Lipoprotein Lipase

The activity of endothelial lipoprotein lipase (LPL) determines the various uptake levels of fatty acids in different tissues. LPL hydrolyzes triglycerides in high-triglyceride lipoproteins like chylomicrons and VLDL to 2-monoglycer-ides and fatty acids. It also effects the transfer of phospholipids and apopro-teins to HDL. Recent research shows that LPL is further responsible for specific binding of lipoproteins to cell surfaces and receptors. These functions point to a central role of the regulation of LPL activity for lipid metabolism. There is presently intense research into the role of LPL malfunctions and mutations in the development of diseases (e.g., atherosclerosis).

LPL can only attach to the cell wall if it binds heparin first. The LPL-heparin complex binds to glycosaminoglycans on the endothelial cell surface. The resulting heparan-sulfate proteogly-cans are long chains that project into the vessel lumen and enable contact between the LPL attached to them and lipoproteins (A). Apoprotein Cn and shorter amino acid sequences at the carboxy terminal end of LPL on the surface of lipoprotein particles provide binding sites. In this, ApoC]] plays the role of a cofactor (colipase) required to enable LPL activity. The subsequent triglyceride hydrolysis frees fatty acids, which are taken up locally by the vessel endothelium. LPL is also generally involved in cell surface-lipoprotein interactions. During lipolysis at the vessel endothelium, a small amount of LPL may dissociate and attach to the lipo-protein particles. This LPL—measurable as plasma LPL—may mediate the attachment to cells (e. g., to the LDL receptor) via binding to surface proteoglycans.

The potentially active LPL is present in dimer form, with its two amino acid chains (twisted at a 180° angle) assuming a shape that makes them cover the active center like an eyelid (B). Contact with lipoprotein particles results in a conformational change, allowing the hydrophobic active center to come in contact with the particle surface and exert its catalytic effect. Overall, LPL activity regulation is still an open question at this point. LPL is produced in most tissues, being most active in fatty tissue, heart muscle, musculature, and lactating mammary glands. Earlier studies showed that regulation must occur on the level of gene expression with subsequent varying LPL-mRNA tissue levels. Since these variations come about more slowly than the change in LPL activity, greater significance has been attributed, recently, to posttranslational regulation. This might mean, for instance, cellular uptake and subsequent intracellu-lar degradation of LPL. It has been established that LPL activity increases postprandially under the influence of insulin and that, on the other hand, its activity is selectively reduced in specific tissues during starvation or fasting.

Lipoprotein Lipase 101

- A. LPL-Lipoprotein Bonding -

Apoprotein E Apoprotein C|j

Lipoprotein

Apoprotein E Apoprotein C|j

Lipoprotein

Lpl Heparan Sulfate

Free cholesterol Apoprotein B Cholesterol ester Phospholipid Triglyceride

Heparan sulfate proteoglycan

Lipoprotein lipase

Products of lipolysis

Lipoprotein LPL particle

Products of lipolysis

Free cholesterol Apoprotein B Cholesterol ester Phospholipid Triglyceride

Heparan sulfate proteoglycan

Lipoprotein lipase

Products of lipolysis

Lipoprotein LPL particle

Products of lipolysis

Lpl Heparan Sulfate
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Responses

  • greta moretti
    How to burn lipoprotein lipase?
    5 years ago
  • cailyn
    How to speed lipoprotein lipase?
    3 years ago

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