Repression of cardiac hypertrophy by KLF15: underlying mechanisms and therapeutic implications

Investigation of coagulation and proteomics profiles in symptomatic feline hypertrophic cardiomyopathy and healthy control cats

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a crucial heart disease in cats. The clinical manifestations of HCM comprise pulmonary edema, dyspnea, syncope, arterial thromboembolism (ATE), and sudden cardiac death. D-dimer and prothrombin time (PT) are powerful biomarkers used to assess coagulation function. Dysregulation in these two biomarkers may be associated with HCM in cats. This study aims to assess D-dimer levels, PT, and proteomic profiling in healthy cats in comparison to cats with symptomatic HCM.

RESULTS

Twenty-nine client-owned cats with HCM were enrolled, including 15 healthy control and 14 symptomatic HCM cats. The D-dimer concentration and PT were examined. Proteomic analysis was conducted by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In symptomatic cats, D-dimer levels were statistically significantly higher (mean ± SEM: 372.19 ng/ml ± 58.28) than in healthy cats (mean ± SEM: 208.54 ng/ml ± 10.92) with P-value of less than 0.01, while PT was statistically significantly lower in symptomatic cats (mean ± SEM: 9.8 s ± 0.15) compared to healthy cats (mean ± SEM: 11.08 s ± 0.23) with P-value of less than 0.0001. The proteomics analysis revealed upregulation of integrin subunit alpha M (ITGAM), elongin B (ELOB), and fibrillin 2 (FBN2) and downregulation of zinc finger protein 316 (ZNF316) and ectonucleoside triphosphate diphosphohydrolase 8 (ENTPD8) in symptomatic HCM cats. In addition, protein-drug interaction analysis identified the Ras signaling pathway and PI3K-Akt signaling pathway.

CONCLUSIONS

Cats with symptomatic HCM have higher D-dimer and lower PT than healthy cats. Proteomic profiles may be used as potential biomarkers for the detection and management of HCM in cats. The use of D-dimer as a biomarker for HCM detection and the use of proteomic profiling for a better understanding of disease mechanisms remain to be further studied in cats.

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.

Amino acid homeostasis is a target of metformin therapy

OBJECTIVE

Unexplained changes in regulation of branched chain amino acids (BCAA) during diabetes therapy with metformin have been known for years. Here we have investigated mechanisms underlying this effect.

METHODS

We used cellular approaches, including single gene/protein measurements, as well as systems-level proteomics. Findings were then cross-validated with electronic health records and other data from human material.

RESULTS

In cell studies, we observed diminished uptake/incorporation of amino acids following metformin treatment of liver cells and cardiac myocytes. Supplementation of media with amino acids attenuated known effects of the drug, including on glucose production, providing a possible explanation for discrepancies between effective doses in vivo and in vitro observed in most studies. Data-Independent Acquisition proteomics identified that SNAT2, which mediates tertiary control of BCAA uptake, was the most strongly suppressed amino acid transporter in liver cells following metformin treatment. Other transporters were affected to a lesser extent. In humans, metformin attenuated increased risk of left ventricular hypertrophy due to the AA allele of KLF15, which is an inducer of BCAA catabolism. In plasma from a double-blind placebo-controlled trial in nondiabetic heart failure (trial registration: NCT00473876), metformin caused selective accumulation of plasma BCAA and glutamine, consistent with the effects in cells.

CONCLUSIONS

Metformin restricts tertiary control of BCAA cellular uptake. We conclude that modulation of amino acid homeostasis contributes to therapeutic actions of the drug.

CRISPR activation and interference as investigative tools in the cardiovascular system

CRISPR activation and interference (CRISPRa/i) technology offers the unprecedented possibility of achieving regulated gene expression both in vitro and in vivo. The DNA pairing specificity of a nuclease dead Cas9 (dCas9) is exploited to precisely target a transcriptional activator or repressor in proximity to a gene promoter. This permits both the study of phenotypes arising from gene modulation for investigative purposes, and the development of potential therapeutics. As with virtually all other organ systems, the cardiovascular system can deeply benefit from a broader utilisation of CRISPRa/i. However, application of this technology is still in its infancy. Significant areas for improvement include the identification of novel and more effective transcriptional regulators that can be docked to dCas9, and the development of more efficient methods for their delivery and expression in vivo.

