A systemic immune challenge to model hospital-acquired infections independently regulates immune responses after pediatric traumatic brain injury

Counteracting immunodepression by extracellular matrix hydrogel to promote brain tissue remodeling and neurological function recovery after traumatic brain injury

Traumatic brain injury (TBI), an intractable disorder of the central nervous system (CNS), is a leading cause of long-term disability and mortality in humans worldwide. However, there is still no effective therapy for TBI, and an important reason for this is TBI-induced immunodepression, which renders TBI patients with low resistance to infections and aggravated brain damage. In this study, a multifunctional extracellular matrix hydrogel was constructed for the treatment of TBI in terms of both counteracting the immunodepression and enhancing neurogenesis. The stromal cell-derived factor-1α (SDF-1α)-loaded hyaluronic acid (HA)/decellularized brain extracellular matrix (BM) hydrogel (SDF@HA/BM) not only mimicked the composition and the biological cues of brain extracellular matrix, but also exhibited the injectability, self-healing, and mechanical properties close to those of brain tissue. The SDF@HA/BM hydrogel protected activated immune cells from dysfunction during the acute phase of TBI for normal levels of inflammatory cytokines, thereby creating a favorable immune microenvironment for subsequent neurogenesis. The SDF-1α and the BM synergistically promoted neurogenesis after TBI by recruiting endogenous neural stem/progenitor cells and inducing their differentiation into neurons. In vivo results demonstrated that the SDF@HA/BM hydrogel exhibited desirable therapeutic effects in severe TBI mice through facilitating brain tissue remodeling and neurological function recovery, including limb balance, autonomous locomotion, and spatial learning and memory abilities, and relieving depression and anxiety. Our work provides a novel strategy for TBI treatment in terms of restoring immune homeostasis and enhancing neurogenesis using advanced biomaterials.

A post-injury immune challenge with lipopolysaccharide following adult traumatic brain injury alters neuroinflammation and the gut microbiome acutely, but has little effect on chronic outcomes

Patients with a traumatic brain injury (TBI) are susceptible to hospital-acquired infections, presenting a significant challenge to an already-compromised immune system. The consequences and mechanisms by which this dual insult worsens outcomes are poorly understood. This study aimed to explore how a systemic immune stimulus (lipopolysaccharide, LPS) influences outcomes following experimental TBI in young adult mice. Male and female C57Bl/6J mice underwent controlled cortical impact or sham surgery, followed by 1 mg/kg i.p. LPS or saline-vehicle at 4 days post-TBI, before behavioral assessment and tissue collection at 6 h, 24 h, 7 days or 6 months. LPS induced acute sickness behaviors including weight loss, transient hypoactivity, and increased anxiety-like behavior. Early systemic immune activation by LPS was confirmed by increased spleen weight and serum cytokines. In brain tissue, gene expression analysis revealed a time course of inflammatory immune activation in TBI or LPS-treated mice (e.g., IL-1β, IL-6, CCL2, TNFα), which was exacerbated in TBI + LPS mice. This group also presented with fecal microbiome dysbiosis at 24 h post-LPS, with reduced bacterial diversity and changes in the relative abundance of key bacterial genera associated with sub-acute neurobehavioral and immune changes. Chronically, TBI induced hyperactivity and cognitive deficits, brain atrophy, and increased seizure susceptibility, similarly in vehicle and LPS-treated groups. Together, findings suggest that an immune challenge with LPS early after TBI, akin to a hospital-acquired infection, alters the acute neuroinflammatory response to injury, but has no lasting effects. Future studies could consider more clinically-relevant models of infection to build upon these findings.

