Entamoeba histolytica Infection and Secreted Proteins Proteolytically Damage Enteric Neurons

Abstract

The enteric protozoan parasite Entamoeba histolytica causes amebic colitis through disruption of the mucus layer, followed by binding to and destruction of epithelial cells. However, it is not known whether ameba infections or ameba components can directly affect the enteric nervous system. Analysis of mucosal innervations in the mouse model of cecal amebiasis showed that axon density was diminished to less than 25% of control. To determine whether amebas directly contributed to axon loss, we tested the effect of either E. histolytica secreted products (Eh-SEC) or soluble components (Eh-SOL) to an established coculture model of myenteric neurons, glia, and smooth muscle cells. Neuronal survival and axonal degeneration were measured after 48 h of exposure to graded doses of Eh-SEC or Eh-SOL (10 to 80 g/ml). The addition of 80 g of either component/ml decreased the neuron number by 30%, whereas the axon number was decreased by 50%. Cytotoxicity was specific to the neuronal population, since the glial and smooth muscle cell number remained similar to that of the control, and was completely abrogated by prior heat denaturation. Neuronal damage was partially prevented by the cysteine protease inhibitor E-64, showing that a heat-labile protease was involved. E. histolytica lysates derived from amebas deficient in the major secreted protease EhCP5 caused a neurotoxicity similar to that of wild-type amebas. We conclude that E. histolytica infection and ameba protease activity can cause selective damage to enteric neurons.Entamoeba histolytica is a protozoan enteric parasite of humans that colonizes the colon, where it typically causes asymptomatic luminal infections. However, in ca. 10% of individuals, the parasite invades the mucosa to cause amoebic colitis, characterized by ulcerative lesions, diarrhea, and fever and, in severe cases can disseminate to soft organs (39). Although normally seldom fatal, the consequences of ameba infection become significant in the immunosuppressed. The mechanism of infection in the intestine is complex and involves dissolution of the mucus layer by motile trophozoites, followed by adhesion and lysis of epithelial cells and invading leukocytes (8,9).Cysteine proteases are important in the differentiation and pathogenicity of E. histolytica, and its genome contains about 50 genes coding for cysteine peptidases (36). A number of in vivo and in vitro studies have implicated cysteine protease activity as a major mechanism of cell death of infected cells, as well as degradation of the extracellular matrix and activation of the complement system (31). Although cell-cell contact is thought to be required for intestinal invasion by E. histolytica trophozoites, amebic proteins have been shown to cause cellular responses in vitro. For example, E. histolytica trophozoitesecreted products caused mucin degradation by proteolytic degradation of cysteine domains (28). In addition, incubation of secreted products and soluble proteins with cultured intestinal epithelial cells resulted in the upregulation...

Enteric Glial Cells: Recent Developments and Future Directions

“…Conversely, other pathogens (eg, Entamoeba histolytica) can elicit neurodegeneration without altering EGCs. 60 Concerning functional bowel disorders, EGC abnormalities have been detailed in 2 severe gut dysmotility disorders: slow transit constipation (STC)/colonic inertia and megacolon. STC refers to a subset of patients characterized by a marked delay of gut transit that usually does not or responds poorly to medical treatment.…”

Effect of the Leptin Receptor Q223R Polymorphism on the Host Transcriptome following Infection with Entamoeba histolytica

“…The cause of this phenomenon is likely complex and multifactorial; however, it is possible that the differences in regulation over time are due to the kinetics of E. histolytica infection. It has been previously suggested that E. histolytica establishes infection sequentially, beginning with attachment to and degradation of the mucus layer, followed by invasion and destruction of the epithelial layer, and finally invasion into the lamina propria and damage of the enteric nervous system (67)(68)(69). Thus, it is likely that at early time points during infection (i.e., at 12 h) transcriptional changes are due to superficial invasion of the mucosa, while later responses represent deeper invasion and more tissue damage.…”

SNAP-25 is abundantly expressed in enteric neuronal networks and upregulated by the neurotrophic factor GDNF

“…While the role of SNAP-25 in the CNS has been extensively studied, little data are available concerning SNAP-25 expression and localization in the human and rat ENS. Previous studies have used SNAP-25 as pan-axonal marker of the ENS in murine cecum and colon (Lourenssen et al 2010;Poli et al 2001) or to characterize membrane specialization between nerve terminals and intestinal cells of Cajal in the murine stomach (Beckett et al 2005). However, a systematic investigation of SNAP-25 in the adult ENS is still missing.…”