Vasopressin-Mediated Enhancement of Adrenergic Vasoconstriction Involves Both the Tyrosine Kinase and the Protein Kinase C Pathways

Plasticity of seven-transmembrane-helix receptor heteromers in human vascular smooth muscle cells

Recently, we reported that the chemokine (C-X-C motif) receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) heteromerize with α_1A/B/D-adrenoceptors (ARs) and arginine vasopressin receptor 1A (AVPR1A) in recombinant systems and in rodent and human vascular smooth muscle cells (hVSMCs). In these studies, we observed that heteromerization between two receptor partners may depend on the presence and the expression levels of other partnering receptors. To test this hypothesis and to gain initial insight into the formation of these receptor heteromers in native cells, we utilized proximity ligation assays in hVSMCs to visualize receptor-receptor proximity and systematically studied how manipulation of the expression levels of individual protomers affect heteromerization patterns among other interacting receptor partners. We confirmed subtype-specific heteromerization between endogenously expressed α_1A/B/D-ARs and detected that AVPR1A also heteromerizes with α_1A/B/D-ARs. siRNA knockdown of CXCR4 and of ACKR3 resulted in a significant re-arrangement of the heteromerization patterns among α₁-AR subtypes. Similarly, siRNA knockdown of AVPR1A significantly increased heteromerization signals for seven of the ten receptor pairs between CXCR4, ACKR3, and α_1A/B/D-ARs. Our findings suggest plasticity of seven transmembrane helix (7TM) receptor heteromerization in native cells and could be explained by a supramolecular organization of these receptors within dynamic clusters in the plasma membrane. Because we previously observed that recombinant CXCR4, ACKR3, α_1a-AR and AVPR1A form hetero-oligomeric complexes composed of 2–4 different protomers, which show signaling properties distinct from individual protomers, re-arrangements of receptor heteromerization patterns in native cells may contribute to the phenomenon of context-dependent GPCR signaling. Furthermore, these findings advise caution in the interpretation of functional consequences after 7TM receptor knockdown in experimental models. Alterations of the heteromerization patterns among other receptor partners may alter physiological and pathological responses, in particular in more complex systems, such as studies on the function of isolated organs or in in vivo experiments.

Class A G protein-coupled receptors assemble into functional higher-order hetero-oligomers

Although class A seven-transmembrane helix (7TM) receptor hetero-oligomers have been proposed, information on the assembly and function of such higher-order hetero-oligomers is not available. Utilizing bioluminescence resonance energy transfer (BRET), bimolecular luminescence/fluorescence complementation (BiLC/BiFC), and BiLC/BiFC BRET in HEK293T cells, we provide evidence that chemokine (C-X-C motif) receptor 4, atypical chemokine receptor 3, α_1a -adrenoceptor, and arginine vasopressin receptor 1A form hetero-oligomers composed of 2-4 different protomers. We show that hetero-oligomerization per se and ligand binding to individual protomers regulate agonist-induced coupling to the signaling transducers of interacting receptor partners. Our findings support the concept that receptor hetero-oligomers form supramolecular machineries with molecular signaling properties distinct from the individual protomers. These findings provide a mechanism for the phenomenon of context-dependent receptor function.

Identification the main molecular mechanism of AT1R Non-desensitization

Angiotensin II Type 1 Receptor Autoantibodies (AT1-AA) as a functional receptor activator can persistently activate Angiotensin II Type 1 Receptor (AT1R) by causing AT1R non-desensitization which is one of the important pathogenesis of preeclampsia (PE). However, the molecular mechanisms of AT1-AA results AT1R non-desensitization remain unknown. In order to explore the background molecular mechanisms of AT1R non-desensitization induced by AT1-AA, we construct dynamical models which are composed of control model (based on the body of healthy pregnant women) and experimental group models (based on the body of pregnant women with PE) in this paper. We also consider the effect of membrane fluidity on the reaction when building the dynamical models. In the experiment group models, we establish two models that caused AT1R non-desensitization: endocytosis disorder model and conformational change model. We write C++ and MATLAB programs to do the data fitting. By comparing the data fitting results and analyzing the images of models and corresponding Bayesian information criterion (BIC) values, we conclude that conformational changes may be the key molecular mechanism of AT1R non-desensitization.

Vasoconstrictor responses to vasopressor agents in human pulmonary and radial arteries: an in vitro study

BACKGROUND

Vasopressor drugs, commonly used to treat systemic hypotension and maintain organ perfusion, may also induce regional vasoconstriction in specialized vascular beds such as the lung. An increase in pulmonary vascular tone may adversely affect patients with pulmonary hypertension or right heart failure. While sympathomimetics constrict pulmonary vessels, and vasopressin does not, a direct comparison between these drugs has not been made. This study investigated the effects of clinically used vasopressor agents on human isolated pulmonary and radial arteries.

METHODS

Isolated pulmonary and radial artery ring segments, mounted in organ baths, were used to study the contractile responses of each vasopressor agent. Concentration-response curves to norepinephrine, phenylephrine, metaraminol, and vasopressin were constructed.

RESULTS

The sympathomimetics norepinephrine, phenylephrine, and metaraminol caused concentration-dependent vasoconstriction in the radial (pEC50: 6.99 ± 0.06, 6.14 ± 0.09, and 5.56 ± 0.07, respectively, n = 4 to 5) and pulmonary arteries (pEC50: 6.86 ± 0.11, 5.94 ± 0.05 and 5.56 ± 0.09, respectively, n = 3 to 4). Vasopressin was a potent vasoconstrictor of the radial artery (pEC50 9.13 ± 0.20, n = 3), whereas in the pulmonary artery, it had no significant effect.

CONCLUSIONS

Sympathomimetic-based vasopressor agents constrict both human radial and pulmonary arteries with similar potency in each. In contrast, vasopressin, although a potent vasoconstrictor of radial vessels, had no effect on pulmonary vascular tone. These findings provide some support for the use of vasopressin in patients with pulmonary hypertension.