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Thinking inside and outside the blood vessel: S1P-mediated control of vascular tone and the impact of CMV infection
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S1P, CMV infection and Vascular tone
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- Author / Creator
- Kerage, Daniel A
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Sphingosine 1–phosphate (S1P), a bioactive lipid, has both endothelial barrier enhancing and disrupting effects, but also regulates vascular tone. The concepts of endothelial permeability and vascular tone have traditionally been studied separately. In this thesis, I demonstrate novel findings that these concepts are interconnected. Using a novel methodology I found that infusion of physiological concentrations of S1P (<1µmol/L) maintained endothelial barrier and had no significant effects on vascular tone in mouse uterine arteries. At a high physiological concentration, 1µmol/L, S1P-induced permeability permitted leakage of a co-infused vasoconstrictor (5 nmol/L U46619, a thromboxane A2 mimetic analog) to the vascular smooth muscle cells (VSMCs) increasing vascular tone. Such endothelial permeability stimulated by S1P, was induced in an S1P3 receptor–dependent manner. These findings reveal a new paradigm of vascular tone control by S1P, in which S1P maintains endothelial barrier that prevents leakage of circulating vasoactive agents to the VSMCs, but also high-end physiological concentrations of S1P (1 µmol/L) induces endothelial permeability that permits leakage of such vasoactive agents to the VSMCs maintaining normal vascular tone. These are important findings as the role of S1P in the control of endothelial barrier has only been previously investigated in cultured endothelial cells and venules. On the other hand, the S1P-induced endothelial permeability at pathophysiological concentrations (10 µmol/L), permitted its own leakage and/or that of co-infused U46619, strongly increasing vascular tone. Equally, endothelial permeability stimulated by thrombin, lipopolysaccharide (LPS) and cytomegalovirus glycoprotein B also facilitated leakage of U46619 to the VSMCs. These findings suggest that excessive increase in endothelial permeability can promote increased vascular tone in uterine arteries. Under pathological conditions, such increased vascular tone could have detrimental effects in reproduction and pregnancy by limiting blood and nutrient supply to important organs for reproduction (ovaries, cervix etc) or to the fetus during pregnancy (leading to pregnancy disorders like intrauterine growth restriction that affect fetal growth). I also found that S1P (3 µmol/L) plays a potentiating role in U46619 (20 nmol/L)-induced vascular tone in mesenteric arteries from female mice. These arteries are however, less reactive to S1P or U46619 than uterine arteries. Such reduced reactivity implies that leakage of vasoconstrictors through the endothelium of systemic arteries is more tightly controlled, meaning that, leakage will likely occur only at pathological concentrations of S1P. Interestingly, I found that mesenteric arteries from male mice were remarkably different. First, their reactivity was similar to that of uterine arteries; secondly, infusion of U46619 (5 nmol/L) or S1P (1 µmol/L) alone, increased vascular tone, each of which was however, significantly lower compared to that induced when the two drugs were co-infused. This means that mesenteric arteries from male mice are likely leakier than those from female mice. This dichotomy of vascular responses found in males and females is not surprising as there are many examples of sex-based differences in vascular responses. Unexpectedly, U46619-induced vascular tone in the bath in mesenteric arteries from S1P3 KO male mice was dramatically decreased compared to the wildtype control, suggesting that in these arteries, U46619-induced responses could be occurring partly through the S1P pathway. Consistent with these assumptions, I provided the first evidence that thromboxane A2 (TXA2) (using U46619), at pathophysiological concentrations (20 nmol/L) could increase endothelial permeability that was accompanied with increased vascular tone in a mechanism that depended on S1P signaling. While these results indicate that TXA2 stimulates downstream S1P signaling, I also demonstrated novel data indicating that cytomegalovirus (CMV) infection enhances the vascular tone induced by TXA2, but also decreases the dependence of TXA2 on the S1P for downstream signaling. CMV infection also opened up an alternative mechanism through which TXA2 increased vascular tone in uterine arteries that was independent of the S1P pathway. Additional studies will be needed to uncover the details of the mechanisms through which CMV infection modulates the vascular tone induced by TXA2.These results indicate that CMV infection can contribute to the pathogenesis of vascular-related complications such as hypertension or pregnancy-related disorders like intrauterine growth restriction Collectively, there is therapeutic promise in targeting the S1P pathway for treatment of vascular disorders caused by TXA2-mediated actions, but also that of CMV infection.
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- Graduation date
- Spring 2016
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.