Apoptotic hepatocyte DNA inhibits hepatic stellate cell chemotaxis via toll-like receptor 9.
Apoptosis of hepatocytes results in the development of liver fibrosis, but the molecular signals mediating this are poorly understood. Degradation and modification of nuclear DNA is a central feature of apoptosis, and DNA from apoptotic mammalian cells is known to activate immune cells via Toll-like receptor 9 (TLR9). We tested if DNA from apoptotic hepatocytes can induce hepatic stellate cell (HSC) differentiation. Our data show that apoptotic hepatocyte DNA and cytidine-phosphate-guanosine oligonucleotides induced up-regulation of transforming growth factor beta1 and collagen 1 messenger RNA both in the human HSC line LX-2 and in primary mouse HSCs. These effects were opposed by TLR9 antagonists. We have recently shown that adenosine inhibits HSC chemotaxis, and we now show that apoptotic hepatocyte DNA also inhibits platelet-derived growth factor (PDGF)-mediated HSC chemotaxis. Inhibition of HSC chemotaxis by PDGF was blocked by TLR9 antagonists, and was absent in primary HSCs from mice deficient in TLR9 or the TLR adaptor molecule MyD88. Stimulation of TLR9 on HSCs blocked signaling by the PDGF signaling molecule inositol 1,4,5-triphosphate and reduced PDGF-mediated increase in cytosolic Ca(2+).


CONCLUSIONS
DNA from apoptotic hepatocytes acts as an important mediator of HSC differentiation by (1) providing a stop signal to mobile HSCs when they have reached an area of apoptosing hepatocytes and (2) inducing a stationary phenotype-associated up-regulation of collagen production.
Watanabe
Azuma
A
Section of Digestive Diseases, Yale University School of Medicine, New Haven, CT, USA.
Hashmi
Ardeshir
A
Gomes
Dawidson Assis
DA
Town
Terrence
T
Badou
Abdallah
A
Flavell
Richard Anthony
RA
Mehal
Wajahat Zafar
WZ
D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D002464:Cell Migration Inhibition / Q000502:physiology*; D024042:Collagen Type I / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008099:Liver / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D008103:Liver Cirrhosis / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051217:Toll-Like Receptor 9 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
D000199:Actins; C408982:CPG-oligonucleotide; D024042:Collagen Type I; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D009838:Oligodeoxyribonucleotides; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D051217:Toll-Like Receptor 9; D053773:Transforming Growth Factor beta1; D015544:Inositol 1,4,5-Trisphosphate; D004247:DNA