Niekamp, P. | bioRxiv Science

bioRxiv2021

Ca2+-activated sphingomyelin scrambling and turnover mediate ESCRT-independent lysosomal repair

Lysosomes are vital organelles vulnerable to injuries from diverse materials. Failure to repair or sequester damaged lysosomes poses a threat to cell viability. Here we report that cells exploit a sphingomyelin-based lysosomal repair pathway that operates independently of ESCRT to reverse potentially lethal membrane damage. Various conditions perturbing organelle integrity trigger a rapid calcium-activated scrambling and cytosolic exposure of sphingomyelin. Subsequent metabolic conversion of sphingomyelin by neutral sphingomyelinases on the cytosolic surface of injured lysosomes promotes their repair, also when ESCRT function is compromised. Conversely, blocking turnover of cytosolic sphingomyelin renders cells more sensitive to lysosome-damaging drugs. Our data indicate that calcium-activated scramblases, sphingomyelin, and neutral sphingomyelinases are core components of a previously unrecognized membrane restoration pathway by which cells preserve the functional integrity of lysosomes.

cell biology↗

bioRxiv2019

Sphingomyelin is critical in organizing phosphoinositide dynamics during phagocytic uptake of Mycobacterium tuberculosis.

Tuberculosis, the pathological result of infection by Mycobacterium tuberculosis (M.tb), represents a massive and persistent global health burden with vast overrepresentation in regions with poor access to healthcare. This pathogen survives intracellularly within lung macrophages, and has been shown to extensively reprogram the host lipid compartment to the effect of enhanced survival and immune evasion. Sphingolipids are a class of lipid with extensive functions in a wide variety of cellular contexts, including apoptosis, autophagy, stress response, and inflammation. There remains a significant knowledge gap surrounding the lipid-mediated interactions between M.tb and its host. Our investigation aims to explore the mechanisms through which M.tb harnesses host-derived sphingolipids to gain entry to the host and to survive intracellularly. To this end, we use chemical and genetic perturbations of the sphingolipid de novo synthesis pathway and fluorescence microscopy to show that sphingolipids are required for efficient phagocytosis of M.tb. We furthermore show that the dynamics of phosphoinositides at the phagosomal synapse are perturbed upon blockade of sphingolipid synthesis. Finally, we demonstrate that perturbing the homeostasis of a specific sphingolipid (sphingomyelin) through both enrichment and depletion at the cell surface reduces M.tb uptake. This work represents a first step in building comprehensive knowledge of the mechanisms of host-pathogen interactions in M.tb, and demonstrates a cohort of methodologies that may be applied to a variety of pathogenic contexts.

microbiology↗