Brain-specific hyaluronate-binding protein: an immunohistological study with monoclonal antibodies of human and bovine central nervous system

Hyaluronan and hyaluronectin in the nervous system

Hyaluronan was studied in extracts of the nervous system and in situ. Extraction yielded larger amounts at neutral or alkaline pH. Protease digestion enhanced the quantitative results obtained with an indirect enzyme immunological assay. It was shown that HA extracted from brain at neutral pH was bound to a glycoprotein component (hyaluronectin, HN) which is in part free at acid pH. Although HN is not restricted to nervous tissue it is mainly expressed in the central nervous system of adult mammals. Its main form has a molecular mass of 68 kDa and binds in vitro to HA and to HA-derived oligosaccharides down to HA10 with a Kd in the 10(-8) M range. HA-HN complexes were found in human cerebrospinal fluids. The HA concentration in cerebral tissue decreases from the fetus to the adult, whereas the HN concentration increases. HA is not however saturated by HN and still binds HN in vitro. In the rat HA decreases sharply at Days 10-11 after birth. In the rat embryo HA forms an extracellular component of the migration and proliferation areas of the cerebral cortex. In the adult typical locations were at the nodes of Ranvier and in perineuronal structures. HN was found in the same locations but seemed to be associated with a restricted category of neurons. In the cerebellum HA-HN was found mainly in the grey nuclei, the granular layer and around Purkinje cells. Cell bodies were not stained but in the electron microscope HN was seen in the cytoplasm and plasma membrane of the perisynaptic glial cell processes. A hypothesis has been proposed that HA-HN is involved in neural GABAergic transmission.

Ultrastructural association of hyaluronan with rat unmyelinated nerve fibres

A potential association between hyaluronan and unmyelinated nerve fibres in the PNS (rat skin and iris) and CNS (rat retinal inner plexiform and nerve fibre layers) was investigated at the ultrastructural level using two different hyaluronan-binding probes (link protein-gold and aggrecan-gold). Neuronal and glial cell plasma membranes, as well as the periaxonal space in between, were specifically labelled, suggesting that hyaluronan is secreted by these cells and utilized locally. Intracelluarly, weak labelling of mitochondrial profiles was observed.

The versican C-type lectin domain recognizes the adhesion protein tenascin-R

The core proteins of large chondroitin sulfate proteoglycans contain a C-type lectin domain. The lectin domain of one of these proteoglycans, versican, was expressed as a recombinant 15-kDa protein and shown to bind to insolubilized fucose and GlcNAc. The lectin domain showed strong binding in a gel blotting assay to a glycoprotein doublet in rat brain extracts. The binding was calcium dependent and abolished by chemical deglycosylation treatment of the ligand glycoprotein. The versican-binding glycoprotein was identified as the cell adhesion protein tenascin-R, and versican and tenascin-R were both found to be localized in the granular layer of rat cerebellum. These results show that the versican lectin domain is a binding domain with a highly targeted specificity. It may allow versican to assemble complexes containing proteoglycan, an adhesion protein, and hyaluronan.

On the existence of a cartilage-like proteoglycan and link proteins in the central nervous system

Monoclonal antibodies (mAbs) against the major constituents of cartilage extracellular matrix, aggrecan and link protein, were screened by indirect immunofluorescence on frozen sections of bovine spinal cord. Antibodies against aggrecan and link protein gave rise to very similar perineuronal labeling in spinal cord gray matter. Aggrecan and link protein reactivities were seen in other regions of the central nervous system (CNS), although their distributions were not always coincident. Pretreatment of the tissue section with Streptomyces hyaluronidase, which is hyaluronate-specific, led to the loss of both reactivities. On Western blots, anti-aggrecan mAbs reacted with a large chondroitin sulfate proteoglycan. The chondroitinase-treated CNS proteoglycan co-migrated with the chondroitinase- and keratanase-treated cartilage proteoglycan. In CNS tissue homogenates, the addition of Streptomyces hyaluronidase brought about the release of the proteoglycan from the tissue. Anti-link protein mAbs were reactive with two species in the bovine CNS, the mobilities of which were very similar to those of the cartilage link proteins. The release of these species from the tissue required hyaluronidase. A rabbit antiserum against aggrecan was used to identify a similar proteoglycan in the rat CNS. In spinal cord-derived cell cultures, the labeled material was associated with astrocytes. An aggrecan cDNA hybridized to a 9.5 kb mRNA in the rat CNS. We conclude that the perineuronal matrix consists, in part, of a hyaluronate-bound aggrecan-like proteoglycan and link proteins, and that the former is produced by astrocytes.

