Basement membrane proteins, interstitial collagens, and fibronectin in neurofibroma

Human cutaneous neurofibroma matrisome revealed by single-cell RNA sequencing

Neurofibromatosis Type I (NF1) is a neurocutaneous genetic syndrome characterized by a wide spectrum of clinical presentations, including benign peripheral nerve sheath tumor called neurofibroma. These tumors originate from the Schwann cell lineage but other cell types as well as extracellular matrix (ECM) in the neurofibroma microenvironment constitute the majority of the tumor mass. In fact, collagen accounts for up to 50% of the neurofibroma's dry weight. Although the presence of collagens in neurofibroma is indisputable, the exact repertoire of ECM genes and ECM-associated genes (i.e. the matrisome) and their functions are unknown. Here, transcriptome profiling by single-cell RNA sequencing reveals the matrisome of human cutaneous neurofibroma (cNF). We discovered that classic pro-fibrogenic collagen I myofibroblasts are rare in neurofibroma. In contrast, collagen VI, a pro-tumorigenic ECM, is abundant and mainly secreted by neurofibroma fibroblasts. This study also identified potential cell type-specific markers to further elucidate the biology of the cNF microenvironment.

A mechanical model for collagen fibril load sharing in peripheral nerve of diabetic and nondiabetic rats

Peripheral neuropathy affects approximately 50% of the 15 million Americans with diabetes. It has been suggested that mechanical effects related to collagen glycation are related to the permanence of neuropathy. In the present paper, we develop a model for load transfer in a whole nerve, using a simple pressure vessel approximation, in order to assess the significant of stiffening of the collagenous nerve sheath on endoneurial fluid pressure. We also develop a fibril-scale mechanics model for the nerve, to model the straightening of wavy fibrils, producing the toe region observed in nerve tissue, and also to interrogate the effects of interfibrillar crosslinks on the overall properties of the tissue. Such collagen crosslinking has been implicated in complications in diabetic tissues. Our fibril-scale model uses a two-parameter Weibull model for fibril strength, in combination with statistical parameters describing fibril modulus, angle, wave-amplitude, and volume fraction to capture both toe region and failure region behavior of whole rat sciatic nerve. The extrema of equal and local load-sharing assumptions are used to map potential differences in diabetic and nondiabetic tissues. This work may ultimately be useful in differentiating between the responses of normal and heavily crosslinked tissue.

Upregulation of tumor suppressor protein neurofibromin in normal human wound healing and in vitro evidence for platelet derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) elicited increase in neurofibromin mRNA steady-state levels in dermal fibroblasts

We first studied expression of neurofibromin by immunohistochemistry in scars obtained from operations involving areas of healing wounds. The results demonstrated increased immunoreactivity for neurofibromin in the fibroblastic cell population of the lesions when compared with fibroblasts of apparently healthy perilesional skin, or those of intact control skin. Furthermore, dermal fibroblasts of 19 and 34 wk-old fetuses displayed a clearly detectable immunosignal for neurofibromin. In vitro studies were designed to investigate the potential effects of selected growth factors--known to be operative in wound healing--on neurofibromin mRNA steady-state levels in cultured fibroblasts. Northern transfer analyses revealed that different isoforms of platelet derived growth factor (PDGF) exerted selective effects on the neurofibromin mRNA levels: PDGF isoform AB elevated neurofibromin mRNA levels in a concentration-dependent manner when concentrations of 0.1, 1, 10, and 30 ng per ml were used. The maximal upregulatory effect of PDGF BB was reached at a concentration of 1 ng per ml. In contrast, PDGF AA did not alter the steady-state levels of neurofibromin mRNA. As estimated by RNase protection assay, transforming growth factor-beta1 (TGF-beta1) upregulated neurofibromin gene expression when concentrations of 0.5 and 5 ng per ml were used. Reverse transcription followed by polymerase chain reaction did not detect apparent alterations in the ratio of type I/type II neurofibromin isoforms in PDGF- or TGF-beta1-treated cultures. Taken together, our results suggest that expression of tumor suppressor protein neurofibromin is upregulated in response to skin injury, and that this upregulation can be mediated through PDGF and TGF-beta.

