This study was directed at characterising the cannabinoid receptor activity modulating the electrical field stimulation (EFS) evoked contractions of the rat isolated ileum myenteric plexus longitudinal muscle (MPLM) preparation, and the capsaicin, nicotine and veratridine evoked secretory responses of the rat isolated colonic submucosal plexus-mucosal (SPM) preparation. EFS of the MPLM preparation with single pulses at a repetition frequency of 0.05 Hz elicited a transient twitch contraction immediately in response to each electrical pulse. In contrast, stimulation of the MPLM preparation with 2 second trains of pulses every minute at a frequency of 30 Hz elicited a rapid transient rebound contraction on termination of each train of EFS. The non-selective cannabinoid receptor agonists AEA, CP 55,940, D9-THC and WIN 55,212-2 inhibited both EFS-evoked twitch and rebound contractions of the rat ileum MPLM elicited by 0.05 Hz and 30 Hz EFS respectively. The inhibition of the twitch contractions was competitively antagonised by the cannabinoid CB1 receptor antagonist / inverse agonist SR 141716 with pKB values of 8.60. In contrast, SR 141716 only antagonised the ability of AEA, D9-THC and WIN 55,212-2 but not CP 55,940 to inhibit the rebound contractions with pA2 values of 6.60. These observations extended to the inhibitory effect of WIN 55,212-2 on the twitch and rebound contractions of the guinea-pig ileum MPLM. The CB2 antagonist / inverse agonist SR 144528 did not alter the effects of the agonists. Additionally, the inhibitory effect of AEA was refractory to the vanilloid TRPV1 receptor antagonist capsazepine. WIN 55,212-3 a stereoisomer of WIN 55,212-2 was without effect on the rat MPLM. SR 141716 alone concentration-dependently increased the twitch contractions but inhibited the rebound contractions. Both types of the EFS-evoked contractions were abolished by the Na+ channel blocker tetrodotoxin or the muscarinic acetylcholine (ACh) receptor antagonist atropine but not the nicotinic ACh receptor antagonist hexamethonium. None of the cannabinoids altered the contractions to exogenously applied ACh. These data suggested that the cannabinoid agonists inhibited the twitch contractions through a stereospecific presynaptic CB1 receptor-mediated reduction in the release of ACh. Additionally, the inhibition of the rebound contractions occurred because of an inhibition of ACh release by a novel stereospecific presynaptic non-CB1 -non CB2 -non -TRPV1 site. The ability of SR 141716 to inhibit the rebound contractions and antagonise AEA, D9-THC and WIN 55,212-2 may be though partial agonism at the non-CB1-non CB2-non-TRPV1 site. The ability of SR 141716 to potentiate the twitch contractions by increasing the release of ACh suggested that the CB1 receptor was constitutively active or was subjected to a tonic activation by endocannabinoid agonists. A comparison between the maximal enhancement of the twitch contractions of the rat and the guinea-pig ileum MPLM caused by three CB1 receptor antagonists/inverse agonists AM 251, SR 141716 and O-2050 showed that each cannabinoid had a different maximum. This suggested inverse agonism. These data were supported with studies showing the lack of effect of three fatty acid amide hydrolase (FAAH) inhibitors AA-5HT, PMSF, URB–597 and VDM-11, an inhibitor of the AEA uptake transporter on EFS-evoked contractions. These studies showed that all three FAAH inhibitors increased the potency of exogenously applied AEA but not WIN 55,212-2, and that VDM-11 had no effect on the potency of exogenously applied AEA. This data suggested that a functional endocannabinoid tone and the uptake transporter were not present in the MPLM, but FAAH was present. These data provide supporting evidence that SR 141716 behaved as an inverse agonist in the MPLM to augment twitch contractions. The interaction between CP 55,940 or WIN 55,212-2 with SR 141716 was investigated using the rat colonic SPM sheet. Both CP 55,940 and WIN 55,212-2 attenuated the secretory responses to capsaicin and nicotine in a SR 141716 sensitive manner. SR 140333, a neurokinin 1 receptor antagonist, abolished the capsaicin and nicotine. This suggested that CP 55,940 and WIN 55,212-2 inhibited the capsaicin and nicotine response through a CB1 receptor-mediated inhibition of the release of substance P or neurokinin A. The sensitivity of the veratridine response to TTX and a-chymotrypsin and the failure of the cannabinoids to attenuate the response suggested the absence of the CB1 receptor on the neurones releasing the undetermined neuropeptide. Together, these data suggest that both the CB1 receptor and non-CB1-non-CB2 -non-TRPV1 receptor can mediate the inhibitory effects of cannabinoid agonists in the rat ileum MPLM depending on the frequency of EFS. These data also show that SR 141716 is an inverse agonist in the MPLM. In the SPM preparation, the CB1 receptor appears to be involved in the modulation of some forms of peptidergic transmission.

