[10] Perlecan is a large multidomain (five domains, labeled I-V)[5] proteoglycan that binds to and cross-links many extracellular matrix (ECM) components and cell-surface molecules.
[12] Perlecan is highly conserved across species and the available data indicate that it has evolved from ancient ancestors by gene duplication and exon shuffling.
[16][17] The dwarfism exhibited by the perlecan null mouse resembles the phenotype produced by activating mutations in the gene for FGFR3,[18] a receptor for fibroblast growth factors.
Perlecan isolated from developing growth plates has been shown to bind to FGF-2 via its heparan sulfate side chains,[19] and to FGF-18 via domain III of its core protein[20] and mediates their action on FGF receptors.
[25] The heparan sulfate chains of perlecan bind growth factors in the ECM, and serve as co-ligands or ligand enhancers when bound to receptors.
Another study showed that release of HS-bound basic FGF in culture could be achieved through treatment with stromelysin, heparitinase I, rat collagenase and plasmin,[26] and these proteolysis sites are illustrated in figure 1.
[27] In a model of explant growth in vitro using corneal epithelium, Matrix Metalloproteinase (MMP) 2 expression correlates with an initial degradation of the original basement membrane.
The laminin-like globular domain contains the active motif of endorepellin, and is unable to be cleaved by cells expressing mutant and inactive forms of the BMP-1 proteins.
[29] This proteolytic process may have significance in disease as a corresponding fragment was found in the urine of patients suffering end-stage renal failure[30] and in the amniotic fluid of pregnant women who have undergone premature rupture of the membrane.
Extracellular perlecan has been observed at the blastocyst stage of mouse embryonic development, specifically upregulated at the point when the embryo reaches “attachment competence”.
Spatio-temporal specificity in trans-activation of the perlecan gene during development is key to the maturation of basement membranes and thus to the complete separation of epithelia from endothelia and stroma.
[34] In the rat embryo, perlecan expression has been shown to increase in vascular smooth muscle cells (VSMCs) post e19 in fetal development.
[38] Perlecan also showed nerve adhesive properties in a previous study, further suggesting that it may act in an attractive role in combination with laminin rather than a repulsive one.
[40] Taken with the data,[41] that mice lacking the pln gene cannot maintain stable cartilage, it is apparent that perlecan is essential to the maturation and stability of cartilaginous structure.
This led to increased mineralization and expression of osteocyte markers, supporting the data showing that loss of heparan sulfate at the COJ is a key factor in osteogenesis.
[45] It is thought that the driving force behind heparanase and chondroitinase activation of osteogenesis is release of bone morphogenetic protein bound in the heparan sulfate chains.
[51][52] Exon 3 knockout mice also showed decreased wound healing and angiogenesis capabilities when challenged by either epidermal injury or FGF-2 addition to the cornea.
Studies from gene knockout mice and human diseases have also revealed critical in vivo roles for perlecan in cartilage development[56] and neuromuscular junction activity.
In human coronary smooth muscle cells in culture, TGF-β1 signaling showed no effect on perlecan expression although it did upregulate other matrix constituents.
[60] In vivo demonstration of the dynamic regulation of perlecan and its control by extracellular signaling pathways is critical to our understanding of the protein's role in development.
[67] Interferon- γ treatment of blastocyst-stage murine embryos leads to a loss of perlecan expression on the trophectoderm, and thus an embryonic morphology and phenotype in cell culture, which is suggestive that these interferon-γ treated blastocysts would be defective in implantation.
[69] Under hypoxic conditions, this study found that perlecan expression by rat cardiac microvascular endothelial cells was decreased sixty-one percent compared to normal controls.
[70] When T84 intestinal epithelial cells are exposed to hypoxic conditions for 24 hours a significant increase in perlecan mRNA and protein production occurs.
[74] This endothelial cell increase in production of VSMC growth inhibitors (i.e. heparin) is reversed in VSMCs, where mechanical stress induces proliferation.
To study the effect of chemical damage on liver cells, Wistar rats were treated with carbon tetrachloride for 48 hours prior to sacrificing.
[77] A similar finding was shown in acetamenophin treatment of mice, where perlecan and other matrix components were heavily expressed in necrotic lesions of the liver.
Human salivary gland ductal and acinar cells have been successfully grown on a bioactive peptide containing a sequence repeated in domain IV of the perlecan protein.
These cells reproduce acini-like structures similar to those found in the native gland and tight junctions, along with complete basement membranes in culture.
[93] These findings of greater tumorigenesis in vivo are supported by data showing that the C-terminus of the perlecan protein acts as an endostatic module now known as endorepellin.
[101][102] Atherosclerosis is most often the culprit in coronary heart disease and other cardiovascular conditions, and a large aggregation of perlecan protein is symptomatic of advanced atherosclerotic plaques.