Adreno–melatonin receptor complexes control ion homeostasis and intraocular pressure ‐ their disruption contributes to hypertensive glaucoma

Abstract

Background and Purpose: Often, glaucoma presents with elevated eye hydrostatic pressure, which is regulated by endogenous melatonin. Phenylephrine increases cytoplasmic [Ca 2+ ], via α 1 -adrenoceptor activation, that is detrimental in glaucoma. The aims of this study were (a) to elucidate the role of melatonin receptors in humour production and intraocular pressure (IOP) maintenance and (b) to identify glaucomarelevant melatonin-adrenoceptor interactions.Experimental Approach: Biophysical and proximity ligation assays were performed to identify interactions in heterologous expression systems, in cell lines and in human eyes. G s /G i /G q signalling was investigated in these systems and in cells producing aqueous humour. IOP was determined in a mice model of glaucoma. Retinography and topically pharmacological treatment were performed in control and in glaucomatous mice.Key Results: α 1 -adreno-and melatonin receptors form functional complexes in which the C-terminal tail of the adrenoceptor plays a role. Remarkably, activation of α 1adrenoceptors in these complexes did not lead to cytosolic Ca 2+ increases, suggesting G s instead of G q coupling is involved. The number of these complexes significantly decreased in models of glaucoma and, importantly, in human samples from glaucoma patients. This has led to hypothesize that melatonin, a hypotensive agent, plus blockade of α 1 -adrenoceptors could normalize pressure in glaucoma. Remarkably, coinstillation of melatonin and prazosin, an α 1 -adrenoceptor antagonist, resulted in long-term decreases in IOP in a well-established animal model of glaucoma.Conclusions and Implications: The findings are instrumental to understand the physiological function of melatonin in the eye and its potential to address eye pathologies by targeting melatonin receptors and their complexes.Abbreviations: 4PPDOT, cis-4-phenyl-2-propionamidotetralin (antagonist of MT2R); AR, adrenoceptor; IIK7, N-[2-(2-methoxy-6H-isoindolo[2,1-a]indol-11-yl)ethyl]butanamide (MT2R selective agonist); IOP, intraocular pressure; MT 1 R, melatonin MT 1 receptor; MT 2 R, melatonin MT 2 receptor; Rluc, Renilla luciferase; YFP, yellow fluorescence protein; α 1A -MT 1 Hets, α 1A -MT 1 receptor heteromers.A first preprint of this paper was deposited in BioRxiv (https://doi.

Influence of Circadian Rhythm in the Eye: Significance of Melatonin in Glaucoma

“…Furthermore, MT2 receptor may interact with serotonin 5-HT2C [243], being of particular interest due to the discover of agomelatine, a potent agonist of the MT1 and MT2 melatonin receptors [230] and a non-selective inhibitor of the 5-HT2C serotonin receptor [231]. Recently, interactions of MT1 and MT2 receptors with α1 antagonist have been shown to increase melatonin hypotensive effect to almost 50% and lasting for 6 h [244].…”

The Old and New Visions of Biased Agonism Through the Prism of Adenosine Receptor Signaling and Receptor/Receptor and Receptor/Protein Interactions

“…Once again, the heteromeric context leads to a change, from G q to G s , in the G protein coupling (see Figure 1 bottom). Glaucoma coursing with elevated intraocular pressure is correlated with a decreased expression of the complexes in stromal cells (Alkozi et al, 2019;Alkozi et al, 2020). Whether this fact is a cause or a consequence of the disease, the melatoninadrenergic heteromers arise as targets for fighting the disease.…”

Assessment of melatonin-alpha adrenergic receptor complexes by molecular docking analysis

“…Crooke et al (2013) confirmed in vitro the indirect action of melatoninergic compounds on adrenergic receptors and their remarkable effect upon the ocular hypotensive action in rabbits mainly of alpha-2 adrenergic receptor agonists but also of beta-adrenergic antagonists. More recently, Alkozi et al (2020) demonstrated that α-adrenergic and melatonin receptors form functional complexes in which the C-terminal tail of the adrenergic receptor play a relevant role, identifying that the number of complexes significantly decreased in models of glaucoma and, more importantly, in human samples of glaucoma patients. Remarkably, coinstillation of melatonin resulted in long-term decreases in the intraocular pressure in a well-established animal model of glaucoma, hypothesizing that melatonin could normalize pressure in glaucoma (Alkozi et al, 2020).…”

“…More recently, Alkozi et al (2020) demonstrated that α-adrenergic and melatonin receptors form functional complexes in which the C-terminal tail of the adrenergic receptor play a relevant role, identifying that the number of complexes significantly decreased in models of glaucoma and, more importantly, in human samples of glaucoma patients. Remarkably, coinstillation of melatonin resulted in long-term decreases in the intraocular pressure in a well-established animal model of glaucoma, hypothesizing that melatonin could normalize pressure in glaucoma (Alkozi et al, 2020). These findings are crucial to understand the potential physiological functions and implications of the melatonin supplementation to address pathological dysfunctions by targeting distinct receptors and their complexes.…”