Alterations in hippocampal neurogenesis following traumatic brain injury in mice

Repetitive traumatic brain injury-induced complement C1-related inflammation impairs long-term hippocampal neurogenesis

JOURNAL/nrgr/04.03/01300535-202503000-00027/figure1/v/2024-06-17T092413Z/r/image-tiff Repetitive traumatic brain injury impacts adult neurogenesis in the hippocampal dentate gyrus, leading to long-term cognitive impairment. However, the mechanism underlying this neurogenesis impairment remains unknown. In this study, we established a male mouse model of repetitive traumatic brain injury and performed long-term evaluation of neurogenesis of the hippocampal dentate gyrus after repetitive traumatic brain injury. Our results showed that repetitive traumatic brain injury inhibited neural stem cell proliferation and development, delayed neuronal maturation, and reduced the complexity of neuronal dendrites and spines. Mice with repetitive traumatic brain injuryalso showed deficits in spatial memory retrieval. Moreover, following repetitive traumatic brain injury, neuroinflammation was enhanced in the neurogenesis microenvironment where C1q levels were increased, C1q binding protein levels were decreased, and canonical Wnt/β-catenin signaling was downregulated. An inhibitor of C1 reversed the long-term impairment of neurogenesis induced by repetitive traumatic brain injury and improved neurological function. These findings suggest that repetitive traumatic brain injury-induced C1-related inflammation impairs long-term neurogenesis in the dentate gyrus and contributes to spatial memory retrieval dysfunction.

A strike to the head: Parallels between the pediatric and adult human and the rodent in traumatic brain injury

Traumatic brain injury (TBI) is a condition that occurs commonly in children from infancy through adolescence and is a global health concern. Pediatric TBI presents with a bimodal age distribution, with very young children (0-4 years) and adolescents (15-19 years) more commonly injured. Because children's brains are still developing, there is increased vulnerability to the effects of head trauma, which results in entirely different patterns of injury than in adults. Pediatric TBI has a profound and lasting impact on a child's development and quality of life, resulting in long-lasting consequences to physical, cognitive, and emotional development. Chronic issues like learning disabilities, behavioral problems, and emotional disturbances can develop. Early intervention and ongoing support are critical for minimizing these long-term deficits. Many animal models of TBI exist, and each varies significantly, displaying different characteristics of clinical TBI. The neurodevelopment differs in the rodent from the human in timing and effect, so TBI outcomes in the juvenile rodent can thus vary from the human child. The current review compares findings from preclinical TBI work in juvenile and adult rodents to clinical TBI research in pediatric and adult humans. We focus on the four brain regions most affected by TBI: the prefrontal cortex, corpus callosum, hippocampus, and hypothalamus. Each has its unique developmental projections and thus is impacted by TBI differently. This review aims to compare the healthy neurodevelopment of these four brain regions in humans to the developmental processes in rodents.

Transcriptional control of neural stem cell activity

In the adult brain, neural stem cells (NSCs) are under the control of various molecular mechanisms to produce an appropriate number of neurons that are essential for specific brain functions. Usually, the majority of adult NSCs stay in a non-proliferative and undifferentiated state known as quiescence, occasionally transitioning to an active state to produce newborn neurons. This transition between the quiescent and active states is crucial for the activity of NSCs. Another significant state of adult NSCs is senescence, in which quiescent cells become more dormant and less reactive, ceasing the production of newborn neurons. Although many genes involved in the regulation of NSCs have been identified using genetic manipulation and omics analyses, the entire regulatory network is complicated and ambiguous. In this review, we focus on transcription factors, whose importance has been elucidated in NSCs by knockout or overexpression studies. We mainly discuss the transcription factors with roles in the active, quiescent, and rejuvenation states of adult NSCs.

Erianin promotes endogenous neurogenesis in traumatic brain injury rats

The objective of this study was to explore the positive influence and potential mechanism of Erianin on the recovery of brain cells following a traumatic brain injury (TBI). TBI rat models were prepared and treated with Erianin injection via tail vein. The assessment included evaluating the rats' levels of oxidative stress, inflammation, neuronal damage, mitochondrial damage, neuronal regeneration, transformation of pro-inflammatory microglial cells, activation status of the ERK signal pathway, and the functionality of their learning and memory. After administering Erianin, there was a suppression of oxidative stress, inflammation, nerve cell damage, and mitochondrial damage in the TBI rats. Additionally, there was an increase in neuronal regeneration in the cortex and hippocampus, inhibition of pro-inflammatory microglial cell transformation in the cortex, improvement in learning and memory function in TBI rats, and simultaneous inhibition of the activation of the ERK1/c-Jun signal pathway. The findings suggest that Erianin has the potential to reduce oxidative stress and inflammatory reaction in rats with TBI, safeguard nerve cells against apoptosis, stimulate the growth of new neural cells, ultimately enhancing the cognitive abilities and memory function of the rats. The inhibition of the ERK signaling pathway could be closely associated with these effects.

Overexpress miR-132 in the Brain Parenchyma by a Non-invasive Way Improves Tissue Repairment and Releases Memory Impairment After Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health problem worldwide, which could lead to an extremely high percentage of mortality and disability. Current treatment strategies mainly concentrate on neuronal protection and reconstruction, among them, exogenous neural stem cell (NSC) transplantation has long been regarded as the most effective curative treatment. However, due to secondary trauma, transplant rejection, and increased incidence of brain malignant tumor, a non-invasive therapy that enhanced endogenous neurogenesis was more suitable for TBI treatment. Our previous work has shown that miR-132 overexpression could improve neuronal differentiation of NSCs in vitro and in vivo. So, we engineered a new kind of AAV vector named AAV-PHP.eB which can transfect brain parenchyma through intravenous injection to overexpress miR-132 in brain after TBI. We found that miR-132 overexpression could reduce impact volume, promote neurogenesis in the dentate gyrus (DG), accelerate neuroblast migrating into the impact cortex, ameliorate microglia-mediated inflammatory reaction, and ultimately restore learning memory function. Our results revealed that AAV-PHP.eB-based miR-132 overexpression could improve endogenous tissue repairment and release clinical symptoms after traumatic brain injury. This work would provide a new therapeutic strategy for TBI treatment and other neurological disorders characterized by markable neuronal loss and memory impairment. miR-132 overexpression accelerates endogenous neurogenesis and releases TBI-induced tissue repairment and memory impairment. Controlled cortical impact onto the cortex would induce serious cortical injury and microglia accumulation in both cortex and hippocampus. Moreover, endogenous neuroblast could migrate around the injury core. miR-132 overexpression could accelerate neuroblast migration toward the injury core and decreased microglia accumulation in the ipsilateral cortex and hippocampus. miR-132 could be a suitable target on neuroprotective therapy after TBI.

Metabolomics reveals the effects of hydroxysafflor yellow A on neurogenesis and axon regeneration after experimental traumatic brain injury

CONTEXT

Hydroxysafflor yellow A (HSYA) is the main bioactive ingredient of safflower (Carthamus tinctorius L., [Asteraceae]) for traumatic brain injury (TBI) treatment.

OBJECTIVE

To explore the therapeutic effects and underlying mechanisms of HSYA on post-TBI neurogenesis and axon regeneration.

MATERIALS AND METHODS

Male Sprague-Dawley rats were randomly assigned into Sham, controlled cortex impact (CCI), and HSYA groups. Firstly, the modified Neurologic Severity Score (mNSS), foot fault test, hematoxylin-eosin staining, Nissl's staining, and immunofluorescence of Tau1 and doublecortin (DCX) were used to evaluate the effects of HSYA on TBI at the 14th day. Next, the effectors of HSYA on post-TBI neurogenesis and axon regeneration were screened out by pathology-specialized network pharmacology and untargeted metabolomics. Then, the core effectors were validated by immunofluorescence.

RESULTS

HSYA alleviated mNSS, foot fault rate, inflammatory cell infiltration, and Nissl's body loss. Moreover, HSYA increased not only hippocampal DCX but also cortical Tau1 and DCX following TBI. Metabolomics demonstrated that HSYA significantly regulated hippocampal and cortical metabolites enriched in 'arginine metabolism' and 'phenylalanine, tyrosine and tryptophan metabolism' including l-phenylalanine, ornithine, l-(+)-citrulline and argininosuccinic acid. Network pharmacology suggested that neurotrophic factor (BDNF) and signal transducer and activator of transcription 3 (STAT3) were the core nodes in the HSYA-TBI-neurogenesis and axon regeneration network. In addition, BDNF and growth-associated protein 43 (GAP43) were significantly elevated following HSYA treatment in the cortex and hippocampus.

DISCUSSION AND CONCLUSIONS

HSYA may promote TBI recovery by facilitating neurogenesis and axon regeneration through regulating cortical and hippocampal metabolism, BDNF and STAT3/GAP43 axis.

