Characterization of a sphingolipid-operated lysosomal repair pathway

• Applicant: Professor Dr. Joost Holthuis
• Subject Area: Biochemistry ; Cell Biology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512783018

Lysosomes are vital organelles vulnerable to injuries from diverse materials. Failure to repair or sequester damaged lysosomes poses a threat to cell viability. We recently identified a sphingomyelin-based lysosomal repair pathway that operates independently of ESCRT to reverse potentially lethal membrane damage. Various conditions perturbing lysosome integrity trigger a rapid Ca2+-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 suggest that Ca2+-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. In this project, we will combine functional assays with organellar lipidomics and correlative 3D electron microscopy to elucidate the mechanistic principles by which sphingomyelin scrambling and turnover promote lysosomal repair. We will also address whether the same principles contribute to the survival of wounded cells.

• DFG Programme: Research Grants