Abstract 18373: Hexokinase II Reduction Exacerbates Cardiac Dysfunction and Reduces HIF-Mediated Angiogenesis in Response to Ischemia-Reperfusion Injury
Background: Cardiomyocytes (CM) switch substrate utilization from fatty acid to glucose in ischemia, however, it is unknown how perturbations in glycolytic enzymes affect cardiac response to ischemia-reperfusion (I/R). Hexokinase (HK) II is a major HK isoform expressed in the heart and can bind to the mitochondrial outer membrane. We studied how HKII and its binding to mitochondria play a role in cardiac response after I/R.
Methods and Results: We subjected the hearts of wild type and heterozygote HKII knockout (HKII+/−) mice to I/R. At baseline, HKII+/− mice have normal cardiac function. However, they displayed greater reduction in fractional shortening 28 days after I/R as determined by echocardiography (16.5 ± 0.9% vs. 21.2 ± 1.2% for HKII+/− and WT, P< 0.05, n=10), and a significant reduction in +dP/dt assessed by invasive hemodynamic measurement (2719 ± 231 mmHg/s vs. 4116 ± 649 mmHg/s for HKII+/− and WT, P< 0.05). The mechanism appears to be through an increase in CM death and fibrosis as HKII+/− mice displayed increased apoptosis in the peri-infarct zone, increased infarct size relative to left ventricular size (41 ± 1% vs. 32 ± 2% for HKII+/− and WT, P< 0.05) and increased lactate dehydrogenase activity. Furthermore, HKII+/− mice displayed a reduction in angiogenesis in the ischemic border zone as measured by Lectin staining, a marker of endothelial cells. The reduction in angiogenesis is through a hypoxia-inducible factor (HIF1)-dependent pathway as HKII knockdown in neonatal rat cardiomyocytes (NRCM) resulted in decreased expression of HIF1α and vascular endothelial growth factor (VEGF) in response to hypoxia. Furthermore, luciferase assay demonstrated reduced induction of HIF1 response elements (HRE) with HKII knockdown. Finally, dissociation of HKII from mitochondria using a competitive peptide led to NRCM death, suggesting that mitochondrial binding of HKII is critical for CM survival.
Conclusion: These results suggest that reduction in HKII levels causes altered remodeling of the heart after I/R by increasing cell death and fibrosis and reducing angiogenesis, and that mitochondrial binding is needed for protection of cardiomyocytes.
- © 2010 by American Heart Association, Inc.