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Cardiac Myocyte KLF5 Regulates Ppara Expression and Cardiac Function.

ABSTRACT: Fatty acid oxidation is transcriptionally regulated by peroxisome proliferator-activated receptor (PPAR)? and under normal conditions accounts for 70% of cardiac ATP content. Reduced Ppara expression during sepsis and heart failure leads to reduced fatty acid oxidation and myocardial energy deficiency. Many of the transcriptional regulators of Ppara are unknown.To determine the role of Krüppel-like factor 5 (KLF5) in transcriptional regulation of Ppara.We discovered that KLF5 activates Ppara gene expression via direct promoter binding. This is blocked in hearts of septic mice by c-Jun, which binds an overlapping site on the Ppara promoter and reduces transcription. We generated cardiac myocyte-specific Klf5 knockout mice that showed reduced expression of cardiac Ppara and its downstream fatty acid metabolism-related targets. These changes were associated with reduced cardiac fatty acid oxidation, ATP levels, increased triglyceride accumulation, and cardiac dysfunction. Diabetic mice showed parallel changes in cardiac Klf5 and Ppara expression levels.Cardiac myocyte KLF5 is a transcriptional regulator of Ppara and cardiac energetics.

SUBMITTER: Drosatos K

PROVIDER: S-EPMC4886555 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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Cardiac Myocyte KLF5 Regulates Ppara Expression and Cardiac Function.

Drosatos Konstantinos K Pollak Nina M NM Pol Christine J CJ Ntziachristos Panagiotis P Willecke Florian F Valenti Mesele-Christina MC Trent Chad M CM Hu Yunying Y Guo Shaodong S Aifantis Iannis I Goldberg Ira J IJ

Circulation research 20151116 2

<h4>Rationale</h4>Fatty acid oxidation is transcriptionally regulated by peroxisome proliferator-activated receptor (PPAR)α and under normal conditions accounts for 70% of cardiac ATP content. Reduced Ppara expression during sepsis and heart failure leads to reduced fatty acid oxidation and myocardial energy deficiency. Many of the transcriptional regulators of Ppara are unknown.<h4>Objective</h4>To determine the role of Krüppel-like factor 5 (KLF5) in transcriptional regulation of Ppara.<h4>Met ...[more]

PMID: 26574507

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Project description:RATIONALE:Loss-of-function studies in cardiac myocytes (CMs) are currently limited by the need for appropriate conditional knockout alleles. The factors that regulate CM maturation are poorly understood. Previous studies on CM maturation have been confounded by heart dysfunction caused by whole organ gene inactivation. OBJECTIVE:To develop a new technical platform to rapidly characterize cell-autonomous gene function in postnatal murine CMs and apply it to identify genes that regulate transverse tubules (T-tubules), a hallmark of mature CMs. METHODS AND RESULTS:We developed CRISPR/Cas9/AAV9-based somatic mutagenesis, a platform in which AAV9 delivers tandem guide RNAs targeting a gene of interest and cardiac troponin-T promoter-driven Cre to RosaCas9GFP/Cas9GFP neonatal mice. When directed against junctophilin-2 (Jph2), a gene previously implicated in T-tubule maturation, we achieved efficient, rapid, and CM-specific JPH2 depletion. High-dose AAV9 ablated JPH2 in 64% CMs and caused lethal heart failure, whereas low-dose AAV9 ablated JPH2 in 22% CMs and preserved normal heart function. In the context of preserved heart function, CMs lacking JPH2 developed T-tubules that were nearly morphologically normal, indicating that JPH2 does not have a major, cell-autonomous role in T-tubule maturation. However, in hearts with severe dysfunction, both adeno-associated virus-transduced and nontransduced CMs exhibited T-tubule disruption, which was more severe in the transduced subset. These data indicate that cardiac dysfunction disrupts T-tubule structure and that JPH2 protects T-tubules in this context. We then used CRISPR/Cas9/AAV9-based somatic mutagenesis to screen 8 additional genes for required, cell-autonomous roles in T-tubule formation. We identified RYR2 (Ryanodine Receptor-2) as a novel, cell-autonomously required T-tubule maturation factor. CONCLUSIONS:CRISPR/Cas9/AAV9-based somatic mutagenesis is a powerful tool to study cell-autonomous gene functions. Genetic mosaics are invaluable to accurately define cell-autonomous gene function. JPH2 has a minor role in normal T-tubule maturation but is required to stabilize T-tubules in the failing heart. RYR2 is a novel T-tubule maturation factor.

Project description:RATIONALE:PGC1? (peroxisome proliferator-activated receptor gamma coactivator 1?) represents an attractive target interfering bioenergetics and mitochondrial homeostasis, yet multiple attempts have failed to upregulate PGC1? expression as a therapy, for instance, causing cardiomyopathy. OBJECTIVE:To determine whether a fine-tuning of PGC1? expression is essential for cardiac homeostasis in a context-dependent manner. METHODS AND RESULTS:Moderate cardiac-specific PGC1? overexpression through a ROSA26 locus knock-in strategy was utilized in WT (wild type) mice and in G3Terc-/- (third generation of telomerase deficient; hereafter as G3) mouse model, respectively. Ultrastructure, mitochondrial stress, echocardiographic, and a variety of biological approaches were applied to assess mitochondrial physiology and cardiac function. While WT mice showed a relatively consistent PGC1? expression from 3 to 12 months old, age-matched G3 mice exhibited declined PGC1? expression and compromised mitochondrial function. Cardiac-specific overexpression of PGC1? (PGC1?OE) promoted mitochondrial and cardiac function in 3-month-old WT mice but accelerated cardiac aging and significantly shortened life span in 12-month-old WT mice because of increased mitochondrial damage and reactive oxygen species insult. In contrast, cardiac-specific PGC1? knock in in G3 (G3 PGC1?OE) mice restored mitochondrial homeostasis and attenuated senescence-associated secretory phenotypes, thereby preserving cardiac performance with age and extending health span. Mechanistically, age-dependent defect in mitophagy is associated with accumulation of damaged mitochondria that leads to cardiac impairment and premature death in 12-month-old WT PGC1?OE mice. In the context of telomere dysfunction, PGC1? induction replenished energy supply through restoring the compromised mitochondrial biogenesis and thus is beneficial to old G3 heart. CONCLUSIONS:Fine-tuning the expression of PGC1? is crucial for the cardiac homeostasis because the balance between mitochondrial biogenesis and clearance is vital for regulating mitochondrial function and homeostasis. These results reinforce the importance of carefully evaluating the PGC1?-boosting strategies in a context-dependent manner to facilitate clinical translation of novel cardioprotective therapies.

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Cardiac Myocyte KLF5 Regulates Ppara Expression and Cardiac Function.

Publications

Cardiac Myocyte KLF5 Regulates Ppara Expression and Cardiac Function.

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