Neospora caninum infection activated autophagy of caprine endometrial epithelial cells via mTOR signaling

Abstract

Neosporosis, caused by infection with the protozoan parasite Neospora caninum, is one of the main causes of abortion in cattle and small ruminants (e.g., goats), negatively influencing animal health and production costs. The uterus is an adhesion organ of placenta that is important for pregnancy and embryonic development. However, the underlying molecular pathogenic mechanisms of N. caninum in the uterus are still unclear. Autophagy regulates innate and adaptive immunity for eliminating pathogens by xenophagy, while pathogens can manipulate autophagy to facilitate their propagation. To study the role of host cell autophagy during N. caninum infection, a N. caninum infection model in caprine endometrial epithelial cells (EECs) was successfully established. In this in vitro model, N. caninum infection increased the expression of LC3-II (a standard marker for autophagosomes) from 6 h post infection (pi) to 48 h pi and the number of autophagosomes in caprine EECs at 48 h pi. Expression of p62 protein (a classical receptor of autophagy) levels were significantly decreased (P < 0.05) in caprine EECs infected with N. caninum tachyzoites at both 24 h pi and 48 h pi. Enhanced autophagic flux was also detected at 48 h pi in caprine EECs infected with N. caninum tachyzoites by transfecting Ad-mCherry-GFP-LC3B recombinant adenovirus. Treatments using a mechanistic target of rapamycin (mTOR)-specific inhibitor (rapamycin) and an autophagy inhibitor (chloroquine) indicated that cell autophagy induced by N. caninum infection promoted the intracellular propagation of parasite tachyzoites. Further studies showed that N. caninum infection induced autophagy through inhibition of mTOR phosphorylation. To the best of our current knowledge, this is the first study to reveal the role of autophagy during N. caninum infection in caprine EECs, and the findings provided significant information for uncovering mechanisms of abortion and pathogenicity caused by N. caninum infection.

Keywords: Autophagy; Caprine endometrial epithelial cells; Mechanistic target of rapamycin; Neospora caninum; Propagation of parasite.