Immunogold quantitation of laminin, type IV collagen, and heparan sulfate proteoglycan in a variety of basement membranes

Urinary biomarkers for amyotrophic lateral sclerosis: candidates, opportunities and considerations

Amyotrophic lateral sclerosis is a relentless neurodegenerative disease that is mostly fatal within 3-5 years and is diagnosed on evidence of progressive upper and lower motor neuron degeneration. Around 15% of those with amyotrophic lateral sclerosis also have frontotemporal degeneration, and gene mutations account for ∼10%. Amyotrophic lateral sclerosis is a variable heterogeneous disease, and it is becoming increasingly clear that numerous different disease processes culminate in the final degeneration of motor neurons. There is a profound need to clearly articulate and measure pathological process that occurs. Such information is needed to tailor treatments to individuals with amyotrophic lateral sclerosis according to an individual's pathological fingerprint. For new candidate therapies, there is also a need for methods to select patients according to expected treatment outcomes and measure the success, or not, of treatments. Biomarkers are essential tools to fulfil these needs, and urine is a rich source for candidate biofluid biomarkers. This review will describe promising candidate urinary biomarkers of amyotrophic lateral sclerosis and other possible urinary candidates in future areas of investigation as well as the limitations of urinary biomarkers.

Effects of Heparan sulfate acetyl-CoA: Alpha-glucosaminide N-acetyltransferase (HGSNAT) inactivation on the structure and function of epithelial and immune cells of the testis and epididymis and sperm parameters in adult mice

Heparan sulfate (HS), an abundant component of the apical cell surface and basement membrane, belongs to the glycosaminoglycan family of carbohydrates covalently linked to proteins called heparan sulfate proteoglycans. After endocytosis, HS is degraded in the lysosome by several enzymes, including heparan-alpha-glucosaminide N-acetyltransferase (HGSNAT), and in its absence causes Mucopolysaccharidosis III type C (Sanfilippo type C). Since endocytosis occurs in epithelial cells of the testis and epididymis, we examined the morphological effects of Hgsnat inactivation in these organs. In the testis, Hgsnat knockout (Hgsnat-Geo) mice revealed statistically significant decrease in tubule and epithelial profile area of seminiferous tubules. Electron microscopy (EM) analysis revealed cross-sectional tubule profiles with normal and moderately to severely altered appearances. Abnormalities in Sertoli cells and blood-testis barrier and the absence of germ cells in some tubules were noted along with altered morphology of sperm, sperm motility parameters and a reduction in fertilization rates in vitro. Along with quantitatively increased epithelial and tubular profile areas in the epididymis, EM demonstrated significant accumulations of electrolucent lysosomes in the caput-cauda regions that were reactive for cathepsin D and prosaposin antibodies. Lysosomes with similar storage materials were also found in basal, clear and myoid cells. In the mid/basal region of the epithelium of caput-cauda regions of KO mice, large vacuolated cells, unreactive for cytokeratin 5, a basal cell marker, were identified morphologically as epididymal mononuclear phagocytes (eMPs). The cytoplasm of the eMPs was occupied by a gigantic lysosome suggesting an active role of these cells in removing debris from the epithelium. Some eMPs were found in proximity to T-lymphocytes, a feature of dendritic cells. Taken together, our results reveal that upon Hgsnat inactivation, morphological alterations occur to the testis affecting sperm morphology and motility parameters and abnormal lysosomes in epididymal epithelial cells, indicative of a lysosomal storage disease.

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 Ultrastructures and Mechanical Properties of the Descement's Membrane in Fuchs Endothelial Corneal Dystrophy

Fuchs endothelial corneal dystrophy (FECD), is the most common corneal endothelial dystrophy, and contributes up to 50% of all corneal transplantations performed in developed countries. FECD develops in Descemet’s membrane (DM) and possibly alters the mechanical properties and internal structures in this basal lamina. In this work, the morphology and mechanical properties of FECD-DMs are studied by transmission electron microscopy (TEM) and quantitative dynamic atomic force microscopy (QD-AFM) at nano scale. Pathological wide-space collagens that are typical of FECD display different mechanical properties in that they are softer than the remaining tissue both for dehydrated- and fully hydrated samples. Additionally, the hydration level has major influence on the mechanical properties. These findings could help to further understand the structural changes in FECD, and possibly be useful for further characterization of the disease, the diagnosis and assessment or even pathologic analysis.

Basement membrane influences intestinal epithelial cell growth and presents a barrier to the movement of macromolecules

This work examines the potential drug delivery barrier of the basement membrane (BM) by assessing the permeability of select macromolecules and nanoparticles. The study further extends to probing the effect of BM on intestinal epithelial cell attachment and monolayer characteristics, including cell morphology. Serum-free cultured Caco-2 cells were grown on BM-containing porous supports, which were obtained by prior culture of airway epithelial cells (Calu-3), shown to assemble and deposit a BM on the growth substrate, followed by decellularisation. Data overall show that the attachment capacity of Caco-2 cells, which is completely lost in serum-free culture, is fully restored when the cells are grown on BM-coated substrates, with cells forming intact monolayers with high electrical resistance and low permeability to macromolecules. Caco-2 cells cultured on BM-coated substrates displayed strikingly different morphological characteristics, suggestive of a higher level of differentiation and closer resemblance to the native intestinal epithelium. BM was found to notably hinder the diffusion of macromolecules and nanoparticles in a size dependent manner. This suggests that the specialised network of extracellular matrix proteins may have a significant impact on transmucosal delivery of certain therapeutics or drug delivery systems.

Fibrinogen, riboflavin, and UVA to immobilize a corneal flap--molecular mechanisms

PURPOSE

Tissue glue containing fibrinogen (FIB) and riboflavin (RF), upon exposure to long wavelength ultraviolet light (UVA, 365 nM) has been proposed potentially to solve long-standing problems presented by corneal wound and epithelial ingrowth side-effects from laser-assisted in situ keratomileuis (LASIK). Data presented in a previous study demonstrated an ability of FIB + RF + UVA to adhere two stromal surfaces; however, to our knowledge no molecular mechanisms have been proposed to account for interactions occurring between corneal extracellular matrix (ECM) and tissue glue molecules. Here, we document several covalent and noncovalent interactions between these classes of macromolecules.

METHODS

SDS-PAGE and Western blot techniques were used to identify covalent interactions between tissue glue molecules and corneal ECM molecules in either the presence or absence of RF and UVA, in vitro and ex vivo. Surface plasmon resonance (SPR) was used to characterize noncovalent interactions, and obtain k(a), k(d), and K(D) binding affinity values.

RESULTS

SDS-PAGE and Western blot analyses indicated that covalent interactions occurred between neighboring FIB molecules, as well as between FIB and collagen type I (Coll-I) proteins (in vitro and ex vivo). These interactions occurred only in the presence of RF and UVA. SPR data demonstrated the ability of FIB to bind noncovalently to corneal stroma molecules, Coll-I, decorin, dermatan sulfate, and corneal basement membrane molecules, laminin and heparan sulfate--only in the presence of Zn(2+).

