Neuroscience
Abstract
Leptin and insulin have been identified as fuel sensors acting in part through their hypothalamic receptors to inhibit food intake and stimulate energy expenditure. As their intracellular signaling converges at the PI3K pathway, we directly addressed the role of phosphatidylinositol3,4,5-trisphosphate–mediated (PIP3-mediated) signals in hypothalamic proopiomelanocortin (POMC) neurons by inactivating the gene for the PIP3 phosphatase Pten specifically in this cell type. Here we show that POMC-specific disruption of Pten resulted in hyperphagia and sexually dimorphic diet-sensitive obesity. Although leptin potently stimulated Stat3 phosphorylation in POMC neurons of POMC cell–restricted Pten knockout (PPKO) mice, it failed to significantly inhibit food intake in vivo. POMC neurons of PPKO mice showed a marked hyperpolarization and a reduction in basal firing rate due to increased ATP-sensitive potassium (KATP) channel activity. Leptin was not able to elicit electrical activity in PPKO POMC neurons, but application of the PI3K inhibitor LY294002 and the KATP blocker tolbutamide restored electrical activity and leptin-evoked firing of POMC neurons in these mice. Moreover, icv administration of tolbutamide abolished hyperphagia in PPKO mice. These data indicate that PIP3-mediated signals are critical regulators of the melanocortin system via modulation of KATP channels.
Authors
Leona Plum, Xiaosong Ma, Brigitte Hampel, Nina Balthasar, Roberto Coppari, Heike Münzberg, Marya Shanabrough, Denis Burdakov, Eva Rother, Ruth Janoschek, Jens Alber, Bengt F. Belgardt, Linda Koch, Jost Seibler, Frieder Schwenk, Csaba Fekete, Akira Suzuki, Tak W. Mak, Wilhelm Krone, Tamas L. Horvath, Frances M. Ashcroft, Jens C. Brüning
Abstract
Hydrocephalus is a common and potentially devastating birth defect affecting the CNS, and its relationship with G protein–coupled receptors (GPCRs) is unknown. We have expressed 2, 4, or 6 copies of a GPCR — the human PAC1 receptor with a 130-kb transgene in the mouse nervous system in a pattern closely resembling that of the endogenous gene. Consistent with PAC1 actions, PKA and PKC activity were elevated in the brains of Tg mice. Remarkably, Tg mice developed dose-dependent hydrocephalus-like characteristics, including enlarged third and lateral ventricles and reduced cerebral cortex, corpus callosum, and subcommissural organ (SCO). Neuronal proliferation and apoptosis were implicated in hydrocephalus, and we observed significantly reduced neuronal proliferation and massively increased neuronal apoptosis in the developing cortex and SCO of Tg embryos, while neurite outgrowth and neuronal migration in vitro remain uncompromised. Ventricular ependymal cilia are crucial for directing cerebrospinal fluid flow, and ependyma of Tg mice exhibited disrupted cilia with increased phospho-CREB immunoreactivity. These data demonstrate that altered neuronal proliferation/apoptosis and disrupted ependymal cilia are the main factors contributing to hydrocephalus in PAC1-overexpressing mice. This is the first report to our knowledge demonstrating that misregulation of GPCRs can be involved in hydrocephalus-related neurodevelopmental disorders.
Authors
Bing Lang, Bing Song, Wendy Davidson, Alastair MacKenzie, Norman Smith, Colin D. McCaig, Anthony J. Harmar, Sanbing Shen
Abstract
Regulation and dysregulation of intracellular calcium (Ca2+) signaling via the inositol 1,4,5-trisphosphate receptor (InsP3R) has been linked to many cellular processes and pathological conditions. In the present study, addition of neuronal calcium sensor-1 (NCS-1), a high-affinity, low-capacity, calcium-binding protein, to purified InsP3R type 1 (InsP3R1) increased the channel activity in both a calcium-dependent and -independent manner. In intact cells, enhanced expression of NCS-1 resulted in increased intracellular calcium release upon stimulation of the phosphoinositide signaling pathway. To determine whether InsP3R1/NCS-1 interaction could be functionally relevant in bipolar disorders, conditions in which NCS-1 is highly expressed, we tested the effect of lithium, a salt widely used for treatment of bipolar disorders. Lithium inhibited the enhancing effect of NCS-1 on InsP3R1 function, suggesting that InsP3R1/NCS-1 interaction is an essential component of the pathomechanism of bipolar disorder.