Indirect immunohistochemistry and immunoelectron microscopy distribution of eight epidermal-dermal junction epitopes in the pig and in isolated perfused skin treated with bis (2-chloroethyl) sulfide

Sulfur mustard (bis [2-chloroethyl] sulfide, HD) is a potent cutaneous vesicant that causes gross blisters by separation of the epidermal-dermal junction (EDJ). The EDJ of the skin is a highly specialized and complex structure composed of several components and plays a major role in the integrity of the skin. The isolated perfused porcine skin flap (IPPSF) was dosed with 0.2 mg/ml (n = 4), 5.0 mg/ml (n = 4), and 10.0 mg/ml (n = 5) HD or ethanol (n = 4) for 8 hr (dose-response study) and 10.0 mg/ml HD or ethanol for 1, 3, 5, and 8 hr (n = 4/treatment) (time-response study). Successful EDJ mapping was carried out in normal pig skin (NPS), ethanol-treated IPPSFs, and HD-treated IPPSFs using the following antibodies: laminin, type IV collagen, fibronectin, GB3 (Nicein), bullous pemphigoid (BP), and epidermolysis bullosa acquisita (EBA). Two mouse anti-human monoclonal antibodies, L3d and 19-DEJ-1 (Uncein), did not cross-react with the EDJ of the pig. Antibody staining in NPS, ranging from very intense for laminin and type IV collagen to weak for fibronectin, was generally more discrete than in the IPPSF. No differences in staining were noted between the ethanol and nonblistered areas of the HD-treated IPPSFs. In HD-blistered areas, BP stained only the epidermal hemidesmosomes, and laminin, fibronectin, and GB3 stained primarily the dermis with fragments attached to the basal pole of the stratum base cells, while type IV collagen and EBA stained only the dermis. Mapping of these epitopes determined that the precise plane of EDJ separation in the HD-treated skin occurred beneath the hemidesmosomes within the upper portion of the lamina lucida. The conservation of human epitopes in the EDJ of the pig further emphasizes the similarities between human skin and pig skin. Therefore, pig skin and the IPPSF may be used to study HD-induced vesication and blistering diseases.

Confocal immunofluorescence localization of collagen types I, III, IV, V and VI and their ultrastructural organization in term human fetal membranes

The distribution of collagen types I, III, IV, V and VI in term human fetal membranes was examined using conventional and confocal indirect immunofluorescence techniques. Collagens I and III were present in most of the layers of fetal membranes except in the trophoblast layer contrary to what has been previously reported. Although collagen IV is considered to be a basement membrane component our study, using monoclonal and polyclonal antibodies, showed its consistent presence in the spongy and reticular layers in high intensity. This was first report on the distribution of type V collagen in the chorion where it was found in the reticular and in the trophoblast layers. Type VI collagen was present mainly in the amnion and the reticular layer. The ultrastructural examination of the extracellular matrix showed that the main fibrous skeleton of the fetal membranes was formed of large banded fibres (Ultrastructurally identical to collagens types I and III) connected together and to the epithelial basement membranes by networks of unbanded filaments (collagen types V, VI and other components). The extensive and continuous networks formed by these collagens may be a major factor responsible for the mechanical integrity of the fetal membranes.

Type VI collagen microfibrils: evidence for a structural association with hyaluronan

Type VI collagen, a widespread structural component of connective tissues, has been isolated in abundance from fetal bovine skin by a procedure involving bacterial collagenase digestion under nonreducing, nondenaturing conditions and gel filtration chromatography. Rotary shadowing electron microscopic analysis revealed that the collagen VI was predominantly in the form of extensive intact microfibrillar arrays. These microfibrils were seen in association with hyaluronan, which was identified by its ability to bind the G1 fragment of cartilage proteoglycan. Treatment with highly purified hyaluronidase largely disrupted the collagen VI microfibrils into component tetramers, double tetramers, and short microfibrillar sections. Subsequent incubation of disrupted collagen VI in the presence of hyaluronan facilitated a partial repolymerization of the microfibrils. In vitro binding studies have also demonstrated that type VI collagen binds hyaluronan with a relatively high affinity. These studies demonstrate that a specific structural relationship exists between type VI collagen and hyaluronan. This association is likely to be of primary importance in the growth and remodeling processes of connective tissues.

