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Evans AD, Pournoori N, Saksala E, Oommen OP. Glycosaminoglycans' for brain health: Harnessing glycosaminoglycan based biomaterials for treating central nervous system diseases and in-vitro modeling. Biomaterials 2024; 309:122629. [PMID: 38797120 DOI: 10.1016/j.biomaterials.2024.122629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 05/06/2024] [Accepted: 05/19/2024] [Indexed: 05/29/2024]
Abstract
Dysfunction of the central nervous system (CNS) following traumatic brain injuries (TBI), spinal cord injuries (SCI), or strokes remains challenging to address using existing medications and cell-based therapies. Although therapeutic cell administration, such as stem cells and neuronal progenitor cells (NPCs), have shown promise in regenerative properties, they have failed to provide substantial benefits. However, the development of living cortical tissue engineered grafts, created by encapsulating these cells within an extracellular matrix (ECM) mimetic hydrogel scaffold, presents a promising functional replacement for damaged cortex in cases of stroke, SCI, and TBI. These grafts facilitate neural network repair and regeneration following CNS injuries. Given that natural glycosaminoglycans (GAGs) are a major constituent of the CNS, GAG-based hydrogels hold potential for the next generation of CNS healing therapies and in vitro modeling of CNS diseases. Brain-specific GAGs not only offer structural and biochemical signaling support to encapsulated neural cells but also modulate the inflammatory response in lesioned brain tissue, facilitating host integration and regeneration. This review briefly discusses different roles of GAGs and their related proteoglycan counterparts in healthy and diseases brain and explores current trends and advancements in GAG-based biomaterials for treating CNS injuries and modeling diseases. Additionally, it examines injectable, 3D bioprintable, and conductive GAG-based scaffolds, highlighting their clinical potential for in vitro modeling of patient-specific neural dysfunction and their ability to enhance CNS regeneration and repair following CNS injury in vivo.
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Affiliation(s)
- Austin D Evans
- Bioengineering and Nanomedicine Group, Faculty of Medicine and Health Technologies, Tampere University, 33720, Tampere, Finland
| | - Negin Pournoori
- Bioengineering and Nanomedicine Group, Faculty of Medicine and Health Technologies, Tampere University, 33720, Tampere, Finland
| | - Emmi Saksala
- Bioengineering and Nanomedicine Group, Faculty of Medicine and Health Technologies, Tampere University, 33720, Tampere, Finland
| | - Oommen P Oommen
- Bioengineering and Nanomedicine Group, Faculty of Medicine and Health Technologies, Tampere University, 33720, Tampere, Finland; School of Pharmacy and Pharmaceutical Sciences, Cardiff University, King Edward VII Avenue, Cardiff CF10 3NB, UK.
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2
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Li M, Li N, Shao F, Wang R, Chen M, Liu YJ, Zhao Y, Li R. Synthesis of a super-low detection limit fluorescent probe for Al 3+ and its application in fluorescence imaging of zebrafish and cells. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 308:123676. [PMID: 38039642 DOI: 10.1016/j.saa.2023.123676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 10/30/2023] [Accepted: 11/21/2023] [Indexed: 12/03/2023]
Abstract
A novel fluorescent probe N'-(2-hydroxybenzylidene)-indole-3-formylhydrazine (JHK) was designed and synthesized based on the condensation reaction of indole-3-formylhydrazine and salicylaldehyde. The probe JHK solution could highly selectively recognize Al3+ by the obvious fluorescence enhancement (288-fold) after adding Al3+. And the probe solution with Al3+ had a very high fluorescence quantum yield (89.29 %). The detection limit was calculated to be 1.135 nM, which was significantly lower than many reported detection limits, indicating that the probe JHK had pretty good sensitivity. The ratio of JHK to Al3+ (1:1) and the sensing mechanism were determined by Job's plot, 1H NMR spectra, FTIR spectra, ESI-MS and Gaussian calculation. The probe solution and medium-speed filter paper were successfully used to make test papers for more convenient detection of Al3+. Furthermore, the probe JHK had been successfully applied to the detection of Al3+ in real water, zebrafish and living cells.