Gliptins normalize posttraumatic hippocampal neurogenesis and restore cognitive function after controlled cortical impact on sensorimotor cortex

Traumatic brain injury (TBI) often leads to long-term neurocognitive dysfunctions. Adult neurogenesis in the hippocampal dentate gyrus (DG) serves critical functions in cognition but can be disrupted by brain injury and insult in serval forms. In the present study, we explore the cellular and molecular targets of DPP-4 inhibitors (or gliptins) as related to hippocampal function and TBI cognitive sequelae. Two structurally different gliptins, sitagliptin and vildagliptin, were examined using a controlled cortical impact (CCI) model of moderate TBI in mice. Sensorimotor CCI, although distal from the hippocampus, impaired hippocampal-dependent cognition without obvious hippocampal tissue destruction. Neurogenic cell proliferation in the DG was increased accompanied by large numbers of reactive astrocyte. Increased numbers of immature granule cells with abnormal dendritic outgrowth were ectopically localized in the outer granule cell layer (GCL) and hilus. Long-term potentiation of dentate immature granule cells was also impaired. Both sitagliptin and vildagliptin attenuated the CCI-induced ectopic migration of doublecortin-positive immature neurons into the outer GCL and hilus, restored the normal dendritic branching pattern of the immature neurons and prevented astrocyte reactivation. Both gliptins prevented loss of normal synaptic integration in the DG after sensorimotor CCI and improved cognitive behavior. Sensorimotor cortical injury thus results in an abnormal neurogenesis pattern and astrocyte reactivation in the distal hippocampus which appears to contribute to the development of cognitive dysfunction after TBI. DPP-4 inhibitors prevent astrocyte reactivation, normalize the posttraumatic hippocampal neurogenesis and help to maintain normal electrophysiology in the DG with positive behavioral effect in a mouse model.

Neurobiochemical, Peptidomic, and Bioinformatic Approaches to Characterize Tauopathy Peptidome Biomarker Candidates in Experimental Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a multidimensional damage, and currently, no FDA-approved medicine is available. Multiple pathways in the cell are triggered through a head injury (e.g., calpain and caspase activation), which truncate tau and generate variable fragment sizes (MW 400-45,000 K). In this study, we used an open-head TBI mouse model generated by controlled cortical impact (CCI) and collected ipsilateral (IC) and contralateral (CC) mice htau brain cortices at one (D1) three (D3), and seven (D7) days post-injury. We implemented immunological (antibody-based detection) and peptidomic approaches (nano-reversed-phase liquid chromatography/tandem mass spectrometry) to investigate proteolytic tau peptidome (low molecular weight (LMW) < 10 K)) and pathological phosphorylation sites (high-molecular-weight (HMW); > 10 K) derived from CCI-TBI animal models. Our immunoblotting analysis verified tau hyperphosphorylation, HMW, and HMW breakdown products (HMW-BDP) formation of tau (e.g., pSer₂₀₂, pThr₁₈₁, pThr₂₃₁, pSer₃₉₆, and pSer₄₀₄), following CCI-TBI. Peptidomic data revealed unique sequences of injury-dependent proteolytic peptides generated from human tau protein. Among the N-terminal tau peptides, EIPEGTTAEEAGIGDTPSLEDEAAGHVTQA (a.a. 96-125) and AQPHTEIPEGTTAEEAGIGDTPSLEDEAAGHVTQARM (a.a. 91-127). Examples of tau C-terminal peptides identified include NVSSTGSIDMVDSPQLATLADEVSASLAKQGL (a.a. 410-441) and QLATLADEVSASLAKQGL (a.a. 424-441). Our peptidomic bioinformatic tools showed the association of proteases, such as CAPN1, CAPN2, and CTSL; CASP1, MMP7, and MMP9; and ELANE, GZMA, and MEP1A, in CCI-TBI tau peptidome. In clinical trials for novel TBI treatments, it might be useful to monitor a subset of tau peptidome as targets for biomarker utility and use them for a "theranostic" approach.

The Role and Mechanism of Transglutaminase 2 in Regulating Hippocampal Neurogenesis after Traumatic Brain Injury

Traumatic brain injury usually results in neuronal loss and cognitive deficits. Promoting endogenous neurogenesis has been considered as a viable treatment option to improve functional recovery after TBI. However, neural stem/progenitor cells (NSPCs) in neurogenic regions are often unable to migrate and differentiate into mature neurons at the injury site. Transglutaminase 2 (TGM2) has been identified as a crucial component of neurogenic niche, and significantly dysregulated after TBI. Therefore, we speculate that TGM2 may play an important role in neurogenesis after TBI, and strategies targeting TGM2 to promote endogenous neural regeneration may be applied in TBI therapy. Using a tamoxifen-induced Tgm2 conditional knockout mouse line and a mouse model of stab wound injury, we investigated the role and mechanism of TGM2 in regulating hippocampal neurogenesis after TBI. We found that Tgm2 was highly expressed in adult NSPCs and up-regulated after TBI. Conditional deletion of Tgm2 resulted in the impaired proliferation and differentiation of NSPCs, while Tgm2 overexpression enhanced the abilities of self-renewal, proliferation, differentiation, and migration of NSPCs after TBI. Importantly, injection of lentivirus overexpressing TGM2 significantly promoted hippocampal neurogenesis after TBI. Therefore, TGM2 is a key regulator of hippocampal neurogenesis and a pivotal therapeutic target for intervention following TBI.

Short-Term Cortical Electrical Stimulation during the Acute Stage of Traumatic Brain Injury Improves Functional Recovery

Functional restoration is an important issue in the treatment of traumatic brain injury (TBI). Various electrical stimulation devices and protocols have been applied in preclinical studies and have shown therapeutic potential for brain trauma. Short-term invasive cortical electrical stimulation during the acute stage of TBI might be a feasible adjuvant therapy for patients with moderate-to-severe brain injury receiving neurosurgical treatment in the intensive care unit. However, the therapeutic effects of short-term multisession cortical electrical stimulation for brain trauma are not clear. This study explored the therapeutic effects of acute-stage short-term cortical electrical stimulation on TBI. We conducted seven sessions of one-hour cortical electrical stimulation from day 0 to day 6 in rats after brain trauma by controlled cortical impact and then evaluated the functional outcome and histopathological changes. Our data showed that short-term cortical electrical stimulation improved motor coordination, short-term memory, and learning ability and attenuated neurological severity after brain trauma. Lesion volume, apoptosis, and gliosis after brain trauma were reduced, and trauma-induced neurogenesis in the hippocampus for the innate neural reparative response was increased. Our study demonstrated that short-term cortical electrical stimulation applied in the acute stage of traumatic brain injury is a potential adjuvant therapy to improve the recovery of neurological deficits.

Post-Traumatic Epilepsy and Comorbidities: Advanced Models, Molecular Mechanisms, Biomarkers, and Novel Therapeutic Interventions

Post-traumatic epilepsy (PTE) is one of the most devastating long-term, network consequences of traumatic brain injury (TBI). There is currently no approved treatment that can prevent onset of spontaneous seizures associated with brain injury, and many cases of PTE are refractory to antiseizure medications. Post-traumatic epileptogenesis is an enduring process by which a normal brain exhibits hypersynchronous excitability after a head injury incident. Understanding the neural networks and molecular pathologies involved in epileptogenesis are key to preventing its development or modifying disease progression. In this article, we describe a critical appraisal of the current state of PTE research with an emphasis on experimental models, molecular mechanisms of post-traumatic epileptogenesis, potential biomarkers, and the burden of PTE-associated comorbidities. The goal of epilepsy research is to identify new therapeutic strategies that can prevent PTE development or interrupt the epileptogenic process and relieve associated neuropsychiatric comorbidities. Therefore, we also describe current preclinical and clinical data on the treatment of PTE sequelae. Differences in injury patterns, latency period, and biomarkers are outlined in the context of animal model validation, pathophysiology, seizure frequency, and behavior. Improving TBI recovery and preventing seizure onset are complex and challenging tasks; however, much progress has been made within this decade demonstrating disease modifying, anti-inflammatory, and neuroprotective strategies, suggesting this goal is pragmatic. Our understanding of PTE is continuously evolving, and improved preclinical models allow for accelerated testing of critically needed novel therapeutic interventions in military and civilian persons at high risk for PTE and its devastating comorbidities.

A role for insulin-like growth factor-1 in hippocampal plasticity following traumatic brain injury

Traumatic brain injury (TBI) initiates a constellation of secondary injury cascades, leading to neuronal damage and dysfunction that is often beyond the scope of endogenous repair mechanisms. Cognitive deficits are among the most persistent morbidities resulting from TBI, necessitating a greater understanding of mechanisms of posttraumatic hippocampal damage and neuroplasticity and identification of therapies that improve recovery by enhancing repair pathways. Focusing here on hippocampal neuropathology associated with contusion-type TBIs, the impact of brain trauma on synaptic structure and function and the process of adult neurogenesis is discussed, reviewing initial patterns of damage as well as evidence for spontaneous recovery. A case is made that insulin-like growth factor-1 (IGF-1), a growth-promoting peptide synthesized in both the brain and the periphery, is well suited to augment neuroplasticity in the injured brain. Essential during brain development, multiple lines of evidence delineate roles in the adult brain for IGF-1 in the maintenance of synapses, regulation of neurotransmission, and modulation of forms of synaptic plasticity such as long-term potentiation. Further, IGF-1 enhances adult hippocampal neurogenesis though effects on proliferation and neuronal differentiation of neural progenitor cells and on dendritic growth of newly born neurons. Post-injury administration of IGF-1 has been effective in rodent models of TBI in improving learning and memory, attenuating death of mature hippocampal neurons and promoting neurogenesis, providing critical proof-of-concept data. More studies are needed to explore the effects of IGF-1-based therapies on synaptogenesis and synaptic plasticity following TBI and to optimize strategies in order to stimulate only appropriate, functional neuroplasticity.