Comparison of various basement membrane components in benign and malignant peripheral nerve tumours

Immunohistochemical methods were used to analyse benign and malignant tumours of peripheral nerve tissue. We tested for the distribution of basement membrane (BM) components collagen IV, laminin, heparan sulphate proteoglycan, fibronectin, for S100 protein and for the presence of interstitial collagens III and V. Laminin was generally noted in association with Schwann cells, but collagen IV occurred with perineural cells. When tested for BM components, fibroblasts were notably non-reactive except for fibronectin. Three specific area-dependent BM patterns were observed in the benign tumours: (a) Schwann cell-like, in fascicular areas (Antoni A areas of schwannoma, central fibrous bundles of plexiform neurofibromas and central areas of cutaneous neurofibroma), (b) perineural cell-like (capsular structures of schwannoma) and (c) fibroblast-like (myxoid and fibrously transformed areas). Most malignant tissues showed a variably fragmentary focal deposition of laminin. Other BM components were present only in well-differentiated areas. Poorly differentiated tumours demonstrated fibronectin reactivity alone. Our results provide evidence that the specific staining pattern for BM components helps to differentiate the various cellular proliferations in neurogenic tumours. Schwann cells are not only distinguishable from perineural cells by S100 protein staining, but also by their specific BM staining. In addition, perineural cells can be separated from fibroblasts, which do not express BM material. The "tropism" of laminin in normal nerves and benign neural tumours--which persists in neurogenic sarcomas--indicates preferential Schwann cell differentiation in these cells.

Acquired progressive lymphangioma

Acquired progressive lymphangioma is rare and can histologically mimic well-differentiated angioendothelioma. In a 9-year-old boy with acquired progressive lymphangioma, we demonstrated that the neoplasm consists of at least a vascular component and a smooth muscle component. The presence of type IV collagen around many vascular channels suggests that an intermediate stage of differentiation between blood vessels and lymphatics may be present. Our findings indicate that acquired progressive lymphangioma is most likely a complex hamartoma composed of vascular channels and smooth muscle.

Epitope mapping of the laminin molecule in murine skin basement membrane zone: demonstration of spatial differences in ultrastructural localization

Results of studies performed to date with polyclonal antilaminin antibodies have been conflicting as to the ultrastructural localization of this glycoprotein in skin basement membrane zone (BMZ). Whereas initial reports suggested its presence solely within the lamina lucida (LL), others have suggested that laminin is instead an exclusive component of the lamina densa (LD). In an attempt to more critically address this issue, we have examined both intact and partially separated (via 1 M NaCl) murine skin BMZ by indirect immunoelectron microscopy via a two-step immunoperoxidase technique on unfixed cryopreserved tissue, utilizing nine well-characterized monoclonal antibodies with binding specificity for laminin. Localization of the sites of the epitopes recognized by these antibodies on isolated laminin molecules was previously determined by rotary shadowing and by biochemical analyses on enzymatic fragments of laminin. Whereas at least faint immunoreactants were detected in both regions with eight of nine antibodies, predominant staining was noted within the LL with three of eight and within (and even sparsely below) the LD in three of eight. One antibody bound solely to the LL; another bound equally within both regions. Although some overlap was noted, it appears that the epitope on the distal portion of the long arm of the laminin molecule resides primarily within the skin LD, whereas epitopes on more central portions of the short arms are present within the LL or within both LL and LD. The findings of stratification of laminin epitopes within skin BMZ supports a similar recent observation in mouse kidney and suggests that portions of the laminin molecule span both LD and LL, and that there may be a non-random spatial orientation for the laminin molecule within murine skin BMZ.

Type VI collagen in experimental atherosclerosis

Diffuse intercellular immunofluorescence staining of type VI collagen was found in the experimentally thickened vascular wall and in control blood vessel tissues as well, superimposed by more intense staining around basement membranes. While the basement membrane staining disappeared in advanced mural thickenings, the diffusely distributed network of type VI collagen remained.