Role of resveratrol in inhibiting pathological cardiac remodeling

Cardiovascular disease is a group of diseases with high mortality in clinic, including hypertension, coronary heart disease, cardiomyopathy, heart valve disease, heart failure, to name a few. In the development of cardiovascular diseases, pathological cardiac remodeling is the most common cardiac pathological change, which often becomes a domino to accelerate the deterioration of the disease. Therefore, inhibiting pathological cardiac remodeling may delay the occurrence and development of cardiovascular diseases and provide patients with greater long-term benefits. Resveratrol is a non-flavonoid polyphenol compound. It mainly exists in grapes, berries, peanuts and red wine, and has cardiovascular protective effects, such as anti-oxidation, inhibiting inflammatory reaction, antithrombotic, dilating blood vessels, inhibiting apoptosis and delaying atherosclerosis. At present, the research of resveratrol has made rich progress. This review aims to summarize the possible mechanism of resveratrol against pathological cardiac remodeling, in order to provide some help for the in-depth exploration of the mechanism of inhibiting pathological cardiac remodeling and the development and research of drug targets.

Postnatal expression of cell cycle promoter Fam64a causes heart dysfunction by inhibiting cardiomyocyte differentiation through repression of Klf15

Introduction of fetal cell cycle genes into damaged adult hearts has emerged as a promising strategy for stimulating proliferation and regeneration of postmitotic adult cardiomyocytes. We have recently identified Fam64a as a fetal-specific cell cycle promoter in cardiomyocytes. Here, we analyzed transgenic mice maintaining cardiomyocyte-specific postnatal expression of Fam64a when endogenous expression was abolished. Despite an enhancement of cardiomyocyte proliferation, these mice showed impaired cardiomyocyte differentiation during postnatal development, resulting in cardiac dysfunction in later life. Mechanistically, Fam64a inhibited cardiomyocyte differentiation by repressing Klf15, leading to the accumulation of undifferentiated cardiomyocytes. In contrast, introduction of Fam64a in differentiated adult wildtype hearts improved functional recovery upon injury with augmented cell cycle and no dedifferentiation in cardiomyocytes. These data demonstrate that Fam64a inhibits cardiomyocyte differentiation during early development, but does not induce de-differentiation in once differentiated cardiomyocytes, illustrating a promising potential of Fam64a as a cell cycle promoter to attain heart regeneration.

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Overexpression of cell cycle promoter Fam64a in cardiomyocytes causes heart failure

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Fam64a inhibits cardiomyocyte differentiation during development by repressing Klf15

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Transient and local induction of Fam64a in adult hearts improves recovery upon injury

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Fam64a activates cardiomyocyte cell cycle without dedifferentiation upon injury

Potential of natural products in the treatment of myocardial infarction: focus on molecular mechanisms

Although conventional drugs are widely used in the prevention and treatment of cardiovascular disease (CVD), they are being used less frequently due to concerns about possible side effects over the long term. There has been a renewed research interest in medicinal plant products, and their role in protecting the cardiovascular system and treating CVD, which are now being considered as potential alternatives to modern drugs. The most important mechanism causing damage to the myocardium after heart attack and reperfusion, is increased levels of free radicals and oxidative stress. Therefore, treatment approaches often focus on reducing free radicals or enhancing antioxidant defense mechanism. It has been previously reported that bioactive natural products can protect the heart muscle in myocardial infarction (MI). Since these compounds are readily available in fruits and vegetables, they could prevent the risk of MI if they are consumed daily. Although the benefits of a healthy diet are well known, many scientific studies have focused on whether pure natural compounds can prevent and treat MI. In this review we summarize the effects of curcumin, resveratrol, quercitin, berberine, and tanshinone on MI and CVD, and focus on their proposed molecular mechanisms of action.

