1
|
Avilés EC, Wang SK, Patel S, Shi S, Lin L, Kefalov VJ, Goodrich LV, Cepko CL, Xue Y. High temporal frequency light response in mouse retina is mediated by ON and OFF bipolar cells and requires FAT3 signaling. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.02.565326. [PMID: 37961274 PMCID: PMC10635074 DOI: 10.1101/2023.11.02.565326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
Vision is initiated by the reception of light by photoreceptors and subsequent processing via parallel retinal circuits. Proper circuit organization depends on the multi-functional tissue polarity protein FAT3, which is required for amacrine cell connectivity and retinal lamination. Here we investigated the retinal function of Fat3 mutant mice and found decreases in physiological and perceptual responses to high frequency flashes. These defects did not correlate with abnormal amacrine cell wiring, pointing instead to a role in bipolar cell subtypes that also express FAT3. Indeed, similar deficits were observed in mice lacking the bipolar cell glutamate receptors GRIK1 (OFF-bipolar cells) and GRM6 (ON-bipolar cells). Mechanistically, FAT3 binds to the synaptic protein PTPσ and is required to localize GRIK1 to OFF-cone bipolar cell synapses with cone photoreceptors. How FAT3 impacts ON-cone bipolar cell function at high temporal frequency remains to be uncovered. These findings expand the repertoire of FAT3's functions and reveal the importance of both ON- and OFF-bipolar cells for high frequency light response.
Collapse
Affiliation(s)
- Evelyn C. Avilés
- Department of Neurobiology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115
- Present address: Facultad de Ciencias Biologicas, Pontificia Universidad Catolica deChile, Santiago, Chile
| | - Sean K. Wang
- Departments of Genetics and Ophthalmology, Harvard Medical School, Boston, MA 02115
- Howard Hughes Medical Institute, Boston, MA 02115
| | - Sarina Patel
- Department of Neurobiology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115
| | - Shuxiang Shi
- Lingang Laboratory, Shanghai, China, 200031
- School of Life Science and Technology, ShanghaiTech University, Shanghai, China, 201210
| | - Lucas Lin
- Departments of Genetics and Ophthalmology, Harvard Medical School, Boston, MA 02115
| | - Vladimir J. Kefalov
- Gavin Herbert Eye Institute & Center for Translational Vision Research, University of California, Irvine, CA 92697
| | - Lisa V. Goodrich
- Department of Neurobiology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115
| | - Constance L. Cepko
- Departments of Genetics and Ophthalmology, Harvard Medical School, Boston, MA 02115
- Howard Hughes Medical Institute, Boston, MA 02115
| | - Yunlu Xue
- Departments of Genetics and Ophthalmology, Harvard Medical School, Boston, MA 02115
- Lingang Laboratory, Shanghai, China, 200031
- Lead contact
| |
Collapse
|
2
|
Farrugia BL, Melrose J. The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour. Int J Mol Sci 2023; 24:14101. [PMID: 37762403 PMCID: PMC10531531 DOI: 10.3390/ijms241814101] [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: 07/24/2023] [Revised: 09/03/2023] [Accepted: 09/05/2023] [Indexed: 09/29/2023] Open
Abstract
This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.
