detection-axonally-localized-mrnas-brain-sections-using-high

Detection of Axonally Localized mRNAs in Brain Sections Using High-Resolution <em>In Situ</em> Hybridization

mRNAs are frequently localized to vertebrate axons and their local translation is required for axon pathfinding or branching during development and for ...

The three-dimensional morphology of the membranous labyrinth of Xenopus laevis is presented from embryonic through late tadpole development (stages 28 to 52, inclusive). This was accomplished by paint-filling the endolymphatic spaces of Xenopus ears at a series of stages, beginning with the embryonic otic vesicle and ending with the complex ear of the late tadpole. At stage 52, the inner ear has expanded approximately 23-fold in its anterior/posterior dimension compared with stage 28 and it is a miniature of the adult form. The paint-filling technique illustrates the dramatic changes required to convert a simple ear vesicle into the elaborate form of the adult, including semicircular canal formation and genesis of vestibular and auditory organs, and it can serve as a basis for phenotype identification in experimentally or genetically manipulated ears.

Three-dimensional morphology of inner ear development in Xenopus laevis.

Dreidimensionale Morphologie Innenohrentwicklung in Xenopus laevis.

A key neurotrophin responsible for the survival and function of basal forebrain (BF) cholinergic neurons is brain-derived neurotrophic factor (BDNF). A number of studies now indicate that a source of this factor may be BF astrocytes. This study was designed to define the role of BF-astrocyte-derived BDNF on cholinergic neurons. Moreover, it investigated regulatory events that modulate BDNF content and release. In initial work BDNF derived from BF-astrocyte-conditioned medium (ACM) was found to increase both numbers of BF acetylcholinesterase (AChE+) cholinergic neurons and the cholinergic synthetic enzyme choline acetyltransferase (ChAT). Western blots, immunocytochemistry and pharmacological inhibition studies revealed that glutamate, through group I metabotropic glutamate receptors (mGluR), increases the intracellular levels of BDNF in BF astrocytes in culture, as well as its release. Furthermore, the release of BDNF is mediated by the actions of PLC, IP3 and internal stores of Ca2+. These results suggest that BF astrocytes serve as local sources of BDNF for cholinergic neurons, and that they may be regulated as such by the neuronal signal, glutamate, through the mediation of group I metabotropic receptors and the PLC pathway.

Glutamate elicits release of BDNF from basal forebrain astrocytes in a process dependent on metabotropic receptors and the PLC pathway.

Recent studies demonstrate that the neuropeptide VGF (nonacronymic) is regulated in the hippocampus by antidepressant therapies and animal models of depression and that acute VGF treatment has antidepressant-like activity in animal paradigms. However, the role of VGF in human psychiatric disorders is unknown. We now demonstrate using in situ hybridization that VGF is downregulated in bipolar disorder in the CA region of the hippocampus and Brodmann's area 9 of the prefrontal cortex. The mechanism of VGF in relation to LiCl was explored. Both LiCl intraperitoneally and VGF intracerebroventricularly reduced latency to drink in novelty-induced hypophagia, and LiCl was not effective in VGF(+/-) mice, suggesting that VGF may contribute to the effects of LiCl in this behavioral procedure that responds to chronic antidepressant treatment. VGF by intrahippocampal injection also had novel activity in an amphetamine-induced hyperlocomotion assay, thus mimicking the actions of LiCl injected intraperitoneally in a system that phenocopies manic-like behavior. Moreover, VGF(+/-) mice exhibited increased locomotion after amphetamine treatment and did not respond to LiCl, suggesting that VGF is required for the effects of LiCl in curbing the response to amphetamine. Finally, VGF delivered intracerebroventricularly in vivo activated the same signaling pathways as LiCl and is necessary for the induction of mitogen-activated protein kinase and Akt by LiCl, thus lending insight into the molecular mechanisms underlying the actions of VGF. The dysregulation of VGF in bipolar disorder as well as the behavioral effects of the neuropeptide similar to LiCl suggests that VGF may underlie the pathophysiology of bipolar disorder.

The neuropeptide VGF is reduced in human bipolar postmortem brain and contributes to some of the behavioral and molecular effects of lithium.

