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Effect of Angiotensin II on gene expression in SHRSP cerebral microcapillaries

ABSTRACT: Renin-angiotensin system (RAS) inhibition reduces stroke and improves brain capillary integrity in stroke prone spontaneously hypertensive rats (SHRSP). We tested the hypothesis that treatment with an angiotensin II receptor subtype 1 (AT1R) antagonist has different effects, compared to an angiotensin converting enzyme (ACE) inhibitor, on gene expression in blood-brain barrier (BBB) capillaries. Six weeks old SHRSP were treated with either olmesartan (4 mg/kg, n=20), lisinopril (6 mg/kg , n=20) or remained untreated (n=20). Blood pressure was controlled by tail-cuff measurement. After 5 weeks the animals were sacrificed and cerebral capillaries were isolated. mRNA was extracted and analyzed with rat GeneChip DNA arrays. Additionally, brain histology and monocyte/macrophage infiltrates were determined. Both treatments similarly reduced neurological signs of stroke, stroke mortality, and monocyte/macrophage infiltration, compared to controls. Blood pressure was not influenced significantly by both drugs. We found 42 transcripts that were regulated by both treatments in the same manner. These genes were mostly related to inflammation. We also observed 39 differentially expressed genes between the two treatment groups that typically contribute to cell growth and differentiation. This study demonstrates that, despite similar effects on cerebral pathology and outcome, ACE inhibition and AT1R blockade have distinct molecular effects on gene expression in BBB capillaries. Keywords = angiotensin II Keywords = gene expression Keywords = microarrays Keywords = brain capillaries Keywords = SHRSP Keywords = olmesartan Keywords = lisinopril Keywords: other

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE1548 | GEO | 2004/08/31

SECONDARY ACCESSION(S): PRJNA89945

REPOSITORIES: GEO

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Project description:Angiotensin converting enzyme (ACE) is known for converting inactive angiotensin I into the potent vasoconstrictor angiotensin II, playing a critical role in blood pressure regulation. However, there is evidence that the dicarboxypeptidase activity of ACE is also essential for other physiological processes likely through processing of various peptide substrates. This study used mass spectrometry for the comprehensive detection and identification of natural substrates and products of ACE within the mouse plasma peptidome. The plasma peptidome of ACE KO mice was obtained through a multi-step purification process which included organic TCA precipitation as well as size exclusion and reversed phase chromatography. The obtained complex mixture of endogenous peptides was then subjected to in vitro cleavage by ACE. ACE-treated and untreated samples were then analyzed by LC/MS on an Orbitrap mass spectrometer, followed by alignment of MS1 data by Progenesis QI software. The MS1 signals that gained or lost intensity after treatment with ACE, were considered as possible products and substrates of ACE, respectively, and were selected for a targeted MS/MS analysis, and subsequently identified with PEAKS 8.5 and Proteome Discoverer software. Results. Close to 250 natural peptides were identified as possible substrates and products of ACE, demonstrating the high promiscuity of the enzyme. The use of internal standards as well as detection of some expected endogenous peptides, such as angiotensin II and bradykinin, supported the validity of the approach. Some of the newly identified substrates of ACE are known for their biological activities. For example, a fragment of complement C3, the 17-amino acid peptide C3f, exhibits spasminogenic activity and was processed by ACE. ACE cleavage of select peptides was further confirmed in vitro. Also, concentrations of ACE substrates in plasma from mice with variant genetic ACE domain backgrounds were determined by LC/MS using multiple reaction monitoring on a triple quadrupole mass spectrometer. The in vivo results were consistent with the in vitro results, in the sense that higher levels of the ACE substrates were observed when the respective processing domain was knocked out. The use of transgenic mice as well as ACE with single active domain allowed clarifying the ACE domain selectivity towards individual peptide substrates. This study resulted in creation of a library of substrates and products of ACE that can be further tested for their biological function and can help to elucidate the link between ACE and the numerous physiological effects attributed to its activity.

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Effect of Angiotensin II on gene expression in SHRSP cerebral microcapillaries

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