Sexual dimorphism in the inflammatory response to traumatic brain injury

Probiotic treatment induces sex-dependent neuroprotection and gut microbiome shifts after traumatic brain injury

BACKGROUND

Recent studies have highlighted the potential influence of gut dysbiosis on traumatic brain injury (TBI) outcomes. Alterations in the abundance and diversity of Lactobacillus species may affect immune dysregulation, neuroinflammatory responses, anxiety- and depressive-like behaviors, and neuroprotective mechanisms activated in response to TBI.

OBJECTIVE

This study aims to evaluate the protective and preventive effects of Pan-probiotic (PP) treatment on the inflammatory response during both the acute and chronic phases of TBI.

METHODS

Males and female mice underwent controlled cortical impact (CCI) injury or sham. They received a PP mixture in drinking water containing strains of Lactobacillus plantarum, L. reuteri, L. helveticas, L. fermentum, L. rhamnosus, L. gasseri, and L. casei. In the acute group, mice received PP or vehicle (VH) treatment for 7 weeks before TBI, continuing until 3 days post-injury (dpi). In the chronic group, treatment began 2 weeks before TBI and was extended through 35 dpi. The taxonomic microbiome profiles of fecal samples were evaluated using 16S rRNA V1-V3 sequencing analysis, and Short-chain fatty acids (SCFAs) were measured. Immunohistochemical, in situ hybridization, and histological analyses were performed to assess neuroinflammation post-TBI, while behavioral assessments were conducted to evaluate sensorimotor and cognitive functions.

RESULTS

Our findings suggest that a 7-week PP administration induces specific microbial changes, including increased abundance of beneficial bacteria such as Lactobacillaceae, Limosilactobacillus, and Lactiplantibacillus. PP treatment reduces lesion volume and cell death at 3 dpi, elevates SCFA levels at 35 dpi, and decreases microglial activation at both time points, particularly in males. Additionally, PP treatment improved motor recovery in males and alleviated depressive-like behaviors in females.

CONCLUSION

Our findings indicate that PP administration modulates microbiome composition, reduces neuroinflammation, and improves motor deficits following TBI, with these effects being particularly pronounced in male mice.

Sex and Genotype Affect Mouse Hippocampal Gene Expression in Response to Blast-Induced Traumatic Brain Injury

Blast-induced traumatic brain injury (bTBI) has been identified as an increasingly prevalent cause of morbidity and mortality in both military and civilian populations over the past few decades. Functional outcomes following bTBI vary widely among individuals, and chronic neurodegenerative effects including cognitive impairments can develop without effective diagnosis and treatment. Genetic predispositions and sex differences may affect gene expression changes in response to bTBI and influence an individual's probability of sustaining long-term damage or exhibiting resilience and tissue repair. Male and female mice from eight genetically diverse and distinct strains (129S1/SvImJ, A/J, C57BL/6J, CAST/EiJ, NOD/ShiLtJ, NZO/HlLtJ, PWK/PhJ, WSB/EiJ) which encompassed 90% of the genetic variability in commercially available laboratory mice were exposed to a single bTBI (180 kPa) using a well-established shock tube system. Subacute changes in hippocampal gene expression due to blast exposure were assessed using RNA-seq at 1-month post-injury. We identified patterns of dysregulation in gene ontology terms and canonical pathways related to mitochondrial function, ribosomal structure, synaptic plasticity, protein degradation, and intracellular signaling that varied by sex and/or strain, including significant changes in genes encoding respiratory complex I of the electron transport chain in male WSB/EiJ mice and the glutamatergic synapse across more than half of our groups. This study represents a multi-level examination of how genetic variability may influence response to bTBI and provides a foundation for the identification of potential therapeutic targets that could be modulated to improve the health of Veterans and others with histories of blast exposures.

Diffuse Traumatic Brain Injury Induced Stimulator of Interferons (STING) Signaling in Microglia Drives Cortical Neuroinflammation, Neuronal Dysfunction, and Impaired Cognition

Neuropsychiatric complications including depression and cognitive impairment develop, persist, and worsen in the years after traumatic brain injury (TBI), negatively affecting life and lifespan. Inflammatory responses mediated by microglia are associated with the transition from acute to chronic neuroinflammation after TBI. Moreover, type I interferon (IFN-I) signaling is a key mediator of inflammation during this transition. Thus, the purpose of this study was to determine the degree to which a microglia-specific knockout of the stimulator of interferons (STING) influenced TBI-induced neuroinflammation, neuronal dysfunction, and cognitive impairment. Here, microglial inducible STING knockout (CX₃CR1Cre/ERT2 x STING fl/fl ) mice were created and validated (mSTING -/- ). Diffuse brain injury (midline fluid percussion) in male and female mice increased STING expression in microglia, promoted microglial morphological restructuring, and induced robust cortical inflammation and pathology 7 days post injury (dpi). These TBI-associated responses were attenuated in mSTING -/- mice. Increased cortical astrogliosis and rod-shaped microglia induced by TBI were independent of mSTING -/- . 7 dpi, TBI induced 237 differentially expressed genes (DEG) in the cortex of functionally wildtype (STING +/+ ) associated with STING, NF- κB, and Interferon Alpha signaling and 85% were attenuated by mSTING -/- . Components of neuronal injury including reduced NeuN expression, increased cortical lipofuscin, and increased neurofilament light chain in plasma were increased by TBI and dependent on mSTING. TBI-associated cognitive tasks (novel object recognition/location, NOR/NOL) at 7 dpi were dependent on mSTING. Notably, the TBI-induced cognitive deficits in NOR/NOL and increased cortical inflammation 7 dpi were unaffected in global interferon-α/β receptor 1 knockout (IFNAR1) mice. In the final study, the RNA profile of neurons after TBI in STING +/+ and mSTING -/- mice was assessed 7 dpi by single nucleus RNA-sequencing. There was a TBI-dependent suppression of cortical neuronal homeostasis with reductions in CREB signaling, synaptogenesis, and oxytocin signaling and increases in cilium assembly and PTEN signaling. Overall, mSTING -/- prevented 50% of TBI-induced DEGs in cortical neurons. Collectively, ablation of STING in microglia attenuates TBI-induced IFN-dependent responses, cortical inflammation, neuronal dysfunction, neuronal pathology, and cognitive impairment.

Sex-based differences in the long-term fate of hippocampal neurons born after a traumatic brain injury

Introduction

Moderate-to-severe traumatic brain injury (TBI) results in an early loss of immature hippocampal granule cells and the activation of typically quiescent neural stem cells (NSCs) in the dentate gyrus. Activation of NSCs leads to a robust increase in proliferation and generation of neural progenitor cells (NPCs), supporting restoration of the immature neuron population of over a period of 1-2 weeks. However, it is unclear if neurons born early after injury develop normally, survive long-term and functionally integrate into the hippocampal network. Although adult hippocampal neurogenesis is regulated in a sex-dependent manner, the majority of pre-clinical TBI studies lack the inclusion of both sexes. The goal of this study was to examine sex differences in hippocampal neurogenesis in response to a moderate controlled cortical impact brain injury.

Methods

In-vivo labeling of NPCs and tracking of their morphological development into a granule cell was achieved using an inducible Cre recombinase driven by the Ascl1 promoter in a CAG-floxStopTom reporter mouse. Ascl1 is a basic helix-loop-helix transcription factor transiently expressed in NPCs and activated NSCs in the dentate gyrus of the adult mammalian brain. To specifically label NPCs born acutely after TBI, tamoxifen was delivered to mice on days 2 and 3 postinjury. Mice survived to 6 weeks after TBI to allow for full neuronal maturation of tdTomato-labeled NPCs.

Results

At 6 weeks postinjury, numbers of tdTomato-positive granule cells were significantly reduced in the ipsilateral hippocampus of brain-injured mice compared to controls, with a more pronounced decrease in males. Further, posttrauma-born neurons in males, but not females, exhibited impaired dendritic development. Neurons born after injury extended axons which formed synaptic terminals within the CA3 region. Numbers of mossy fiber boutons were significantly decreased in injured males compared to naïve males or to injured females. Potential forms of plasticity were observed in brain-injured females, including increased neurogenesis in the contralateral hippocampus and increased mossy fiber bouton volume. Together these data suggest a neurogenic advantage in females after injury.

Discussion

This study is the first to report sex differences in posttraumatic hippocampal neurogenesis and to demonstrate modification of synaptic terminals formed by neurons born after TBI.

Glutamate uptake is transiently compromised in the perilesional cortex following controlled cortical impact

Glutamate, the primary excitatory neurotransmitter in the central nervous system (CNS), is regulated by the excitatory amino acid transporters glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST). Following traumatic brain injury, extracellular glutamate levels increase, contributing to excitotoxicity, circuit dysfunction, and morbidity. Increased neuronal glutamate release and compromised astrocyte-mediated uptake contribute to elevated glutamate, but the mechanistic and spatiotemporal underpinnings of these changes are not well established. Using the controlled cortical impact model of TBI and iGluSnFR glutamate imaging, we quantified extracellular glutamate dynamics after injury. Three days postinjury, glutamate release was increased, and glutamate uptake and GLT-1 expression were reduced. Seven and 14 days postinjury, glutamate dynamics were comparable between sham and controlled cortical impact animals. Changes in peak glutamate response were unique to specific cortical layers and proximity to injury. This was likely driven by increases in glutamate release, which was spatially heterogeneous, rather than reduced uptake, which was spatially uniform. The astrocyte K+ channel, Kir4.1, regulates activity-dependent slowing of glutamate uptake. Surprisingly, Kir4.1 was unchanged after controlled cortical impact and accordingly, activity-dependent slowing of glutamate uptake was unaltered. This dynamic glutamate dysregulation after traumatic brain injury underscores a brief period in which disrupted glutamate uptake may contribute to dysfunction and highlights a potential therapeutic window to restore glutamate homeostasis.

