P1516Novel cardiotropic AAV variant C102 vectors show superior gene delivery & reduced immunogenicity in non-human primates, transduction of human cardiomyocytes, & correction of Fabry disease phenotype

Background

Cardiac-targeted gene therapy vectors are needed. Fabry disease is a rare, X-linked disorder caused by mutations in the GLA gene, which encodes α-galactosidase A (GLA). Storage and accumulation of glycolipid substrates of GLA leads to organ damage. Cardiovascular disease is the most common cause of mortality in Fabry disease (75% of deaths). Enzyme replacement therapy (ERT; first line treatment for most patients) demonstrates clearance of Gb3 from capillary endothelial cells. However, Gb3 accumulation in podocytes, cardiomyocytes, and vascular smooth muscle cells persists. Gene replacement strategies leveraging adeno-associated virus (AAV) vectors with high tropism for affected organs (namely the heart) may directly address the underlying pathophysiology of Fabry disease.

Purpose

To unlock the full potential of cardiac gene therapy, novel targeted vectors are needed with enhanced tropism for specific target tissues when delivered in vivo.

Methods

An industrialized “directed evolution” approach (Therapeutic Vector Evolution) was applied in the most relevant animal species (non-human primate; NHP) which led to the discovery of C102, a novel AAV variant capable of efficient gene delivery throughout the primate heart following a single intravenous (IV) administration. C102 biodistribution using a ubiquitous promoter was evaluated in mice and NHP at doses at least 10-fold lower than current AAV-based clinical trials for neuromuscular gene therapy. Animal studies conformed to the NIH Principles of Laboratory Animal Care. To evaluate the ability of the C102 capsid to transduce human target cells relevant to Fabry disease, human pluripotent stem cell-derived cardiomyocytes were transduced. To evaluate the ability of C102 to correct Fabry disease, cultured patient fibroblasts were transduced with the C102.GLA product.

Results

Following a single IV administration in mice, the onset of C102.luciferase expression was rapid (14 days) and durable. Dose-dependent luciferase activity was observed in Fabry disease target tissues, including heart and liver. Following a single IV administration in NHP, superior delivery to heart was demonstrated and immunogenicity was markedly reduced compared to first generation wild-type vectors (AAV8,9), and genomes were present throughout the heart and skeletal muscle groups. In human cardiomyocytes in vitro, C102.EGFP demonstrated significantly higher transduction compared to wild-type AAV1 and 9 vectors (immunofluorescence imaging and quantification by flow cytometry) at all doses. Following transduction with increasing doses of the C102.GLA product in Fabry patient fibroblasts, dose-dependent GLA expression and function was observed.

C102 Genome Delivery in NHP

Conclusion

The data generated using the novel C102 capsid and the C102.GLA Fabry product validate the Therapeutic Vector Evolution approach for cardiac tissue targeting in vivo and provide a strong preclinical data package to enable clinical translation.

Nox2 contributes to age-related oxidative damage to neurons and the cerebral vasculature

Oxidative stress plays an important role in aging-related neurodegeneration. This study used littermates of WT and Nox2-knockout (Nox2KO) mice plus endothelial cell–specific human Nox2 overexpression–transgenic (HuNox2Tg) mice to investigate Nox2-derived ROS in brain aging. Compared with young WT mice (3–4 months), aging WT mice (20–22 months) had obvious metabolic disorders and loss of locomotor activity. Aging WT brains had high levels of angiotensin II (Ang II) and ROS production; activation of ERK1/2, p53, and γH2AX; and losses of capillaries and neurons. However, these abnormalities were markedly reduced in aging Nox2KO brains. HuNox2Tg brains at middle age (11–12 months) already had high levels of ROS production and activation of stress signaling pathways similar to those found in aging WT brains. The mechanism of Ang II–induced endothelial Nox2 activation in capillary damage was examined using primary brain microvascular endothelial cells. The clinical significance of Nox2-derived ROS in aging-related loss of cerebral capillaries and neurons was investigated using postmortem midbrain tissues of young (25–38 years) and elderly (61–85 years) adults. In conclusion, Nox2 activation is an important mechanism in aging-related cerebral capillary rarefaction and reduced brain function, with the possibility of a key role for endothelial cells.

Transthoracic Echocardiographic Examination in the Rabbit Model

Large animal models such as the rabbit are valuable for translational preclinical research. Rabbits have a similar cardiac electrophysiology compared to that of humans and that of other large animal models such as dogs and pigs. However, the rabbit model has the additional advantage of lower maintenance costs compared to other large animal models. The longitudinal evaluation of cardiac function using echocardiography, when appropriately implemented, is a useful methodology for preclinical assessment of novel therapies for heart failure with reduced ejection fraction (e.g. cardiac regeneration). The correct use of this non-invasive tool requires the implementation of a standardized examination protocol following international guidelines. Here we describe, step by step, a detailed protocol supervised by veterinary cardiologists for performing echocardiography in the rabbit model, and demonstrate how to correctly obtain the different echocardiographic views and imaging planes, as well as the different imaging modes available in a clinical echocardiography system routinely used in human and veterinary patients.

