Neuroscience
Abstract
Vertebrate cells require a very narrow pH range for survival. Cells accordingly possess sensory and defense mechanisms for situations where the pH deviates from the viable range. Although the monitoring of acidic pH by sensory neurons has been attributed to several ion channels, including transient receptor potential vanilloid 1 channel (TRPV1) and acid-sensing ion channels (ASICs), the mechanisms by which these cells detect alkaline pH are not well understood. Here, using Ca2+ imaging and patch-clamp recording, we showed that alkaline pH activated transient receptor potential cation channel, subfamily A, member 1 (TRPA1) and that activation of this ion channel was involved in nociception. In addition, intracellular alkalization activated TRPA1 at the whole-cell level, and single-channel openings were observed in the inside-out configuration, indicating that alkaline pH activated TRPA1 from the inside. Analyses of mutants suggested that the two N-terminal cysteine residues in TRPA1 were involved in activation by intracellular alkalization. Furthermore, intraplantar injection of ammonium chloride into the mouse hind paw caused pain-related behaviors that were not observed in TRPA1-deficient mice. These results suggest that alkaline pH causes pain sensation through activation of TRPA1 and may provide a molecular explanation for some of the human alkaline pH–related sensory disorders whose mechanisms are largely unknown.
Authors
Fumitaka Fujita, Kunitoshi Uchida, Tomoko Moriyama, Asako Shima, Koji Shibasaki, Hitoshi Inada, Takaaki Sokabe, Makoto Tominaga
Abstract
Neurotoxic amyloid β peptide (Aβ) accumulates in the brains of individuals with Alzheimer disease (AD). The APOE4 allele is a major risk factor for sporadic AD and has been associated with increased brain parenchymal and vascular amyloid burden. How apoE isoforms influence Aβ accumulation in the brain has, however, remained unclear. Here, we have shown that apoE disrupts Aβ clearance across the mouse blood-brain barrier (BBB) in an isoform-specific manner (specifically, apoE4 had a greater disruptive effect than either apoE3 or apoE2). Aβ binding to apoE4 redirected the rapid clearance of free Aβ40/42 from the LDL receptor–related protein 1 (LRP1) to the VLDL receptor (VLDLR), which internalized apoE4 and Aβ-apoE4 complexes at the BBB more slowly than LRP1. In contrast, apoE2 and apoE3 as well as Aβ-apoE2 and Aβ-apoE3 complexes were cleared at the BBB via both VLDLR and LRP1 at a substantially faster rate than Aβ-apoE4 complexes. Astrocyte-secreted lipo-apoE2, lipo-apoE3, and lipo-apoE4 as well as their complexes with Aβ were cleared at the BBB by mechanisms similar to those of their respective lipid-poor isoforms but at 2- to 3-fold slower rates. Thus, apoE isoforms differentially regulate Aβ clearance from the brain, and this might contribute to the effects of APOE genotype on the disease process in both individuals with AD and animal models of AD.
Authors
Rashid Deane, Abhay Sagare, Katie Hamm, Margaret Parisi, Steven Lane, Mary Beth Finn, David M. Holtzman, Berislav V. Zlokovic
Abstract
Spinal muscular atrophy (SMA), a motor neuron disease (MND) and one of the most common genetic causes of infant mortality, currently has no cure. Patients with SMA exhibit muscle weakness and hypotonia. Stem cell transplantation is a potential therapeutic strategy for SMA and other MNDs. In this study, we isolated spinal cord neural stem cells (NSCs) from mice expressing green fluorescent protein only in motor neurons and assessed their therapeutic effects on the phenotype of SMA mice. Intrathecally grafted NSCs migrated into the parenchyma and generated a small proportion of motor neurons. Treated SMA mice exhibited improved neuromuscular function, increased life span, and improved motor unit pathology. Global gene expression analysis of laser-capture-microdissected motor neurons from treated mice showed that the major effect of NSC transplantation was modification of the SMA phenotype toward the wild-type pattern, including changes in RNA metabolism proteins, cell cycle proteins, and actin-binding proteins. NSC transplantation positively affected the SMA disease phenotype, indicating that transplantation of NSCs may be a possible treatment for SMA.
