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Abstract
BackgroundSepsis-associated encephalopathy (SAE), a diffuse cerebral dysfunction in the absence of direct CNS infection, is associated with increased rates of mortality and morbidity in patients with sepsis. Increased cytokine production and disruption of the blood-brain barrier (BBB) are implicated in the pathogenesis of SAE. The induction of pro-inflammatory mediators is driven, in part, by activation of NF-κΒ. Lipopolysaccharide (LPS), an endotoxin produced by gram-negative bacteria, potently activates NF-κΒ and its downstream targets, including cyclooxygenase-2 (Cox-2). Cox-2 catalyzes prostaglandin synthesis and in the brain prostaglandin, E2 is capable of inducing endothelial permeability. Depletion of polymerase δ-interacting protein 2 (Poldip2) has previously been reported to attenuate BBB disruption, possibly via regulation of NF-κΒ, in response to ischemic stroke. Here we investigated Poldip2 as a novel regulator of NF-κΒ/cyclooxygenase-2 signaling in an LPS model of SAE.MethodsIntraperitoneal injections of LPS (18 mg/kg) were used to induce BBB disruption in Poldip2+/+ and Poldip2+/− mice. Changes in cerebral vascular permeability and the effect of meloxicam, a selective Cox-2 inhibitor, were assessed by Evans blue dye extravasation. Cerebral cortices of Poldip2+/+ and Poldip2+/− mice were further evaluated by immunoblotting and ELISA. To investigate the role of endothelial Poldip2, immunofluorescence microscopy and immunoblotting were performed to study the effect of siPoldip2 on LPS-mediated NF-κΒ subunit p65 translocation and Cox-2 induction in rat brain microvascular endothelial cells. Finally, FITC-dextran transwell assay was used to assess the effect of siPoldip2 on LPS-induced endothelial permeability.ResultsHeterozygous deletion of Poldip2 conferred protection against LPS-induced BBB permeability. Alterations in Poldip2+/+ BBB integrity were preceded by induction of Poldip2, p65, and Cox-2, which was not observed in Poldip2+/− mice. Consistent with these findings, prostaglandin E2 levels were significantly elevated in Poldip2+/+ cerebral cortices compared to Poldip2+/− cortices. Treatment with meloxicam attenuated LPS-induced BBB permeability in Poldip2+/+ mice, while having no significant effect in Poldip2+/− mice. Moreover, silencing of Poldip2 in vitro blocked LPS-induced p65 nuclear translocation, Cox-2 expression, and endothelial permeability.ConclusionsThese data suggest Poldip2 mediates LPS-induced BBB disruption by regulating NF-κΒ subunit p65 activation and Cox-2 and prostaglandin E2 induction. Consequently, targeted inhibition of Poldip2 may provide clinical benefit in the prevention of sepsis-induced BBB disruption.
Highlights
Sepsis-associated encephalopathy (SAE), a diffuse cerebral dysfunction in the absence of direct Central nervous system (CNS) infection, is associated with increased rates of mortality and morbidity in patients with sepsis
We report that Polymerase delta-interacting protein 2 (Poldip2) is a novel regulator of Nuclear factor kappa Β (NF-κΒ)/Cox-2 signaling in a model of SAE
We previously reported that Poldip2 mediates breakdown of the blood-brain barrier (BBB) following ischemic injury [26]
Summary
Sepsis-associated encephalopathy (SAE), a diffuse cerebral dysfunction in the absence of direct CNS infection, is associated with increased rates of mortality and morbidity in patients with sepsis. Lipopolysaccharide (LPS), an endotoxin produced by gram-negative bacteria, potently activates NF-κΒ and its downstream targets, including cyclooxygenase-2 (Cox-2). To investigate the role of endothelial Poldip, immunofluorescence microscopy and immunoblotting were performed to study the effect of siPoldip on LPS-mediated NF-κΒ subunit p65 translocation and Cox-2 induction in rat brain microvascular endothelial cells. The endotoxin lipopolysaccharide (LPS), a cell wall component of gram-negative bacteria, is a potent mediator of sepsis pathogenesis [1, 2]. Sepsis-associated encephalopathy (SAE), which is a diffuse cerebral dysfunction in the absence of direct central nervous system infection, is a frequent sequela of sepsis [1, 2]. Long-term neurocognitive deficits in memory, learning, and behavior have been reported; treatment of SAE remains limited to the management of the underlying infection [2, 7, 8]
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