Minimally invasive serial collection of cerebrospinal fluid reveals sex-dependent differences in neuroinflammation in a rat model of mild traumatic brain injury

Traumatic brain injuries (TBI) are the seventh leading cause of disability globally with 48.99 million prevalent cases and 7.08 million years lived with diability. Approximately 80 % of TBI patients are diagnosed with mild TBI (mTBI), or concussion, caused by nonpenetrating mechanical trauma to the head or body along with sudden rotational motion of the head. Studies investigating the temporal dynamics of neuroinflammation after mTBI are greatly needed. Without longitudinal studies, translating preclinical studies to clinical studies remains challenging as the difference in timing remains poorly understood. In this study, we describe a method of minimally invasive serial cerebrospinal fluid (CSF) collection that enables longitudinal investigation of CSF inflammation. The method described in this study can easily be adapted by any laboratory prepared for animal studies. Multiplex immunoassay of serially collected and singly collected CSF samples show collection frequency does not alter protein expression in the CSF. Further, sex-dependent differences in TBI have been reported, but remain poorly understood. This study establishes a framework for assessing sex difference in neuroinflammation after a concussion. We showed that results vary based on the framing of the statistical test. However, it is evident that males experience a more robust inflammatory response to a single concussion than females.

P2X7R antagonism suppresses long-lasting brain hyperexcitability following traumatic brain injury in mice

Purpose: Post-traumatic epilepsy (PTE) is one of the most common life-quality reducing consequences of traumatic brain injury (TBI). However, to date there are no pharmacological approaches to predict or to prevent the development of PTE. The P2X7 receptor (P2X7R) is a cationic ATP-dependent membrane channel that is expressed throughout the brain. While increasing evidence suggests a role for the P2X7R during seizures and epilepsy, it is unclear if changes in P2X7R expression can predict TBI-induced epilepsy development, and whether P2X7R antagonism can protect against long-lasting brain hyperexcitability caused by TBI. Methods: TBI was induced in adult male mice using the controlled cortical impact model (CCI). To test the anti-epileptogenic effects of P2X7R antagonism, mice were treated with brain-penetrant P2X7R antagonists JNJ-54175446 (30 mg/kg) or AFC-5128 (30 mg/kg) for 7 days post-CCI. The cell-type specific effects of P2X7Rs on TBI-induced hyperexcitability were analyzed in mice lacking exon 2 of the P2rx7 gene selectively in microglia (P2rx7:Cx3cr1-Cre). Static positron emission tomography (PET) via an intravenous injection of the P2X7R radioligand 18F-JNJ-64413739 and magnetic resonance imaging (MRI) were conducted twice during the first- and third-week post-injury. Results: Following TBI, while there were no obvious changes in P2X7R protein levels in the ipsilateral hippocampus post-injury, there was a delayed increase in P2X7R protein levels in the ipsilateral cortex at 3 months post-injury. Treatment with P2X7R antagonists shortly after TBI reduced long-lasting brain hyperexcitability, reduced cortical contusion volume, and normalized injury-induced hyperactivity to control sham-levels at 3 weeks post-TBI. Notably, mice lacking P2rx7 in microglia had an increased seizure threshold after TBI, suggesting that P2X7R contributed to brain hyperexcitability via its effects on microglia. Finally, P2X7R radioligand uptake after TBI correlated with seizure threshold at 3 weeks post-injury. Conclusions: Our results demonstrate the antiepileptogenic potential of P2X7R antagonism to prevent TBI-induced epilepsy and indicate that P2X7R-based PET imaging may be a useful diagnostic tool to identify people at risk of developing PTE.

Translational Outcomes Project in Neurotrauma (TOP-NT) Pre-Clinical Consortium Study: A Synopsis

Traumatic brain injury (TBI) has long been a leading cause of death and disability, yet research has failed to successfully translate findings from the pre-clinical, animal setting into the clinic. One factor that contributes significantly to this struggle is the heterogeneity observed in the clinical setting where patients present with injuries of varying types, severities, and comorbidities. Modeling this highly varied population in the laboratory remains challenging. Given feasibility constraints, individual laboratories often focus on single injury types and are limited to an abridged set of outcome measures. Furthermore, laboratories tend to use different injury or outcome methodologies from one another, making it difficult to compare studies and identify which pre-clinical findings may be best suited for clinical translation. The NINDS-funded Translational Outcomes Project in Neurotrauma (TOP-NT) is a multi-site consortium designed to address the reproducibility, rigor, and transparency of pre-clinical development and validation of clinically relevant biomarkers for TBI. The current overview article provides a detailed description of the infrastructure and strategic approach undertaken by the consortium. We outline the TOP-NT strategy to address three goals: (1) selection and cross-center validation of biomarker tools, (2) development and population of a data infrastructure to allow for the sharing and reuse of pre-clinical, animal research following findable, accessible, interoperable, and reusable data guidelines, and (3) demonstration of feasibility, reproducibility, and transparency in conducting a multi-center, pre-clinical research trial for TBI biomarker development. The synthesized scientific analysis and results of the TOP-NT efforts will be the topic of future articles.

Microstructural Alterations of Gray and White Matter in Active Young Boxers with Sports-Related Concussions

The existing research on the microstructural alterations associated with sport-related concussions (SRCs) has primarily focused on deep white matter (DWM) fibers, while the impact of SRCs on the superficial white matter (SWM) and gray matter (GM) remains unknown. This study aimed to characterize the altered metrics obtained from neurite orientation dispersion and density imaging (NODDI) in boxers with SRCs, and thereby determine whether distinct regional patterns of microstructural alterations can offer valuable insights for accurate diagnosis and prognosis. Concussed boxers (n = 56) and healthy controls (HCs) with typically developing (n = 72) underwent comprehensive neuropsychological assessment and magnetic resonance imaging (MRI) examinations. The tract-based spatial statistics approach was used to investigate alterations in the DWM and SWM, while the gray matter-based spatial statistics approach was used to examine changes in the GM. The median time from the last SRC to MRI in the SRC group was 33.5 days (interquartile range, 45.25). In comparison with HCs, the SRC group exhibited lower fractional anisotropy (FA), neurite density index (NDI), and isotropic volume fraction (ISOVF), as well as higher mean diffusivity, axial diffusivity (AD), and radial diffusivity in both the DWM and SWM. Moreover, the SRC group exhibited lower FA, NDI, orientation dispersion index, and ISOVF in the GM, as well as higher AD. The altered microstructure of both gray and white matter was found to be associated with deficits in working memory and vocabulary memory among boxers. In addition to characterizing the DWM impairment, NODDI further elucidated the effects of SRCs on the microstructure of GM and SWM, offering a reliable imaging biomarker for SRC diagnosis and shedding light on the pathophysiological changes underlying SRCs.

Chronic glial activation and behavioral alterations induced by acute/subacute pioglitazone treatment in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a disabling neurotraumatic condition and the leading cause of injury-related deaths and disability in the United States. Attenuation of neuroinflammation early after TBI is considered an important treatment target; however, while these inflammatory responses can induce secondary brain injury, they are also involved in the repair of the nervous system. Pioglitazone, which activates peroxisome proliferator-activated receptor gamma, has been shown to decrease inflammation acutely after TBI, but the long-term consequences of its use remain unknown. For this reason, the impacts of treatment with pioglitazone during the acute/subacute phase (30 min after injury and each subsequent 24 h for 5 days) after TBI were interrogated during the chronic phase (30- and 274-days post-injury (DPI)) in mice using the controlled cortical impact model of experimental TBI. Acute/subacute pioglitazone treatment after TBI results in long-term deleterious consequences, including disruption of tau homeostasis, chronic glial cell activation, neuronal pathology, and worsened injury severity particularly at 274 DPI, with male mice being more susceptible than female mice. Further, male pioglitazone-treated TBI mice exhibited increased dominant and offensive-like behavior while having a decreased non-social exploring behavior at 274 DPI. After TBI, both sexes exhibited glial activation at 30 DPI when treated with pioglitazone; however, while injury severity was increased in females it was not impacted in male mice. This work reveals that although pioglitazone has been shown to lead to attenuated TBI outcomes acutely, sex-based differences, timing and long-term consequences of treatment with glitazones must be considered and further studied prior to their clinical use for TBI therapy.

Characterization of focused ultrasound blood-brain barrier disruption effect on inflammation as a function of treatment parameters

The technology of focused ultrasound-mediated disruption of the blood-brain barrier (FUS-BBB opening) has now been used in over 20 Phase 1 clinical trials to validate the safety and feasibility of BBB opening for drug delivery in patients with brain tumors and neurodegenerative diseases. The primary treatment parameters, FUS intensity and microbubble dose, are chosen to balance sufficient BBB disruption to achieve drug delivery against potential acute vessel damage leading to microhemorrhage. However, other safety considerations due to second order effects caused by BBB disruption, such as inflammation and alteration of neurovascular function, are only beginning to be understood. This study builds on previous work that has investigated the inflammatory response following FUS-BBB opening. In this study, we characterize the effect of FUS intensity, microbubble dose and single vs multiple treatments on the extent of BBB disruption, observed level of microhemorrhage, and degree of inflammatory response at acute post-treatment time points in the wild-type mouse brain. Results show that upregulation of pro-inflammatory markers is primarily driven by microbubble dose, with peak effects seen at 24 hours post-treatment. We additionally saw significantly elevated levels of cytokine and chemokine markers in female vs male mice, despite no sex differences in level of BBB disruption or microglia activation. Multiple treatments did not result in increased levels of pro-inflammatory markers compared to single treatment baseline. However, we did see an interesting elevation of the anti-inflammatory molecule eNOS after multiple treatments, indicating active mechanisms were at work to restore homeostasis in the brain environment.

