Endothelial Gi protein expression is markedly low in human coronary microvessels

Endothelium-derived hyperpolarizing factor mediated relaxations in pig coronary arteries do not involve Gi/o proteins

AIM

Endothelium-dependent relaxations to certain neurohumoral substances are mediated by pertussis toxin-sensitive Gi/o protein. Our experiments were designed to determine the role, if any, of pertussis toxin-sensitive G-proteins in relaxations attributed to endothelium-derived hyperpolarizing factor (EDHF).

METHODS

Pig coronary arterial rings with endothelia were suspended in organ chambers filled with Krebs-Ringer bicarbonate solution maintained at 37 degrees and continuously aerated with 95%O2 and 5% CO2. Isometric tension was measured during contractions to prostaglandin F2alpha in the presence of indomethacin and N(omega)- nitro-L-arginine methyl ester (L-NAME).

RESULTS

Thrombin, the thrombin receptor- activating peptide SFLLRN, bradykinin, substance P, and calcimycin produced dose-dependent relaxations. These relaxations were not inhibited by prior incubation with pertussis toxin, but were abolished upon the addition of charybdotoxin plus apamin. Relaxations to the alpha2-adrenergic agonist UK14304 and those to serotonin were abolished in the presence of indomethacin and L-NAME.

CONCLUSION

Unlike nitric oxide-mediated relaxations, EDHF-mediated relaxations of pig coronary arteries do not involve pertussis toxin-sensitive pathways and are Gi/o protein independent.

[Development of genetically engineered mice lacking all three nitric oxide synthase isoforms]

The nitric oxide (NO) synthases (NOSs) system consists of three different isoforms, including neuronal (nNOS), inducible (iNOS), and endothelial NOSs (eNOS). The roles of NO in vivo have been extensively investigated in pharmacological studies with NOS inhibitors and in studies with mice lacking each NOS isoform. However, in the pharmacological studies, the specificity of NOS inhibitors continues to be an issue of debate, while in the studies with mice lacking each NOS isoform, compensatory mechanism by other NOSs appears to be involved. Thus, the ultimate roles of endogenous NO in our body still remain to be fully elucidated. To address this important issue, we have successfully developed mice in which all three NOS genes are completely disrupted. NOS expression and activities were totally absent in the triply n/i/eNOS(-/-) mice before and after treatment with lipopolysaccharide. While the triply n/i/eNOS(-/-) mice were viable, their survival and fertility rates were markedly reduced as compared with wild-type mice. The first noticeable phenotypes were polyuria, polydipsia, and renal unresponsiveness to vasopressin, characteristics consistent with nephrogenic diabetes insipidus. We subsequently observed that in those mice, arteriosclerosis is spontaneously developed with a clustering of cardiovascular risk factors. These results provide the first evidence that genetic disruption of all three NOSs causes a variety of cardiovascular diseases in mice in vivo, demonstrating the critical role of the endogenous NOSs system in maintaining cardiovascular homeostasis.

Development of genetically engineered mice lacking all three nitric oxide synthases

Nitric oxide (NO) is produced in almost all tissues and organs, exerting multiple biological actions under both physiological and pathological conditions. NO is synthesized by three different isoforms of NO synthase (NOS): neuronal, inducible, and endothelial NOSs. Due to the substantial compensatory interactions among the NOS isoforms, the ultimate roles of endogenous NO in our body still remain to be fully elucidated. To address this point, we have successfully developed mice in which all three NOS genes are completely disrupted. NOS expression and activities were totally absent in the triply n/i/eNOS(-/-) mice before and after treatment with lipopolysaccharide. While the triply n/i/eNOS(-/-) mice were viable, their survival and fertility rates were markedly reduced as compared with wild-type mice. The phenotypes of those mice that we first noticed were polyuria, polydipsia, and renal unresponsiveness to vasopressin, characteristics consistent with nephrogenic diabetes insipidus. We subsequently observed that in those mice, arteriosclerosis is spontaneously developed with a clustering of cardiovascular risk factors. These results provide the first evidence that the systemic deletion of all three NOSs causes a variety of cardiovascular diseases in mice, demonstrating a critical role of the endogenous NOSs system in maintaining cardiovascular homeostasis.

