Early detection of subclinical visual damage after blast-mediated TBI enables prevention of chronic visual deficit by treatment with P7C3-S243

Henle fiber layer thickening and deficits in objective retinal function in participants with a history of multiple traumatic brain injuries

Introduction

This study tested whether multiple traumatic brain injuries (TBIs) alter the structure of the Henle fiber layer (HFL) and degrade cell-specific function in the retinas of human participants.

Methods

A cohort of case participants with multiple TBIs and a cohort of pair-matched control participants were prospectively recruited. Directional optical coherence tomography and scanning laser polarimetry measured HFL thickness and phase retardation, respectively. Full-field flash electroretinography (fERG) assessed retinal function under light-adapted (LA) 3.0, LA 30 Hz, dark-adapted (DA) 0.01, DA 3.0, and DA 10 conditions. Retinal imaging and fERG outcomes were averaged between both eyes, and paired t-tests or Wilcoxon signed-rank tests analyzed inter-cohort differences.

Results

Global HFL thickness was significantly (p = 0.02) greater in cases (8.4 ± 0.9 pixels) than in controls (7.7 ± 1.1 pixels). There was no statistically significant difference (p = 0.91) between the cohorts for global HFL phase retardation. For fERG, LA 3.0 a-wave amplitude was significantly reduced (p = 0.02) in cases (23.5 ± 4.2 μV) compared to controls (29.0 ± 8.0 μV). There were no other statistically significant fERG outcomes between the cohorts.

Discussion

In summary, the HFL thickens after multiple TBIs, but phase retardation remains unaltered in the macula. Multiple TBIs may also impair retinal function, indicated by a reduction in a-wave amplitude. These results support the potential of the retina as a site to detect TBI-associated pathology.

Increasing the number and intensity of shock tube generated blast waves leads to earlier retinal ganglion cell dysfunction and regional cell death

The purpose of this study was to examine the effect of a blast exposure generated from a shock tube on retinal ganglion cell (RGC) function and structure. Mice were exposed to one of three blast conditions using a shock tube; a single blast wave of 20 PSI, a single blast wave of 30 PSI, or three blast waves of 30 PSI given on three consecutive days with a one-day inter-blast interval. The structure and function of the retina were analyzed using the pattern electroretinogram (PERG), the optomotor reflex (OMR), and optical coherence tomography (OCT). The in vivo parameters were examined at baseline, and then again 1-week, 4-weeks, and 16-weeks following blast exposure. The number of surviving RGCs was quantified at the end of the study. Analysis of mice receiving a 20 PSI injury showed decreased PERG and OMR responses 16-weeks post blast, without evidence of changed retinal thickness or RGC death. Mice subjected to a 30 PSI injury showed decreased PERG responses 4 weeks and 16 weeks after injury, without changes in the retinal thickness or RGC density. Mice subjected to 30 PSI X 3 blast exposures had PERG deficits 1-week and 4-weeks post exposure. There was also significant change in retinal thickness 1-week and 16-weeks post blast exposure. Mice receiving 30 PSI X 3 blast injuries had regional loss of RGCs in the central retina, but not in the mid-peripheral or peripheral retina. Overall, this study has shown that increasing the number of blast exposures and the intensity leads to earlier functional loss of RGCs. We have also shown regional RGC loss only when using the highest blast intensity and number of blast injuries.

Higher concentration of P7C3 than required for neuroprotection suppresses renal cell carcinoma growth and metastasis

Background: P7C3 is a novel compound that has been widely applied in neurodegenerative diseases and nerve injury repair. Here, we show that higher concentrations of P7C3 than are required for in vivo neuroprotection have the novel function of suppressing renal cell carcinoma (RCC) proliferation and metastasis. Methods: Colony formation, CCK-8 and EdU assay were applied to evaluate RCC cell proliferation. Wound healing and transwell assay were used to measure RCC cell migration and invasion. Flow cytometry assay was employed to detect RCC cell apoptosis and cell cycle. qRT-PCR assay was carried out to measure ribonucleotide reductase subunit M2 (RRM2) mRNA expression level, while western blot assay was utilized to detect the expression level of target proteins. RCC cell growth in vivo was determined by xenografts in mice. Results: We observed that high concentrations of P7C3 could restrain the proliferation and metastasis of RCC cells and promote cell apoptosis. Mechanistically, this new effect of higher dose of P7C3 was associated with reduced expression of RRM2, and the beneficial efficacy of P7C3 in RCC was blocked when suppression of RRM2 was prevented. When RRM2 suppression was permitted, the cGAS-STING pathway was activated by virtue of RRM2/Bcl-2/Bax signaling. Lastly, intraperitoneal injection of this high level of P7C3 in mice potently inhibited tumor growth. Conclusion: In conclusion, we show here that P7C3 that exerts an anti-cancer effect in RCC. Our study indicated that P7C3 might act as a novel drug for RCC in the future. The regulatory signal pathway RRM2/Bcl-2/BAX/cGAS-STING might present novel insight to the potential mechanism of RCC development.

Application of P7C3 Compounds to Investigating and Treating Acute and Chronic Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading worldwide cause of disability, and there are currently no medicines that prevent, reduce, or reverse acute or chronic neurodegeneration in TBI patients. Here, we review the target-agnostic discovery of nicotinamide adenine dinucleotide (NAD+)/NADH-stabilizing P7C3 compounds through a phenotypic screen in mice and describe how P7C3 compounds have been applied to advance understanding of the pathophysiology and potential treatment of TBI. We summarize how P7C3 compounds have been shown across multiple laboratories to mitigate disease progression safely and effectively in a broad range of preclinical models of disease related to impaired NAD+/NADH metabolism, including acute and chronic TBI, and note the reported safety and neuroprotective efficacy of P7C3 compounds in nonhuman primates. We also describe how P7C3 compounds facilitated the recent first demonstration that chronic neurodegeneration 1 year after TBI in mice, the equivalent of many decades in people, can be reversed to restore normal neuropsychiatric function. We additionally review how P7C3 compounds have facilitated discovery of new pathophysiologic mechanisms of neurodegeneration after TBI. This includes the role of rapid TBI-induced tau acetylation that drives axonal degeneration, and the discovery of brain-derived acetylated tau as the first blood-based biomarker of neurodegeneration after TBI that directly correlates with the abundance of a therapeutic target in the brain. We additionally review the identification of TBI-induced tau acetylation as a potential mechanistic link between TBI and increased risk of Alzheimer's disease. Lastly, we summarize historical accounts of other successful phenotypic-based drug discoveries that advanced medical care without prior recognition of the specific molecular target needed to achieve the desired therapeutic effect.

Current and future therapeutic strategies for Alzheimer's disease: an overview of drug development bottlenecks

Alzheimer's disease (AD) is the most common chronic neurodegenerative disease worldwide. It causes cognitive dysfunction, such as aphasia and agnosia, and mental symptoms, such as behavioral abnormalities; all of which place a significant psychological and economic burden on the patients' families. No specific drugs are currently available for the treatment of AD, and the current drugs for AD only delay disease onset and progression. The pathophysiological basis of AD involves abnormal deposition of beta-amyloid protein (Aβ), abnormal tau protein phosphorylation, decreased activity of acetylcholine content, glutamate toxicity, autophagy, inflammatory reactions, mitochondria-targeting, and multi-targets. The US Food and Drug Administration (FDA) has approved five drugs for clinical use: tacrine, donepezil, carbalatine, galantamine, memantine, and lecanemab. We have focused on the newer drugs that have undergone clinical trials, most of which have not been successful as a result of excessive clinical side effects or poor efficacy. Although aducanumab received rapid approval from the FDA on 7 June 2021, its long-term safety and tolerability require further monitoring and confirmation. In this literature review, we aimed to explore the possible pathophysiological mechanisms underlying the occurrence and development of AD. We focused on anti-Aβ and anti-tau drugs, mitochondria-targeting and multi-targets, commercially available drugs, bottlenecks encountered in drug development, and the possible targets and therapeutic strategies for future drug development. We hope to present new concepts and methods for future drug therapies for AD.

Longitudinal in vivo monitoring of axonal degeneration after brain injury

Traumatic brain injury (TBI)-induced axonal degeneration leads to acute and chronic neuropsychiatric impairment, neuronal death, and accelerated neurodegenerative diseases of aging, including Alzheimer's and Parkinson's diseases. In laboratory models, axonal degeneration is traditionally studied through comprehensive postmortem histological evaluation of axonal integrity at multiple time points. This requires large numbers of animals to power for statistical significance. Here, we developed a method to longitudinally monitor axonal functional activity before and after injury in vivo in the same animal over an extended period. Specifically, after expressing an axonal-targeting genetically encoded calcium indicator in the mouse dorsolateral geniculate nucleus, we recorded axonal activity patterns in the visual cortex in response to visual stimulation. In vivo aberrant axonal activity patterns after TBI were detectable from 3 days after injury and persisted chronically. This method generates longitudinal same-animal data that substantially reduces the number of required animals for preclinical studies of axonal degeneration.