Type 1 neurofibromatosis: selective expression of extracellular matrix genes by Schwann cells, perineurial cells, and fibroblasts in mixed cultures

Cutaneous neurofibromas, characteristic lesions of neurofibromatosis 1, are composed of an abundant extracellular matrix and nerve connective tissue-derived cell types: Schwann cells, perineurial cells, and fibroblasts. In this study, the extracellular matrix gene expression by these cells was examined under culture conditions that allowed them to be metabolically active and readily identifiable by morphologic and immunocytochemical criteria. Northern hybridizations demonstrated expression of genes for type I, III, IV, and VI collagens, as well as for fibronectin, laminin, and elastin. In situ hybridizations revealed that all three cell types expressed pro alpha 1 (I), pro alpha 2 (VI), and laminin B1 chain genes. However, fibroblasts did not contain [35S]cDNA-mRNA hybrids specific for type IV collagen, whereas both Schwann cells and perineurial cells expressed these genes. Perineurial cells and fibroblasts readily expressed the fibronectin gene whereas Schwann cells were essentially devoid of the corresponding mRNA. Perineurial cells also expressed the gene for laminin A chain. The results indicate that the extracellular matrix gene expression profiles of Schwann cells, perineurial cells, and fibroblasts are distinct: all three cell types are capable of expressing some of the genes for extracellular matrix components, such as type I and VI collagens, whereas Schwann cells and perineurial cells may have the primary role in synthesizing basement membrane zone components, type IV collagen and laminin. These observations potentially relate to the mechanisms of growth and development of human neurofibromas. The results attest to the applicability of the methodology utilized here to study other human tumors with mixed cell populations.

Ultrastructure of type VI collagen in human skin and cartilage suggests an anchoring function for this filamentous network

An mAb was used in conjunction with immunoelectron microscopy to study the ultrastructure and distribution of the type VI collagen network. Type VI collagen in femoral head and costal cartilage was found distributed throughout the matrix but concentrated in areas surrounding chondrocytes. Three-dimensional information gained from high voltage stereo pair electron microscopy showed that the type VI collagen network in skin was organized into a highly branched, open, filamentous network that encircled interstitial collagen fibers, but did not appear to interact directly with them. Type VI collagen was also found concentrated near basement membranes of nerves, blood vessels, and fat cells although in a less organized state. Labeling was conspicuously reduced close to the epithelial basement membrane in the region of the anchoring fibrils. No labeling of basement membranes was seen. Based on these observations it is suggested that the type VI collagen forms a flexible network that anchors large interstitial structures such as nerves, blood vessels, and collagen fibers into surrounding connective tissues.

High resolution immunoelectron microscopic localization of functional domains of laminin, nidogen, and heparan sulfate proteoglycan in epithelial basement membrane of mouse cornea reveals different topological orientations

Thin and ultrathin cryosections of mouse cornea were labeled with affinity-purified antibodies directed against either laminin, its central segments (domain 1), the end of its long arm (domain 3), the end of one of its short arms (domain 4), nidogen, or low density heparan sulfate proteoglycan. All basement membrane proteins are detected by indirect immunofluorescence exclusively in the epithelial basement membrane, in Descemet's membrane, and in small amorphous plaques located in the stroma. Immunoelectron microscopy using the protein A-gold technique demonstrated laminin domain 1 and nidogen in a narrow segment of the lamina densa at the junction to the lamina lucida within the epithelial basement membrane. Domain 3 shows three preferred locations at both the cellular and stromal boundaries of the epithelial basement membrane and in its center. Domain 4 is located predominantly in the lamina lucida and the adjacent half of the lamina densa. The low density heparan sulfate proteoglycan is found all across the basement membrane showing a similar uniform distribution as with antibodies against the whole laminin molecule. In Descemet's membrane an even distribution was found with all these antibodies. It is concluded that within the epithelial basement membrane the center of the laminin molecule is located near the lamina densa/lamina lucida junction and that its long arm favors three major orientations. One is close to the cell surface indicating binding to a cell receptor, while the other two are directed to internal matrix structures. The apparent codistribution of laminin domain 1 and nidogen agrees with biochemical evidence that nidogen binds to this domain.

