Basic structure of basement membranes is a fine network of "cords," irregular anastomosing strands

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.

Topographical influence of electrospun basement membrane mimics on formation of cellular monolayer

Functional unit of many organs like lung, kidney, intestine, and eye have their endothelial and epithelial monolayers physically separated by a specialized extracellular matrix called the basement membrane. The intricate and complex topography of this matrix influences cell function, behavior and overall homeostasis. In vitro barrier function replication of such organs requires mimicking of these native features on an artificial scaffold system. Apart from chemical and mechanical features, the choice of nano-scale topography of the artificial scaffold is integral, however its influence on monolayer barrier formation is unclear. Though studies have reported improved single cell adhesion and proliferation in presence of pores or pitted topology, corresponding influence on confluent monolayer formation is not well reported. In this work, basement membrane mimic with secondary topographical cues is developed and its influence on single cells and their monolayers is investigated. We show that single cells cultured on fibers with secondary cues form stronger focal adhesions and undergo increased proliferation. Counterintuitively, absence of secondary cues promoted stronger cell-cell interaction in endothelial monolayers and promoted formation of integral tight barriers in alveolar epithelial monolayers. Overall, this work highlights the importance of choice of scaffold topology to develop basement barrier function in in vitro models.

Biomimetic stochastic topography and electric fields synergistically enhance directional migration of corneal epithelial cells in a MMP-3-dependent manner

Directed migration of corneal epithelial cells (CECs) is critical for maintenance of corneal homeostasis as well as wound healing. Soluble cytoactive factors and the intrinsic chemical attributes of the underlying extracellular matrix (ECM) participate in stimulating and directing migration. The central importance of the intrinsic biophysical attributes of the microenvironment of the cell in modulating an array of fundamental epithelial behaviors including migration has been widely documented. Among the best measures of these attributes are the intrinsic topography and stiffness of the ECM and electric fields (EFs). How cells integrate these multiple simultaneous inputs is not well understood. Here, we present a method that combines the use of (i) topographically patterned substrates (mean pore diameter 800nm) possessing features that approximate those found in the native corneal basement membrane; and (ii) EFs (0-150mVmm(-1)) mimicking those at corneal epithelial wounds that the cells experience in vivo. We found that topographic cues and EFs synergistically regulated directional migration of human CECs and that this was associated with upregulation of matrix metalloproteinase-3 (MMP3). MMP3 expression and activity were significantly elevated with 150mVmm(-1) applied-EF while MMP2/9 remained unaltered. MMP3 expression was elevated in cells cultured on patterned surfaces against planar surfaces. The highest single-cell migration rate was observed with 150mVmm(-1) applied EF on patterned and planar surfaces. When cultured as a confluent sheet, EFs induced collective cell migration on stochastically patterned surfaces compared with dissociated single-cell migration on planar surfaces. These results suggest significant interaction of biophysical cues in regulating cell behaviors and will help define design parameters for corneal prosthetics and help to better understand corneal wound healing.

A cell culture substrate with biologically relevant size-scale topography and compliance of the basement membrane

A growing body of literature broadly documents that a wide array of fundamental cell behaviors are modulated by the physical attributes of the cellular microenvironment, yet in vitro assays are typically carried out using tissue culture plastic or glass substrates that lack the 3-dimensional topography present in vivo and have stiffness values that far exceed that of cellular and stromal microenvironments. This work presents a method for the fabrication of thin hydrogel films that can replicate arbitrary topographies with a resolution of 400 nm that possess an elastic modulus of approximately 250 kPa. Material characterization including swelling behavior and mechanics were performed and reported. Cells cultured on these surfaces patterned with anisotropic ridges and grooves react to the biophysical cues present and show an alignment response.

