Spatiotemporal distribution of chondroitin sulfate proteoglycans after optic nerve injury in rodents

The function of astrocytes and their role in neurological diseases

Astrocytes have countless links with neurons. Previously, astrocytes were only considered a scaffold of neurons; in fact, astrocytes perform a variety of functions, including providing support for neuronal structures and energy metabolism, offering isolation and protection and influencing the formation, function and elimination of synapses. Because of these functions, astrocytes play an critical role in central nervous system (CNS) diseases. The regulation of the secretiory factors, receptors, channels and pathways of astrocytes can effectively inhibit the occurrence and development of CNS diseases, such as neuromyelitis optica (NMO), multiple sclerosis, Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease. The expression of aquaporin 4 in AS is directly related to NMO and indirectly involved in the clearance of Aβ and tau proteins in AD. Connexin 43 has a bidirectional effect on glutamate diffusion at different stages of stroke. Interestingly, astrocytes reduce the occurrence of PD through multiple effects such as secretion of related factors, mitochondrial autophagy and aquaporin 4. Therefore, this review is focused on the structure and function of astrocytes and the correlation between astrocytes and CNS diseases and drug treatment to explore the new functions of astrocytes with the astrocytes as the target. This, in turn, would provide a reference for the development of new drugs to protect neurons and promote the recovery of nerve function.

Increased Cerebral Serum Amyloid A2 and Parameters of Oxidation in Arylsulfatase B (N-Acetylgalactosamine-4-Sulfatase)-Null Mice

Background

Chondroitin sulfate and chondroitin sulfate proteoglycans have been associated with Alzheimer's disease (AD), and the impact of modified chondroitin sulfates is being investigated in several animal and cell-based models of AD. Published reports have shown the role of accumulation of chondroitin 4-sulfate and decline in Arylsulfatase B (ARSB; B-acetylgalactosamine-4-sulfatase) in other pathology, including nerve injury, traumatic brain injury, and spinal cord injury. However, the impact of ARSB deficiency on AD pathobiology has not been reported, although changes in ARSB were associated with AD in two prior reports. The enzyme ARSB removes 4-sulfate groups from the non-reducing end of chondroitin 4-sulfate and dermatan sulfate and is required for their degradation. When ARSB activity declines, these sulfated glycosaminoglycans accumulate, as in the inherited disorder Mucopolysaccharidosis VI.

Objective

Reports about chondroitin sulfate, chondroitin sulfate proteoglycans, and chondroitin sulfatases in AD were reviewed.

Methods

Measurements of SAA2, iNOS, lipid peroxidation, chondroitin sulfate proteoglycan 4 (CSPG4), and other parameters were performed in cortex and hippocampus from ARSB-null mice and controls by QRT-PCR, ELISA, and other standard assays.

Results

SAA2 mRNA expression and protein, CSPG4 mRNA, chondroitin 4-sulfate, and iNOS were increased significantly in ARSB-null mice. Measures of lipid peroxidation and redox state were significantly modified.

Conclusion

Findings indicate that decline in ARSB leads to changes in expression of parameters associated with AD in the hippocampus and cortex of the ARSB-deficient mouse. Further investigation of the impact of decline in ARSB on the development of AD may provide a new approach to prevent and treat AD.

Increased Cerebral Serum Amyloid A2 and Parameters of Oxidation in Arylsulfatase B (N-Acetylgalactosamine-4-Sulfatase)-Null Mice

Introduction

Chondroitin sulfate and chondroitin sulfate proteoglycans have been associated with Alzheimer's Disease (AD), and the impact of modified chondroitin sulfates is being investigated in several animal and cell-based models of AD. Published reports have shown the role of accumulation of chondroitin 4-sulfate and decline in Arylsulfatase B (ARSB; B-acetylgalactosamine-4-sulfatase) in other pathology, including nerve injury, traumatic brain injury, and spinal cord injury. However, the impact of ARSB deficiency on AD pathobiology has not been reported, although changes in ARSB were associated with AD in two prior reports. The enzyme ARSB removes 4-sulfate groups from the non-reducing end of chondroitin 4-sulfate and dermatan sulfate and is required for their degradation. When ARSB activity declines, these sulfated glycosaminoglycans accumulate, as in the inherited disorder Mucopolysaccharidosis VI.

