# A new mechanism regulating microglial NLRP3 inflammasome: FMR1 mediates NLRP3 mRNA stability

## TL;DR

This study shows that FMR1 reduces NLRP3 inflammasome activity in microglia, which could help treat multiple sclerosis by lowering harmful inflammation.

## Contribution

FMR1 is identified as a novel regulator of NLRP3 mRNA stability in microglia, offering a new therapeutic target for MS.

## Key findings

- FMR1 overexpression in EAE mice reduced microglial activation and NLRP3 expression.
- FMR1 binds to NLRP3 mRNA, causing its destabilization and suppressing NLRP3 protein levels.
- FMR1 inhibits NLRP3 inflammasome activation, reducing neuroinflammation in MS models.

## Abstract

The NLRP3 inflammasome drives chronic inflammation and contributes to the pathogenesis of multiple sclerosis (MS). This study aimed to elucidate a novel post-transcriptional regulatory mechanism controlling NLRP3 expression in microglia under lipopolysaccharide (LPS) stimulation.

The experimental autoimmune encephalomyelitis (EAE) mouse model of MS was established and divided into four groups: Sham, EAE, EAE + Lv-con (control lentivirus), and EAE + Lv-FMR1 (FMR1-overexpressing lentivirus). BV2 microglial cells were stimulated with LPS and adenosine triphosphate (ATP). mRNA and protein levels were assessed by qPCR, western blot, immunofluorescence, and immunohistochemistry. Caspase-1 activity and IL-1β/IL-18 levels were quantified using commercial assay kits. RNA-binding proteins (RBPs) interacting with NLRP3 mRNA were identified by RNA pull-down combined with mass spectrometry. NLRP3 mRNA stability was analyzed using Actinomycin D.

NLRP3 inflammasome activation was confirmed in the spinal cords of EAE mice and in LPS/ATP-stimulated BV2 cells. Lentivirus-mediated overexpression of FMR1 in EAE mice attenuated microglial activation (reduced IBA-1) and decreased NLRP3 expression compared to the EAE + Lv-con control group. Immunohistochemistry confirmed reduced caspase-1 deposition in the EAE + Lv-FMR1 group. Mechanistically, FMR1 directly interacted with the 3’ untranslated region (3’UTR) of NLRP3 mRNA in LPS/ATP-treated BV2 cells, leading to mRNA destabilization and consequent suppression of NLRP3 protein expression. Functionally, FMR1 inhibited NLRP3 inflammasome activation by downregulating NLRP3.

FMR1 suppresses NLRP3 inflammasome activation in both EAE mice and microglial cell models by destabilizing NLRP3 mRNA. This suggests that FMR1 possesses therapeutic potential for MS by dually regulating neuroinflammation and NLRP3-driven pathology.