Increased Risk of Aging-Related Neurodegenerative Disease after Traumatic Brain Injury

Traumatic brain injury (TBI) survivors frequently suffer from chronically progressive complications, including significantly increased risk of developing aging-related neurodegenerative disease. As advances in neurocritical care increase the number of TBI survivors, the impact and awareness of this problem are growing. The mechanisms by which TBI increases the risk of developing aging-related neurodegenerative disease, however, are not completely understood. As a result, there are no protective treatments for patients. Here, we review the current literature surrounding the epidemiology and potential mechanistic relationships between brain injury and aging-related neurodegenerative disease. In addition to increasing the risk for developing all forms of dementia, the most prominent aging-related neurodegenerative conditions that are accelerated by TBI are amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Parkinson's disease (PD), and Alzheimer's disease (AD), with ALS and FTD being the least well-established. Mechanistic links between TBI and all forms of dementia that are reviewed include oxidative stress, dysregulated proteostasis, and neuroinflammation. Disease-specific mechanistic links with TBI that are reviewed include TAR DNA binding protein 43 and motor cortex lesions in ALS and FTD; alpha-synuclein, dopaminergic cell death, and synergistic toxin exposure in PD; and brain insulin resistance, amyloid beta pathology, and tau pathology in AD. While compelling mechanistic links have been identified, significantly expanded investigation in the field is needed to develop therapies to protect TBI survivors from the increased risk of aging-related neurodegenerative disease.

Immune responses in mice after blast-mediated traumatic brain injury TBI autonomously contribute to retinal ganglion cell dysfunction and death

PURPOSE

The purpose of this study was to examine the role of the immune system and its influence on chronic retinal ganglion cell (RGC) dysfunction following blast-mediated traumatic brain injury (bTBI).

METHODS

C57BL/6J and B6.129S7-Rag1^tm1Mom/J (Rag^-/-) mice were exposed to one blast injury of 140 kPa. A separate cohort of C57BL/6J mice was exposed to sham-blast. Four weeks following bTBI mice were euthanized, and splenocytes were collected. Adoptive transfer (AT) of splenocytes into naïve C57BL/6J recipient mice was accomplished via tail vein injection. Three groups of mice were analyzed: those receiving AT of splenocytes from C57BL/6J mice exposed to blast (AT-TBI), those receiving AT of splenocytes from C57BL/6J mice exposed to sham (AT-Sham), and those receiving AT of splenocytes from Rag^-/- mice exposed to blast (AT-Rag^-/-). The visual function of recipient mice was analyzed with the pattern electroretinogram (PERG), and the optomotor response (OMR). The structure of the retina was evaluated using optical coherence tomography (OCT), and histologically using BRN3A-antibody staining.

RESULTS

Analysis of the PERG showed a decreased amplitude two months post-AT that persisted for the duration of the study in AT-TBI mice. We also observed a significant decrease in the retinal thickness of AT-TBI mice two months post-AT compared to sham, but not at four or six months post-AT. The OMR response was significantly decreased in AT-TBI mice 5- and 6-months post-AT. BRN3A staining showed a loss of RGCs in AT-TBI and AT-Rag^-/- mice.

CONCLUSION

These results suggest that the immune system contributes to chronic RGC dysfunction following bTBI.

Impairments of retinal hemodynamics and oxygen metrics in ocular hypertension-induced ischemia-reperfusion

Ischemia-reperfusion (I/R) is an established model for retinal neurodegeneration. However, there is limited knowledge of retinal physiological metrics and their relationships to retinal function and morphology in the I/R model. The purpose of the study was to test the hypotheses that retinal hemodynamic and oxygen metrics are impaired and associated with visual dysfunction, retinal thinning, and retinal ganglion cell (RGC) loss due to I/R injury. Intraocular pressure (IOP) was increased in one eye of 10 rats for 90 min followed by reperfusion. Fellow eyes served as controls. After one week of reperfusion, multimodal imaging was performed to quantify total retinal blood flow (TRBF) and retinal vascular oxygen contents. Retinal oxygen delivery (DO2) and metabolism (MO2) were calculated. Pattern-evoked electroretinography (PERG) and optical coherence tomography were performed to measure RGC function and retinal thicknesses, respectively. RGCs were counted from retina whole mounts. After one week of reperfusion, TRBF was lower in study eyes than in control eyes (p < 0.0003). Similarly, DO2 and MO2 were reduced in study eyes compared to control eyes (p < 0.003). PERG amplitude, TRT, IRT, ORT, and RGCs were also lower in study eyes (p ≤ 0.01). DO2 and MO2 were correlated with PERG amplitude, TRT, IRT, and ORT (r ≥ 0.6, p ≤ 0.005). The findings improve knowledge of physiological metrics affected by I/R injury and have the potential for identifying biomarkers of injury and outcomes for evaluating experimental treatments.

Biological Correlations and Confounders for Quantification of Retinal Ganglion Cells by Optical Coherence Tomography Based on Studies of Outbred Mice

Purpose

Despite popularity of optical coherence tomography (OCT) in glaucoma studies, it's unclear how well OCT-derived metrics compare to traditional measures of retinal ganglion cell (RGC) abundance. Here, Diversity Outbred (J:DO) mice are used to directly compare ganglion cell complex (GCC) thickness measured by OCT to metrics of retinal anatomy measured ex vivo with retinal wholemounts and optic nerve histology.

Methods

J:DO mice (n = 48) underwent fundoscopic and OCT examinations, with automated segmentation of GCC thickness. RGC axons were quantified from para-phenylenediamine-stained optic nerve cross-sections and somas from BRN3A-immunolabeled retinal wholemounts, with total inner retinal cellularity assessed by TO-PRO and subsequent hematoxylin staining.

Results

J:DO tissues lacked overt disease. GCC thickness, RGC abundance, and total cell abundance varied broadly across individuals. GCC thickness correlated significantly to RGC somal density (r = 0.58) and axon number (r = 0.44), but not total cell density. Retinal area and nerve cross-sectional area varied widely. No metrics were significantly influenced by sex. In bilateral comparisons, GCC thickness (r = 0.95), axon (r = 0.72), and total cell density (r = 0.47) correlated significantly within individuals.

Conclusions

Amongst outbred mice, OCT-derived measurements of GCC thickness correlate significantly to RGC somal and axon abundance. Factors limiting correlation are likely both biological and methodological, including differences in retinal area that distort sampling-based estimates of RGC abundance.

Translational Relevance

There are significant-but imperfect-correlations between GCC thickness and RGC abundance across genetic contexts in mice, highlighting valid uses and ongoing challenges for meaningful use of OCT-derived metrics.

Structure and function of retinal ganglion cells in subjects with a history of repeated traumatic brain injury

This study tested whether repeated traumatic brain injuries (TBIs) alter the objective structure or the objective function of retinal ganglion cells (RGCs) in human subjects recruited from an optometry clinic. Case subjects (n = 25) with a history of repeated TBIs (4.12 ± 2.76 TBIs over 0-41 years) and healthy pair-matched control subjects (n = 30) were prospectively recruited. Retinal nerve fiber layer (RNFL) thickness was quantified with spectral-domain optical coherence tomography, and scanning laser polarimetry measured RNFL phase retardation. Measurements of the photopic negative response were made using full-field flash electroretinography. There was no statistically significant difference (p = 0.42) in global RNFL thickness between the case cohort (96.6 ± 9.4 microns) and the control cohort (94.9 ± 7.0 microns). There was no statistically significant difference (p = 0.80) in global RNFL phase retardation between the case cohort (57.9 ± 5.7 nm) and the control cohort (58.2 ± 4.6 nm). There were no statistically significant differences in the peak time (p = 0.95) of the PhNR or in the amplitude (p = 0.11) of the PhNR between the case cohort (69.9 ± 6.9 ms and 24.1 ± 5.1 μV, respectively) and the control cohort (70.1 ± 8.9 ms and 27.8 ± 9.1 μV, respectively). However, PhNR amplitude was more variable (p < 0.025) in the control cohort than in the case cohort. Within the case cohort, there was a strong positive (r = 0.53), but not statistically significant (p = 0.02), association between time since last TBI and PhNR amplitude. There was also a modest positive (r = 0.45), but not statistically significant (p = 0.04), association between time since first TBI and PhNR amplitude. Our results suggest that there were no statistically significant differences in the objective structure or in the objective function of RGCs between the case cohort and the control cohort. Future large, longitudinal studies will be necessary to confirm our negative results and to more fully investigate the potential interaction between PhNR amplitude and time since first or last TBI.

Neuro-Visual and Vestibular Manifestations of Concussion and Mild TBI

PURPOSE OF REVIEW

Mild traumatic brain injury, or concussion, is a major cause of disability. Vestibular and visual dysfunction following concussion is common and can negatively affect patients' well-being and prolong recovery. Etiologies of visual and vestibular symptoms are numerous, including ocular, neuro-ophthalmic, otologic, and neuro-vestibular conditions. Some etiologies are benign and may be treatable, while others are potentially vision or life-threatening, making a focused history and examination essential. This review offers an approach to the evaluation and treatment of the most common neuro-visual and vestibular impairments that may result from concussion.

