No abstract

Autism spectrum disorders (ASDs) are associated with mutations affecting synaptic components, including GluN2B-NMDA receptors (NMDARs) and neurobeachin (NBEA). NBEA participates in biosynthetic pathways to regulate synapse receptor targeting, synaptic function, cognition, and social behavior. However, the role of NBEA-mediated transport in specific trafficking routes is unclear. Here, we highlight an additional function for NBEA in the local delivery and surface re-insertion of synaptic receptors in mouse neurons. NBEA dynamically interacts with Rab4-positive recycling endosomes, transiently enters spines in an activity-dependent manner, and regulates GluN2B-NMDAR recycling. Furthermore, we show that the microtubule growth inhibitor kinesin KIF21B constrains NBEA dynamics and is present in the NBEA-recycling endosome-NMDAR complex. Notably, Kif21b knockout decreases NMDAR surface expression and alters social behavior in mice, consistent with reported social deficits in Nbea mutants. The influence of NBEA-KIF21B interactions on GluN2B-NMDAR local recycling may be relevant to mechanisms underlying ASD etiology.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system with continuous neuronal loss. Treatment of clinical progression remains challenging due to lack of insights into inflammation-induced neurodegenerative pathways. Here, we show that an imbalance in the neuronal receptor interactome is driving glutamate excitotoxicity in neurons of MS patients and identify the MS risk–associated metabotropic glutamate receptor 8 (GRM8) as a decisive modulator. Mechanistically, GRM8 activation counteracted neuronal cAMP accumulation, thereby directly desensitizing the inositol 1,4,5-trisphosphate receptor (IP3R). This profoundly limited glutamate-induced calcium release from the endoplasmic reticulum and subsequent cell death. Notably, we found Grm8-deficient neurons to be more prone to glutamate excitotoxicity, whereas pharmacological activation of GRM8 augmented neuroprotection in mouse and human neurons as well as in a preclinical mouse model of MS. Thus, we demonstrate that GRM8 conveys neuronal resilience to CNS inflammation and is a promising neuroprotective target with broad therapeutic implications.

Neuroinflammation leads to neuronal stress responses that contribute to neuronal dysfunction and loss. However, treatments that stabilize neurons and prevent their destruction are still lacking. Here, we identify the histone methyltransferase G9a as a druggable epigenetic regulator of neuronal vulnerability to inflammation. In murine experimental autoimmune encephalomyelitis (EAE) and human multiple sclerosis (MS), we found that the G9a-catalyzed repressive epigenetic mark H3K9me2 was robustly induced by neuroinflammation. G9a activity repressed anti-ferroptotic genes, diminished intracellular glutathione levels, and triggered the iron-dependent programmed cell death pathway ferroptosis. Conversely, pharmacological treatment of EAE mice with a G9a inhibitor restored anti-ferroptotic gene expression, reduced inflammation-induced neuronal loss, and improved clinical outcome. Similarly, neuronal anti-ferroptotic gene expression was reduced in MS brain tissue and was boosted by G9a inhibition in human neuronal cultures. This study identifies G9a as a critical transcriptional enhancer of neuronal ferroptosis and potential therapeutic target to counteract inflammation-induced neurodegeneration.