The −318 C>G Single-Nucleotide Polymorphism in GNAI2 Gene Promoter Region Impairs Transcriptional Activity through Specific Binding of Sp1 Transcription Factor and Is Associated with High Blood Pressure in Caucasians from Italy

Inhibiting Galpha subunit 2 protein, which is encoded by the GNAI2 gene, is suggested to be pathogenic for essential hypertension and/or insulin resistance. The aim of this study was to determine whether GNAI2 variations modulate the risk for these abnormalities. Seven single-nucleotide polymorphisms (SNP) at the GNAI2 locus were identified. Because of either low allelic frequency or unlikely biologic relevance (i.e., synonymous or intronic), six SNP were not studied further. The -318C>G SNP (allelic frequency 6%) in the promoter region was studied for association with adiposity, systolic BP (SBP) and diastolic BP, fasting insulin and glucose, and lipids levels in 655 nondiabetic Caucasians from Italy. As compared with individuals who carry the C/C genotype, G carriers (i.e., individuals who carry either the G/G or the C/G genotype) had higher SBP (117.8 +/- 16 versus 113.6 +/- 12.6 mmHg; P = 0.010) and were at increased risk for hypertension (odds ratio 2.2; 95% confidence interval 1.1 to 4.5). Compared with the C, the G allele had 2.5-fold reduced transcriptional activity in transfected HEK293 cells. As predicted by the TRANSFAC database, competition with YY1 or Sp1 transcription factors specifically reduced the binding of HeLa cell nuclear proteins to -318C or -318G allele, respectively, as indicated by shifted electrophoretic mobility. A "supershift" of the nuclear proteins/-318G allele complex was observed after anti-Sp1 was added but not anti-YY1 antibody. The GNAI2 -318 C>G SNP impairs transcriptional activity through specific binding of Sp1 and is associated with high SBP in Caucasians from Italy.

Coronary artery endothelial dysfunction after ischemia-reperfusion and acute untreated rejection in a canine heterotopic heart transplantation model

BACKGROUND

Acute rejection is a common problem in heart transplantation and may contribute to the development of cardiac allograft vasculopathy. This study was designed to evaluate the mechanisms of coronary endothelial dysfunction associated with ischemia-reperfusion and acute untreated rejection.

METHODS

Two groups of mongrel dogs (n=7 per group) underwent heterotopic cervical heart transplantation without immunosuppression. Allografts were harvested on posttransplant day 1 (group 1) and day 5 (group 2). A third group of unoperated dogs served as control (group 3). After harvesting, epicardial coronary arteries were studied in organ chamber for endothelium-dependent and independent reactivity.

RESULTS

Group 1 displayed multifocal ischemic damage without any rejection while hearts from group 2 reached grade IV rejection. Immunohistochemical studies for von Willebrand factor showed expression on coronary endothelial cells in all animals with scattered areas of denudation in transplanted groups. Endothelium-dependent responses to acetylcholine, calcium ionophore A23147, and bradykinin were unaffected in groups 1 and 2. Endothelial relaxations to sodium fluoride (Gi-protein activator) was significantly reduced in group 1 and significantly increased in group 2 compared with control. Responses to serotonin and UK14304 (receptors linked to Gi-protein) were significantly increased in group 2. Responses to thrombin were decreased in both groups. Endothelium-independent responses were unaffected.

CONCLUSIONS

In the canine model of heterotopic heart transplantation, the early (24 hr) endothelial dysfunction seen after transplantation is specific to the thrombin receptor and the Gi-protein signaling pathway. Acute untreated rejection did not modify the alteration in endothelial reactivity to thrombin but enhanced the sensibility of the Gi-protein signaling pathways.