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Benson CA, Olson KL, Patwa S, Kauer SD, King JF, Waxman SG, Tan AM. Conditional Astrocyte Rac1KO Attenuates Hyperreflexia after Spinal Cord Injury. J Neurosci 2024; 44:e1670222023. [PMID: 37963762 PMCID: PMC10851682 DOI: 10.1523/jneurosci.1670-22.2023] [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: 09/01/2022] [Revised: 08/24/2023] [Accepted: 09/19/2023] [Indexed: 11/16/2023] Open
Abstract
Spasticity is a hyperexcitability disorder that adversely impacts functional recovery and rehabilitative efforts after spinal cord injury (SCI). The loss of evoked rate-dependent depression (RDD) of the monosynaptic H-reflex is indicative of hyperreflexia, a physiological sign of spasticity. Given the intimate relationship between astrocytes and neurons, that is, the tripartite synapse, we hypothesized that astrocytes might have a significant role in post-injury hyperreflexia and plasticity of neighboring neuronal synaptic dendritic spines. Here, we investigated the effect of selective Rac1KO in astrocytes (i.e., adult male and female mice, transgenic cre-flox system) on SCI-induced spasticity. Three weeks after a mild contusion SCI, control Rac1wt animals displayed a loss of H-reflex RDD, that is, hyperreflexia. In contrast, transgenic animals with astrocytic Rac1KO demonstrated near-normal H-reflex RDD similar to pre-injury levels. Reduced hyperreflexia in astrocytic Rac1KO animals was accompanied by a loss of thin-shaped dendritic spine density on α-motor neurons in the ventral horn. In SCI-Rac1wt animals, as expected, we observed the development of dendritic spine dysgenesis on α-motor neurons associated with spasticity. As compared with WT animals, SCI animals with astrocytic Rac1KO expressed increased levels of the glial-specific glutamate transporter, glutamate transporter-1 in the ventral spinal cord, potentially enhancing glutamate clearance from the synaptic cleft and reducing hyperreflexia in astrocytic Rac1KO animals. Taken together, our findings show for the first time that Rac1 activity in astrocytes can contribute to hyperreflexia underlying spasticity following SCI. These results reveal an opportunity to target cell-specific molecular regulators of H-reflex excitability to manage spasticity after SCI.Significance Statement Spinal cord injury leads to stretch reflex hyperexcitability, which underlies the clinical symptom of spasticity. This study shows for the first time that astrocytic Rac1 contributes to the development of hyperreflexia after SCI. Specifically, astrocytic Rac1KO reduced SCI-related H-reflex hyperexcitability, decreased dendritic spine dysgenesis on α-motor neurons, and elevated the expression of the astrocytic glutamate transporter-1 (GLT-1). Overall, this study supports a distinct role for astrocytic Rac1 signaling within the spinal reflex circuit and the development of SCI-related spasticity.
