, as binding is lost with glutamate substitution (Iismaa, S. E., Wu, M.-J., Nanda, N., Church, W. B., and Graham, R. M. (2000) J. Biol. Chem. 275, 18259-18265). Here, we have shown that alanine substitution of homologous residues in rat TG2 (Phe174 in the core domain or Arg476, Arg478, or Arg579 in barrel 1) does not affect TG activity but reduces or abolishes GTP binding and GTPgammaS inhibition of TG activity in vitro, indicating that these residues are important in GTP binding. Alanine substitution of Ser171 does not impair GTP binding, indicating this residue does not interact directly with GTP. Arg579 is particularly important for GTP binding, as isothermal titration calorimetry demonstrated a 100-fold reduction in GTP binding affinity by the R579A mutant. Unlike wild-type TG2 or its S171E or F174A mutants, which are sensitive to both trypsin and mu-calpain digestion, R579A is inherently more resistant to mu-calpain, but not trypsin, digestion, indicating reduced accessibility and/or flexibility of this mutant in the region of the calpain cleavage site(s). Basal TG activity of intact R579A stable SH-SY5Y neuroblastoma cell transfectants was slightly increased relative to wild-type transfectants and, in contrast to the TG activity of the latter, was further stimulated by muscarinic receptor-activated calcium mobilization. Thus, loss of GTP binding sensitizes TG2 to intracellular calcium concentrations. These findings are consistent with the notion that intracellularly, under physiological conditions, TG2 is maintained largely as a latent enzyme, its calcium-activated cross-linking activity being suppressed allosterically by guanine nucleotide binding.

Sustained augmentation of cardiac alpha1A-adrenergic drive results in pathological remodeling with contractile dysfunction, progressive fibrosis and reactivation of matricellular protein genes

We previously reported that transgenic (TG) mice with cardiac-restricted alpha(1A)-adrenergic receptor (alpha(1A)-AR)-overexpression showed enhanced contractility, but no hypertrophy. Since chronic inotropic enhancement may be deleterious, we investigated if long-term, cardiac function and longevity are compromised. alpha(1A)-TG mice, but not their non-TG littermates (NTLs), showed progressive loss of left ventricular (LV) hypercontractility (dP/dt(max): 14,567+/-603 to 11,610+/-915 mmHg/s, P<0.05, A1A1 line: 170-fold overexpression; and 13,625+/-826 to 8322+/-682 mmHg/s, respectively, P<0.05, A1A4 line: 112-fold overexpression, at 2 and 6 months, respectively). Both TG lines developed LV fibrosis, but not LV dilatation or hypertrophy, despite activation of hypertrophic signaling pathways. Microarray and real time RT-PCR analyses revealed activation of matricellular protein genes, including those for thrombospondin 1, connective tissue growth factor and tenascin C, but not transforming growth factor beta1. Life-span was markedly shortened (mean age at death: 155 days, A1A1 line; 224 days, A1A4 line compared with NTLs: >300 days). Telemetric electrocardiography revealed that death in the alpha(1A)-AR TG mice was due to cardiac standstill preceded by a progressive diminution in QRS amplitude, but not by arrhythmias. The QRS changes and sudden death could be mimicked by alpha(1)-AR activation, and reversed preterminally by alpha(1)-AR blockade, suggesting a relationship to stress- or activity-associated catecholamine release. Thus, long-term augmentation of cardiac alpha(1A)-adrenergic drive leads to premature death and progressive LV fibrosis with reactivation of matricellular protein genes. To our knowledge this is the first evidence in vivo for a role of the alpha(1A)-AR in ventricular fibrosis and in pathological cardiac remodeling.

The alpha(1D)-adrenergic receptor: cinderella or ugly stepsister

This Perspective focuses on the alpha(1D)-adrenergic receptor (AR), the often neglected sibling of the alpha(1)-AR family. This neglect is due in part to its poor cell-surface expression. However, it has recently been shown that dimerization of the alpha(1D)-AR with either the alpha(1B)-AR or the beta(2)-AR increases alpha(1D)-AR cell-surface expression, and in this issue of Molecular Pharmacology, Hague et al. (p. 45) demonstrate that dimerization of the alpha(1D)-AR with the alpha(1B)-AR not only leads to increased cell-surface expression but also results in the formation of a novel functional entity.