CONCLUSIONS

Covalent and (zinc-mediated) noncovalent mechanisms involving FIB and stromal ECM molecules contribute to the adhesion created by FIB + RF + UVA.

Fibrinogen, riboflavin, and UVA to immobilize a corneal flap--conditions for tissue adhesion

PURPOSE

Laser-assisted in situ keratomileus (LASIK) creates a permanent flap that remains non-attached to the underlying laser-modified stroma. This lack of permanent adhesion is a liability. To immobilize a corneal flap, a protocol using fibrinogen (FIB), riboflavin (RF), and ultraviolet (UVA) light (FIB+RF+UVA) was devised to re-adhere the flap to the stroma.

METHODS

A model flap was created using rabbit (Oryctolagus cuniculus) and shark (Squalus acanthias) corneas. Solutions containing FIB and RF were applied between corneal strips as glue. Experimental corneas were irradiated with long wavelength (365 nm) UVA. To quantify adhesive strength between corneal strips, the glue-tissue interface was subjected to a constant force while a digital force gauge recorded peak tension.

RESULTS

In the presence of FIB, substantive non-covalent interactions occurred between rabbit corneal strips. Adhesiveness was augmented if RF and UVA also were applied, suggesting formation of covalent bonds. Additionally, exposing both sides of rabbit corneas to UVA generated more adhesion than exposure from one side, suggesting that RF in the FIB solution catalyzes formation of covalent bonds at only the interface between stromal molecules and FIB closest to the UVA. In contrast, in the presence of FIB, shark corneal strips interacted non-covalently more substantively than those of rabbits, and adhesion was not augmented by applying RF+UVA, from either or both sides. Residual RF could be rinsed away within 1 hour.

CONCLUSIONS

Glue solution containing FIB and RF, together with UVA treatment, may aid immobilization of a corneal flap, potentially reducing risk of flap dislodgement.

Localization and distribution of laminin in the basal lamina of certain mechanoreceptors—an immunogold study

The applied immunogold cytochemical technique in investigating the cytologic distribution of the laminin (LAM) molecule in the capsulated Pacinian and Herbst mechanoreceptors shows the presence of LAM around most elements of the receptor structures. The LAM immunoreactivity (LAM-IR) is best expressed in the vicinity of the perineural capsule cells of both receptor types, where it is primarily concentrated around the perinuclear regions as well as the cytoplasmic lamellae. Such a localization overlaps with the already known ultrastructural localization of a basal lamina (BL) around these cells. Laminin immunoreactivity is less well expressed around the modified Schwann cells. Even in these cells, however, there is an apparent immunoreaction around the cytoplasmic lamellae regardless of the lamellar location. In both receptor types, there is no LAM-IR in the cells of the subcapsular space. Of particular significance we consider the localization of gold particles (respectively the presence of a BL) between the innermost lamellae of the modified Schwann cells and the non-myelinated part of the receptor nerve fiber and their endings, as well as around the axoplasmic protrusions of the nerve endings. We discuss the role of the BL and LAM in the investigated rapidly adapting mechanoreceptors and their trophic influence upon the sensory regions. We also assume the arresting and selective effect of these membranes in building up the ion channels of the axolemma which probably has a certain importance in mechanotransduction.

Development of the corneal stroma, and the collagen-proteoglycan associations that help define its structure and function

The cornea of the eye is a unique, transparent connective tissue. It is comprised predominantly of collagen fibrils, remarkably uniform in diameter and regularly spaced, organized into an intricate lamellar array. Its establishment involves a precisely controlled sequence of developmental events in which the embryonic cornea undergoes major structural transformations that ultimately determine tissue form and function. In this article, we will review corneal developmental dynamics from a structural perspective, consider the roles and interrelationships of collagens and proteoglycans, and comment on contemporary concepts and current challenges pertinent to developmental processes that result in an optically clear, mature cornea.

Ultrastructure and composition of basement membrane separating mature ameloblasts from enamel

At a late stage of amelogenesis, a basement-membrane-like (BML) structure appears between mature ameloblasts and the enamel surface. Although this BML structure is known to contain certain basement membrane components, its detailed nature and role were not well defined. As such, this study examined the BML structure using high-resolution electron microscopy combined with immunohistochemical staining. Mandibular rat incisors were processed for the preparation of Epon sections for ultrastructural observations, and frozen sections were used for immunostaining laminin, heparan sulphate proteoglycan (HSPG) and type IV collagen. The BML structure was characterized by the presence of abundant ribbon-like 'double tracks', 4.5-5.0 nm wide; the form known to be taken by HSPG in basal laminae. The main ultrastructural component of basal laminae, known as 'cords', was replaced by fine filaments of type IV collagen. Immunohistochemical staining of the BML structure showed an intense reaction for HSPG, moderate staining for type IV collagen and negligible staining for laminin. These observations indicate that this structure is an atypical basement membrane in which the cord network is replaced by type IV collagen filaments. However, the BML structure was found to be unusually rich in HSPG, similar to kidney glomerular basement membrane. It is likely that this specialized basement membrane mediates firm attachment of mature ameloblasts to the enamel surface, and filters the influx and efflux of materials to and from enamel during maturation.

Sodium hyaluronate (hyaluronic acid) promotes migration of human corneal epithelial cells in vitro

PURPOSE

Sodium hyaluronate (hyaluronic acid) is known to promote corneal epithelial wound healing in vivo and in vitro, in animal experiments. Sodium hyaluronate is the ligand for CD44, a cell surface adhesion molecule which has been found on normal human corneal epithelial cells. The purpose of this study was to investigate the effect of sodium hyaluronate on human corneal epithelial cell migration, proliferation, and CD44 receptor expression.

METHODS

Human corneal epithelial cell cultures were established from 32 donor corneoscleral rims and maintained separately in three different culture conditions: (1) culture medium only, (2) sodium hyaluronate enriched (0.6 mg/ml) medium, and (3) hydroxypropylmethylcellulose enriched (2.5 mg/ml) medium. The total area of migrating epithelial cell sheets in each case was measured by planimetry on days 4, 8, 12, and 16. Cytospin preparations of cells cultured in the different culture conditions were examined immunohistochemically for proliferation and CD44 receptor expression using antibodies directed against Ki67 and CD44 respectively.

RESULTS

Cells cultured in the presence of sodium hyaluronate showed significantly increased migration at days 12 and 16 (Friedmen test: p = 0.0012, day 16; p = <0.001, day 12) compared with cells cultured in the other media. There was no difference in cell proliferation (Ki67) or CD44 expression on cells cultured in the different culture conditions.

CONCLUSIONS

Sodium hyaluronate promotes migration but not proliferation or CD44 expression on human corneal epithelial cells in vitro. The beneficial effect of sodium hyaluronate in corneal wound healing is likely to be related to rapid migration of cells leading to rapid wound closure. This may be facilitated by the adhesion between CD44 on the cells and hyaluronic acid, which coats the surface of the denuded cornea.