In memory of Amico Bignami (1930-1994)

Amico Bignami, neuropathologist and neuroscientist, professor of Neuropathology at Harvard Medical School, died on August 5, 1994. He is best known for his pioneering work on spongiform encephalopathies and intermediate filaments, in particular glial fibrillary acidic protein (GFAP).

Identification of Gal(beta 1-3)GalNAc bearing glycoproteins at the nodes of Ranvier in peripheral nerve

A subset of human anti-GM1 ganglioside antibodies cross-reacts with Gal(beta 1-3)GalNAc bearing glycoproteins in peripheral nerve and spinal cord. The same oligosaccharide determinant is recognized by the lectin peanut agglutinin (PNA) which binds at the nodes of Ranvier in intact peripheral nerve. The Gal(beta 1-3)GalNAc bearing glycoproteins were isolated using PNA lectin affinity chromatography followed by separation on Western blot, and the proteins were subjected to partial amino acid sequence analysis. Two major PNA binding glycoproteins were identified in peripheral nerve and spinal cord; one had an approximate molecular weight of 120 kD and had sequence homology to the oligodendrocyte-myelin glycoprotein (OMgp). The other migrated between 70 and 80 kD and had sequence homology to the hyaluronate binding domain of versican, which has been reported to share sequence homology with the 70 kD proteins hyaluronectin and the glial hyaluronic acid binding protein (GHAP). By immunocytochemistry, OMgp was localized to the paranodal region of myelin, and the protein homologous to the hyaluronate binding domain of versican was localized to the nodal gap in peripheral nerve. These PNA binding glycoproteins might be target antigens for autoantibodies in peripheral nerve.

A role for extracellular matrix degradation and matrix metalloproteinases in senile dementia?

In brain as in cartilage, the extracellular matrix contains aggregates formed by hyaluronic acid (HA) and proteoglycans. In osteoarthritic cartilage, release of the proteoglycans from the aggregates by cleavage of the HA-binding region results in the accumulation of the HA-binding region and in the fragmentation of the released proteoglycans. Stromelysin, a matrix neutral metalloproteinase, is one of the enzymes responsible for the cleavage of the HA-binding region. We suggest that a similar process also occurs in senile dementia. The brain proteoglycan contains sequences identical to those of aggrecan, which are recognized and cleaved by stromelysin, and is, in fact, susceptible to stromelysin digestion. Monoclonal antibodies reacting with glial HA-binding protein, but not with the parent protein, stained several senile plaques as defined by their reactivity with antibodies to the amyloid-beta protein in double-labeling experiments.

Colocalization of tenascin with versican, a hyaluronate-binding chondroitin sulfate proteoglycan

Rabbit antisera against tenascin, a large extracellular matrix protein, in conjunction with monoclonal antibodies of mouse origin against versican, a large hyaluronate-binding proteoglycan, were used to make a comparative study of the distribution of the two antigens in the same cryostat sections by double immunofluorescence. In the central nervous system, tenascin was invariably associated with versican, but the reverse was not true, in that versican was also found where tenascin was not detectable, particularly in gray matter. There were major species differences in the distribution of tenascin in the central nervous system. In the cow, tenascin was found in cerebral and spinal cord white matter and in the granule cell layer of the cerebellum. In the human brain, tenascin was found in cerebral white matter but not in the cerebellum. In the rat, tenascin was mainly confined to brain periventricular layer and spinal cord white matter. During the development of the cerebellum of the rat, the tenascin immunoreactivity decreased, and a lower molecular weight band appeared (J1-160/180/restrictin?) and persisted throughout adulthood. Tenascin expression was a relatively late event in the development of the rat central nervous system, immunoreactivity being first observed after birth. In the rat embryo, tenascin was found to co-localize with versican in precartilaginous mesenchyme and in connective tissue underlying epithelia. The colocalization of versican with tenascin suggests that versican may be the tenascin (cytotactin)-associated proteoglycan reported in the literature.