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Affiliation(s)
- Curtis A Benson
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Kai-Lan Olson
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Siraj Patwa
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Sierra D Kauer
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Jared F King
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Stephen G Waxman
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Andrew M Tan
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510,
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
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Benson CA, King JF, Kauer SD, Waxman SG, Tan AM. Increased astrocytic GLT-1 expression in tripartite synapses is associated with SCI-induced hyperreflexia. J Neurophysiol 2023; 130:1358-1366. [PMID: 37877184 DOI: 10.1152/jn.00234.2023] [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: 06/12/2023] [Revised: 10/06/2023] [Accepted: 10/22/2023] [Indexed: 10/26/2023] Open
Abstract
Spasticity is a chronic neurological complication associated with spinal cord injury (SCI), characterized by increased muscle tone and stiffness. A physiological sign of spasticity is hyperreflexia, evident by the loss of evoked rate-dependent depression (RDD) in the H-reflex. Although previous work has shown that SCI-induced astrogliosis contributes to hyperexcitability disorders, including neuropathic pain and spasticity, it is unclear how reactive astrocytes can modulate synaptic transmission within the injured spinal cord. To study astrocytes' role in post-SCI hyperreflexia, we examined glutamate transporter-1 (GLT-1) and postsynaptic density protein 95 (PSD-95) proteins in astrocytes and neurons, respectively, within the ventral horn (lamina IX) below the level of injury (spinal segment L4-5). The close juxtaposition of GLT-1 and PSD-95 markers is a molecular correlate of tripartite synapses and is thought to be a key element in the astrocyte-induced plasticity of neuronal synapses. Our study compared animals with and without SCI-induced hyperreflexia and spasticity and investigated potential synaptic abnormalities associated with astrocyte involvement. As expected, 4 wk after SCI, we observed a loss in evoked H-reflex RDD in hindlimb electromyogram recordings, i.e., hyperreflexia, in contrast to uninjured sham. Importantly, our main findings show a significant increase in the presence of GLT-1-PSD-95 tripartite synapses in the ventral spinal cord motor regions of animals exhibiting SCI-induced hyperreflexia. Taken together, our study suggests the involvement of astrocyte-neuron synaptic complexes in the plasticity-driven progression of chronic spasticity.NEW & NOTEWORTHY The role of astrocytes in H-reflex hyperexcitability following SCI remains understudied. Our findings establish a relationship between GLT-1 expression, its proximity to neuronal PSD-95 in the spinal cord ventral horn, and the loss of H-reflex RDD, i.e., hyperreflexia. Our findings provide a new perspective on synaptic alterations and the development of SCI-related spasticity.
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Affiliation(s)
- Curtis A Benson
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut, United States
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut, United States
| | - Jared F King
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut, United States
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut, United States
| | - Sierra D Kauer
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut, United States
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut, United States
| | - Stephen G Waxman
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut, United States
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut, United States
| | - Andrew M Tan
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut, United States
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut, United States
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Alexander MS, Velinov M. DOCK3-Associated Neurodevelopmental Disorder-Clinical Features and Molecular Basis. Genes (Basel) 2023; 14:1940. [PMID: 37895289 PMCID: PMC10606569 DOI: 10.3390/genes14101940] [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: 09/11/2023] [Revised: 10/09/2023] [Accepted: 10/12/2023] [Indexed: 10/29/2023] Open
Abstract
The protein product of DOCK3 is highly expressed in neurons and has a role in cell adhesion and neuronal outgrowth through its interaction with the actin cytoskeleton and key cell signaling molecules. The DOCK3 protein is essential for normal cell growth and migration. Biallelic variants in DOCK3 associated with complete or partial loss of function of the gene were recently reported in six patients with intellectual disability and muscle hypotonia. Only one of the reported patients had congenital malformations outside of the CNS. Further studies are necessary to better determine the prevalence of DOCK3-associated neurodevelopmental disorders and the frequency of non-CNS clinical manifestations in these patients. Since deficiency of the DOCK3 protein product is now an established pathway of this neurodevelopmental condition, supplementing the deficient gene product using a gene therapy approach may be an efficient treatment strategy.
