Regensburg, Univ., Diss., 2002.

Boston University. University Professors Program Senior theses. / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2031-01-02

Currently, it is reported that ~65% and 34% of the U.S. population is overweight and obese, respectively. Obesity is a major risk factor for cardiovascular disease. Overweight and obese individuals are also at an increased risk of developing hypertension. Whole-body insulin sensitivity is reduced in obesity, resulting in insulin resistance and increased risk of type 2 diabetes. One possible mechanism contributing to insulin resistance in obesity hypertension is renin-angiotensin system (RAS) overactivation. The RAS exhibits vasocontricting and sodium-retaining properties, yet in vivo and in vitro animal experiments suggest impairment of whole-body insulin sensitivity with increased angiotensin II (Ang II) exposure. Furthermore, evidence from clinical studies indicates Ang II receptor blockers (ARBs) may reduce the incidence of new-onset diabetes compared to other antihypertensive agents in at-risk hypertensive patients. However, it is unclear if whole-body insulin sensitivity is improved with Ang II receptor blockade in humans. Thus, we tested the hypothesis that 8-week Ang II receptor blockade with olmesartan would improve whole-body insulin sensitivity in overweight and obese individuals with elevated blood pressure (BP). Olmesartan was selected for the present study because it is devoid of partial PPARγ agonist activity. To test our hypothesis, intravenous glucose tolerance tests were performed to measure insulin sensitivity before and after control and ARB treatment in a randomized crossover manner. Because skeletal muscle tissue accounts for ~75-90% of insulin-stimulated glucose uptake, a secondary exploratory aim was to examine skeletal muscle inflammatory and collagen response in relation to insulin sensitivity during ARB treatment. No baseline differences were observed between treatments (P>0.05). Both systolic (-11.7 mmHg; P=0.008) and diastolic (-12.1 mmHg; P=0.000) BP were reduced with ARB treatment. Insulin sensitivity was not different between treatments (P>0.05). No correlates of insulin sensitivity were identified. In addition, skeletal muscle inflammatory and collagen gene expression did not change from pre- to post-ARB treatment (P>0.05). Our findings suggest that short-term RAS blockade in overweight and obese adults with elevated BP does not improve whole-body insulin sensitivity, despite a significant BP reduction. Further studies are needed to clarify the role of individual RAS blockers on insulin sensitivity during RAS inhibition in obesity hypertension. / Ph. D.

Fetal pancreatic tissues can be a promising source for pancreatic progenitor cells (PPCs). In this regard, we have successfully isolated and characterized a population of fetal PPCs from first trimester human fetal pancreas using a previously established basic protocol. Upon exposure to a cocktail of conventional growth factors, these PPCs are amenable to differentiate into insulin-secreting islet-like cell clusters (ICCs); however, these ICCs have yet to exert additional efforts to direct to glucose-responsive cells. To address this issue, we have proposed two novel morphogenic factors in the present study, namely PDZ-domain-containing 2 (PDZD2) and angiotensin II (Ang II), a physiologically active peptide of the renin-angiotensin system (RAS), that potentially promote the differentiation and maturation of PPCs/ICCs. / In light of these findings, we conclude that we have discovered two novel mechanisms, the PDZD2 and Ang II/AT2 receptor signaling pathways, in the regulation of the development of PPCs/ICCs, thus implying their novel roles during islet development in vivo. The present study provides a "proof-of-principle" that a local RAS is critically involved in governing islet cell development. This work may contribute to devising protocols for maturation of pancreatic progenitors for clinical islet transplantation. / Local RASs have been reported to regulate the differentiation of tissue progenitor cells. It has yet to be confirmed whether such systems exist and govern the PPC development. To address this issue, we herein provided evidence that expression of RAS components was highly regulated throughout PPC differentiation. Locally generated Ang II was found to maintain PPC growth and differentiation via mediation of the Ang II type 1 and type 2 (AT1 and AT 2) receptors. We found that the AT2, but not AT1, receptor was a key mediator of Ang II-induced upregulation of beta-cell transcription factors. Transplantation of AT2 receptor-depleted ICCs into immune-privileged diabetic mice failed to ameliorate hyperglycemia, implying that AT2 receptors are indispensable during ICC maturation in vivo. / PDZD2 and its secreted form (sPDZD2) have been found to express in our fetal PPCs. We first evaluated the potential role of sPDZD2 in stimulating PPC differentiation and established an optimal concentration for such stimulation. We found that 10-9 M sPDZD2 promoted PPC differentiation, as evidenced by the up-regulation of the pancreatic endocrine markers and C-peptide content in the ICCs. It enhanced their expression of the L-type voltage-gated calcium ion channel (Cav1.2) and conferred an ability to secrete insulin in response to membrane depolarization. Yet these ICCs remained glucose-unresponsive because of the minimal expression of GLUT-2. We thus attempted to study another potential morphogenic candidate, Ang II. / To further test whether a functional RAS is present and if so, whether it regulates islet development in vivo, we employed a mouse embryo model at different embryonic days and reported a stronger AT2 receptor expression during the 2nd developmental transition of pancreas development. AT2 receptor blockade from e8.0 resulted in abnormalities in fetal pancreatic development. Neonates from these mother mice displayed destructed pancreas/islet architecture, a hampered ability in glucose-stimulated insulin-secretion possibly attributed to a decreased ratio of beta-cell to alpha-cell, and an impaired glucose tolerance at 4-wk old. / Leung, Kwan Keung. / Adviser: Po Sing Leung. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 254-284). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Eine der häufigsten kardiovaskulären Erkrankungen ist die Atherosklerose. Bei der Entstehung einer Atherosklerose spielt eine Hyperlipoproteinämie eine entscheidende Rolle. Ein weiterer Faktor für die Entstehung kardiovaskulärer Erkrankungen ist ein hoher Blutdruck. In dieser Arbeit wurde eine mögliche Interaktion zwischen Lipoproteinen und den blutdruckregulierenden Endothelin- und Renin-Angiotensin-Systemen untersucht. Weiterführende Analysen erfolgten an Rezeptoren für die Aufnahme von nLDL und oxLDL. Abschließend wurden Signalwege untersucht, die durch nLDL und oxLDL aktiviert werden. Tierexperimentielle Untersuchungen in Aorten und Herzen fettreich gefütterter Wildtyp- Mäuse unterstützen die Zellkultur-Ergebnisse einer Induzierung des Endothelin-Systems durch erhöhte Lipoproteine. Zusammenfassend zeigt diese Arbeit neue Mechanismen der Interaktion von Lipoproteinen und blutdruckregulierenden Systemen in Endothelzellen. Die Rezeptoren scheinen dabei eine Schlüsselrolle zu spielen. Dies spricht für eine Potenzierung von Hyperlipoproteinämie und Hypertonie bei der Entstehung von Herz-Kreislauf-Erkrankungen.

