Klf15 deficiency is a molecular link between heart failure and aortic aneurysm formation

Downregulation of MLF1 safeguards cardiomyocytes against senescence-associated chromatin opening

Aging-associated cardiac hypertrophy (AACH) increases susceptibility to heart failure in the elderly. Chromatin remodeling contributes to the gene reprogramming in AACH; however, the intrinsic regulations remain elusive. We performed a transcriptome analysis for AACH in comparison with pressure-overload-induced pathological cardiac hypertrophy in mice and identified myeloid leukemia factor 1 (MLF1) as an aging-sensitive factor whose expression was reduced during aging but could be reversed by anti-aging administrations. In human AC16 cardiomyocytes, silencing MLF1 suppressed H2O2-induced cell senescence while the phenotype was exacerbated by MLF1 overexpression. RNA-seq analysis revealed that MLF1 functioned as a transcription activator, regulating genomic-clustered genes that mainly involved in inflammation and development. ATAC-seq analysis showed a prominent reduction in chromatin accessibility at the promoter regions of senescence effectors, like IL1B and p21, after MLF1 knockdown. Despite a potential interaction of MLF1 with the histone methyltransferase PRC2, its inhibition failed to reverse the impact of MLF1 knockdown. Instead, MLF1-mediated regulation was blunted by inhibiting the acetyltransferase EP300. CUT&Tag analysis showed that MLF1 bound to target promoters and recruited EP300 to promote H3K27ac deposition. Collectively, we identify MLF1 as a pro-aging epigenetic orchestrator that recruits EP300 to facilitate opening of the condensed chromatin encompassing senescence effectors.

Glucocorticoid chronopharmacology promotes glucose metabolism in heart through a cardiomyocyte-autonomous transactivation program

Circadian time of intake gates the cardioprotective effects of glucocorticoid administration in both healthy and infarcted hearts. The cardiomyocyte-specific glucocorticoid receptor (GR) and its cofactor, Krüppel-like factor 15 (KLF15), play critical roles in maintaining normal heart function in the long term and serve as pleiotropic regulators of cardiac metabolism. Despite this understanding, the cardiomyocyte-autonomous metabolic targets influenced by the concerted epigenetic action of the GR/KLF15 axis remain undefined. Here, we demonstrated the critical roles of the cardiomyocyte-specific GR and KLF15 in orchestrating a circadian-dependent glucose oxidation program within the heart. Combining integrated transcriptomics and epigenomics with cardiomyocyte-specific inducible ablation of GR or KLF15, we identified their synergistic role in the activation of adiponectin receptor expression (Adipor1) and the mitochondrial pyruvate complex (Mpc1/2), thereby enhancing insulin-stimulated glucose uptake and pyruvate oxidation. Furthermore, in obese diabetic (db/db) mice exhibiting insulin resistance and impaired glucose oxidation, light-phase prednisone administration, as opposed to dark-phase prednisone dosing, restored cardiomyocyte glucose oxidation and improved diastolic function. These effects were blocked by combined in vivo knockdown of GR and KLF15 levels in db/db hearts. In summary, this study leveraged the circadian-dependent cardioprotective effects of glucocorticoids to identify cardiomyocyte-autonomous targets for the GR/KLF15 axis in glucose metabolism.

Glucocorticoid chrono-pharmacology unveils novel targets for the cardiomyocyte-specific GR-KLF15 axis in cardiac glucose metabolism

Circadian time-of-intake gates the cardioprotective effects of glucocorticoid administration in both healthy and infarcted hearts. The cardiomyocyte-specific glucocorticoid receptor (GR) and its co-factor, Krüppel-like factor (Klf15), play critical roles in maintaining normal heart function in the long-term and serve as pleiotropic regulators of cardiac metabolism. Despite this understanding, the cardiomyocyte-autonomous metabolic targets influenced by the concerted epigenetic action of GR-Klf15 axis remain undefined. Here, we demonstrate the critical roles of the cardiomyocyte-specific GR and Klf15 in orchestrating a circadian-dependent glucose oxidation program within the heart. Combining integrated transcriptomics and epigenomics with cardiomyocyte-specific inducible ablation of GR or Klf15, we identified their synergistic role in the activation of adiponectin receptor expression (Adipor1) and the mitochondrial pyruvate complex (Mpc1/2), thereby enhancing insulin-stimulated glucose uptake and pyruvate oxidation. Furthermore, in obese diabetic (db/db) mice exhibiting insulin resistance and impaired glucose oxidation, light-phase prednisone administration, as opposed to dark-phase prednisone dosing, effectively restored cardiomyocyte glucose oxidation and improved diastolic function towards control-like levels in a sex-independent manner. Collectively, our findings uncover novel cardiomyocyte-autonomous metabolic targets of the GR-Klf15 axis. This study highlights the circadian-dependent cardioprotective effects of glucocorticoids on cardiomyocyte glucose metabolism, providing critical insights into chrono-pharmacological strategies for glucocorticoid therapy in cardiovascular disease.

KLF15 maintains contractile phenotype of vascular smooth muscle cells and prevents thoracic aortic dissection by interacting with MRTFB

Thoracic aortic dissection (TAD) is a highly dangerous cardiovascular disorder caused by weakening of the aortic wall, resulting in a sudden tear of the internal face. Progressive loss of the contractile apparatus in vascular smooth muscle cells (VSMCs) is a major event in TAD. Exploring the endogenous regulators essential for the contractile phenotype of VSMCs may aid the development of strategies to prevent TAD. Krüppel-like factor 15 (KLF15) overexpression was reported to inhibit TAD formation; however, the mechanisms by which KLF15 prevents TAD formation and whether KLF15 regulates the contractile phenotype of VSMCs in TAD are not well understood. Therefore, we investigated these unknown aspects of KLF15 function. We found that KLF15 expression was reduced in human TAD samples and β-aminopropionitrile monofumarate-induced TAD mouse model. Klf15KO mice are susceptible to both β-aminopropionitrile monofumarate- and angiotensin II-induced TAD. KLF15 deficiency results in reduced VSMC contractility and exacerbated vascular inflammation and extracellular matrix degradation. Mechanistically, KLF15 interacts with myocardin-related transcription factor B (MRTFB), a potent serum response factor coactivator that drives contractile gene expression. KLF15 silencing represses the MRTFB-induced activation of contractile genes in VSMCs. Thus, KLF15 cooperates with MRTFB to promote the expression of contractile genes in VSMCs, and its dysfunction may exacerbate TAD. These findings indicate that KLF15 may be a novel therapeutic target for the treatment of TAD.

The role of transcription factors in the pathogenesis and therapeutic targeting of vascular diseases

Transcription factors (TFs) constitute an essential component of epigenetic regulation. They contribute to the progression of vascular diseases by regulating epigenetic gene expression in several vascular diseases. Recently, numerous regulatory mechanisms related to vascular pathology, ranging from general TFs that are continuously activated to histiocyte-specific TFs that are activated under specific circumstances, have been studied. TFs participate in the progression of vascular-related diseases by epigenetically regulating vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). The Krüppel-like family (KLF) TF family is widely recognized as the foremost regulator of vascular diseases. KLF11 prevents aneurysm progression by inhibiting the apoptosis of VSMCs and enhancing their contractile function. The presence of KLF4, another crucial member, suppresses the progression of atherosclerosis (AS) and pulmonary hypertension by attenuating the formation of VSMCs-derived foam cells, ameliorating endothelial dysfunction, and inducing vasodilatory effects. However, the mechanism underlying the regulation of the progression of vascular-related diseases by TFs has remained elusive. The present study categorized the TFs involved in vascular diseases and their regulatory mechanisms to shed light on the potential pathogenesis of vascular diseases, and provide novel insights into their diagnosis and treatment.

