The hyaluronidase of brain

Engineered glycomaterial implants orchestrate large-scale functional repair of brain tissue chronically after severe traumatic brain injury

Severe traumatic brain injury (sTBI) survivors experience permanent functional disabilities due to significant volume loss and the brain's poor capacity to regenerate. Chondroitin sulfate glycosaminoglycans (CS-GAGs) are key regulators of growth factor signaling and neural stem cell homeostasis in the brain. However, the efficacy of engineered CS (eCS) matrices in mediating structural and functional recovery chronically after sTBI has not been investigated. We report that neurotrophic factor functionalized acellular eCS matrices implanted into the rat M1 region acutely after sTBI significantly enhanced cellular repair and gross motor function recovery when compared to controls 20 weeks after sTBI. Animals subjected to M2 region injuries followed by eCS matrix implantations demonstrated the significant recovery of "reach-to-grasp" function. This was attributed to enhanced volumetric vascularization, activity-regulated cytoskeleton (Arc) protein expression, and perilesional sensorimotor connectivity. These findings indicate that eCS matrices implanted acutely after sTBI can support complex cellular, vascular, and neuronal circuit repair chronically after sTBI.

A modified flavonoid accelerates oligodendrocyte maturation and functional remyelination

Myelination delay and remyelination failure following insults to the central nervous system (CNS) impede axonal conduction and lead to motor, sensory and cognitive impairments. Both myelination and remyelination are often inhibited or delayed due to the failure of oligodendrocyte progenitor cells (OPCs) to mature into myelinating oligodendrocytes (OLs). Digestion products of the glycosaminoglycan hyaluronan (HA) have been implicated in blocking OPC maturation, but how these digestion products are generated is unclear. We tested the possibility that hyaluronidase activity is directly linked to the inhibition of OPC maturation by developing a novel modified flavonoid that functions as a hyaluronidase inhibitor. This compound, called S3, blocks some but not all hyaluronidases and only inhibits matrix metalloproteinase activity at high concentrations. We find that S3 reverses HA-mediated inhibition of OPC maturation in vitro, an effect that can be overcome by excess recombinant hyaluronidase. Furthermore, we find that hyaluronidase inhibition by S3 accelerates OPC maturation in an in vitro model of perinatal white matter injury. Finally, blocking hyaluronidase activity with S3 promotes functional remyelination in mice with lysolecithin-induced demyelinating corpus callosum lesions. All together, these findings support the notion that hyaluronidase activity originating from OPCs in CNS lesions is sufficient to prevent OPC maturation, which delays myelination or blocks remyelination. These data also indicate that modified flavonoids can act as selective inhibitors of hyaluronidase activity and can promote OPC maturation, making them excellent candidates to accelerate myelination or promote remyelination following perinatal and adult CNS insults.

Pyrrole-hyaluronic acid conjugates for decreasing cell binding to metals and conducting polymers

Surface modification of electrically conductive biomaterials has been studied to improve biocompatibility for a number of applications, such as implantable sensors and microelectrode arrays. In this study we electrochemically coated electrodes with biocompatible and non-cell adhesive hyaluronic acid (HA) to reduce cellular adhesion for potential use in neural prostheses. To this end, pyrrole-conjugated hyaluronic acid (PyHA) was synthesized and employed to electrochemically coat platinum, indium-tin oxide and polystyrene sulfonate-doped polypyrrole electrodes. This PyHA conjugate consisted of (1) a pyrrole moiety that allowed the compound to be electrochemically polymerized onto a conductive substrate and (2) non-adhesive HA to minimize cell adhesion and to potentially decrease inflammatory tissue responses. Our characterization results showed the presence of a hydrophilic p(PyHA) layer on the modified electrode, and impedance measurements revealed an impedance that was statistically the same as the unmodified electrode. We found that the p(PyHA)-coated electrodes minimized adhesion and migration of fibroblasts and astrocytes for a minimum of up to 3 months. Also, the coating was stable in physiological solution for 3 months and was stable against enzymatic degradation by hyaluronidase. These studies suggest that this p(PyHA) coating has the potential to be used to mask conducting electrodes from adverse glial responses that occur upon implantation. In addition, electrochemical coating with PyHA could potentially be extended for the surface modification of other metallic and conducting substances, such as stents and biosensors.

