Prep1 deficiency induces protection from diabetes and increased insulin sensitivity through a p160-mediated mechanism

Resveratrol Improves Endothelial Function by A PREP1-Mediated Pathway in Mouse Aortic Endothelial Cells

PREP1 is a homeodomain transcription factor that impairs metabolism and is involved in age-related aortic thickening. In this study, we evaluated the role of PREP1 on endothelial function. Mouse Aortic Endothelial Cells (MAECs) transiently transfected with a Prep1 cDNA showed a 1.5- and 1.6-fold increase in eNOSThr495 and PKCα phosphorylation, respectively. Proinflammatory cytokines Tnf-α and Il-6 increased by 3.5 and 2.3-fold, respectively, in the presence of Prep1, while the antioxidant genes Sod2 and Atf4 were significantly reduced. Bisindolylmaleimide reverted the effects induced by PREP1, suggesting PKCα to be a mediator of PREP1 action. Interestingly, resveratrol, a phenolic micronutrient compound, reduced the PREP1 levels, eNOSThr495, PKCα phosphorylation, and proinflammatory cytokines and increased Sod2 and Atf4 mRNA levels. The experiments performed on the aorta of 18-month-old Prep1 hypomorphic heterozygous mice (Prep1i/+) expressing low levels of this protein showed a 54 and 60% decrease in PKCα and eNOSThr495 phosphorylation and a 45% reduction in Tnf-α levels, with no change in Il-6, compared to same-age WT mice. However, a significant decrease in Sod2 and Atf4 was observed in Prep1i/+ old mice, indicating the lack of age-induced antioxidant response. These results suggest that Prep1 deficiency partially improved the endothelial function in aged mice and suggested PREP1 as a novel target of resveratrol.

Interleukin 6 reduces vascular smooth muscle cell apoptosis via Prep1 and is associated with aging

Aging exacerbates neointimal formation by reducing apoptosis of vascular smooth muscle cells (VSMCs) and induces inflammation within vascular wall. Prep1 is a homeodomain transcription factor which stimulates the expression of proinflammatory cytokines in aortic endothelial cell models and plays a primary role in the regulation of apoptosis. In this study, we have investigated the role of Prep1 in aorta of Prep1 hypomorphic heterozygous mice (Prep1^i/+ ) and in VSMCs, and its correlation with aging. Histological analysis from Prep1^i/+ aortas revealed a 25% reduction in medial smooth muscle cell density compared to WT animals. This result paralleled higher apoptosis, caspase 3, caspase 9 and p53 levels in Prep1^i/+ mice and lower Bcl-xL. Prep1 overexpression in VSMCs decreased apoptosis by 25% and caspase 3 and caspase 9 expression by 40% and 37%. In parallel, Bcl-xL inhibition by BH3I-1 and p53 induction by etoposide reverted the antiapoptotic effect of Prep1. Experiments performed in aorta from 18 months old WT mice showed a significant increase in Prep1, p16^INK4 , p21^Waf1 and interleukin 6 (IL-6) compared to youngest animals. Similar results have been observed in H₂ O₂ -induced senescent VSMCs. Interestingly, the synthetic Prep1 inhibitory peptide Prep1 (54-72) reduced the antiapoptotic effects mediated by IL-6, particularly in senescent VSMCs. These results indicate that IL-6-Prep1 signaling reduces apoptosis, by modulating Bcl-xL and p53 both in murine aorta and in VSMCs. In addition, age-dependent increase in IL-6 and Prep1 in senescent VSMCs and in old mice may be involved in the aging-related vascular dysfunction.

Leptin and TGF-β1 Downregulate PREP1 Expression in Human Adipose-Derived Mesenchymal Stem Cells and Mature Adipocytes

