Inositol phosphorylceramide synthase null Leishmania are viable and virulent in animal infections where salvage of host sphingomyelin predominates

Many pathogens synthesize inositol phosphorylceramide (IPC) as the major sphingolipid (SL), differing from the mammalian host where sphingomyelin (SM) or more complex SLs predominate. The divergence between IPC synthase and mammalian SL synthases has prompted interest as a potential drug target. However, in the trypanosomatid protozoan Leishmania, cultured insect stage promastigotes lack de novo SL synthesis (Aspt2-) and SLs survive and remain virulent, as infective amastigotes salvage host SLs and continue to produce IPC. To further understand the role of IPC, we generated null IPCS mutants in Leishmania major (Aipcs-). Unexpectedly and unlike fungi where IPCS is essential, Aipcs- was remarkably normal in culture and highly virulent in mouse infections. Both IPCS activity and IPC were absent in Aipcs- promastigotes and amastigotes, arguing against an alternative route of IPC syn-thesis. Notably, salvaged mammalian SM was highly abundant in purified amastigotes from both WT and Aipcs-, and salvaged SLs could be further metabolized into IPC. SM was about 7-fold more abundant than IPC in WT amastigotes, estab-lishing that SM is the dominant amastigote SL, thereby rendering IPC partially redundant. These data suggest that SM salvage likely plays key roles in the survival and virulence of both WT and Aipcs- parasites in the infected host, confirma-tion of which will require the development of methods or mutants deficient in host SL/SM uptake in the future. Our findings call into question the suitability of IPCS as a target for chemotherapy, instead suggesting that approaches targeting SM/SL uptake or catabolism may warrant further emphasis.

Automated summary

Leishmania parasites can survive without synthesizing sphingolipids themselves, instead salvaging and metabolizing sphingolipids from the host to produce inositol phosphorylceramide (IPC). This calls into question the suitability of targeting IPC synthesis for chemotherapy and suggests that targeting the salvage and catabolism of host sphingolipids may be a more effective approach.