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Affiliation(s)
- Min Li
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China
| | - Na Li
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China
| | - Feng Shao
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China
| | - Rui Wang
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China
| | - Miao Chen
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China
| | - Yuan-Jun Liu
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China
| | - Yu Zhao
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, PR China.
| | - Rong Li
- Qingdao Women and Children 's Hospital, No. 217 Liaoyang West Road, Qingdao, Shandong 226034, PR China.
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Downs M, Zaia J, Sethi MK. Mass spectrometry methods for analysis of extracellular matrix components in neurological diseases. MASS SPECTROMETRY REVIEWS 2023; 42:1848-1875. [PMID: 35719114 PMCID: PMC9763553 DOI: 10.1002/mas.21792] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 04/12/2022] [Accepted: 05/24/2022] [Indexed: 06/15/2023]
Abstract
The brain extracellular matrix (ECM) is a highly glycosylated environment and plays important roles in many processes including cell communication, growth factor binding, and scaffolding. The formation of structures such as perineuronal nets (PNNs) is critical in neuroprotection and neural plasticity, and the formation of molecular networks is dependent in part on glycans. The ECM is also implicated in the neuropathophysiology of disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and Schizophrenia (SZ). As such, it is of interest to understand both the proteomic and glycomic makeup of healthy and diseased brain ECM. Further, there is a growing need for site-specific glycoproteomic information. Over the past decade, sample preparation, mass spectrometry, and bioinformatic methods have been developed and refined to provide comprehensive information about the glycoproteome. Core ECM molecules including versican, hyaluronan and proteoglycan link proteins, and tenascin are dysregulated in AD, PD, and SZ. Glycomic changes such as differential sialylation, sulfation, and branching are also associated with neurodegeneration. A more thorough understanding of the ECM and its proteomic, glycomic, and glycoproteomic changes in brain diseases may provide pathways to new therapeutic options.
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Affiliation(s)
- Margaret Downs
- Department of Biochemistry, Center for Biomedical Mass Spectrometry, Boston University, Boston, Massachusetts, USA
| | - Joseph Zaia
- Department of Biochemistry, Center for Biomedical Mass Spectrometry, Boston University, Boston, Massachusetts, USA
- Bioinformatics Program, Boston University, Boston, Massachusetts, USA
| | - Manveen K Sethi
- Department of Biochemistry, Center for Biomedical Mass Spectrometry, Boston University, Boston, Massachusetts, USA
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John U, Patro N, Patro IK. Astrogliosis and associated CSPG upregulation adversely affect dendritogenesis, spinogenesis and synaptic activity in the cerebellum of a double-hit rat model of protein malnutrition (PMN) and lipopolysaccharide (LPS) induced bacterial infection. J Chem Neuroanat 2023; 131:102286. [PMID: 37169039 DOI: 10.1016/j.jchemneu.2023.102286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 05/07/2023] [Accepted: 05/08/2023] [Indexed: 05/13/2023]
Abstract
The extracellular matrix (ECM) plays a vital role in growth, guidance and survival of neurons in the central nervous system (CNS). The chondroitin sulphate proteoglycans (CSPGs) are a type of ECM proteins that are crucial for CNS homeostasis. The major goal of this study was to uncover the effects of astroglial activation and associated intensified expression of CSPGs on dendritogenesis, spinogenesis as well as on synaptic activity in cerebellum following protein malnutrition (PMN) and lipopolysaccharide (LPS) induced bacterial infection. Female Wistar albino rats (3 months old) were switched to control (20% protein) or low protein (LP, 8% protein) diet for 15 days followed by breeding. A set of pups born to control/LP mothers and maintained on respective diets throughout the experimental period constituted the control and LP groups, while a separate set of both control and LP group pups exposed to bacterial infection by a single intraperitoneal injection of LPS (0.3 mg/ kg body weight) on postnatal day-9 (P-9) constituted control+LPS and LP+LPS groups respectively. The consequences of astrogliosis induced CSPG upregulation on cerebellar cytoarchitecture and synaptic activity were studied using standard immunohistochemical and histological tools on P-21 and 6 months of age. The results revealed reactive astrogliosis and associated CSPG upregulation in a double-hit model of PMN and LPS induced bacterial infection resulted in disrupted dendritogenesis, reduced postsynaptic density protein (PSD-95) levels and a deleterious impact on normal spine growth. Such alterations frequently have the potential to cause synaptic dysregulation and inhibition of plasticity both during development as well as adulthood. At the light of our results, we can envision that upregulation of CSPGs in PMN and LPS co-challenged individuals might emerge as an important modulator of brain circuitry and a major causative factor for many neurological disorders.
