Inhibition of metabotropic glutamate receptor 5 induces cellular stress through pertussis toxin-sensitive Gi-proteins in murine BV-2 microglia cells

Microglia are critical immune cells in the central nervous system, and their dysregulation is linked to numerous neurodegenerative conditions. Previous research established that activating the metabotropic glutamate receptor 5 (mGluR5) with agonists like CHPG can dampen neuroinflammation and oxidative stress. However, the consequences of inhibiting mGluR5 in these cells remained largely unexplored. This study aimed to determine if the mGluR5 antagonist MPEP induces inflammatory responses and cellular stress in microglia.

The researchers utilized BV-2 murine microglia, a common cell model for studying neuroinflammatory pathways. They treated these cells with MPEP and employed high-content imaging, qPCR, ELISA, and Western blotting to monitor indicators of cellular health. Key metrics included reactive oxygen species (ROS) levels, mitochondrial mass, inflammatory mediator expression (IL-6, iNOS), and markers of endoplasmic reticulum (ER) stress (CHOP, GRP78). They also used various chemical inhibitors and chelators to systematically dissect the signaling cascade responsible for the observed stress.

Treatment with the mGluR5 inhibitor MPEP induced a marked increase in oxidative stress, mitochondrial dysfunction, and the production of inflammatory cytokines. Mechanistically, this stress response was preceded by a rapid release of calcium from the endoplasmic reticulum. The researchers discovered that this calcium efflux was mediated by Gi-proteins and the activation of phospholipase C (PLC). Inhibiting this pathway with pertussis toxin (a Gi-protein inhibitor) or U-73122 (a PLC inhibitor) effectively prevented the MPEP-induced cellular stress and inflammation, confirming that mGluR5 antagonism can paradoxically promote pro-inflammatory states through this specific signaling route.