CCL20-CCR6 axis modulated traumatic brain injury-induced visual pathologies

Blast injury: Impact to the cornea

Visual disorders are common even after mild traumatic brain injury (mTBI) or blast exposure. The cost of blast-induced vision loss in civilians, military personnel, and veterans is significant. The visual consequences of blasts associated with TBI are elusive. Active military personnel and veterans report various ocular pathologies including corneal disorders post-combat blasts. The wars and conflicts in Afghanistan, Iraq, Syria, and Ukraine have significantly increased the number of corneal and other ocular disorders among military personnel and veterans. Binocular vision, visual fields, and other visual functions could be impaired following blast-mediated TBI. Blast-associated injuries can cause visual disturbances, binocular system problems, and visual loss. About 25% of veterans exposed to blasts report corneal injury. Blast exposure induces corneal edema, corneal opacity, increased corneal thickness, damage of corneal epithelium, corneal abrasions, and stromal and endothelial abnormality including altered endothelial density, immune cell infiltration, corneal neovascularization, Descemet membrane rupture, and increased pain mediators in animal models and the blast-exposed military personnel including veterans. Immune response exacerbates blast-induced ocular injury. TBI is associated with dry eyes and pain in veterans. Subjects exposed to blasts that cause TBI should undergo immediate clinical visual and ocular examinations. Delayed visual care may lead to progressive vision loss, lengthening/impairing rehabilitation and ultimately may lead to permanent vision problems and blindness. Open-field blast exposure could induce corneal injuries and immune responses in the cornea. Further studies are warranted to understand corneal pathology after blast exposure. A review of current advancements in blast-induced corneal injury will help elucidate novel targets for potential therapeutic options. This review discusses the impact of blast exposure-associated corneal disorders.

Visual Impairment in Pre-Clinical Models of Mild Traumatic Brain Injury

Impairment in visual function is common after traumatic brain injury (TBI) in the clinical setting, a phenomenon that translates to pre-clinical animal models as well. In Morris et al. (2021), we reported histological changes following weight-drop-induced TBI in a rodent model including retinal ganglion cell (RGC) loss, decreased electroretinogram (ERG) evoked potential, optic nerve diameter reduction, induced inflammation and gliosis, and loss of myelin accompanied by markedly impaired visual acuity. In this review, we will describe several pre-clinical TBI models that result in injuries to the visual system, indicating that visual function may be impaired following brain injury induced by a number of different injury modalities. This underscores the importance of understanding the role of the visual system and the potential detrimental sequelae to this sensory modality post-TBI. Given that most commonly employed behavioral tests such as the Elevated Plus Maze and Morris Water Maze rely on an intact visual system, interpretation of functional deficits in diffuse models may be confounded by off- target effects on the visual system.

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.

CC Chemokine Family Members' Modulation as a Novel Approach for Treating Central Nervous System and Peripheral Nervous System Injury-A Review of Clinical and Experimental Findings

Despite significant progress in modern medicine and pharmacology, damage to the nervous system with various etiologies still poses a challenge to doctors and scientists. Injuries lead to neuroimmunological changes in the central nervous system (CNS), which may result in both secondary damage and the development of tactile and thermal hypersensitivity. In our review, based on the analysis of many experimental and clinical studies, we indicate that the mechanisms occurring both at the level of the brain after direct damage and at the level of the spinal cord after peripheral nerve damage have a common immunological basis. This suggests that there are opportunities for similar pharmacological therapeutic interventions in the damage of various etiologies. Experimental data indicate that after CNS/PNS damage, the levels of 16 among the 28 CC-family chemokines, i.e., CCL1, CCL2, CCL3, CCL4, CCL5, CCL6, CCL7, CCL8, CCL9, CCL11, CCL12, CCL17, CCL19, CCL20, CCL21, and CCL22, increase in the brain and/or spinal cord and have strong proinflammatory and/or pronociceptive effects. According to the available literature data, further investigation is still needed for understanding the role of the remaining chemokines, especially six of them which were found in humans but not in mice/rats, i.e., CCL13, CCL14, CCL15, CCL16, CCL18, and CCL23. Over the past several years, the results of studies in which available pharmacological tools were used indicated that blocking individual receptors, e.g., CCR1 (J113863 and BX513), CCR2 (RS504393, CCX872, INCB3344, and AZ889), CCR3 (SB328437), CCR4 (C021 and AZD-2098), and CCR5 (maraviroc, AZD-5672, and TAK-220), has beneficial effects after damage to both the CNS and PNS. Recently, experimental data have proved that blockades exerted by double antagonists CCR1/3 (UCB 35625) and CCR2/5 (cenicriviroc) have very good anti-inflammatory and antinociceptive effects. In addition, both single (J113863, RS504393, SB328437, C021, and maraviroc) and dual (cenicriviroc) chemokine receptor antagonists enhanced the analgesic effect of opioid drugs. This review will display the evidence that a multidirectional strategy based on the modulation of neuronal-glial-immune interactions can significantly improve the health of patients after CNS and PNS damage by changing the activity of chemokines belonging to the CC family. Moreover, in the case of pain, the combined administration of such antagonists with opioid drugs could reduce therapeutic doses and minimize the risk of complications.

