The endocannabinoid 2-arachidonoylglycerol regulates oligodendrocyte progenitor cell migration.

While the endocannabinoid 2-arachidonoylglycerol (2-AG) is thought to enhance the proliferation and differentiation of oligodendrocyte progenitor cells (OPCs) in vitro, less is known about how endogenous 2-AG may influence the migration of these cells. When we assessed this in Agarose drop and Boyden chemotaxis chamber assays, inhibiting the sn-1-diacylglycerol lipases α and ß (DAGLs) that are responsible for 2-AG synthesis significantly reduced the migration of OPCs stimulated by platelet-derived growth factor-AA (PDGF) and basic fibroblast growth factor (FGF). Likewise, antagonists of the CB1 and CB2 cannabinoid receptors (AM281 and AM630, respectively) produced a similar inhibition of OPC migration. By contrast, increasing the levels of endogenous 2-AG by blocking its degradation (impairing monoacylglycerol lipase activity with JZL-184) significantly increased OPC migration, as did agonists of the CB1, CB2 or CB1/CB2 cannabinoid receptors. This latter effect was abolished by selective CB1 or CB2 antagonists, strongly suggesting that cannabinoid receptor activation specifically potentiates OPC chemotaxis and chemokinesis in response to PDGF/FGF. Furthermore, the chemoattractive activity of these cannabinoid receptor agonists on OPCs was even evident in the absence of PDGF/FGF. In cultured brain slices prepared from the corpus callosum of postnatal rat brains, DAGL or cannabinoid receptor inhibition substantially diminished the in situ migration of Sox10+ OPCs. Overall, these results reveal a novel function of endogenous 2-AG in PDGF and FGF induced OPC migration, highlighting the importance of the endocannabinoid system in regulating essential steps in oligodendrocyte development.

A Basal Tone of 2-Arachidonoylglycerol Contributes to Early Oligodendrocyte Progenitor Proliferation by Activating Phosphatidylinositol 3-Kinase (PI3K)/AKT and the Mammalian Target of Rapamycin (MTOR) Pathways.

A basal tone of the endocannabinoid 2-arachidonoylglycerol (2-AG) enhances late oligodendrocyte progenitor cell (OPC) differentiation. Here, we investigated whether endogenous 2-AG may also promote OPC proliferation in earlier stages. We found that the blockade of 2-AG synthesizing enzymes, sn-1-diacylglycerol lipases α and ß (DAGLs), with RHC-80267 or the antagonism of either CB1 or CB2 cannabinoid receptors with AM281 and AM630, respectively, impaired early OPC proliferation stimulated by platelet-derived growth factor (PDGF-AA) and basic fibroblast growth factor (bFGF). On the contrary, increasing the levels of endogenous 2-AG by blocking the degradative enzyme monoacylglycerol lipase (MAGL) with JZL-184, significantly increased OPC proliferation as did agonists of cannabinoid receptor CB1 (ACEA), CB2 (JWH133) or both (HU-210). To elucidate signaling pathways underlying OPC proliferation, we studied the involvement of phosphatidylinositol 3-kinase (PI3K)/Akt and its downstream target mammalian target of rapamycin (mTOR). We show that phosphorylation of Akt and mTOR is required for OPC proliferation stimulated by growth factors (PDGF-AA and bFGF) or by CB1/CB2 agonists (ACEA/JWH133), since it was strongly decreased after LY294002 or rapamycin treatment. In line with this, blockade of CB1 (AM281), CB2 (AM630) or DAGLs (RHC-80267), decreased phosphorylation of Akt, mTOR and 4E-BP1, diminished cyclin E-cdk2 complex association and increased p27(kip1) levels. Our data suggest that proliferation of early OPCs stimulated by PDGF-AA and bFGF depends on the tonic activation of cannabinoid receptors by endogenous 2-AG and provide further evidence on the role of endocannabinoids in oligodendrocyte development, being important for the maintenance and self-renewal of the OPCs. The results highlight the therapeutic potential of the endocannabinoid signaling in the emerging field of brain repair.