Angiogenesis is confined to the transient period of VEGF expression that follows adenoviral gene delivery to ischemic muscle

Therapeutic angiogenesis involves the introduction of exogenous growth factor proteins and genes into ischemic tissues to augment endogenous factors and promote new vessel growth. Positive results from studies in animal models of peripheral arterial disease (PAD) and coronary artery disease over the past decade have supported the implementation of clinical trials testing vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) proteins and genes. Although several clinical trials reported positive results, others have been disappointing and results of a recent Phase II trial of VEGF delivered by adenovirus (the RAVE trial) were negative. It has been suggested that the duration of gene expression following delivery by adenovirus may be insufficient to produce stable vessels. Here we present direct evidence in support of this using the rabbit ischemic hindlimb model injected with adenovirus encoding VEGF165. Immunohistology indicated an activation of endothelial cell cycling and proliferation 2-3 days after VEGF delivery that coincided closely with transient VEGF expression. Ki-67-positive endothelial nuclei were evident at high levels in capillaries and large vessels in muscles from treated animals. Angiography indicated increased density of both large and small vessels in Ad-VEGF-treated muscle at 1 week, but no significant differences thereafter. The early burst of endothelial proliferation was accompanied by increased nuclear fragmentation and condensation in VEGF-treated muscles, suggesting coincident apoptosis. No further endothelial cell proliferation took place after 1 week although there was still evidence of apoptosis. The results suggest that angiogenesis is confined to the short period of VEGF expression produced by adenovirus and early gains in collateralization rapidly regress to control levels when VEGF production ceases.

Update on the use of stem cells for cardiac disease

Major advances have recently been made in our understanding of stem cell biology, and in the application of stem cells to treat cardiac disease. Resident cardiac stem cells have now been described and the long-accepted paradigm of the adult mammalian heart as an organ without regenerative capacity has been questioned. Various stem-cell-based approaches for ameliorating cardiac disease have been shown to be beneficial in animal models and are now being trialled in humans, with several phase I clinical studies already completed. Although these clinical studies lacked adequate placebo controls, they have consistently shown promising results. If confirmed by larger phase II/III trials, it is possible that within a few years a powerful new therapeutic option may be available for the burgeoning number of patients suffering from myocardial ischaemia and/or other cardiac disorders.

Genetic enhancement of ventricular contractility protects against pressure-overload-induced cardiac dysfunction

In response to pressure-overload, cardiac function deteriorates and may even progress to fulminant heart failure and death. Here we questioned if genetic enhancement of left ventricular (LV) contractility protects against pressure-overload. Transgenic (TG) mice with cardiac-restricted overexpression (66-fold) of the alpha(1A)-adrenergic receptor (alpha(1A)-AR) and their non-TG (NTG) littermates, were subjected to transverse aorta constriction (TAC)-induced pressure-overload for 12 weeks. TAC-induced hypertrophy was similar in the NTG and TG mice but the TG mice were less likely to die of heart failure compared to the non-TG animals (P <0.05). The hypercontractile phenotype of the TG mice was maintained over the 12-week period following TAC with LV fractional shortening being significantly greater than in the NTG mice (42+/-2 vs 29+/-1%, P <0.01). In the TG animals, 11-week beta-AR-blockade with atenolol neither induced hypertrophy nor suppressed the hypercontractile phenotype. The hypertrophic response to pressure-overload was not altered by cardiac alpha(1A)-AR overexpression. Moreover, the inotropic phenotype of alpha(1A)-AR overexpression was well maintained under conditions of pressure overload. Although the functional decline in contractility with pressure overload was similar in the TG and NTG animals, given that contractility was higher before TAC in the TG mice, their LV function was better preserved and heart failure deaths were fewer after induction of pressure overload.