Methods

Reports about chondroitin sulfate, chondroitin sulfate proteoglycans and chondroitin sulfatases in Alzheimer's Disease were reviewed. Measurements of SAA2, iNOS, lipid peroxidation, chondroitin sulfate proteoglycan 4, and other parameters were performed in cortex and hippocampus from ARSB-null mice and controls by QRT-PCR, ELISA, and other standard assays.

Results

SAA2 mRNA expression and protein, CSPG4 mRNA, chondroitin 4-sulfate and i-NOS were increased significantly in ARSB-null mice. Measures of lipid peroxidation and redox state were significantly modified.

Discussion

Findings indicate that decline in ARSB leads to changes in expression of parameters associated with AD in the hippocampus and cortex of the ARSB-deficient mouse.

Conclusions

Further investigation of the impact of decline in ARSB on the development of AD may provide a new approach to prevent and treat AD.

Advances in transcorneal electrical stimulation: From the eye to the brain

The mammalian brain is reported to contain about 10⁶-10⁹ neurons linked together to form complex networks. Physiologically, the neuronal networks interact in a rhythmic oscillatory pattern to coordinate the brain's functions. Neuromodulation covers a broad range of techniques that can alter neuronal network activity through the targeted delivery of electrical or chemical stimuli. Neuromodulation can be used to potentially treat medical conditions and can serve as a research tool for studying neural functions. Typically, the main method of neuromodulation is to electrically stimulate specific structures in both the central and peripheral nervous systems via surgically implanted electrodes. Therefore, it is imperative to explore novel and safer methods for altering neuronal network activity. Transcorneal electrical stimulation (TES) has rapidly emerged as a non-invasive neuromodulatory technique that can exert beneficial effects on the brain through the eyes. There is substantial evidence to show that TES can change the brain oscillations in rodents. Moreover, the molecular data clearly shows that TES can also activate non-visual brain regions. In this review, we first summarize the use of TES in the retina and then discuss its effects in the brain through the eye-brain connection. We then comprehensively review the substantial evidence from electrophysiological, behavioral, and molecular studies on the role of TES on modulating neurons in the brain. Lastly, we discuss the implications and possible future directions of the research on TES as a non-invasive tool for neuromodulation of the brain via directly stimulating the mammalian eye.

Auricular cartilage regeneration using different types of mesenchymal stem cells in rabbits

BACKGROUND

Cartilaginous disorders comprise a wide range of diseases that affect normal joint movement, ear and nose shape; and they have great social and economic impact. Mesenchymal stem cells (MSCs) provide a promising regeneration alternative for treatment of degenerative cartilaginous disorders. This study aimed to compare therapeutic potential of different types of laser activated MSCs to promote auricular cartilage regeneration. Twelve adult rabbit allocated equally in four groups, all animals received a surgical mid auricular cartilage defect in one ear; Group I (Positive control) injected sub-perichondrially with phosphate-buffered saline (PBS), Group II (ADMSC-transplanted group) injected adipose-derived MSCs (ADMSCs), Group III (BMMSCs-transplanted group) received bone marrow-derived MSCs (BMMSCs), and Group IV (EMSC-transplanted group) received ear MSCs (EMSCs) in the defected ear. The auricular defect was analyzed morphologically, histopathologically and immunohistochemically after 4 weeks. In addition, a quantitative real-time polymerase chain reaction was used to examine expression of the collagen type II (Col II) and aggrecan as cartilage growth factors.