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Affiliation(s)
- Urmilla John
- School of Studies in Neuroscience, Jiwaji University, Gwalior, India; School of Studies in Zoology, Jiwaji University, Gwalior, India
| | - Nisha Patro
- School of Studies in Neuroscience, Jiwaji University, Gwalior, India
| | - Ishan K Patro
- School of Studies in Neuroscience, Jiwaji University, Gwalior, India; School of Studies in Zoology, Jiwaji University, Gwalior, India.
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Xu T, Liu C, Deng S, Gan L, Zhang Z, Yang GY, Tian H, Tang Y. The roles of microglia and astrocytes in myelin phagocytosis in the central nervous system. J Cereb Blood Flow Metab 2023; 43:325-340. [PMID: 36324281 PMCID: PMC9941857 DOI: 10.1177/0271678x221137762] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Revised: 10/03/2022] [Accepted: 10/05/2022] [Indexed: 11/06/2022]
Abstract
Myelination is an important process in the central nervous system (CNS). Oligodendrocytes (OLs) extend multiple layers to densely sheath on axons, composing the myelin to achieve efficient electrical signal conduction. The myelination during developmental stage maintains a balanced state. However, numerous CNS diseases including neurodegenerative and cerebrovascular diseases cause demyelination and disrupt the homeostasis, resulting in inflammation and white matter deficits. Effective clearance of myelin debris is needed in the region of demyelination, which is a key step for remyelination and tissue regeneration. Microglia and astrocytes are the major resident phagocytic cells in the brain, which may play different or collaborative roles in myelination. Microglia and astrocytes participate in developmental myelination through engulfing excessive unneeded myelin. They are also involved in the clearance of degenerated myelin debris for accelerating remyelination, or engulfing healthy myelin sheath for inhibiting remyelination. This review focuses on the roles of microglia and astrocytes in phagocytosing myelin in the developmental brain and diseased brain. In addition, the interaction between microglia and astrocytes to mediate myelin engulfment is also summarized.
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Affiliation(s)
- Tongtong Xu
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Chang Liu
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Shiyu Deng
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Lin Gan
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Zhijun Zhang
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Guo-Yuan Yang
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Hengli Tian
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
| | - Yaohui Tang
- Shanghai Jiao Tong Affiliated Sixth People’s
Hospital, School of Biomedical Engineering, Shanghai Jiao Tong University,
Shanghai, China
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Du B, Zheng M, Ma H, Huang J, Jiao Q, Bai Y, Zhao M, Zhou J. Nanozyme-natural enzymes cascade catalyze cholesterol consumption and reverse cancer multidrug resistance. J Nanobiotechnology 2022; 20:209. [PMID: 35501796 PMCID: PMC9063293 DOI: 10.1186/s12951-022-01406-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 03/30/2022] [Indexed: 11/10/2022] Open
Abstract
Multidrug resistance is still a major obstacle to cancer treatment. The most studies are to inhibit the activity of the drug transporter P-glycoprotein (P-gp), but the effect is not ideal. Herein, a nanosystem was built based on cascade catalytic consumption of cholesterol. Cholesterol oxidase (natural enzyme, COD) was immobilized on the carrier (NH2-MIL-88B, MOF) through amide reaction, COD catalyzed the consumption of cholesterol, the reaction product H2O2 was further produced by the MOF with its peroxidase-like activity to produce hydroxyl radicals (•OH) with killing effect. Due to the high expression of CD44 receptor on the surface of tumor cells, we encapsulated chondroitin sulfate gel shell (CS-shell) with CD44 targeting and apoptosis promoting effect on the surface of DOX@MOF-COD nanoparticles, which can accurately and efficiently deliver the drugs to the tumor site and improve the effect of reversing drug resistance. Taking drug-resistant cell membrane as "breakthrough", this paper will provide a new idea for reversing multidrug resistance of tumor.
