In-vivo effects of knocking-down metabotropic glutamate receptor 5 in the SOD1 mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder due to loss of upper and lower motor neurons (MNs). The mechanisms of neuronal death are largely unknown, thus prejudicing the successful pharmacological treatment. One major cause for MN degeneration in ALS is represented by glutamate(Glu)-mediated excitotoxicity. We have previously reported that activation of Group I metabotropic Glu receptors (mGluR1 and mGluR5) at glutamatergic spinal cord nerve terminals produces abnormal Glu release in the widely studied SOD1 mouse model of ALS. We also demonstrated that halving mGluR1 expression in the SOD1 mouse had a positive impact on survival, disease onset, disease progression, and on a number of cellular and biochemical readouts of ALS. We generated here SOD1 mice with reduced expression of mGluR5 (SOD1Grm5) by crossing the SOD1 mutant mouse with the mGluR5 heterozigous Grm5 mouse. SOD1Grm5 mice showed prolonged survival probability and delayed pathology onset. These effects were associated to enhanced number of preserved MNs, decreased astrocyte and microglia activation, reduced cytosolic free Ca concentration, and regularization of abnormal Glu release in the spinal cord of SOD1Grm5 mice. Unexpectedly, only male SOD1Grm5 mice showed improved motor skills during disease progression vs. SOD1 mice, while SOD1Grm5 females did not. These results demonstrate that a lower constitutive level of mGluR5 has a significant positive impact in mice with ALS and support the idea that blocking Group I mGluRs may represent a potentially effective pharmacological approach to the disease.