Heme Oxygenase-1 Deficiency Diminishes Methicillin-Resistant Staphylococcus aureus Clearance Due to Reduced TLR9 Expression in Pleural Mesothelial Cells

• Published in: PloS one 2017-01, Vol.12 (1), p.e0169245-e0169245
• Main Authors: Gahlot, Satindra, Nasreen, Najmunnisa, Johnson, Judith A, Sahn, Steven A, Mohammed, Kamal A
• Format: Article
• Language: English
• Subjects: Activation; Anemia, Hemolytic - genetics; Anemia, Hemolytic - metabolism; Animals; Antimicrobial agents; Bacteria; Bacterial diseases; Bacterial infections; Biology and life sciences; Carbon monoxide; Chemokines; Cobalt; Critical care; Cytokines; Dendritic cells; Deoxyribonucleic acid; DNA; Drug resistance; Empyema; Epithelial Cells - enzymology; Epithelial Cells - metabolism; Female; Growth Disorders - genetics; Growth Disorders - metabolism; Health aspects; Heme; Heme oxygenase (decyclizing); Heme Oxygenase-1 - deficiency; Heme Oxygenase-1 - genetics; Heme Oxygenase-1 - metabolism; Immune clearance; Immunity; Immunity, Innate - genetics; Immunity, Innate - physiology; Immunology; Infection; Infections; Infectious diseases; Inflammation; Innate immunity; Iron Metabolism Disorders - genetics; Iron Metabolism Disorders - metabolism; Kinases; Male; Medicine; Medicine and health sciences; Methicillin; Methicillin-Resistant Staphylococcus aureus - pathogenicity; Mice; Mice, Knockout; Microbial drug resistance; Oxygenase; Pathogenesis; Pathogens; Pleura; Pleura - enzymology; Pleura - metabolism; Pleura - microbiology; Pneumonia; Polymerase chain reaction; Proteins; Protoporphyrin; Research and Analysis Methods; Reverse Transcriptase Polymerase Chain Reaction; Sepsis; Signal Transduction - genetics; Signal Transduction - physiology; Skin; Staphylococcus aureus; Staphylococcus aureus infections; Staphylococcus infections; TLR1 protein; TLR4 protein; TLR9 protein; Toll-Like Receptor 9 - genetics; Toll-Like Receptor 9 - metabolism; Toll-like receptors; Veterans; Zinc
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0169245

Methicillin Resistant Staphylococcus aureus (MRSA) cause pneumonia and empyema thoraces. TLR9 activation provides protection against bacterial infections and Heme oxygenase-1 (HO-1) is known to enhance host innate immunity against bacterial infections. However, it is still unclear whether HO-1 regulates TLR-9 expression in the pleura and modulates the host innate defenses during MRSA empyema. In order to determine if HO-1 regulates host innate immune functions via modulating TLR expression, in MRSA empyema, HO-1+/+ and HO-1-/- mouse pleural mesothelial cells (PMCs) were infected with MRSA (1:10, MOI) in the presence or absence of Cobalt Protoporphyrin (CoPP) and Zinc Protoporphyrin (ZnPP) or CORM-2 (a Carbon monoxide donor) and the expression of mTLR9 and mBD14 was assessed by RT-PCR. In vivo, HO-1+/+ and HO-1-/- mice were inoculated with MRSA (5x106 CFU) intra-pleurally and host bacterial load was measured by CFU, and TLR9 expression in the pleura was determined by histochemical-immunostaining. We noticed MRSA inducing differential expression of TLR9 in HO-1+/+ and HO-1 -/- PMCs. In MRSA infected HO-1+/+ PMCs, TLR1, TLR4, and TLR9 expression was several fold higher than MRSA infected HO-1-/- PMCs. Particularly TLR9 expression was very low in MRSA infected HO-1-/- PMCs both in vivo and in vitro. Bacterial clearance was significantly higher in HO-1+/+ PMCs than compared to HO-1-/- PMCs in vitro, and blocking TLR9 activation diminished MRSA clearance significantly. In addition, HO-1-/- mice were unable to clear the MRSA bacterial load in vivo. MRSA induced TLR9 and mBD14 expression was significantly high in HO-1+/+ PMCs and it was dependent on HO-1 activity. Our findings suggest that HO-1 by modulating TLR9 expression in PMCs promotes pleural innate immunity in MRSA empyema.