RESULTS

The auricles of all treatments appeared completely healed with smooth surfaces and similar tissue color. Histopathologically, defective areas of control positive group, ADMSCs and EMSCs treated groups experienced a small area of immature cartilage. While BMMSCs treated group exhibited typical features of new cartilage formation with mature chondrocytes inside their lacunae and dense extracellular matrix (ECM). In addition, BMMSC treated group showed a positive reaction to Masson's trichrome and orcein stains. In contrary, control positive, ADMSC and EMSC groups revealed faint staining with Masson's trichrome and Orcein. Immunohistochemically, there was an intense positive S100 expression in BMMSCs (with a significant increase of area percentage + 21.89 (P < 0.05), a moderate reaction in EMSCs (with an area percentage + 17.97, and a mild reaction in the control group and ADMSCs (area percentages + 8.02 and + 11.37, respectively). The expression of relative col II and aggrecan was substantially highest in BMMSCs (± 0.91 and ± 0.89, respectively). While, Control positive, ADMSCs and EMSCs groups recorded (± 0.41: ± 0.21, ± 0.6: ± 0.44, ± 0.61: ± 0.63) respectively.

CONCLUSION

BMMSCs showed the highest chondrogenic potential compared to ADMSCs and EMSCs and should be considered the first choice in treatment of cartilaginous degenerative disorders.

Proteoglycan Sulphation in the Function of the Mature Central Nervous System

Chondroitin sulphate and heparan sulphate proteoglycans (CSPGS and HSPGs) are found throughout the central nervous system (CNS). CSPGs are ubiquitous in the diffuse extracellular matrix (ECM) between cells and are a major component of perineuronal nets (PNNs), the condensed ECM present around some neurons. HSPGs are more associated with the surface of neurons and glia, with synapses and in the PNNs. Both CSPGs and HSPGs consist of a protein core to which are attached repeating disaccharide chains modified by sulphation at various positions. The sequence of sulphation gives the chains a unique structure and local charge density. These sulphation codes govern the binding properties and biological effects of the proteoglycans. CSPGs are sulphated along their length, the main forms being 6- and 4-sulphated. In general, the chondroitin 4-sulphates are inhibitory to cell attachment and migration, while chondroitin 6-sulphates are more permissive. HSPGs tend to be sulphated in isolated motifs with un-sulphated regions in between. The sulphation patterns of HS motifs and of CS glycan chains govern their binding to the PTPsigma receptor and binding of many effector molecules to the proteoglycans, such as growth factors, morphogens, and molecules involved in neurodegenerative disease. Sulphation patterns change as a result of injury, inflammation and ageing. For CSPGs, attention has focussed on PNNs and their role in the control of plasticity and memory, and on the soluble CSPGs upregulated in glial scar tissue that can inhibit axon regeneration. HSPGs have key roles in development, regulating cell migration and axon growth. In the adult CNS, they have been associated with tau aggregation and amyloid-beta processing, synaptogenesis, growth factor signalling and as a component of the stem cell niche. These functions of CSPGs and HSPGs are strongly influenced by the pattern of sulphation of the glycan chains, the sulphation code. This review focuses on these sulphation patterns and their effects on the function of the mature CNS.

A comprehensive atlas of Aggrecan, Versican, Neurocan and Phosphacan expression across time in wildtype retina and in retinal degeneration

As photoreceptor cells die during retinal degeneration, the surrounding microenvironment undergoes significant changes that are increasingly recognized to play a prominent role in determining the efficacy of therapeutic interventions. Chondroitin Sulphate Proteoglycans (CSPGs) are a major component of the extracellular matrix that have been shown to inhibit neuronal regrowth and regeneration in the brain and spinal cord, but comparatively little is known about their expression in retinal degeneration. Here we provide a comprehensive atlas of the expression patterns of four individual CSPGs in three models of inherited retinal degeneration and wildtype mice. In wildtype mice, Aggrecan presented a biphasic expression, while Neurocan and Phosphacan expression declined dramatically with time and Versican expression remained broadly constant. In degeneration, Aggrecan expression increased markedly in Aipl1-/- and Pde6brd1/rd1, while Versican showed regional increases in the periphery of Rho-/- mice. Conversely, Neurocan and Phosphacan broadly decrease with time in all models. Our data reveal significant heterogeneity in the expression of individual CSPGs. Moreover, there are striking differences in the expression patterns of specific CSPGs in the diseased retina, compared with those reported following injury elsewhere in the CNS. Better understanding of the distinct distributions of individual CSPGs will contribute to creating more permissive microenvironments for neuro-regeneration and repair.

Promoting axon regeneration in the central nervous system by increasing PI3-kinase signaling

Much research has focused on the PI3-kinase and PTEN signaling pathway with the aim to stimulate repair of the injured central nervous system. Axons in the central nervous system fail to regenerate, meaning that injuries or diseases that cause loss of axonal connectivity have life-changing consequences. In 2008, genetic deletion of PTEN was identified as a means of stimulating robust regeneration in the optic nerve. PTEN is a phosphatase that opposes the actions of PI3-kinase, a family of enzymes that function to generate the membrane phospholipid PIP₃ from PIP₂ (phosphatidylinositol (3,4,5)-trisphosphate from phosphatidylinositol (4,5)-bisphosphate). Deletion of PTEN therefore allows elevated signaling downstream of PI3-kinase, and was initially demonstrated to promote axon regeneration by signaling through mTOR. More recently, additional mechanisms have been identified that contribute to the neuron-intrinsic control of regenerative ability. This review describes neuronal signaling pathways downstream of PI3-kinase and PIP₃, and considers them in relation to both developmental and regenerative axon growth. We briefly discuss the key neuron-intrinsic mechanisms that govern regenerative ability, and describe how these are affected by signaling through PI3-kinase. We highlight the recent finding of a developmental decline in the generation of PIP₃ as a key reason for regenerative failure, and summarize the studies that target an increase in signaling downstream of PI3-kinase to facilitate regeneration in the adult central nervous system. Finally, we discuss obstacles that remain to be overcome in order to generate a robust strategy for repairing the injured central nervous system through manipulation of PI3-kinase signaling.

Knock-Out of Tenascin-C Ameliorates Ischemia-Induced Rod-Photoreceptor Degeneration and Retinal Dysfunction

Retinal ischemia is a common pathomechanism in various eye diseases. Recently, evidence accumulated suggesting that the extracellular matrix (ECM) glycoprotein tenascin-C (Tnc) plays a key role in ischemic degeneration. However, the possible functional role of Tnc in retinal ischemia is not yet known. The aim of our study was to explore retinal function and rod-bipolar/photoreceptor cell degeneration in wild type (WT) and Tnc knock-out (KO) mice after ischemia/reperfusion (I/R) injury. Therefore, I/R was induced by increasing intraocular pressure in the right eye of wild type (WT I/R) and Tnc KO (KO I/R) mice. The left eye served as untreated control (WT CO and KO CO). Scotopic electroretinogram (ERG) recordings were performed to examine rod-bipolar and rod-photoreceptor cell function. Changes of Tnc, rod-bipolar cells, photoreceptors, retinal structure and apoptotic and synaptic alterations were analyzed by immunohistochemistry, Hematoxylin and Eosin staining, Western blot, and quantitative real time PCR. We found increased Tnc protein levels 3 days after ischemia, while Tnc immunoreactivity decreased after 7 days. Tnc mRNA expression was comparable in the ischemic retina. ERG measurements after 7 days showed lower a-/b-wave amplitudes in both ischemic groups. Nevertheless, the amplitudes in the KO I/R group were higher than in the WT I/R group. We observed retinal thinning in WT I/R mice after 3 and 7 days. Although compared to the KO CO group, retinal thinning was not observed in the KO I/R group until 7 days. The number of PKCα⁺ rod-bipolar cells, recoverin⁺ photoreceptor staining and Prkca and Rcvrn expression were comparable in all groups. However, reduced rhodopsin protein as well as Rho and Gnat1 mRNA expression levels of rod-photoreceptors were found in the WT I/R, but not in the KO I/R retina. Additionally, a lower number of activated caspase 3⁺ cells was observed in the KO I/R group. Finally, both ischemic groups displayed enhanced vesicular glutamate transporter 1 (vGlut1) levels. Collectively, KO mice showed diminished rod-photoreceptor degeneration and retinal dysfunction after I/R. Elevated vGlut1 levels after ischemia could be related to an impaired glutamatergic photoreceptor-bipolar cell signaling and excitotoxicity. Our study provides novel evidence that Tnc reinforces ischemic retinal degeneration, possibly by synaptic remodeling.