Comparative ultrastructural localization of collagen types III, IV, VI and laminin in rat uterus and kidney

Antibodies against collagen types III and VI have been localized by electron immunohistochemistry with two different techniques in normal rat uterus and kidney. Antibodies directed against two components of the extracellular matrix with known localization, laminin and type IV collagen, were used as controls for the specificity of the localization. The results demonstrate that types III and VI are found in the interstitium as fine (10- to 15-nm), beaded fibrils and filaments (6- to 10-nm), respectively. Both are often found associated with thick, crossbanded type I collagen fibers (30- to 35-nm) and occasionally associated with some basement membranes adjacent to the interstitium. Further, the findings suggest that collagens III and VI may connect the various components of the extracellular matrix, such as type I fibers with basement membranes and other structures, thus forming an integrated functional unit.

Chondroitin-6-sulfate-containing proteoglycan: a new component of human skin dermoepidermal junction

A murine monoclonal antibody (3B3) has been produced with specificity for chondroitin-6-sulfate (C-6-S) and proven binding to rodent basement membranes, presumably detecting a population of C-6-S-containing proteoglycans. Utilizing this antibody, we sought to determine whether a basement membrane chondroitin sulfate proteoglycan is present in adult, neonatal, and/or fetal skin, and if present, its ultrastructural localization. Indirect immunofluorescence was performed on human adult, neonatal, and fetal skin. To detect the antigen, specimens were pretreated with chondroitinase ABC; absence of enzyme treatment served as negative control. Chondroitin sulfate proteoglycan was detectable in linear homogeneous array along the dermoepidermal junction and within vascular (and when present, adnexal) basement membranes in both adult and neonatal skin. In fetal skin, basement membrane staining was noted as early as 54 gestational days. Indirect immunoelectron microscopy and NaCl-split skin studies were performed to ultrastructurally localize the antigen; immune deposits were detectable within the lamina densa in chondroitinase-treated skin. These findings demonstrate that chondroitin sulfate proteoglycan is present within all skin basement membranes; that it is present in the region of the lamina densa; and that similar to some other ubiquitous basement membrane antigens, it is present early in the developing fetus.

Nidogen and heparan sulfate proteoglycan: detection of newly isolated basement membrane components in normal and epidermolysis bullosa skin

The epidermal basement membrane zone comprises various biochemical constituents, some of which may be affected or involved in certain forms of mechanobullous diseases. Recently, nidogen and a low density form of heparan sulfate proteoglycan--two ubiquitous, noncollagenous components of basement membranes--were isolated and characterized, and affinity-purified antibodies to each component were prepared. These antibodies were used to study the distribution of both antigens in normal and diseased human skin. By immunofluorescence, both nidogen and heparan sulfate proteoglycan were linearly distributed along the basement membrane of the dermal-epidermal junction, adnexal structures, and blood vessels of normal human skin. On suction-induced blisters of normal skin, both antigens were found at the base of the blister, indicating that each was within or below the lamina lucida. By indirect immunoelectron microscopy, both antigens were ultrastructurally located within the lamina densa. The staining patterns for nidogen and heparan sulfate proteoglycan were examined in 11 patients with either junctional, dominant dystrophic, or recessive dystrophic epidermolysis bullosa, and were found to be not different from the patterns observed in normal skin.

Histopathological and immunohistochemical changes in neurosurgically resected epileptic foci

Neurosurgical resection of an epileptic focus was performed in eleven patients suffering from drug resistant focal epilepsy. The clinical result was favourable in nine cases and corresponds to the earlier results. The routinely processed biopsy specimens obtained from the brain resections were stained with haematoxylin-eosin and with specific antisera to GFAP, S-100, NSE, laminin, and fibronectin using the peroxidase-antiperoxidase technique. The main pathological finding was gliosis in eight cases, neuronal degeneration in two cases, and a vascular malformation in one case. The anti-GFAP as a specific marker of astrocytes made the astroglial proliferation clearly visible, demonstrating an astroglial scar in four cases and a moderately to strongly increased amount of astroglial cells in another four cases. Anti-S-100 and anti-fibronectin are not as specific markers. They stained both neurones and glial cells with comparable results to that of anti-GFAP but with a lower specificity and sensitivity. Anti-NSE showed decreased amounts of neurones in most of the heavily gliotic lesions and also stained glial cells in some cases. Anti-laminin stained the pial and vascular basement membranes and revealed an increased vasculature in two cases. From these results, it appears that GFAP immunostaining is a highly demonstrative means for the visualization of astrogliosis in epileptic lesions and may be of help in identifying slight focal changes. An exact demonstration of neuronal loss or other neuronal changes still waits for a more specific marker than NSE. A favourable clinical outcome after neurosurgery seems to be associated with the patients showing a clearly gliotic brain lesion in one temporal lobe.

