Mouse retinal ganglion cell signalling is dynamically modulated through parallel anterograde activation of cannabinoid and vanilloid pathways

Abstract

How retinal ganglion cells (RGCs) process and integrate synaptic, mechanical, swelling stimuli with light inputs is an area of intense debate. The nociceptive cation channel TRPV1 (transient receptor potential vanilloid type 1) modulates RGC Ca signals and excitability yet the proportion of RGCs that express it remains unclear. Furthermore, TRPV1's response to endocannabinoids (eCBs), the putative endogenous retinal activators, is unknown, as is the potential modulation by cannabinoid receptors (CBRs). The density of TRPV1-expressing RGCs in the Ai9:Trpv1 reporter mouse peaked in the mid-peripheral retina. TRPV1 agonists including capsaicin (CAP) and the eCBs anandamide and N-arachidonoyl-dopamine elevated [Ca ] in 30-40% of wild-type RGCs, with effects suppressed by TRPV1 antagonists capsazepine (CPZ) and BCTC ((4-(3-chloro-2-pyridinyl)-N-[4-(1,1-dimethylethyl)phenyl]-1-piperazinecarboxamide), and lacking in Trpv1 cells. The cannabinoid receptor type 1 (CB1R) colocalized with TRPV1:tdTomato expression. Its agonists 2-arachidonoylglycerol (2-AG) and WIN55,122 inhibited CAP-induced [Ca ] signals in adult, but not early postnatal, RGCs. The suppressive effect of 2-AG on TRPV1 activation was emulated by positive modulators of the protein kinase A (PKA) pathway, inhibited by the CB1R antagonist rimonabant and G uncoupler pertussis toxin, and absent in Cnr1 RGCs. We conclude that TRPV1 is a modulator of Ca homeostasis in a subset of RGCs that show non-uniform distribution across the mouse retina. Non-retrograde eCB-mediated modulation of RGC signalling involves a dynamic push-pull between direct TRPV1 activation and PKA-dependent regulation of channel inactivation, with potential functions in setting the bandwidth of postsynaptic responses, sensitivity to mechanical/excitotoxic stress and neuroprotection.

Calcium influx through TRPV4 channels modulates the adherens contacts between retinal microvascular endothelial cells

“…Unfortunately, currently available TRPV1 antibodies are not sufficiently selective to label mammalian retinal tissue (Jo et al . ).…”

TRPV1 Tunes Optic Nerve Axon Excitability in Glaucoma

“…TRPV1 channels densely accumulate in nociceptor cells of dorsal root ganglia to transduce noxious sensory input into the electrochemical responses of the spinal nerve (Simone et al, 1989;Caterina et al, 1997Caterina et al, , 2000Bolcskei et al, 2005). Recent evidence shows widespread TRPV1 expression in the central nervous system (CNS) tissues, including the cortex, hippocampus, hypothalamus, and retina (Mezey et al, 2000;Roberts et al, 2004;Cristino et al, 2006;Sappington et al, 2009Sappington et al, , 2015Jo et al, 2017;Lakk et al, 2018). TRPV1 has also been implicated in neurodegenerative disorders such as Alzheimer's disease (Jayant et al, 2016;Balleza-Tapia et al, 2018), Parkinson's disease (Marinelli et al, 2003;Morgese et al, 2007;Nam et al, 2015;Chung et al, 2017), Huntington's disease (Lastres-Becker et al, 2003), and glaucomatous optic neuropathy, or glaucoma (Ward et al, 2014;Weitlauf et al, 2014).…”

“…Glaucoma is the leading cause of irreversible blindness (Quigley and Broman, 2006), involving sensitivity to intraocular pressure (IOP) that stresses retinal ganglion cell (RGC) axons as they form the optic nerve (Calkins, 2012). Many RGCs express TRPV1 channels (Jo et al, 2017;Lakk et al, 2018), localizing to dendrites, unmyelinated axon segment, and cell body, where it increases with short-term elevations in IOP (Sappington et al, 2009(Sappington et al, , 2015Weitlauf et al, 2014) but is negligible within the optic nerve itself (Choi et al, 2015). Even so, Trpv1 −/− accelerates optic nerve degeneration with elevated IOP and increases the depolarization necessary for RGCs to produce action potentials (Ward et al, 2014;Weitlauf et al, 2014).…”

Polymodal Sensory Transduction in Mouse Corneal Epithelial Cells

“…Animal handling and experiments were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research, with the project also approved by the Institutional Animal Care and Use Committee at the University of Utah. C57BL/6 (C57), TRPV4 −/− , 30 and B6.Cg-Gt(ROSA)26Sortm9(CAGtdTomato) Hze/J (Ai9) in which the LoxP-STOP-LoxP TdTomato construct is knocked in at the Gt(ROSA)26Sor locus (referred to as TRPV1 tdT ) 31 and bacterial artificial chromosome (BAC)-transgenic Tg(TRPV4-EGFP)MT43Gsat mice (referred to as TRPV4 eGFP ) mice 32 were maintained in a pathogen-free facility with a 12-hour light/dark cycle and unrestrained access to food and water. Data were gathered from 1-to 3-month-old male and female animals with no noted gender differences.…”

“…Detached CE sheets and acutely dissociated cells were used for optical imaging as described. 20,31 Single cells were obtained after enzymatic digestion with papain (15 U/mL) and plated onto coverslips coated with concanavalin A (0.5 mg/mL). Epithelial sheets were carefully peeled off enucleated corneas and placed in the recording chamber (Warner Instruments (Hamden, CT, USA)).…”