Infection and characterization of Toxoplasma gondii in human induced neurons from patients with brain disorders and healthy controls

Abstract

Toxoplasma gondii is a protozoan parasite capable of establishing persistent infection within the brain. Serological studies in humans have linked exposure to Toxoplasma to neuropsychiatric disorders. However, serological studies have not elucidated the related molecular mechanisms within neuronal cells. To address this question, we used human induced neuronal cells derived from peripheral fibroblasts of healthy individuals and patients with genetically-defined brain disorders (i.e. childhood-onset schizophrenia with disease-associated copy number variations). Parasite infection was characterized by differential detection of tachyzoites and tissue cysts in induced neuronal cells. This approach may aid study of molecular mechanisms underlying individual predisposition to Toxoplasma infection linked to neuropathology of brain disorders.

Keywords: Brain disorders; Cysts; Induced neuronal cells; Schizophrenia; Tachyzoites; Toxoplasma gondii.

Fig. 1

T. gondii infection in iN cells with tachyzoites. (A) Immunostaining of infected iN cells (MAP2, green) with tachyzoites (SAG1, red), the high replicative form of T. gondii. Tachyzoites were located in the soma. Nuclei were stained with DAPI (blue). Nuclei are outlined by dashed white lines. Scale bar, 10 μm. (B) Percentage tachyzoites-positive iN cells over total infected iN cells. Healthy control, circles; 16p11.2 duplication, pluses; 22q11.21 deletion, triangles. (C) Average number of tachyzoites in each iN cell. Healthy control, circles; 16p11.2 duplication, pluses; 22q11.21 deletion, triangles. A total of 118 iN cells were counted. *p<0.05.

Fig. 2

T. gondii infection in iN cells with cysts. (A) Immunostaining of infected iN cells (MAP2, green) carrying cysts (DBA, pink), the dormant form of T. gondii. Cysts in the soma pushed the nucleus (DAPI, blue) to the side. Nuclei are outlined by dashed white lines. Scale bar, 10 μm. (B) Percentage of cysts-positive iN cells. Healthy control, circles; 16p11.2 duplication, pluses; 22q11.21 deletion, triangles. (C) Average number of cysts in each iN cell. Healthy control, circles; 16p11.2 duplication, pluses; 22q11.21 deletion, triangles. A total of 149 iN cells were counted. (D) Average diameter (μm) of cysts. Healthy control, circles; 16p11.2 duplication, pluses; 22q11.21 deletion, triangles. A total of 69 cysts were measured. **p<0.01.