The crosstalk of hyaluronan-based extracellular matrix and synapses

Many neurons and their synapses are enwrapped in a brain-specific form of the extracellular matrix (ECM), the so-called perineuronal net (PNN). It forms late in the postnatal development around the time when synaptic contacts are stabilized. It is made of glycoproteins and proteoglycans of glial as well as neuronal origin. The major organizing polysaccharide of brain extracellular space is the polymeric carbohydrate hyaluronic acid (HA). It forms the backbone of a meshwork consisting of CNS proteoglycans such as the lectican family of chondroitin sulphate proteoglycans (CSPG). This family comprises four abundant components of brain ECM: aggrecan and versican as broadly expressed CSPGs and neurocan and brevican as nervous-system-specific family members. In this review, we intend to focus on the specific role of the HA-based ECM in synapse development and function.

Enzymic pathways of hyaluronan catabolism

The enzymic degradation of hyaluronan in mammalian tissues takes place in two phases, encompassing breakdown of the polysaccharide to its monosaccharide constituents and subsequent utilization of the monosaccharide products. Degradation to the monosaccharide components is effected by the concerted action of three enzymes, hyaluronidase, beta-D-glucuronidase and beta-N-acetyl-D-hexosaminidase. The relative contributions of hyaluronidase and the two exoglycosidases to the physiological catabolism of hyaluronan are not yet known but consideration of the kinetic properties of the three enzymes clearly indicates that hyaluronidase is best suited for the initial attack on the polysaccharide, inasmuch as its Km for hyaluronan is 1000- to 10,000-fold lower than that estimated for beta-D-glucuronidase. Recent investigations in the authors' laboratories have been focused on the catabolism of hyaluronan and other complex carbohydrates in liver, since the sinusoidal endothelial cells in this organ are the main sites for degradation of circulating hyaluronan. Assay of ten lysosomal hydrolases in isolated rat liver cells showed considerably higher activities in Kupffer cells and endothelial cells than in hepatocytes for nine of the enzymes, including beta-D-glucuronidase and beta-N-acetyl-D-hexosaminidase. The activity of N-acetylglucosamine-6-phosphate deacetylase, a key enzyme in the metabolism of the N-acetylglucosamine released by the lysosomal degradation of hyaluronan and other complex carbohydrates, has also been determined. High deacetylase activities were observed in both Kupffer cells and endothelial cells but, surprisingly, virtually no activity was detected in hepatocytes. This finding implies that N-acetylglucosamine cannot be degraded in hepatocytes and must be largely reutilized in the synthesis of new macromolecules. Further studies of the enzymes involved in hyaluronan degradation and N-acetylglucosamine utilization in the liver are under way.

Human hyaluronidases: electrophoretic multiple forms in somatic tissues and body fluids. Evidence for conserved hyaluronidase potential N-glycosylation sites in different mammalian species

Some properties of the multiple forms of human hyaluronidases in somatic tissues and in body fluids were investigated. Liver and placenta exhibited seven hyaluronidase forms when analyzed electrophoretically on a polyacrylamide-hyaluronan gel. Ovary, breast, myometrium, endometrium, skin, leukocytes and platelets displayed distinct patterns of enzymatic micropolydispersity. The most acidic forms of hyaluronidase were in synovial fluid and serum, some serum exhibited an additional basic form. Following sialidase treatment, the number of forms decreased to two in placenta, three in liver and to a broad basic form in serum. The native serum and placental hyaluronidases remained fully active after thermal inactivation but desialylated hyaluronidase was inactivated slowly in serum, and quickly in placenta suggesting a higher overall glycosylation of the plasma enzyme. Potential N-glycosylation sites were searched in the amino acid sequences of six human hyaluronidases and several hyaluronidases from different mammalian species using the PROSITE motif database. A potential N-glycosylation site (site 1) with similar tripeptide patterns was observed at the same position in human plasma (HYAL1), human lysosomes (HYAL2) and in two newly reported hyaluronidases (HYAL4 and HYALP1). The same site was also present in mouse plasma (HYAL1) and mouse lysosomes (HYAL2), and in rat lysosomes (HYAL2). This site was absent in human HYAL3 and in all sperm hyaluronidases (PH-20) studied (human, macaque, mouse, guinea pig, rabbit and fox). A second potential N-glycosylation site was observed at a location further in the polypeptide chain. This site is present in all mammalian hyaluronidase isoenzymes reported in the present study whatever the species and organ localization. The pattern at site 2 is NVT for all hyaluronidases except for hyaluronidases of lysosomal origin where it is NVS. Such conserved sites strongly suggest that they may represent actual N-glycosylation sites.