Peripheral immune cell dysregulation following diffuse traumatic brain injury in pigs

Traumatic brain injury (TBI) is a global health problem affecting millions of individuals annually, potentially resulting in persistent neuropathology, chronic neurological deficits, and death. However, TBI not only affects neural tissue, but also affects the peripheral immune system's homeostasis and physiology. TBI disrupts the balanced signaling between the brain and the peripheral organs, resulting in immunodysregulation and increasing infection susceptibility. Indeed, secondary infections following TBI worsen neurological outcomes and are a major source of mortality and morbidity. Despite the compelling link between the damaged brain and peripheral immune functionality, little is known about how injury severity affects the peripheral immune system in closed-head diffuse TBI, the most common clinical presentation including all concussions. Therefore, we characterized peripheral blood mononuclear cells (PBMCs) and plasma changes over time and across injury severity using an established large-animal TBI model of closed-head, non-impact diffuse rotational acceleration in pigs. Across all timepoints and injury levels, we did not detect any changes to plasma cytokine concentrations. However, changes to the PBMCs were detectable and much more robust. We observed the concentration and physiology of circulating PBMCs changed in an injury severity-dependent manner, with most cellular changes occurring within the first 10 days following a high rotational velocity injury. Here, we report changes in the concentrations of myeloid and T cells, changes in PBMC composition, and changes in phagocytic clearance over time. Together, these data suggest that following a diffuse brain injury in a clinically relevant large-animal TBI model, the immune system exhibits perturbations that are detectable into the subacute timeframe. These findings invite future investigations into therapeutic interventions targeting peripheral immunity and the potential for peripheral blood cellular characterization as a diagnostic tool.

Single episode of moderate to severe traumatic brain injury leads to chronic neurological deficits and Alzheimer's-like pathological dementia

Traumatic brain injury (TBI) is one of the foremost causes of disability and mortality globally. While the scientific and medical emphasis is to save lives and avoid disability during acute period of injury, a severe health problem can manifest years after injury. For instance, TBI increases the risk of cognitive impairment in the elderly. Remote TBI history was reported to be a cause of the accelerated clinical trajectory of Alzheimer's disease-related dementia (ADRD) resulting in earlier onset of cognitive impairment and increased AD-associated pathological markers like greater amyloid deposition and cortical thinning. It is not well understood whether a single TBI event may increase the risk of dementia. Moreover, the cellular signaling pathways remain elusive for the chronic effects of TBI on cognition. We have hypothesized that a single TBI induces sustained neuroinflammation and disrupts cellular communication in a way that results later in ADRD pathology. To test this, we induced TBI in young adult CD1 mice and assessed the behavioral outcomes after 11 months followed by pathological, histological, transcriptomic, and MRI assessment. On MRI scans, these mice showed significant loss of tissue, reduced CBF, and higher white matter injury compared to sham mice. We found these brains showed progressive atrophy, markers of ADRD, sustained astrogliosis, loss of neuronal plasticity, and growth factors even after 1-year post-TBI. Because of progressive neurodegeneration, these mice had motor deficits, showed cognitive impairments, and wandered randomly in open field. We, therefore, conclude that progressive pathology after adulthood TBI leads to neurodegenerative conditions such as ADRD and impairs neuronal functions.

Lactobacillus Helveticus Improves Controlled Cortical Impact Injury-Generated Neurological Aberrations by Remodeling of Gut-Brain Axis Mediators

Considerable studies augured the potential of gut microbiota-based interventions in brain injury-associated complications. Based on our earlier study results, we envisaged the sex-specific neuroprotective effect of Lactobacillus helveticus by remodeling of gut-brain axis. In this study, we investigated the effect of L. helveticus on neurological complications in a mouse model of controlled cortical impact (CCI). Adult, male and female, C57BL/6 mice underwent CCI surgery and received L. helveticus treatment for six weeks. Sensorimotor function was evaluated via neurological severity score and rotarod test. Long-term effects on anxiety-like behavior and cognition were assessed using the elevated-zero maze (EZM) and novel object recognition test (NORT). Brain perilesional area, blood, colon, and fecal samples were collected post-CCI for molecular biology analysis. CCI-operated mice displayed significant neurological impairments at 1-, 3-, 5-, and 7-days post-injury (dpi) and exhibited altered behavior in EZM and NORT compared to sham-operated mice. However, these behavioral changes were ameliorated in mice receiving L. helveticus. GFAP, Iba-1, TNF-α, and IL-1β expressions and corticotrophin-releasing hormone (CRH) levels were elevated in the perilesional cortex of CCI-operated male/female mice. These elevated biomarkers and decreased BDNF levels in both male/female mice were modified by L. helveticus treatment. Additionally, L. helveticus treatment restored altered short-chain fatty acids (SCFAs) levels in fecal samples and improved intestinal integrity but did not affect decreased plasma levels of progesterone and testosterone in CCI mice. These results indicate that L. helveticus exerts beneficial effects in the CCI mouse model by mitigating inflammation and remodeling of gut microbiota-brain mediators.

Piezo2 Contributes to Traumatic Brain Injury by Activating the RhoA/ROCK1 Pathways

Traumatic brain injury (TBI) can lead to short-term and long-term physical and cognitive impairments, which have significant impacts on patients, families, and society. Currently, treatment outcomes for this disease are often unsatisfactory, due at least in part to the fact that the molecular mechanisms underlying the development of TBI are largely unknown. Here, we observed significant upregulation of Piezo2, a key mechanosensitive ion channel protein, in the injured brain tissue of a mouse model of TBI induced by controlled cortical impact. Pharmacological inhibition and genetic knockdown of Piezo2 after TBI attenuated neuronal death, brain edema, brain tissue necrosis, and deficits in neural function and cognitive function. Mechanistically, the increase in Piezo2 expression contributed to TBI-induced neuronal death and subsequent production of TNF-α and IL-1β, likely through activation of the RhoA/ROCK1 pathways in the central nervous system. Our findings suggest that Piezo2 is a key player in and a potential therapeutic target for TBI.

Connecting cellular mechanisms and extracellular vesicle cargo in traumatic brain injury

Traumatic brain injury is followed by a cascade of dynamic and complex events occurring at the cellular level. These events include: diffuse axonal injury, neuronal cell death, blood-brain barrier break down, glial activation and neuroinflammation, edema, ischemia, vascular injury, energy failure, and peripheral immune cell infiltration. The timing of these events post injury has been linked to injury severity and functional outcome. Extracellular vesicles are membrane bound secretory vesicles that contain markers and cargo pertaining to their cell of origin and can cross the blood-brain barrier. These qualities make extracellular vesicles intriguing candidates for a liquid biopsy into the pathophysiologic changes occurring at the cellular level post traumatic brain injury. Herein, we review the most commonly reported cargo changes in extracellular vesicles from clinical traumatic brain injury samples. We then use knowledge from animal and in vitro models to help infer what these changes may indicate regrading cellular responses post traumatic brain injury. Future research should prioritize labeling extracellular vesicles with markers for distinct cell types across a range of timepoints post traumatic brain injury.

A single-cell atlas deconstructs heterogeneity across multiple models in murine traumatic brain injury and identifies novel cell-specific targets

Traumatic brain injury (TBI) heterogeneity remains a critical barrier to translating therapies. Identifying final common pathways/molecular signatures that integrate this heterogeneity informs biomarker and therapeutic-target development. We present the first large-scale murine single-cell atlas of the transcriptomic response to TBI (334,376 cells) across clinically relevant models, sex, brain region, and time as a foundational step in molecularly deconstructing TBI heterogeneity. Results were unique to cell populations, injury models, sex, brain regions, and time, highlighting the importance of cell-level resolution. We identify cell-specific targets and previously unrecognized roles for microglial and ependymal subtypes. Ependymal-4 was a hub of neuroinflammatory signaling. A distinct microglial lineage shared features with disease-associated microglia at 24 h, with persistent gene-expression changes in microglia-4 even 6 months after contusional TBI, contrasting all other cell types that mostly returned to naive levels. Regional and sexual dimorphism were noted. CEREBRI, our searchable atlas (https://shiny.crc.pitt.edu/cerebri/), identifies previously unrecognized cell subtypes/molecular targets and is a leverageable platform for future efforts in TBI and other diseases with overlapping pathophysiology.

Glutamate uptake is transiently compromised in the perilesional cortex following controlled cortical impact

Glutamate, the primary excitatory neurotransmitter in the CNS, is regulated by the excitatory amino acid transporters (EAATs) GLT-1 and GLAST. Following traumatic brain injury (TBI), extracellular glutamate levels increase, contributing to excitotoxicity, circuit dysfunction, and morbidity. Increased neuronal glutamate release and compromised astrocyte-mediated uptake contribute to elevated glutamate, but the mechanistic and spatiotemporal underpinnings of these changes are not well established. Using the controlled cortical impact (CCI) model of TBI and iGluSnFR glutamate imaging, we quantified extracellular glutamate dynamics after injury. Three days post-injury, glutamate release was increased, and glutamate uptake and GLT-1 expression were reduced. 7- and 14-days post-injury, glutamate dynamics were comparable between sham and CCI animals. Changes in peak glutamate response were unique to specific cortical layers and proximity to injury. This was likely driven by increases in glutamate release, which was spatially heterogenous, rather than reduced uptake, which was spatially uniform. The astrocyte K + channel, Kir4.1, regulates activity-dependent slowing of glutamate uptake. Surprisingly, Kir4.1 was unchanged after CCI and accordingly, activity-dependent slowing of glutamate uptake was unaltered. This dynamic glutamate dysregulation after TBI underscores a brief period in which disrupted glutamate uptake may contribute to dysfunction and highlights a potential therapeutic window to restore glutamate homeostasis.