Authors
Stefania Corti, Monica Nizzardo, Martina Nardini, Chiara Donadoni, Sabrina Salani, Dario Ronchi, Francesca Saladino, Andreina Bordoni, Francesco Fortunato, Roberto Del Bo, Dimitra Papadimitriou, Federica Locatelli, Giorgia Menozzi, Sandra Strazzer, Nereo Bresolin, Giacomo P. Comi
Abstract
Parkinson disease (PD) is characterized by dopaminergic neurodegeneration and intracellular inclusions of α-synuclein amyloid fibers, which are stable and difficult to dissolve. Whether inclusions are neuroprotective or pathological remains controversial, because prefibrillar oligomers may be more toxic than amyloid inclusions. Thus, whether therapies should target inclusions, preamyloid oligomers, or both is a critically important issue. In yeast, the protein-remodeling factor Hsp104 cooperates with Hsp70 and Hsp40 to dissolve and reactivate aggregated proteins. Metazoans, however, have no Hsp104 ortholog. Here we introduced Hsp104 into a rat PD model. Remarkably, Hsp104 reduced formation of phosphorylated α-synuclein inclusions and prevented nigrostriatal dopaminergic neurodegeneration induced by PD-linked α-synuclein (A30P). An in vitro assay employing pure proteins revealed that Hsp104 prevented fibrillization of α-synuclein and PD-linked variants (A30P, A53T, E46K). Hsp104 coupled ATP hydrolysis to the disassembly of preamyloid oligomers and amyloid fibers composed of α-synuclein. Furthermore, the mammalian Hsp70 and Hsp40 chaperones, Hsc70 and Hdj2, enhanced α-synuclein fiber disassembly by Hsp104. Hsp104 likely protects dopaminergic neurons by antagonizing toxic α-synuclein assemblies and might have therapeutic potential for PD and other neurodegenerative amyloidoses.
Authors
Christophe Lo Bianco, James Shorter, Etienne Régulier, Hilal Lashuel, Takeshi Iwatsubo, Susan Lindquist, Patrick Aebischer
Abstract
Neuronal ceroid lipofuscinoses represent the most common childhood neurodegenerative storage disorders. Infantile neuronal ceroid lipofuscinosis (INCL) is caused by palmitoyl protein thioesterase-1 (PPT1) deficiency. Although INCL patients show signs of abnormal neurotransmission, manifested by myoclonus and seizures, the molecular mechanisms by which PPT1 deficiency causes this abnormality remain obscure. Neurotransmission relies on repeated cycles of exo- and endocytosis of the synaptic vesicles (SVs), in which several palmitoylated proteins play critical roles. These proteins facilitate membrane fusion, which is required for neurotransmitter exocytosis, recycling of the fused SV membrane components, and regeneration of fresh vesicles. However, palmitoylated proteins require depalmitoylation for recycling. Using postmortem brain tissues from an INCL patient and tissue from the PPT1-knockout (PPT1-KO) mice that mimic INCL, we report here that PPT1 deficiency caused persistent membrane anchorage of the palmitoylated SV proteins, which hindered the recycling of the vesicle components that normally fuse with the presynaptic plasma membrane during SV exocytosis. Thus, the regeneration of fresh SVs, essential for maintaining the SV pool size at the synapses, was impaired, leading to a progressive loss of readily releasable SVs and abnormal neurotransmission. This abnormality may contribute to INCL neuropathology.
