Complement C3 Inhibition Modulates Neurodegeneration in Chronic Traumatic Brain Injury

Increased Pan-Type, A1-Type, and A2-Type Astrocyte Activation and Upstream Inflammatory Markers Are Induced by the P2X7 Receptor

This study asked whether the P2X7 receptor was necessary and sufficient to trigger astrocyte polarization into neuroinflammatory activation states. Intravitreal injection of agonist BzATP increased gene expression of pan-astrocyte activation markers Gfap, Steap4, and Vim and A1-type astrocyte activation markers C3, Serping1, and H2T23, but also the Cd14 and Ptx3 genes usually associated with the A2-type astrocyte activation state and Tnfa, IL1a, and C1qa, assumed to be upstream of astrocyte activation in microglia. Correlation analysis of gene expression suggested the P2X7 receptor induced a mixed A1/A2-astrocyte activation state, although A1-state genes like C3 increased the most. A similar pattern of mixed glial activation genes occurred one day after intraocular pressure (IOP) was elevated in wild-type mice, but not in P2X7-/- mice, suggesting the P2X7 receptor is necessary for the glial activation that accompanies IOP elevation. In summary, this study suggests stimulation of the P2X7R is necessary and sufficient to trigger the astrocyte activation in the retina following IOP elevation, with a rise in markers for pan-, A1-, and A2-type astrocyte activation. The P2X7 receptor is expressed on microglia, optic nerve head astrocytes, and retinal ganglion cells (RGCs) in the retina, and can be stimulated by the mechanosensitive release of ATP that accompanies IOP elevation. Whether the P2X7 receptor connects this mechanosensitive ATP release to microglial and astrocyte polarization in glaucoma remains to be determined.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Circadian disruption and psychostimulants dysregulates plasma acute-phase proteins and circulating cell-free mitochondrial DNA

Background

Previous studies have indicated a close link between the inflammatory response, exacerbated by circadian disruption and psychostimulants such as cocaine and methamphetamine (METH). Indicators of this inflammation include cortisol and acute-phase proteins (APPs) like C-reactive protein (CRP), complement C3 (C3), and serum amyloid A (SAA). The connection between these inflammation markers and circulating mitochondrial DNA (mtDNA) has been gaining attention. However, the specific influence of cocaine and METH on APP, cortisol, and mtDNA levels in mice with disturbed circadian rhythm has yet to be explored, which is the main aim of this research.

Methods

In our study, we employed 10-12-week-old male C57BL/6J mice, which underwent an imposed 6-h phase advance every six days for a total of eight cycles. This process led to the formation of mice with disrupted circadian rhythm and sleep disorders (CRSD). We administered 11 dosages of cocaine and METH 15 mg/kg and 20 mg/kg, respectively to these CRSD mice over the course of 22 days. Quantitative assessments of CRP, C3, SAA, cortisol, and cell-free circulating mtDNA were conducted using enzyme-linked immunosorbent assay (ELISA), Western Blot, and quantitative real-time polymerase chain reaction (qRT-PCR) techniques.

Results

The experiment revealed that disruption in circadian rhythm alone or cocaine or METH on their own increased CRP, C3, SAA, and cortisol levels in comparison with the control group. CRSD mice, exposed to cocaine and METH, showed a significant rise in CRP, C3, and SAA, while those without exposure remained stable. We also found a reduction in circulating cell-free mtDNA in all CRSD mice, regardless of cocaine and METH exposure.

Conclusions

The findings of our study affirm that the levels of CRP, C3, SAA, and cortisol, which reflect inflammation, are enhanced by circadian disruption, cocaine, and METH, and these levels show a strong correlation with the content of circulating cell-free mtDNA. Furthermore, it also shows the potential link between the disruption of the circadian clock and the inflammatory response triggered by cocaine and METH.

In vivo spatiotemporal dynamics of astrocyte reactivity following neural electrode implantation

Brain computer interfaces (BCIs), including penetrating microelectrode arrays, enable both recording and stimulation of neural cells. However, device implantation inevitably causes injury to brain tissue and induces a foreign body response, leading to reduced recording performance and stimulation efficacy. Astrocytes in the healthy brain play multiple roles including regulating energy metabolism, homeostatic balance, transmission of neural signals, and neurovascular coupling. Following an insult to the brain, they are activated and gather around the site of injury. These reactive astrocytes have been regarded as one of the main contributors to the formation of a glial scar which affects the performance of microelectrode arrays. This study investigates the dynamics of astrocytes within the first 2 weeks after implantation of an intracortical microelectrode into the mouse brain using two-photon microscopy. From our observation astrocytes are highly dynamic during this period, exhibiting patterns of process extension, soma migration, morphological activation, and device encapsulation that are spatiotemporally distinct from other glial cells, such as microglia or oligodendrocyte precursor cells. This detailed characterization of astrocyte reactivity will help to better understand the tissue response to intracortical devices and lead to the development of more effective intervention strategies to improve the functional performance of neural interfacing technology.

