Diacylglycerol Lipaseα (DAGLα) and DAGLβ Cooperatively Regulate the Production of 2-Arachidonoyl Glycerol in Autaptic Hippocampal Neurons

Abstract

Cannabinoids are part of an endogenous signaling system consisting of cannabinoid receptors and endogenous cannabinoids as well as the enzymatic machinery for their synthesis and degradation. Depolarization-induced suppression of excitation (DSE) is a form of cannabinoid CB 1 receptor-mediated inhibition of synaptic transmission that involves the production of the endogenous cannabinoid 2-arachidonoyl glycerol (2-AG). Both diacylglycerol lipase a (DAGLa) and DAGLb can produce 2-AG in vitro, but evidence from knockout animals argues strongly for a predominant, even exclusive, role for DAGLa in regulation of 2-AG-mediated synaptic plasticity. What role, if any, might be played by DAGLb remains largely unknown. Cultured autaptic hippocampal neurons exhibit robust DSE. With the ability to rapidly modulate expression of DAGLa and DAGLb in these neurons with short hairpin RNA, they are well suited for a comparative study of the roles of each isoform in mediating DSE. We find that RNA interference knockdown of DAGLa substantially reduces autaptic DSE, shifting the "depolarizationresponse curve" from an ED 50 value of 1.7 seconds to 3.0 seconds. Surprisingly, DAGLb knockdown diminishes DSE as much or more (ED 50 6.4 seconds), suggesting that DAGLb is also responsible for a portion of 2-AG production in autaptic neurons. Similarly, the two DAGLs both contribute to the production of 2-AG via group I metabotropic glutamate receptors. Our results provide the first explicit evidence for a role of DAGLb in modulating neurotransmission.

Inhibiting endocannabinoid biosynthesis: a novel approach to the treatment of constipation

“…Full details are found in the http://onlinelibrary.wiley.com/doi/10.1111/bph.13114/suppinfo. Briefly, whole‐mount preparations were incubated with the primary rabbit antibody against DAGLα or DAGLβ (1:50–1:500, optimal dilution 1:100) raised by Ken Mackie, Indiana University, Indianapolis, IN, USA (Katona et al ., ; Jain et al ., ) alone or in double‐labelling experiments with the vesicular acetylcholine transporter (vAChT; Phoenix Pharmaceuticals Inc., Burlingame, CA, USA), substance P (Medicorp Inc., Montreal, QC, Canada) or neuronal NOS (Sigma‐Aldrich Ltd., Oakville, ON, Canada). Positive DAGLα labelling was completely abolished by pre‐absorption with 100 μg·mL −1 of the immunizing peptide.…”

Parsing the players: 2‐arachidonoylglycerol synthesis and degradation in the CNS

“…A recent study using RNAi knockdown in cultured hippocampal neurons suggests that DAGLα and DAGLβ can cooperate to mediate two forms of endocannabinoid plasticity: DSE and metabotropic suppression of excitation (MSE) (Jain et al ., ). In these experiments, DSE was diminished by knockdown of either DAGL and reduced almost completely when both enzymes were knocked down, consistent with a cooperative effect.…”

An Introduction to the Endogenous Cannabinoid System

“…Anatomical studies place receptors such as mGluR5 and DAGLα in close proximity to one another in dendritic spines, apposed to presynaptic CB1 receptors (60–62). While DAGLα seems the dominant 2-AG producing lipase in adult CNS, DAGLβ may contribute to synaptic 2-AG under certain conditions (63) and plays an important role in the generation of 2-AG during immune responses (64). A secondary pathway for 2-AG synthesis could be cleavage of the phosphatidyl inositol precursor by a phospholipase A, followed by hydrolysis of the phosphate ester bond by a lyso-phospholipase C, however the importance of this pathway in brain remains to be established.…”