A Novel Rat Model with Long Range Optic Nerve Injury to Study Retinal Ganglion Cells Endogenous Regeneration

In adult mammals, axon regeneration is limited within the lesion site after injury to the optic nerve. Changes in the microenvironment of lesion sites play an important role in retinal ganglion cells (RGCs) axon regeneration along with other intrinsic factors. In this study, the effect of the lesion site on the microenvironment and axon growth was evaluated using a refined optic nerve crush (ONC) injury model, in which the injury range was extended compared to classical injury. The number of regenerated axons labeled anterogradely with cholera toxin B fragment (CTB) was significantly increased in the long-range crush injury (LI) group compared to the ONC group at distances of 500, 1000 and 1500 µm from the initial site of the injury. These data confirmed that RGC axons can regenerate inside the lesion site. Immunofluorescence and proteomic analysis showed that the microenvironment at the lesion site was highly heterogeneous. The levels of myelin-associated inhibitors, chondroitin-sulfate proteoglycans (CSPGs) and other axon growth inhibitors decreased inside the lesion site compared to the posterior segment of the optic nerve lesion site. The expression of multiple lysosome-related enzymes, metabolic inhibitors including cholesterol esterase, cathepsin B, D, Z and arylsulfatase B (ARSB) were significantly increased inside the lesion site for the LI group compared to the normal optic nerves. Our results suggest that the model of long range optic nerve injury is more useful towards understanding the lesion microenvironment and the endogenous regeneration of RGCs. Also, we showed that myelin and neurocan (a CSPG) are differently expressed in the optic nerve between the interior and posterior lesion sites and may explain why axons cannot reach the brain through the lesion site.

Extracellular Matrix Remodeling in the Retina and Optic Nerve of a Novel Glaucoma Mouse Model

Simple Summary

Glaucoma is a leading cause of blindness worldwide, and increased age and intraocular pressure (IOP) are the major risk factors. Glaucoma is characterized by the death of nerve cells and the loss of optic nerve fibers. Recently, evidence has accumulated indicating that proteins in the environment of nerve cells, called the extracellular matrix (ECM), play an important role in glaucomatous neurodegeneration. Depending on its constitution, the ECM can influence either the survival or the death of nerve cells. Thus, the aim of our study was to comparatively explore alterations of various ECM molecules in the retina and optic nerve of aged control and glaucomatous mice with chronic IOP elevation. Interestingly, we observed elevated levels of blood vessel and glial cell-associated ECM components in the glaucomatous retina and optic nerve, which could be responsible for various pathological processes. A better understanding of the underlying signaling mechanisms may help to develop new diagnostic and therapeutic strategies for glaucoma patients.

