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Andreas Barthel - One of the best experts on this subject based on the ideXlab platform.
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Cellular models for the analysis of signaling by protein kinase B and the forkhead Transcription Factor FKHR (Foxo1a).
Regulatory Peptides, 2004Co-Authors: Hans-martin Orth, Dieter Schmoll, Rolf Grempler, Klaus-dieter Krüger, Hans-georg Joost, Werner A. Scherbaum, Stefan R. Bornstein, Andreas BarthelAbstract:The Transcription Factor FKHR (FOXO1a) is regulated by protein kinase B (PKB) and insulin controls the expression of hepatic genes like glucose-6-phosphatase (G6Pase) at least in part via these proteins. However, insulin is known to activate several pathways and it is therefore difficult to establish which effects of the hormone are attributed to PKB and FKHR signaling. The aim of the present study was the generation of cellular models which allow the specific analysis of molecular events controlled by PKB and FKHR, respectively. We generated two H4IIEC3 rat hepatoma cell lines stably expressing either a hydroxytamoxifen-regulatable form of PKB (myristoylated PKB estrogen receptor chimera; MER-PKB) or FKHR (FKHR estrogen receptor chimera; FKHR-ER) by retroviral infection and determined the regulation of the G6Pase transcript by Northern blotting and enzyme assays. Activation of the regulatable PKB fusion protein almost completely reduced the dexamethasone/cAMP-stimulated G6Pase mRNA levels comparable to the effect of insulin. In contrast, stimulation of FKHR-ER with tamoxifen increased the expression of the dexamethasone/cAMP-induced G6Pase mRNA and the G6Pase enzymatic activity about 2.5- to 3-fold. The present data demonstrate that activation of PKB is sufficient to mimic the effect of insulin on the expression of G6Pase and that FKHR acts as an activator of the G6Pase gene indicating that the established cellular models are suitable for the specific analysis of downstream targets of these signaling molecules. Therefore, these cell systems might serve as useful tools for the development of anti-diabetic drugs.
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dyrk1 is a co activator of FKHR foxo1a dependent glucose 6 phosphatase gene expression
Biochemical and Biophysical Research Communications, 2003Co-Authors: Florian Von Grootebidlingmaier, Dieter Schmoll, Andreas Barthel, Hans-martin Orth, H G Joost, Walter BeckerAbstract:Expression of glucose-6-phosphatase (G6Pase), one of the rate-limiting enzymes of hepatic gluconeogenesis, has recently been shown to be transactivated by the Transcription Factor FKHR. One of the proteins known to directly interact with FKHR is the nuclear protein kinase DYRK1A. In order to study the effects of DYRK1A on G6Pase gene expression, we generated a H4IIEC3 rat hepatoma cell line stably expressing DYRK1A by retroviral infection. Overexpression of DYRK1A increased the expression of G6Pase about threefold, as determined by Northern blotting. In transiently transfected HepG2 cells, co-expression of DYRK1A and a G6Pase promoter construct increased G6Pase promoter activity about twofold. This effect of DYRK1A was independent of its kinase activity, since a kinase-dead DYRK1A mutant as well as a point mutant of the phosphorylation site of DYRK1A in FKHR (Ser329Ala) failed to affect the effect of DYRK1A on the G6Pase expression. The effect of DYRK on the G6Pase promoter activity was produced by the isoforms DYRK1A and DYRK1B, which are localized in the nucleus, but not by DYRK2. Mutations of the FKHR-binding sites in the G6Pase promoter markedly reduced the effect of DYRK1 on the G6Pase promoter activity. In summary, the data suggest that DYRK1 is a specific co-activator of FKHR, independent of its kinase activity.
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Akt modulates STAT3-mediated gene expression through a FKHR (FOXO1a)-dependent mechanism.
