Molecular weight of different angiotensin II polymers directly determines: density of endothelial membrane AT1 receptors and coronary vasoconstriction

Limited AT1 Receptor Internalization Is a Novel Mechanism Underlying Sustained Vasoconstriction Induced by AT1 Receptor Autoantibody From Preeclampsia

Background

Angiotensin II type 1 receptor (AT₁R) autoantibody (AT1‐AA) was first identified as a causative factor in preeclampsia. Unlike physiological ligand angiotensin II (Ang II), AT1‐AA can induce vasoconstriction in a sustained manner, causing a series of adverse effects, such as vascular injury and poor placental perfusion. However, its underlying mechanisms remain unclear. Here, from the perspective of AT₁R internalization, the present study investigated the molecular mechanism of sustained vasoconstriction induced by AT₁R autoantibody.

Methods and Results

In the current study, we used the vascular‐ring technique to determine that AT1‐AA‐positive IgG, which was obtained from the sera of preeclamptic patients, induced long‐term vasoconstriction in endothelium‐intact or endothelium‐denuded rat thoracic arteries. The effect was caused by prolonged activation of AT₁R downstream signals in vascular smooth muscle cells, including Ca²⁺, protein kinase C, and extracellular signal‐regulated kinase 1 and 2. Then, using subcellular protein fractionation, cell surface protein biotinylation, and total internal reflection fluorescence, we found that AT1‐AA‐positive IgG resulted in significantly less AT₁R internalization than in the Ang II treatment group. Moreover, through use of fluorescent tracing and bioluminescence resonance energy transfer, we found that AT1‐AA‐positive IgG cannot induce the recruitment of β‐arrestin1/2, which mediated receptor internalization. Then, the effect of sustained AT₁R activation induced by AT1‐AA‐positive IgG was rescued by overexpression of β‐arrestin2.

Conclusions

These data suggested that limited AT₁R internalization resulting from the inhibition of β‐arrestin1/2 recruitment played an important role in sustained vasoconstriction induced by AT1‐AA‐positive IgG, which may set the stage for avoiding AT₁R overactivation in the management of preeclampsia.

Novel high molecular weight albumin-conjugated angiotensin II activates β-arrestin and G-protein pathways

PURPOSE

To study the ability of a novel bovine serum albumin-angiotensin II (BSA-Ang II) conjugate to effect responses of the AT₁ angiotensin II receptor subtype mediated by the G-protein-coupled and the beta-arrestin pathways.

METHODS

Angiotensin II (Ang II) was conjugated with bovine serum albumin and compared with Ang II for competition binding to AT₁ receptors, to stimulate aldosterone release from adrenocortical cells, to promote beta-arrestin binding to AT₁ receptors, to promote calcium mobilization, and stimulate drinking of water and saline by rats.

RESULTS

The BSA-Ang II conjugate was less potent competing for AT₁R binding, but was equally efficacious at stimulating aldosterone release from H295R adrenocortical cells. Both BSA-Ang II and Ang II stimulated calcium mobilization and beta-arrestin binding to AT₁ receptors. BSA-Ang II and Ang II stimulated water appetite equivalently but BSA-Ang II stimulated saline appetite more than Ang II. Both BSA-Ang II and Ang II were considerably more potent at causing calcium mobilization than β-arrestin binding.

CONCLUSIONS

Addition of a high molecular weight molecule to Ang II reduced its AT₁ receptor binding affinity, but did not significantly alter stimulation of aldosterone release or water consumption. The BSA-Ang II conjugate caused a greater saline appetite than Ang II suggesting that it may be a more efficacious agonist of this beta-arrestin-mediated response than Ang II. The higher potency calcium signaling response suggests that the G-protein-coupled responses predominate at physiological concentrations of Ang II, while the beta-arrestin response requires pathophysiological or pharmacological concentrations of Ang II to occur.