Neuere Studien zeigen, dass das Neuropeptid VGF (Nonacronymic) im Hippocampus durch antidepressive Therapien und Tiermodellen f&uuml;r Depression Regeln und VGF Akutbehandlung Antidepressivum viren&auml;hnliche Tier Paradigmenwechsel hat. Die Rolle der VGF in psychiatrischen St&ouml;rungen des Menschen ist jedoch unbekannt. Wir zeigen jetzt in situ-Hybridisierung, dass VGF Downregulated in bipolaren St&ouml;rung in der CA-Region des Hippocampus und Brodmanns-Areal 9 des pr&auml;frontalen Cortex ist. Der Mechanismus der VGF in Bezug auf LiCl wurde erforscht. Beide LiCl intraperitoneal VGF Intracerebroventricularly reduzierte Latenz Neuheit-induzierte Hypophagia zu trinken und LiCl war nicht wirksam bei VGF(+/-) M&auml;use, was darauf hindeutet, dass VGF auf die Auswirkungen der LiCl in diesem verhaltensbasierten Verfahren beitragen kann, die auf chronische antidepressiven Behandlung reagiert. VGF durch Intrahippocampal Injektion hatte auch neuartige Aktivit&auml;t in ein Amphetamin-induzierte Hyperlocomotion-Assay, so imitiert die Aktionen der LiCl injiziert intraperitoneal in einem System, dass Ph&auml;nokopien manisch-&auml;hnliches Verhalten. Dar&uuml;ber hinaus VGF(+/-) M&auml;use erh&ouml;hte Fortbewegung nach Amphetamin Behandlung ausgestellt und reagierte nicht auf LiCl, darauf hindeutet, dass die VGF f&uuml;r die Auswirkungen der LiCl erforderlich ist, die Reaktion auf Amphetamine einzuschr&auml;nken. Schlie&szlig;lich VGF geliefert Intracerebroventricularly in-vivo aktiviert die gleichen Signalwege als LiCl und ist notwendig f&uuml;r die Induktion von Mitogen-aktivierte Proteinkinase und Akt von LiCl, somit Einblick in die molekularen Mechanismen der Aktionen der VGF Kreditvergabe. Die Dysregulation der VGF in bipolaren St&ouml;rung sowie die verhaltensbasierten Auswirkungen das Neuropeptid LiCl &auml;hnlich zufolge VGF die Pathophysiologie der bipolaren St&ouml;rung zugrunde liegen k&ouml;nnten.

Das Neuropeptid VGF bipolar Post-mortem Gehirn reduziert ist und tr&auml;gt zur die Verhaltens- und Molekulare Effekte von Lithium.

Caspases, initially identified as a family of proteases regulating cell death, have been found to have nonapoptotic functions as well. Some family members are critical for mediating programmed cell death in development. After development, caspases are downregulated in the nervous system, but continue to perform important nonapoptotic functions relevant for neurogenesis and synaptic plasticity. In neurodegenerative diseases, where aberrant neuronal death is an outstanding feature, there is an increase in caspase activity. The specific caspase death pathways leading to dysfunction and death have still not been fully clarified, despite the plethora of scientific literature addressing these issues. In this chapter, we will present the current knowledge of caspase activation and activity pathways, the current tools for examining caspases, and functions of caspases in the nervous system in health and in disease. Alzheimer's Disease, the most common neurodegenerative disorder, and cerebral ischemia, the most common cause of neurologic death, are used to illustrate our current understanding of death signaling in neurodegenerative diseases. A better understanding of how caspases function in health and disease would provide appropriate specific targets for the development of therapeutic interventions for these diseases. Life and death are exquisitely regulated at the cellular level from development through maturity. During development, neuronal death is the major factor shaping the nervous system. This death is mainly caspase-mediated apoptosis. Once the waves of developmental death have passed (death occurs at different times in different parts of the nervous system), there is downregulation of the death machinery, as the postmitotic neurons should live for the life of the organism. Aberrant neuronal death is a major part of neurodegenerative disorders, but there is still no clear understanding of the processes leading to the phenotypes of the various diseases. Even the type of death that occurs continues to be debated, whether it is apoptotic, necrotic, or autophagic, or some combination of these death mechanisms. Here, we will discuss the role that the caspases play in neuronal function, dysfunction, and death. First, we will discuss the regulation of caspase activation and activity. We will examine the current understanding of caspase function in developmental neuronal death and then illustrate the role of caspases in neuronal death in disease employing two diseases of neuronal loss, Alzheimer's Disease (AD), which is the most common chronic neurodegenerative disorder, and cerebral ischemia/stroke, the third most common cause of death in Western society, which is an acute neuronal disorder with chronic sequelae.

Regulation of caspases in the nervous system implications for functions in health and disease.

Caspase 2 was initially identified as a neuronally expressed developmentally down-regulated gene (HUGO gene nomenclature CASP2) and has been shown to be required for neuronal death induced by several stimuli, including NGF (nerve growth factor) deprivation and Aβ (β-amyloid). In non-neuronal cells the PIDDosome, composed of caspase 2 and two death adaptor proteins, PIDD (p53-inducible protein with a death domain) and RAIDD {RIP (receptor-interacting protein)-associated ICH-1 [ICE (interleukin-1β-converting enzyme)/CED-3 (cell-death determining 3) homologue 1] protein with a death domain}, has been proposed as the caspase 2 activation complex, although the absolute requirement for the PIDDosome is not clear. To investigate the requirement for the PIDDosome in caspase-2-dependent neuronal death, we have examined the necessity for each component in induction of active caspase 2 and in execution of caspase-2-dependent neuronal death. We find that both NGF deprivation and Aβ treatment of neurons induce active caspase 2 and that induction of this activity depends on expression of RAIDD, but is independent of PIDD expression. We show that treatment of wild-type or PIDD-null neurons with Aβ or NGF deprivation induces formation of a complex of caspase 2 and RAIDD. We also show that caspase-2-dependent execution of neurons requires RAIDD, not PIDD. Caspase 2 activity can be induced in neurons from PIDD-null mice, and NGF deprivation or Aβ use caspase 2 and RAIDD to execute death of these neurons.

