Autocrine Endocannabinoid Signaling through CB₁Receptors Potentiates OX₁Orexin Receptor Signaling

Abstract

It has been proposed that OX 1 orexin receptors and CB 1 cannabinoid receptors can form heteromeric complexes, which affect the trafficking of OX 1 receptors and potentiate OX 1 receptor signaling to extracellular signal-regulated kinase (ERK). We have recently shown that OX 1 receptor activity releases high levels of the endocannabinoid 2-arachidonoyl glycerol (2-AG), suggesting an alternative route for OX 1 -CB 1 receptor interaction in signaling, for instance, in retrograde synaptic transmission. In the current study, we set out to investigate this possibility utilizing recombinant Chinese hamster ovary K1 cells. 2-AG released from OX 1 receptor-expressing cells acted as a potent paracrine messenger stimulating ERK activity in neighboring CB 1 receptor-expressing cells. When OX 1 and CB 1 receptors were expressed in the same cells, OX 1 stimulation-induced ERK phosphorylation and activity were strongly potentiated. The potentiation but not the OX 1 response as such was fully abolished by specific inhibition of CB 1 receptors or the enzyme responsible for 2-AG generation, diacylglycerol lipase (DAGL). Although the results do not exclude the previously proposed OX 1 -CB 1 heteromerization, they nevertheless unequivocally identify DAGL-dependent 2-AG generation as the pivotal determinant of the OX 1 -CB 1 synergism and thus suggest a functional rather than a molecular interaction of OX 1 and CB 1 receptors.

Cannabinoid-hypocretin cross-talk in the central nervous system: what we know so far

“…Besides the heteromerization, an additional mechanism has been proposed to explain the increase in the potency of hypocretin-1 to activate the ERK pathway in the presence of CB1 (Jäntti et al, 2013; Kukkonen and Leonard, 2013). Recent studies report that HcrtR1-expressing CHO cells may release 2-AG in response to hypocretin-1 stimulation.…”

CB1 cannabinoid receptor-mediated increases in cyclic AMP accumulation are correlated with reduced Gi/o function

“…In any biological system, the abundance of endogenously-produced endocannabinoids is an important determinant of whether the CB 1 R is under the influence of high “endocannabinoid tone” that could be reversed by a competitive antagonist (for discussion, see [42]). CHO cells express phospholipase C and diacylglycerol lipase [43;44], as do neuronal cell lines (Howlett, unpublished observations), enzymes that govern production of the endocannabinoid 2-AG. This suggests the necessity of testing responses to a diaceylglycerol lipase inhibitor to demonstrate whether forskolin-activated cAMP accumulation can be influenced by endocannabinoids produced by the cultured cells.…”

New horizons on the role of cannabinoid CB1 receptors in palatable food intake, obesity and related dysmetabolism

“…25 In an in vitro study, it was demonstrated that the coexpression of CB1 and OX1 receptors results in a higher potentiation of ERK signalling, possibly because of heterodimerization/oligomerization of these two receptors. 26 Recently, however, it was also shown that 2-AG produced and released through the activation of OX1 receptor acts as both a paracrine and autocrine messenger via CB1 receptors, 23,27 thus possibly explaining the above-mentioned findings in the rat dorsal raphe nucleus and periaqueductal gray, as well as the potentiation of ERK phoshorylation that follows OX1/CB1 receptor coexpression. These data suggest the involvement of 2-AG and CB1 receptors not only in orexin-A release but also in orexin-mediated regulation of synaptic transmission.…”