Fentanyl dysregulates neuroinflammation and disrupts blood-brain barrier integrity in HIV-1 Tat transgenic mice

Opioid overdose deaths have dramatically increased by 781% from 1999 to 2021. In the setting of HIV, opioid drug abuse exacerbates neurotoxic effects of HIV in the brain, as opioids enhance viral replication, promote neuronal dysfunction and injury, and dysregulate an already compromised inflammatory response. Despite the rise in fentanyl abuse and the close association between opioid abuse and HIV infection, the interactive comorbidity between fentanyl abuse and HIV has yet to be examined in vivo. The HIV-1 Tat-transgenic mouse model was used to understand the interactive effects between fentanyl and HIV. Tat is an essential protein produced during HIV that drives the transcription of new virions and exerts neurotoxic effects within the brain. The Tat-transgenic mouse model uses a glial fibrillary acidic protein (GFAP)-driven tetracycline promoter which limits Tat production to the brain and this model is well used for examining mechanisms related to neuroHIV. After 7 days of fentanyl exposure, brains were harvested. Tight junction proteins, the vascular cell adhesion molecule, and platelet-derived growth factor receptor-β were measured to examine the integrity of the blood brain barrier. The immune response was assessed using a mouse-specific multiplex chemokine assay. For the first time in vivo, we demonstrate that fentanyl by itself can severely disrupt the blood-brain barrier and dysregulate the immune response. In addition, we reveal associations between inflammatory markers and tight junction proteins at the blood-brain barrier.

Lifelong Chronic Sleep Disruption in a Mouse Model of Traumatic Brain Injury

Chronic sleep/wake disturbances (SWDs) are strongly associated with traumatic brain injury (TBI) in patients and are being increasingly recognized. However, the underlying mechanisms are largely understudied and there is an urgent need for animal models of lifelong SWDs. The objective of this study was to develop a chronic TBI rodent model and investigate the lifelong chronic effect of TBI on sleep/wake behavior. We performed repetitive midline fluid percussion injury (rmFPI) in 4-month-old mice and monitored their sleep/wake behavior using the non-invasive PiezoSleep system. Sleep/wake states were recorded before injury (baseline) and then monthly thereafter. We found that TBI mice displayed a significant decrease in sleep duration in both the light and dark phases, beginning at 3 months post-TBI and continuing throughout the study. Consistent with the sleep phenotype, these TBI mice showed circadian locomotor activity phenotypes and exhibited reduced anxiety-like behavior. TBI mice also gained less weight, and had less lean mass and total body water content, compared to sham controls. Further, TBI mice showed extensive brain tissue loss and increased glial fibrillary acidic protein and ionized calcium-binding adaptor molecule 1 levels in the hypothalamus and vicinity of the injury, indicative of chronic neuropathology. In summary, our study identified a critical time window of TBI pathology and associated circadian and sleep/wake phenotypes. Future studies should leverage this mouse model to investigate the molecular mechanisms underlying the chronic sleep/wake phenotypes post-TBI early in life.

