Avirulence and lysozyme secretion in Paneth cells after infection of BALB/c mice with oocysts of Toxoplasma gondii strains TgCatCHn2 (ToxoDB#17) and TgCatCHn4 (ToxoDB#9).

Toxoplasma gondii has a complex life cycle and pathogenic mechanisms. Acute T. gondii infections in mice often result in death, whereas in chronic infections, the parasites may persist in the host tissues as intraneuronal or intramuscular cysts. However, the virulence of T. gondii strains in mice varies with its genetic background. The present study investigated the pathogenicity and pathological lesions of two T. gondii isolates from China: namely, TgCatCHn2 (ToxoDB#17) and TgCatCHn4 (ToxoDB#9). The virulent (ToxoDB#216) and avirulent (VEG) strains were employed as controls. Toxoplasmosis was induced by inoculating BALB/c mice with oocysts of the strains of T. gondii VEG, ToxoDB#216, TgCatCHn2 (ToxoDB#17), and TgCatCHn4 (ToxoDB#9), respectively. As a result, one oocyst of ToxoDB#216 could kill a mouse within 10 days post inoculation (DPI). The survival time of the mice for T. gondii TgCatCHn2 and TgCatCHn4 was >60 DPI for 106/mL oocysts, but this concentration (106/mL oocysts) of VEG strain could kill mice within 11 DPI. Compared with the strains of T. gondii ToxoDB#216 and VEG, the lesions in the small intestines of the strains of TgCatCHn2- and TgCatCHn4-infected mice were significantly smaller (P < 0.01). The positive area of T. gondii antigen in the ileum of mice infected with the strains of T. gondii VEG, TgCatCHn2 and TgCatCHn4 were significantly lower than that T. gondii ToxoDB#216 at 8 DPI (P < 0.01). Paneth cells (PCs) in the small intestines was eliminated by ToxoDB#216 (5-6 DPI) (P < 0.05). The strains of T. gondii TgCatCHn2-, TgCatCHn4- and VEG-infected mice, the number of PCs and granules decreased in the intestines, compared to T. gondii free mice, but the difference was not significant (8 DPI, P > 0.05). However, the granules in the PCs showed negative lysozyme expression in the intestines of mice infected with T. gondii TgCatCHn2 and TgCatCHn4. Thus, T. gondii strains of TgCatCHn2 (ToxoDB#17) and TgCatCHn4 (ToxoDB#9) were avirulent strains, they triggered an inhibition of lysozyme expression in the granules of PCs of the mouse intestine. These effects may in turn lead to intestinal dysbiosis, which may be related to further parasitic invasion of the intestines. The findings of the present study further expand the spectrum of the pathogenic features of various Chinese isolates of T. gondii.

Antibody Detection, Isolation, Genotyping, and Virulence of Toxoplasma gondii in Captive Felids from China.

The felids are the only definitive hosts of Toxoplasma gondii, which could excrete oocysts into the environment and provide an infection source for toxoplasmosis in various warm-blooded animal species, particularly the captive felids that live close to human communities. The infection rate of the captive felids is a perfect standard in detecting the presence of Toxoplasma gondii oocysts in the environment. In this study, sera or tissue samples from zoo (1 young tiger, 2 adult tigers, 6 young lions), farm (10 masked palm civets), and pet hospital (28 cats) from Henan Province (China) were collected. The sera (n = 47) were tested for immunoglobulin G (IgG) antibodies against T. gondii by using modified agglutination test (MAT), whereas the hearts tissue (n = 40) were bioassayed in mice to isolate T. gondii strains. The genotype was distinguished by using PCR-RFLP of 10 loci (SAG1, SAG2, SAG3, GRA6, BTUB, L358, c22-8, PK1, c29-2, and Apico). The detection rate for the T. gondii antibody in captive felids was 21.3% (10/47). One viable T. gondii strain (TgCatCHn4) was obtained from a cat heart tissue, and its genotype was ToxoDB#9. The oocysts of ToxoDB#9 were collected from a T. gondii-free cat. The virulence of TgCatCHn4 was low and no cysts were detected in the brain of mice at 60 days post-inoculation. The finding of the present study suggested a widespread exposure of T. gondii for felids in Henan Province of central China, particularly those from the zoological gardens and homes. ToxoDB#9 was the predominant strain in China. Preventive measures against T. gondii oocyst contamination of various components of the environment should thus be implemented, including providing pre-frozen meat, well-cooked cat food, cleaned fruits and vegetables, monitoring birds and rodents, inactive T. gondii oocysts in felids feces, and proper hygiene.

G protein coupled receptor 50 promotes self-renewal and neuronal differentiation of embryonic neural progenitor cells through regulation of notch and wnt/ß-catenin signalings.

G protein-coupled receptor 50 (GPR50), a risk factor for major depressive disorder and bipolar affective disorder, is expressed in both the developmental and adult brain. However, the function of GPR50 in the brain remains unknown. We here show GPR50 is expressed by neural progenitor cells (NPCs) in the ventricular zone of embryonic brain. Knockdown of GPR50 with a small interference RNA (siRNA) decreased self-renewal and neuronal differentiation, but not glial differentiation of NPCs. Moreover, overexpression of either full-length GPR50 or the intracellular domain of GPR50, rather than the truncated GPR50 in which the intracellular domain is deleted in, increased neuronal differentiation, indicating that GPR50 promotes neuronal differentiation of NPCs in an intracellular domain-dependent manner. We further described that the transcriptional activity of the intracellular domain of notch on Hes1 gene was repressed by overexpression of GPR50. In addition, decreased levels of transcription factor 7-like 2 (TCF7L2) mRNA was observed in GPR50 siRNA-transfected NPCs, suggesting that knockdown of GPR50 impairs wnt/ß-catenin signaling. Moreover, the mRNA levels of neurogenin (Ngn) 1, Ngn2 and cyclin D1, the target genes of notch and wnt/ß-catenin signalings, in NPCs were reduced by knockdown of GPR50. Therefore, GPR50 promotes self-renewal and neuronal differentiation of NPCs possibly through regulation of notch and wnt/ß-catenin signalings.