Neuronal TLR4 upregulation activates the cGAS-STING pathway to induce ferroptosis in EAE mice.

INTRODUCTION: Progressive neurofunctional impairment in multiple sclerosis (MS) is largely driven by neuronal damage and loss, yet the underlying molecular mechanisms remain poorly understood. This study aimed to investigate the role of neuronal Toll-like receptor 4 (TLR4) in promoting ferroptosis, an iron-dependent cell death pathway, during experimental autoimmune encephalomyelitis (EAE). METHODS: We leveraged a MOG35-55-induced EAE mouse model (n = 10 per group) alongside in vitro LPS-stimulated SH-SY5Y mono- and co-culture systems (n = 3 biological replicates) to interrogate the crosstalk between TLR4 signaling and ferroptosis. This link was comprehensively evaluated via biochemical assays, Western blotting, RT-qPCR, co-immunoprecipitation, immunofluorescence analyses, and transmission electron microscopy. Furthermore, we mechanistically dissected the underlying signaling cascades using siRNA-mediated gene silencing and co-immunoprecipitation. RESULTS: Both in vivo and in vitro models recapitulated classical ferroptosis features, including NCOA4-mediated ferritinophagy, lipid peroxidation, and iron overload. Mechanistically, we suggest that neuronal TLR4 activation may provoke the release of mitochondrial DNA into the cytosol, thereby potentially engaging the cGAS-STING axis and precipitating dysregulated iron metabolism. Observations indicate that the TLR4 signaling contributes to ferroptosis even within the complex inflammatory microenvironment of microglia-neuron co-cultures. In EAE mice, pharmacological blockade of ferroptosis via Liproxstatin-1 appeared to ameliorate clinical severity, associated with restored neuronal GPX4 expression in the brain and spinal cord, and concomitantly suppressed lipid peroxidation. DISCUSSION: This study proposes a specific TLR4-mtDNA-cGAS-STING-NCOA4 signaling cascade that may facilitate neuronal ferroptosis in EAE mice. These findings suggest a novel mechanism of neuronal injury in MS and underscore that targeting this intrinsic neuronal pathway could represent a promising therapeutic strategy to ameliorate progressive neurodegeneration.