The role of visfatin in peripheral immune organs and intestines of weaned piglets under lipopolysaccharide induced immune stress

To investigate the regulatory mechanisms and pathways of visfatin under immune stress injury in weaned piglets, we established a lipopolysaccharide-induced immune stress model in weaned piglets to study how visfatin affects peripheral immune organs and intestinal function. The results revealed that visfatin improved the inflammatory response in immune-stressed weaned piglets by reducing the levels of pro-inflammatory cytokines interleukin-1β, interleukin-6 and monocyte chemoattractant protein-1, as well as decreasing the neutrophil/lymphocyte ratio. Visfatin ameliorated oxidative stress in piglets by promoting the expression of superoxide dismutase and glutathione peroxidase. It also enhanced cell proliferation in peripheral immune organs (spleen and mesenteric lymph nodes) and suppressed cell apoptosis in these organs through the death receptor apoptosis pathway, thereby improving the immune function of weaned piglets under immune stress. Moreover, it alleviated intestinal villi damage, increased the abundance of beneficial bacteria, and elevated the levels of short-chain fatty acids, thus preserving the intestinal barrier's integrity and the balance of intestinal microbiota. Hence, these data indicate that visfatin can ameliorate immune stress injury in weaned piglets by exerting anti-inflammatory and antioxidant effects, enhancing immune organ and intestinal function.

Gut Microbiota and Immune System Dynamics in Parkinson's and Alzheimer's Diseases

The gut microbiota, a diverse collection of microorganisms in the gastrointestinal tract, plays a critical role in regulating metabolic, immune, and cognitive functions. Disruptions in the composition of these microbial communities, termed dysbiosis, have been linked to various neurodegenerative diseases (NDs), such as Parkinson's disease (PD) and Alzheimer's disease (AD). One of the key pathological features of NDs is neuroinflammation, which involves the activation of microglia and peripheral immune cells. The gut microbiota modulates immune responses through the production of metabolites and interactions with immune cells, influencing the inflammatory processes within the central nervous system. This review explores the impact of gut dysbiosis on neuroinflammation, focusing on the roles of microglia, immune cells, and potential therapeutic strategies targeting the gut microbiota to alleviate neuroinflammatory processes in NDs.

Fabrication of pH-stimuli hydrogel as bioactive materials for wound healing applications

Hydrogels exhibit exceptional suitability as wound dressing due to their remarkable three-dimensional (3D) characteristics. Here, we have reported the fabrication of hydrogels from biopolymers carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and gelatin via a simple blending method to mimic the natural extracellular matrix. Scanning electron microscopy (SEM), water contact meters (WCM), and Fourier-transform infrared spectroscopy (FTIR) were used to evaluate the chemical structural, morphological, and wettability behavior. The wetting and degradation behavior were also found to be different for different formulations (Min. (51.60o) and Max. (113.60o)) and (Min. (38.82 mg) and Max. (3.72 mg)), respectively. Swelling was investigated in different media, including phosphate buffer saline solution (PBS) and aqueous media. It was observed that the hydrogel displayed the highest degree of swelling in an aqueous medium (Min. (597.32-1121.49 %) and Max. (1089.51-2139.73 %)) compared to PBS media (Min. (567.01-1021.85 %) and Max. (899.13-1639.17 %)). The release of Neomycin was studied in a PBS medium via the Franz diffusion method at 37 °C. The maximal release in various media demonstrated pH-responsive behavior. The viability and proliferation of fibroblast (3T3) cell lines were examined in vitro to evaluate cytocompatibility. Human Embryonic Kidney (HEK) 293 cells were used to evaluate the hydrogels' ability to promote vascularization and angiogenesis. Therefore, the data demonstrate that hydrogels that have been manufactured have qualities that make them promising for use as wound dressings in wound healing applications.

Modelling lung infection with Klebsiella pneumoniae after murine traumatic brain injury

Pneumonia is a common comorbidity in patients with severe traumatic brain injury (TBI), and is associated with increased morbidity and mortality. In this study, we established a model of intratracheal Klebsiella pneumoniae administration in young adult male and female mice, at 4 days following an experimental TBI, to investigate how K. pneumoniae infection influences acute post-TBI outcomes. A dose-response curve determined the optimal dose of K. pneumoniae for inoculation (1 x 10^6 colony forming units), and administration at 4 days post-TBI resulted in transient body weight loss and sickness behaviors (hypoactivity and acute dyspnea). K. pneumoniae infection led to an increase in pro-inflammatory cytokines in serum and bronchoalveolar lavage fluid at 24 h post-infection, in both TBI and sham (uninjured) mice. By 7 days, when myeloperoxidase + neutrophil numbers had returned to baseline in all groups, lung histopathology was observed with an increase in airspace size in TBI + K. pneumoniae mice compared to TBI + vehicle mice. In the brain, increased neuroinflammatory gene expression was observed acutely in response to TBI, with an exacerbated increase in Ccl2 and Hmox1 in TBI + K. pneumoniae mice compared to either TBI or K. pneumoniae alone. However, the presence of neuroinflammatory immune cells in the injured brain, and the extent of damage to cortical and hippocampal brain tissue, was comparable between K. pneumoniae and vehicle-treated mice by 7 days. Examination of the fecal microbiome across a time course did not reveal any pronounced effects of either injury or K. pneumoniae on bacterial diversity or abundance. Together, these findings demonstrate that K. pneumoniae lung infection after TBI induces an acute and transient inflammatory response, primarily localized to the lungs with some systemic effects. However, this infection had minimal impact on secondary injury processes in the brain following TBI. Future studies are needed to evaluate the potential longer-term consequences of this dual-hit insult.