RECENT FINDINGS

Treatment of concussion including exercise, computerized programs, transcranial magnetic stimulation, gene therapy, stem cell therapy, and nanoparticles has shown promise. Many novel therapies are in the pipework for visual and vestibular recovery after concussion; however, the treatment mainstay remains therapy and evaluation for co-existing diseases.

Mesenchymal stem cell secretome protects against oxidative stress-induced ocular blast visual pathologies

Visual deficits are a common concern among subjects with head trauma. Stem cell therapies have gained recent attention in treating visual deficits following head trauma. Previously, we have shown that adipose-derived stem cell (ASC) concentrated conditioned medium (ASC-CCM), when delivered via an intravitreal route, yielded a significant improvement in vision accompanied by a decrease in retinal neuroinflammation in a focal cranial blast model that indirectly injures the retina. The purpose of the current study is to extend our previous studies to a direct ocular blast injury model to further establish the preclinical efficacy of ASC-CCM. Adult C57BL/6J mice were subjected to repetitive ocular blast injury (rOBI) of 25 psi to the left eye, followed by intravitreal delivery of ASC-CCM (∼200 ng protein/2 μl) or saline within 2-3 h. Visual function and histological changes were measured 4 weeks after injury and treatment. In vitro, Müller cells were used to evaluate the antioxidant effect of ASC-CCM. Visual acuity, contrast sensitivity, and b-wave amplitudes in rOBI mice receiving saline were significantly decreased compared with age-matched sham blast mice. Immunohistological analyses demonstrated a significant increase in glial fibrillary acidic protein (a retinal injury marker) in Müller cell processes, DNA/RNA damage, and nitrotyrosine (indicative of oxidative stress) in the retina, while qPCR analysis revealed a >2-fold increase in pro-inflammatory cytokines (TNF-α, ICAM1, and Ccl2) in the retina, as well as markers for microglia/macrophage activation (IL-1β and CD86). Remarkably, rOBI mice that received ASC-CCM demonstrated a significant improvement in visual function compared to saline-treated rOBI mice, with visual acuity, contrast sensitivity, and b-wave amplitudes that were not different from those in sham mice. This improvement in visual function also was associated with a significant reduction in retinal GFAP, neuroinflammation markers, and oxidative stress compared to saline-treated rOBI mice. In vitro, Müller cells exposed to oxidative stress via increasing doses of hydrogen peroxide demonstrated decreased viability, increased GFAP mRNA expression, and reduced activity for the antioxidant catalase. On the other hand, oxidatively stressed Müller cells pre-incubated with ASC-CCM showed normalized GFAP, viability, and catalase activity. In conclusion, our study demonstrates that a single intravitreal injection of ASC-CCM in the rOBI can significantly rescue retinal injury and provide significant restoration of visual function. Our in vitro studies suggest that the antioxidant catalase may play a major role in the protective effects of ASC-CCM, uncovering yet another aspect of the multifaceted benefits of ASC secretome therapies in neurotrauma.

Peering into the Brain through the Retrosplenial Cortex to Assess Cognitive Function of the Injured Brain

The retrosplenial cortex (RSC) is a posterior cortical area that has been drawing increasing interest in recent years, with a growing number of studies studying its contribution to cognitive and sensory functions. From an anatomical perspective, it has been established that the RSC is extensively and often reciprocally connected with the hippocampus, neocortex, and many midbrain regions. Functionally, the RSC is an important hub of the default-mode network. This endowment, with vast anatomical and functional connections, positions the RSC to play an important role in episodic memory, spatial and contextual learning, sensory-cognitive activities, and multi-modal sensory information processing and integration. Additionally, RSC dysfunction has been reported in cases of cognitive decline, particularly in Alzheimer's disease and stroke. We review the literature to examine whether the RSC can act as a cortical marker of persistent cognitive dysfunction after traumatic brain injury (TBI). Because the RSC is easily accessible at the brain's surface using in vivo techniques, we argue that studying RSC network activity post-TBI can shed light into the mechanisms of less-accessible brain regions, such as the hippocampus. There is a fundamental gap in the TBI field about the microscale alterations occurring post-trauma, and by studying the RSC's neuronal activity at the cellular level we will be able to design better therapeutic tools. Understanding how neuronal activity and interactions produce normal and abnormal activity in the injured brain is crucial to understanding cognitive dysfunction. By using this approach, we expect to gain valuable insights to better understand brain disorders like TBI.

AxonDeep: Automated Optic Nerve Axon Segmentation in Mice With Deep Learning

Purpose

Optic nerve damage is the principal feature of glaucoma and contributes to vision loss in many diseases. In animal models, nerve health has traditionally been assessed by human experts that grade damage qualitatively or manually quantify axons from sampling limited areas from histologic cross sections of nerve. Both approaches are prone to variability and are time consuming. First-generation automated approaches have begun to emerge, but all have significant shortcomings. Here, we seek improvements through use of deep-learning approaches for segmenting and quantifying axons from cross-sections of mouse optic nerve.

Methods

Two deep-learning approaches were developed and evaluated: (1) a traditional supervised approach using a fully convolutional network trained with only labeled data and (2) a semisupervised approach trained with both labeled and unlabeled data using a generative-adversarial-network framework.

Results

From comparisons with an independent test set of images with manually marked axon centers and boundaries, both deep-learning approaches outperformed an existing baseline automated approach and similarly to two independent experts. Performance of the semisupervised approach was superior and implemented into AxonDeep.

Conclusions

AxonDeep performs automated quantification and segmentation of axons from healthy-appearing nerves and those with mild to moderate degrees of damage, similar to that of experts without the variability and constraints associated with manual performance.

Translational Relevance

Use of deep learning for axon quantification provides rapid, objective, and higher throughput analysis of optic nerve that would otherwise not be possible.

A Tropomycin-Related Kinase B Receptor Activator for the Management of Ocular Blast-Induced Vision Loss

Pressure waves from explosions or other traumatic events can damage the neurons of the eye and visual centers of the brain, leading to functional loss of vision. There are currently few treatments for such injuries that can be deployed rapidly to mitigate damage. Brain-derived neurotrophic factor (BDNF) and activation of its receptor tropomycin-related kinase B (TrkB) have neuroprotective effects in a number of degeneration models. Small molecule activators of TrkB, such as N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC), cross the blood-brain and blood-retina barriers after systemic administration. We characterize the effects of blast-induced ocular trauma on retinal and visual function. We show that systemic administration of HIOC, a potent small molecule activator of the BDNF/TrkB receptor, preserves visual function in mice exposed to ocular blast injury. The HIOC treatment for one week preserves visual function for at least four months. The HIOC treatment effectively protected vision when the initial dose was administered up to 3 h after blast, but not if the initial treatment was delayed for 24 h. We provide evidence that the therapeutic effect of HIOC is mediated by activation of BDNF/TrkB receptors. The results indicate that HIOC may be useful for managing ocular blast injury and other forms of traumatic optic neuropathy.

Effects of intravitreal injection of siRNA against caspase-2 on retinal and optic nerve degeneration in air blast induced ocular trauma

Ocular repeated air blast injuries occur from low overpressure blast wave exposure, which are often repeated and in quick succession. We have shown that caspase-2 caused the death of retinal ganglion cells (RGC) after blunt ocular trauma. Here, we investigated if caspase-2 also mediates RGC apoptosis in a mouse model of air blast induced indirect traumatic optic neuropathy (b-ITON). C57BL/6 mice were exposed to repeated blasts of overpressure air (3 × 2 × 15 psi) and intravitreal injections of siRNA against caspase-2 (siCASP2) or against a control enhanced green fluorescent protein (siEGFP) at either 5 h after the first 2 × 15 psi ("post-blast") or 48 h before the first blast exposure ("pre-blast") and repeated every 7 days. RGC counts were unaffected by the b-ITON or intravitreal injections, despite increased degenerating ON axons, even in siCASP2 "post-blast" injection groups. Degenerating ON axons remained at sham levels after b-ITON and intravitreal siCASP2 "pre-blast" injections, but with less degenerating axons in siCASP2 compared to siEGFP-treated eyes. Intravitreal injections "post-blast" caused greater vitreous inflammation, potentiated by siCASP2, with less in "pre-blast" injected eyes, which was abrogated by siCASP2. We conclude that intravitreal injection timing after ocular trauma induced variable retinal and ON pathology, undermining our candidate neuroprotective therapy, siCASP2.

