Human cord blood stem cell paracrine factors activate the survival protein kinase Akt and inhibit death protein kinases JNK and p38 in injured cardiomyocytes

Background aims. We hypothesized that paracrine factors from human umbilical cord blood mononuclear cells (hUCBC) activate in injured cardiomyocytes the survival protein kinase Akt and limit activation of death protein kinases INK and p38. Methods. We treated hUCBC with H2O2 and measured growth factors and cytokines secreted by hUCBC. We then treated cardiomyocytes with H2O2 for 24 h and measured Akt, JNK and p38 activation by means of Western blots. We also measured myocyte viability and apoptosis with the use of fluorescence-activated cell-sorting cytometry. We then investigated myocytes treated for 24 h with H2O2 plus hUCBC and myocytes without hUCBC or H2O2. Four million hUCBC were placed in transwells permeable only to hUCBC paracrine factors, and the transwells were placed in flasks with H2O2+Dulbecco's modified Eagle's medium or in flasks with myocytes plus H2O2+Dulbecco's modified Eagle's medium. Results. hUCBC increased.secretion during H2O2 of hepatocyte growth factor by 338%, insulin-like growth factor by 200%, interleukin-4 by 200%, vascular endothelial cell growth factor by 192%, placental growth factor by 150%, interleukin-10 by 150% and angiogenin by 121%. H2O2 increased myocyte JNK activation by 237% and p38 activation by 60%, decreased myocyte viability by 38% and increased necrosis by 34% (all P < 0.01). hUCBC paracrine factors increased in myocytes with H2O2 Akt activation by >= 25%, decreased JNK and p38 activation by >= 35%, increased viability by >22% and decreased apoptosis by >33% (all P < 0.05). Akt inhibitor API-1 prevented the effects of hUCBC and enhanced H2O2 decrease of myocyte viability. Addition of JNK inhibitor SP600125 or p38 inhibitor SB203580 to myocytes plus H2O2 prevented H2O2 decrease in viability and increased hUCBC beneficial effects. Conclusions. During free radical stress, hUCBC paracrine factors activate myocyte Akt, which increases myocyte viability by decreasing activation of death-promoting protein kinases JNK and p38.