The role of neuroinflammation in neurodegenerative diseases: current understanding and future therapeutic targets

Neuroinflammation refers to a highly complicated reaction of the central nervous system (CNS) to certain stimuli such as trauma, infection, and neurodegenerative diseases. This is a cellular immune response whereby glial cells are activated, inflammatory mediators are liberated and reactive oxygen and nitrogen species are synthesized. Neuroinflammation is a key process that helps protect the brain from pathogens, but inappropriate, or protracted inflammation yields pathological states such as Parkinson's disease, Alzheimer's, Multiple Sclerosis, and other neurodegenerative disorders that showcase various pathways of neurodegeneration distributed in various parts of the CNS. This review reveals the major neuroinflammatory signaling pathways associated with neurodegeneration. Additionally, it explores promising therapeutic avenues, such as stem cell therapy, genetic intervention, and nanoparticles, aiming to regulate neuroinflammation and potentially impede or decelerate the advancement of these conditions. A comprehensive understanding of the intricate connection between neuroinflammation and these diseases is pivotal for the development of future treatment strategies that can alleviate the burden imposed by these devastating disorders.

Bi-directional neuro-immune dysfunction after chronic experimental brain injury

BACKGROUND

It is well established that traumatic brain injury (TBI) causes acute and chronic alterations in systemic immune function and that systemic immune changes contribute to posttraumatic neuroinflammation and neurodegeneration. However, how TBI affects bone marrow (BM) hematopoietic stem/progenitor cells chronically and to what extent such changes may negatively impact innate immunity and neurological function has not been examined.

METHODS

To further understand the role of BM cell derivatives on TBI outcome, we generated BM chimeric mice by transplanting BM from chronically injured or sham (i.e., 90 days post-surgery) congenic donor mice into otherwise healthy, age-matched, irradiated CD45.2 C57BL/6 (WT) hosts. Immune changes were evaluated by flow cytometry, multiplex ELISA, and NanoString technology. Moderate-to-severe TBI was induced by controlled cortical impact injury and neurological function was measured using a battery of behavioral tests.

RESULTS

TBI induced chronic alterations in the transcriptome of BM lineage-c-Kit+Sca1+ (LSK+) cells in C57BL/6 mice, including modified epigenetic and senescence pathways. After 8 weeks of reconstitution, peripheral myeloid cells from TBI→WT mice showed significantly higher oxidative stress levels and reduced phagocytic activity. At eight months after reconstitution, TBI→WT chimeric mice were leukopenic, with continued alterations in phagocytosis and oxidative stress responses, as well as persistent neurological deficits. Gene expression analysis revealed BM-driven changes in neuroinflammation and neuropathology after 8 weeks and 8 months of reconstitution, respectively. Chimeric mice subjected to TBI at 8 weeks and 8 months post-reconstitution showed that longer reconstitution periods (i.e., time post-injury) were associated with increased microgliosis and leukocyte infiltration. Pre-treatment with a senolytic agent, ABT-263, significantly improved behavioral performance of aged C57BL/6 mice at baseline, although it did not attenuate neuroinflammation in the acutely injured brain.

CONCLUSIONS

TBI causes chronic activation and progressive dysfunction of the BM stem/progenitor cell pool, which drives long-term deficits in hematopoiesis, innate immunity, and neurological function, as well as altered sensitivity to subsequent brain injury.