Dependence of visual and cognitive outcomes on animal holder configuration in a rodent model of blast overpressure exposure

Blast-induced traumatic brain injury is the signature injury of modern military conflicts. To more fully understand the effects of blast exposure, we placed rats in different holder configurations, exposed them to blast overpressure, and assessed the degree of eye and brain injury. Anesthetized Long-Evans rats received blast exposures directed at the head (63 kPa, 195 dB-SPL) in either an "open holder" (head and neck exposed; n = 7), or an "enclosed holder" (window for blast exposure to eye; n = 15) and were compared to non-blast exposed (control) rats (n = 22). Outcomes included optomotor response (OMR), electroretinography (ERG), and spectral domain optical coherence tomography (SD-OCT) at 2, 4, and 6 months post-blast, and cognitive function (Y-maze) at 3 months. Spatial frequency and contrast sensitivity were reduced in ipsilateral blast-exposed eyes in both holders (p < 0.01), while contralateral eyes showed greater deficits with the enclosed holder (p < 0.05). Thinner retinas (p < 0.001) and reduced ERG a- and b- wave amplitudes (p < 0.05) were observed for both ipsilateral and contralateral eyes with the enclosed, but not the open, holder. Rats in the open holder showed cognitive deficits compared to rats in the enclosed holder (p < 0.05). Overall, the animal holder configuration used in blast exposure studies can significantly affect outcomes. Enclosed holders may cause secondary damage to the contralateral eye by concussive injury or blast wave reflection off the holder wall. Open holders may damage the brain via rapid head movement (contrecoup injury). These results highlight additional factors to be considered when evaluating patients with blast exposure or developing models of blast injury.

Traumatic brain injury and sight loss in military and veteran populations- a review

War and combat exposure pose great risks to the vision system. More recently, vision related deficiencies and impairments have become common with the increased use of powerful explosive devices and the subsequent rise in incidence of traumatic brain injury (TBI). Studies have looked at the effects of injury severity, aetiology of injury and the stage at which visual problems become apparent. There was little discrepancy found between the frequencies or types of visual dysfunctions across blast and non-blast related groups, however complete sight loss appeared to occur only in those who had a blast-related injury. Generally, the more severe the injury, the greater the likelihood of specific visual disturbances occurring, and a study found total sight loss to only occur in cases with greater severity. Diagnosis of mild TBI (mTBI) is challenging. Being able to identify a potential TBI via visual symptoms may offer a new avenue for diagnosis.

The Retinal Ganglion Cell Response to Blast-Mediated Traumatic Brain Injury Is Genetic Background Dependent

Purpose

The purpose of this study was to examine the influence of genetic background on the retinal ganglion cell (RGC) response to blast-mediated traumatic brain injury (TBI) in Jackson Diversity Outbred (J:DO), C57BL/6J and BALB/cByJ mice.

Methods

Mice were subject to one blast injury of 137 kPa. RGC structure was analyzed by optical coherence tomography (OCT), function by the pattern electroretinogram (PERG), and histologically using BRN3A antibody staining.

Results

Comparison of the change in each group from baseline for OCT and PERG was performed. There was a significant difference in the J:DOΔOCT compared to C57BL/6J mice (P = 0.004), but not compared to BALB/cByJ (P = 0.21). There was a significant difference in the variance of the ΔOCT in J:DO compared to both C57BL/6J and BALB/cByJ mice. The baseline PERG amplitude was 20.33 ± 9.32 µV, which decreased an average of −4.14 ± 12.46 µV following TBI. Baseline RGC complex + RNFL thickness was 70.92 ± 4.52 µm, which decreased an average of −1.43 ± 2.88 µm following blast exposure. There was not a significant difference in the ΔPERG between J:DO and C57BL/6J (P = 0.13), although the variances of the groups were significantly different. Blast exposure in J:DO mice results in a density change of 558.6 ± 440.5 BRN3A-positive RGCs/mm² (mean ± SD).

Conclusions

The changes in retinal outcomes had greater variance in outbred mice than what has been reported, and largely replicated herein, for inbred mice. These results demonstrate that the RGC response to blast injury is highly dependent upon genetic background.

Axonopathy precedes cell death in ocular damage mediated by blast exposure

Traumatic brain injuries (TBI) of varied types are common across all populations and can cause visual problems. For military personnel in combat settings, injuries from blast exposures (bTBI) are prevalent and arise from a myriad of different situations. To model these diverse conditions, we are one of several groups modeling bTBI using mice in varying ways. Here, we report a refined analysis of retinal ganglion cell (RGC) damage in male C57BL/6J mice exposed to a blast-wave in an enclosed chamber. Ganglion cell layer thickness, RGC density (BRN3A and RBPMS immunoreactivity), cellular density of ganglion cell layer (hematoxylin and eosin staining), and axon numbers (paraphenylenediamine staining) were quantified at timepoints ranging from 1 to 17-weeks. RNA sequencing was performed at 1-week and 5-weeks post-injury. Earliest indices of damage, evident by 1-week post-injury, are a loss of RGC marker expression, damage to RGC axons, and increase in glial markers expression. Blast exposure caused a loss of RGC somas and axons—with greatest loss occurring by 5-weeks post-injury. While indices of glial involvement are prominent early, they quickly subside as RGCs are lost. The finding that axonopathy precedes soma loss resembles pathology observed in mouse models of glaucoma, suggesting similar mechanisms.

Inflammatory Regulation of CNS Barriers After Traumatic Brain Injury: A Tale Directed by Interleukin-1

Several barriers separate the central nervous system (CNS) from the rest of the body. These barriers are essential for regulating the movement of fluid, ions, molecules, and immune cells into and out of the brain parenchyma. Each CNS barrier is unique and highly dynamic. Endothelial cells, epithelial cells, pericytes, astrocytes, and other cellular constituents each have intricate functions that are essential to sustain the brain's health. Along with damaging neurons, a traumatic brain injury (TBI) also directly insults the CNS barrier-forming cells. Disruption to the barriers first occurs by physical damage to the cells, called the primary injury. Subsequently, during the secondary injury cascade, a further array of molecular and biochemical changes occurs at the barriers. These changes are focused on rebuilding and remodeling, as well as movement of immune cells and waste into and out of the brain. Secondary injury cascades further damage the CNS barriers. Inflammation is central to healthy remodeling of CNS barriers. However, inflammation, as a secondary pathology, also plays a role in the chronic disruption of the barriers' functions after TBI. The goal of this paper is to review the different barriers of the brain, including (1) the blood-brain barrier, (2) the blood-cerebrospinal fluid barrier, (3) the meningeal barrier, (4) the blood-retina barrier, and (5) the brain-lesion border. We then detail the changes at these barriers due to both primary and secondary injury following TBI and indicate areas open for future research and discoveries. Finally, we describe the unique function of the pro-inflammatory cytokine interleukin-1 as a central actor in the inflammatory regulation of CNS barrier function and dysfunction after a TBI.

Different forms of traumatic brain injuries cause different tactile hypersensitivity profiles

ABSTRACT

Chronic complications of traumatic brain injury represent one of the greatest financial burdens and sources of suffering in the society today. A substantial number of these patients suffer from posttraumatic headache (PTH), which is typically associated with tactile allodynia. Unfortunately, this phenomenon has been understudied, in large part because of the lack of well-characterized laboratory animal models. We have addressed this gap in the field by characterizing the tactile sensory profile of 2 nonpenetrating models of PTH. We show that multimodal traumatic brain injury, administered by a jet-flow overpressure chamber that delivers a severe compressive impulse accompanied by a variable shock front and acceleration-deceleration insult, produces long-term tactile hypersensitivity and widespread sensitization. These are phenotypes reminiscent of PTH in patients, in both cephalic and extracephalic regions. By contrast, closed head injury induces only transient cephalic tactile hypersensitivity, with no extracephalic consequences. Both models show a more severe phenotype with repetitive daily injury for 3 days, compared with either 1 or 3 successive injuries in a single day, providing new insight into patterns of injury that may place patients at a greater risk of developing PTH. After recovery from transient cephalic tactile hypersensitivity, mice subjected to closed head injury demonstrate persistent hypersensitivity to established migraine triggers, including calcitonin gene-related peptide and sodium nitroprusside, a nitric oxide donor. Our results offer the field new tools for studying PTH and preclinical support for a pathophysiologic role of calcitonin gene-related peptide in this condition.

