Preeclampsia is a pregnancy related disorder, characterized by proteinuria and hypertension. The pathogenesis of preeclampsia is poorly understood; however, two proteins, called sFlt-1 and sEng, were found to be highly elevated in the maternal plasma weeks prior to the onset of clinical symptoms. sFlt-1 and sEng are thought to inhibit VEGF and TGF-β receptor signalling respectively. In order to elucidate how these proteins may contribute to preeclampsia, we looked at their ability to affect the secretion of endothelin-1 (ET-1), a powerful vasoconstrictor, shown to be dysregulated in preeclampsia. We found that both TGF-β1 and BMP9, a recently described ligand for sEng, induce ET-1 secretion through Smad1/5/8 and p38 pathways. Moreover, we report that sEng and VEGF can efficiently block ET-1 secretion, induced by BMP9. We propose that the balance between VEGF and BMP9 signalling is disturbed during preeclampsia, leading to excessive release of ET-1, which in turn may cause hypertension.

Preeclampsia is a pregnancy related disorder, characterized by proteinuria and hypertension. The pathogenesis of preeclampsia is poorly understood; however, two proteins, called sFlt-1 and sEng, were found to be highly elevated in the maternal plasma weeks prior to the onset of clinical symptoms. sFlt-1 and sEng are thought to inhibit VEGF and TGF-β receptor signalling respectively. In order to elucidate how these proteins may contribute to preeclampsia, we looked at their ability to affect the secretion of endothelin-1 (ET-1), a powerful vasoconstrictor, shown to be dysregulated in preeclampsia. We found that both TGF-β1 and BMP9, a recently described ligand for sEng, induce ET-1 secretion through Smad1/5/8 and p38 pathways. Moreover, we report that sEng and VEGF can efficiently block ET-1 secretion, induced by BMP9. We propose that the balance between VEGF and BMP9 signalling is disturbed during preeclampsia, leading to excessive release of ET-1, which in turn may cause hypertension.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted.

Freiburg, Univ., Diss., 1998.

Tübingen, Univ., Diss., 2005.

University, Diss., 2004--Frankfurt (Main).

