Background Overexpression of the inducible hsp70 protects against ischemic cardiac damage. However, it is unclear whether the small heat shock proteins hsp27 and αB-crystallin protect against ischemic injury.

Methods and Results Our aim was to examine whether the overexpression of hsp27 and αB-crystallin in neonatal and adult rat cardiomyocytes would protect against ischemic injury. Recombinant adenovirus expressing hsp27 or αB-crystallin under the control of the cytomegalovirus promoter was used to infect cardiac myocytes at high efficiency as assessed by immunostaining. Overexpression was confirmed by Western blot analysis. Cardiomyocytes were subjected to simulated ischemic stress, and survival was estimated through assessment of lactate dehydrogenase and creatine phosphokinase release. The hsp27 overexpression decreased lactate dehydrogenase release by 45±7.5% in adult cardiomyocytes but had no effect in the neonatal cells. In contrast, αB-crystallin overexpression was associated with a decrease in cytosolic enzyme release in both adult (29±6.6%) and neonatal (32±5.4%) cardiomyocytes. Decreased endogenous hsp25 with an antisense adenovirus produced a 29±9.9% increase in damage with simulated ischemia. Overexpression of the inducible hsp70 in adult cardiomyocytes was associated with a 34±4.6% decrease in lactate dehydrogenase release and is in line with our previous results in neonatal cardiomyocytes.

Conclusions The increased expression of hsp27 and αB-crystallin through an adenovirus vector system protects against ischemic injury in adult cardiomyocytes. Likewise, the overexpression of αB-crystallin protects against ischemic damage in neonatal cardiomyocytes. Decreasing the high levels of endogenous hsp25 present in neonatal cardiomyocytes renders them more susceptible to damage caused by simulated ischemia.