Abstract P1148: Glucocorticoid Receptor - Klf9 Axis Regulates Cardiomyocyte Metabolic Homeostasis

Abstract

Glucocorticoids (GCs) through activation of the Glucocorticoid receptor (GR) plays an essential role in cellular homeostasis during physiological variations and in response to stress. GC-GR signaling is involved in regulating several cellular processes including metabolism, circadian rhythm and inflammation for diurnal adaptations. Our genomic GR binding (ChIP) and transcriptome (RNAseq) data from Dexamethasone (Dex) treatment in cardiomyocytes show an early (1hr) differential regulation of mostly transcription factors, followed by sequential change in downstream signaling pathways (6-12hr). Here, we examine the role of an early direct target of GR in cardiomyocytes, Krüppel-like factor 9 (Klf9) in metabolic homeostasis. Our Klf9-ChIPseq identified 4100 genes with change in promoter Klf9 binding in response to Dex. Functional annotation of these genes lists metabolic pathway on the top of KEGG pathway, along with genes regulating transcription and survival. Interestingly, integration of GR and Klf9 data show overlapping targets (1181), suggesting that Klf9 could be serving as feedback regulator for these genes. Further, our transcriptome analysis of Dex treated cardiomyocytes with knockdown of Klf9 reveal differential regulation of 1777 genes (Dex+siKLf9 vs Dex+siLUC), of which a reversal in expression is seen in 1640 (92%) genes with siKlf9 vs. Dex. Conversely, only 137 (8%) genes show further dysregulation in expression with siKLf9 as Dex. Gene ontology of these 1640 genes show metabolic pathway on the top, including genes involved in glycolysis and oxidative phosphorylation. Conversely, mostly immuno-regulatory genes are among those 137 genes. Expectedly, knockdown of Klf9 in cardiomyocytes inhibits Dex induced increase in glycolysis and glycolytic capacity by 24%, and spare respiratory capacity by 50%, as measured by ECAR and OCR with glycolysis and mito stress tests, respectively. Thus, we conclude that cyclic, diurnal GC mediated GR activation, through Klf9 -dependent feedforward signaling plays a central role in maintaining cellular metabolic homeostasis. With hypertrophic stress a decrease in cardiac GR and dysregulated Klf9 signaling might result in metabolic crisis, contributing to mitochondrial and cardiac dysfunction