Antinociceptive effect of intrathecal P7C3 via GABA in a rat model of inflammatory pain

The recently identified molecule P7C3 has been highlighted in the field of pain research. We examined the effect of intrathecal P7C3 in tissue injury pain evoked by formalin injection and determined the role of the GABA system in the activity of P7C3 at the spinal level. Male Sprague-Dawley rats with intrathecal catheters implanted for experimental drug delivery were studied. The effects of intrathecal P7C3 and nicotinamide phosphoribosyltransferase (NAMPT) administered 10 min before the formalin injection were examined. Animals were pretreated with bicuculline, a GABA-A receptor antagonist; saclofen, a GABA-B receptor antagonist; L-allylglycine, a glutamic acid decarboxylase (GAD) blocker; and CHS 828, an NAMPT inhibitor; to observe involvement in the effects of P7C3. The effects of P7C3 alone and the mixture of P7C3 with GABA receptor antagonists on KCl-induced calcium transients were examined in rat dorsal root ganglion (DRG) neurons. The expression of GAD and the concentration of GABA in the spinal cord were evaluated. Intrathecal P7C3 and NAMPT produced an antinociceptive effect in the formalin test. Intrathecal bicuculline, saclofen, L-allylglycine, and CHS 828 reversed the antinociception of P7C3 in both phases. P7C3 decreased the KCl-induced calcium transients in DRG neurons. Both bicuculline and saclofen reversed the blocking effect of P7C3. The levels of GAD expression and GABA concentration decreased after formalin injection and were increased by P7C3. These results suggest that P7C3 increases GAD activity and then increases the GABA concentration in the spinal cord, which in turn may act on GABA receptors causing the antinociceptive effect against pain evoked by formalin injection.

Blast mild traumatic brain injury is associated with increased myopia and chronic convergence insufficiency

While chronic visual symptom complaints are common among Veterans with a history of mild traumatic brain injury (mTBI), research is still ongoing to characterize the pattern of visual deficits that is most strongly associated with mTBI and specifically, the impact of blast-related mTBI on visual functioning. One area that has not been well explored is the potential impact of blast mTBI on refractive error. While myopic shifts have been documented following head injuries in civilian populations, posttraumatic myopic shifts have not been explored in participants with military mTBI. This study investigated the impact of blast mTBIs on a range of visual function measures including distance acuity and refractive error, in a well-characterized cohort of thirty-one Post-9/11 veterans for whom detailed clinical interviews regarding military and TBI history were available. Seventeen participants had a history of blast-related mTBI (blast mTBI + group) while 14 did not (blast mTBI- group). Results show an increased frequency of convergence insufficiency and myopia in the blast mTBI + group relative to the blast mTBI- group. Linear regression analyses further show that deficits in distance acuity and refractive error are associated with the number of blast mTBIs during military service but not the number of non-blast mTBIs or the number of lifetime non-blast TBIs and cannot be accounted for by PTSD. These results are consistent with long-lasting damage following blast mTBI to subcortical visual structures that support both vergence movements and the accommodative functions needed to see clearly objects at varying distances.

Sex Does Not Influence Visual Outcomes After Blast-Mediated Traumatic Brain Injury but IL-1 Pathway Mutations Confer Partial Rescue

Purpose

In a mouse model of blast-mediated traumatic brain injury (bTBI), interleukin-1 (IL-1)-pathway components were tested as potential therapeutic targets for bTBI-mediated retinal ganglion cell (RGC) dysfunction. Sex was also evaluated as a variable for RGC outcomes post-bTBI.

Methods

Male and female mice with null mutations in genes encoding IL-1α, IL-1β, or IL-1RI were compared to C57BL/6J wild-type (WT) mice after exposure to three 20-psi blast waves given at an interblast interval of 1 hour or to mice receiving sham injury. To determine if genetic blockade of IL-1α, IL-1β, or IL-1RI could prevent damage to RGCs, the function and structure of these cells were evaluated by pattern electroretinogram and optical coherence tomography, respectively, 5 weeks following blast or sham exposure. RGC survival was also quantitatively assessed via immunohistochemical staining of BRN3A at the completion of the study.

Results

Our results showed that male and female WT mice had a similar response to blast-induced retinal injury. Generally, constitutive deletion of IL-1α, IL-1β, or IL-1RI did not provide full protection from the effects of bTBI on visual outcomes; however, injured WT mice had significantly worse visual outcomes compared to the injured genetic knockout mice.

Conclusions

Sex does not affect RGC outcomes after bTBI. The genetic studies suggest that deletion of these IL-1 pathway components confers some protection, but global deletion from birth did not result in a complete rescue.

Visual Outcomes in Experimental Rodent Models of Blast-Mediated Traumatic Brain Injury

Blast-mediated traumatic brain injuries (bTBI) cause long-lasting physical, cognitive, and psychological disorders, including persistent visual impairment. No known therapies are currently utilized in humans to lessen the lingering and often serious symptoms. With TBI mortality decreasing due to advancements in medical and protective technologies, there is growing interest in understanding the pathology of visual dysfunction after bTBI. However, this is complicated by numerous variables, e.g., injury location, severity, and head and body shielding. This review summarizes the visual outcomes observed by various, current experimental rodent models of bTBI, and identifies data showing that bTBI activates inflammatory and apoptotic signaling leading to visual dysfunction. Pharmacologic treatments blocking inflammation and cell death pathways reported to alleviate visual deficits in post-bTBI animal models are discussed. Notably, techniques for assessing bTBI outcomes across exposure paradigms differed widely, so we urge future studies to compare multiple models of blast injury, to allow data to be directly compared.

Reducing acetylated tau is neuroprotective in brain injury

Traumatic brain injury (TBI) is the largest non-genetic, non-aging related risk factor for Alzheimer's disease (AD). We report here that TBI induces tau acetylation (ac-tau) at sites acetylated also in human AD brain. This is mediated by S-nitrosylated-GAPDH, which simultaneously inactivates Sirtuin1 deacetylase and activates p300/CBP acetyltransferase, increasing neuronal ac-tau. Subsequent tau mislocalization causes neurodegeneration and neurobehavioral impairment, and ac-tau accumulates in the blood. Blocking GAPDH S-nitrosylation, inhibiting p300/CBP, or stimulating Sirtuin1 all protect mice from neurodegeneration, neurobehavioral impairment, and blood and brain accumulation of ac-tau after TBI. Ac-tau is thus a therapeutic target and potential blood biomarker of TBI that may represent pathologic convergence between TBI and AD. Increased ac-tau in human AD brain is further augmented in AD patients with history of TBI, and patients receiving the p300/CBP inhibitors salsalate or diflunisal exhibit decreased incidence of AD and clinically diagnosed TBI.

Characterization of the Jet-Flow Overpressure Model of Traumatic Brain Injury in Mice

The jet-flow overpressure chamber (OPC) has been previously reported as a model of blast-mediated traumatic brain injury (bTBI). However, rigorous characterization of the features of this injury apparatus shows that it fails to recapitulate exposure to an isolated blast wave. Through combined experimental and computational modeling analysis of gas-dynamic flow conditions, we show here that the jet-flow OPC produces a collimated high-speed jet flow with extreme dynamic pressure that delivers a severe compressive impulse. Variable rupture dynamics of the diaphragm through which the jet flow originates also generate a weak and infrequent shock front. In addition, there is a component of acceleration-deceleration injury to the head as it is agitated in the headrest. Although not a faithful model of free-field blast exposure, the jet-flow OPC produces a complex multi-modal model of TBI that can be useful in laboratory investigation of putative TBI therapies and fundamental neurophysiological processes after brain injury.

Antibodies Against Lysophosphatidic Acid Protect Against Blast-Induced Ocular Injuries

Exposure to blast overpressure waves is implicated as the major cause of ocular injuries and resultant visual dysfunction in veterans involved in recent combat operations. No effective therapeutic strategies have been developed so far for blast-induced ocular dysfunction. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells, and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid have been reported to increase acutely in patients with traumatic brain injury (TBI) as well as in a controlled cortical impact (CCI) TBI model in mice. In the present study, we have evaluated the efficacy of a single intravenous administration of a monoclonal LPA antibody (25 mg/kg) given at 1 h post-blast for protection against injuries to the retina and associated ocular dysfunctions. Our results show that a single 19 psi blast exposure significantly increased the levels of several species of LPA in blood plasma at 1 and 4 h post-blast. The anti-LPA antibody treatment significantly decreased glial cell activation and preserved neuronal cell morphology in the retina on day 8 after blast exposure. Optokinetic measurements indicated that anti-LPA antibody treatment significantly improved visual acuity in both eyes on days 2 and 6 post-blast exposure. Anti-LPA antibody treatment significantly increased rod photoreceptor and bipolar neuronal cell signaling in both eyes on day 7 post-blast exposure. These results suggest that blast exposure triggers release of LPAs, which play a major role promoting blast-induced ocular injuries, and that a single early administration of anti-LPA antibodies provides significant protection.

P7C3-A20 treatment one year after TBI in mice repairs the blood-brain barrier, arrests chronic neurodegeneration, and restores cognition

Chronic neurodegeneration, a major cause of the long-term disabilities that afflict survivors of traumatic brain injury (TBI), is linked to an increased risk for late-life neurodegenerative disorders, including Alzheimer’s disease, Parkinson’s disease, vascular dementia, and chronic traumatic encephalopathy. Here, we report on the restoration of blood–brain barrier (BBB) structure and function by P7C3-A20 when administered 12 mo after TBI. This pharmacotherapy was associated with cessation of chronic neurodegeneration and recovery of normal cognitive function, benefits that persisted long after treatment cessation. Pharmacologic renewal of BBB integrity may thus provide a new treatment option for patients who have suffered a remote TBI, or other neurological conditions associated with BBB deterioration.