Hyaluronidase expression in human skin fibroblasts

Hyaluronidase activity has been detected for the first time in normal human dermal fibroblasts (HS27), as well as in fetal fibroblasts (FF24) and fibrosarcoma cells (HT1080). Enzymatic activity was secreted predominantly into the culture media, with minor amounts of activity associated with the cell layer. In both classes of fibroblasts, hyaluronidase expression was confluence-dependent, with highest levels of activity occurring in quiescent, post-confluent cells. However, in the fibrosarcoma cell cultures, expression was independent of cell density. The enzyme had a pH optimum of 3.7 and on hyaluronan substrate gel zymography, activity occurred as a single band corresponding to an approximate molecular size of 57 kDa. The enzyme could be immunoprecipitated in its entirety using monoclonal antibodies raised against Hyal-1, human plasma hyaluronidase. PCR confirmed that fibroblast hyaluronidase was identical to Hyal-1. The conclusion by previous investigators using earlier technologies that fibroblasts do not contain hyaluronidase activity should be reevaluated.

Plasma hyaluronidase activity in mucolipidoses II and III: marked differences from other lysosomal enzymes

A nearly pathognomonic finding of the lysosomal storage disorders mucolipidoses II and III is the marked increase of plasma lysosomal enzyme activities. The genetic lesion in ML II and III causes defective function of the enzyme UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. Defective function of this enzyme results in deficient phosphorylation of lysosomal enzyme asparagine-linked oligosaccharides and a consequent misrouting of many newly synthesized lysosomal enzymes. These enzymes are secreted from cells instead of being targeted to lysosomes, with resultant marked elevations of multiple lysosomal enzyme activities in plasma. We report here that plasma hyaluronidase activity, an endoglycosidase of presumably lysosomal origin, is not increased in the plasma from individuals with mucolipidoses II and III, unlike most lysosomal enzymes. Our data suggest the possibility that hyaluronidase is not targeted to lysosomes by a lysosomal enzyme phosphosmannosyl recognition mechanism. Alternatively, hyaluronidase activity may not be present in the cell type(s) responsible for the lysosomal enzyme hypersecretion in mucolipidoses II and III which, along with its deficiency in fibroblasts and leukocytes, would constitute an unusual tissue distribution of activity for a soluble lysosomal enzyme.

Developing rat cerebellum--II. Effects of abnormal thyroid states and undernutrition on hyaluronic acid

The early postnatal pattern of hyaluronic acid (HA) deposition in rat cerebellum is affected by thyroid deficiency, thyroxine treatment and undernutrition. The modification of HA ontogenesis apparently reflects the smaller number of cells formed in undernourished rats, or alterations of cell maturation (accelerated in thyroxine-treated and slowed down in thyroid-deficient rats). The developmentally regulated loss of tissue water is also affected in the three conditions; this can be correlated with the roughly simultaneous disappearance of extracellular, but not of total, HA.

Mucopolysaccharidase activity and glycosaminoglycan content in traumatized resorbing deciduous teeth

The periodontal ligaments from traumatized deciduous teeth, while undergoing rapid resorption, were analyzed biochemically for mucopolysaccharidase activity and for total glycosaminoglycan content of dentin and cementum. Enzyme activity was present only in resorbing teeth. A concomitant 65 percent decrease in glycosaminoglycans from these teeth occurred as well.

Mucopolysaccharidase activity in traumatized human deciduous teeth undergoing accelerated resorption: isolation and characterization

Mucopolysaccharidase activity was observed in traumatized human decidous teeth. Histochemical analysis of the periodontal ligaments from these teeth revealed a loss of film substrate metachromasia during incubation, indicating enzyme activity. Routine histology of these ligaments showed the presence of an inflammatory infiltrate throughout this tissue. Biochemical analysis of the ligaments revealed a 10-fold increase of enzyme activity when incubation time was increased from 1 to 8 h. When compared to the enzyme activity measured during physiologic resorption, activity was increased. This suggests that the presence of an inflammatory infiltrate not observed in the tissues undergoing physiologic resorption may be responsible for the rapid resorption seen in traumatized deciduous teeth.

Brain hyaluronidase: changes in activity during chick development

Development of embryonic chick brain is characterized by high levels of hyaluronidase activity and of hyaluronate, both of which decrease rapidly soon after the chick hatches. By analogy to other systems, it is proposed that the sequence of hyaluronate production and its enzymatic removal may have a developmental role in brain formation.