Acute intermittent hypoxia activates myocardial cell survival signaling

Abstract

Intermittent hypoxia (IH) with repeated episodes of hypoxia-normoxia cycle has been shown to exert preconditioning-like cardioprotective effects. To understand the mechanism of these events, we investigated the changes in cardiac gene expression in response to acute IH. Mice were subjected to five cycles of 2 min of 10% O(2) plus 2 min of 21% O(2). RNA was isolated, and gene array analysis was performed. Results show that the expression of antiapoptotic genes, such as Bcl-2 and Bcl-x(L), were increased after acute IH. GATA-4 regulates transcription of these genes, and, consistently, GATA-4 activity was increased by acute IH. Although the phosphorylation of GATA-4 has been shown to regulate its activity, no changes in GATA-4 phosphorylation status by acute IH were noted. Gene transcription of gata4 was increased by acute IH, and this might be responsible for the enhanced GATA activity. To understand the mechanism of acute IH activation of gata4 gene transcription, we identified a promoter region of the mouse gata4 gene that is 1,000 bp immediately upstream from the transcriptional start site. In cardiac muscle cells, truncation of 1,000 to 250 bp did not alter the transcriptional activity, suggesting that the proximal 250-bp region contains important transcriptional regulatory sites. We further found that acute IH activates factors which bind to the proximal 100-bp region. Thus acute IH activates not yet identified factors that bind to the proximal 100-bp region of the gata4 promoter and, in turn, increases gata4 gene transcription, leading to enhanced expression of Bcl-2 and Bcl-x(L).