The basement membrane of the isolated rat colonic mucosa. A light, electron and atomic force microscopy study

Basement membranes (BM) are structures of the extracellular matrix (ECM), which are involved in epithelial barriers, but also play an important role in processes such as cell adhesion, cell growth and tissue healing. The aim of this study was to investigate possible effects of cell removal on the structure of the BM of the colonic mucosa. The superficial epithelium was removed with EDTA and the samples were then mechanically fixed for immunohistochemistry, TEM, SEM and AFM. For SEM and AFM, some samples were also prepared according to the OTO method. BM marker proteins were detected after cell removal by immunohistochemistry, indicating that BM remains. However, a lamina lucida (LL) was no longer visible in TEM, it disappeared and the BM became slightly thinner. The surface topography of the BM is characterized by the presence of globules, fenestrations and pore-like structures, which were visualized with SEM and AFM. Noteworthy is the visualization for the first time with AFM of a 3D network of fine fibers and filaments ("cords"), which very much resembled that described with TEM by Inoue (1994). An unresolved question is whether the pore-like structures observed in this study, especially with SEM, actually correspond to the pores of the BM whose existence has been demonstrated functionally. In conclusion, the structural patterns and changes described could be considered as a reference to evaluate the effects of other decellularization protocols on BMs, such as those used in tissue engineering.

The influence of a biologically relevant substratum topography on human aortic and umbilical vein endothelial cells

A topographically patterned substrate with stochastic surface order that closely mimics the topographic features of native basement membranes has been fabricated to investigate the influence of topographic biophysical cueing on human aortic and umbilical vein endothelial cells. The stochastic substrate was fabricated by first generating a highly porous polyelectrolyte multilayer film of poly(acrylic acid) and poly(allylamine hydrochloride) followed by replicate production of this biomimetic topography via soft lithography. These substrates, which are easy to prepare and replicate, possess a number of prominent features associated with in vivo vascular basement membrane (interwoven ridges and grooves, bumps, and pores), which have typically been studied as singular features that frequently possess anisotropic surface order (e.g., alternating ridges and grooves). When compared to a flat surface of identical chemistry, these biomimetic topographies influenced a number of important cellular behaviors associated with the homeostasis and degradation of vascular tissues. These include modulating cell migration rate and directional persistence, proliferation rate, and gene expression associated with regulation and remodeling of vascular tissues as well as inflammation.

Sensing and modulation of invadopodia across a wide range of rigidities

Recent studies have suggested that extracellular matrix rigidity regulates cancer invasiveness, including the formation of cellular invadopodial protrusions; however, the relevant mechanical range is unclear. Here, we used a combined analysis of tissue-derived model basement membrane (BM) and stromal matrices and synthetic materials to understand how substrate rigidity regulates invadopodia. Urinary bladder matrix-BM (UBM-BM) was found to be a rigid material with elastic moduli of 3-8 MPa, as measured by atomic force microscopy and low-strain tensile testing. Stromal elastic moduli were ∼6-fold lower, indicating a more compliant material. Using synthetic substrates that span kPa-GPa moduli, we found a peak of invadopodia-associated extracellular matrix degradation centered around 30 kPa, which also corresponded to a peak in invadopodia/cell. Surprisingly, we observed another peak in invadopodia numbers at 2 GPa as well as gene expression changes that indicate cellular sensing of very high moduli. Based on the measured elastic moduli of model stroma and BM, we expected to find more invadopodia formation on the stroma, and this was verified on the stromal versus BM side of UBM-BM. These data suggest that cells can sense a wide range of rigidities, up into the GPa range. Furthermore, there is an optimal rigidity range for invadopodia activity that may be limited by BM rigidity.

Toward managing chronic rejection after lung transplant: the fate and effects of inhaled cyclosporine in a complex environment

The fate and effects of inhaled cyclosporine A (CsA) are considered after deposition on the lung surface. Special emphasis is given to a post-lung transplant environment and to the potential effects of the drug on the various cell types it is expected to encounter. The known stability, metabolism, pharmacokinetics and pharmacodynamics of the drug have been reviewed and discussed in the context of the lung microenvironment. Arguments support the contention that the immuno-inhibitory and anti-inflammatory effects of CsA are not restricted to T-cells. It is likely that pharmacologically effective concentrations of CsA can be sustained in the lungs but due to the complexity of uptake and action, the elucidation of effective posology must ultimately rely on clinical evidence.