Expressions and relationship of Krüppel-like factor 15 and endothelial nitric oxide synthase in experimental deep venous thrombosis

Background

Deep vein thrombosis (DVT) is an early postoperative complication. Thrombosis formation, which is potentially life-threatening, seriously affects the rehabilitation of patients after surgery. We aimed to establish a C57 mouse model of DVT and to examine the changes in the expression of Krüppel-like factor 15 (KLF15) and endothelial nitric oxide synthase (eNOS) in venous wall tissues, and we also investigated the regulatory relationship of KLF15 and eNOS in the thrombin-induced human umbilical vein endothelial cell (HUVEC) injury cell model.

Methods

The DVT model was established using the inferior vena cava (IVC) stenosis method. The expression levels of KLF15 and eNOS were analyzed using quantitative reverse transcription–polymerase chain reaction (qRT-PCR). In cell experiments, the expression of KLF15 and eNOS was analyzed in the model of thrombin-induced HUVEC injury with KLF15 siRNA.

Results

Compared to the control and sham-operated groups, KLF15 in the DVT group was upregulated, while eNOS was downregulated. The results of cell experiments revealed that KLF15 was downregulated in the thrombin+KLF15 siRNA group compared with the thrombin group. Meanwhile, eNOS was upregulated in the thrombin+KLF15 siRNA group compared with the thrombin group. These findings suggested that KLF15 regulated the expression of eNOS in the DVT model.

Conclusions

We successfully constructed a DVT mouse model. In the early stage of DVT formation, KLF15 regulated the expression and inhibited the antithrombotic effect of eNOS, resulting in thrombi formation.

Impact of short-term starvation and refeeding on the expression of KLF15 and regulatory mechanism of branched-chain amino acids metabolism in muscle of Chinese soft-shelled turtle (Pelodiscus sinensis)

The branched-chain amino acids (BCAA) play an important role in muscle energy metabolism, and Krüppel-like factor 15 (KLF15) is an essential regulator of BCAA metabolism in muscle under nutritional deficiency. In this study, we analyzed the effect of normal feeding (starvation for 0 day), starvation for 3, 7, 10, 15 days, and refeeding for 7 days after 15 days of starvation on the expression of KLF15 and BCAA metabolism in muscle of Chinese soft-shelled turtles by a fasting-refeeding trial. The results showed that the level of KLF15 transcription was increased first and then decreased in muscle during short-term starvation, and the protein level was gradually increased. Both the mRNA and protein level of the KLF15 returned to normal feeding level after refeeding for 7 days. The changing trend of the activities of branched-chain aminotransferase (BCAT) and alanine aminotransferase (ALT) was consistent to that of KLF15 mRNA, but at the transcription level, the expression of BCAT mRNA was consistent with the change of enzyme activity as well as ALT continued to increase in muscle under starvation. In addition, BCAA content showed a trend that decreased first and then increased under starvation, while the alanine (Ala) was the contrary. The above results indicated that the regulatory role of KLF15 in BCAA catabolism of muscle in Chinese soft-shelled turtles under nutritional deficiency, which might be activated the catabolism of BCAA in muscle to provide energy and maintain the homeostasis by KLF15-BACC signaling axis.

MiR-125a-3p-KLF15-BCAA Regulates the Skeletal Muscle Branched-Chain Amino Acid Metabolism in Nile Tilapia (Oreochromis niloticus) During Starvation

The branched-chain amino acids (BCAAs) play a key role in the energy metabolism of the muscle tissue and the Krüppel-like factor 15 (KLF15) as a transcription factor, which is a key regulator of BCAA metabolism in the skeletal muscle. This study assessed the effect of starvation for 0, 3, 7, and 15 days on BCAA metabolism in the skeletal muscle of Nile tilapia. The results showed that the expression of KLF15 showed a trend of increasing first and then decreasing during starvation, as well as the expression and activity of branched-chain aminotransferase 2 (BCAT2) and alanine aminotransferase (ALT). On the other hand, the content of BCAA was at first decreased and then upregulated, and it reached the lowest level after starvation for 3 days. In addition, through dual-luciferase reporter assay and injection experiments, it was found that KLF15 is the target gene of miR-125a-3p, which further verified that miR-125a-3p can regulate the BCAA metabolism by targeting KLF15 in the skeletal muscle. Thus, our work investigated the possible mechanisms of BCAA metabolism adapting to nutritional deficiency in the skeletal muscle of Nile tilapia and illustrated the regulation of BCAA metabolism through the miR-125a-3p-KLF15-BCAA pathway in the skeletal muscle.

