Hippocampal Expression of Cytochrome P450 1B1 in Penetrating Traumatic Brain Injury

Hippocampal dysfunction contributes to multiple traumatic brain injury sequala. Female rodents’ outcome is superior to male which has been ascribed the neuroprotective sex hormones 17β-estradiol and progesterone. Cytochrome P450 1B1 (CYP1B1) is an oxidative enzyme influencing the neuroinflammatory response by creating inflammatory mediators and metabolizing neuroprotective 17β-estradiol and progesterone. In this study, we aimed to describe hippocampal CYP1B1 mRNA expression, protein presence of CYP1B1 and its key redox partner Cytochrome P450 reductase (CPR) in both sexes, as well as the effect of penetrating traumatic brain injury (pTBI). A total 64 adult Sprague Dawley rats divided by sex received pTBI or sham-surgery and were assigned survival times of 1-, 3-, 5- or 7 days. CYP1B1 mRNA was quantified using in-situ hybridization and immunohistochemistry performed to verify protein colocalization. CYP1B1 mRNA expression was present in all subregions but greatest in CA2 irrespective of sex, survival time or intervention. At 3-, 5- and 7 days post-injury, expression in CA2 was reduced in male rats subjected to pTBI compared to sham-surgery. Females subjected to pTBI instead exhibited increased expression in all CA subregions 3 days post-injury, the only time point expression in CA2 was greater in females than in males. Immunohistochemical analysis confirmed neuronal CYP1B1 protein in all hippocampal subregions, while CPR was limited to CA1 and CA2. CYP1B1 mRNA is constitutively expressed in both sexes. In response to pTBI, females displayed a more urgent but brief regulatory response than males. This indicates there may be sex-dependent differences in CYP1B1 activity, possibly influencing inflammation and neuroprotection in pTBI.

Innate immunity pathways activate cell proliferation after penetrating traumatic brain injury in adult Drosophila

We are utilizing an adult penetrating traumatic brain injury (PTBI) model in Drosophila to investigate regenerative mechanisms after damage to the central brain. We focused on cell proliferation as an early event in the regenerative process. To identify candidate pathways that may trigger cell proliferation following PTBI, we utilized RNA-Seq. We find that transcript levels for components of both Toll and Immune Deficiency (Imd) innate immunity pathways are rapidly and highly upregulated post-PTBI. We then tested mutants for the NF-κB transcription factors of the Toll and Imd pathways, Dorsal-related immunity factor (Dif) and Relish (Rel) respectively. We find that loss of either or both Dif and Rel results in loss of cell proliferation after injury. We then tested canonical downstream targets of Drosophila innate immune signaling, the antimicrobial peptides (AMPs), and find that they are not required for cell proliferation following PTBI. This suggests that there are alternative targets of Toll and Imd signaling that trigger cell division after injury. Furthermore, we find that while AMP levels are substantially elevated after PTBI, their levels revert to near baseline within 24 hours. Finally, we identify tissue-specific requirements for Dif and Rel. Taken together, these results indicate that the innate immunity pathways play an integral role in the regenerative response. Innate immunity previously has been implicated as both a potentiator and an inhibitor of regeneration. Our work suggests that modulation of innate immunity may be essential to prevent adverse outcomes. Thus, this work is likely to inform future experiments to dissect regenerative mechanisms in higher organisms.

Comparing the medical coverage provided by four contemporary military combat helmets against penetrating traumatic brain injury