Hypertonie ist die häufigste adipositas-assoziierte Erkrankung. Das vermehrt vorhandene Fettgewebe könnte von pathophysiologischer Bedeutung sein, da es eine Reihe von Substanzen sezerniert, die die Blutdruckregulation beeinflussen. Hinweise auf eine Rolle des adipocytären Renin-Angiotensin Systems für die Hypertonie ergeben sich aus der Assoziation von Adipositas und einer gesteigerten systemischen Aktivität des Renin-Angiotensin Systems, sowie aus dem Nachweis im Tiermodell, dass adipocytär gebildetes Angiotensinogen in die systemische Zirkulation gelangt. In der vorliegenden Untersuchung wurden 12 schlanke Normotonikerinnen, 8 adipöse Normotonikerinnen und 10 adipöse Hypertonikerinnen charakterisiert und die adipocytäre Genexpression des Renin-Angiotensin Systems untersucht. Adipocyten wurden mittels Nadelbiopsie und Kollagenaseverdau gewonnen, die Genexpression wurde durch real-time RT-PCR bestimmt. Der Vergleich der drei Gruppen zeigt, dass Adipositas mit einer Reduktion der Angiotensinogen-Expression einhergeht, die adipositas-assoziierte Hypertonie mit einer gesteigerten Expression von Renin, Angiotensin-Converting-Enzyme und Angiotensin II-Typ 1-Rezeptor. Dies führt zu der Hypothese, dass im Fettgewebe adipöser Hypertoniker vermehrt Angiotensin II gebildet wird und könnte den positiven Einfluß von ACE-Hemmern auf die Insulinresistenz und die Verringerung der Neuerkrankungsrate an Diabetes mellitus Typ 2 erklären. / Adipose tissue secretes vasoactive substances which may contribute to the development of obesity-related hypertension. We aimed to study the differential expression of renin-angiotensin system genes in subcutaneous abdominal adipocytes of 12 lean normotensive, 8 obese normotensive, and 10 obese hypertensive women in a cross-sectional study. 24h ambulatory blood pressure measurement, clinical chemistry, and anthropometry were used to characterize the volunteers. Adipocytes were obtained by abdominal subcutaneous needle biopsy and collagenase digestion. Gene expression was studied by quantitative real time RT-PCR. While expression of the angiotensinogen gene was significantly lower in adipocytes from both obese groups, the renin, angiotensin-converting enzyme and angiotensin II-type 1-receptor genes were significantly upregulated in obese hypertensives. In conclusion, renin-angiotensin system genes are differentially regulated in human obesity and hypertension. The data obtained suggest increased formation of angiotensin II in adipose tissue of obese hypertensive subjects. The role of the adipose-tissue renin-angiotensin system in the development of obesity-associated hypertension or metabolic disease clearly warrants further study.

