Abstract 1121: Importance of Small Heat Shock Protein 20 C-terminal Extension in Cardioprotection and Calcium Handling of Rat Cardiomyocytes
Recent studies show that overexpression of small heat shock protein 20 (Hsp20) in mouse hearts reduces infarct size and improves cardiac performance. However, it is not known whether Hsp20 exerts its protective action through calcium handling or chaperone activity. The C-terminal extensions of some small heat shock proteins, such as alphaB-crystallin and Hsp25, are implicated in chaperoning activity. Through adenovirus mediated overexpression of Hsp20 with C-terminal extension deletion we delineated the mechanism of protection. Overexpressing Hsp20 with a C-terminus deletion did not protect against simulated ischemia/reperfusion in either adult (98±8.8% lactate dehydrogenase (LDH) release of control) or neonatal cardiomy-ocytes (103±1.8% creatine kinase (CK) release of control) as measured by CK and LDH cell viability assays. However, this Hsp20 C-terminal deletion mutant increased calcium transients from 0.09±0.01 to 0.12±0.01 and cell contraction amplitude from 4.74±0.73 to 7.55±0.79 as quantified through confocal microscopy. In contrast, overexpression of the full length Hsp20 protected cultured adult (53±8.5% LDH release of control) and neonatal rat (57±8.3% CK release of control) cardiomyocytes from simulated ischemia/reperfusion injury. This overex-pression also increased calcium transients from 0.09±0.01 to 0.14±0.01 and cell contraction fractional shortening from 9.49±1.14 to 11.08±1.12. This novel data suggests that the C-terminal extension of Hsp20 is essential for cardioprotection and that Hsp20 renders this protection through its chaperoning activity. All adult rat experiments comprised of n=16 to 34 cells per heart from 4 to 5 hearts. All neonatal rat experiments comprised of an n=4. All data compared are significantly different (P<0.05).