Contusion brain damage in mice for modelling of post-traumatic epilepsy with contralateral hippocampus sclerosis: Comprehensive and longitudinal characterization of spontaneous seizures, neuropathology, and neuropsychiatric comorbidities

Traumatic brain injury (TBI) is a leading cause of acquired epilepsy referred to as post-traumatic epilepsy (PTE), characterized by spontaneous recurrent seizures (SRS) that start in the months or years following TBI. There is a critical need to develop small animal models for advancing the neurotherapeutics of PTE, which accounts for 20% of all acquired epilepsy cases. Despite many previous attempts, there are few PTE models with demonstrated consistency or longitudinal incidence of SRS, a critical feature for creating models for investigation of novel therapeutics for preventing PTE. Over the past few years, we have made in-depth updates and several advances to our mouse model of TBI in which SRS consistently occurs upon 24/7 monitoring for 4 months. Here, we show that an advanced cortical contusion damage in mice elicits a chronic state of PTE with SRS and robust epileptiform activity, along with cognitive comorbidities. We observed SRS in 33% and 87% of moderate and severe injury cohorts, respectively. Though incidence was higher in the severe cohort, moderate injury elicited a robust epileptogenesis. Progressive neuronal damage, neurodegeneration, and inflammation signals were evident in many brain regions; comorbid behavior and cognitive deficits were observed for up to 4-months. SRS onset was correlated with the inception of interneuron loss after TBI. Contralateral hippocampal sclerosis was unique and well correlated with SRS, confirming a potential network basis for epileptogenesis. Collectively, this mouse model exhibits a number of hallmark TBI sequelae reminiscent of human PTE. This model provides a vital tool for probing molecular pathological mechanisms and therapeutic interventions for post-traumatic epileptogenesis. SIGNIFICANCE STATEMENT: TBI is a leading cause of post-traumatic epilepsy (PTE). Despite many attempts to create PTE in animals, success has been limited due to a lack of consistent spontaneous "epileptic" seizures after TBI. We present a comprehensive phenotype of PTE after contusion brain injury in mice, which exhibits robust spontaneous seizures along with neuronal loss, inflammation, and cognitive dysfunction. Our broad profiling of a TBI mouse reveals features of progressive, long-lasting epileptic activity, unique contralateral hippocampal sclerosis, and comorbid mood and memory deficits. The PTE mouse shows a striking consistency in recapitulating major pathological sequelae of human PTE. This mouse model will be helpful in assessing mechanisms and interventions for TBI-induced epilepsy and mood dysfunction.

Co-Ultra PEALut Enhances Endogenous Repair Response Following Moderate Traumatic Brain Injury

This study aimed to assess the neuro-regenerative properties of co-ultramicronized PEALut (Glialia^®), composed of palmitoylethanolamide (PEA) and the flavonoid luteolin (Lut), in an in vivo model of traumatic brain injury (TBI) and patients affected by moderate TBI. An increase in neurogenesis was seen in the mice at 72 h and 7 d after TBI. The co-ultra PEALut treatment helped the neuronal reconstitution process to restore the basal level of both novel and mature neurons; moreover, it induced a significant upregulation of the neurotrophic factors, which ultimately led to progress in terms of memory recall during behavioral testing. Moreover, our preliminary findings in a clinical trial suggested that Glialia^® treatment facilitated neural recovery on working memory. Thus, co-ultra PEALut (Glialia^®) could represent a valuable therapeutic agent for intensifying the endogenous repair response in order to better treat TBI.

Moderate Intensity Treadmill Exercise Increases Survival of Newborn Hippocampal Neurons and Improves Neurobehavioral Outcomes after Traumatic Brain Injury

Physician-prescribed rest after traumatic brain injury (TBI) is both commonplace and an increasingly scrutinized approach to TBI treatment. Although this practice remains a standard of patient care for TBI, research of patient outcomes reveals little to no benefit of prescribed rest after TBI, and in some cases prolonged rest has been shown to interfere with patient well-being. In direct contrast to the clinical advice regarding physical activity after TBI, animal models of brain injury consistently indicate that exercise is neuroprotective and promotes recovery. Here, we assessed the effect of low and moderate intensity treadmill exercise on functional outcome and hippocampal neural proliferation after brain injury. Using the controlled cortical impact (CCI) mouse model of TBI, we show that 10 days of moderate intensity treadmill exercise initiated after CCI reduces anxiety-like behavior, improves hippocampus-dependent spatial memory, and promotes hippocampal proliferation and newborn neuronal survival. Pathophysiological measures including lesion volume and axon degeneration were not altered by exercise. Taken together, these data reveal that carefully titrated physical activity may be a safe and effective approach to promoting recovery after brain injury.

IGF1-Stimulated Posttraumatic Hippocampal Remodeling Is Not Dependent on mTOR

Adult hippocampal neurogenesis is stimulated acutely following traumatic brain injury (TBI). However, many hippocampal neurons born after injury develop abnormally and the number that survive long-term is debated. In experimental TBI, insulin-like growth factor-1 (IGF1) promotes hippocampal neuronal differentiation, improves immature neuron dendritic arbor morphology, increases long-term survival of neurons born after TBI, and improves cognitive function. One potential downstream mediator of the neurogenic effects of IGF1 is mammalian target of rapamycin (mTOR), which regulates proliferation as well as axonal and dendritic growth in the CNS. Excessive mTOR activation is posited to contribute to aberrant plasticity related to posttraumatic epilepsy, spurring preclinical studies of mTOR inhibitors as therapeutics for TBI. The degree to which pro-neurogenic effects of IGF1 depend upon upregulation of mTOR activity is currently unknown. Using immunostaining for phosphorylated ribosomal protein S6, a commonly used surrogate for mTOR activation, we show that controlled cortical impact TBI triggers mTOR activation in the dentate gyrus in a time-, region-, and injury severity-dependent manner. Posttraumatic mTOR activation in the granule cell layer (GCL) and dentate hilus was amplified in mice with conditional overexpression of IGF1. In contrast, delayed astrocytic activation of mTOR signaling within the dentate gyrus molecular layer, closely associated with proliferation, was not affected by IGF1 overexpression. To determine whether mTOR activation is necessary for IGF1-mediated stimulation of posttraumatic hippocampal neurogenesis, wildtype and IGF1 transgenic mice received the mTOR inhibitor rapamycin daily beginning at 3 days after TBI, following pulse labeling with bromodeoxyuridine. Compared to wildtype mice, IGF1 overexpressing mice exhibited increased posttraumatic neurogenesis, with a higher density of posttrauma-born GCL neurons at 10 days after injury. Inhibition of mTOR did not abrogate IGF1-stimulated enhancement of posttraumatic neurogenesis. Rather, rapamycin treatment in IGF1 transgenic mice, but not in WT mice, increased numbers of cells labeled with BrdU at 3 days after injury that survived to 10 days, and enhanced the proportion of posttrauma-born cells that differentiated into neurons. Because beneficial effects of IGF1 on hippocampal neurogenesis were maintained or even enhanced with delayed inhibition of mTOR, combination therapy approaches may hold promise for TBI.

New Insight of Circular RNAs' Roles in Central Nervous System Post-Traumatic Injury

The central nervous system (CNS) post-traumatic injury can cause severe nerve damage with devastating consequences. However, its pathophysiological mechanisms remain vague. There is still an urgent need for more effective treatments. Circular RNAs (circRNAs) are non-coding RNAs that can form covalently closed RNA circles. Through second-generation sequencing technology, microarray analysis, bioinformatics, and other technologies, recent studies have shown that a number of circRNAs are differentially expressed after traumatic brain injury (TBI) or spinal cord injury (SCI). These circRNAs play important roles in the proliferation, inflammation, and apoptosis in CNS post-traumatic injury. In this review, we summarize the expression and functions of circRNAs in CNS in recent studies, as well as the circRNA–miRNA–mRNA interaction networks. The potential clinical value of circRNAs as a therapeutic target is also discussed.