Η μελέτη αυτή είναι από τις πρώτες που ασχολήθηκαν με τη διερεύνηση του ρόλου της ενδοθηλίνης στη νεφρική νόσο, καθώς και με την παραγωγή της στο νεφρικό ιστό. Στο πρώτο μέρος της διατριβής επιλέχθηκαν δύο ομάδες ασθενών στις οποίες προσδιορίστηκαν τα επίπεδα ενδοθηλίνης-1 στο πλάσμα και στα ούρα: α) ασθενείς με νεφρωσικό σύνδρομο και β) ασθενείς με ΧΝΑ, χωρίς πρωτεϊνουρία. Στη συνέχεια εξετάστηκε κατά πόσο υπήρχε συσχετισμός των επιπέδων της ΕΤ-1 με διαφορετικές νεφρικές παραμέτρους μεγέθη όπως η κάθαρση της κρεατινίνης, η πρωτεϊνουρία και η ροή των ούρων. Τα πρώτα αποτελέσματα παρείχαν ενδείξεις για αυξημένη νεφρική παραγωγή ενδοθηλίνης-1 σε ασθενείς με σπειραματική βλάβη και η απεκκρινόμενη ΕΤ-1 είχε θετική συσχέτιση με το βαθμό της πρωτεϊνουρίας. Στη συνέχεια μελετήθηκε η έκφραση της στο νεφρικό ιστό και ακόμα ειδικότερα, στο σπείραμα, στα σωληνάρια και στο διάμεσο ιστό, καθώς και η μεταβολή των επιπέδων της απεκκρινόμενης ΕΤ-1 κατά τη θεραπευτική αντιμετώπιση της πρωτεϊνουρίας. Πιο αναλυτικά τα αποτελέσματα της διατριβής ήταν τα παρακάτω: α) Τα επίπεδα ΕΤ-1 στο πλάσμα ασθενών με νεφρική νόσο είναι αυξημένα και περίπου τριπλάσια από τα φυσιολογικά. Η αύξηση αυτή είναι ανεξάρτητη από την κάθαρση της κρεατινίνης και από το βαθμό ή την ύπαρξη της πρωτεϊνουρίας. β) Η απεκκρινόμενη ΕΤ-1 στα ούρα ασθενών με νεφρική νόσο, είναι αυξημένη στο διπλάσιο σε σύγκριση με τα φυσιολογικά επίπεδα και αντικατοπτρίζει τη νεφρική της παραγωγή. γ) Η ΕΤ-1 εντοπίζεται στο κυτταρόπλασμα των ενδοθηλιακών κυττάρων του σπειράματος και στα αγγεία του διάμεσου ιστού στο φυσιολογικό νεφρικό παρέγχυμα. δ) Στο νεφρικό ιστό των νεφρωσικών ασθενών η ΕΤ-1 εκτός από το σπείραμα και τα αγγεία του διάμεσου ιστού, εντοπίζεται και στο κυτταρόπλασμα των επιθηλιακών κυττάρων των σωληναρίων (εγγύς και άπω). ε) Δεν παρατηρείται καμία διαφορά στην κατανομή της ΕΤ-1 στις διάφορες τομές μεταξύ των ασθενών με νεφρωσικό σύνδρομο. Η κατανομή της ΕΤ-1 είναι ίδια και είναι ανεξάρτητη από τις διάφορες σπειραματικές νόσους στις οποίες οφείλεται η πρωτεϊνουρία. στ) Συνοπτικά, η έκφραση της ΕΤ-1 είναι μεγαλύτερη στο νεφρικό ιστό των ασθενών με πρωτεϊνουρία σε σύγκριση με την ομάδα των τομών από φυσιολογικό νεφρικό ιστό. ζ) Η απεκκρινόμενη ΕΤ-1 στα ούρα είναι ανάλογη του βαθμού της πρωτεϊνουρίας σε ασθενείς με νεφρωσικό σύνδρομο και μειώνεται παράλληλα με την πρωτεϊνουρία μετά από θεραπευτική αγωγή. / This study investigates the role of endothelin-1 (ET-1) and its production in the renal tissue. Endothelin-1 was determined in plasma and urine in two groups of renal patients: a) patients with nephrotic syndrome and b) patients with chronic renal failure without proteinuria. Endothelin levels were correlated with several renal function parameters such as creatinin clearance, proteinuria and urinary flow. Results showed an increased endothelin renal production in patients with glomerular injury and a positive correlation between endothelin renal excretion and proteinuria. The endothelin expression in the renal tissue was studied and particularly in the glomerulus, tubules and interstitial tissue. Further more, changes in endothelin renal excretion were investigated during immunosuppressive treatment of proteinuria. The results of this study are as follow: a) Endothelin-1 plasma levels in patients with renal disease are increased compared to controls. This increase was independent compared to creatinine clearance and the severity of proteinuria. b) The endothelin renal excretion in patients with renal disease is increased compared to controls and represents its renal production. c) ΕΤ-1 is localized in the cytoplasm of glomerular endothelial cells and in the vessel walls in the interstitial tissue in normal renal parenchyma. d) In patients with neprotic syndrome, ET-1 is also localized in the cytoplasm of epithelial cells in proximal and distal tubules. e) No differences in the renal distribution of ET-1 were observed among tissue samples of nephrotic patients with different primary causes of proteinuria. f) The ΕΤ-1 expression was increased in the renal tissue of patients with proteinuria compared to controls. g) The ΕΤ-1 excretion in urine was positive correlated to the degree of proteinuria and decreases with the reduction of proteinuria after immunosuppressive treatment.

