The angiopoietins are protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 growth factors that promote angiogenesis

Angiogenesis

Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...

, the formation of blood vessels from pre-existing blood vessels. There are now four identified angiopoietins:
Ang1, Ang2

ANGPT2

Angiopoietin-2 is a protein that in humans is encoded by the ANGPT2 gene.-Interactions:ANGPT2 has been shown to interact with TEK tyrosine kinase.-Further reading:...

, Ang3

ANGPTL1

Angiopoietin-related protein 1 is a protein that in humans is encoded by the ANGPTL1 gene.-Further reading:...

, Ang4

ANGPT4

Angiopoietin-4 is a protein that in humans is encoded by the ANGPT4 gene.-Further reading:...

. In addition, there are a number of proteins that are closely related to angiopoietins (ANGPTL2

ANGPTL2

Angiopoietin-related protein 2 is a protein that in humans is encoded by the ANGPTL2 gene.-Further reading:...

, ANGPTL3

ANGPTL3

Angiopoietin-like 3, also known as ANGPTL3, is a protein which in humans is encoded by the ANGPTL3 gene.- Function :The protein encoded by this gene is a member of the angiopoietin-like family of secreted factors...

, ANGPTL4

ANGPTL4

Angiopoietin-related protein 4 is a protein that in humans is encoded by the ANGPTL4 gene. ANGPTL4 inhibits lipoprotein lipase, LPL, by breaking the dimer molecule. ANGPTL3 and ANGPTL4 have been unambiguously established as potent inhibitors of blood plasma Triglyceride clearance, causing...

, , , ANGPTL7

ANGPTL7

Angiopoietin-related protein 7 is a protein that in humans is encoded by the ANGPTL7 gene.-Further reading:...

). Ang1 and Ang2 are required for the formation of mature blood vessels, as demonstrated by mouse knock out studies.

Angiopoietin receptors

The TIE receptors are tyrosine kinases, so named because they mediate cell signals by inducing the phosphorylation of key tyrosines, thus initiating the binding and activation of downstream, intracellular enzymes; this process is called cell signalling, and it is the method by which cells are induced to activate or inhibit key regulatory functions. It is somewhat controversial which of the TIE receptors mediate functional signals downstream of Ang stimulation - but it is clear that at least TIE-2 is capable of physiologic activation as a result of binding the angiopoietins. The angiopoietins are the secreted ligands of the TIE family of protein receptor tyrosine kinases.

Clinical relevance

Angiopoietin 2 is elevated in patients with angiosarcoma

Hemangiosarcoma

Hemangiosarcoma is a rare, rapidly growing, highly invasive variety of cancer. It is a sarcoma arising from the lining of blood vessels; that is, blood-filled channels and spaces are commonly observed microscopically...

.

Vaccination against TIE-2-positive cells appears to reduce atheroma formation in experimental animals.

There are changes in circulating levels and ratios of angiopoietins during pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

, but not during the menstrual cycle and in controlled ovarian hyperstimulation.