Transcriptomic Analysis of Mouse Brain After Traumatic Brain Injury Reveals That the Angiotensin Receptor Blocker Candesartan Acts Through Novel Pathways

Traumatic brain injury (TBI) results in complex pathological reactions, where the initial lesion is followed by secondary inflammation and edema. Our laboratory and others have reported that angiotensin receptor blockers (ARBs) have efficacy in improving recovery from traumatic brain injury in mice. Treatment of mice with a subhypotensive dose of the ARB candesartan results in improved functional recovery, and reduced pathology (lesion volume, inflammation and gliosis). In order to gain a better understanding of the molecular mechanisms through which candesartan improves recovery after controlled cortical impact injury (CCI), we performed transcriptomic profiling on brain regions after injury and drug treatment. We examined RNA expression in the ipsilateral hippocampus, thalamus and hypothalamus at 3 or 29 days post injury (dpi) treated with either candesartan (0.1 mg/kg) or vehicle. RNA was isolated and analyzed by bulk mRNA-seq. Gene expression in injured and/or candesartan treated brain region was compared to that in sham vehicle treated mice in the same brain region to identify genes that were differentially expressed (DEGs) between groups. The most DEGs were expressed in the hippocampus at 3 dpi, and the number of DEGs reduced with distance and time from the lesion. Among pathways that were differentially expressed at 3 dpi after CCI, candesartan treatment altered genes involved in angiogenesis, interferon signaling, extracellular matrix regulation including integrins and chromosome maintenance and DNA replication. At 29 dpi, candesartan treatment reduced the expression of genes involved in the inflammatory response. Some changes in gene expression were confirmed in a separate cohort of animals by qPCR. Fewer DEGs were found in the thalamus, and only one in the hypothalamus at 3 dpi. Additionally, in the hippocampi of sham injured mice, 3 days of candesartan treatment led to the differential expression of 384 genes showing that candesartan in the absence of injury had a powerful impact on gene expression specifically in the hippocampus. Our results suggest that candesartan has broad actions in the brain after injury and affects different processes at acute and chronic times after injury. These data should assist in elucidating the beneficial effect of candesartan on recovery from TBI.

Diffusion Tensor Imaging Detects Acute Pathology-Specific Changes in the P301L Tauopathy Mouse Model Following Traumatic Brain Injury

Traumatic brain injury (TBI) has been linked with tauopathy. However, imaging methods that can non-invasively detect tau-protein abnormalities following TBI need further investigation. This study aimed to investigate the potential of diffusion tensor imaging (DTI) to detect tauopathy following TBI in P301L mutant-tau-transgenic-pR5-mice. A total of 24 9-month-old pR5 mice were randomly assigned to sham and TBI groups. Controlled cortical injuries/craniotomies were performed for TBI/sham groups followed by DTI data acquisition on days 1 and 7 post-injury. DTI data were analyzed by using voxelwise analysis and track-based spatial statistics for gray matter and white matter. Further, immunohistochemistry was performed for total-tau and phosphorylated-tau, astrocytes, and microglia. To detect the association of DTI with these pathological markers, a correlation analysis was performed between DTI and histology findings. At day 1 post-TBI, DTI revealed a widespread reduction in fractional anisotropy (FA) and axial diffusivity (AxD) in the TBI group compared to shams. On day 7, further reduction in FA, AxD, and mean diffusivity and increased radial diffusivity were observed. FA was significantly increased in the amygdala and cortex. Correlation results showed that in the ipsilateral hemisphere FA reduction was associated with increased phosphorylated-tau and glial-immunoreactivity, whereas in the contralateral regions, the FA increase was associated with increased immunostaining for astrocytes. This study is the first to exploit DTI to investigate the effect of TBI in tau-transgenic mice. We show that alterations in the DTI signal were associated with glial activity following TBI and would most likely reflect changes that co-occur with/without phosphorylated-tau. In addition, FA may be a promising measure to identify discrete pathological processes such as increased astroglia activation, tau-hyperphosphorylation or both in the brain following TBI.

Deficits in pattern separation and dentate gyrus proliferation after rodent lateral fluid percussion injury

It has been demonstrated that adult born granule cells are generated after traumatic brain injury (TBI). There is evidence that these newly generated neurons are aberrant and are poised to contribute to poor cognitive function after TBI. Yet, there is also evidence that these newly generated neurons are important for cognitive recovery. Pattern separation is a cognitive task known to be dependent on the function of adult generated granule cells. Performance on this task and the relation to dentate gyrus dysfunction after TBI has not been previously studied. Here we subjected Sprague Dawley rats to lateral fluid percussion injury or sham and tested them on the dentate gyrus dependent task pattern separation. At 2 weeks after injury, we examined common markers of dentate gyrus function such as GSK3ß phosphorylation, Ki-67 immunohistochemistry, and generation of adult born granule cells. We found that injured animals have deficits in pattern separation. We additionally found a decrease in proliferative capacity at 2 weeks indicated by decreased phosphorylation of GSK3ß and Ki-67 immunopositivity as compared to sham animals. Lastly we found an increase in numbers of new neurons generated during the pattern separation task. These findings provide evidence that dentate gyrus dysfunction may be an important contributor to TBI pathology.

Mild Traumatic Brain Injury Induces Transient, Sequential Increases in Proliferation, Neuroblasts/Immature Neurons, and Cell Survival: A Time Course Study in the Male Mouse Dentate Gyrus

Mild traumatic brain injuries (mTBIs) are prevalent worldwide. mTBIs can impair hippocampal-based functions such as memory and cause network hyperexcitability of the dentate gyrus (DG), a key entry point to hippocampal circuitry. One candidate for mediating mTBI-induced hippocampal cognitive and physiological dysfunction is injury-induced changes in the process of DG neurogenesis. There are conflicting results on how TBI impacts the process of DG neurogenesis; this is not surprising given that both the neurogenesis process and the post-injury period are dynamic, and that the quantification of neurogenesis varies widely in the literature. Even within the minority of TBI studies focusing specifically on mild injuries, there is disagreement about if and how mTBI changes the process of DG neurogenesis. Here we utilized a clinically relevant rodent model of mTBI (lateral fluid percussion injury, LFPI), gold-standard markers and quantification of the neurogenesis process, and three time points post-injury to generate a comprehensive picture of how mTBI affects adult hippocampal DG neurogenesis. Male C57BL/6J mice (6-8 weeks old) received either sham surgery or mTBI via LFPI. Proliferating cells, neuroblasts/immature neurons, and surviving cells were quantified via stereology in DG subregions (subgranular zone [SGZ], outer granule cell layer [oGCL], molecular layer, and hilus) at short-term (3 days post-injury, dpi), intermediate (7 dpi), and long-term (31 dpi) time points. The data show this model of mTBI induces transient, sequential increases in ipsilateral SGZ/GCL proliferating cells, neuroblasts/immature neurons, and surviving cells which is suggestive of mTBI-induced neurogenesis. In contrast to these ipsilateral hemisphere findings, measures in the contralateral hemisphere were not increased in key neurogenic DG subregions after LFPI. Our work in this mTBI model is in line with most literature on other and more severe models of TBI in showing TBI stimulates the process of DG neurogenesis. However, as our DG data in mTBI provide temporal, subregional, and neurogenesis-stage resolution, these data are important to consider in regard to the functional importance of TBI-induction of the neurogenesis process and future work assessing the potential of replacing and/or repairing DG neurons in the brain after TBI.

Traumatic brain injury and hippocampal neurogenesis: Functional implications

In the adult brain, self-renewing radial-glia like (RGL) progenitor cells have been shown to reside in the subventricular zone and the subgranular zone of the hippocampus. A large body of evidence shows that experiences such as learning, enriched environment and stress can alter proliferation and differentiation of RGL progenitor cells. The progenitor cells present in the subgranular zone of the hippocampus divide to give rise to newborn neurons that migrate to the dentate gyrus where they differentiate into adult granule neurons. These newborn neurons have been found to have a unique role in certain types of hippocampus-dependent learning and memory, including goal-directed behaviors that require pattern separation. Experimental traumatic brain injury (TBI) in rodents has been shown to alter hippocampal neurogenesis, including triggering the acute loss of newborn neurons, as well as progenitor cell hyper-proliferation. In this review, we discuss the role of hippocampal neurogenesis in learning and memory. Furthermore, we review evidence for the molecular mechanisms that contribute to newborn neuron loss, as well as increased progenitor cell proliferation after TBI. Finally, we discuss strategies aimed at enhancing neurogenesis after TBI and their possible therapeutic benefits.

Acid Sphingomyelinase Inhibition Mitigates Histopathological and Behavioral Changes in a Murine Model of Traumatic Brain Injury

Traumatic brain injury (TBI) can lead to the development of chronic traumatic encephalopathy as a result of neuronal phosphorylated tau (p-tau) protein aggregation and neuroinflammation. Acid sphingomyelinase (Asm) may also contribute to post-TBI neurodegenerative disorders. We hypothesized that Asm inhibition would ameliorate p-tau aggregation, neuroinflammation, and behavioral changes after TBI in a murine model. TBI was generated using a weight-drop method. Asm inhibition in wild-type mice was achieved with a single injection of amitriptyline 1 h after TBI. Genetic Asm ablation was achieved using Asm-deficient mice (Asm^-/-). Thirty days after TBI, mice underwent behavioral testing with the forced swim test for symptoms of depression or were euthanized for neurohistological analysis. Neuroinflammation was quantified using the microglial markers, ionized calcium-binding adaptor molecule 1 and transmembrane protein 119. Compared to sham mice, TBI mice demonstrated increased hippocampal p-tau. Mice that received amitriptyline after TBI demonstrated decreased p-tau compared to mice that received a saline control. Further, post-TBI Asm^-/- mice demonstrated lower levels of p-tau compared to wild-type mice. Though a decrease in neuroinflammation was observed at 1 month post-TBI, no change was demonstrated with mice treated with amitriptyline. Similarly, TBI mice were more likely to show depression compared to mice that received amitriptyline after TBI. Utilizing a weight-drop method to induce moderate TBI, we have shown that genetic deficiency or pharmacological inhibition of Asm prevented hippocampal p-tau aggregation 1 month after injury as well as decreased symptoms of depression. These findings highlight an opportunity to potentially reduce the long-term consequences of TBI.