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Affiliation(s)
- Matthew S. Alexander
- Department of Pediatrics, Division of Neurology, University of Alabama at Birmingham and Children’s of Alabama, Birmingham, AL 35294, USA;
- UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA
- Department of Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
- UAB Civitan International Research Center (CIRC), University of Alabama at Birmingham, Birmingham, AL 35233, USA
- UAB Center for Neurodegeneration and Experimental Therapeutics (CNET), University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Milen Velinov
- Department of Pediatrics, Division of Genetics, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ 08901, USA
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Ji B, Wojtaś B, Skup M. Molecular Identification of Pro-Excitogenic Receptor and Channel Phenotypes of the Deafferented Lumbar Motoneurons in the Early Phase after SCT in Rats. Int J Mol Sci 2022; 23:ijms231911133. [PMID: 36232433 PMCID: PMC9569670 DOI: 10.3390/ijms231911133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 09/19/2022] [Accepted: 09/19/2022] [Indexed: 02/07/2023] Open
Abstract
Spasticity impacts the quality of life of patients suffering spinal cord injury and impedes the recovery of locomotion. At the cellular level, spasticity is considered to be primarily caused by the hyperexcitability of spinal α-motoneurons (MNs) within the spinal stretch reflex circuit. Here, we hypothesized that after a complete spinal cord transection in rats, fast adaptive molecular responses of lumbar MNs develop in return for the loss of inputs. We assumed that early loss of glutamatergic afferents changes the expression of glutamatergic AMPA and NMDA receptor subunits, which may be the forerunners of the developing spasticity of hindlimb muscles. To better understand its molecular underpinnings, concomitant expression of GABA and Glycinergic receptors and serotoninergic and noradrenergic receptors, which regulate the persistent inward currents crucial for sustained discharges in MNs, were examined together with voltage-gated ion channels and cation-chloride cotransporters. Using quantitative real-time PCR, we showed in the tracer-identified MNs innervating extensor and flexor muscles of the ankle joint multiple increases in transcripts coding for AMPAR and 5-HTR subunits, along with a profound decrease in GABAAR, GlyR subunits, and KCC2. Our study demonstrated that both MNs groups similarly adapt to a more excitable state, which may increase the occurrence of extensor and flexor muscle spasms.
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Affiliation(s)
- Benjun Ji
- Group of Restorative Neurobiology, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland
| | - Bartosz Wojtaś
- Laboratory of Sequencing, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland
| | - Małgorzata Skup
- Group of Restorative Neurobiology, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland
- Correspondence:
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Adler M, Pellett S, Sharma SK, Lebeda FJ, Dembek ZF, Mahan MA. Preclinical Evidence for the Role of Botulinum Neurotoxin A (BoNT/A) in the Treatment of Peripheral Nerve Injury. Microorganisms 2022; 10:microorganisms10050886. [PMID: 35630331 PMCID: PMC9148055 DOI: 10.3390/microorganisms10050886] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 03/29/2022] [Accepted: 04/17/2022] [Indexed: 01/27/2023] Open
Abstract
Traumatic peripheral nerve injuries tend to be more common in younger, working age populations and can lead to long-lasting disability. Peripheral nerves have an impressive capacity to regenerate; however, successful recovery after injury depends on a number of factors including the mechanism and severity of the trauma, the distance from injury to the reinnervation target, connective tissue sheath integrity, and delay between injury and treatment. Even though modern surgical procedures have greatly improved the success rate, many peripheral nerve injuries still culminate in persistent neuropathic pain and incomplete functional recovery. Recent studies in animals suggest that botulinum neurotoxin A (BoNT/A) can accelerate nerve regeneration and improve functional recovery after injury to peripheral nerves. Possible mechanisms of BoNT/A action include activation or proliferation of support cells (Schwann cells, mast cells, and macrophages), increased angiogenesis, and improvement of blood flow to regenerating nerves.
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Affiliation(s)
- Michael Adler
- Neuroscience Department, Medical Toxicology Division, U.S. Army Medical Research Institute of Chemical Defense, 8350 Ricketts Point Rd., Aberdeen Proving Ground, MD 21010, USA
- Correspondence: ; Tel.: +1-410-436-1913
| | - Sabine Pellett
- Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Drive, Madison, WI 53706, USA;
| | - Shashi K. Sharma
- Division of Microbiology, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA;
| | - Frank J. Lebeda
- Biotechnology, Protein Bioinformatics, Zanvyl Krieger School of Arts & Sciences, Johns Hopkins University, Advanced Academic Programs, 9601 Medical Center Drive, Rockville, MD 20850, USA;
| | - Zygmunt F. Dembek
- Department of Military and Emergency Medicine, Uniformed Services University of Health Sciences, 3154 Jones Bridge Rd., Bethesda, MD 20814, USA;
| | - Mark A. Mahan
- Department of Neurosurgery, Clinical Neurosciences, University of Utah, 175 N Medical Drive East, Salt Lake City, UT 84132, USA;
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