Percutaneous Contrast Echocardiography-guided Intramyocardial Injection and Cell Delivery in a Large Preclinical Model

Cell and gene therapy are exciting and promising strategies for the purpose of cardiac regeneration in the setting of heart failure with reduced ejection fraction (HFrEF). Before they can be considered for use, and implemented in humans, extensive preclinical studies are required in large animal models to evaluate the safety, efficacy, and fate of the injectate (e.g., stem cells) once delivered into the myocardium. Small rodent models offer advantages (e.g., cost effectiveness, amenability for genetic manipulation); however, given inherent limitations of these models, the findings in these rarely translate into the clinic. Conversely, large animal models such as rabbits, have advantages (e.g., similar cardiac electrophysiology compared to humans and other large animals), whilst retaining a good cost-effective balance. Here, we demonstrate how to perform a percutaneous contrast echocardiography-guided intramyocardial injection (IMI) technique, which is minimally invasive, safe, well tolerated, and very effective in the targeted delivery of injectates, including cells, into several locations within the myocardium of a rabbit model. For the implementation of this technique, we also have taken advantage of a widely available clinical echocardiography system. After putting in practice the protocol described here, a researcher with basic ultrasound knowledge will become competent in the performance of this versatile and minimally invasive technique for routine use in experiments, aimed at hypothesis testing of the capabilities of cardiac regenerative therapeutics in the rabbit model. Once competency is achieved, the whole procedure can be performed within 25 min after anaesthetizing the rabbit.

Aging-associated metabolic disorder induces Nox2 activation and oxidative damage of endothelial function

Oxidative stress attributable to the activation of a Nox2-containing NADPH oxidase is involved in the development of vascular diseases and in aging. However, the mechanism of Nox2 activation in normal aging remains unclear. In this study, we used age-matched wild-type (WT) and Nox2 knockout (KO) mice at 3-4 months (young); 11-12 months (middle-aged) and 21-22 months (aging) to investigate age-related metabolic disorders, Nox2 activation and endothelial dysfunction. Compared to young mice, middle-aged and aging WT mice had significant hyperglycaemia, hyperinsulinaemia, increased systemic oxidative stress and higher blood pressure. Endothelium-dependent vessel relaxation to acetylcholine was significantly impaired in WT aging aortas, and this was accompanied by increased Nox2 and ICAM-1 expressions, MAPK activation and decreased insulin receptor expression and signaling. However, these aging-associated disorders were significantly reduced or absent in Nox2KO aging mice. The effect of metabolic disorder on Nox2 activation and endothelial dysfunction was further confirmed using high-fat diet-induced obesity and insulin resistance in middle-aged WT mice treated with apocynin (a Nox2 inhibitor). In vitro experiments showed that in response to high glucose plus high insulin challenge, WT coronary microvascular endothelial cells increased significantly the levels of Nox2 expression, activation of stress signaling pathways and the cells were senescent, e.g. increased p53 and β-galactosidase activity. However, these changes were absent in Nox2KO cells. In conclusion, Nox2 activation in response to aging-associated hyperglycaemia and hyperinsulinaemia plays a key role in the oxidative damage of vascular function. Inhibition or knockout of Nox2 preserves endothelial function and improves global metabolism in old age.

p22phox C242T Single-Nucleotide Polymorphism Inhibits Inflammatory Oxidative Damage to Endothelial Cells and Vessels

BACKGROUND

The NADPH oxidase, by generating reactive oxygen species, is involved in the pathophysiology of many cardiovascular diseases and represents a therapeutic target for the development of novel drugs. A single-nucleotide polymorphism, C242T of the p22(phox) subunit of NADPH oxidase, has been reported to be negatively associated with coronary heart disease and may predict disease prevalence. However, the underlying mechanisms remain unknown.

METHODS AND RESULTS

With the use of computer molecular modeling, we discovered that C242T single-nucleotide polymorphism causes significant structural changes in the extracellular loop of p22(phox) and reduces its interaction stability with Nox2 subunit. Gene transfection of human pulmonary microvascular endothelial cells showed that C242T p22(phox) significantly reduced Nox2 expression but had no significant effect on basal endothelial O2 (.-) production or the expression of Nox1 and Nox4. When cells were stimulated with tumor necrosis factor-α (or high glucose), C242T p22(phox) significantly inhibited tumor necrosis factor-α-induced Nox2 maturation, O2 (.-) production, mitogen-activated protein kinases and nuclear factor κB activation, and inflammation (all P<0.05). These C242T effects were further confirmed using p22(phox) short-hairpin RNA-engineered HeLa cells and Nox2(-/-) coronary microvascular endothelial cells. Clinical significance was investigated by using saphenous vein segments from non-coronary heart disease subjects after phlebotomies. TT (C242T) allele was common (prevalence of ≈22%) and, in comparison with CC, veins bearing TT allele had significantly lower levels of Nox2 expression and O2 (.-) generation in response to high-glucose challenge.

CONCLUSIONS

C242T single-nucleotide polymorphism causes p22(phox) structural changes that inhibit endothelial Nox2 activation and oxidative response to tumor necrosis factor-α or high-glucose stimulation. C242T single-nucleotide polymorphism may represent a natural protective mechanism against inflammatory cardiovascular diseases.

