Abstract P3012: Syndecan 1 Regulates Lung Endothelial Barrier Function In Homeostatic And Injury Conditions

Abstract

Introduction: Acute lung injury (ALI) is an inflammatory syndrome that may occur secondarily to bacterial infection. Pulmonary edema is a severe complication of ALI and it may result from endothelial barrier disruption. The mechanisms that initiate ALI during bacterial infection remains unresolved. Syndecan 1 (Sdc1) is a heparan sulfate proteoglycan that contributes to endothelial barrier stability and is cleaved during inflammatory processes. Whether Sdc1 contributes to ALI progression is unresolved. Herein we investigated if Sdc1 mediates LPS-induced ALI in mice. Methods: Male and Female Sdc1 knockout (Sdc1KO) and wild type (WT) mice, with 5-8 weeks of age, were injected with lipopolysaccharide (LPS, 10mg/Kg, IP) or PBS and euthanized after 6hr. Bronchoalveolar lavage fluid (BAL) and lung tissue were collected and assessed for myeloperoxidase (MPO) activity, albumin content, RhoA activity using commercially available spectrometric and ELISA kits. Lung edema was assessed by lung wet/dry ratio (W/D). Results and Conclusions: LPS increased lung W/D by 1.5-fold (p=0.0042, n≥5/group) in WT but not Sdc1KO mice. Sdc1KO showed higher basal lung W/D vs WT (Sdc1KO=3.55 vs WT=2.21, p=0.044, n≥5/group). Similarly, a trend increase in basal lung MPO activity was seen in Sdc1KO when compared to WT (p=0.33, n≥5/group). A significant increase in MPO activity was seen in LPS-treated WT (LPS=0.47±0.03 vs. PBS=0.26±0.03, p=0.003) but not LPS-treated Sdc1KO mice (p=0.11; n≥5/group) when compared to matched PBS-treated strain controls. Albumin content was increased by LPS only in WT BAL (LPS=106.9±8.9 vs PBS=63.65±6.15, p=0.03, n≥5/group). LPS increased RhoA activity exclusively in WT lungs. (LPS=0.04±0.002 vs PBS= 0.02±0.003, p=0.04, n≥5/group). A trend increase in RhoA activity was seen in PBS-treated Sdc1KO when compared to PBS-treated WT (p=0.06, n≥4/group). Collectively, our data suggest that Sdc1KO show basal lung endothelial barrier failure. This phenotype is associated with decreased response to LPS. The mechanisms whereby Sdc1 regulate barrier function may involve RhoA-dependent pathway. Sdc1 may participate in lung edema development during ALI.