Patients with Chronic Spinal Cord Injury Display a Progressive Alteration over the Years of the Activation Stages of the T Lymphocyte Compartment

Spinal cord injury (SCI) is a serious medical condition associated with severe morbidities and disability. Chronic SCI patients present an enhanced susceptibility to infections and comorbidities with inflammatory pathogenesis. Chronic SCI appears to be associated with a systemic dysfunction of the immune system. We investigated the alteration of the pivotal CD4+ and CD8+ T lymphocytes in patients with chronic SCI at different years of evolution. A clinically homogenous population of 105 patients with chronic SCI (31 with time of evolution less than 5 years (SCI SP); 32 early chronic (SCI ECP) with time of evolution between 5 and 15 years; and 42 late chronic (SCI LCP) with time of evolution more than 15 years) and 38 healthy controls were enrolled. SCI ECP and SCI LCP patients showed significant CD4+ and CD8+ T lymphopenia, ascribed to a reduction in naïve and CM subsets. Furthermore, SCI ECP and SCI LCP patients showed a significant reduction in the expression of CD28 on CD8+ T lymphocytes. The expression of CCR6 by CD4+ T lymphocytes was decreased during the evolution of chronic SCI, but on CD8+ T lymphocytes, it was observed during the first 15 years of evolution. In conclusion, the chronic SCI course with severe damage to T lymphocytes mainly worsens over the years of disease evolution.

Microglia-derived CCL20 deteriorates neurogenesis following intraventricular hemorrhage

Intraventricular hemorrhage (IVH) commonly occurs as an extension of intracerebral hemorrhage (ICH) into the brain ventricular system, leading to worse outcomes without effective management. Using a mouse model of IVH, we found that impaired neurogenesis is evident in the subventricular zone (SVZ), along with persistent microglia activation, leukocyte infiltration and cell death. Pharmacological depletion of microglia using PLX3397, an inhibitor of colony stimulating factor 1 receptor (CSF1R), promotes neurogenesis, and alleviated delayed functional impairments in IVH mice. Meanwhile, an elevated level of microglia-derived CC chemokine ligand 20 (CCL20) is observed in the SVZ following IVH, which can induce the upregulation of pro-inflammatory factors in microglia and impair the proliferation and survival of neural stem cells (NSCs) in vitro. Blocking CCL20 in microglia leads to downregulation of protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/the nuclear factor-κB (NF-κB) signaling pathway, which may contribute to CCL20-dependent pro-inflammatory responses and neural injury. These findings demonstrate a detrimental role of microglia in the neurogenesis and neurorepair after IVH in which CCL20 likely plays a role.

Window into the mind: Advanced handheld spectroscopic eye-safe technology for point-of-care neurodiagnostic

Traumatic brain injury (TBI), a major cause of morbidity and mortality worldwide, is hard to diagnose at the point of care with patients often exhibiting no clinical symptoms. There is an urgent need for rapid point-of-care diagnostics to enable timely intervention. We have developed a technology for rapid acquisition of molecular fingerprints of TBI biochemistry to safely measure proxies for cerebral injury through the eye, providing a path toward noninvasive point-of-care neurodiagnostics using simultaneous Raman spectroscopy and fundus imaging of the neuroretina. Detection of endogenous neuromarkers in porcine eyes' posterior revealed enhancement of high-wave number bands, clearly distinguishing TBI and healthy cohorts, classified via artificial neural network algorithm for automated data interpretation. Clinically, translating into reduced specialist support, this markedly improves the speed of diagnosis. Designed as a hand-held cost-effective technology, it can allow clinicians to rapidly assess TBI at the point of care and identify long-term changes in brain biochemistry in acute or chronic neurodiseases.

Sleep Disruption in a Mouse Model of Chronic Traumatic Brain Injury

Chronic sleep/wake disturbances are strongly associated with traumatic brain injury (TBI) in patients and are being increasingly recognized. However, the underlying mechanisms are largely understudied and there is an urgent need for animal models of lifelong sleep/wake disturbances. The objective of this study was to develop a chronic TBI rodent model and investigate the lifelong chronic effect of TBI on sleep/wake behavior. We performed repetitive midline fluid percussion injury (rmFPI) in four months old mice and monitored their sleep/wake behavior using the non-invasive PiezoSleep system. The sleep/wake states were recorded before injury (baseline) and then monthly thereafter. We found that TBI mice displayed a significant decrease in sleep duration in both the light and dark phases, beginning at three months post-TBI and continuing throughout the study. Consistent with the sleep phenotype, these TBI mice showed circadian locomotor activity phenotypes and exhibited reduced anxiety-like behavior. TBI mice also gained less weight, and had less lean mass and total body water content, compared to sham controls. Furthermore, TBI mice showed extensive brain tissue loss and increased GFAP and IBA1 levels in the hypothalamus and the vicinity of the injury, indicative of chronic neuropathology. In summary, our study identified a critical time window of TBI pathology and associated circadian and sleep/wake phenotypes. Future studies should leverage this mouse model to investigate the molecular mechanisms underlying the chronic sleep/wake phenotypes following TBI early in life.

