Genome-wide Transcriptome Analysis And MicroRNA Markers In Hosts Infected With Toxoplasma Gondii

Toxoplasma gondii （T. gondii） is an obligatory intracellular parasite thatcauses diverse pathological effects in humans and other warm-blooded vertebrates. T.gondii has an unusual clonal population structure which exists with limited geneticdiversity but belongs to three distinct clonal lineages and displays markedly differentlevels of virulence in mice. Type I strain, such as RH strain, is considered as themost virulent strain in mice, and it has been frequently found in individuals at risk ofatypical ocular toxoplasmosis. Type II strain, like ME49strain is less pathogenicwith lower LD50value than that of RH strain and this strain has been found in themajority of human infection. Type III strain is rarely found in humans, but thereason is unclear. The investigation showed that more than90%of the patientssuffered from systemic toxoplasmosis died of toxoplasmic encephalitis. Manyresearchers have established animal model to explore the pathogenesis oftoxoplasmic encephalitis. Microarray represents the first generation of analyticaltools with the capacity of global gene expression profiling in both pathogendevelopment and host-pathogen interactions. It has been extensively used to identifyalterations in gene expression of bacterial and viral infection. Microarray has alsobeen used to investigate gene expression of parasites such as Eimeria maxima andPlasmodium falciparum. However, all these studies were performed with cell linesinfected by T. gondii, whereas little is known about changes in hosts in vivo.Furthermore, several studies have indicated that parasite infection in the host neuralcells may cause behavioral alterations, but no conclusive evidence has beenidentified. More studies are still necessary in order to increase our understanding ofhost–parasite interactions in T. gondii infection.In this study, we systematically analyzed the transcriptomes in both brain tissues and peripheral lymphocytes in BALB/c mice infected with Type I (RH strain)and II (ME49strain) T. gondii respectively. Total RNA of brain tissues andperipheral lymphocytes of BALB/c mice infected with RH and ME49strain T.gondii as well as that of healthy mice were purified and converted to cRNA withincorporated Cy3. The labeled cRNA probes were hybridized to the Whole MouseGenome Microarray. The impact of parasite infection on gene expression in bothbrain tissues and peripheral lymphocytes were analyzed. Differentially expressedgenes were revalidated with real-time quantitative reverse transcriptase-polymerasechain reaction (Q-PCR). Data indicated that the genes associated with immunitywere up-regulated after infection by the two parasite strains, but significantup-regulation was observed in both brain tissues and peripheral lymphocytes of miceinfected with ME49strain compared to that infected by RH strain. The pathwaysrelated to pathogenesis of the nervous system were more significantly up-regulatedin mice infected with RH strain. Genetically distinct T. gondii strains showed cleardifferences in modulation of host pathophysiological and immunological responsesin both brain tissues and peripheral lymphocytes. It was likely that some of the hostresponses to T. gondii infection were universal, but the immune response and CNSreaction were in a strain-specific manner.Toxoplasmosis caused by T. gondii is a worldwide intracellular parasitic diseasethat varies from Asian, Africa, South America to Europe. Detection of early-stagetoxoplasmosis is a key measure to reduce toxoplasmosis-related health damage. Theparasite can cause severe disease in immunocompromised patients and mothersduring pregnancy. Toxoplasmosis may cause serious consequences for a new bornbaby, such as hearing and sight impairment, neurological symptoms. Early treatmentof pregnant women could reduce the incidence of sequelae in infected infants.Therefore, an ideal method with high specificity and sensitivity for diagnosis oftoxoplasmosis has been asked for urgently. microRNAs (miRNAs) are21-25nucleotides noncoding RNA molecules that could play important roles in physiological and pathologic processes. Recently, it has been reported that miRNAsare stably detectable in plasma. It has been confirmed that plasma miRNAs werediagnosis biomarkers for human cancer. But to our knowledge, there is no report onthe role of circulating miRNAs in the plasma of host infected with T. gondii.In this study, real-time PCR array was applied to measure414miRNAs fromplasma of mice infected by T. gondii. We focused on mmu-miR-712-3p,mmu-miR-511-5p and mmu-miR-217-5p, which were detected abundantly in miceinfected with T. gondii. Quantitative analysis of these miRNAs in a large set plasmaof mice, rats and human showed that mmu-miR-712-3p, mmu-miR-511-5p andmmu-miR-217-5p were potentially useful for diagnosis with a satisfactory degree ofsensitivity and specificity. In conclusion, plasma miR-712-3p, miR-511-5p andmiR-217-5p appear to be novel biomarkers for detection of toxoplasmosis. Our datamay serve as basis for further research to predict the clinical toxoplasmosis.