Cyclic AMP‐dependent protein kinase and D1 dopamine receptors regulate diacylglycerol lipase‐α and synaptic 2‐arachidonoyl glycerol signaling

Abstract

Abbreviations: 2-AG, 2-arachidonoyl glycerol; ACSF, artificial cerebrospinal fluid; CaMKII, calcium/calmodulin-dependent protein kinase II; CB1R, type 1 cannabinoid receptor; d/iMSN, striatal medium spiny neurons projecting via the direct/indirect output pathways, respectively; D1R, D1-dopamine receptor; D2R, D2-dopamine receptor; DGLα, diacylglycerol lipase-α; DSE, depolarization-enhanced suppression of excitation; eCB, endocannabinoid; eEPSC, evoked excitatory post-synaptic current; IBMX, 3-isobutyl-1-methylxanthine; PKA, cyclic AMP-dependent protein kinase. AbstractBrain endocannabinoids serve as retrograde neurotransmitters, being synthesized in post-synaptic neurons "on demand" and released to bind pre-synaptic cannabinoid receptors and suppress glutamatergic or GABAergic transmission. The most abundant brain endocannabinoid, 2 arachidonoyl glycerol (2-AG), is primarily synthesized by diacylglycerol lipase-α (DGLα), which is activated by poorly understood mechanisms in response to calcium influx following post-synaptic depolarization and/or the activation of G q -coupled group 1 metabotropic glutamate receptors. However, the impact of other neurotransmitters and their downstream signaling pathways on synaptic 2-AG signaling has not been intensively studied. Here, we found that DGLα activity in membrane fractions from transfected HEK293T cells was significantly increased by in vitro phosphorylation using cyclic AMP-dependent protein kinase (PKA). Moreover, PKA directly phosphorylated DGLα at Ser798 in vitro. Elevation of cAMP levels in HEK293 cells expressing DGLα increased Ser798 phosphorylation, as detected using a phospho-Ser798-specific antibody, and enhanced DGLα activity; this in situ enhancement of DGLα activity was prevented by mutation of Ser798 to Ala. We investigated the impact of PKA on synaptic 2-AG mobilization in mouse striatal slices by manipulating D1-dopamine receptor (D1R) signaling and assessing depolarization-induced suppression of excitation, a DGLα-and 2-AG-dependent form of short-term synaptic depression. The magnitude of depolarization-enhanced suppression of excitation in direct pathway medium spiny neurons was increased by pre-incubation with a D1R agonist, and this enhancement was blocked by postsynaptic inhibition of PKA. Taken together, these findings provide new molecular insights into the complex mechanisms regulating synaptic endocannabinoid signaling. K E Y W O R D S D1 dopamine receptor, diacylglycerol lipase, endocannabinoid, PKA, protein phosphorylation Read the Editorial Highlight for this article on page 297. | 335 SHONESY Et al.

Cannabinoid Modulation of Dopamine Release During Motivation, Periodic Reinforcement, Exploratory Behavior, Habit Formation, and Attention

“…Individual FSIs innervate hundreds of MSNs and, when excited, inhibit their collective output ( Tepper et al, 2008 ). Within the NAc, eCBs are synthesized and released from MSNs following activation of either D1 ( Shonesy et al, 2020 ) or D2 ( Lerner and Kreitzer, 2012 ) receptors. Also noteworthy is recent evidence suggesting that tyrosine receptor kinase B activation augments intracellular calcium transients to promote eCB synthesis and spike-timing dependent plasticity in the striatum ( Gangarossa et al, 2020 ).…”

Autocrine regulation of adult neurogenesis by the endocannabinoid 2-arachidonoylglycerol (2-AG)

“…It is currently not known which signaling mechanisms act upstream of the endocannabinoid system in the modulation of adult neurogenesis. In addition to growth factor receptor activation these may include metabotropic receptors, such as dopamine receptor D1 which has been shown to regulate DAGLa activity (Shonesy et al, 2020) as well as NPC proliferation (Takamura et al, 2014) that there is a redundancy of pathways and compensation by other factors regulating these crucial developmental stages. In the adulthood, however, there seems to be less plasticity and potential for compensation.…”

“…It is currently not known which signaling mechanisms act upstream of the endocannabinoid system in the modulation of adult neurogenesis. In addition to growth factor receptor activation these may include metabotropic receptors, such as dopamine receptor D1 which has been shown to regulate DAGLa activity (Shonesy et al, 2020) as well as NPC proliferation (Takamura et al, 2014) or the well-established upstream regulator of DAGLa, the glutamate receptor. We propose that an autocrine endocannabinoid signaling in NSCs/NPCs may either serve in signal potentiation or, alternatively, function as a signal integrator, for example for coincidence detection of several neurogenic signals.…”

Dopamine Receptors and the Kidney: An Overview of Health- and Pharmacological-Targeted Implications

“…In particular, D1 receptors have a high affinity for benzazepine antagonists, while D2 receptors have a high affinity for benzamides and butiferone antagonists such as sulpiride and spiperone [ 5 , 6 ]. D1 receptors are involved in stimulation of adenylate cyclase and accumulation of cyclic AMP (cAMP), while D2 receptors inhibit these enzymes [ 7 , 8 ]. Furthermore, D1 and D2 receptors have different DNA sequences and protein structures and are distributed differently in different tissues [ 9 ].…”