Exercise-induced increases in cell free DNA in human plasma originate predominantly from cells of the haematopoietic lineage

The role of cell free DNA (cfDNA) has been intensively discussed under various pathological conditions and after acute bouts of exercise. To date, there is still no conclusive evidence concerning the cellular origin of cfDNA and the entire mechanism leading to elevated cfDNA concentrations in human plasma and serum. Here, we investigated the cellular origin of cfDNA in sex-mismatched haematopoietic stem cell transplantation (HSCT) and liver transplantation (LT) patients by determining the relative proportion of Y-chromosomal to total nuclear cfDNA. Total nuclear cfDNA and Y-chromosomal cfDNA concentrations were determined in blood plasma before and after an incremental exercise test via quantitative real-time PCR (qPCR). Female HSCT patients showed high proportions of Y-chromosomal cfDNA. Both total nuclear and Y-chromosomal cfDNA increased significantly and in a highly correlated fashion due to exercise. In male HSCT patients with female donors less than 10% of the cfDNA was of Y-chromosomal origin at any point in time and even though the total amount of cfDNA increased during exercise, no increases in Y-chromosomal DNA could be detected. The percentage of Y-chromosomal cfDNA in female LT patients with male donors was very low and levels remained unchanged during exercise. This indicates that cells not derived from the bone marrow, in this case transplanted liver cells, represented only a minor fraction of cfDNA in blood plasma and were not released during acute physical exercise. Even though many physiological conditions may be altered in transplant patients versus healthy people, our results strongly suggest that cells from the haematopoietic lineage are the main source of cfDNA released during acute bouts of exercise.