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

Is the Cis-Element CACCC-Box a Master Regulatory Element during Cardiovascular Disease? A Bioinformatics Approach from the Perspective of the Krüppel-like Family of Transcription Factors

The CACCC-box motif emerges as a pivotal cis-regulatory element implicated in diverse developmental processes and diseases, particularly cardiovascular diseases (CVDs). This study centers on the intricate interplay between the CACCC-box and its binding proteins such as: the Krüppel-Like Family (KLF) of transcription factors as primary effectors in the context of CVDs. Our analysis was through a bioinformatics approach, which revealed significant transcriptional activity among KLF subgroup 2, exhibiting the highest number of interactions focusing on the established roles: pluripotency, cancer, and cardiovascular development and diseases. Our analysis reveals KLF's interactions with GATA4, MEF2C, NKX2.5 and other ~90 potential genes that participate in the regulation of the hypertrophic environment (or CVDs' Environment). Also, the GO analysis showed that genes containing the motif CACCC were enriched for multiple CVDs; in combination with STRING analysis, these results pointed to a link between KLFs and these diseases. The analysis further identifies other potential CACCC-box binding factors, such as SP family members, WT1, VEZF1, and -SALL4, which are implicated in cardiac contraction, remodeling, and inflammation processes.

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.

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.

Metformin: evidence from preclinical and clinical studies for potential novel applications in cardiovascular disease

INTRODUCTION

For a long time, metformin has been the first-line treatment for glycaemic control in type 2 diabetes, however, the results of recent cardiovascular outcome trials of sodium-glucose co-transporter 2 inhibitors and glucagon-like peptide 1 receptor agonists have caused many to question metformin's position in the guidelines. Although there are several plausible mechanisms by which metformin might have beneficial cardiovascular effects, for example its anti-inflammatory effects and metabolic properties, and numerous observational data suggesting improved cardiovascular outcomes with metformin use, the main randomised clinical trial data for metformin was published over 20 years ago. Nevertheless, the overwhelming majority of participants in contemporary type 2 diabetes trials were prescribed metformin.

AREAS COVERED

In this review we will summarise the potential mechanisms of cardiovascular benefit with metformin, before discussing clinical data in individuals with or without diabetes.

EXPERT OPINION

Metformin may have some cardiovascular benefit in patients with and without diabetes, however the majority of clinical trials were small and are before the use SGLT2 inhibitors and GLP1-RAs. Larger contemporary randomised trials with metformin evaluating its cardiovascular benefit are warranted.

The Involvement of Krüppel-like Factors in Cardiovascular Diseases

Krüppel-like factors (KLFs) are a set of DNA-binding proteins belonging to a family of zinc-finger transcription factors, which have been associated with many biological processes related to the activation or repression of genes, inducing cell growth, differentiation, and death, and the development and maintenance of tissues. In response to metabolic alterations caused by disease and stress, the heart will undergo cardiac remodeling, leading to cardiovascular diseases (CVDs). KLFs are among the transcriptional factors that take control of many physiological and, in this case, pathophysiological processes of CVD. KLFs seem to be associated with congenital heart disease-linked syndromes, malformations because of autosomal diseases, mutations that relate to protein instability, and/or loss of functions such as atheroprotective activities. Ischemic damage also relates to KLF dysregulation because of the differentiation of cardiac myofibroblasts or a modified fatty acid oxidation related to the formation of a dilated cardiomyopathy, myocardial infarctions, left ventricular hypertrophy, and diabetic cardiomyopathies. In this review, we describe the importance of KLFs in cardiovascular diseases such as atherosclerosis, myocardial infarction, left ventricle hypertrophy, stroke, diabetic cardiomyopathy, and congenital heart diseases. We further discuss microRNAs that have been involved in certain regulatory loops of KLFs as they may act as critical in CVDs.

