Cultured Rat Microglial Cells Synthesize the Endocannabinoid 2-Arachidonylglycerol, Which Increases Proliferation via a CB₂Receptor-Dependent Mechanism

Abstract

Microglia, as phagocytes and antigen-presenting cells in the central nervous system, are activated in such disease processes as stroke and multiple sclerosis. Because peripheral macrophages are capable of producing endocannabinoids, we have examined endocannabinoid production in a macrophage-colony stimulating factor (M-CSF)-dependent rat microglial cell line (RTMGL1) using reversed phase high-pressure liquid chromatography and liquid chromatography-mass spectroscopy. We determined that cultured microglial cells produce the endocannabinoid 2-arachidonylglycerol (2-AG) as well as anandamide in smaller quantities. When 2-AG, but not anandamide, is added exogenously, RT-MGL1 microglia increase their proliferation. This increased proliferation is blocked by an antagonist of the CB 2 receptor N-[(1S)-endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) and mimicked by the CB 2 receptor-specific agonist 1,1-dimethylbutyl-1-deoxy-⌬ 9 -tetrahydrocannabinol (JWH133). Accompanying the increase in proliferation seen with 2-AG is an increase in active ERK1 that is also blocked with SR144528. The RTMGL1 microglial cells, which exist in a primed state, express the CB 1 and CB 2 receptors as demonstrated by reverse transcription-polymerase chain reaction and immunostaining. The CB 2 receptor in untreated cells is expressed both at the cell surface and internally, and exposure of the cells to 2-AG significantly increases receptor internalization. These data suggest that 2-AG activation of CB 2 receptors may contribute to the proliferative response of microglial cells, as occurs in neurodegenerative disorders.

Brain injury activates microglia that induce neural stem cell proliferation ex vivo and promote differentiation of neurosphere-derived cells into neurons and oligodendrocytes

“…Several mitogens are also known to positively regulate the proliferation of NSPCs in the SVZ, e.g., erythropoietin (Wang et al, 2004), vascular endothelial growth factor (VEGF) (Jin et al, 2002) and endocannabinoids (Carrier et al, 2004, Aguado et al, 2005. We found that microgliaconditioned medium had additive effects on cell proliferation in the neurospheres in the presence of high concentrations of EGF/bFGF, suggesting that the unknown factor acts via a different pathway.…”

The endocannabinoid system in normal and pathological brain ageing

“…These data suggest that cannabinoids regulate glial activity primarily through CB2 receptors. Glial cells not only receive cannabinoid signals but can themselves produce cannabinoids such as anandamide [189], 2-AG [190] and palmitoylethanolamide [191], and also express the enzymes involved in the synthesis and degradation of endocannabinoids [192][193][194]. Because both neurons and glia express elements of the cannabinoid system, it was hypothesized that the cannabinoid system plays an important role in neuron-glia communication.…”

The Cannabinoid CB2 Receptor as a Target for Inflammation-Dependent Neurodegeneration

“…The effects of endocannabinoids on microglia proliferation were studied by Carrier et al [8], who found that 2-AG, but not anandamide, stimulated a concentration-dependent increase in proliferation in microglial cells cultured in the presence of mononuclear colony stimulating factor (M-CSF). This is in contrast to McKallip et al [39], who showed that cannabinoids inhibit the proliferation of cultured macrophages.…”