Knocking down metabotropic glutamate receptor 1 improves survival and disease progression in the SOD1G93A mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease reflecting degeneration of upper and lower motoneurons (MNs). The cause of ALS and the mechanisms of neuronal death are still largely obscure, thus impairing the establishment of efficacious therapies. Glutamate (Glu)-mediated excitotoxicity plays a major role in MN degeneration in ALS. We recently demonstrated that the activation of Group I metabotropic Glu autoreceptors, belonging to both type 1 and type 5 receptors (mGluR1 and mGluR5), at glutamatergic spinal cord nerve terminals, produces excessive Glu release in mice over-expressing human superoxide-dismutase carrying the G93A point mutation (SOD1^G93A), a widely used animal model of human ALS. To establish whether these receptors are implicated in ALS, we generated mice expressing half dosage of mGluR1 in the SOD1^G93A background (SOD1^G93AGrm1^crv4/+), by crossing the SOD1^G93A mutant mouse with the Grm1^crv4/+ mouse, lacking mGluR1 because of a spontaneous recessive mutation. SOD1^G93AGrm1^crv4/+ mice showed prolonged survival probability, delayed pathology onset, slower disease progression and improved motor performances compared to SOD1^G93A mice. These effects were associated to reduction of mGluR5 expression, enhanced number of MNs, decreased astrocyte and microglia activation, normalization of metallothionein and catalase mRNA expression, reduced mitochondrial damage, and decrease of abnormal Glu release in spinal cord of SOD1^G93AGrm1^crv4/+compared to SOD1^G93A mice. These results demonstrate that a lower constitutive level of mGluR1 has a significant positive impact on mice with experimental ALS, thus providing the rationale for future pharmacological approaches to ALS by selectively blocking Group I metabotropic Glu receptors.