sphingosine-kinase and Cryptococcosis

Cryptococcus neoformans is a fungal pathogen that causes pulmonary infections, which may progress into life-threatening meningitis. In commonly used mouse models of C. neoformans infections, fungal cells are not contained in the lungs, resulting in dissemination to the brain. We have previously reported the generation of an engineered C. neoformans strain (C. neoformans Δgcs1) which can be contained in lung granulomas in the mouse model and have shown that granuloma formation is dependent upon the enzyme sphingosine kinase 1 (SK1) and its product, sphingosine 1-phosphate (S1P). In this study, we have used four mouse models, CBA/J and C57BL6/J (both immunocompetent), Tgε26 (an isogenic strain of strain CBA/J lacking T and NK cells), and SK(-/-) (an isogenic strain of strain C57BL6/J lacking SK1), to investigate how the granulomatous response and SK1-S1P pathway are interrelated during C. neoformans infections. S1P and monocyte chemotactic protein-1 (MCP-1) levels were significantly elevated in the bronchoalveolar lavage fluid of all mice infected with C. neoformans Δgcs1 but not in mice infected with the C. neoformans wild type. SK1(-/-) mice did not show elevated levels of S1P or MCP-1. Primary neutrophils isolated from SK1(-/-) mice showed impaired antifungal activity that could be restored by the addition of extracellular S1P. In addition, high levels of tumor necrosis factor alpha were found in the mice infected with C. neoformans Δgcs1 in comparison to the levels found in mice infected with the C. neoformans wild type, and their levels were also dependent on the SK1-S1P pathway. Taken together, these results suggest that the SK1-S1P pathway promotes host defense against C. neoformans infections by regulating cytokine levels, promoting extracellular killing by phagocytes, and generating a granulomatous response.

Topics: Animals; Bronchoalveolar Lavage Fluid; Cryptococcosis; Cryptococcus neoformans; Disease Models, Animal; Female; Gene Deletion; Granuloma; Lung; Lysophospholipids; Male; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Knockout; Phosphotransferases (Alcohol Group Acceptor); Sphingosine

Cryptococcus neoformans is a fungal pathogen causing pulmonary infection and a life-threatening meningoencephalitis in human hosts. The fungus infects the host through inhalation, and thus, the host response in the lung environment is crucial for containment or dissemination of C. neoformans to other organs. In the lung, alveolar macrophages (AMs) are key players in the host lung immune response, and upon phagocytosis, they can kill C. neoformans by evoking an effective immune response through a variety of signaling molecules. On the other hand, under conditions not yet fully defined, the fungus is able to survive and proliferate within macrophages. Since the host sphingosine kinase 1 (SK1) regulates many signaling functions of immune cells, particularly in macrophages, in this study we determined the role of SK1 in the host response to C. neoformans infection. Using wild-type (SK1/2(+/+)) and SK1-deficient (SK1(-/-)) mice, we found that SK1 is dispensable during infection with a facultative intracellular wild-type C. neoformans strain. However, SK1 is required to form a host lung granuloma and to prevent brain infection by a C. neoformans mutant strain lacking the cell wall-associated glycosphingolipid glucosylceramide (Delta gcs1), previously characterized as a mutant able to replicate only intracellularly. Specifically, in contrast to those from SK1/2(+/+) mice, lungs from SK1(-/-) mice have no collagen deposition upon infection with C. neoformans Delta gcs1, and AMs from these mice contain significantly more C. neoformans cells than AMs from SK1/2(+/+) mice, suggesting that under conditions in which C. neoformans is more internalized by AMs, SK1 may become important to control C. neoformans infection. Indeed, when we induced immunosuppression, a host condition in which wild-type C. neoformans cells are increasingly found intracellularly, SK1(-/-) survived significantly less than SK1/2(+/+) mice infected with a facultative intracellular wild-type strain, suggesting that SK1 has an important role in controlling C. neoformans infection under conditions in which the fungus is predominantly found intracellularly.

Topics: Animals; Colony Count, Microbial; Cryptococcosis; Cryptococcus neoformans; Female; Granuloma; Lung; Macrophages, Alveolar; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphotransferases (Alcohol Group Acceptor); Survival Analysis