POSTER NO: 365

DNA microarray analysis of the in vivo progression mechanism to heart failure in Dahl salt-sensitive rats

¹Shuichi Ueno, ¹Ruri Ohki, ¹Keiji Yamamoto, ¹Uichi Ikeda, ¹Kazuyuki Shimada, ²Hiroyuki Mano
¹Division of Cardiology, Jichi Medical School, Minamikawachi-machi, Tochigi 329-0498, Japan, ²Division of Functional Genomics, Jichi Medical School, Minamikawachi-machi, Tochigi 329-0498, Japan

A variety of conditions including pressure or volume overload lead to hypertrophy of cardiac muscles, which is often accompanied with an increase in systemic blood pressure (BP). The hypertrophic change is in some cases the result of a compensatory mechanism, and in other cases due to yet unidentified causes. Regardless of the etiology, however, sustained hypertrophy of cardiac myocytes eventually induces a reduction in contractile ability and/or a decrease in the number of viable myocytes; the condition is referred to as 'heart failure'. Even today, it is difficult to control the function of failed heart, and this condition remains one of the leading causes of human death. The possibility of preventing the progression from cardiac hypertrophy to heart failure would be greatly increased by characterization of this process at the molecular level. To address this issue, analysis of in vivo changes in heart would be indispensable. Dahl rats are genetically sensitive to sodium loading, and, therefore, high salt diet (HSD) renders the rats hypertensive, cardiac hypertrophy and heart failure in a sequential manner. Thus, Dahl rats would be a suitable tool to investigate the molecular mechanism of how pumping failure is induced in myocytes in vivo. HSD or low salt diet (LSD) was started at the age of 6 weeks in Dahl rats. Only in the rats with HSD, a gradual increase of blood pressure became apparent at 8 weeks, followed by the development of cardiac hypertrophy at 8-11 weeks as measured by echocardiography. Decrease of ejection fraction in heart began at 13-15 weeks, and most rats died shortly after. These pathological consequences were not observed in the Dahl rats with LSD. To reveal the progressive change of transcriptomes in the affected and control myocytes, RNAs were prepared from the rats at every time point (n=2), and were converted to double strand cDNA to prepare biotin-labeled cRNA. Hybridization of every cRNA with the 'Rat Genome U34A' GeneChip (Affymetrix) has revealed the transcriptomes of ~8,800 genes throughout the disease progression. For instance, induced with HSD were the genes for atrial natriuretic peptide, and alpha-myosin heavy chain. On the contrary, the gene for beta-actin was induced in hypertensive and hypertrophic states, but declined in the failing hearts. A number of other genes including enzymes for lipid as well as unknown ones showed a similar expression profile. We also confirmed by the 'real-time' PCR method such expression changes in representative genes. Our analysis has provided a wealth of information for the molecular mechanism of cardiac hypertrophy and on the initiation of heart failure. Our current data may also be useful for the identification of biomarkers to determine or predict the function of given hearts.