Lipid phosphate phosphohydrolase 3 (LPP3), also known as phospholipid phosphatase 3 (PLPP3) and phosphatidic acid phosphatase type 2B (PAP-2b or PPAP2B), is an enzyme that in humans is encoded by the PPAP2B gene on chromosome 1. [5] [6] [7] It is ubiquitously expressed in many tissues and cell types. [8] LPP3 is a cell-surface glycoprotein that hydrolyzes extracellular lysophosphatidic acid (LPA) and short-chain phosphatidic acid. [9] Its function allows it to regulate vascular and embryonic development by inhibiting LPA signaling, which is associated with a wide range of human diseases, including cardiovascular disease and cancer, as well as developmental defects. [10] The PPAP2B gene also contains one of 27 loci associated with increased risk of coronary artery disease. [11]
The PPAP2B gene resides on chromosome 1 at the band 1p32.2 and includes 6 exons. [6]
LPP3 is a member of the PAP-related phosphoesterase family. [7] It is a type 2 activity PAP, which localizes to the plasma membrane, and is one of four known LPP isoforms. As an integral membrane protein, LPP3 contains six hydrophobic transmembrane domains and a hydrophilic catalytic site composed of three conserved domains. [12] [13] One catalytic domain is proposed to bind the substrate while the other two contribute to dephosphorylation of the substrate. The catalytic site typically faces the extracellular matrix when located on the cell membrane and faces the lumen when located in intracellular membranes. This protein can form homo- and hetero-oligomers. [13]
This protein is a membrane glycoprotein localized at the cell plasma membrane. It has been shown to actively hydrolyze extracellular lysophosphatidic acid (LPA) and short-chain phosphatidic acid. [5] As an LPA inhibitor, PPAP2B is known to suppress LPA receptor mediated cellular signaling, which is associated with activation of vascular and blood cells and epithelial cell migration and proliferation. [14] [15] In response to dynamic athero relevant-flows, PPAP2B can promote anti-inflammatory phenotype via inhibition of LPA signaling and maintain vascular integrity of endothelial monolayer. This flow-sensitive PPAP2B expression is inhibited by microRNA-92a and activated by transcription factor KLF2. [16] In addition to LPA receptor-mediated signaling, PPAP2B is also associated with Wnt signaling, functioning in embryonic development for proper formation of important tissues including bone, heart and muscle. The phenotype of axis duplication in mice globally lacking PPAP2B resembles that observed in animals with altered Wnt signaling. [17] Furthermore, Wnt signaling mediated TCF/LEF-transcription via β-catenin is upregulated in PPAP2B null embryonic stem cells, implicating LPP3 as a negative regulator of the Wnt pathway. [18]
Due to the regulatory role of LPP3 in vascular and embryonic development, inactivation of this protein can contribute to cardiovascular disease and developmental complications. For example, inducible inactivation of LPP3 in both endothelial and hematopoietic cells leads to atherosclerosis due to accumulation of LPA in human plaques. [10] [19] Likewise, plasma LPA levels are significantly elevated in patients with acute coronary syndromes. [20] It was further observed that reduced levels of endothelial LPP3 is associated with disturbed flow and mechano-regulation in blood vessels. [16] During embryonic development in mice, inactivation of LPP3 results in early lethality in part due to failure of extra-embryonic vascular development. [17] Abnormal activation of LPA signaling has also been implicated in cancer, fibrotic disorders, and metabolic syndrome (involving insulin resistance). [21] [22]
In humans, PPAP2B emerged as 1 of 13 new loci associated with coronary artery disease by genome-wide association studies (GWAS). [23] [24] This prediction appears to be independent of traditional risk factors for cardiovascular disease such as high cholesterol levels, high blood pressure, obesity, smoking, and diabetes mellitus.
Additionally, a multi-locus genetic risk score study, based on a combination of 27 loci including the PPAP2B gene, identified individuals at increased risk for both incident and recurrent coronary artery disease events, as well as an enhanced clinical benefit from statin therapy. The study was based on a community cohort study (the Malmo Diet and Cancer study) and four additional randomized controlled trials of primary prevention cohorts (JUPITER and ASCOT) and secondary prevention cohorts (CARE and PROVE IT-TIMI 22). [11]
Taken together, these findings also suggest that PPAP2B and LPA may serve a role in predicting and screening coronary artery disease for early prevention. [14]
LPP3 participates in interactions within the triacylglyceride synthesis and sphingolipid metabolism pathways.
Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty acids. They constitute about 0.25% of phospholipids in the bilayer.
Lipid signaling, broadly defined, refers to any biological cell signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses. Lipid signaling is thought to be qualitatively different from other classical signaling paradigms because lipids can freely diffuse through membranes. One consequence of this is that lipid messengers cannot be stored in vesicles prior to release and so are often biosynthesized "on demand" at their intended site of action. As such, many lipid signaling molecules cannot circulate freely in solution but, rather, exist bound to special carrier proteins in serum.
