Nuclear Factor-κB Activation in Axons and Schwann Cells in Experimental Sciatic Nerve Injury and Its Role in Modulating Axon Regeneration: Studies With Etanercept

Abstract

Early inflammatory events may inhibit functional recovery after injury in both the peripheral and central nervous systems. We investigated the role of the inflammatory tumor necrosis factor/nuclear factor-kappaB (NF-kappaB) axis on events subsequent to sciatic nerve crush injury in adult rats. Electrophoretic mobility shift assays revealed that within 6 hours after crush, NF-kappaB DNA-binding activity increased significantly in a 1-cm section around the crush site. By immunofluorescence staining, there was increased nuclear localization of the NF-kappaB subunits p50 but not p65 or c-Rel in Schwann cells but no obvious inflammatory cell infiltration. In rats injected subcutaneously with etanercept, a tumor necrosis factor receptor chimera that binds free cytokine, the injury-induced rise in NF-kappaB DNA-binding activity was inhibited, and nuclear localization of p50 in Schwann cells was lowered after the injury. Axonal growth 3 days after nerve crush assessed with immunofluorescence for GAP43 demonstrated that the regeneration distance of leading axons from the site of nerve crush was greater in etanercept-treated animals than in saline-treated controls. These data indicate that tumor necrosis factor mediates rapid activation of injury-induced NF-kappaB DNA binding in Schwann cells and that these events are associated with inhibition of postinjury axonal sprouting.

Abnormal Regenerative Responses and Impaired Axonal Outgrowth after Nerve Crush in TDP-43 Transgenic Mouse Models of Amyotrophic Lateral Sclerosis

“…Evaluation of immunostaining. Immunoreactivity (IR) scores were assigned as described previously (Ravizza et al, 2006;Iyer et al, 2010) by a blinded investigator. Assigned scores represent averages for all cells in the sciatic motor neuron pool.…”

“…Neuronal overexpression at high levels of wild-type (WT) or mutant TDP-43 in transgenic mice caused a dose-dependent degeneration of cortical and spinal motor neurons but with no cytoplasmic TDP-43 aggregates (Wegorzewska et al, 2009;Stallings et al, 2010;Wils et al, 2010;Xu et al, 2010), raising the possibility that an upregulation of TDP-43 in the nucleus rather than TDP-43 cytoplasmic aggregates may contribute to neurodegeneration. In fact, TDP-43 has been reported to be upregulated in the CSF of patients with ALS (Kasai et al, 2009) and in peripheral blood lymphocytes from ALS patients (Mougeot et al, 2011;Nardo et al, 2011). Recently, we reported that TDP-43 is upregulated in the spinal cord of sporadic ALS cases at both the mRNA and protein levels (Swarup et al 2011b).…”

“…Tar DNA binding protein 43 (TDP-43), a DNA/RNA-binding 43 kDa protein, has been implicated in ALS (Arai et al, 2006;Neumann et al, 2006), and dominant mutations in TARDBP, which codes for TDP-43, were reported by several groups as a primary cause of ALS (Gitcho et al, 2008;Kabashi et al, 2008;Sreedharan et al, 2008;Van Deerlin et al, 2008) and may account for ϳ3% of familial ALS cases and ϳ1.5% of sporadic cases. TDP-43, normally observed in the nucleus, is detected in pathological inclusions in the cytoplasm and nucleus of both neurons and glial cells of ALS and frontotemporal lobar degeneration with ubiquitin inclusions cases (Arai et al, 2006;Neumann et al, 2006). The inclusions consist prominently of TDP-43 C-terminal fragments of ϳ25 kDa.…”

Growth/differentiation factor-15 and its role in peripheral nervous system lesion and regeneration

“…Through TNFR1, NF-κB is activated by TNF-α, leading to a pro-inflammatory process. NF-κB is a key modulator of Wallerian degeneration for successful axon regeneration (Smith et al, 2009). …”

“…To investigate whether there was a difference between WT and KO animals in terms of demyelination and regeneration, representative genes were studied, including Krox-20 for demyelination , NF-κB for activation of glial cells (Nickols et al, 2003;Smith et al, 2009), MAC-2 for macrophage-Schwann cell interaction (Saada et al, 1996;Stoll and Muller, 1999) and NCAM for SC migration (Hansen et al, 2008;Thomaidou et al, 2001). After SN crush, the distal Segments C from WT and KO animals were collected at different time points, RNAs and proteins were isolated for qRT-PCR and Western blot analysis.…”