A structural constitutive model for the human lens capsule

Published data on the mechanical performance of the human lens capsule when tested under uniaxial and biaxial conditions are reviewed. It is concluded that two simple phenomenological constitutive models (namely a linear elastic model and a Fung-type hyperelastic model) are unable to provide satisfactory representations of the mechanical behaviour of the capsule for both of these loading conditions. The possibility of resolving these difficulties using a structural constitutive model for the capsule, of a form that is inspired by the network of collagen IV filaments that exist within the lens capsule, is explored. The model is implemented within a rectangular periodic cell. Prescribed stretches are imposed on the periodic cell and the network is allowed to deform in a non-affine manner. The performance of the constitutive model correlates well with previously published test data. One possible application of the model is in the development of a multi-scale analysis of the mechanics of the human lens capsule.

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.

Ultrastructural characterization of an artificial basement membrane produced by cultured keratinocytes

A recent study in our laboratories on the growth of keratinocytes at the culture medium/air interface has led to the identification of a novel thin sheet-like matrix that supports adherent cells. This novel matrix consists of components secreted by keratinocytes, including type IV collagen, and laminins 1 and 5, that self-assembled to a membrane structure. In the present study, a detailed ultrastructural characterization of this membrane was done with high-resolution electron microscopy after negative staining. The basic organization of the membrane was found to be a dense network of 8- to 10-nm-wide irregular rod-like elements. High-resolution examination and immunolabeling showed that type IV collagen filaments form the core of these elements, and other components including heparan sulfate proteoglycan in the form of 4.5- to 5-nm-wide ribbon-like "double tracks" are aggregated around it. These detailed features of the membrane strikingly resembled those of the basement membrane in vivo. These ultrastructural similarities indicate that the membrane may also have basement membrane-like functional properties, and suggest that it should be considered for testing in future medical applications.

A basement membrane-like matrix formed by cell-released proteins at the medium/air interface supports growth of keratinocytes

Epithelial cells require adherence to a matrix for regular growth. During standard keratinocyte cell culture in serum-free medium, we observed that cell colonies formed not only on the bottom of the culture vessels but also at the medium/air interface. Coomassie blue staining detected a protein membrane that extended up to several centimeters between the colonies of floating cells. Ultrastructural investigation of this membrane revealed structures closely resembling those of basement membranes, and immunochemical staining confirmed the presence of laminins-1 and -5 as well as collagen IV, representative components of basement membranes. Cells attached to the floating membrane proliferated and could be cultivated for up to six months. When keratinocyte-conditioned medium was filtered and transferred to a culture vessel without cells, the protein membrane at the liquid/air interface formed within one week suggesting self-assembly of cell-released proteins. Our findings provide a basis for the production of epidermal basement membranes for potential medical uses.

Epithelial contact guidance on well-defined micro- and nanostructured substrates

The human corneal basement membrane has a rich felt-like surface topography with feature dimensions between 20 nm and 200 nm. On the basis of these findings, we designed lithographically defined substrates to investigate whether nanotopography is a relevant stimulus for human corneal epithelial cells. We found that cells elongated and aligned along patterns of grooves and ridges with feature dimensions as small as 70 nm, whereas on smooth substrates, cells were mostly round. The percentage of aligned cells was constant on substrate tomographies with lateral dimensions ranging from the nano- to the micronscale, and increased with groove depth. The presence of serum in the culture medium resulted in a larger percentage of cells aligning along the topographic patterns than when no serum was added to the basal medium. When present, actin microfilaments and focal adhesions were aligned along the substrate topographies. The width of the focal adhesions was determined by the width of the ridges in the underlying substrate. This work documents that biologic length-scale topographic features that model features encountered in the native basement membrane can profoundly affect epithelial cell behavior.

Honeycomb structure in the lamina lucida of epidermal basement membrane during metamorphosis of Rana temporaria ornativentris

In this study we examine the structure of the lamina lucida during metamorphosis of Rana temporaria ornativentris. During the metamorphosis of anuran larvae, both the epidermal cells and the dermal connective tissues in the tail regenerate. The basal surface of the epidermis becomes irregular and the epidermal basement membrane detaches from the epidermal cells, showing a widened lamina lucida. In this widened lamina we observed a geometrical honeycomb structure and a ladder structure. Each side of the honeycomb structure was approximately 40 nm and the intervals of the ladder structure were approximately 50 nm. From our observations we believe that the honeycomb and ladder appearances are different aspects of the same structure. At the beginning of metamorphosis anchoring filaments were prominent in the lamina lucida and, when the lamina lucida was tangentially cut, the lamina lucida showed the honeycomb structure. These results suggest that both the honeycomb and the ladder structures observed in the widened lamina lucida originate from constituents of the lamina lucida and become morphologically evident during the epidermal-dermal separation.

