Neuroscience
Abstract
Local anesthetics (LAs) block the generation and propagation of action potentials by interacting with specific sites of voltage-gated Na+ channels. LAs can also excite sensory neurons and be neurotoxic through mechanisms that are as yet undefined. Nonspecific cation channels of the transient receptor potential (TRP) channel family that are predominantly expressed by nociceptive sensory neurons render these neurons sensitive to a variety of insults. Here we demonstrated that the LA lidocaine activated TRP channel family receptors TRPV1 and, to a lesser extent, TRPA1 in rodent dorsal root ganglion sensory neurons as well as in HEK293t cells expressing TRPV1 or TRPA1. Lidocaine also induced a TRPV1-dependent release of calcitonin gene–related peptide (CGRP) from isolated skin and peripheral nerve. Lidocaine sensitivity of TRPV1 required segments of the putative vanilloid-binding domain within and adjacent to transmembrane domain 3, was diminished under phosphatidylinositol 4,5-bisphosphate depletion, and was abrogated by a point mutation at residue R701 in the proximal C-terminal TRP domain. These data identify TRPV1 and TRPA1 as putative key elements of LA-induced nociceptor excitation. This effect is sufficient to release CGRP, a key component of neurogenic inflammation, and warrants investigation into the role of TRPV1 and TRPA1 in LA-induced neurotoxicity.
Authors
Andreas Leffler, Michael J. Fischer, Dietlinde Rehner, Stephanie Kienel, Katrin Kistner, Susanne K. Sauer, Narender R. Gavva, Peter W. Reeh, Carla Nau
Abstract
Altered degradation of α-synuclein (α-syn) has been implicated in the pathogenesis of Parkinson disease (PD). We have shown that α-syn can be degraded via chaperone-mediated autophagy (CMA), a selective lysosomal mechanism for degradation of cytosolic proteins. Pathogenic mutants of α-syn block lysosomal translocation, impairing their own degradation along with that of other CMA substrates. While pathogenic α-syn mutations are rare, α-syn undergoes posttranslational modifications, which may underlie its accumulation in cytosolic aggregates in most forms of PD. Using mouse ventral medial neuron cultures, SH-SY5Y cells in culture, and isolated mouse lysosomes, we have found that most of these posttranslational modifications of α-syn impair degradation of this protein by CMA but do not affect degradation of other substrates. Dopamine-modified α-syn, however, is not only poorly degraded by CMA but also blocks degradation of other substrates by this pathway. As blockage of CMA increases cellular vulnerability to stressors, we propose that dopamine-induced autophagic inhibition could explain the selective degeneration of PD dopaminergic neurons.
Authors
Marta Martinez-Vicente, Zsolt Talloczy, Susmita Kaushik, Ashish C. Massey, Joseph Mazzulli, Eugene V. Mosharov, Roberto Hodara, Ross Fredenburg, Du-Chu Wu, Antonia Follenzi, William Dauer, Serge Przedborski, Harry Ischiropoulos, Peter T. Lansbury, David Sulzer, Ana Maria Cuervo
Abstract
Astrogliosis is a pathological hallmark of the epileptic brain. The identification of mechanisms that link astrogliosis to neuronal dysfunction in epilepsy may provide new avenues for therapeutic intervention. Here we show that astrocyte-expressed adenosine kinase (ADK), a key negative regulator of the brain inhibitory molecule adenosine, is a potential predictor and modulator of epileptogenesis. In a mouse model of focal epileptogenesis, in which astrogliosis is restricted to the CA3 region of the hippocampus, we demonstrate that upregulation of ADK and spontaneous focal electroencephalographic seizures were both restricted to the affected CA3. Furthermore, spontaneous seizures in CA3 were mimicked in transgenic mice by overexpression of ADK in this brain region, implying that overexpression of ADK without astrogliosis is sufficient to cause seizures. Conversely, after pharmacological induction of an otherwise epileptogenesis-precipitating acute brain injury, transgenic mice with reduced forebrain ADK were resistant to subsequent epileptogenesis. Likewise, ADK-deficient ES cell–derived brain implants suppressed astrogliosis, upregulation of ADK, and spontaneous seizures in wild-type mice when implanted after the epileptogenesis-precipitating brain injury. Our findings suggest that astrocyte-based ADK provides a critical link between astrogliosis and neuronal dysfunction in epilepsy.
