Perineurial cells coexpress genes encoding interstitial collagens and basement membrane zone components

Alk1 acts in non-endothelial VE-cadherin+ perineurial cells to maintain nerve branching during hair homeostasis

Vascular endothelial (VE)-cadherin is a well-recognized endothelial cell marker. One of its interacting partners, the TGF-β receptor Alk1, is essential in endothelial cells for adult skin vasculature remodeling during hair homeostasis. Using single-cell transcriptomics, lineage tracing and gene targeting in mice, we characterize the cellular and molecular dynamics of skin VE-cadherin+ cells during hair homeostasis. We describe dynamic changes of VE-cadherin+ endothelial cells specific to blood and lymphatic vessels and uncover an atypical VE-cadherin+ cell population. The latter is not a predicted adult endovascular progenitor, but rather a non-endothelial mesenchymal perineurial cell type, which forms nerve encapsulating tubular structures that undergo remodeling during hair homeostasis. Alk1 acts in the VE-cadherin+ perineurial cells to maintain proper homeostatic nerve branching by enforcing basement membrane and extracellular matrix molecular signatures. Our work implicates the VE-cadherin/Alk1 duo, classically known as endothelial-vascular specific, in perineurial-nerve homeostasis. This has broad implications in vascular and nerve disease.

Expression of JCAD and EGFR in Perineurial Cell-Cell Junctions of Human Inferior Alveolar Nerve

Although perineurium has an important role in maintenance of the blood-nerve barrier, understanding of perineurial cell-cell junctions is insufficient. The aim of this study was to analyze the expression of junctional cadherin 5 associated (JCAD) and epidermal growth factor receptor (EGFR) in the perineurium of the human inferior alveolar nerve (IAN) and investigate their roles in perineurial cell-cell junctions using cultured human perineurial cells (HPNCs). In human IAN, JCAD was strongly expressed in endoneurial microvessels. JCAD and EGFR were expressed at various intensities in the perineurium. In HPNCs, JCAD was clearly expressed at cell-cell junctions. EGFR inhibitor AG1478 treatment changed cell morphology and the ratio of JCAD-positive cell-cell contacts of HPNCs. Therefore, JCAD and EGFR may have a role in the regulation of perineurial cell-cell junctions.

Characterization of a Novel Aspect of Tissue Scarring Following Experimental Spinal Cord Injury and the Implantation of Bioengineered Type-I Collagen Scaffolds in the Adult Rat: Involvement of Perineurial-like Cells?

Numerous intervention strategies have been developed to promote functional tissue repair following experimental spinal cord injury (SCI), including the bridging of lesion-induced cystic cavities with bioengineered scaffolds. Integration between such implanted scaffolds and the lesioned host spinal cord is critical for supporting regenerative growth, but only moderate-to-low degrees of success have been reported. Light and electron microscopy were employed to better characterise the fibroadhesive scarring process taking place after implantation of a longitudinally microstructured type-I collagen scaffold into unilateral mid-cervical resection injuries of the adult rat spinal cord. At long survival times (10 weeks post-surgery), sheets of tightly packed cells (of uniform morphology) could be seen lining the inner surface of the repaired dura mater of lesion-only control animals, as well as forming a barrier along the implant–host interface of the scaffold-implanted animals. The highly uniform ultrastructural features of these scarring cells and their anatomical continuity with the local, reactive spinal nerve roots strongly suggest their identity to be perineurial-like cells. This novel aspect of the cellular composition of reactive spinal cord tissue highlights the increasingly complex nature of fibroadhesive scarring involved in traumatic injury, and particularly in response to the implantation of bioengineered collagen scaffolds.