Alterations in the lens capsule contribute to cataractogenesis in SPARC-null mice

The lens capsule, which is also called the lens basement membrane, is a specialized extracellular matrix produced anteriorly by the lens epithelium and posteriorly by newly differentiated fiber cells. SPARC (secreted protein,acidic and rich in cysteine) is a matricellular glycoprotein that regulates cell-cell and cell-matrix interactions, cellular proliferation and differentiation, and the expression of genes encoding extracellular matrix components. SPARC-null mice exhibit lens opacity 1 month after birth and mature cataract and capsular rupture at 5-7 months. In this study, we report disruption of the structural integrity of the lens capsule in mice lacking SPARC. The major structural protein of basement membrane, collagen type IV, in the lens capsule was substantially altered in the absence of SPARC. The lens cells immediately beneath the capsule showed aberrant morphology, with numerous protrusions into the lens basement membrane. SPARC-null lenses at 1 month of age exhibited an increased penetration of dye or radioactive tracer through the capsule, as well as a higher content of water than their wild-type counterparts. Moreover, SPARC-null fibers exhibited swelling as early as 1 month of age; by 3 months, all the fiber cells appeared swollen to a marked degree. By contrast, the absence of SPARC had no apparent morphological effect on the early stages of lens formation, cell proliferation or fiber cell differentiation. Degradation of crystallins and MIP 26, or changes in the levels of these proteins, were not detected. These results underscore the importance of the capsular extracellular matrix in the maintenance of lens transparency and indicate that SPARC participates in the synthesis, assembly and/or stabilization of the lens basement membrane.

Basement membrane and beta amyloid fibrillogenesis in Alzheimer's disease

High-resolution ultrastructural and immunohistochemical studies revealed that in situ beta amyloid fibrils of Alzheimer's disease were made up of a core consisting of a solid column of amyloid P component (AP) and associated chondroitin sulfate proteoglycan, and a heparan sulfate proteoglycan surface layer with externally associated fine filaments of beta protein. The main body of beta amyloid fibrils closely resembled that of microfibrils. Abundant microfibrils were reported to be present at the basement membrane of capillaries with "leaky" blood-urine or blood-air barriers. Similarly, abundant microfibril-like beta amyloid fibrils are formed at the microvascular basement membrane in cerebrovascular amyloid angiopathy with altered blood-brain barrier. Since AP is an indispensable major component of microfibrils and microfibril-like structures, the formation of microfibrils may depend on, among other factors, the availability of AP. Thus, in beta amyloid fibrillogenesis fibrils may be built around AP which continuously leaks out from circulation into vascular basement membrane, and beta amyloid fibrils may be regarded as pathologically altered basement membrane-associated microfibrils. With no source of AP around them, senile plaque fibrils may also be derived from perivascular amyloid.

Basement membrane of mouse bone marrow sinusoids shows distinctive structure and proteoglycan composition: a high resolution ultrastructural study

Venous sinusoids in bone marrow are the site of a large-scale traffic of cells between the extravascular hemopoietic compartment and the blood stream. The wall of the sinusoids consists solely of a basement membrane interposed between a layer of endothelial cells and an incomplete covering of adventitial cells. To examine its possible structural specialization, the basement membrane of bone marrow sinusoids has now been examined by high resolution electron microscopy of perfusion-fixed mouse bone marrow. The basement membrane layer was discontinuous, consisting of irregular masses of amorphous material within a uniform 60-nm-wide space between apposing endothelial cells and adventitial cell processes. At maximal magnifications, the material was resolved as a random arrangement of components lacking the "cord network" formation seen in basement membranes elsewhere. Individual components exhibited distinctive ultrastructural features whose molecular identity has previously been established. By these morphological criteria, the basement membrane contained unusually abundant chondroitin sulfate proteoglycan (CSPG) revealed by 3-nm-wide "double tracks," and moderate amounts of both laminin as dense irregular coils and type IV collagen as 1-1.5-nm-wide filaments, together with less conspicuous amounts of amyloid P forming pentagonal frames. In contrast, 4.5-5-nm-wide "double tracks" characteristic of heparan sulfate proteoglycan (HSPG) were absent. The findings demonstrate that, in comparison with "typical" basement membranes in other tissues, the bone marrow sinusoidal basement membrane is uniquely specialized in several respects. Its discontinuous nature, lack of network organization, and absence of HSPG, a molecule that normally helps to maintain membrane integrity, may facilitate disassembly and reassembly of basement membrane material in concert with movements of adventitial cell processes as maturing hemopoietic cells pass through the sinusoidal wall: the exceptionally large quantity of CSPG may represent a reservoir of CD44 receptor for use in hemopoiesis.