An Upgrade on the Rabbit Model of Anthracycline-Induced Cardiomyopathy: Shorter Protocol, Reduced Mortality, and Higher Incidence of Overt Dilated Cardiomyopathy

Current protocols of anthracycline-induced cardiomyopathy in rabbits present with high premature mortality and nephrotoxicity, thus rendering them unsuitable for studies requiring long-term functional evaluation of myocardial function (e.g., stem cell therapy). We compared two previously described protocols to an in-house developed protocol in three groups: Group DOX2 received doxorubicin 2 mg/kg/week (8 weeks); Group DAU3 received daunorubicin 3 mg/kg/week (10 weeks); and Group DAU4 received daunorubicin 4 mg/kg/week (6 weeks). A cohort of rabbits received saline (control). Results of blood tests, cardiac troponin I, echocardiography, and histopathology were analysed. Whilst DOX2 and DAU3 rabbits showed high premature mortality (50% and 33%, resp.), DAU4 rabbits showed 7.6% premature mortality. None of DOX2 rabbits developed overt dilated cardiomyopathy; 66% of DAU3 rabbits developed overt dilated cardiomyopathy and quickly progressed to severe congestive heart failure. Interestingly, 92% of DAU4 rabbits showed overt dilated cardiomyopathy and 67% developed congestive heart failure exhibiting stable disease. DOX2 and DAU3 rabbits showed alterations of renal function, with DAU3 also exhibiting hepatic function compromise. Thus, a shortened protocol of anthracycline-induced cardiomyopathy as in DAU4 group results in high incidence of overt dilated cardiomyopathy, which insidiously progressed to congestive heart failure, associated to reduced systemic compromise and very low premature mortality.

Dual-site sampling improved detection rates for MRSA colonization in patients with cutaneous abscesses

Extranasal sites are common reservoirs of Staphylococcus aureus colonization and may be relevant for methicillin-resistant S. aureus (MRSA) screening and infection control strategies. The objective here was to determine whether inguinal specimens could also be screened using Xpert SA Nasal Complete assay for MRSA. Results were compared to broth enrichment culture. Among 162 consented adults seeking care in the emergency department for cutaneous abscesses, inguinal specimens were found positive for MRSA more often than nares specimens, 24% and 26% by PCR or culture, respectively, compared to 19% each by PCR or culture. Overall, 6% of adults colonized with MRSA would have been missed by nares screening alone. Compared to culture, Xpert SA Nasal Complete assay demonstrated sensitivity and specificity of 89% and 97%, respectively, for detecting nares and/or inguinal MRSA colonization. In conclusion, inguinal specimens were a more common reservoir for MRSA than nares specimens in this population of patients.

Ibuprofen inhibits migration and proliferation of human coronary artery smooth muscle cells by inducing a differentiated phenotype: role of peroxisome proliferator-activated receptor γ

OBJECTIVES

The search for agents that are capable of preventing restenosis and reduce the risk of late thrombosis is of utmost importance. In this study we aim to evaluate the in vitro effects of ibuprofen on proliferation and migration of human coronary artery smooth muscle cells and on endothelial cells.

METHODS

Cell proliferation was evaluated by trypan blue exclusion. Cell migration was assessed by wound-healing 'scratch' assay and time-lapse video microscopy. Protein expression was assessed by immunoblotting, and morphology by immunocytochemistry. The involvement of the PPARγ pathway was studied with the agonist troglitazone, and the use of selective antagonists such as PGF2α and GW9662.

KEY FINDINGS

We demonstrate that ibuprofen inhibits proliferation and migration of HCASMCs and induces a switch in HCASMCs towards a differentiated and contractile phenotype, and that these effects are mediated through the PPARγ pathway. Importantly we also show that the effects of ibuprofen are cell type-specific as it does not affect migration and proliferation of endothelial cells.

CONCLUSIONS

Taken together, our results suggest that ibuprofen could be an effective drug for the development of novel drug-eluting stents that could lead to reduced rates of restenosis and potentially other complications of DES implantation.

Limitations of the MRL mouse as a model for cardiac regeneration

OBJECTIVE

Myocardial repair following injury in mammals is restricted such that damaged areas are replaced by scar tissue, impairing cardiac function. MRL mice exhibit exceptional regenerative healing in an ear punch wound model. Some myocardial repair with restoration of heart function has also been reported following cryoinjury. Increased cardiomyocyte proliferation and a foetal liver stem cell population were implicated. We investigated molecular mechanisms facilitating myocardial repair in MRL mice to identify potential therapeutic targets in non-regenerative species.

METHODS

Expressions of specific cell-cycle regulators that might account for regeneration (CDKs 1, 2, 4 and 6; cyclins A, E, D1 and B1; p21, p27 and E2F5) were compared by immunoblotting in MRL and control C57BL/6 ventricles during development. Flow cytometry was used to investigate stem cell populations in livers from foetal mice, and infarct sizes were compared in coronary artery-ligated and sham-treated MRL and C57BL/6 adult mice.

KEY FINDINGS

No differences in the expressions of cell cycle regulators were observed between the two strains. Expressions of CD34+Sca1+ckit-, CD34+Sca1+ckit+ and CD34+Sca1-ckit+ increased in livers from C57BL/6 vs MRL mice. No differences were observed in infarct sizes, levels of fibrosis, Ki67 staining or cardiac function between MRL and C57BL/6 mice.

CONCLUSIONS

No intrinsic differences were observed in cell cycle control molecules or stem cell populations between MRL and control C57BL mouse hearts. Pathophysiologically relevant ischaemic injury is not repaired more efficiently in MRL myocardium, questioning the use of the MRL mouse as a reliable model for cardiac regeneration in response to pathophysiologically relevant forms of injury.

Characterisation and regulation of E2F-6 and E2F-6b in the rat heart: a potential target for myocardial regeneration?

The E2F transcription factors are instrumental in regulating cell cycle progression and growth, including that in cardiomyocytes, which exit the cell cycle shortly after birth. E2F-6 has been demonstrated to act as a transcriptional repressor; however, its potential role in normal cardiomyocyte proliferation and hypertrophy has not previously been investigated. Here we report the isolation and characterisation of E2F-6 and E2F-6b in rat cardiomyocytes and consider its potential as a target for myocardial regeneration following injury. At the mRNA level, both rat E2F-6 and the alternatively spliced variant, E2F-6b, were expressed in E18 myocytes and levels were maintained throughout development into adulthood. Interestingly, E2F-6 protein expression was down-regulated during myocyte development suggesting that it is regulated post-transcriptionally in these cells. During myocyte hypertrophy, the mRNA expressions of E2F-6 and E2F-6b were not regulated whereas E2F-6 protein was up-regulated significantly. Indeed, E2F-6 protein expression levels closely parallel the developmental withdrawal of myocytes from the cell cycle and the subsequent reactivation of their cell cycle machinery during hypertrophic growth. Furthermore, depletion of E2F-6, using anti-sense technology, results in death of cultured neonatal myocytes. Taken together, abrogation of E2F-6 expression in neonatal cardiomyocytes leads to a significant decrease in their viability, consistent with the notion that E2F-6 might be required for maintaining normal myocyte growth.

The use of proteomics to identify novel therapeutic targets for the treatment of disease

The completion of the Human Genome Project has revealed a multitude of potential avenues for the identification of therapeutic targets. Extensive sequence information enables the identification of novel genes but does not facilitate a thorough understanding of how changes in gene expression control the molecular mechanisms underlying the development and regulation of a cell or the progression of disease. Proteomics encompasses the study of proteins expressed by a population of cells, and evaluates changes in protein expression, post-translational modifications, protein interactions, protein structure and splice variants, all of which are imperative for a complete understanding of protein function within the cell. From the outset, proteomics has been used to compare the protein profiles of cells in healthy and diseased states and as such can be used to identify proteins associated with disease development and progression. These candidate proteins might provide novel targets for new therapeutic agents or aid the development of assays for disease biomarkers. This review provides an overview of the current proteomic techniques available and focuses on their application in the search for novel therapeutic targets for the treatment of disease.

Over expression of Plk1 does not induce cell division in rat cardiac myocytes in vitro

BACKGROUND

Mammalian cardiac myocytes withdraw from the cell cycle during post-natal development, resulting in a non-proliferating, fully differentiated adult phenotype that is unable to repair damage to the myocardium, such as occurs following a myocardial infarction. We and others previously have shown that forced expression of certain cell cycle molecules in adult cardiac myocytes can promote cell cycle progression and division in these cells. The mitotic serine/threonine kinase, Polo-like kinase-1 (Plk1), is known to phosphorylate and activate a number of mitotic targets, including Cdc2/Cyclin B1, and to promote cell division.

PRINCIPAL FINDINGS

The mammalian Plk family are all differentially regulated during the development of rat cardiac myocytes, with Plk1 showing the most dramatic decrease in both mRNA, protein and activity in the adult. We determined the potential of Plk1 to induce cell cycle progression and division in cultured rat cardiac myocytes. A persistent and progressive loss of Plk1 expression was observed during myocyte development that correlated with the withdrawal of adult rat cardiac myocytes from the cell cycle. Interestingly, when Plk1 was over-expressed in cardiac myocytes by adenovirus infection, it was not able to promote cell cycle progression, as determined by cell number and percent binucleation.

CONCLUSIONS

We conclude that, in contrast to Cdc2/Cyclin B1 over-expression, the forced expression of Plk1 in adult cardiac myocytes is not sufficient to induce cell division and myocardial repair.

Inhibition of human mesangial cell proliferation by targeting T-type calcium channels

BACKGROUND

Aberrant glomerular mesangial cell (MC) proliferation is a common finding in renal diseases. T-type calcium channels (T-CaCN) play an important role in the proliferation of a number of cell types, including vascular smooth muscle cells. The hypothesis that T-CaCN may play a role in the proliferation of human MC was investigated.

METHODS

The presence of T-CaCN in primary cultures of human MC was examined using voltage clamping and by RT-PCR. The effect of calcium channel inhibitors, and of siRNA directed against the Cav3.2 T-CaCN isoform, on MC proliferation was assessed using the microculture tetrazolium assay and nuclear BrdU incorporation.

