Regulation of Adipocyte Lipolysis

• Catecholamines– Epinephrine & Norepinephrine

• Beta Adrenergic Receptors– Stimulate

• Alpha Adrenergic Receptors– Inhibit

• Insulin– Inhibitory

Catecholamines

• Stimulatory– B-Adrenergic Receptors– Activates Stimulatory G-

Protein– Activates Adenylate Cyclase– Generates cAMP– Activates cAMP-dependent

protein kinase– Phosphorylates HSL &

Perilipins– Break down triglycerides

• Inhibitory– A-Adrenergic Receptors– Activates Inhibitory G-protein– Inhibits Adenylate Cyclase

•Catecholamines stimulate HSL to break down triglycerides to fatty acids and glycerol

•Fatty acids and glycerol are released into the blood and circulated to other body tissues

ATGL

• Adipose Triglyceride Lipase– Enzyme that may be responsible for

catalyzing the initial steps of triglyceride hydrolysis.

– Zimmermann et al. (2004)• HSL knock-out mice showed an accumulation

of diglycerides, suggesting that additional lipases may be present that can hydrolyze the first ester bond of triglycerides

– Still controversial

Insulin

Lipoprotein Lipase (LPL)

Phosphatidylinositol 3-Kinase (PI3K)

Phosphodiesterase-3

Degrades

cAMP

Hydrolyzes

Plasma Triglycerides

Into

FFA

Phosphorylates

Insulin & LPL

Insulin

• LPL– Hydrolyzes

triglycerides in the blood to increase FFA levels

• PI3K– Inhibits lipolysis in

adipose cells– Mediates insulin-

stimulated glucose uptake

PI3K

Phosphodiestesterase-3

Phosphorylates

Degrades