Adipose tissue is widely recognized as an extremely active endocrine organ producing adipokines as leptin that bridge metabolism and the immune system. Pre-B-cell leukemia homeobox (Pbx)-regulating protein-1 (PREP1) is a ubiquitous homeodomain transcription factor involved in the adipogenic differentiation and insulin-sensitivity processes. Leptin, as pleiotropic adipokine, and TGF-β, known to be expressed by primary pre-adipocytes [adipose-derived stem cells (ASCs)] and mature differentiated adipocytes, modulate inflammatory responses. We aimed to assess for the first time if leptin and TGF-β interfere with PREP1 expression in both ASCs and mature differentiated adipocytes. Human ASCs were isolated from subcutaneous adipose liposuction and, after expansion, fully differentiated to mature adipocytes. In both ASCs and adipocytes, leptin and TGF-β1 significantly decreased the expression of PREP1, alone and following concurrent Toll-like receptor 4 (TLR4) activation. Moreover, in adipocytes, but not in ASCs, leptin increased TLR4 and IL-33 expression, whereas TGF-β1 enhanced TLR4 and IL-6 expression. Taken together, we provide evidence for a direct regulation of PREP1 by leptin and TGF-β1 in ASCs and mature adipocytes. The effects of leptin and TGF-β1 on immune receptors and cytokines, however, are limited to mature adipocytes, suggesting that modulating immune responses depends on the differentiation of ASCs. Further studies are needed to fully understand the regulation of PREP1 expression and its potential for the development of new therapeutic approaches in obesity-related diseases.

The Tumor Suppressor Roles of MYBBP1A, a Major Contributor to Metabolism Plasticity and Stemness

The MYB binding protein 1A (MYBBP1A, also known as p160) acts as a co-repressor of multiple transcription factors involved in many physiological processes. Therefore, MYBBP1A acts as a tumor suppressor in multiple aspects related to cell physiology, most of them very relevant for tumorigenesis. We explored the different roles of MYBBP1A in different aspects of cancer, such as mitosis, cellular senescence, epigenetic regulation, cell cycle, metabolism plasticity and stemness. We especially reviewed the relationships between MYBBP1A, the inhibitory role it plays by binding and inactivating c-MYB and its regulation of PGC-1α, leading to an increase in the stemness and the tumor stem cell population. In addition, MYBBP1A causes the activation of PGC-1α directly and indirectly through c-MYB, inducing the metabolic change from glycolysis to oxidative phosphorylation (OXPHOS). Therefore, the combination of these two effects caused by the decreased expression of MYBBP1A provides a selective advantage to tumor cells. Interestingly, this only occurs in cells lacking pVHL. Finally, the loss of MYBBP1A occurs in 8%–9% of renal tumors. tumors, and this subpopulation could be studied as a possible target of therapies using inhibitors of mitochondrial respiration.

Prep1 regulates angiogenesis through a PGC-1α-mediated mechanism

Angiogenesis depends on a delicate balance between the different transcription factors, and their control should be considered necessary for preventing or treating diseases. Pre-B-cell leukemia transcription factor regulating protein 1 (Prep1) is a homeodomain transcription factor that plays a primary role in organogenesis and metabolism. Observations performed in a Prep1 hypomorphic mouse model, expressing 3-5% of the protein, show an increase of embryonic lethality due, in part, to defects in angiogenesis. In this study, we provide evidence that overexpression of Prep1 in mouse aortic endothelial cells (MAECs) stimulates migration, proliferation, and tube formation. These effects are paralleled by an increase of several proangiogenic factors and by a decrease of the antiangiogenic gene neurogenic locus notch homolog protein 1 (Notch1). Prep1-mediated angiogenesis involves the activation of the p160 Myb-binding protein (p160)/peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) pathway. Indeed, Prep1 overexpression increases its binding with p160 and induces a 4-fold increase of p160 and 70% reduction of PGC-1α compared with control cells. Incubation of MAECs with a synthetic Prep1(54-72) peptide, mimicking the Prep1 region involved in the interaction with p160, reverts the proangiogenic effects mediated by Prep1. In addition, Prep1 levels increase by 3.2-fold during the fibroblast growth factor β (bFGF)-mediated endothelial colony-forming cells' activation, whereas Prep1(54-72) peptide reduces the capability of these cells to generate tubular-like structures in response to bFGF, suggesting a possible role of Prep1 both in angiogenesis from preexisting vessels and in postnatal vasculogenesis. Finally, Prep1 hypomorphic heterozygous mice, expressing low levels of Prep1, show attenuated placental angiogenesis and vessel formation within Matrigel plugs. All of these observations indicate that Prep1, complexing with p160, decreases PGC-1α and stimulates angiogenesis.-Cimmino, I., Margheri, F., Prisco, F., Perruolo, G., D'Esposito, V., Laurenzana, A., Fibbi, G., Paciello, O., Doti, N., Ruvo, M., Miele, C., Beguinot, F., Formisano, P., Oriente, F. Prep1 regulates angiogenesis through a PGC-1α-mediated mechanism.