RESULTS

Human MC express only the Cav3.2 T-CaCN isoform. Co-incubation of MC with a T-CaCN inhibitor (mibefradil, TH1177 or Ni(2+)) results in a concentration-dependent attenuation of proliferation. This effect cannot be attributed to direct drug-induced cytotoxicity or apoptosis and is not seen with verapamil, an L-type channel blocker. Transfection of MC with siRNA results in knockdown of T-CaCN Cav3.2 mRNA and a clear attenuation of MC proliferation.

CONCLUSIONS

These results demonstrate for the first time an important role for T-CaCN in human MC proliferation. This could potentially lead to a novel therapy in the treatment of proliferative renal diseases.

Viral nucleolar localisation signals determine dynamic trafficking within the nucleolus

Localisation of both viral and cellular proteins to the nucleolus is determined by a variety of factors including nucleolar localisation signals (NoLSs), but how these signals operate is not clearly understood. The nucleolar trafficking of wild type viral proteins and chimeric proteins, which contain altered NoLSs, were compared to investigate the role of NoLSs in dynamic nucleolar trafficking. Three viral proteins from diverse viruses were selected which localised to the nucleolus; the coronavirus infectious bronchitis virus nucleocapsid (N) protein, the herpesvirus saimiri ORF57 protein and the HIV-1 Rev protein. The chimeric proteins were N protein and ORF57 protein which had their own NoLS replaced with those from ORF57 and Rev proteins, respectively. By analysing the sub-cellular localisation and trafficking of these viral proteins and their chimeras within and between nucleoli using confocal microscopy and photo-bleaching we show that NoLSs are responsible for different nucleolar localisations and trafficking rates.

Reprogramming the cell cycle machinery to treat cardiovascular disease

Coronary artery disease is one of the most common heart pathologies. Restriction of blood flow to the heart by atherosclerotic lesions, leading to angina pectoris and myocardial infarction, damages the heart, resulting in impaired cardiac function. Damaged myocardium is replaced by scar tissue since surviving cardiomyocytes are unable to proliferate to replace lost heart tissue. Although narrowing of the coronary arteries can be treated successfully using coronary revascularisation procedures, re-occlusion of the treated vessels remains a significant clinical problem. Cell cycle control mechanisms are key in both the impaired cardiac repair by surviving cardiomyocytes and re-narrowing of treated vessels by maladaptive proliferation of vascular smooth muscle cells. Strategies targeting the cell cycle machinery in the heart and vasculature offer promise both for the improvement of cardiac repair following MI and the prevention of restenosis and bypass graft failure following revascularisation procedures.

Nox2 regulates endothelial cell cycle arrest and apoptosis via p21cip1 and p53

Endothelial cells (EC) express constitutively two major isoforms (Nox2 and Nox4) of the catalytic subunit of NADPH oxidase, which is a major source of endothelial reactive oxygen species. However, the individual roles of these Noxes in endothelial function remain unclear. We have investigated the role of Nox2 in nutrient deprivation-induced cell cycle arrest and apoptosis. In proliferating human dermal microvascular EC, Nox2 mRNA expression was low relative to Nox4 (Nox2:Nox4 approximately 1:13), but was upregulated 24 h after starvation and increased to 8+/-3.5-fold at 36 h of starvation. Accompanying the upregulation of Nox2, there was a 2.28+/-0.18-fold increase in O2.- production, a dramatic induction of p21cip1 and p53, cell cycle arrest, and the onset of apoptosis (all p<0.05). All these changes were inhibited significantly by in vitro deletion of Nox2 expression and in coronary microvascular EC isolated from Nox2 knockout mice. In Nox2 knockout cells, although there was a 3.8+/-0.5-fold increase in Nox4 mRNA expression after 36 h of starvation (p<0.01), neither O2.- production nor the p21cip1 or p53 expression was increased significantly and only 0.46% of cells were apoptotic. In conclusion, Nox2-derived O2.-, through the modulation of p21cip1 and p53 expression, participates in endothelial cell cycle regulation and apoptosis.

Regulation of cell cycle and stress responses to hydrostatic pressure in fission yeast

We have investigated the cellular responses to hydrostatic pressure by using the fission yeast Schizosaccharomyces pombe as a model system. Exposure to sublethal levels of hydrostatic pressure resulted in G2 cell cycle delay. This delay resulted from Cdc2 tyrosine-15 (Y-15) phosphorylation, and it was abrogated by simultaneous disruption of the Cdc2 kinase regulators Cdc25 and Wee1. However, cell cycle delay was independent of the DNA damage, cytokinesis, and cell size checkpoints, suggesting a novel mechanism of Cdc2-Y15 phosphorylation in response to hydrostatic pressure. Spc1/Sty1 mitogen-activated protein (MAP) kinase, a conserved member of the eukaryotic stress-activated p38, mitogen-activated protein (MAP) kinase family, was rapidly activated after pressure stress, and it was required for cell cycle recovery under these conditions, in part through promoting polo kinase (Plo1) phosphorylation on serine 402. Moreover, the Spc1 MAP kinase pathway played a key role in maintaining cell viability under hydrostatic pressure stress through the bZip transcription factor, Atf1. Further analysis revealed that prestressing cells with heat increased barotolerance, suggesting adaptational cross-talk between these stress responses. These findings provide new insight into eukaryotic homeostasis after exposure to pressure stress.

