Biomedical subjects

Ryo Suzuki

Publications and source records attributed to Ryo Suzuki.

At least 37 records · Page 2Linked to original sources

PubMed2004

SH2-containing inositol phosphatase 2 predominantly regulates Akt2, and not Akt1, phosphorylation at the plasma membrane in response to insulin in 3T3-L1 adipocytes.

SH2-containing inositol phosphatase 2 (SHIP2) is a physiologically important negative regulator of insulin signaling by hydrolyzing the phosphatidylinositol (PI) 3-kinase product PI 3,4,5-trisphosphate in the target tissues of insulin. Targeted disruption of the SHIP2 gene in mice resulted in increased insulin sensitivity without affecting biological systems other than insulin signaling. Therefore, we investigated the molecular mechanisms by which SHIP2 specifically regulates insulin-induced metabolic signaling in 3T3-L1 adipocytes. Insulin-induced phosphorylation of Akt, one of the molecules downstream of PI3-kinase, was inhibited by expression of wild-type SHIP2, whereas it was increased by expression of 5'-phosphatase-defective (DeltaIP) SHIP2 in whole cell lysates. The regulatory effect of SHIP2 was mainly seen in the plasma membrane (PM) and low density microsomes but not in the cytosol. In this regard, following insulin stimulation, a proportion of Akt2, and not Akt1, appeared to redistribute from the cytosol to the PM. Thus, insulin-induced phosphorylation of Akt2 at the PM was predominantly regulated by SHIP2, whereas the phosphorylation of Akt1 was only minimally affected. Interestingly, insulin also elicited a subcellular redistribution of both wild-type and DeltaIP-SHIP2 from the cytosol to the PM. The degree of this redistribution was inhibited in part by pretreatment with PI3-kinase inhibitor. Although the expression of a constitutively active form of PI3-kinase myr-p110 also elicited a subcellular redistribution of SHIP2 to the PM, expression of SHIP2 appeared to affect the myr-p110-induced phosphorylation, and not the translocation, of Akt2. Furthermore, insulin-induced phosphorylation of Akt was effectively regulated by SHIP2 in embryonic fibroblasts derived from knockout mice lacking either insulin receptor substrate-1 or insulin receptor substrate-2. These results indicate that insulin specifically stimulates the redistribution of SHIP2 from the cytosol to the PM independent of 5'-phosphatase activity, thereby regulating the insulin-induced translocation and phosphorylation of Akt2 at the PM.

3T3-L1 Cells↗

PubMed2004

Obesity in insulin receptor substrate-2-deficient mice: disrupted control of arcuate nucleus neuropeptides.

OBJECTIVE: Disturbances in insulin signaling have been shown to induce obesity and/or hyperphagia in brain insulin receptor or insulin receptor substrate-2 (IRS-2) knockout (KO) mice. This study aimed to examine the central and peripheral mechanisms underlying the phenotype in IRS-2 KO mice. RESEARCH METHODS AND PROCEDURES: We measured the histological characterization of adipose tissues, mRNA levels of pro-opiomelanocortin, agouti-related protein, and neuropeptide Y in the hypothalamus and uncoupling proteins (UCPs) in peripheral tissues of IRS-2 KO mice. RESULTS: Female IRS-2 KO mice showed increased daily food intake. Body weight and adiposity were increased in both sexes, although these differences were more pronounced in female than in male IRS-2 KO mice. Both male and female IRS-2 KO mice showed decreased UCP1 mRNA expression in brown adipose tissue with defective thermoregulation, and UCP2 mRNA expression was increased in the white adipose tissue of female knockout mice. Furthermore, arcuate nucleus mRNA expression of pro-opiomelanocortin, was decreased in both male and female IRS-2 KO mice, whereas expression of agouti-related protein and neuropeptide Y were increased in female IRS-2 KO mice. DISCUSSION: In IRS-2 KO mice, disrupted control of hypothalamic neuropeptide levels and UCP mRNA expression may contribute to the development of obesity.

