Lcn10 in Sepsis-Induced Vascular Leakage and Heart Failure

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Vascular hyperpermeability is well-recognized to be responsible for sepsis-triggered organ failure and patient mortality. Despite decades of intensive study, there is no specific treatment available for targeting such vascular leakage thus far. This is due in part to the incomplete knowledge of the mediators and mechanisms underlying sepsis-elicited disruption of the endothelial barrier integrity. At present, most prior work has focused on pulmonary vascular leakage that results in lung edema and acute respiratory distress syndrome. Few studies have investigated coronary vascular leakage, which is a major cause of heart failure and death in human patients with septic shock. We recently discovered that expression of lipocalin 10 (Lcn10), a poorly characterized member of the lipocalin superfamily, was significantly downregulated in the hearts of both endotoxin LPS- and cecal ligation- puncture (CLP)-treated mice, compared to their controls. Interestingly, further cell-type specific analysis showed that such reduction of Lcn10 did not occur in either cardiomyocytes or fibroblasts but only in cardiac endothelial cells (ECs). These compelling data implicate a potential role of Lcn10 in sepsis-induced cardiovascular leakage. Indeed, using a global knockout mouse model, we observed that deficiency of Lcn10 significantly augmented LPS- induced vascular leakage, leading to greater cardiac depression and higher mortality, compared to LPS-treated wild-type control mice. By contrast, in vitro forced overexpression of Lcn10 in ECs showed greater resistance to LPS-induced monolayer leak relative to control cells. An initial mechanistic analysis by RNA-sequencing and RT- qPCR showed that both endogenous and exogenous elevation of Lcn10 in ECs caused significant upregulation of slingshot homolog 1 (Ssh1). Ssh1 is a phosphatase known to dephosphorylate and thus activate Cofilin, a key actin-binding protein that plays an essential role in controlling actin filament dynamics. Most importantly, knockdown of Ssh1 in ECs offsets the Lcn10-induced reduction of monolayer leakage upon LPS exposure. Based on these preliminary data, we hypothesize that Lcn10 is critical for protecting against sepsis-induced vascular leak via the activation of the Ssh1-Cofilin pathway. This hypothesis will be tested by pursuing three specific aims: 1) Define the precise role of Lcn10 in vascular permeability during polymicrobial sepsis, using a global knockout and an EC-specific Lcn10-transgenic mouse model; 2) Identify the mechanism by which Lcn10- elicited reduction of cardiovascular leakage is dependent on Ssh1-mediated actin dynamics, using a cross mouse model by mating EC-specific Lcn10-transgenic mice with Ssh1-KO mice; and 3) Investigate the therapeutic potential of recombinant Lcn10 protein in treating sepsis. The proposed studies are expected to identify Lcn10 as a potent and novel regulator of vascular permeability and a new protector against sepsis-induced heart failure. If completed, the findings from this proposal are likely to provide new therapeutic options for reducing vascular leakage during sepsis, with the hope of improving the survival of septic patients.