Phospholipase D (EC 3.1.4.4, lipophosphodiesterase II, lecithinase D, choline phosphatase, PLD; systematic name phosphatidylcholine phosphatidohydrolase) is an anesthetic sensitive and mechanosensitive enzyme of the phospholipase superfamily that catalyses the following reaction
sn-Glycerol 3-phosphate is the organic ion with the formula HOCH2CH(OH)CH2OPO32-. It is one of two stereoisomers of the ester of dibasic phosphoric acid (HOPO32-) and glycerol. It is a component of bacterial and eukaryotic glycerophospholipids. From a historical reason, it is also known as L-glycerol 3-phosphate, D-glycerol 1-phosphate, L-α-glycerophosphoric acid.
A lysophosphatidic acid (LPA) is a phospholipid derivative that can act as a signaling molecule.
The lysophospholipid receptor (LPL-R) group are members of the G protein-coupled receptor family of integral membrane proteins that are important for lipid signaling. In humans, there are eleven LPL receptors, each encoded by a separate gene. These LPL receptor genes are also sometimes referred to as "Edg".
Autotaxin, also known as ectonucleotide pyrophosphatase/phosphodiesterase family member 2, is an enzyme that in humans is encoded by the ENPP2 gene.
Endothelial lipase (LIPG) is a form of lipase secreted by vascular endothelial cells in tissues with high metabolic rates and vascularization, such as the liver, lung, kidney, and thyroid gland. The LIPG enzyme is a vital component to many biological processes. These processes include lipoprotein metabolism, cytokine expression, and lipid composition in cells. Unlike the lipases that hydrolyze Triglycerides, endothelial lipase primarily hydrolyzes phospholipids. Due to the hydrolysis specificity, endothelial lipase contributes to multiple vital systems within the body. On the contrary to the beneficial roles that LIPG plays within the body, endothelial lipase is thought to play a potential role in cancer and inflammation. Knowledge obtained in vitro and in vivo suggest the relations to these conditions, but human interaction knowledge lacks due to the recent discovery of endothelial lipase. Endothelial lipase was first characterized in 1999. The two independent research groups which are notable for this discovery cloned the endothelial lipase gene and identified the novel lipase secreted from endothelial cells. The anti-Atherosclerosis opportunity through alleviating plaque blockage and prospective ability to raise High-density lipoprotein (HDL) have gained endothelial lipase recognition.
Lysophosphatidic acid receptor 1 also known as LPA1 is a protein that in humans is encoded by the LPAR1 gene. LPA1 is a G protein-coupled receptor that binds the lipid signaling molecule lysophosphatidic acid (LPA).
Sphingosine-1-phosphate receptor 3 also known as S1PR3 is a human gene which encodes a G protein-coupled receptor which binds the lipid signaling molecule sphingosine 1-phosphate (S1P). Hence this receptor is also known as S1P3.
Lysophosphatidic acid receptor 2 also known as LPA2 is a protein that in humans is encoded by the LPAR2 gene. LPA2 is a G protein-coupled receptor that binds the lipid signaling molecule lysophosphatidic acid (LPA).
The enzyme phosphatidate phosphatase (PAP, EC 3.1.3.4) is a key regulatory enzyme in lipid metabolism, catalyzing the conversion of phosphatidate to diacylglycerol:
Lysophosphatidic acid receptor 3 also known as LPA3 is a protein that in humans is encoded by the LPAR3 gene. LPA3 is a G protein-coupled receptor that binds the lipid signaling molecule lysophosphatidic acid (LPA).
Lipid phosphate phosphohydrolase 1 also known as phosphatidic acid phosphatase 2a is an enzyme that in humans is encoded by the PPAP2A gene.
Lipid phosphate phosphohydrolase 2 is an enzyme that in humans is encoded by the PPAP2C gene.
1-acyl-sn-glycerol-3-phosphate acyltransferase alpha is an enzyme that in humans is encoded by the AGPAT1 gene.
The human gene AGK encodes the enzyme mitochondrial acylglycerol kinase.
Vascular endothelial growth factor A (VEGF-A) is a protein that in humans is encoded by the VEGFA gene.
Soluble epoxide hydrolase (sEH) is a bifunctional enzyme that in humans is encoded by the EPHX2 gene. sEH is a member of the epoxide hydrolase family. This enzyme, found in both the cytosol and peroxisomes, binds to specific epoxides and converts them to the corresponding diols. A different region of this protein also has lipid-phosphate phosphatase activity. Mutations in the EPHX2 gene have been associated with familial hypercholesterolemia.
Lysophosphatidic acid phosphatase type 6 is an acid phosphatase enzyme that is encoded in humans by the ACP6 gene.