The Role of Prep1 in the Regulation of Mesenchymal Stromal Cells

Molecular mechanisms governing cell fate decision events in bone marrow mesenchymal stromal cells (MSC) are still poorly understood. Herein, we investigated the homeobox gene Prep1 as a candidate regulatory molecule, by adopting Prep1 hypomorphic mice as a model to investigate the effects of Prep1 downregulation, using in vitro and in vivo assays, including the innovative single cell RNA sequencing technology. Taken together, our findings indicate that low levels of Prep1 are associated to enhanced adipogenesis and a concomitant reduced osteogenesis in the bone marrow, suggesting Prep1 as a potential regulator of the adipo-osteogenic differentiation of mesenchymal stromal cells. Furthermore, our data suggest that in vivo decreased Prep1 gene dosage favors a pro-adipogenic phenotype and induces a "browning" effect in all fat tissues.

c-MYB- and PGC1a-dependent metabolic switch induced by MYBBP1A loss in renal cancer

The tumor microenvironment may alter the original tumorigenic potential of tumor cells. Under harsh environmental conditions, genetic alterations conferring selective advantages may initiate the growth of tumor subclones, providing new opportunities for these tumors to grow. We performed a genetic loss-of-function screen to identify genetic alterations able to promote tumor cell growth in the absence of glucose. We identified that downregulation of MYBBP1A increases tumorigenic properties under nonpermissive conditions. MYBBP1A downregulation simultaneously activates PGC1α, directly by alleviating direct repression and indirectly by increasing PGC1α mRNA levels through c-MYB, leading to a metabolic switch from glycolysis to OXPHOS and increased tumorigenesis in low-glucose microenvironments. We have also identified reduced MYBBP1A expression in human renal tumor samples, which show high expression levels of genes involved in oxidative metabolism. In summary, our data support the role of MYBBP1A as a tumor suppressor by regulating c-MYB and PGC1α. Therefore, loss of MYBBP1A increases adaptability spanning of tumors through metabolic switch.

Targeting Mybbp1a suppresses HCC progression via inhibiting IGF1/AKT pathway by CpG islands hypo-methylation dependent promotion of IGFBP5

BACKGROUND

Myb-binding protein 1A (Mybbp1a) is a nucleolar protein that can regulate rRNA metabolism, the stress response and carcinogenesis. However, the function of Mybbp1a in the progression of hepatocellular carcinoma (HCC) is unclear. We aimed to determine the role of Mybbp1a in HCC and the underlying mechanism.

METHODS

We investigated the function of Mybbp1a in HCC cell models and the xenograft mouse model. The relationship between Mybbp1a and IGFBP5 was found through expression profile chip. The molecular mechanism of Mybbp1a regulating IGFBP5 was proved through CO-IP, CHIP, Bisulfite Sequencing and Pyrosequencing.

FINDINGS

In this study, we observed that Mybbp1a was overexpressed in HCC tissues and associated with the poor prognosis of HCC patients. Suppression of Mybbp1a led to a reduction in the proliferation and migration ability of HCC cells through inhibiting the IGF1/AKT signaling pathway. Further study found that Mybbp1a could form a complex with DNMT1 and induce aberrant hyper-methylation of CpG islands of IGFBP5, which inhibits secretion of IGFBP5 and then activates IGF1/AKT signaling pathway.

INTERPRETATION

These findings extend our understanding of the function of Mybbp1a in the progression of HCC. The newly identified Mybbp1a may provide a novel biomarker for developing potential therapeutic targets of HCC. FUND: Science Technology Department of Zhejiang Province (No. 2015C03034), National Health and Family Planning Commission of China (No. 2016138643), Innovative Research Groups of National Natural Science Foundation of China (No. 81721091), Major program of National Natural Science Foundation of China (No. 91542205).

