Targeting glial cannabinoid CB 2 receptors to delay the progression of the pathological phenotype in TDP-43 (A315T) transgenic mice, a model of amyotrophic lateral sclerosis.

BACKGROUND AND PURPOSE: Cannabinoid CB2 receptors are up-regulated in reactive microglia in the spinal cord of TDP-43 (A315T) transgenic mice, an experimental model of amyotrophic lateral sclerosis. To determine whether this up-regulation can be exploited pharmacologically, we investigated the effects of different treatments that affect CB2 receptor function.

EXPERIMENTAL APPROACH: We treated TDP-43 (A315T) transgenic mice with the non-selective agonist WIN55,212-2, alone or combined with selective CB1 or CB2 antagonists, as well as with the selective CB2 agonist HU-308, and evaluated their effects on the pathological phenotype.

KEY RESULTS: WIN55,212-2 had modest beneficial effects in the rotarod test, Nissl staining of motor neurons, and GFAP and Iba-1 immunostainings in the spinal cord, which were mediated in part by CB2 receptor activation. HU-308 significantly improved the rotarod performance of the transgenic mice, with complete preservation of Nissl-stained motor neurons in the ventral horn. Reactive astrogliosis labelled with GFAP was also attenuated by HU-308 in the dorsal and ventral horns, in which CB2 receptors colocalize with this astroglial marker. Furthermore, HU-308 reduced the elevated Iba-1 immunostaining in the ventral horn of TDP-43 transgenic mice, but did not affect this immunoreactivity in white matter, in which CB2 receptors also colocalize with this microglial marker.

CONCLUSIONS AND IMPLICATIONS: Our study shows an important role for glial CB2 receptors in limiting the progression of the pathological phenotype in TDP-43 (A315T) transgenic mice. Such benefits appear to derive from the activation of CB2 receptors concentrated in astrocytes and reactive microglia located in spinal dorsal and ventral horns.