Adipose Tissue↗

PubMed2004

Insulin receptor substrate 2 plays a crucial role in beta cells and the hypothalamus.

We previously demonstrated that insulin receptor substrate 2 (Irs2) KO mice develop diabetes associated with hepatic insulin resistance, lack of compensatory beta cell hyperplasia, and leptin resistance. To more precisely determine the roles of Irs2 in beta cells and the hypothalamus, we generated beta cell-specific Irs2 KO and hypothalamus-specific Irs2 knockdown (betaHT-IRS2) mice. Expression of Irs2 mRNA was reduced by approximately 90% in pancreatic islets and was markedly reduced in the arcuate nucleus of the hypothalamus. By contrast, Irs2 expression in liver, muscle, and adipose tissue of betaHT-IRS2 mice was indistinguishable from that of control mice. The betaHT-IRS2 mice displayed obesity and leptin resistance. At 4 weeks of age, the betaHT-IRS2 mice showed normal insulin sensitivity, but at 8 and 12 weeks, they were insulin resistant with progressive obesity. Despite their normal insulin sensitivity at 8 weeks with caloric restriction, the betaHT-IRS2 mice exhibited glucose intolerance and impaired glucose-induced insulin secretion. beta Cell mass and beta cell proliferation in the betaHT-IRS2 mice were reduced significantly at 8 and 12 weeks but not at 10 days. Insulin secretion, normalized by cell number per islet, was significantly increased at high glucose concentrations in the betaHT-IRS2 mice. We conclude that, in beta cells and the hypothalamus, Irs2 is crucially involved in the regulation of beta cell mass and leptin sensitivity.

Animals↗

PubMed2004

N-cadherin plays a role in the synapse-like structures between mast cells and neurites.

Communication between nerves and mast cells is a prototypic demonstration of neuro-immune interaction. Numerous studies have shown that the stimulation of nerves (or addition of neurotransmitters) can evoke activation of mast cells, and that mast cell-derived mediators can influence neuronal activity. However, the molecules involved in the membrane-membrane contacts between nerves and mast cells are still unknown. Here, we used an in vitro co-culture approach comprising interaction between immune (bone marrow-derived mast cell, BMMC) and nerve cells (superior cervical ganglia, SCG). The experiments showed clearly that the nerve-mast cell communication was supported by synapse-like structure and that N-cadherin, not E-cadherin, played an essential role in the synapse-like structure. In addition, we found that the synapse-like structure was assisted by clustering of beta-catenin to N-cadherin.

Animals↗

PubMed2004

Resection of giant right atrial lymphoma using vacuum-assisted cardiopulmonary bypass without snaring the inferior vena cava.

A 53-year-old man sustained hemodynamic collapse due to a huge right atrial tumor and was transferred to our hospital and underwent a life-saving emergency operation. The tumor arose from the inferolateral wall of the right atrium, occupying almost the whole right atrial cavity and obstructing not only the inflow of the right ventricle but also the orifice of the inferior vena cava. Venous cannulation via the right atrial wall and placing a snare around the inferior vena cava were impossible. With a cardiopulmonary bypass using vacuum-assisted venous drainage, the tumor was successfully resected and the tricuspid valve was replaced with a bioprosthetic valve without snaring the inferior vena cava. Postoperative histological examination demonstrated the tumor to be a large B-cell non-Hodgkin type malignant lymphoma. When the tumor is large and it is difficult to establish total cardiopulmonary bypass, the vacuum-assisted cardiopulmonary bypass is a useful option. This can achieve a bloodless operative field and is not blocked by the incoming air, due to the venous drainage being continually pressure-regulated.

Cardiopulmonary Bypass↗

PubMed2003

Combination effects of complement regulatory proteins and anti-complement polymer.

