Browsing by Author "Alexander, Thomas D."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Axotomy-induced target disconnection promotes an additional death mechanism involved in motoneuron degeneration in amyotrophic lateral sclerosis transgenic mice
    (Wiley, 2014-07) Haulcomb, Melissa M.; Mesnard, Nichole A.; Batka, Richard J.; Alexander, Thomas D.; Sanders, Virginia M.; Jones, Kathryn J.; Department of Anatomy & Cell Biology, School of Medicine
    The target disconnection theory of amyotrophic lateral sclerosis (ALS) pathogenesis suggests that disease onset is initiated by a peripheral pathological event resulting in neuromuscular junction loss and motoneuron (MN) degeneration. Presymptomatic mSOD1(G93A) mouse facial MN (FMN) are more susceptible to axotomy-induced cell death than wild-type (WT) FMN, which suggests additional CNS pathology. We have previously determined that the mSOD1 molecular response to facial nerve axotomy is phenotypically regenerative and indistinguishable from WT, whereas the surrounding microenvironment shows significant dysregulation in the mSOD1 facial nucleus. To elucidate the mechanisms underlying the enhanced mSOD1 FMN loss after axotomy, we superimposed the facial nerve axotomy model on presymptomatic mSOD1 mice and investigated gene expression for death receptor pathways after target disconnection by axotomy vs. disease progression. We determined that the TNFR1 death receptor pathway is involved in axotomy-induced FMN death in WT and is partially responsible for the mSOD1 FMN death. In contrast, an inherent mSOD1 CNS pathology resulted in a suppressed glial reaction and an upregulation in the Fas death pathway after target disconnection. We propose that the dysregulated mSOD1 glia fail to provide support the injured MN, leading to Fas-induced FMN death. Finally, we demonstrate that, during disease progression, the mSOD1 facial nucleus displays target disconnection-induced gene expression changes that mirror those induced by axotomy. This validates the use of axotomy as an investigative tool in understanding the role of peripheral target disconnection in the pathogenesis of ALS.
  • Thumbnail Image
    Item
    CD4+ T cell-mediated neuroprotection is independent of T cell-derived BDNF in a mouse facial nerve axotomy model
    (Elsevier, 2012) Xin, Junping; Mesnard, Nichole A.; Beahrs, Taylor; Wainwright, Derek A.; Serpe, Craig J.; Alexander, Thomas D.; Sanders, Virginia M.; Jones, Kathryn J.; Anatomy, Cell Biology and Physiology, School of Medicine
    Background: The production of neurotrophic factors, such as BDNF, has generally been considered an important mechanism of immune-mediated neuroprotection. However, the ability of T cells to produce BDNF remains controversial. Methods: In the present study, we examined mRNA and protein of BDNF using RT-PCR and western blot, respectively, in purified and reactivated CD4(+) T cells. In addition, to determine the role of BDNF derived from CD4(+) T cells, the BDNF gene was specifically deleted in T cells using the Cre-lox mouse model system. Results: Our results indicate that while both mRNA expression and protein secretion of BDNF in reactivated T cells were detected at 24 h, only protein could be detected at 72 h after reactivation. The results suggest a transient up-regulation of BDNF mRNA in reactivated T cells. Furthermore, in contrast to our hypothesis that the BDNF expression is necessary for CD4(+) T cells to mediate neuroprotection, mice with CD4(+) T cells lacking BDNF expression demonstrated a similar level of facial motoneuron survival compared to their littermates that expressed BDNF, and both levels were comparable to wild-type. The results suggest that the deletion of BDNF did not impair CD4(+) T cell-mediated neuroprotection. Conclusion: Collectively, while CD4(+) T cells are a potential source of BDNF after nerve injury, production of BDNF is not necessary for CD4(+) T cells to mediate their neuroprotective effects.