Insulin-like growth factor-1 overexpression increases long-term survival of posttrauma-born hippocampal neurons while inhibiting ectopic migration following traumatic brain injury

Cellular damage associated with traumatic brain injury (TBI) manifests in motor and cognitive dysfunction following injury. Experimental models of TBI reveal cell death in the granule cell layer (GCL) of the hippocampal dentate gyrus acutely after injury. Adult-born neurons residing in the neurogenic niche of the GCL, the subgranular zone, are particularly vulnerable. Injury-induced proliferation of neural progenitors in the subgranular zone supports recovery of the immature neuron population, but their development and localization may be altered, potentially affecting long-term survival. Here we show that increasing hippocampal levels of insulin-like growth factor-1 (IGF1) is sufficient to promote end-stage maturity of posttrauma-born neurons and improve cognition following TBI. Mice with conditional overexpression of astrocyte-specific IGF1 and wild-type mice received controlled cortical impact or sham injury and bromo-2'-deoxyuridine injections for 7d after injury to label proliferating cells. IGF1 overexpression increased the number of GCL neurons born acutely after trauma that survived 6 weeks to maturity (NeuN+BrdU+), and enhanced their outward migration into the GCL while significantly reducing the proportion localized ectopically to the hilus and molecular layer. IGF1 selectively affected neurons, without increasing the persistence of posttrauma-proliferated glia in the dentate gyrus. IGF1 overexpressing animals performed better during radial arm water maze reversal testing, a neurogenesis-dependent cognitive test. These findings demonstrate the ability of IGF1 to promote the long-term survival and appropriate localization of granule neurons born acutely after a TBI, and suggest these new neurons contribute to improved cognitive function.

Chronic Regulation of miR-124-3p in the Perilesional Cortex after Experimental and Human TBI

Traumatic brain injury (TBI) dysregulates microRNAs, which are the master regulators of gene expression. Here we investigated the changes in a brain-enriched miR-124-3p, which is known to associate with major post-injury pathologies, such as neuroinflammation. RT-qPCR of the rat tissue sampled at 7 d and 3 months in the perilesional cortex adjacent to the necrotic lesion core (aPeCx) revealed downregulation of miR-124-3p at 7 d (fold-change (FC) 0.13, p < 0.05 compared with control) and 3 months (FC 0.40, p < 0.05) post-TBI. In situ hybridization confirmed the downregulation of miR-124-3p at 7 d and 3 months post-TBI in the aPeCx (both p < 0.01). RT-qPCR confirmed the upregulation of the miR-124-3p target Stat3 in the aPeCx at 7 d post-TBI (7-fold, p < 0.05). mRNA-Seq revealed 312 downregulated and 311 upregulated miR-124 targets (p < 0.05). To investigate whether experimental findings translated to humans, we performed in situ hybridization of miR-124-3p in temporal lobe autopsy samples of TBI patients. Our data revealed downregulation of miR-124-3p in individual neurons of cortical layer III. These findings indicate a persistent downregulation of miR-124-3p in the perilesional cortex that might contribute to post-injury neurodegeneration and inflammation.

dBcAMP Rescues the Neurons From Degeneration in Kainic Acid-Injured Hippocampus, Enhances Neurogenesis, Learning, and Memory

Dibutyryl cyclic adenosine monophosphate (dBcAMP) is a cell-permeable synthetic analog of cyclic adenosine monophosphate (cAMP). Although the elevation of cAMP levels was reported to promote the functional recovery in spinal cord injury, its role in neurogenesis or functional recovery after hippocampal injury is unknown. The objective of the study was to investigate the effects of dBcAMP on learning, memory, and hippocampal neurogenesis in the excitotoxically lesioned hippocampus. An excitotoxic lesion was induced in the hippocampi of 4-month-old male BALB/c mice by injecting 0.25 μg/μl into the lateral ventricles of both sides. The lesioned mice (L) were divided into L+dBcAMP and L+phosphate-buffered saline (PBS) groups. Sham surgery (S) was done by the injection of 1 μl of sterile saline into the lateral ventricles. The sham surgery mice were divided into S+dBcAMP and S+PBS groups. Mice in the L+dBcAMP and S+dBcAMP groups were treated with dBcAMP for 1 week (i.p., 50 mg/kg), whereas mice in the L+PBS and S+PBS groups were treated with PBS. The mice in all groups were subjected to water maze and passive avoidance tests at the end of the 4th week. Cresyl violet staining and NeuN and doublecortin immunostaining were done to analyze the morphology and neurogenesis. The water maze learning sessions did not show a significant difference in escape latency between the groups, suggesting an unimpaired learning ability of mice in all groups. The L+dBcAMP mice had significantly short entry latency and higher target quadrant time/distance traveled compared to the L+PBS group, suggesting better memory retention. The L+dBcAMP group had a significantly improved memory retention compared to the L+PBS mice during the passive avoidance test. Morphological studies showed significantly greater adult neurons and increased hippocampal neurogenesis in the hippocampus of mice in the L+dBcAMP group compared to those in the L+PBS group. There was no significant difference between the S+dBcAMP and S+PBS groups in the water maze/passive avoidance tests and the number of neurons. In conclusion, dBcAMP protects the hippocampal neuron from degeneration and enhances hippocampal neurogenesis, learning, and memory.

Apolipoprotein E regulates the maturation of injury-induced adult-born hippocampal neurons following traumatic brain injury

Various brain injuries lead to the activation of adult neural stem/progenitor cells in the mammalian hippocampus. Subsequent injury-induced neurogenesis appears to be essential for at least some aspects of the innate recovery in cognitive function observed following traumatic brain injury (TBI). It has previously been established that Apolipoprotein E (ApoE) plays a regulatory role in adult hippocampal neurogenesis, which is of particular interest as the presence of the human ApoE isoform ApoE4 leads to significant risk for the development of late-onset Alzheimer's disease, where impaired neurogenesis has been linked with disease progression. Moreover, genetically modified mice lacking ApoE or expressing the ApoE4 human isoform have been shown to impair adult hippocampal neurogenesis under normal conditions. Here, we investigate how controlled cortical impact (CCI) injury affects dentate gyrus development using hippocampal stereotactic injections of GFP-expressing retroviruses in wild-type (WT), ApoE-deficient and humanized (ApoE3 and ApoE4) mice. Infected adult-born hippocampal neurons were morphologically analyzed once fully mature, revealing significant attenuation of dendritic complexity and spine density in mice lacking ApoE or expressing the human ApoE4 allele, which may help inform how ApoE influences neurological diseases where neurogenesis is defective.

Histone Deacetylase 4 Downregulation Elicits Post-Traumatic Psychiatric Disorders through Impairment of Neurogenesis

An enduring deficit in neurogenesis largely contributes to the development of severe post-traumatic psychiatric disorders such as anxiety, depression, and memory impairment following traumatic brain injury (TBI); however, the mechanism remains obscure. Here we have shown that an imbalance in the generation of γ-aminobutyric acid (GABA)ergic and glutamatergic neurons due to aberrant induction of vesicular glutamate transporter 1 (vGlut1)-positive glutamatergic cells is responsible for impaired neuronal differentiation in the hippocampus following TBI. To elucidate the molecular mechanism, we found that TBI activates a transcription factor, Pax3, by increasing its acetylation status, and subsequently induces Ngn2 transcription. This event, in turn, augments the vGlut1-expressing glutamatergic neurons and accumulation of excess glutamate in the hippocampus that can affect neuronal differentiation. In our study the acetylation of Pax3 was increased due to loss of its interaction with a deacetylase, histone deacetylase 4 (HDAC4), which was downregulated after TBI. TBI-induced activation of GSK3β was responsible for the degradation of HDAC4. We also showed that overexpression of HDAC4 before TBI reduces Pax3 acetylation by restoring an interaction between HDAC4 and Pax3 in the hippocampus. This event prevents the aberrant induction of vGlut1-positive glutamatergic neurons by decreasing the Ngn2 level and subsequently reinforces the balance between GABAergic and glutamatergic neurons following TBI. Further, we found that overexpression of HDAC4 in the hippocampus improves anxiety, depressive-like behavior, and memory functions following TBI.

