Toll-like receptor 4 mediates mitochondrial DNA damage and biogenic responses after heat-inactivated E. coli.
An important site of cellular damage in bacterial sepsis is mitochondrial DNA (mtDNA), which we proposed is caused by reactive oxygen and nitrogen species generated by activation of signaling through specific toll-like receptors (TLR). In wild-type (Wt) mice injected with heat-inactivated E. coli, hepatic TLR4 and TLR2 proteins were up-regulated with TLR-dependent increases in transcript levels for tumor necrosis factor (TNF-alpha), interleukin 6, nitric oxide synthase-II (iNOS), and NADPH oxidase 2 (Nox2). The accompanying stress significantly depleted hepatic mtDNA despite eight- and fourfold increases in manganese superoxide dismutase (MnSOD) and mitochondrial transcription factor A (Tfam) expression, respectively. The identical E. coli dose generated significantly less TNF-alpha, NO, and Nox2 in TLR4-/- and TLR2/4-/- but not in TLR2-/- mice. TLR4-/- and TLR2/4-/- compared with Wt mice were protected from mtDNA oxidation but showed no Tfam up-regulation and little copy number restoration. A critical role in the mtDNA damage was determined for TLR4-mediated iNOS transcription through the MyD88 pathway. In Wt mice, mtDNA depletion was avoided by selective iNOS blockade, and residual mtDNA loss was linked to NF-kappaB-dependent TNF-alpha expression. These data disclose the dual role of TLR4 in mtDNA damage and compensatory mitochondrial biogenic responses after innate immune activation.
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
Hagir B
HB
Suliman
Karen E
KE
Welty-Wolf
Martha Sue
MS
Carraway
David A
DA
Schwartz
John W
JW
Hollingsworth
Claude A
CA
Piantadosi
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D004249:DNA Damage; D004272:DNA, Mitochondrial / Q000032:analysis / Q000378:metabolism*; D004926:Escherichia coli / Q000472:pathogenicity*; D053592:Interleukin-1 Receptor-Associated Kinases; D015850:Interleukin-6 / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000235:genetics; D018384:Oxidative Stress; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000032:analysis / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000032:analysis / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D004272:DNA, Mitochondrial; D015850:Interleukin-6; D047908:Intracellular Signaling Peptides and Proteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D012333:RNA, Messenger; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D052247:Nitric Oxide Synthase Type II; D053592:Interleukin-1 Receptor-Associated Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt