Genetic analysis of Kruppel-like zinc finger 11 variants in 5864 Danish individuals: potential effect on insulin resistance and modified signal transducer and activator of transcription-3 binding by promoter variant -1659G>C

Cardiometabolic Risk Factors and Benign Gynecologic Disorders

Importance

While it has long been known that polycystic ovarian syndrome is associated with cardiometabolic risk factors (CMRFs), there is emerging evidence that other benign gynecologic conditions, such as uterine leiomyomas, endometriosis, and even hysterectomy without oophorectomy, can be associated with CMRFs. Understanding the evidence and mechanisms of these associations can lead to novel preventive and therapeutic interventions.

Objective

This article discusses the evidence and the potential mechanisms mediating the association between CMRFs and benign gynecologic disorders.

Evidence Acquisition

We reviewed PubMed, EMBASE, Scopus, and Google Scholar databases to obtain plausible clinical and biological evidence, including hormonal, immunologic, inflammatory, growth factor-related, genetic, epigenetic, atherogenic, vitamin D-related, and dietary factors.

Results

Cardiometabolic risk factors appear to contribute to uterine leiomyoma pathogenesis. For example, obesity can modulate leiomyomatous cellular proliferation and extracellular matrix deposition through hyperestrogenic states, chronic inflammation, insulin resistance, and adipokines. On the other hand, endometriosis has been shown to induce systemic inflammation, thereby increasing cardiometabolic risks, for example, through inducing atherosclerotic changes.

Conclusion and Relevance

Clinical implications of these associations are 2-fold. First, screening and early modification of CMRFs can be part of a preventive strategy for uterine leiomyomas and hysterectomy. Second, patients diagnosed with uterine leiomyomas or endometriosis can be screened and closely followed for CMRFs and cardiovascular disease.

TGF-β Induces Endometriotic Progression via a Noncanonical, KLF11-Mediated Mechanism

Endometriosis, a chronic disease of heterogeneous etiopathology affects 10% of young women and is characterized by ectopic implantation of endometrial cells. Growth and spread of endometriosis lesions involves biological interplay between intrinsic lesion-driven and extrinsic host-responsive mechanisms. We propose a role for TGFβ and its target transcription factor Krüppel-like factor 11 (KLF11) in mediating such mechanisms. Although TGFβ, a pleiotropic cytokine implicated in endometriosis potentially, mediates its pathological phenotypes, KLF11 is associated with endocrine and reproductive tract diseases, specifically progression of endometriosis. In Ishikawa cells, TGFβ1 treatment resulted in noncanonical SMAD-mediated transient up-regulation and sustained repression of KLF11. KLF11 recruits histone deacetylases to epigenetically repress multiple synthetic and metabolic cytochrome P450 (CYP) enzymes such as CYP3A4, which affects endometrial metabolism and pathophysiology. In contrast to KLF11, TGFβ1 treatment caused transient repression and sustained activation of CYP3A4 expression. CYP3A4 increased endometrial cell proliferation and was also increased in human endometriosis lesions compared with eutopic endometrium. To determine whether dysregulation of TGFβ/Klf11/Cyp3a signaling affected endometriotic progression, we treated wild-type control and Klf11-/- mice with a Tgfβ type 1 receptor inhibitor (TGFβR1I) that inhibits Tgfβ signaling upstream of the canonical Smad proteins or a combination of TGFβR1I and a histone acetyltransferase inhibitor that additionally inhibits Klf11 signaling. Disease progression and lesional Cyp3a expression was diminished in TGFβR1I-treated animals and more so in animals treated synergistically with TGFβR1I and histone acetyltransferase inhibitor. TGFβ and KLF11 thus mediate critical, translationally relevant host and lesion-driven responses that enable establishment and progression of endometriosis.

Phenotypic Characterization of Mice Carrying Homozygous Deletion of KLF11, a Gene in Which Mutations Cause Human Neonatal and MODY VII Diabetes

We have previously shown that amino acid changes in the human Kruppel-Like Factor (KLF) 11 protein is associated with the development of maturity onset diabetes of the young VII, whereas complete inactivation of this pathway by the -331 human insulin mutation causes neonatal diabetes mellitus. Here, we report that Klf11-/- mice have decreased circulating insulin levels, alterations in the control of blood glucose and body weight, as well as serum dyslipidemia, but do not develop diabetes. Functional assays using ex vivo liver tissue sections demonstrate that Klf11-/- mice display increased insulin sensitivity. Genome-wide experiments validated by pathway-specific quantitative PCR arrays reveal that the Klf11-/- phenotype associates to alterations in the regulation of gene networks involved in lipid metabolism, in particular those regulated by peroxisome proliferator-activated receptor-γ. Combined, these results demonstrate that the major phenotype given by the whole-body deletion of Klf11 in mouse is not diabetes but increased insulin sensitivity, likely due to altered transcriptional regulation in target tissues. The absence of diabetes in the Klf11-/- mouse either indicates an interspecies difference for the role of this transcription factor in metabolic homeostasis between mouse and humans, or potentially highlights the fact that other molecular factors can compensate for its absence. Nevertheless, the data of this study, gathered at the whole-organism level, further support a role for KLF11 in metabolic processes like insulin sensitivity, which regulation is critical in several forms of diabetes.

