Neuroscience
Abstract
Painful diabetic neuropathy (PDN) is an intractable complication of diabetes that affects 25% of patients. PDN is characterized by neuropathic pain and small-fiber degeneration, accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability and loss of their axons within the skin. The molecular mechanisms underlying DRG nociceptor hyperexcitability and small-fiber degeneration in PDN are unknown. We hypothesize that chemokine CXCL12/CXCR4 signaling is central to this mechanism, as we have shown that CXCL12/CXCR4 signaling is necessary for the development of mechanical allodynia, a pain hypersensitivity behavior common in PDN. Focusing on DRG neurons expressing the sodium channel Nav1.8, we applied transgenic, electrophysiological, imaging, and chemogenetic techniques to test this hypothesis. In the high-fat diet mouse model of PDN, we were able to prevent and reverse mechanical allodynia and small-fiber degeneration by limiting CXCR4 signaling or neuronal excitability. This study reveals that excitatory CXCR4/CXCL12 signaling in Nav1.8-positive DRG neurons plays a critical role in the pathogenesis of mechanical allodynia and small-fiber degeneration in a mouse model of PDN. Hence, we propose that targeting CXCR4-mediated DRG nociceptor hyperexcitability is a promising therapeutic approach for disease-modifying treatments for this currently intractable and widespread affliction.
Authors
Nirupa D. Jayaraj, Bula J. Bhattacharyya, Abdelhak A. Belmadani, Dongjun Ren, Craig A. Rathwell, Sandra Hackelberg, Brittany E. Hopkins, Herschel R. Gupta, Richard J. Miller, Daniela M. Menichella
Abstract
Spinocerebellar ataxia type 1 (SCA1) is an adult-onset neurodegenerative disease caused by a polyglutamine expansion in the protein ATXN1, which is involved in transcriptional regulation. Although symptoms appear relatively late in life, primarily from cerebellar dysfunction, pathogenesis begins early, with brain-wide transcriptional changes detectable as early as a week after birth in SCA1 knock-in mice. Given the importance of this postnatal period for cerebellar development, we asked whether this region might be developmentally altered by mutant ATXN1. We found that expanded ATXN1 stimulates the proliferation of postnatal cerebellar stem cells in SCA1 mice. These hyper-proliferating stem cells tended to differentiate into GABAergic inhibitory interneurons rather than astrocytes; this significantly increased the GABAergic inhibitory interneuron synaptic connections, disrupting cerebellar Purkinje cell function in a non-cell autonomous manner. We confirmed the increased basket cell-Purkinje cell connectivity in human SCA1 patients. Mutant ATXN1 thus alters the neural circuitry of the developing cerebellum, setting the stage for the later vulnerability of Purkinje cells to SCA1. We propose that other late-onset degenerative diseases may also be rooted in subtle developmental derailments.
Authors
Chandrakanth Reddy Edamakanti, Jeehaeh Do, Alessandro Didonna, Marco Martina, Puneet Opal
Abstract
Increasing evidence suggests that synapse dysfunctions are a major determinant of several neurodevelopmental and neurodegenerative diseases. Here we identify protein kinase N1 (PKN1) as a novel key player in fine-tuning the balance between axonal outgrowth and presynaptic differentiation in the parallel fiber (PF)-forming cerebellar granule cells (Cgc). Postnatal Pkn1–/– animals showed a defective PF-Purkinje cell (PC) synapse formation. In vitro, Pkn1–/– Cgc exhibited deregulated axonal outgrowth, elevated AKT phosphorylation and higher levels of neuronal differentiation-2 (NeuroD2), a transcription factor preventing presynaptic maturation. Concomitantly Pkn1–/– Cgc had a reduced density of presynaptic sites. By inhibiting AKT with MK-2206 and siRNA-mediated knockdown, we found that AKT hyperactivation is responsible for the elongated axons, higher NeuroD2 levels and the reduced density of presynaptic specifications in Pkn1–/– Cgc. In line with our in vitro data, Pkn1–/– mice showed AKT hyperactivation, elevated NeuroD2 levels and reduced expression of PF-PC synaptic markers during stages of PF maturation in vivo. The long-term effect of Pkn1 knockout was further seen in cerebellar atrophy and mild ataxia. In summary, our results demonstrate that PKN1 functions as a developmentally active gatekeeper of AKT activity, thereby fine-tuning axonal outgrowth and presynaptic differentiation of Cgc and subsequently the correct PF-PC synapse formation.