Developmental expression of myostatin in cardiomyocytes and its effect on foetal and neonatal rat cardiomyocyte proliferation

OBJECTIVES

Myostatin, a member of the transforming growth factor-beta (TGF-beta) family, plays a key role in skeletal muscle myogenesis by limiting hyperplastic and hypertrophic muscle growth. In cardiac muscle, myostatin has been shown to limit agonist-induced cardiac hypertrophic growth. However, its role in cardiac hyperplastic growth remains undetermined. The aim of this study was to characterise the expression of myostatin in developing myocardium, determine its effect on cardiomyocyte proliferation, and explore the signalling mechanisms affected by myostatin in dividing cardiomyocytes.

METHODS

We used quantitative PCR and Western blotting to study the expression of myostatin in cardiomyocytes isolated from rat myocardium at different developmental ages. We determined the effect of recombinant myostatin on proliferation and cell viability in dividing cardiomyocytes in culture. We analysed myostatin's effect on cardiomyocyte cell cycle progression by flow cytometry and used Western blotting to explore the signalling mechanisms involved.

RESULTS

Myostatin is expressed differentially in cardiomyocytes during cardiac development such that increasing expression correlated with a low cardiomyocyte proliferation index. Proliferating foetal cardiomyocytes, from embryos at 18 days of gestation, expressed low levels of myostatin mRNA and protein, whereas isolated cardiomyocytes from postnatal day 10 hearts, wherein the majority of cardiomyocytes have lost their ability to proliferate, displayed a 6-fold increase in myostatin expression. Our in vitro studies demonstrated that myostatin inhibited proliferation of dividing foetal and neonatal cardiomyocytes. Flow cytometric analysis showed that this inhibition occurs mainly via a block in the G1-S phase transition of the cardiomyocyte cell cycle. Western blot analysis showed that part of the mechanism underpinning the inhibition of cardiomyocyte proliferation by myostatin involves phosphorylation of SMAD2 and altered expressions of the cell cycle proteins p21 and CDK2.

CONCLUSIONS

We conclude that myostatin is an inhibitor of cardiomyocyte proliferation with the potential to limit cardiomyocyte hyperplastic growth by altering cardiac cell cycle progression.

Characterisation of cyclin D1 down-regulation in coronavirus infected cells

The positive strand RNA coronavirus, infectious bronchitis virus (IBV), induces a G2/M phase arrest and reduction in the G1 and G1/S phase transition regulator cyclin D1. Quantitative real-time RT-PCR and Western blot analysis demonstrated that cyclin D1 was reduced post-transcriptionally within infected cells independently of the cell-cycle stage at the time of infection. Confocal microscopy revealed that cyclin D1 decreased in IBV-infected cells as infection progressed and inhibition studies indicated that a population of cyclin D1 could be targeted for degradation by a virus mediated pathway. In contrast to the SARS-coronavirus, IBV nucleocapsid protein did not interact with cyclin D1.

Can the cardiomyocyte cell cycle be reprogrammed?

Cardiac repair following myocardial injury is restricted due to the limited proliferative potential of adult cardiomyocytes. The ability of mammalian cardiomyocytes to proliferate is lost shortly after birth as cardiomyocytes withdraw from the cell cycle and differentiate. We do not fully understand the molecular and cellular mechanisms that regulate this cell cycle withdrawal, although if we could it might lead to the discovery of novel therapeutic targets for improving cardiac repair following myocardial injury. For the last decade, researchers have investigated cardiomyocyte cell cycle control, commonly using transgenic mouse models or recombinant adenoviruses to manipulate cell cycle regulators in vivo or in vitro. This review discusses cardiomyocyte cell cycle regulation and summarises recent data from studies manipulating the expressions and activities of cell cycle regulators in cardiomyocytes. The validity of therapeutic strategies that aim to reinstate the proliferative potential of cardiomyocytes to improve myocardial repair following injury will be discussed.

Changes in nucleolar morphology and proteins during infection with the coronavirus infectious bronchitis virus

The nucleolus is a dynamic subnuclear structure involved in ribosome subunit biogenesis, cell cycle control and mediating responses to cell stress, among other functions. While many different viruses target proteins to the nucleolus and recruit nucleolar proteins to facilitate virus replication, the effect of infection on the nucleolus in terms of morphology and protein content is unknown. Previously we have shown that the coronavirus nucleocapsid protein will localize to the nucleolus. In this study, using the avian infectious bronchitis coronavirus, we have shown that virus infection results in a number of changes to the nucleolus both in terms of gross morphology and protein content. Using confocal microscopy coupled with fluorescent labelled nucleolar marker proteins we observed changes in the morphology of the nucleolus including an enlarged fibrillar centre. We found that the tumour suppressor protein, p53, which localizes normally to the nucleus and nucleolus, was redistributed predominately to the cytoplasm.