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.

A mutation in mouse Krüppel-like factor 15 alters the gut microbiome and response to obesogenic diet

We identified a mouse strain, HLB444, carrying an N-ethyl-N-nitrosourea (ENU)-induced mutation in a highly conserved C2H2 zinc-finger DNA binding motif of the transcriptional regulator KLF15 that exhibits resistance to diet-induced obesity. Characterization of the HLB444 mutant model on high-fat and chow diets revealed a number of phenotypic differences compared to wild-type controls. When fed a high fat diet, HLB444 had lower body fat, resistance to hepatosteatosis, lower circulating glucose and improved insulin sensitivity compared to C57BL/6J controls. Gut microbial profiles in HLB444 generated from 16S rRNA sequencing of fecal samples differed from controls under both chow and high fat diets. HLB444 shares similar phenotypic traits with engineered full- and adipose-specific Klf15 knockout strains; however, some phenotypic differences between this mutant and the other models suggest that the Klf15 mutation in HLB444 is a hypomorphic variant. The HLB444 model will inform further annotation of transcriptional functions of KLF15, especially with respect to the role of the first zinc-finger domain.

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.

Testosterone deficiency reduces cardiac hypertrophy in a rat model of severe volume overload

The aim of the study was to characterize if the development of cardiac hypertrophy (CH) caused by severe left ventricle (LV) volume overload (VO) from chronic aortic valve regurgitation (AR) in male rats was influenced by androgens. We studied Wistar rats with/without orchiectomy (Ocx) either sham-operated (S) or with severe AR for 26 weeks. Loss of testosterone induced by Ocx decreased general body growth. Cardiac hypertrophy resulting from AR was relatively more important in intact (non-Ocx) animals than in Ocx ones compared to their respective S group (60% vs. 40%; P = 0.019). The intact AR group had more LV dilation, end-diastolic LV diameter being increased by 37% over S group and by 17% in AROcx rats (P < 0.0001). Fractional shortening (an index of systolic function) decreased only by 15% in AROcx compared to 26% for intact AR animals (P = 0.029). Changes in LV gene expression resulting from CH were more marked in intact rats than in AROcx animals, especially for genes linked to extracellular matrix remodeling and energy metabolism. The ratio of hydroxyacyl-Coenzyme A dehydrogenase activity over hexokinase activity, an index of the shift of myocardial substrate use toward glucose from the preferred fatty acids, was significantly decreased in the AR group but not in AROcx. Finally, pJnk2 LV protein content was more abundant in AR than in AROcx rats, indicating decreased activation of this stress pathway in the absence of androgens. In summary, testosterone deficiency in rats with severe LV VO resulted in less CH and a normalization of the LV gene expression profile.

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.

Genome-wide DNA methylation encodes cardiac transcriptional reprogramming in human ischemic heart failure