Therapeutic effect of transplantation of human bone marrow‑derived mesenchymal stem cells on neuron regeneration in a rat model of middle cerebral artery occlusion

Human bone marrow-derived mesenchymal stromal cells (hBMSCs) have been revealed to be beneficial for the regeneration of tissues and cells in several diseases. The present study aimed to elucidate the mechanisms underlying the effect of hBMSC transplantation on neuron regeneration in a rat model of middle cerebral artery occlusion (MCAO). The hBMSCs were isolated, cultured and identified. A rat model of MCAO was induced via the modified Longa method. Neurological severity scores (NSS) were adopted for the evaluation of neuronal function in the model rats after cell transplantation. Next, the expression levels of nestin, β-III-tubulin (β-III-Tub), glial fibrillary acidic protein (GFAP), HNA and neuronal nuclear antigen (NeuN) were examined, as well as the positive expression rates of human neutrophil alloantigen (HNA), nestin, NeuN, β-III-Tub and GFAP. The NSS, as well as the mRNA and protein expression of nestin, decreased at the 1st, 2nd, 4 and 8th weeks, while the mRNA and protein expression of NeuN, β-III-Tub and GFAP increased with time. In addition, after treatment, the MCAO rats showed decreased NSS and mRNA and protein expression of nestin, but elevated mRNA and protein expression of NeuN, β-III-Tub and GFAP at the 2nd, 4 and 8th weeks, and decreased positive expression of HNA and nestin with enhanced expression of NeuN, β-III-Tub and GFAP. Therefore, the present findings demonstrated that hBMSC transplantation triggered the formation of nerve cells and enhanced neuronal function in a rat model of MCAO.

A single injection of imipramine affected proliferation in the hippocampus of adult Swiss mice depending on the route of administration, doses, survival time and lodging conditions

Swiss mice may be valuable for the screening of antidepressants in preclinical trials. Acute treatment with antidepressants may affect the behaviour of Swiss mice, but the effects on their hippocampal neurogenesis remain unknown. The present work aims to assess the influence of acute treatment with antidepressants on cell proliferation in the dentate gyrus of the hippocampus of adult Swiss mice. Cell proliferation was estimated by ex vivo counting of Ki-67 immunoreactive nuclei (Ki-67-ir) in the dentate gyrus of Swiss mice housed in standard or enriched environments, at survival-times 2 or 24 h after imipramine injection Independent of the experimental group, intraperitoneal imipramine (0 or 30 mg/kg) failed to change the number of Ki-67-ir in the hippocampus of mice. Through intracerebroventricular route, imipramine reduced the number of Ki-67-ir in the hippocampus of Swiss mice at the dose of 0.06 nmol and increased it at the dose 0.2 nmol. At the dose 0.2 nmol, not 0.06 nmol, imipramine increased the immunoreactivity to doublecortin (a marker for immature neurons) in the hippocampus of mice. The effects of intracerebroventricular injection of imipramine on neurogenesis markers were seen 24 h after the injection in mice housed in standard conditions. The effects of intracerebroventricular injection of imipramine on neurogenesis markers were absent in mice housed in enrichment or 2 h after the injection. These data suggest that acute treatment with imipramine may affect proliferation in the hippocampus of adult Swiss mice depending on the route of administration, doses, survival time and lodging conditions.

Acute histopathological responses and long-term behavioral outcomes in mice with graded controlled cortical impact injury

While animal models of controlled cortical impact often display short-term motor dysfunction after injury, histological examinations do not show severe cortical damage. Thus, this model requires further improvement. Mice were subjected to injury at three severities using a Pin-Point™-controlled cortical impact device to establish secondary brain injury mouse models. Twenty-four hours after injury, hematoxylin-eosin staining, Fluoro-Jade B histofluorescence, and immunohistochemistry were performed for brain slices. Compared to the uninjured side, we observed differences of histopathological findings, neuronal degeneration, and glial cell number in the CA2 and CA3 regions of the hippocampus on the injured side. The Morris water maze task and beam-walking test verified long-term (14–28 days) spatial learning/memory and motor balance. To conclude, the histopathological responses were positively correlated with the degree of damage, as were the long-term behavioral manifestations after controlled cortical impact. All animal procedures were approved by the Institutional Animal Care and Use Committee at Shanghai Jiao Tong University School of Medicine.

Diffusion Magnetic Resonance Imaging Unveils the Spatiotemporal Microstructural Gray Matter Changes following Injury in the Rodent Brain

Traumatic brain injury (TBI) is associated with gray and white matter alterations in brain tissue. Gray matter alterations are not yet as well studied as those of the white matter counterpart. This work utilized T2-weighted structural imaging, diffusion tensor imaging (DTI), and diffusion kurtosis imaging to unveil the gray matter changes induced in a controlled cortical impact (CCI) mouse model of TBI at 5 h, 1 day, 3 days, 7 days, 14 days, and 30 days post-CCI. A cross-sectional histopathology approach was used to confer validity of the magnetic resonance imaging (MRI) data by performing cresyl violet staining and glial fibrillary acidic protein (GFAP) immunohistochemistry. The results demonstrated a significant increase in lesion volume up to 3 days post-injury followed by a significant decrease in the cavity volume for the period of 1 month. GFAP signals peaked on Day 7 and persisted until Day 30 in both ipsilateral and contralateral hippocampus, ipsilateral cortex, and thalamic areas. An increase in fractional anisotropy (FA) was seen at Day 7 in the pericontusional area but decreased FA in the contralateral cortex, hippocampus, and thalamus. Mean diffusivity (MD) was significantly lower in the pericontusional cortex. Increased MD and decreased mean kurtosis were limited to the injury site on Days 7 to 30 and to the contralateral hippocampus and thalamus on Days 3 and 7. This work is one of the few cross-sectional studies to demonstrate a link between MRI measures and histopathological readings to track gray matter changes in the progression of TBI.

Significant changes in circular RNA in the mouse cerebral cortex around an injury site after traumatic brain injury

BACKGROUND AND OBJECTIVE

Circular RNA (circRNA) is an important type of non-coding RNA that has not been widely researched in traumatic brain injury (TBI). The present study aimd to detect the altered circRNA expression around an injury site in the mouse cerebral cortex after TBI and explore its potential functions.

METHOD

C57BL/6 mice were used to construct a controlled cortical impact (CCI) model to simulate TBI. At 24 h post-TBI, the cortex around the injury site was collected, and the total RNA was extracted to perform RNA sequencing (RNA-seq). The differentially expressed circRNAs were determined according to the following criteria: |log₂^{(fold change)}| > 1, P < .05 and FDR < 0.05. Among them, circRNA chr8_87,859,283-87,904,548 was preliminarily explored to determine its function.

RESULTS

A total of 8036 altered circRNAs were discovered, and among them, 16 were significantly changed (5 up-regulated and 11 down-regulated). The circRNA chr8_87,859,283-87,904,548 significantly increased by approximately 4 times in the cerebral cortex around the injury site after TBI and promoted neuro-inflammation through increasing the CXCR2 protein by sponging mmu-let-7a-5p. As a result, the increased circRNA chr8_87,859,283-87,904,548 blocked the restoration of neurological function after TBI.

CONCLUSION

Many circRNAs are significantly up-regulated or down-regulated in the traumatic cerebral penumbra cortex after TBI. Among them, the circRNA chr8_87,859,283-87,904,548 potentially plays a pro-inflammatory role, which may have a deleterious effect on neurological restoration after TBI. .

miR-124-3p is a chronic regulator of gene expression after brain injury

Traumatic brain injury (TBI) initiates molecular and cellular pathologies that underlie post-injury morbidities, including hippocampus-related memory decline and epileptogenesis. Non-coding small RNAs are master regulators of gene expression with the potential to affect multiple molecular pathways. To evaluate whether hippocampal gene expression networks are chronically regulated by microRNAs after TBI, we sampled the dentate gyrus of rats with severe TBI induced by lateral fluid-percussion injury 3 months earlier. Ingenuity pathway analysis revealed 30 upregulated miR-124-3p targets, suggesting that miR-124-3p is downregulated post-TBI (z-score = - 5.146, p < 0.05). Droplet digital polymerase chain reaction (ddPCR) and in situ hybridization confirmed the chronic downregulation of miR-124-3p (p < 0.05). Quantitative PCR analysis of two targets, Plp2 and Stat3, indicated that their upregulation correlated with the miR-124-3p downregulation (r = - 0.647, p < 0.05; r = - 0.629, p < 0.05, respectively). Immunohistochemical staining of STAT3 confirmed the increased protein expression. STRING analysis showed that 9 of the 30 miR-124-3p targets belonged to a STAT3 network. Reactome analysis and data mining connected the targets especially to inflammation and signal transduction. L1000CDS2 software revealed drugs (e.g., importazole, trichostatin A, and IKK-16) that could reverse the observed molecular changes. The translational value of our data was emphasized by in situ hybridization showing chronic post-traumatic downregulation of miR-124-3p in the dentate gyrus of TBI patients. Analysis of another brain injury model, status epilepticus, highlighted the fact that chronic downregulation of miR-124 is a common phenomenon after brain injury. Together, our findings indicate that miR-124-3p is a chronic modulator of molecular networks relevant to post-injury hippocampal pathologies in experimental models and in humans.

