A variety of neurologic illnesses including peripheral and cranial neuropathies, central vestibular disease, seizures and coma have been associated with hypothyroidism in dogs. Repeated studies have shown that there is loss of blood brain barrier (BBB) integrity in these animals. Current research has also shown the development cerebrospinal fluid abnormalities in neurologically normal hypothyroid dogs; a finding that is related to BBB degradation. This derangement may be secondary to atherosclerosis and vascular accidents. One possible mediator of vasospasm and ischemic brain injury is endothelin-1 (ET-1). Another group of mediators of vascular dysfunction that has been found in CSF of dogs with various other CNS diseases is matrix metalloproteinases (MMP). The purpose of this study was to assay molecular markers that may contribute to disruption in the blood brain barrier in chronically hypothyroid canines. We hypothesized that BBB disruption in hypothyroidism is mediated by ET-1 and MMPs, as evidenced by increased concentrations of these proteins in CSF compared to controls. Cerebrospinal fluid (CSF) previously collected from 9 control and 9 experimentally induced hypothyroid dogs was used. Administration of I-131 was used to create the experimental model. CSF from time points 0, 6, 12, and 18 months post-induction were evaluated using an ELISA kit for endothelin-1. CSF from each time point was also evaluated using gelatinase zymography to detect MMP-2,9, and 14. The endothelin assay was able to detect ET-1 in CSF as determined by a spike and recovery method. However, ET-1 was undetectable in CSF of control and hypothyroid dogs at all time points. Constitutively expressed MMP-2 was detectable in all dogs at all time points. No other MMPs were detectable in CSF. ET-1 and gelatinase MMP,-9, and -14 are not primary mediators of BBB damage in chronically hypothyroid dogs. They could be involved secondarily and may be better evaluated with different assays or in temporal association with the development of clinical signs of neurologic dysfunction. Additional research is needed to confirm this finding and to evaluate biomarkers of non-vascular components of the BBB. / Master of Science

No / We have examined whether melanin affects Ca2+ homeostasis in cultured normal human melanocytes. Intracellular Ca2+ concentrations ([Ca2+]i), were measured in four Caucasian and in three Negroid melanocyte cultures. Under resting conditions [Ca2+]i was around 100 nM in all cultures, but differences between cells within cultures were observed. All cultures responded to endothelin-1 (ET-1) with increases in [Ca2+]i and there were no differences between Caucasian and Negroid cultures. However, large differences in responses between cells within cultures were observed, indicating that melanocyte cultures are very heterogeneous. The addition of 2.5 mM CaCl2 to melanocytes kept in Ca2+-free medium resulted in rapid and transient increases in [Ca2+]i of up to 1500 nM. These increases were on average more than two times smaller in melanocyte cultures established from Negroid donors compared with Caucasian cultures. In addition, well melanized Caucasian melanocytes, cultured in the presence of 400 ¿M tyrosine and 10 mM NH4Cl, showed a reduced increase in cytoplasmic Ca2+ concentration upon the addition of extracellular Ca2+. The difference in maintaining Ca2+ homeostasis between poorly and well melanized melanocytes may be the result of the clearance of cytoplasmic Ca2+ into melanosomes and the greater capacity for this in the more pigmented melanocytes.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

No description available.

Endothelin receptor b (Ednrb) and its ligand Endothelin 3 (Edn3) have been implicated in melanoma. Several studies have shown an upregulation of EDNRB and EDN3 at both the protein and mRNA levels, as melanoma becomes more aggressive. This study investigated the putative role played by Edn3 over-expression in melanoma progression and angiogenesis in vivo. We crossed Tg(Grm1)Epv transgenic mice that aberrantly express metabotropic glutamate receptor1 under the Dopachrome tautomerase promoter, leading to spontaneous melanocytic lesions in the ears and tails that do not metastasize, with transgenics that overexpress Edn3 under the Keratin 5 promoter (K5-Edn3) or overexpress Ednrb in melanocytes (Tg(Ednrb)1Lk). In both the Tg(Grm1)Epv/K5-Edn3 and Tg(Grm1)Epv/Tg(Ednrb)1Lk mice, tumors appeared earlier and grew significantly larger and faster when compared to Tg(Grm1)Epv mice. Approximately eighty-one percent of Tg(Grm1)Epv/ K5-Edn3 mice and 76% of Tg(Grm1)Epv/Tg(Ednrb)1Lk mice had pigmented lesions in distant organs such as the lung and brain. Real-Time PCR analysis showed higher expression levels of genes involved in cell-cell and cell-matrix interactions and angiogenesis in lesions of Tg(Grm1)Epv/K5-Edn3 when compared to controls. Considering the rapid tumor growth rate of in the Tg(Grm1)Epv/K5-Edn3 mice, differences in the angiogenic response compared to control mice were investigated. Immunofluorescence analysis with the endothelial cell marker CD31 showed that there were more endothelial cells per tumor area in the Tg(Grm1)Epv/K5-Edn3 mice than the controls. Proteome analysis showed that the Dct-Grm1/K5-Edn3 mice had significant increases in other angiogenic related genes such as Angiogenin, CXCL 16 and Endoglin, when compared to controls, while real time PCR analysis of tail tumors also showed higher expression levels of angiogenic related genes such as Hif-1α. The results of this study showed that the EDNRB/EDN3 axis is sufficient to alter the kinetics of melanocytic tumors’ progression, lead them to a fully malignant state, and increase the tumor angiogenic response.

