Lipid droplet questions

Unique membrane structure of a lipid droplet

Phospholipid monolayer surrounding a hydrophobic neutral lipid core

Primary lipids found in the LD core

Triacylglycerols (TAGs) and Sterol Esters (SEs)

Most abundant phospholipid on the LD surface

Phosphatidylcholine (PC)

How LDs prevent lipotoxicity

By sequestering excess free fatty acids into inert neutral lipids

Organelle of origin for lipid droplets

Endoplasmic Reticulum (ER)

Function of Seipin (BSCL2)

Forms a bridge at ER-LD contact sites to facilitate budding and size control

Reaction catalyzed by DGAT1 and DGAT2

Final step of TAG synthesis (converting DAG and fatty acyl-CoA to TAG)

Function of ACAT1 and ACAT2

Synthesize Cholesterol Esters (CEs) from free cholesterol and fatty acids

Role of FIT2 protein

Partitions neutral lipids into nascent LDs within the ER bilayer

Product of AGPAT enzymes

Phosphatidic Acid (PA), a precursor for TAG and phospholipids

Primary function of Perilipins (PLIN1-5)

Coat the LD surface to regulate lipase access and lipid mobilization

Tissue expression of PLIN1

Specific to adipocytes

Tissue expression of PLIN2 (Adipophilin)

Ubiquitous expression across most cell types

Role of PLIN5

Promotes LD-mitochondria interaction in oxidative tissues (heart, muscle)

Function of CIDE proteins (e.g., CIDEC/FSP27)

Facilitate LD fusion to form large unilocular droplets

Role of Rab18 on LDs

Regulates trafficking and ER recruitment to the LD surface

Rate-limiting enzyme of TAG breakdown

ATGL (Adipose Triglyceride Lipase)

Function of CGI-58 (ABHD5)

Acts as a co-activator of ATGL

Enzyme that hydrolyzes diacylglycerol (DAG)

Hormone-Sensitive Lipase (HSL)

Enzyme for the final step of TAG breakdown

MGL (Monoacylglycerol Lipase)

Definition of Lipophagy

Autophagic degradation of lipid droplets via the lysosome

Purpose of ER-LD contact sites

Transfer of lipids and proteins during droplet growth

Reason for LD-Mitochondria interaction

Direct supply of fatty acids for beta-oxidation (ATP production)

Link between LDs and Peroxisomes

Coordination for the breakdown of very-long-chain fatty acids

Impact of LD upregulation in cancer

Provides energy and membrane building blocks for rapid proliferation