Collapse
Affiliation(s)
- Brooke L. Farrugia
- Department of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Melbourne, Melbourne, VIC 3010, Australia;
| | - James Melrose
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW 2052, Australia
- Raymond Purves Laboratory of Bone and Joint Research, Kolling Institute of Medical Research, Northern Sydney Local Health District, Royal North Shore Hospital, St. Leonards, NSW 2065, Australia
- Sydney Medical School (Northern), University of Sydney at Royal North Shore Hospital, St. Leonards, NSW 2065, Australia
| |
Collapse
|
3
|
Sclip A, Südhof TC. Combinatorial expression of neurexins and LAR-type phosphotyrosine phosphatase receptors instructs assembly of a cerebellar circuit. Nat Commun 2023; 14:4976. [PMID: 37591863 PMCID: PMC10435579 DOI: 10.1038/s41467-023-40526-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Accepted: 07/20/2023] [Indexed: 08/19/2023] Open
Abstract
Synaptic adhesion molecules (SAMs) shape the structural and functional properties of synapses and thereby control the information processing power of neural circuits. SAMs are broadly expressed in the brain, suggesting that they may instruct synapse formation and specification via a combinatorial logic. Here, we generate sextuple conditional knockout mice targeting all members of the two major families of presynaptic SAMs, Neurexins and leukocyte common antigen-related-type receptor phospho-tyrosine phosphatases (LAR-PTPRs), which together account for the majority of known trans-synaptic complexes. Using synapses formed by cerebellar Purkinje cells onto deep cerebellar nuclei as a model system, we confirm that Neurexins and LAR-PTPRs themselves are not essential for synapse assembly. The combinatorial deletion of both neurexins and LAR-PTPRs, however, decreases Purkinje-cell synapses on deep cerebellar nuclei, the major output pathway of cerebellar circuits. Consistent with this finding, combined but not separate deletions of neurexins and LAR-PTPRs impair motor behaviors. Thus, Neurexins and LAR-PTPRs are together required for the assembly of a functional cerebellar circuit.
Collapse
Affiliation(s)
- Alessandra Sclip
- Department of Cellular and Molecular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA.
| | - Thomas C Südhof
- Department of Cellular and Molecular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA.
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA, 94305, USA.
| |
Collapse
|
4
|
Khaspekov LG, Frumkina LE. Molecular Mechanisms of Astrocyte Involvement in Synaptogenesis and Brain Synaptic Plasticity. BIOCHEMISTRY. BIOKHIMIIA 2023; 88:502-514. [PMID: 37080936 DOI: 10.1134/s0006297923040065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/22/2023]
Abstract
Astrocytes perform a wide range of important functions in the brain. As structural and functional components of synapses, astrocytes secrete various factors (proteins, lipids, small molecules, etc.) that bind to neuronal receptor and contribute to synaptogenesis and regulation of synaptic contacts. Astrocytic factors play a key role in the formation of neural networks undergoing short- and long-term synaptic morphological and functional rearrangements essential in the memory formation and behavior. The review summarizes the data on the molecular mechanisms mediating the involvement of astrocyte-secreted factors in synaptogenesis in the brain and provides up-to-date information on the role of astrocytes and astrocytic synaptogenic factors in the long-term plastic rearrangements of synaptic contacts.
Collapse
|
5
|
Dhume SH, Connor SA, Mills F, Tari PK, Au-Yeung SHM, Karimi B, Oku S, Roppongi RT, Kawabe H, Bamji SX, Wang YT, Brose N, Jackson MF, Craig AM, Siddiqui TJ. Distinct but overlapping roles of LRRTM1 and LRRTM2 in developing and mature hippocampal circuits. eLife 2022; 11:64742. [PMID: 35662394 PMCID: PMC9170246 DOI: 10.7554/elife.64742] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 05/20/2022] [Indexed: 01/21/2023] Open
Abstract
LRRTMs are postsynaptic cell adhesion proteins that have region-restricted expression in the brain. To determine their role in the molecular organization of synapses in vivo, we studied synapse development and plasticity in hippocampal neuronal circuits in mice lacking both Lrrtm1 and Lrrtm2. We found that LRRTM1 and LRRTM2 regulate the density and morphological integrity of excitatory synapses on CA1 pyramidal neurons in the developing brain but are not essential for these roles in the mature circuit. Further, they are required for long-term-potentiation in the CA3-CA1 pathway and the dentate gyrus, and for enduring fear memory in both the developing and mature brain. Our data show that LRRTM1 and LRRTM2 regulate synapse development and function in a cell-type and developmental-stage-specific manner, and thereby contribute to the fine-tuning of hippocampal circuit connectivity and plasticity.