Astrocytic Kir6.1 deletion aggravates neurodegeneration in the lipopolysaccharide-induced mouse model of Parkinson's disease via astrocyte-neuron cross talk through complement C3-C3R signaling

Complement pathway over-activation has been implicated in a variety of neurological diseases. However, the signaling pathways governing astrocytic complement activation in Parkinson's disease (PD) are poorly understood. Kir6.1, a pore-forming subunit of ATP-sensitive potassium (K-ATP) channel, is prominently expressed in astrocytes and exhibits anti-inflammatory effects. Therefore, we hypothesize that Kir6.1/K-ATP channel may regulate astrocytic complement activation in the pathogenesis of PD. In this study, astrocytic Kir6.1 knockout (KO) mice were used to examine the effect of astrocytic Kir6.1/K-ATP channel on astrocytic complement activation triggered by the lipopolysaccharide (LPS). Here, we found that astrocytic Kir6.1 KO mice showed more dopaminergic neuron loss and more astrocyte reactivity in substantia nigra compacta than controls. We also found that astrocytic Kir6.1 KO increased the expression of complement C3 in astrocytes in LPS-induced mouse model of PD. Mechanistically, astrocytic Kir6.1 KO promoted astroglial NF-κB activation to elicit extracellular release of C3, which in turn interacted with neuronal C3aR to induce neuron death. Blocking complement function by NF-κB inhibitor or C3aR antagonist rescued the aggravated neuron death induced by Kir6.1 KO. Collectively, our findings reveal that astrocytic Kir6.1/K-ATP channel prevents neurodegeneration in PD via astrocyte-neuron cross talk through NF-κB/C3/C3aR signaling and suggest that targeting astroglial Kir6.1/K-ATP channel-NF-κB-C3-neuronal C3aR signaling represents a novel therapeutic strategy for PD.

Complement mediates neuroinflammation and cognitive decline at extended chronic time points after traumatic brain injury

Traumatic brain injury (TBI) can result in progressive cognitive decline occurring for years after the initial insult, and for which there is currently no pharmacological treatment. An ongoing chronic inflammatory response after TBI is thought to be an important factor in driving this cognitive decline. Here, we investigate the role of complement in neuroinflammation and cognitive decline for up to 6 months after murine TBI. Male C57BL/6 mice were subjected to open head injury using a controlled cortical impact device. At 2 months post TBI, mice were moved to large cages with an enriched environment to simulate rehabilitation therapy, and assigned to one of three treatment groups: 1. vehicle (PBS), 2. CR2Crry (3 doses over 1 week), 3. CR2Crry (continuous weekly dose until the end of the study). The study was terminated at 6 months post-TBI for all groups. Motor and cognitive function was analyzed, with histopathological analysis of brain tissue. Measured at 6 months after TBI, neither of the complement inhibition paradigms improved motor performance. However, mice receiving continuous CR2Crry treatment showed improved spatial learning and memory compared to both mice receiving only 3 doses and to mice receiving vehicle control. Analysis of brain sections at 6 months after injury revealed ongoing complement activation in the control group, with reduced complement activation and C3 deposition in the continuous CR2Crry treatment group. The ipsilateral hemisphere of continuously treated animals also showed a decrease in microglia/macrophage and astrocyte activation compared to vehicle. There was also increased astrocytosis in the contralateral hippocampus of vehicle treated vs. naïve mice, which was reduced in mice continuously treated with CR2Crry. This study demonstrates continued complement mediated neuroinflammation at extended chronic time points after TBI, and extends the potential treatment window for complement inhibition, which has previously been shown to improve outcomes after murine TBI.

Effect of Weight Class on Regional Brain Volume, Cognition, and Other Neuropsychiatric Outcomes among Professional Fighters