The Journal of biological chemistry, 2002Co-Authors: Marcin Kortylewski, Richard A Roth, Klaus-dieter Krüger, Hans-georg Joost, Gregor Bahrenberg, Florian Feld, Peter C. Heinrich, Iris Behrmann, Andreas BarthelAbstract:The phosphatidylinositol 3-kinase/Akt pathway plays an important role in the signaling of insulin and other growth Factors, which reportedly attenuate the interleukin-6 (IL-6)-mediated stimulation of acute phase plasma protein genes. We investigated the effect of the protein kinase Akt on IL-6-mediated Transcriptional activation. The transient expression of constitutively active Akt inhibited the IL-6-dependent activity of the alpha(2)-macroglobulin promoter in HepG2 cells, whereas expression of an inactive mutant of phosphatidylinositol-dependent kinase 1 had the opposite effect. Since Akt is known to regulate gene expression through inactivation of the Transcription Factor FKHR (forkhead in rhabdomyosarcoma), we examined the effect of FKHR on STAT3-mediated Transcriptional regulation. Indeed, the overexpression of FKHR specifically enhanced the activity of STAT3-dependent promoters but not that of a STAT5-responsive promoter. The effect of FKHR required the presence of functional STAT3 and was abrogated by the expression of dominant negative STAT3 mutants. Furthermore, FKHR and STAT3 were shown to coimmunoprecipitate and to colocalize in the nuclear regions of IL-6-treated HepG2 cells. Our results indicate that FKHR can modulate the IL-6-induced Transcriptional activity by acting as a coactivator of STAT3.
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Construction and characterization of a conditionally active construct of the insulin-regulated forkhead Transcription Factor FKHR.
Experimental and clinical endocrinology & diabetes : official journal German Society of Endocrinology [and] German Diabetes Association, 2002Co-Authors: Andreas Barthel, Dieter Schmoll, Hans-martin Orth, Klaus-dieter Krüger, Hans-georg JoostAbstract:Summary. Insulin is known to inhibit glucose-6-phosphatase gene expression through PI 3-kinase/PKB mediated phosphorylation and inactivation of the forkhead Transcription Factor FKHR, which is a potent transactivator of the glucose-6-phosphatase gene. To study the function and regulation of the Transcription Factor FKHR in hepatic cells, we constructed a hydroxytamoxifen-inducible version of FKHR by fusing a part of the hormone binding domain of the estrogen receptor (ER) to the C-terminus of FKHR (FKHR-ER). In HepG2-cells transiently transfected with plasmids encoding the FKHR-ER fusion protein and a glucose-6-phosphatase reporter construct, hydroxytamoxifen induced a marked induction of glucose-6-phosphatase promoter activity, whereas no effect was observed in control cells. We next generated a H4IIEC3 rat hepatoma cell line stably expressing both FKHR-ER and a glucose-6-phosphatase promoter-based reporter construct. After 2h stimulation with hydroxytamoxifen, the promoter activity was stimulated 3-5 fold, and continued to increase up to 100-fold after 15 h. The response was half maximal at 0.5 microM hydroxytamoxifen. Insulin (1 nM) decreased the hydroxytamoxifen induced promoter activity by about 70% of the maximal response. This cell system can be used for (1) the identification of FKHR dependent genes and for (2) high throughput screening (HTS) of agents affecting the activity of FKHR and its regulation by insulin. Abbreviations used: FKHR, forkhead in rhabdomyosarcoma; G6Pase, glucose-6-phosphatase; PKB, protein kinase B; PI 3-kinase, phosphatidyl-inositol 3-kinase; IRU, insulin-responsive unit; Tx, 4-hydroxytamoxifen, ER, estrogen receptor; HBD, hormone binding domain
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Regulation of the forkhead Transcription Factor FKHR (FOXO1a) by glucose starvation and AICAR, an activator of AMP-activated protein kinase.
