Chondroitin sulfate proteoglycan phosphacan/RPTPbeta in the hypothalamic magnocellular nuclei

Extracellular diffusion quantified by magnetic resonance imaging during rat C6 glioma cell progression

Solution reflux and edema hamper the convection-enhanced delivery of the standard treatment for glioma. Therefore, a real-time magnetic resonance imaging (MRI) method was developed to monitor the dosing process, but a quantitative analysis of local diffusion and clearance parameters has not been assessed. The objective of this study was to compare diffusion into the extracellular space (ECS) at different stages of rat C6 gliomas, and analyze the effects of the extracellular matrix (ECM) on the diffusion process. At 10 and 20 days, after successful glioma modeling, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) was introduced into the ECS of rat C6 gliomas. Diffusion parameters and half-life of the reagent were then detected using MRI, and quantified according to the mathematical model of diffusion. The main ECM components [chondroitin sulfate proteoglycans (CSPGs), collagen IV, and tenascin C] were detected by immunohistochemical and immunoblot analyses. In 20-day gliomas, Gd-DTPA diffused more slowly and derived higher tortuosity, with lower clearance rate and longer half-life compared to 10-day gliomas. The increased glioma ECM was associated with different diffusion and clearance parameters in 20-day rat gliomas compared to 10-day gliomas. ECS parameters were altered with C6 glioma progression from increased ECM content. Our study might help better understand the glioma microenvironment and provide benefits for interstitial drug delivery to treat brain gliomas.

Activity-dependent remodeling of chondroitin sulfate proteoglycans extracellular matrix in the hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) consisting of arginine vasopressin (AVP) and oxytocin (OXT) magnocellular neurons shows the structural plasticity including the rearrangement of synapses, dendrites, and neurovascular contacts during chronic physiological stimulation. In this study, we examined the remodeling of chondroitin sulfate proteoglycans (CSPGs), main extracellular matrix (ECM), in the HNS after salt loading known as a chronic stimulation to cause the structural plasticity. In the supraoptic nucleus (SON), confocal microscopic observation revealed that the immunoreactivity of 6B4 proteoglycans (PG) was observed mainly at AVP-positive magnocellular neurons but that of neurocan was seen chiefly at OXT-positive magnocellular neurons. The immunoreactivity of phosphacan and aggrecan was seen at both AVP- and OXT-positive magnocellular neurons. Electron microscopic observation further showed that the immunoreactivity of phosphacan and neurocan was observed at astrocytic processes to surround somata, dendrites, and terminals, but not synaptic junctions. In the neurohypophysis (NH), the immunoreactivity of phosphacan, 6B4 PGs, and neurocan was observed at AVP-positive magnocellular terminals, but the reactivity of Wisteria floribunda agglutinin lectin was seen at OXT-positive ones. The immunoreactivity of versican was found at microvessel and that of aggrecan was not detected in the NH. Quantitative morphometrical analysis showed that the chronic physiological stimulation by 7-day salt loading decreased the level of 6B4 PGs in the SON and the level of phosphacan, 6B4 PGs, and neurocan in the NH. These results suggest that the extracellular microenvironment of CSPGs is different between AVP and OXT magnocellular neurons and activity-dependent remodeling of CSPGs could be involved in the structural plasticity of the HNS.

Synaptic localization of receptor-type protein tyrosine phosphatase zeta/beta in the cerebral and hippocampal neurons of adult rats

Receptor-type protein tyrosine phosphatase (RPTP) zeta/beta is a nervous tissue-specific chondroitin sulfate proteoglycan. In this study, we investigated the immunohistochemical localization of RPTPzeta/beta in adult rat cerebral cortex and hippocampus at light and electron microscopic levels. Double labeling immunofluorescence microscopy revealed that the immunoreactivity of RPTPzeta/beta was observed at MAP2-positive dendrites and PSD-95-positive spines of pyramidal neurons in the cerebral cortex and hippocampus. Electron microscopic observation demonstrated a strong immunoreactivity of RPTPzeta/beta at the postsynaptic membrane of dendritic spines and shafts, and its moderate immunoreactivity at the dendritic membrane. In cultured cortical neurons, the immunoreactivity of RPTPzeta/beta was observed at some of PSD-95-positive spines. These results demonstrate that RPTPzeta/beta is localized mainly at the postsynaptic membrane of pyramidal neurons in adult cerebral cortex and hippocampus.

