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Brahimi F, Galan A, Jmaeff S, Barcelona PF, De Jay N, Dejgaard K, Young JC, Kleinman CL, Thomas DY, Saragovi HU. Alternative Splicing of a Receptor Intracellular Domain Yields Different Ectodomain Conformations, Enabling Isoform-Selective Functional Ligands. iScience 2020; 23:101447. [PMID: 32829283 PMCID: PMC7452315 DOI: 10.1016/j.isci.2020.101447] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 05/13/2020] [Accepted: 08/06/2020] [Indexed: 01/04/2023] Open
Abstract
Events at a receptor ectodomain affect the intracellular domain conformation, activating signal transduction (out-to-in conformational effects). We investigated the reverse direction (in-to-out) where the intracellular domain may impact on ectodomain conformation. The primary sequences of naturally occurring TrkC receptor isoforms (TrkC-FL and TrkC.T1) only differ at the intracellular domain. However, owing to their differential association with Protein Disulfide Isomerase the isoforms have different disulfide bonding and conformations at the ectodomain. Conformations were exploited to develop artificial ligands, mAbs, and small molecules, with isoform-specific binding and biased activation. Consistent, the physiological ligands NT-3 and PTP-sigma bind both isoforms, but NT-3 activates all signaling pathways, whereas PTP-sigma activates biased signals. Our data support an "in-to-out" model controlling receptor ectodomain conformation, a strategy that enables heterogeneity in receptors, ligands, and bioactivity. These concepts may be extended to the many wild-type or oncogenic receptors with known isoforms.
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Affiliation(s)
- Fouad Brahimi
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
| | - Alba Galan
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
| | - Sean Jmaeff
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
- Department of Pharmacology, McGill University, Montreal, QC, Canada
| | - Pablo F. Barcelona
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
| | - Nicolas De Jay
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
- Department of Human Genetics, McGill University, Montreal, QC, Canada
| | - Kurt Dejgaard
- Department of Biochemistry, McGill University, Montreal, QC, Canada
| | - Jason C. Young
- Department of Biochemistry, McGill University, Montreal, QC, Canada
| | - Claudia L. Kleinman
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
- Department of Human Genetics, McGill University, Montreal, QC, Canada
| | - David Y. Thomas
- Department of Biochemistry, McGill University, Montreal, QC, Canada
| | - H. Uri Saragovi
- Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
- Department of Pharmacology, McGill University, Montreal, QC, Canada
- Department of Ophthalmology and Visual Science, McGill University, Montreal, QC, Canada
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Szobota S, Mathur PD, Siegel S, Black K, Saragovi HU, Foster AC. BDNF, NT-3 and Trk receptor agonist monoclonal antibodies promote neuron survival, neurite extension, and synapse restoration in rat cochlea ex vivo models relevant for hidden hearing loss. PLoS One 2019; 14:e0224022. [PMID: 31671109 PMCID: PMC6822712 DOI: 10.1371/journal.pone.0224022] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Accepted: 10/03/2019] [Indexed: 12/21/2022] Open
Abstract
Neurotrophins and their mimetics are potential treatments for hearing disorders because of their trophic effects on spiral ganglion neurons (SGNs) whose connections to hair cells may be compromised in many forms of hearing loss. Studies in noise or ototoxin-exposed animals have shown that local delivery of NT-3 or BDNF has beneficial effects on SGNs and hearing. We evaluated several TrkB or TrkC monoclonal antibody agonists and small molecules, along with BDNF and NT-3, in rat cochlea ex vivo models. The TrkB agonists BDNF and a monoclonal antibody, M3, had the greatest effects on SGN survival, neurite outgrowth and branching. In organotypic cochlear explants, BDNF and M3 enhanced synapse formation between SGNs and inner hair cells and restored these connections after excitotoxin-induced synaptopathy. Loss of these synapses has recently been implicated in hidden hearing loss, a condition characterized by difficulty hearing speech in the presence of background noise. The unique profile of M3 revealed here warrants further investigation, and the broad activity profile of BDNF observed underpins its continued development as a hearing loss therapeutic.