Decrease in laminin content and protein excretion rate after five sixths nephrectomy and low-dose irradiation in the rat

The effect of low-dose irradiation on laminin distribution and urine protein excretion in the remnant rat kidney has been studied. The rat remnant kidney formed after 5/6 nephrectomy is an experimental model of chronic renal failure. In the remnant kidney, focal segmental glomerulosclerosis is developed characterized by focal or segmental sclerosis in glomeruli, alterations in the tubules and thickening of the glomerular basement membrane. Low dose irradiation has been presumed to suppress sclerotic processes. In this study 24 male Wistar rats were subdivided into the nephrectomized group, nephrectomized and irradiated groups (1 or 3 Grey), and healthy control group. Animals were sacrificed at 2, 4 and 8 weeks after beginning the experiment. Laminin immunohistochemical staining was found along the tubular and glomerular basement membranes in all experimental groups, but with varying intensity. Laminin content in the basement membranes was decreased in early stages (week 2), especially after irradiation followed by increase during the later stages with relatively high levels at the end of the experiment (week 8). Irradiation at a dose of 3 Grey decreased protein excretion compared to the nephrectomized rats at all stages, while 1 Grey dose was ineffective. Based on decreased proteinuria we conclude that moderate low-dose irradiation has beneficial effects on the rat remnant kidney and that laminin in basement membranes is probably not the most crucial component in regulating membrane permeability.

Immunoelectron microscopic study of PECAM-1 expression on lymphatic endothelium of the human tongue

The expression of platelet-endothelial cell adhesion molecule-1 (PECAM-1) on lymphatic and blood vessels of the human tongue was examined with fluorescence and transmission electron microscopy (TEM). The study used anti-desmoplakins antiserum for light microscopic identification of the lymphatic vessels, plus a pre-embedding immunogold electron microscopic technique for TEM observations. Before making TEM observations, cryostat serial sections were immunostained with anti-desmoplakins or anti-PECAM-1 and then embedded. Semithin sections from each cryostat section were photographed under a light microscope and compared in order to identify the lymphatic vessels expressing PECAM-1. In fluorescence microscopy, PECAM-1 expression on lymphatic vessels was weaker than that on blood vessels. TEM observations showed that PECAM-1 expression on the blood vessels was observed only on the luminal surface of the endothelium. In lymphatic vessels, PECAM-1 expression was found both on the luminal and abluminal surfaces of the endothelium. The density of the PECAM-1 reaction products was lower in lymphatic vessels than in blood vessels. The density of PECAM-1 reaction products on the luminal surface of lymphatic vessels was higher than on the abluminal surfaces. The results suggest that blood vessels are more active than lymphatic vessels in leukocyte migration. The expression of PECAM-1 on the abluminal surface of lymphatic endothelium may allow leukocytes to adhere to the endothelium and interact in their migration from tissue into lymphatic vessels.

Desmoplakin as a specific marker of lymphatic vessels

The usefulness of immunostaining with anti-desmoplakin antibody for light microscopic identification of lymphatic vessels was examined in cryostat sections of the human tongue. The results were compared with laminin, 5'-nucleotidase (5'-Nase), and factor VIII staining. Immunoelectron microscopic observation was also performed to confirm that the vessels reacting with anti-desmoplakin were lymphatic vessels. Under the immunoelectron microscopic, the vessels reacting with anti-desmoplakin showed ultrastructural features characteristic of lymphatic vessels: thin endothelial walls, no or incomplete basal lamina, open junctions, and overlapping endothelium. In general, lymphatic vessels identified by anti-desmoplakin reacted strongly with 5'-Nase, but showed weak or no reactivity with anti-laminin and anti-factor VIII. Blood vessels showed no reactivity with anti-desmoplakin, but reacted strongly with anti-laminin and anti-factor VIII. However, some blood and lymphatic vessels showed intermediate reactivity with anti-laminin, anti-factor VIII, and 5'-Nase. It was difficult to identify these as blood or lymphatic vessels only by the reactivity differences. The results indicate that anti-desmoplakin antibody specifically distinguishes lymphatic vessels and is useful for studying the fine distribution of lymphatic vessels under light microscopy.

Nidogen-1. Expression and ultrastructural localization during the onset of mesoderm formation in the early mouse embryo

Nidogen-1, a key component of basement membranes, is considered to function as a link between laminin and collagen Type IV networks and is expressed by mesenchymal cells during embryonic and fetal development. It is not clear which cells produce nidogen-1 in early developmental stages when no mesenchyme is present. We therefore localized nidogen-1 and its corresponding mRNA at the light and electron microscopic level in Day 7 mouse embryos during the onset of mesoderm formation by in situ hybridization, light microscopic immunostaining, and immunogold histochemistry. Nidogen-1 mRNA was found not only in the cells of the ectoderm-derived mesoderm but also in the cytoplasm of the endoderm and ectoderm, indicating that all three germ layers express it. Nidogen-1 was localized only in fully developed basement membranes of the ectoderm and was not seen in the developing endodermal basement membrane or in membranes disrupted during mesoderm formation. In contrast, laminin-1 and collagen Type IV were present in all basement membrane types at this developmental stage. The results indicate that, in the early embryo, nidogen-1 may be expressed by epithelial and mesenchymal cells, that both cell types contribute to embryonic basement membrane formation, and that nidogen-1 might serve to stabilize basement membranes in vivo. (J Histochem Cytochem 48:229-237, 2000)

Ultrastructural triple localization of laminin-1, nidogen-1, and collagen type IV helps elucidate basement membrane structure in vivo

The basement membrane models which have been proposed to date are generally based on biochemical data, mainly binding studies and artificially synthesized polymers in vitro. Basically these have led to models proposing two three-dimensional laminin-1 and collagen type IV networks interconnected by nidogen-1. Whether they reflect the in vivo basement membrane structure is still not clear. We localized laminin-1, nidogen-1, and collagen type IV ultrastructurally in adult and fetal mouse kidney basement membranes with the help of immunogold-histochemistry performing double and triple localization to try to elucidate the molecular organization of basement membranes in vivo. We found laminin-1, nidogen-1, and collagen type IV distributed over the entire basement membranes in adult and fetal kidneys. This contradicts earlier studies ascribing laminin-1 to the lamina lucida and collagen type IV to the lamina densa. In addition, various basement membrane segments exhibited an organized labeling pattern for the BM components. Double-labeling revealed co-localization of laminin-1 and nidogen-1. We conclude that the combination of laminin-1 with collagen type IV as double-network basement membrane partially interconnected by nidogen-1 is found already in the early fetal kidney in vivo. However, our data cannot exclude the possibility of other variants of basement membrane assemblages. This is also indicated by a changing structure even in individual segments of one basement membrane type which renders a more flexible basement membrane architecture plausible.