Abstract

Glaucoma is a neurodegenerative disease that is characterized by the loss of retinal ganglion cells (RGC) and optic nerve fibers. Increased age and intraocular pressure (IOP) elevation are the main risk factors for developing glaucoma. Mice that are heterozygous (HET) for the mega-karyocyte protein tyrosine phosphatase 2 (PTP-Meg2) show chronic and progressive IOP elevation, severe RGCs loss, and optic nerve damage, and represent a valuable model for IOP-dependent primary open-angle glaucoma (POAG). Previously, evidence accumulated suggesting that glaucomatous neurodegeneration is associated with the extensive remodeling of extracellular matrix (ECM) molecules. Unfortunately, little is known about the exact ECM changes in the glaucomatous retina and optic nerve. Hence, the goal of the present study was to comparatively explore ECM alterations in glaucomatous PTP-Meg2 HET and control wild type (WT) mice. Due to their potential relevance in glaucomatous neurodegeneration, we specifically analyzed the expression pattern of the ECM glycoproteins fibronectin, laminin, tenascin-C, and tenascin-R as well as the proteoglycans aggrecan, brevican, and members of the receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) family. The analyses were carried out in the retina and optic nerve of glaucomatous PTP-Meg2 HET and WT mice using quantitative real-time PCR (RT-qPCR), immunohistochemistry, and Western blot. Interestingly, we observed increased fibronectin and laminin levels in the glaucomatous HET retina and optic nerve compared to the WT group. RT-qPCR analyses of the laminins α4, β2 and γ3 showed an altered isoform-specific regulation in the HET retina and optic nerve. In addition, an upregulation of tenascin-C and its interaction partner RPTPβ/ζ/phosphacan was found in glaucomatous tissue. However, comparable protein and mRNA levels for tenascin-R as well as aggrecan and brevican were observed in both groups. Overall, our study showed a remodeling of various ECM components in the glaucomatous retina and optic nerve of PTP-Meg2 HET mice. This dysregulation could be responsible for pathological processes such as neovascularization, inflammation, and reactive gliosis in glaucomatous neurodegeneration.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Decellularization optimizes the inhibitory microenvironment of the optic nerve to support neurite growth

Allogeneic or homologous tissue transplantation is an effective strategy to repair tissue injury. However, the central nervous tissues like the brain, spinal cord, and optic nerve are not ideal materials for nervous tissue regeneration due to the excessive axonal inhibitor cues in their microenvironments. In the present study, we found that decellularization optimizes the function of the adult optic nerve in supporting the oriented outgrowth of dorsal root ganglion (DRG) neurites. The neurites growing on the decellularized optic nerve (DON) showed longer extension distances than those growing on the normal optic nerve (ON). Neurite branching was also significantly increased on the DON compared to on the ON. Decellularization selectively removed some axon-inhibitory molecules such as myelin-associated glycoprotein (basically not detected in DON) and chondroitin sulfate proteoglycans (detected in DON at a level less than 0.3 fold that in ON) and preserved some axon-promoted extracellular matrix (ECM) proteins, including collagen IV and laminin (detected at levels 6.0-fold higher in DON than in ON). Furthermore, collagen IV and laminin were shown to be preserved in DON, and their binding activities with integrin α1 were retained to promote the extension of DRG neurites. Together, the findings provide a feasible way to optimize the axon-inhibited microenvironment of central nervous tissues and establish a theoretical basis for the application of DON scaffolds in repairing central nervous injury.

Role of Chondroitin Sulfation Following Spinal Cord Injury

Traumatic spinal cord injury produces long-term neurological damage, and presents a significant public health problem with nearly 18,000 new cases per year in the U.S. The injury results in both acute and chronic changes in the spinal cord, ultimately resulting in the production of a glial scar, consisting of multiple cells including fibroblasts, macrophages, microglia, and reactive astrocytes. Within the scar, there is an accumulation of extracellular matrix (ECM) molecules—primarily tenascins and chondroitin sulfate proteoglycans (CSPGs)—which are considered to be inhibitory to axonal regeneration. In this review article, we discuss the role of CSPGs in the injury response, especially how sulfated glycosaminoglycan (GAG) chains act to inhibit plasticity and regeneration. This includes how sulfation of GAG chains influences their biological activity and interactions with potential receptors. Comprehending the role of CSPGs in the inhibitory properties of the glial scar provides critical knowledge in the much-needed production of new therapies.