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Affiliation(s)
- Stephanie Szobota
- Otonomy, Inc., San Diego, California, United States of America
- * E-mail:
| | | | - Sairey Siegel
- Otonomy, Inc., San Diego, California, United States of America
| | | | - H. Uri Saragovi
- Lady Davis Institute-Jewish General Hospital, McGill University, Montreal, Quebec, Canada
| | - Alan C. Foster
- Otonomy, Inc., San Diego, California, United States of America
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Saragovi HU, Galan A, Levin LA. Neuroprotection: Pro-survival and Anti-neurotoxic Mechanisms as Therapeutic Strategies in Neurodegeneration. Front Cell Neurosci 2019; 13:231. [PMID: 31244606 PMCID: PMC6563757 DOI: 10.3389/fncel.2019.00231] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Accepted: 05/08/2019] [Indexed: 12/14/2022] Open
Abstract
Neurotrophins (NTs) are a subset of the neurotrophic factor family. These growth factors were originally named based on the nerve growth functional assays used to identify them. NTs act as paracrine or autocrine factors for cells expressing NT receptors. The receptors and their function have been studied primarily in cells of the nervous system, but are also present in the cardiovascular, endocrine, and immune systems, as well as in many neoplastic cells. The signals activated by NTs can be varied, depending on cellular stage and context, healthy or disease states, and depending on whether the specific NTs and their receptors are expressed in the relevant cells. In the healthy central and peripheral adult nervous systems, NTs drive neuronal survival, phenotype, synaptic maintenance, and function. Deficiencies of the NT/NT receptor axis are causally associated with disease onset or disease progression. Paradoxically, NTs can also drive synaptic loss and neuronal death. In the embryonic stage this activity is essential for proper developmental pruning of the nervous system, but in the adult it can be associated with neurodegenerative disease. Given their key role in neuronal survival and death, NTs and NT receptors have long been considered therapeutic targets to achieve neuroprotection. The first neuroprotective approaches consisted of enhancing neuronal survival signals using NTs. Later strategies selectively targeted receptors to induce survival signals specifically, while avoiding activation of death signals. Recently, the concept of selectively targeting receptors to reduce neuronal death signals has emerged. Here, we review the rationale of each neuroprotective strategy with respect to the complex cell biology and pharmacology of each target receptor.
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Affiliation(s)
- Horacio Uri Saragovi
- Lady Davis Institute, Montreal, QC, Canada.,Jewish General Hospital, Montreal, QC, Canada.,Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC, Canada
| | - Alba Galan
- Lady Davis Institute, Montreal, QC, Canada.,Jewish General Hospital, Montreal, QC, Canada
| | - Leonard A Levin
- Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC, Canada.,McGill University Health Centre, Montreal, QC, Canada.,Montreal Neurological Institute, Mcgill University, Montreal, QC, Canada
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Brahimi F, Maira M, Barcelona PF, Galan A, Aboulkassim T, Teske K, Rogers ML, Bertram L, Wang J, Yousefi M, Rush R, Fabian M, Cashman N, Saragovi HU. The Paradoxical Signals of Two TrkC Receptor Isoforms Supports a Rationale for Novel Therapeutic Strategies in ALS. PLoS One 2016; 11:e0162307. [PMID: 27695040 PMCID: PMC5047590 DOI: 10.1371/journal.pone.0162307] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 08/19/2016] [Indexed: 12/14/2022] Open
Abstract
Full length TrkC (TrkC-FL) is a receptor tyrosine kinase whose mRNA can be spliced to a truncated TrkC.T1 isoform lacking the kinase domain. Neurotrophin-3 (NT-3) activates TrkC-FL to maintain motor neuron health and function and TrkC.T1 to produce neurotoxic TNF-α; hence resulting in opposing pathways. In mouse and human ALS spinal cord, the reduction of miR-128 that destabilizes TrkC.T1 mRNA results in up-regulated TrkC.T1 and TNF-α in astrocytes. We exploited conformational differences to develop an agonistic mAb 2B7 that selectively activates TrkC-FL, to circumvent TrkC.T1 activation. In mouse ALS, 2B7 activates spinal cord TrkC-FL signals, improves spinal cord motor neuron phenotype and function, and significantly prolongs life-span. Our results elucidate biological paradoxes of receptor isoforms and their role in disease progression, validate the concept of selectively targeting conformational epitopes in naturally occurring isoforms, and may guide the development of pro-neuroprotective (TrkC-FL) and anti-neurotoxic (TrkC.T1) therapeutic strategies.