Hyaluronic acid and hyaluronic acid-binding proteins in brain extracellular matrix

Hyaluronic acid (HA) plays the main structural role in the formation of brain extracellular matrix (ECM). The extracellular space appears empty by electron microscopy because HA is readily dissolved during the preparation of tissues for ultrastructural studies. The HA-binding proteins so far identified in brain ECM are versican, aggrecan and the glial HA-binding protein. Versican is a large fibroblast proteoglycan preferentially expressed in embryonic cartilage at the time of mesenchymal condensation. Glial HA-binding protein (GHAP) is probably a proteolytic product of versican corresponding to its HA-binding amino-terminal domain. It is mainly a white-matter protein, suggesting that the proteinase responsible for its cleavage from versican is normally activated in this location. Versican is found in both white matter and gray matter, where it forms pericellular coats around large neurons. Aggrecan, the aggregating proteoglycan of mature cartilage, co-localizes with versican in this location. In white matter, the localization of GHAP and versican is identical to that of the glial fibrillary acid protein, suggesting that both proteins are produced by astrocytes. An important difference between GHAP and versican is that GHAP but not versican is released from the tissues by hyaluronidase digestion, which suggests that versican is anchored to the cell membranes lining the extracellular space. GHAP was localized at the ultrastructural level in the granule cell layer of rat cerebellum, the only region of gray matter that is positive for GHAP in this species. Rats were perfused with aqueous fixatives containing cetylpyridinium chloride or tannic acid to prevent the solubilization of HA. GHAP is found throughout the extracellular space, the synaptic clefts being a notable exception. GHAP appears late in development, and the same is true for versican, the characteristic perineuronal coats first becoming apparent in the third postnatal week. It is suggested that a marked change occurs in the structure of brain ECM when HA-binding proteins first appear, and that the change is similar to that observed in prechondrogenic mesenchyme, i.e., reduction of the extracellular space and cell aggregation.

Versican, a hyaluronate-binding proteoglycan of embryonal precartilaginous mesenchyma, is mainly expressed postnatally in rat brain

The localization of versican, a large hyaluronate-binding fibroblast proteoglycan, was studied in rat prenatal and postnatal development. In adult rat white matter and cerebellum, the distribution of versican was identical to that previously reported for brain-specific glial hyaluronate-binding protein (GHAP). Versican was also found in gray matter where it formed characteristic coats around large neurons. It was also found in peripheral tissues, namely, kidney medulla, myotendinous junctions, and endoneurial and endomysial sheaths. In rat embryo the most notable finding was the presence of large amounts of versican immunoreactive material in precartilaginous mesenchyma. In embryonal CNS, versican was mainly confined to the marginal zone on the surface of the cerebral hemispheres. Versican expression mainly occurred postnatally in brain and spinal cord. In spinal cord white matter, versican immunoreactivity was already present in 3-day-old rats and preceded the appearance of GHAP, which was first detected on day 13 after the onset of myelination. Versican expression was markedly delayed in gray matter. The characteristic perineuronal coats were first observed on day 21 in the cerebral cortex. It is concluded that, with the exception of hyaluronate, brain extracellular matrix (ECM) is mainly produced postnatally and that the ECM protein produced by brain cells, most likely astrocytes, is similar to that produced by precartilaginous mesenchyma.

