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postgraduate thesis: The role of secretin receptor in the angiotensin II-induced aldosterone biosynthesis and salt conservation
Title | The role of secretin receptor in the angiotensin II-induced aldosterone biosynthesis and salt conservation |
---|---|
Authors | |
Issue Date | 2017 |
Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
Citation | Bai, J. [白娟]. (2017). The role of secretin receptor in the angiotensin II-induced aldosterone biosynthesis and salt conservation. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. |
Abstract | Secretin (SCT) and its receptor (SCTR) play an important role in fluid-regulating through
controlling the trafficking and expression of renal aquaporin 2 (AQP2), and mediating the
central actions of angiotensin II (ANGII) in inducing water-drinking behavior and vasopressin
(Vp) release. The indispensable role of this SCT/SCTR axis in the central ANGII-induced
water-drinking behavior is achieved through SCTR/AT1aR heterodimer. However, if this axis
is also involved in regulating periphery functions of ANGII, such as ANGII-induced
aldosterone biosynthesis/release, remains unknown. In addition, whether SCTR/AT1aR
complex is functional in mediating other actions of ANGII has not been explored. The
homeostasis of water and sodium is usually closely associated, and ANGII is a crucial regulator
ii
in maintenance of the both homeostasis. Therefore, in the present study, systemic studies were
carried out to investigate the potential role of SCT/SCTR axis and SCTR/AT1aR heterodimeric
complex in ANGII-conducted regulations on sodium homeostasis. As ANGII-controlled
aldosterone dominates renal epithelial sodium channels (ENaCs), therefore in this study it was
firstly tested if SCT/SCTR can regulate sodium homeostasis via the renin-angiotensinaldosterone system (RAAS). SCTR knockout (SCTR-/-) mice showed impaired aldosterone
synthase (CYP11B2) expression and consequent aldosterone release upon intraperitoneal (IP)
injected ANGII. Endogenous ANGII production induced by dietary sodium restriction was
higher in SCTR-/- than in C57BL/6N (WT), but CYP11B2 and aldosterone synthesis were not
increased accordingly. Cholesteryl ester providing the precursor of aldosterone was not
properly accumulated in the adrenal glands of SCTR-/- fed low Na+ diet. Absence of SCTR
resulted in elevated adrenal basal CYP11B2 and renal basal ENaCs transcripts. Although the
transcript and protein levels of ENaCs were similar in WT/ and SCTR-/-/low Na+, ENaCs in
SCTR-/- were less sensitive to amiloride hydrochloride. Next, the hypothesis that SCTR/AT1R
mediates the ANGII-inducible aldosterone synthesis/release was extensively examined.
Primary zona glomerulosa (ZG) cells were obtained from WT and SCTR-/- mice. Aldosterone
release from primary ZG cells exposed to ANGII (10 nM) was determined by enzyme
immunoassay (EIA). The primary SCTR-/- adrenal cortical cells showed impaired ANGIIinduced aldosterone secretion, compared with WT. The Fluo-4 AM-loaded primary WT
adrenal ZG cells displayed a dose-dependently increased intracellular calcium ([Ca2+]i)
responding to ANGII, but not in SCTR-/-, indicating the absence of SCTR has attenuated the
ANGII-induced Ca2+ which is EGTA-chelated. Using synthetic transmembrane (TM) peptides,
it was found that the SCTR/AT1R heteromers mediated the majority of ANGII-induced Ca2+
influx. Consistently, SCTR TM-II pre-incubated primary ZG cells failed to secrete aldosterone
upon ANGII, while the mutated STM-II peptide (STM-IIm) did not show this inhibitory effects.
In summary, the data from this study have collectively showed that the knockout of SCTR
resulted in defective aldosterone biosynthesis/release and less amiloride-sensitive ENaCs, and
the SCT/SCTR axis is required for aldosterone precursor uptake, expression of CYP11B2.