Sphingolipid Metabolism: New Insight into Ceramide-Induced Lipotoxicity in Muscle Cells

Insulin-resistance is a characteristic feature of type 2 diabetes (T2D) and plays a major role in the pathogenesis of this disease. Skeletal muscles are quantitatively the biggest glucose users in response to insulin and are considered as main targets in development of insulin-resistance. It is now clear that circulating fatty acids (FA), which are highly increased in T2D, play a major role in the development of muscle insulin-resistance. In healthy individuals, excess FA are stored as lipid droplets in adipocytes. In situations like obesity and T2D, FA from lipolysis and food are in excess and eventually accumulate in peripheral tissues. High plasma concentrations of FA are generally associated with increased risk of developing diabetes. Indeed, ectopic fat accumulation is associated with insulin-resistance; this is called lipotoxicity. However, FA themselves are not involved in insulin-resistance, but rather some of their metabolic derivatives, such as ceramides. Ceramides, which are synthetized de novo from saturated FA like palmitate, have been demonstrated to play a critical role in the deterioration of insulin sensitivity in muscle cells. This review describes the latest progress involving ceramides as major players in the development of muscle insulin-resistance through the targeting of selective actors of the insulin signaling pathway.

Type 2 diabetes and metabolic syndrome: identification of the molecular mechanisms, key signaling pathways and transcription factors aimed to reveal new therapeutical targets

Type 2 diabetes mellitus (T2DM) is a socially important disease with only symptomatic therapy developed due to lack of knowledge about its pathogenesis and underlying mechanism. Insulin resistance (IR) is the first link of T2DM pathogenesis and results in decrease of ability of insulin to stimulate glucose uptake by target cells. Development of IR involves genetic predisposition, excessive nutrition, stress, obesity or chronic inflammation due to disruption of insulin signaling within cells. Molecular mechanisms and markers of IR are characterized rather poorly, which prevents early diagnosis and creation of preventive therapy. Euglycemic clamp test is still a golden standard for IR diagnosis in clinic. Hyperglycemia is a distant consequence of IR in which damaging effect of oxidative and carbonyl stress is realized and diagnosis of T2DM is stipulated. Molecular chaperones and small heat-shock proteins have a protective effect at the early stages of T2DM pathogenesis, preventing development of reticulum stress and apoptosis. Endothelial dysfunction is related to T2DM and its cardiovascular complications, however, it is unknown on which stage of pathogenesis these changes occur and what are their molecular inductors. Finally, transcriptional activity and adipogenic differentiation play an important role in formation of new fat depots from predecessor cells and activation of brown and beige fat demonstrating hypolipidemic and hypoglycemic properties. The aim of this study was investigation of pathophysiological mechanisms of development of IR and endothelial dysfunction, role of transcription factor Prep1 and small heat shock proteins, evaluation of novel methods of diagnostics of IR and therapeutic potential of brown and beige fat, determination of biotargets for new antidiabetic drugs.

MiR-17 family-mediated regulation of Pknox1 influences hepatic steatosis and insulin signaling

The aberrant expression of Pknox1 is associated with hepatic glucose and lipid dysmetabolism status of type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). However, the underlying mechanism causing Pknox1 overexpression in this pathological status remains unclear. By using miRNA target prediction programs, we found that the 3′‐UTR of the Pknox1 mRNA sequence contains highly conserved target sites of miR‐17 family. In a rat model of streptozotocin and high‐fat diet‐induced T2DM and NAFLD complication, the increased hepatic expression of Pknox1 was consistent with decreased expressions of miR‐17 family, especially miR‐17 and miR‐20a. Furthermore, an inverse correlation was observed between Pknox1 and miR‐17 and miR‐20a in free fatty acids‐induced hepatocyte steatosis. Dual‐luciferase reporter assay further showed that Pknox1 was a valid target gene of miR‐17 family. The ectopic expression of miR‐17 or miR‐20a could markedly suppress Pknox1 expression in hepatocytes. MiR‐17 or miR‐20a overexpression also resulted in significantly enhanced insulin sensitivity and reduced hepatocyte steatosis in HepG2 and L02 cells, which were determined by altered phosphorylation on insulin receptor signaling pathway proteins and decreased intracellular triglyceride and lipid accumulation, respectively. These data implicate the upregulated hepatic expression of Pknox1 in T2DM complicated with NAFLD may be caused by the reduced expression of miR‐17 family, indicating that developing miRNA‐mediated regulation strategies on Pknox1 may provide new therapeutic options for metabolic disease.