Das Renin-Angiotensin-System ist nachweislich in die Entwicklung der schwangerschaftsspezifischen Erkrankung Präeklampsie involviert. Ziel der Arbeit ist die Charakterisierung der Effekte des zirkulierenden sowie uteroplazentaren Renin-Angiotensin-Systems im Rattenmodell. Wurden weibliche Ratten, transgen für humanes Angiotensinogen, mit männlichen Ratten, transgen für humanes Renin verpaart, so entwickelten sie während der Schwangerschaft Bluthochdruck und Proteinurie, während die umgekehrte Kreuzung diese Hauptsymptome der Präeklampsie nicht zeigte. Weiterhin wurde mit einer Kontrollgruppe sowie einer Angiotensin II behandelten Gruppe gearbeitet. Chronisch, systemische Angiotensin II Infusion (1000 ng/kg/min) erhöhte zirkulierendes Angiotensin II während in der umgekehrten, Präeklampsie-negativen Kreuzung uteroplazentares Angiotensin II erhöht war. In der Präeklampsie-positiven Gruppe war Angiotensin II zirkulär und uteroplazentar erhöht. Bluthochdruck und Albuminurie waren alleinig in den Tiermodellen mit erhöhtem zirkulierendem Angiotensin II nachweisbar. In der Kontrollgruppe kam es während der Schwangerschaft zu einer physiologischen Herzhypertrophie, während in der Präeklampsie-positiven Gruppe Anzeichen einer pathologischen Herzhypertrophie nachweisbar waren. Weiterhin unterstützte uteroplazentares Angiotensin II die tiefe Invasion von Trophoblasten in plazentafernen Spiralarterien, während zirkulierendes Angiotensin II die Trophoblasteninvasion im gesamten mesometrialen Dreieck diffus förderte. In Zellkulturexperimenten konnte gezeigt werden, dass Angiotensin II die Mobilität und die Invasion einer Trophoblastenzelllinie förderte. Ebenso erhöhte Angiotensin II die Migration von Trophoblasten in Plazentakulturen. Diese Ergebnisse verdeutlichen den unterschiedlichen Einfluss des zirkulierenden und uteroplazentaren Renin-Angiotensin-Systems auf die Schwangerschaft und tragen damit zum Verständnis pathologischer Prozesse bei, die zu Präeklampsie führen. / Dysregulation of the renin-angiotensin-system is important in preeclampsia, a pregnancy specific disorder, characterized by high blood pressure and albuminuria. Aim of this study is to characterize the effects of circulation and uteroplacental renin-angiotensin-system during pregnancy in a rat model. Female rats transgenic for the human angiotensinogen gene crossed with males transgenic for the human renin gene develop preeclampsia, whereas those of the opposite cross do not. We used this model to study the role of angiotensin II in trophoblast invasion, which is shallow in human preeclampsia but deeper in this model. We investigated the following groups: preeclampsia rats, opposite-cross rats, angiotensin II–infused rats and control rats. Angiotensin II infusion increased only circulating angiotensin II levels, opposite cross influenced only uteroplacental angiotensin II and preeclampsia rats showed increased circulating and uteroplacental angiotensin II. Blood pressure and albuminuria occurred in the models with high circulating angiotensin II but not in other models. Control rats showed physiological heart hypertrophy during pregnancy whereas pathological heart hypertrophy occurred in preeclampsia rats. High uteroplacental angiotensin II influenced deep trophoblast invasion in distant spiral arteries whilst the effect of circulating angiotensin II was more diffuse. We then studied human trophoblast cell line and villous explants derived from first-trimester pregnancy. Local angiotensin II dose-dependently increased migration, invasion and motility. The data suggest that angiotensin II stimulates trophoblast invasion in vivo in the rat and in vitro in human cells, a hitherto fore unrecognized function.