Immunohistochemical demonstration of lymphatic vessels in human dental pulp

The existence of lymphatic vessels in dental pulp has been a matter of continuing controversy because of the difficulty of discriminating them in ordinary stained tissue sections. Recently, we have succeeded in establishing a new identification method for lymphatic vessels in human frozen sections by using a commercial monoclonal antibody specific for the human thoracic duct and anti-human laminin antiserum. The present study aimed to examine the lymphatic vessels in human dental pulp using the new immunostaining method, and compared the results with those in human small intestine. The study clearly demonstrated the distribution of lymphatic vessels in human dental pulp. Large lymphatic vessels are located in the central part of the pulp and there are small lymphatic vessels in the periphery of the pulp. This suggests that lymphatic drainage of the human dental pulp starts from the periphery of the pulp and collects in the central part of the pulp. A notable difference between the small intestine and dental pulp was found in the immunoreactivity of lymphatic vessels to anti-human laminin anti-serum. In small intestine, immunoreactivity was significantly weaker than that of the blood vessels, whereas in dental pulp, that of lymphatic vessels was almost the same as blood vessels, except for some lymphatic vessels showing very weak reactivity. These findings suggest that the development of the basement membrane in both the lymphatic and blood vessels of human dental pulp is not as marked as in other tissue.

Immunocytochemistry of extracellular matrix components in the rat seminiferous tubule: electron microscopic localization with improved methodology

BACKGROUND

Cell-cell interactions between Sertoli, myoid, Leydig, and germ cells are thought to be essential for spermatogenesis. These cells interact with each other through the extracellular matrices (ECMs) of the testicular lamina propria, which thus may have an important function in spermatogenesis. For an understanding of the role of ECMs in spermatogenesis, it is important to investigate the molecular constitution of the testicular ECM. We examined the distribution of type IV, V, and VI collagens (Cols), laminin (LM), fibronectin (FN), and heparan sulfate proteoglycan (HSPG) in the rat testicular lamina propria.

METHODS

Adult rat testes were fixed with 4% paraformaldehyde and 0.2% glutaraldehyde. Ultrathin frozen sections were made and immunolabeling was performed according to the method of Tokuyasu (1986 J. Microsc., 143:139-149). Alternatively, for preembedding immunocytochemistry, we used labeling with nanogold, followed by silver enhancement and gold toning. The tissues were then fixed with osmium and embedded in Epon (Sawada and Esaki 1994 J. Electron Microsc., 43:361-366). These specimens were examined in a JEOL JEM-100C transmission electron microscope operated at 80 kV.

RESULTS

Col IV, LM, and HSPG were localized in the basement membranes of the seminiferous tubule (ST-BM) and in the BM of myoid cells. Cols V and VI, and FN were localized both in the connective tissue between the seminiferous tubule and the myoid cells (tubule-myoid connective tissue) and in the connective tissue between the myoid cells and the lymphatic endothelial cells (myoid-endothelium connective tissue). Furthermore, statistical analysis of the micrographs of immunogold labeling for Col IV, LM, and FN around the ST-BM suggested that the Col IV molecule is located uniformly in the ST-BM, whereas the LM molecule is distributed mainly in the lamina rara of ST-BM, and the FN molecule appears to be present predominantly in the tubule-myoid connective tissue.

CONCLUSIONS

Distinct distribution patterns were observed for each antigen within the testicular lamina propria at the ultrastructural level. However, localization of some components was not consistent with localizations reported by others.

Identification of lymphatic vessels by using a monoclonal antibody specific for the human thoracic duct

Light microscopic identification of lymphatic vessels of the human small intestine was studied immuno-histochemically with a monoclonal antibody specific for human thoracic duct (mAb-D) and rabbit anti-human laminin antibody (anti-L). Two types of vessels were observed with anti-L; one strongly reacted with regularly outlined vessels and the other weakly reacted with irregularly outlined vessels and thin walls. Immunoreactivity to mAb-D was strong in the weakly reacting vessels, and the strongly reacting vessels did not react to mAb-D. Immunoreactivity of lymphatic vessels to anti-L has been reported to be weaker than that of the blood vessels; only irregularly outlined vessels which were weakly immunostained with anti-L reacted to mAb-D and no cross-reaction to mAb-D was observed in the regularly outlined vessels. This indicates that the vessels strongly reacting with anti-L are blood vessels and the vessels immunostained with mAb-D must be lymphatics. The study shows that it is possible to identify lymphatic vessels light microscopically by mAb-D. This method will be useful in studying the fine distribution of lymphatic vessels in normal tissue and also in pathological tissue such as metastasis of malignant tumors.

Immunolocalization of transforming growth factor-alpha and its receptor in the normal and hyperoxia-exposed neonatal rat retina

PURPOSE

Transforming growth factor-alpha (TGF-alpha) is a mitogenic polypeptide for a variety of different cells types including retinal neurons and glial cells. We have examined the temporal and spatial expression of TGF-alpha and its receptor in the normal and hyperoxia-exposed neonatal rat retina to determine if the expression is consistent with a role in retinal development and response to retinal injury.

METHODS

We have used immunohistochemistry to examine TGF-alpha and epidermal growth factor receptor (EGF-R) on postnatal days (1, 5, 10, 14, 18, and 25). To examine TGF-alpha and EGF-R expression after retinal injury we studied the retinas from rats which were exposed to 80% oxygen for 10 days and then recovered in room air. Immunolocalization of type IV collagen was performed to examine the retinal vasculature development after hyperoxia.

RESULTS

The pattern of TGF-alpha and EGF-R expression in the neural retina evolved from a diffuse pattern on postnatal day 1 to restricted sites on postnatal day 14. The TGF-alpha immunoreactivity was consistent with localization in Müller cells on postnatal day 14. Both TGF-alpha and EGF-R patterns were altered in the retinas from rats that had been exposed to hyperoxia and recovered in room air for 4 days. The type IV confirmed immunostaining confirmed vaso-obliteration in the deep layer of retinal vessels after hyperoxia.

CONCLUSIONS

Our findings of altered expression of TGF-alpha and EGF-R during retinal development suggests a biological function for this growth factor, possibly promoting retinal cell proliferation, differentiation, and survival. The altered immunolocalization of TGF-alpha and EGF-R in the hyperoxia-exposed retina suggest that TGF-alpha is likely involved in the retinal response to injury.

Laminin stimulates rapid epithelial restitution of rabbit duodenal mucosa in vitro

BACKGROUND

This study investigated the effect of the basal lamina constituents fibronectin, collagen IV, and laminin on epithelial restitution of rabbit duodenum in vitro.

METHODS

Rabbit duodenal mucosal sheets were mounted in Ussing chambers, luminally exposed to 10 mM HCI for 10 min, and incubated with buffer or luminal buffer containing 25-100 micrograms/ml of collagen IV, fibronectin, laminin, or polyclonal antisera directed against these proteins (diluted 1:50-1:20) for 3 h. Resistance was calculated from potential difference and short-circuit current. Mucosal damage was assessed by morphometry on hematoxylin- and eosin-stained sections.