Krüpple-like factors in cardiomyopathy: emerging player and therapeutic opportunities

Cardiomyopathy, a heterogeneous pathological condition characterized by changes in cardiac structure or function, represents a significant risk factor for the prevalence and mortality of cardiovascular disease (CVD). Research conducted over the years has led to the modification of definition and classification of cardiomyopathy. Herein, we reviewed seven of the most common types of cardiomyopathies, including Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), diabetic cardiomyopathy, Dilated Cardiomyopathy (DCM), desmin-associated cardiomyopathy, Hypertrophic Cardiomyopathy (HCM), Ischemic Cardiomyopathy (ICM), and obesity cardiomyopathy, focusing on their definitions, epidemiology, and influencing factors. Cardiomyopathies manifest in various ways ranging from microscopic alterations in cardiomyocytes, to tissue hypoperfusion, cardiac failure, and arrhythmias caused by electrical conduction abnormalities. As pleiotropic Transcription Factors (TFs), the Krüppel-Like Factors (KLFs), a family of zinc finger proteins, are involved in regulating the setting and development of cardiomyopathies, and play critical roles in associated biological processes, including Oxidative Stress (OS), inflammatory reactions, myocardial hypertrophy and fibrosis, and cellular autophagy and apoptosis, particularly in diabetic cardiomyopathy. However, research into KLFs in cardiomyopathy is still in its early stages, and the pathophysiologic mechanisms of some KLF members in various types of cardiomyopathies remain unclear. This article reviews the roles and recent research advances in KLFs, specifically those targeting and regulating several cardiomyopathy-associated processes.

Targeting mitochondrial circadian rhythms: The potential intervention strategies of Traditional Chinese medicine for myocardial ischaemia‒reperfusion injury

Coronary artery disease has one of the highest mortality rates in the country, and methods such as thrombolysis and percutaneous coronary intervention (PCI) can effectively improve symptoms and reduce mortality, but most patients still experience symptoms such as chest pain after PCI, which seriously affects their quality of life and increases the incidence of adverse cardiovascular events (myocardial ischaemiareperfusion injury, MIRI). MIRI has been shown to be closely associated with circadian rhythm disorders and mitochondrial dysfunction. Mitochondria are a key component in the maintenance of normal cardiac function, and new research shows that mitochondria have circadian properties. Traditional Chinese medicine (TCM), as a traditional therapeutic approach characterised by a holistic concept and evidence-based treatment, has significant advantages in the treatment of MIRI, and there is an interaction between the yin-yang theory of TCM and the circadian rhythm of Western medicine at various levels. This paper reviews the clinical evidence for the treatment of MIRI in TCM, basic experimental studies on the alleviation of MIRI by TCM through the regulation of mitochondria, the important role of circadian rhythms in the pathophysiology of MIRI, and the potential mechanisms by which TCM regulates mitochondrial circadian rhythms to alleviate MIRI through the regulation of the biological clock transcription factor. It is hoped that this review will provide new insights into the clinical management, basic research and development of drugs to treat MIRI.

A defect in mitochondrial protein translation influences mitonuclear communication in the heart

The regulation of the informational flow from the mitochondria to the nucleus (mitonuclear communication) is not fully characterized in the heart. We have determined that mitochondrial ribosomal protein S5 (MRPS5/uS5m) can regulate cardiac function and key pathways to coordinate this process during cardiac stress. We demonstrate that loss of Mrps5 in the developing heart leads to cardiac defects and embryonic lethality while postnatal loss induces cardiac hypertrophy and heart failure. The structure and function of mitochondria is disrupted in Mrps5 mutant cardiomyocytes, impairing mitochondrial protein translation and OXPHOS. We identify Klf15 as a Mrps5 downstream target and demonstrate that exogenous Klf15 is able to rescue the overt defects and re-balance the cardiac metabolome. We further show that Mrps5 represses Klf15 expression through c-myc, together with the metabolite L-phenylalanine. This critical role for Mrps5 in cardiac metabolism and mitonuclear communication highlights its potential as a target for heart failure therapies.

The KLF7/PFKL/ACADL axis modulates cardiac metabolic remodelling during cardiac hypertrophy in male mice

The main hallmark of myocardial substrate metabolism in cardiac hypertrophy or heart failure is a shift from fatty acid oxidation to greater reliance on glycolysis. However, the close correlation between glycolysis and fatty acid oxidation and underlying mechanism by which causes cardiac pathological remodelling remain unclear. We confirm that KLF7 simultaneously targets the rate-limiting enzyme of glycolysis, phosphofructokinase-1, liver, and long-chain acyl-CoA dehydrogenase, a key enzyme for fatty acid oxidation. Cardiac-specific knockout and overexpression KLF7 induce adult concentric hypertrophy and infant eccentric hypertrophy by regulating glycolysis and fatty acid oxidation fluxes in male mice, respectively. Furthermore, cardiac-specific knockdown phosphofructokinase-1, liver or overexpression long-chain acyl-CoA dehydrogenase partially rescues the cardiac hypertrophy in adult male KLF7 deficient mice. Here we show that the KLF7/PFKL/ACADL axis is a critical regulatory mechanism and may provide insight into viable therapeutic concepts aimed at the modulation of cardiac metabolic balance in hypertrophied and failing heart.

Branched-chain amino acids in cardiovascular disease

Research conducted in the past 15 years has yielded crucial insights that are reshaping our understanding of the systems physiology of branched-chain amino acid (BCAA) metabolism and the molecular mechanisms underlying the close relationship between BCAA homeostasis and cardiovascular health. The rapidly evolving literature paints a complex picture, in which numerous tissue-specific and disease-specific modes of BCAA regulation initiate a diverse set of molecular mechanisms that connect changes in BCAA homeostasis to the pathogenesis of cardiovascular diseases, including myocardial infarction, ischaemia-reperfusion injury, atherosclerosis, hypertension and heart failure. In this Review, we outline the current understanding of the major factors regulating BCAA abundance and metabolic fate, highlight molecular mechanisms connecting impaired BCAA homeostasis to cardiovascular disease, discuss the epidemiological evidence connecting BCAAs with various cardiovascular disease states and identify current knowledge gaps requiring further investigation.

Effect of forsythoside A on the transcriptional profile of bovine mammary epithelial cells challenged with lipoteichoic acid

Mastitis is a common disease of the dairy cattle, which affects the development of the dairy industry and leads to huge economic losses. Forsythoside A (FTA) has anti-inflammatory, antioxidant, antiviral and anti-apoptotic effects. However, the therapeutic effect and molecular mechanism of FTA on dairy cow mastitis remain unclear. In this study, bovine mammary epithelial cells (BMECs) were stimulated with lipoteichoic acid (LTA), a key virulence factor of Staphylococcus aureus (S. aureus), to construct in vitro models, and then treated with FTA. Subsequently, the differentially expressed genes (DEGs) in different groups were determined by RNA sequencing (RNA-Seq) analysis. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to analyse the possible function of the DEGs, real-time quantitative PCR (RT-qPCR) was used to verify whether the expression levels of these DEGs were consistent with RNA-Seq results. The results showed that cell division cycle 20B (CDC20B), endothelial cell surface expressed chemotaxis and apoptosis regulator (ECSCR), complement factor H-related 5 (CFHR5) and phospholipase A2 group IVA (PLA2G4A) were down-regulated after FTA treatment. In contrast, Kruppel-like factor 15 (KLF15) and Metallothionein 1E (MT1E) were up-regulated. These DEGs are involved in processes such as apoptosis, inflammation and development of cancer. This study provides valuable insights into the transcriptome changes in BMECs after FTA treatment. Further analysis may help identify the underlying molecular mechanisms.

SREBP1 regulates Lgals3 activation in response to cholesterol loading

Aberrant smooth muscle cell (SMC) plasticity is etiological to vascular diseases. Cholesterol induces SMC phenotypic transition featuring high LGALS3 (galectin-3) expression. This proatherogenic process is poorly understood for its molecular underpinnings, in particular, the mechanistic role of sterol regulatory-element binding protein-1 (SREBP1), a master regulator of lipid metabolism. Herein we show that cholesterol loading stimulated SREBP1 expression in mouse, rat, and human SMCs. SREBP1 positively regulated LGALS3 expression (and vice versa), whereas Krüppel-like factor-15 (KLF15) acted as a negative regulator. Both bound to the Lgals3 promoter, yet at discrete sites, as revealed by chromatin immunoprecipitation-qPCR and electrophoretic mobility shift assays. SREBP1 and LGALS3 each abated KLF15 protein, and blocking the bromo/extraterminal domain-containing proteins (BETs) family of acetyl-histone readers abolished cholesterol-stimulated SREBP1/LGALS3 protein production. Furthermore, silencing bromodomain protein 2 (BRD2; but not other BETs) reduced SREBP1; endogenous BRD2 co-immunoprecipitated with SREBP1's transcription-active domain, its own promoter DNA, and that of L gals 3. Thus, results identify a previously uncharacterized cholesterol-responsive dyad-SREBP1 and LGALS3, constituting a feedforward circuit that can be blocked by BETs inhibition. This study provides new insights into SMC phenotypic transition and potential interventional targets.