Ischemic cardiomyopathy (ICM) is the clinical endpoint of coronary heart disease and a leading cause of heart failure. Despite growing demands to develop personalized approaches to treat ICM, progress is limited by inadequate knowledge of its pathogenesis. Since epigenetics has been implicated in the development of other chronic diseases, the current study was designed to determine whether transcriptional and/or epigenetic changes are sufficient to distinguish ICM from other etiologies of heart failure. Specifically, we hypothesize that genome-wide DNA methylation encodes transcriptional reprogramming in ICM. RNA-sequencing analysis was performed on human ischemic left ventricular tissue obtained from patients with end-stage heart failure, which enriched known targets of the polycomb methyltransferase EZH2 compared to non-ischemic hearts. Combined RNA sequencing and genome-wide DNA methylation analysis revealed a robust gene expression pattern consistent with suppression of oxidative metabolism, induced anaerobic glycolysis, and altered cellular remodeling. Lastly, KLF15 was identified as a putative upstream regulator of metabolic gene expression that was itself regulated by EZH2 in a SET domain-dependent manner. Our observations therefore define a novel role of DNA methylation in the metabolic reprogramming of ICM. Furthermore, we identify EZH2 as an epigenetic regulator of KLF15 along with DNA hypermethylation, and we propose a novel mechanism through which coronary heart disease reprograms the expression of both intermediate enzymes and upstream regulators of cardiac metabolism such as KLF15.

Novel molecular therapeutic targets in cardiac fibrosis: a brief overview 1

Cardiac fibrosis, characterized by excessive accumulation of extracellular matrix, abolishes cardiac contractility, impairs cardiac function, and ultimately leads to heart failure. In recent years, significant evidence has emerged that supports the highly dynamic and responsive nature of the cardiac extracellular matrix. Although our knowledge of cardiac fibrosis has advanced tremendously over the past decade, there is still a lack of specific therapies owing to an incomplete understanding of the disease etiology and process. In this review, we attempt to highlight some of the recently investigated molecular determinants of ischemic and non-ischemic fibrotic remodeling of the myocardium that present as promising avenues for development of anti-fibrotic therapies.

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.

Protective effect of KLF15 on vascular endothelial dysfunction induced by TNF‑α

Atherosclerosis (AS) is a cardiovascular disease with a relatively high incidence rate. Krüppel-like factor 15 (KLF15) has a role in numerous pathological processes, including nephropathy, abnormal glucose metabolism and myocardial injury. The aim of the present study was to investigate the function of KLF15 in vascular endothelial dysfunction. MTT analyses, nitric oxide (NO) detection and cell adhesion detection kits were used to investigate the viability and adhesion of, and quantity of NO released by Eahy926 cells induced by tumor necrosis factor (TNF)-α, respectively. Reverse transcription-quantitative polymerase chain reaction and western blot analyses were performed to determine the expression levels of KLF15, endothelial nitric oxide synthase, monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), transforming growth factor-β1 (TGF-β1), phosphorylated (p-)transcription factor p65 (p65) and nuclear factor erythroid 2-related factor 2 (Nrf2). The results of the present study demonstrated that TNF-α was able to induce vascular endothelial dysfunction in Eahy926 cells at an optimum concentration of 10 ng/ml. Overexpression of KLF15 markedly enhanced cell viability in addition to the quantity of released NO of TNF-α-induced Eahy926 cells, and increased the expression levels of eNOS and Nrf2. Furthermore, overexpression of KLF15 markedly suppressed the rate of cellular adhesion, and downregulated levels of MCP-1, ICAM-1, TGF-β1 and p-p65 in TNF-α induced Eahy926 cells. In conclusion, the results of the present study suggested that overexpression of KLF15 in Eahy926 cells exhibited a protective effect against TNF-α induced dysfunction via activation of Nrf2 signaling and inhibition of nuclear factor κB signaling.

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.

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.

KLF 15 Works as an Early Anti-Fibrotic Transcriptional Regulator in Ang II-Induced Renal Fibrosis via Down-Regulation of CTGF Expression

BACKGROUND/AIMS

Angiotensin II (Ang II) has been regarded as an important profibrogenic cytokine in renal fibrosis. Krüppel-like factor 15 (KLF15) has been identified as an important negative transcription factor in renal fibrosis. However, little is known about the role of KLF15 in Ang II-induced renal fibrosis.

METHODS

In this study, we randomized mice into a control group, Ang II group or Ang II plus losartan group. KLF15 expression was examined with real-time PCR and immunofluorescence in these groups. In vitro, KLF15 expression was examined by Western blot in rat renal fibroblasts (NRK-49F) stimulated with Ang II, and the effect of altered KLF15 expression on the regulation of the profibrotic factor connective tissue growth factor (CTGF) was further explored with co-immunoprecipitation (CoIP) and chromatin immunoprecipitation (ChIP) analyses.