Ultrastructure and composition of basement membranes in the tooth

The tooth, the hardest organ in the body, is known to be formed through highly elaborate, unique processes of differentiation and development. Basement membranes play critical roles in fundamentally important biological processes such as growth and differentiation, and for better understanding of the mechanism of development and maintenance of the tooth, specializations of tooth basement membranes are reviewed in detail in relation to their roles. The basement membrane at such diverse locations in the tooth as the inner enamel epithelium, maturation-stage ameloblasts, and junctional epithelium at the dentogingival border are specialized in their own highly unique ways for anchoring, firm binding, or mediation in the transport of substances. Thus, the role of basement membranes in the developing and mature tooth is manifold and for these roles individual basement membranes are specialized in their own specific ways which are rare or not seen in nondental tissues, and these specializations are essential for successful development and maintenance of the tooth.

Nanoscale topography of the corneal epithelial basement membrane and Descemet's membrane of the human

PURPOSE

Quantitatively define and compare the nanoscale topography of the corneal epithelial basement membrane (anterior basement membrane) and Descemet's membrane (posterior basement membrane) of the human.

METHODS

Human corneas not suitable for transplantation were obtained from the Wisconsin Eye Bank. The corneas were placed in 2.5 mM EDTA for 2.5 h or 30 min. for removal of the epithelium or endothelium, respectively. After removal of the overlying cells, specimens were fixed in 2% glutaraldehyde and either examined in this state by atomic force microscopy only or dehydrated through an ethanol series and prepared for transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).

RESULTS

The subepithelial and subendothelial basement membrane surfaces have a similar appearance that consists of an interwoven meshwork of fibers and pores. Topographic feature sizes were found to be in the nanometer size range with the epithelial basement membrane features larger and less densely packed than Descemet's membrane features. The topographic features are fractile in nature and increase surface area for cell contact.

CONCLUSION

With the use of the TEM, SEM, and AFM, a detailed description of the surface topography of corneal epithelial basement membrane and Descemet's membrane of the human cornea are provided. The significance of differences in corneal basement membrane topography may reflect differences in function of the overlying cells or may be related to differences in cell migration and turnover patterns between the epithelium and endothelium.

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.

Pressure-permeability relationships in basement membrane: effects of static and dynamic pressures

The glomerular basement membrane (GBM) is an important component of the filtration barrier that is the glomerular capillary wall. Previously GBM permeability has been investigated only under static pressures and often within a supraphysiological range. We used Matrigel as a model of GBM and formed membranes at the base of filtration chamber. We measured membrane permeability under static and dynamic pressures. Matrigel membranes were size and charge selective toward neutrally and negatively charged dextrans. Their permeability (as measured by hydraulic conductivity) was found to decrease from 1.61 +/- 0.06 to 0.75 +/- 0.07 x 10(-6) cm.s-1.cmH2O-1 as static pressure increased from 6 to 78 cmH2O, an effect attributed to membrane compression. In comparison to static pressure, sinusoidal pressure waves with a mean pressure of 50 cmH2O decreased membrane permeability, e.g., fluid flux was reduced by a maximum of 2% to a value of 5.47 +/- 0.38 x 10(-5) cm/s; albumin clearance was reduced by a maximum of 5.2% to a value of 9.63 +/- 1.06 x 10(-6) ml.cm-2.s-1. Such changes were affected by the frequency of pressure wave application and could be attributed to a switching on and off of the membrane compression effect.