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Affiliation(s)
- Fouad Brahimi
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
| | - Mario Maira
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
| | - Pablo F. Barcelona
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
| | - Alba Galan
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
| | - Tahar Aboulkassim
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
| | - Katrina Teske
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
| | - Mary-Louise Rogers
- Flinders University, Department of Human Physiology, Centre for Neuroscience, Adelaide, Australia
| | - Lisa Bertram
- University of British Columbia. Brain Research Centre, Vancouver, Canada
| | - Jing Wang
- University of British Columbia. Brain Research Centre, Vancouver, Canada
| | - Masoud Yousefi
- University of British Columbia. Brain Research Centre, Vancouver, Canada
| | - Robert Rush
- Flinders University, Department of Human Physiology, Centre for Neuroscience, Adelaide, Australia
| | - Marc Fabian
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
- Department of Biochemistry. McGill University, Montréal, QC, Canada
| | - Neil Cashman
- University of British Columbia. Brain Research Centre, Vancouver, Canada
| | - H. Uri Saragovi
- Lady Davis Institute-Jewish General Hospital, Translational Center, McGill University, Montréal, QC, Canada
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC, Canada
- * E-mail:
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Kamkaew A, Burgess K. Double-targeting using a TrkC ligand conjugated to dipyrrometheneboron difluoride (BODIPY) based photodynamic therapy (PDT) agent. J Med Chem 2013; 56:7608-14. [PMID: 24063347 DOI: 10.1021/jm4012142] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A molecule 1 (IY-IY-PDT) was designed to contain a fragment (IY-IY) that targets the TrkC receptor and a photosensitizer that acts as an agent for photodynamic therapy (PDT). Molecule 1 had submicromolar photocytotoxicities to cells that were engineered to stably express TrkC (NIH3T3-TrkC) or that naturally express high levels of TrkC (SY5Y neuroblastoma lines). Control experiments showed that 1 is not cytotoxic in the dark and has significantly less photocytotoxicity toward cells that do not express TrkC (NIH3T3-WT). Other controls featuring a similar agent 2 (YI-YI-PDT), which is identical and isomeric with 1 except that the targeting region is scrambled (a YI-YI motif, see text), showed that 1 is considerably more photocytotoxic than 2 on TrkC(+) cells. Imaging live TrkC(+) cells after treatment with a fluorescent agent 1 (IY-IY-PDT) proved that 1 permeates into TrkC(+) cells and is localized in the lysosomes. This observation indirectly indicates that agent 1 enters the cells via the TrkC receptor. Consistent with this, the dose-dependent PDT effects of 1 can be competitively reduced by the natural TrkC ligand, neurotrophin NT3.
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Affiliation(s)
- Anyanee Kamkaew
- Department of Chemistry, Texas A & M University , Box 30012, College Station, Texas 77842, United States
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Small-molecule modulation of neurotrophin receptors: a strategy for the treatment of neurological disease. Nat Rev Drug Discov 2013; 12:507-25. [PMID: 23977697 DOI: 10.1038/nrd4024] [Citation(s) in RCA: 198] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Neurotrophins and their receptors modulate multiple signalling pathways to regulate neuronal survival and to maintain axonal and dendritic networks and synaptic plasticity. Neurotrophins have potential for the treatment of neurological diseases. However, their therapeutic application has been limited owing to their poor plasma stability, restricted nervous system penetration and, importantly, the pleiotropic actions that derive from their concomitant binding to multiple receptors. One strategy to overcome these limitations is to target individual neurotrophin receptors — such as tropomyosin receptor kinase A (TRKA), TRKB, TRKC, the p75 neurotrophin receptor or sortilin — with small-molecule ligands. Such small molecules might also modulate various aspects of these signalling pathways in ways that are distinct from the programmes triggered by native neurotrophins. By departing from conventional neurotrophin signalling, these ligands might provide novel therapeutic options for a broad range of neurological indications.
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Cazorla M, Arrang JM, Prémont J. Pharmacological characterization of six trkB antibodies reveals a novel class of functional agents for the study of the BDNF receptor. Br J Pharmacol 2011; 162:947-60. [PMID: 21039416 DOI: 10.1111/j.1476-5381.2010.01094.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND AND PURPOSE By interacting with trkB receptors, brain-derived neurotrophic factor (BDNF) triggers various signalling pathways responsible for neurone survival, differentiation and modulation of synaptic transmission. Numerous reports have implicated BDNF and trkB in the pathogenesis of various central nervous system affections and in cancer, thus representing trkB as a promising therapeutic target. In this study, we used an antibody-based approach to search for trkB-selective functional reagents. EXPERIMENTAL APPROACH Six commercially available polyclonal and monoclonal antibodies were tested on recombinant and native, human and rodent trkB receptors. Functional and pharmacological characterization was performed using a modified version of the KIRA-elisa method and radioligand binding studies. Western blot analyses and neurite outgrowth assays were carried out to determine the specificity and selectivity of antibody effects. The survival properties of one antibody were further assessed on cultured neurones in a serum-deprived paradigm. KEY RESULTS The functional trkB-selective antibodies showed distinct pharmacological profiles, ranging from partial agonists to antagonists, acting on trkB receptors through allosteric modulations. The same diversity of effects was observed on the mitogen-activated protein kinase signalling pathway downstream of trkB and on the subsequent neurite outgrowth. One antibody with partial agonist activity demonstrated cell survival properties by activating the Akt pathway. Finally, these antibodies were functionally validated as true trkB-selective ligands because they failed activating trkA or trkC, and contrary to BDNF, none of them bind to p75(NTR). CONCLUSIONS AND IMPLICATIONS These trkB-selective antibodies represent a novel class of pharmacological tools to explore the pathophysiological roles of trkB and its potential therapeutic relevance for the treatment of various disorders.
