Toxoplasma gondii Proliferation Require Down-Regulation of Host Nox4 Expression via Activation of PI3 Kinase/Akt Signaling Pathway

PLoS One. 2013 Jun 18;8(6):e66306. doi: 10.1371/journal.pone.0066306. Print 2013.

Abstract

Toxoplasma gondii results in ocular toxoplasmosis characterized by chorioretinitis with inflammation and necrosis of the neuroretina, pigment epithelium, and choroid. After invasion, T. gondii replicates in host cells before cell lysis, which releases the parasites to invade neighboring cells to repeat the life cycle and establish a chronic retinal infection. The mechanism by which T. gondii avoids innate immune defense, however, is unknown. Therefore, we determined whether PI3K/Akt signaling pathway activation by T. gondii is essential for subversion of host immunity and parasite proliferation. T. gondii infection or excretory/secretory protein (ESP) treatment of the human retinal pigment epithelium cell line ARPE-19 induced Akt phosphorylation, and PI3K inhibitors effectively reduced T. gondii proliferation in host cells. Furthermore, T. gondii reduced intracellular reactive oxygen species (ROS) while activating the PI3K/Akt signaling pathway. While searching for the main source of these ROS, we found that NADPH oxidase 4 (Nox4) was prominently expressed in ARPE-19 cells, and this expression was significantly reduced by T. gondii infection or ESP treatment along with decreased ROS levels. In addition, artificial reduction of host Nox4 levels with specific siRNA increased replication of intracellular T. gondii compared to controls. Interestingly, these T. gondii-induced effects were reversed by PI3K inhibitors, suggesting that activation of the PI3K/Akt signaling pathway is important for suppression of both Nox4 expression and ROS levels by T. gondii infection. These findings demonstrate that manipulation of the host PI3K/Akt signaling pathway and Nox4 gene expression is a novel mechanism involved in T. gondii survival and proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cell Proliferation
  • Down-Regulation*
  • Enzyme Activation
  • Humans
  • NADPH Oxidase 4
  • NADPH Oxidases / genetics
  • NADPH Oxidases / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Proto-Oncogene Proteins c-akt / metabolism*
  • RNA, Small Interfering / genetics
  • Reactive Oxygen Species / metabolism
  • Signal Transduction*
  • Toxoplasma / cytology*
  • Toxoplasma / enzymology
  • Toxoplasma / metabolism

Substances

  • RNA, Small Interfering
  • Reactive Oxygen Species
  • NADPH Oxidase 4
  • NADPH Oxidases
  • NOX4 protein, human
  • Phosphatidylinositol 3-Kinases
  • Proto-Oncogene Proteins c-akt

Grant support

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology (2007-0054932, 2009-0068747, 2011-0006228, 2011-0023501) and Korea Health Technology Research & Development Project, Ministry of Health & Welfare, Republic of Korea (A100876-1102-0000100). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.