Functional complexes of Angiotensin-converting enzyme 2 and renin-angiotensin system receptors: expression in adult but not fetal lung tissue

Angiotensin-converting enzyme 2 (ACE2) is a membrane peptidase and a componentof the renin-angiotensin system (RAS) that has been found in cells of all organs, including thelungs. While ACE2 has been identified as the receptor for severe acute respiratory syndrome (SARS)coronaviruses, the mechanism underlying cell entry remains unknown. Human immunodeficiencyvirus infects target cells via CXC chemokine receptor 4 (CXCR4)-mediated endocytosis. Furthermore,CXCR4 interacts with dipeptidyl peptidase-4 (CD26/DPPIV), an enzyme that cleaves CXCL12/SDF-1,which is the chemokine that activates this receptor. By analogy, we hypothesized that ACE2 mightalso be capable of interactions with RAS-associated G-protein coupled receptors. Using resonanceenergy transfer and cAMP and mitogen-activated protein kinase signaling assays, we found thathuman ACE2 interacts with RAS-related receptors, namely the angiotensin II type 1 receptor (AT1R),the angiotensin II type 2 receptor (AT2R), and the MAS1 oncogene receptor (MasR). Although theseinteractions led to various alterations of signal transduction, but, more importantly, ligand binding toAT1R resulted in the downregulation of ACE2 cell surface expression, while ligand binding to AT2R,but not to MasR, resulted in upregulation of ACE2 cell surface expression. Proximity ligation assaysperformed in situ revealed macromolecular complexes containing ACE2 and AT1R, AT2R or MasR inadult but not fetal mouse lung tissue. These findings highlight the relevance of RAS in SARS-CoV-2infection and the role of ACE2-containing complexes as potential therapeutic targets

Angiotensin AT1 and AT2 receptors heteromer expression in microglia correlates with Parkinson's disease progression in the hemilesioned rat model of the disease

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. Proximity ligation assays was used to quantify receptor expression in microglial cells and brain striatal slices. 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 show a cross-potentiation, i.e. candesartan, the antagonist of AT 1 increases the effect of AT 2 receptor agonists. In addition, the level of expression in the unilateral 6-OH-dopamine lesion rat PD model increases upon disease progression and is maximal in dyskinetic animals. 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

Angiotensin AT 1 and AT 2 receptor heteromer expression in the hemilesioned rat model of Parkinson's disease that increases with levodopa-induced dyskinesia

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 AT1 and AT2 receptors, mainly known for their role in regulating water homeostasis and blood pressure and able to form heterodimers (AT1/2Hets), are present in the central nervous system. We assessed the functionality and expression of AT1/2Hets in Parkinson disease (PD). Methods: Immunocytochemistry was used to analyze the colocalization between angiotensin receptors; bioluminescence resonance energy transfer was used to detect AT1/2Hets. 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 AT1 and AT2 receptors form AT1/2Hets that are expressed in cells of the central nervous system. AT1/2Hets 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, AT1/2Hets that are expressed in both striatal neurons and microglia make possible that candesartan, the antagonist of AT1, increases the effect of AT2 receptor agonists. In addition, the level of striatal expression increased in the unilateral 6-OH-dopamine 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 AT2 receptors using an AT1 receptor antagonist constitutes a promising therapeutic strategy in PD. Keywords: Dyskinesia; G-protein-coupled receptor (GPCR); Heteromer; Levodopa; Neuroinflammation

Cannabidiol skews biased agonism at cannabinoid CB1 and CB2 receptors with smaller effect in CB1-CB2 heteroreceptor complexes

