Restoration of CB1 receptor function in hippocampal GABAergic neurons rescues memory deficits in Huntington's disease models.

Background: Dysregulation of the endocannabinoid system (eCBS) and the loss of CB1 receptors (CB1R) in the basal ganglia are well-established hallmarks of Huntington's disease (HD). As a result, significant research efforts have focused on targeting the eCBS to alleviate motor disturbances associated with the disease. Beyond its role in motor control, the eCBS is a complex signaling network critically involved in regulating learning and memory. Despite this, the potential involvement of eCBS dysfunction in the cognitive decline characteristic of HD, often manifested well before motor dysfunction, has remained largely unexplored.

Methods: CB1R expression in the hippocampus was evaluated in both human HD samples and HD mouse models (R6/1 and Hdh^Q7/Q111 models, including both sexes) using Western blotting, immunohistochemistry, and radioligand binding assays. To restore CB1R function, CB1R agonist WIN-55212-2 was systemically administered, or viral vectors encoding CB1R were locally infused into the hippocampus of HD mice. A multidisciplinary approach combining behavioral, biochemical, electrophysiological, and morphological analyses, was employed to investigate the molecular mechanisms underlying the effects of CB1R activation in the context of HD-related cognitive dysfunction.

Results: In both human HD samples and HD mouse models, CB1R protein levels were reduced in the hippocampus, accompanied by structural synaptic alterations and impairment in spatial, recognition and working memory. Moreover, hippocampal depolarization-induced suppression of inhibition was significantly disrupted in R6/1 mice. Administration of WIN-55212-2 successfully restored these synaptic and cognitive deficits. Immunohistochemical analysis revealed that the CB1R decrease was specifically localized to GABAergic interneurons within the hippocampus. Notably, targeted restoration of CB1R expression in these interneurons via viral vector delivery was sufficient to rescue hippocampal-dependent memory deficits in HD mice.

Conclusion: This study suggests that impaired CB1R function in hippocampal GABAergic interneurons contributes to memory dysfunction in HD.