Cardiovascular diseases are a major cause of death worldwide. Aneurysmal rupture in cerebral arteries or loss of endothelial integrity in the course of atherosclerosis or therapeutic angioplasty lead to exposure of vascular smooth muscle cells (SMC) to blood components such as sphingolipids. Sphingosylphosphorylcholine (SPC) and sphingosine 1-phosphate (S1P) are two naturally occurring sphingolipids, which are vasoprotective in the healthy endothelium-lined vessel, but may promote vascular disease by causing functional changes of SMC. Vascular inflammation is an important factor in various pathologies. SPC can activate pro-inflammatory signalling pathways in rat cerebral artery. Here these observations are extended by showing that SPC elicits monocyte chemoattractant protein-1 production in rat cerebral artery SMC ex vivo. Thus, in addition to being a vasoconstrictor, SPC may promote the development of life-threatening prolonged cerebral vasospasm following subarachnoid haemorrhage by supporting vascular inflammation. It is also demonstrated that SPC prevents tumour necrosis factor-a (TNF)-stimulated adhesion of macrophages to rat aortic SMC in vitro by interfering with adhesive properties of SMC, but not macrophages. While this effect appeared to be mediated by the S1P receptor S1P2, S1P itself did not reduce macrophage adhesion. The anti-adhesive action of SPC also depended on lipid rafts. However, SPC did neither prevent TNF-induced nuclear factor kB activation nor cell adhesion molecule expression in SMC. SPC-induced cyclooxygenase 2 expression in aortic SMC was dispensable for its anti-adhesive effect. In contrast, the inhibitory effect of SPC on TNFinduced expression of inducible nitric oxide synthase is probably involved in its anti-adhesive effect because it was mimicked by respective pharmacological blockade. The results also demonstrate that nitric oxide promotes leukocyte adhesion to vascular SMC, while it has the opposite effect on endothelial cells. These findings may help understand cardiovascular diseases and define novel treatment approaches.

No description available.

Subarachnoid hemorrhage (SAH) following cerebral aneurysm rupture is associated with substantial morbidity and mortality. The ability of SAH to induce vasospasm in large diameter pial arteries has been extensively studied, although the contribution of this phenomenon to patient outcome is unclear. Conversely, little is known regarding the impact of SAH on intracerebral (parenchymal) arterioles, which are critical for regulation of cerebral blood flow. To assess the function of parenchymal arterioles following SAH, measurements of diameter, intracellular Ca2+ ([Ca2+]i) and membrane potential were performed in intact arterioles from unoperated (control), sham-operated and SAH model rats. At physiological intravascular pressure, parenchymal arterioles from SAH animals exhibited significantly elevated [Ca2+]i and enhanced constriction compared with arterioles from control and sham-operated animals. Elevated [Ca2+]i and enhanced tone following SAH were observed in the absence of vascular endothelium and were abolished by the L-type voltage-dependent Ca2+ channel (VDCC) inhibitor nimodipine. Molecular assessment of the L-type VDCC CaV1.2 indicated unchanged mRNA and protein expression in arterioles from SAH animals. Increased CaV1.2 activity following SAH may also reflect enhanced pressure-induced membrane potential depolarization of arteriolar smooth muscle. Membrane potential measurements in arteriolar myocytes using intracellular microelectrodes revealed approximately 7 mV depolarization at 40 mmHg in myocytes from SAH animals. Further, when membrane potential was adjusted to similar values, arteriolar [Ca2+]i and tone were similar between groups. These results demonstrate that greater pressure-dependent membrane potential depolarization results in increased activity of CaV1.2 channels, elevated [Ca2+]i and enhanced constriction of parenchymal arterioles from SAH animals. Thus, impaired regulation of parenchymal arteriolar [Ca2+]i and diameter may restrict cerebral blood flow in SAH patients. Although nimodipine is used clinically to prevent delayed neurological deficits in SAH patients, the use of this drug has been limited by hypotension and treatment options remain inadequate. Therefore, our next objective was to explore strategies to selectively suppress CaV1.2 channels in the cerebral vasculature. To do so, we examined the physiological role of smooth muscle CaV1.2 splice variants containing the alternatively-spliced exon 9* in cerebral artery constriction. Using antisense oligonucleotides, we demonstrate that suppression of exon 9*-containing CaV1.2 splice variants results in substantially reduced cerebral artery constriction to elevated extracellular [K+]. In addition, no further reduction in constriction was observed following suppression of all Cav1.2 splice variants, suggesting that exon 9* splice variants are functionally dominant in cerebral artery constriction. In summary, results shown in this dissertation demonstrate that increased CaV1.2 activity following SAH results in enhanced constriction of parenchymal arterioles. Furthermore, evidence is provided supporting the concept that CaV1.2 splice variants with exon 9* are critical for cerebral artery constriction and may provide a novel target for the prevention of delayed ischemic deficits in SAH patients.

