Lam, Chen‐Fuh

The mechanisms underlying regenerative function of endothelial progenitor cells (EPCs) are not completely understood. Since previous studies from several groups including ours suggest that biosynthesis of NO in EPCs is low, the present study was designed to determine ability of EPCs to produce and release prostacyclin (PGI 2 ). Outgrowth (“late”) EPCs were obtained from peripheral blood of healthy subjects. Enzymatic activity of eNOS was significantly lower in EPCs as compared to eNOS activity in human coronary endothelial cells (CAECs) (n=4‐6 subjects, P<0.05). In contrast, production and release of PGI 2 was four fold higher in EPCs as compared to CAECs (n=3, P<0.05). This was associated with significantly higher expression of cyclooxygenase‐1 (COX‐1) protein in EPCs whereas levels of COX‐2 protein were not different between progenitor and mature endothelial cells. Production of thromboxane A 2 and prostaglandin E 2 were low and identical in EPCs and CAECs. Most importantly, inhibition of COX isoforms with indomethacin impaired pro‐angiogenic effect of EPCs as assessed by in vitro tube formation assay (n=4‐6, P<0.05). Cell proliferation was also significantly reduced after inhibition of COX isoforms with indomethacin or inactivation of PGI 2 ‐synthase by siRNA (n=4‐6, P<0.05). Our findings suggest that production and release PGI 2 is an important mechanism contributing to regenerative capability of EPCs.

Sepsis, the systemic inflammatory response to infection, imposes a high demand for bodily adaptation, with the cardiovascular response a key determinant of outcome. The homeostatic elements that secure cardiac tolerance in the setting of the sepsis syndrome are poorly understood. Here, in a model of acute septic shock induced by endotoxin challenge with Escherichia coli lipopolysaccharide (LPS), knockout of the KCNJ8 gene encoding the vascular Kir6.1 K ATP channel pore predisposed to an early and profound survival disadvantage. The exaggerated susceptibility provoked by disruption of this stress‐responsive sensor of cellular metabolism was linked to progressive deterioration in cardiac activity, ischemic myocardial damage, and contractile dysfunction. Deletion of KCNJ8 blunted the responsiveness of coronary vessels to cytokine‐ or metabolic‐mediated vasodilation necessary to support myocardial perfusion in the wild‐type (WT), creating a deficit in adaptive response in the Kir6.1 knockout. Application of a K ATP channel opener drug improved survival in the endotoxic WT but had no effect in the Kir6.1 knockout. Restoration of the dilatory capacity of coronary vessels was required to rescue the Kir6.1 knockout phenotype and reverse survival disadvantage in lethal endotoxemia. Thus, the Kir6.1containing K ATP channel, by coupling vasoreactivity with metabolic demand, provides a vital feedback element for cardiovascular tolerance in endotoxic shock.—Kane, G. C., Lam, C‐F., O'Cochlain, F., Hodgson, D. M., Reyes, S., Liu, X‐K., Miki, T., Seino, S., Katusic, Z. S., Terzic, A. Gene knockout of the KCNJ8encoded Kir6.1 KATP channel imparts fatal susceptibility to endotoxemia. FASEB J. 20, 2271–2280 (2006)