Molecular basis of exopeptidase activity in the C-terminal domain of human angiotensin I-converting enzyme: insights into the origins of its exopeptidase activity

Proteolytic processing is a primary means of biological control. Exopeptidases use terminal anchoring interactions to restrict cleavage at peptide substrate N or C termini. In contrast, internal peptide bond targeting by endopeptidases is through context-driven recognition. Angiotensin I-converting enzyme (ACE), a zinc metalloproteinase, has tandem duplicate catalytic domains, N- and C-terminal, each of which is a dual specificity enzyme with exo- and endocarboxypeptidase activities. The mechanisms by which ACE evolved from its endopeptidase ancestors as a dual specificity enzyme have not been defined. Based on kinetic studies of wild-type and mutant forms of the C-terminal catalytic domain of human ACE and of the ACE substrates angiotensin I, substance P, and bradykinin, as well as considerations of the ACE x-ray structure, we provide evidence that the acquisition of its exopeptidase activity is due to novel evolutionary specializations. These involve not only interactions between the S(2)' subsite cognate for the C-terminal substrate P(2)' side chain, acting in concert with carboxylate-docking interactions with Lys(1087) and Tyr(1096), but also electrostatic selection against a cationic C-terminal substrate carboxylate. With a blocked C terminus, substrate side chain interactions are dominant in cleavage site selection. In the evolution of obligate exopeptidases from endopeptidase ancestors, mutations that destroy context-driven peptide bond targeting are likely to have followed the acquisition of terminal docking interactions. Evolutionary intermediates between endopeptidases and obligate exopeptidases could therefore have been dual specificity proteinases like ACE.

Synthesis and biological evaluation of bicyclic and tricyclic substituted nortropane derivatives: discovery of a novel selective α1D-adrenergic receptor ligand

A range of 3,6,6-trisubstituted nortropane derivatives based upon 6beta-phenyltropane-3beta,6 alpha-diol have been synthesised from 6beta-hydroxytropinone, including some novel related tricyclic hemi-ketal and tricyclic ketal compounds. Derivatives were assessed for pharmacological affinity and selectivity at alpha(1)-adrenergic receptors, and 6beta-phenyl-8-azabicyclo[3.2.1]octan-3-spiro-2'-(1',3'-dioxolane)-6-ol, a novel lead compound selective for the alpha(1D)-adrenergic receptor, is reported.

Involvement of chymase-mediated angiotensin II generation in blood pressure regulation

Angiotensin I-converting enzyme (ACE) inhibitors are thought to lower blood pressure in hypertensive patients, mainly by decreasing angiotensin II (Ang II) formation. Chymase, a human mast cell protease, has recently been proposed to play a role in blood pressure regulation because of its Ang II-forming activity. Here we show that the predominant chymase mRNA species in the mouse aorta are those for types 4 and 5 isoforms, and that both are efficient Ang II-forming enzymes. Evaluation of ACE-dependent and ACE-independent Ang II-forming pathways in mast cell-deficient (Kit(w)/Kit(w-v)) mice and their mast cell-sufficient littermate (MC(+/+)) controls revealed that, in contrast to the latter, Kit(w)/Kit(w-v) mice fail to express chymase mRNAs in the vasculature and have almost no ACE-independent Ang II-forming activity in either isolated blood vessels or homogenates. Moreover, in MC(+/+) but not in Kit(w)/Kit(w-v) mice, a contribution of ACE-independent Ang II generation to blood pressure regulation was evident by a 1.6-fold greater maximal reduction in mean arterial pressure with acute ACE inhibition plus AT(1) receptor blockade than with ACE inhibition alone. Thus, mast cells are the source of the vascular ACE-independent pathway, and the antihypertensive benefit of combining ACE inhibitor therapy with AT(1) receptor antagonist therapy is most likely due to negation of chymase-catalyzed Ang II generation.