We previously reported the development of a "cytomedicine" that consists of cells trapped in alginate-poly-L-lysine-alginate (APA) microcapsules and agarose microbeads. The functional cells that are entrapped in semipermeable polymer are completely isolated from cellular immune system. However, the ability of cytomedicine to isolate cells from the humoral immune system, which plays an essential role in xenograft rejection, is low. Therefore, the goal of the present study was to develop a novel cytomedicine that could protect the entrapped cells from injury of the complement system. We investigated the applicability of the complement regulatory protein (CRP), Crry, to cytomedicine. Crry-transfected cells entrapped within agarose microbeads resisted injury by complement to a degree, while entrapment of Crry transfected cells within agarose microbeads containing polyvinyl sulfate (PVS), a novel cytomedical device with anti-complement activity, clearly protected against complement attack. These data indicate that the combination of a CRP and a cytomedical device with anti-complement activity is a superior device for cytomedical therapy.

Animals↗

PubMed2003

Pdx1 expression in Irs2-deficient mouse beta-cells is regulated in a strain-dependent manner.

We previously demonstrated that Irs2-/- mice develop diabetes due to beta-cell growth failure and insulin resistance; however, glucose-induced insulin secretion was increased in islets isolated from Irs2-/- mice. Pdx-1, a transcription factor important for maintenance of the beta-cell function, was recently reported to be severely reduced in Irs2-/- murine beta-cells. We report herein that Pdx-1 expression, including the amount of Pdx-1 localized in the nucleus, is not down-regulated in our Irs2-/- murine beta-cells with a C57BL/6 background. We have also demonstrated the expression of upstream genes of Pdx-1, such as HNF3beta and HNF1alpha, as well as its downstream genes, including insulin, Glut2, and Nkx6.1, to be well preserved. We have further demonstrated Pdx-1 expression to also be preserved in beta-cells of 30-week-old diabetic Irs2-/- mice. In addition, surprisingly, even in Irs2-/- mice on a high fat diet with markedly elevated blood glucose, exceeding 400 mg/dl, Pdx-1 expression was not reduced. Furthermore, we found Pdx-1 to be markedly decreased in certain severely diabetic Irs2-/- mice with a mixed C57BL/6J x 129Sv background. We conclude that 1) Pdx-1 expression in Irs2-/- mice is regulated in a strain-dependent manner, 2) Irs2-/- mice develop diabetes associated with beta-cell growth failure even when Pdx1 expression is preserved, and 3) Pdx-1 expression is preserved in severely hyperglycemic Irs2-/- mice with a C57BL/6 background on a high fat diet.

Animal Feed↗

PubMed2003

Lack of insulin receptor substrate-2 causes progressive neointima formation in response to vessel injury.

BACKGROUND: Insulin resistance is associated with atherosclerosis, but its mechanism is unknown. It has been reported that insulin receptor substrate (IRS)-1 deficient (IRS-1-/-) mice showed insulin resistance without type 2 diabetes, whereas the IRS-2 deficient (IRS-2-/-) mice showed insulin resistance with type 2 diabetes. METHODS AND RESULTS: We investigated neointima formation in the IRS-1-/- and IRS-2-/- mice at 8 and 20 weeks. The IRS-2-/- mice showed much greater neointima formation than the IRS-1-/- and wild-type mice at 8 weeks. At 20 weeks, the IRS-2-/- mice had greater neointima formation than the IRS-1-/- mice, which showed more enhanced neointima formation than the wild-type mice. The IRS-1-/- and IRS-2-/- mice had dyslipidemia, hypertension, and insulin resistance. The IRS-2-/- mice had more metabolic abnormalities than the IRS-1-/- mice at 8 and 20 weeks. IRS-2 expression was detected, but IRS-1 expression was not detected in the vessels. CONCLUSIONS: The neointima formation in the IRS-1-/- and IRS-2-/- mice appears to be related to abnormalities induced by the altered metabolic milieu in insulin-resistant states. Moreover, because neointima formation was much greater in the IRS-2-/- mice than in the IRS-1-/- mice at 8 and 20 weeks, it is suggested that a lack of IRS-2 renders the vasculature more susceptible to injury in the abnormal metabolic milieu, and IRS-2 may have a protective effect on neointima formation. We conclude that IRS-2 is protective and retards the development of neointima formation in insulin-resistant states.