IntroductionModern military combat helmets vary in their shapes and features, but all are designed to protect the head from traumatic brain injury. Recent recommendations for protection against energised projectiles that are characteristic of secondary blast injury is to ensure coverage of both the brain and brainstem.MethodGraphical representations of essential coverage of the head (cerebral hemispheres, cerebellum and brainstem) within an anthropometrically sized model were superimposed over two standard coverage helmets (VIRTUS helmet, Advanced Combat Helmet (ACH)) and two ‘high-cut’ helmets (a Dismounted Combat Helmet (DCH)) and Combat Vehicle Crewman (CVC) helmet), both of which are designed to be worn with communications devices. Objective shotline coverage from representative directions of projectile travel (−30 to +30 degrees) was determined using the Coverage of Armour Tool (COAT).ResultsVIRTUS and ACH demonstrated similar overall coverage (68.7% and 69.5%, respectively), reflecting their similar shell shapes. ACH has improved coverage from below compared with VIRTUS (23.3% vs 21.7%) due to its decreased standoff from the scalp. The ‘high-cut’ helmets (DCH and CVC) had reduced overall coverage (57.9% and 52.1%), which was most pronounced from the side.ConclusionsBoth the VIRTUS and ACH helmets provide excellent overall coverage of the brain and brainstem against ballistic threats. Coverage of both would be improved at the rear by using a nape protector and the front using a visor. This is demonstrated with the analysis of the addition of the nape protector in the VIRTUS system. High-cut helmets provide significantly reduced coverage from the side of the head, as the communication devices they are worn with are not designed to provide protection from ballistic threats. Unless absolutely necessary, it is therefore recommended that high-cut helmets be worn only by those users with defined specific requirements, or where the risk of injury from secondary blast is low.

New lymphatic cell formation is associated with damaged brain tissue clearance after penetrating traumatic brain injury

We characterized the tissue repair response after penetrating traumatic brain injury (pTBI) in this study. Seventy specific pathogen-free Kunming mice were randomly divided into the following groups: normal control, 1, 3, 7, 15, 21, and 30 days after pTBI. Hematoxylin and eosin (H&E) staining, immunohistochemistry, and immunofluorescence were performed to examine and monitor brain tissue morphology, and the distribution and expression of lymphatic-specific markers lymphatic vessel endothelial receptor-1 (LYVE-1), hematopoietic precursor cluster of differentiation 34 (CD34) antigen, and Prospero-related homeobox-1 (PROX1) protein. H&E staining revealed that damaged and necrotic tissues observed on day 1 at and around the injury site disappeared on day 7, and there was gradual shrinkage and disappearance of the lesion on day 30, suggesting a clearance mechanism. We explored the possibility of lymphangiogenesis causing this clearance as part of the post-injury response. Notably, expression of lymphangiogenesis markers LYVE-1, CD34, and PROX1 was detected in damaged mouse brain tissue but not in normal tissue. Moreover, new lymphatic cells and colocalization of LYVE-1/CD34 and LYVE-1/PROX1 were also observed. Our findings of the formation of new lymphatic cells following pTBI provide preliminary insights into a post-injury clearance mechanism in the brain. Although we showed that lymphatic cells are implicated in brain tissue repair, further research is required to clarify the origin of these cells.

518 New In Vitro Model of Traumatic Brain Injury to Assess Biomaterial Based Regenerative Strategies

Introduction Penetrating traumatic brain injury (pTBI) management is largely supportive, with no clinically established regenerative therapies. Neurocompatible biomaterials offer a high potential to promote regenerative mechanisms but facile, high throughput, pathomimetic in vitro pTBI models for the developmental testing of neuro-materials is lacking. Method A mouse mixed glial culture system was utilised within which penetrating injuries could be induced. DuraGen PlusTM – an FDA approved neurosurgical grade biomaterial could be implanted into lesions to assess cell-biomaterial responses. Reactive gliosis (astrocytic morphological responses/GFAP expression) and microglial infiltration (Iba1 expression) were assessed/quantified. Results Key pathological features of pTBI were observed in the model, with the ability to (i) introduce reproducible lesions (diameter 949 ± 26 μm) and (ii) for DuraGen PlusTM to be implanted into lesions. Peri-lesional astrocytes displayed hypertrophic palisading morphologies and GFAP upregulation, analogous to gliosis in vivo. Significant microglial numbers infiltrated the DuraGen PlusTM implant at 7 days post-lesion (132.41 ± 15.83 cells/mm2) versus lesion only (82.04 ± 5.11 cells/mm2), p < 0.05). Conclusions We have developed a novel, neuropathomimetic pTBI model, wherein biomaterial implantation enables investigation of neural cell-biomaterial responses. This model can facilitate early-stage evaluation of novel biomaterials as high throughput, inexpensive and facile screening tool.