Quantified Morphology of the Cervical and Subdiaphragmatic Vagus Nerves of Human, Pig, and Rat

It is necessary to understand the morphology of the vagus nerve (VN) to design and deliver effective and selective vagus nerve stimulation (VNS) because nerve morphology influences fiber responses to electrical stimulation. Specifically, nerve diameter (and thus, electrode-fiber distance), fascicle diameter, fascicular organization, and perineurium thickness all significantly affect the responses of nerve fibers to electrical signals delivered through a cuff electrode. We quantified the morphology of cervical and subdiaphragmatic VNs in humans, pigs, and rats: effective nerve diameter, number of fascicles, effective fascicle diameters, proportions of endoneurial, perineurial, and epineurial tissues, and perineurium thickness. The human and pig VNs were comparable sizes (∼2 mm cervically; ∼1.6 mm subdiaphragmatically), while the rat nerves were ten times smaller. The pig nerves had ten times more fascicles-and the fascicles were smaller-than in human nerves (47 vs. 7 fascicles cervically; 38 vs. 5 fascicles subdiaphragmatically). Comparing the cervical to the subdiaphragmatic VNs, the nerves and fascicles were larger at the cervical level for all species and there were more fascicles for pigs. Human morphology generally exhibited greater variability across samples than pigs and rats. A prior study of human somatic nerves indicated that the ratio of perineurium thickness to fascicle diameter was approximately constant across fascicle diameters. However, our data found thicker human and pig VN perineurium than those prior data: the VNs had thicker perineurium for larger fascicles and thicker perineurium normalized by fascicle diameter for smaller fascicles. Understanding these differences in VN morphology between preclinical models and the clinical target, as well as the variability across individuals of a species, is essential for designing suitable cuff electrodes and stimulation parameters and for informing translation of preclinical results to clinical application to advance the therapeutic efficacy of VNS.

Tight Junction Proteins and Perineurial Cells in Neurofibromas

Cutaneous neurofibromas consist of axonal processes, Schwann cells, fibroblasts, perineurial cells, mast cells, and abundant extracellular matrix. The distribution and role of perineurial cells in neurofibromas has been uncertain, partly because there has not been a specific immunohistochemical marker for perineurial cells. In this study, tight junctions (TJs) of 16 neurofibromas from 12 patients with neurofibromatosis type 1 (NF1) were analyzed using electron microscopy, immunohistochemistry, and Western transfer analysis. Cell-cell contacts with typical ultrastructural morphology of TJs were seen between adjacent perineurial cells surrounding the small nerves and between contacting perineurial cell processes embedded in tumor stroma. Immunohistochemistry showed expression of claudin-1, claudin-3, and ZO-1 in the intercellular junctions of a subpopulation of tumor cells. Occludin was present mainly in perineurium and claudin-5 localized to the blood vessels. Double immunolabelings were used to identify the cell types expressing claudin-1. The results showed that claudin-1 positive cells were also positive for type IV collagen and epithelial membrane antigen but not for S-100 protein. This labeling pattern is consistent with perineurial cell phenotype. Using claudin-1 as a marker, our results showed that clusters of perineurial cells are distributed around the rudimentary nerves within cutaneous neurofibromas and at the periphery of some neurofibromas.

Perineurial glia

Although the ultrastructure of peripheral nerves has been known for nearly 200 years, the developmental origins and functional roles of all five main components of these specialized nervous system conduits are still poorly understood. One of these understudied nerve elements, the perineurium, is a component of the blood-nerve barrier and is essential for protecting axons and their associated Schwann cells from ionic flux, toxins, and infection. However, until recently, it was thought that this vital nerve tissue was derived from the mesoderm and simply served a structural/barrier function with no other influence on the development, maintenance, or regeneration of peripheral nerves. Recent work in zebrafish using in vivo time-lapse imaging, genetic manipulation, and laser axotomy is shedding light on the origin and roles of this previously ignored glial nerve component and is changing how we view development of the nervous system.

