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Endothelial deletion of EPH receptor A4 alters single-cell profile and Tie2/Akap12 signaling to preserve blood-brain barrier integrity

ABSTRACT: Neurobiological consequences of traumatic brain injury (TBI) result from a complex interplay of secondary injury responses and sequela that mediates chronic disability. Endothelial cells are important regulators of the cerebrovascular response to TBI. Our work demonstrates that genetic deletion of endothelial cell (EC)-specific EPH receptor A4 (EphA4) using conditional EphA4f/f/Tie2-Cre and EphA4f/f/VE-Cadherin-CreERT2 knockout (KO) mice, promotes blood-brain barrier (BBB) integrity and tissue protection, which correlates with improved motor function and cerebral blood flow recovery following controlled cortical impact (CCI) injury. scRNAseq of capillary-derived KO ECs showed increased differential gene expression of BBB-related junctional and actin cytoskeletal regulators, namely, A-kinase anchor protein 12, Akap12, whose presence at Tie2 clustering domains is enhanced in KO microvessels. Transcript and protein analysis of CCI-injured whole cortical tissue or cortical-derived ECs suggests EphA4 limits the expression of Cldn5, Akt, and Akap12 and promotes Ang2. Blocking the Tie2 receptor using sTie2-Fc, attenuated BBB and tissue protection and reversed Akap12 mRNA and protein levels in KO compared to WT cortical-derived ECs. Conversely, direct stimulation of Tie2 using Vasculotide, an angiopoietin-1 memetic peptide, phenocopied the neuroprotection. Finally, we report a noteworthy rise in soluble Ang2 in the sera of individuals with acute TBI, highlighting its promising role as a vascular biomarker for early detection of BBB disruption. Overall, we describe a novel contribution of the axon guidance molecule, EphA4, in mediating TBI microvascular dysfunction through negative regulation of Tie2/Akap12 signaling.

ORGANISM(S): Mus musculus

PROVIDER: GSE240430 | GEO | 2023/09/24

REPOSITORIES: GEO

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Project description:Traumatic brain injury (TBI) initiates not only complex neurovascular and glial changes within the brain but also pathophysiological responses that extend beyond the central nervous system. The peripheral response to TBI has become an intensive area of research, as these systemic perturbations can induce dysfunction in multiple organ systems. As there are no approved therapeutics for TBI, it is imperative that we investigate the peripheral response to TBI to identify targets for future intervention. Of particular interest is the gastrointestinal (GI) system. Even in the absence of polytrauma, brain-injured individuals are at increased risk of suffering from GI-related morbidity and mortality. Symptoms such as intestinal dysmotility, inflammation, ulceration, and fecal incontinence can drastically diminish quality of life. The GI tract is inhabited by trillions of microbes that have been implicated as modulators of many neurological disorders. Clinical and preclinical studies implicate gut dysbiosis, a pathological imbalance in the normally symbiotic microbiota, as both a consequence of TBI as well as a contributing factor to brain damage. However, our understanding of this interplay is still limited. While relatively little is known about the effects of TBI on the structure and function of the GI tract, prior studies report that experimental TBI induces intestinal barrier dysfunction and morphological changes. To confirm these findings in the current model of TBI, male C57BL/6J mice underwent a sham control or a controlled cortical impact (CCI) procedure to induce a contusive brain injury, and intestinal permeability was assessed at 4 h, 8 h, 1 d, and 3 d post-injury. An acute, transient increase in permeability was observed at 4 h after CCI. Histological analyses of the ileum and colon at multiple time points from 4 h to 4 wks revealed no overt morphological changes, suggesting that CCI induced a short-lived physiologic dysfunction without major structural alterations to the GI tract. As the microbiome is a modulator of GI physiology, we performed 16s gene sequencing on fecal samples collected prior to and over the first month after CCI or sham injury. Microbial community diversity was assessed using common metrics of alpha and beta diversity. Alpha diversity was lower in the CCI injury group and beta diversity differed among groups, although these effects were not observed in all metrics. Subsequent differential abundance analysis revealed that the phylum Verrucamicrobiota was increased in CCI mice at 1, 2, and 3 d post-injury when compared to sham mice. Subsequent qPCR identified the Verrucamicrobiota species as Akkermansia Muciniphila, an obligate anaerobe that resides in and helps regulate the intestinal mucus layer and barrier. To determine whether TBI promotes changes to the GI tract favorable for the proliferation of A. muciniphila, mucus-producing goblet cells and the level of GI hypoxia were evaluated. Goblet cell density in the medial colon was significantly increased at 1 d, while colon hypoxia was significantly increased at 3 d. Taken together, these studies show that CCI induces transient intestinal barrier dysfunction followed by increased goblet cell density and hypoxia in the colon with a concomitant increase in A. muciniphila that may suggest a compensatory response to systemic stress after TBI.