Epigenetic regulation of uterine biology by transcription factor KLF11 via posttranslational histone deacetylation of cytochrome p450 metabolic enzymes

Endocrine regulation of uterine biology is critical for embryo receptivity and human reproduction. Uterine endometrium depends on extrinsic sex steroid input and hence likely has mechanisms that enable adaptation to hormonal variation. Emerging evidence suggests that sex steroid bioavailability in the endometrium is determined by adjusting their metabolic rate and fate via regulation of cytochrome (CYP) p450 enzymes. The CYP enzymes are targeted by ubiquitously expressed Sp/Krüppel-like (Sp/KLF) transcription factors. Specifically, KLF11 is highly expressed in reproductive tissues, regulates an array of endocrine/metabolic pathways via epigenetic histone-based mechanisms and, when aberrantly expressed, is associated with diabetes and reproductive tract diseases, such as leiomyoma and endometriosis. Using KLF11 as a model to investigate epigenetic regulation of endometrial first-pass metabolism, we evaluated the expression of a comprehensive array of metabolic enzymes in Ishikawa cells. KLF11 repressed most endometrial CYP enzymes. To characterize KLF11-recruited epigenetic regulatory mechanisms, we focused on the estrogen-metabolizing enzyme CYP3A4. KLF11 expression declined in secretory phase endometrial epithelium associated with increased CYP3A4 expression. Additionally, KLF11 bound to CYP3A4 promoter GC elements and thereby repressed promoter, message, protein as well as enzymatic function. This repression was epigenetically mediated, because KLF11 colocalized with and recruited the corepressor SIN3A/histone deacetylase resulting in selective deacetylation of the CYP3A4 promoter. Repression was reversed by a mutation in KLF11 that abrogated cofactor recruitment and binding. This repression was also pharmacologically reversible with an histone deacetylase inhibitor. Pharmacological alteration of endometrial metabolism could have long-term translational implications on human reproduction and uterine disease.

Involvement of KLF11 in hepatic glucose metabolism in mice via suppressing of PEPCK-C expression

BACKGROUND

Abnormal hepatic gluconeogenesis is related to hyperglycemia in mammals with insulin resistance. Despite the strong evidences linking Krüppel-like factor 11 (KLF11) gene mutations to development of Type 2 diabetes, the precise physiological functions of KLF11 in vivo remain largely unknown.

RESULTS

In current investigation, we showed that KLF11 is involved in modulating hepatic glucose metabolism in mice. Overexpression of KLF11 in primary mouse hepatocytes could inhibit the expression of gluconeogenic genes, including phosphoenolpyruvate carboxykinase (cytosolic isoform, PEPCK-C) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), subsequently decreasing the cellular glucose output. Diabetic mice with overexpression of KLF11 gene in livers significantly ameliorated hyperglycemia and glucose intolerance; in contrast, the knockdown of KLF11 expression in db/m and C57BL/6J mice livers impaired glucose tolerance.

CONCLUSIONS

Our data strongly indicated the involvement of KLF11 in hepatic glucose homeostasis via modulating the expression of PEPCK-C.

Human Krüppel-like factor 11 differentially regulates human insulin promoter activity in β-cells and non-β-cells via p300 and PDX1 through the regulatory sites A3 and CACCC box

Human Krüppel-like factor 11 (hKLF11) has been characterised to both activate and inhibit human insulin promoter (hInsP) activity. Since KLF11 is capable to differentially regulate genes dependent on recruited cofactors, we investigated the effects of hKLF11 on cotransfected hInsP in both β-cells and non-β-cells. hKLF11 protein interacts with hp300 but not with hPDX1. Overexpressed hKLF11 stimulates PDX1-transactivation of hInsP in HEK293 non-β-cells, but confers inhibition in INS-1E β-cells. Both hKLF11 functions can be neutralised by the p300 inhibitor E1A, increased hp300 levels (INS-1E), dominant negative (DN)-PDX1 and by mutation of the PDX1 binding site A3 or the CACCC box. In summary, hKLF11 differentially regulates hInsP activity depending on the molecular context via modulation of p300:PDX1 interactions with the A3 element and CACCC box. We postulate that KLF11 has a role in fine-tuning insulin transcription in certain cellular situations rather than representing a major transcriptional activator or repressor of the insulin gene.