CTRP12 alleviates cardiomyocyte ischemia‑reperfusion injury via regulation of KLF15

Myocardial ischemia-reperfusion (I/R) serves a crucial role in myocardial infarction. C1q/TNF-related protein 12 (CTRP12) is a secretory protein involved in metabolism. It has been reported that CTRP12 participates in the regulation of numerous cardiovascular diseases. However, its role in myocardial I/R injury remains unclear. In the present study, the left anterior descending coronary artery in mice was ligated to establish a mouse I/R model. A myocardial hypoxia-reoxygenation (H/R) cell model was also established. Cardiomyocyte injury was evaluated using hematoxylin and eosin staining, Cell Counting Kit-8 and a lactate dehydrogenase (LDH) kit. The expression levels of CTRP12 and Krueppel-like factor 15 (KLF15) in murine myocardial tissues and H9c2 cells were determined using reverse transcription-quantitative PCR and western blotting, as KLF15 was previously reported to protect against I/R-induced cardiomyocyte damage. Furthermore, inflammatory factors TNF-α, IL-1β and IL-6 were analyzed using ELISA while apoptosis was assessed using TUNEL assays and western blotting. Moreover, the activity of the CTRP12 promoter was determined using a dual-luciferase reporter assay. The results demonstrated that I/R surgery markedly exacerbated myocardial tissue damage, whereas H/R treatment significantly reduced cell viability and significantly increased LDH activity as well as the release of inflammatory factors and apoptosis. I/R and H/R induction significantly reduced the expression levels of CTRP12 and KLF15. CTRP12 overexpression significantly alleviated H/R-induced cell injury and significantly inhibited inflammation and apoptosis. Further analysis demonstrated that KLF15 could significantly promote the activity of the CTRP12 promoter. However, following CTRP12 knockdown, KLF15 overexpression exacerbated cell injury, inflammation and apoptosis. In conclusion, the present study demonstrated that CTRP12 may mitigate inflammation and apoptosis in H/R-induced cardiomyocytes, possibly via the regulation of KLF15, which provided a theoretical basis for the potential treatment of I/R-induced myocardial infarction.

Activation of PKG-CREB-KLF15 by melatonin attenuates Angiotensin II-induced vulnerability to atrial fibrillation via enhancing branched-chain amino acids catabolism

Mitochondrial reactive oxygen species (ROS) damage and atrial remodeling serve as the crucial substrates for the genesis of atrial fibrillation (AF). Branched-chain amino acids (BCAAs) catabolic defect plays critical roles in multiple cardiovascular diseases. However, the alteration of atrial BCAA catabolism and its role in AF remain largely unknown. This study aimed to explore the role of BCAA catabolism in the pathogenesis of AF and to further evaluate the therapeutic effect of melatonin with a focus on protein kinase G (PKG)-cAMP response element binding protein (CREB)-Krüppel-like factor 15 (KLF15) signaling. We found that angiotensin II-treated atria exhibited significantly elevated BCAA level, reduced BCAA catabolic enzyme activity, increased AF vulnerability, aggravated atrial electrical and structural remodeling, and enhanced mitochondrial ROS damage. These deleterious effects were attenuated by melatonin co-administration while exacerbated by BCAA oral supplementation. Melatonin treatment ameliorated BCAA-induced atrial damage and reversed BCAA-induced down-regulation of atrial PKGIα expression, CREB phosphorylation as well as KLF15 expression. However, inhibition of PKG partly abolished melatonin-induced beneficial actions. In summary, these data demonstrated that atrial BCAA catabolic defect contributed to the pathogenesis of AF by aggravating tissue fibrosis and mitochondrial ROS damage. Melatonin treatment ameliorated Ang II-induced atrial structural as well as electrical remodeling by activating PKG-CREB-KLF15. The present study reveals additional mechanisms contributing to AF genesis and highlights the opportunity of a novel therapy for AF by targeting BCAA catabolism. Melatonin may serve as a potential therapeutic agent for AF intervention.

High protein diet-induced metabolic changes are transcriptionally regulated via KLF15-dependent and independent pathways

High protein diet (HPD) is an affordable and positive approach in prevention and treatment of many diseases. It is believed that transcriptional regulation is responsible for adaptation after HPD feeding and Kruppel-like factor 15 (KLF15), a zinc finger transcription factor that has been proved to perform transcriptional regulation over amino acid, lipid and glucose metabolism, is known to be involved at least in part in this HPD response. To gain more insight into molecular mechanisms by which HPD controls expressions of genes involved in amino acid metabolism in the liver, we performed RNA-seq analysis of mice fed HPD for a short period (3 days). Compared to a low protein diet, HPD feeding significantly increased hepatic expressions of enzymes involved in the breakdown of all the 20 amino acids. Moreover, using KLF15 knockout mice and in vivo Ad-luc analytical system, we were able to identify Cth (cystathionine gamma-lyase) as a new target gene of KLF15 transcription as well as Ast (aspartate aminotransferase) as an example of KLF15-independent gene despite its remarkable responsiveness to HPD. These findings provide us with a clue to elucidate the entire transcriptional regulatory mechanisms of amino acid metabolic pathways.

KLF2 regulates neutrophil activation and thrombosis in cardiac hypertrophy and heart failure progression

It is widely recognized that inflammation plays a critical role in cardiac hypertrophy and heart failure. However, clinical trials targeting cytokines have shown equivocal effects, indicating the need for a deeper understanding of the precise role of inflammation and inflammatory cells in heart failure. Leukocytes from human subjects and a rodent model of heart failure were characterized by a marked reduction in expression of Klf2 mRNA. Using a mouse model of angiotensin II–induced nonischemic cardiac dysfunction, we showed that neutrophils played an essential role in the pathogenesis and progression of heart failure. Mechanistically, chronic angiotensin II infusion activated a neutrophil KLF2/NETosis pathway that triggered sporadic thrombosis in small myocardial vessels, leading to myocardial hypoxia, cell death, and hypertrophy. Conversely, targeting neutrophils, neutrophil extracellular traps (NETs), or thrombosis ameliorated these pathological changes and preserved cardiac dysfunction. KLF2 regulated neutrophil activation in response to angiotensin II at the molecular level, partly through crosstalk with HIF1 signaling. Taken together, our data implicate neutrophil-mediated immunothrombotic dysregulation as a critical pathogenic mechanism leading to cardiac hypertrophy and heart failure. This neutrophil KLF2-NETosis-thrombosis mechanism underlying chronic heart failure can be exploited for therapeutic gain by therapies targeting neutrophils, NETosis, or thrombosis.

Acetyltransferase p300 Is a Putative Epidrug Target for Amelioration of Cellular Aging-Related Cardiovascular Disease

Cardiovascular disease is the leading cause of accelerated as well as chronological aging-related human morbidity and mortality worldwide. Genetic, immunologic, unhealthy lifestyles including daily consumption of high-carb/high-fat fast food, lack of exercise, drug addiction, cigarette smoke, alcoholism, and exposure to environmental pollutants like particulate matter (PM)-induced stresses contribute profoundly to accelerated and chronological cardiovascular aging and associated life threatening diseases. All these stressors alter gene expression epigenetically either through activation or repression of gene transcription via alteration of chromatin remodeling enzymes and chromatin landscape by DNA methylation or histone methylation or histone acetylation. Acetyltransferase p300, a major epigenetic writer of acetylation on histones and transcription factors, contributes significantly to modifications of chromatin landscape of genes involved in cellular aging and cardiovascular diseases. In this review, the key findings those implicate acetyltransferase p300 as a major contributor to cellular senescence or aging related cardiovascular pathologies including vascular dysfunction, cardiac hypertrophy, myocardial infarction, cardiac fibrosis, systolic/diastolic dysfunction, and aortic valve calcification are discussed. The efficacy of natural or synthetic small molecule inhibitor targeting acetyltransferase p300 in amelioration of stress-induced dysregulated gene expression, cellular aging, and cardiovascular disease in preclinical study is also discussed.