Ultrastructural aspects of human cystic duct epithelium as a result of cholelithiasis and cholesterolosis

Although there is a large body of data on the gallbladder and the importance of the cystic duct in surgical procedures, there is insufficient data regarding the morphology of the human cystic duct. In the present study, transmission electron microscopic (TEM) and scanning electron microscopic (SEM) survey of several surgical and autopsy cystic ducts in cholelithiasis and cholesterolosis is reported. In cholelithiasis, similar to gallbladder epithelium, the cystic duct epithelial cells display minor-to-severe alterations of the epithelial surface accompanied by variable erosion of the epithelium. Areas of intact surface epithelium demonstrate microvilli-covered cells coated by a rich glycocalyx and mucous production. In other areas, apical excrescences are associated with mucus hyperproduction and secretory events. Lipoid bodies are also present in many cells and especially in many of the cells' subliminal apical areas. In cholesterolosis, mucous secretory granules appear dilated, fatty deposits are infrequent, and peculiar intracellular cholesterol deposits can be detected in the apical and subapical region of cells and around condensed mitochondria. Following elective cholecystectomies, predominantly in association with cholelithiasis, eroded areas were detected; therefore, it appears that the action of intraluminal calculi may be a principal causative factor in discrete epithelial erosions of the cystic duct. Intraluminal calculi/ debris, along with the alteration of mucus, cell sloughing, and a decreased pool of bile acids and motility may participate in the gallstone nucleation process. The peculiar cholesterol inclusions may also play a role in that nucleating process.

Three-dimensional distribution of extracellular matrix in the mouse small intestinal villi. Laminin and tenascin

To investigate the three-dimensional distribution of laminin and tenascin in the villi of the mouse small intestine, we designed a new tissue preparation procedure for confocal laser scanning microscopy. Fixed tissue was pretreated with sodium deoxycholate and immunostained. The specimens displayed intense immunofluorescence even in the deeper sites of the lamina propria. Laminin was distributed like a sheet in the basement membrane of the epithelium as well as that of the capillaries. Additionally, it was associated with some tubular structures in the lamina propria. Many pores were found in the laminin sheet. By comparison, tenascin was distributed at the epithelial basement membrane and in the underlying connective tissue exhibiting a striped pattern. Tenascin was observed wrapping around the capillary wall in a spiral but was absent at the tip of the villi except in the capillary wall. Pores in the staining pattern of tenascin were also found as was the case for laminin. This three-dimensional reconstruction made it possible to observe more clearly the localization of these two extracellular matrix molecules.

Basement-membrane stromal relationships: interactions between collagen fibrils and the lamina densa

Collagens, the most abundant molecules in the extracellular space, predominantly form either fibrillar or sheet-like structures-the two major supramolecular conformations that maintain tissue integrity. In connective tissues, other than cartilage, collagen fibrils are mainly composed of collagens I, III, and V at different molecular ratios, exhibiting a D-periodic banding pattern, with diameters ranging from 30 to 150 nm, that can form a coarse network in the extracellular matrix in comparison with a fine meshwork of lamina densa. The lamina densa represents a stable sheet-like meshwork composed of collagen IV, laminin, nidogen, and perlecan compartmentalizing tissue from one another. We hypothesize that the interactions between collagen fibrils and the lamina densa are crucial for maintaining tissue-tissue interactions. A detailed analysis of these interactions forms the basis of this review article. Here, we demonstrate that there is a direct connection between collagen fibrils and the lamina densa and propose that collagen V may play a crucial role in this connection. Collagen V might also be involved in regulation of collagen fibril diameter and anchoring of epithelia to underlying connective tissues.

