Ultrastructural localization of the core protein of a basement membrane-specific chondroitin sulfate proteoglycan in adult rat skin

Basement membrane and interstitial proteoglycans produced by MDCK cells correspond to those expressed in the kidney cortex

Multiple proteoglycans (PGs) are present in all basement membranes (BM) and may contribute to their structure and function, but their effects on cell behavior are not well understood. Their postulated functions include: a structural role in maintaining tissue histoarchitecture, or aid in selective filtration processes; sequestration of growth factors; and regulation of cellular differentiation. Furthermore, expression PGs has been found to vary in several disease states. In order to elucidate the role of PGs in the BM, a well-characterized model of polarized epithelium, Madin-Darby canine kidney (MDCK) cells has been utilized. Proteoglycans were prepared from conditioned medium by DEAE anion exchange chromatography. The eluted PGs were treated with heparitinase or chondroitinase ABC (cABC), separately or combined, followed by SDS-PAGE. Western blot analysis, using antibodies specific for various PG core proteins or CS stubs generated by cABC treatment, revealed that both basement membrane and interstitial PGs are secreted by MDCK cells. HSPGs expressed by MDCK cells are perlecan, agrin, and collagen XVIII. Various CSPG core proteins are made by MDCK cells and have been identified as biglycan, bamacan, and versican (PG-M). These PGs are also associated with mammalian kidney tubules in vivo.

Basement membranes, microfibrils and beta amyloid fibrillogenesis in Alzheimer's disease: high resolution ultrastructural findings

It is known that beta amyloid fibrils are deposited at the basement membrane of the cerebromicrovasculature in the brains of patients with Alzheimer's disease, and the assembly of the fibrils may be in continuation with the core of senile plaques. The fibrils accumulate in a manner similar to that in which microfibrils accumulate in the glomerular basement membrane of the rat kidney during long-term experimental diabetes, and in the alveolar-capillary basement membrane of the normal lung. beta amyloid fibrils in-situ are known to be about 10 nm wide tubular structures and they closely resemble connective tissue microfibrils. Our recent high resolution ultrastructural studies combined with immunogold labeling demonstrated that beta amyloid fibrils in-situ are indeed microfibril-like structures, and the beta protein is associated with their surface in the form of loose assemblies of 1 nm wide flexible filaments. Thus, the result of this study indicates that in-situ a major component of the beta amyloid deposit is the microfibril-like structure. The elucidation of the mechanism of cerebral beta amyloid fibrillogenesis in Alzheimer's disease may therefore require understanding the mechanism of 'normal' microfibrils biogenesis.

Morphogenesis of the glomerular filter: the synchronous assembly and maturation of two distinct extracellular matrices

The morphogenesis of the glomerular filtration apparatus during pre- and postnatal development in the rodent involves the coordinated assembly of two closely apposed but morphologically different extracellular matrices, the glomerular capillary basement membrane and the mesangial matrix. The cellular origin of these matrices is known to be distinct and complex; however, the mechanisms by which these matrices are assembled during morphogenesis are not entirely understood. It has been shown that in the earliest stages of glomerular morphogenesis the nascent glomerular basement membrane exists as a four-layered structure, the product of both the visceral epithelium and capillary endothelium. During the latter stages of glomerular development, the quadrilaminar structure becomes a trilaminar basement membrane, the event thought to occur by fusion of closely apposed basement membrane layers. In subsequent stages of maturation and throughout the life of the animal, the visceral epithelial cells, which line the periphery of the glomerular capillary, are the primary source of newly synthesized basement membrane material. The mesangial matrix, which lacks the specific organization of a basement membrane, first occurs in the developing glomerulus as a diffuse matrix central to the developing glomerular capillaries. During glomerular maturation the mesangial matrix undergoes a compaction/arborization coincident with the ramification of the vascular histoarchitecture of the glomerular tuft. Recent advances in the cell biology of basement membrane now demonstrate that there is a divergence in isoforms of the molecules that comprise the glomerular capillary basement membrane and mesangial matrices during development, possibly coincidental with functional specialization during the process of glomerular maturation.

Basement membrane proteoglycans are of epithelial origin in rodent skin

Basement membrane proteoglycans in mammalian skin comprise at least one chondroitin sulfate proteoglycan and heparan sulfate proteoglycans, including perlecan. In this study, the origins of basement membrane chondroitin sulfate proteoglycan and perlecan were investigated both in vivo and in vitro. For in vivo experiments, pieces of newborn rat epidermis obtained by dispase treatment were grafted onto athymic nude mice. Three and six weeks after grafting, immunofluorescence analysis of the grafted skin was carried out, using monoclonal antibodies specific for rat basement membrane chondroitin sulfate proteoglycan and rat and mouse perlecan. While the isolated rat epidermis was shown to completely lack rat basement membrane chondroitin sulfate proteoglycan and rat basement membrane heparan sulfate proteoglycans, including perlecan, immunofluorescence staining of tissue sections from the grafted sites on mice demonstrated the presence of rat basement membrane chondroitin sulfate proteoglycan and rat perlecan on interfollicular and follicular basement membranes including that separating dermal papillae from adjacent hair follicle epithelium. In contrast, the basement membranes of all dermal capillaries were positive for mouse perlecan, but negative for rat basement membrane chondroitin sulfate proteoglycan and rat perlecan, including the basement membranes of papillary dermal capillaries beneath the rat epidermis. These data suggest that basement membrane proteoglycans of the dermal-epidermal junction and hair follicle epithelium are of epidermal (epithelial) origin in vivo. Stratified rat keratinocytes cultured on a collagen matrix at the air-liquid interface showed the synthesis of perlecan, laminin 1, and type IV collagen in basement membranes, but not clearly detectable basement membrane chondroitin sulfate proteoglycan.

Distribution of heparan sulfate proteoglycans in embryonic chicken neural retina and isolated inner limiting membrane

Quantitative distribution of proteoglycans was studied in retinal neural epithelium and its basement membrane (inner limiting membrane). Heparan sulfate proteoglycans (HSPGs) were primarily associated with both inner and outer plexiform (synaptic) layers, and inner limiting membrane (ILM), as determined by autoradiographs of lyase-digested cryosections. Based on distribution of 35S-sulfate-labeled proteoglycans, the isolated ILM contained on average approximately three fourths of its proteoglycans as HSPGs and one fourth as chondroitin sulfate/dermatan sulfate proteoglycans (CS/DSPGs), whereas the remaining retina contained approximately equal amounts of the two proteoglycans (PGs). Immunohistochemical staining indicates that the core proteins of the HSPGs in the ILM are distinct from those of the plexiform layers. The photoreceptor layer, which other studies have shown to contain much of the extracellular CS/DSPGs, was not examined. Enrichment of distinct HSPGs in the ILM and plexiform layers support the conclusion that the HSPGs may be intimately involved in the different developmental events characterizing the two regions: development and extension of ganglion cell axons in the former, synaptogenesis and neuronal function in the latter.

Structure and antigenicity of the skin basement membrane zone

The skin basement membrane zone is comprised of two major ultrastructural regions, four associated structures, and at least 17 different antigens. In this brief review, the ultrastructure, antigenicity, and ontogeny of normal human skin will be discussed in detail, as will alterations in expression or immune response to selected basement membrane components in specific mechanobullous and autoimmune diseases.