Cyclooxygenase-2 plays a crucial role during myocardial patterning of developing chick.

Cyclooxygenase-2 (COX-2), a member of the Cyclooxygenase family, initiates the biosynthesis of prostanoids that regulates various cellular functions. Our pilot attempt revealed that the administration of etoricoxib, an inhibitor specific for COX-2, induces abnormal looping in the chicken heart. The present study attempts to reveal the mechanistic details of etoricoxib-induced abnormal cardiac looping. The activity of COX-2 was inhibited by administering 3.5 μg of etoricoxib into the egg's air cell on day zero of incubation. The gene and protein expression patterns of key mediators of heart development were then analyzed on day 2 (HH12) and day 3 (HH20). Reduced COX-2 activity altered the expressions of upstream regulators of organogenesis like Wnt11, BMP4, and SHH in the etoricoxib-exposed embryos. The observed expression shifts in the downstream regulators of myocardial patterning (MYOCD, HAND2, GATA4, GATA5, and GATA6) in the treated embryos corroborate the above results. In addition, the reduction in COX-2 activity hampered cardiomyocyte proliferation with a concomitant increase in the apoptosis rate. In conclusion, the collective effect of altered expression of signaling molecules of myocardial patterning and compromised cardiomyocyte turnover rate could be the reason behind the looping defects observed in the heart of etoricoxib-treated chick embryos.