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Very-low-density lipoprotein (VLDL), density relative to extracellular water, is a type of
lipoprotein A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, su ...
made by the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
. VLDL is one of the five major groups of lipoproteins ( chylomicrons, VLDL,
intermediate-density lipoprotein Intermediate-density lipoproteins (IDLs) belong to the lipoprotein particle family and are formed from the degradation of very low-density lipoproteins as well as high-density lipoproteins. IDL is one of the five major groups of lipoproteins (chyl ...
,
low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densit ...
,
high-density lipoprotein High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are t ...
) that enable fats and cholesterol to move within the water-based solution of the bloodstream. VLDL is assembled in the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
from
triglycerides A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...
, cholesterol, and
apolipoprotein Apolipoproteins are proteins that bind lipids (oil-soluble substances such as fats, cholesterol and fat soluble vitamins) to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph. The lipid components of lipoprotei ...
s. VLDL is converted in the bloodstream to
low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densit ...
(LDL) and
intermediate-density lipoprotein Intermediate-density lipoproteins (IDLs) belong to the lipoprotein particle family and are formed from the degradation of very low-density lipoproteins as well as high-density lipoproteins. IDL is one of the five major groups of lipoproteins (chyl ...
(IDL). VLDL particles have a diameter of 30–80 nm. VLDL transports
endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, es ...
products, whereas chylomicrons transport
exogenous In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, the fact of being influenced within a system. Economics In an economic model, an exogeno ...
(dietary) products. In the early 2010s both the lipid composition and protein composition of this lipoprotein were characterised in great detail.


Function

Very-low-density lipoproteins transport endogenous
triglycerides A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...
,
phospholipids Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typi ...
, cholesterol, and cholesteryl esters. It functions as the body's internal transport mechanism for lipids. In addition it serves for long-range transport of hydrophobic intercellular messengers, like the morphogen
Indian hedgehog (protein) Indian hedgehog homolog (Drosophila), also known as IHH, is a protein which in humans is encoded by the ''IHH'' gene. This cell signaling protein is in the hedgehog signaling pathway. The several mammalian variants of the '' Drosophila'' hedgehog ...
.


Changes during circulation

Nascent VLDL released from the liver contains
apolipoprotein B100 Apolipoprotein B (ApoB) is a protein that in humans is encoded by the gene. Function Apolipoprotein B is the primary apolipoprotein of chylomicrons, VLDL, Lp(a), IDL, and LDL particles (LDL—commonly known as "bad cholesterol" when in re ...
,
apolipoprotein C1 Apolipoprotein C-I is a protein component of lipoproteins that in humans is encoded by the ''APOC1'' gene. Function The protein encoded by this gene is a member of the apolipoprotein C family. This gene is expressed primarily in the liver, a ...
(apoC1), apolipoprotein E (apoE), cholesterol,
cholesteryl ester 300px, Cholesterol oleate, a member of the cholesteryl ester family Cholesteryl ester, a dietary lipid, is an ester of cholesterol. The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol. Cho ...
s, and
triglycerides A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...
. As it circulates in blood, it picks up
apolipoprotein C-II Apolipoprotein C-II (Apo-CII, or Apoc-II), or apolipoprotein C2 is a protein that in humans is encoded by the gene. The protein encoded by this gene is secreted in plasma where it is a component of very low density lipoproteins and chylomicron ...
(apoC-II) and additional apoE donated from
high-density lipoprotein High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are t ...
(HDL). At this point, nascent VLDL becomes a mature VLDL. Once in circulation, VLDL will come in contact with
lipoprotein lipase Lipoprotein lipase (LPL) (EC 3.1.1.34, systematic name triacylglycerol acylhydrolase (lipoprotein-dependent)) is a member of the lipase gene family, which includes pancreatic lipase, hepatic lipase, and endothelial lipase. It is a water-soluble ...
(LPL) in the capillary beds in the body (adipose, cardiac, and skeletal muscle). LPL will remove triglycerides from VLDL for storage or energy production. VLDL now meets back up with HDL where apoC-II is transferred back to HDL (but keeps apoE). HDL also transfers cholesteryl esters to the VLDL in exchange for phospholipids and triglycerides via
cholesterylester transfer protein Cholesteryl ester transfer protein (CETP), also called plasma lipid transfer protein, is a plasma protein that facilitates the transport of cholesteryl esters and triglycerides between the lipoproteins. It collects triglycerides from very-low-d ...
(CETP). As more and more triglycerides are removed from the VLDL because of the action of LPL and CETP enzymes, the composition of the molecule changes, and it becomes intermediate-density lipoprotein (IDL). Fifty percent of IDLs are recognized by receptors in the liver cells because of the apolipoprotein B-100 (apoB-100) and apoE they contain and are endocytosed. The other 50% of IDL lose apoE; when their cholesterol content becomes greater than the content of triglyceride, they become LDL, with apoB-100 as the primary apolipoprotein. The LDL is taken into a cell via the LDL receptor via endocytosis, where the contents are either stored, used for cell membrane structure, or converted into other products such as steroid hormones or bile acids.


See also

* Combined hyperlipidemia * Lipid profile


Notes and references

{{DEFAULTSORT:Very Low-Density Lipoprotein Lipoproteins