Abstract 10609: Loss of Function of Heat Shock Protein 60 (hsp60) Increases Susceptibility to Atrio-ventricular (av) Block
Background: Acquired atrio-ventricular (AV) block commonly develops after the fifth decade of life and associates with degeneration of the conduction system. Heat shock protein 60 (Hsp60) is a well-characterized chaperone that prevents stress-induced protein damage and is upregulated in heart failure. This study aimed to determine whether hsp60 dysfunction leads to AV block.
Methods and Results: We previously developed a zebrafish mutant, nbl, which had a V324E missense mutation in exon 7 of hsp60 leading to the loss of function. In zebrafish, slow conduction tissue develops in the AV border, around 42 hours post fertilization (hpf), where strong expression of Hsp60 was observed. To assess the contribution of Hsp60 in the developing cardiac conduction system, embryos were raised at 33°C. Although 81% of wild-type zebrafish reached adulthood, few nbl mutants attained this stage at 33°C, and 63% of mutants showed a progressive AV block. Apoptotic cells were frequently observed in the AV border area of nbl mutants especially in acetylcholinestrase-positive cells. To investigate whether this cardiac phenotype was specifically resulted from hsp60 dysfunction rather than from the heat shock, we injected wild-type embryos with hsp60 morpholino targeting the splice donor site of exon 7, which contains the V324E mutation. When embryos were transferred to hypoxic conditions after the injection of morpholino, 37% of them developed the AV block phenotype. To evaluate the formation of AV conduction tissue, we performed microarray, RT-PCR, and in situ hybridization analysis of the heart. Connexin40 and 43 expressions were unchanged. Notch1b mRNA level was upregulated in the nbl heart, although notch1b was not localized in the AV endocardium. In vivo calcium imaging showed a failure in AV delay development in the nbl mutants. Analysis of genetically unrelated patients with familial DCM, who had no mutations in the known DCM-causing genes, identified a hsp60 mutation in one DCM family in which two of four mutation prone individuals died suddenly. These data suggested that Hsp60 dysfunction led to the AV block under certain environmental stress-through loss of conduction cells.
Conclusion: Loss of Hsp60 function may increase the susceptibility to AV block.
- © 2012 by American Heart Association, Inc.