Abstract 386: Lipocalin 10 Protects Against Sepsis-triggered Vascular Leakage Through Activation Of The Ssh1-cofilin Signaling Pathway

Abstract

Background: The increased vascular leakage seen in sepsis patients is well-recognized to be responsible for sepsis-triggered organ failure and patient mortality. Prior work suggests that lipocalin 10 (Lcn10), a member of the lipocalin superfamily, is significantly downregulated in the blood of non-survival septic patients when comparing to the survival group. Nonetheless, whether Lcn10 affects endothelial barrier integrity in sepsis remains unknown. Methods and Results: First, we observed that the expression of Lcn10 was remarkably down-regulated in the hearts of both endotoxin LPS- and cecal ligation/puncture (CLP)-induced septic mice, compared to their controls. Interestingly, further analysis of Lcn10 expression in different cell types isolated from LPS- and CLP-hearts showed that reduction of Lcn10 occurred only in cardiac endothelial cells (ECs) but not in cardiomyocytes or fibroblasts. Using a global Lcn10-knockout (KO) mouse model, we found that loss of Lcn10 greatly increased vascular permeability, which correlated with more severe cardiac depression and higher mortality following LPS challenge or CLP surgery, compared to LPS- or CLP-treated wild-type (WT) mice. By contrast, in vitro overexpression of Lcn10 in ECs provided greater resistance to LPS-caused monolayer leak, compared to control cells. A mechanistic analysis by RNA-sequencing and RT-qPCR revealed that both endogenous and exogenous elevation of Lcn10 in ECs could greatly upregulate slingshot homolog 1 (Ssh1) expression. Ssh1 is a phosphatase known to activate Cofilin, a key actin-binding protein that plays an essential role in controlling actin filament dynamics. Accordingly, phosphorylated Cofilin levels were significantly reduced and thereby, reorganized F-actin to cortical actin for stabilizing tight junction molecules in Lcn10-treated ECs, compared to control cells. Finally, knockdown of Ssh1 in ECs by siRNA greatly offsets Lcn10-induced reduction of monolayer leakage upon LPS insult. Conclusions: Endothelial Lcn10 is critical for protecting against sepsis-induced cardiovascular leakage, and its underlying mechanism involves the activation of Ssh1-Cofilin pathway. Our study suggests that Lcn10 could be a novel regulator of vascular barrier integrity.