KLF15 suppresses tumor growth and metastasis in Triple-Negative Breast Cancer by downregulating CCL2 and CCL7

Kruppel like factor 15 (KLF15), a transcriptional factor belonging to the Kruppel-like factor (KLF) family of genes, has recently been reported as a tumor suppressor gene in breast cancer. However, the specific mechanisms by which KLF15 inhibits BrCa have not been elucidated. Here we investigated the role and mechanism of KLF15 in triple-negative breast cancer (TNBC). KLF15 expression and methylation were detected by RT-qPCR, RT-PCR and methylation-specific PCR in breast cancer cell lines and tissues. The effects of KLF15 on TNBC cell functions were examined via various cellular function assays. The specific anti-tumor mechanisms of KLF15 were further investigated by RNA sequence, RT-qPCR, Western blotting, luciferase assay, ChIP, and bioinformatics analysis. As the results showed that KLF15 is significantly downregulated in breast cancer cell lines and tissues, which promoter methylation of KLF15 partially contributes to. Exogenous expression of KLF15 induced apoptosis and G2/M phase cell cycle arrest, suppressed cell proliferation, metastasis and in vivo tumorigenesis of TNBC cells. Mechanism studies revealed that KLF15 targeted and downregulated C-C motif chemokine ligand 2 (CCL2) and CCL7. Moreover, transcriptome and metabolome analysis revealed that KLF15 is involved in key anti-tumor regulatory and metabolic pathways in TNBC. In conclusion, KLF15 suppresses cell growth and metastasis in TNBC by downregulating CCL2 and CCL7. KLF15 may be a prognostic biomarker in TNBC.

Quercetin alleviates diastolic dysfunction and suppresses adverse pro-hypertrophic signaling in diabetic rats

INTRODUCTION

Quercetin (Que) is a potent anti-inflammatory and antioxidant flavonoid with cardioprotective potential. However, very little is known about the signaling pathways and gene regulatory proteins Que may interfere with, especially in diabetic cardiomyopathy. Therefore, we aimed to study the potential cardioprotective effects of Que on the cardiac phenotype of type 2 diabetes mellitus (T2DM) accompanied by obesity.

METHODS

For this experiment, we used Zucker Diabetic Fatty rats (fa/fa) and their age-matched lean controls (fa/+) that were treated with either vehicle or 20 mg/kg/day of Que for 6 weeks. Animals underwent echocardiographic (echo) examination before the first administration of Que and after 6 weeks.

RESULTS

After the initial echo examination, the diabetic rats showed increased E/A ratio, a marker of left ventricular (LV) diastolic dysfunction, in comparison to the control group which was selectively reversed by Que. Following the echo analysis, Que reduced LV wall thickness and exhibited an opposite effect on LV luminal area. In support of these results, the total collagen content measured by hydroxyproline assay was decreased in the LVs of diabetic rats treated with Que. The follow-up immunoblot analysis of proteins conveying cardiac remodeling pathways revealed that Que was able to interfere with cardiac pro-hypertrophic signaling. In fact, Que reduced relative protein expression of pro-hypertrophic transcriptional factor MEF2 and its counter-regulator HDAC4 along with pSer²⁴⁶-HDAC4. Furthermore, Que showed potency to decrease GATA4 transcription factor, NFAT3 and calcineurin, as well as upstream extracellular signal-regulated kinase Erk5 which orchestrates several pro-hypertrophic pathways.

DISCUSSION

In summary, we showed for the first time that Que ameliorated pro-hypertrophic signaling on the level of epigenetic regulation and targeted specific upstream pathways which provoked inhibition of pro-hypertrophic signals in ZDF rats. Moreover, Que mitigated T2DM and obesity-induced diastolic dysfunction, therefore, might represent an interesting target for future research on novel cardioprotective agents.

