Basement membrane: carbohydrates and x-ray diffraction

Basement Membrane Type IV Collagen and Laminin: An Overview of Their Biology and Value as Fibrosis Biomarkers of Liver Disease

Basement membranes provide structural support to epithelium, endothelium, muscles, fat cells, Schwann cells, and axons. Basement membranes are multifunctional: they modulate cellular behavior, regulate organogenesis, promote tissue repair, form a barrier to filtration and tumor metastasis, bind growth factors, and mediate angiogenesis. All basement membranes contain type IV collagen (Col IV), laminin, nidogen, and perlecan. Col IV and laminin self-assemble into two independent supramolecular networks that are linked to nidogen and perlecan to form a morphological discernable basement membrane/basal lamina. The triple helical region, 7S domain and NCI domain of Col IV, laminin and laminin fragment P1 have been evaluated as noninvasive fibrosis biomarkers of alcoholic liver disease, viral hepatitis, and nonalcoholic fatty liver disease. Elevated serum Col IV and laminin are related to degrees of fibrosis and severity of hepatitis, and may reflect hepatic basement membrane metabolism. But the serum assays have not been linked to disclosing the anatomical sites and lobular distribution of perisinusoidal basement membrane formation in the liver. Hepatic sinusoids normally lack a basement membrane, although Col IV is a normal matrix component of the space of Disse. In liver disease, laminin deposits in the space of Disse and codistributes with Col IV, forming a perisinusoidal basement membrane. Concomitantly, the sinusoidal endothelium loses its fenestrae and is transformed into vascular type endothelium. These changes lead to capillarization of hepatic sinusoids, a significant pathology that impairs hepatic function. Accordingly, codistribution of Col IV and laminin serves as histochemical marker of perisinusoidal basement membrane formation in liver disease. Anat Rec, 300:1371-1390, 2017. © 2017 Wiley Periodicals, Inc.

The hepatic extracellular matrix. I. Components and distribution in normal liver

The unique nature of the hepatic extracellular matrix (ECM) is predicated by the special configuration of the space of Disse. Whereas other epithelial organs have two basement membranes (BM) and a substantial ECM interposed between endothelial and epithelial cells, the liver lobule has no BM and only an attenuated ECM, consisting mostly of fibronectin, some collagen type I, and minor quantities of types III, IV, V, and VI. This configuration, together with the abundant fenestrations and gaps of the sinusoidal endothelial cells, seems ideally suited to facilitate the rapid bidirectional exchange of macromolecules normally taking place between plasma and hepatocytes. During organogenesis, the liver anlage is vascularized by continuous capillaries with BM, but by day 13.5 of development (in the rat) the vessels in the immediate proximity of hepatocytes become fenestrated, lacking specialized junctions and BM, suggesting that the hepatocytes produce signals capable of modulating the endothelial phenotype. In regeneration, hepatocyte proliferation precedes vascular proliferation resulting in the formation of hepatocyte clusters that, temporarily, lack sinusoids. Eventually, vascular proliferation follows and the normal hepatocyte-vascular relationships are restored. During this period laminin synthesis by Ito cells is prominent. As soon as hepatocytes become stable, secretion of the sinusoid phenotype-maintaining factors resumes and laminin synthesis and secretion terminates. The interplay between extracellular matrix and liver cells is essential for normal homeostasis and its modification results in deranged hepatic function.

Biosynthesis of basement membrane by parietal yolk sac cells

The biosynthesis of basement membrane (Reichert's membrane) by parietal yolk sac cells of the mouse embryo was studied using immunohistochemistry and autoradiography with the electron microscope. Fab' fragments of characterized antisera to either a mixture of type IV collagen and laminin, or to type IV collagen alone, were conjugated to horseradish peroxidase for the immunohistochemical study; radiolabeled proline, leucine, and glucosamine were utilized either in vivo or in isolated yolk sac membranes in vitro for autoradiography. Whereas neither of the two antisera employed localized in either the Golgi apparatus or in the cytosol, both localized in the rough endoplasmic reticulum (RER) and in the extracellular basement membrane. Furthermore, no evidence of passage of isotopically labeled precursors of basement membrane from the RER to the Golgi apparatus was observed. Consequently, it is concluded that the basement membrane precursors are synthesized in the RER of parietal yolk sac cells and neither traverse the Golgi apparatus nor diffuse across the cytosol of the cell in the process of secretion. By elimination, secretion must be via direct communications between RER and plasma membrane or via small vesicles observed in the cytosol between RER and plasma membrane. These data are not in accord with the concept of the universality of the Golgi apparatus in the biosynthesis of glycoprotein. Parietal yolk sac cells do not use the Golgi apparatus in the biosynthesis of basement membrane, but do use the Golgi apparatus for the biosynthesis of other proteins.

Properties of a basement membrane-related glycoprotein synthesized in culture by a mouse embryonal carcinoma-derived cell line

Two glycoproteins, GP-1 and GP-2, have been isolated from an extracellular membrane synthesized in cell culture by an embryonal carcinoma-derived cell line. The amino acid and carbohydrate compositions have been determined. Both proteins are rich in half-cystine residues and contain approximately 12-15% carbohydrate. Antibodies have been obtained against one of the glycoproteins, GP-2, in rabbits. The antibody reacts with basement membranes from adult mouse and human kidney glomeruli and tubules, and all basement membranes tested from mouse embryonic tissues. The molecular properties of GP-2 are superficially similar to LETS protein; however, immunological and other criteria show that they are distinct proteins. The presence of LETS protein and GP-2 in basement membranes suggests that there are subtle interactions which are important in adhesion of epithelial cells to basement membranes.

Basement membrane changes under neoplastic oral mucous membrane. Ultrastructural observations, review of the literature, and a unifying concept

This study explores the morphologic nature of the basement membrane under neoplastic oral mucous membrane. Of particular interest is the progression of changes associated with dysplasia, carcinoma in situ, and invasive carcinoma. On the basis of a critical review of the literature and our own ultrastructural observations, we present a unifying concept for the development of these basement membrane changes. This concept proposes that neoplastic epithelial cells may produce a collagenolytic enzyme which is released into the epithelial intercellular spaces. This enzyme permeates to the basement membrane, causes breaks in the basement membrane, and focal loss of stromal area contiguous with intercellular spaces. The neoplastic basal cells develop pseudopodia that eventually extend through the breaks in the basement membrane. This concept suggests that the basement membrane changes herald the progression of carcinoma in situ to invasive carcinoma.