Sphingosine Kinase and Cryptococcal Granuloma

ABSTRACT The goal of this project is to study the role of the host sphingosine kinase 1 (SK1) pathway in controlling infection by the fungus Cryptococcus neoformans (Cn) during immunodeficiency. A mouse model of lung cryptococcal granuloma that recapitulates the human granuloma was developed. When these mice become immunocompromised, the fungus disseminates to the brain, causing meningo-encephalitis.1 Thus, our mouse model mimics the physiopathology of the infection in immunocompromised subjects with which cryptococcosis is mostly associated.2 In recent years, patients treated with FTY720 (Fingolimod) for multiple sclerosis3 (MS) have developed cryptococcosis.4-9 Studies using the animal model in the lab showed that host sphingosine kinase 1 (SK1) and its product sphingosine-1- phosphate (S1P) are critical for the formation of the lung granuloma against Cn.1, 10, 11 In addition, treatment with FTY720 reactivated Cn infection from the lung granuloma, and fungal cells that disseminate to the brain cause lethal meningo- encephalitis.12 This reactivation does not occur when mice were treated with BAF312 or AUY954, which are also used to treat MS patients by targeting sphingosine-1-phosphate receptors (S1Prs). FTY720 is a sphingosine analog that, once phosphorylated, mimics S1P and binds to S1P receptors S1Pr1, S1Pr3 and S1Pr513 whereas BAF312 or AUY954 binds to S1Pr1 and S1Pr5,14 or only to S1Pr1,15 respectively. These results suggest that SK1-S1P may regulate the containment of Cn cells within the lung granuloma through the activation of a specific S1P receptor(s), such as S1Pr3, as this is one of the receptors blocked by FTY720 but not by the other compounds. Treatment with FTY720, but not with BAF312, was associated with disorganization of macrophages and with M2 polarization at the granuloma site.12 In a cell system, Cn cells are poorly internalized or killed by macrophages lacking S1Pr3. Very interestingly, both internalization and killing by macrophages can be inhibited by S1Pr3 antagonists and enhanced by S1Pr3 agonists.12 Based on these findings, the hypothesis is that the S1P-S1Pr pathway regulates the host cellular immunity against Cn at the granuloma and that antagonizing S1Pr3 is detrimental for the host and may lead to reactivation of cryptococcosis during lymphopenia. Thus, the following aims are proposed: 1) Determine the immune mechanism by which of SK1-S1P regulates the organization of Cn granuloma; and 2) Define the immune response by which by SK1-S1P protects from Cn reactivation.