Abstract Cardiac hypertrophy is an adaptive response of the heart to a variety of mechanical, hemodynamic, neurohumoral, and pathologic stimuli. Prolonged pathophysiological load leads to development of left ventricular hypertrophy and ultimately to heart failure. The natriuretic peptides including the B-type natriuretic peptide (BNP) provide the physiological feedback mechanism to suppress the load signal. The aim of the present study was to evaluate the cis elements within the BNP promoter that mediate the cardiac load responses in vivo, and to study the involvement of paracrine factors, such as endothelin-1 (ET-1) and angiotensin II (Ang II) in activating these transcription factors. In this study, cardiac overload was produced by bilateral nephrectomy, and infusions of arginine8-vasopressin (AVP) or Ang II. In isolated perfused rat heart, the direct wall stretch was achieved by inflating the left ventricular balloon. To identify the cis elements within the BNP promoter that mediate hemodynamic overload response, the approach of DNA injection into the myocardium was used. Mutation or deletion of proximal BNP GATA sites abrogated the response to nephrectomy. AVP-induced acute pressure overload increased left ventricular BNP mRNA and peptide levels. In gel mobility shift assays, pressure overload produced rapid activation of transcription factor GATA4 DNA binding, which was completely inhibited by the ET-1 receptor antagonist bosentan. Both ET-1 and Ang II receptor antagonism inhibited the wall stretch-induced increases in left ventricular GATA4 and AP-1 binding activities in isolated perfused heart preparation. BNP promoter activity and BNP mRNA and peptide levels were regulated distinctly in chronic hemodynamic overload produced by Ang II. In conclusion, GATA4 appears to be necessary and sufficient to confer transcriptional activation of BNP gene during hemodynamic stress in vivo. ET-1 is a signaling molecule mediating the cardiac response to acute pressure overload in vivo. In isolated rat heart, Ang II and ET-1 are required for the stimulation of GATA4 and AP-1 binding activity in response to direct left ventricular wall stretch. Finally, posttranscriptional mechanisms play an important role in the regulation of BNP gene expression in pressure overload produced by Ang II in vivo.

Chronic kidney disease (CKD) is an important independent risk factor in the development of cardiovascular disease (CVD). Indeed, patients with CKD are far more likely to die from CVD than reach end stage renal disease. Conventional cardiovascular risk factors and co-morbidity contribute to this increased risk of CVD. However, emerging evidence suggests other novel factors including inflammation, oxidative stress, and a shift in the balance of the vasodilator nitric oxide and vasoconstrictor endothelin system, are also important contributors. Despite increasing evidence that the endothelin system plays an important role in the development of CKD and CVD, there has been little research examining possible therapeutic benefits of its modification in patients with CKD. The overall aims of the work presented within this thesis were to examine CVD risk in patients with renal impairment and then to see what impact chronic inhibition of the endothelin system would have on risk factors for CVD and CKD progression. In the first two studies I examined markers of arterial stiffness (AS) and endothelial function in a cohort of patients with immune-mediated renal disease. I was able to show in the acute setting that improvement in renal function following treatment for these conditions leads to significant improvements in AS. Interestingly, in patients who were in remission from their renal disease, only classical cardiovascular risk factors appear to be linked to AS. In the next study I was able to prove that sitaxsentan, a selective oral ETA antagonist, did not cause functional blockade of the ETB receptor in man. This was the first study of its kind to confirm that a “selective” endothelin antagonist truly is selective in vivo: a finding that will allow more accurate mechanistic investigation of the ET system. In the final studies, I showed that in subjects with stable non-diabetic proteinuric CKD, chronic selective ETA receptor antagonism reduces blood pressure and AS, and that these systemic benefits are associated with an increase in renal blood flow and reduction in proteinuria. The reduction in proteinuria is most likely haemodynamic and linked to a fall in GFR and filtration fraction, similar to what is seen with ACE inhibitors. Importantly, these benefits were seen in patients already taking maximally tolerated renin-angiotensin aldosterone system blockade, suggesting that chronic endothelin antagonism could be an important future therapy in the management of CKD. In summary, I have shown that renal impairment can directly affect markers of arterial function and by inference increase the risk of CVD. Chronic antagonism of the endothelin system with ETA receptor blockers would appear to improve many of these biomarkers, including reductions in BP, AS and proteinuria. There were no adverse effects reported in these studies, suggesting that selective ETA antagonism may be safe enough for clinical development in CKD patients. Further larger clinical trials are warranted.