Endocrinology, 2002Co-Authors: Andreas Barthel, Richard A Roth, Dieter Schmoll, Klaus-dieter Krüger, Hans-georg JoostAbstract:Expression of the catalytic subunit of glucose-6-phosphatase (G6Pase) has recently been shown to be transactivated by the Transcription Factor FKHR. Insulin and conditions of energy depletion are known repressors of the G6Pase gene. Whereas insulin is known to inhibit G6Pase expression by phosphorylation and nuclear exclusion of FKHR, the mechanism of repression of G6Pase by energy depletion is unknown. Here, we have studied the effect of glucose starvation and AICAR, an activator of AMP-activated protein kinase (AMPK) on G6Pase expression and the expressional level of FKHR-protein in hepatic cells. Using a H4-hepatoma cell line stably overexpressing FKHR, we found that both glucose starvation and treatment of cells with AICAR strongly repressed G6Pase expression and led to an almost complete disappearance of the FKHR protein, whereas the levels of control proteins and FKHR mRNA were not affected. Our data suggest that AICAR and glucose starvation inhibit G6Pase expression by a reduction of the cellular level of FKHR, presumably mediated by specific degradation of the protein.
Gabriel Nunez - One of the best experts on this subject based on the ideXlab platform.
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Regulation of the forkhead Transcription Factor FKHR, but not the PAX3-FKHR fusion protein, by the serine/threonine kinase Akt
Oncogene, 1999Co-Authors: Luis Del Peso, Frederic G Barr, Victor M Gonzalez, Ruben Hernandez, Gabriel NunezAbstract:Akt, a proto-oncogene that encodes a cytosolic serine/threonine kinase, can phosphorylate and modulate the activity of several proteins involved in cellular metabolism and survival. Recently, two mammalian highly related forkhead Transcription Factors FKHRL1 and AFX and their nematode homologue Daf-16 have been found to be targets of this kinase. Here we show that Akt, but not inactive Akt, represses the Transcriptional activity of FKHR, another member of the forkhead family. FKHR mutants with alanine substitutions at three Akt phosphorylation consensus sites (T24, S256 and S319) were inhibited by Akt, but mutation of all three sites rendered FKHR resistant to suppression. By contrast, the Transcriptional activity of the oncogenic PAX3 – FKHR fusion protein, containing two consensus phosphorylation sites, was not inhibited by Akt. Importantly, Akt inhibited the translocation of FKHR to the nucleus, providing a mechanism by which Akt might regulate the Transcriptional activity of FKHR. Consistent with this model, the localization of the PAX3 – FKHR fusion protein was nuclear and was not altered by Akt. These results provide evidence that Akt inhibits the Transcriptional activity of FKHR by controlling its trafficking into the nucleus and that oncogenic PAX3 – FKHR can escape this negative regulation by Akt.
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regulation of the forkhead Transcription Factor FKHR but not the pax3 FKHR fusion protein by the serine threonine kinase akt
Oncogene, 1999Co-Authors: Luis Del Peso, Frederic G Barr, Victor M Gonzalez, Ruben Hernandez, Gabriel NunezAbstract:Akt, a proto-oncogene that encodes a cytosolic serine/threonine kinase, can phosphorylate and modulate the activity of several proteins involved in cellular metabolism and survival. Recently, two mammalian highly related forkhead Transcription Factors FKHRL1 and AFX and their nematode homologue Daf-16 have been found to be targets of this kinase. Here we show that Akt, but not inactive Akt, represses the Transcriptional activity of FKHR, another member of the forkhead family. FKHR mutants with alanine substitutions at three Akt phosphorylation consensus sites (T24, S256 and S319) were inhibited by Akt, but mutation of all three sites rendered FKHR resistant to suppression. By contrast, the Transcriptional activity of the oncogenic PAX3 – FKHR fusion protein, containing two consensus phosphorylation sites, was not inhibited by Akt. Importantly, Akt inhibited the translocation of FKHR to the nucleus, providing a mechanism by which Akt might regulate the Transcriptional activity of FKHR. Consistent with this model, the localization of the PAX3 – FKHR fusion protein was nuclear and was not altered by Akt. These results provide evidence that Akt inhibits the Transcriptional activity of FKHR by controlling its trafficking into the nucleus and that oncogenic PAX3 – FKHR can escape this negative regulation by Akt.