The extracellular matrix of cerebral gray matter: Golgi's pericellular net and Nissl's nervösen grau revisited

Glial hyaluronate-binding protein (GHAP) and a large aggregating chondroitin sulfate proteoglycan (Ag-Pg) similar to a fibroblast proteoglycan (versican) were localized in bovine, dog and cat central nervous system (CNS) gray matter by indirect immunofluorescence. The distribution of the two hyaluronate-binding proteins was identical with that of hyaluronate, an extracellular glycosaminoglycan. All substances formed a finely reticulated mesh in the neuropil with a condensation of the stain around large neurons. It is concluded that in gray matter, as in white matter, the extracellular matrix (ECM) contains hyaluronate-protein aggregates. We suggest that the hyaluronate-protein aggregates correspond to the pericellular network first described by Golgi.

The astrocyte--extracellular matrix complex in CNS myelinated tracts: a comparative study on the distribution of hyaluronate in rat, goldfish and lamprey

The localization of hyaluronate was studied in the CNS of rat, goldfish and lamprey. Cryostat sections were incubated with glial hyaluronate-binding protein of human origin and stained by indirect immunofluorescence with glial hyaluronate binding protein antibodies not reaching with rat and fish. As previously reported for glial hyaluronate-binding protein and glial fibrillary acidic protein, hyaluronate and glial fibrillary acidic protein had a similar distribution in rat spinal cord and optic nerve, both substances forming ring-like structures around individual myelinated axons. A similar periaxonal distribution was observed in goldfish spinal cord and medulla, except that the rings were much wider, to accommodate the large goldfish axons. The glial fibrillary acidic protein-positive neuroglial tissue forming distinctive structures in goldfish vagal lobes also stained for hyaluronate. In both rat and goldfish spinal cord, motoneurons were surrounded by a hyaluronate coat. Goldfish optic nerve and lamprey spinal cord were hyaluronate-negative and, as previously reported, they stained for keratin but not for glial fibrillary acidic protein. The findings suggest that hyaluronate in CNS fibre tracts in a product of glial fibrillary acidic protein-positive neuroglia. They also suggest that the appearance of glial fibrillary acidic protein-positive neuroglia and the formation of a hyaluronate-bound extracellular matrix are related phenomena in phylogeny.

Some observations on the localization of hyaluronic acid in adult, newborn and embryonal rat brain

Hyaluronic acid was localized in acetone-fixed cryostat sections of brain and spinal cord obtained from adult, newborn and embryonal rat. The sections were incubated with glial hyaluronate-binding protein (GHAP) of human origin and the protein was visualized by indirect immunofluorescence with monoclonal antibodies raised to human GHAP and not staining rat brain by immunofluorescence. GHAP is a brain extracellular matrix (ECM) glycoprotein, approximately 60,000 molecular weight, which is structurally related to the HA-binding region of cartilage ECM proteins. The distribution of hyaluronate in adult brain white matter and cerebellar cortex was similar to that previously reported for GHAP. In both cases, the reaction product formed a mesh surrounding myelinated axons and granule cells. Hyaluronate was also found in parts of the brain that did not contain GHAP. A finely reticulated mesh was observed in the neuropil between cell bodies in cerebral cortex and basal ganglia. Scattered cortical neurons were surrounded by a rim of reactive material. Perineural staining was the rule rather than the exception in spinal cord anterior horn motoneurons, inferior olivary nucleus, large bulbar reticular neurons and dentate nucleus of cerebellum. The only part of the brain which appeared relatively free of hyaluronate was the molecular layer of the cerebellum. In newborn and embryonal rat, the densely packed cell bodies in cerebral gray matter, periventricular germinal layer and external granular layer of cerebellum were surrounded by hyaluronate. Small droplets of hyaluronate were observed in between the cylindrical epithelial cells lining the neural tube in 11 day embryos. Non-myelinated fiber tracts and the molecular layer of the developing cerebellum were relatively unstained. No hyaluronate was detected in the ependyma lining the cerebral ventricles and the central canal of the spinal cord.

