Microglial NLRP3 inflammasome activation leads to perineuronal net loss in cocultured neurons

Background: Microglia play a crucial role in maintaining the health of the central nervous system (CNS) through synaptic pruning, debris clearance, and pathogen elimination; however, sustained microglial inflammation can lead to neuronal damage. The NLRP3 inflammasome, a key regulator of inflammatory responses, has been implicated in various CNS diseases. Perineuronal nets (PNNs) are specialized structures that encase neuron somas, protect neurons from oxidative stress, and stabilize synaptic connections. While inflammatory microglia can degrade PNNs, the specific role of inflammasomes in this degradation process remains unclear.

Methods and results: To investigate the role of inflammasomes in degradation of PNNs, neurons were derived from the murine Neuro-2a cell line using retinoic acid. Subsequently, we induced the NLRP3 inflammasome in the murine N9 microglial cell line via exposure to lipopolysaccharide and ATP. The effect of NLRP3 activation on degradation of PNNs was examined by coculturing neurons and microglia with and without NLRP3 inhibition for 24 h. PNNs were quantified using immunofluorescence staining with Wisteria floribunda agglutinin and neurocan antibodies, both of which bind to PNNs. Our findings demonstrate that coculture with NLRP3-activated microglia reduces the percentage of WFA- and neurocan-positive neurons whereas the inhibition of NLRP3 reverses this effect.

Conclusions: Our findings highlight the significant role of the NLRP3 inflammasome in the degradation of PNNs in inflammatory states. Moreover, our research suggests that targeting the NLRP3 inflammasome could protect PNN-positive neurons from the damaging effects of inflammation. These findings might provide insight into the inflammatory mechanisms underlying loss of PNNs.

Clinical trial number: Not applicable.

Inflammation; Microglia; Neuroinflammation; Neuron; Perineuronal net.