Das akute Lungenversagen ist gekennzeichnet durch eine schwere Störung des Gasaustausches mit ausgeprägter arterieller Hypoxämie. Die inhalative Gabe von Stickstoffmonoxid (iNO) erfolgt in der Therapie zur Verbesserung der arteriellen Oxygenierung, der Effekt ist jedoch variabel. Bisher existieren nur wenige Studien zur Identifikation von Faktoren, die die Effektivität von iNO bestimmen. Die positive Wirkung von iNO auf den Gasaustausch lässt eine Vasokonstriktion in beatmeten Lungenarealen vermuten. Wir untersuchten eine mögliche Wechselwirkung zwischen dem endogenen Vasokonstriktor Endothelin-1 (ET-1) und iNO in einem tierexperimentellen Modell des akuten Lungenversagens. Sechzehn Schweine wurden narkotisiert, invasiv beatmet und nach Induktion des akuten Lungenschadens (ALI) mittels repetitiver Surfactantauswaschung (Lavagemodell nach Lachmann) zwei Gruppen zugeteilt. Die NO-Gruppe (n=8) erhielt eine Inhalation von 30ppm NO, die Kontrolltiere (CTR-Gruppe, n=8) blieben ohne weitere Intervention. Während der nächsten vier Stunden wurden Messungen von Gasaustausch und ET-1 Konzentrationen im arteriellen Blut durchgeführt. Bei allen Tieren führte die Induktion des ALI zu einer signifikanten Verschlechterung des Gasaustausches. Die Gabe von iNO bewirkte in der NO-Gruppe eine signifikante Erhöhung des PaO2. Die ET-1 Plasmaspiegel stiegen im Verlauf an und waren nach drei Stunden in der NO-Gruppe signifikant niedriger als in der CTR-Gruppe. Dabei zeigte sich eine signifikante, moderate Korrelation zwischen den ET-1 Plasmaspiegeln und den durch iNO induzierten Änderungen in PaO2 und Shunt. Damit konnte ET-1 als ein Einflussfaktor auf die durch iNO induzierte Verbesserung des Gasaustausches identifiziert werden.

Neointimal hyperplasia, the proliferative growth of the innermost layer of the blood vessel wall, is a key process in the response to vascular injury, underlying conditions such as post-interventional restenosis and vein/arterial graft disease. One of the many mediators implicated in this process is endothelin-1 (ET-1), a potent vasoconstrictor with pro-inflammatory and pro-mitogenic actions, which acts through ETA and ETB receptor subtypes. It is well established that ET-1 increases, and ETA blockade reduces, neointima formation following vascular injury. The role of ETB is less clear because these receptors mediate potentially beneficial actions in endothelial cells (EC; such as nitric oxide production, and ET-1 clearance) but detrimental effects elsewhere (such as vascular smooth muscle) and it has been recently reported that non-cell-specific ETB deficiency is associated with increased neointimal lesion size following injury. The work described in this thesis addressed the hypothesis that endogenous ET-1 contributes to neointimal hyperplasia by activation of the ETA receptor, and that this action is moderated by concurrent activation of the ETB receptor expressed in EC. The role of ET receptors in neointimal lesion development was assessed using two models of femoral arterial injury in the mouse: (i) an established method of intraluminal wire-injury, and (ii) adaptation of a model of ligation injury that induces robust neointimal lesion formation without physical damage to the endothelium. Lesion development was assessed using standard histological techniques and this was augmented by development of quantitative optical projection tomography (OPT) to allow three-dimensional analysis of lesions. The role of ETA and ETB receptors in these models was addressed using suitable pharmacological ET receptor antagonists. Following wire-injury, selective ETB blockade (A192621; 30mg.kg-1.day-1; 35 days) increased lesion size and blood pressure without significant altering lesion composition. In contrast, selective ETA blockade (atrasentan; 10mg.kg-1.day-1; 35 days) reduced lesion size and blood pressure. Combined ETA+ETB antagonism had no effect on lesion size, despite reducing blood pressure, and reducing collagen content of the lesions. In the ligation model, neither ETA selective, ETB selective nor ETA+ETB blockade altered lesion size as assessed by standard histology but analysis by OPT indicated that ETA blockade, with or without concurrent ETB blockade, reduced lesion volume. The influence of ETB receptors expressed by ECs on lesion formation was addressed using EC-specific ETB knockout mice. Small vessel myography indicated that endothelium-dependent relaxation was unaltered in femoral arteries from these mice. In addition, no effect on lesion size or rate of development was observed in either wire- or ligation-injury models of neointima formation (although subtle effects on lesion and medial composition were apparent after intra-luminal injury). These results indicate that ETB receptor activation can moderate the detrimental actions of the ETA receptor on neointimal lesion progression, and that this role is dependent on the mode of vascular injury. Furthermore, in this setting, this beneficial action is not primarily mediated by ETB expressed by EC, suggesting that ETB in other cell types can reduce lesion development through another, unidentified mechanism. Therefore, while both ETA selective and non-selective ETA/B antagonists are currently in clinical use, in conditions where similar arterial remodelling processes occur, selective ETA receptor antagonists might be preferred.

