Regulation of Adipocyte Lipolysis Catecholamines Epinephrine Norepinephrine Beta

Regulation of Adipocyte Lipolysis • Catecholamines – Epinephrine & Norepinephrine • Beta Adrenergic Receptors – Stimulate • Alpha Adrenergic Receptors – Inhibit • Insulin – Inhibitory

Catecholamines • Stimulatory – B-Adrenergic Receptors – Activates Stimulatory GProtein – Activates Adenylate Cyclase – Generates c. AMP – Activates c. AMP-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) Hydrolyzes Plasma Triglycerides Phosphatidylinositol 3 -Kinase (PI 3 K) Phosphorylates Phosphodiesterase-3 Into Degrades FFA c. AMP

Insulin & LPL

PI 3 K Insulin Phosphorylates • LPL – Hydrolyzes triglycerides in the blood to increase FFA levels • PI 3 K – Inhibits lipolysis in adipose cells – Mediates insulinstimulated glucose uptake Phosphodiestesterase-3 Degrades