BackgroundNeurodegenerative diseases including AD is currently one of intractable problems globally due to the insufficiency of intervention strategies. Long-term infection of Toxoplasma gondii (T. gondii) can induce cognitive impairment in hosts, which is closely implicated in the pathogenesis of neurodegenerative diseases. Aconitate decarboxylase 1 (Acod1) and its produced metabolite itaconate (termed Acod1/itaconate axis), have recently attracted extensive interests due to its anti-inflammatory role in macrophages. However, whether the axis can influence cognitive function remains unknown. MethodsA chronic T. gondii-infected mice (C57BL/6J) model was established via administration of cysts by gavage. Novel location (NL), novel object recognition (NOR), Y-maze spatial memory and nest building tests were used to evaluate the behavior performance. Transmission electron microscopy, immunofluorescence, RT-PCR, western-blotting and RNA sequencing were utilized to determine the pathological changes, neuroinflammation and transcription profile in hippocampus tissues post infection, respectively. Moreover, the protective effect of Acod1/itaconate axis in T. gondii-induced cognitive deficits was evaluated.ResultsWe found that the latent infection of the parasite impaired the cognitive function, which was assessed behaviorally by novel location (NL), novel object recognition (NOR), Y-maze spatial memory and nest building tests. RNA sequencing of hippocampus showed that the infection downregulated the expression of genes related to synaptic plasticity, transmission and cognitive behavior. To our attention, the infection robustly upregulated the expression of genes associated with pro-inflammatory responses, which was characterized by microglia activation and disorder of Acod1/itaconate axis. Interestingly, administration of dimethyl itaconate (DI, an itaconate derivative with cell membrane permeability) could significantly ameliorate the cognitive deficits induced by T. gondii, which was proved by improvement of behavior performance and synaptic ultrastructure impairment, and lower accumulation of pro-inflammatory microglia. Notably, DI administration had a potential therapeutic effect on the cognitive deficits and synaptic impairment induced by the parasitic infection.ConclusionsOverall, these findings provide a novel insight for the pathogenesis of T. gondii-related cognitive deficits in hosts, and also provide a novel clue for the potential therapeutic strategies.

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BackgroundThe phagocytic S100 protein, which mediates inflammatory responses and recruits inflammatory cells to sites of tissue damage, has long been known to be expressed in cells of myeloid origin. S100A6 belongs to the A group of the S100 protein family of Ca2+-binding proteins. Currently, the mechanism by which S100A6 mediates the inflammatory response and recruits inflammatory cells to the tissue injury site is unknown.MethodsA mouse model of carbon tetrachloride (CCl4)-induced acute liver injury (ALI) was established, and the transcriptomes of postinjury 2d and 5d liver tissues were sequenced. Enzyme-linked immunosorbent assay was used to determine the expression of inflammatory factors (TNF-α, IL-1β, IL-6, and IL-8) in the supernatant of the liver. Immunohistochemical analysis confirmed the expression of S100A6 in the liver cells. In vitro experiments proved the pro-inflammatory function of S100A6, and western blotting (WB) showed that the pathways were activated. The transwell experiment showed the infiltration of mononuclear/macrophages.ResultsWe found that S100A6 is highly expressed in liver cells during the most severe period of ALI, suggesting that it acts as an endogenous danger signal and has a pro-inflammatory function. In vitro, the mouse S100A6 recombinant protein was used to stimulate liver Kupffer cells to promote the secretion of TNF-α, IL-1β, IL-6, and IL-8. Further mechanistic experiments revealed that S100A6 acts as an endogenous danger signal to activate p-P38 and p-JNK downstream of the TLR4 and P65 pathways. Similarly, transcriptome data showed that S100A6 can activate the inflammatory response in Kuffer cells. WB revealed that S100A6 had no significant effect on cell apoptosis. To continue to explore the mechanism of monocyte/macrophage infiltration, we found that TNF-α stimulates liver cells as the main source of CCL2. TNF-α can initiate the p-P38 and p-JNK pathways of liver cells to produce CCL2, thereby recruiting the infiltration of mononuclear/macrophages. ConclusionsTaken together, S100A6 is an endogenous danger signal that mediates inflammatory responses and recruits inflammatory cells to sites of tissue damage.

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