DNA-release by Streptococcus pneumoniae autolysin LytA induced Krueppel-like factor 4 expression in macrophages

Abstract

The recruitment of myeloid cells to the lung is of utmost importance for the elimination of invading pathogens. We investigated the Streptococcus pneumoniae-dependent induction mechanism of KLF4 in macrophages as a potential regulator of the macrophage immune response. We demonstrated that only viable pneumococci, which have direct contact to the host cells and release LytA-dependent DNA, induced KLF4. Exogenous supplementation of pneumococcal, other bacterial, eukaryotic foreign (human) or self (mouse) DNA to autolysis-deficient pneumococci restored (at least in part) pneumococci-related KLF4 induction. Experiments using TLR9, TRIF and MyD88 knockout macrophages revealed that TLR9, TRIF and MyD88 were partly involved in the S. pneumoniae-induced KLF4 expression. BMMs missing important DNA receptor related molecules (ASC−/−, STING−/−) showed no differences in pneumococci-related KLF4 expression. Similar results were observed with IFNAR−/− BMMs and Type I IFN stimulated cells. LyzMcre mediated knockdown of KLF4 in BMMs resulted in a decreased secretion of proinflammatory cytokines and enhanced IL-10 release. In summary, we showed that pneumococci-related KLF4 induction in macrophages is mediated via a PAMP-DAMP induction mechanism involving a hitherto unknown host cell DNA sensor leading to a more proinflammatory macrophage phenotype.

Impact of the myeloid Krüppel like factor4 during pneumococcal pneumonia

“…10. Further, unlike in epithelial cells, there is no induction of KLF4 with bacterial DNA alone 136 but the signal was partly back when the cells were stimulated with the combination of pneumococcal strain R6x∆lytA and bacterial DNA, the inducing factor for KLF4 in macrophages 169 . It has been reported that S. pneumoniae autolysin LytA (N-acetylmuramoyl-L-alanine amidase) activates immunomodulatory signaling pathways in macrophages by releasing bacterial cell wall constituents such as peptidoglycan and diconic acid 187 .…”

“…Zahlten et al and Herta et al have previously shown that LytA (autolysin) dependent release of bacterial DNA was a controlling factor in the induction of KLF4 in epithelial cells and macrophages during S. pneumoniae infection 167,169 . The present experiment was done to see whether the induction of KLF4 was also dependent on autolysin like in the other cell types.…”

“…Since we have already seen an increased expression of KLF4 in BMMs during pneumococcal pneumonia from previous studies, which had a functional role 169 , experiments were done to see whether neutrophils showed any KLF4 expression during bacterial pneumonia. Human neutrophils were isolated from whole blood obtained from healthy individuals.…”

KLF4 upregulation is involved in alternative macrophage activation during secondary Echinococcus granulosus infection

“…During mycobacterium tuberculosis infection and alcoholic liver disease, upregulation of KLF4 favored M2 polarization. However, Str eptococcus pneumoniae induced KLF4 expression in macrophages, leading to a more proinflammatory macrophage phenotype . In a murine experimental model of autoimmune encephalomyelitis, the increased and sustained expression of KLF4 was found to reduce numbers of proinflammatory T cells and M1 macrophages, as well as to suppress central nervous system inflammation .…”

“…However, Streptococcus pneumoniae induced KLF4 expression in macrophages, leading to a more proinflammatory macrophage phenotype. 18 In a murine experimental model of autoimmune encephalomyelitis, the increased and sustained expression of KLF4 was found to reduce numbers of proinflammatory T cells and M1 macrophages, as well as to suppress central nervous system inflammation. 19 23 The mRNA expression of KLF4 remained unaltered in peripheral blood monocytes and macrophages of patients with visceral leishmaniasis.…”