A pre-existing Toxoplasma gondii infection exacerbates the pathophysiological response and extent of brain damage after traumatic brain injury in mice

Traumatic brain injury (TBI) is a key contributor to global morbidity that lacks effective treatments. Microbial infections are common in TBI patients, and their presence could modify the physiological response to TBI. It is estimated that one-third of the human population is incurably infected with the feline-borne parasite, Toxoplasma gondii, which can invade the central nervous system and result in chronic low-grade neuroinflammation, oxidative stress, and excitotoxicity-all of which are also important pathophysiological processes in TBI. Considering the large number of TBI patients that have a pre-existing T. gondii infection prior to injury, and the potential mechanistic synergies between the conditions, this study investigated how a pre-existing T. gondii infection modified TBI outcomes across acute, sub-acute and chronic recovery in male and female mice. Gene expression analysis of brain tissue found that neuroinflammation and immune cell markers were amplified in the combined T. gondii + TBI setting in both males and females as early as 2-h post-injury. Glutamatergic, neurotoxic, and oxidative stress markers were altered in a sex-specific manner in T. gondii + TBI mice. Structural MRI found that male, but not female, T. gondii + TBI mice had a significantly larger lesion size compared to their uninfected counterparts at 18-weeks post-injury. Similarly, diffusion MRI revealed that T. gondii + TBI mice had exacerbated white matter tract abnormalities, particularly in male mice. These novel findings indicate that a pre-existing T. gondii infection affects the pathophysiological aftermath of TBI in a sex-dependent manner, and may be an important modifier to consider in the care and prognostication of TBI patients.

Regulation of microglial responses after pediatric traumatic brain injury: exploring the role of SHIP-1

Introduction

Severe traumatic brain injury (TBI) is the world's leading cause of permanent neurological disability in children. TBI-induced neurological deficits may be driven by neuroinflammation post-injury. Abnormal activity of SH2 domain-containing inositol 5' phosphatase-1 (SHIP-1) has been associated with dysregulated immunological responses, but the role of SHIP-1 in the brain remains unclear. The current study investigated the immunoregulatory role of SHIP-1 in a mouse model of moderate-severe pediatric TBI.

Methods

SHIP-1+/- and SHIP-1-/- mice underwent experimental TBI or sham surgery at post-natal day 21. Brain gene expression was examined across a time course, and immunofluorescence staining was evaluated to determine cellular immune responses, alongside peripheral serum cytokine levels by immunoassays. Brain tissue volume loss was measured using volumetric analysis, and behavior changes both acutely and chronically post-injury.

Results

Acutely, inflammatory gene expression was elevated in the injured cortex alongside increased IBA-1 expression and altered microglial morphology; but to a similar extent in SHIP-1-/- mice and littermate SHIP-1+/- control mice. Similarly, the infiltration and activation of CD68-positive macrophages, and reactivity of GFAP-positive astrocytes, was increased after TBI but comparable between genotypes. TBI increased anxiety-like behavior acutely, whereas SHIP-1 deficiency alone reduced general locomotor activity. Chronically, at 12-weeks post-TBI, SHIP-1-/- mice exhibited reduced body weight and increased circulating cytokines. Pro-inflammatory gene expression in the injured hippocampus was also elevated in SHIP-1-/- mice; however, GFAP immunoreactivity at the injury site in TBI mice was lower. TBI induced a comparable loss of cortical and hippocampal tissue in both genotypes, while SHIP-1-/- mice showed reduced general activity and impaired working memory, independent of TBI.

Conclusion

Together, evidence does not support SHIP-1 as an essential regulator of brain microglial morphology, brain immune responses, or the extent of tissue damage after moderate-severe pediatric TBI in mice. However, our data suggest that reduced SHIP-1 activity induces a greater inflammatory response in the hippocampus chronically post-TBI, warranting further investigation.