Cognitive dysfunction following brain trauma results from sex-specific reactivation of the developmental pruning processes

Cognitive losses resulting from severe brain trauma have long been associated with the focal region of tissue damage, leading to devastating functional impairment. For decades, researchers have focused on the sequelae of cellular alterations that exist within the perilesional tissues; however, few clinical trials have been successful. Here, we employed a mouse brain injury model that resulted in expansive synaptic damage to regions outside the focal injury. Our findings demonstrate that synaptic damage results from the prolonged increase in D-serine release from activated microglia and astrocytes, which leads to hyperactivation of perisynaptic NMDARs, tagging of damaged synapses by complement components, and the reactivation of developmental pruning processes. We show that this mechanistic pathway is reversible at several stages within a prolonged and progressive period of synaptic loss. Importantly, these key factors are present in acutely injured brain tissue acquired from patients with brain injury, which supports a therapeutic neuroprotective strategy.

The Uncoupling Effect of 17β-Estradiol Underlies the Resilience of Female-Derived Mitochondria to Damage after Experimental TBI

Current literature finds females have improved outcomes over their male counterparts after severe traumatic brain injury (TBI), while the opposite seems to be true for mild TBI. This begs the question as to what may be driving these sex differences after TBI. Estrogen is thought to be neuroprotective in certain diseases, and its actions have been shown to influence mitochondrial function. Mitochondrial impairment is a major hallmark of TBI, and interestingly, this dysfunction has been shown to be more severe in males than females after brain injury. This suggests estrogen could be playing a role in promoting "mitoprotection" following TBI. Despite the existence of estrogen receptors in mitochondria, few studies have examined the direct role of estrogen on mitochondrial function, and no studies have explored this after TBI. We hypothesized ex vivo treatment of isolated mitochondria with 17β-estradiol (E2) would improve mitochondrial function after experimental TBI in mice. Total mitochondria from the ipsilateral (injured) and contralateral (control) cortices of male and female mice were isolated 24 h post-controlled severe cortical impact (CCI) and treated with vehicle, 2 nM E2, or 20 nM E2 immediately before measuring reactive oxygen species (ROS) production, bioenergetics, electron transport chain complex (ETC) activities, and β-oxidation of palmitoyl carnitine. Protein expression of oxidative phosphorylation (OXPHOS) complexes was also measured in these mitochondrial samples to determine whether this influenced functional outcomes with respect to sex or injury. While mitochondrial ROS production was affected by CCI in both sexes, there were other sex-specific patterns of mitochondrial injury 24 h following severe CCI. For instance, mitochondria from males were more susceptible to CCI-induced injury with respect to bioenergetics and ETC complex activities, whereas mitochondria from females showed only Complex II impairment and reduced β-oxidation after injury. Neither concentration of E2 influenced ETC complex activities themselves, but 20 nM E2 appeared to uncouple mitochondria isolated from the contralateral cortex in both sexes, as well as the injured ipsilateral cortex of females. These studies highlight the significance of measuring mitochondrial dysfunction in both sexes after TBI and also shed light on another potential neuroprotective mechanism in which E2 may attenuate mitochondrial dysfunction after TBI in vivo.

Characterization of focused ultrasound blood-brain barrier disruption effect on inflammation as a function of treatment parameters

The technology of focused ultrasound-mediated disruption of the blood-brain barrier (FUS- BBB opening) has now been used in over 20 Phase 1 clinical trials to validate the safety and feasibility of BBB opening for drug delivery in patients with brain tumors and neurodegenerative diseases. The primary treatment parameters, FUS intensity and microbubble dose, are chosen to balance sufficient BBB disruption to achieve drug delivery against potential acute vessel damage leading to microhemorrhage. This can largely be achieved based on both empirical results from animal studies and by monitoring the microbubble cavitation signal in real time during the treatment. However, other safety considerations due to second order effects caused by BBB disruption, such as inflammation and alteration of neurovascular function, are not as easily measurable, may take longer to manifest and are only beginning to be understood. This study builds on previous work that has investigated the inflammatory response following FUS-BBB opening. In this study, we characterize the effect of FUS intensity and microbubble dose on the extent of BBB disruption, observed level of microhemorrhage, and degree of inflammatory response at three acute post-treatment time points in the wild-type mouse brain. Additionally, we evaluate differences related to biological sex, presence and degree of the anti- inflammatory response that develops to restore homeostasis in the brain environment, and the impact of multiple FUS-BBB opening treatments on this inflammatory response.

Sex-specific and cell-specific regulation of ER stress and neuroinflammation after traumatic brain injury in juvenile mice

Endoplasmic reticulum (ER) stress and neuroinflammation play an important role in secondary brain damage after traumatic brain injury (TBI). Due to the complex brain cytoarchitecture, multiple cell types are affected by TBI. However, cell type-specific and sex-specific responses to ER stress and neuroinflammation remain unclear. Here we investigated differential regulation of ER stress and neuroinflammatory pathways in neurons and microglia during the acute phase post-injury in a mouse model of impact acceleration TBI in both males and females. We found that TBI resulted in significant weight loss only in males, and sensorimotor impairment and depressive-like behaviors in both males and females at the acute phase post-injury. By concurrently isolating neurons and microglia from the same brain sample of the same animal, we were able to evaluate the simultaneous responses in neurons and microglia towards ER stress and neuroinflammation in both males and females. We discovered that the ER stress and anti-inflammatory responses were significantly stronger in microglia, especially in female microglia, compared with the male and female neurons. Whereas the degree of phosphorylated-tau (pTau) accumulation was significantly higher in neurons, compared with the microglia. In conclusion, TBI resulted in behavioral deficits and cell type-specific and sex-specific responses to ER stress and neuroinflammation, and abnormal protein accumulation at the acute phase after TBI in immature mice.

Effects of poloxamer 188 on traumatic brain injury

Traumatic Brain Injury (TBI) is a major cause of severe disability and death, resulting in significant health care and economic burden. Poloxamer 188, a synthetic tri-block copolymer approved by the FDA, has been studied for its potential effects on traumatic brain injury (TBI). The neuroprotective abilities of P188 have attracted significant attention. This systematic review aims to compile evidence of P188's effect on the treatment of TBI. A comprehensive literature search was conducted using PubMed, SCOPUS, and Google Scholar databases, which yielded 20 articles that satisfied the inclusion criteria. These articles have shown direct protective effects of P188 on brain tissue following TBI, including restitution of the increase cell membrane permeability, attenuation of neuronal necrosis and apoptosis, improvement of mitochondrial viability, reduction in axonal disruption, and restoration of the blood brain barrier. In animals, P188 has been shown to improve sensorimotor functions, as well as spatial learning and memory.

Sex-dependent improvement in traumatic brain injury outcomes after liposomal delivery of dexamethasone in mice

Traumatic brain injury (TBI) can have long-lasting physical, emotional, and cognitive consequences due to the neurodegeneration caused by its robust inflammatory response. Despite advances in rehabilitation care, effective neuroprotective treatments for TBI patients are lacking. Furthermore, current drug delivery methods for TBI treatment are inefficient in targeting inflamed brain areas. To address this issue, we have developed a liposomal nanocarrier (Lipo) encapsulating dexamethasone (Dex), an agonist for the glucocorticoid receptor utilized to alleviate inflammation and swelling in various conditions. In vitro studies show that Lipo-Dex were well tolerated in human and murine neural cells. Lipo-Dex showed significant suppression of inflammatory cytokines, IL-6 and TNF-α, release after induction of neural inflammation with lipopolysaccharide. Further, the Lipo-Dex were administered to young adult male and female C57BL/6 mice immediately after controlled cortical impact injury (a TBI model). Our findings demonstrate that Lipo-Dex can selectively target the injured brain, thereby reducing lesion volume, cell death, astrogliosis, the release of pro-inflammatory cytokines, and microglial activation compared to Lipo-treated mice in a sex-dependent manner, showing a major impact only in male mice. This highlights the importance of considering sex as a crucial variable in developing and evaluating new nano-therapies for brain injury. These results suggest that Lipo-Dex administration may effectively treat acute TBI.

Brain-Bone Crosstalk in a Murine Polytrauma Model Promotes Bone Remodeling but Impairs Neuromotor Recovery and Anxiety-Related Behavior

Traumatic brain injury (TBI) and long bone fractures are a common injury pattern in polytrauma patients and modulate each other's healing process. As only a limited number of studies have investigated both traumatic sites, we tested the hypothesis that brain-bone polytrauma mutually impacts neuro- and osteopathological outcomes. Adult female C57BL/6N mice were subjected to controlled cortical impact (CCI), and/or osteosynthetic stabilized femoral fracture (FF), or sham surgery. Neuromotor and behavioral impairments were assessed by neurological severity score, open field test, rotarod test, and elevated plus maze test. Brain and bone tissues were processed 42 days after trauma. CCI+FF polytrauma mice had increased bone formation as compared to FF mice and increased mRNA expression of bone sialoprotein (BSP). Bone fractures did not aggravate neuropathology or neuroinflammation assessed by cerebral lesion size, hippocampal integrity, astrocyte and microglia activation, and gene expression. Behavioral assessments demonstrated an overall impaired recovery of neuromotor function and persistent abnormalities in anxiety-related behavior in polytrauma mice. This study shows enhanced bone healing, impaired neuromotor recovery and anxiety-like behavior in a brain-bone polytrauma model. However, bone fractures did not aggravate TBI-evoked neuropathology, suggesting the existence of outcome-relevant mechanisms independent of the extent of brain structural damage and neuroinflammation.