Neutrophils for Revascularization Require Activation of CCR6 and CCL20 by TNFα

BACKGROUND

Activation of immune-inflammatory pathways involving TNFα (tumor necrosis factor alpha) signaling is critical for revascularization and peripheral muscle tissue repair after ischemic injury. However, mechanisms of TNFα-driven inflammatory cascades directing recruitment of proangiogenic immune cells to sites of ischemia are unknown.

METHODS

Muscle tissue revascularization after permanent femoral artery ligation was monitored in mutant mice by laser Doppler imaging and light sheet fluorescence microscopy. TNFα-mediated signaling and the role of the CCL20 (C-C motif chemokine ligand 20)-CCR6 (C-C chemokine receptor 6) axis for formation of new vessels was studied in vitro and in vivo using bone marrow transplantation, flow cytometry, as well as biochemical and molecular biological techniques.

RESULTS

TNFα-mediated activation of TNFR (tumor necrosis factor receptor) 1 but not TNFR2 was found to be required for postischemic muscle tissue revascularization. Bone marrow-derived CCR6+ neutrophil granulocytes were identified as a previously undescribed TNFα-induced population of proangiogenic neutrophils, characterized by increased expression of VEGFA (vascular endothelial growth factor A). Mechanistically, postischemic activation of TNFR1 induced expression of the CCL20 in vascular cells and promoted translocation of the CCL20 receptor CCR6 to the cell surface of neutrophils, essentially conditioning VEGFA-expressing proangiogenic neutrophils for CCL20-dependent recruitment to sites of ischemia. Moreover, impaired revascularization of ischemic peripheral muscle tissue in diabetic mice was associated with reduced numbers of proangiogenic neutrophils and diminished CCL20 expression. Administration of recombinant CCL20 enhanced recruitment of proangiogenic neutrophils and improved revascularization of diabetic ischemic skeletal muscles, which was sustained by sequential treatment with fluvastatin.

CONCLUSIONS

We demonstrate that site-specific activation of the CCL20-CCR6 axis via TNFα recruits proangiogenic VEGFA-expressing neutrophils to sites of ischemic injury for initiation of muscle tissue revascularization. The findings provide an attractive option for tissue revascularization, particularly under diabetic conditions.

A mouse model of repeated traumatic brain injury-induced hearing impairment: Early cochlear neurodegeneration in the absence of hair cell loss

PURPOSE

Traumatic Brain Injury (TBI) is a major cause of death and disability worldwide. Mounting evidence suggests that even mild TBI injuries, which comprise >75% of all TBIs, can cause chronic post-concussive neurological symptoms, especially when experienced repetitively (rTBI). The most common post-concussive symptoms include auditory dysfunction in the form of hearing loss, tinnitus, or impaired auditory processing, which can occur even in the absence of direct damage to the auditory system at the time of injury. The mechanism by which indirect damage causes loss of auditory function is poorly understood, and treatment is currently limited to symptom management rather than preventative care. We reasoned that secondary injury mechanisms, such as inflammation, may lead to damage of the inner ear and parts of the brain used for hearing after rTBI. Herein, we established a model of indirect damage to the auditory system induced by rTBI and characterized the pathology of hearing loss.

METHODS

We established a mouse model of rTBI in order to determine a timeline of auditory pathology following multiple mild injuries. Mice were subject to controlled cortical impact at the skull midline once every 48 h, for a total of 5 hits. Auditory function was assessed via the auditory brainstem response (ABR) at various timepoints post injury. Brain and cochleae were collected to establish a timeline of cellular pathology.

RESULTS

We observed increased ABR thresholds and decreased (ABR) P1 amplitudes in rTBI vs sham animals at 14 days post-impact (dpi). This effect persisted for up to 60 days (dpi). Auditory temporal processing was impaired beginning at 30 dpi. Spiral ganglion degeneration was evident at 14 dpi. No loss of hair cells was detected at this time, suggesting that neuronal loss is one of the earliest notable events in hearing loss caused by this type of rTBI.