Animals↗

PubMed2003

A novel cytomedical vehicle capable of protecting cells against complement.

We have developed "Cytomedicine," which consists of functional cells entrapped in semipermeable polymer, and previously reported that APA microcapsules could protect the entrapped cells from injury by cellular immune system. However, microencapsulated cells were not protected from humoral immune system. Here, we developed a novel APA microcapsule, in which APA microbeads (APA(Ba) microbeads) were modified to contain a barium alginate hydrogel within their centers in an attempt to make it more difficult for antibody and complement to permeate the microcapsules. The permeability of APA(Ba) microbeads was clearly less than that of APA microcapsules, presumably due to the presence of barium alginate hydrogel. Cells encapsulated within APA(Ba) microbeads were protected against treatment with xenogeneic anti-serum. Furthermore, murine pancreatic beta-cells encapsulated in APA(Ba) microbeads remained viable and continued to secrete insulin in response to glucose. Therefore, APA(Ba) microbeads may be a useful carrier for developing anti-complement device for cytomedical therapy.

Alginates↗

PubMed2003

Natural denitrification in the Kakamigahara groundwater basin, Gifu prefecture, central Japan.

Although nitrate is recognized as the most common groundwater contaminant due to growing anthropogenic sources, such as agriculture in particular, its adverse effects on human and animal health are debatable. The current issue, however, is to control and reduce nitrate contamination with regards to the long residence time of groundwater within aquifers. Denitrification has recently been recognized for its ability to reduce high nitrate concentrations in groundwater. The Kakamigahara groundwater basin, Gifu prefecture, Japan, witnessed rising levels of nitrate (>12 mg/l NO(3)-N) originating from agricultural sources. Chemical analyses for the determination of major constituents of groundwater and delta(15)N of residual nitrate were performed on representative groundwater samples in order to fulfill two main objectives. One is to investigate the current situation of nitrate groundwater pollution. The second objective is to determine whether the denitrification is a potential natural mechanism, which eliminates nitrate pollution in the Kakamigahara aquifer. Agricultural nitrate contamination of groundwater was obvious from characteristically high concentrations of Ca(2+), Mg(2+), NO(3)(-) and SO(4)(2-). High nitrate concentrations were found on the eastern side of the basin in association with vegetable cultivation fields, and decreased gradually towards the west of the basin along the direction of groundwater flow. The decrease of nitrate concentration was conveniently coupled with increase of HCO(3)(-) (the heterotrophic denitrification product), pH and delta(15)N of residual nitrate (due to isotopic fractionation) from east to west. Therefore, denitrification in situ is continuously removing nitrate from the Kakamigahara groundwater system.

Agriculture↗

PubMed2003

Human-derived vascular smooth muscle cells produce angiotensin II by changing to the synthetic phenotype.