The brain-bone marrow axis and its implications for chronic traumatic brain injury

Traumatic brain injury (TBI) causes acute and chronic alterations in systemic immune function which contribute to posttraumatic neuroinflammation and neurodegeneration. However, how TBI affects bone marrow (BM) hematopoietic stem/progenitor cells chronically and to what extent such changes may negatively impact innate immunity and neurological function has not been examined. To further understand the role of BM cell derivatives on TBI outcome, we generated BM chimeric mice by transplanting BM from chronically injured or sham congenic donor mice into otherwise healthy, age-matched, irradiated hosts. After 8 weeks of reconstitution, peripheral myeloid cells from TBI→WT mice showed significantly higher oxidative stress levels and reduced phagocytic activity. At eight months after reconstitution, TBI→WT chimeric mice were leukopenic, with continued alterations in phagocytosis and oxidative stress responses, as well as persistent neurological deficits. Gene expression analysis revealed BM-driven changes in neuroinflammation and neuropathology after 8 weeks and 8 months of reconstitution, respectively. Chimeric mice subjected to TBI showed that longer reconstitution periods were associated with increased microgliosis and leukocyte infiltration. Thus, TBI causes chronic activation and progressive dysfunction of the BM stem/progenitor cell pool, which drives long-term deficits in innate immunity and neurological function, as well as altered sensitivity to subsequent brain injury.

Modulating chronic outcomes after pediatric traumatic brain injury: Distinct effects of social and environmental enrichment

Impairments in social and cognitive function are a common consequence of pediatric traumatic brain injury (TBI). Rehabilitation has the potential to promote optimal behavioral recovery. Here, we evaluated whether an enhanced social and/or cognitive environment could improve long-term outcomes in a preclinical model of pediatric TBI. Male C57Bl/6 J mice received a moderately-severe TBI or sham procedure at postnatal day 21. After one week, mice were randomized to different social conditions (minimal socialization, n = 2/cage; or social grouping, n = 6/cage), and housing conditions (standard cage, or environmental enrichment (EE), incorporating sensory, motor, and cognitive stimuli). After 8 weeks, neurobehavioral outcomes were assessed, followed by post-mortem neuropathology. We found that TBI mice exhibited hyperactivity, spatial memory deficits, reduced anxiety-like behavior, and reduced sensorimotor performance compared to age-matched sham controls. Pro-social and sociosexual behaviors were also reduced in TBI mice. EE increased sensorimotor performance, and the duration of sociosexual interactions. Conversely, social housing reduced hyperactivity and altered anxiety-like behavior in TBI mice, and reduced same-sex social investigation. TBI mice showed impaired spatial memory retention, except for TBI mice exposed to both EE and group housing. In the brain, while TBI led to significant regional tissue atrophy, social housing had modest neuroprotective effects on hippocampal volumes, neurogenesis, and oligodendrocyte progenitor numbers. In conclusion, manipulation of the post-injury environment has benefit for chronic behavioral outcomes, but the benefits are specific to the type of enrichment available. This study improves understanding of modifiable factors that may be harnessed to optimize long-term outcomes for survivors of early-life TBI.

Temporal changes in the microglial proteome of male and female mice after a diffuse brain injury using label-free quantitative proteomics

Traumatic brain injury (TBI) triggers neuroinflammatory cascades mediated by microglia, which promotes tissue repair in the short-term. These cascades may exacerbate TBI-induced tissue damage and symptoms in the months to years post-injury. However, the progression of the microglial function across time post-injury and whether this differs between biological sexes is not well understood. In this study, we examined the microglial proteome at 3-, 7-, or 28-days after a midline fluid percussion injury (mFPI) in male and female mice using label-free quantitative proteomics. Data are available via ProteomeXchange with identifier PXD033628. We identified a reduction in microglial proteins involved with clearance of neuronal debris via phagocytosis at 3- and 7-days post-injury. At 28 days post-injury, pro-inflammatory proteins were decreased and anti-inflammatory proteins were increased in microglia. These results indicate a reduction in microglial clearance of neuronal debris in the days post-injury with a shift to anti-inflammatory function by 28 days following TBI. The changes in the microglial proteome that occurred across time post-injury did not differ between biological sexes. However, we did identify an increase in microglial proteins related to pro-inflammation and phagocytosis as well as insulin and estrogen signaling in males compared with female mice that occurred with or without a brain injury. Although the microglial response was similar between males and females up to 28 days following TBI, biological sex differences in the microglial proteome, regardless of TBI, has implications for the efficacy of treatment strategies targeting the microglial response post-injury.

