Lipid droplets in stress protection: distinct mechanisms of lipid droplet microautophagy

Abstract

Lipid droplets (LDs) are organelles that function as sites for lipid storage. LDs have also been implicated in the cellular response to proteotoxic or lipotoxic stress as sites for sequestering dysfunctional or excess proteins or lipids, and targeting those cargos for degradation by LD microautophagy (microlipophagy, µLP). Here, we describe two mechanisms for µLP in yeast, which are triggered by different stressors. µLP occurs at raft-like liquid ordered microdomains in the vacuolar membrane in yeast exposed to severe nutrient limitations. In contrast, in yeast exposed to ER stress or less severe nutrient limitations, LD uptake at the vacuole is liquid ordered (Lo) microdomain-independent and dependent upon vacuolar membrane remodeling mediated by endosomal sorting complexes required for transport (ESCRT).