Fredrik Clausen

Traumatic brain injury (TBI) increases the risk of delayed neurodegenerative processes, including Parkinson’s disease (PD). Interleukin-1beta (IL-1β), a key pro-inflammatory cytokine, may promote secondary injury development after TBI. Conversely, neutralizing IL-1β was found to improve functional recovery following experimental TBI. However, the mechanisms underlying the behavioral improvements observed by IL-1β neutralization are still poorly understood. The present study investigated the role of IL-1β on the microglia response and neuronal changes in the globus pallidus in response to diffuse TBI. Mice were subjected to sham injury or the central fluid percussion injury (cFPI) (a model of traumatic axonal injury), and were randomly administered an IL-1β neutralizing or a control antibody at 30 min post-injury. The animals were analyzed at 2, 7, or 14 days post-injury. When compared to controls, mice subjected to cFPI TBI had increased microglia activation and dopaminergic innervation in the globus pallidus, and a decreased number of parvalbumin (PV) positive interneurons in the globus pallidus. Neutralization of IL-1β attenuated the microglia activation, prevented the loss of PV+ interneurons and normalized dopaminergic fiber density in the globus pallidus of brain-injured animals. These findings argue for an important role for neuro-inflammation in the PD-like pathology observed in TBI.

Alzheimer’s disease (AD) is the leading cause of dementia worldwide, affecting over 10% of the elderly population. Epidemiological evidence indicates that traumatic brain injury (TBI) is an important risk factor for developing AD later in life. Howev

Traumatic brain injury (TBI) is followed by secondary injury mechanisms strongly involving neuroinflammation. To monitor the complex inflammatory cascade in human TBI, we used cerebral microdialysis (MD) and multiplex proximity extension assay (PEA) technology and simultaneously measured levels of 92 protein biomarkers of inflammation in MD samples every three hours for five days in 10 patients with severe TBI under neurointensive care. One μL MD samples were incubated with paired oligonucleotide-conjugated antibodies binding to each protein, allowing quantification by real-time quantitative polymerase chain reaction. Sixty-nine proteins were suitable for statistical analysis. We found five different patterns with either early (96 h; e.g., CD40, MCP2, MCP3), biphasic peaks (e.g., CXCL1, CXCL5, IL8) or stable (e.g., CCL4, DNER, VEGFA)/low trends. High protein levels were observed for e.g., CXCL1, CXCL10, MCP1, MCP2, IL8, while e.g., CCL28 and MCP4 were detected at low levels. Several proteins (CCL8, -19, -20, -23, CXCL1, -5, -6, -9, -11, CST5, DNER, Flt3L, and SIRT2) have not been studied previously in human TBI. Cross-correlation analysis revealed that LIF and CXCL5 may play a central role in the inflammatory cascade. This study provides a unique data set with individual temporal trends for potential inflammatory biomarkers in patients with TBI. We conclude that the combination of MD and PEA is a powerful tool to map the complex inflammatory cascade in the injured human brain. The technique offers new possibilities of protein profiling of complex secondary injury pathways.

Background/Objectives: Motor impairment induced by traumatic brain injury (TBI) may be mediated through changes in spinal molecular systems regulating neuronal plasticity. We assessed whether a focal controlled cortical impact (CCI) TBI in the rat alters expression of the Tgfb1, c-Fos, Bdnf, and Gap43 neuroplasticity genes in lumbar spinal cord. Approach/Methods: Adult male Sprague-Dawley rats ( n = 8) were subjected to a right-side CCI over the anterior sensorimotor hindlimb representation area or sham-injury ( n = 8). Absolute expression levels of Tgfb1, c-Fos, Bdnf, and Gapd43 genes were measured by droplet digital PCR in ipsi-and contralesional, dorsal and ventral quadrants of the L4 and L5 spinal cord. The neuronal activity marker c-Fos was analysed by immunohistochemistry in the dorsal L4 and L5 segments. The contra- vs. ipsilesional expression pattern was examined as the asymmetry index, AI. Results: The Tgfb1 mRNA levels were significantly higher in the CCI vs. sham-injured rats, and in the contra- vs. ipsilesional dorsal domains in the CCI group. The number of c-Fos-positive cells was elevated in the L4 and L5 segments; and on the contralesional compared to the ipsilesional side in the CCI group. The c-Fos AI in the dorsal laminae was significantly increased by CCI. Conclusions: The results support the hypothesis that focal TBI induces plastic alterations in the lumbar spinal cord that may contribute to either motor recovery or maladaptive motor responses.

Neuroinflammation is a major contributor to the progressive brain injury process induced by traumatic brain injury (TBI), and may play an important role in the pathophysiology of axonal injury. The immediate neuroinflammatory cascade cannot be characterized in the human setting. Therefore, we used the midline fluid percussion injury model of diffuse TBI in rats and a novel microdialysis (MD) method providing stable diffusion-driven biomarker sampling. Immediately post-injury, bilateral amphiphilic tri-block polymer coated MD probes (100 kDa cut off membrane) were inserted and perfused with Dextran 500 kDa-supplemented artificial CSF to optimize protein capture. Six hourly samples were analyzed for 27 inflammatory biomarkers (9 chemokines, 13 cytokines and 5 growth factors) using a commercial multiplex biomarker kit. TBI (n=6) resulted in a significant increase compared to sham-injured controls (n=6) for 5 chemokines (Eotaxin/CCL11, Fractalkine/CX3CL1, LIX/CXCL5, MCP1α/CCL2, MIP1α /CCL3), 10 cytokines (IL-1α, IL-1β, IL-4, IL-6, IL-10, IL-13, IL-17α, IL-18, IFN-γ, TNF-α), and 4 growth factors (EGF, GM-CSF, Leptin, VEGF). Thus, diffuse TBI was associated with an increased level of 18 of the 27 inflammatory biomarkers at 1-6 time points during the observation period whereas the remaining 9 biomarkers were unaltered. The study shows that diffuse TBI induces an acute increase of a number of inflammatory biomarkers. The novel MD technique provides stable MD sampling suitable for further studies on the early neuroinflammatory cascade in TBI.

