Abstract 417: Phosphorylation of Small Heat Shock Protein 20 at Serine 16 Is Essential in Cardiac Protection against Ischemia/Reperfusion Injury
Recent studies show that the cardiac small heat shock protein 20 (Hsp20) protects hearts against β-adrenergic-receptor agonist induced apoptosis and ischemia/reperfusion injury. Importantly, Hsp20 can be phosphorylated at Serine 16 by PKA. To examine the in vivo effects of Hsp20 phosphorylation at this residue, we generated transgenic mice with cardiac-specific expression (7x and 5x) of the non-phosphorylated Hsp20 form (Hsp20-S16A). Using a Langendorff perfusion model, we subjected hearts to 45 minutes of ischemia followed by 1 hour of reperfusion. During reperfusion, negative and positive pressure derivatives (−dP/dt and + dP/dt) as well as left ventricular developed pressure (LVDP) were significantly lower in Hsp20-S16A transgenic compared with wild type hearts (P<0.01). After 1 hour reperfusion, +dP/dt, −dP/dt and LVDP values in TG hearts reached around 54.2 ± 4.7%, 48.9 ± 4.4% and 58.7 ± 4.3% of their pre-ischemic levels, while these values recovered by 70.1 ± 4.2% (+dP/dt), 68.2 ± 5.0% (−dP/dt) and 63.6 ± 5.1% (LVDP) in wild-type hearts (n = 10, p<0.01). Lactate dehydrogenase release, an index of myocyte death, during reperfusion was 2-fold higher in transgenic mice than controls (P<0.01). Furthermore, TUNEL staining of the hearts, subjected to ischemia/ reperfusion (I/R) injury, revealed 2.5-fold increase of apoptotic cells in Hsp20-S16A compared with wild types (p<0.05). Importantly, Hsp20 (MW 20kD) appeared to form oligomers of ~150kD in WT hearts, whereas this mass was increased to ~300KD in Hsp20-S16A hearts. These findings suggest that phosphorylation of Ser 16 in Hsp20 may regulate its oligomerization state and may influence its protective effects against cellular stress.