Life and Death in the Nervous System. Role of Neurotrophic Factors and Their Receptors

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https://sversufguwatho.ml/gade-chatea-gratis.php GFP shows the efficiency of cell transfection. C Cell viability determined by the criterion of propidium iodide exclusion [52] after 4 DIV. At least 50 neurons were scored for each condition. Double immunofluorescence of adult RGC showing the distribution of NF displaying neuronal shape and myc marker of transfection with cDNA encoding for a constitutively active form of the PI3K regulatory subunit p Cells were transfected and cultured for 4 days.

Within the developing hippocampus, passage from stage 2 of differentiation prior to the appearance of a discernible axon to stage 3 appearance of an identifiable axon is marked by the segregation of activatable IGF-1R to one neurite with the subsequent activation of PI3K, axonal specification and outgrowth [13]. Several studies have demonstrated the involvement of IGF-1R and downstream signaling pathways, including PI3K and cdc42, in the regulation of axonal specification and outgrowth during differentiation in at least two types of central neurons: hippocampal pyramidal neurons [13] and corticospinal motor neurons [30].

This receptor system is also involved in axonal regeneration in adult peripheral nervous system [17] , [18]. In order to perform these studies we chose RGCs as a model for mature neurons for the following reasons: i the axons of these cells, located in the optic nerve, are affected in many disorders including traumatic optic neuropathy [32] , ischemic optic neuropathy [33] , optic neuritis [34] and glaucoma [35]. Functional recovery after these insults requires overcoming several barriers compromising RGC axonal outgrowth potential; ii all the retinal neurons, including RGC, are able to survive and develop neurites in primary cultures including those from adult animals and humans [19] , [23] , [36] ; iii retinal cells in culture have been extensively used to study the cellular and molecular mechanisms involved in axonal regeneration [37] , [38] ; iv retina cells express IGF and IGF-1R widely [20] , [21] ; and v the optic nerve is a readily accessible region of the CNS in which to further explore these studies in vivo.

The expression of IGF-1R is developmentally regulated in brain, reaching highest levels at embryonic and early postnatal stages [39] , [40]. Expression of IGF-1R is relatively low in the adult retina.

Background

Life and Death in the Nervous System. Role of Neurotrophic Factors and Their Receptors. Book • Edited by: C.F. IBÁÑEZ, T. HÖKFELT, D. OTTOSON. Life and Death in the Nervous System: Role of Neurotrophic Factors and Their Receptors. C. F. Ibanez, T. Hokfelt, L. Olson, K. Fuxe, H. Jornvall, D. Ottoson.

We observed a significant increase in the expression of this receptor after disaggregation and culture of adult RGC. The fact that polarized activation of the IGF-1R at the growth cone and distal axon is sufficient to stimulate axonal regeneration in the absence of any other growth factor is a novel observation.

By Jennifer McDowall

This is somewhat in contradiction to the observation that CNS neurons, using RGC as an experimental model, require a cocktail of trophic factors in order to survive and regenerate neurites in vitro [41]. There is a notable down-regulation of endogenous IGF-1 expression by the RGC during postnatal maturation [43] , which may be one of the reasons of the very limited axonal regeneration in adult optic nerve. In keeping with this idea, IGF-1 delivery into postnatal rat eyes partly rescues RGC from programmed cell death and maintains higher numbers of axons within the optic nerve [44].

Several neurotrophic factors have been implicated in ameliorating survival and axonal regeneration in adult RGC. Hepatocyte growth factor improves both RGC survival and axonal regeneration in vivo and in vitro , and also exerts its effects through activation of Akt [46]. Although there are numerous similarities between axon outgrowth in embryonic and adult CNS, there are also some differences.

While BDNF acting through the PI3K pathway has been shown to be involved in adult RGC process regeneration [47] , this factor does not trigger axonal specification and outgrowth in embryonic hippocampal neurons [13] or cortical motor neurons [30]. Moreover, transfection with a constitutively active form of PI3K was sufficient to trigger axonal regeneration in the absence of any other extracellular stimulus.

Research Area

It has also been shown that PI3K activation significantly increases axonal regeneration over the level induced by pten phosphatase and tensin homolog deletion [50]. This could be very interesting in the field of gene therapy directed towards promotion of re-growth of damaged RGC axons in several neurodegenerative conditions.

This is especially cogent given that up-regulation of IGF-1 within the eye leads to appearance of diabetes-like alterations [51] , which cautions against direct use of this growth factor in promoting axonal repair. Wrote the paper: DH SQ. Browse Subject Areas?

The Nervous System, Part 1: Crash Course A&P #8

Click through the PLOS taxonomy to find articles in your field. Abstract Axonal regeneration is an essential condition to re-establish functional neuronal connections in the injured adult central nervous system CNS , but efficient regrowth of severed axons has proven to be very difficult to achieve. Introduction The functional repair of the adult central nervous system CNS constitutes a major challenge for modern medicine. Cell Culture Retinal cultures were prepared essentially as previously described [19] , [24] , [25].

