Neuroprotective effects of metabotropic glutamate receptor group II and III activators against MPP(+)-induced cell death in human neuroblastoma SH-SY5Y cells: The impact of cell differentiation state

• mGluR II/III activators are neuroprotective against MPP(+)-induced toxicity.
• The neuroprotective effect of mGluR II/III activators is caspase-3 independent.
• The highest neuroprotection is mediated by mGluR8-specific ligands.
• Necrostatin-1 inhibits the protection mediated by mGluR III ligands.

Recent studies have documented that metabotropic glutamate receptors from group II and III (mGluR II/III) are a potential target in the symptomatic treatment of Parkinson's disease (PD), however, the neuroprotective effects of particular mGluR II/III subtypes in relation to PD pathology are recognized only partially. In the present study, we investigated the effect of various mGluR II/III activators in the in vitro model of PD using human neuroblastoma SH-SY5Y cell line and mitochondrial neurotoxin MPP(+). We demonstrated that all tested mGluR ligands: mGluR II agonist – LY354740, mGluR III agonist – ACPT-I, mGluR4 PAM – VU0361737, mGluR8 agonist – (S)-3,4-DCPG, mGluR8 PAM – AZ12216052 and mGluR7 allosteric agonist – AMN082 were protective against MPP(+)-evoked cell damage in undifferentiated (UN-) SH-SY5Y cells with the highest neuroprotection mediated by mGluR8-specific agents. However, in retinoic acid- differentiated (RA-) SH-SY5Y cells we found protection mediated only by mGluR8 activators. We also demonstrated the cell proliferation stimulating effect for mGluR4 and mGluR8 PAMs. Next, we showed that the protection mediated by mGluR II/III activators in UN-SH-SY5Y was not accompanied by the modulation of caspase-3 activity, however, a decrease in the number of apoptotic nuclei was found. Finally, we showed that the inhibitor of necroptosis, necrostatin-1 blocked the mGluR III-mediated protection. Altogether our comparative in vitro data add a further proof to neuroprotective effects of mGluR agonists or PAMs and point to mGluR8 as a promising target for neuroprotective interventions in PD. The results also suggest the participation of necroptosis-related molecular pathways in neuroprotective effects of mGluR III activation.