CCAAT/enhancer-binding protein δ (C/EBPδ) aggravates inflammation and bacterial dissemination during pneumococcal meningitis

Sern et al. Journal of Neuroinflammation CCAAT/enhancer-binding protein (C/EBP) aggravates inflammation and bacterial dissemination during pneumococcal meningitis Mercedes Valls Sern 0 JanWillem Duitman 1 Madelijn Geldhoff 0 JooYeon Engelen-Lee 0 Stefan R Havik 0 Matthijs C Brouwer 0 Diederik van de Beek 0 C Arnold Spek 1 0 Department of Neurology, Center of Infection and Immunity Amsterdam (CINIMA), Academic Medical Center, University of Amsterdam , Meibergdreef 9, PO Box 22660, 1100DD Amsterdam , The Netherlands 1 Center for Experimental and Molecular Medicine (CEMM), Academic Medical Center , Meibergdreef 9, 1105 AZ Amsterdam , The Netherlands Background: The prognosis of bacterial meningitis largely depends on the severity of the inflammatory response. The transcription factor CAAT/enhancer-binding protein (C/EBP) plays a key role in the regulation of the inflammatory response during bacterial infections. Consequently, we assessed the role of C/EBP during experimental meningitis. Methods: Wild-type and C/EBP-deficient mice (C/EBP/) were intracisternally infected with Streptococcus pneumoniae and sacrificed after 6 or 30 h, or followed in a survival study. Results: In comparison to wild-type mice, C/EBP/ mice showed decreased bacterial loads at the primary site of infection and decreased bacterial dissemination to lung and spleen 30 h after inoculation. Expression levels of the inflammatory mediators IL-10 and KC were lower in C/EBP/ brain homogenates, whereas IL-6, TNF-, IL-1, and MIP-2 levels were not significantly different between the two genotypes. Moreover, C/EBP/ mice demonstrated an attenuated systemic response as reflected by lower IL-10, IL-6, KC, and MIP-2 plasma levels. No differences in clinical symptoms or in survival were observed between wild-type and C/EBP/ mice. Conclusion: C/EBP in the brain drives the inflammatory response and contributes to bacterial dissemination during pneumococcal meningitis. C/EBP does, however, not affect clinical parameters of the disease and does not confer a survival benefit. Experimental meningitis; C/EBP; Infection; Streptococcus pneumoniae - Introduction Bacterial meningitis remains an important cause of mortality and morbidity worldwide, despite the implementation of vaccination strategies, effective antibiotic therapy and adjunctive dexamethasone treatment [1,2]. Pneumococcal meningitis is the most common and most severe form of meningitis: 16% to 35% of the patients die and up to 50% of survivors suffer from long-term sequelae, including hearing loss, cognitive impairment, and focal neurological deficits [3,4]. The pathophysiology of bacterial meningitis is characterized by a strong inflammatory response in the subarachnoid space, and this host inflammatory response seems to cause adverse events during bacterial meningitis [5,6]. The severity of the inflammatory response largely has been shown to determine the prognosis in experimental pneumococcal meningitis [7] and novel therapeutic agents may thus target the inflammatory response. However, the inflammatory response during meningitis is complex and has only been partially elucidated. CAAT/enhancer-binding protein (C/EBP), a member of the C/EBP family of transcription factors that is upregulated during the acute phase response, recently emerged as an essential player in the inflammatory response to bacterial infections [8]. C/EBP levels rapidly increase after pro-inflammatory stimuli such as lipopolysaccharide (LPS), interleukin (IL)-1, IL-6, interferon (IFN-), and tumor necrosis factor- (TNF-) [9-11]. Reciprocally, C/ EBP enhances cytokine production and C/EBP-induced inflammation contributes to elimination of bacteria during infectious disease. C/EBP was shown to limit bacterial dissemination and prolong survival during a lethal model of Escherichia coli-induced peritonitis and during Klebsiella pneumoniae-induced pulmonary infection [12,13]. During Streptococcus pneumoniae-induced pulmonary infection, however, C/EBP exaggerated bacterial dissemination and wild-type mice succumbed earlier to the disease as compared to C/EBP/ mice [14]. Furthermore, C/EBP did not affect disease progression during non-lethal models of E. coli-induced peritonitis or urinary tract infection [12,15]. C/EBP therefore seems to play a complex and potential dual role during infectious disease most likely depending on the causing pathogen, the severity of the infection and the infection site. In the present study, we assessed the role of C/EBP in experimental pneumococcal meningitis. Materials and methods Mice Eight- to 12-week-old female C57BL/6 mice were obtained from Charles River (Sulzfeld, Germany), whereas C/EBP/ mice, generated as described previously [16], were bred and maintained at the animal facility at the Academic Medical Center of Amsterdam. The mice were kept to a controlled 12 h light/dark cycle and food and water were provided ad libitum. All experiments were approved by the Institutional Animal Care and Use Committee of the Academic Medical Center, Amsterdam. Experimental pneumococcal meningitis model Pneumococcal meningitis was induced by intracisternal inoculation with S. pneumoniae (serotype 3, American Type Culture Collection #6303; Rockville, MD) as described previously [17]. In brief, wild-type and C/EBP/ mice (n = 12 per group) were inoculated with 1 L bacterial suspension containing 1 104 CFU S. pneumoniae into the cisterna magna under isoflurane anesthesia. Six mice per group inoculated with sterile saline were used as controls. Immediately after intracisternal inoculation, mice were assessed for neurologic damage as a result of the puncture, and if present, these mice were excluded from further analysis. Clinical signs of meningitis were scored at 24 and 30 h post infection as previously described [17]. At 6 and 30 h post infection, mice were anesthetized by intraperitoneal injection of 190 mg/kg ketamine (Eurovet Animal Health, Bladel, The Netherlands) and 0.3 mg/kg dexmedetomidine (Pfizer Animal Health, Capelle aan den Ijssel, The Netherlands) followed by cardiac puncture for blood collection and perfusion of organs with sterile isotonic saline via the left ventricle. CSF was collected by puncture of the cisterna magna. Brain, lung, and spleen were harvested, placed on ice, processed, and stored as described before [17]. EDTA blood was centrifuged at 2,000g for 15 min. Plasma was stored at 80C for further analysis. Determination of cytokines and chemokines The cytokines IL-1, IL-6, IL-10, and TNF- and the chemokines KC and MIP-2 were determined in plasma and brain homogenates by Luminex technology using a mouse Bioplex kit (Bio-Rad Laboratories, Veenendaal, The Netherlands) as described before [17]. Organ damage markers Plasma aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase levels were determined as described before [18]. Murine histopathology and immunohistochemistry Histopathology was performed on the ri (...truncated)