RESULTS

Acid exposure caused a 40% drop in resistance (119 +/- 5 versus 71 +/- 5 Ohm.cm2 before versus after injury; P < 0.05, n = 6) and mucosal damage of 58 +/- 4% (n = 6). Three hours after injury resistance was 102 +/- 6, 117 +/- 4, and 48 +/- 5 Ohm.cm2 in the control, laminin, and anti-laminin groups, respectively. Furthermore, 36 +/- 2%, 16 +/- 2%, and 64 +/- 5% of the mucosa was damaged in the control, laminin, and anti-laminin groups, respectively, 3 h after injury (P < 0.05 versus controls). Laminin promoted epithelial wound closure by stimulation of enterocyte migration, which was inhibited by anti-laminin. Fibronectin, collagen IV, anti-fibronectin, and anti-collagen IV did not impair restitution.

CONCLUSION

Our results show that laminin promotes electrophysiologic restoration and epithelial restitution of rabbit duodenum in vitro. We therefore suggest that laminin plays an important part in the orchestration of epithelial integrity and barrier function.

Immunohistochemistry of human cutaneous Meissner and pacinian corpuscles

This paper reviews the immunohistochemical characteristics of two kinds of human cutaneous sensory nerve formations (SNFs), the Meissner and Pacinian corpuscles. In both kinds of SNF the central axon might be easily identifiable because it displays immunoreactivity (IR) for the neuroendocrine markers neuron-specific enolase and protein gene product 9.5, as well as for neuron-specific intermediate filament proteins, i.e., neurofilaments. Other intermediate filament proteins such as vimentin are localized in the lamellar cells of Meissner corpuscles, and in the inner core, outer core and capsule of Pacinian corpuscles. However, they lack cytokeratins or glial fibrillary acidic protein IR. On the other hand, and in agreement with ultrastructural data, IR for basement membrane constituents laminin and type IV collagen is found underlying all SNF constituents, with the exception of the axon. One of the mechanisms involved in the maintenance of intracellular calcium ions (Ca2+) homeostasis is the calcium binding proteins. Ca2+ play a key role in the mechanoelectric transduction and have been localized in SNFs. In this way IR for the Ca(2+)-binding proteins calbindin D28K, parvalbumin and calretinin, is present and colocalized in both Meissner and Pacinian corpuscles; furthermore, S-100 protein is exclusively localized in the lamellar cells and the inner core. On the other hand, the skin is a main source of neurotrophins for a subset of neural crest sensory neurons, some of which end forming SNF. These factors are conveyed via retrograde axonal transport from the skin to the cell body of the responsive neurons. Interestingly, Meissner and Pacinian corpuscles also display IR for the pan-neurotrophin low-affinity receptor (p75), and for the trkA receptor protein, a basic constituent of the high-affinity receptor for some neurotrophins. Moreover, they express IR for the epidermal growth factor receptor. Finally, other antigens not proper to the cells forming human cutaneous SNF, such as the epithelial membrane antigen and the leucocytary antigen-7, have also been detected.

Cellular distribution patterns of lanthanum and morphometry of rat hearts exposed to different degrees of ischemic stress

BACKGROUND

The element lanthanum (La) can be used as a tracer for verification of membrane permeability. The aim of this study was to establish whether 1) distribution of La in the myocardium of rat hearts depends on the degree of ischemic stress and 2) morphometrically determined cell and mitochondrial swelling correlates with the La distribution.

MATERIALS AND METHODS

Isolated beating rat hearts were arrested by coronary perfusion with the cardioplegic solution Custodiol (controls) or by aortic cross clamping followed by exposure to different degrees of ischemic stress. The solutions for perfusion-and postfixation as well as for rinsing contained 1.1% La(NO3)3. Cellular and mitochondrial swelling were determined morphometrically and myocytes exhibiting intracellular La were quantified and stated as percentage of test fields.

RESULTS

Immediately after cardiac arrest La was present as precipitates only in a few myocytes adjacent to the outer mitochondrial membrane as seen by cTEM and ESI. In such cells La was also detected by EELS in mitochondrial matrix and myofibrils. Advanced ischemic stress led to an increase of the percentage of myocytes containing detectable intracellular La. After 45 min ischemia at 30 degrees C, myocytes and mitochondria showed a remarkable edema and different intracellular distribution patterns of La. After 90 min of ischemia at 20 degrees C interruptions of sarcolemma could only be detected in a few of the swollen myocytes. Roundish La granules were seen in the myofibrils. The percentage of myocytes containing intracellular La and the extent of cellular and mitochondrial swelling showed a significant correlation.

CONCLUSIONS

Patterns of intracellular La distribution depend on the degree of ischemic stress and correspond to the degree of cellular as well as mitochondrial edema. These results point at a direct relation between alterations of membrane permeability and development of edema.

The biology of perlecan: the multifaceted heparan sulphate proteoglycan of basement membranes and pericellular matrices

Images

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.

Distribution of basal lamina type IV collagen and laminin in normal rat tongue mucosa and experimental oral carcinoma: ultrastructural immunolocalization and immunogold quantitation

The relationship of basal lamina, a form of specialised extracellular matrix which separates epithelial cells and other cell types from adjacent stroma, to the behaviour of malignant neoplasms of epithelial origin is not well understood. However, it is widely acknowledged that the properties of local invasion and metastasis of carcinomas are linked to extracellular matrix (including basal lamina) changes. In the present study, the distribution of the major basal lamina components, type IV collagen and laminin, in normal rat tongue mucosa and experimentally induced oral carcinomas was investigated using post-embedding immunogold techniques and electron microscopy. The expression of these components was also quantitatively analysed using morphometry and immunocytochemistry. Results indicated that type IV collagen and laminin were confined to the lamina densa of normal oral epithelial basal lamina, and that both components were also detected in the lamina densa of basal lamina associated with carcinomas, and in the extracellular matrix of tumours. Furthermore, laminin was detected within stromal fibroblasts in normal tissues and experimental carcinomas. Quantitative analysis indicated that expression of laminin was significantly increased in carcinomas. In contrast, type IV collagen expression was significantly decreased. The quantitative changes observed in the two basal lamina constituents may be related to the process of tumour invasion, reflecting altered metabolic activities of tumour and stromal cells. These observations may be of use in understanding the architectural characteristics of oral mucosa basal lamina and in assessing the malignant potential of epithelial dysplasias or "premalignant" lesions.

