Characterization of Metabolically Quiescent Leishmania Parasites in Murine Lesions Using Heavy Water Labeling
Fig 5
Lesion amastigotes utilize both salvage and de novo biosynthetic pathways to supply their fatty acid needs.
A. The maximum level of 2H-enrichment (EM1, %) in major cellular fatty acids of Prolog and Amalesion were determined after labeling for 7 days and >6 weeks, respectively. 2H-enrichment in the total plasma lipid of infected mice was also measured to determine the potential contribution of labeled host fatty acids to the parasite labeling. Note that while saturated and unsaturated C18 fatty acids are predominant fatty acids in both stages, the fatty acid composition of Amalesion differs from cultured promastigotes in containing elevated levels of C20:4 n-6, and polyunsaturated very long chain fatty acids (C22:4 n-6, C22:6 n-3) (S8 Fig.). The C:D nomenclature refers to overall chain length and number of double bonds in each fatty acid, respectively. n-3 and n-6 refers to the two major biosynthetic pathways involved in unsaturated fatty acid biosynthesis (where-3 and-6 refer to the position of double bond relative to the methyl carbon). B. Stage-specific differences in the levels of 2H-enrichment in fatty acid pools can be used to infer the contributions of de novo biosynthesis and salvage pathways. In particular, levels of 2H-enrichment in the major Amalesion C18 fatty acids, C18:1 (oleic acid) and C18:2 (linoleic acid), were appreciably higher than in host plasma, indicating that these stages are dependent on de novo biosynthesis. Conversely, the elevated levels of 2H-enrichment in C20:4 n-6 and C22:6n-3 compared to C18:1 precursor (comparable to plasma pools) indicate that these very long chain polyunsaturated fatty acids are primarily scavenged from the host cell.