Delayed and Abbreviated Environmental Enrichment after Brain Trauma Promotes Motor and Cognitive Recovery That Is Not Contingent on Increased Neurogenesis

Environmental enrichment (EE) confers motor and cognitive recovery in pre-clinical models of traumatic brain injury (TBI), and neurogenesis has been attributed to mediating the benefits. Whether that ascription is correct has not been fully investigated. Hence, the goal of the current study is to further clarify the possible role of learning-induced hippocampal neurogenesis on functional recovery after cortical impact or sham injury by utilizing two EE paradigms (i.e., early + continuous, initiated immediately after TBI and presented 24 h/day; and delayed + abbreviated, initiated 4 days after TBI for 6 h/day) and comparing them to one another as well as to standard (STD) housed controls. Motor and cognitive performance was assessed on post-operative Days 1-5 and 14-19, respectively, for the STD and early + continuous EE groups and on Days 4-8 and 17-22, for the delayed + abbreviated EE groups. Rats were injected with bromodeoxyuridine (BrdU, 500 mg/ kg; intraperitoneally) for 3 days (12 h apart) before cognitive training and sacrificed 1 week later for quantification of BrdU+ and doublecortin (DCX+) labeled cells. Both early + continuous and delayed + abbreviated EE promoted motor and cognitive recovery after TBI, relative to STD (p < 0.05), and did not differ from one another (p > 0.05). However, only early + continuous EE increased DCX+ cells beyond the level of STD-housed controls (p < 0.05). No effect of EE on non-injured controls was observed. Based on these data, two novel conclusions emerged. First, EE does not need to be provided early and continuously after TBI to confer benefits, which lends credence to the delayed + abbreviated EE paradigm as a relevant pre-clinical model of neurorehabilitation. Second, the functional recovery observed after TBI in the delayed + abbreviated EE paradigm is not contingent on increased hippocampal neurogenesis. Future studies will elucidate alternate viable mechanisms mediating the benefits induced by EE.

Assessment of systemic administration of PEGylated IGF-1 in a mouse model of traumatic brain injury

BACKGROUND

Traumatic brain injury can result in lasting cognitive dysfunction due to degeneration of mature hippocampal neurons as well as the loss of immature neurons within the dentate gyrus. While endogenous neurogenesis affords a partial recovery of the immature neuron population, hippocampal neurogenesis may be enhanced through therapeutic intervention. Insulin-like growth factor-1 (IGF-1) has the potential to improve cognitive function and promote neurogenesis after TBI, but its short half-life in the systemic circulation makes it difficult to maintain a therapeutic concentration. IGF-1 modified with a polyethylene glycol moiety (PEG-IGF-1) exhibits improved stability and half-life while retaining its ability to enter the brain from the periphery, increasing its viability as a translational approach.

OBJECTIVE

The goal of this study was to evaluate the ability of systemic PEG-IGF-1 administration to attenuate acute neuronal loss and stimulate the recovery of hippocampal immature neurons in brain-injured mice.

METHODS

In a series of studies utilizing a well-established contusion brain injury model, PEG-IGF-1 was administered subcutaneously after injury. Serum levels of PEG were verified using ELISA and histological staining was used to investigate numbers of degenerating neurons and cortical contusion size at 24 h after injury. Immunofluorescent staining was used to evaluate numbers of immature neurons at 10 d after injury.

RESULTS

Although subcutaneous injections of PEG-IGF-1 increased serum IGF-1 levels in a dose-dependent manner, no effects were observed on cortical contusion size, neurodegeneration within the dentate gyrus, or recovery of hippocampal immature neuron numbers.

CONCLUSIONS

In contrast to its efficacy in rodent models of neurodegenerative diseases, PEG- IGF-1 was not effective in ameliorating early neuronal loss after contusion brain trauma.

Brain Phospholipid Precursors Administered Post-Injury Reduce Tissue Damage and Improve Neurological Outcome in Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) leads to cellular loss, destabilization of membranes, disruption of synapses and altered brain connectivity, and increased risk of neurodegenerative disease. A significant and long-lasting decrease in phospholipids (PLs), essential membrane constituents, has recently been reported in plasma and brain tissue, in human and experimental TBI. We hypothesized that supporting PL synthesis post-injury could improve outcome post-TBI. We tested this hypothesis using a multi-nutrient combination designed to support the biosynthesis of PLs and available for clinical use. The multi-nutrient, Fortasyn^® Connect (FC), contains polyunsaturated omega-3 fatty acids, choline, uridine, vitamins, cofactors required for PL biosynthesis, and has been shown to have significant beneficial effects in early Alzheimer's disease. Male C57BL/6 mice received a controlled cortical impact injury and then were fed a control diet or a diet enriched with FC for 70 days. FC led to a significantly improved sensorimotor outcome and cognition, reduced lesion size and oligodendrocyte loss, and it restored myelin. It reversed the loss of the synaptic protein synaptophysin and decreased levels of the axon growth inhibitor, Nogo-A, thus creating a permissive environment. It decreased microglia activation and the rise in ß-amyloid precursor protein and restored the depressed neurogenesis. The effects of this medical multi-nutrient suggest that support of PL biosynthesis post-TBI, a new treatment paradigm, has significant therapeutic potential in this neurological condition for which there is no satisfactory treatment. The multi-nutrient tested has been used in dementia patients and is safe and well tolerated, which would enable rapid clinical exploration in TBI.

Central Infusion of Insulin-Like Growth Factor-1 Increases Hippocampal Neurogenesis and Improves Neurobehavioral Function after Traumatic Brain Injury

Traumatic brain injury (TBI) produces neuronal dysfunction and cellular loss that can culminate in lasting impairments in cognitive and motor abilities. Therapeutic agents that promote repair and replenish neurons post-TBI hold promise in improving recovery of function. Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor capable of mediating neuroprotective and neuroplasticity mechanisms. Targeted overexpression of IGF-1 enhances the generation of hippocampal newborn neurons in brain-injured mice; however, the translational neurogenic potential of exogenously administered IGF-1 post-TBI remains unknown. In a mouse model of controlled cortical impact, continuous intracerebroventricular infusion of recombinant human IGF-1 (hIGF) for 7 days, beginning 15 min post-injury, resulted in a dose-dependent increase in the number of immature neurons in the hippocampus. Infusion of 10 μg/day of IGF-1 produced detectable levels of hIGF-1 in the cortex and hippocampus and a concomitant increase in protein kinase B activation in the hippocampus. Both motor function and cognition were improved over 7 days post-injury in IGF-1-treated cohorts. Vehicle-treated brain-injured mice showed reduced hippocampal immature neuron density relative to sham controls at 7 days post-injury. In contrast, the density of hippocampal immature neurons in brain-injured mice receiving acute onset IGF-1 infusion was significantly higher than in injured mice receiving vehicle and equivalent to that in sham-injured control mice. Importantly, the neurogenic effect of IGF-1 was maintained with as much as a 6-h delay in the initiation of infusion. These data suggest that central infusion of IGF-1 enhances the generation of immature neurons in the hippocampus, with a therapeutic window of at least 6 h post-injury, and promotes neurobehavioral recovery post-TBI.

Transcriptome-Wide Identification of Differentially Expressed Genes and Long Non-coding RNAs in Aluminum-Treated Rat Hippocampus

Aluminum (Al) is an environmental neurotoxicant with a wide exposure, but the molecular mechanism underlying its toxicity remains unclear. We used RNA sequencing (RNA-seq) in the hippocampus of Al-treated rats to identify 96 upregulated and 652 downregulated mRNAs, and 37 dysregulated long non-coding (lnc)RNAs. Gene ontology analysis showed that dysregulated genes were involved in glial cell differentiation, neural transmission, and vesicle trafficking. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed clustering of differentially expressed mRNAs and lncRNA target genes in several pathways, including the "adenosine monophosphate-activated protein kinase signaling pathway," "extracellular matrix receptor interaction," "the phosphatidylinositol 3 kinase-protein kinase B signaling pathway," and "focal adhesion" signaling pathway. RNA-seq results were validated by reverse transcription (RT)-PCR. Additionally, Al induced changes to the number and morphology of glial cells in the hippocampus of rats, as shown by glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1 (Iba1) immunochemistry. RT-PCR and western blotting validated the significant increase in expression of glial cell-related genes GFAP and SOX10 following Al exposure compared with control rats, consistent with RNA-seq results. Collectively, these results suggest that aberrant mRNAs and lncRNAs respond to Al neurotoxicity, and that glial cell-related genes play important roles in the Al neurotoxicity mechanism. These findings provide the basis for designing targeted approaches for the treatment or prevention of Al-induced neurotoxicity.

Implantation of Neuronal Stem Cells Enhances Object Recognition without Increasing Neurogenesis after Lateral Fluid Percussion Injury in Mice

Cognitive deficits after traumatic brain injury (TBI) are debilitating and contribute to the morbidity and loss of productivity of over 10 million people worldwide. Cell transplantation has been linked to enhanced cognitive function after experimental traumatic brain injury, yet the mechanism of recovery is poorly understood. Since the hippocampus is a critical structure for learning and memory, supports adult neurogenesis, and is particularly vulnerable after TBI, we hypothesized that stem cell transplantation after TBI enhances cognitive recovery by modulation of endogenous hippocampal neurogenesis. We performed lateral fluid percussion injury (LFPI) in adult mice and transplanted embryonic stem cell-derived neural progenitor cells (NPC). Our data confirm an injury-induced cognitive deficit in novel object recognition, a hippocampal-dependent learning task, which is reversed one week after NPC transplantation. While LFPI alone promotes hippocampal neurogenesis, as revealed by doublecortin immunolabeling of immature neurons, subsequent NPC transplantation prevents increased neurogenesis and is not associated with morphological maturation of endogenous injury-induced immature neurons. Thus, NPC transplantation enhances cognitive recovery early after LFPI without a concomitant increase in neuron numbers or maturation.