KLF15 Regulates Oxidative Stress Response in Cardiomyocytes through NAD. Metabolites 2021;11:metabo11090620. [PMID: 34564436 PMCID: PMC8468172 DOI: 10.3390/metabo11090620]

KLF15 has recently emerged as a central regulator of metabolism. Although its connection to oxidative stress has been suspected, there has not been any study to date that directly demonstrates the molecular link. In this study, we sought to determine the role of KLF15 in cardiac oxidative stress. We found that KLF15 deficiency in the heart is associated with increased oxidative stress. Acute deficiency of KLF15 in neonatal rat ventricular myocytes (NRVMs) leads to the defective clearance of reactive oxygen species (ROS) and an exaggerated cell death following a variety of oxidative stresses. Mechanistically, we found that KLF15 deficiency leads to reduced amounts of the rate-limiting NAD⁺ salvage enzyme NAMPT and to NAD⁺ deficiency. The resultant SIRT3-dependent hyperacetylation and the inactivation of mitochondrial antioxidants can be rescued by MnSOD mimetics or NAD⁺ precursors. Collectively, these findings suggest that KLF15 regulates cardiac ROS clearance through the regulation of NAD⁺ levels. Our findings establish KLF15 as a central coordinator of cardiac metabolism and ROS clearance.

Krüppel-like factor 15 reduces ischemia-induced apoptosis involving regulation of p38/MAPK signaling

Background Cardiomyocyte apoptosis is a characteristic of a variety of cardiac diseases including myocardial infarction (MI). Krüppel-like factor 15 (KLF15) is a transcription factor of Krüppel family that plays an important part in cardiovascular diseases. However, the function and the underlying mechanism of KLF15 in MI remain unknown. Methods and Results The expression of KLF15 was downregulated both in ischemic myocardium of MI mice model and hypoxia-treated neonatal rat ventricular myocytes (NRVCs). KLF15 overexpression mediated by adeno-associated virus significantly abrogated the ischemia-induced cardiac dysfunction, increased the survival rate and reduced infarct size after MI. Meanwhile, KLF15 overexpression dramatically reduced the myocardial apoptosis, regulated apoptosis-related genes such as Bcl2 and Bax, diminished the activities of caspase-9/3 and inactivated p38/MAPK signaling in the border zone. Similar results were observed in NRVCs exposed to hypoxia. Conclusions We demonstrated for the first time that KLF15 overexpression could reduce cardiomyocyte apoptosis and improve cardiac dysfunction in MI mice at least partially by inhibiting p38/MAPK signaling pathway.

Inhibition of miR-431-5p attenuated liver apoptosis through KLF15/p53 signal pathway in S100 induced autoimmune hepatitis mice

AIMS

The purpose of this study was to investigate the effects of miR-431-5p on hepatocyte apoptosis in AIH.

MATERIALS AND METHODS

We used intraperitoneal injection of S100 to establish AIH mouse model and injected AAV into tail vein on day 14 of modeling to regulate miR-431-5p expression. The expression of ALT, AST, IgG and apoptosis-related proteins Bax, Bcl-2 and cleaved caspase 3 were measured in each group. Cellular experiments were performed using miR-431-5p mimics or inhibitors to transfect LPS-stimulated AML12 cells, and apoptosis was verified using Western blot and Hoechst 33342/PI Double Staining. The target of miR-431-5p, KLF15, was screened using databases and verified by the luciferase reporter assay. The relationship between KLF15 and p53 was verified by si-KLF15 and PFTβ (a p53-specific inhibitor).

KEY FINDINGS

Here, we observed that the increase in the level of miR-431-5p was accompanied by a decrease in the expression of Krüppel-like zinc finger transcription factor 15 (KLF15). In addition, the deletion of miR-431-5p significantly reduced hepatocyte apoptosis in AIH mice induced by liver S100 and apoptosis of AML12 cells induced by LPS stimulation, accompanied by decreased expression of Bax and cleaved caspase-3 as well as increased expression of Bcl-2. Moreover, KLF15 was the direct and functional target of miR-431-5p. Furthermore, miR-431-5p negatively regulated the expression of KLF15, and KLF15 deletion partially abolished the inhibitory effect of miR-431-5p deletion on apoptosis by activating p53 signaling.

SIGNIFICANCE

In summary, miR-431-5p may be a potential therapeutic target for AIH.

Molecular link between circadian clocks and cardiac function: a network of core clock, slave clock, and effectors

The circadian rhythm has a strong influence on both cardiac physiology and disease in humans. Preclinical studies primarily using tissue-specific transgenic mouse models have contributed to our understanding of the molecular mechanism of the circadian clock in the cardiovascular system. The core clock driven by CLOCK:BMAL1 complex functions as a universal timing machinery that primarily sets the pace in all mammalian cell types. In one specific cell or tissue type, core clock may control a secondary transcriptional oscillator, conceptualized as slave clock, which confers the oscillatory expression of tissue-specific effectors. Here, we discuss a core clock-slave clock-effectors network, which links the molecular clock to cardiac function.

p300 in Cardiac Development and Accelerated Cardiac Aging

The heart is the first functional organ that develops during embryonic development. While a heartbeat indicates life, cessation of a heartbeat signals the end of life. Heart disease, due either to congenital defects or to acquired dysfunctions in adulthood, remains the leading cause of death worldwide. Epigenetics plays a key role in both embryonic heart development and heart disease in adults. Stress-induced vascular injury activates pathways involved in pathogenesis of accelerated cardiac aging that includes cellular dysfunction, pathological cardiac hypertrophy, diabetic cardiomyopathy, cardiac matrix remodeling, cardiac dysfunction and heart failure. Acetyltransferase p300 (p300), a major epigenetic regulator, plays a pivotal role in heart development during embryogenesis, as deficiency or abnormal expression of p300 leads to embryonic death at early gestation periods due to deformation of the heart and neural tube. Acetyltransferase p300 controls heart development through histone acetylation-mediated chromatin remodeling and transcriptional regulation of genes required for cardiac development. In adult hearts, p300 is differentially expressed in different chambers and epigenetically controls cardiac gene expression. Deregulation of p300, in response to prohypertrophic and profibrogenic stress signals, is associated with increased recruitment of p300 to several genes including transcription factors, increased acetylation of specific lysines in histones and transcription factors, altered chromatin organization, and increased hypertrophic and fibrogenic gene expression. Cardiac hypertrophy and myocardial fibrogenesis are common pathological manifestations of several stress-induced accelerated cardiac aging-related pathologies, including high blood pressure-induced or environmentally induced cardiac hypertrophy, myocardial infarction, diabetes-induced cardiomyopathy, and heart failure. Numerous studies using cellular and animal models clearly indicate that pharmacologic or genetic normalization of p300 activity has the potential to prevent or halt the progression of cardiac aging pathologies. Based on these preclinical studies, development of safe, non-toxic, small molecule inhibitors/epidrugs targeting p300 is an ideal approach to control accelerated cardiac aging-related deaths worldwide.

Metabolic Regulation of Human Pluripotent Stem Cell-Derived Cardiomyocyte Maturation

PURPOSE OF REVIEW

This review summarizes the important role that metabolism plays in driving maturation of human pluripotent stem cell-derived cardiomyocytes.

RECENT FINDINGS

Human pluripotent stem cell-derived cardiomyocytes provide a model system for human cardiac biology. However, these models have been unable to fully recapitulate the maturity observed in the adult heart. By simulating the glucose to fatty acid transition observed in neonatal mammals, human pluripotent stem cell-derived cardiomyocytes undergo structural and functional maturation also accompanied by transcriptional changes and cell cycle arrest. The role of metabolism in energy production, signaling, and epigenetic modifications illustrates that metabolism and cellular phenotype are intimately linked. Further understanding of key metabolic factors driving cardiac maturation will facilitate the generation of more mature human pluripotent stem cell-derived cardiomyocyte models. This will increase our understanding of cardiac biology and potentially lead to novel therapeutics to enhance heart function.

KLF15-Wnt-Dependent Cardiac Reprogramming Up-Regulates SHISA3 in the Mammalian Heart

BACKGROUND

The combination of cardiomyocyte (CM) and vascular cell (VC) fetal reprogramming upon stress culminates in end-stage heart failure (HF) by mechanisms that are not fully understood. Previous studies suggest KLF15 as a key regulator of CM hypertrophy.

OBJECTIVES

This study aimed to characterize the impact of KLF15-dependent cardiac transcriptional networks leading to HF progression, amenable to therapeutic intervention in the adult heart.

METHODS

Transcriptomic bioinformatics, phenotyping of Klf15 knockout mice, Wnt-signaling-modulated hearts, and pressure overload and myocardial ischemia models were applied. Human KLF15 knockout embryonic stem cells and engineered human myocardium, and human samples were used to validate the relevance of the identified mechanisms.