Authors
Stephanie zur Nedden, Rafaela Eith, Christoph Schwarzer, Lucia Zanetti, Hartwig Seitter, Friedrich Fresser, Alexandra Koschak, Angus J.M. Cameron, Peter J. Parker, Gottfried Baier, Gabriele Baier-Bitterlich
Abstract
Transient vanilloid potential 1 (TRPV1) agonists are emerging as highly efficacious non-opioid analgesics in preclinical studies. These drugs selectively lesion TRPV1+ primary sensory afferents, which are responsible for the transmission of many noxious stimulus modalities. Resiniferatoxin (RTX) is a very potent and selective TRPV1 agonist and is a promising candidate for treating many types of pain. Recent work establishing intrathecal application of RTX for the treatment of pain resulting from advanced cancer has demonstrated profound analgesia in client-owned dogs with osteosarcoma. The present study uses transcriptomics and histochemistry to examine the molecular mechanism of RTX action in rats, in clinical canine subjects, and in one human subject with advanced cancer treated for pain using intrathecal RTX. In all three species we observe a strong analgesic action, yet this was accompanied by limited transcriptional alterations at the level of the DRG. Functional and neuroanatomical studies demonstrated that intrathecal RTX largely spares susceptible neuronal perikarya, which remain active peripherally, but unable to transmit signals to the spinal cord. The results demonstrate that central chemo-axotomy of the TRPV1+ afferents underlies RTX analgesia and refine the neurobiology underlying effective clinical use of TRPV1 agonists for pain control.
Authors
Matthew R. Sapio, John K. Neubert, Danielle M. LaPaglia, Dragan Maric, Jason M. Keller, Stephen J. Raithel, Eric L. Rohrs, Ethan M. Anderson, John A. Butman, Robert M. Caudle, Dorothy C. Brown, John D. Heiss, Andrew J. Mannes, Michael J. Iadarola
Abstract
Tuberous sclerosis complex (TSC) is a dominantly inherited disease, caused by hyperactivation of the mTORC1 pathway and characterized by the development of hamartomas and benign tumors, also in the brain. Among the neurological manifestations associated with TSC, the tumor progression of static subependymal nodules (SENs) into subependymal giant cell astrocytomas (SEGAs) is one of the major causes of morbidity and shortened life expectancy. To date, mouse modeling has failed in reproducing these two lesions. Here we report that simultaneous hyperactivation of mTORC1 and Akt pathways by codeletion of Tsc1 and Pten, selectively in postnatal neural stem cells (pNSCs), is required for the formation of bona fide SENs and SEGAs. Notably, both lesions closely recapitulate the pathognomonic morphological and molecular features of the corresponding human abnormalities. The establishment of long-term expanding pNSC lines from mouse SENs and SEGAs made possible the identification of mTORC2 as one of the mediators conferring tumorigenic potential to SEGA pNSCs. Of note, in spite of concurrent Akt hyperactivation in mouse brain lesions, single mTOR inhibition by rapamycin was sufficient to strongly impair mouse SEGA growth. This study provides the first evidence that, concomitant with mTORC1 hyperactivation, sustained activation of Akt and mTORC2 in pNSCs is a mandatory step for the induction of SENs and SEGAs and, at the same time, makes available an unprecedented NSC-based in vivo/in vitro model to be exploited for identifying actionable targets in TSC.