PTSD-Related Behavioral Traits in a Rat Model of Blast-Induced mTBI Are Reversed by the mGluR2/3 Receptor Antagonist BCI-838

Battlefield blast exposure related to improvised explosive devices (IEDs) has become the most common cause of traumatic brain injury (TBI) in the recent conflicts in Iraq and Afghanistan. Mental health problems are common after TBI. A striking feature in the most recent veterans has been the frequency with which mild TBI (mTBI) and posttraumatic stress disorder (PTSD) have appeared together, in contrast to the classical situations in which the presence of mTBI has excluded the diagnosis of PTSD. However, treatment of PTSD-related symptoms that follow blast injury has become a significant problem. BCI-838 (MGS0210) is a Group II metabotropic glutamate receptor (mGluR2/3) antagonist prodrug, and its active metabolite BCI-632 (MGS0039) has proneurogenic, procognitive, and antidepressant activities in animal models. In humans, BCI-838 is currently in clinical trials for refractory depression and suicidality. The aim of the current study was to determine whether BCI-838 could modify the anxiety response and reverse PTSD-related behaviors in rats exposed to a series of low-level blast exposures designed to mimic a human mTBI or subclinical blast exposure. BCI-838 treatment reversed PTSD-related behavioral traits improving anxiety and fear-related behaviors as well as long-term recognition memory. Treatment with BCI-838 also increased neurogenesis in the dentate gyrus (DG) of blast-exposed rats. The safety profile of BCI-838 together with the therapeutic activities reported here, make BCI-838 a promising drug for the treatment of former battlefield Warfighters suffering from PTSD-related symptoms following blast-induced mTBI.

Behavioral and pathophysiological outcomes associated with caffeine consumption and repetitive mild traumatic brain injury (RmTBI) in adolescent rats

Given that caffeine consumption is exponentially rising in adolescents and they are at increased risk for repetitive mild traumatic brain injury (RmTBI), we sought to examine the pathophysiological outcomes associated with early life caffeine consumption and RmTBI. Adolescent male and female Sprague Dawley rats received either caffeine in the drinking water or normal water and were then randomly assigned to 3 mild injuries using our lateral impact device or 3 sham procedures. Following injury induction, behavioral outcomes were measured with a test battery designed to examine symptoms consistent with clinical manifestation of PCS (balance and motor coordination, anxiety, short-term working memory, and depressive-like behaviours). In addition, pathophysiological outcomes were examined with histological measures of volume and cellular proliferation in the dentate gyrus, as well as microglia activation in the ventromedial hypothalamus. Finally, modifications to expression of 12 genes (Adora2a, App, Aqp4, Bdnf, Bmal1, Clock, Cry, Gfap, Orx1, Orx2, Per, Tau), in the prefrontal cortex, hippocampus, and/or the hypothalamus were assessed. We found that chronic caffeine consumption in adolescence altered normal developmental trajectories, as well as recovery from RmTBI. Of particular importance, many of the outcomes exhibited sex-dependent responses whereby the sex of the animal modified response to caffeine, RmTBI, and the combination of the two. These results suggest that caffeine consumption in adolescents at high risk for RmTBI should be monitored.

Stem cell transplantation therapy for multifaceted therapeutic benefits after stroke

One of the exciting advances in modern medicine and life science is cell-based neurovascular regeneration of damaged brain tissues and repair of neuronal structures. The progress in stem cell biology and creation of adult induced pluripotent stem (iPS) cells has significantly improved basic and pre-clinical research in disease mechanisms and generated enthusiasm for potential applications in the treatment of central nervous system (CNS) diseases including stroke. Endogenous neural stem cells and cultured stem cells are capable of self-renewal and give rise to virtually all types of cells essential for the makeup of neuronal structures. Meanwhile, stem cells and neural progenitor cells are well-known for their potential for trophic support after transplantation into the ischemic brain. Thus, stem cell-based therapies provide an attractive future for protecting and repairing damaged brain tissues after injury and in various disease states. Moreover, basic research on naïve and differentiated stem cells including iPS cells has markedly improved our understanding of cellular and molecular mechanisms of neurological disorders, and provides a platform for the discovery of novel drug targets. The latest advances indicate that combinatorial approaches using cell based therapy with additional treatments such as protective reagents, preconditioning strategies and rehabilitation therapy can significantly improve therapeutic benefits. In this review, we will discuss the characteristics of cell therapy in different ischemic models and the application of stem cells and progenitor cells as regenerative medicine for the treatment of stroke.

Modulation of gap junction-associated Cx43 in neural stem/progenitor cells following traumatic brain injury

Restoration of learning and memory deficits following traumatic brain injury (TBI) is attributed, in part, to enhanced neural stem/progenitor cell (NSPCs) function. Recent findings suggest gap junction (GJ)-associated connexin 43 (Cx43) plays a key role in the cell cycle regulation and function of NSPCs and is modulated following TBI. Here, we demonstrate that Cx43 is up-regulated in the dentate gyrus following TBI and is expressed on vimentin-positive cells in the subgranular zone. To test the role of Cx43 on NSPCs, we exposed primary cultures to the α-connexin Carboxyl Terminal (αCT1) peptide which selectively modulates GJ-associated Cx43. Treatment with αCT1 substantially reduced proliferation and increased caspase 3/7 expression on NSPCs in a dose-dependent manner. αCT1 exposure also reduced overall expression of Cx43 and phospho (p)-Serine368. These findings demonstrate that Cx43 positively regulates adult NPSCs; the modulation of which may influence changes in the dentate gyrus following TBI.

Trehalose improves traumatic brain injury-induced cognitive impairment

Traumatic brain Injury (TBI) is a significant cause of death and long-term disability for which there are currently no effective pharmacological treatment options. In this study then, we utilized a mouse model of TBI to assess the therapeutic potential of the stable disaccharide trehalose, which is known to protect against oxidative stress, increase levels of chaperone molecules and enhance autophagy. Furthermore, trehalose has demonstrated neuroprotective properties in numerous animal models and has been proposed as a potential treatment for neurodegeneration. As TBI (and associated neurodegenerative disorders) is complicated by a sudden and dramatic change in brain metal concentrations, including iron (Fe) and zinc (Zn), the collective accumulation and translocation of which has been hypothesized to contribute to the pathogenesis of TBI, then we also sought to determine whether trehalose modulated the metal dyshomeostasis associated with TBI. In this study three-month-old C57Bl/6 wildtype mice received a controlled cortical impact TBI, and were subsequently treated for one month with trehalose. During this time animals were assessed on multiple behavioral tasks prior to tissue collection. Results showed an overall significant improvement in the Morris water maze, Y-maze and open field behavioral tests in trehalose-treated mice when compared to controls. These functional benefits occurred in the absence of any change in lesion volume or any significant modulation of biometals, as assessed by laser ablation inductively coupled plasma mass spectrometry. Western blot analysis, however, revealed an upregulation of synaptophysin, doublecortin and brain derived neurotrophic factor protein in trehalose treated mice in the contralateral cortex. These results indicate that trehalose may be efficacious in improving functional outcomes following TBI by a previously undescribed mechanism of action that has relevance to multiple disorders of the central nervous system.

Increased Amyloid Precursor Protein and Tau Expression Manifests as Key Secondary Cell Death in Chronic Traumatic Brain Injury

In testing the hypothesis of Alzheimer's disease (AD)‐like pathology in late stage traumatic brain injury (TBI), we evaluated AD pathological markers in late stage TBI model. Sprague–Dawley male rats were subjected to moderate controlled cortical impact (CCI) injury, and 6 months later euthanized and brain tissues harvested. Results from H&E staining revealed significant 33% and 10% reduction in the ipsilateral and contralateral hippocampal CA3 interneurons, increased MHCII‐activated inflammatory cells in many gray matter (8–20‐fold increase) and white matter (6–30‐fold increased) regions of both the ipsilateral and contralateral hemispheres, decreased cell cycle regulating protein marker by 1.6‐ and 1‐fold in the SVZ and a 2.3‐ and 1.5‐fold reductions in the ipsilateral and contralateral dentate gyrus, diminution of immature neuronal marker by two‐ and onefold in both the ipsilateral and contralateral SVZ and dentate gyrus, and amplified amyloid precursor protein (APP) distribution volumes in white matter including corpus callosum, fornix, and internal capsule (4–38‐fold increase), as well as in the cortical gray matter, such as the striatum hilus, SVZ, and dentate gyrus (6–40‐fold increase) in TBI animals compared to controls (P's < 0.001). Surrogate AD‐like phenotypic markers revealed a significant accumulation of phosphorylated tau (AT8) and oligomeric tau (T22) within the neuronal cell bodies in ipsilateral and contralateral cortex, and dentate gyrus relative to sham control, further supporting the rampant neurodegenerative pathology in TBI secondary cell death. These findings indicate that AD‐like pathological features may prove to be valuable markers and therapeutic targets for late stage TBI. J. Cell. Physiol. 232: 665–677, 2017. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.