Matrix-degrading enzymes tissue plasminogen activator and matrix metalloprotease-3 in the hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS), synthesizing arginine vasopressin (AVP) and oxytocin (OXT), is well known to show structural plasticity during chronic physiological stimulation such as salt loading and lactation. In the present study, we undertook in the HNS to study localization and activity-dependent changes in the expression of matrix-degrading enzymes such as tissue plasminogen activator (tPA) and matrix metalloprotease-3 (MMP-3). Double labeling confocal microscopy demonstrated that the immunoreactivity of tPA was localized at AVP-positive dendrites in the supraoptic nucleus (SON) and AVP-positive terminals in the neurohypophysis (NH). The immunoreactivity of tPA was also seen at astrocytic processes in the HNS. Likewise, the immunoreactivity of MMP-3 was observed at AVP-positive dendrites and terminals. High magnification observation further revealed punctate distribution of tPA and MMP-3 immunoreactivity at dendrites and terminals, suggesting that they are localized at neurosecretory granules. Salt loading, known as the chronic stimulation to cause the structural plasticity, increased protein and mRNA levels of tPA in the SON but reduced protein levels of it in the NH. The chronic stimulation also increased protein levels of urokinase plasminogen activator in the SON, but the stimulation did not change protein levels of MMP-3 in the SON and NH. Depolarizing agent KCl released tPA from isolated neurosecretosomes, and this depolarization-dependent release was abolished by verapamil, a Ca(2+) channel blocker. These results demonstrate that tPA and MMP-3 are localized mainly at dendrites and terminals of AVP-expressing magnocellular neurons and tPA is released in an activity-dependent manner, suggesting that matrix-degrading proteases are candidate molecules to be concerned with the structural plasticity in the HNS.

Chondroitin sulfate proteoglycan phosphacan associates with parallel fibers and modulates axonal extension and fasciculation of cerebellar granule cells

Phosphacan is a nervous system-specific chondroitin sulfate proteoglycan and one of the major components of extracellular matrix in the brain. In the present study, we examined its spatiotemporal expression, ultrastructural localization, binding manner, and in vitro analysis on cell adhesion, axonal extension, and fasciculation in rat cerebellum. The present light microscopic immunohistochemistry showed that phosphacan immunoreactivity was localized mainly at the molecular layer in the cerebellum, but not at the external granular layer. Further double labeling immunohistochemical and immunoelectron microscopic studies revealed that phosphacan was localized around parallel fibers, but not at synapses. The binding of phosphacan to membrane and/or extracellular matrix partly required Ca2+ and was mediated through its core glycoprotein. Phosphacan inhibited adhesion and axonal extension of cerebellar granule cells in dissociated culture, while it promoted axonal fasciculation of their aggregated culture. These results indicate that phosphacan around parallel fibers may be the repulsive substratum for adhesion and extension of granule cells and promote the fasciculation of parallel fibers.

Neuronal expression of the chondroitin sulfate proteoglycans receptor-type protein-tyrosine phosphatase beta and phosphacan

Receptor-type protein-tyrosine phosphatase beta (RPTPbeta) and its spliced variant phosphacan are major components of chondroitin sulfate proteoglycans in the CNS. In this study, expression and localization of RPTPbeta and phosphacan were examined in developing neurons by immunological analyses using 6B4, 3F8, and anti-PTP antibodies and reverse transcription-polymerase chain reaction (RT-PCR). Light microscopic immunohistochemistry showed that 6B4 RPTPbeta/phosphacan immunoreactivity was observed around neurons in the cortical plate. Further ultrastructural observation showed that 6B4 RPTPbeta/phosphacan immunoreactivity was observed mainly at the membrane of migrating neurons and radial glia. Immunocytochemical analysis revealed that RPTPbeta immunoreactivity was observed in cultured cerebral, hippocampal, and cerebellar neurons in addition to type-1 and type-2 astrocytes. Western analysis further demonstrated that the shorter receptor form of RPTPbeta (sRPTPbeta) was detected from cell lysate of cortical and hippocampal neurons using 6B4 and anti-PTP antibodies, while sRPTPbeta of cerebellar neurons and type-1 astrocytes was recognized only by anti-PTP antibody. Phosphacan was detected from neuronal culture supernatants of cortical, hippocampal, and cerebellar neurons, but not from type-1 astrocytes using 6B4 and 3F8 antibodies. RT-PCR analysis demonstrated the prominent expression of sRPTPbeta and phosphacan mRNAs in cortical neurons, and that of sRPTPbeta mRNA in type-1 astrocytes. During culture development of cortical neurons, the immunoreactivity of 6B4 sRPTPbeta was observed entirely on the neuronal surface including somata, dendrites, axons, and growth cones at earlier stages of cortical neuronal culture such as stages 2 and 3, while, after longer culture, 6B4 sRPTPbeta immunoreactivity in stages 4 and 5 neurons was detected at dendrites and somata and disappeared from axons, and was not observed over axonal terminals and postsynaptic spines. These results demonstrate that neurons are able to express sRPTPbeta on their cellular surface and to secrete phosphacan, and neuronal expression of sRPTPbeta may modulate neuronal differentiation including neuritogenesis and synaptogenesis.