Jiang, Lili. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 215-235). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Chronic treatment with enalapril and valsartan significantly improved endothelium-dependent relaxations of aortas from ovariectomized rats. The present results clearly point to that chronic treatment with enalapril or valsartan reduced expression and function of RAS and associated oxidative stress, thereby augmented NO bioavailability and improved endothelium-dependent relaxations. These results provided novel evidence supporting a potential application of ACEI and ARB in the treatment of endothelial dysfunction-associated vascular complications in postmenopausal women. / Functional studies showed that acetylcholine-induced relaxations in isolated aortas were impaired in a time-dependent manner, from the 4th-week to the 12th-week after ovariectomy. The impaired relaxations were partially restored by acute treatment with losartan [angiotensin II type 1 receptor (AT1R) blocker] and apocynin [NAD(P)H oxidase inhibitor]. The present results demonstrate that estrogen deficiency blunted endothelium-dependent relaxations due to impaired the NO bioavailability, which is closely associated with the reduced eNOS activity and elevated RAS expression and associated NAD(P)H oxidase-mediated oxidative stress in the vascular wall. / The present study shows that chronic consumption of cranberry juice restored the endothelium-dependent relaxations in aortas from ovariectomized rats. In ovariectomized rats, the phenylephrine-induced a higher active vascular tension; which was prevented by chronic consumption of cranberry juice. The present data also shows that cranberry juice administration significantly reduces the elevated serum levels of total cholesterol, triglyceride, high density lipoprotein (HDL) cholesterol, non-HDL (nHDL) cholesterol, and nHDL/HDL. The active ingredients in the cranberry juice organic extract accounting for the vascular benefit remain to be further examined even though the extract causes endothelial NO-dependent relaxations in normal rat aortas and contains several bioactive compounds, some of which may protect the vascular function. This study provides the first line of evidence concerning a significant vascular benefit of chronic consumption of cranberry juice during estrogen deficiency. (Abstract shortened by UMI.) / The present study used ovariectomized female rats that mimic the "equivalent" state of menopause in human and investigated whether dysregulation of RAS components contribute to endothelial dysfunction and whether chronic treatment with ACEI (enalapril) or ARB (valsartan) could restore endothelial function in ovariectomized rats. / The second objective of the present study was to investigate whether or not consumption of cranberry juice, a popular drink in Western countries, could restore endothelial function during estrogen deficiency and to elucidate the cellular mechanisms underlying the improved endothelial function. / Yung, Lai Ming. / Adviser: Huana Yu. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3252. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 148-168). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

In the first study, I aimed to compare the angiotensin II type 1 receptor (AT1R) expression levels of the isolated pancreatic islets from normal and mouse model of T2DM. In addition, 4-week-old diabetic mice were orally treated with AT1R antagonist losartan for 8 weeks. It is found that AT1R mRNA was upregulated markedly in diabetic islets and double-immunolabeling confirmed that AT1R was localized to beta-cells. Losartan selectively improved glucose-induced insulin release and (pro)insulin biosynthesis in diabetic islets. Oral losartan treatment delayed the onset of diabetes, and reduced hyperglycemia and glucose intolerance in diabetic mice. These data indicate that AT1R antagonism improves beta-cell function and glucose tolerance in young T2DM mice. / In the second study, I aimed to examine how the upregulated RAS could impair beta-cell function, where oxidative stress is the potential mediator. Meanwhile, T2DM results in oxidative stress-mediated activation of uncoupling protein 2 (UCP2), a negative regulator of islet function. Thus, it was postulated that some of the protective effects of AT1R antagonism might be mediated through interference with this pathway and tested this hypothesis in a mouse model of T2DM. In order to achieve this, losartan was given to 4-week-old diabetic mice for 8 weeks. UCP2-driven oxidative damage and apoptosis were analyzed in isolated islets. Results showed that losartan selectively inhibited oxidative stress via NADPH oxidase downregulation; this in turn suppressed UCP2 expression, thus improving beta-cell insulin secretion while decreasing apoptosis-induced beta-cell mass loss in diabetic mice islets. These data indicate that islet AT1R activation in young diabetic mice can lead to progressive islet beta-cell failure through UCP2-driven oxidative damage and apoptosis. / The mechanisms by which chronic hyperglycemia associated with glucotoxicity causes beta-cell dysfunction and apoptosis remain ambiguous. Voltage-gated outward potassium (Kv) current, which mediates beta-cell membrane potential and limits insulin secretion, could play a role in glucotoxicity. Meanwhile the RAS has been shown to be upregulated by prolonged exposure to high glucose. In the third part of my study, I therefore investigated the effects of prolonged exposure to high glucose and angiotensin II (Ang II) on the expression and activity of Kv channels in mouse pancreatic beta-cell. Dissociated mice beta-cells, incubated in 5.6 mM or 28 mM glucose for 3-5 days, were used for electrophysiological study; while isolated islets cultured for 1-7 days were proceeded for gene/protein expression analysis. Both Kv channel expression and current were markedly increased by prolonged glucose incubation. Simultaneously, Ang II reduced Kv current under normal glucose condition, while high glucose incubation abolished the effect of Ang II. Moreover, the ability of Ang II on Kv current reduction was eliminated by inhibiting AT2R but not AT1R. These data indicated that Ang II reduced Kv current via AT2R, which was abolished by prolonged high glucose incubation. On the other hand, high glucose increased Kv channel expression and current, which might alter the ability of insulin secretion in beta-cell. (Abstract shortened by UMI.) / Chu, Kwan Yi. / Adviser: P. S. Leung. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3246. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 163-188). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.