Neuronal caspase 2 activity and function requires RAIDD, but not PIDD.

Neuronal apoptotic death generally requires de novo transcription, and activation of the transcription factor c-Jun has been shown to be necessary in multiple neuronal death paradigms. Caspase-2 has been implicated in death of neuronal and non-neuronal cells, but its relationship to transcriptional activation has not been clearly elucidated. In the present study, using two different neuronal apoptotic paradigms, β-amyloid treatment and NGF (nerve growth factor) withdrawal, we examined the hierarchical role of caspase-2 activation in the transcriptional control of neuron death. Both paradigms induce rapid activation of caspase-2 as well as activation of the transcription factor c-Jun and subsequent induction of the pro-apoptotic BH3 (Bcl-homology domain 3)-only protein Bim (Bcl-2-interacting mediator of cell death). Caspase-2 activation is dependent on the adaptor protein RAIDD {RIP (receptor-interacting protein)-associated ICH-1 [ICE (interleukin-1β-converting enzyme)/CED-3 (cell-death determining 3) homologue 1] protein with a death domain}, and both caspase-2 and RAIDD are required for c-Jun activation and Bim induction. The present study thus shows that rapid caspase-2 activation is essential for c-Jun activation and Bim induction in neurons subjected to apoptotic stimuli. This places caspase-2 at an apical position in the apoptotic cascade and demonstrates for the first time that caspase-2 can regulate transcription.

Caspase-2 is essential for c-Jun transcriptional activation and Bim induction in neuron death.

In Alzheimer's disease (AD) brain, exposure of axons to Aβ causes pathogenic changes that spread retrogradely by unknown mechanisms, affecting the entire neuron. We found that locally applied Aβ1-42 initiates axonal synthesis of a defined set of proteins including the transcription factor ATF4. Inhibition of local translation and retrograde transport or knockdown of axonal Atf4 mRNA abolished Aβ-induced ATF4 transcriptional activity and cell loss. Aβ1-42 injection into the dentate gyrus (DG) of mice caused loss of forebrain neurons whose axons project to the DG. Protein synthesis and Atf4 mRNA were upregulated in these axons, and coinjection of Atf4 siRNA into the DG reduced the effects of Aβ1-42 in the forebrain. ATF4 protein and transcripts were found with greater frequency in axons in the brain of AD patients. These results reveal an active role for intra-axonal translation in neurodegeneration and identify ATF4 as a mediator for the spread of AD pathology.

Axonally synthesized ATF4 transmits a neurodegenerative signal across brain regions.

Specific therapies for neurologic diseases such as Alzheimer's disease provide the potential for better clinical outcomes. Expression of caspases in the brain is developmentally regulated, and dysregulated in neurologic disease, supporting that caspases may be therapeutic targets. The activity of caspases is carefully regulated via binding partners, cleavage, or endogenous inhibitors to prevent spontaneous activation, which could lead to aberrant cell death. This review serves as a brief examination of the current understanding of the regulation and function of caspases, and approaches to specifically target aberrant caspase activity. The use of proper tools to investigate individual caspases is addressed. Moreover, it summarizes the reports of various caspases in Alzheimer's disease studies. A better understanding of specific caspase pathways in heath and neurodegenerative disease is crucial for identifying specific targets for the development of therapeutic interventions.

Article	Year
Three-dimensional morphology of inner ear development in Xenopus laevis. Developmental dynamics : an official publication of the American Association of Anatomists\| PubMed ID: 12815629	2003
Glutamate elicits release of BDNF from basal forebrain astrocytes in a process dependent on metabotropic receptors and the PLC pathway. Neuron glia biology\| PubMed ID: 19267952	2008
The neuropeptide VGF is reduced in human bipolar postmortem brain and contributes to some of the behavioral and molecular effects of lithium. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 20631166	2010
Regulation of caspases in the nervous system implications for functions in health and disease. Progress in molecular biology and translational science\| PubMed ID: 21238939	2011
Neuronal caspase 2 activity and function requires RAIDD, but not PIDD. The Biochemical journal\| PubMed ID: 22515271	2012
Caspase-2 is essential for c-Jun transcriptional activation and Bim induction in neuron death. The Biochemical journal\| PubMed ID: 23815625	2013
Axonally synthesized ATF4 transmits a neurodegenerative signal across brain regions. Cell\| PubMed ID: 25171414	2014
Caspases: therapeutic targets in neurologic disease. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics\| PubMed ID: 25339539	2015

Ying Jean

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