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negative regulation of the forkhead Transcription Factor FKHR by akt
Journal of Biological Chemistry, 1999Co-Authors: Eric D Tang, Gabriel Nunez, Frederic G Barr, Kunliang GuanAbstract:The FKHR gene was first identified from its disruption by the t(2;13) chromosomal translocation seen in the pediatric tumor alveolar rhabdomyosarcoma. It encodes for a member of the forkhead family of Transcription Factors. Recently, a homolog of FKHR in the nematode Caenorhabditis elegans was identified called DAF-16, which is a downstream target of two Akt homologs in an insulin-related signaling pathway. We have examined the possible role of Akt in the regulation of FKHR. We find that FKHR can bind in vitro to the insulin-responsive sequence (IRS) in the insulin-like growth Factor-binding protein 1 promoter and can activate Transcription from a reporter plasmid containing multiple copies of the IRS. Expression of active but not inactive Akt can suppress FKHR-mediated Transcriptional activation. Akt can phosphorylate FKHR in vitro on three phosphoacceptor sites, at least a subset of which can also be phosphorylated by Akt in vivo. Importantly, mutation of these three sites to alanine residues enhances the Transcriptional activity of FKHR and renders it resistant to inhibition by Akt. Expression of an Akt-resistant mutant of FKHR causes apoptosis in 293T cells in a manner dependent on DNA binding. These results suggest that FKHR may be a direct nuclear regulatory target for Akt in both metabolic and cell survival pathways.
M. S. Felix - One of the best experts on this subject based on the ideXlab platform.
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Activation of Akt/FKHR in the medulla oblongata contributes to ă spontaneous respiratory recovery after incomplete spinal cord injury in ă adult rats
Neurobiology of Disease, 2014Co-Authors: M. S. Felix, F. Darlot, F Muscatelli, Anne Kästner, S. Bauer, P. Gauthier, Vito MatarazzoAbstract:After incomplete spinal cord injury (SCI), patients and animals may ă exhibit some spontaneous functional recovery which can be partly ă attributed to remodeling of injured neural circuitry. This post-lesion ă plasticity implies spinal remodeling but increasing evidences suggest ă that supraspinal structures contribute also to the functional recovery. ă Here we tested the hypothesis that partial SCI may activate ă cell-signaling pathway(s) at the supraspinal level and that this ă molecular response may contribute to spontaneous recovery. With this ă aim, we used a rat model of partial cervical hemisection which injures ă the bulbospinal respiratory tract originating from the medulla oblongata ă of the brainstem but leads to a time-dependent spontaneous functional ă recovery of the paralyzed hemidiaphragm. We first demonstrate that after ă SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata ă of the brainstem, resulting in an inactivation of its pro-apoptotic ă downstream target, forkhead Transcription Factor (FKHR/FOXO1A). ă Retrograde labeling of medullary premotoneurons including respiratory ă ones which project to phrenic motoneurons reveals an increased FKHR ă phosphorylation in their cell bodies together with an unchanged cell ă number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the ă SCI-induced Akt and FKHR phosphorylations and activates one of its ă death-promoting downstream targets, Fas ligand. Quantitative EMG ă analyses of diaphragmatic contractility demonstrate that the inhibition ă of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery ă normally observed after partial cervical SCI. Such inhibition does not ă however affect either baseline contractile frequency or the ventilatory ă reactivity under acute respiratory challenge. Together, these findings ă provide novel evidence of supraspinal cellular contribution to the ă spontaneous respiratory recovery after partial SCI. (C) 2014 Elsevier ă Inc All rights reserved.