Phospholipase C-delta1 rescues intracellular Ca2+ overload in ischemic heart and hypoxic neonatal cardiomyocytes

Ischemia and simulated ischemic conditions cause intracellular Ca2+ overload in the myocardium. The relationship between ischemia injury and Ca2+ overload has not been fully characterized. The aim of the present study was to investigate the expression and characteristics of PLC isozymes in myocardial infarction-induced cardiac remodeling and heart failure. In normal rat heart tissue, PLC-delta1 (about 44 ng/mg of heart tissue) was most abundant isozymes compared to PLC-gamma1 (6.8 ng/mg) and PLC-beta1 (0.4 ng/mg). In ischemic heart and hypoxic neonatal cardiomyocytes, PLC-delta1, but not PLC-beta1 and PLC-gamma1, was selectively degraded, a response that could be inhibited by the calpain inhibitor, calpastatin, and by the caspase inhibitor, zVAD-fmk. Overexpression of the PLC-delta1 in hypoxic neonatal cardiomyocytes rescued intracellular Ca2+ overload by ischemic conditions. In the border zone and scar region of infarcted myocardium, and in hypoxic neonatal cardiomyocytes, the selective degradation of PLC-delta1 by the calcium sensitive proteases may play important roles in intracellular Ca2+ regulations under the ischemic conditions. It is suggested that PLC isozyme-changes may contribute to the alterations in calcium homeostasis in myocardial ischemia.

Validity of mouse models for the study of tissue transglutaminase in neurodegenerative diseases

Tissue transglutaminase (tTG) is a multifunctional enzyme that catalyzes peptide cross-linking and polyamination reactions, and also is a signal-transducing GTPase. tTG protein content and enzymatic activity are upregulated in the brain in Huntington's disease and in other neurological diseases and conditions. Since mouse models are currently being used to study the role of tTG in Huntington's disease and other neurodegenerative diseases, it is critical that the level of its expression in the mouse forebrain be determined. In contrast to human forebrain where tTG is abundant, tTG can only be detected in mouse forebrain by immunoblotting a GTP-binding-enriched protein fraction. tTG mRNA content and transamidating activity are approximately 70% lower in mouse than in human forebrain. However, tTG contributes to the majority of transglutaminase activity within mouse forebrain. Thus, although tTG is expressed at lower levels in mouse compared with human forebrain, it likely plays important roles in neuronal function.

Evolutionary specialization of a tryptophan indole group for transition-state stabilization by eukaryotic transglutaminases

Covalent posttranslational protein modifications by eukaryotic transglutaminases proceed by a kinetic pathway of acylation and deacylation. Ammonia is released as the acylenzyme is formed, whereas the cross-linked product is released later in the deacylation step. Superposition of the active sites of transglutaminase type 2 (TG2) and the structurally related cysteine protease, papain, indicates that in the formation of tetrahedral intermediates, the backbone nitrogen of the catalytic Cys-277 and the N1 nitrogen of Trp-241 of TG2 could contribute to transition-state stabilization. The importance of this Trp-241 side chain was demonstrated by examining the kinetics of dansylcadaverine incorporation into a model peptide. Although substitution of the Trp-241 side chain with Ala or Gly had only a small effect on the Michaelis constant Km (1.5-fold increase), it caused a >300-fold lowering of the catalytic rate constant kcat. The wild-type and mutant TG2-catalyzed release of ammonia showed kinetics similar to the kinetics for the formation of cross-linked product, indicating that transition-state stabilization in the acylation step was rate-limiting. In papain, a Gln residue is at the position of TG2-Trp-241. The conservation of Trp-241 in all eukaryotic transglutaminases and the finding that W241Q-TG2 had a much lower kcat than wild-type enzyme suggest evolutionary specialization in the use of the indole group. This notion is further supported by the observation that transition-state-stabilizing side chains of Tyr and His that operate in some serine and metalloproteases only partially substituted for Trp.