RESULTS

The authors identified a sequential, postnatal transcriptional repression mediated by KLF15 of pathways implicated in pathological tissue remodeling, including distinct Wnt-pathways that control CM fetal reprogramming and VC remodeling. The authors further uncovered a vascular program induced by a cellular crosstalk initiated by CM, characterized by a reduction of KLF15 and a concomitant activation of Wnt-dependent transcriptional signaling. Within this program, a so-far uncharacterized cardiac player, SHISA3, primarily expressed in VCs in fetal hearts and pathological remodeling was identified. Importantly, the KLF15 and Wnt codependent SHISA3 regulation was demonstrated to be conserved in mouse and human models.

CONCLUSIONS

The authors unraveled a network interplay defined by KLF15-Wnt dynamics controlling CM and VC homeostasis in the postnatal heart and demonstrated its potential as a cardiac-specific therapeutic target in HF. Within this network, they identified SHISA3 as a novel, evolutionarily conserved VC marker involved in pathological remodeling in HF.

Transcriptome analysis of Klf15‑mediated inhibitory functions in a mouse deep venous thrombosis model

Krüppel-like family (KLF) members are important regulators of proinflammatory activation in the vasculature. A transcriptome study involving RNA sequencing (RNA-seq) and quantitative PCR (qPCR) was performed to investigate Klf15 and Klf15-regulated gene levels in C57BL/6 mice with inferior vena cava thrombi and in control (Blank) mice. A total of 2,206 differentially expressed genes (DEGs), including 1,330 upregulated and 876 downregulated genes, were identified between the deep venous thrombosis (DVT) group and the Blank group. Additionally, 1,041 DEGs (235 upregulated and 806 downregulated) were identified between the Klf15-small interfering RNA (siRNA) and Klf15-negative control (NC) groups. The DEGs were subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses, and qPCR was conducted to validate the results. A total of seven significant DEGs were selected from the RNA-seq results. Matrix metalloproteinases (Mmp)12, Mmp13, Mmp19, Arg1, Ccl2, heme oxygenase-1 and Fmo3 levels were significantly higher, while Klf15 levels were lower, in the DVT group than in the Blank group. Fmo3 and Mmp19 have not been previously identified as DVT-associated DEGs. Klf15, Mmp12 and Mmp13 levels were compared between the Klf15-siRNA and Klf15-NC groups. Mmp12 and Mmp13 expression was significantly higher, while that of Klf15 was lower, in the Klf15-siRNA group than in the Klf15-NC group. Critical roles of Klf15, Mmp12 and Mmp13 have been identified, which have not previously been shown to help regulate DVT initiation and progression. Moreover, Klf15-mediated regulation of DVT may be modulated by downregulation of various genes, such as Mmp12 and Mmp13, potentially providing a theoretical foundation and diagnostic criteria for DVT treatment.

KLF15 is a protective regulatory factor of heart failure induced by pressure overload

The aim of the present study was to investigate the protective effect of Kruppel‑like factor 15 (KLF15) overexpression on heart failure (HF) induced by left ventricular (LV) pressure overload in mice. Wild‑type (WT) mice and cardiac‑specific KLF15‑overexpressed transgenic (TG) mice were selected as research subjects, and an LV pressure overload model was constructed by ascending aortic constriction surgery. Changes in cardiac morphology and function, and ultrastructure and molecular expression were observed via M‑mode echocardiography, histological and immunohistochemical staining, ELISA and western blotting at 2 and 6 weeks of LV overload. WT and TG mice subjected to 2 weeks of overload displayed adaptive LV hypertrophy characterized by ventricular thickness, cardiomyocyte size, ejection fraction and fractional shortening of heart‑lung weight ratio and KLF15, and increases in vascular endothelial growth factor (VEGF) expression without other pathological changes. WT mice subjected to 6 weeks of overload displayed enlargement of the LV chamber, severe interstitial remodeling, and HW/LW, cardiac capillary and heart function decline, accompanied by downregulated expression of KLF15 and VEGF, and upregulated expression of connective tissue growth factor, phosphorylated p38 (p‑p38) and phosphorylated Smad3 (p‑Smad3). In contrast, TG mice exhibited improved resistance to 6 weeks of overload and a slighter molecular expression response compared with WT mice. KLF15 was revealed to be a critical factor regulating the expression of CTGF, VEGF, p‑p38 and p‑Smad3, and could alleviate the progression from adaptive LV hypertrophy to decompensatory cardiac insufficiency.

MiR-137-3p exacerbates the ischemia-reperfusion injured cardiomyocyte apoptosis by targeting KLF15

Ischemia-reperfusion (I/R) injury is a kind of the tissue damage caused by an abrupt re-supplying tissue with blood after a period of ischemia or hypoxia. It contributes to a wide range of pathological processes including kidney injury, circulatory arrest, and especially cardiovascular disease. However, the underlying pathological mechanism is not fully elucidated. Previously, extensive studies demonstrated that miRNAs participate in the pathogenesis of I/R injury, such as I/R-induced cardiomyocyte apoptosis. Here, we found that miR-137-3p, a mature form of miR-137, was up-regulated in I/R-injured cardiomyocytes of myocardial infarction patients. Deficiency of miR-137-3p partly alleviated the cardiomyocyte apoptosis and oxidative stress induced by hypoxia-reoxygenation (H/R) treatment in H9c2 cells. Also, we provided evidences that miR-137-3p directly targeted the 3' UTR of KLF15 mRNA to down-regulate its expression, and loss function of KLF15 significantly abolished the deleterious effects of ectopic miR-137-3p on cardiomyocytes both in vitro and in vivo. Collectively, these observations highlight a molecular perturbation in the pathogenesis of I/R injury in cardiomyocytes.

Impaired branched chain amino acid oxidation contributes to cardiac insulin resistance in heart failure

BACKGROUND

Branched chain amino acids (BCAA) can impair insulin signaling, and cardiac insulin resistance can occur in the failing heart. We, therefore, determined if cardiac BCAA accumulation occurs in patients with dilated cardiomyopathy (DCM), due to an impaired catabolism of BCAA, and if stimulating cardiac BCAA oxidation can improve cardiac function in mice with heart failure.

METHOD

For human cohorts of DCM and control, both male and female patients of ages between 22 and 66 years were recruited with informed consent from University of Alberta hospital. Left ventricular biopsies were obtained at the time of transplantation. Control biopsies were obtained from non-transplanted donor hearts without heart disease history. To determine if stimulating BCAA catabolism could lessen the severity of heart failure, C57BL/6J mice subjected to a transverse aortic constriction (TAC) were treated between 1 to 4-week post-surgery with either vehicle or a stimulator of BCAA oxidation (BT2, 40 mg/kg/day).

RESULT

Echocardiographic data showed a reduction in ejection fraction (54.3 ± 2.3 to 22.3 ± 2.2%) and an enhanced formation of cardiac fibrosis in DCM patients when compared to the control patients. Cardiac BCAA levels were dramatically elevated in left ventricular samples of patients with DCM. Hearts from DCM patients showed a blunted insulin signalling pathway, as indicated by an increase in P-IRS1ser636/639 and its upstream modulator P-p70S6K, but a decrease in its downstream modulators P-AKT ser473 and in P-GSK3β ser9. Cardiac BCAA oxidation in isolated working hearts was significantly enhanced by BT2, compared to vehicle, following either acute or chronic treatment. Treatment of TAC mice with BT2 significantly improved cardiac function in both sham and TAC mice (63.0 ± 1.8 and 56.9 ± 3.8% ejection fraction respectively). Furthermore, P-BCKDH and BCKDK expression was significantly decreased in the BT2 treated groups.

CONCLUSION

We conclude that impaired cardiac BCAA catabolism and insulin signaling occur in human heart failure, while enhancing BCAA oxidation can improve cardiac function in the failing mouse heart.

Molecular Pharmacological Approaches for Treating Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is considered to be a potent life-threatening disorder in elderly individuals. Although many patients with a small AAA are detected during routine abdominal screening, there is no effective therapeutic option to prevent the progression or regression of AAA in the clinical setting. Recent advances in molecular biology have led to the identification of several important molecules, including microRNA and transcription factor, in the process of AAA formation. Regulation of these factors using nucleic acid drugs is expected to be a novel therapeutic option for AAA. Nucleic acid drugs can bind to target factors, mRNA, microRNA, and transcription factors in a sequence-specific fashion, resulting in a loss of function of the target molecule at the transcriptional or posttranscriptional level. Of note, inhibition of a transcription factor using a decoy strategy effectively suppresses experimental AAA formation, by regulating the expression of several genes associated with the disease progression. This review focuses on recent advances in molecular therapy of using nucleic acid drugs to treat AAA.