Characterization of the Han:SPRD rat model for hereditary polycystic kidney disease

The Han:SPRD rat model for inherited polycystic kidney disease (PKD) was characterized (clinical parameters, morphology, immunohistochemistry and in situ hybridization). Homozygous animals died of uremia after three to four weeks with severe cystic transformation of virtually all nephrons and collecting ducts (serum urea: 616 +/- 195 mg/dl; kidney-to-body weight ratio: > 20%). In heterozygotes, slow progression of the disease led to death between the 12th and 21st month (median: 17 months; serum urea levels above 200 mg/dl). Kidney enlargement was moderate, and cysts were restricted to the cortex and outer medulla. Immunohistochemical markers showed that approximately 75% of the cysts were derived from the proximal tubule. Cystic transformation started in the proximal tubule with a sharp onset of basement membrane alteration and a loss of epithelial differentiation restricted to small focal areas. In these areas, alpha 1(IV) collagen and laminin B1 mRNA were enhanced as revealed by isotopic and non-isotopic in situ hybridization. Fibroblasts underlying the affected tubular portions were involved in matrix overexpression resulting in subepithelial accumulation of immunoreactive collagen IV and laminin. In later stages of cystic transformation distal nephron segments were affected as well. A reversal in epithelial polarity as judged from Na,K-ATPase-immunoreactivity was not observed. Renal immunoreactive renin-status was significantly decreased. Hematocrit was lowered in heterozygotes (40.4 +/- 5.8 vol% compared to 46.7 +/- 1.99 vol% in controls; P < 0.05) and total renal EPO mRNA was reduced to 36 +/- 14% of the mean value of control animals, whereas serum EPO levels were not significantly altered. We conclude that the Han:SPRD rat is a useful model for the study of human ADPKD since both diseases are similar in several aspects. The model is particularly suitable for the study of epithelial-mesenchymal interactions at the beginning of tubular cystic transformation.

Application of cationic probes for the ultrastructural localization of proteoglycans in basement membranes

The application of cationic probes for the ultrastructural detection of proteoglycans in basement membranes is reviewed. Proteoglycans are highly negatively charged macromolecules due to their glycosaminoglycan side chains. The interaction of cationic probes with proteoglycans is of an electrostatic nature. Methods are discussed to increase the specificity of probes for proteoglycans. The use of phthalocyanin-like dyes such as Cuprolinic blue, according to the critical electrolyte concentration method, results in a selective staining of proteoglycans. Enzymatic or chemical digestions, however, should be done to validate the proteoglycan nature of the dye-positive granules/filaments, and to establish the class of proteoglycan. The value of cationic probes in basement membrane research on development and pathology is discussed. The potential for deducting molecular information from the ultrastructural appearance of stained proteoglycans is indicated.

Morphology of the basement membrane

The aim of this contribution is to summarize our knowledge of the morphology of the basement membrane (BM). The first step in this direction is the attempt to define this term. The BM is composed of the Lamina lucida, densa, and fibroreticularis. Subsequently, the historical development of this term is discussed. Our main interest is, of course, focused on the description of the BM-structure up to the macromolecular level and the special forms of this structure. This is supplemented by discussing its chemical composition and establishing a relationship between morphology and biochemistry. The obtained findings yielded some indications as to the molecular composition of the BM which may serve for the construction of "models." The composition of the Lamina lucida (L.l.) and the Lamina or Pars fibroreticularis (L.f.) must be discussed separately, since, if present, they show a different and strongly varying structure (L.f.). An important aspect is the function of this extracellular layer which comprises mechanical tasks up to inductive effects. Finally, the concepts of the formation of the BM, especially of the Lamina densa (L.d.), are summarized. It obviously consists of a sequence of individual steps which starts with expression and secretion of the L.d.-components and is followed by an induction of integrin expression.

Alterations in the glomerular charge barrier in human lupus nephritis

Renal tissue taken from ten patients with proteinuria and diagnosed as suffering from human lupus nephritis was examined by a post-embedding charge labelling method using cationic gold (CG). The method allows localization of the anionic charge in the glomerular epithelial cell coat and/or glomerular basement membrane (GBM). Our results demonstrate that in human lupus nephritis there are gaps in the charge barrier associated with immune deposits found in the lamina rara externa of the GBM. These data suggest that the loss of glomerular fixed anionic charges in the GBM may play an important role in the development of proteinuria in patients suffering from lupus nephritis.

Glomerular distribution of type IV collagen in diabetes by high resolution quantitative immunochemistry

We examined type IV collagen distribution and density in human diabetic kidneys by quantitative immunogold electron microscopy. We studied normal kidney transplant donors and "slow-track" and "fast-track" insulin dependent diabetic (IDDM) patients. The "slow-track" patients had IDDM for > or = 20 years and mesangial volume fraction (VvMes/glom) of < or = 0.32. The "fast-track" patients had IDDM for < or = 20 years and VvMes/glom > or = 0.37. Renal biopsies were embedded in Lowicryl, reacted with polyclonal anti-type IV collagen (in the distribution of the classical alpha 1(IV) and alpha 2(IV) collagen chains) and monoclonal anti-alpha 4(IV) collagen chain antibody followed by gold conjugated secondary antibody. We found, by morphometric techniques, a decrease in the immunogold densities of anti-type IV collagen in the subendothelial zone of the GBM in the "fast-track" IDDM patients. There was a trend towards a decrease in mesangial matrix (MM) particle density in the "fast-track" (P = 0.07) but not in the "slow-track" patients. However, because of the marked increase in MM in the "fast-track" patients, the per glomerulus estimated quantity of these antigens in MM was increased. In contrast, the density of alpha 4(IV) collagen chain was increased in the epithelial zone of the GBM in the "fast-track" IDDM patients. It is not known whether these changes in glomerular type IV collagen represent markers of advanced diabetic lesions or whether these changes might be detected earlier in diabetic patients destined for the later development of serious lesions.

Cytological and immunocytochemical approaches to the study of corneal endothelial wound repair

The vertebrate corneal endothelium represents a unique model system for investigating many cellular aspects of wound repair within an organized tissue in situ. The tissue exists as a cell monolayer that resides upon its own natural basement membrane that can be prepared as a flat mount to observe the entire cell population. Thus, it readily avails itself to many cytological and immunocytochemical methods at both the light microscopic and ultrastructural levels. In addition, the tissue is easily explanted into organ culture where further investigations can be carried out. These techniques have enabled investigators to use many approaches to explore function and changes in response to injury. In vivo, the endothelium acts as a transport tissue to actively pump Na+ and bicarbonate ions from the corneal stroma into the aqueous humor to control corneal transparency. Physiological findings indicate that fluid diffuses back into the stroma, across the endothelium, and thus hydration is said to be controlled by a pump-leak mechanism. Ultrastructural investigations, some employing horseradish peroxidase and lanthanum, have established the morphological basis for this mechanism as apical focal junctions that are not the classical tight junctions and do not constitute a complete zona occludens. Along with these apical focal junctions are gap junctions that appear identical to their counterparts in other cell types. Cytochemical studies localized both Na+K(+)-ATPase and carbonic anhydrase, the main pump enzymes associated with corneal hydration, to the lateral plasma membranes. Corneal endothelial cells of noninjured tissue do not traverse the cell cycle and are considered to be in the "Go" phase of the cell cycle as determined by microfluorometric analysis with DNA binding dyes such as auramin O and pararosaniline-Feulgen. However, injury can initiate cell cycle transverse and histochemical and cytological methods have been used to understand the tissue's response. Classical histochemical studies revealed that increased staining was observed for metabolic (NADase and NADPase) and lysosomal enzymes in cells bordering the wound area. The use of radiolabelled agents has further lead to an understanding of the endothelial wound response. Autoradiographic analyses of 3H-actinomycin D incorporation indicated that injury initiates changes in chromatin leading to increased binding levels of the drug in cells surrounding the wound. This change suggests that those cells undergo heightened macromolecular synthesis and this was confirmed by examining 3H-uridine and 3H-thymidine incorporation. The major mechanism involved in corneal endothelial repair is cell migration. Cytochemical and immunocytochemical investigations have allowed investigators an opportunity to gain some insight into changes that occur during this cellular process.(ABSTRACT TRUNCATED AT 400 WORDS)

