Search

Objective: The endothelial surface layer (ESL), a layer of macromolecules on the surface of endothelial cells, can both impede and facilitate leukocyte recruitment. However, its role in monocyte and neutrophil recruitment in glomerular capillaries is unknown. Methods: We used multiphoton intravital microscopy to examine monocyte and neutrophil behavior in the glomerulus following ESL disruption with hyaluronidase. Results: Constitutive retention and migration of monocytes and neutrophils within the glomerular microvasculature was unaltered by hyaluronidase. Consistent with this, inhibition of the hyaluronan‐binding molecule CD44 also failed to modulate glomerular trafficking of these immune cells. To investigate the contribution of the ESL during acute inflammation, we induced glomerulonephritis via in situ immune complex deposition. This resulted in increases in glomerular retention of monocytes and neutrophils but did not induce marked reduction in the glomerular ESL. Furthermore, hyaluronidase treatment did not modify the prolonged retention of monocytes and neutrophils in the acutely inflamed glomerular microvasculature. Conclusions: These observations indicate that, despite evidence that the ESL has the capacity to inhibit leukocyte‐endothelial cell interactions while also containing adhesive ligands for immune cells, neither of these functions modulate trafficking of monocytes and neutrophils in steady‐state or acutely‐inflamed glomeruli. [ABSTRACT FROM AUTHOR]

Deciphering the molecular basis of leukocyte recruitment is critical to the understanding of inflammation. In this study, we investigated the contribution of the tetraspanin CD37 to this key process. CD37-deficient mice showed impaired neutrophil recruitment in a peritonitis model. Intravital microscopic analysis indicated that the absence of CD37 impaired the capacity of leukocytes to follow a CXCL1 chemotactic gradient accurately in the interstitium. Moreover, analysis of CXCLl-induced leukocyte-endothelial cell interactions in postcapillary venules revealed that CXCLl-induced neutrophil adhesion and transmigration were reduced in the absence of CD37, consistent with a reduced capacity to undergo β2 integrin-dependent adhesion. This result was supported by in vitroflow chamber experiments that demonstrated an impairment in adhesion of CD37-deficient neutrophils to the β2 integrin ligand, ICAM-1, despite the normal display of high-affinity β2 integrins. Superresolution microscopic assessment of localization of CD37 and CD18 in ICAM-1-adherent neutrophils demonstrated that these molecules do not significantly cocluster in the cell membrane, arguing against the possibility that CD37 regulates β2 integrin function via a direct molecular interaction. Moreover, CD37 ablation did not affect β2 integrin clustering. In contrast, the absence of CD37 in neutrophils impaired actin polymerization, cell spreading and polarization, dysregulated Rac-1 activation, and accelerated β2 integrin internalization. Together, these data indicate that CD37 promotes neutrophil adhesion and recruitment via the promotion of cytoskeletal function downstream of integrin-mediated adhesion. [ABSTRACT FROM AUTHOR]

Aims: Acute myocardial infarction rapidly increases blood neutrophils (<2 h). Release from bone marrow, in response to chemokine elevation, has been considered their source, but chemokine levels peak up to 24 h after injury, and after neutrophil elevation. This suggests that additional non-chemokine-dependent processes may be involved. Endothelial cell (EC) activation promotes the rapid (<30 min) release of extracellular vesicles (EVs), which have emerged as an important means of cell-cell signalling and are thus a potential mechanism for communicating with remote tissues., Methods and Results: Here, we show that injury to the myocardium rapidly mobilizes neutrophils from the spleen to peripheral blood and induces their transcriptional activation prior to arrival at the injured tissue. Time course analysis of plasma-EV composition revealed a rapid and selective increase in EVs bearing VCAM-1. These EVs, which were also enriched for miRNA-126, accumulated preferentially in the spleen where they induced local inflammatory gene and chemokine protein expression, and mobilized splenic-neutrophils to peripheral blood. Using CRISPR/Cas9 genome editing, we generated VCAM-1-deficient EC-EVs and showed that its deletion removed the ability of EC-EVs to provoke the mobilization of neutrophils. Furthermore, inhibition of miRNA-126 in vivo reduced myocardial infarction size in a mouse model., Conclusions: Our findings show a novel EV-dependent mechanism for the rapid mobilization of neutrophils to peripheral blood from a splenic reserve and establish a proof of concept for functional manipulation of EV-communications through genetic alteration of parent cells., Competing Interests: Conflict of interest: none declared., (© The Author(s) 2022. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Endocrine cells are continually regulating the balance between hormone biosynthesis, secretion, and intracellular degradation to ensure that cellular hormone stores are maintained at optimal levels. In pancreatic beta-cells, intracellular insulin stores in beta-granules are mostly upheld by efficiently up-regulating proinsulin biosynthesis at the translational level to rapidly replenish the insulin lost via exocytosis. Under normal circumstances, intracellular degradation of insulin plays a relatively minor janitorial role in retiring aged beta-granules, apparently via crinophagy. However, this mechanism alone is not sufficient to maintain optimal insulin storage in beta-cells when insulin secretion is dysfunctional. Here, we show that despite an abnormal imbalance of glucose/glucagon-like peptide 1 regulated insulin production over secretion in Rab3A(-/-) mice compared with control animals, insulin storage levels were maintained due to increased intracellular beta-granule degradation. Electron microscopy analysis indicated that this was mediated by a significant 12-fold up-regulation of multigranular degradation vacuoles in Rab3A(-/-) mouse islet beta-cells (P