Traumatic brain injury (TBI) is a common source of functional impairment among athletes, military personnel, and the general population. Professional fighters in both boxing and mixed martial arts (MMA) are at particular risk for repetitive TBI and may provide valuable insight into both the pathophysiology of TBI and its consequences. Currently, effects of fighter weight class on brain volumetrics (regional and total) and functional outcomes are unknown. Fifty-three boxers and 103 MMA fighters participating in the Professional Fighters Brain Health Study (PRBHS) underwent volumetric magnetic resonance imaging (MRI) and neuropsychological testing. Fighters were divided into lightweight (≤139.9 lb), middleweight (140.0–178.5 lb), and heavyweight (>178.5 lb). Compared with lightweight fighters, heavyweights displayed greater yearly reductions in regional brain volume (boxers: bilateral thalami; MMA: left thalamus, right putamen) and functional performance (boxers: processing speed, simple and choice reaction; MMA: Trails A and B tests). Lightweights suffered greater reductions in regional brain volume on a per-fight basis (boxers: left thalamus; MMA: right putamen). Heavyweight fighters bore greater yearly burden of regional brain volume and functional decrements, possibly related to differing fight dynamics and force of strikes in this division. Lightweights demonstrated greater volumetric decrements on a per-fight basis. Although more research is needed, greater per-fight decrements in lightweights may be related to practices of weight-cutting, which may increase vulnerability to neurodegeneration post-TBI. Observed decrements associated with weight class may result in progressive impairments in fighter performance, suggesting interventions mitigating the burden of TBI in professional fighters may both improve brain health and increase professional longevity.

Hippocampal atrophy is associated with psychotic symptom severity following traumatic brain injury

Psychosis is a rare, but particularly serious sequela of traumatic brain injury. However, little is known as to the neurobiological processes that may contribute to its onset. Early evidence suggests that psychotic symptom development after traumatic brain injury may co-occur with hippocampal degeneration, invoking the possibility of a relationship. Particularly regarding the hippocampal head, these degenerative changes may lead to dysregulation in dopaminergic circuits, as is reported in psychoses due to schizophrenia, resulting in the positive symptom profile typically seen in post-injury psychosis. The objective of this study was to examine change in hippocampal volume and psychotic symptoms across time in a sample of moderate-to-severe traumatic brain injury patients. We hypothesized that hippocampal volume loss would be associated with increased psychotic symptom severity. From a database of n = 137 adult patients with prospectively collected, longitudinal imaging and neuropsychiatric outcomes, n = 24 had complete data at time points of interest (5 and 12 months post-traumatic brain injury) and showed increasing psychotic symptom severity on the Personality Assessment Inventory psychotic experiences subscale of the schizophrenia clinical scale across time. Secondary analysis employing stepwise regression with hippocampal volume change (independent variable) and Personality Assessment Inventory psychotic symptom change (dependent variable) from 5 to 12 months post-injury was conducted including age, sex, marijuana use, family history of schizophrenia, years of education and injury severity as control variables. Total right hippocampal volume loss predicted an increase in the Personality Assessment Inventory psychotic experiences subscale (F_{(1, 22)} = 5.396, adjusted R² = 0.161, P = 0.030; β = −0.017, 95% confidence interval = −0.018, −0.016) as did volume of the right hippocampal head (F_{(1, 22)} = 5.764, adjusted R² = 0.172, P = 0.025; β = −0.019, 95% confidence interval = −0.021, −0.017). Final model goodness-of-fit was confirmed using k-fold (k = 5) cross-validation. Consistent with our hypotheses, the current findings suggest that hippocampal degeneration in the chronic stages of moderate-to-severe traumatic brain injury may play a role in the delayed onset of psychotic symptoms after traumatic brain injury. These findings localized to the right hippocampal head are supportive of a proposed aetiological mechanism whereby atrophy of the hippocampal head may lead to the dysregulation of dopaminergic networks following traumatic brain injury; possibly accounting for observed clinical features of psychotic disorder after traumatic brain injury (including prolonged latency period to symptom onset and predominance of positive symptoms). If further validated, these findings may bear important clinical implications for neurorehabilitative therapies following traumatic brain injury.

Traumatic brain injury alters neuropsychiatric symptomatology in all-cause dementia

INTRODUCTION

Traumatic brain injury (TBI) may alter the course of neuropsychiatric symptom (NPS) onset during dementia development. The connection among TBI, NPS, and dementia progression is of increasing interest to researchers and clinicians.

METHODS

Incidence of NPS was examined in participants with normal cognition who progressed to all-cause dementia based on whether TBI history was present (n = 130) or absent (n = 849). Survival analyses were used to examine NPS incidence across 7.6 ± 3.0 years of follow-up.

RESULTS

Participants with TBI history had increased prevalence and incidence of apathy (44.7% vs 29.9%, P = .0062; HR_adj. = 1.708, P = .0018) and motor disturbances (17.2% vs 9.5%, P = .0458; HR_adj. = 2.023, P = .0168), controlling for demographics and type of dementia diagnosis. Earlier anxiety onset was associated with TBI (692 days prior to dementia diagnosis vs 161 days, P = .0265).

DISCUSSION

History of TBI is associated with increased risk for and earlier onset of NPS in the trajectory of dementia development.