Activity-dependent regulation of a chondroitin sulfate proteoglycan 6B4 phosphacan/RPTPbeta in the hypothalamic supraoptic nucleus

The hypothalamic magnocellular neurons, synthesizing arginine vasopressin (AVP) and oxytocin, are well known to show structural plasticity during chronic physiological stimulation. We have previously reported that 6B4 phosphacan/receptor-type protein-tyrosine phosphatasebeta (RPTPbeta), a chondroitin sulfate proteoglycan is highly expressed in the supraoptic nucleus (SON) of adult hypothalamus. Here, we undertook to study the activity-dependent regulation of 6B4 phosphacan/RPTPbeta in this system. Double labeling confocal microscopy demonstrated in the SON that 6B4 phosphacan/RPTPbeta-immunoreactive perineuronal nets were seen around AVP-containing somata and dendrites and its distribution pattern was well coincided with that of TAG-1. Quantitative immunohistochemical and Western analyses showed that 1-week salt loading, known as the chronic physiological stimulation for inducing the structural changes such as synaptic remodeling and direct neuronal membrane apposition, decreased 6B4 phosphacan/RPTPbeta levels in the SON, but did not alter TAG-1 levels. The 6B4 phosphacan/RPTPbeta levels were returned to control basal values within 3 weeks after the cessation of the chronic stimulation. Activity-dependent decreases in 6B4 phosphacan/RPTPbeta levels of the SON were confirmed when Western and immunohistochemical samples were digested with chondroitinase ABC, indicating that the decrease in 6B4 phosphacan/RPTPbeta levels was due to disappearance of 6B4 phosphacan/RPTPbeta core protein rather than increase in chondroitin sulfate glycosaminoglycans. With electron microscopy, the electron-dense immunoproducts for 6B4 phosphacan/RPTPbeta were found on the membrane surface of axons and glial processes, but not at synaptic junctions in control SON, and its immunoreactivity was eliminated with the chronic salt loading. The present results indicate that the levels of 6B4 phosphacan/RPTPbeta are regulated with activity-dependent manner and may be concerned with the structural plasticity seen in the SON.

Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries

The formation of misaligned scar tissue by a variety of cell types expressing multiple axon growth inhibitory proteoglycans presents a physical and molecular barrier to axon regeneration after adult spinal cord injuries. Decorin is a small, leucine-rich proteoglycan that has previously been shown to reduce astrogliosis and basal lamina formation in acute cerebral cortex stab injuries. We have therefore tested whether mini pump infusion of hr-decorin into acute stab injuries of the adult rat spinal cord can not only inhibit formation of an astroglial limitans but also deposition of the axon growth inhibitory proteoglycans neurocan, NG2, phosphacan and brevican. Combined immunohistochemical and quantitative Western blot analysis revealed major reductions in levels of core protein expression (>80% for 130-kDa neurocan, 145/80-kDa brevican, 300-kDa phosphacan) and immunoreactivity for all four chondroitin sulfate proteoglycans (CSPGs) within decorin-treated injuries compared with untreated controls. Astrogliosis within lesion margins and the accumulation of OX42+ macrophages/microglia within lesion centres were also significantly reduced. These decorin-induced changes in scar formation combined to promote the striking ability of axons from microtransplanted adult sensory neurons to enter, grow within and exit decorin-infused spinal cord injuries, in sharp contrast to the complete failure of axons to cross untreated, CSPG-rich lesions. Decorin pretreatment of meningial fibroblasts in vitro also resulted in a three-fold increase in neurite outgrowth from co-cultured adult sensory neurons and suppression of NG2 immunoreactivity. The ability of decorin to promote axon growth across acute spinal cord injuries via a coordinated suppression of inflammation, CSPG expression and astroglial scar formation make decorin treatment a promising component of future spinal cord regeneration strategies.