RESULTS

Compared with the control group, the murine model of Ang II-induced renal fibrosis demonstrated a significant decrease in renal KLF15 expression at 4 weeks and presented with progressive renal fibrosis at 6 weeks. Meanwhile, losartan, an angiotensin type 1 (AT1) receptor antagonist, effectively prevented the down-regulation of KLF15 expression induced by Ang II infusion. In vitro, NRK-49F cells stimulated with Ang II exhibited a significant decrease in KLF15 expression, accompanied by a marked increase in the expression of profibrotic factors and in the production of extracellular matrix. The up-regulation of CTGF expression induced by Ang II stimulation was inhibited by KLF15 overexpression in NRK-49F cells, and losartan treatment prevented the down-regulation of KLF15 expression and the up-regulation of CTGF expression induced by Ang II stimulation. Furthermore, CoIP and ChIP assays revealed that the transcription regulator KLF15 directly bound to the co-activator P/CAF and repressed its recruitment to the CTGF promoter.

CONCLUSIONS

Ang II down-regulates KLF15 expression via the AT1 receptor, and KLF15 is likely to inhibit Ang II-induced CTGF expression by repressing the recruitment of the co-activator P/CAF to the CTGF promoter.

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.

ZNF307 (Zinc Finger Protein 307) Acts as a Negative Regulator of Pressure Overload–Induced Cardiac Hypertrophy

Pathological cardiac hypertrophy is a key risk factor for heart failure. We found that the protein expression levels of the ZNF307 (zinc finger protein 307) were significantly increased in heart samples from both human patients with dilated cardiomyopathy and mice subjected to aortic banding. Therefore, we aimed to elucidate the role of ZNF307 in the development of cardiac hypertrophy and to explore the signal transduction events that mediate the effect of ZNF307 on cardiac hypertrophy, using cardiac-specific ZNF307 transgenic (ZNF307-TG) mice and ZNF307 global knockout (ZNF307-KO) mice. The results showed that the deletion of ZNF307 potentiated aortic banding–induced pathological cardiac hypertrophy, fibrosis, and cardiac dysfunction; however, the aortic banding–induced cardiac hypertrophic phenotype was dramatically diminished by ZNF307 overexpression in mouse heart. Mechanistically, the antihypertrophic effects mediated by ZNF307 in response to pathological stimuli were associated with the direct inactivation of NF-κB (nuclear factor-κB) signaling and blockade of the nuclear translocation of NF-κB subunit p65. Furthermore, the overexpression of a degradation-resistant mutant of IκBα (IκBα S32A/S36A ) reversed the exacerbation of cardiac hypertrophy, fibrosis, and dysfunction shown in aortic banding–treated ZNF307-KO mice. In conclusion, our findings demonstrate that ZNF307 ameliorates pressure overload–induced cardiac hypertrophy by inhibiting the activity of NF-κB–signaling pathway.

Genetic Variation in Kruppel like Factor 15 Is Associated with Left Ventricular Hypertrophy in Patients with Type 2 Diabetes: Discovery and Replication Cohorts