We investigated whether vascular smooth muscle cells (VSMC)-derived from human produce angiotensin (Ang) II upon change from the contractile phenotype to the synthetic phenotype by incubation with fibronectin (FN). Expression of alpha-smooth muscle (SM) actin, apparent in the contractile phenotype, was decreased by FN. Expressions of matrix Gla and osteopontin, apparent in the synthetic phenotype, were increased by FN. Ang II measured by radioimmunoassay (RIA) was significantly increased in human VSMC by FN. Expression of mRNAs for Ang II-generating proteases cathepsin D, cathepsin G, ACE, and chymase was increased by FN. Expressions of cathepsin D and cathepsin G proteins were also increased by FN. Ang I-generating activity, which was inhibited by an aspartyl protease inhibitor pepstatin A, was readily detected in the conditioned medium from human VSMC. Antisense oligodeoxynucleotides (ODNs) that hybridize with cathepsin D and cathepsin G significantly inhibited FN-increased Ang II in conditioned medium and cell extracts. In VSMC conditioned medium, FN-induced elevation of Ang II was significantly inhibited by temocapril but not by chymostatin. Ang II type 1 receptor antagonist CV11974 completely, and antisense cathepsin D and cathepsin G ODNs partially inhibited the FN-stimulated growth of human VSMC. These results indicate that the change of homogeneous cultures of human VSMC from the contractile to the synthetic phenotype sequentially increases expression of proteases cathepsin D, cathepsin G, and ACE, production of Ang II and productions of growth factors, culminating in VSMC proliferation. These findings implicate a new mechanism for the pathogenesis of human vascular proliferative diseases.

Angiotensin I↗

PubMed2003

Effects of antisense peptide nucleic acid to platelet-derived growth factor A-chain on growth of vascular smooth muscle cells.

To investigate antisense peptide nucleic acid (PNA) as a gene therapy for the arterial proliferative diseases, the authors designed and examined the effects of an antisense PNA targeting platelet-derived growth factor (PDGF) A-chain on expression of PDGF A-chain and growth of vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats. A 15-mer antisense PNA complementary to the initiation codon of rat and human PDGF A-chain mRNA was synthesized and purified by high-performance liquid chromatography. Gel-shift assay and biomolecular interaction analysis (BIAcore) revealed that the antisense PNA bound weakly to the target RNA, whereas it bound strongly to the target DNA. Fluorescein-isothiocyanate-labeled antisense PNA to PDGF A-chain was taken up slowly and maintained in VSMCs for a prolonged period of time. Antisense PNA inhibited expression of PDGF A-chain mRNA and protein as well as DNA synthesis in VSMCs in a dose-independent manner. Inhibition of DNA synthesis by the antisense PNA was greater than that by the antisense DNA at a low concentration (0.5 micromol/L). These results suggest that antisense PNA to PDGF A-chain will be used as a gene therapy for vascular proliferative diseases such as hypertensive vascular diseases, restenosis of coronary arteries after angioplasty, and atherosclerosis.

Animals↗

PubMed2002

Impact of genetic background and ablation of insulin receptor substrate (IRS)-3 on IRS-2 knock-out mice.

Although we and others have generated IRS-2 knock-out (IRS-2(-/-)) mice, significant differences were seen between the two lines of IRS-2(-/-) mice in the severity of diabetes and alterations of beta-cell mass. It has been reported that although IRS-1 and IRS-3 knock-out mice showed normal blood glucose levels, IRS-1/IRS-3 double knock-out mice exhibited marked hyperglycemia. Thus, IRS-1 and IRS-3 compensate each other's functions in maintaining glucose homeostasis. To assess the effect of genetic background and also ablation of IRS-3 on IRS-2(-/-), we generated IRS-2/IRS-3 double knock-out (IRS-2(-/-)IRS-3(-/-)) mice by crossing IRS-3(-/-) mice (129/Sv and C57Bl/6 background) with our IRS-2(-/-) mice (CBA and C57Bl/6 background). Intercrosses of IRS-2(+/-)IRS-3(+/-) mice yielded nine genotypes, and all of them including IRS-2(-/-)IRS-3(-/-) mice were apparently healthy and showed normal growth. However, at 10-20 weeks of age, 20-30% mice carrying a null mutation for the IRS-2 gene, irrespective of the IRS-3 genotype, developed diabetes. When mice with diabetes were excluded from the analysis of glucose and insulin tolerance test, IRS-2(-/-)IRS-3(-/-) showed a degree of glucose intolerance and insulin resistance similar to those of IRS-2(-/-) mice. Both IRS-2(-/-) and IRS-2(-/-)IRS-3(-/-) mice had moderately reduced beta-cell mass despite having insulin resistance. Insulin-positive beta-cells were decreased to nearly zero in IRS-2(-/-) mice with diabetes. Although Pdx1 and glucose transporter 2 expressions were essentially unaltered in islets from IRS-2(-/-) mice without diabetes, they were dramatically decreased in IRS-2(-/-) mice with diabetes. Taken together, these observations indicate that IRS-3 does not play a role compensating for the loss of IRS-2 in maintaining glucose homeostasis and that the severity of diabetes in IRS-2(-/-) mice depends upon genetic background, suggesting the existence of modifier gene(s) for diabetes in mice of the 129/Sv genetic strain.

