Comparative transcriptomic and proteomic investigation of host cell responses during Toxoplasma gondii and Neospora caninum invasion of human astrocytes

• Main Author: Al-Twaim, Sarah
• Published: University of Liverpool 2014
• Subjects: 616.9; Q Science (General)
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.666698

Toxoplasma gondii and Neospora caninum are intracellular protozoan parasites from the phylum Apicomplexa. Both parasites share many morphological and genetic features, but have diverse host preferences. While T. gondii can infect any warm-blooded animal including humans, N. caninum does not. The basis of host preference in these two parasites is unknown, but could be due to differences in tropism to specific host cells. The discovery of differences between host cell responses could lead to a better understanding to why T. gondii can lead to disease in humans and N. caninum cannot, specifically related to infection of the CNS. To investigate the differences in host cell response, the differential expression patterns of host-cell transcripts and proteins as well as protein secretions and dopamine level during the invasion of human astrocyte (HA) cells by both Toxoplasma and Neospora were investigated. Proteomic investigations were achieved by global proteomic profiling of human astrocytes during infection using two dimensional difference gel electrophoresis (2D-DIGE) and a quantitative label-free approach. Transcriptomic investigation of infected human astrocytes was carried out using an RNA-Seq approach. A number of differences in host cell response genes/proteins were noted between Toxoplasma and Neospora infection. Transcriptome analysis revealed differential expression of host cells transcripts associated with cell adhesion and cytokine receptor interaction pathways. Differences were observed in cell adhesion molecules (such as VCAM1 and NCAM2) and chemokines (such as CCL2), which were up-regulated in T. gondii infected cells compared to N. caninum infection. Whereas up-regulation of neutrophil activation was identified in N. caninum infected cells compared to T. gondii infection. Host cell secretome analysis during infection identified significant changes in many secreted proteins such as cytokines chemokines and cell adhesion molecules (i.e. CXCL1, CXCL2, IL8 and ICAM1). This data suggested that the two parasites stimulate different host cell responses. Dopamine acts as a neurotransmitter in the brain and the induction of dopamine has been found to provoke behavioural changes in the host during infection by T. gondii. Dopamine levels were measured in dopaminergic PC-12 cells during infection by T. gondii and N. caninum through tachyzoite conversion to the bradyzoite stage. Increased levels in dopamine production was observed in dopaminergic cells infected with T. gondii, compared to no changes in cells infected with N. caninum. This result suggested that T. gondii modifies the host’s behaviour (rodents), whereas the successful vertical transmission of N. caninum in cattle has led the parasite to not need to alter changes in the host’ brain. Overall, differences were mostly observed in molecules associated with cell adhesion and cytokine receptor signalling pathway, which may suggest why T. gondii is more successful in host cell infection of the CNS compared to N. caninum. Dopamine measurements of host cells during infection has also confirmed that T. gondii induces significant production of dopamine in infected host cells compared to N. caninum infection, suggesting different modulation of the host cell between the parasites in the CNS.