Traumatic brain injury (TBI) commonly results in injury to the components of the white matter tracts, causing post-injury cognitive deficits. The myelin-producing oligodendrocytes (OLs) are vulnerable to TBI, although may potentially be replaced by proliferating oligodendrocyte progenitor cells (OPCs). The cytokine interleukin-1β (IL-1β) is a key mediator of the complex inflammatory response, and when neutralized in experimental TBI, behavioral outcome was improved. To evaluate the role of IL-1β on oligodendrocyte cell death and OPC proliferation, 116 adult male mice subjected to sham injury or the central fluid percussion injury (cFPI) model of traumatic axonal injury, were analyzed at two, seven, and 14 days post-injury. At 30 min post-injury, mice were randomly administered an IL-1β neutralizing or a control antibody. OPC proliferation (5-ethynyl 2′- deoxyuridine (EdU)/Olig2 co-labeling) and mature oligodendrocyte cell loss was evaluated in injured white matter tracts. Microglia/macrophages immunohistochemistry and ramification using Sholl analysis were also evaluated. Neutralizing IL-1β resulted in attenuated cell death, indicated by cleaved caspase-3 expression, and attenuated loss of mature OLs from two to seven days post-injury in brain-injured animals. IL-1β neutralization also attenuated the early, two day post-injury increase of microglia/macrophage immunoreactivity and altered their ramification. The proliferation of OPCs in brain-injured animals was not altered, however. Our data suggest that IL-1β is involved in the TBI-induced loss of OLs and early microglia/macrophage activation, although not the OPC proliferation. Attenuated oligodendrocyte cell loss may contribute to the improved behavioral outcome observed by IL-1β neutralization in this mouse model of diffuse TBI.

A synthetic peptide with antisecretory activity, AF-16, improves injury-related deficits in water and ion transport and decreases intracranial pressure after experimental cold lesion injury and encephalitis although its role in traumatic brain injury (TBI) is unknown. AF-16 or an inactive reference peptide was administrated intranasally 30 min following midline fluid percussion injury (mFPI; n=52), a model of mild-moderate diffuse TBI in rats. Sham-injured (n=14) or naïve (n=24) animals were used as controls. The rats survived for either 48 h or 15 days. At 48 h, the animals were tested in Morris water maze (MWM) for memory function and brains analyzed for cerebral edema. Here, mFPI induced brain edema compared to sham or naïve controls that was significantly reduced by AF-16 treatment (p<0.05) although MWM performance was not altered. In the 15-day survival groups, the MWM learning and memory abilities as well as histological changes were analyzed. AF-16 treated brain-injured animals shortened both MWM latency and swim path in the learning trials and improved probe trial performance compared to brain-injured controls treated with the inactive reference peptide (p<0.05). A modest decrease by AF-16 on TBI-induced changes in hippocampal glial acidic fibrillary protein (GFAP) staining (p=0.11) was observed. AF-16 treatment did not alter any other immunohistochemical analyses (degenerating neurons, beta-amyloid precursor protein (β-APP) and Olig2). In conclusion, intranasal AF-16 attenuated brain edema and enhanced visuospatial learning and memory following diffuse TBI in the rat. Intranasal administration early post-injury of a promising neuroprotective substance offers a novel treatment approach for TBI.

Background: Injury to the white matter may lead to impaired neuronal signaling and is commonly observed following traumatic brain injury (TBI). Although endogenous repair of TBI-induced white matter pathology is limited, oligodendrocyte progenitor cells (OPCs) may be stimulated to proliferate and regenerate functionally myelinating oligodendrocytes. Even though OPCs are present throughout the adult brain, little is known about their proliferative activity following axonal injury caused by TBI. Objective: We hypothesized that central fluid percussion injury (cFPI) in mice, a TBI model causing wide-spread axonal injury, results in OPC proliferation. Methods: Proliferation of OPCs was evaluated in 27 cFPI mice using 5-ethynyl-2′-deoxyuridine (EdU) labeling and a cell proliferation assay at 2 ( n = 9), 7 ( n = 8) and 21 ( n = 10) days post injury (dpi). Sham-injured mice ( n = 14) were used as controls. OPC proliferation was quantified by immunohistochemistry using the OPC markers NG2 and Olig2 in several white matter loci including the corpus callosum, external capsule, fimbriae, the internal capsule and cerebral peduncle. Results: The number of EdU/DAPI/Olig2-positive cells were increased in the cFPI group compared to sham-injured animals at 7 days post-injury (dpi; p≤0.05) in the majority of white matter regions. The OPC proliferation had subsided by 21 dpi. The number of EdU/DAPI/NG2 cells was also increase at 7 dpi in the external capsule and fimbriae. Conclusion: These results suggest that traumatic axonal injury in the mouse induces a transient proliferative response of residing OPCs. These proliferating OPCs may replace dead oligodendrocytes and contribute to remyelination, which needs evaluation in future studies.