Sphingolipid Degradation by Leishmania major Is Required for Its Resistance to Acidic pH in the Mammalian Host

Abstract

Leishmania parasites alternate between flagellated promastigotes in sand flies and nonflagellated amastigotes in mammals, causing a spectrum of serious diseases. To survive, they must resist the harsh conditions in phagocytes (including acidic pH, elevated temperature, and increased oxidative/nitrosative stress) and evade the immune response. Recent studies have highlighted the importance of sphingolipid (SL) metabolism in Leishmania virulence. In particular, we have generated a Leishmania major iscl ؊ mutant which is deficient in SL degradation but grows normally as promastigotes in culture. Importantly, iscl ؊ mutants cannot induce pathology in either immunocompetent or immunodeficient mice yet are able to persist at low levels. In this study, we investigated how the degradation of SLs might contribute to Leishmania infection. First, unlike wild-type (WT) L. major, iscl ؊ mutants do not trigger polarized T cell responses in mice. Second, like WT parasites, iscl ؊ mutants possess the ability to downregulate macrophage activation by suppressing the production of interleukin-12 (IL-12) and nitric oxide. Third, during the stationary phase, iscl ؊ promastigotes were extremely vulnerable to acidic pH but not to other adverse conditions, such as elevated temperature and oxidative/nitrosative stress. In addition, inhibition of phagosomal acidification significantly improved iscl ؊ survival in murine macrophages. Together, these findings indicate that SL degradation by Leishmania is essential for its adaption to the acidic environment in phagolysosomes but is not required for the suppression of host cell activation. Finally, our studies with iscl ؊ mutant-infected mice suggest that having viable, persistent parasites is not sufficient to provide immunity against virulent Leishmania challenge.

Developmentally Regulated Sphingolipid Degradation in Leishmania major

“…This hypersensitivity to acid shock is responsible for the poor survival of iscl − in macrophages, as the pretreatment of macrophages with chemicals that inhibit phagolysosomal acidification significantly improved the viability of iscl − in host cells [22]. Because ISCL is both a SMase and an IPCase, we investigated which activity is required for acid resistance in stationary phase promastigotes.…”

“…This result suggests that SL degradation is important for conferring acid resistance [22]. The hypersensitivity of iscl − to acidic pH is responsible for its poor survival in murine macrophages [22], the definitive host cells for Leishmania .…”

“…This result suggests that SL degradation is important for conferring acid resistance [22]. The hypersensitivity of iscl − to acidic pH is responsible for its poor survival in murine macrophages [22], the definitive host cells for Leishmania . Since ISCL is both a neutral SMase and an IPCase, it is of interest to determine which activity is required for acid tolerance and whether the restoration of acid resistance is sufficient to recover the virulence of iscl − in mammals.…”

Leishmania parasites possess a platelet-activating factor acetylhydrolase important for virulence

“…Deletion of ISCL led to a mild defect in morphology during the promastigote phase [10]. Importantly, these ISCL-null mutants were hypersensitive to acidic pH [11] and lacked virulence in mice [10]. Infectivity was restored when ISCL-null mutants were complemented with a functional sphingomyelinase [10, 12].…”

Comparison Between Plethysmometer and Caliper Methods to Monitor Lesion-Size Induced by <i>Leishmania major</i> Infection in BALB/c Mouse Experimental Model

“…Several previous [11,12] as well as new [13][14][15] studies used routinely the caliper to monitor the lesion development induced in the footpad of animals. This measure represents the difference between the widths and/or the thicknesses of the infected and the uninfected paws of the same mouse.…”