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 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)
Hydrolyzes
Plasma Triglycerides
Phosphatidylinositol
3-Kinase (PI3K)
Phosphorylates
Phosphodiesterase-3
Into
Degrades
FFA
cAMP
Insulin & LPL
PI3K
Insulin
Phosphorylates
• LPL
– Hydrolyzes
triglycerides in the
blood to increase
FFA levels
• PI3K
– Inhibits lipolysis in
adipose cells
– Mediates insulinstimulated glucose
uptake
Phosphodiestesterase-3
Degrades