Currently, biased agonism is at the center stage of drug development approaches. We analyzed effects of a battery of cannabinoids plus/minus cannabidiol (CBD) in four functional parameters (cAMP levels, phosphorylation of extracellular signal–regulated kinases (ERK1/2), β-arrestin recruitment and label-free/DMR) in HEK-293T cells expressing cannabinoid receptors, CB or CB, or CB-CB heteroreceptor complexes. In all cases two natural agonists plus two selective synthetic agonists were used. Furthermore, the effect of cannabidiol, at a dose (100 nM) that does not allow significant binding to the orthosteric center of either receptor, was measured. From the huge amount of generated data, we would like to highlight that the two psychotropic molecules (Δ-tetrahydrocannabinol/THC and CP-55940) showed similar bias in CBR and that the bias of THC was particularly relevant toward MAPK pathway. Furthermore, THC did not activate the G protein coupled to CBR. Interestingly, the biased agonism was reduced when assays were performed in cells expressing the two receptors, thus suggesting that the heteromer allows less functional selectivity. In terms of cannabidiol action, the phytocannabinoid altered the functional responses, likely by allosteric means, and modified potency, agonist IC/EC values and biased agonism in qualitative and/or quantitative different ways depending on the agonist. The effect of cannabidiol on anandamide actions on both cannabinoid receptors was particularly noteworthy as was significantly different from that of other compounds. Results are a compendium of data on biased agonism on cannabinoid receptors in the absence and presence of cannabidiol. In addition, for the first time, GPCR biased agonism is characterized in an heteromeric context.This work was partially supported by grants from the Spanish Ministry of Economy and Competitiveness (Ref. no. BFU2015-64405-R and SAF2017-84117-R; they may include FEDER funds) and by grant 201413-30 from: Fundació la Marató de TV3Peer Reviewe

Molecular and functional interaction between GPR18 and cannabinoid CB2 G-protein-coupled receptors. Relevance in neurodegenerative diseases

GPR18, still considered an orphan receptor, may respond to endocannabinoids, whose canonical receptors are CB1 and CB2. GPR18 and CB2 receptors share a role in peripheral immune response regulation and are co-expressed in microglia, which are immunocompetent cells in the central nervous system (CNS). We aimed at identifying heteroreceptor complexes formed by GPR18 and CB1R or CB2R in resting and activated microglia. Receptor-receptor interaction was assessed using energy-transfer approaches, and receptor function by determining cAMP levels and ERK1/2 phosphorylation in heterologous cells and primary cultures of microglia. Heteroreceptor identification in primary cultures of microglia was achieved by in situ proximity ligation assays. Energy transfer results showed interaction of GPR18 with CB2R but not with CB1R. CB2-GPR18 heteroreceptor complexes displayed particular functional properties (heteromer prints) often consisting of negative cross-talk (activation of one receptor reduces signaling arising from the partner receptor) and cross-antagonism (the response of one of the receptors is blocked by a selective antagonist of the partner receptor). Activated microglia showed the heteromer print (negative cross-talk and bidirectional cross-antagonism) and increased expression of CB2R and GPR18. Due to the important role of CB2R in neuroprotection, we further investigated heteroreceptor occurrence in primary cultures of microglia from transgenic mice overexpressing human APPSw,Ind, an Alzheimer's disease model. Microglial cells from transgenic mice showed the heteromer print and functional interactions that were similar to those found in cells from wild-type animals that were activated by treatment with lipopolysaccharide and interferon-ɤ. Our results show that GPR18 and its heteromers may play important roles in neurodegenerative processes

Cannabigerol Action at Cannabinoid CB1 and CB2 Receptors and at CB1–CB2 Heteroreceptor Complexes

Cannabigerol (CBG) is one of the major phytocannabinoids present in Cannabis sativa L. that is attracting pharmacological interest because it is non-psychotropic and is abundant in some industrial hemp varieties. The aim of this work was to investigate in parallel the binding properties of CBG to cannabinoid CB1 (CB1R) and CB2 (CB2R) receptors and the effects of the compound on agonist activation of those receptors and of CB1–CB2 heteroreceptor complexes. Using [3H]-CP-55940, CBG competed with low micromolar Ki values the binding to CB1R and CB2R. Homogeneous binding in living cells, which is only technically possible for the CB2R, provided a 152 nM Ki value. Also interesting, CBG competed the binding of [3H]-WIN-55,212-2 to CB2R but not to CB1R (Ki: 2.7 versus >30 μM). The phytocannabinoid modulated signaling mediated by receptors and receptor heteromers even at low concentrations of 0.1–1 μM. cAMP, pERK, β-arrestin recruitment and label-free assays in HEK-293T cells expressing the receptors and treated with endocannabinoids or selective agonists proved that CBG is a partial agonist of CB2R. The action on cells expressing heteromers was similar to that obtained in cells expressing the CB2R. The effect of CBG on CB1R was measurable but the underlying molecular mechanisms remain uncertain. The results indicate that CBG is indeed effective as regulator of endocannabinoid signaling

Expression of Melatonin and Dopamine D Receptor Heteromers in Eye Ciliary Body Epithelial Cells and Negative Correlation with Ocular Hypertension