Animals↗

PubMed2002

Cyotomedical therapy for insulinopenic diabetes using microencapsulated pancreatic beta cell lines.

Current therapy for type 1 diabetes mellitus involves a daily regimen of multiple subcutaneous or intramuscular injections of recombinant human insulin. To achieve long-term insulin delivery in vivo, we investigated the applicability of cytomedical therapy using beta TC6 cells or MIN6 cells, both of which are murine pancreatic beta cell lines that secrete insulin in a subphysiologically or physiologically regulated manner, respectively. We examined this therapy in the insulinopenic diabetic mice intraperitoneally injected with beta TC6 cells or MIN6 cells microencapsulated within alginate-poly(L)lysine-alginate membranes (APA-beta TC6 cells or APA-MIN6 cells). The diabetic mice treated with APA-beta TC6 cells fell into hypoglycemia, whereas those injected with APA-MIN6 cells maintained normal blood glucose concentrations for over 2 months without developing hypoglycemia. In addition, we also conducted an oral glucose tolerance test using these mice. The blood glucose concentrations of normal and of diabetic mice injected with APA-MIN6 cells similarly changed over time, although the blood insulin concentration increased later in the injected diabetic mice than in the former. These results suggest that cytomedicine utilizing microencapsulated pancreatic beta cell lines with a physiological glucose sensor may be a beneficial and safe therapy with which to treat diabetes mellitus.

Alginates↗

PubMed2002

A new functional screening system for identification of regulators for the generation of amyloid beta-protein.

Presenilin (PS) is essential for gamma-cleavage, which is required for the generation of amyloid beta-protein (Abeta) from the beta-amyloid precursor protein. However, it remains to be clarified how gamma-cleavage is regulated. To elucidate the regulation of PS-mediated gamma-cleavage, we developed a new functional screening method for identifying cDNA that enhances gamma-cleavage. This screening system utilizes our own developed cell line, where the expression of cDNA that enhances gamma-cleavage confers puromycin resistance. The cDNA library is retrovirally delivered to the above-mentioned cell line, allowing the identification of our target cDNAs by a combination of puromycin resistance selection and Abeta assay screening. With this screening method, we isolated several cDNAs enhancing gamma-cleavage, including the previously reported Herp. Here we also demonstrate that Rab1A, identified with this screening, can be a regulator of Abeta generation. Thus, our established screening method is a powerful tool for identifying multiple regulators involved in gamma-cleavage in the Abeta generation pathway, including modulators of gamma-secretase activity or the intracellular trafficking of factors necessary for gamma-cleavage.

Amyloid Precursor Protein Secretases↗

PubMed2002

Endoplasmic reticulum stress-inducible protein, Herp, enhances presenilin-mediated generation of amyloid beta-protein.

