Existence of a mutation of angiotensin AT1 receptor gene promoter region involved in inhibition of AT1 receptor gene transcription in spontaneously hypertensive rats

[Mechanisms of hypertension in the central nervous system]

This article reviews studies by the author on central mechanisms of hypertension. Spontaneously hypertensive rats (SHR) have been developed as a rat model of genetic hypertension, and central acetylcholine has been implicated in hypertension in SHR. The rostral ventrolateral medulla (RVL), a major source of efferent sympathetic activity, has cholinergic pressor systems. The release of acetylcholine is enhanced in the RVL of SHR, leading to hypertension. The alteration of the RVL cholinergic system in SHR results from enhanced angiotensin systems in the anterior hypothalamic area (AHA). Angiotensin II-sensitive neurons are present in the AHA and they are tonically activated by endogenous angiotensins. The basal activity of AHA angiotensin II-sensitive neurons is enhanced in SHR, mainly due to enhanced sensitivity of AHA neurons to angiotensin II. The AHA angiotensin system is also responsible for hypertension induced by emotional stress and central Na(+) increases. These findings suggest that the AHA angiotensin system may play a critical role in the development of hypertension.

Basal transcriptional regulation of rat AT1 angiotensin II receptor gene expression

1. Angiotensin II AT1A receptors are thought to play an important role in the development of hypertension. The transcriptional factor Sp1 is a ubiquitous transcriptional factor associated with GC-rich promoters and involved in basal promoter activity. 2. To examine basal transcriptional levels regulation of the rat AT1A receptor gene, we determined whether two GC-box-related regions within 100 bp of the rat AT1A receptor gene promoter are involved in the basal expression of the gene in A10 cells, a vascular smooth muscle cell line. 3. The electrophoretic mobility shift assay demonstrated that incubation of the -98/-79 region and -58/-34 region sequence oligonucleotides with nuclear extracts of rat hypothalamus, liver and adrenal formed DNA-protein complexes and that the addition of unlabelled oligonucleotides containing the Sp1 consensus sequence blocked the formation of the DNA-protein complex. The addition of antibody against Sp1 also blocked the formation of the DNA-protein complex. 4. The promoter/luciferase reporter assay demonstrated that the reporter activity of AT1A receptor promoters mutated either within the -98/-79 or the -58/-34 region was lower than that of intact AT1A receptor promoters. 5. The promoter activity of AT1A receptor promoters mutated within those two regions was lower than that of promoters mutated within either the -98/-79 or the -58/-34 region. 6. These findings suggest that GC-box-regulated sequences within the -98/-79 region and the -58/-34 region are additively involved in basal expression level of the AT1A receptor gene in A10 cells.

Sp1 decoy oligodeoxynucleotide decreases angiotensin receptor expression and blood pressure in spontaneously hypertensive rats

The transcriptional factor Sp1 is associated with GC-rich promoters and involved in basal promoter activity. A GC-box-related sequence is located within the -58 to -34 base pair region of the angiotensin type 1 receptor gene promoter. We examined whether Sp1 in the hypothalamus was increased in spontaneously hypertensive rats (SHR) and whether inhibition of Sp1 binding sites suppressed angiotensin type 1 receptor expression and thus decreased blood pressure in SHR. Western blot analysis showed that Sp1 protein levels were increased in nuclear extracts of hypothalamus from SHR. Electrophoretic mobility shift assay (EMSA) using oligonucleotides containing Sp1 consensus sequence and -58 to -34 region sequence oligonucleotides showed that DNA-protein complexes were greater in nuclear extracts of hypothalamus from SHR than those of Wistar Kyoto rats (WKY). Sp1 decoy phosphorothioate oligodeoxynucleotides injected into the lateral ventricle produced a decrease in blood pressure in SHR, and decreased angiotensin type 1 receptor mRNA levels and number of angiotensin receptors in the hypothalamus of SHR. Pressor responses to angiotensin II but not to carbachol injected into the lateral ventricle were decreased in the Sp1 decoy-treated SHR. The results of the present study suggest that Sp1 levels in the hypothalamus of SHR are increased, and that inhibition of the binding of Sp1 to its binding sites decreases angiotensin type 1 receptor expression and blood pressure in SHR. The possibility cannot be ruled out that the Sp1 decoy oligodeoxynucleotides (ODN) also suppressed transcriptions of genes other than the angiotensin type 1 receptor gene.