Download: PPT. Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. References 1. Annu Rev Neurosci — View Article Google Scholar 2. Caroni P Intrinsic neuronal determinants that promote axonal sprouting and elongation. Bioessays — View Article Google Scholar 3. Restor Neurol Neurosci 85— View Article Google Scholar 4. J Neurochem — View Article Google Scholar 5. Bouquet C, Nothias F Molecular mechanisms of axonal growth.

Introduction

The VGF gene has been highly conserved throughout evolution and is located on chromosome 7q22 in humans and chromosome 5 in mice. Arrows indicate stained cells. In addition, because simultaneous expression of both the neurotrophic ligand and its receptor has been reported for a number of neuronal subpopulations, disturbances in such auto- and paracrine loops might contribute to neurodegeneration. Nat Rev Drug Discov Longo FM, Massa SM Small-molecule modulation of neurotrophin receptors: a strategy for the treatment of neurological disease. In MDD patients, serum NGF level is higher than in controls, and has been associated with the severity of depressive symptoms in women [ ].

Adv Exp Med Biol 1— All NTFs can bind to the p75 receptor. Although both the Trk receptor and the p75NTR receptor have a ligand-binding region and a cytoplasmic region, the sequences of the two have no similarities. After NTF dimerization, it binds to the Trk receptor, dimerizing the receptor and activating the catalytic tyrosine protein kinase region.

The dimerized Trk receptor auto phosphorylates several signaling pathways within the cell. These are tyrosine phosphorylated after recognition of a specific ligand at a recognition site, and they contain a phosphoserine-binding motif such as Src homology region 2 SH2. The SH2 binding protein linkage activates the Trk receptor to achieve its neurotrophic activity primarily through two distinct intracellular signaling pathways. The major neuronal survival pathways, including the SH2-linked Trk receptor, activate PI3K kinase, increase its phosphorylation level, and then sequentially activate downstream Akts that have multiple functions in the apoptotic program.

CREB proteins play multiple roles in cell cycle, neurite outgrowth, and synaptic plasticity. Activation of the Trk receptor can further activate multiple downstream pathways. And it interacts with Trk receptors to enhance the recognition of different neurotrophic factors. There is extensive programmed cell death during the development of the nervous system, which determines the number of cells and the correct distribution of neurons during development. NTF is highly expressed early in development and is essential for neuronal survival and selection at different developmental stages.

The neurotrophic hypothesis provides a functional analysis of the role of NTF in the development of the nervous system. The nervous system shapes itself to maintain the most competitive and appropriate synaptic connections. A small amount of NTF produced by neurons compressing target cells indicates selective cell survival. In the central nervous system, repeated expression of multiple NTF receptors and cognate ligands allows for a variety of different linkages that allow the neural network to expand into maturity. In addition, current research has shown that NTF secreted by neurons can also act on itself autocrine transmission , or it can be transported down to the axon to act on adjacent neurons.

At the same time, glial cells can also secrete NTF to neurons through paracrine secretion. In the peripheral nerve, the information transmitted by the NTF reverse signaling pathway must be effectively transmitted over long distances, sometimes even over 1 minute.

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NTF promotes neuronal survival and differentiation during development, but they can also guide the death of neurons. While a great deal remains to be discovered about the wide ranging functions of the p75 NTR , studies summarized in this review highlight the immense potential for development of novel neuroprotective and neurorestorative therapies. Users Online: Neuron Bernabeu RO, Longo FM The p75 neurotrophin receptor is expressed by adult mouse dentate progenitor cells and regulates neuronal and non-neuronal cell genesis. BMC Neurosci ASN Neuro 1.

Chu GK, Yu W, Fehlings MG The p75 neurotrophin receptor is essential for neuronal cell survival and improvement of functional recovery after spinal cord injury. Neuroscience Embo J Ann Neurol Trends Neurosci Neurology Mol Cell Neurosci Friedman WJ Neurotrophins induce death of hippocampal neurons via the p75 receptor. J Neurosci Hannila SS, Kawaja MD Nerve growth factor-mediated collateral sprouting of central sensory axons into deafferentated regions of the dorsal horn is enhanced in the absence of the p75 neurotrophin receptor.

J Comp Neurol Nature Ibanez CF, Simi A p75 neurotrophin receptor signaling in nervous system injury and degeneration: paradox and opportunity.

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Neurotoxicology Brain Res Mol Brain Res Handb Exp Pharmacol Longo FM, Massa SM Small-molecule modulation of neurotrophin receptors: a strategy for the treatment of neurological disease. Nat Rev Drug Discov Meeker R, Williams K Dynamic nature of the p75 neurotrophin receptor in response to injury and disease.

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J Neuroimmune Pharmacol Nat Neurosci J Alzheimers Dis Neuropathol Appl Neurobiol Laryngoscope Cell Death Dis 3:e PLoS One 9:e Stem Cells J Neurochem Sorensen B, Tandrup T, Koltzenburg M, Jakobsen J No further loss of dorsal root ganglion cells after axotomy in p75 neurotrophin receptor knockout mice. Glia Role of caspases. J Biol Chem Int J Biochem Cell Biol Neurosci Lett