Prep1 deficiency improves metabolic response in white adipose tissue

Prep1 is a gene encoding for a homeodomain transcription factor which induces hepatic and muscular insulin resistance. In this study, we show that Prep1 hypomorphic heterozygous (Prep1^i/+) mice, expressing low levels of protein, featured a 23% and a 25% reduction of total body lipid content and epididymal fat, respectively. The percentage of the small adipocytes (25-75 μm) was 30% higher in Prep1^i/+ animals than in the WT, with a reciprocal difference in the large adipose cells (100-150 and >150 μm). Insulin-stimulated insulin receptor tyrosine and Akt serine phosphorylation markedly increased in Prep1^i/+ mice, paralleled by 3-fold higher glucose uptake and a significant increase of proadipogenic genes such as C/EBPα, GLUT4, and FABP4. Moreover, T cells infiltration and TNF-α, IFNγ and leptin expression were reduced in adipose tissue from Prep1^i/+ mice, while adiponectin levels were 2-fold higher. Furthermore, Prep1^i/+ mature adipocytes released lower amounts of pro-inflammatory cytokines and higher amount of adiponectin compared to WT cells. Incubation of murine liver cell line (NMuLi) with conditioned media (CM) from mature adipocytes of Prep1^i/+ mice improved glucose metabolism, while those from WT mice had no effect. Consistent with these data, Prep1 overexpression in 3T3-L1 adipocytes impaired adipogenesis and insulin signaling, and increased proinflammatory cytokine secretion. All these findings suggest that Prep1 silencing reduces inflammatory response and increases insulin sensitivity in adipose tissue. In addition, CM from mature adipocytes of Prep1^i/+ mice improve metabolism in hepatic cells.

Prep1 Deficiency Affects Olfactory Perception and Feeding Behavior by Impairing BDNF-TrkB Mediated Neurotrophic Signaling

Prep1 is a homeodomain transcription factor which has an important role in hindbrain development. Prep1 expression is also kept in adult mouse brain and in particular within the olfactory bulbs. Moreover, many Prep1 neurons co-localize with Calbindin-positive periglomerular interneurons in olfactory glomerular layer. However, Prep1 function in this brain region is still unknown. In this study, we show that Prep1 hypomorphic heterozygous (Prep1^i/+) mice express low levels of protein and feature a 30% reduction of olfactory bulb area, compared to WT mice. In addition, Prep1^i/+ mice olfactory bulb histological analysis indicated a 20% lower cytochrome C oxidase activity within the glomerular layer, accompanied by a reduced number of periglomerular interneurons, compared to the WT littermates. Consistently, olfactory perception test highlighted that Prep1 hypomorphic heterozygous mice display a scant ability to distinguish odors, which significantly impacts on feeding behavior, as Prep1^i/+ mice revealed a reduced preference for high-fat food. Analysis of BDNF signaling, which represents the main molecular mediator of olfactory plasticity, showed that Prep1^i/+ mouse olfactory bulbs feature a 30% reduction of TrkB receptor levels and a decreased activation of ERK1/2. Similarly, overexpression of Prep1 in mouse neuronal cells (N2A) caused an increase of TrkB expression levels, BDNF-induced ERK phosphorylation, and cell viability, compared to control cells. We conclude that Prep1 deficiency alters olfactory morpho-functional integrity and olfaction-mediated eating behavior by affecting BDNF-TrkB signaling. Prep1 could, therefore, play a crucial role in behavioral dysfunctions associated to impaired responsiveness to BDNF.

Prep1, A Homeodomain Transcription Factor Involved in Glucose and Lipid Metabolism

The three-amino acid loop extension (TALE) homeodomain proteins are a family of transcription factor including the mammalian Pbx, MEIS and Prep proteins. TALE proteins can bind other transcription factors such as Pdx-1 and play an important role in the regulation of glucose metabolism. Experiments performed in mutant mice have shown that while the single Pbx1 or Pdx-1 knockout mice feature pancreatic islet malformations, impaired glucose tolerance and hypoinsulinemia, the trans-heterozygous Pbx1^+/-Pdx1^+/- mice develop age-dependent overt diabetes mellitus. In contrast, Prep1 plays a different role with respect to these proteins. Indeed, Prep1 hypomorphic mice, expressing low levels of protein, feature pancreatic islet hypoplasia accompanied by hypoinsulinemia similar to Pbx1 or Pdx1. Nevertheless, these animals show increased insulin sensitivity in skeletal muscle, liver and adipose tissue accompanied by protection from streptozotocin-induced diabetes. In addition, Prep1 hypomorphic mice feature reduced triglyceride synthesis and do not develop steatohepatitis after a methionine and coline deficient diet. In this review we have underlined how important metabolic functions are controlled by TALE proteins, in particular by Prep1, leading to hypothesis that its suppression might represent beneficial effect in the care of metabolic diseases.