Mammalian Nkx2.2+ perineurial glia are essential for motor nerve development

BACKGROUND

All vertebrate peripheral nerves connect the central nervous system (CNS) with targets in the periphery and are composed of axons, layers of ensheathing glia and connective tissue. Although the structure of these conduits is well established, very little is known about the origin and developmental roles of some of their elements. One understudied component, the perineurium, ensheaths nerve fascicles and is a component of the blood-nerve-barrier. In zebrafish, the motor nerve perineurium is composed of CNS-derived nkx2.2a(+) perineurial glia, which establish the motor exit point (MEP) during development. To determine if mouse perineurial cells also originate within the CNS and perform a similar function, we created a Nkx2.2:EGFP transgenic reporter line.

RESULTS

In conjunction with RNA expression analysis and antibody labeling, we observed Nkx2.2(+) cells along peripheral motor nerves at all stages of development and in adult tissue. Additionally, in mice lacking Nkx2.2, we demonstrate that Nkx2.2(+) perineurial glia are essential for motor nerve development and Schwann cell differentiation.

CONCLUSIONS

Our studies reveal that a subset of mouse perineurial cells are CNS-derived, express Nkx2.2, and are essential for motor nerve development. This work highlights an under-appreciated but essential contribution of CNS-derived cells to the development of the mammalian peripheral nervous system (PNS).

Barriers of the peripheral nerve

This review introduces the traditionally defined anatomic compartments of the peripheral nerves based on light and electron microscopic topography and then explores the cellular and the most recent molecular basis of the different barrier functions operative in peripheral nerves. We also elucidate where, and how, the homeostasis of the normal human peripheral nerve is controlled in situ and how claudin-containing tight junctions contribute to the barriers of peripheral nerve. Also, the human timeline of the development of the barriers of the peripheral nerve is depicted. Finally, potential future therapeutic modalities interfering with the barriers of the peripheral nerve are discussed.

Endoneurial fibroblast-like cells

Endoneurial fibroblast-like cells (EFLCs) have been described for more than 60 years, but the embryology, functions, and pathology of these cells are not well defined. Several hypotheses of their origin have been proposed. A previous study suggesting that they were of neural crest origin is supported by our data in humans. This lineage might account for EFLCs having multiple biologic functions and involvement in pathological processes. Here, we review what is known about the origin; functions in collagen synthesis, phagocytosis, inflammatory responses, and immune surveillance; and the pathological alterations of EFLCs based on the literature and on our personal observations.

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.

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.

The neurofibromatosis type 2 gene is mutated in perineurial cell tumors: a molecular genetic study of eight cases

Perineurial cell tumors (PNTs) are rare neoplasms derived from or showing differentiation toward specialized lining cells of the nerve sheath, the perineurial cells. In this study, we have evaluated neurofibromatosis type 2 (NF2) gene alterations in eight PNTs using archival formaldehyde-fixed, paraffin-embedded tissue. Two conventional soft-tissue PNTs from the upper back and chest wall, one retiform soft tissue variant from the scapular region, and five sclerosing PNTs from the fingers and palm were studied. All cases showed histological features of PNTs, and the neoplastic cells were positive for epithelial membrane antigen and negative for S100 protein. The coding sequences (exons 1 to 15) of the NF2 gene were polymerase chain reaction (PCR) amplified and evaluated for mutations by direct sequencing of the PCR products. Five NF2 point mutations, two in the 5'-untranslated region (UTR) and three in exons 3, 6, and 8, were identified in four of eight cases (50%) studied. Exon mutations resulted in changes of predicted amino acids sequences: Asp-->Asn at codon 83, Glu-->Asp at codon 182, and Leu-->Val at codon 241. In two cases (one with a missense mutation in codon 241), the same point mutation in the 5'-UTR at the nucleotide position 8958 was identified. A loss of heterozygosity (LOH) study was performed in three cases. LOH at the NF2 locus was found in one case with a mutation in the 5'-UTR. However, in another case with exon 8 and 5'-UTR mutations, deletion of one allele of the NF2 gene was previously documented by fluorescence in situ hybridization. The coexistence of NF2 gene mutations and LOH at the NF2 locus indicates that the NF2 tumor suppressor gene is altered in PNTs by the two-hit mechanism.

