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Intracellular surveillance for systemic microbial components during homeostasis and infections governs host physiology and immunity. However, a long-standing question is how circulating microbial ligands become accessible to intracellular receptors. Here we show a role for host-derived extracellular vesicles (EVs) in this process; human and murine plasma-derived and cell culture-derived EVs have an intrinsic capacity to bind bacterial lipopolysaccharide (LPS). Remarkably, circulating host EVs capture blood-borne LPS in vivo, and the LPS-laden EVs confer cytosolic access for LPS, triggering non-canonical inflammasome activation of gasdermin D and pyroptosis. Mechanistically, the interaction between the lipid bilayer of EVs and the lipid A of LPS underlies EV capture of LPS, and the intracellular transfer of LPS by EVs is mediated by CD14. Overall, this study demonstrates that EVs capture and escort systemic LPS to the cytosol licensing inflammasome responses, uncovering EVs as a previously unrecognized link between systemic microbial ligands and intracellular surveillance.

Endothelial cells are important contributors to brain development, physiology, and disease. Although RNA sequencing has contributed to the understanding of brain endothelial cell diversity, bulk analysis and single-cell approaches have relied on fresh tissue digestion protocols for the isolation of single endothelial cells and flow cytometry-based sorting on surface markers or transgene expression. These approaches are limited in the analysis of the endothelium in human brain tissues, where fresh samples are difficult to obtain. Here, we developed an approach to examine endothelial RNA expression by using an endothelial-specific marker to isolate nuclei from abundant archived frozen brain tissues. We show that this approach rapidly and reliably extracts endothelial nuclei from frozen mouse brain samples, and importantly, from archived frozen human brain tissues. Furthermore, isolated RNA transcript levels are closely correlated with expression in whole cells from tissue digestion protocols and are enriched in endothelial markers and depleted of markers of other brain cell types. As high-quality RNA transcripts could be obtained from as few as 100 nuclei in archived frozen human brain tissues, we predict that this approach should be useful for both bulk analysis of endothelial RNA transcripts in human brain tissues as well as single-cell analysis of endothelial sub-populations.

Endothelial cells are important contributors to brain development, physiology, and disease. Although RNA sequencing has contributed to the understanding of brain endothelial cell diversity, bulk analysis and single-cell approaches have relied on fresh tissue digestion protocols for the isolation of single endothelial cells and flow cytometry-based sorting on surface markers or transgene expression. These approaches are limited in the analysis of the endothelium in human brain tissues, where fresh samples are difficult to obtain. Here, we developed an approach to examine endothelial RNA expression by using an endothelial-specific marker to isolate nuclei from abundant archived frozen brain tissues. We show that this approach rapidly and reliably extracts endothelial nuclei from frozen mouse brain samples, and importantly, from archived frozen human brain tissues. Furthermore, isolated RNA transcript levels are closely correlated with expression in whole cells from tissue digestion protocols and are enriched in endothelial markers and depleted of markers of other brain cell types. As high-quality RNA transcripts could be obtained from as few as 100 nuclei in archived frozen human brain tissues, we predict that this approach should be useful for both bulk analysis of endothelial RNA transcripts in human brain tissues as well as single-cell analysis of endothelial sub-populations.

Globoid cell leukodystrophy (GLD) or Krabbe’s disease is a fatal genetic demyelinating disease of the central nervous system caused by loss-of-function mutations in the galactosylceramidase (galc) gene. While the metabolic basis for disease is known, the understanding of how this results in neuropathology is not well understood. Herein, we report that the rapid and protracted elevation of CD8+ cytotoxic T lymphocytes occurs coincident with clinical disease in a mouse model of GLD. Administration of a function-blocking antibody against CD8α effectively prevented disease onset, reduced morbidity and mortality, and prevented CNS demyelination in mice. These data indicate that subsequent to the genetic cause of disease, neuropathology is driven by pathogenic CD8+ T cells, thus offering novel therapeutic potential for treatment of GLD.

NFκB mediated endothelial activation drives leukocyte recruitment and atherosclerosis, in part through upregulation of adhesion molecules Icam1 and Vcam. The endothelium is primed for cytokine activation of NFκB by exposure to low and disturbed blood flow (LDF). While priming leads to an exaggerated expression of Icam1 and Vcam following cytokine stimulation, the molecular underpinnings are not understood. In a model of LDF, platelets were required for the increased expression of several RNA-binding splice factors, including Polypyrimidine tract binding protein (Ptbp1). This was coordinated with changes in RNA splicing in the NFκB pathway in primed cells, leading us to examine splice factors as mediators of priming. Using Icam1 and Vcam induction by TNFα stimulation as a readout, we performed a CRISPR-Cas9 screen of these factors and identified a requirement for Ptbp1 in priming. Deletion of Ptbp1 had no obvious effect on cell proliferation or viability, but reversed LDF splicing patterns and inhibited NFκB nuclear translocation and transcriptional activation of nearly all downstream targets, including Icam1 and Vcam. In human coronary arteries, elevated PTBP1 correlates with expression of TNF pathway genes and plaque. In vivo, endothelial specific deletion of Ptbp1 reduced Icam1 expression and myeloid cell infiltration at regions of LDF in atherosclerotic mice and limited atherosclerosis. Together, our data show that Ptbp1, which is induced in a subset of the endothelium by innate immune cell recruitment at regions of LDF, is required for priming of the endothelium for subsequent NFκB activation, myeloid cell recruitment and atherosclerosis.

ABSTRACTß2 (CD18) integrins with a-chains CD11a, -b, -c, and -d are important adhesion molecules necessary for leukocyte migration and cellular interactions. CD18 deficiency leads to recurrent bacterial infections and poor wound healing due to reduced migration of leukocytes to inflammatory sites. CD8 T cells also upregulate CD11a, CD11b, and CD11c upon activation. However, the role these molecules play for CD8 T cells in vivois not known. To determine the function of individual ß2 integrins, we examined CD8 T cell responses to Listeria monocytogenesinfection in CD11a-, CD11b-, and CD11c-deficient mice. The absence of CD11b or CD11c had no effect on the generation of antigen-specific CD8 T cells. In contrast, the magnitude of the primary CD8 T cell response in CD11a-deficient mice was significantly reduced. Moreover, the response in CD11a-/-mice exhibited reduced differentiation of short-lived effector cells (KLRG1hiCD127lo), although cytokine and granzyme B production levels were unaffected. Notably, CD11a deficiency resulted in greatly enhanced generation of CD62L+central memory cells. Surprisingly, CD8 T cells lacking CD11a mounted a robust secondary response to infection. Taken together, these findings demonstrated that CD11a expression contributes to expansion and differentiation of primary CD8 T cells but may be dispensable for secondary responses to infection.