Collapse
Affiliation(s)
- Shreya H Dhume
- Neuroscience Research Program, Kleysen Institute for Advanced Medicine, Health Sciences Centre, Winnipeg, Canada.,Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada
| | - Steven A Connor
- Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, Canada.,Department of Biology, York University, Toronto, Canada
| | - Fergil Mills
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada
| | - Parisa Karimi Tari
- Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, Canada.,Department of Biology, York University, Toronto, Canada
| | - Sarah H M Au-Yeung
- Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, Canada
| | - Benjamin Karimi
- Neuroscience Research Program, Kleysen Institute for Advanced Medicine, Health Sciences Centre, Winnipeg, Canada.,Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada
| | - Shinichiro Oku
- Neuroscience Research Program, Kleysen Institute for Advanced Medicine, Health Sciences Centre, Winnipeg, Canada.,Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada.,Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, Canada
| | - Reiko T Roppongi
- Neuroscience Research Program, Kleysen Institute for Advanced Medicine, Health Sciences Centre, Winnipeg, Canada.,Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada
| | - Hiroshi Kawabe
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.,Division of Pathogenetic Signaling, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Kobe, Japan.,Department of Gerontology, Laboratory of Molecular Life Science, Institute of Biomedical Research and Innovation, Foundation for Biomedical Research and Innovation at Kobe, Kobe, Japan.,Department of Pharmacology, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Shernaz X Bamji
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada
| | - Yu Tian Wang
- Division of Neurology, Department of Medicine and Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, Canada
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Michael F Jackson
- Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, Canada
| | - Ann Marie Craig
- Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, Canada
| | - Tabrez J Siddiqui
- Neuroscience Research Program, Kleysen Institute for Advanced Medicine, Health Sciences Centre, Winnipeg, Canada.,Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada.,The Children's Hospital Research Institute of Manitoba, Winnipeg, Canada.,Program in Biomedical Engineering, University of Manitoba, Winnipeg, Canada
| |
Collapse
|
6
|
Kamimura K. Roles of Glypican and Heparan Sulfate at the Synapses. TRENDS GLYCOSCI GLYC 2021. [DOI: 10.4052/tigg.2017.1e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Keisuke Kamimura
- Department of Brain and Neurosciences, Tokyo Metropolitan Institute of Medical Science
| |
Collapse
|
7
|
Kamimura K. Roles of Glypican and Heparan Sulfate at the Synapses. TRENDS GLYCOSCI GLYC 2021. [DOI: 10.4052/tigg.2017.1j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Keisuke Kamimura
- Department of Brain and Neurosciences, Tokyo Metropolitan Institute of Medical Science
| |
Collapse
|
8
|
Shan L, Zhang T, Fan K, Cai W, Liu H. Astrocyte-Neuron Signaling in Synaptogenesis. Front Cell Dev Biol 2021; 9:680301. [PMID: 34277621 PMCID: PMC8284252 DOI: 10.3389/fcell.2021.680301] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2021] [Accepted: 06/14/2021] [Indexed: 01/10/2023] Open
Abstract
Astrocytes are the key component of the central nervous system (CNS), serving as pivotal regulators of neuronal synapse formation and maturation through their ability to dynamically and bidirectionally communicate with synapses throughout life. In the past 20 years, numerous astrocyte-derived molecules promoting synaptogenesis have been discovered. However, our understanding of the cell biological basis underlying intra-neuron processes and astrocyte-mediated synaptogenesis is still in its infancy. Here, we provide a comprehensive overview of the various ways astrocytes talk to neurons, and highlight astrocytes’ heterogeneity that allow them to displays regional-specific capabilities in boosting synaptogenesis. Finally, we conclude with promises and future directions on how organoids generated from human induced pluripotent stem cells (hiPSCs) effectively address the signaling pathways astrocytes employ in synaptic development.