CONCLUSIONS

We conclude that rTBI results in chronic auditory dysfunction via damage to the spiral ganglion which occurs in the absence of any reduction in hair cell number. This suggests early neuronal damage that may be caused by systemic mechanisms similar to those leading to the spread of neuronal death in the brain following TBI. This TBI-hearing loss model provides an important first step towards identifying therapeutic targets to attenuate damage to the auditory system following head injury.

Human amnionic progenitor cell secretome mitigates the consequence of traumatic optic neuropathy in a mouse model

Traumatic optic neuropathy (TON) is a condition in which acute injury to the optic nerve from direct or indirect trauma results in vision loss. The most common cause of TON is indirect injury to the optic nerve caused by concussive forces that are transmitted to the optic nerve. TON occurs in up to 5% of closed-head trauma patients and there is currently no known effective treatment. One potential treatment option for TON is ST266, a cell-free biological solution containing the secretome of amnion-derived multipotent progenitor (AMP) cells. We investigated the efficacy of intranasal ST266 in a mouse model of TON induced by blunt head trauma. Injured mice treated with a 10-day regimen of ST266 showed an improvement in spatial memory and learning, a significant preservation of retinal ganglion cells, and a decrease in neuropathological markers in the optic nerve, optic tract, and dorsal lateral geniculate nucleus. ST266 treatment effectively downregulated the NLRP3 inflammasome-mediated neuroinflammation pathway after blunt trauma. Overall, treatment with ST266 was shown to improve functional and pathological outcomes in a mouse model of TON, warranting future exploration of ST266 as a cell-free therapeutic candidate for testing in all optic neuropathies.

Multispectral optoacoustic tomography (MSOT): Monitoring neurovascular changes in a mouse repetitive traumatic brain injury model

BACKGROUND

Evidence suggests that mild TBI injuries, which comprise > 75% of all TBIs, can cause chronic post-concussive symptoms, especially when experienced repetitively (rTBI). rTBI is a major cause of cognitive deficit in athletes and military personnel and is associated with neurovascular changes. Current methods to monitor neurovascular changes in detail are prohibitively expensive and invasive for patients with mild injuries.

NEW METHOD

We evaluated the potential of multispectral optoacoustic tomography (MSOT) to monitor neurovascular changes and assess therapeutic strategies in a mouse model of rTBI. Mice were subjected to rTBI or sham via controlled cortical impact and administered pioglitazone (PG) or vehicle. Oxygenated and deoxygenated hemoglobin were monitored using MSOT. Indocyanine green clearance was imaged via MSOT to evaluate blood-brain-barrier (BBB) integrity.

RESULTS

Mice subjected to rTBI show a transient increase in oxygenated/total hemoglobin ratio which can be mitigated by PG administration. rTBI mice also show BBB disruption shortly after injury and reduction of oxygenated/total hemoglobin in the chronic stage, neither of which were affected by PG intervention.

COMPARISON WITH EXISTING METHODS

MSOT imaging has the potential as a noninvasive in vivo imaging method to monitor neurovascular changes and assess therapeutics in mouse models of rTBI. In comparison to standard methods of tracking inflammation and BBB disruption, MSOT can be used multiple times throughout the course of injury without the need for surgery. Thus, MSOT is especially useful in research of rTBI models for screening therapeutics, and with further technological improvements may be extended for use in rTBI patients.

Identification of immune associated potential molecular targets in proliferative diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and causes of blindness in developed countries. Our study was designed to identify immune-related genes involved in the progression of proliferative diabetic retinopathy (PDR).

METHODS

The "GSE102485" dataset of neovascular membrane samples (NVMs) from type 1 and 2 diabetes mellitus patients was downloaded from the Gene Expression Omnibus database. Functional enrichment analyses, protein-protein interaction network (PPI) construction, and module analysis of immune pathways in NVMs and controls were conducted via Gene Set Enrichment Analysis and Metascape.