Authors
Christina Schlecker, Wolfgang Boehmerle, Andreas Jeromin, Brenda DeGray, Anurag Varshney, Yogendra Sharma, Klara Szigeti-Buck, Barbara E. Ehrlich
Abstract
There is no treatment for the neurodegenerative disorder Huntington disease (HD). Cystamine is a candidate drug; however, the mechanisms by which it operates remain unclear. We show here that cystamine increases levels of the heat shock DnaJ-containing protein 1b (HSJ1b) that are low in HD patients. HSJ1b inhibits polyQ-huntingtin–induced death of striatal neurons and neuronal dysfunction in Caenorhabditis elegans. This neuroprotective effect involves stimulation of the secretory pathway through formation of clathrin-coated vesicles containing brain-derived neurotrophic factor (BDNF). Cystamine increases BDNF secretion from the Golgi region that is blocked by reducing HSJ1b levels or by overexpressing transglutaminase. We demonstrate that cysteamine, the FDA-approved reduced form of cystamine, is neuroprotective in HD mice by increasing BDNF levels in brain. Finally, cysteamine increases serum levels of BDNF in mouse and primate models of HD. Therefore, cysteamine is a potential treatment for HD, and serum BDNF levels can be used as a biomarker for drug efficacy.
Authors
Maria Borrell-Pagès, Josep M. Canals, Fabrice P. Cordelières, J. Alex Parker, José R. Pineda, Ghislaine Grange, Elzbieta A. Bryson, Martine Guillermier, Etienne Hirsch, Philippe Hantraye, Michael E. Cheetham, Christian Néri, Jordi Alberch, Emmanuel Brouillet, Frédéric Saudou, Sandrine Humbert
Abstract
The role of activated microglia (MG) in demyelinating neurodegenerative diseases such as multiple sclerosis is controversial. Here we show that high, but not low, levels of IFN-γ (a cytokine associated with inflammatory autoimmune diseases) conferred on rodent MG a phenotype that impeded oligodendrogenesis from adult neural stem/progenitor cells. IL-4 reversed the impediment, attenuated TNF-α production, and overcame blockage of IGF-I production caused by IFN-γ. In rodents with acute or chronic EAE, injection of IL-4–activated MG into the cerebrospinal fluid resulted in increased oligodendrogenesis in the spinal cord and improved clinical symptoms. The newly formed oligodendrocytes were spatially associated with MG expressing MHC class II proteins and IGF-I. These results point to what we believe to be a novel role for MG in oligodendrogenesis from the endogenous stem cell pool.
Authors
Oleg Butovsky, Gennady Landa, Gilad Kunis, Yaniv Ziv, Hila Avidan, Nadav Greenberg, Adi Schwartz, Igor Smirnov, Ayala Pollack, Steffen Jung, Michal Schwartz
Abstract
Disruption of cholinergic neurotransmission contributes to the memory impairment that characterizes Alzheimer disease (AD). Since the amyloid cascade hypothesis of AD pathogenesis postulates that amyloid β (Aβ) peptide accumulation in critical brain regions also contributes to memory impairment, we assessed cholinergic function in transgenic mice where the human Aβ peptide is overexpressed. We first measured hippocampal acetylcholine (ACh) release in young, freely moving PDAPP mice, a well-characterized transgenic mouse model of AD, and found marked Aβ-dependent alterations in both basal and evoked ACh release compared with WT controls. We also found that Aβ could directly interact with the high-affinity choline transporter which may impair steady-state and on-demand ACh release. Treatment of PDAPP mice with the anti-Aβ antibody m266 rapidly and completely restored hippocampal ACh release and high-affinity choline uptake while greatly reducing impaired habituation learning that is characteristic of these mice. Thus, soluble “cholinotoxic” species of the Aβ peptide can directly impair cholinergic neurotransmission in PDAPP mice leading to memory impairment in the absence of overt neurodegeneration. Treatment with certain anti-Aβ antibodies may therefore rapidly reverse this cholinergic dysfunction and relieve memory deficits associated with early AD.
Authors
Kelly R. Bales, Eleni T. Tzavara, Su Wu, Mark R. Wade, Frank P. Bymaster, Steven M. Paul, George G. Nomikos
Abstract
Accumulation and aggregation of amyloid β peptide 1–42 (Aβ42) in the brain has been hypothesized as triggering a pathological cascade that causes Alzheimer disease (AD). To determine whether selective targeting of Aβ42 versus Aβ40 or total Aβ is an effective way to prevent or treat AD, we compared the effects of passive immunization with an anti-Aβ42 mAb, an anti-Aβ40 mAb, and multiple Aβ1–16 mAbs. We established in vivo binding selectivity of the anti-Aβ42 and anti-Aβ40 mAbs using novel TgBRI-Aβ mice. We then conducted a prevention study in which the anti-Aβ mAbs were administered to young Tg2576 mice, which have no significant Aβ deposition, and therapeutic studies in which mAbs were administered to Tg2576 or CRND8 mice with modest levels of preexisting Aβ deposits. Anti-Aβ42, anti-Aβ40, and anti-Aβ1–16 mAbs attenuated plaque deposition in the prevention study. In contrast, anti-Aβ42 and anti-Aβ40 mAbs were less effective in attenuating Aβ deposition in the therapeutic studies and were not effective in clearing diffuse plaques following direct injection into the cortex. These data suggest that selective targeting of Aβ42 or Aβ40 may be an effective strategy to prevent amyloid deposition, but may have limited benefit in a therapeutic setting.