Background: Experiments in the late nineties showed an inverse relationship in the eye levels of melatonin and dopamine, thereby constituting an example of eye parameters that are prone to circadian variations. The underlying mechanisms are not known but these relevant molecules act via specific cell surface dopamine and melatonin receptors. This study investigated whether these receptors formed heteromers whose function impact on eye physiology. We performed biophysical assays to identify interactions in heterologous systems. Particular heteromer functionality was detected using Gi coupling, MAPK activation, and label-free assays. The expression of the heteroreceptor complexes was assessed using proximity ligation assays in cells producing the aqueous humor and human eye samples. Dopamine D receptors (DRs) were identified in eye ciliary body epithelial cells. We discovered heteromers formed by DR and either MT (MTR) or MT (MTR) melatonin receptors. Heteromerization led to the blockade of DR-Gi coupling and regulation of signaling to the MAPK pathway. Heteromer expression was negatively correlated with intraocular hypertension. Conclusions: Heteromers likely mediate melatonin and dopamine actions in structures regulating intraocular pressure. Significant expression of DR-MTR and DR-MTR was associated with normotensive conditions, whereas expression diminished in a cell model of hypertension. A clear trend of expression reduction was observed in samples from glaucoma cases. The trend was marked but no statistical analysis was possible as the number of available eyes was 2

Cannabigerol action at cannabinoid CB1 and CB2 receptors and at CB1-CB2 heteroreceptor complexes

Cannabigerol (CBG) is one of the major phytocannabinoids present in Cannabis sativa L. that is attracting pharmacological interest because it is non-psychotropic and is abundant in some industrial hemp varieties. The aim of this work was to investigate in parallel the binding properties of CBG to cannabinoid CB1 (CB1R) and CB2 (CB2R) receptors and the effects of the compound on agonist activation of those receptors and of CB1-CB2 heteroreceptor complexes. Using [3H]-CP-55940, CBG competed with low micromolar Ki values the binding to CB1R and CB2R. Homogeneous binding in living cells, which is only possible for the CB2R, provided a nanomolar Ki value. In contrast, CBG competed the binding of [3H]-WIN-55,212-2 to CB2R but not to CB1R (2.7 versus >30 µM). The phytocannabinoid modulated signaling mediated by receptors and receptor heteromers even at low concentrations of 0.1-1 µM. cAMP, pERK, ÿ-arrestin recruitment and label-free assays in HEK-293T cells expressing the receptors and treated with endocannabinoids or selective agonists proved that CBG is a partial agonist of CB2R. The action on cells expressing heteromers was similar to that obtained in cells expressing the CB2R. The effect of CBG on CB1R was measurable but the underlying molecular mechanisms remain uncertain. The results indicate that CBG is indeed effective as regulator of endocannabinoid signaling

Binding and Signaling Studies Disclose a Potential Allosteric Site for Cannabidiol in Cannabinoid CB2 Receptors

The mechanism of action of cannabidiol (CBD), the main non-psychotropic component of Cannabis sativa L., is not completely understood. First assumed that the compound was acting via cannabinoid CB2 receptors (CB(2)Rs) it is now suggested that it interacts with non-cannabinoid G-protein-coupled receptors (GPCRs); however, CBD does not bind with high affinity to the orthosteric site of any GPCR. To search for alternative explanations, we tested CBD as a potential allosteric ligand of CB2R. Radioligand and non-radioactive homogeneous binding, intracellular cAMP determination and ERK1/2 phosphorylation assays were undertaken in heterologous systems expressing the human version of CB2R. Using membrane preparations from CB2R-expressing HEK-293T (human embryonic kidney 293T) cells, we confirmed that CBD does not bind with high affinity to the orthosteric site of the human CB2R where the synthetic cannabinoid, [H-3]-WIN 55,212-2, binds. CBD was, however, able to produce minor but consistent reduction in the homogeneous binding assays in living cells using the fluorophore-conjugated CB2R-selective compound, CM-157. The effect on binding to CB2R-expressing living cells was different to that exerted by the orthosteric antagonist, SR144528, which decreased the maximum binding without changing the K-D. CBD at nanomolar concentrations was also able to significantly reduce the effect of the selective CB2R agonist, JWH133, on forskolin-induced intracellular cAMP levels and on activation of the MAP kinase pathway. These results may help to understand CBD mode of action and may serve to revisit its therapeutic possibilities