Interleukin-13 (IL-13) has been implicated as a critical inducer of a number of features of allergy and asthma including the induction of nonspecific airway hyperresponsiveness (AHR), eosinophilic inflammatory response, eotaxin production, excess mucus formation, and fibrosis. Determining the mechanism(s) of AHR, a hallmark of asthma, is crucial to our understanding of both the pathogenesis and successful treatment of asthma. After carrying out initial experiments to determine the effect of IL-13-induced AHR on murine and rat tracheal rings, mice tissues were chosen for subsequent experiments due to their consistent results and the fact that the mouse genetic map was completed in 1996, which will enable subsequent gene therapy work. Human and mouse share a high percentage of their genes with an average of 85% homology. Numerous IL-13 signalling studies have concentrated on the JAK/STAT6 pathway. IL-13 also activates phosphoinositide 3-kinase (PI3K) and downstream effector molecules. In experiments presented in this thesis pharmacological and genetic approaches implicate the involvement of PI3K and its individual isoform PI3Kδ in IL-13 induced AHR in vitro and this involvement was confirmed using a small interference RNA (siRNA) technology approach. However, IL-13 induced an early activation of PI3K, whereas increased responsiveness was not observed until overnight incubation. Arginase I induction was demonstrated to be another PI3K-dependent potential mechanism of IL-13-induced hyperresponsiveness. The epithelium is also implicated in IL-13-induced hyperresponsiveness, however, the induction of arginase I was demonstrated in both intact and denuded epithelium tracheal rings. The siRNA approach was also employed in 9HTEo-, A549 and BEAS-2B cell lines using different transfecting agents. From these findings, it is concluded that class IA p110δ could be a useful target for the treatment of asthma by preventing IL-13-induced airway smooth muscle hyperresponsiveness and also that arginase I may be involved in IL-13-induced hyperresponsiveness through PI3K- and epithelial-dependent pathways.

FOXO3a is a pro-apoptotic transcription factor which shows increased activation in vascular smooth muscle cells (VSMCs) of advanced atherosclerotic plaques, specifically within the intimal layer. Since VSMC apoptosis plays a crucial role in the pathophysiology of atherosclerosis, we investigated the mechanisms underlying FOXO3a-mediated cell death in this particular cell type. We aimed to characterise a novel VSMC system (FOXO3aA3ERTM) and use these cells to validate MMP-13 and TIMP3 as new FOXO3a target genes. Also, we sought to determine the mechanisms of FOXO3aA3ERTM-mediated VSMC apoptosis, particularly regarding MMP-13 and TIMP3, potential MMP-13 substrates in the extracellular matrix and the precise apoptotic signalling involved. Furthermore, we aimed to investigate whether VSMC-specific activation of FOXO3aA3ERTM in mouse affects vascular remodelling during injury and whether this is reliant on MMP-13. Lastly, we aimed to address if endogenous FOXO3a upregulates MMP-13 in mouse and human VSMCs. Our laboratory has created a transgenic rat VSMC line which stably expresses an inducible FOXO3a mutant allele known as FOXO3aA3ERTM and previous microarray experiments identified matrix metalloproteinase 13 (MMP-13) as a potential novel FOXO3a target gene. Initially, we described several key features of the FOXO3aA3ERTM VSMCs used throughout this thesis, and subsequently demonstrated that MMP-13 is a bona fide target whose expression is rapidly upregulated upon FOXO3a activation, leading to markedly higher levels of protein, cleavage and proteolytic capacity. This induction of MMP-13 was responsible for the vast majority of FOXO3a-mediated apoptosis which was accompanied by prominent degradation of fibronectin, a glycoprotein found in the extracellular matrix. However, we could not identify a terminal apoptotic pathway. FOXO3a also downregulated the endogenous MMP inhibitor TIMP3, the recombinant protein of which reduced both MMP-13 proteolysis and FOXO3a-mediated apoptosis. Activation of FOXO3aA3ERTM in the VSMCs of medium and large arteries in mice resulted in heightened expression of MMP-13 in the vessel wall, which contributed to enhanced neointimal formation during carotid ligation. Finally, endogenous FOXO3a activation leads to increased MMP-13 expression in human VSMCs, but not mouse. Overall, we have shown that FOXO3a promotes VSMC apoptosis through MMP-13 both in vitro and in vivo, a novel pathway that has important implications for the pathogenesis and treatment of vascular disease.

No description available.

No description available.

Atherosclerosis is the leading cause of death in the Western world. Although mitochondrial DNA (mtDNA) damage has been implicated in atherosclerosis, it is unclear whether the damage is sufficient to impair mitochondrial respiration, and mitochondrial dysfunction has not been demonstrated. Treatment of vascular smooth muscle cells (VSMCs) with an atherogenic lipid, oxidised low-density lipoprotein (OxLDL), dose dependently decreased basal and maximal respiration and fat-feeding of apolipoprotein E deficient (ApoE-/-) mice reduced mitochondrial DNA copy number relative to nuclear DNA in aortas. Mitochondrial respiration of ApoE-/- mouse aortas, assessed through a 24-well Seahorse extracellular flux analyser, was not affected prior to the development of atherosclerotic plaques. Developed human carotid atherosclerotic plaques were dissected into defined regions including healthy media, shoulder region, fibrous cap and core and their respiration was investigated. The respiratory reserve capacity (RRC) of the shoulder region was similar to the media. However, the cap RRC was significantly reduced compared to healthy media. In contrast, the extracellular acidification rates (ECAR) of the media, shoulder, cap and core regions were similar. In addition, mtDNA copy number was significantly reduced in tissues derived from human plaques compared to healthy arteries and expression of complexes I and II of the electron transfer chain (ETC) were significantly reduced in plaque VSMCs. OxLDL induced mitophagy in human VSMCs and plaque VSMCs demonstrated increased levels of mitophagy without compensatory upregulation of proteins involved in mitochondrial biogenesis. Understanding the role of mitochondrial metabolism and signalling is important for our understanding of disease progression and may lead to future therapeutic targets.

Neointimal proliferation is a key process underlying many cardiovascular diseases such as atherosclerosis and angioplasty-induced restenosis. Vascular smooth muscle cells (SMC) are significant contributors to the development and stability of the neointimal lesion. This is due, in part, to their capacity to be phenotypically modulated, facilitating SMC proliferation in response to mechanical injury, their subsequent migration, and deposition of extracellular matrix. The aim of this thesis was to characterize the function of two genes identified in our laboratory to be upregulated shortly after mechanical injury of vascular SMC and their exposure to fibroblast growth factor (FGF)-2, an injury-induced cytokine. The first is activation transcription factor (ATF) 4, which is upregulated by FGF-2 and mechanical injury in vascular SMC in vitro, and by balloon-injury in the artery wall. The induction of ATF4 by FGF-2 was shown to be mediated through the PI3K pathway, and preceded by phoshorylation of eIF2alpha, a known upstream effector of ATF4 activation. Knock-down of ATF4 expression inhibited balloon-injury induced neointimal hyperplasia, suggesting that ATF4 is a key player in the SMC response to injury. Furthermore, microarray analysis identified several genes whose transcription in response to FGF-2 may be regulated by ATF4. In particular, this work demonstrates that ATF4 is necessary for VEGF-A upregulation in SMC in response to FGF-2 and mechanical injury in vitro and in the artery wall following balloon-injury. The second is a translation factor, YrdC203. Using confocal fluorescence microscopy, YrdC203 was found to localize partially to the ER, and with RPL12, a component of the 60S ribosomal subunit. Immunoprecipitation studies demonstrate that YrdC203 also interacts with an initiation factor, eIF5B. Mutation of an initiation factor’s signature on the exterior of YrdC203 perturbed its interaction with RPL12 and eIF5B, and inhibited the increase in protein synthesis observed with overexpression of YrdC203. This implicates YrdC203 as a translation factor responsible for ensuring protein synthesis in vascular SMC in response to injury. The present work provides evidence for new molecular mechanisms, transcriptional and translational, regulating the response of vascular SMC to injury. This would provide leads for future therapeutic targets.