An investigation of the role of lysosomes in amebic trogocytosis and cell killing

Entamoeba histolytica is a protozoan parasite that is prevalent in low-income countries where it causes potentially fatal diarrhea, dysentery and liver abscesses. The parasite ingests fragments of live host cells in a nibbling-like process termed amebic trogocytosis. Amebic trogocytosis is required for cell killing and contributes to tissue invasion, which is a hallmark of invasive amebic colitis. Trogocytosis has been observed in other organisms, however little is known about the mechanism in any system. In the current work, we show that acidified lysosomes are required for amebic trogocytosis and cell killing. Interfering with lysosome acidification using ammonium chloride, a weak base, or concanamycin A, a vacuolar H+ ATPase inhibitor, decreased amebic trogocytosis and amebic cytotoxicity. Our data suggest that the inhibitors do not impair the ingestion of an initial fragment, but rather block continued trogocytosis and the ingestion of multiple fragments. The acidification inhibitors also decreased phagocytosis, but not fluid-phase endocytosis. These data suggest that amebic lysosomes play a crucial role in amebic trogocytosis, phagocytosis and cell killing.

I found that the disruption of lysosomal digestion by the inhibition of amebic cysteine proteases significantly reduced both amebic trogocytosis and cell killing. These observations provide further evidence that amebic lysosomes play an important role amebic trogocytosis and cell killing. They also suggest that amebic lysosomes are crucial for trogocytosis because they are required for efficient degradation of ingested material. Additionally, I observed that there was a significant decrease in the amount of Gal/GalNAc lectin on the surface of inhibitor-treated parasite compared to control parasites following trogocytosis, implicating amebic lysosomes in the rapid recycling of internalized amebic surface receptors. Interestingly, I found that impairing lysosomal digestion through the inhibition of amebic cysteine proteases did not impact phagocytosis, suggesting that there may be distinct lysosomal functions required for amebic trogocytosis. This work will provide a foundation for future studies to understand the mechanism of amebic trogocytosis.