Spingolipid metabolism in a reptillian protozoan, Entamoeba invadens

Entamoeba invadens (hereinafter E. invadens ) is an anaerobic parasitic protozoan that can be found in water and soil. Although the host organisms for this parasite are snakes, lizards, and other reptile species, the parasite is morphologically identical to Entamoeba histolytica, a causative agent of human amebiasis. Entamoeba inavdens exists in two morphological forms—(1) a replicative trophozoite, and (2) a relatively dormant cyst. While the transformation of cyst to trophozoites (called excystation ) takes place in the stomach, the differentiation of trophozoites to cyst (known as encystation ), occurs in the small intestine. Unlike the cyst, a trophozoite is unable to survive outside the host and therefore must encyst to survive. Various factors in the milieu of the small intestine trigger encystation. Newly encysted cysts are then excreted from the host and infect a new a host to continue the life cycle. In recent years, sphingolipids (SLs) have emerged as important molecules in biological systems, and, in particular, these molecules are involved in regulating the encystation of a related intestinal protozoan, Giardia lamblia. Therefore, the major goal of my thesis is to examine whether SLs also play an important role in determining the growth and encystation of E. inavdens. My first hypothesis is that serine-palmitoyltransferase (SPT), a rate-limiting enzyme of SL biosynthesis, regulates the growth and encystation of E. invadens. I also hypothesize that blocking of SPT activity with a suitable small molecule inhibitor should interrupt the life cycle of this intestinal pathogen. In Specific Aim-1, I asked whether myriocin, an inhibitor of SPT, inhibits the growth of E. invadens trophozoites in culture. The goal of Aim-2 was to investigate whether the inactivation of SPT can interfere with encystation and cyst production. Briefly, I found that SPT is an important Entamoeba enzyme and that manipulating its activity by myriocin has a profound effect on its life cycle. The knowledge generated from the current study will shed light on the possible role of SLs in regulating the growth and viability of Entamoeba histolytica, a parasite that infects over 50 million people worldwide every year