Chronic neurodegeneration in survivors of traumatic brain injury (TBI) is a major cause of morbidity, with no effective therapies to mitigate this progressive and debilitating form of nerve cell death. Here, we report that pharmacologic restoration of the blood–brain barrier (BBB), 12 mo after murine TBI, is associated with arrested axonal neurodegeneration and cognitive recovery, benefits that persisted for months after treatment cessation. Recovery was achieved by 30 d of once-daily administration of P7C3-A20, a compound that stabilizes cellular energy levels. Four months after P7C3-A20, electron microscopy revealed full repair of TBI-induced breaks in cortical and hippocampal BBB endothelium. Immunohistochemical staining identified additional benefits of P7C3-A20, including restoration of normal BBB endothelium length, increased brain capillary pericyte density, increased expression of BBB tight junction proteins, reduced brain infiltration of immunoglobulin, and attenuated neuroinflammation. These changes were accompanied by cessation of TBI-induced chronic axonal degeneration. Specificity for P7C3-A20 action on the endothelium was confirmed by protection of cultured human brain microvascular endothelial cells from hydrogen peroxide-induced cell death, as well as preservation of BBB integrity in mice after exposure to toxic levels of lipopolysaccharide. P7C3-A20 also protected mice from BBB degradation after acute TBI. Collectively, our results provide insights into the pathophysiologic mechanisms behind chronic neurodegeneration after TBI, along with a putative treatment strategy. Because TBI increases the risks of other forms of neurodegeneration involving BBB deterioration (e.g., Alzheimer’s disease, Parkinson’s disease, vascular dementia, chronic traumatic encephalopathy), P7C3-A20 may have widespread clinical utility in the setting of neurodegenerative conditions.

Assessment of necroptosis in the retina in a repeated primary ocular blast injury mouse model

Primary blast injury (caused by the initial rapid increase in pressure following an explosive blast) to the retina and optic nerve (ON) causes progressive visual loss and neurodegeneration. Military personnel are exposed to multiple low-overpressure blast waves, which may be in quick succession, such as during breacher training or in combat. We investigated the necroptotic cell death pathway in the retina in a mouse repeated primary ocular blast injury (rPBI) model using immunohistochemistry. We further evaluated whether intravitreal injections of a potent necroptosis inhibitor, Necrostatin-1s (Nec-1s), protects the retina and ON axons by retinal ganglion cells (RGC) counts, ON axonal counting and optical coherence tomography (OCT) analysis of vitreous haze. Receptor interacting protein kinase (RIPK) 3, increased in the inner plexiform layer 2 days post injury (dpi) and persisted until 14 dpi, whilst RIPK1 protein expression did not change after injury. The number of degenerating ON axons was increased at 28 dpi but there was no evidence of a reduction in the number of intact ON axons or RNA-binding protein with multiple splicing (RBPMS)⁺ RGC in the retina by 28 dpi in animals not receiving any intravitreal injections. But, when intravitreal injections (vehicle or Nec-1s) were given there was a significant reduction in RBPMS⁺ RGC numbers, suggesting that rPBI with intraocular injections is damaging to RGC. There were fewer RGC lost after Nec-1s than vehicle injection, but there was no effect of Nec-1s or vehicle treatment on the number of degenerating axons. OCT analysis demonstrated no effect of rPBI on vitreous haze, but intravitreal injection combined with rPBI increased vitreous haze (P = 0.004). Whilst necroptosis may be an active cell death signalling pathway after rPBI, its inhibition did not prevent cell death, and intravitreal injections in combination with rPBI increased vitreous inflammation and reduced RBPMS⁺ RGC numbers, implying intravitreal injection is not an ideal method for drug delivery after rPBI.

Modulation of Post-Traumatic Immune Response Using the IL-1 Receptor Antagonist Anakinra for Improved Visual Outcomes

The purpose of this study was to characterize acute changes in inflammatory pathways in the mouse eye after blast-mediated traumatic brain injury (bTBI) and to determine whether modulation of these pathways could protect the structure and function of retinal ganglion cells (RGC). The bTBI was induced in C57BL/6J male mice by exposure to three 20 psi blast waves directed toward the head with the body shielded, with an inter-blast interval of one hour. Acute cytokine expression in retinal tissue was measured through reverse transcription-quantitative polymerase chain reaction (RT-qPCR) four hours post-blast. Increased retinal expression of interleukin (lL)-1β, IL-1α, IL-6, and tumor necrosis factor (TNF)α was observed in bTBI mice exposed to blast when compared with shams, which was associated with activation of microglia and macroglia reactivity, assessed via immunohistochemistry with ionized calcium binding adaptor molecule 1 and glial fibrillary acidic protein, respectively, one week post-blast. Blockade of the IL-1 pathway was accomplished using anakinra, an IL-1RI antagonist, administered intra-peritoneally for one week before injury and continuing for three weeks post-injury. Retinal function and RGC layer thickness were evaluated four weeks post-injury using pattern electroretinogram (PERG) and optical coherence tomography (OCT), respectively. After bTBI, anakinra treatment resulted in a preservation of RGC function and RGC structure when compared with saline treated bTBI mice. Optic nerve integrity analysis demonstrated a trend of decreased damage suggesting that IL-1 blockade also prevents axonal damage after blast. Blast exposure results in increased retinal inflammation including upregulation of pro-inflammatory cytokines and activation of resident microglia and macroglia. This may explain partially the RGC loss we observed in this model, as blockade of the acute inflammatory response after injury with the IL-1R1 antagonist anakinra resulted in preservation of RGC function and RGC layer thickness.

Identification of chronic brain protein changes and protein targets of serum auto-antibodies after blast-mediated traumatic brain injury

In addition to needing acute emergency management, blast-mediated traumatic brain injury (TBI) is also a chronic disorder with delayed-onset symptoms that manifest and progress over time. While the immediate consequences of acute blast injuries are readily apparent, chronic sequelae are harder to recognize. Indeed, the identification of individuals with mild-TBI or TBI-induced symptoms is greatly impaired in large part due to the lack of objective and robust biomarkers. The purpose of this study was to address these need by identifying candidates for serum-based biomarkers of blast TBI, and also to identify unique or differentially regulated protein expression in the thalamus in C57BL/6J mice exposed to blast using high throughput qualitative screens of protein expression. To identify thalamic proteins differentially or uniquely associated with blast exposure, we utilized an antibody-based affinity-capture strategy (referred to as "proteomics-based analysis of depletomes"; PAD) to deplete thalamic lysates from blast-treated mice of endogenous thalamic proteins also found in control mice. Analysis of this "depletome" detected 75 unique proteins, many with associations to the myelin sheath. To identify blast-associated proteins eliciting production of circulating autoantibodies, serum antibodies of blast-treated mice were immobilized, and their immunogens subsequently identified by proteomic analysis of proteins specifically captured following incubation with thalamic lysates (a variant of a strategy referred to as "proteomics-based expression library screening"; PELS). This analysis identified 46 blast-associated immunogenic proteins, including 6 shared in common with the PAD analysis (ALDOA, PHKB, HBA-A1, DPYSL2, SYN1, and CKB). These proteins and their autoantibodies are appropriate for further consideration as biomarkers of blast-mediated TBI.

Blast-Mediated Traumatic Brain Injury Exacerbates Retinal Damage and Amyloidosis in the APPswePSENd19e Mouse Model of Alzheimer's Disease

Purpose

Traumatic brain injury (TBI) is a risk factor for developing chronic neurodegenerative conditions including Alzheimer's disease (AD). The purpose of this study was to examine chronic effects of blast TBI on retinal ganglion cells (RGC), optic nerve, and brain amyloid load in a mouse model of AD amyloidosis.

Methods

Transgenic (TG) double-mutant APPswePSENd19e (APP/PS1) mice and nontransgenic (Non-TG) littermates were exposed to a single blast TBI (20 psi) at age 2 to 3 months. RGC cell structure and function was evaluated 2 months later (average age at endpoint = 4.5 months) using pattern electroretinogram (PERG), optical coherence tomography (OCT), and the chromatic pupil light reflex (cPLR), followed by histologic analysis of retina, optic nerve, and brain amyloid pathology.

Results

APP/PS1 mice exposed to blast TBI (TG-Blast) had significantly lower PERG and cPLR responses 2 months after injury compared to preblast values and compared to sham groups of APP/PS1 (TG-Sham) and nontransgenic (Non-TG-Sham) mice as well as nontransgenic blast-exposed mice (Non-TG-Blast). The TG-Blast group also had significantly thinner RGC complex and more optic nerve damage compared to all groups. No amyloid-β (Aβ) deposits were detected in retinas of APP/PS1 mice; however, increased amyloid precursor protein (APP)/Aβ-immunoreactivity was seen in TG-Blast compared to TG-Sham mice, particularly near blood vessels. TG-Blast and TG-Sham groups exhibited high variability in pathology severity, with a strong, but not statistically significant, trend for greater cerebral cortical Aβ plaque load in the TG-Blast compared to TG-Sham group.

