Abstract
The retina is the primary site of Toxoplasma gondii infection in the eye, and choroidal neovascularization in ocular toxoplasmosis is one of the most important causes of visual impairment. Vascular endothelial growth factor (VEGF) is one of the key regulators of blood vessel development, however, little is known about the mechanisms of T. gondii-induced VEGF production in ocular toxoplasmosis. Here, we investigate the effect of T. gondii on VEGF production regulation in human retinal pigment epithelium ARPE-19 cells and attempted to unveil the underlying mechanism of this event by focusing on the interaction between parasite and the selected host intracellular signaling pathways. T. gondii infection increased the expression of VEGF mRNA and protein in ARPE-19 cells in parasite burden- and infection time-dependent manner. The proportional increase of VEGF upstream regulators, HIF-1α and HO-1, was also observed. T. gondii induced the activation of host p-AKT, p-ERK1/2, and p-p38 MAPK in ARPE-19 cells in a parasite-burden dependent manner. However, VEGF expression decreased after the pre-treatment with PI3K inhibitors (LY294002 and GDC-0941), ERK1/2 inhibitor (PD098059), and p38 MAPK inhibitor (SB203580), but not JNK inhibitor (SP600125), in a dose-dependent manner. The anti-VEGF agent bevacizumab or VEGF siRNA transfection prominently inhibited the activation of p-AKT and p-ERK1/2, but not p-p38 MAPK and JNK1/2 in T. gondii-infected ARPE-19 cells. Bevacizumab treatment or VEGF siRNA transfection significantly inhibited the proliferation of T. gondii tachyzoites in the host cell, dose-dependently, but not invasion of parasites. VEGF-receptor 2 (VEGF-R2) antagonist, SU5416, attenuated VEGF production and tachyzoite proliferation in T. gondii-infected ARPE-19 cells in a dose-dependent manner. Collectively, T. gondii prominently induces VEGF production in ARPE-19 cells, and VEGF and AKT/ERK1/2 signaling pathways mutually regulate each other in T. gondii-infected ARPE-19 cells, but not p38 MAPK and JNK1/2 signaling pathways. VEGF and VEGF-R2 control the parasite proliferation in T. gondii-infected ARPE-19 cells. From this study, we revealed the putative mechanisms for VEGF induction as well as the existence of positive feedback between VEGF and PI3K/MAPK signaling pathways in T. gondii-infected retinal pigment epithelium.
Highlights
Toxoplasma gondii is an obligate intracellular protozoan parasite that infects one-third of the world’s population (RobertGangneux and Dard, 2012)
The primary antibodies against phosphorylated ERK1/2, total ERK1/2 (ERK1/2), p-JNK1/2, JNK1/2, p-p38 MAPK, p38 MAPK, phosphospecific AKT (p-AKT), total AKT (AKT), hypoxia-inducible factor-1α (HIF-1α) and heme oxygenase-1 (HO-1) were purchased from Cell Signaling Technology Inc. (Danvers, MA)
When ARPE-19 cells were infected with T. gondii at an multiplicity of infection (MOI) of 1, 5, and 10 for 24 h, vascular endothelial growth factor (VEGF) mRNA levels were significantly increased in a parasite dose-dependent manner (Figure 1B)
Summary
Toxoplasma gondii is an obligate intracellular protozoan parasite that infects one-third of the world’s population (RobertGangneux and Dard, 2012). Almost 80–90% of primary T. gondii infections are asymptomatic in immunocompetent individuals (Halonen and Weiss, 2013); toxoplasmic retinochoroiditis is a progressive, recurring disease that can cause severe morbidity (Commodaro et al, 2009). The retina is the primary site of T. gondii infection in the eye, and choroidal neovascularization in ocular toxoplasmosis is one of the most important causes of visual impairment (Commodaro et al, 2009). VEGF represents a growth factor with important pro-angiogenic activity, having a mitogenic and an anti-apoptotic effect on endothelial cells, increasing the vascular permeability, promoting cell migration, and so on (Ferrara, 2004; Melincovici et al, 2018; Apte et al, 2019). There is insufficient information regarding VEGF expression in T. gondiiinfected retina
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
