The m6A demethylase FTO regulates TNF-α expression in human macrophages following Toxoplasma gondii infection

Toxoplasma gondii (T. gondii) is an opportunistic parasite. After infection, macrophages finely regulate the immune response to restrict parasite proliferation. It is well-known that N6-methyladenosine (m6A) plays a critical role in fine-tuning gene expression. To investigate whether m6A modification is involved in regulating the anti-infection immune response in human macrophages against T. gondii, this study utilized T. gondii tachyzoites from the RH strain to infect human THP-1 macrophages. qPCR and ELISA results show that T. gondii infection mounted the expression of TNF-α, IL-1β, and IL-6. Transcriptomic data suggest that the infection of T. gondii induced differential gene expression in pathways associated with TNF signaling and cytokine-cytokine receptor interaction. Meanwhile, expression of m6A regulators were evaluated using qPCR and Western blotting. T. gondii infection increased the abundance of m6A demethylase FTO and methyltransferase WTAP. Joint analysis of RNA-seq and m6A-seq data was utilized for enriching differentially expressed genes (DEGs) with significantly altered m6A modifications. Intriguingly, following T. gondii infection, the m6A levels of DEGs associated with toxoplasmosis, TNF signaling pathway, and NF-κB signaling pathway were significantly different. The m6A-IP-qPCR assay further confirmed that T. gondii infection led to the decrease in the levels of m6A modification in the 3'UTR and 5'UTR regions of TNF-α mRNA. Knocking-down of FTO retarded the infection induced-decrease in the levels of m6A modification in TNF-α transcripts, accompanied by dampened immune response and uncontrolled T. gondii proliferation. Furthermore, the YTHDF2 RIP assay indicates that T. gondii infection remarkably weakened the binding of YTHDF2 to TNF-α mRNA, which could mount TNF-α expression by inhibiting the degradation of TNF-α mRNA. Overall, these findings suggest that m6A plays a role in the T. gondii infection-induced immune response in human macrophages, uncovering a new molecular mechanism for the regulation of TNF-α expression from an epitranscriptomic aspect.