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Affiliation(s)
- M Cazorla
- Laboratory of Neurobiology & Molecular Pharmacology, Centre de Psychiatrie et Neurosciences, UMR-894 INSERM/Université Paris Descartes, 2Ter rue d'Alésia, Paris, France.
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Bai Y, Shi Z, Zhuo Y, Liu J, Malakhov A, Ko E, Burgess K, Schaefer H, Esteban PF, Tessarollo L, Saragovi HU. In glaucoma the upregulated truncated TrkC.T1 receptor isoform in glia causes increased TNF-alpha production, leading to retinal ganglion cell death. Invest Ophthalmol Vis Sci 2010; 51:6639-51. [PMID: 20574020 DOI: 10.1167/iovs.10-5431] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
PURPOSE Glaucoma is a distinct neuropathy characterized by the chronic and progressive death of retinal ganglion cells (RGCs). The etiology of RGC death remains unknown. Risk factors for glaucomatous RGC death are elevated intraocular pressure and glial production of tumor necrosis factor-alpha (TNF-α). Previously, the authors showed that glaucoma causes a rapid upregulation of a neurotrophin receptor truncated isoform lacking the kinase domain, TrkC.T1, in retina. Here they examined the biological role of TrkC.T1 during glaucoma progression. METHODS Rat and mouse models of chronic ocular hypertension were used. Immunofluorescence Western blot analysis and in situ mRNA hybridization were used to identify cells upregulating TrkC.T1. A genetic model of engineered mice lacking TrkC.T1 (TrkC.T1(-/-)) was used to validate a role for this receptor in glaucoma. Pharmacologic studies were conducted to evaluate intravitreal delivery of agonists or antagonists of TrkC.T1, compared with controls, during glaucoma. Surviving RGCs were quantified by retrograde-labeling techniques. Production of neurotoxic TNF-α and α2 macroglobulin were quantified. RESULTS TrkC.T1 was upregulated in retinal glia, with a pattern similar to that of TNF-α. TrkC.T1(-/-) mice had normal retinas. However, during experimental glaucoma, TrkC.T1(-/-) mice had lower rates of RGC death and produced less TNF-α than wild-type littermates. In rats with glaucoma, the pharmacologic use of TrkC antagonists delayed RGC death and reduced the production of retinal TNF-α. CONCLUSIONS TrkC.T1 is implicated in glaucomatous RGC death through the control of glial TNF-α production. Overall, the data point to a paracrine mechanism whereby elevated intraocular pressure upregulated glial TrkC.T1 expression in glia; TrkC.T1 controlled glial TNF-α production, and TNF-α caused RGC death.
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Affiliation(s)
- Yujing Bai
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
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Brahimi F, Liu J, Malakhov A, Chowdhury S, Purisima EO, Ivanisevic L, Caron A, Burgess K, Saragovi HU. A monovalent agonist of TrkA tyrosine kinase receptors can be converted into a bivalent antagonist. Biochim Biophys Acta Gen Subj 2010; 1800:1018-26. [PMID: 20600627 DOI: 10.1016/j.bbagen.2010.06.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 05/28/2010] [Accepted: 06/11/2010] [Indexed: 01/18/2023]
Abstract
BACKGROUND Receptor tyrosine kinases (RTK) act through dimerization. Previously it was thought that only bivalent ligands could be agonistic, whereas monovalent ligands should be antagonistic. This notion changed after the demonstration that monovalent ligands can be agonistic, including our report of a small molecule monovalent ligand "D3" that is a partial agonist of the NGF receptor TrkA. A bivalent "D3-linker-D3" was expected to increase agonism. METHODS Dimeric analogs were synthesized and tested in binding, biochemical, and biological assays. RESULTS One analog, 1-ss, binds TrkA with higher affinity than D3 and induces or stabilizes receptor dimers. However, 1-ss exhibited antagonistic activity, through two mechanisms. One mechanism is that 1-ss blocks NGF binding, unlike D3 which is non-competitive. Inhibition of NGF binding may be due to the linker of 1-ss filling the inter-receptor space that NGF traverses before docking. In a second mechanism, 1-ss acts as a pure antagonist, inhibiting NGF-independent TrkA activity in cells over-expressing receptors. Inhibition is likely due to 1-ss "freezing" the TrkA dimer in the inactive state. CONCLUSIONS Dimerization of an RTK can result in antagonism, through two independent mechanisms. GENERAL SIGNIFICANCE we report a small molecule monovalent agonist being converted to a bivalent antagonist.
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Affiliation(s)
- Fouad Brahimi
- Lady Davis Institute-Jewish General Hospital, Pharmacology and Therapeutics, Oncology and the Cancer Center. McGill University, Canada
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