Myostatin regulates cardiomyocyte growth through modulation of Akt signaling

Myostatin is a highly conserved, potent negative regulator of skeletal muscle hypertrophy in many species, from rodents to humans, although its mechanisms of action are incompletely understood. Transcript profiling of hearts from a genetic model of cardiac hypertrophy revealed dramatic upregulation of myostatin, not previously recognized to play a role in the heart. Here we show that myostatin abrogates the cardiomyocyte growth response to phenylephrine in vitro through inhibition of p38 and the serine-threonine kinase Akt, a critical determinant of cell size in many species from drosophila to mammals. Evaluation of male myostatin-null mice revealed that their cardiomyocytes and hearts overall were slightly smaller at baseline than littermate controls but exhibited more exuberant growth in response to chronic phenylephrine infusion. The increased cardiac growth in myostatin-null mice corresponded with increased p38 phosphorylation and Akt activation in vivo after phenylephrine treatment. Together, these data demonstrate that myostatin is dynamically regulated in the heart and acts more broadly than previously appreciated to regulate growth of multiple types of striated muscle.

Delineation and modelling of a nucleolar retention signal in the coronavirus nucleocapsid protein

Unlike nuclear localization signals, there is no obvious consensus sequence for the targeting of proteins to the nucleolus. The nucleolus is a dynamic subnuclear structure which is crucial to the normal operation of the eukaryotic cell. Studying nucleolar trafficking signals is problematic as many nucleolar retention signals (NoRSs) are part of classical nuclear localization signals (NLSs). In addition, there is no known consensus signal with which to inform a study. The avian infectious bronchitis virus (IBV), coronavirus nucleocapsid (N) protein, localizes to the cytoplasm and the nucleolus. Mutagenesis was used to delineate a novel eight amino acid motif that was necessary and sufficient for nucleolar retention of N protein and colocalize with nucleolin and fibrillarin. Additionally, a classical nuclear export signal (NES) functioned to direct N protein to the cytoplasm. Comparison of the coronavirus NoRSs with known cellular and other viral NoRSs revealed that these motifs have conserved arginine residues. Molecular modelling, using the solution structure of severe acute respiratory (SARS) coronavirus N‐protein, revealed that this motif is available for interaction with cellular factors which may mediate nucleolar localization. We hypothesise that the N‐protein uses these signals to traffic to and from the nucleolus and the cytoplasm.

Cell cycle perturbations induced by infection with the coronavirus infectious bronchitis virus and their effect on virus replication

In eukaryotic cells, cell growth and division occur in a stepwise, orderly fashion described by a process known as the cell cycle. The relationship between positive-strand RNA viruses and the cell cycle and the concomitant effects on virus replication are not clearly understood. We have shown that infection of asynchronously replicating and synchronized replicating cells with the avian coronavirus infectious bronchitis virus (IBV), a positive-strand RNA virus, resulted in the accumulation of infected cells in the G2/M phase of the cell cycle. Analysis of various cell cycle-regulatory proteins and cellular morphology indicated that there was a down-regulation of cyclins D1 and D2 (G1 regulatory cyclins) and that a proportion of virus-infected cells underwent aberrant cytokinesis, in which the cells underwent nuclear, but not cytoplasmic, division. We assessed the impact of the perturbations on the cell cycle for virus-infected cells and found that IBV-infected G2/M-phase-synchronized cells exhibited increased viral protein production when released from the block when compared to cells synchronized in the G0 phase or asynchronously replicating cells. Our data suggested that IBV induces a G2/M phase arrest in infected cells to promote favorable conditions for viral replication.

Launching the Tidal Model: evaluating the evidence

Launching the Tidal Model: evaluating the evidence This paper reports on two evaluations of the Tidal Model, in the context of two separate acute admission wards, one in Birmingham (2004) and the other in Newcastle (2001), and makes recommendations concerning the criteria and type of reasoning appropriate to evaluating the evidence the two projects have generated. In the Birmingham study, results showed that in the year following the introduction of the Tidal Model, the total number of serious untoward incidents such as physical assault, violence and harassment, decreased by 57%. Nurse satisfaction with their work also improved with nurses rating the model superior to their previous way of working. Inpatient service user assessment of the overall quality of their care was also positive. These findings are then compared with the positive results of an earlier study of the Tidal Model undertaken in Newcastle in 2001. That study was criticized, however, for not showing conclusively that the positive results of the evaluation correlated with the introduction of the Tidal Model. This criticism is briefly examined in the light of both ancient (Aristotle) and modern (Charles Peirce) understandings of the nature of evidence and suggests that such criticism begs the question of the nature of proof. The paper concludes by arguing that, according to both Aristotle and the procedures of abductive reasoning advocated by Charles Peirce, inferring a positive correlation between the results of both studies and the introduction of Tidal Model is a good example of reasonable inference to the best explanation. The available evidence suggests that the results of both studies render the conclusion probable and thus 'good enough' to warrant serious consideration for implementing the Tidal Model more widely within and across Mental Health NHS Trusts.