Expression of laminin and type IV collagen by basement membrane-producing EHS tumors in streptozotocin-induced diabetic mice: in vivo modulation by low-molecular-weight heparin fragments

The biosynthesis of basement membrane components in Engelberth Holm Swarm-bearing mice with or without streptozotocin-induced diabetes and the effect of low-molecular-weight heparin derivatives (CY222, Sanofi Recherche/Institut Choay) on the relative rates of these synthetic activities were studied. In diabetic mice, the laminin mRNA level increased, whereas type IV collagen mRNA decreased. In vivo treatment with heparin fragments decreased the mRNA level of laminin to control values without altering the mRNA level of collagen IV. Biosynthetic studies with radiolabeled precursors ([3H]-proline for collagen and [35S]-methionine for laminin) confirmed these results. Laminin protein biosynthesis increased in diabetic mice. Treatment with CY222 corrected this alteration. Our results suggested an increased labeling of polymeric forms of collagen IV in diabetic mice. In addition, we showed that biosynthesis of acid-extractable collagen IV decreased in diabetic mice and that CY222 treatment corrected this disturbance. These experiments suggest that low-molecular-weight heparin fragments CY222 can modulate the biosynthesis of extracellular matrix macromolecules altered in diabetic animals by different pathways, including pretranslational and posttranslational steps.

Ultrastructural characterization of internal basement membrane of junctional epithelium at dentogingival border

BACKGROUND

Although a number of electron microscopic observations of the dentogingival border have been reported, observation of the detailed ultrastructure of the internal basement membrane of the junctional epithelium at the border has not yet been done.

METHODS

The internal basement membrane of a rhesus monkey (Macaca mulatta) was ultrastructurally characterized with high-resolution electron microscopy. The head and neck region of a 5-year-old animal was perfused with a fixative containing 1.25% glutaraldehyde, 0.75% formaldehyde, and 0.04% CaCl2 in 0.1 M phosphate buffer, pH 7.4. Isolated mandibular segments were further fixed with 2.5% glutaraldehyde, 2% formaldehyde, and CaCl2 (300 mg/l) in 0.1 M sodium cacodylate buffer, pH 7.4, for 24 hr at 4 degrees C. The segments were then demineralized and cut into small pieces that were postfixed with 1% osmium tetroxide and further processed for electron microscopy.

RESULTS

The internal basement membrane takes the form of both a common basement membrane and, in places, a multilayered basement membrane. This basement membrane was found to have fundamental ultrastructural features common to other basement membranes. That is, the bulk of the basement membrane is composed of a network of irregular anastomosing strands referred to as "cords." Heparan sulfate proteoglycan-containing ribbonlike 4.5-5-nm-wide "double tracks" were also present in this basement membrane. However, the lamina densa of this basement membrane was unusually thick (160 nm) compared with the thickness (30-60 nm) in other basement membranes, and the cords were also much thicker (8.3 +/- 1.9 nm vs. the usual 3-5 nm).

CONCLUSIONS

From these results, it is concluded that this particular basement membrane is specialized for mechanical strength. This specialization is likely to be suitable for the purpose of the tight sealing of the periodontal tissues from the oral environment.

High-resolution ultrastructural study of the rat glomerular basement membrane in aminonucleoside nephrosis

In the initial stages of aminonucleoside nephrosis, functional alterations in the glomerular basement membrane occur, as evidenced by the development of proteinuria. However, it has not been possible to observe important ultrastructural modifications at the level of the basement membrane, probably because the changes are taking place at the molecular level. In this study, by the use of high-resolution electron microscopy, an attempt was made to evaluate such changes in rat glomerular basement membrane during acute aminonucleoside nephrosis. As previously reported, in control animals the glomerular basement membrane is composed of a network of 4-nm-wide irregular anastomosing strands, referred to as "cords," which are known to contain a core filament of type IV collagen surrounded by a "sheath" of other components, such as laminin and heparan sulfate proteoglycan (HSPG). The most conspicuous ultrastructural alteration of the nephrotic glomerular basement membrane, recognizable only at high magnification, is that the cords were denuded leaving only the core filament through the loss of the sheath material. Thus, the cord network was transformed, with the progress of pathological conditions, into a network of fine filaments. On the other hand, abundance and distribution of HSPG molecules known to be present in the form of 4.5- to 5-nm-wide ribbon-like "double tracks," were found to be similar in control and nephrotic tissues. Since HSPG is one of the charge proteins of the basement membrane, the little changes observed for HSPG are difficult to interpret in view of reported decreases in basement membrane anionic sites in nephrosis. In conclusion, the glomerular basement membrane in aminonucleoside nephrosis loses its cord network components and replaces them with a more perforated network, which could be a cause for the increased permeability of this basement membrane.