Authors
Sung-Jo Kim, Zhongjian Zhang, Chinmoy Sarkar, Pei-Chih Tsai, Yi-Ching Lee, Louis Dye, Anil B. Mukherjee
Abstract
Calpains are calcium-dependent enzymes that determine the fate of proteins through regulated proteolytic activity. Calpains have been linked to the modulation of memory and are key to the pathogenesis of Alzheimer disease (AD). When abnormally activated, calpains can also initiate degradation of proteins essential for neuronal survival. Here we show that calpain inhibition through E64, a cysteine protease inhibitor, and the highly specific calpain inhibitor BDA-410 restored normal synaptic function both in hippocampal cultures and in hippocampal slices from the APP/PS1 mouse, an animal model of AD. Calpain inhibition also improved spatial-working memory and associative fear memory in APP/PS1 mice. These beneficial effects of the calpain inhibitors were associated with restoration of normal phosphorylation levels of the transcription factor CREB and involved redistribution of the synaptic protein synapsin I. Thus, calpain inhibition may prove useful in the alleviation of memory loss in AD.
Authors
Fabrizio Trinchese, Mauro Fa’, Shumin Liu, Hong Zhang, Ariel Hidalgo, Stephen D. Schmidt, Hisako Yamaguchi, Narihiko Yoshii, Paul M. Mathews, Ralph A. Nixon, Ottavio Arancio
Abstract
Stress-induced analgesia (SIA) is a key component of the defensive behavioral “fight-or-flight” response. Although the neural substrates of SIA are incompletely understood, previous studies have implicated the hypocretin/orexin (Hcrt) and nociceptin/orphanin FQ (N/OFQ) peptidergic systems in the regulation of SIA. Using immunohistochemistry in brain tissue from wild-type mice, we identified N/OFQ-containing fibers forming synaptic contacts with Hcrt neurons at both the light and electron microscopic levels. Patch clamp recordings in GFP-tagged mouse Hcrt neurons revealed that N/OFQ hyperpolarized, decreased input resistance, and blocked the firing of action potentials in Hcrt neurons. N/OFQ postsynaptic effects were consistent with opening of a G protein–regulated inwardly rectifying K+ (GIRK) channel. N/OFQ also modulated presynaptic release of GABA and glutamate onto Hcrt neurons in mouse hypothalamic slices. Orexin/ataxin-3 mice, in which the Hcrt neurons degenerate, did not exhibit SIA, although analgesia was induced by i.c.v. administration of Hcrt-1. N/OFQ blocked SIA in wild-type mice, while coadministration of Hcrt-1 overcame N/OFQ inhibition of SIA. These results establish what is, to our knowledge, a novel interaction between the N/OFQ and Hcrt systems in which the corticotropin-releasing factor and N/OFQ systems coordinately modulate the Hcrt neurons to regulate SIA.
Authors
Xinmin Xie, Jonathan P. Wisor, Junko Hara, Tara L. Crowder, Robin LeWinter, Taline V. Khroyan, Akihiro Yamanaka, Sabrina Diano, Tamas L. Horvath, Takeshi Sakurai, Lawrence Toll, Thomas S. Kilduff
Abstract
Murine olfactory ensheathing cells (OECs) promote central nervous system axonal regeneration in models of spinal cord injury. We investigated whether OECs could induce a neuroplastic effect to improve the neurological dysfunction caused by hypoxic/ischemic stress. In this study, human OECs/olfactory nerve fibroblasts (hOECs/ONFs) specifically secreted trophic factors including stromal cell–derived factor–1α (SDF-1α). Rats with intracerebral hOEC/ONF implantation showed more improvement on behavioral measures of neurological deficit following stroke than control rats. [18F]fluoro-2-deoxyglucose PET (FDG-PET) showed increased glucose metabolic activity in the hOEC/ONF-treated group compared with controls. In mice, transplanted hOECs/ONFs and endogenous homing stem cells including intrinsic neural progenitor cells and bone marrow stem cells colocalized with specific neural and vascular markers, indicating stem cell fusion. Both hOECs/ONFs and endogenous homing stem cells enhanced neuroplasticity in the rat and mouse ischemic brain. Upregulation of SDF-1α and CXCR4 in hOECs/ONFs promoted neurite outgrowth of cocultured primary cortical neurons under oxygen glucose deprivation conditions and in stroke animals through upregulation of cellular prion protein (PrPC) expression. Therefore, the upregulation of SDF-1α and the enhancement of CXCR4 and PrPC interaction induced by hOEC/ONF implantation mediated neuroplastic signals in response to hypoxia and ischemia.