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Affiliation(s)
- Bin Du
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China.,Key Laboratory of Targeting Therapy and Diagnosis for Critical Diseases, 100 Science Road, Zhengzhou, 450001, Henan Province, People's Republic of China
| | - Mei Zheng
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China
| | - Huizhen Ma
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China
| | - Jingshu Huang
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China
| | - Qingqing Jiao
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China
| | - Yimeng Bai
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China
| | - Mengmeng Zhao
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China
| | - Jie Zhou
- School of Pharmaceutical Sciences, Zhengzhou University, 100 Science Road, Zhengzhou, 450001, People's Republic of China. .,Key Laboratory of Targeting Therapy and Diagnosis for Critical Diseases, 100 Science Road, Zhengzhou, 450001, Henan Province, People's Republic of China.
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Basu A, Patel NG, Nicholson ED, Weiss RJ. Spatiotemporal diversity and regulation of glycosaminoglycans in cell homeostasis and human disease. Am J Physiol Cell Physiol 2022; 322:C849-C864. [PMID: 35294848 PMCID: PMC9037703 DOI: 10.1152/ajpcell.00085.2022] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Glycosaminoglycans (GAGs) are long, linear polysaccharides that are ubiquitously expressed on the cell surface and in the extracellular matrix of all animal cells. These complex carbohydrates play important roles in many cellular processes and have been implicated in many disease states, including cancer, inflammation, and genetic disorders. GAGs are among the most complex molecules in biology with enormous information content and extensive structural and functional heterogeneity. GAG biosynthesis is a nontemplate-driven process facilitated by a large group of biosynthetic enzymes that have been extensively characterized over the past few decades. Interestingly, the expression of the enzymes and the consequent structure and function of the polysaccharide chains can vary temporally and spatially during development and under certain pathophysiological conditions, suggesting their assembly is tightly regulated in cells. Due to their many key roles in cell homeostasis and disease, there is much interest in targeting the assembly and function of GAGs as a therapeutic approach. Recent advances in genomics and GAG analytical techniques have pushed the field and generated new perspectives on the regulation of mammalian glycosylation. This review highlights the spatiotemporal diversity of GAGs and the mechanisms guiding their assembly and function in human biology and disease.