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activation of akt FKHR in the medulla oblongata contributes to spontaneous respiratory recovery after incomplete spinal cord injury in adult rats
Neurobiology of Disease, 2014Co-Authors: M. S. Felix, F. Darlot, F Muscatelli, Anne Kästner, S. Bauer, P. Gauthier, Valéry MatarazzoAbstract:Abstract After incomplete spinal cord injury (SCI), patients and animals may exhibit some spontaneous functional recovery which can be partly attributed to remodeling of injured neural circuitry. This post-lesion plasticity implies spinal remodeling but increasing evidences suggest that supraspinal structures contribute also to the functional recovery. Here we tested the hypothesis that partial SCI may activate cell-signaling pathway(s) at the supraspinal level and that this molecular response may contribute to spontaneous recovery. With this aim, we used a rat model of partial cervical hemisection which injures the bulbospinal respiratory tract originating from the medulla oblongata of the brainstem but leads to a time-dependent spontaneous functional recovery of the paralyzed hemidiaphragm. We first demonstrate that after SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata of the brainstem, resulting in an inactivation of its pro-apoptotic downstream target, forkhead Transcription Factor (FKHR/FOXO1A). Retrograde labeling of medullary premotoneurons including respiratory ones which project to phrenic motoneurons reveals an increased FKHR phosphorylation in their cell bodies together with an unchanged cell number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the SCI-induced Akt and FKHR phosphorylations and activates one of its death-promoting downstream targets, Fas ligand. Quantitative EMG analyses of diaphragmatic contractility demonstrate that the inhibition of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery normally observed after partial cervical SCI. Such inhibition does not however affect either baseline contractile frequency or the ventilatory reactivity under acute respiratory challenge. Together, these findings provide novel evidence of supraspinal cellular contribution to the spontaneous respiratory recovery after partial SCI.
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Activation of Akt/FKHR in the medulla oblongata contributes to spontaneous respiratory recovery after incomplete spinal cord injury in adult rats.
Neurobiology of disease, 2014Co-Authors: M. S. Felix, F. Darlot, F Muscatelli, Anne Kästner, S. Bauer, P. Gauthier, Valéry MatarazzoAbstract:After incomplete spinal cord injury (SCI), patients and animals may exhibit some spontaneous functional recovery which can be partly attributed to remodeling of injured neural circuitry. This post-lesion plasticity implies spinal remodeling but increasing evidences suggest that supraspinal structures contribute also to the functional recovery. Here we tested the hypothesis that partial SCI may activate cell-signaling pathway(s) at the supraspinal level and that this molecular response may contribute to spontaneous recovery. With this aim, we used a rat model of partial cervical hemisection which injures the bulbospinal respiratory tract originating from the medulla oblongata of the brainstem but leads to a time-dependent spontaneous functional recovery of the paralyzed hemidiaphragm. We first demonstrate that after SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata of the brainstem, resulting in an inactivation of its pro-apoptotic downstream target, forkhead Transcription Factor (FKHR/FOXO1A). Retrograde labeling of medullary premotoneurons including respiratory ones which project to phrenic motoneurons reveals an increased FKHR phosphorylation in their cell bodies together with an unchanged cell number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the SCI-induced Akt and FKHR phosphorylations and activates one of its death-promoting downstream targets, Fas ligand. Quantitative EMG analyses of diaphragmatic contractility demonstrate that the inhibition of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery normally observed after partial cervical SCI. Such inhibition does not however affect either baseline contractile frequency or the ventilatory reactivity under acute respiratory challenge. Together, these findings provide novel evidence of supraspinal cellular contribution to the spontaneous respiratory recovery after partial SCI.
Paul J Coffer - One of the best experts on this subject based on the ideXlab platform.
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FKHR l1 can act as a critical effector of cell death induced by cytokine withdrawal protein kinase b enhanced cell survival through maintenance of mitochondrial integrity
Journal of Cell Biology, 2002Co-Authors: Pascale F Dijkers, Leo Koenderman, Janwillem J Lammers, Kim U Birkenkamp, Shaun N B Thomas, Paul J CofferAbstract:Survival signals elicited by cytokines include the activation of phosphatidylinositol 3-kinase (PI3K), which in turn promotes the activation of protein kinase B (PKB). Recently, PKB has been demonstrated to phosphorylate and inactivate forkhead Transcription Factor FKHR-L1, a potent inducer of apoptosis. To explore the mechanisms underlying the induction of apoptosis after cytokine withdrawal or FKHR-L1 activation, we used a cell line in which FKHR-L1 activity could be specifically induced. Both cytokine withdrawal and FKHR-L1 activation induced apoptosis, which was preceded by an upregulation in p27 KIP1 and a concomitant decrease in cells entering the cell cycle. Induction of apoptosis by both cytokine withdrawal and activation of FKHR-L1 correlated with the disruption of mitochondrial membrane integrity and cytochrome c release. This was preceded by upregulation of the pro-apoptotic Bcl-2 family member Bim. Ectopic expression of an inhibitory mutant of FKHR-L1 substantially reduced the levels of apoptosis observed after cytokine withdrawal. Activation of PKB alone was sufficient to promote cell survival, as measured by maintenance of mitochondrial integrity and the resultant inhibition of effector caspases. Furthermore, hematopoietic stem cells isolated from Bim −/− mice exhibited reduced levels of apoptosis upon inhibition of PI3K/PKB signaling. These data demonstrate that activation of FKHR-L1 alone can recapitulate all known elements of the apoptotic program normally induced by cytokine withdrawal. Thus PI3K/PKB–mediated inhibition of this Transcription Factor likely provides an important mechanism by which survival Factors act to prevent programmed cell death.
