Skull bone marrow-derived immune cells infiltrate the injured cerebral cortex and exhibit anti-inflammatory properties.

Identifying the origins and contributions of peripheral-derived immune cell populations following brain injury is crucial for understanding their roles in neuroinflammation and tissue repair. This study investigated the infiltration and phenotypic characteristics of skull bone marrow-derived immune cells in the murine brain after traumatic brain injury (TBI). We performed calvarium transplantation from GFP donor mice and subjected the recipients to controlled cortical impact (CCI) injury 14 days post-transplant. Confocal imaging at 3 days post-CCI revealed GFP+ calvarium-derived cells were present in the ipsilateral injured cortex, expressing CD45 and CD11b immune markers. These cells included Ly6G-positive neutrophil or Ccr2-positive monocyte identities. Calvarium-derived GFP+/Iba1+ monocyte/macrophages expressed the efferocytosis receptor MERTK and displayed engulfment of NeuN+ and cleaved caspase 3+ apoptotic cells. Phenotypic analysis showed that greater calvarium-derived monocytes/macrophages disproportionately express the anti-inflammatory arginase-1 marker than pro-inflammatory CD86. To differentiate the responses of blood- and calvarium-derived macrophages, we transplanted GFP calvarium skull bone into tdTomato bone marrow chimeric mice, then performed CCI injury 14 days post-transplant. Calvarium-derived GFP+cells predominantly infiltrated the lesion boundary, while blood-derived tdTomato+ cells dispersed throughout the lesion and peri-lesion. Compared to calvarium-derived cells, more blood-derived cells expressed pro-inflammatory CD86 and displayed altered 3D morphologic traits. These findings uniquely demonstrate that skull bone marrow-derived immune cells infiltrate the brain after injury and contribute to the neuroinflammatory milieu, representing a novel immune cell source that may be further investigated for their causal role in functional outcomes.

Peripheral loss of EphA4 ameliorates TBI-induced neuroinflammation and tissue damage.

BACKGROUND: The continuum of pro- and anti-inflammatory response elicited by traumatic brain injury (TBI) is suggested to play a key role in the outcome of TBI; however, the underlying mechanisms remain ill -defined. METHODS: Here, we demonstrate that using bone marrow chimeric mice and systemic inhibition of EphA4 receptor shifts the pro-inflammatory milieu to pro-resolving following acute TBI. RESULTS: EphA4 expression is increased in the injured cortex as early as 2 h post-TBI and on CX3CR1gfp-positive cells in the peri-lesion. Systemic inhibition or genetic deletion of EphA4 significantly reduced cortical lesion volume and shifted the inflammatory profile of peripheral-derived immune cells to pro-resolving in the damaged cortex. These findings were consistent with in vitro studies showing EphA4 inhibition or deletion altered the inflammatory state of LPS-stimulated monocyte/macrophages towards anti-inflammatory. Phosphoarray analysis revealed that EphA4 may regulate pro-inflammatory gene expression by suppressing the mTOR, Akt, and NF-κB pathways. Our human metadata analysis further demonstrates increased EPHA4 and pro-inflammatory gene expression, which correlates with reduced AKT concurrent with increased brain injury severity in patients. CONCLUSIONS: Overall, these findings implicate EphA4 as a novel mediator of cortical tissue damage and neuroinflammation following TBI.

Lactobacillus rescues postnatal neurobehavioral and microglial dysfunction in a model of maternal microbiome dysbiosis.

Increasing reports of pregnancy events leading to maternal microbiome dysbiosis (MMD) show strong correlates with atypical neurodevelopmental outcomes. However, the mechanism(s) driving microbiome-mediated behavioral dysfunction in offspring remain understudied. Here, we demonstrate the presence of a novel gut commensal bacterium strain, Lactobacillus murinus HU-1, was sufficient to rescue behavioral deficits and brain region-specific microglial activationobserved in MMD-reared murine offspring. We furtheridentified a postnatal window of susceptibility that could prevent social impairments with timed maternal administration of the symbiotic bacterium. Moreover, MMD increased expression of microglial senescence genes, Trp53 and Il1ß, and Cx3cr1 protein in the prefrontal cortex, which correlated with dysfunctional modeling of synapses and accompanied dysbiosis-induced microglial activation. MMD male offspring harboring Lactobacillus murinus HU-1 or lacking Cx3cr1 showed amelioration of these effects. The current study describes a new avenue of influence by which maternally transferred Lactobacillus drives proper development of social behavior in the offspring through microglia-specific regulation of Cx3cr1 signaling.