A peptide antagonist of Prep1-p160 interaction improves ceramide-induced insulin resistance in skeletal muscle cells

Prep1 is a homeodomain transcription factor belonging to the TALE protein family. Its overexpression affects glucose metabolism in several tissues. In particular, in skeletal muscle tissue the interaction of Prep1 with its cofactor p160 impairs GLUT4 expression and glucose uptake. In this study, we show that ceramides (C2cer), a class of lipids antagonizing insulin signalling, increase the levels of Prep1 and p160 in a dose and time-dependent fashion in L6 cells and induce their association by 80%. We find that C2cer exposure inhibits insulin receptor, IRS1 and Akt phosphorylation and reduces insulin-stimulated glycogen content and glucose uptake by 1.3- and 2.1-fold, respectively. The synthetic Prep1(54-72) peptide, mimicking the Prep1 region involved in the interaction with p160, reduces in vitro Prep1-p160 binding in a dose-dependent way (IC₅₀ = 0.20μM). In C2cer-treated L6 cells, 10μM Prep1(54-72) restores insulin signalling impaired by ceramide treatment. Prep1 overexpressing L6 cells display similar metabolic alterations observed in ceramide-treated L6 cells and the presence of Prep1(54-72) mitigates these events. All these findings suggest that disruption of the Prep1/p160 molecular interaction enhances insulin sensitivity impaired by ceramides in skeletal muscle cells and indicate this complex as an important target for type 2 diabetes.

The transcription factor Prep1 controls hepatic insulin sensitivity and gluconeogenesis by targeting nuclear localization of FOXO1

Liver plays a key role in controlling body carbohydrate homeostasis by switching between accumulation and production of glucose and this way maintaining constant level of glucose in blood. Increased blood glucose level triggers release of insulin from pancreatic β-cells. Insulin represses hepatic glucose production and increases glucose accumulation. Insulin resistance is the main cause of type 2 diabetes and hyperglycemia. Currently thiazolidinediones (TZDs) targeting transcriptional factor PPARγ are used as insulin sensitizers for treating patients with type 2 diabetes. However, TZDs are reported to be associated with cardiovascular and liver problems and stimulate obesity. Thus, it is necessary to search new approaches to improve insulin sensitivity. A promising candidate is transcriptional factor Prep1, as it was shown earlier it could affect insulin sensitivity in variety of insulin-sensitive tissues. The aim of the present study was to evaluate a possible involvement of transcriptional factor Prep1 in control of hepatic glucose accumulation and production. We created mice with liver-specific Prep1 knockout and discovered that hepatocytes derived from these mice are much more sensitive to insulin, comparing to their WT littermates. Incubation of these cells with 100 nM insulin results in almost complete inhibition of gluconeogenesis, while in WT cells this repression is only partial. However, Prep1 doesn't affect gluconeogenesis in the absence of insulin. Also, we observed that nuclear content of gluconeogenic transcription factor FOXO1 was greatly reduced in Prep1 knockout hepatocytes. These findings suggest that Prep1 may control hepatic insulin sensitivity by targeting FOXO1 nuclear stability.