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Affiliation(s)
- Amrita Basu
- 1Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia
| | - Neil G. Patel
- 1Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia,2Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia
| | - Elijah D. Nicholson
- 2Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia
| | - Ryan J. Weiss
- 1Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia,2Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia
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Hayes AJ, Melrose J. Neural Tissue Homeostasis and Repair Is Regulated via CS and DS Proteoglycan Motifs. Front Cell Dev Biol 2021; 9:696640. [PMID: 34409033 PMCID: PMC8365427 DOI: 10.3389/fcell.2021.696640] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 07/13/2021] [Indexed: 01/04/2023] Open
Abstract
Chondroitin sulfate (CS) is the most abundant and widely distributed glycosaminoglycan (GAG) in the human body. As a component of proteoglycans (PGs) it has numerous roles in matrix stabilization and cellular regulation. This chapter highlights the roles of CS and CS-PGs in the central and peripheral nervous systems (CNS/PNS). CS has specific cell regulatory roles that control tissue function and homeostasis. The CNS/PNS contains a diverse range of CS-PGs which direct the development of embryonic neural axonal networks, and the responses of neural cell populations in mature tissues to traumatic injury. Following brain trauma and spinal cord injury, a stabilizing CS-PG-rich scar tissue is laid down at the defect site to protect neural tissues, which are amongst the softest tissues of the human body. Unfortunately, the CS concentrated in gliotic scars also inhibits neural outgrowth and functional recovery. CS has well known inhibitory properties over neural behavior, and animal models of CNS/PNS injury have demonstrated that selective degradation of CS using chondroitinase improves neuronal functional recovery. CS-PGs are present diffusely in the CNS but also form denser regions of extracellular matrix termed perineuronal nets which surround neurons. Hyaluronan is immobilized in hyalectan CS-PG aggregates in these perineural structures, which provide neural protection, synapse, and neural plasticity, and have roles in memory and cognitive learning. Despite the generally inhibitory cues delivered by CS-A and CS-C, some CS-PGs containing highly charged CS disaccharides (CS-D, CS-E) or dermatan sulfate (DS) disaccharides that promote neural outgrowth and functional recovery. CS/DS thus has varied cell regulatory properties and structural ECM supportive roles in the CNS/PNS depending on the glycoform present and its location in tissue niches and specific cellular contexts. Studies on the fruit fly, Drosophila melanogaster and the nematode Caenorhabditis elegans have provided insightful information on neural interconnectivity and the role of the ECM and its PGs in neural development and in tissue morphogenesis in a whole organism environment.
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Affiliation(s)
- Anthony J. Hayes
- Bioimaging Research Hub, Cardiff School of Biosciences, Cardiff University, Wales, United Kingdom
| | - James Melrose
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia
- Raymond Purves Bone and Joint Research Laboratories, Kolling Institute of Medical Research, Royal North Shore Hospital and The Faculty of Medicine and Health, The University of Sydney, St. Leonard’s, NSW, Australia
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Type IIa RPTPs and Glycans: Roles in Axon Regeneration and Synaptogenesis. Int J Mol Sci 2021; 22:ijms22115524. [PMID: 34073798 PMCID: PMC8197235 DOI: 10.3390/ijms22115524] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/18/2021] [Accepted: 05/20/2021] [Indexed: 02/06/2023] Open
Abstract
Type IIa receptor tyrosine phosphatases (RPTPs) play pivotal roles in neuronal network formation. It is emerging that the interactions of RPTPs with glycans, i.e., chondroitin sulfate (CS) and heparan sulfate (HS), are critical for their functions. We highlight here the significance of these interactions in axon regeneration and synaptogenesis. For example, PTPσ, a member of type IIa RPTPs, on axon terminals is monomerized and activated by the extracellular CS deposited in neural injuries, dephosphorylates cortactin, disrupts autophagy flux, and consequently inhibits axon regeneration. In contrast, HS induces PTPσ oligomerization, suppresses PTPσ phosphatase activity, and promotes axon regeneration. PTPσ also serves as an organizer of excitatory synapses. PTPσ and neurexin bind one another on presynapses and further bind to postsynaptic leucine-rich repeat transmembrane protein 4 (LRRTM4). Neurexin is now known as a heparan sulfate proteoglycan (HSPG), and its HS is essential for the binding between these three molecules. Another HSPG, glypican 4, binds to presynaptic PTPσ and postsynaptic LRRTM4 in an HS-dependent manner. Type IIa RPTPs are also involved in the formation of excitatory and inhibitory synapses by heterophilic binding to a variety of postsynaptic partners. We also discuss the important issue of possible mechanisms coordinating axon extension and synapse formation.
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