Antibiotic treatment induces microbiome dysbiosis and reduction of neuroinflammation following traumatic brain injury in mice

Background

The gut microbiome is linked to brain pathology in cases of traumatic brain injury (TBI), yet the specific bacteria that are implicated are not well characterized. To address this gap, in this study, we induced traumatic brain injury (TBI) in male C57BL/6J mice using the controlled cortical impact (CCI) injury model. After 35 days, we administered a broad-spectrum antibiotics (ABX) cocktail (ampicillin, gentamicin, metronidazole, vancomycin) through oral gavage for 2 days to diminish existing microbiota. Subsequently, we inflicted a second TBI on the mice and analyzed the neuropathological outcomes five days later.

Results

Longitudinal analysis of the microbiome showed significant shifts in the diversity and abundance of bacterial genera during both acute and chronic inflammation. These changes were particularly dramatic following treatment with ABX and after the second TBI. ABX treatment did not affect the production of short-chain fatty acids (SCFA) but did alter intestinal morphology, characterized by reduced villus width and a lower count of goblet cells, suggesting potential negative impacts on intestinal integrity. Nevertheless, diminishing the intestinal microbiome reduced cortical damage, apoptotic cell density, and microglial/macrophage activation in the cortical and thalamic regions of the brain.

Conclusions

Our findings suggest that eliminating colonized gut bacteria via broad-spectrum ABX reduces neuroinflammation and enhances neurological outcomes in TBI despite implications to gut health.

Escape from X-chromosome inactivation and sex differences in Alzheimer's disease

Sex differences exist in the onset and progression of Alzheimer's disease. Globally, women have a higher prevalence, while men with Alzheimer's disease experience earlier mortality and more pronounced cognitive decline than women. The cause of sex differences in Alzheimer's disease remains unclear. Accumulating evidence suggests the potential role of X-linked genetic factors in the sex difference of Alzheimer's disease (AD). During embryogenesis, a remarkable process known as X-chromosome inactivation (XCI) occurs in females, leading to one of the X chromosomes undergoing transcriptional inactivation, which balances the effects of two X chromosomes in females. Nevertheless, certain genes exceptionally escape from XCI, which provides a basis for dual expression dosage of specific genes in females. Based on recent research findings, we explore key escape genes and their potential therapeutic use associated with Alzheimer's disease. Also, we discuss their possible role in driving the sex differences in Alzheimer's disease. This will provide new perspectives for precision medicine and gender-specific treatment of AD.

Complement propagates visual system pathology following traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is associated with the development of visual system disorders. Visual deficits can present with delay and worsen over time, and may be associated with an ongoing neuroinflammatory response that is known to occur after TBI. Complement system activation is strongly associated with the neuroinflammatory response after TBI, but whether it contributes to vision loss after TBI is unexplored.

METHODS

Acute and chronic neuroinflammatory changes within the dorsal lateral geniculate nucleus (dLGN) and retina were investigated subsequent to a moderate to severe murine unilateral controlled cortical impact. Neuroinflammatory and histopathological outcomes were interpreted in the context of behavioral and visual function data. To investigate the role of complement, cohorts were treated after TBI with the complement inhibitor, CR2-Crry.

RESULTS

At 3 days after TBI, complement component C3 was deposited on retinogeniculate synapses in the dLGN both ipsilateral and contralateral to the lesion, which was reduced in CR2-Crry treated animals. This was associated with microglia morphological changes in both the ipsilateral and contralateral dLGN, with a less ramified phenotype in vehicle compared to CR2-Crry treated animals. Microglia in vehicle treated animals also had a greater internalized VGlut2 + synaptic volume after TBI compared to CR2-Crry treated animals. Microglia morphological changes seen acutely persisted for at least 49 days after injury. Complement inhibition also reduced microglial synaptic internalization in the contralateral dLGN and increased the association between VGLUT2 and PSD95 puncta, indicating preservation of intact synapses. Unexpectedly, there were no changes in the thickness of the inner retina, retinal nerve fiber layer or retinal ganglion layer. Neuropathological changes in the dLGN were accompanied by reduced visual acuity at subacute and chronic time points after TBI, with improvement seen in CR2-Crry treated animals.

CONCLUSION

TBI induces complement activation within the dLGN and promotes microglial activation and synaptic internalization. Complement inhibition after TBI in a clinically relevant paradigm reduces complement activation, maintains a more surveillance-like microglia phenotype, and preserves synaptic density within the dLGN. Together, the data indicate that complement plays a key role in the development of visual deficits after TBI via complement-dependent microglial phagocytosis of synapses within the dLGN.

Sex Dependent Disparities in the Central Innate Immune Response after Moderate Spinal Cord Contusion in Rat

Subacute spinal cord injury (SCI) displays a complex pathophysiology associated with pro-inflammation and ensuing tissue damage. Microglia, the resident innate immune cells of the CNS, in concert with infiltrating macrophages, are the primary contributors to SCI-induced inflammation. However, subpopulations of activated microglia can also possess immunomodulatory activities that are essential for tissue remodeling and repair, including the production of anti-inflammatory cytokines and growth factors that are vital for SCI recovery. Recently, reports have provided convincing evidence that sex-dependent differences exist in how microglia function during CNS pathologies and the extent to which these cells contribute to neurorepair and endogenous recovery. Herein we employed flow cytometry and immunohistochemical methods to characterize the phenotype and population dynamics of activated innate immune cells within the injured spinal cord of age-matched male and female rats within the first week (7 days) following thoracic SCI contusion. This assessment included the analysis of pro- and anti-inflammatory markers, as well as the expression of critical immunomodulatory kinases, including P38 MAPK, and transcription factors, such as NFκB, which play pivotal roles in injury-induced inflammation. We demonstrate that activated microglia from the injured spinal cord of female rats exhibited a significantly diminutive pro-inflammatory response, but enhanced anti-inflammatory activity compared to males. These changes included lower levels of iNOS and TLR4 expression but increased levels of ARG-1 and CD68 in females after SCI. The altered expression of these markers is indicative of a disparate secretome between the microglia of males and females after SCI and that the female microglia possesses higher phagocytic capabilities (increased CD68). The examination of immunoregulatory kinases and transcription factors revealed that female microglia had higher levels of phosphorylated P38Thr180/Tyr182 MAPK and nuclear NFκB pp50Ser337 but lower amounts of nuclear NFκB pp65Ser536, suggestive of an attenuated pro-inflammatory phenotype in females compared to males after SCI. Collectively, this work provides novel insight into some of the sex disparities that exist in the innate immune response after SCI and indicates that sex is an important variable when designing and testing new therapeutic interventions or interpretating positive or negative responses to an intervention.

Shared inflammatory glial cell signature after stab wound injury, revealed by spatial, temporal, and cell-type-specific profiling of the murine cerebral cortex

Traumatic brain injury leads to a highly orchestrated immune- and glial cell response partially responsible for long-lasting disability and the development of secondary neurodegenerative diseases. A holistic understanding of the mechanisms controlling the responses of specific cell types and their crosstalk is required to develop an efficient strategy for better regeneration. Here, we combine spatial and single-cell transcriptomics to chart the transcriptomic signature of the injured male murine cerebral cortex, and identify specific states of different glial cells contributing to this signature. Interestingly, distinct glial cells share a large fraction of injury-regulated genes, including inflammatory programs downstream of the innate immune-associated pathways Cxcr3 and Tlr1/2. Systemic manipulation of these pathways decreases the reactivity state of glial cells associated with poor regeneration. The functional relevance of the discovered shared signature of glial cells highlights the importance of our resource enabling comprehensive analysis of early events after brain injury.

Probiotic treatment causes sex-specific neuroprotection after traumatic brain injury in mice

Background

Recent studies have shed light on the potential role of gut dysbiosis in shaping traumatic brain injury (TBI) outcomes. Changes in the levels and types of Lactobacillus bacteria present might impact the immune system disturbances, neuroinflammatory responses, anxiety and depressive-like behaviors, and compromised neuroprotection mechanisms triggered by TBI.

Objective

This study aimed to investigate the effects of a daily pan-probiotic (PP) mixture in drinking water containing strains of Lactobacillus plantarum, L. reuteri, L. helveticus, L. fermentum, L. rhamnosus, L. gasseri, and L. casei, administered for either two or seven weeks before inducing TBI on both male and female mice.

Methods

Mice were subjected to controlled cortical impact (CCI) injury. Short-chain fatty acids (SCFAs) analysis was performed for metabolite measurements. The taxonomic profiles of murine fecal samples were evaluated using 16S rRNA V1-V3 sequencing analysis. Histological analyses were used to assess neuroinflammation and gut changes post-TBI, while behavioral tests were conducted to evaluate sensorimotor and cognitive functions.

Results

Our findings suggest that PP administration modulates the diversity and composition of the microbiome and increases the levels of SCFAs in a sex-dependent manner. We also observed a reduction of lesion volume, cell death, and microglial and macrophage activation after PP treatment following TBI in male mice. Furthermore, PP-treated mice show motor function improvements and decreases in anxiety and depressive-like behaviors.

Conclusion

Our findings suggest that PP administration can mitigate neuroinflammation and ameliorate motor and anxiety and depressive-like behavior deficits following TBI. These results underscore the potential of probiotic interventions as a viable therapeutic strategy to address TBI-induced impairments, emphasizing the need for gender-specific treatment approaches.