Authors
Paola Zordan, Manuela Cominelli, Federica Cascino, Elisa Tratta, Pietro L. Poliani, Rossella Galli
Abstract
The nonerythrocytic α-spectrin-1 (SPTAN1) gene encodes the cytoskeletal protein αII spectrin. Mutations in SPTAN1 cause early infantile epileptic encephalopathy type 5 (EIEE5); however, the role of αII spectrin in neurodevelopment and EIEE5 pathogenesis is unknown. Prior work suggests that αII spectrin is absent in the axon initial segment (AIS) and contributes to a diffusion barrier in the distal axon. Here, we have shown that αII spectrin is expressed ubiquitously in rodent and human somatodendritic and axonal domains. CRISPR-mediated deletion of Sptan1 in embryonic rat forebrain by in utero electroporation caused altered dendritic and axonal development, loss of the AIS, and decreased inhibitory innervation. Overexpression of human EIEE5 mutant SPTAN1 in embryonic rat forebrain and mouse hippocampal neurons led to similar developmental defects that were also observed in EIEE5 patient-derived neurons. Additionally, patient-derived neurons displayed aggregation of spectrin complexes. Taken together, these findings implicate αII spectrin in critical aspects of dendritic and axonal development and synaptogenesis, and support a dominant-negative mechanism of SPTAN1 mutations in EIEE5.
Authors
Yu Wang, Tuo Ji, Andrew D. Nelson, Katarzyna Glanowska, Geoffrey G. Murphy, Paul M. Jenkins, Jack M. Parent
Abstract
Parkinson’s disease is characterized by the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc). DA neurons in the ventral tegmental area are more resistant to this degeneration than those in the SNc, though the mechanisms for selective resistance or vulnerability remain poorly understood. A key to elucidating these processes may lie within the subset of DA neurons that corelease glutamate and express the vesicular glutamate transporter VGLUT2. Here, we addressed the potential relationship between VGLUT expression and DA neuronal vulnerability by overexpressing VGLUT in DA neurons of flies and mice. In Drosophila, VGLUT overexpression led to loss of select DA neuron populations. Similarly, expression of VGLUT2 specifically in murine SNc DA neurons led to neuronal loss and Parkinsonian behaviors. Other neuronal cell types showed no such sensitivity, suggesting that DA neurons are distinctively vulnerable to VGLUT2 expression. Additionally, most DA neurons expressed VGLUT2 during development, and coexpression of VGLUT2 with DA markers increased following injury in the adult. Finally, conditional deletion of VGLUT2 made DA neurons more susceptible to Parkinsonian neurotoxins. These data suggest that the balance of VGLUT2 expression is a crucial determinant of DA neuron survival. Ultimately, manipulation of this VGLUT2-dependent process may represent an avenue for therapeutic development.
Authors
Thomas Steinkellner, Vivien Zell, Zachary J. Farino, Mark S. Sonders, Michael Villeneuve, Robin J. Freyberg, Serge Przedborski, Wei Lu, Zachary Freyberg, Thomas S. Hnasko
Abstract
Dravet syndrome (DS) is a severe childhood-onset epilepsy commonly due to mutations of the sodium channel gene SCN1A. DS patients have a high risk of sudden unexplained death in epilepsy (SUDEP), believed to be due to cardiac mechanisms. Here we show that DS patients have peri-ictal respiratory dysfunction. One patient who had severe and prolonged postictal hypoventilation later died of SUDEP. Mice with an Scn1aR1407X/+ loss of function mutation died after spontaneous and heat-induced seizures due to central apnea followed by progressive bradycardia. Death could be prevented with mechanical ventilation after seizures induced by hyperthermia or maximal electroshock. Muscarinic receptor antagonists did not prevent bradycardia or death when given at doses selective for peripheral parasympathetic blockade, whereas apnea was prevented at doses known to be high enough to cross the blood brain barrier. Anoxia causes bradycardia due to a direct effect on the heart. We conclude that SUDEP in DS may result in some cases from primary central apnea, which can cause bradycardia presumably via an effect of hypoxemia on cardiac muscle.