Multiple roles of KLF15 in the heart: Underlying mechanisms and therapeutic implications

Although there is an increasing understanding of the signaling pathways that promote cardiac hypertrophy, negative regulatory factors of this process have received less attention. Increasing evidence indicates that Krüppel-like factor 15 (KLF15) plays an important role in maintaining cardiac function by controlling the transcriptional pathways that regulating cardiac metabolism. Recent studies have also revealed a vital role for KLF15 as an inhibitor of pathological cardiac hypertrophy and fibrosis via its effects on factors such as myocyte enhancer factor 2 (MEF2), GATA-binding protein 4 (GATA4), transforming growth factor-β (TGF-β), and myocardin. KLF15 may therefore be an effective therapeutic target for the treatment of heart failure and other cardiovascular diseases. In this review, we focus on the physiological and pathophysiological roles of KLF15 in the heart and the potential mechanisms through which KLF15 is regulated in various cardiac diseases.

The Krüppel-Like Factors and Control of Energy Homeostasis

Nutrient handling by higher organisms is a complex process that is regulated at the transcriptional level. Studies over the past 15 years have highlighted the critical importance of a family of transcriptional regulators termed the Krüppel-like factors (KLFs) in metabolism. Within an organ, distinct KLFs direct networks of metabolic gene targets to achieve specialized functions. This regulation is often orchestrated in concert with recruitment of tissue-specific transcriptional regulators, particularly members of the nuclear receptor family. Upon nutrient entry into the intestine, gut, and liver, KLFs control a range of functions from bile synthesis to intestinal stem cell maintenance to effect nutrient acquisition. Subsequently, coordinated KLF activity across multiple organs distributes nutrients to sites of storage or liberates them for use in response to changes in nutrient status. Finally, in energy-consuming organs like cardiac and skeletal muscle, KLFs tune local metabolic programs to precisely match substrate uptake, flux, and use, particularly via mitochondrial function, with energetic demand; this is achieved in part via circulating mediators, including glucocorticoids and insulin. Here, we summarize current understanding of KLFs in regulation of nutrient absorption, interorgan circulation, and tissue-specific use.

Targeting the glucagon receptor improves cardiac function and enhances insulin sensitivity following a myocardial infarction

Background

In heart failure the myocardium becomes insulin resistant which negatively influences cardiac energy metabolism and function, while increasing cardiac insulin signalling improves cardiac function and prevents adverse remodelling in the failing heart. Glucagon’s action on cardiac glucose and lipid homeostasis counteract that of insulin’s action. We hypothesised that pharmacological antagonism of myocardial glucagon action, using a human monoclonal antibody (mAb A) against glucagon receptor (GCGR), a G-protein coupled receptor, will enhance insulin sensitivity and improve cardiac energy metabolism and function post myocardial infarction (MI).

Methods

Male C57BL/6 mice were subjected to a permanent left anterior descending coronary artery ligation to induce MI, following which they received either saline or mAb A (4 mg kg⁻¹ week⁻¹ starting at 1 week post-MI) for 3 weeks.

Results

Echocardiographic assessment at 4 weeks post-MI showed that mAb A treatment improved % ejection fraction (40.0 ± 2.3% vs 30.7 ± 1.7% in vehicle-treated MI heart, p < 0.05) and limited adverse remodelling (LV mass: 129 ± 7 vs 176 ± 14 mg in vehicle-treated MI hearts, p < 0.05) post MI. In isolated working hearts an increase in insulin-stimulated glucose oxidation was evident in the mAb A-treated MI hearts (1661 ± 192 vs 924 ± 165 nmol g dry wt⁻¹ min⁻¹ in vehicle-treated MI hearts, p < 0.05), concomitant with a decrease in ketone oxidation and fatty acid oxidation rates. The increase in insulin stimulated glucose oxidation was accompanied by activation of the IRS-1/Akt/AS160/GSK-3β pathway, an increase in GLUT4 expression and a reduction in pyruvate dehydrogenase phosphorylation. This enhancement in insulin sensitivity occurred in parallel with a reduction in cardiac branched chain amino acids content (374 ± 27 vs 183 ± 41 µmol g protein⁻¹ in vehicle-treated MI hearts, p < 0.05) and inhibition of the mTOR/P70S6K hypertrophic signalling pathway. The MI-induced increase in the phosphorylation of transforming growth factor β-activated kinase 1 (p-TAK1) and p38 MAPK was also reduced by mAb A treatment.

Conclusions

mAb A-mediated cardioprotection post-myocardial infarction is associated with improved insulin sensitivity and a selective enhancement of glucose oxidation via, at least in part, enhancing branched chain amino acids catabolism. Antagonizing glucagon action represents a novel and effective pharmacological intervention to alleviate cardiac dysfunction and adverse remodelling post-myocardial infarction.

Absence of miR-223-3p ameliorates hypoxia-induced injury through repressing cardiomyocyte apoptosis and oxidative stress by targeting KLF15

Apoptosis of cardiomyocytes and oxidant stress are considered essential processes in the progression of cardiovascular diseases. A hypoxic stress which causes apoptosis of cardiomyocytes is the main problem in ischemic heart disease. The aim of the present study was to explore the functional role and potential mechanisms of miR-223-3p in hypoxia-induced cardiomyocyte apoptosis and oxidative stress. Here, we observed a increment of miR-223-3p level accompanied by the decrease of Krüppel-like zinc-finger transcription factor 15 (KLF15) expression in response to hypoxia. Additionally, absence of miR-223-3p manifestly dampened hypoxia-induced cardiomyocyte injury in H9c2 cells, including improving cell viability, attenuating the LDH leakage and preventing cardiomyocyte apoptosis accompanied by an increase in the expression of Bcl-2 and a decrease in the expression of Bax and C-caspase 3 in the setting of hypoxia. Moreover, depletion of miR-223-3p evidently retarded oxidant stress by inhibiting reactive oxygen species generation and lipid peroxidation, as well as enhancing antioxidant enzyme activity in H9c2 cells following exposure to hypoxia. More importantly, KLF15 was a direct and functional target of miR-223-3p. Further data validated that miR-223-3p negatively regulated the expression of KLF15. Mechanistically, deletion of KLF15 partly abrogated the suppressive effects of miR-223-3p deletion on hypoxia-induced cardiomyocyte apoptosis and oxidative stress. Taken all data together, our findings established that our study defines a novel mechanism by which miR-223-3p protects against cardiomyocyte apoptosis and oxidative stress by targeting KLF15, suggesting that the miR-223-3p/KLF15 may be a potential therapeutic target for ischemic heart conditions.

Estrogen receptor beta maintains expression of KLF15 to prevent cardiac myocyte hypertrophy in female rodents

Maintaining a healthy, anti-hypertrophic state in the heart prevents progression to cardiac failure. In humans, angiotensin II (AngII) indirectly and directly stimulates hypertrophy and progression, while estrogens acting through estrogen receptor beta (ERβ) inhibit these AngII actions. The KLF15 transcription factor has been purported to provide anti-hypertrophic action. In cultured neonatal rat cardiomyocytes, we found AngII inhibited KLF1 expression and nuclear localization, substantially prevented by estradiol (E2) or β-LGND2 (β-LGND2), an ERβ agonist. AngII stimulation of transforming growth factor beta expression in the myocytes activated p38α kinase via TAK1 kinase, inhibiting KLF15 expression. All was comparably reduced by E2 or β-LGND2. Knockdown of KLF15 in the myocytes induced myocyte hypertrophy and limited the anti-hypertrophic actions of E2 and β-LGND2. Key aspects were confirmed in an in-vivo model of cardiac hypertrophy. Our findings define additional anti-hypertrophic effects of ERβ supporting testing specific receptor agonists in humans to prevent progression of cardiac disease.

Left ventricular hypertrophy in experimental chronic kidney disease is associated with reduced expression of cardiac Kruppel-like factor 15

Background

Left ventricular hypertrophy (LVH) increases the risk of death in chronic kidney disease (CKD). The transcription factor Kruppel-like factor 15 (KLF15) is expressed in the heart and regulates cardiac remodelling through inhibition of hypertrophy and fibrosis. It is unknown if KLF15 expression is changed in CKD induced LVH, or whether expression is modulated by blood pressure reduction using angiotensin converting enzyme (ACE) inhibition.