Altered distribution of Schwann cells in the periodontal ligament of the rat incisor following resection of the inferior alveolar nerve: an immunohistochemical study on S-100 proteins

The present study employed immunohistochemistry for the detection of S-100 proteins to reveal the alteration in the distribution of Schwann cells in the periodontal ligament of the rat incisor following resection of the inferior alveolar nerve (IAN). In normal animals, S-100-immunostaining demonstrated the profiles of Ruffini endings, primary mechanoreceptors in the periodontal ligament, in the alveolus-related part of the ligament. Under the electron microscope, S-100-like immunoreactivity (-LI) was observed in the cytoplasm of the terminal Schwann cell elements and in some axon profiles of the Ruffini endings. During the regeneration, S-100-like immunoreactive (-IR) terminal Schwann cells in the alveolus-related part of the ligament gradually decreased in number. In contrast, S-100-LI was found in the spindle-shaped cells at the shear zone (the border between alveolus-related and tooth-related parts) and in the tooth-related part, where S-100-LI was rarely detected in normal animals. Immunoelectron microscopic observations revealed that some S-100-IR spindle-shaped cells contained fibrous long spacing (FLS) fibers, suggesting that they were Schwann cells. Some regenerating axons were observed at the shear zone, but were rarely found in the tooth-related part. With the progress of the regeneration of the periodontal Ruffini endings, S-100-IR terminal Schwann cells became rearranged in the alveolus-related part by 42-56 days post injury, whereas the S-100-IR spindle-shaped Schwann cells in the shear zone and tooth-related part disappeared when the regeneration was complete.

Spatial pattern of type I collagen expression in injured peripheral nerve

The authors studied the spatial expression and regulation of messenger RNA for the alpha subunit of collagen type I in crushed rat sciatic nerve to provide a basis for future therapeutic manipulation. Sciatic nerves in 20 male or female adult Lewis rats were crushed for 60 seconds; the unharmed contralateral sciatic nerves served as controls. Twenty-one days after injury the experimental animals were killed and their tissue was harvested. The spatial expression of collagen type I was determined by using in situ hybridization techniques. Quantification of fibroblast number and total signal was performed through computerized morphometry. Collagen upregulation was evident in epineurial and perineurial layers, with the epineurium displaying higher activity. The cells responsible for procollagen type I production were fibroblasts. No activity was seen in the endoneurium. Morphometric findings indicated that collagen upregulation in the epineurium and perineurium occurred at both pretranscriptional and posttranslational levels when compared to controls; a paired t-test analysis confirmed statistical significance for all comparisons between injured and control tissues. Epineurial fibroblasts are responsible for the collagen production associated with crushed peripheral nerve injury in the rat. Regulation occurs pretranscriptionally as well as posttranslationally. It is interesting to speculate that the delivery of agents directed against collagen production (such as neutralizing antibodies to growth factors) into epineurial tissues proximate to the time and location of clinical nerve injury might mitigate later deleterious effects of excess collagen production in axonal regeneration.

Immunohistochemical localization of laminin and type IV collagen in human cutaneous sensory nerve formations

We used immunohistochemical techniques and monoclonal antibodies to localize two basement membrane components (laminin and type IV collagen) in the nerves and sensory nerve formations, or corpuscles, supplying human digital skin. Furthermore, neurofilament proteins, S-100 protein and epithelial membrane antigen were studied in parallel. In dermal nerve trunks, immunostaining for laminin and type IV collagen was found to be co-localized in the perineurium and the Schwann cells, the stronger immunoreactivity being at the external surface of the cells. In the Meissner digital corpuscles, the immunoreactivity for laminin and type IV collagen was mainly observed underlying the cell surface of lamellar cells, while the cytoplasm was weakly immunolabelled or unlabelled. Finally, within Pacinian corpuscles co-localization of the two basement membrane molecules was encountered in the inner core, intermediate layer, outer core and capsule. Laminin and type IV collagen immunoreactivities were also found in blood vessels and sweat glands, apparently labelling basement membrane structures. The present results provide evidence for the presence of basement membrane in all periaxonic cells forming human cutaneous sensory nerve formations, and suggest that all of them are able to synthesize and release some basement membrane components, such as laminin and type IV collagen. The possible role of laminin in sensory nerve formations is discussed.