Extracellular matrix of central nervous system white matter: demonstration of an hyaluronate-protein complex

Monoclonal antibodies were raised against human glial hyaluronate-binding protein (GHAP), a major CNS-specific glycoprotein known to bind hyaluronate in vitro. Frozen sections of dog and human spinal cord were digested with Streptomyces hyaluronidase in order to ascertain whether GHAP is bound to hyaluronate in vivo. Digestion with hyaluronidase, prior to staining of the sections by conventional indirect immunofluorescence, led to a drastic reduction in the intensity of the staining reaction. Chondroitinase ABC (protease-free) was also effective in bringing about the release of GHAP from tissue sections. This enzyme also degrades hyaluronate. The effects of the chondroitinase were completely reversed by the addition of 1 mM Zn2+, a known inhibitor of this enzyme. The intact protein was released into the soluble fraction of human brain homogenates by testicular hyaluronidase. An immunoreactive species of 70 kD was released into the soluble fraction of dog spinal cord homogenates by Streptomyces hyaluronidase. Dog GHAP was isolated from spinal cord by means of ion exchange and affinity chromatography. This protein bound efficiently to hyaluronate in vitro. Dog and human GHAP had identical isoelectric points and similar peptide maps but different molecular weights. Dog GHAP (70 kD) was larger than its human counterpart (60 kD). These findings imply that GHAP exists in association with hyaluronate in CNS white matter. Immunoelectron microscopy revealed that GHAP fills the space between myelin sheaths in dog spinal cord white matter. One is led to conclude therefore that an hyaluronate based extracellular matrix exists in CNS white matter.

Permissive and non-permissive reactive astrocytes: immunofluorescence study with antibodies to the glial hyaluronate-binding protein

Two distinct types of reactive astrocytes were studied in rat CNS. Reactive astrocytes secondary to penetrating trauma (anisomorphic gliosis) were induced by stab wounds to the brain. Reactive astrocytes secondary to Wallerian degeneration (isomorphic gliosis) were induced in spinal cord dorsal columns by dorsal rhizotomy proximal to dorsal root ganglia. Anisomorphic glial scars did not stain with antibodies to the glial hyaluronate-binding protein (GHAP), a structural glycoprotein of white matter extracellular matrix. Conversely, isomorphic glial scars were still GHAP-positive 3 months after dorsal root transection. Only after 5 months did GHAP immunoreactivity start to disappear from the isomorphic glial scar. Extensive dorsal rhizotomy was performed at the lumbar level to produce Wallerian degeneration of spinal cord dorsal columns. One month later, the rats were reoperated and two thoracic dorsal roots were implanted in the degenerated dorsal columns. The rats were examined 1 month after grafting. As expected, there was a dense anisomorphic glial scar at the site of surgery, while the dorsal columns above the graft showed isomorphic gliosis. Extensive axonal growth was observed in the dense glial scar surrounding the graft. Conversely, no axonal growth was observed in the degenerated dorsal columns undergoing isomorphic gliosis above the implant. The findings suggested that GHAP-negative astrocytes responding to traumatic injury are permissive for axonal growth and that GHAP-positive astrocytes responding to Wallerian degeneration are not permissive.

Glial hyaluronate-binding protein in dysmyelinating mice mutants: jimpy, quaking and shiverer

Cryostat sections of cerebral hemispheres, cerebellum and spinal cord from dysmyelinating mice mutants (quaking, jimpy and shiverer) and littermate controls were stained by indirect immunofluorescence with polyclonal antibodies to the glial hyaluronate-binding protein (GHAP), a brain-specific extracellular matrix glycoprotein produced by astrocytes. In normal mice, the distribution of GHAP was similar to that previously reported in human, calf, pig and dog. The antigen was mainly localized in white matter, the granular layer of the cerebellum being the main exception. No differences were observed between mutants and littermate controls, except that with both GHAP and glial fibrillary acidic protein antibodies the glial framework was denser in the mutants, probably due to the reduction in myelin. The findings suggest that GHAP expression by astrocytes is not induced by myelination and that white matter astrocytes constitute a distinct glial population.