Authors
YuJaung Kim, Eduardo Bravo, Caitlin K. Thirnbeck, Lori A. Smith-Mellecker, Se Hee Kim, Brian K. Gehlbach, Linda C. Laux, Douglas R. Nordli Jr., George B. Richerson
Abstract
Macrophages are a source of both proinflammatory and restorative functions in damaged tissue through complex dynamic phenotypic changes. Here, we sought to determine whether monocyte-derived macrophages (MDMs) contribute to recovery after acute sterile brain injury. By profiling the transcriptional dynamics of MDMs in the murine brain after experimental intracerebral hemorrhage (ICH), we found robust phenotypic changes in the infiltrating MDMs over time and demonstrated that MDMs are essential for optimal hematoma clearance and neurological recovery. Next, we identified the mechanism by which the engulfment of erythrocytes with exposed phosphatidylserine directly modulated the phenotype of both murine and human MDMs. In mice, loss of receptor tyrosine kinases AXL and MERTK reduced efferocytosis of eryptotic erythrocytes and hematoma clearance, worsened neurological recovery, exacerbated iron deposition, and decreased alternative activation of macrophages after ICH. Patients with higher circulating soluble AXL had poor 1-year outcomes after ICH onset, suggesting that therapeutically augmenting efferocytosis may improve functional outcomes by both reducing tissue injury and promoting the development of reparative macrophage responses. Thus, our results identify the efferocytosis of eryptotic erythrocytes through AXL/MERTK as a critical mechanism modulating macrophage phenotype and contributing to recovery from ICH.
Authors
Che-Feng Chang, Brittany A. Goods, Michael H. Askenase, Matthew D. Hammond, Stephen C. Renfroe, Arthur F. Steinschneider, Margaret J. Landreneau, Youxi Ai, Hannah E. Beatty, Luís Henrique Angenendt da Costa, Matthias Mack, Kevin N. Sheth, David M. Greer, Anita Huttner, Daniel Coman, Fahmeed Hyder, Sourav Ghosh, Carla V. Rothlin, J. Christopher Love, Lauren H. Sansing
Abstract
The underlying cellular mechanisms of catatonia, an executive “psychomotor” syndrome that is observed across neuropsychiatric diseases, have remained obscure. In humans and mice, reduced expression of the structural myelin protein CNP is associated with catatonic signs in an age-dependent manner, pointing to the involvement of myelin-producing oligodendrocytes. Here, we showed that the underlying cause of catatonic signs is the low-grade inflammation of white matter tracts, which marks a final common pathway in Cnp-deficient and other mutant mice with minor myelin abnormalities. The inhibitor of CSF1 receptor kinase signaling, PLX5622, depleted microglia and alleviated the catatonic symptoms of Cnp mutants. Thus, microglia and low-grade inflammation of myelinated tracts emerged as the trigger of a previously unexplained mental condition. We observed a very high (25%) prevalence of individuals with catatonic signs in a deeply phenotyped schizophrenia sample (n = 1095). Additionally, we found the loss-of-function allele of a myelin-specific gene (CNP rs2070106-AA) associated with catatonia in 2 independent schizophrenia cohorts and also associated with white matter hyperintensities in a general population sample. Since the catatonic syndrome is likely a surrogate marker for other executive function defects, we suggest that microglia-directed therapies may be considered in psychiatric disorders associated with myelin abnormalities.
Authors
Hana Janova, Sahab Arinrad, Evan Balmuth, Marina Mitjans, Johannes Hertel, Mohamad Habes, Robert A. Bittner, Hong Pan, Sandra Goebbels, Martin Begemann, Ulrike C. Gerwig, Sönke Langner, Hauke B. Werner, Sarah Kittel-Schneider, Georg Homuth, Christos Davatzikos, Henry Völzke, Brian L. West, Andreas Reif, Hans Jörgen Grabe, Susann Boretius, Hannelore Ehrenreich, Klaus-Armin Nave
Copyright © 2018 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)