Collapse
Affiliation(s)
- Lili Shan
- Guangzhou Laboratory, Guangzhou, China.,Bioland Laboratory (Guangzhou Regenerative Medicine and Health Guangdong Laboratory), Guangzhou, China
| | - Tongran Zhang
- Guangzhou Laboratory, Guangzhou, China.,Bioland Laboratory (Guangzhou Regenerative Medicine and Health Guangdong Laboratory), Guangzhou, China
| | - Kevin Fan
- Department of Radiology, University of Wisconsin-Madison, Madison, WI, United States.,Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, United States
| | - Weibo Cai
- Department of Radiology, University of Wisconsin-Madison, Madison, WI, United States.,Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, United States
| | - Huisheng Liu
- Guangzhou Laboratory, Guangzhou, China.,Bioland Laboratory (Guangzhou Regenerative Medicine and Health Guangdong Laboratory), Guangzhou, China
| |
Collapse
|
9
|
Montoliu-Gaya L, Tietze D, Kaminski D, Mirgorodskaya E, Tietze AA, Sterky FH. CA10 regulates neurexin heparan sulfate addition via a direct binding in the secretory pathway. EMBO Rep 2021; 22:e51349. [PMID: 33586859 PMCID: PMC8024894 DOI: 10.15252/embr.202051349] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 12/21/2020] [Accepted: 01/13/2021] [Indexed: 12/29/2022] Open
Abstract
Neurexins are presynaptic adhesion molecules that shape the molecular composition of synapses. Diversification of neurexins in numerous isoforms is believed to confer synapse-specific properties by engaging with distinct ligands. For example, a subset of neurexin molecules carry a heparan sulfate (HS) glycosaminoglycan that controls ligand binding, but how this post-translational modification is controlled is not known. Here, we observe that CA10, a ligand to neurexin in the secretory pathway, regulates neurexin-HS formation. CA10 is exclusively found on non-HS neurexin and CA10 expressed in neurons is sufficient to suppress HS addition and attenuate ligand binding and synapse formation induced by ligands known to recruit HS. This effect is mediated by a direct interaction in the secretory pathway that blocks the primary step of HS biosynthesis: xylosylation of the serine residue. NMR reveals that CA10 engages residues on either side of the serine that can be HS-modified, suggesting that CA10 sterically blocks xylosyltransferase access in Golgi. These results suggest a mechanism for the regulation of HS on neurexins and exemplify a new mechanism to regulate site-specific glycosylations.
Collapse
Affiliation(s)
- Laia Montoliu-Gaya
- Department of Laboratory Medicine, Institute for Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.,Wallenberg Centre for Molecular and Translational Medicine, University of Gothenburg, Gothenburg, Sweden
| | - Daniel Tietze
- Wallenberg Centre for Molecular and Translational Medicine, University of Gothenburg, Gothenburg, Sweden.,Department of Chemistry and Molecular Biology, Faculty of Science, University of Gothenburg, Gothenburg, Sweden
| | - Debora Kaminski
- Department of Laboratory Medicine, Institute for Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.,Wallenberg Centre for Molecular and Translational Medicine, University of Gothenburg, Gothenburg, Sweden.,Department of Clinical Chemistry, Sahlgrenska University Hospital, Gothenburg, Sweden
| | | | - Alesia A Tietze
- Wallenberg Centre for Molecular and Translational Medicine, University of Gothenburg, Gothenburg, Sweden.,Department of Chemistry and Molecular Biology, Faculty of Science, University of Gothenburg, Gothenburg, Sweden
| | - Fredrik H Sterky
- Department of Laboratory Medicine, Institute for Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.,Wallenberg Centre for Molecular and Translational Medicine, University of Gothenburg, Gothenburg, Sweden.,Department of Clinical Chemistry, Sahlgrenska University Hospital, Gothenburg, Sweden
| |
Collapse
|
10
|
Kamimura K, Maeda N. Glypicans and Heparan Sulfate in Synaptic Development, Neural Plasticity, and Neurological Disorders. Front Neural Circuits 2021; 15:595596. [PMID: 33679334 PMCID: PMC7928303 DOI: 10.3389/fncir.2021.595596] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 01/11/2021] [Indexed: 12/16/2022] Open
Abstract
Heparan sulfate proteoglycans (HSPGs) are components of the cell surface and extracellular matrix, which bear long polysaccharides called heparan sulfate (HS) attached to the core proteins. HSPGs interact with a variety of ligand proteins through the HS chains, and mutations in HSPG-related genes influence many biological processes and cause various diseases. In particular, recent findings from vertebrate and invertebrate studies have raised the importance of glycosylphosphatidylinositol-anchored HSPGs, glypicans, as central players in the development and functions of synapses. Glypicans are important components of the synapse-organizing protein complexes and serve as ligands for leucine-rich repeat transmembrane neuronal proteins (LRRTMs), leukocyte common antigen-related (LAR) family receptor protein tyrosine phosphatases (RPTPs), and G-protein-coupled receptor 158 (GPR158), regulating synapse formation. Many of these interactions are mediated by the HS chains of glypicans. Neurexins (Nrxs) are also synthesized as HSPGs and bind to some ligands in common with glypicans through HS chains. Therefore, glypicans and Nrxs may act competitively at the synapses. Furthermore, glypicans regulate the postsynaptic expression levels of ionotropic glutamate receptors, controlling the electrophysiological properties and non-canonical BMP signaling of synapses. Dysfunctions of glypicans lead to failures in neuronal network formation, malfunction of synapses, and abnormal behaviors that are characteristic of neurodevelopmental disorders. Recent human genetics revealed that glypicans and HS are associated with autism spectrum disorder, neuroticism, and schizophrenia. In this review, we introduce the studies showing the roles of glypicans and HS in synapse formation, neural plasticity, and neurological disorders, especially focusing on the mouse and Drosophila as potential models for human diseases.
