Lipocalin2 is an early marker of endothelial activation during sepsis

Association of infection with systemic inflammation defines sepsis. It affects 950,000 patients per year in Europe and the mortality varies from 26% to 60%. In 60% of cases, sepsis induces acute brain dysfunction (SIBD) clinically characterized by altered consciousness ranging from confusion to coma. SIBD is correlated with long-term psycho-cognitive dysfunctions and dementia, and represents a major public health issue. Interestingly, SIBD is not due to direct brain infection, but rather driven by peripheral inflammatory mediators. These mediators affect primarily blood-brain barrier functions causing endothelial activation and microvascular dysfunctions, leading then to intraparenchymal glial dysfunctions and ultimately neurotoxicical effects. However, neither a clear scenario of these events nor molecular key drivers of SIBD have been defined, compromising the design of targeted therapies. Our project is to define key pathophysiological targets of SIBD. We focused on Lipocalin2 (Lcn2), a protein recently found to be upregulated in several neuroinflammatory contexts. Here, we studied the expression of Lcn2 in the brain during sepsis. Experiments were performed in the cecal ligation and puncture (CLP) mouse model for sepsis, which consists of an induced fecal peritonitis. Control mice (Sham) were submitted to skin incision only. In the cortex, hippocampus, and cerebellum, we found a 1000-fold increase in Lcn2 mRNA in CLP mice compared to Sham, associated to the upregulation of inflammatory cytokines TNF-alpha and IL-1beta. We localized Lcn2 upregulation by in situ hybridization and immunohistochemistry mostly in endothelial cells. We confirmed the Lcn2 upreglation performing qPCR on purified brain vessels 4 h post-CLP, which paralleled the upregulation of ICAM, an endothelial activation marker. Altogether, these results suggest that endothelial activation is probably one of the earliest mechanisms induced by peritonitis in the brain, and that Lcn2 upregulation may participate to this regulation. Together, they might therefore be instrumental in neuroinflammatory processes leading to SIBD.