Methods

CKD was induced in Sprague–Dawley rats by subtotal nephrectomy (STNx), and rats received vehicle (n = 10) or ACE inhibition (ramipril, 1 mg/kg/day, n = 10) for 4 weeks. Control, sham-operated rats (n = 9) received vehicle. Cardiac structure and function and expression of KLF15 were assessed.

Results

STNx caused impaired kidney function (P < 0.001), hypertension (P < 0.01), LVH (P < 0.001) and fibrosis (P < 0.05). LVH was associated with increased gene expression of hypertrophic markers, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP, P < 0.01) and connective tissue growth factor (CTGF) (P < 0.05). Cardiac KLF15 mRNA and protein expression were reduced (P < 0.05) in STNx and levels of the transcription regulator, GATA binding protein 4 were increased (P < 0.05). Ramipril reduced blood pressure (P < 0.001), LVH (P < 0.001) and fibrosis (P < 0.05), and increased cardiac KLF15 gene (P < 0.05) and protein levels (P < 0.01). This was associated with reduced ANP, BNP and CTGF mRNA (all P < 0.05).

Conclusion

This is the first evidence that loss of cardiac KLF15 in CKD induced LVH is associated with unchecked trophic and fibrotic signalling, and that ACE inhibition ameliorates loss of cardiac KLF15.

Advances in the relationship between Kruppel-like factor 15 and cardiovascular disease research

Kruppel-like factor 15 (KLF15) is a subtype of the Kruppel-like family of transcription factors (KLFs). KLFs have three high-fidelity zinc fingers at the carboxyl terminus that enable them to regulate the biological processes of proliferation, differentiation, cellular development, and apoptosis. KLF15 is highly expressed in the kidney, pancreas, and cardiac and skeletal muscle, and plays an essential role in the development and occurrence of multiple system diseases. In this paper, we underscored the important relationship between KLF15 and cardiovascular diseases such as atherosclerosis, heart failure, arrhythmia, aortic lesions, etc. On this basis, we identified KLF15 as a potential therapeutic target for the treatment of cardiovascular disease.

A Leveraged Signal-to-Noise Ratio (LSTNR) Method to Extract Differentially Expressed Genes and Multivariate Patterns of Expression From Noisy and Low-Replication RNAseq Data

To life scientists, one important feature offered by RNAseq, a next-generation sequencing tool used to estimate changes in gene expression levels, lies in its unprecedented resolution. It can score countable differences in transcript numbers among thousands of genes and between experimental groups, all at once. However, its high cost limits experimental designs to very small sample sizes, usually N = 3, which often results in statistically underpowered analysis and poor reproducibility. All these issues are compounded by the presence of experimental noise, which is harder to distinguish from instrumental error when sample sizes are limiting (e.g., small-budget pilot tests), experimental populations exhibit biologically heterogeneous or diffuse expression phenotypes (e.g., patient samples), or when discriminating among transcriptional signatures of closely related experimental conditions (e.g., toxicological modes of action, or MOAs). Here, we present a leveraged signal-to-noise ratio (LSTNR) thresholding method, founded on generalized linear modeling (GLM) of aligned read detection limits to extract differentially expressed genes (DEGs) from noisy low-replication RNAseq data. The LSTNR method uses an agnostic independent filtering strategy to define the dynamic range of detected aggregate read counts per gene, and assigns statistical weights that prioritize genes with better sequencing resolution in differential expression analyses. To assess its performance, we implemented the LSTNR method to analyze three separate datasets: first, using a systematically noisy in silico dataset, we demonstrated that LSTNR can extract pre-designed patterns of expression and discriminate between "noise" and "true" differentially expressed pseudogenes at a 100% success rate; then, we illustrated how the LSTNR method can assign patient-derived breast cancer specimens correctly to one out of their four reported molecular subtypes (luminal A, luminal B, Her2-enriched and basal-like); and last, we showed the ability to retrieve five different modes of action (MOA) elicited in livers of rats exposed to three toxicants under three nutritional routes by using the LSTNR method. By combining differential measurements with resolving power to detect DEGs, the LSTNR method offers an alternative approach to interrogate noisy and low-replication RNAseq datasets, which handles multiple biological conditions at once, and defines benchmarks to validate RNAseq experiments with standard benchtop assays.

Kruppel-Like Factor 15 Is Critical for the Development of Left Ventricular Hypertrophy

Left ventricular hypertrophy (LVH) is an independent risk factor for adverse cardiovascular events and is often present in patients with hypertension. Treatment to reduce blood pressure and regress LVH is key to improving health outcomes, but currently available drugs have only modest cardioprotective effects. Improved understanding of the molecular mechanisms involved in the development of LVH may lead to new therapeutic targets in the future. There is now compelling evidence that the transcription factor Kruppel-like factor 15 (KLF15) is an important negative regulator of cardiac hypertrophy in both experimental models and in man. Studies have reported that loss or suppression of KLF15 contributes to LVH, through lack of inhibition of pro-hypertrophic transcription factors and stimulation of trophic and fibrotic signaling pathways. This review provides a summary of the experimental and human studies that have investigated the role of KLF15 in the development of cardiac hypertrophy. It also discusses our recent paper that described the contribution of genetic variants in KLF15 to the development of LVH and heart failure in high-risk patients.

Hypoxia Triggers SENP1 (Sentrin-Specific Protease 1) Modulation of KLF15 (Kruppel-Like Factor 15) and Transcriptional Regulation of Arg2 (Arginase 2) in Pulmonary Endothelium

OBJECTIVE

KLF15 (Kruppel-like factor 15) has recently been shown to suppress activation of proinflammatory processes that contribute to atherogenesis in vascular smooth muscle, however, the role of KLF15 in vascular endothelial function is unknown. Arginase mediates inflammatory vasculopathy and vascular injury in pulmonary hypertension. Here, we tested the hypothesis that KLF15 is a critical regulator of hypoxia-induced Arg2 (arginase 2) transcription in human pulmonary microvascular endothelial cells (HPMEC).

APPROACH AND RESULTS

Quiescent HPMEC express ample amounts of full-length KLF15. HPMECs exposed to 24 hours of hypoxia exhibited a marked decrease in KLF15 protein levels and a reciprocal increase in Arg2 protein and mRNA. Chromatin immunoprecipitation indicated direct binding of KLF15 to the Arg2 promoter, which was relieved with HPMEC exposure to hypoxia. Furthermore, overexpression of KLF15 in HPMEC reversed hypoxia-induced augmentation of Arg2 abundance and arginase activity and rescued nitric oxide (NO) production. Ectopic KLF15 also reversed hypoxia-induced endothelium-mediated vasodilatation in isolated rat pulmonary artery rings. Mechanisms by which hypoxia regulates KLF15 abundance, stability, and compartmentalization to the nucleus in HPMEC were then investigated. Hypoxia triggered deSUMOylation of KLF15 by SENP1 (sentrin-specific protease 1), and translocation of KLF15 from nucleus to cytoplasm.

CONCLUSIONS

KLF15 is a critical regulator of pulmonary endothelial homeostasis via repression of endothelial Arg2 expression. KLF15 abundance and nuclear compartmentalization are regulated by SUMOylation/deSUMOylation-a hypoxia-sensitive process that is controlled by SENP1. Strategies including overexpression of KLF15 or inhibition of SENP1 may represent novel therapeutic targets for pulmonary hypertension.

Kruppel-like factor 15 is required for the cardiac adaptive response to fasting

Cardiac metabolism is highly adaptive in response to changes in substrate availability, as occur during fasting. This metabolic flexibility is essential to the maintenance of contractile function and is under the control of a group of select transcriptional regulators, notably the nuclear receptor family of factors member PPARα. However, the diversity of physiologic and pathologic states through which the heart must sustain function suggests the possible existence of additional transcriptional regulators that play a role in matching cardiac metabolism to energetic demand. Here we show that cardiac KLF15 is required for the normal cardiac response to fasting. Specifically, we find that cardiac function is impaired upon fasting in systemic and cardiac specific Klf15-null mice. Further, cardiac specific Klf15-null mice display a fasting-dependent accumulation of long chain acylcarnitine species along with a decrease in expression of the carnitine translocase Slc25a20. Treatment with a diet high in short chain fatty acids relieves the KLF15-dependent long chain acylcarnitine accumulation and impaired cardiac function in response to fasting. Our observations establish KLF15 as a critical mediator of the cardiac adaptive response to fasting through its regulation of myocardial lipid utilization.

