Endothelial LSP1 is involved in endothelial dome formation, minimizing vascular permeability changes during neutrophil transmigration in vivo

Abstract

The endothelium actively participates in neutrophil migration out of the vasculature via dynamic, cytoskeleton-dependent rearrangements leading to the formation of transmigratory cups in vitro, and to domes that completely surround the leukocyte in vivo. Leukocyte-specific protein 1 (LSP1), an F-actin-binding protein recently shown to be in the endothelium, is critical for effective transmigration, although the mechanism has remained elusive. Herein we show that endothelial LSP1 is expressed in the nucleus and cytosol of resting endothelial cells and associates with the cytoskeleton upon endothelial activation. Two-photon microscopy revealed that endothelial LSP1 was crucial for the formation of endothelial domes in vivo in response to neutrophil chemokine keratinocyte-derived chemokine (KC) as well as in response to endogenously produced chemokines stimulated by cytokines (tumor necrosis factor ␣ [TNF␣] or interleukin-1␤ [IL-1␤]). Endothelial domes were significantly reduced in Lsp1 ؊/؊ compared with wildtype (WT) mice. Lsp1 ؊/؊ animals not only showed impaired neutrophil emigration after KC and TNF␣ stimulation, but also had disproportionate increases in vascular permeability. We demonstrate that endothelial LSP1 is recruited to the cytoskeleton in inflammation and plays an important role in forming endothelial domes thereby regulating neutrophil transendothelial migration. The permeability data may underscore the physiologic relevance of domes and the role for LSP1 in endothelial barrier integrity. IntroductionRecruitment of circulating neutrophils from the bloodstream to sites of tissue injury and infection is the hallmark feature of the inflammatory response. This process involves multiple, interdependent, regulated molecular interactions between the neutrophils and the vascular endothelium. 1,2 Initial tethering and rolling of leukocytes along the vessel wall is followed by firm adhesion to the vascular endothelium caused by chemokine activation of leukocyte integrins. 3,4 The neutrophils then crawl to sites where they migrate through the vascular endothelium, 5 a process known as transendothelial migration or diapedesis. A growing body of literature suggests that transendothelial migration is an interactive process between leukocytes and endothelial cells, in which endothelial cells are not passive bystanders but rather active participants that regulate this process. [6][7][8][9] There is also evidence that leukocyte adhesion molecules binding to endothelial adhesion molecules 2,10 induce intracellular signaling, stimulating the endothelial cytoskeleton and regulatory proteins to initiate transendothelial migration. 1,11,12 One such regulatory protein in endothelial cells is leukocytespecific protein 1 (LSP1), which was initially characterized in lymphocytes and thymocytes. 13,14 LSP1 has now been identified in monocytes, macrophages, dendritic cells, Langerhans cells, and neutrophils [15][16][17] and in both murine and human endothelium. 18 LSP1 is a cytoplasmic intracellular Ca 2ϩ -and F-actin-binding ...

Leukocyte transendothelial migration: A local affair

“…transmigratory cups, apical cups, dome structures, ICAM-1-enriched contact areas, or actin dynamic structures. 14,[67][68][69][70][71] The names were based on the hypothesized function or morphology of these structures. Work of Carman and coworkers showed that these structures, that formed both during para-and transcellular diapedesis (Fig.…”

Dynamic interactions ofPlasmodiumspp. with vascular endothelium

“…Moreover, transmigrating cups around neutrophils has been shown to be a mechanism for the maintenance rather than disruption of barrier function. 64 These discrepancies will need to be resolved in future studies.…”

Intravascular Leukocyte Chemotaxis: The Rules of Attraction

“…Using in vivo spinning disk or multi-photon confocal microscopy, profound anatomical changes of the endothelium that facilitated leukocyte extravasation without compromising vascular barrier integrity were observed Petri B. et al, 2011). Docking cup-like structures were formed by endothelial cells (endothelial projections) at the base of the transmigrating neutrophil, which has also been described for T-lymphocytes in vitro (Carman C. V., Springer T. A., 2004).…”

“…The endothelial projections extended towards the top of the neutrophil and eventually formed a dome that surrounded the entire neutrophil, prior to basolateral opening and neutrophil migration further into tissue. If the dome formations were prevented, neutrophil transmigration was delayed (Petri B. et al, 2011), further implicating an active role of endothelium during leukocyte diapedesis, while maintaining the barrier function and vascular permeability.…”