Up-regulation of CB2 receptors in reactive astrocytes in canine degenerative myelopathy, a disease model of amyotrophic lateral sclerosis

Targeting of the CB 2 receptor results in neuroprotection in the SOD1 G93A mutant mouse model of amyotrophic lateral sclerosis (ALS). The neuroprotective effects of CB 2 receptors are facilitated by their upregulation in the spinal cord of the mutant mice. Here, we investigated whether similar CB 2 receptor upregulation, as well as parallel changes in other endocannabinoid elements, is evident in the spinal cord of dogs with degenerative myelopathy (DM), caused by mutations in the superoxide dismutase 1 gene ( SOD1 ). We used well-characterized post-mortem spinal cords from unaffected and DM-affected dogs. Tissues were used first to confirm the loss of motor neurons using Nissl staining, which was accompanied by glial reactivity (elevated GFAP and Iba-1 immunoreactivity). Next, we investigated possible differences in the expression of endocannabinoid genes measured by qPCR between DM-affected and control dogs. We found no changes in expression of the CB 1 receptor (confirmed with CB 1 receptor immunostaining) or NAPE-PLD, DAGL, FAAH and MAGL enzymes. In contrast, CB 2 receptor levels were significantly elevated in DM-affected dogs determined by qPCR and western blotting, which was confirmed in the grey matter using CB 2 receptor immunostaining. Using double-labelling immunofluorescence, CB 2 receptor immunolabelling colocalized with GFAP but not Iba-1, indicating upregulation of CB 2 receptors on astrocytes in DM-affected dogs. Our results demonstrate a marked upregulation of CB 2 receptors in the spinal cord in canine DM, which is concentrated in activated astrocytes. Such receptors could be used as a potential target to enhance the neuroprotective effects exerted by these glial cells.