IGF-1 enhances a store-operated Ca2+ channel in skeletal muscle myoblasts: involvement of a CD20-like protein

Overexpression of IGF-1 in C2C12 myoblasts causes hypertrophy when myoblasts fuse to form myotubes, a response that requires elevated intracellular calcium. We show that myoblasts contain a store-operated Ca2+ channel (SOCC) whose activity is enhanced with IGF-1 overexpression. A membrane protein, CD20, can cause Ca2+ entry, which is increased by IGF-1. We therefore tested whether CD20 mediates the SOCC activity in myoblasts. An antibody to the extracellular loop of CD20 detected a protein in myoblasts and this antibody also inhibited Ca2+ entry through SOCC. Overexpression of CD20 in myoblasts increased SOCC activity. However, we could not detect mRNA for CD20 in myoblasts and an antibody to the intracellular C-terminus of CD20 was unable to detect CD20 in these cells. These studies demonstrate that CD20 is a novel SOCC or modulates SOCC activity. However, the SOCC activity observed in C2C12 myoblasts is mediated not by CD20, but by a CD20-like protein. Activation of this SOCC may contribute to IGF-1-induced hypertrophy in these cells.

Allosteric alpha 1-adrenoreceptor antagonism by the conopeptide rho-TIA

A peptide contained in the venom of the predatory marine snail Conus tulipa, rho-TIA, has previously been shown to possess alpha1-adrenoreceptor antagonist activity. Here, we further characterize its pharmacological activity as well as its structure-activity relationships. In the isolated rat vas deferens, rho-TIA inhibited alpha1-adrenoreceptor-mediated increases in cytosolic Ca2+ concentration that were triggered by norepinephrine, but did not affect presynaptic alpha2-adrenoreceptor-mediated responses. In radioligand binding assays using [125I]HEAT, rho-TIA displayed slightly greater potency at the alpha 1B than at the alpha 1A or alpha 1D subtypes. Moreover, although it did not affect the rate of association for [3H]prazosin binding to the alpha 1B-adrenoreceptor, the dissociation rate was increased, indicating non-competitive antagonism by rho-TIA. N-terminally truncated analogs of rho-TIA were less active than the full-length peptide, with a large decline in activity observed upon removal of the fourth residue of rho-TIA (Arg4). An alanine walk of rho-TIA confirmed the importance of Arg4 for activity and revealed a number of other residues clustered around Arg4 that contribute to the potency of rho-TIA. The unique allosteric antagonism of rho-TIA resulting from its interaction with receptor residues that constitute a binding site that is distinct from that of the classical competitive alpha1-adrenoreceptor antagonists may allow the development of inhibitors that are highly subtype selective.

Structural details (kinks and non-alpha conformations) in transmembrane helices are intrahelically determined and can be predicted by sequence pattern descriptors

One of the promising methods of protein structure prediction involves the use of amino acid sequence-derived patterns. Here we report on the creation of non-degenerate motif descriptors derived through data mining of training sets of residues taken from the transmembrane-spanning segments of polytopic proteins. These residues correspond to short regions in which there is a deviation from the regular alpha-helical character (i.e. pi-helices, 3(10)-helices and kinks). A 'search engine' derived from these motif descriptors correctly identifies, and discriminates amongst instances of the above 'non-canonical' helical motifs contained in the SwissProt/TrEMBL database of protein primary structures. Our results suggest that deviations from alpha-helicity are encoded locally in sequence patterns only about 7-9 residues long and can be determined in silico directly from the amino acid sequence. Delineation of such variations in helical habit is critical to understanding the complex structure-function relationships of polytopic proteins and for drug discovery. The success of our current methodology foretells development of similar prediction tools capable of identifying other structural motifs from sequence alone. The method described here has been implemented and is available on the World Wide Web at http://cbcsrv.watson.ibm.com/Ttkw.html.

