Traumatic Spinal Cord Injury Induces Nuclear Factor-κB Activation

Abstract

Inflammatory responses are a major component of secondary injury and play a central role in mediating the pathogenesis of acute and chronic spinal cord injury (SCI). The nuclear factor-kappaB (NF-kappaB) family of transcription factors is required for the transcriptional activation of a variety of genes regulating inflammatory, proliferative, and cell death responses of cells. In this study we examined the temporal and cellular expression of activated NF-kappaB after traumatic SCI. We used a contusion model (N.Y.U. Impactor) to initiate the early biochemical and molecular changes that occur after traumatic injury to reproduce the pathological events associated with acute inflammation after SCI. The activation and cellular distribution of activated NF-kappaB was evaluated by using a monoclonal antibody that selectively recognizes activated p65 in a NF-kappaB dimer. Immunohistochemical and Western blot analyses demonstrated that NF-kappaB activation occurred as early as 0.5 hr postinjury and persisted for at least 72 hr. Using electrophoretic mobility shift assays (EMSA), we demonstrate that NF-kappaB is activated after SCI. In our immunohistochemical, Western, and EMSA experiments there are detectable levels of activated NF-kappaB in our control animals. Using double-staining protocols, we detected activated NF-kappaB in macrophages/microglia, endothelial cells, and neurons within the injured spinal cord. Colocalization of activated NF-kappaB with the NF-kappaB-dependent gene product, inducible nitric oxide synthase (iNOS), suggests functional implications for this transcription factor in the pathogenesis of acute spinal cord injury. Although there is considerable evidence for the involvement of an inflammatory reaction after traumatic SCI, this is the first evidence for the activation of NF-kappaB after trauma. Strategies directed at blocking the initiation of this cascade may prove beneficial as a therapeutic approach for the treatment of acute SCI.

Roles for NF-κB in nerve cell survival, plasticity, and disease

“…71 Traumatic injury to the brain and spinal cord results in increased levels of NF-kB activity in cells within and surrounding the site of injury including neurons, astrocytes, and microglia. 72 NF-kB activity can remain elevated for long time periods (weeks to months) following a traumatic injury and likely contributes to associated inflammatory processes. Damage to cortical neurons and the blood-brain barrier were exacerbated in mice lacking TNFa receptors, which was associated with reduced NF-kB activation, 73 consistent with an adaptive neuroprotective function of NF-kB.…”

Post-traumatic inflammation following spinal cord injury

“…29 Activation of nuclear factor kappaB (NF-kB) by TNF-a induces transcriptional activation of iNOS, thus causing further cell damage. 3 This effect is partially blocked by the NMDA receptor antagonist MK-801 in the spinal cord white and grey matter and offers a potential therapeutic target. 88 In the CNS, apoptosis involves predominantly nonneuronal cells such as oligodendrocytes.…”

“…[1][2][3][4][5][6][7][8] SCIinduced inflammation may result in further reduction in functional recovery because of the development of scar tissue, as well as necrosis or apoptosis of neurons and oligodendrocytes. However, a potentially beneficial role of the inflammatory process has also been reported, illustrating the dual nature of post-traumatic inflammation.…”

“…14 The infiltration of the CNS by leucocytes is orchestrated by specific cell adhesion molecules that promote cell-to-cell interactions between astrocytes, endothelial cells, microglia, and macrophages. 3 Interestingly, it has been shown that the acute inflammatory response to traumatic injury is greater in the spinal cord than in the cerebral cortex. 9,10 Following a comparable mechanical injury, the number of neutrophils and activated microglia/macrophage, as well as the extent of their infiltration, was much less in the cerebral cortex than in the spinal cord.…”

Inflammation and spinal cord injury: Infiltrating leukocytes as determinants of injury and repair processes

“…Neutrophils release reactive oxygen and nitrosyl radicals as well as cytokines, chemokines, and a variety of proteases, including metalloproteinases and neutrophil elastase, and as such are key determinants in secondary tissue damage (Table 1) (22)(23)(24)(25) . The damaging effects of neutrophils in spinal cord injury are perhaps best illustrated in studies showing that either depletion of circulating neutrophils, inhibition of neutrophil-related proteolytic enzyme activities (19,23) , or inhibition of neutrophil adhesion (26) confer neuroprotection.…”