| Abstract No.: | A-C1106 |
| Country: | Canada |
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| Title: | REGULATION OF FOXO3A TRANSCRIPTION FACTOR EXPRESSION AND NUCLEAR LOCALIZATION IN SENSORY NEURONS IN RESPONSE TO CELLULAR STRESS |
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| Authors/Affiliations: | 1 Jovan Hasmatali*; 2 Mohammad Hossein Noyan Ashraf ; 1 Bernhard Juurlink; 1 Valerie Verge;
1 University of Saskatchewan, Saskatoon, SK, Canada; 2 University of Toronto, ON, Canada
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| Content: | Cellular stress is a well-known modifier of gene expression and protein activation in cells of the nervous system. Activation of stress pathways associated with neuropathologies may benefit or hinder successful recovery. The expression and activation of the forkhead box transcription factor, class O 3a (FOXO3a) is strongly implicated in this pathway and induction of this transcription factor may lead to the activation of apoptotic genes and cell death. FOXO3a’s activity is regulated by phosphorylation in a PI3K/Akt dependent manner and remains cytoplasmic when phosphorylated. However when signaling is decreased, the serine/threonine residues are dephosphorylated, thereby facilitating nuclear localization. The proteins functional reaction to stress has been characterized in a variety of neuronal cell types, such as motoneurons, hippocampal, and neuroblastoma cells where induction of this transcription factor leads to cell death. However, the role of FOXO3a in the stress response regulation of sensory neurons has not been elucidated. Objective: To investigate the effect of nerve injury on the temporal FOXO3a expression and nuclear localization in dorsal root ganglion (DRG) neurons using a chronic injury time course model. Materials and Methods: The right L4-L6 spinal nerves of adult male Wistar rats were axotomized and corresponding ipsilateral and contralateral formaldehyde perfused DRGs were dissected and examined after 1-hour, 1-day, 2-day and 1-week time points. Ten µm sections of collected DRG were thaw mounted on microscope slides and processed for immunohistochemistry using a rabbit anti-FOXO3a antibody and in situ hybridization with an S35 labeled DNA probe. Results: Preliminary analysis of protein suggests that FOXO3a expression levels are higher in the small-med sized presumably nociceptive neurons. Unilateral peripheral nerve injury results in an initial bilateral increase in nuclear localization in virtually all small-med neurons at 1-hour followed by an overall decrease in both cytoplasmic and nuclear staining ipsilaterally by 1-day. This low level continued up to 1-week post-injury. Interestingly, FOXO3a nuclear localization in DRG contralateral to injury showed a biphasic response where localization increased from 1-hour to 1-day, was decreased by 2-days and elevated again by 1-week. In situ hybridization studies on the same tissue revealed that message levels largely paralleled that observed for protein. Glial perineuronal cells show increased levels of the protein over-time ipsilaterally and FOXO3a also appears to be localized to neuronal fiber tracts. Conclusions: The temporal spatial responses of FOXO3a to axotomy implicate it in the acute response of sensory neurons to injury, while diminished expression at subsequent timepoints is consistent with the reduced neurotrophin signaling associated with this state. The bilateral and contralateral alterations in FOXO3a may be due to humeral factors implying a systemic response to the injury. Peripheral nerve injury also appears to regulate glial expression of FOXO3a and its localization to fibre tracts indicates that it may be transported. Furthermore, the fact that levels appeared higher in small-med sized neurons implicate that this protein in nociception. |
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