Distinct transglutaminase 2-independent and transglutaminase 2-dependent pathways mediate articular chondrocyte hypertrophy

Altered chondrocyte differentiation, including development of chondrocyte hypertrophy, mediates osteoarthritis and pathologic articular cartilage matrix calcification. Similar changes in endochondral chondrocyte differentiation are essential for physiologic growth plate mineralization. In both articular and growth plate cartilages, chondrocyte hypertrophy is associated with up-regulated expression of certain protein-crosslinking enzymes (transglutaminases (TGs)) including the unique dual-functioning TG and GTPase TG2. Here, we tested if TG2 directly mediates the development of chondrocyte hypertrophic differentiation. To do so, we employed normal bovine chondrocytes and mouse knee chondrocytes from recently described TG2 knockout mice, which are phenotypically normal. We treated chondrocytes with the osteoarthritis mediator IL-1 beta, with the all-trans form of retinoic acid (ATRA), which promotes endochondral chondrocyte hypertrophy and pathologic calcification, and with C-type natriuretic peptide, an essential factor in endochondral development. IL-1 beta and ATRA induced TG transamidation activity and calcification in wild-type but not in TG2 (-/-) mouse knee chondrocytes. In addition, ATRA induced multiple features of hypertrophic differentiation (including type X collagen, alkaline phosphatase, and MMP-13), and these effects required TG2. Significantly, TG2 (-/-) chondrocytes lost the capacity for ATRA-induced expression of Cbfa1, a transcription factor necessary for ATRA-induced chondrocyte hypertrophy. Finally, C-type natriuretic peptide, which did not modulate TG activity, comparably promoted Cbfa1 expression and hypertrophy (without associated calcification) in TG2 (+/+) and TG2 (-/-) chondrocytes. Thus, distinct TG2-independent and TG2-dependent mechanisms promote Cbfa1 expression, articular chondrocyte hypertrophy, and calcification. TG2 is a potential site for intervention in pathologic calcification promoted by IL-1 beta and ATRA.

Transglutaminases: crosslinking enzymes with pleiotropic functions

Blood coagulation, skin-barrier formation, hardening of the fertilization envelope, extracellular-matrix assembly and other important biological processes are dependent on the rapid generation of covalent crosslinks between proteins. These reactions--which are catalysed by transglutaminases--endow the resulting supramolecular structure with extra rigidity and resistance against proteolytic degradation. Some transglutaminases function as molecular switches in cytoskeletal scaffolding and modulate protein-protein interactions. Having knowledge of these enzymes is essential for understanding the aetiologies of diverse hereditary diseases of the blood and skin, and various autoimmune, inflammatory and degenerative conditions.

Keratosis pilaris atrophicans in mother and daughter

We report two cases of keratosis follicularis spinulosa decalvans in a Caucasian family involving a 28-year-old woman and her mother. This is an unusual family in that no male relatives are similarly affected. Secondly, both patients have no significant eye changes but quite extensive scarring alopecia. To the best of our knowledge this is the second reported family in the UK.

Mutation of a single TMVI residue, Phe(282), in the beta(2)-adrenergic receptor results in structurally distinct activated receptor conformations

We showed previously that Phe(303) in transmembrane segment (TM) VI of the alpha(1B)-adrenergic receptor (alpha(1B)-AR), a residue conserved in many G protein-coupled receptors (GPCRs), is critically involved in coupling agonist binding with TM helical movement and G protein activation. Here the equivalent residue, Phe(282), in the beta(2)-AR was evaluated by mutation to glycine, asparagine, alanine, or leucine. Except for F282N, which exhibits attenuated basal and maximal isoproterenol stimulation, the Phe(282) mutants display varying degrees of constitutive activity (F282L > F282A > F282G), and as shown by the results of substituted cysteine accessibility method (SCAM) studies, induce movement of endogenous cysteine(s) into the water-accessible ligand-binding pocket. For F282A, movement is confined to Cys(285) in TMVI, whereas F282L induces movement of both Cys(285) in TMVI and Cys(327) in TMVII. Further, engineered cysteine-sensor studies indicate that F282L causes movement of TMVI, both above and below an apparent kink-inducing TMVI proline (Pro(288)), whereas that due to F282A is confined to the domain below Pro(288). A plausible interpretation of these data is that receptor activation involves rigid body movement of TMVI which, because of its Pro(288)-induced kink, acts as a pivot to transduce and amplify the agonist-induced conformational change in the upper domain, to a change in the lower domain required for productive receptor-G protein coupling.