Authors
Yona Levites, Pritam Das, Robert W. Price, Marjorie J. Rochette, Lisa A. Kostura, Eileen M. McGowan, Michael P. Murphy, Todd E. Golde
Abstract
Degeneration of peripheral motor axons is a common feature of several debilitating diseases including complicated forms of hereditary spastic paraplegia. One such form is caused by loss of the mitochondrial energy-dependent protease paraplegin. Paraplegin-deficient mice display a progressive degeneration in several axonal tracts, characterized by the accumulation of morphological abnormal mitochondria. We show that adenoassociated virus–mediated (AAV-mediated) intramuscular delivery of paraplegin halted the progression of neuropathological changes and rescued mitochondrial morphology in the peripheral nerves of paraplegin-deficient mice. One single injection before onset of symptoms improved the motor performance of paraplegin-deficient mice for up to 10 months, indicating that the peripheral neuropathy contributes to the clinical phenotype. This study provides a proof of principle that gene transfer may be an effective therapeutic option for patients with paraplegin deficiency and demonstrates that AAV vectors can be successfully employed for retrograde delivery of an intracellular protein to spinal motor neurons, opening new perspectives for several hereditary axonal neuropathies of the peripheral nerves.
Authors
Marinella Pirozzi, Angelo Quattrini, Gennaro Andolfi, Giorgia Dina, Maria Chiara Malaguti, Alberto Auricchio, Elena I. Rugarli
Abstract
Hereditary spastic paraplegias (HSPs) are a group of neurodegenerative diseases characterized by progressive weakness and spasticity of the lower limbs. Dominant mutations in the human SPG4 gene, encoding spastin, are responsible for the most frequent form of HSP. Spastin is an ATPase that binds microtubules and localizes to the spindle pole and distal axon in mammalian cell lines. Furthermore, its Drosophila homolog, Drosophila spastin (Dspastin), has been recently shown to regulate microtubule stability and synaptic function at the Drosophila larval neuromuscular junction. Here we report the generation of a spastin-linked HSP animal model and show that in Drosophila, neural knockdown of Dspastin and, conversely, neural overexpression of Dspastin containing a conserved pathogenic mutation both recapitulate some phenotypic aspects of the human disease, including adult onset, locomotor impairment, and neurodegeneration. At the subcellular level, neuronal expression of both Dspastin RNA interference and mutant Dspastin cause an excessive stabilization of microtubules in the neuromuscular junction synapse. In addition, we provide evidence that administration of the microtubule targeting drug vinblastine significantly attenuates these phenotypes in vivo. Our findings demonstrate that loss of spastin function elicits HSP-like phenotypes in Drosophila, provide novel insights into the molecular mechanism of spastin mutations, and raise the possibility that therapy with Vinca alkaloids may be efficacious in spastin-associated HSP and other disorders related to microtubule dysfunction.
Authors
Genny Orso, Andrea Martinuzzi, Maria Giovanna Rossetto, Elena Sartori, Mel Feany, Andrea Daga
Abstract
The hippocampal dentate gyrus in the adult mammalian brain contains neural stem/progenitor cells (NS/PCs) capable of generating new neurons, i.e., neurogenesis. Most drugs of abuse examined to date decrease adult hippocampal neurogenesis, but the effects of cannabis (marijuana or cannabinoids) on hippocampal neurogenesis remain unknown. This study aimed at investigating the potential regulatory capacity of the potent synthetic cannabinoid HU210 on hippocampal neurogenesis and its possible correlation with behavioral change. We show that both embryonic and adult rat hippocampal NS/PCs are immunoreactive for CB1 cannabinoid receptors, indicating that cannabinoids could act on CB1 receptors to regulate neurogenesis. This hypothesis is supported by further findings that HU210 promotes proliferation, but not differentiation, of cultured embryonic hippocampal NS/PCs likely via a sequential activation of CB1 receptors, Gi/o proteins, and ERK signaling. Chronic, but not acute, HU210 treatment promoted neurogenesis in the hippocampal dentate gyrus of adult rats and exerted anxiolytic- and antidepressant-like effects. X-irradiation of the hippocampus blocked both the neurogenic and behavioral effects of chronic HU210 treatment, suggesting that chronic HU210 treatment produces anxiolytic- and antidepressant-like effects likely via promotion of hippocampal neurogenesis.
Authors
Wen Jiang, Yun Zhang, Lan Xiao, Jamie Van Cleemput, Shao-Ping Ji, Guang Bai, Xia Zhang
Copyright © 2020 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)