Effects of hypoxia on stress proteins in the piglet heart at birth.

Hypoxia at birth represents a very stressful event that can result in severe lifelong consequences in different tissues, including those of the heart. Heat shock and other associated stress proteins are involved in cellular protection, but their roles are not clearly defined at the time of birth. Newborn piglets were subjected to 5% oxygen and 95% nitrogen for either 1 or 4 hours. They were allowed to recover over periods of 1 to 68 hours. The relative levels of alphaB-crystallin, HspB8, Hsp20, Hsp27, Hsp60, and Hsp70 as well as nitric oxide synthases (NOS) (endothelial NOS, inducible NOS, neuronal NOS) were examined by Western blot analysis. Surprisingly, alphaB-crystallin expression was drastically increased in animals submitted to hypoxia. The hypoxia-associated factor HIFlalpha was also strongly and rapidly overexpressed. Heme oxygenase 1 was also increased. To a lesser extent, neuronal NOS was also increased in the left ventricle of animals submitted to hypoxia. This work clearly shows that the Hsp chaperone alphaB-crystallin is strongly overexpressed in the left ventricle of animals submitted to hypoxia. This observation dissociates the response to low oxygenation of alphaB-crystallin and other stress-associated proteins including Hsp27, and it indicates that heme oxygenase is not alone among HSPs in its oxygen-related gene expression.