Authors
Tianfu Li, Gaoying Ren, Theresa Lusardi, Andrew Wilz, Jing Q. Lan, Takuji Iwasato, Shigeyoshi Itohara, Roger P. Simon, Detlev Boison
Abstract
Recent epidemiological evidence suggests that some antihypertensive medications may reduce the risk for Alzheimer disease (AD). We screened 55 clinically prescribed antihypertensive medications for AD-modifying activity using primary cortico-hippocampal neuron cultures generated from the Tg2576 AD mouse model. These agents represent all drug classes used for hypertension pharmacotherapy. We identified 7 candidate antihypertensive agents that significantly reduced AD-type β-amyloid protein (Aβ) accumulation. Through in vitro studies, we found that only 1 of the candidate drugs, valsartan, was capable of attenuating oligomerization of Aβ peptides into high-molecular-weight (HMW) oligomeric peptides, known to be involved in cognitive deterioration. We found that preventive treatment of Tg2576 mice with valsartan significantly reduced AD-type neuropathology and the content of soluble HMW extracellular oligomeric Aβ peptides in the brain. Most importantly, valsartan administration also attenuated the development of Aβ-mediated cognitive deterioration, even when delivered at a dose about 2-fold lower than that used for hypertension treatment in humans. These preclinical studies suggest that certain antihypertensive drugs may have AD-modifying activity and may protect against progressive Aβ-related memory deficits in subjects with AD or in those at high risk of developing AD.
Authors
Jun Wang, Lap Ho, Linghong Chen, Zhong Zhao, Wei Zhao, Xianjuan Qian, Nelson Humala, Ilana Seror, Sadie Bartholomew, Clive Rosendorff, Giulio Maria Pasinetti
Abstract
Glutaric acidemia type I (GA-I) is an inherited disorder of lysine and tryptophan metabolism presenting with striatal lesions anatomically and symptomatically similar to Huntington disease. Affected children commonly suffer acute brain injury in the context of a catabolic state associated with nonspecific illness. The mechanisms underlying injury and age-dependent susceptibility have been unknown, and lack of a diagnostic marker heralding brain injury has impeded intervention efforts. Using a mouse model of GA-I, we show that pathologic events began in the neuronal compartment while enhanced lysine accumulation in the immature brain allowed increased glutaric acid production resulting in age-dependent injury. Glutamate and GABA depletion correlated with brain glutaric acid accumulation and could be monitored in vivo by proton nuclear magnetic resonance (1H NMR) spectroscopy as a diagnostic marker. Blocking brain lysine uptake reduced glutaric acid levels and brain injury. These findings provide what we believe are new monitoring and treatment strategies that may translate for use in human GA-I.
Authors
William J. Zinnanti, Jelena Lazovic, Cathy Housman, Kathryn LaNoue, James P. O’Callaghan, Ian Simpson, Michael Woontner, Stephen I. Goodman, James R. Connor, Russell E. Jacobs, Keith C. Cheng
Abstract
The slow-channel myasthenic syndrome (SCS) is a hereditary disorder of the acetylcholine receptor (AChR) of the neuromuscular junction (NMJ) that leads to prolonged AChR channel opening, Ca2+ overload, and degeneration of the NMJ. We used an SCS transgenic mouse model to investigate the role of the calcium-activated protease calpain in the pathogenesis of synaptic dysfunction in SCS. Cleavage of a fluorogenic calpain substrate was increased at the NMJ of dissociated muscle fibers. Inhibition of calpain using a calpastatin (CS) transgene improved strength and neuromuscular transmission. CS caused a 2-fold increase in the frequency of miniature endplate currents (MEPCs) and an increase in NMJ size, but MEPC amplitudes remained reduced. Persistent degeneration of the NMJ was associated with localized activation of the non-calpain protease caspase-3. This study suggests that calpain may act presynaptically to impair NMJ function in SCS but further reveals a role for other cysteine proteases whose inhibition may be of additional therapeutic benefit in SCS and other excitotoxic disorders.