Proteoglycans of basement membranes

Proteoglycans carrying either heparan sulfate and/or chondroitin sulfate side chains are typical constituents of basement membranes. The most prominent proteoglycan (perlecan) consists of a 400-500 kDa core protein and three heparan sulfate chains. Electron microscopy and cDNA sequencing show a complex and elongated domain structure for the core protein which in part is homologous to that of the laminin A chain. This structure may be varied by alternative splicing and proteolysis. Integration into basement membranes probably occurs by heparan sulfate binding to laminin and collagen IV, core protein binding to nidogen and by limited self assembly. The proteoglycan is in addition a cell-adhesive protein which is recognized by beta 1 integrins. Several more proteoglycans with smaller core proteins (10-160 kDa) apparently exist in basement membranes but are less well characterized. Biological functions include control of filtration through basement membranes and binding of growth factors and protease inhibitors.

Asymmetric origins of the mature glomerular basement membrane

Renal plasma filtration is a critical physiologic function that depends upon the precise composition and arrangement of the constituent extracellular matrix proteins within the glomerular basement membrane (GBM). The GBM develops during renal embryogenesis by the fusion of discrete basement membranes produced independently by endothelial and visceral epithelial cells, and, possibly from matrix secreted by the mesangial cells. In the mature animal, however, the epithelial cell has generally been accepted as the sole source of all GBM constituent proteins. Although the final structures and distributions of the component proteins have been defined by histochemical techniques, the individual contributions of the three resident glomerular cell types to the maintenance and turnover of the mature GBM remain uncertain. We report the application of a new technique, in situ reverse transcription (ISRT), for the localization of RNA transcripts of nine major GBM protein components within the closely apposed cells of the glomerulus. Using this technique, we demonstrate that in normal adult rat glomeruli the RNA transcripts for heparan sulfate proteoglycan and the laminin-S chain are primarily expressed by visceral epithelial cells, while Type IV alpha-1 and alpha-2 collagen transcripts were restricted to the endothelial cells in a heterogeneous pattern. RNA transcripts for entactin and the laminin-A and -B2 chains were expressed by all three glomerular cell types, while laminin-B1 and fibronectin transcripts were limited to the mesangium. These findings demonstrate that GBM synthesis in the mature animal is not restricted to the epithelial cell and that all intrinsic glomerular cells contribute to the production of GBM protein components. The ISRT technique also provided the additional, and unexpected, finding that appreciable synthetic heterogeneity exists within individual glomerular cell types.

Ultrastructural localization of lectin-binding sites in different basement membranes

In the present work we localized binding sites for the lectins WGA, RCA I, con A and SBA at the ultrastructural levels in morphologically different basement membranes. These different basement membranes included (a) thin ones, for example, tubular basement membrane of the mouse kidney which separates epithelial cell layers from mesenchymal cells and glomerular basement membrane which separates epithelial cells from other epithelial cells, (b) thick multilayered ones, for example. Reichert's membrane which is built up during the embryonic development of rodents and as an example of a pathologically thickened basement membrane, the basement membrane of the Engelbreth-Holm-Swarm (EHS) sarcoma. We were able to show that, in contrast to the thick multilayered basement membranes, the thin ones showed a strong positive SBA-binding pattern. Thick basement membranes otherwise revealed very strong labelling with the lectins WGA and RCA I. Our findings lead us to conclude that thin and thick basement membranes differ markedly in the quality and quantity of the carbohydrates which they contain.

Proteoglycans of basement membranes

Proteoglycans carrying either heparan sulfate and/or chondroitin sulfate side chains are typical constituents of basement membranes. The most prominent proteoglycan (perlecan) consists of a 400-500 kDa core protein and three heparan sulfate chains. Electron microscopy and cDNA sequencing show a complex and elongated domain structure for the core protein which in part is homologous to that of the laminin A chain. This structure may be varied by alternative splicing and proteolysis. Integration into basement membranes probably occurs by heparan sulfate binding to laminin and collagen IV, core protein binding to nidogen and by limited self assembly. The proteoglycan is in addition a cell-adhesive protein which is recognized by beta 1 integrins. Several more proteoglycans with smaller core proteins (10-160 kDa) apparently exist in basement membranes but are less well characterized. Biological functions include control of filtration through basement membranes and binding of growth factors and protease inhibitors.

Cryofixation of basement membranes followed by freeze substitution or freeze drying demonstrates that they are composed of a tridimensional network of irregular cords

Since conventional chemical fixation may extract tissue components and thus alter structural organization, cryofixation was used to reexamine the ultrastructure of three thick basement membranes: lens capsule, Reichert's membrane, and Engelbreth-Holm-Swarm (EHS) tumor matrix, and two thin basement membranes, those of epididymis and semi-niferous tubules. Cryofixation was achieved by slam freezing followed by either freeze substitution in dry acetone containing 1% osmium tetroxide and 0.05% uranyl acetate or freeze drying in a molecular distillation dryer. The results by both procedures demonstrate that thick basement membranes and the lamina densa of thin basement membranes are composed of a network of anastomosing strands referred to as cords. The cords vary in density and distinctiveness, but their thickness averages 3 to 5 nm in every tissue examined. The spaces separating the cords vary within wide limits, but their mean diameter is approximately 15 nm in every case. Two other common features are 1) the presence within the network of a few 1.5-3.0-nm-thick filaments and 2) 4.5-nm-wide sets of parallel lines referred to as double tracks. When these results are compared with those previously described after conventional fixation, no significant difference is observed in either the cord network or the associated filaments and "double tracks." However, in the thin basement membranes processed by cryofixation, the lamina densa is in direct contact with epithelial cells, whereas, after conventional fixation, the lamina densa is separated from the epithelial cells by a pale layer referred to as lamina lucida or lamina rara. Immunogold labeling of three basement membranes after cryofixation and freeze substitution in acetone containing 0.3% glutaraldehyde yields strong reactions for laminin, type IV collagen, and heparan sulfate proteoglycan. Comparison with previous results indicates that conventional formaldehyde fixation adequately preserves laminin and type IV collagen but causes the loss of some proteoglycan. It is concluded that, except for this loss and the absence of lamina lucida in cryofixed thin basement membranes, the morphological and antigenic features obtained after cryofixation are similar to those observed in the past after conventional fixation.

