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A2778 - Heparan Sulfate Fragments Released During Sepsis Initiate Persistent Neurocognitive Dysfunction Through Sequestration of Hippocampal Brain-Derived Neurotrophic Factor
Author Block: J. A. Hippensteel1, J. E. Orfila2, J. A. Ford1, G. Su3, F. Zhang4, X. Liu4, X. Han4, J. Liu3, R. J. Linhardt4, P. Herson2, E. P. Schmidt1; 1Pulmonary and Critical Care, University of Colorado Denver, Aurora, CO, United States, 2Anesthesiology, University of Colorado Denver, Aurora, CO, United States, 3Pharmacy, University of North Carolina, Chapel Hill, NC, United States, 4Chemistry, Rensselaer Polytechnic Institute, Troy, NY, United States.
Introduction: Persistent neurocognitive dysfunction is common in sepsis survivors yet its underlying pathophysiology remains poorly understood. We have previously shown that sepsis induces degradation of the endothelial glycocalyx, releasing constituent heparan sulfate (HS) octasaccharides into the circulation. We hypothesized that these circulating fragments, in a sulfation sequence-specific pattern, sequester brain-derived neurotrophic factor (BDNF) and cause cognitive impairment. Methods: We modeled sepsis by intraperitoneal injection of lipopolysaccharide (LPS) or cecal ligation and puncture (CLP) in C57BL/6 mice. We measured circulating HS concentration and structure via mass spectrometry. We determined if circulating HS fragments penetrate the hippocampus via intravital microscopy and immunofluorescence through intravenous injection of fluorescently labeled HS fragments in these sepsis models. We determined the cognitive effects of HS by performing ex vivo hippocampal electrophysiology experiments to evaluate long-term potentiation (LTP), the synaptic correlate of learning. BDNF-dependence of HS effects on LTP was evaluated by performing these electrophysiology experiments in the presence or absence of the BDNF receptor (TrkB) activating agent 7,8 DHF. We corroborated these effects with behavioral measures of learning (e.g. contextual fear conditioning, CFC). Finally, we performed a glycoarray experiment to determine the HS sulfation sequence-specificity of BDNF inhibition. Results: LPS-induced sepsis (similar to CLP) induced release of HS fragments in the plasma. HS penetrated the hippocampus in vivo as demonstrated by histology and intravital microscopy; ex vivo, we observed that fragments directly inhibited LTP when compared to controls. HS-mediated inhibition of LTP was reversible with 7,8 DHF ex vivo, demonstrating BDNF specificity of HS-induced loss of LTP. Administration of 7,8 DHF to septic mice congruently improved memory (CFC) in vivo. Finally, four specific HS fragment subtypes were found to have a high affinity for BDNF using our glycoarray analysis. Conclusions: HS fragments are shed during sepsis and, through their ability to sequester BDNF, directly inhibit hippocampal-dependent memory formation. There are specific HS substructures with a high affinity for BDNF. We believe that identification of this subset of highly BDNF-avid HS sequences is a major step in developing predictive biomarkers and novel therapies for the management of persistent neurocognitive dysfunction after sepsis.