Authors
Woei-Cherng Shyu, Demeral David Liu, Shinn-Zong Lin, Wen-Wen Li, Ching-Yuan Su, Ying-Chen Chang, Hsiao-Jung Wang, Hsing-Won Wang, Chang-Hai Tsai, Hung Li
Abstract
Hereditary sensory and autonomic neuropathy type II (HSANII) is an early-onset autosomal recessive disorder characterized by loss of perception to pain, touch, and heat due to a loss of peripheral sensory nerves. Mutations in hereditary sensory neuropathy type II (HSN2), a single-exon ORF originally identified in affected families in Quebec and Newfoundland, Canada, were found to cause HSANII. We report here that HSN2 is a nervous system–specific exon of the with-no-lysine(K)–1 (WNK1) gene. WNK1 mutations have previously been reported to cause pseudohypoaldosteronism type II but have not been studied in the nervous system. Given the high degree of conservation of WNK1 between mice and humans, we characterized the structure and expression patterns of this isoform in mice. Immunodetections indicated that this Wnk1/Hsn2 isoform was expressed in sensory components of the peripheral nervous system and CNS associated with relaying sensory and nociceptive signals, including satellite cells, Schwann cells, and sensory neurons. We also demonstrate that the novel protein product of Wnk1/Hsn2 was more abundant in sensory neurons than motor neurons. The characteristics of WNK1/HSN2 point to a possible role for this gene in the peripheral sensory perception deficits characterizing HSANII.
Authors
Masoud Shekarabi, Nathalie Girard, Jean-Baptiste Rivière, Patrick Dion, Martin Houle, André Toulouse, Ronald G. Lafrenière, Freya Vercauteren, Pascale Hince, Janet Laganiere, Daniel Rochefort, Laurence Faivre, Mark Samuels, Guy A. Rouleau
Abstract
Neuroprotection can be achieved by preventing apoptotic death of postmitotic cells. Apoptotic death can occur by either a caspase-dependent mechanism, involving cytochrome c, apoptosis protease-activating factor–1 (Apaf-1), and caspase-9, or a caspase-independent mechanism, involving apoptosis-inducing factor (AIF). HIV protease inhibitors (PIs) avert apoptosis in part by preventing mitochondrial outer membrane permeabilization (MOMP), but the precise mechanism by which they work is not known. Here, we evaluated the impact of the PIs in a mouse model of retinal detachment (RD) in vivo and in murine primary retinal cell cultures in vitro. Oral administration of the PIs nelfinavir and ritonavir significantly inhibited photoreceptor apoptosis, while preventing the translocation of AIF from mitochondria to the nucleus as well as the activation of caspase-9. RD-induced photoreceptor apoptosis was similarly inhibited in mice carrying hypomorphic mutations of the genes encoding AIF or Apaf-1. Nelfinavir attenuated apoptosis as well as mitochondrial release of AIF and cytochrome c, and subsequent activation of caspase-9 in vitro, in photoreceptor cultures exposed to starvation or monocyte chemoattractant protein–1–stimulated (MCP-1–stimulated) macrophages. Our results suggest that the MOMP inhibition by PIs involved interruption of both caspase-dependent and caspase-independent apoptosis pathways and that PIs may be clinically useful for the treatment of diseases caused by excessive apoptosis.
Authors
Toshio Hisatomi, Toru Nakazawa, Kousuke Noda, Lama Almulki, Shinsuke Miyahara, Shintaro Nakao, Yasuhiro Ito, Haicheng She, Riichiro Kohno, Norman Michaud, Tatsuro Ishibashi, Ali Hafezi-Moghadam, Andrew D. Badley, Guido Kroemer, Joan W. Miller
Copyright © 2021 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)