cAMP-dependent differential regulation of extracellular matrix (ECM) gene expression in cultured rat Schwann cells

cAMP-dependent regulation of the steady-state mRNA levels for the ECM components, laminin A, B1 and B2 chains, collagen types I, III and IV were examined by Northern blot analysis in cultured rat Schwann cells. ECM mRNAs of laminin B1 chain and collagen types I and IV were expressed at high levels in the control Schwann cells, while laminin B2 chain and collagen type III mRNA levels were low, and laminin A chain mRNA was not detectable. When Schwann cells were treated with forskolin or cAMP derivatives, the gene expression for the ECM molecules constituting the Schwann cell basement membrane, laminin B1 and B2 chains, and collagen type IV, was enhanced in time- and dose-dependent manners for exogenously administered forskolin or cAMP derivatives, while the mRNA levels for the ECM molecules, which are not the major components of the basement membrane, fibrillary collagen types I and III were significantly suppressed. This cAMP-dependent differential regulation of Schwann cell ECM gene expression may be related to the role of each ECM molecule in the peripheral nerve development and regeneration.

Hyperglycemic glucose concentrations up-regulate the expression of type VI collagen in vitro. Relevance to alterations of peripheral nerves in diabetes mellitus

Electron microscopy of peripheral nerves obtained from two diabetic patients revealed large deposits of microfibrils and the presence of Luse bodies in the vicinity of perineurial cells. Microfibrils were found to accumulate also in the sciatic nerves of diabetic BB rats; these microfibrillar deposits were shown to contain type VI collagen by immunoelectron microscopy. Connective tissue cells cultured from rat sciatic nerves were exposed to high glucose concentrations. High glucose concentrations up-regulated the mRNA steady-state levels of alpha 1(VI), alpha 2(VI), and alpha 3(VI) chains of type VI collagen and caused accumulation of type VI collagen-containing fibrils in the cultures. Immunostaining and in situ hybridizations demonstrated that perineurial cells, Schwann cells, and fibroblasts expressed type VI collagen at the mRNA and protein levels. The results suggest that the turnover and supramolecular assembly of type VI collagen are perturbed in diabetic nerves and that glucose per se increases the expression of type VI collagen in vitro.

Basement membranes during development of human nerve: Schwann cells and perineurial cells display marked changes in their expression profiles for laminin subunits and beta 1 and beta 4 integrins

The formation of the connective tissue compartments of human sciatic and tibial nerves was studied with special reference to the maturation of the basement membranes during foetal development (11-35 weeks of gestation). All Schwann cells were surrounded by continuous basement membranes as early as at week 11, while the perineurial cells became covered by basement membranes gradually between weeks 17 and 35, as estimated by electron microscopy. The first laminin subunits detectable within the nerve were the B1, B2 and M chains. These laminin subunits were present in Schwann cell basement membrane zone at week 11, and in the perineurium at week 17 and later. Laminin A and S chains were first detected at 26 weeks in the perineurium, and at a later stage (35 weeks) on Schwann cells. In mature nerves, all these five laminin chains could be demonstrated in both Schwann cell and perineurial cell basement membrane zones, although A, S and B2 chains predominated in the perineurium, and M, B1 and B2 were the predominant chains in Schwann cell basement membranes. Beta 1 and beta 4 integrins were expressed by all Schwann cells in samples from the youngest foetuses (11-17 weeks). At 22-35 weeks, however, only a subpopulation of Schwann cells stained positively for beta 1 and beta 4 integrins. Perineurial cells expressed beta 1 integrins at all ages studied. Staining for beta 4 integrin in perineurium became detectable and intensified concomitant with the formation of structural basement membranes. The results demonstrate that Schwann cells and perineurial cells change their laminin and integrin expression profiles during the maturation of peripheral nerve.