Exploration of the anti-inflammatory, analgesic, and wound healing activities of Bletilla Striata polysaccharide

Bletilla Striata (BS) Polysaccharide (BSP) is one of the main components of the traditional Chinese medicinal plant Bletilla striata Rchb. F. BSP has been widely used in antimicrobial and hemostasis treatments in clinics. Despite its use in skin disease treatment and cosmetology, the effects of BSP on wound healing remain unclear. Here we investigated the anti-inflammatory, antioxidant, and analgesic effects of BSP and explored its impact on morphological changes and inflammatory mediators during wound healing. A carrageenan-induced mouse paw edema model was established to evaluate the anti-inflammatory effect of BSP. Antioxidant indicators, including NO, SOD, and MDA, were measured in the blood and liver. The increased pain threshold induced by BSP was also determined using the hot plate test. A mouse excisional wound model was applied to evaluate the wound healing rate, and HE staining and Masson staining were used to detect tissue structure changes. In addition, ELISA was employed to detect the expression of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β in serum. BSP significantly decreased the concentration of NO and MDA in serum and liver while increasing SOD activity. It exhibited a notable improvement in mouse paw edema induced by carrageenan. BSP dose-dependently delayed the appearance of licking behavior in mice, indicating its analgesic effect. Compared to the control group, the wound healing rate was significantly improved in the BSP treatment group. HE and Masson staining results showed that the BSP and 'Jingwanhong' ointment groups had slightly milder inflammatory responses and significantly promoted more new granulation tissue formation. The levels of serum inflammatory mediators TNF-α, IL-1β, and IL-6 were reduced to varying degrees. The results demonstrated that BSP possesses anti-inflammatory, antioxidant, analgesic, and wound healing properties, and it may promote wound healing through inhibition of inflammatory cytokine synthesis and release.

Sex specific effects of buprenorphine on adult hippocampal neurogenesis and behavioral outcomes during the acute phase after pediatric traumatic brain injury in mice

Traumatic brain injury (TBI) in children often causes cognitive and mental dysfunctions, as well as acute and chronic pain. Adult hippocampal neurogenesis plays a key role in cognition, depression, and pain. Adult hippocampal neurogenesis can be modulated by genetic and environmental factors, such as TBI and opioids. Buprenorphine (BPN), a semisynthetic opioid, is commonly used for pain management in children, however, the effects of BPN on adult hippocampal neurogenesis after pediatric TBI are still unclear. This study investigated the sex-specific effects of BPN on adult hippocampal neurogenesis during acute phase after pediatric TBI. Male and female littermates were randomized on postnatal day 20-21(P20-21) into Sham, TBI+saline and TBI+BPN groups. BPN was administered intraperitoneally to the TBI+BPN mice at 30 min after injury, and then every 6-12 h (h) for 2 days (d). Bromodeoxyuridine (BrdU) was administered intraperitoneally to all groups at 2, 4, 6, and 8-h post-injury. All outcomes were evaluated at 3-d post-BrdU administration. We found that TBI induced significant cognitive impairment, depression, and reduced adult hippocampal neurogenesis in both male and female mice, with more prominent effects in females. BPN significantly improved adult hippocampal neurogenesis and depression in males, but not in females. We further demonstrated that differential expressions of opioid receptors, transcription factors and neuroinflammatory markers at the neurogenic niche might be responsible for the differential effects of BPN in males and females. In conclusion, this study elucidates the effects of BPN on adult hippocampal neurogenesis and behavioral outcomes at the acute phase after pediatric TBI.

Reactive gliosis in traumatic brain injury: a comprehensive review

Traumatic brain injury (TBI) is one of the most common pathological conditions impacting the central nervous system (CNS). A neurological deficit associated with TBI results from a complex of pathogenetic mechanisms including glutamate excitotoxicity, inflammation, demyelination, programmed cell death, or the development of edema. The critical components contributing to CNS response, damage control, and regeneration after TBI are glial cells-in reaction to tissue damage, their activation, hypertrophy, and proliferation occur, followed by the formation of a glial scar. The glial scar creates a barrier in damaged tissue and helps protect the CNS in the acute phase post-injury. However, this process prevents complete tissue recovery in the late/chronic phase by producing permanent scarring, which significantly impacts brain function. Various glial cell types participate in the scar formation, but this process is mostly attributed to reactive astrocytes and microglia, which play important roles in several brain pathologies. Novel technologies including whole-genome transcriptomic and epigenomic analyses, and unbiased proteomics, show that both astrocytes and microglia represent groups of heterogenic cell subpopulations with different genomic and functional characteristics, that are responsible for their role in neurodegeneration, neuroprotection and regeneration. Depending on the representation of distinct glia subpopulations, the tissue damage as well as the regenerative processes or delayed neurodegeneration after TBI may thus differ in nearby or remote areas or in different brain structures. This review summarizes TBI as a complex process, where the resultant effect is severity-, region- and time-dependent and determined by the model of the CNS injury and the distance of the explored area from the lesion site. Here, we also discuss findings concerning intercellular signaling, long-term impacts of TBI and the possibilities of novel therapeutical approaches. We believe that a comprehensive study with an emphasis on glial cells, involved in tissue post-injury processes, may be helpful for further research of TBI and be the decisive factor when choosing a TBI model.

Complement propagates visual system pathology following traumatic brain injury

Background

Traumatic brain injury (TBI) is associated with the development of visual system disorders. Visual deficits can present with delay and worsen over time, and may be associated with an ongoing neuroinflammatory response that is known to occur after TBI. Complement activation is strongly associated with the neuroinflammatory response after TBI, but whether it contributes to vision loss after TBI is unexplored.

Methods

Acute and chronic neuroinflammatory changes within the dorsal lateral geniculate nucleus (dLGN) and retina were investigated subsequent to murine controlled unilateral cortical impact. Neuroinflammatory and histopathological data were interpreted in the context of behavioral and visual function data. To investigate the role of complement, cohorts were treated after TBI with the complement inhibitor, CR2-Crry.

Results

At 3 days after TBI, complement C3 was deposited on retinogeniculate synapses in the dLGN both ipsilateral and contralateral to the lesion, which was reduced in CR2-Crry treated animals. This was associated with microglia morphological changes in both the ipsilateral and contralateral dLGN, with a more amoeboid phenotype in vehicle compared to CR2-Crry treated animals. Microglia in vehicle treated animals also had a greater internalized VGlut2+ synaptic volume after TBI compared to CR2-Crry treated animals. Microglia morphological changes seen acutely persisted for at least 49 days after injury. Complement inhibition also reduced microglial synaptic internalization in the contralateral dLGN and increased the association between VGLUT2 and PSD95 puncta, indicating preservation of intact synapses. Unexpectedly, there were no changes in the thickness of the inner retina, retinal nerve fiber layer or retinal ganglion layer. Pathologies were accompanied by reduced visual acuity at subacute and chronic time points after TBI, with improvement seen in CR2-Crry treated animals.

Conclusion

TBI induces complement activation within the dLGN and promotes microglial activation and synaptic internalization. Complement inhibition after TBI in a clinically relevant paradigm reduces complement activation, maintains a more surveillance-like microglia phenotype, and preserves synaptic density within the dLGN. Together, the data indicate that complement plays a key role in the development of visual deficits after TBI via complement-dependent microglial phagocytosis of synapses within the dLGN.

Deplete and repeat: microglial CSF1R inhibition and traumatic brain injury

Traumatic brain injury (TBI) is a public health burden affecting millions of people. Sustained neuroinflammation after TBI is often associated with poor outcome. As a result, increased attention has been placed on the role of immune cells in post-injury recovery. Microglia are highly dynamic after TBI and play a key role in the post-injury neuroinflammatory response. Therefore, microglia represent a malleable post-injury target that could substantially influence long-term outcome after TBI. This review highlights the cell specific role of microglia in TBI pathophysiology. Microglia have been manipulated via genetic deletion, drug inhibition, and pharmacological depletion in various pre-clinical TBI models. Notably, colony stimulating factor 1 (CSF1) and its receptor (CSF1R) have gained much traction in recent years as a pharmacological target on microglia. CSF1R is a transmembrane tyrosine kinase receptor that is essential for microglia proliferation, differentiation, and survival. Small molecule inhibitors targeting CSF1R result in a swift and effective depletion of microglia in rodents. Moreover, discontinuation of the inhibitors is sufficient for microglia repopulation. Attention is placed on summarizing studies that incorporate CSF1R inhibition of microglia. Indeed, microglia depletion affects multiple aspects of TBI pathophysiology, including neuroinflammation, oxidative stress, and functional recovery with measurable influence on astrocytes, peripheral immune cells, and neurons. Taken together, the data highlight an important role for microglia in sustaining neuroinflammation and increasing risk of oxidative stress, which lends to neuronal damage and behavioral deficits chronically after TBI. Ultimately, the insights gained from CSF1R depletion of microglia are critical for understanding the temporospatial role that microglia develop in mediating TBI pathophysiology and recovery.

Sex-driven variability in TSPO-expressing microglia in MS patients and healthy individuals

Background

Males with multiple sclerosis (MS) have a higher risk for disability progression than females, but the reasons for this are unclear.

Objective

We hypothesized that potential differences in TSPO-expressing microglia between female and male MS patients could contribute to sex differences in clinical disease progression.

Methods

The study cohort consisted of 102 MS patients (mean (SD) age 45.3 (9.7) years, median (IQR) disease duration 12.1 (7.0-17.2) years, 72% females, 74% relapsing-remitting MS) and 76 age- and sex-matched healthy controls. TSPO-expressing microglia were measured using the TSPO-binding radioligand [11C](R)-PK11195 and brain positron emission tomography (PET). TSPO-binding was quantified as distribution volume ratio (DVR) in normal-appearing white matter (NAWM), thalamus, whole brain and cortical gray matter (cGM).

Results

Male MS patients had higher DVRs compared to female patients in the whole brain [1.22 (0.04) vs. 1.20 (0.02), p = 0.002], NAWM [1.24 (0.06) vs. 1.21 (0.05), p = 0.006], thalamus [1.37 (0.08) vs. 1.32 (0.02), p = 0.008] and cGM [1.25 (0.04) vs. 1.23 (0.04), p = 0.028]. Similarly, healthy men had higher DVRs compared to healthy women except for cGM. Of the studied subgroups, secondary progressive male MS patients had the highest DVRs in all regions, while female controls had the lowest DVRs.