Besides, the results here clearly provide evidence that the SCTR/AT1R heterodimer is required
for fully functioned ANGII to induce aldosterone biosynthesis/release through mediating the
ANGII-triggered Ca2+ influx in the ZG cells. |
Degree | Doctor of Philosophy |
Subject | Secretin - Receptors Aldosterone |
Dept/Program | Biological Sciences |
Persistent Identifier | http://hdl.handle.net/10722/239929 |
HKU Library Item ID | b5846373 |
DC Field | Value | Language |
---|---|---|
dc.contributor.author | Bai, Juan | - |
dc.contributor.author | 白娟 | - |
dc.date.accessioned | 2017-04-08T23:13:12Z | - |
dc.date.available | 2017-04-08T23:13:12Z | - |
dc.date.issued | 2017 | - |
dc.identifier.citation | Bai, J. [白娟]. (2017). The role of secretin receptor in the angiotensin II-induced aldosterone biosynthesis and salt conservation. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. | - |
dc.identifier.uri | http://hdl.handle.net/10722/239929 | - |
dc.description.abstract | Secretin (SCT) and its receptor (SCTR) play an important role in fluid-regulating through controlling the trafficking and expression of renal aquaporin 2 (AQP2), and mediating the central actions of angiotensin II (ANGII) in inducing water-drinking behavior and vasopressin (Vp) release. The indispensable role of this SCT/SCTR axis in the central ANGII-induced water-drinking behavior is achieved through SCTR/AT1aR heterodimer. However, if this axis is also involved in regulating periphery functions of ANGII, such as ANGII-induced aldosterone biosynthesis/release, remains unknown. In addition, whether SCTR/AT1aR complex is functional in mediating other actions of ANGII has not been explored. The homeostasis of water and sodium is usually closely associated, and ANGII is a crucial regulator ii in maintenance of the both homeostasis. Therefore, in the present study, systemic studies were carried out to investigate the potential role of SCT/SCTR axis and SCTR/AT1aR heterodimeric complex in ANGII-conducted regulations on sodium homeostasis. As ANGII-controlled aldosterone dominates renal epithelial sodium channels (ENaCs), therefore in this study it was firstly tested if SCT/SCTR can regulate sodium homeostasis via the renin-angiotensinaldosterone system (RAAS). SCTR knockout (SCTR-/-) mice showed impaired aldosterone synthase (CYP11B2) expression and consequent aldosterone release upon intraperitoneal (IP) injected ANGII. Endogenous ANGII production induced by dietary sodium restriction was higher in SCTR-/- than in C57BL/6N (WT), but CYP11B2 and aldosterone synthesis were not increased accordingly. Cholesteryl ester providing the precursor of aldosterone was not properly accumulated in the adrenal glands of SCTR-/- fed low Na+ diet. Absence of SCTR resulted in elevated adrenal basal CYP11B2 and renal basal ENaCs transcripts. Although the transcript and protein levels of ENaCs were similar in WT/ and SCTR-/-/low Na+, ENaCs in SCTR-/- were less sensitive to amiloride hydrochloride. Next, the hypothesis that SCTR/AT1R mediates the ANGII-inducible aldosterone synthesis/release was extensively examined. Primary zona glomerulosa (ZG) cells were obtained from WT and SCTR-/- mice. Aldosterone release from primary ZG cells exposed to ANGII (10 nM) was determined by enzyme immunoassay (EIA). The primary SCTR-/- adrenal cortical cells showed impaired ANGIIinduced aldosterone secretion, compared with WT. The Fluo-4 AM-loaded primary WT adrenal ZG cells displayed a dose-dependently increased intracellular calcium ([Ca2+]i) responding to ANGII, but not in SCTR-/-, indicating the absence of SCTR has attenuated the ANGII-induced Ca2+ which is EGTA-chelated. Using synthetic transmembrane (TM) peptides, it was found that the SCTR/AT1R heteromers mediated the majority of ANGII-induced Ca2+ influx. Consistently, SCTR TM-II pre-incubated primary ZG cells failed to secrete aldosterone upon ANGII, while the mutated STM-II peptide (STM-IIm) did not show this inhibitory effects. In summary, the data from this study have collectively showed that the knockout of SCTR resulted in defective aldosterone biosynthesis/release and less amiloride-sensitive ENaCs, and the SCT/SCTR axis is required for aldosterone precursor uptake, expression of CYP11B2. Besides, the results here clearly provide evidence that the SCTR/AT1R heterodimer is required for fully functioned ANGII to induce aldosterone biosynthesis/release through mediating the ANGII-triggered Ca2+ influx in the ZG cells. | - |
dc.language | eng | - |
dc.publisher | The University of Hong Kong (Pokfulam, Hong Kong) | - |
dc.relation.ispartof | HKU Theses Online (HKUTO) | - |
dc.rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works. | - |
dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
dc.subject.lcsh | Secretin - Receptors | - |
dc.subject.lcsh | Aldosterone | - |
dc.title | The role of secretin receptor in the angiotensin II-induced aldosterone biosynthesis and salt conservation | - |
dc.type | PG_Thesis | - |
dc.identifier.hkul | b5846373 | - |
dc.description.thesisname | Doctor of Philosophy | - |
dc.description.thesislevel | Doctoral | - |
dc.description.thesisdiscipline | Biological Sciences | - |
dc.description.nature | published_or_final_version | - |
dc.identifier.mmsid | 991022011759703414 | - |