RESULTS

The significantly upregulated hallmark gene sets in DR2 and DR1 groups were involved in five immune pathways. Only CCR4, CXCR6, C3AR1, LPAR1, C5AR1, and P2RY14 were not previously reported in the context of PDR molecular pathophysiology. Except for P2RY14, all of the above were upregulated in retinal samples from experimental diabetes mouse models and human retina microvascular endothelial cells (HRMECs) treated with high glucose (HG) by quantitative Real Time Polymerase Chain Reaction (qRT-PCR).

CONCLUSION

The genes identified herein provide insight into immune-related differential gene expression during DR progression.

CCL20/CCR6 Mediated Macrophage Activation and Polarization Can Promote Adenoid Epithelial Inflammation in Adenoid Hypertrophy

Background

Adenoid hypertrophy (AH) is a chronic or acute obstruction-related ailment of the upper respiratory tract that arises as an inflammatory response to exposure of bacteria, viruses or allergies. Activation and polarization of macrophages are key processes in inflammation-related disorders like AH and CCL20/CCR6 axis is a critical therapeutic target.

Purpose

To determine that CCL20/CCR6 mediated macrophage activation and polarization can promote adenoid epithelial inflammation in AH.

Methods

To support this claim, CCL20 and CCR6 expressions were studied in clinical AH samples. In addition, the expressions of cytokines such as TNF-α, IL-1β, IL-6, IL-17, IL-10 and TGF-β were analysed. In vitro, human adenoid epithelial cells were co-cultured with polarized THP-1 and T lymphocyte H9 cells to study the expressions of several inflammatory markers.

Results

The expressions of M1 macrophage markers CD86 and IL-17 were significantly increased, whereas the expressions of M2 macrophage markers CD206 and FOXP3 were significantly decreased. The THP-1 cells were successfully polarized to M0, M1 and M2 macrophages. The survival of macrophages improved after 24 hr of induction and enhanced TGF-β expression was observed. The expressions of the inflammatory cytokines IL-6, TNF-α, IL-1β and CCL20 increased significantly.

Conclusion

Collectively, these results suggest that the CCL20/CCR6 mediated macrophage activation and polarization into M1-type macrophages can promote adenoid epithelial inflammation in AH. Further studies are warranted to determine the roles of inflammatory markers in the pathophysiology of AH and identifying potential targets.

Ischemic stroke: From pathological mechanisms to neuroprotective strategies

Ischemic stroke (IS) has complex pathological mechanisms, and is extremely difficult to treat. At present, the treatment of IS is mainly based on intravenous thrombolysis and mechanical thrombectomy, but they are limited by a strict time window. In addition, after intravenous thrombolysis or mechanical thrombectomy, damaged neurons often fail to make ideal improvements due to microcirculation disorders. Therefore, finding suitable pathways and targets from the pathological mechanism is crucial for the development of neuroprotective agents against IS. With the hope of making contributions to the development of IS treatments, this review will introduce (1) how related targets are found in pathological mechanisms such as inflammation, excitotoxicity, oxidative stress, and complement system activation; and (2) the current status and challenges in drug development.

Traumatic Brain Injury-Related Optic Nerve Damage

Vision disorders are associated with traumatic brain injury (TBI) in 20%-40% of clinical cases and involve a diverse set of potential symptoms that can present acutely or chronically. Due to its structure and position, the optic nerve is vulnerable to multiple forms of primary injury, which can result in traumatic optic neuropathy (TON). Multiple studies have shown that the optic tract may also be injured during TBI, though data regarding the temporospatial resolution of injury to the optic nerve are sparse. We evaluated the time course of optic nerve injury and visual impairments in our closed head impact acceleration mouse model of mild TBI (mTBI) designed to mimic repetitive injuries experienced in the context of sport. Our results show that inflammation and gliosis occur acutely in response to injury. Additionally, indications of optic nerve degeneration and functional loss of vision beginning at 1-month postinjury, and retinal ganglion cell loss at 7 months, revealed that the degeneration is continuous and permanent. Together, this study demonstrated that the optic nerve is vulnerable to damage during mTBI, which can cause TON and vision loss. These findings will be important for clinicians to consider to determine whether optic nerve is injured in the TBI patients with vision problems.