Laminin B1 and collagen type IV gene expression in transected peripheral nerve: reinnervation compared to denervation

The expression of B1 laminin and type IV collagen was followed in the microsurgically isolated endoneurium of transected rat sciatic nerves from 3 days until 8 weeks. Northern hybridizations revealed that after nerve transection the proximal stumps of denervated, as well as freely regenerating, nerves showed a markedly increased expression of laminin and type IV collagen which lasted from 3 days up to 8 weeks. In the distal stumps, close to the site of transection (2-7 mm), the expression of laminin, and to a certain extent that of type IV collagen, seemed to be enhanced if free axonal reinnervation was allowed. Further distally (10-15 mm), the patterns of B1 laminin and type IV collagen expression were similar in both experimental groups, so that an increased expression was noticed during the first 2 weeks. The present results suggest that laminin and type IV collagen gene expression is markedly different in different parts of transected rat sciatic nerve. During peripheral nerve regeneration, there is a long-lasting basement membrane gene expression in the proximal stump. In the distal part of the transected nerve, the axonal reinnervation possibly up-regulates, but is not essential for, the expression of B1 laminin and type IV collagen.

The enigmatic perineurial cell and its participation in tumors and in tumorlike entities

The perineurial cells that make up the perineurium of peripheral nerve fascicles are characterized by distinct ultrastructural features, including non-branching thin cytoplasmic processes coated by an external lamina and joined at their ends by a tight junction, few organelles, actin and vimentin filaments, and numerous pinocytotic vesicles. Perineurial cells are immunoreactive for vimentin and epithelial membrane antigen (EMA) but not for the Schwann cell markers S-100 protein and Leu-7. The cytogenesis of the perineurium remains disputable, with morphologic, immunohistochemical, and experimental evidence supporting origin from the fibroblast, Schwann cell, and arachnoid cap cell. Ultrastructural studies more recently supported by immunolocalization of EMA have detected hyperplastic and neoplastic perineuriallike cells in a number of pseudoneoplastic lesions and true neoplasms, notably localized hypertrophic neuropathy, neurofibromas of various types, and perineurioma.

Plasticity of integrin expression by nerve-derived connective tissue cells. Human Schwann cells, perineurial cells, and fibroblasts express markedly different patterns of beta 1 integrins during nerve development, neoplasia, and in vitro

Strikingly selective expression patterns of beta 1, alpha 2, alpha 3, and alpha 5 integrin subunits were revealed in endoneurium, perineurium, and epineurium of fetal and adult human peripheral nerve by immunostaining with specific antibodies. The alpha 2 subunit was expressed only on Schwann cells both in fetal and adult nerve, whereas the alpha 3 epitopes were expressed exclusively in the adult tissue and were primarily present on perineurial cells. The alpha 5 epitopes were expressed only on the innermost cell layer of perineurium of fetal and adult nerve. The tumor cells within schwannomas and cutaneous neurofibromas expressed both alpha 2 and alpha 3 subunits, indicating that Schwann cells have the potential to express also the alpha 3 subunit in vivo. Cell cultures established from human fetal nerve and neurofibromas revealed expression of the alpha 2 and alpha 5 epitopes on Schwann cells, perineurial cells, and fibroblasts, whereas only Schwann cells contained the alpha 3 epitopes which were occasionally concentrated on the adjacent Schwann cells at cell-cell contacts. Our findings emphasize that nerve connective tissue cells change their profiles for expression of extracellular matrix receptors under conditions which have different regulatory control signals exerted by, for example, axons, humoral factors, or the extracellular matrix of the peripheral nerve. This plasticity may play an important role during nerve development and in neoplastic processes affecting the connective tissue compartments of peripheral nerve.

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.