The cytokine temporal profile in rat cortex after controlled cortical impact

Strain influences on inflammatory pathway activation, cell infiltration and complement cascade after traumatic brain injury in the rat

Increasing evidence suggests that genetic background affects outcome of traumatic brain injuries (TBI). Still, there is limited detailed knowledge on what pathways/processes are affected by genetic heterogeneity. The inbred rat strains DA and PVG differ in neuronal survival following TBI. We here carried out global expressional profiling to identify differentially regulated pathways governing the response to an experimental controlled brain contusion injury. One of the most differentially regulated molecular networks concerned immune cell trafficking. Subsequent characterization of the involved cells using flow cytometry demonstrated greater infiltration of neutrophils and monocytes, as well as a higher degree of microglia activation in DA compared to PVG rats. In addition, DA rats displayed a higher number of NK cells and a higher ratio of CD161bright compared to CD161dim NK cells. Local expression of complement pathway molecules such as C1 and C3 was higher in DA and both the key complement component C3 and membrane-attack complex (MAC) could be demonstrated on axons and nerve cells. A stronger activation of the complement system in DA was associated with higher cerebrospinal fluid levels of neurofilament-light, a biomarker for nerve/axonal injury. In summary, we demonstrate substantial differences between DA and PVG rats in activation of inflammatory pathways; in particular, immune cell influx and complement activation associated with neuronal/axonal injury after TBI. These findings suggest genetic influences acting on inflammatory activation to be of importance in TBI and motivate further efforts using experimental forward genetics to identify genes/pathways that affect outcome.

Understanding the neuroinflammatory response following concussion to develop treatment strategies

Mild traumatic brain injuries (mTBI) have been associated with long-term cognitive deficits relating to trauma-induced neurodegeneration. These long-term deficits include impaired memory and attention, changes in executive function, emotional instability, and sensorimotor deficits. Furthermore, individuals with concussions show a high co-morbidity with a host of psychiatric illnesses (e.g., depression, anxiety, addiction) and dementia. The neurological damage seen in mTBI patients is the result of the impact forces and mechanical injury, followed by a delayed neuroimmune response that can last hours, days, and even months after the injury. As part of the neuroimmune response, a cascade of pro- and anti-inflammatory cytokines are released and can be detected at the site of injury as well as subcortical, and often contralateral, regions. It has been suggested that the delayed neuroinflammatory response to concussions is more damaging then the initial impact itself. However, evidence exists for favorable consequences of cytokine production following traumatic brain injuries as well. In some cases, treatments that reduce the inflammatory response will also hinder the brain's intrinsic repair mechanisms. At present, there is no evidence-based pharmacological treatment for concussions in humans. The ability to treat concussions with drug therapy requires an in-depth understanding of the pathophysiological and neuroinflammatory changes that accompany concussive injuries. The use of neurotrophic factors [e.g., nerve growth factor (NGF)] and anti-inflammatory agents as an adjunct for the management of post-concussion symptomology will be explored in this review.

Controlled cortical impact and craniotomy induce strikingly similar profiles of inflammatory gene expression, but with distinct kinetics

An immediate consequence of traumatic brain injury (TBI) is the induction of an inflammatory response. Mounting data suggest that inflammation is a major contributor to TBI-induced brain damage. However, much remains unknown regarding the induction and regulation of the inflammatory response to TBI. In this study we compared the TBI-induced inflammatory response to severe parenchymal injury (controlled cortical impact) vs. mild brain injury (craniotomy) over a 21-day period. Our data show that both severe and mild brain injury induce a qualitatively similar inflammatory response, involving highly overlapping sets of effector molecules. However, kinetic analysis revealed that the inflammatory response to mild brain injury is of much shorter duration than the response to severe TBI. Specifically, the inflammatory response to severe brain injury persists for at least 21 days, whereas the response to mild brain injury returns to near baseline values within 10 days post-injury. Our data therefore imply that the development of accurate diagnostic tests of TBI severity that are based on imaging or biomarker analysis of the inflammatory response may require repeated measures over at least a 10-day period, post-injury.

CCL20 Is Associated with Neurodegeneration Following Experimental Traumatic Brain Injury and Promotes Cellular Toxicity In Vitro

Traumatic brain injury (TBI) is complex and involves multiple processes that contribute to functional decline. Progressive neuropathies result from delayed cellular death following the initial impact. Although the precise mechanisms responsible for delayed injury are unknown, numerous data implicate a role for the peripheral immune system in perpetuating neuroinflammation after TBI. A previous report demonstrated that splenic CCL20 chemokine expression was upregulated 24 h after lateral fluid percussive impact (LFPI), prior to neuronal expression but consistent with neurodegeneration. Here, we expand on those data to report increased CCL20 protein expression in white matter 48 h after LFPI and demonstrate that CCL20 is directly toxic to primary neurons and oligodendrocytes subjected to oxygen glucose deprivation. The temporal expression profile of CCL20, coupled with in vitro toxicity to primary cells, suggests that this chemokine exerts deleterious effects on cell viability following TBI. These findings warrant further investigations into the use of CCL20 as a potential biomarker and/or therapeutic target.

Chemokines in CNS injury and repair

Recruitment of inflammatory cells is known to drive the secondary damage cascades that are common to injuries of the central nervous system (CNS). Cell activation and infiltration to the injury site is orchestrated by changes in the expression of chemokines, the chemoattractive cytokines. Reducing the numbers of recruited inflammatory cells by the blocking of the action of chemokines has turned out be a promising approach to diminish neuroinflammation and to improve tissue preservation and neovascularization. In addition, several chemokines have been shown to be essential for stem/progenitor cell attraction, their survival, differentiation and cytokine production. Thus, chemokines might indirectly participate in remyelination, neovascularization and neuroprotection, which are important prerequisites for CNS repair after trauma. Moreover, CXCL12 promotes neurite outgrowth in the presence of growth inhibitory CNS myelin and enhances axonal sprouting after spinal cord injury (SCI). Here, we review current knowledge about the exciting functions of chemokines in CNS trauma, including SCI, traumatic brain injury and stroke. We identify common principles of chemokine action and discuss the potentials and challenges of therapeutic interventions with chemokines.