Collapse
Affiliation(s)
- Keisuke Kamimura
- Developmental Neuroscience Project, Department of Brain and Neurosciences, Tokyo Metropolitan Institute of Medical Science, Setagaya, Japan
| | - Nobuaki Maeda
- Developmental Neuroscience Project, Department of Brain and Neurosciences, Tokyo Metropolitan Institute of Medical Science, Setagaya, Japan
| |
Collapse
|
11
|
SPARCL1 Promotes Excitatory But Not Inhibitory Synapse Formation and Function Independent of Neurexins and Neuroligins. J Neurosci 2020; 40:8088-8102. [PMID: 32973045 DOI: 10.1523/jneurosci.0454-20.2020] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 06/17/2020] [Accepted: 07/12/2020] [Indexed: 12/17/2022] Open
Abstract
Emerging evidence supports roles for secreted extracellular matrix proteins in boosting synaptogenesis, synaptic transmission, and synaptic plasticity. SPARCL1 (also known as Hevin), a secreted non-neuronal protein, was reported to increase synaptogenesis by simultaneously binding to presynaptic neurexin-1α and to postsynaptic neuroligin-1B, thereby catalyzing formation of trans-synaptic neurexin/neuroligin complexes. However, neurexins and neuroligins do not themselves mediate synaptogenesis, raising the question of how SPARCL1 enhances synapse formation by binding to these molecules. Moreover, it remained unclear whether SPARCL1 acts on all synapses containing neurexins and neuroligins or only on a subset of synapses, and whether it enhances synaptic transmission in addition to boosting synaptogenesis or induces silent synapses. To explore these questions, we examined the synaptic effects of SPARCL1 and their dependence on neurexins and neuroligins. Using mixed neuronal and glial cultures from neonatal mouse cortex of both sexes, we show that SPARCL1 selectively increases excitatory but not inhibitory synapse numbers, enhances excitatory but not inhibitory synaptic transmission, and augments NMDAR-mediated synaptic responses more than AMPAR-mediated synaptic responses. None of these effects were mediated by SPARCL1-binding to neurexins or neuroligins. Neurons from triple neurexin-1/2/3 or from quadruple neuroligin-1/2/3/4 conditional KO mice that lacked all neurexins or all neuroligins were fully responsive to SPARCL1. Together, our results reveal that SPARCL1 selectively boosts excitatory but not inhibitory synaptogenesis and synaptic transmission by a novel mechanism that is independent of neurexins and neuroligins.SIGNIFICANCE STATEMENT Emerging evidence supports roles for extracellular matrix proteins in boosting synapse formation and function. Previous studies demonstrated that SPARCL1, a secreted non-neuronal protein, promotes synapse formation in rodent and human neurons. However, it remained unclear whether SPARCL1 acts on all or on only a subset of synapses, induces functional or largely inactive synapses, and generates synapses by bridging presynaptic neurexins and postsynaptic neuroligins. Here, we report that SPARCL1 selectively induces excitatory synapses, increases their efficacy, and enhances their NMDAR content. Moreover, using rigorous genetic manipulations, we show that SPARCL1 does not require neurexins and neuroligins for its activity. Thus, SPARCL1 selectively boosts excitatory synaptogenesis and synaptic transmission by a novel mechanism that is independent of neurexins and neuroligins.
Collapse
|