Conclusions

When combined with a genetic susceptibility for developing amyloidosis of AD, blast TBI exposure leads to earlier RGC and optic nerve damage associated with modest but detectable increase in cerebral cortical Aβ pathology. These findings suggest that genetic risk factors for AD may increase the sensitivity of the retina to blast-mediated damage.

Blast Preconditioning Protects Retinal Ganglion Cells and Reveals Targets for Prevention of Neurodegeneration Following Blast-Mediated Traumatic Brian Injury

Purpose

The purpose of this study was to examine the effect of multiple blast exposures and blast preconditioning on the structure and function of retinal ganglion cells (RGCs), to identify molecular pathways that contribute to RGC loss, and to evaluate the role of kynurenine-3-monooxygenase (KMO) inhibition on RGC structure and function.

Methods

Mice were subjected to sham blast injury, one single blast injury, or three blast injuries separated by either 1 hour or 1 week, using a blast intensity of 20 PSI. To examine the effect of blast preconditioning, mice were subjected to sham blast injury, one single 20-PSI injury, or three blast injuries separated by 1 week (5 PSI, 5 PSI, 20 PSI and 5 PSI, 5 PSI, 5 PSI). RGC structure was analyzed by optical coherence tomography (OCT) and function was analyzed by the pattern electroretinogram (PERG). BRN3A-positive cells were quantified to determine RGC density. RNA-seq analysis was used to identify transcriptional changes between groups.

Results

Analysis of mice with multiple blast exposures of 20 PSI revealed no significant differences compared to one 20-pounds per square inch (PSI) exposure using OCT, PERG, or BRN3A cell counts. Analysis of mice exposed to two preconditioning 5-PSI blasts prior to one 20-PSI blast showed preservation of RGC structure and function. RNA-seq analysis of the retina identified multiple transcriptomic changes between conditions. Pharmacologic inhibition of KMO preserved RGC responses compared to vehicle-treated mice.

Conclusions

Preconditioning protects RGC from blast injury. Protective effects appear to involve changes in KMO activity, whose inhibition is also protective.

Vision impairment after traumatic brain injury: present knowledge and future directions

Traumatic brain injury (TBI) is a major cause of mortality and morbidity in the USA as well as in the world. As a result of TBI, the visual system is also affected often causing complete or partial visual loss, which in turn affects the quality of life. It may also lead to ocular motor dysfunction, defective accommodation, and impaired visual perception. As a part of the therapeutic strategy, early rehabilitative optometric intervention is important. Orthoptic therapy, medication, stem cell therapy, motor and attention trainings are the available treatment options. Gene therapy is one of the most promising emerging strategies. Use of state-of-the-art nanomedicine approaches to deliver drug(s) and/or gene(s) might enhance the therapeutic efficacy of the present and future modalities. More research is needed in these fields to improve the outcome of this debilitating condition. This review focuses on different visual pathologies caused by TBI, advances in pre-clinical and clinical research, and available treatment options.

Neuroprotective Efficacy of a Sigma 2 Receptor/TMEM97 Modulator (DKR-1677) after Traumatic Brain Injury

Compounds targeting the sigma 2 receptor, which we recently cloned and showed to be identical with transmembrane protein 97 (σ2R/TMEM97), are broadly applicable therapeutic agents currently in clinical trials for imaging in breast cancer and for treatment of Alzheimer's disease and schizophrenia. These promising applications coupled with our previous observation that the σ2R/TMEM97 modulator SAS-0132 has neuroprotective attributes and improves cognition in wild-type mice suggests that modulating σ2R/TMEM97 may also have therapeutic benefits in other neurodegenerative conditions such as traumatic brain injury (TBI). Herein, we report that DKR-1677, a novel derivative of SAS-0132 with increased affinity and selectivity for σ2R/Tmem97 ( K_i = 5.1 nM), is neuroprotective after blast-induced and controlled cortical impact (CCI) TBI in mice. Specifically, we discovered that treatment with DKR-1677 decreases axonal degeneration after blast-induced TBI and enhances survival of cortical neurons and oligodendrocytes after CCI injury. Furthermore, treatment with DKR-1677 preserves cognition in the Morris water maze after blast TBI. Our results support an increasingly broad role for σ2R/Tmem97 modulation in neuroprotection and suggest a new approach for treating patients suffering from TBI.

Benefits of Enhancing Nicotinamide Adenine Dinucleotide Levels in Damaged or Diseased Nerve Cells

Three unbiased lines of research have commonly pointed to the benefits of enhanced levels of nicotinamide adenine dinucleotide (NAD⁺) to diseased or damaged neurons. Mice carrying a triplication of the gene encoding the culminating enzyme in NAD⁺ salvage from nicotinamide, NMNAT, are protected from a variety of insults to axons. Protection from Wallerian degeneration of axons is also observed in flies and mice bearing inactivating mutations in the SARM1 gene. Functional studies of the SARM1 gene product have revealed the presence of an enzymatic activity directed toward the hydrolysis of NAD⁺ Finally, an unbiased drug screen performed in living mice led to the discovery of a neuroprotective chemical designated P7C3. Biochemical studies of the P7C3 chemical show that it can enhance recovery of NAD⁺ from nicotinamide by activating NAMPT, the first enzyme in the salvage pathway. In combination, these three unrelated research endeavors offer evidence of the benefits of enhanced NAD⁺ levels to damaged neurons.

P7C3-A20 neuroprotection is independent of Wallerian degeneration in primary neuronal culture

The antiapoptotic, neuroprotective compound P7C3-A20 reduces neurological deficits when administered to murine in-vivo models of traumatic brain injury. P7C3-A20 is thought to exert its activity through small-molecule activation of the enzyme nicotinamide phosphoribosyltransferase. This enzyme converts nicotinamide to nicotinamide mononucleotide, the precursor to nicotinamide adenine dinucleotide synthesis. Alterations to this bioenergetic pathway have been shown to induce Wallerian degeneration (WD) of the distal neurite following injury. This study aimed to establish whether P7C3-A20, through induction of nicotinamide phosphoribosyltransferase activity, would affect the rate of WD. The model systems used were dissociated primary cortical neurons, dissociated superior cervical ganglion neurons and superior cervical ganglion explants. P7C3-A20 failed to show any protection against WD induced by neurite transection or vincristine administration. Furthermore, there was a concentration-dependent neurotoxicity. These findings are important in understanding the mechanism by which P7C3-A20 mediates its effects - a key step before moving to human clinical trials.

(-)-P7C3-S243 Protects a Rat Model of Alzheimer's Disease From Neuropsychiatric Deficits and Neurodegeneration Without Altering Amyloid Deposition or Reactive Glia

BACKGROUND

In addition to cognitive deficits, Alzheimer's disease (AD) is associated with other neuropsychiatric symptoms, including severe depression. Indeed, depression often precedes cognitive deficits in patients with AD. Unfortunately, the field has seen only minimal therapeutic advances, underscoring the critical need for new treatments. P7C3 aminopropyl carbazoles promote neuronal survival by enhancing nicotinamide adenine dinucleotide flux in injured neurons. Neuroprotection with P7C3 compounds has been demonstrated in preclinical models of neurodegeneration by virtue of promoting neuronal survival independently of early disease-specific pathology, resulting in protection from cognitive deficits and depressive-like behavior. We hypothesize that P7C3 compounds might be uniquely applicable to patients with AD, given the comorbid presentation of depression and cognitive deficits.

METHODS

Aging male and female wild-type and TgF344-AD rats, a well-characterized preclinical AD model, were administered (-)-P7C3-S243 daily for 9 and 18 months, beginning at 6 months of age. Behavioral phenotypes related to cognition and depression were assessed at 15 and 24 months, and brain pathology and biochemistry were assessed at 24 months.

RESULTS

(-)-P7C3-S243 safely protected aging male and female wild-type and TgF344-AD rats from cognitive deficits and depressive-like behavior. Depressive-like behavior occurred earlier than cognitive deficits in TgF344-AD rats, consistent with AD in many patients. Treatment with (-)-P7C3-S243 blocked neurodegeneration in TgF344-AD rats, without altering amyloid deposition or indicators of neuroinflammation.

CONCLUSIONS

Neuronal cell death-specific treatment approaches, such as P7C3 compounds, may represent a new treatment approach for patients experiencing the combination of cognitive deficits and depression associated with AD.

