Chlamydia trachomatis exploits sphingolipid metabolic pathways during infection of phagocytes

Abstract

Chlamydiae are obligate intracellular pathogens that utilize host cell metabolites for catabolic and anabolic processes. The bacteria replicate in epithelial cells from which they take up sphingolipids (SL) and incorporate them into the chlamydial membrane and the vacuole (termed inclusion). SL uptake is essential for Chlamydia trachomatis (Ctr) in epithelial cells; however, they can also infect phagocytes, but the consequences for the SL metabolism have not yet been investigated in these cells. We performed a quantitative sphingolipidome analysis of infected primary neutrophils, macrophages, and immortalized fallopian tube epithelial cells. Sphingosine (Sph) levels are elevated in primary M2-like macrophages and human neutrophils infected with C. trachomatis. Human neutrophils respond to the pathogen by markedly upregulating sphingosine kinase 1 (SPHK1). We show in M2-like macrophages, by RNAseq, that two counteracting pathways involving upregulation of SPHK1, but also sphingosine-1-phosphate phosphatases 1 and 2 (SGPP1 and SGPP2) and sphingosine-1-phosphate lyase (SGPL1), maintain a steady pool of S1P. Using click chemistry, we show that exogenously added sphingomyelin (SM) and ceramide (Cer) are efficiently taken up into the chlamydial inclusion and are integrated into bacterial membranes in infected M2-like macrophages. Exogenous Sph reduces chlamydial infectivity, is transported into the inclusion lumen, and integrates into chlamydial membranes, suggesting that this particular SL species could represent a host defense mechanism. Taken together, our data indicate an important role for Sph/Sph kinase vs S1P/S1P phosphatase balance in infected phagocytes and a previously unrecognized role for sphingosine in the immune defense against chlamydial infection.