Ccr2 Gene Ablation Does Not Influence Seizure Susceptibility, Tissue Damage, or Cellular Inflammation after Murine Pediatric Traumatic Brain Injury

Pediatric traumatic brain injury (TBI) is a major public health issue, and a risk factor for the development of post-traumatic epilepsy that may profoundly impact the quality of life for survivors. As the majority of neurotrauma research is focused on injury to the adult brain, our understanding of the developing brain's response to TBI remains incomplete. Neuroinflammation is an influential pathophysiological mechanism in TBI, and is thought to increase neuronal hyperexcitability, rendering the brain more susceptible to the onset of seizures and/or epileptogenesis. We here hypothesized that peripheral blood-derived macrophages, recruited into the injured brain via C-C motif ligand 2 (CCL2) chemokine/C-C chemokine receptor type 2 (CCR2) signaling, contributes to neuroinflammation and thus seizure susceptibility after experimental pediatric TBI. Using Ccr2 gene-deficient mice in the controlled cortical impact (CCI) model of TBI, in 3-week-old male mice we found that TBI led to an increase in susceptibility to pentylenetetrazol (PTZ)-evoked seizures, associated with considerable cortical tissue loss, a robust cellular neuroinflammatory response, and oxidative stress. Intriguingly, although Ccr2-deficiency increased CCL2 levels in serum, it did not exacerbate seizure susceptibility or the neuroinflammatory cellular response after pediatric TBI. Similarly, acute post-injury treatment with a CCR2 antagonist did not influence seizure susceptibility or the extent of tissue damage in wild-type (WT) mice. Together, our findings suggest that CCR2 is not a crucial driver of epileptogenesis or neuroinflammation after TBI in the developing brain. We propose that age may be an important factor differentiating our findings from previous studies in which targeting CCL2/CCR2 has been reported to be anti-inflammatory, neuroprotective or anti-seizure.

Pre-existing Toxoplasma gondii infection increases susceptibility to pentylenetetrazol-induced seizures independent of traumatic brain injury in mice

Introduction

Post-traumatic epilepsy (PTE) is a debilitating chronic outcome of traumatic brain injury (TBI), and neuroinflammation is implicated in increased seizure susceptibility and epileptogenesis. However, how common clinical factors, such as infection, may modify neuroinflammation and PTE development has been understudied. The neurotropic parasite, Toxoplasma gondii (T. gondii) incurably infects one-third of the world's population. Thus, many TBI patients have a pre-existing T. gondii infection at the time of injury. T. gondii infection results in chronic low-grade inflammation and altered signaling pathways within the brain, and preliminary clinical evidence suggest that it may be a risk factor for epilepsy. Despite this, no studies have considered how a pre-existing T. gondii infection may alter the development of PTE.

Methods

This study aimed to provide insight into this knowledge gap by assessing how a pre-existing T. gondii infection alters susceptibility to, and severity of, pentylenetetrazol (PTZ)-induced seizures (i.e., a surrogate marker of epileptogenesis/PTE) at a chronic stage of TBI recovery. We hypothesized that T. gondii will increase the likelihood and severity of seizures following PTZ administration, and that this would occur in the presence of intensified neuroinflammation. To test this, 6-week old male and female C57BL/6 Jax mice were intraperitoneally injected with 50,000 T. gondii tachyzoites or with the PBS vehicle only. At 12-weeks old, mice either received a severe TBI via controlled cortical impact or sham injury. At 18-weeks post-injury, mice were administered 40 mg/kg PTZ and video-recorded for evaluation of seizure susceptibility. Fresh cortical tissue was then collected for gene expression analyses.

Results

Although no synergistic effects were evident between infection and TBI, chronic T. gondii infection alone had robust effects on the PTZ-seizure response and gene expression of markers related to inflammatory, oxidative stress, and glutamatergic pathways. In addition to this, females were more susceptible to PTZ-induced seizures than males. While TBI did not impact PTZ responses, injury effects were evident at the molecular level.

Discussion

Our data suggests that a pre-existing T. gondii infection is an important modifier of seizure susceptibility independent of brain injury, and considerable attention should be directed toward delineating the mechanisms underlying this pro-epileptogenic factor.