Neuroprotective efficacy of P7C3 compounds in primate hippocampus

There is a critical need for translating basic science discoveries into new therapeutics for patients suffering from difficult to treat neuropsychiatric and neurodegenerative conditions. Previously, a target-agnostic in vivo screen in mice identified P7C3 aminopropyl carbazole as capable of enhancing the net magnitude of postnatal neurogenesis by protecting young neurons from death. Subsequently, neuroprotective efficacy of P7C3 compounds in a broad spectrum of preclinical rodent models has also been observed. An important next step in translating this work to patients is to determine whether P7C3 compounds exhibit similar efficacy in primates. Adult male rhesus monkeys received daily oral P7C3-A20 or vehicle for 38 weeks. During weeks 2-11, monkeys received weekly injection of 5'-bromo-2-deoxyuridine (BrdU) to label newborn cells, the majority of which would normally die over the following 27 weeks. BrdU+ cells were quantified using unbiased stereology. Separately in mice, the proneurogenic efficacy of P7C3-A20 was compared to that of NSI-189, a proneurogenic drug currently in clinical trials for patients with major depression. Orally-administered P7C3-A20 provided sustained plasma exposure, was well-tolerated, and elevated the survival of hippocampal BrdU+ cells in nonhuman primates without adverse central or peripheral tissue effects. In mice, NSI-189 was shown to be pro-proliferative, and P7C3-A20 elevated the net magnitude of hippocampal neurogenesis to a greater degree than NSI-189 through its distinct mechanism of promoting neuronal survival. This pilot study provides evidence that P7C3-A20 safely protects neurons in nonhuman primates, suggesting that the neuroprotective efficacy of P7C3 compounds is likely to translate to humans as well.

GSK-3 inhibition through GLP-1R allosteric activation mediates the neurogenesis promoting effect of P7C3 after cerebral ischemic/reperfusional injury in mice

An aminopropyl carbazole compound, P7C3, has been shown to be a potent neurogenesis promoting agent; however, its fundamental signaling action has yet to be elucidated. A cerebral ischemic/reperfusional (CI/R) injury model in mice was implemented to elucidate the neuronal protective mechanism(s) of P7C3. Treating CI/R mice using P7C3 (50-100 μg/kg, i.v.) significantly improved tracking distance and walking behavior, and reduced brain damage. Specifically, P7C3 promoted the expression of neurogenesis-associated proteins, including doublecortin, beta tubulin III (β-tub3), adam11 and adamts20, near the peri-infarct cortex, accompanied by glycogen synthase kinase 3 (GSK-3) inhibition and β-catenin upregulation. The application of a specific inhibitor against glucagon-like peptide 1 receptor (GLP-1R), exendin(9-39), revealed that the beneficial effects of P7C3 involved triggering the activation of GLP-1R-associated PKA/Akt signaling. P7C3 elicited the GLP-1R-dependent intracellular cAMP increment and the insulin secretion in cellular models. Surface plasmon resonance assay of P7C3 showed a Kd value of 0.53 μM for GLP-1R binding, and the docking of P7C3 to the putative active site on GLP-1R was successfully predicted by molecular modeling. Our findings indicate that P7C3 promotes the expression of neurogenesis proteins by activation of the cAMP/PKA-dependent and Akt/GSK3-associated β-catenin through positive allosteric stimulation of GLP-1R. Within the P7C3 class of neuroprotective molecules, this mechanism appears to be unique to the prototypical P7C3 molecule, as other active derivatives such as P7C2-A20 and P7C3-S243 they do not engage this same pathway and have been shown to work by nicotinamide phosphoribosyltransferase (NAMPT) stimulation.

Long-Term Functional and Structural Consequences of Primary Blast Overpressure to the Eye

Acoustic blast overpressure (ABO) injury in military personnel and civilians is often accompanied by delayed visual deficits. However, most animal model studies dealing with blast-induced visual defects have focused on short-term (≤1 month) changes. Here, we evaluated long-term (≤8 months) retinal structure and function deficits in rats with ABO injury. Adult male Long-Evans rats were subjected to ABO from a single blast (approximately 190 dB SPL, ∼63 kPa, @80 psi), generated by a shock tube device. Retinal function (electroretinography; ERG), visual function (optomotor response), retinal thickness (spectral domain-optical coherence tomography; SD-OCT), and spatial cognition/exploratory motor behavior (Y-maze) were measured at 2, 4, 6, and 8 months post-blast. Immunohistochemical analysis of glial fibrillary acidic protein (GFAP) in retinal sections was performed at 8 months post-blast. Electroretinogram a- and b-waves, oscillatory potentials, and flicker responses showed greater amplitudes with delayed implicit times in both eyes of blast-exposed animals, relative to controls. Contrast sensitivity (CS) was reduced in both eyes of blast-exposed animals, whereas spatial frequency (SF) was decreased only in ipsilateral eyes, relative to controls. Total retinal thickness was greater in both eyes of blast-exposed animals, relative to controls, due to increased thickness of several retinal layers. Age, but not blast exposure, altered Y-maze outcomes. GFAP was greatly increased in blast-exposed retinas. ABO exposure resulted in visual and retinal changes that persisted up to 8 months post-blast, mimicking some of the visual deficits observed in human blast-exposed patients, thereby making this a useful model to study mechanisms of injury and potential treatments.

Therapeutic Potential of NAD-Boosting Molecules: The In Vivo Evidence

Nicotinamide adenine dinucleotide (NAD), the cell's hydrogen carrier for redox enzymes, is well known for its role in redox reactions. More recently, it has emerged as a signaling molecule. By modulating NAD⁺-sensing enzymes, NAD⁺ controls hundreds of key processes from energy metabolism to cell survival, rising and falling depending on food intake, exercise, and the time of day. NAD⁺ levels steadily decline with age, resulting in altered metabolism and increased disease susceptibility. Restoration of NAD⁺ levels in old or diseased animals can promote health and extend lifespan, prompting a search for safe and efficacious NAD-boosting molecules that hold the promise of increasing the body's resilience, not just to one disease, but to many, thereby extending healthy human lifespan.

Visual problems associated with traumatic brain injury

Traumatic brain injury (TBI) and its associated concussion are major causes of disability and death. All ages can be affected but children, young adults and the elderly are particularly susceptible. A decline in mortality has resulted in many more individuals living with a disability caused by TBI including those affecting vision. This review describes: (1) the major clinical and pathological features of TBI; (2) the visual signs and symptoms associated with the disorder; and (3) discusses the assessment of quality of life and visual rehabilitation of the patient. Defects in primary vision such as visual acuity and visual fields, eye movement including vergence, saccadic and smooth pursuit movements, and in more complex aspects of vision involving visual perception, motion vision ('akinopsia'), and visuo-spatial function have all been reported in TBI. Eye movement dysfunction may be an early sign of TBI. Hence, TBI can result in a variety of visual problems, many patients exhibiting multiple visual defects in combination with a decline in overall health. Patients with chronic dysfunction following TBI may require occupational, vestibular, cognitive and other forms of physical therapy. Such patients may also benefit from visual rehabilitation, including reading-related oculomotor training and the prescribing of spectacles with a variety of tints and prism combinations.

Pyridine Dinucleotides from Molecules to Man

SIGNIFICANCE

Pyridine dinucleotides, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), were discovered more than 100 years ago as necessary cofactors for fermentation in yeast extracts. Since that time, these molecules have been recognized as fundamental players in a variety of cellular processes, including energy metabolism, redox homeostasis, cellular signaling, and gene transcription, among many others. Given their critical role as mediators of cellular responses to metabolic perturbations, it is unsurprising that dysregulation of NAD and NADP metabolism has been associated with the pathobiology of many chronic human diseases. Recent Advances: A biochemistry renaissance in biomedical research, with its increasing focus on the metabolic pathobiology of human disease, has reignited interest in pyridine dinucleotides, which has led to new insights into the cell biology of NAD(P) metabolism, including its cellular pharmacokinetics, biosynthesis, subcellular localization, and regulation. This review highlights these advances to illustrate the importance of NAD(P) metabolism in the molecular pathogenesis of disease.

CRITICAL ISSUES

Perturbations of NAD(H) and NADP(H) are a prominent feature of human disease; however, fundamental questions regarding the regulation of the absolute levels of these cofactors and the key determinants of their redox ratios remain. Moreover, an integrated topological model of NAD(P) biology that combines the metabolic and other roles remains elusive.

FUTURE DIRECTIONS

As the complex regulatory network of NAD(P) metabolism becomes illuminated, sophisticated new approaches to manipulating these pathways in specific organs, cells, or organelles will be developed to target the underlying pathogenic mechanisms of disease, opening doors for the next generation of redox-based, metabolism-targeted therapies. Antioxid. Redox Signal. 28, 180-212.

An insight into the vision impairment following traumatic brain injury

Traumatic brain injury (TBI) is one of the major cause of morbidity and mortality and it affects more than 1.7 million Americans each year. Depending on its location and severity, TBI leads to structural and functional damage in several parts of the brain such as cranial nerves, optic nerve tract or other circuitry involved in vision, and occipital lobe. As a result, the function associated with vision processing and perception are significantly affected and cause blurred vision, double vision, decreased peripheral vision and blindness. In this mini-review, we will focus the recent progress made to understand the pathology and underlying cellular/molecular mechanisms involved in the impairment of the integrity of visual systems following TBI.