Left ventricular (LV) hypertrophy (LVH) is a heritable trait that is common in type 2 diabetes and is associated with the development of heart failure. The transcriptional factor Kruppel like factor 15 (KLF15) is expressed in the heart and acts as a repressor of cardiac hypertrophy in experimental models. This study investigated if KLF15 gene variants were associated with LVH in type 2 diabetes. In stage 1 of a 2-stage approach, patients with type 2 diabetes and no known cardiac disease were prospectively recruited for a transthoracic echocardiographic assessment (Melbourne Diabetes Heart Cohort) (n = 318) and genotyping of two KLF15 single nucleotide polymorphisms (SNPs) (rs9838915, rs6796325). In stage 2, the association of KLF15 SNPs with LVH was investigated in the Genetics of Diabetes Audit and Research in Tayside Scotland (Go-DARTS) type 2 diabetes cohort (n = 5631). The KLF15 SNP rs9838915 A allele was associated in a dominant manner with LV mass before (P = 0.003) and after (P = 0.001) adjustment for age, gender, body mass index (BMI) and hypertension, and with adjusted septal (P < 0.0001) and posterior (P = 0.004) wall thickness. LVH was present in 35% of patients. Over a median follow up of 5.6 years, there were 22 (7%) first heart failure hospitalizations. The adjusted risk of heart failure hospitalization was 5.5-fold greater in those with LVH and the rs9838915 A allele compared to those without LVH and the GG genotype (hazard ratio (HR) 5.5 (1.6–18.6), P = 0.006). The association of rs9838915 A allele with LVH was replicated in the Go-DARTS cohort. We have identified the KLF15 SNP rs9838915 A allele as a marker of LVH in patients with type 2 diabetes, and replicated these findings in a large independent cohort. Studies are needed to characterize the functional importance of these results, and to determine if the SNP rs9838915 A allele is associated with LVH in other high risk patient cohorts.

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KLF15 SNP rs9838915 A allele is associated with increased LV mass in patients with 2 diabetes.

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KLF15 SNP rs9838915 predicts incident heart failure hospitalization.

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Genotyping KLF15 SNP rs9838915 allowed more precise stratification of the risk of heart failure hospitalization.

Left ventricular hypertrophy (LVH) is a heritable trait that is common in patients with diabetes. The Kruppel like factor 15 (KLF15) is expressed in the heart and acts as a repressor of cardiac hypertrophy and fibrosis. Our study provides evidence that genetic variation in KLF15 is associated with LVH in patients with type 2 diabetes and these findings were then replicated in an independent cohort of patients with type 2 diabetes. The KLF15 genetic variant was also associated with first heart failure hospitalization. These findings add to our understanding of the molecular mechanisms that contribute to increased LV mass.

Resveratrol-Mediated Expression of KLF15 in the Ischemic Myocardium is Associated with an Improved Cardiac Phenotype

PURPOSE

Myocardial infarction results in physiological derangements that lead to structural and functional alterations to the myocardium. In addition, oxidative stress potentiates cardiac remodeling and drives disease progression. Unfortunately, treatment with antioxidants in clinical trials have failed to show any therapeutic benefits despite the positive results reported in animal studies, which warrants further investigation into their mechanism(s) of action. Accordingly, the aim of this study was to elucidate a previously unknown mechanism of action for the antioxidant, resveratrol, in the treatment of the ischemic heart.

METHODS

Male Sprague-Dawley rats underwent four weeks of chronic myocardial ischemia with or without daily resveratrol treatment (10 mg/kg/day). The expression and signaling of Krüppel-like factor 15 (KLF15) were determined by immunoblot and qPCR analyses, respectively.

RESULTS

Chronic myocardial ischemia reduced the protein expression of KLF15. In parallel, mRNA transcripts of KLF15 gene targets actively involved in cardiac remodeling were robustly increased in untreated hearts. Importantly, daily treatment with resveratrol stimulated KLF15 expression, which was associated with attenuated gene expression and an improved cardiac phenotype. Additionally, we describe a novel role for KLF15 in the regulation of redox homeostasis.

CONCLUSION

Based on our current findings, it appears that resveratrol treatment induces KLF15 expression, which may, in part, explain its therapeutic efficacy to improve the cardiac phenotype following ischemic injury.