Conclusion

We observed higher TSPO-binding in males compared to females among people with MS and in healthy individuals. This sex-driven inherent variability in TSPO-expressing microglia may predispose male MS patients to greater likelihood of disease progression.

Acute brain injury and nanomedicine: sex as a biological variable

Sex as a biological variable has been recognized for decades to be a critical aspect of the drug development process, as differences in drug pharmacology and toxicity in female versus male subjects can drive the success or failure of new therapeutics. These concepts in development of traditional drug systems have only recently begun to be applied for advancing nanomedicine systems that are designed for drug delivery or imaging in the central nervous system (CNS). This review provides a comprehensive overview of the current state of two fields of research - nanomedicine and acute brain injury-centering on sex as a biological variable. We highlight areas of each field that provide foundational understanding of sex as a biological variable in nanomedicine, brain development, immune response, and pathophysiology of traumatic brain injury and stroke. We describe current knowledge on female versus male physiology as well as a growing number of empirical reports that directly address sex as a biological variable in these contexts. In sum, the data make clear two key observations. First, the manner in which sex affects nanomedicine distribution, toxicity, or efficacy is important, complex, and depends on the specific nanoparticle system under considerations; second, although field knowledge is accumulating to enable us to understand sex as a biological variable in the fields of nanomedicine and acute brain injury, there are critical gaps in knowledge that will need to be addressed. We anticipate that understanding sex as a biological variable in the development of nanomedicine systems to treat acute CNS injury will be an important determinant of their success.

Association of Blood Biomarkers of Inflammation With Acute Concussion in Collegiate Athletes and Military Service Academy Cadets

BACKGROUND AND OBJECTIVES

The objective was to characterize the acute effects of concussion (a subset of mild traumatic brain injury) on serum interleukin (IL)-6 and IL-1 receptor antagonist (RA) and 5 additional inflammatory markers in athletes and military service academy members from the Concussion Assessment, Research, and Education Consortium and to determine whether these markers aid in discrimination of concussed participants from controls.

METHODS

Athletes and cadets with concussion and matched controls provided blood at baseline and postinjury visits between January 2015 and March 2020. Linear models investigated changes in inflammatory markers measured using Meso Scale Discovery assays across time points (baseline and 0-12, 12-36, 36-60 hours). Subanalyses were conducted in participants split by sex and injury population. Logistic regression analyses tested whether acute levels of IL-6 and IL-1RA improved discrimination of concussed participants relative to brain injury markers (glial fibrillary acidic protein, tau, neurofilament light, ubiquitin c-terminal hydrolase-L1) or clinical data (Sport Concussion Assessment Tool-Third Edition, Standardized Assessment of Concussion, Balance Error Scoring System).

RESULTS

Participants with concussion (total, N = 422) had elevated IL-6 and IL-1RA at 0-12 hours vs controls (n = 345; IL-6: mean difference [MD] (standard error) = 0.701 (0.091), p < 0.0001; IL-1RA: MD = 0.283 (0.042), p < 0.0001) and relative to baseline (IL-6: MD = 0.656 (0.078), p < 0.0001; IL-1RA: MD = 0.242 (0.038), p < 0.0001), 12-36 hours (IL-6: MD = 0.609 (0.086), p < 0.0001; IL-1RA: MD = 0.322 (0.041), p < 0.0001), and 36-60 hours (IL-6: MD = 0.818 (0.084), p < 0.0001; IL-1RA: MD = 0.317 (0.040), p < 0.0001). IL-6 and IL-1RA were elevated in participants with sport (IL-6: MD = 0.748 (0.115), p < 0.0001; IL-1RA: MD = 0.304 (0.055), p < 0.0001) and combative-related concussions (IL-6: MD = 0.583 (0.178), p = 0.001; IL-1RA: MD = 0.312 (0.081), p = 0.0001). IL-6 was elevated in male (MD = 0.734 (0.105), p < 0.0001) and female participants (MD = 0.600 (0.177), p = 0.0008); IL-1RA was only elevated in male participants (MD = 0.356 (0.047), p < 0.0001). Logistic regression showed the inclusion of IL-6 and IL-1RA at 0-12 hours improved the discrimination of participants with concussion from controls relative to brain injury markers (χ2(2) = 17.855, p = 0.0001; area under the receiver operating characteristic curve [AUC] 0.73 [0.66-0.80] to 0.78 [0.71-0.84]), objective clinical measures (balance and cognition; χ2(2) = 40.661, p < 0.0001; AUC 0.81 [0.76-0.86] to 0.87 [0.83-0.91]), and objective and subjective measures combined (χ2(2) = 13.456, p = 0.001; AUC 0.97 [0.95-0.99] to 0.98 [0.96-0.99]), although improvement in AUC was only significantly relative to objective clinical measures.

DISCUSSION

IL-6 and IL-1RA (male participants only) are elevated in the early-acute window postconcussion and may aid in diagnostic decisions beyond traditional blood markers and common clinical measures. IL-1RA results highlight sex differences in the immune response to concussion which should be considered in future biomarker work.

Neurobehavioral and inflammatory responses following traumatic brain injury in male and female mice

Traumatic brain injury (TBI) is a leading cause of mortality and is associated with a high rate of functional comorbidities, including motor, cognitive, anxiety, depression, and emotional disorders. TBI pathophysiology and recovery are complicated and involve several mechanistic pathways that control neurobehavioral outcomes. In this study, male and female C57Bl/6 J mice were subjected to a controlled cortical impact model of TBI or sham injury and evaluated for different neurobehavioral and inflammatory outcomes over a month. We demonstrate that TBI mice have increased motor dysfunction at early and late time points following the injury as compared to the sham group. Anxiety-like symptoms were time- and task-dependent, with both sexes having increased anxiety-like behavior 2 weeks post-injury. Cognitive functions measured by T-maze presented greater deficits in TBI mice, while there was no sex or injury-related difference in depressive-like behaviors. Notably, a significant effect of sex was found in empathy-like behavior, with females showing more allogrooming and freezing behavior in the consoling and fear observational tests, respectively. Evaluating the impact of the injury-induced brain damage demonstrated a greater injury volume and neuronal degeneration in males compared to females one month after TBI. Moreover, male mice showed higher peripheral inflammatory responses, as represented by elevated serum levels of peripheral leukocytes and inflammatory markers. These results will have significant implications for understanding TBI's long-term consequences on neurobehavioral and inflammatory responses, which are sex-specific and can be considered for individualized therapeutic strategies in treating TBI.

Neuroprotection or Sex Bias: A Protective Response to Traumatic Brain Injury in the Females

Traumatic brain injury (TBI) is a major healthcare problem and a common cause of mortality and morbidity. Clinical and preclinical research suggests sex-related differences in short- and longterm outcomes following TBI; however, males have been the main focus of TBI research. Females show a protective response against TBI. Female animals in preclinical studies and women in clinical trials have shown comparatively better outcomes against mild, moderate, or severe TBI. This reflects a favorable protective nature of the females compared to the males, primarily attributed to various protective mechanisms that provide better prognosis and recovery in the females after TBI. Understanding the sex difference in the TBI pathophysiology and the underlying mechanisms remains an elusive goal. In this review, we provide insights into various mechanisms related to the anatomical, physiological, hormonal, enzymatic, inflammatory, oxidative, genetic, or mitochondrial basis that support the protective nature of females compared to males. Furthermore, we sought to outline the evidence of multiple biomarkers that are highly potential in the investigation of TBI's prognosis, pathophysiology, and treatment and which can serve as objective measures and novel targets for individualized therapeutic interventions in TBI treatment. Implementations from this review are important for the understanding of the effect of sex on TBI outcomes and possible mechanisms behind the favorable response in females. It also emphasizes the critical need to include females as a biological variable and in sufficient numbers in future TBI studies.

Repurposing of pexidartinib for microglia depletion and renewal

Pexidartinib (PLX3397) is a small molecule receptor tyrosine kinase inhibitor of colony stimulating factor 1 receptor (CSF1R) with moderate selectivity over other members of the platelet derived growth factor receptor family. It is approved for treatment of tenosynovial giant cell tumors (TGCT). CSF1R is highly expressed by microglia, which are macrophages of the central nervous system (CNS) that defend the CNS against injury and pathogens and contribute to synapse development and plasticity. Challenged by pathogens, apoptotic cells, debris, or inflammatory molecules they adopt a responsive state to propagate the inflammation and eventually return to a homeostatic state. The phenotypic switch may fail, and disease-associated microglia contribute to the pathophysiology in neurodegenerative or neuropsychiatric diseases or long-lasting detrimental brain inflammation after brain, spinal cord or nerve injury or ischemia/hemorrhage. Microglia also contribute to the growth permissive tumor microenvironment of glioblastoma (GBM). In rodents, continuous treatment for 1-2 weeks via pexidartinib food pellets leads to a depletion of microglia and subsequent repopulation from the remaining fraction, which is aided by peripheral monocytes that search empty niches for engraftment. The putative therapeutic benefit of such microglia depletion or forced renewal has been assessed in almost any rodent model of CNS disease or injury or GBM with heterogeneous outcomes, but a tendency of partial beneficial effects. So far, microglia monitoring e.g. via positron emission imaging is not standard of care for patients receiving Pexidartinib (e.g. for TGCT), so that the depletion and repopulation efficiency in humans is still largely unknown. Considering the virtuous functions of microglia, continuous depletion is likely no therapeutic option but short-lasting transient partial depletion to stimulate microglia renewal or replace microglia in genetic disease in combination with e.g. stem cell transplantation or as part of a multimodal concept in treatment of glioblastoma appears feasible. The present review provides an overview of the preclinical evidence pro and contra microglia depletion as a therapeutic approach.

iDISCO Tissue Clearing Whole-Brain and Light Sheet Microscopy for High-Throughput Imaging in a Mouse Model of Traumatic Brain Injury

Immunolabeling-enabled imaging of solvent-cleared organs (iDISCO) (Renier N, Wu Z, Simon DJ, Yang J, Ariel P, Tessier-Lavigne M, Cell 159:896-910, 2014) aims to match the refractive index (RI) of tissue to the surrounding medium, thereby facilitating three-dimensional (3D) imaging and quantification of cellular points and tissue structures. Once cleared, transparent tissue samples allow for rapid imaging with no mechanical sectioning. This imaging technology enables us to visualize brain tissue in situ and quantify the morphology and extent of glial cell branches or neuronal processes extending from the epicenter of a traumatic brain injury (TBI). In this way, we can more accurately assess and quantify the damaging consequences of TBI not only in the impact region but also in the extended pericontusional regions.