KLF15 negatively regulates cardiac fibrosis by which SDF-1β attenuates cardiac fibrosis in type 2 diabetic mice

Diabetic cardiomyopathy (DCM) is a serious diabetic complication that lacks effective preventive or therapeutic approaches. Wild-type and Klf15 knockout (Klf15-KO) mice were fed with either high fat diet (HFD, 60% kcal from fat) or normal diet (ND, 10% kcal from fat) for 3 months and then injected with streptozotocin or vehicle, to induce type 2 diabetes (T2D). All T2D and age-matched control mice were treated with or without SDF-1β at 5 mg/kg body-weight twice a week and also continually received HFD or ND for 3 months. At the end of 6-month study, after cardiac functions were measured, mice were euthanized to collect heart tissue. For in vitro mechanistic study, H9c2 cells were exposed to palmitate to mimic in vivo condition of T2D. SDF-1β prevented T2D-induced cardiac dysfunction and fibrosis and T2D-down-regulated KLF15 expression in wild-type diabetic heart tissue. However, the preventive effects of SDF-1β on both KLF15 expression and fibrosis was abolished, with partial cardiac protection in Klf15-KO/T2D mice. These results demonstrate partial KLF15-dependence for SDF-1β's cardiac fibrotic protection from T2D, but not on SDF-1β's protective effects on T2D-induced cardiac dysfunction. Further study showed that SDF-1β inhibited palmitate-induced cardiomyocyte fibrosis through its receptor CXCR7-mediated activation of p38β MAPK signaling pathway.

KLF15 Loss-of-Function Mutation Underlying Atrial Fibrillation as well as Ventricular Arrhythmias and Cardiomyopathy

Atrial fibrillation (AF) represents the most common type of clinical cardiac arrhythmia and substantially increases the risks of cerebral stroke, heart failure and death. Accumulating evidence has convincingly demonstrated the strong genetic basis of AF, and an increasing number of pathogenic variations in over 50 genes have been causally linked to AF. Nevertheless, AF is of pronounced genetic heterogeneity, and the genetic determinants underpinning AF in most patients remain obscure. In the current investigation, a Chinese pedigree with AF as well as ventricular arrhythmias and hypertrophic cardiomyopathy was recruited. Whole exome sequencing and bioinformatic analysis of the available family members were conducted, and a novel heterozygous variation in the KLF15 gene (encoding Krüppel-like factor 15, a transcription factor critical for cardiac electrophysiology and structural remodeling), NM_014079.4: c.685A>T; p.(Lys229*), was identified. The variation was verified by Sanger sequencing and segregated with autosomal dominant AF in the family with complete penetrance. The variation was absent from 300 unrelated healthy subjects used as controls. In functional assays using a dual-luciferase assay system, mutant KLF15 showed neither transcriptional activation of the KChIP2 promoter nor transcriptional inhibition of the CTGF promoter, alone or in the presence of TGFB1, a key player in the pathogenesis of arrhythmias and cardiomyopathies. The findings indicate KLF15 as a new causative gene responsible for AF as well as ventricular arrhythmias and hypertrophic cardiomyopathy, and they provide novel insight into the molecular mechanisms underlying cardiac arrhythmias and hypertrophic cardiomyopathy.

Muscle Krüppel-like factor 15 regulates lipid flux and systemic metabolic homeostasis

Skeletal muscle is a major determinant of systemic metabolic homeostasis that plays a critical role in glucose metabolism and insulin sensitivity. By contrast, despite being a major user of fatty acids, and evidence that muscular disorders can lead to abnormal lipid deposition (e.g., nonalcoholic fatty liver disease in myopathies), our understanding of skeletal muscle regulation of systemic lipid homeostasis is not well understood. Here we show that skeletal muscle Krüppel-like factor 15 (KLF15) coordinates pathways central to systemic lipid homeostasis under basal conditions and in response to nutrient overload. Mice with skeletal muscle-specific KLF15 deletion demonstrated (a) reduced expression of key targets involved in lipid uptake, mitochondrial transport, and utilization, (b) elevated circulating lipids, (c) insulin resistance/glucose intolerance, and (d) increased lipid deposition in white adipose tissue and liver. Strikingly, a diet rich in short-chain fatty acids bypassed these defects in lipid flux and ameliorated aspects of metabolic dysregulation. Together, these findings establish skeletal muscle control of lipid flux as critical to systemic lipid homeostasis and metabolic health.

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.

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.

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.