Blockade on Lin28a Prevents Cognitive Impairment and Disruption of the Blood-Brain Barrier Induced by Chronic Cerebral Hypoperfusion

Lin28a is an RNA-binding protein involved in the translation and regulation of multiple mRNAs. Lin28a is overexpressed in animal models of brain injury. Similarly, our preliminary study found increased Lin28a expression levels in the animal models four to seven days after chronic cerebral hypoperfusion. Therefore, this current study aimed to evaluate the effects of modulating Lin28a on cognition and brain functions. Vascular dementia (VaD) was induced in 12-week-old male Wistar rats using permanent bilateral common carotid artery occlusion (BCCAO), and these rats were treated with Lin28a siRNA on the fourth and seventh day after BCCAO. From the 42nd day after BCCAO, cognitive behavioral experiments were performed for two weeks. VaD induced by BCCAO resulted in cognitive impairment and microglial activation. Lin28a expression was upregulated after BCCAO. Lin28a siRNA treatment alleviated cognitive impairment and overexpression of GFAP and Iba-1 in the brain. Furthermore, the treatment ameliorated the VaD-induced damage to the blood-brain barrier (BBB) components, including PECAM-1, PDGFRβ, occludin, claudin-9, and ZO-1. CCR6 activation after VaD, associated with BBB disruption, was diminished by treatment with Lin28a siRNA. The treatment inhibited VaD-induced microglial activity and alleviated BBB damage. Thus, blocking Lin28a may alleviate cognitive impairment caused by VaD.

Raloxifene Modulates Microglia and Rescues Visual Deficits and Pathology After Impact Traumatic Brain Injury

Mild traumatic brain injury (TBI) involves widespread axonal injury and activation of microglia, which initiates secondary processes that worsen the TBI outcome. The upregulation of cannabinoid type-2 receptors (CB2) when microglia become activated allows CB2-binding drugs to selectively target microglia. CB2 inverse agonists modulate activated microglia by shifting them away from the harmful pro-inflammatory M1 state toward the helpful reparative M2 state and thus can stem secondary injury cascades. We previously found that treatment with the CB2 inverse agonist SMM-189 after mild TBI in mice produced by focal cranial blast rescues visual deficits and the optic nerve axon loss that would otherwise result. We have further shown that raloxifene, which is Food and Drug Administration (FDA)-approved as an estrogen receptor modulator to treat osteoporosis, but also possesses CB2 inverse agonism, yields similar benefit in this TBI model through its modulation of microglia. As many different traumatic events produce TBI in humans, it is widely acknowledged that diverse animal models must be used in evaluating possible therapies. Here we examine the consequences of TBI created by blunt impact to the mouse head for visual function and associated pathologies and assess raloxifene benefit. We found that mice subjected to impact TBI exhibited decreases in contrast sensitivity and the B-wave of the electroretinogram, increases in light aversion and resting pupil diameter, and optic nerve axon loss, which were rescued by daily injection of raloxifene at 5 or 10 mg/ml for 2 weeks. Raloxifene treatment was associated with reduced M1 activation and/or enhanced M2 activation in retina, optic nerve, and optic tract after impact TBI. Our results suggest that the higher raloxifene dose, in particular, may be therapeutic for the optic nerve by enhancing the phagocytosis of axonal debris that would otherwise promote inflammation, thereby salvaging less damaged axons. Our current work, together with our prior studies, shows that microglial activation drives secondary injury processes after both impact and cranial blast TBI and raloxifene mitigates microglial activation and visual system injury in both cases. The results thus provide a strong basis for phase 2 human clinical trials evaluating raloxifene as a TBI therapy.

Repetitive Traumatic Brain Injury Is Associated With TDP-43 Alterations, Neurodegeneration, and Glial Activation in Mice

Increasing evidence points to a relationship between repetitive mild traumatic brain injury (mTBI), the Tar DNA binding protein 43 (TDP-43) pathology and some neurodegenerative diseases, but the underlying pathophysiological mechanisms are still unknown. We examined TDP-43 regulation, neurodegeneration, and glial responses following repetitive mTBI in nontransgenic mice and in animals with overexpression of human mutant TDP-43 protein (TDP-43G348C). In the frontal cortices of the injured nontransgenic animals, early TDP-43 cytoplasmatic translocation and overexpression of the protein and its pathological forms were detected. In the injured animals of both genotypes, neurodegeneration and pronounced glial activity were detected in the optic tract. In TDP-43G348C mice, these changes were significantly higher at day 7 after the last mTBI compared with the values in the nontransgenic animals. Results of this study suggest that the changes in the TDP-43 regulation in the frontal cortices of the nontransgenic animals were a transient stress response to the brain injury. Repetitive mTBI did not produce additional TDP-43 dysregulation or neurodegeneration or pronounced gliosis in the frontal cortex of TDP-43G348C mice. Our research also suggests that overexpression of mutated human TDP-43 possibly predisposes the brain to more intense neurodegeneration and glial activation in the optic tract after repetitive mTBI.

