Degradation of Host Sphingomyelin Is Essential for Leishmania Virulence

Abstract

In eukaryotes, sphingolipids (SLs) are important membrane components and powerful signaling molecules. In Leishmania, the major group of SLs is inositol phosphorylceramide (IPC), which is common in yeast and Trypanosomatids but absent in mammals. In contrast, sphingomyelin is not synthesized by Leishmania but is abundant in mammals. In the promastigote stage in vitro, Leishmania use SL metabolism as a major pathway to produce ethanolamine (EtN), a metabolite essential for survival and differentiation from non-virulent procyclics to highly virulent metacyclics. To further probe SL metabolism, we identified a gene encoding a putative neutral sphingomyelinase (SMase) and/or IPC hydrolase (IPCase), designated ISCL (Inositol phosphoSphingolipid phospholipase C-Like). Despite the lack of sphingomyelin synthesis, L. major promastigotes exhibited a potent SMase activity which was abolished upon deletion of ISCL, and increased following over-expression by episomal complementation. ISCL-dependent activity with sphingomyelin was about 20 fold greater than that seen with IPC. Null mutants of ISCL (iscl−) showed modest accumulation of IPC, but grew and differentiated normally in vitro. Interestingly, iscl− mutants did not induce lesion pathology in the susceptible BALB/c mice, yet persisted indefinitely at low levels at the site of infection. Notably, the acute virulence of iscl− was completely restored by the expression of ISCL or heterologous mammalian or fungal SMases, but not by fungal proteins exhibiting only IPCase activity. Together, these findings strongly suggest that degradation of host-derived sphingomyelin plays a pivotal role in the proliferation of Leishmania in mammalian hosts and the manifestation of acute disease pathology.

A plate-based assay system for analyses and screening of the Leishmania major inositol phosphorylceramide synthase

“…IPC synthase activity is evident in both the insect and mammalian stages of the L. major lifecycle, however in the intra-macrophage form the parasite is predicted to scavenge host cell ceramide for use as substrate by LmjIPCS (Zhang, et al 2005;Zhang, et al 2009). …”

Two Major Inositol Transporters and Their Role in Cryptococcal Virulence

“…Enzymes involved in sphingolipid biosynthesis and degradation pathways, such as inositol-phosphoryl ceramide synthase 1 (Ipc1) (35) and inositol phosphosphingolipid-phospholipase C1 (Isc1) (53), have been found to promote pathogenicity in C. neoformans. The importance of sphingolipids for pathogenicity has also been recognized in some parasitic pathogens, including Leishmania and Trypanosoma species, and related enzymes have been proposed as potential drug targets (36,37,45,60,67). The diacyglycerol (DAG)-protein kinase C1 (Pkc1) signaling pathway is critical for virulence factor production and pathogenicity in C. neoformans (18,19,24,25).…”

Sphingolipid Degradation by Leishmania major Is Required for Its Resistance to Acidic pH in the Mammalian Host

“…Despite their lack of sphingomyelin synthesis, Leishmania parasites possess a potent neutral sphingomyelinase (SMase) called inositol phosphosphingolipid phospholipase C-like (ISCL), which is responsible for the degradation of both host-derived sphingomyelin and parasite-derived IPC (35). ISCL null mutants (iscl Ϫ mutants, generated from wild-type [WT] L. major) had only minor defects during the promastigote stage in culture but completely failed to multiply or cause disease in susceptible BALB/c mice (35). Importantly, this deficiency can be corrected only by other SMases and not IPC hydrolases (IPCases), suggesting that the degradation of host-derived sphingomyelin (not parasite-synthesized IPC) is essential for Leishmania growth in mammals (35).…”

“…ISCL null mutants (iscl Ϫ mutants, generated from wild-type [WT] L. major) had only minor defects during the promastigote stage in culture but completely failed to multiply or cause disease in susceptible BALB/c mice (35). Importantly, this deficiency can be corrected only by other SMases and not IPC hydrolases (IPCases), suggesting that the degradation of host-derived sphingomyelin (not parasite-synthesized IPC) is essential for Leishmania growth in mammals (35).…”

“…Because ISCL is localized in mitochondria during the promastigote stage (35), it may play a role in respiration or energy production under low-sugar conditions (such as late stationary phase in culture or inside the phagolysosome of macrophages). Alternatively, the degradation of host sphingomyelin may be important for the uptake of nutrients or the adaptation to hostile conditions in the mammalian host.…”