KLF15 protects against isoproterenol-induced cardiac hypertrophy via regulation of cell death and inhibition of Akt/mTOR signaling

Increasing evidence indicate that the Krüppel-like factor KLF15, a member of Cys2/His2 zinc-finger DNA-binding proteins, attenuates cardiac hypertrophy. However, the role of KLF15 in cardiovascular system is largely unknown and the exact molecular mechanism of its protective function is not fully elucidated. In the present study, we established a mouse model of cardiac hypertrophy and found that KLF15 expression was down-regulated in hypertrophic hearts. To evaluate the roles of KLF15 in cardiac hypertrophy, we generated transgenic mice overexpressing KLF15 of KLF15 knockdown mice and subsequently induced cardiac hypertrophy. The results indicated that KLF15 overexpression protects mice from ISO-induced cardiac hypertrophy, with reduced ratios of heart weight (HW)/body weight (BW) and cross-sectional area. We also observed that KLF15 overexpression attenuated cardiac fibrosis, inhibited apoptosis and induced autophagy in cardiomyocytes compared with KLF15 knockdown mice. More importantly, we found that the KLF15 overexpression inhibited the Akt/mTOR signaling pathway. Taken together, our findings imply that KLF15 possesses potential anti-hypertrophic and anti-fibrotic functions, possibly via regulation of cell death pathways and the inhibition of Akt/mTOR axis. KLF15 may constitute an efficient candidate drug for the treatment of heart failure and other cardiovascular diseases.

KLF15 suppresses cell proliferation and extracellular matrix expression in mesangial cells under high glucose

Excess mesangial extracellular matrix (ECM) and mesangial cell (MC) proliferation is the major pathologic feature of diabetic nephropathy. Kruppel-like factor 15 (KLF15) is a member of the KLF transcription factor family that plays a critical role in regulating renal fibrosis. However, the role of KLF15 in diabetic nephropathy remains poorly understood. This study was conducted to explore the role of KLF15 in the development and progress of diabetic nephropathy in high glucose (HG)-stimulated human MCs. Here, we found down-regulated expression of KLF15 in MCs induced by HG. Overexpression of KLF15 significantly inhibited MCs proliferation and ECM production induced by HG. Moreover, overexpression of KLF15 inhibited HG-induced ERK1/2 phosphorylation in MCs. In summary, our data demonstrate that KLF15 can suppress HG-induced cell proliferation and ECM protein fibronectin expression in human MCs via ERK1/2 MAPK signaling. The results provide evidence that KLF15 might be a potential molecular target for the treatment of diabetic nephropathy.

KLF15 is an essential negative regulatory factor for the cardiac remodeling response to pressure overload

OBJECTIVE

To investigate the mechanism of Krüppel-like factor 15 (KLF15) in cardiac remodeling and interstitial fibrosis.

METHODS

A rat model was established by in vivo aortic coarctation followed by a period of pressure unloading and used to measure heart function, myocardial pathological changes, and KLF15, transforming growth factor-β (TGF-β), connective tissue growth factor (CTGF), and myocardin-related transcription factor A (MRTF-A) expression levels. In addition, cardiac fibroblasts were cultured in vitro and treated with KLF15-shRNA or KLF15 recombinant adenovirus to establish a TGF-β-mediated cardiac fibroblast hypertrophy model and analyze cell morphology, collagen secretion, and changes in the expression levels of 4 cytokines.

RESULTS

In vivo pressure overload impaired cardiac function and resulted in myocardial hypertrophy and fibrosis. These changes were accompanied by the downregulation of KLF15 mRNA levels and increased expression of the other factors. The response to unloading was the opposite. In in vitro cell experiments, by specifically targeting the KLF15 gene, changes in the expression levels of the 4 cytokines and the amounts of collagen I and III were observed.

CONCLUSIONS

In myocardial remodeling processes induced by mechanical or metabolic factors, KLF15 regulates TGF-β, CTGF, and MRTF-A expression and can ameliorate or even reverse myocardial fibrosis and improve cardiac function.

Cardiospheres and cardiosphere-derived cells as therapeutic agents following myocardial infarction

Heart disease is a major cause of morbidity and mortality. Cellular therapies hold significant promise for patients with heart disease. Heart-derived progenitor cells are capable of repairing a diseased heart through modulation of growth factor milieu and temporary engraftment leading to endogenous repair. The proof-of-concept CADUCEUS clinical trial using cardiosphere-derived cells has shown evidence of therapeutic cardiac tissue regeneration. Future clinical trials are now being planned to generate additional safety and efficacy data in the hopes of building toward an approved cellular therapy for heart disease.