impairs CX3CL1/fractalkine shedding from mouse cortical neurons, leading to microglia activation.

UNLABELLED

Toxoplasmosis is caused by infection with and is one of the most prevalent food-borne parasitic disease worldwide. disseminates through the host organism and forms a latency-specific structure called bradyzoite cysts, found primarily in muscle and neuronal cells. In mice, Toxoplasma leads to sustained brain microvascular abnormalities, including capillary rarefaction, microglial activation, and blood-brain barrier (BBB) breakdown, resulting in synaptic and neuronal loss, behavioral and cognitive damages. We hypothesized that cyst-bearing neurons could signal distinct classes of molecules that would orchestrate neurovascular and neuroinflammatory processes. Primary mouse cortical neurons were infected with (ME49 strain) tachyzoites, which, 7 days post infection, generated cysts. We determined angiogenic-regulating factors from the neuronal conditioned media (nCM) using a proteome array and found nine molecules, belonging to four main functional clusters: (i) angiogenic signaling (VEGFA); (ii) endothelial-regulating growth factors (IGFBP-2, -3, -9 and PDGF-AA), (iii) chemoattractants (CCL-2, CCL-3, and CXCL12), and (iv) fractalkine signaling (CX3CL1). The main targets were validated in neuronal culture samples and in brain cortices by ELISA, RT-qPCR, or immunoblotting. CX3CL1 secretion was reduced in infected cultures and accumulated on neuronal surface. , the CX3CL1 receptor (CX3CR1) was upregulated, whereas the CX3CL1 soluble fraction was decreased. Recombinant CX3CL1 decreased arginase-1 and increased iNOS expression in nCM-treated microglial cells, indicating that CX3CL1 polarizes microglia to a pro-resolutive state. Our data suggest that CX3CL1 plays a key role in regulating neuroinflammatory signaling in acquired Toxoplasmosis, highlighting its potential to prevent the neurocognitive damage observed in infected individuals.

IMPORTANCE

is a widespread parasite that forms latent cysts in neurons during chronic brain infection. How these infected neurons contribute to long-term brain damage is not well understood. In this study, we used a neuron-specific culture system and a mouse model to show that infection alters the release of key signaling molecules by neurons. We found that infected neurons reduce secretion of fractalkine, a molecule that normally helps keep brain immune cells (microglia) in a resting state. At the same time, infected neurons showed increased expression of inflammatory and vascular-related genes, but not always matching increases in protein levels, pointing to complex regulation. These changes may contribute to blood-brain barrier dysfunction and persistent inflammation seen in chronic infection. Our findings highlight the role of neuron-derived signals in driving -induced brain pathology and identify fractalkine as a potential target to reduce inflammation.