Long-Term Effects of Repetitive Mild Traumatic Injury on the Visual System in Wild-Type and TDP-43 Transgenic Mice

Little is known about the impairments and pathological changes in the visual system in mild brain trauma, especially repetitive mild traumatic brain injury (mTBI). The goal of this study was to examine and compare the effects of repeated head impacts on the neurodegeneration, axonal integrity, and glial activity in the optic tract (OT), as well as on neuronal preservation, glial responses, and synaptic organization in the lateral geniculate nucleus (LGN) and superior colliculus (SC), in wild-type mice and transgenic animals with overexpression of human TDP-43 mutant protein (TDP-43^G348C) at 6 months after repeated closed head traumas. Animals were also assessed in the Barnes maze (BM) task. Neurodegeneration, axonal injury, and gliosis were detected in the OT of the injured animals of both genotypes. In the traumatized mice, myelination of surviving axons was mostly preserved, and the expression of neurofilament light chain was unaffected. Repetitive mTBI did not induce changes in the LGN and the SC, nor did it affect the performance of the BM task in the traumatized wild-type and TDP-43 transgenic mice. Differences in neuropathological and behavioral assessments between the injured wild-type and TDP-43^G348C mice were not revealed. Results of the current study suggest that repetitive mTBI was associated with chronic damage and inflammation in the OT in wild-type and TDP-43^G348C mice, which were not accompanied with behavioral problems and were not affected by the TDP-43 genotype, while the LGN and the SC remained preserved in the used experimental conditions.

Altered Secretome and ROS Production in Olfactory Mucosa Stem Cells Derived from Friedreich's Ataxia Patients

Friedreich’s ataxia is the most common hereditary ataxia for which there is no cure or approved treatment at present. However, therapeutic developments based on the understanding of pathological mechanisms underlying the disease have advanced considerably, with the implementation of cellular models that mimic the disease playing a crucial role. Human olfactory ecto-mesenchymal stem cells represent a novel model that could prove useful due to their accessibility and neurogenic capacity. Here, we isolated and cultured these stem cells from Friedreich´s ataxia patients and healthy donors, characterizing their phenotype and describing disease-specific features such as reduced cell viability, impaired aconitase activity, increased ROS production and the release of cytokines involved in neuroinflammation. Importantly, we observed a positive effect on patient-derived cells, when frataxin levels were restored, confirming the utility of this in vitro model to study the disease. This model will improve our understanding of Friedreich´s ataxia pathogenesis and will help in developing rationally designed therapeutic strategies.

Treatment with shCCL20-CCR6 nanodendriplexes and human mesenchymal stem cell therapy improves pathology in mice with repeated traumatic brain injury

Traumatic brain injury (TBI) is a devastating neurological disorder, although the underlying pathophysiology is poorly understood. TBI causes blood-brain barrier (BBB) disruption, immune cell trafficking, neuroinflammation and neurodegeneration. CCL20 is an important chemokine mediating neuroinflammation. Human mesenchymal stem cell (hMSC) therapy is a promising regenerative approach but the inflammatory microenvironment in the brain tends to decrease the efficacy of the hMSC transplantation. Reducing the inflammation prior to hMSC therapy improves the outcome. We developed a combined nano-cell therapy by using dendrimers complexed with plasmids (dendriplexes) targeting CCL20 and its sole receptor CCR6 to reduce inflammation followed by hMSC transplantation. Treatment of TBI mice with shRNA conjugated dendriplexes followed by hMSC administration downregulated the inflammatory markers and significantly increased brain-derived neurotrophic factor (BDNF) expression in the cerebral cortex indicating future possible neurogenesis and improved behavioral deficits. Taken together, this nano-cell therapy ameliorates neuroinflammation and promotes brain tissue repair after TBI.