Abstract 162: Hypoxia Inducible Factor Regulates Cardiac Ribonucleic Acid Splicing
Ischemic cardiomyopathy is associated with elevated levels of hypoxia inducible factor (HIF)-1, a transcription factor that plays a key role in the response to hypoxia. We have created a transgenic mouse model with inducible cardiomyocyte-specific expression of an oxygen-stable form of HIF-1α to better understand the role of HIF-1 in ischemic cardiomyopathy. We performed RNAseq on polyA selected cardiac RNA before and after three days of transgene expression, with 10 million processed reads per sample. Genes were considered possibly differentially expressed if, following adjustment for multiple testing, p-value for the comparison to uninduced was less than 0.05. Genes having evidence of alternative splicing (those with a q-value <0.05 suggesting a change in the relative abundance of the different transcripts deriving from a single transcription start site) were identified. A total of 22 alternatively spliced genes were investigated. One transcript in particular, that for Calmodulin-dependent protein kinase II isoform gamma 2 (CaMKIIγ) was of particular interest because CaMKII homologs are involved in the phosphorylation of both RyR2 and PLB, and might thus be important in excitation-contraction coupling and cardiac contractility. The reference RNA sequence for CaMKIIγ was down regulated 11.7-fold, while variant 1 (missing Exons 7 and 8), and variant 2 (missing Exon 8) were up regulated 2.6-fold and 1.7-fold, respectively. Real-time PCR validation of the RNAseq data has been obtained in the transgenic hearts, and, to a lesser extent, in wild type mice subjected to LAD ligation. The cardiac effects of CaMKIIγ have been little studied in the response to hypoxia. Taken together with our prior observations of SERCA2a down-regulation and increased phosphorylation of PLB in the transgenic model, this new evidence suggests that another way in which HIF-1 may be modulating calcium flux is by reconfiguring the abundance of CaMKIIγ splice variants. The biochemical effect(s) of this variation in splice variants remains unknown, but seems likely to be connected to the decrement in cardiac contractility seen with HIF expression, and in ischemic cardiomyopathy. The surprising role of HIF in regulating splicing will also be a fertile area for further investigation.
- © 2013 by American Heart Association, Inc.