The assembly of lipid droplets and its relation to cellular insulin sensitivity.
The assembly of lipid droplets is dependent on PtdIns(4,5)P(2) that activates PLD(1) (phospholipase D(1)), which is important for the assembly process. ERK2 (extracellular-signal-regulated kinase 2) phosphorylates the motor protein dynein and sorts it to lipid droplets, allowing them to be transported on microtubules. Lipid droplets grow in size by fusion, which is dependent on dynein and the transfer on microtubules, and is catalysed by the SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) proteins SNAP-23 (23 kDa synaptosome-associated protein), syntaxin-5 and VAMP-4 (vesicle-associated protein 4). SNAP-23 is also involved in the insulin-dependent translocation of the glucose transporter GLUT4 to the plasma membrane. Fatty acids induce a missorting of SNAP-23, from the plasma membrane to the interior of the cell, resulting in cellular insulin resistance that can be overcome by increasing the levels of SNAP-23. The same missorting of SNAP-23 occurs in vivo in skeletal-muscle biopsies from patients with T2D (Type 2 diabetes). Moreover, there was a linear relation between the amount of SNAP-23 in the plasma membrane from human skeletal-muscles biopsies and the systemic insulin-sensitivity. Syntaxin-5 is low in T2D patients, which leads to a decrease in the insulin-dependent phosphorylation of Akt (also known as protein kinase B). Thus both SNAP-23 and syntaxin-5 are highly involved in the development of insulin resistance.
Boström
Pontus
P
Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Gothenburg, Sweden.
Andersson
Linda
L
Li
Lu
L
Perkins
Rosie
R
Højlund
Kurt
K
Borén
Jan
J
Olofsson
Sven-Olof
SO
D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance; D050356:Lipid Metabolism; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism; D015388:Organelles / Q000737:chemistry / Q000378:metabolism; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D050766:Qb-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D050767:Qc-SNARE Proteins / Q000235:genetics / Q000378:metabolism*
D005227:Fatty Acids; D007328:Insulin; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; C100493:SNAP23 protein, human