Multicompartmental Trauma Induces Persistent Inflammation and Organ Injury

INTRODUCTION

Previous preclinical models of multicompartmental injury have investigated its effects for durations of less than 72 h and the long-term effects have not been defined. We hypothesized that a model of multicompartmental injury would result in systemic inflammation and multiorgan dysfunction that persists at 1 wk.

METHODS

Male and proestrus female Sprague-Dawley rats (n = 16/group) underwent polytrauma (PT) (unilateral right lung contusion, hemorrhagic shock, cecectomy, bifemoral pseudofractures) and were compared to naive controls. Weight, hemoglobin, plasma neutrophil gelatinase-associated lipocalin, and plasma toll-like receptor 4 were evaluated on days two and seven. Bilateral lungs were sectioned, stained and assessed for injury at day seven. Comparisons were performed in Graphpad with significance defined as ∗P <0.05.

RESULTS

Rats who underwent PT had significant weight loss and anemia at day 2 (P = 0.001) compared to naïve rats which persisted at day 7 (P = 0.001). PT rats had elevated plasma neutrophil gelatinase-associated lipocalin at day 2 compared to naïve (P <0.0001) which remained elevated at day 7 (P <0.0001). Plasma toll-like receptor 4 was elevated in PT compared to naïve at day 2 (P = 0.03) and day 7 (P = 0.01). Bilateral lungs showed significant injury in PT cohorts at day 7 compared to naïve (P <0.0004). PT males had worse renal function at day seven compared to females (P = 0.02).

CONCLUSIONS

Multicompartmental trauma induces systemic inflammation and multiorgan dysfunction without recovery by day seven. However, females demonstrate improved renal recovery compared to males. Long-term assessment of preclinical PT models are crucial to better understand and evaluate future therapeutic immunomodulatory and anti-inflammatory treatments.

Sex-Specific and Traumatic Brain Injury Effects on Dopamine Receptor Expression in the Hippocampus

Traumatic brain injury (TBI) is a major health concern. Each year, over 50 million individuals worldwide suffer from TBI, and this leads to a number of acute and chronic health issues. These include affective and cognitive impairment, as well as an increased risk of alcohol and drug use. The dopaminergic system, a key component of reward circuitry, has been linked to alcohol and other substance use disorders, and previous research indicates that TBI can induce plasticity within this system. Understanding how TBI modifies the dopaminergic system may offer insights into the heightened substance use and reward-seeking behavior following TBI. The hippocampus, a critical component of the reward circuit, is responsible for encoding and integrating the spatial and salient aspects of rewarding stimuli. This study explored TBI-related changes in neuronal D2 receptor expression within the hippocampus, examining the hypothesis that sex differences exist in both baseline hippocampal D2 receptor expression and its response to TBI. Utilizing D2-expressing tdTomato transgenic male and female mice, we implemented either a sham injury or the lateral fluid percussion injury (FPI) model of TBI and subsequently performed a region-specific quantification of D2 expression in the hippocampus. The results show that male mice exhibit higher baseline hippocampal D2 expression compared to female mice. Additionally, there was a significant interaction effect between sex and injury on the expression of D2 in the hippocampus, particularly in regions of the dentate gyrus. Furthermore, TBI led to significant reductions in hippocampal D2 expression in male mice, while female mice remained mostly unaffected. These results suggest that hippocampal D2 expression varies between male and female mice, with the female dopaminergic system demonstrating less susceptibility to TBI-induced plasticity.

Experimental traumatic brain injury increases epichaperome formation

Under normal conditions, heat shock proteins work in unison through dynamic protein interactions collectively referred to as the "chaperome." Recent work revealed that during cellular stress, the functional interactions of the chaperome are modified to form the "epichaperome," which results in improper protein folding, degradation, aggregation, and transport. This study is the first to investigate this novel mechanism of protein dishomeostasis in traumatic brain injury (TBI). Male and female adult, Sprague-Dawley rats received a lateral controlled cortical impact (CCI) and the ipsilateral hippocampus was collected 24 h 1, 2, and 4 weeks after injury. The epichaperome complex was visualized by measuring HSP90, HSC70 and HOP expression in native-PAGE and normalized to monomeric protein expression. A two-way ANOVA examined the effect of injury and sex at each time-point. Native HSP90, HSC70 and HOP protein expression showed a significant effect of injury effect across all time-points. Additionally, HSC70 and HOP showed significant sex effects at 24 h and 4 weeks. Altogether, controlled cortical impact significantly increased formation of the epichaperome across all proteins measured. Further investigation of this pathological mechanism can lead to a greater understanding of the link between TBI and increased risk of neurodegenerative disease and targeting the epichaperome for therapeutics.

Repeated mild traumatic brain injury causes sex-specific increases in cell proliferation and inflammation in juvenile rats

Childhood represents a period of significant growth and maturation for the brain, and is also associated with a heightened risk for mild traumatic brain injuries (mTBI). There is also concern that repeated-mTBI (r-mTBI) may have a long-term impact on developmental trajectories. Using an awake closed head injury (ACHI) model, that uses rapid head acceleration to induce a mTBI, we investigated the acute effects of repeated-mTBI (r-mTBI) on neurological function and cellular proliferation in juvenile male and female Long-Evans rats. We found that r-mTBI did not lead to cumulative neurological deficits with the model. R-mTBI animals exhibited an increase in BrdU + (bromodeoxyuridine positive) cells in the dentate gyrus (DG), and that this increase was more robust in male animals. This increase was not sustained, and cell proliferation returning to normal by PID3. A greater increase in BrdU + cells was observed in the dorsal DG in both male and female r-mTBI animals at PID1. Using Ki-67 expression as an endogenous marker of cellular proliferation, a robust proliferative response following r-mTBI was observed in male animals at PID1 that persisted until PID3, and was not constrained to the DG alone. Triple labeling experiments (Iba1+, GFAP+, Brdu+) revealed that a high proportion of these proliferating cells were microglia/macrophages, indicating there was a heightened inflammatory response. Overall, these findings suggest that rapid head acceleration with the ACHI model produces an mTBI, but that the acute neurological deficits do not increase in severity with repeated administration. R-mTBI transiently increases cellular proliferation in the hippocampus, particularly in male animals, and the pattern of cell proliferation suggests that this represents a neuroinflammatory response that is focused around the mid-brain rather than peripheral cortical regions. These results add to growing literature indicating sex differences in proliferative and inflammatory responses between females and males. Targeting proliferation as a therapeutic avenue may help reduce the short term impact of r-mTBI, but there may be sex-specific considerations.

The Renin Angiotensin System as a Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health problem, with limited pharmacological options available beyond symptomatic relief. The renin angiotensin system (RAS) is primarily known as a systemic endocrine regulatory system, with major roles controlling blood pressure and fluid homeostasis. Drugs that target the RAS are used to treat hypertension, heart failure and kidney disorders. They have now been used chronically by millions of people and have a favorable safety profile. In addition to the systemic RAS, it is now appreciated that many different organ systems, including the brain, have their own local RAS. The major ligand of the classic RAS, Angiotensin II (Ang II) acts predominantly through the Ang II Type 1 receptor (AT1R), leading to vasoconstriction, inflammation, and heightened oxidative stress. These processes can exacerbate brain injuries. Ang II receptor blockers (ARBs) are AT1R antagonists. They have been shown in several preclinical studies to enhance recovery from TBI in rodents through improvements in molecular, cellular and behavioral correlates of injury. ARBs are now under consideration for clinical trials in TBI. Several different RAS peptides that signal through receptors distinct from the AT1R, are also potential therapeutic targets for TBI. The counter regulatory RAS pathway has actions that oppose those stimulated by AT1R signaling. This alternative pathway has many beneficial effects on cells in the central nervous system, bringing about vasodilation, and having anti-inflammatory and anti-oxidative stress actions. Stimulation of this pathway also has potential therapeutic value for the treatment of TBI. This comprehensive review will provide an overview of the various components of the RAS, with a focus on their direct relevance to TBI pathology. It will explore different therapeutic agents that modulate this system and assess their potential efficacy in treating TBI patients.

Neurosteroid Receptor Modulators for Treating Traumatic Brain Injury

Traumatic brain injury (TBI) triggers wide-ranging pathology that impacts multiple biochemical and physiological systems, both inside and outside the brain. Functional recovery in patients is impeded by early onset brain edema, acute and chronic inflammation, delayed cell death, and neurovascular disruption. Drug treatments that target these deficits are under active development, but it seems likely that fully effective therapy may require interruption of the multiplicity of TBI-induced pathological processes either by a cocktail of drug treatments or a single pleiotropic drug. The complex and highly interconnected biochemical network embodied by the neurosteroid system offers multiple options for the research and development of pleiotropic drug treatments that may provide benefit for those who have suffered a TBI. This narrative review examines the neurosteroids and their signaling systems and proposes directions for their utility in the next stage of TBI drug research and development.