A Disintegrin and Metalloproteinase 15‐Mediated Glycocalyx Disruption Contributes to Vascular Leakage During Septic Injury

Abstract

Disruption of vascular endothelial barrier results in excessive accumulation of plasma proteins and fluid within the interstitial space, exacerbating tissue injury caused by infection or sepsis. There is an urgent need to explore effective strategies to restore vascular barrier integrity in patients with sepsis. Glycocalyx, an endothelial surface coating matrix composed of glycoproteins and proteinglycans attached to glycoaminoglycan chains, has been shown to be protective of vascular barrier function. Degradation of glycocalyx has been implicated in the progression of septic injury, evidenced by increased serum levels of glycocalyx degradation products, including soluble CD44 and hyaluronic acid in sepsis patients, correlating with severity of injury. Currently, the molecular mechanisms underlying glycocalyx degradation are poorly understood. Here, we investigated whether and how this process involves a disintegrin and metalloproteinase 15 (ADAM15), a transmembrane sheddase capable of cleaving the ectodomains of membrane‐bounded proteins. Based on intravital microscopic measurements of dextran (150 kD) exclusion, we comparatively assessed glycocalyx thickness in wild‐type and ADAM15 knockout mice subjected to septic insult via lipopolysaccharides (LPS) injection. Our results indicated that LPS treatment induced a remarkable reduction in glycocalyx thickness in wide type mice, a response significantly attenuated in ADAM15−/− mice, suggesting the critical role of ADAM15 in LPS‐induced glycocalyx injury. Moreover, glycocalyx in mouse pulmonary microvasculature was observed by electron microscopy. Consistently, ADAM15 deficiency prevented the loss of glycocalyx coverage on the endothelial surface in pulmonary vessels following LPS challenge. To elucidate the underlying molecular details, we performed an in vitro cleavage assay, which confirmed the ability of recombinant ADAM15 to cleave CD44, an important glycoprotein expressed in glycocalyx, in a dose‐dependent manner. Further proteomic analysis revealed that the cleavage site of CD44 fell within the membrane‐proximal region of its ectodomain. Functionally, incubating endothelial cells with CD44 ectodomain resulted in barrier dysfunction and adherens junction disorganization. In line with these in vitro findings, mice with impaired glycocalyx exhibited vascular hyperpermeability after LPS challenge, as indicated by increased Evans Blue‐bound albumin extravasation in the lungs as well as enhanced albumin leakage from mesenteric vessels. In contrast, microvessels from ADAM15−/− mice with well‐preserved glycocalyx structure displayed an attenuated permeability response. Taken together, our studies suggest a novel function of ADAM15 in mediating glycocalyx injury during septic challenge.Support or Funding InformationThis work was supported by the National Institutes of Health Grants GM097270 and HL070752.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.