Fat inclusions strongly alter membrane mechanics

Neutral lipids (NLs) are apolar oil molecules synthesized in the endoplasmic reticulum bilayer upon diverse biological stimuli. NLs synthesized are released in the hydrophobic core of the bilayer. At a critical concentration, NLs condense by phase separation and nucleate a lipid droplet (LD). After an LD forms, a fraction of NLs can be present in the bilayer but at a concentration below that of the nucleation. Here, we study whether and how the accumulation of NLs alters a lipid bilayer's mechanical properties. In synthetic systems, we found that NLs proffer unusual bilayer stretching capacities, especially in the presence of negatively curved phospholipids. This impact becomes spectacular when an LD is contiguous with the bilayer and supplies it with NLs. The tested NLs markedly decrease the bilayer area expansion modulus and significantly increase lysis tension but had opposite effects on membrane bending rigidity. Our data unveil how NL molecules modify overall membrane mechanics, the alteration of which may be linked to pathologies or anticancer treatments targeting NLs.

Automated summary

Neutral lipids (NLs) synthesized in the endoplasmic reticulum can alter a lipid bilayer's mechanical properties, especially in the presence of negatively curved phospholipids. The presence of NLs, especially when supplied by lipid droplets (LDs), can decrease the bilayer's area expansion modulus and increase lysis tension while impacting membrane bending rigidity in different ways. Understanding how NLs modify membrane mechanics may have implications for disease pathologies or anticancer treatments targeting NLs.