Krüppel-like factor-11, a transcription factor involved in diabetes mellitus, suppresses endothelial cell activation via the nuclear factor-κB signaling pathway

OBJECTIVE

Endothelial cell (EC) inflammatory status is critical to many vascular diseases. Emerging data demonstrate that mutations of Krüppel-like factor-11 (KLF11), a gene coding maturity-onset diabetes mellitus of the young type 7 (MODY7), contribute to the development of neonatal diabetes mellitus. However, the function of KLF11 in the cardiovascular system still remains to be uncovered. In this study, we aimed to investigate the role of KLF11 in vascular endothelial inflammation.

METHODS AND RESULTS

KLF11 is highly expressed in vascular ECs and induced by proinflammatory stimuli. Adenovirus-mediated KLF11 overexpression inhibits expression of tumor necrosis factors-α-induced adhesion molecules. Moreover, small interfering RNA-mediated KLF11 knockdown augments the proinflammatory status in ECs. KLF11 inhibits promoter activity of adhesion molecules induced by tumor necrosis factor-α and nuclear factor-κB p65 overexpression. Mechanistically, KLF11 potently inhibits nuclear factor-κB signaling pathway via physical interaction with p65. Furthermore, KLF11 knockdown results in increased binding of p65 to vascular cell adhesion molecule-1 and E-selectin promoters. At the whole organism level, KLF11(-/-) mice exhibit a significant increase in leukocyte recruitment to ECs after lipopolysaccharide administration.

CONCLUSIONS

Taken together, our data demonstrate for the first time that KLF11 is a suppressor of EC inflammatory activation, suggesting that KLF11 constitutes a novel potential molecular target for inhibition of vascular inflammatory diseases.

Detailed structural-functional analysis of the Krüppel-like factor 16 (KLF16) transcription factor reveals novel mechanisms for silencing Sp/KLF sites involved in metabolism and endocrinology

Krüppel-like factor (KLF) proteins have elicited significant attention due to their emerging key role in metabolic and endocrine diseases. Here, we extend this knowledge through the biochemical characterization of KLF16, unveiling novel mechanisms regulating expression of genes involved in reproductive endocrinology. We found that KLF16 selectively binds three distinct KLF-binding sites (GC, CA, and BTE boxes). KLF16 also regulated the expression of several genes essential for metabolic and endocrine processes in sex steroid-sensitive uterine cells. Mechanistically, we determined that KLF16 possesses an activation domain that couples to histone acetyltransferase-mediated pathways, as well as a repression domain that interacts with the histone deacetylase chromatin-remodeling system via all three Sin3 isoforms, suggesting a higher level of plasticity in chromatin cofactor selection. Molecular modeling combined with molecular dynamic simulations of the Sin3a-KLF16 complex revealed important insights into how this interaction occurs at an atomic resolution level, predicting that phosphorylation of Tyr-10 may modulate KLF16 function. Phosphorylation of KLF16 was confirmed by in vivo³²P incorporation and controlled by a Y10F site-directed mutant. Inhibition of Src-type tyrosine kinase signaling as well as the nonphosphorylatable Y10F mutation disrupted KLF16-mediated gene silencing, demonstrating that its function is regulatable rather than constitutive. Subcellular localization studies revealed that signal-induced nuclear translocation and euchromatic compartmentalization constitute an additional mechanism for regulating KLF16 function. Thus, this study lends insights on key biochemical mechanisms for regulating KLF sites involved in reproductive biology. These data also contribute to the new functional information that is applicable to understanding KLF16 and other highly related KLF proteins.

Disruption of a novel Kruppel-like transcription factor p300-regulated pathway for insulin biosynthesis revealed by studies of the c.-331 INS mutation found in neonatal diabetes mellitus

Krüppel-like transcription factors (KLFs) have elicited significant attention because of their regulation of essential biochemical pathways and, more recently, because of their fundamental role in the mechanisms of human diseases. Neonatal diabetes mellitus is a monogenic disorder with primary alterations in insulin secretion. We here describe a key biochemical mechanism that underlies neonatal diabetes mellitus insulin biosynthesis impairment, namely a homozygous mutation within the insulin gene (INS) promoter, c.-331C>G, which affects a novel KLF-binding site. The combination of careful expression profiling, electromobility shift assays, reporter experiments, and chromatin immunoprecipitation demonstrates that, among 16 different KLF proteins tested, KLF11 is the most reliable activator of this site. Congruently, the c.-331C>G INS mutation fails to bind KLF11, thus inhibiting activation by this transcription factor. Klf11^−/− mice recapitulate the disruption in insulin production and blood levels observed in patients. Thus, these data demonstrate an important role for KLF11 in the regulation of INS transcription via the novel c.-331 KLF site. Lastly, our screening data raised the possibility that other members of the KLF family may also regulate this promoter under distinct, yet unidentified, cellular contexts. Collectively, this study underscores a key role for KLF proteins in biochemical mechanisms of human diseases, in particular, early infancy onset diabetes mellitus.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.