Renal basement membranes by ultrahigh resolution scanning electron microscopy

Three-dimensional ultrastructures of basement membranes of the rat kidney were investigated with an ultrahigh resolution scanning electron microscope (HSEM) equipped with a resolving power of 0.5 nm. All cellular components were extracted from renal cortical tissues by sequential-detergent treatment. Four types of acellular basement membranes were observed after tannin-osmium conductive staining: the glomerular basement membrane (GBM) associated with the mesangial matrix, the tubular basement membrane (TBM), the Bowman's capsule basement membrane (BCBM), and the peritubular capillary basement membrane (PTCBM). We could demonstrate the polygonal meshwork structures composed of strands in the respective basement membranes. The strands averaged 6 to 7 nm wide, whereas the pore sizes within the meshworks were variable and differed according to the basement membrane type. Moreover, we confirmed the presence of the heterogeneity of the GBM suggested by several approaches. Present data support the proposition that a polygonal meshwork structure may represent the basic structure of basement membrane. Some of the observed architectural dissimilarities in basement membrane types may reflect their different functional properties, which in turn may reflect the heterogeneous distribution of major basement membrane components as demonstrated by immunohistochemical and biochemical studies.

Basement membrane lectin binding sites are decreased in the esophageal endoderm during the arrival of presumptive muscle mesenchyme in the developing asteroid Pisaster ochraceus

Basement membranes (BMs) of vertebrates and invertebrates have been shown to contain glycoproteins and proteoglycans, which include oligosaccharides and glycosaminoglycans. Lectin binding sites were characterized in the BM of gastrulating embryos of the starfish, Pisaster ochraceus. In early and mid-gastrulae, the fluorescein isothiocyanate (FITC)-lectin conjugates of concanavalin A (Con A) and wheat germ agglutinin (WGA) reveal the presence of mannose/glucose and glucosamine/sialic acid residues in the BM of all regions of the embryos. However, in the late gastrula embryo, an apparent reduction of these components is observed over the esophageal BM. Ultrastructural studies using the lectin-gold conjugates Con A, Limax flavus agglutinin (LFA), specific for sialic acid, and Dolichos biflorus agglutinin (DBA), specific for galactosamine, demonstrate that most mannose/glucose and galactosamine-containing residues lie in the lamina densa, whereas most sialic acid residues are located over the lamina lucida. In addition, a statistical analysis of lectin binding in the late gastrula embryo reveals that the amount of labelling with both Con A and LFA is significantly reduced in the esophageal region, suggesting that mannose/glucose and sialic acid residues are reduced in this region. These results confirm the observations of the FITC-lectin studies described above. They also confirm earlier studies that demonstrated a difference in BM morphology of the esophageal region (Crawford, '88). Mesenchyme cells, some of which arise from the forming coeloms (Crawford, '90), and which may represent a distinct population, colonize exclusively on this esophageal BM, where they later differentiate into muscle. Quantitative differences in BM glycoconjugates may act to direct the presumptive muscle cells to the region of the esophagus.

Structural variations of different oral basement membranes revealed by cationic dyes and detergent added to aldehyde fixative solution

The ultrastructural appearance of different types of basement membrane was studied using histochemical methods for visualizing glycosaminoglycans. Samples of rat gingiva and mouse molar germ tissue were fixed either with glutaraldehyde, glutaraldehyde-ruthenium hexammine trichloride (RHT), glutaraldehyde-Cuprolinic Blue (CB) or cetylpyridinium chloride-glutaraldehyde (CPC). Ultrathin sections were stained with uranyl acetate and lead citrate. The results showed that the conventional trilaminar structure of the basement membrane was observed after glutaraldehyde and CB fixation. In contrast, after CPC or RHT fixation, the appearance of the basement membrane was homogeneous without any evidence of a lamina lucida. Furthermore, after single fixation with CPC, the ultrastructure of different basement membranes from oral tissues showed some differences in appearance which were related to their localizations, functions, or both.

Diabetic glomerulosclerosis--immunogold ultrastructural studies on the glomerular distribution of type IV collagen and heparan sulphate proteoglycan

We have undertaken an ultrastructural immunogold investigation of the distribution of type IV collagen and heparan sulphate proteoglycan (HSPG) in glomeruli from the kidneys of one normal control and three patients with diabetes mellitus and proteinuria. The sample included both diffuse and nodular diabetic glomerulosclerosis. In the control and diabetic kidneys, the type IV collagen was present predominantly on the endothelial aspect of the glomerular basement membrane (GBM), and by contrast the HSPG was found mainly on the epithelial side. In the mesangium in both control and diabetic glomeruli, type IV collagen was found predominantly in the central regions, while HSPG was mostly restricted to the region beneath the epithelial cells. Consequently, where there is a marked increase in mesangial matrix with nodule formation in diabetics there is a corresponding increase in the amount of type IV collagen but not of HSPG. Although the three diabetic patients were proteinuric, the HSPG was not decreased in the thickened GBMs.

Immunolocalization of laminin, heparan-sulfate proteoglycan, entactin, and type IV collagen in the rat anterior pituitary. I. An in vivo study

The distribution of three components of basement membranes (BM): heparan-sulfate proteoglycan (HSPG), entactin (ENT), and type IV collagen (Coll. IV), was studied in the adult rat anterior pituitary and compared to the distribution of laminin (LAM) described in an earlier report (Vila-Porcile et al., 1987, J. Histochem. Cytochem., 35, 287). Several immunocytochemical methods were applied at both light and electron microscope levels. The three components were detected in all the pituitary BM and in endothelial and perivascular connective cells, as previously observed for LAM. In contrast to the prominent labeling previously observed for LAM within epithelial cells, however, only a faint immunoreaction could be detected for the other components, with nonetheless a discrete signal for Coll. IV. These findings indicate that 1) the four studied components are present in all the BM of the rat anterior pituitary; 2) pituitary endocrine cells contain LAM, and to a lesser extent Coll. IV, and thus could participate to the elaboration of the BM; and 3) the presence of the four components in non-epithelial cells also suggests their cooperation in BM building. The questions of the turnover and intracellular pathways of each of these components were addressed but remain unanswered.

Collagen biosynthesis in cultured rat testicular Sertoli and peritubular myoid cells

The incorporation of 3H-proline into protein was regarded as a measure of total protein synthesis and the incorporation into hydroxyproline as indicative of collagen synthesis. Relative collagen synthesis (expressed as percent of total protein synthesized) by Sertoli and peritubular myoid cells cultured from 20-22 day old rat testis was estimated. In both secreted and cellular pools, relative collagen synthesis by Sertoli cells was significantly greater than by peritubular myoid cells. Coculture of Sertoli and myoid cells resulted in a significant increase in relative collagen synthesis when compared to monocultures of each cell type. Addition of serum to peritubular myoid cells resulted in a stronger stimulation of relative collagen production. Sertoli cell extracellular matrix inhibited relative collagen synthesis by peritubular myoid cells in the presence or absence of serum. Radioactivity into hydroxyproline as corrected per cellular DNA also showed similar results. Immunolocalization studies confirmed that both cell types synthesize type I and type IV collagens. These results indicate that stimulation of collagen synthesis observed in Sertoli-myoid cell cocultures is due to humoral interactions, rather than extracellular matrix, and Sertoli cell extracellular matrix regulates serum-induced increase in collagen synthesis by peritubular myoid cells.