Krüppel-Like Factors in Vascular Inflammation: Mechanistic Insights and Therapeutic Potential

The role of inflammation in vascular disease is well recognized, involving dysregulation of both circulating immune cells as well as the cells of the vessel wall itself. Unrestrained vascular inflammation leads to pathological remodeling that eventually contributes to atherothrombotic disease and its associated sequelae (e.g., myocardial/cerebral infarction, embolism, and critical limb ischemia). Signaling events during vascular inflammation orchestrate widespread transcriptional programs that affect the functions of vascular and circulating inflammatory cells. The Krüppel-like factors (KLFs) are a family of transcription factors central in regulating vascular biology in states of homeostasis and disease. Given their abundance and diversity of function in cells associated with vascular inflammation, understanding the transcriptional networks regulated by KLFs will further our understanding of the pathogenesis underlying several pervasive health concerns (e.g., atherosclerosis, stroke, etc.) and consequently inform the treatment of cardiovascular disease. Within this review, we will discuss the role of KLFs in coordinating protective and deleterious responses during vascular inflammation, while addressing the potential targeting of these critical transcription factors in future therapies.

Identification of transcriptome signature for myocardial reductive stress

The nuclear factor erythroid 2 like 2 (Nfe2l2/Nrf2) is a master regulator of antioxidant gene transcription. We recently identified that constitutive activation of Nrf2 (CaNrf2) caused reductive stress (RS) in the myocardium. Here we investigate how chronic Nrf2 activation alters myocardial mRNA transcriptome in the hearts of CaNrf2 transgenic (TG-low and TG-high) mice using an unbiased integrated systems approach and next generation RNA sequencing followed by qRT-PCR methods. A total of 246 and 1031 differentially expressed genes (DEGs) were identified in the heart of TGL and TGH in relation to NTG littermates at ~ 6 months of age. Notably, the expression and validation of the transcripts were gene-dosage dependent and statistically significant. Ingenuity Pathway Analysis identified enriched biological processes and canonical pathways associated with myocardial RS in the CaNrf2-TG mice. In addition, an overrepresentation of xenobiotic metabolic signaling, glutathione-mediated detoxification, unfolded protein response, and protein ubiquitination was observed. Other, non-canonical signaling pathways identified include: eNOS, integrin-linked kinase, glucocorticoid receptor, PI3/AKT, actin cytoskeleton, cardiac hypertrophy, and the endoplasmic reticulum stress response. In conclusion, this mRNA profiling identified a "biosignature" for pro-reductive (TGL) and reductive stress (TGH) that can predict the onset, rate of progression, and clinical outcome of Nrf2-dependent myocardial complications. We anticipate that this global sequencing analysis will illuminate the undesirable effect of chronic Nrf2 signaling leading to RS-mediated pathogenesis besides providing important guidance for the application of Nrf2 activation-based cytoprotective strategies.

KLF15 regulates in vitro chondrogenic differentiation of human mesenchymal stem cells by targeting SOX9

Mesenchymal stem cells (MSCs) are multipotent stromal cells residing in the bone marrow. MSCs have the potential to differentiate into adipocytes, chondrocytes, and other types of cells. However, the mechanism underlying MSC differentiation is still not fully understood. Here we aimed to investigate the function of the Kruppel-like factor (KLF) transcriptional factor family in regulating chondrogenic differentiation from human MSCs. Among the KLF family members, KLF15 was activated during different models of chondrogenic differentiation in a time-dependent manner. Lentivirus-mediated knockdown of KLF15 in MSCs repressed chondrogenic differentiation whereas KLF15 overexpression facilitated chondrogenic differentiation. KLF15 promoted the chondrogenic differentiation of human MSCs by activating the expression of SOX9, which is critically involved in KLF15 function during chondrogenic differentiation. Our mechanism study demonstrated that KLF15 bound the promoter of SOX9 and promoted the activation of the SOX9 promoter. Taken together, our findings show that KLF15 promotes chondrogenic differentiation of human MSCs by activating SOX9.

Krüppel-like factors in mammalian stem cells and development

Krüppel-like factors (KLFs) are a family of zinc-finger transcription factors that are found in many species. Recent studies have shown that KLFs play a fundamental role in regulating diverse biological processes such as cell proliferation, differentiation, development and regeneration. Of note, several KLFs are also crucial for maintaining pluripotency and, hence, have been linked to reprogramming and regenerative medicine approaches. Here, we review the crucial functions of KLFs in mammalian embryogenesis, stem cell biology and regeneration, as revealed by studies of animal models. We also highlight how KLFs have been implicated in human diseases and outline potential avenues for future research.

Regulatory network changes between cell lines and their tissues of origin

BACKGROUND

Cell lines are an indispensable tool in biomedical research and often used as surrogates for tissues. Although there are recognized important cellular and transcriptomic differences between cell lines and tissues, a systematic overview of the differences between the regulatory processes of a cell line and those of its tissue of origin has not been conducted. The RNA-Seq data generated by the GTEx project is the first available data resource in which it is possible to perform a large-scale transcriptional and regulatory network analysis comparing cell lines with their tissues of origin.

RESULTS

We compared 127 paired Epstein-Barr virus transformed lymphoblastoid cell lines (LCLs) and whole blood samples, and 244 paired primary fibroblast cell lines and skin samples. While gene expression analysis confirms that these cell lines carry the expression signatures of their primary tissues, albeit at reduced levels, network analysis indicates that expression changes are the cumulative result of many previously unreported alterations in transcription factor (TF) regulation. More specifically, cell cycle genes are over-expressed in cell lines compared to primary tissues, and this alteration in expression is a result of less repressive TF targeting. We confirmed these regulatory changes for four TFs, including SMAD5, using independent ChIP-seq data from ENCODE.

CONCLUSIONS

Our results provide novel insights into the regulatory mechanisms controlling the expression differences between cell lines and tissues. The strong changes in TF regulation that we observe suggest that network changes, in addition to transcriptional levels, should be considered when using cell lines as models for tissues.

Short-term administration of Nicotinamide Mononucleotide preserves cardiac mitochondrial homeostasis and prevents heart failure

Heart failure is associated with mitochondrial dysfunction so that restoring or improving mitochondrial health is of therapeutic importance. Recently, reduction in NAD⁺ levels and NAD⁺-mediated deacetylase activity has been recognized as negative regulators of mitochondrial function. Using a cardiac specific KLF4 deficient mouse line that is sensitive to stress, we found mitochondrial protein hyperacetylation coupled with reduced Sirt3 and NAD⁺ levels in the heart before stress, suggesting that the KLF4-deficient heart is predisposed to NAD⁺-associated defects. Further, we demonstrated that short-term administration of Nicotinamide Mononucleotide (NMN) successfully protected the mutant mice from pressure overload-induced heart failure. Mechanically, we showed that NMN preserved mitochondrial ultrastructure, reduced ROS and prevented cell death in the heart. In cultured cardiomyocytes, NMN treatment significantly increased long-chain fatty acid oxidation despite no direct effect on pyruvate oxidation. Collectively, these results provide cogent evidence that hyperacetylation of mitochondrial proteins is critical in the pathogenesis of cardiac disease and that administration of NMN may serve as a promising therapy.

BET bromodomain inhibition suppresses innate inflammatory and profibrotic transcriptional networks in heart failure

Despite current standard of care, the average 5-year mortality after an initial diagnosis of heart failure (HF) is about 40%, reflecting an urgent need for new therapeutic approaches. Previous studies demonstrated that the epigenetic reader protein bromodomain-containing protein 4 (BRD4), an emerging therapeutic target in cancer, functions as a critical coactivator of pathologic gene transactivation during cardiomyocyte hypertrophy. However, the therapeutic relevance of these findings to human disease remained unknown. We demonstrate that treatment with the BET bromodomain inhibitor JQ1 has therapeutic effects during severe, preestablished HF from prolonged pressure overload, as well as after a massive anterior myocardial infarction in mice. Furthermore, JQ1 potently blocks agonist-induced hypertrophy in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Integrated transcriptomic analyses across animal models and human iPSC-CMs reveal that BET inhibition preferentially blocks transactivation of a common pathologic gene regulatory program that is robustly enriched for NFκB and TGF-β signaling networks, typified by innate inflammatory and profibrotic myocardial genes. As predicted by these specific transcriptional mechanisms, we found that JQ1 does not suppress physiological cardiac hypertrophy in a mouse swimming model. These findings establish that pharmacologically targeting innate inflammatory and profibrotic myocardial signaling networks at the level of chromatin is effective in animal models and human cardiomyocytes, providing the critical rationale for further development of BET inhibitors and other epigenomic medicines for HF.