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FKHR-L1 can act as a critical effector of cell death induced by cytokine withdrawal: protein kinase B–enhanced cell survival through maintenance of mitochondrial integrity
The Journal of cell biology, 2002Co-Authors: Pascale F Dijkers, Leo Koenderman, Janwillem J Lammers, Eric Lam, Kim U Birkenkamp, N. Shaun B. Thomas, Paul J CofferAbstract:Survival signals elicited by cytokines include the activation of phosphatidylinositol 3-kinase (PI3K), which in turn promotes the activation of protein kinase B (PKB). Recently, PKB has been demonstrated to phosphorylate and inactivate forkhead Transcription Factor FKHR-L1, a potent inducer of apoptosis. To explore the mechanisms underlying the induction of apoptosis after cytokine withdrawal or FKHR-L1 activation, we used a cell line in which FKHR-L1 activity could be specifically induced. Both cytokine withdrawal and FKHR-L1 activation induced apoptosis, which was preceded by an upregulation in p27 KIP1 and a concomitant decrease in cells entering the cell cycle. Induction of apoptosis by both cytokine withdrawal and activation of FKHR-L1 correlated with the disruption of mitochondrial membrane integrity and cytochrome c release. This was preceded by upregulation of the pro-apoptotic Bcl-2 family member Bim. Ectopic expression of an inhibitory mutant of FKHR-L1 substantially reduced the levels of apoptosis observed after cytokine withdrawal. Activation of PKB alone was sufficient to promote cell survival, as measured by maintenance of mitochondrial integrity and the resultant inhibition of effector caspases. Furthermore, hematopoietic stem cells isolated from Bim −/− mice exhibited reduced levels of apoptosis upon inhibition of PI3K/PKB signaling. These data demonstrate that activation of FKHR-L1 alone can recapitulate all known elements of the apoptotic program normally induced by cytokine withdrawal. Thus PI3K/PKB–mediated inhibition of this Transcription Factor likely provides an important mechanism by which survival Factors act to prevent programmed cell death.
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expression of the pro apoptotic bcl 2 family member bim is regulated by the forkhead Transcription Factor FKHR l1
Current Biology, 2000Co-Authors: Pascale F Dijkers, Leo Koenderman, Janwillem J Lammers, Rene H. Medema, Paul J CofferAbstract:Cell death is regulated mainly through an evolutionarily conserved form of cell suicide termed apoptosis [1]. Deregulation of apoptosis has been associated with cancer, autoimmune diseases and degenerative disorders. Many cells, particularly those of the hematopoietic system, have a default program of cell death and survival that is dependent on the constant supply of survival signals. The Bcl-2 family, which has both pro- and anti-apoptotic members, plays a critical role in regulating cell survival [2]. One family member, the Bcl-2 interacting mediator of cell death (Bim), contains only a protein-interaction motif known as the BH3 domain, allowing it to bind pro-survival Bcl-2 molecules, neutralizing their function [3]. Disruption of the bim gene results in resistance to apoptosis following cytokine withdrawal in leukocytes, indicating that regulation of the pro-apoptotic activity of Bim is critical for maintenance of the default apoptotic program [4]. Here, we report that withdrawal of cytokine results in upregulation of Bim expression concomitant with induction of the apoptotic program in lymphocytes. Activation of the forkhead Transcription Factor FKHR-L1, previously implicated in regulation of apoptosis in T lymphocytes [5], was sufficient to induce Bim expression. We propose a mechanism by which cytokines promote lymphocyte survival by inhibition of FKHR-L1, preventing Bim expression.