Axonal regeneration in old multiple sclerosis plaques. Immunohistochemical study with monoclonal antibodies to phosphorylated and non-phosphorylated neurofilament proteins

Cryostat sections of two old plaques removed at autopsy from the spinal cord of a 62-year-old man with multiple sclerosis of 24-year duration were studied by indirect immunofluorescence with antibodies to neurofilament proteins, glial fibrillary acidic protein (GFAP), glial hyaluronate-binding protein (GHAP), vimentin and laminin. The neurofilament monoclonal antibodies used in this study reacted with phosphorylated epitopes of the two large polypeptides of the neurofilament triplet (NF 150K, NF 200K). As previously reported [Dahl D, Labkovsky B, Bignami A (1989) Brain Res Bull 22:225-232], the neurofilament antibodies either stained axons in the distal stump of transected sciatic nerve in the early stages of regeneration or late in the process, i.e., after regenerating axons had reached the distal stump of the transected sciatic nerve. Both multiple sclerosis plaques were positive for GFAP and vimentin, but negative for GHAP, while astrocytes in myelinated spinal cord white matter stained with both GFAP and GHAP antibodies. Laminin immunoreactivity in the plaques and normal spinal cord was confined to blood vessels. One plaque was almost devoid of axons as evidenced by indirect immunofluorescence with neurofilament antibodies. Another plaque was packed with bundles of thin axons running an irregular course in the densely gliosed tissue. Axons in the plaque only stained with neurofilament antibodies reacting with sciatic nerve in the early stages of regeneration while axons in the surrounding myelinated white matter were decorated by all neurofilament antibodies, regardless of the time of appearance of immunoreactivity in crushed sciatic nerve. It is concluded that reactive astrocytes forming glial scars do not constitute a non-permissible substrate for axonal growth.

Glial hyaluronate-binding protein in Wallerian degeneration of dog spinal cord

Wallerian degeneration of spinal cord dorsal columns was produced in three dogs by unilateral extradural dorsal rhizotomy at the lower thoracic level. The spinal cord was studied 1 month, 2 months, and 3 months after surgery. Transverse cryostat sections at the site rhizotomy and at the mid-thoracic level were stained by indirect immunofluorescence with antibodies to the glial fibrillary acidic protein (GFAP) and to the glial hyaluronate-binding protein (GHAP). GHAP immunoreactivity was almost unchanged in the degenerated dorsal column 1 month after rhizotomy. After 2 and 3 months, staining with GHAP antibodies was markedly decreased in the gliosed dorsal column at the site of rhizotomy, but it still persisted at the mid-thoracic level. It is concluded that GHAP persists for long periods of time in dorsal columns undergoing Wallerian degeneration, a finding consistent with its putative role as a nonpermissive substrate preventing nerve regeneration in CNS white matter.

Brain-specific hyaluronate-binding protein. A product of white matter astrocytes?

The distribution of glial fibrillary acidic (GFA) protein and hyaluronectin, a hyaluronate-binding protein isolated from human brain, was compared in brain, spinal cord and optic nerves of pigs and dogs by indirect immunofluorescence with monoclonal antibodies. In spinal cord white matter the localization of the two proteins was similar, both antigens forming a mesh surrounding myelinated axons. A similar distribution of the two proteins was also observed in the periventricular glia as well as in the glia limitans of spinal cord and optic nerves. Cerebral white matter was hyaluronectin-positive, but the GFA-positive stellate astrocytes did not stain with hyaluronectin antibodies in this location. Hyaluronectin antibodies did not stain grey matter, the granular layer of the cerebellum excepted. The astrocytes identified with GFA antibodies in hyaluronectin-negative grey matter were: the fibrous astrocytes forming the glia limitans on the surface of the cerebral hemispheres; the protoplasmic astrocytes of cerebral isocortex and basal ganglia; the fibrous astrocytes of cerebral allocortex (hippocampus); Bergmann radial glia in the molecular layer of the cerebellar cortex; and fibrous astrocytes of spinal cord anterior and posterior horns. It is concluded that the hyaluronectin fraction reacting with the monoclonal antibodies is a brain-specific protein probably produced by white matter astrocytes. We propose to call this fraction brain-specific hyaluronectin, to be distinguished from other fractions reacting with polyclonal antibodies and with different localizations.