Abstract:

Objective To investigate the effects of Toxoplasma gondii infection on the expression of microRNA-155 (miR-155) in microglia and the role of miR-155 in the microglial activation. Methods BV-2 murine microglial cells were divided into four groups, namely, PRU infection group (infected with T. gondii PRU strain tachyzoites), miR-155 mimics group (transfected with miR-155 mimics), PRU + miR-155 inhibitor group (infection followed by miR-155 inhibitor transfection), and control group (transfection reagent only). Cellular miR-155, IL-1β, IL-12, and inducible nitric oxide synthase (iNOS) mRNA levels were detected by qPCR. Protein levels of IL-1β, IL-12, and nitric oxide (NO) in supernatants were measured by ELISA. Western blotting was performed to analyze the suppressor of cytokine signaling 1 (SOCS1) protein expression. Flow cytometry was used to assess the apoptosis in N2a neuronal cells cultured with conditioned medium prepared from each group′s supernatants. Results Compared with control group and PRU + miR-155 inhibitor group, both PRU-infected and miR-155 mimics groups showed significantly upregulated miR-155 expression, accompanied by increased IL-1β, IL-12, iNOS mRNA levels, and elevated NO production, whereas protein SOCS1 expression was markedly downregulated (all P < 0.05). Neuronal apoptosis rates in PRU-infected (22.37%±1.88%) and miR-155 mimics groups (29.87%± 0.67%) were significantly higher than those in the control group (9.84%±0.57%), yet the PRU + inhibitor group (10.91%±2.01%) showed similar apoptosis rates to the controls. Conclusion Toxoplasma gondii infection may result in upregulated miR-155 expression in the microglia, which further suppresses SOCS1 protein expression and subsequently promotes release of proinflammatory cytokines IL-1β, IL-12 and iNOS, ultimately inducing neuronal apoptosis.

Key words: Toxoplasma gondii, Microglia, miR-155, Apoptosis