Lipid Body Organelles within the Parasite Trypanosoma cruzi: A Role for Intracellular Arachidonic Acid Metabolism

Abstract

Most eukaryotic cells contain varying amounts of cytosolic lipidic inclusions termed lipid bodies (LBs) or lipid droplets (LDs). In mammalian cells, such as macrophages, these lipid-rich organelles are formed in response to host-pathogen interaction during infectious diseases and are sites for biosynthesis of arachidonic acid (AA)-derived inflammatory mediators (eicosanoids). Less clear are the functions of LBs in pathogenic lower eukaryotes. In this study, we demonstrated that LBs, visualized by light microscopy with different probes and transmission electron microscopy (TEM), are produced in trypomastigote forms of the parasite Trypanosoma cruzi, the causal agent of Chagas’ disease, after both host interaction and exogenous AA stimulation. Quantitative TEM revealed that LBs from amastigotes, the intracellular forms of the parasite, growing in vivo have increased size and electron-density compared to LBs from amastigotes living in vitro. AA-stimulated trypomastigotes released high amounts of prostaglandin E2 (PGE2) and showed PGE2 synthase expression. Raman spectroscopy demonstrated increased unsaturated lipid content and AA incorporation in stimulated parasites. Moreover, both Raman and MALDI mass spectroscopy revealed increased AA content in LBs purified from AA-stimulated parasites compared to LBs from unstimulated group. By using a specific technique for eicosanoid detection, we immunolocalized PGE2 within LBs from AA-stimulated trypomastigotes. Altogether, our findings demonstrate that LBs from the parasite Trypanosoma cruzi are not just lipid storage inclusions but dynamic organelles, able to respond to host interaction and inflammatory events and involved in the AA metabolism. Acting as sources of PGE2, a potent immunomodulatory lipid mediator that inhibits many aspects of innate and adaptive immunity, newly-formed parasite LBs may be implicated with the pathogen survival in its host.

Fat, fight, and beyond: The multiple roles of lipid droplets in infections and inflammation

“…In Leishmania, the presence of PLA 2 and prostaglandin F 2α synthase on parasite LDs has been identified . In addition to the presence of PGE synthase on LDs, the accumulation of arachidonic acid and PGE 2 formation on LDs was also reported in T. cruzi . The production of inflammatory mediators by parasite LDs suggests that this organelle participates in an elaborate form of evasion of the immune system, and it is even suggested that parasite LDs could be classified as a mechanism of pathogenicity …”

“…In both infections, PGE 2 production was reported as permissive to pathogens and probably downmodulate macrophage antimicrobial response . Furthermore, PGE 2 not only affects infected leukocytes but may also inhibit Th1 responses, which would favor pathogen proliferation and dissemination . Moreover, LDs in colon cancer cells are active organelles involved in PGE 2 synthesis and may have implications in the pathogenesis of adenocarcinoma of the colon …”

“…Parasite cells have their own LDs, as well as those of the host cells, and parasite LDs are dynamic structures able to respond to host interaction and inflammatory events . Moreover, parasite LDs were also reported as being a platform of compartmentalization of the eicosanoid pathway . In Leishmania, the presence of PLA 2 and prostaglandin F 2α synthase on parasite LDs has been identified .…”

Lipid droplet functions beyond energy storage

“…Inhibition of ATGL, genetically or pharmacologically, also impairs eicosanoid release in other types of immune cells, such as neutrophils [79]. In the intracellular parasites Leishmania and Trypanosoma , LDs can also act as a source of immunomodulatory prostaglandins implicated in improving the survival of the parasite within its host [80, 81]. The available evidence suggests that the enzymatically released AA is locally metabolized, as both eicosanoid precursors and eicosanoid producing enzymes have been found associated with LDs [75].…”

Gradient Temperature Raman Spectroscopy of Fatty Acids with One to Six Double Bonds Identifies Specific Carbons and Provides Systematic Three Dimensional Structures

“…While conventional Raman analysis can be useful, to first order the long-chain polyunsaturated fatty acids (LC-PUFA) appear nearly identical, with the vibrational modes of most moieties degenerate, redundant or very broad [5] [6] [7] [8] [9]. But logically this cannot be the case, because the LC-PUFA are so vastly different biochemically.…”