Distinct regulation of nNOS and iNOS by CB2 receptor in remote delayed neurodegeneration

Hemicerebellectomy results in remote delayed degeneration of precerebellar neurons. We have reported that such a lesion induces type 2 cannabinoid receptor (CB2) expression in precerebellar neurons and that stimulation of CB2, but not CB1, has neuroprotective effects. In this study, we found that in the same model, the CB2 agonist JWH-015 enhances neuronal nitric oxide synthase (nNOS) expression in axotomized neurons and that CB2-mediated neuroprotection is abrogated by pharmacological inhibition of nNOS. JWH-015 prevented the axotomy-induced upregulation of inducible NOS (iNOS) in astrocytes but had no effect on endothelial NOS (eNOS). In addition, we observed that JWH-015 significantly reduces hemicerebellectomy-induced neuroinflammatory responses and oxidative/nitrative stress. With regard to the signaling pathways of CB2/nNOS-mediated neuroprotection, we noted nNOS-dependent modulation of the expression of anti-oxidative (Hsp70) and anti-apoptotic (Bcl-2) proteins. These findings shed light on the interactions between the endocannabinoid and nitrergic systems after focal brain injury, implicating distinct functions of nNOS activation and iNOS inhibition in CB2 signaling, which protect neurons from axotomy-induced cell death.