Cell-free DNA in blood circulation is generated by DNase1L3 and caspase-activated DNase

Cell-free DNA (cfDNA) (e.g. fetal- or tumor-derived DNA) is DNA found in the blood circulation. It is now widely investigated as a biomarker for prenatal screening, tumor diagnosis, and tumor monitoring as "liquid biopsies". However, the biological and biochemical aspects of cfDNA remain unclear. Although cfDNA is considered to be mainly derived from dead cells, information is scarce as to whether it is apoptotic or necrotic and what kinds of endonucleases or DNases are involved. We induced in vivo hepatocyte necrosis and apoptosis in mice deficient in DNase1L3 (also named DNase γ) and/or caspase-activated DNase (CAD) genes with acetaminophen overdose and anti-Fas antibody treatments. We found that (i) DNase1L3 was the endonuclease responsible for generating cfDNA in acetaminophen-induced hepatocyte necrosis and (ii) CAD and DNase1L3 cooperated in producing cfDNA for anti-Fas mediated hepatocyte apoptosis.