Stroke or cerebral vascular accident (CVA) is the 4th leading cause of mortality and the principle cause of long-term disability in the United States. Unfortunately, current reperfusion-based treatments (e.g. thrombolysis, tPA) cannot be administered to the majority of patients presenting with ischemic stroke. Accordingly, new treatments for ischemic stroke are desperately needed. Reactive astrocytes perform key roles in tissue repair and remodeling following stroke such as preservation and repair of the blood-brain barrier, modulation of immune cell invasion, glutamate uptake and neuroprotection, and glial scar formation. The proliferative subpopulation of reactive astrocytes found immediately adjacent to the infarct core after stroke (known as the peri-infarct area) is particularly important for protecting the brain parenchyma from ischemic damage and inflammation. Defining the signaling network that controls reactive astrocyte formation and function has potential to provide new treatment strategies for patients ineligible for reperfusion therapy. Notch1 signaling is required for the proliferation of peri-infarct reactive astrocytes after stroke. To identify downstream targets and potential functional effectors of Notch1 signaling in reactive astrocytes, we developed an ex vivo forward signaling screen. To generate large quantities of adult reactive astrocytes, we employed adult Reactive astrocyte-derived Neural Stem Cells (Rad-NSCs) isolated from the peri-infarct area of mice after stroke. Astrocytes re-differentiated from Rad-NSCs (AstroRad-NSC) were then exposed to immobilized Jagged-1, a Notch1 ligand. In response to Jagged-1, many genes involved in reactive astrocyte-mediated tissue protection, metabolic regulation, angiogenesis and glial scar formation were up-regulated. Of special interest, several genes for proteins that regulate with glutamate uptake and metabolism were increased by Jagged-1/Notch signaling, including the glial-specific GLutamate-ASpartate Transporter (GLAST). With loss-of-function experiments, we determined that deletion of Notch1 decreased GLAST transcript and protein levels in cultured AstroRad-NSC. Furthermore, we isolated reactive astrocytes directly from cerebral cortex after stroke and confirmed the effects of Notch1 on GLAST in vivo. Our results suggest that treatments designed to stimulate Notch1 signaling after stroke may promote glutamate uptake, thereby decreasing excitotoxicity and neuronal cell death. Binding of Endothelin peptides to the type B Endothelin receptor (ETBR) has been shown to alter cell proliferation. Investigating a possible relationship between Jagged-1/Notch1 and Endothelin signaling in reactive astrocytes, we determined that Notch1 signaling regulated ETBR indirectly, by activating STAT3, an unidentified transcriptional activator of ETBR. Using inducible transgenic astrocyte-specific conditional knockout (cKO) mice (GFAP-ETBR-cKO), we found that specific deletion of ETBR in reactive astrocytes phenocopied the defect in reactive astrocyte proliferation observed in our previous work with GFAP-Notch1-cKO mice. Notably, the Notch1-STAT3-ETBR axis we identified is likely to control reactive astrocyte proliferation in most, if not all, forms of CNS injury. The experimental results presented in this doctoral dissertation provide novel insight into signaling mechanisms that may someday be exploited to improve care for patients with stroke and other forms of CNS injury or disease.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.