Authors
Jason S. Groshong, Melissa J. Spencer, Bula J. Bhattacharyya, Elena Kudryashova, Bhupinder P.S. Vohra, Roberto Zayas, Robert L. Wollmann, Richard J. Miller, Christopher M. Gomez
Abstract
Authors
Yi Dai, Shenglan Wang, Makoto Tominaga, Satoshi Yamamoto, Tetsuo Fukuoka, Tomohiro Higashi, Kimiko Kobayashi, Koichi Obata, Hiroki Yamanaka, Koichi Noguchi
Abstract
Ependymal overexpression of brain-derived neurotrophic factor (BDNF) stimulates neuronal addition to the adult striatum, from subependymal progenitor cells. Noggin, by suppressing subependymal gliogenesis and increasing progenitor availability, potentiates this process. We asked whether BDNF/Noggin overexpression might be used to recruit new striatal neurons in R6/2 huntingtin transgenic mice. R6/2 mice injected with adenoviral BDNF and adenoviral Noggin (AdBDNF/AdNoggin) recruited BrdU+βIII-tubulin+ neurons, which developed as DARPP-32+ and GABAergic medium spiny neurons that expressed either enkephalin or substance P and extended fibers to the globus pallidus. Only AdBDNF/AdNoggin-treated R6/2 mice harbored migrating doublecortin-defined neuroblasts in their striata, and the new neurons expressed p27 as a marker of mitotic quiescence after parenchymal integration. AdBDNF/AdNoggin-treated R6/2 mice sustained their rotarod performance and open-field activity and survived longer than did AdNull-treated and untreated controls. Neither motor performance nor survival improved in R6/2 mice treated only with AdBDNF, and intraventricular infusion of the mitotic inhibitor Ara-C completely blocked the performance and survival effects of AdBDNF/AdNoggin, suggesting that the benefits of AdBDNF/AdNoggin derived from neuronal addition. Thus, BDNF and Noggin induced striatal neuronal regeneration, delayed motor impairment, and extended survival in R6/2 mice, suggesting a new therapeutic strategy in Huntington disease.
Authors
Sung-Rae Cho, Abdellatif Benraiss, Eva Chmielnicki, Amer Samdani, Aris Economides, Steven A. Goldman
Abstract
Acute spinal cord injury (SCI) causes progressive hemorrhagic necrosis (PHN), a poorly understood pathological process characterized by hemorrhage and necrosis that leads to devastating loss of spinal cord tissue, cystic cavitation of the cord, and debilitating neurological dysfunction. Using a rodent model of severe cervical SCI, we tested the hypothesis that sulfonylurea receptor 1–regulated (SUR1-regulated) Ca2+-activated, [ATP]i-sensitive nonspecific cation (NCCa-ATP) channels are involved in PHN. In control rats, SCI caused a progressively expansive lesion with fragmentation of capillaries, hemorrhage that doubled in volume over 12 hours, tissue necrosis, and severe neurological dysfunction. SUR1 expression was upregulated in capillaries and neurons surrounding necrotic lesions. Patch clamp of cultured endothelial cells exposed to hypoxia showed that upregulation of SUR1 was associated with expression of functional SUR1-regulated NCCa-ATP channels. Following SCI, block of SUR1 by glibenclamide or repaglinide or suppression of Abcc8, which encodes for SUR1 by phosphorothioated antisense oligodeoxynucleotide essentially eliminated capillary fragmentation and progressive accumulation of blood, was associated with significant sparing of white matter tracts and a 3-fold reduction in lesion volume, and resulted in marked neurobehavioral functional improvement compared with controls. We conclude that SUR1-regulated NCCa-ATP channels in capillary endothelium are critical to development of PHN and constitute a major target for therapy in SCI.
Authors
J. Marc Simard, Orest Tsymbalyuk, Alexander Ivanov, Svetlana Ivanova, Sergei Bhatta, Zhihua Geng, S. Kyoon Woo, Volodymyr Gerzanich
Abstract
Proinflammatory agents trypsin and mast cell tryptase cleave and activate PAR2, which is expressed on sensory nerves to cause neurogenic inflammation. Transient receptor potential A1 (TRPA1) is an excitatory ion channel on primary sensory nerves of pain pathway. Here, we show that a functional interaction of PAR2 and TRPA1 in dorsal root ganglion (DRG) neurons could contribute to the sensation of inflammatory pain. Frequent colocalization of TRPA1 with PAR2 was found in rat DRG neurons. PAR2 activation increased the TRPA1 currents evoked by its agonists in HEK293 cells transfected with TRPA1, as well as DRG neurons. Application of phospholipase C (PLC) inhibitors or phosphatidylinositol-4,5-bisphosphate (PIP2) suppressed this potentiation. Decrease of plasma membrane PIP2 levels through antibody sequestration or PLC-mediated hydrolysis mimicked the potentiating effects of PAR2 activation at the cellular level. Thus, the increased TRPA1 sensitivity may have been due to activation of PLC, which releases the inhibition of TRPA1 from plasma membrane PIP2. These results identify for the first time to our knowledge a sensitization mechanism of TRPA1 and a novel mechanism through which trypsin or tryptase released in response to tissue inflammation might trigger the sensation of pain by TRPA1 activation.
Authors
Yi Dai, Shenglan Wang, Makoto Tominaga, Satoshi Yamamoto, Tetsuo Fukuoka, Tomohiro Higashi, Kimiko Kobayashi, Koichi Obata, Hiroki Yamanaka, Koichi Noguchi
Copyright © 2025 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)