Presenilin (PS) is essential for the gamma-cleavage required for the generation of the C terminus of amyloid beta-protein (Abeta). However, the mechanism underlying PS-mediated gamma-cleavage remains unclear. We have identified Herp cDNA by our newly developed screening method for the isolation of cDNAs that increase the degree of gamma-cleavage. Herp was originally identified as a homocysteine-responsive protein, and its expression is up-regulated by endoplasmic reticulum stress. Herp is an endoplasmic reticulum-localized membrane protein that has a ubiquitin-like domain. Here, we report that a high expression of Herp in cells increases the level of Abeta generation, although not in PS-deficient cells. We found that Herp interacts with both PS1 and PS2. Thus, Herp regulates PS-mediated Abeta generation, possibly through its binding to PS. Immunohistochemical analysis of a normal human brain section with an anti-Herp antibody revealed the exclusive staining of neurons and vascular smooth muscle cells. Moreover, the antibody strongly stained activated microglia in senile plaques in the brain of patients with Alzheimer disease. Taken together, Herp could be involved in Abeta accumulation, including the formation of senile plaques and vascular Abeta deposits.

Amyloid beta-Peptides↗

PubMed2002

Inhibitory effect of a novel angiotensin II type 1 receptor antagonist RNH-6270 on growth of vascular smooth muscle cells from spontaneously hypertensive rats: different anti-proliferative effect to angiotensin-converting enzyme inhibitor.

The current study was undertaken to evaluate the anti-proliferative effect of a novel angiotensin II type 1 (AT1) receptor antagonist, RNH-6270, on exaggerated growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR), in comparison with the effects of an angiotensin-converting enzyme (ACE) inhibitor. RNH-6270 and temocapril significantly inhibited basal DNA synthesis in VSMCs from SHRs in a dose-dependent manner, but not in cells from Wistar-Kyoto (WKY) rats. SHR-derived VSMC showed a hyperresponse of DNA synthesis to serum and angiotensin II compared with that of WKY rats-derived VSMC. RNH-6270 did not affect serum-stimulated DNA synthesis in VSMCs from both rat strains. RNH-6270 abolished angiotensin II-stimulated DNA synthesis in VSMC from both rat strains. RNH-6270 significantly inhibited proliferation of VSMC from both rat strains, but the ACE inhibitor temocapril did not exert such an effect. RNH-6270 decreased the specific binding of angiotensin II to VSMC in a competitive manner for angiotensin II receptors in both rat strains. RNH-6270 and temocapril significantly decreased the expression of growth factor mRNAs and proteins in VSMC from SHR, but not in cells from WKY rats. These results suggest that RNH-6270 is a potent AT1 receptor antagonist and has anti-proliferative effects on VSMCs from SHR, which was not seen with an ACE inhibitor. The growth inhibitory effect of RNH-6270 may be associated with the inhibition of growth factors via antagonism to AT1 receptors.

Angiotensin II↗

PubMed2002

Angiotensin II type 2 receptor gene transfer downregulates angiotensin II type 1a receptor in vascular smooth muscle cells.

Two distinct subtypes of angiotensin (Ang) II receptors, type 1 (AT(1)) and type 2 (AT(2)), have been identified. Vascular smooth muscle cells (VSMCs) usually express AT(1) receptor. To elucidate the direct effects of the AT(2) receptor on the AT(1) receptor in VSMCs, we transfected AT(2) receptor gene into cultured rat VSMCs. Overexpression of AT(2) receptor significantly decreased expression of AT(1a) receptor at both the mRNA and protein levels in the presence and absence of Ang II in VSMCs. Overexpression of AT(2) receptor increased expression of bradykinin and inducible NO in the presence and absence of Ang II in VSMCs. Bradykinin B(2) receptor antagonist HOE-140 and NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) inhibited the decreases in AT(1a) receptor expression by the overexpression of AT(2) receptor in VSMCs. L-Arginine augmented the decrease in AT(1a) receptor expression. Overexpression of AT(2) receptor suppressed basal DNA synthesis and proliferation of VSMCs and abolished response of DNA synthesis to Ang II in VSMCs. Our results demonstrate that overexpression of the AT(2) receptor downregulates AT(1a) receptor expression in rat VSMCs in a ligand-independent manner that is mediated by the bradykinin/NO pathway. Downregulation of AT(1a) receptor is a novel mechanism by which the AT(2) receptor regulates growth and metabolism of VSMCs.

Angiotensin II↗