Endocannabinoids alleviate proinflammatory conditions by modulating innate immune response in muller glia during inflammation

Abstract

Muller cells play a prominent role in inflammatory conditions of the retina. They are part of the retinal innate immune response. The endocannabinoid system functions as an immune modulator in both the peripheral immune system as well as the central nervous system. We hypothesized that the neuroprotective ability of exogenous endocannabinoids in the retina is partially mediated through Muller glia. This study reports that exposure to endocannabinoids in activated but not resting primary human Muller glia inhibit production of several proinflammatory cytokines, while elevating anti-inflammatory mediators. Cytokine generation in activated Muller glia is regulated by endocannabinoids through the mitogen-activated protein kinase (MAPK) family at multiple signaling stages. Anandamide (AEA) acts to control MAPK phosphorylation through MKP-1. Both AEA and 2-arachidonoylglycerol (2-AG) inhibit the transcription factor NF-κB and increases the regulatory protein, IL1-R-associated kinase 1-binding protein 1. Endocannabinoids also increase expression of Tristetraprolin in activated Muller cells, which is implicated in affecting AU-rich proinflammatory cytokine mRNA. We demonstrate that exogenous application of AEA and 2-AG aid in retinal cell survival under inflammatory conditions by creating an anti-inflammatory milieu. Endocannabinoids or synthetic cannabinoid therapy may therefore orchestrate a molecular switch to bias the innate immune system suchthat the balance of pro- and anti-inflammatory cytokine generation creates a prosurvival milieu.

Anandamide rescues retinal barrier properties in Müller glia through nitric oxide regulation

“…5B), almost as much as addition of AEA. Earlier work from the authors had identified the mitogen-activated protein kinases (MAPK) pathway as a fulcrum during inflammation in Mu¨ller glia (Krishnan and Chatterjee, 2012), with the phosphatase, MKP-1 emerging as critical in limiting excessive production of pro-inflammatory factors. Existing reports show the inhibition of iNOS expression via the MKP-1/MEK/ERK pathways (Liu et al, 2013).…”

“…AEA was used at 10 lM unless mentioned otherwise. We had earlier optimized that exposure to 10 lM AEA is necessary for regulation of pro-inflammatory cytokines in Mu¨ller cells (Krishnan and Chatterjee, 2012). Five micromole DAF-2DA and 10 mM Lucifer Yellow were used for imaging studies.…”

“…RT-PCR was performed according to Krishnan and Chatterjee (2012). Total RNA was collected according to the manufacturer's instructions (Qiagen RNeasy Kit, Limburg, Netherlands).…”

“…Mu¨ller glia were isolated according to Krishnan and Chatterjee (2012) with no modifications. Cultures were enriched for Mu¨ller glia.…”

“…Cannabidiol, a non-psychoactive cannabinoid, is also known to suppress NO production independent of cannabinoid receptor type 1 (CB1) or cannabinoid receptor type 2 (CB2), in activated microglia from rats with endotoxin-induced uveitis (EIU) (El-Remessy et al, 2008). While action of endocannabinoids in the retina is relatively unexplored, it has been demonstrated that Mu¨ller glia are active players in retinal innate immunity (Shamsuddin and Kumar, 2011;Krishnan and Chatterjee, 2012).…”