Nucleolin is regulated both at the level of transcription and translation

Nucleolin is a multi-functional protein that is located to the nucleolus. In tissue culture cells, the stability of nucleolin is related to the proliferation status of the cell. During development, rat cardiomyocytes proliferate actively with increases in the mass of the heart being due to both hyperplasia and hypertrophy. The timing of this shift in the phenotype of the myocyte from one capable of undergoing hyperplasia to one that can grow only by hypertrophy occurs within 4 days of post-natal development. Thus, cardiomyocytes are an ideal model system in which to study the regulation of nucleolin during growth in vivo. Using Western blot and quantitative RT-PCR (TaqMan) we found that the amount of nucleolin is regulated both at the level of transcription and translation during the development of the cardiomyocyte. However, in cells which had exited the cell cycle and were subsequently given a hypertrophic stimulus, nucleolin was regulated post-transcriptionally.

Functional interactions of antiapoptotic proteins and tumor necrosis factor in the context of a replication-competent adenovirus

Replication-selective oncolytic adenoviruses hold promise, but novel mechanisms must be identified to maximize intratumoral virus persistence, spread and therapeutic transgene-carrying capacity while maintaining safety. One of the main approaches to engineering cancer-selectivity has been to delete a viral gene that is theoretically expendable in cancer cells. Results with this approach have been mixed, however, as evidenced by controversy over Onyx-015 (E1B-55kD(-)) selectivity. We hypothesized that the functional redundancy between viral gene products might limit selectivity and/or potency with this approach. Antiviral immune inducers of apoptosis (eg TNF-alpha) have not been thoroughly investigated in previous studies. We therefore explored whether deletion of functionally redundant viral genes, E1B-19kD and E3B, both independently antagonize TNF-alpha, could lead to enhanced oncolytic potency while maintaining selectivity. Since tumors have numerous blocks in apoptotic pathways, we hypothesized that deletion of one or both gene regions would result in cancer-selectivity in the presence of TNF-alpha. We have previously shown that the E1B-19kD deletion resulted in enhanced viral spread in vitro and in immunocompetent tumor models in vivo. In contrast, the impact of E3B deletion, especially its in vitro selectivity and potency, was not thoroughly characterized, although it resulted in rapid immune-mediated viral clearance in vivo. Furthermore, previous publications indicated that double-deleted mutants have selectivity but unsatisfactory efficacy. We compared the selectivity and potency of E1B-19kD(-), E3B(-) and E1B-19kD(-)/E3B(-) mutants to wild-type adenovirus. In cancer cells, the E1B-19kD(-) mutant had superior replication, spread and cytolysis (+) or (-) TNF-alpha; deletion of both E1B-19kD and E3B was relatively deleterious. In normal cells without TNF-alpha, similar results were obtained. In contrast, all three mutants were significantly inhibited in the presence of TNF-alpha. In immunocompetent mice, all three mutants were significantly inhibited in normal tissue. In tumors, only the E1B-19kD(-) mutant demonstrated enhanced replication, spread and antitumoral efficacy. Therefore, E1B-19kD deletion and E3B retention should be incorporated in oncolytic adenoviruses for enhanced safety and efficacy. In addition, functional redundant viral genes and their biological mediators/targets need to be carefully examined for the next generation of gene-deleted oncolytic viruses.

The role of voltage gated T-type Ca2+ channel isoforms in mediating "capacitative" Ca2+ entry in cancer cells

The mechanism by which Ca2+ enters electrically non-excitable cells is unclear. The sensitivity of the Ca2+ entry pathway in electrically non-excitable cells to inhibition by extracellular Ni2+ was used to direct the synthesis of a library of simple, novel compounds. These novel compounds inhibit Ca2+ entry into and, consequently, proliferation of several cancer cell lines. They showed stereoselective inhibition of proliferation and Ca2+ influx with identical stereoselective inhibition of heterologously expressed Cav3.2 isoform of T-type Ca2+ channels. Proliferation of human embryonic kidney (HEK)293 cells transfected with the Cav3.2 Ca2+ channel was also blocked. Cancer cell lines sensitive to our compounds express message for the Cav3.2 T-type Ca2+ channel isoform, its delta25B splice variant, or both, while a cell line resistant to our compounds does not. These observations raise the possibility that clinically useful drugs can be designed based upon the ability to block these Ca2+ channels.

The mammalian cell cycle: an overview

In recent years, we have witnessed major advances in our understanding of the mammalian cell cycle and how it is regulated. Normal mammalian cellular proliferation is tightly regulated at each phase of the cell cycle by the activation and deactivation of a series of proteins that constitute the cell cycle machinery. This review article describes the various phases of the mammalian cell cycle and focuses on the cell cycle regulatory molecules that act at each stage to ensure normal cellular progression.

Cyclins, cyclin-dependent kinases, and cyclin-dependent kinase inhibitors: detection methods and activity measurements

The cyclin/cyclin-dependent kinase (Cdk) complexes and the Cdk inhibitors (CDKI) are crucial regulators of cell cycle progression in all eukaryotic cells. Using rat cardiac myocytes as a model system, this chapter provides a detailed account of methods that can be employed to measure both cyclin/Cdk activity in cells and the extent of CDKI inhibitory activity present in a particular cell type.