Abstract 3648: A Dual Role for Granulocyte-Colony Stimulating Factor in Promotion of Coronary Collateral Growth and Production of Cardiomyocyte Reactive Oxygen Species
Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic cytokine that promotes proliferation and differentiation of neutrophil progenitors. Because G-CSF ameliorates myocar-dial ischemic injury, we projected this effect would also translate into stimulating myocardial adaptations to ischemia. Accordingly, we hypothesized that G-CSF stimulates coronary collateral growth (CCG) in a rat model of repetitive episodic ischemia (RI): 40 sec LAD occlusion every 20 min for 2h20min, 3 times/day for 5 days. CCG was deduced from collateral-dependent flow (flow to LAD region during occlusion [neutron activated microspheres]) and expressed as the increase in the ratio between collateral-dependent and normal zone flows from the initial measurement to that after 5 days of RI. Following RI, G-CSF (100 microg/Kg/day) increased CCG (P<0.01) (0.47 +− 0.15) versus vehicle (0.14 +− 0.06). Surprisingly, G-CSF treatment without RI increased CCG (0.57 +− 0.18, P<0.01 vs vehicle) equal to G-CSF +RI. Because redox signaling is critical for CCG and neutrophils are a rich source of NADPH oxidase and reactive oxygen species (ROS), we hypothesized that G-CSF stimulates production of ROS. We evaluated ROS by dihydroethidine (DHE) fluorescence (LV injection, 60 microg/kg, during two episodes of ischemia). DHE fluorescence was double in G-CSF+RI vs vehicle+RI (P<0.01), and even higher in G-CSF without RI (P<0.01). Interestingly, the DHE signal did not co-localize with myeloperoxidase (immunostaining, neutrophil marker) but appeared in cardiac myocytes. To unequivocally determine if G-CSF stimulates ROS production in cardiac myocytes, we studied isolated cardiac myocytes and found the cytokine stimulates ROS. In addition to affecting neutrophils, G-CSF directly targets cardiac myocytes to produce ROS. In conclusion, G-CSF stimulates production of ROS by cardiac myocytes, which likely plays a pivotal role in adaptations of the heart to ischemia including growth of the coronary collateral circulation.