Angiotensin AT1 and AT2 receptor heteromer expression in the hemilesioned rat model of Parkinson’s disease that increases with levodopa-induced dyskinesia

Abstract

Background/aims: The renin-angiotensin system (RAS) is altered in Parkinson's disease (PD), a disease due to substantia nigra neurodegeneration and whose dopamine-replacement therapy, using the precursor levodopa, leads to dyskinesias as the main side effect. Angiotensin AT 1 and AT 2 receptors, mainly known for their role in regulating water homeostasis and blood pressure and able to form heterodimers (AT 1/2 Hets), are present in the central nervous system. We assessed the functionality and expression of AT 1/2 Hets in Parkinson disease (PD). Methods: Immunocytochemistry was used to analyze the colocalization between angiotensin receptors; bioluminescence resonance energy transfer was used to detect AT 1/2 Hets. Calcium and cAMP determination, MAPK activation, and label-free assays were performed to characterize signaling in homologous and heterologous systems. Proximity ligation assays were used to quantify receptor expression in mouse primary cultures and in rat striatal sections. Results: We confirmed that AT 1 and AT 2 receptors form AT 1/2 Hets that are expressed in cells of the central nervous system. AT 1/2 Hets are novel functional units with particular signaling properties. Importantly, the coactivation of the two receptors in the heteromer reduces the signaling output of angiotensin. Remarkably, AT 1/2 Hets that are expressed in both striatal neurons and microglia make possible that candesartan, the antagonist of AT 1 , increases the effect of AT 2 receptor agonists. In addition, the level of striatal expression increased in the unilateral 6-OHdopamine lesioned rat PD model and was markedly higher in parkinsonian-like animals that did not become dyskinetic upon levodopa chronic administration if compared with expression in those that became dyskinetic. Conclusion: The results indicate that boosting the action of neuroprotective AT 2 receptors using an AT 1 receptor antagonist constitutes a promising therapeutic strategy in PD.

Investigation of Receptor Heteromers Using NanoBRET Ligand Binding

“…AT 1 -β 2 AR heteromers have been described in several studies [ 9 , 24 , 25 ] and are involved in the mediation of cardiomyocyte contractility and heart rate in intact mice [ 24 ]. The pharmacology of the AT 1 -AT 2 heteromer has been extensively studied [ 4 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ], and most recently, has been implicated in Parkinson’s disease [ 27 ].…”

Novel Interactions Involving the Mas Receptor Show Potential of the Renin–Angiotensin system in the Regulation of Microglia Activation: Altered Expression in Parkinsonism and Dyskinesia

“…Heteromers containing adenosine and cannabinoid receptors are among those relevant to striatal function [ 65 – 71 ]. The occurrence of angiotensin receptors in the nigra and the striatum was followed by the identification of complexes formed by AT 1 R and AT 2 R [ 39 , 42 ]. In this paper, we showed that the Mas receptor forms heteroreceptor complexes with AT 1 R and AT 2 R and that such complexes are relevant for better understanding the role of RAS in neuroinflammation.…”

“…In addition, MasR is key for microglia-driven development of the retinal vasculature [ 87 ]. The results presented here and those related to expression of AT 1 R-AT 2 R heteromers in striatal cells [ 42 ] suggest that MasR-related therapies to delay progression of PD should consider RAS components in microglia, with the ultimate goal of attenuating inflammation or skewing microglia toward the M2 neuroprotective phenotype [ 64 ]. RAS is well positioned to be targeted to polarization of microglia activated upon neuroinflammation [ 82 ].…”

“…In microglia, a differential pharmacological trend, when Ang II receptor heteromers are compared with AT 1 -MasHets or AT 2 -MasHets, is cross-antagonism, which is not found in the former but in the latter. This is promising from a therapeutic point of view, because cross-antagonism in AT 1 R-AT 2 R heteromers would lead to a dead end in terms of neuroprotection; instead, the antagonist of one Ang II receptor releases the brake on activation of the partner Ang II receptor within the AT 1 R-AT 2 R heteromer [ 42 ].…”

“…The aim of this study was to demonstrate the presence of Mas and AT 1 /AT 2 receptor heterodimerization in neurons and microglia. The function of the MasR-AT 1 R/AT 2 R complexes in resting and activated microglia was investigated to complement our recent findings on AT 1 R-AT 2 R heteromer function in neural cells [ 42 ]. Importantly, we assessed the expression of heteroreceptor complexes in animal models of parkinsonian and dyskinesia.…”