Valéry Matarazzo - One of the best experts on this subject based on the ideXlab platform.
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activation of akt FKHR in the medulla oblongata contributes to spontaneous respiratory recovery after incomplete spinal cord injury in adult rats
Neurobiology of Disease, 2014Co-Authors: M. S. Felix, F. Darlot, F Muscatelli, Anne Kästner, S. Bauer, P. Gauthier, Valéry MatarazzoAbstract:Abstract After incomplete spinal cord injury (SCI), patients and animals may exhibit some spontaneous functional recovery which can be partly attributed to remodeling of injured neural circuitry. This post-lesion plasticity implies spinal remodeling but increasing evidences suggest that supraspinal structures contribute also to the functional recovery. Here we tested the hypothesis that partial SCI may activate cell-signaling pathway(s) at the supraspinal level and that this molecular response may contribute to spontaneous recovery. With this aim, we used a rat model of partial cervical hemisection which injures the bulbospinal respiratory tract originating from the medulla oblongata of the brainstem but leads to a time-dependent spontaneous functional recovery of the paralyzed hemidiaphragm. We first demonstrate that after SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata of the brainstem, resulting in an inactivation of its pro-apoptotic downstream target, forkhead Transcription Factor (FKHR/FOXO1A). Retrograde labeling of medullary premotoneurons including respiratory ones which project to phrenic motoneurons reveals an increased FKHR phosphorylation in their cell bodies together with an unchanged cell number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the SCI-induced Akt and FKHR phosphorylations and activates one of its death-promoting downstream targets, Fas ligand. Quantitative EMG analyses of diaphragmatic contractility demonstrate that the inhibition of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery normally observed after partial cervical SCI. Such inhibition does not however affect either baseline contractile frequency or the ventilatory reactivity under acute respiratory challenge. Together, these findings provide novel evidence of supraspinal cellular contribution to the spontaneous respiratory recovery after partial SCI.
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Activation of Akt/FKHR in the medulla oblongata contributes to spontaneous respiratory recovery after incomplete spinal cord injury in adult rats.
Neurobiology of disease, 2014Co-Authors: M. S. Felix, F. Darlot, F Muscatelli, Anne Kästner, S. Bauer, P. Gauthier, Valéry MatarazzoAbstract:After incomplete spinal cord injury (SCI), patients and animals may exhibit some spontaneous functional recovery which can be partly attributed to remodeling of injured neural circuitry. This post-lesion plasticity implies spinal remodeling but increasing evidences suggest that supraspinal structures contribute also to the functional recovery. Here we tested the hypothesis that partial SCI may activate cell-signaling pathway(s) at the supraspinal level and that this molecular response may contribute to spontaneous recovery. With this aim, we used a rat model of partial cervical hemisection which injures the bulbospinal respiratory tract originating from the medulla oblongata of the brainstem but leads to a time-dependent spontaneous functional recovery of the paralyzed hemidiaphragm. We first demonstrate that after SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata of the brainstem, resulting in an inactivation of its pro-apoptotic downstream target, forkhead Transcription Factor (FKHR/FOXO1A). Retrograde labeling of medullary premotoneurons including respiratory ones which project to phrenic motoneurons reveals an increased FKHR phosphorylation in their cell bodies together with an unchanged cell number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the SCI-induced Akt and FKHR phosphorylations and activates one of its death-promoting downstream targets, Fas ligand. Quantitative EMG analyses of diaphragmatic contractility demonstrate that the inhibition of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery normally observed after partial cervical SCI. Such inhibition does not however affect either baseline contractile frequency or the ventilatory reactivity under acute respiratory challenge. Together, these findings provide novel evidence of supraspinal cellular contribution to the spontaneous respiratory recovery after partial SCI.