Molecular Insights into Tachyphylaxis Phenomenon in the Angiotensin II Type 1 Receptor

Abstract

Tachyphylaxis is a phenomenon characterized as a progressive decrease in drug response after prolonged or repetitive administration; however, the precise mechanism behind such phenomenon remains unclear. Here, we assessed the molecular bases of tachyphylaxis using the Angiotensin II (AngII) type 1 receptor (AT1R) and two AngII analogs, named #001 and #002, which function as non‐tachyphylactic agonists. The affinity of both analogs for the AT1R was obtained by radioligand competition binding assays, and they were pharmacologically characterized by prolonged and short stimulation using bioluminescence resonance energy transfer (BRET) assays in Human Embryonic Kidney (HEK) 293T cells expressing the AT1R. Analogs #001 and #002 presented low affinity for the AT1R as compared with AngII, but behaved as full agonists for Gq protein activation, intracellular calcium mobilization, as well as concerning to β‐arrestin recruitment, with potencies similar to those of AngII. We also showed that the activation of Gq protein and the translocation of β‐arrestins to the plasma membrane triggered by the analogs were rapidly reversed either by washout or addition of the antagonist Losartan, whereas AngII induced a sustained response even after washout or addition of Losartan. Furthermore, the internalization of the AT1R induced by analogs #001 or #002 showed a faster recycling and to be more sensitive to washout or addition of Losartan than when induced by AngII. Our results suggest that the molecular bases of AngII tachyphylaxis are linked to distinct kinetics of sustained signaling, which we believe could be due to a higher dissociation rate of the analogs. According to our hypothesis, the non‐tachyphylactic AngII analogs activate the AT1R in a fast but transient manner, consequently leading the AT1R to be quickly recycled to the plasma membrane, becoming available to a new cycle of activation. On the other hand, the sustained activation of AT1R by AngII and the low dissociation rate of AngII seem to lead to a sustained internalization of the AT1R in endosomes, retarding their recycling to the plasma membrane. We believe that understanding the molecular mechanisms involved in tachyphylaxis may ultimately contribute to improve the efficiency of drugs and therapies.Support or Funding InformationFAPESP (process numbers 2014/09893‐0 and 2012/20148‐0)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.