Light microscopic immunolocalization of laminin, type IV collagen, nidogen, heparan sulphate proteoglycan and fibronectin in the enteric nervous system of rat and guinea pig

The localization of the extracellular matrix components laminin, fibronectin and type IV collagen in the enteric nervous system and the surrounding smooth muscle was investigated by immunohistochemical methods, using tissue sections of rat and guinea pig large intestine. None of these molecules were detectable inside the enteric ganglia. In contrast, they were easily demonstrable in association with the basement membrane of satellite cells within sensory and sympathetic ganglia. All of these molecules were, however, present in or nearby the basement membrane that surrounds each enteric ganglion. This agrees with previous ultrastructural observations that, in small mammals, neither basement membranes nor large connective tissue spaces are found inside enteric ganglia. The matrix molecules under study were also detected in the basement membrane of the nearby smooth muscle cells that make up the muscle layer of the gut wall. Fibronectin was frequently observed as a broad staining pattern suggesting its localization in the lamina reticularis rather than in the lamina densa. In addition, nidogen and heparan sulphate proteoglycan were demonstrated in the basement membrane of both enteric ganglia and Schwann cells.

Basement membrane proteins produced by Schwann cells and in neurofibromatosis

Mouse Schwann cells and rat RN22 schwannoma cells cultured in the absence of neurons and fibroblasts produce typical basement membrane proteins. Heparan sulfate proteoglycan (low density form), nidogen, and protein BM-40 were identified by radioimmunoassays, immunoblotting, and by immunoprecipitation after metabolic labeling. The cells also produce a laminin-like protein that differs from authentic laminin by a reduced A chain content and lack of antigenic determinants located in the long arm of laminin. Laminin possessing A and B chains is, however, produced by PYS-2 teratocarcinoma cells grown under the same conditions. Laminin from Schwann cell culture medium promotes neurite outgrowth, and this activity could be immunoprecipitated but not blocked by various antibodies against authentic laminin. In addition, Schwann cell laminin is found complexed noncovalently with nidogen. Sulfate incorporation revealed the synthesis of proteoglycans and entactin. A similar set of proteins and in addition collagen IV could be demonstrated in neurofibroma tissue by immunohistology, and were localized to the laminae densae of the multilayered basement membranes around Schwann cells and capillaries. Laminin purified from 0.5 M NaCl neurofibroma tissue extracts possessed both A and B chains. Nidogen was identified in a partially degraded form.

The extracellular matrix is an integrated unit: ultrastructural localization of collagen types I, III, IV, V, VI, fibronectin, and laminin in human term placenta

The human term placenta is used extensively as a source of extracellular matrix components. To elucidate the tissue distribution and interrelationships of seven of these components, monospecific antibodies directed against collagen types I, III, IV, V, VI, fibronectin, and laminin were reacted with human term placenta and studied by light and electron immunohistochemistry. Type I collagen was the basic structural unit of human term placenta, present as 30-35 nm, cross-banded fibers, often in the form of large fiber bundles. Type III collagen was present as thin 10-15 nm, beaded fibers often forming a meshwork which encased type I collagen fibers. Types V and VI collagen were present as 6-10 nm filaments, often closely associated with types I and III collagen. Type VI collagen also coated collagen fibers of all diameters, enhancing their periodicity, providing a staining pattern often similar to that observed with anti-fibronectin antibodies. Fibronectin was present in both maternal and fetal plasma and throughout the stroma of the chorionic villus, as both free filaments and coating collagen fibers. Basement membranes contained laminin and type IV collagen, but no fibronectin. In summary, the non-basement membrane proteins studied often codistributed with type I collagen, between and apparently attached to fibers, suggesting that they may act as binding proteins, linking type I fibers and bundles, to themselves and to other structures.