Transcriptomic alterations in cortical astrocytes following the development of post-traumatic epilepsy.

Post-traumatic epilepsy (PTE) stands as one of the numerous debilitating consequences that follow traumatic brain injury (TBI). Despite its impact on many individuals, the current landscape offers only a limited array of reliable treatment options, and our understanding of the underlying mechanisms and susceptibility factors remains incomplete. Among the potential contributors to epileptogenesis, astrocytes, a type of glial cell, have garnered substantial attention as they are believed to promote hyperexcitability and the development of seizures in the brain following TBI. The current study evaluated the transcriptomic changes in cortical astrocytes derived from animals that developed seizures as a result of severe focal TBI. Using RNA-Seq and ingenuity pathway analysis (IPA), we unveil a distinct gene expression profile in astrocytes, including alterations in genes supporting inflammation, early response modifiers, and neuropeptide-amidating enzymes. The findings underscore the complex molecular dynamics in astrocytes during PTE development, offering insights into therapeutic targets and avenues for further exploration.

Inhibitory checkpoint molecule mRNA expression in canine soft tissue sarcoma.

Canine soft tissue sarcomas (STS) are common neoplasms and considered immune deserts. Tumour infiltrating lymphocytes are sparse in STS and, when present, tend to organize around blood vessels or at the periphery of the neoplasm. This pattern is associated with an immunosuppressive tumour microenvironment linked to overexpression of molecules of the PD-axis. PD-1, PD-L1 and PD-L2 expression correlates with malignancy and poor prognosis in other neoplasms in humans and dogs, but little is known about their role in canine STS, their relationship to tumour grade, and how different therapies affect expression. The objective of this study was to evaluate the expression of checkpoint molecules across STS tumour grades and after tumour ablation treatment. Gene expression analysis was performed by reverse-transcriptase real-time quantitative PCR in soft tissue sarcomas that underwent histotripsy and from histologic specimens of STS from the Virginia Tech Animal Laboratory Services archives. The expression of PD-1, PD-L1 and PD-L2 was detected in untreated STS tissue representing grades 1, 2, and 3. Numerically decreased expression of all markers was observed in tissue sampled from the treatment interface relative to untreated areas of the tumour. The relatively lower expression of these checkpoint molecules at the periphery of the treated area may be related to liquefactive necrosis induced by the histotripsy treatment, and would potentially allow TILs to infiltrate the tumour. Relative increases of these checkpoint molecules in tumours of a higher grade and alongside immune cell infiltration are consistent with previous reports that associate their expression with malignancy.

Atypical Neurogenesis, Astrogliosis, and Excessive Hilar Interneuron Loss Are Associated with the Development of Post-Traumatic Epilepsy.

BACKGROUND: Traumatic brain injury (TBI) remains a significant risk factor for post-traumatic epilepsy (PTE). The pathophysiological mechanisms underlying the injury-induced epileptogenesis are under investigation. The dentate gyrus-a structure that is highly susceptible to injury-has been implicated in the evolution of seizure development. METHODS: Utilizing the murine unilateral focal control cortical impact (CCI) injury, we evaluated seizure onset using 24/7 EEG video analysis at 2-4 months post-injury. Cellular changes in the dentate gyrus and hilus of the hippocampus were quantified by unbiased stereology and Imaris image analysis to evaluate Prox1-positive cell migration, astrocyte branching, and morphology, as well as neuronal loss at four months post-injury. Isolation of region-specific astrocytes and RNA-Seq were performed to determine differential gene expression in animals that developed post-traumatic epilepsy (PTE+) vs. those animals that did not (PTE-), which may be associated with epileptogenesis. RESULTS: CCI injury resulted in 37% PTE incidence, which increased with injury severity and hippocampal damage. Histological assessments uncovered a significant loss of hilar interneurons that coincided with aberrant migration of Prox1-positive granule cells and reduced astroglial branching in PTE+ compared to PTE- mice. We uniquely identified Cst3 as a PTE+-specific gene signature in astrocytes across all brain regions, which showed increased astroglial expression in the PTE+ hilus. CONCLUSIONS: These findings suggest that epileptogenesis may emerge following TBI due to distinct aberrant cellular remodeling events and key molecular changes in the dentate gyrus of the hippocampus.