Inflammation and the role of infection: Complications and treatment options following neurotrauma

Traumatic brain injury can have devastating consequences for patients and extended hospital stays and recovery course. Recent data indicate that the initial insult causes profound changes to the immune system and leads to a pro-inflammatory state. This alteration in homeostasis predisposes patients to an increased risk of infection and underlying autoimmune conditions. Increased emphasis has been placed on understanding this process both in the clinical and preclinical literature. This review highlights the intrinsic inflammatory conditions that can occur within the initial hospital stay, discusses long-term immune consequences, highlights emerging treatment options, and delves into important pathways currently being investigated with preclinical models.

Pediatric traumatic brain injury and a subsequent transient immune challenge independently influenced chronic outcomes in male mice

Traumatic brain injury (TBI) is a major contributor to death and disability worldwide. Children are at particularly high risk of both sustaining a TBI and experiencing serious long-term consequences, such as cognitive deficits, mental health problems and post-traumatic epilepsy. Severe TBI patients are highly susceptible to nosocomial infections, which are mostly acquired within the first week of hospitalization post-TBI. Yet the potential chronic impact of such acute infections following pediatric TBI remains unclear. In this study, we hypothesized that a peripheral immune challenge, such as lipopolysaccharide (LPS)-mimicking a hospital-acquired infection-would worsen inflammatory, neurobehavioral, and seizure outcomes after experimental pediatric TBI. To test this, three-week old male C57Bl/6J mice received a moderate controlled cortical impact or sham surgery, followed by 1 mg/kg i.p. LPS (or 0.9% saline vehicle) at 4 days TBI. Mice were randomized to four groups; sham-saline, sham-LPS, TBI-saline or TBI-LPS (n = 15/group). Reduced general activity and increased anxiety-like behavior were observed within 24 h in LPS-treated mice, indicating a transient sickness response. LPS-treated mice also exhibited a reduction in body weights, which persisted chronically. From 2 months post-injury, mice underwent a battery of tests for sensorimotor, cognitive, and psychosocial behaviors. TBI resulted in hyperactivity and spatial memory deficits, independent of LPS; whereas LPS resulted in subtle deficits in spatial memory retention. At 5 months post-injury, video-electroencephalographic recordings were obtained to evaluate both spontaneous seizure activity as well as the evoked seizure response to pentylenetetrazol (PTZ). TBI increased susceptibility to PTZ-evoked seizures; whereas LPS appeared to increase the incidence of spontaneous seizures. Post-mortem analyses found that TBI, but not LPS, resulted in robust glial reactivity and loss of cortical volume. A TBI × LPS interaction in hippocampal volume suggested that TBI-LPS mice had a subtle increase in ipsilateral hippocampus tissue loss; however, this was not reflected in neuronal cell counts. Both TBI and LPS independently had modest effects on chronic hippocampal gene expression. Together, contrary to our hypothesis, we observed minimal synergy between TBI and LPS. Instead, pediatric TBI and a subsequent transient immune challenge independently influenced chronic outcomes. These findings have implications for future preclinical modeling as well as acute post-injury patient management.

Traumatic Brain Injury: An Age-Dependent View of Post-Traumatic Neuroinflammation and Its Treatment

Traumatic brain injury (TBI) is a leading cause of death and disability all over the world. TBI leads to (1) an inflammatory response, (2) white matter injuries and (3) neurodegenerative pathologies in the long term. In humans, TBI occurs most often in children and adolescents or in the elderly, and it is well known that immune responses and the neuroregenerative capacities of the brain, among other factors, vary over a lifetime. Thus, age-at-injury can influence the consequences of TBI. Furthermore, age-at-injury also influences the pharmacological effects of drugs. However, the post-TBI inflammatory, neuronal and functional consequences have been mostly studied in experimental young adult animal models. The specificity and the mechanisms underlying the consequences of TBI and pharmacological responses are poorly understood in extreme ages. In this review, we detail the variations of these age-dependent inflammatory responses and consequences after TBI, from an experimental point of view. We investigate the evolution of microglial, astrocyte and other immune cells responses, and the consequences in terms of neuronal death and functional deficits in neonates, juvenile, adolescent and aged male animals, following a single TBI. We also describe the pharmacological responses to anti-inflammatory or neuroprotective agents, highlighting the need for an age-specific approach to the development of therapies of TBI.