Abstract 156: Hsp20 Inhibits Doxorubicin-triggered Cardiac Injury Via PI3 Kinase-Akt Dependent Pathway
Background Doxorubicin (Dox) is a highly effective chemotherapeutic agent used in the treatment of tumors. However, multiple intravenous Dox treatments lead to heart failure in humans, which is mainly caused by increased oxidant production that induces cardiomyocyte apoptosis. Our recent studies indicated that the small heat-shock protein Hsp20 may protect cardiomyocytes against apoptosis, induced by ischemia/reperfusion injury or by prolonged β-agonist stimulation. Thus, it was important to investigate whether Hsp20 may also exert protective effects on Dox-induced cardiac injury, and determine the underlying mechanism(s).
Methods and Results 8-week-old wild-type (WT) and Hsp20-transgenic (TG, 10-fold overexpression) mice were subjected to one intraperitoneal injection of 20 μg/g of doxorubicin. Four days later, cardiac function was assessed by Langendorff perfusion and indicated depressed left ventricular developed pressure (LVDP), as well as rates of contraction (−dP/dt) and relaxation (−dP/dt) in both Dox-treated WT and TG mice. However, the decreases were more prominent in WTs than in TGs (n=8, p<0.05). Furthermore, the hearts of Dox-treated WTs, but not those of Dox-treated TGs, displayed typical ladder formation of fragmented DNA and increases in the cleaved form of caspase-3. More importantly, all WT mice died (n=11) within 7 days, while TGs (55%, n=14) survived up to 10 days after treatment with Dox. Parallel in vitro experiments showed that transduction of adult rat cardiomyocytes with Ad.Hsp20 led to resistance to Dox-triggered cell death. However, both pre-incubation of cardiomyocytes with the PI3-kinase inhibitors LY294002 and infection with a dominant-negative Akt adenovirus significantly attenuated the anti-apoptotic actions of Hsp20, as determined by Hoechst staining, TUNEL staining, and DNA fragmentation. In contrast, pre-incubation with MEK1/2 inhibitor PD98059, p38 MAPK inhibitor SB203580 and JNK inhibitor II had no effects on the protection of Hsp20 against Dox-induced cardiomyocyte apoptosis.
Conclusions: Taken together, our findings suggest that DOX-triggered cardiac injury is suppressed by overexpression of Hsp20 and these beneficial effects appear to be dependent on the PI3 kinase-Akt pathway.