Characterization of the Expression of Angiogenic Factors in Cutaneous Squamous Cell Carcinoma of Domestic Cats.

Cutaneous squamous cell carcinoma (CSCC) is a common malignant skin cancer with a significant impact on health, and it is important to determine the degree of reliance of CSCC on angiogenesis for growth and metastasis. Major regulators of angiogenesis are the vascular endothelial growth factor (VEGF) family and their associated receptors. Alternative pre-mRNA splicing produces multiple isoforms of VEGF-A and PLGF with distinct biological properties. Several studies highlight the function of VEGF-A in CSCC, but there are no studies of the different isoforms of VEGF-A and PLGF for this neoplasm. We characterized the expression of three isoforms of VEGF-A, two isoforms of PLGF, and their receptors in cat CSCC biopsies compared to normal haired skin (NHS). Although our results revealed no significant changes in transcript levels of panVEGF-A or their isoforms, the mRNA levels of PLGF I and the receptors Flt-1 and KDR were downregulated in CSCC compared to NHS. Differences were observed in ligand:receptor mRNA expression ratio, with the expression of VEGF-A relative to its receptor KDR higher in CSCC, which is consistent with our hypothesis and prior human SCC studies. Immunolocalization in tissue showed increased expression of all measured factors and receptors in tumor cells compared to NHS and surrounding vasculature. We conclude that the factors measured may play a pivotal role in CSCC growth, although further studies are needed to clarify the role of angiogenic factors in feline CSCC.

Type I Interferon Response Is Mediated by NLRX1-cGAS-STING Signaling in Brain Injury.

Background: Inflammation is a significant contributor to neuronal death and dysfunction following traumatic brain injury (TBI). Recent evidence suggests that interferons may be a key regulator of this response. Our studies evaluated the role of the Cyclic GMP-AMP Synthase-Stimulator of Interferon Genes (cGAS-STING) signaling pathway in a murine model of TBI. Methods: Male, 8-week old wildtype, STING knockout (-/-), cGAS -/-, and NLRX1 -/- mice were subjected to controlled cortical impact (CCI) or sham injury. Histopathological evaluation of tissue damage was assessed using non-biased stereology, which was complemented by analysis at the mRNA and protein level using qPCR and western blot analysis, respectively. Results: We found that STING and Type I interferon-stimulated genes were upregulated after CCI injury in a bi-phasic manner and that loss of cGAS or STING conferred neuroprotection concomitant with a blunted inflammatory response at 24 h post-injury. cGAS -/- animals showed reduced motor deficits 4 days after injury (dpi), and amelioration of tissue damage was seen in both groups of mice up to 14 dpi. Given that cGAS requires a cytosolic damage- or pathogen-associated molecular pattern (DAMP/PAMP) to prompt downstream STING signaling, we further demonstrate that mitochondrial DNA is present in the cytosol after TBI as one possible trigger for this pathway. Recent reports suggest that the immune modulator NLR containing X1 (NLRX1) may sequester STING during viral infection. Our findings show that NLRX1 may be an additional regulator that functions upstream to regulate the cGAS-STING pathway in the brain. Conclusions: These findings suggest that the canonical cGAS-STING-mediated Type I interferon signaling axis is a critical component of neural tissue damage following TBI and that mtDNA may be a possible trigger in this response.