Myotubes derived from human-induced pluripotent stem cells mirror in vivo insulin resistance

Induced pluripotent stem cells (iPS cells) represent a unique tool for the study of the pathophysiology of human disease, because these cells can be differentiated into multiple cell types in vitro and used to generate patient- and tissue-specific disease models. Given the critical role for skeletal muscle insulin resistance in whole-body glucose metabolism and type 2 diabetes, we have created a novel cellular model of human muscle insulin resistance by differentiating iPS cells from individuals with mutations in the insulin receptor (IR-Mut) into functional myotubes and characterizing their response to insulin in comparison with controls. Morphologically, IR-Mut cells differentiated normally, but had delayed expression of some muscle differentiation-related genes. Most importantly, whereas control iPS-derived myotubes exhibited in vitro responses similar to primary differentiated human myoblasts, IR-Mut myotubes demonstrated severe impairment in insulin signaling and insulin-stimulated 2-deoxyglucose uptake and glycogen synthesis. Transcriptional regulation was also perturbed in IR-Mut myotubes with reduced insulin-stimulated expression of metabolic and early growth response genes. Thus, iPS-derived myotubes from individuals with genetically determined insulin resistance demonstrate many of the defects observed in vivo in insulin-resistant skeletal muscle and provide a new model to analyze the molecular impact of muscle insulin resistance.

Glucose-induced expression of the homeotic transcription factor Prep1 is associated with histone post-translational modifications in skeletal muscle

AIMS/HYPOTHESIS

Chronic hyperglycaemia worsens insulin resistance in individuals with type 2 diabetes. Whether this effect is contributed by epigenetic dysregulation and which genes are involved remain unclear. Prep1 (also known as Pknox1) is a gene exerting major effects on the sensitivity of the glucose transport machinery to insulin. Here, we show that dysregulation of Prep1 expression by high glucose levels is associated with histone modifications at its 5' regulatory region.

METHODS

We used mouse and cell models to investigate Prep1 transcriptional regulation by glucose.

RESULTS

Differentiated L6 skeletal muscle cells were grown in the presence of either 5.5 or 25 mmol/l glucose (normal [NG] and high glucose [HG], respectively). The HG exposure increased nuclear factor κ light chain enhancer of activated B cells (NF-κB) p65 binding and recruitment of the su(var)3-9, enhancer-of-zeste, trithorax domain-containing lysine methyltransferase 7 (SET7) histone methyltransferase and p300 acetyltransferase to the 5' region of Prep1, leading to enhanced transcription. In addition, chromatin immunoprecipitation assays revealed concomitantly increased histone H3 mono- and dimethylation and acetylation at Lys4 and Lys9/14, respectively. Skeletal muscle tissue from streptozotocin-treated diabetic mice also showed Prep1 overexpression accompanied by similarly increased recruitment of NF-κB p65 and histone modifications at the 5' region of Prep1. In these same mice, as well as in Prep1-overexpressing L6 cells, Prep1-induced recruitment of the repressor complex myocyte enhancer factor 2 (MEF2)/histone deacetylase 5 (HDAC5) at the Glut4 promoter was also increased, leading to reduced Glut4 expression.

CONCLUSIONS/INTERPRETATION

These studies indicate that HG exposure induces NF-κB recruitment and histone modification at the Prep1 5' region, thereby enhancing the transcription of Prep1 and repressing that of Glut4. Histone changes at the Prep1 gene may contribute to insulin resistance in individuals with type 2 diabetes.

Understanding type 2 diabetes: from genetics to epigenetics

The known genetic variability (common DNA polymorphisms) does not account either for the current epidemics of type 2 diabetes or for the family transmission of this disorder. However, clinical, epidemiological and, more recently, experimental evidence indicates that environmental factors have an extraordinary impact on the natural history of type 2 diabetes. Some of these environmental hits are often shared in family groups and proved to be capable to induce epigenetic changes which alter the function of genes affecting major diabetes traits. Thus, epigenetic mechanisms may explain the environmental origin as well as the familial aggregation of type 2 diabetes much easier than common polymorphisms. In the murine model, exposure of parents to environmental hits known to cause epigenetic changes reprograms insulin sensitivity as well as beta-cell function in the progeny, indicating that certain epigenetic changes can be transgenerationally transmitted. Studies from different laboratories revealed that, in humans, lifestyle intervention modulates the epigenome and reverts environmentally induced epigenetic modifications at specific target genes. Finally, specific human epigenotypes have been identified which predict adiposity and type 2 diabetes with much greater power than any polymorphism so far identified. These epigenotypes can be recognized in easily accessible white cells from peripheral blood, indicating that, in the future, epigenetic profiling may enable effective type 2 diabetes prediction. This review discusses recent evidence from the literature supporting the immediate need for further investigation to uncover the power of epigenetics in the prediction, prevention and treatment of type 2 diabetes.

ChIP-Seq and RNA-Seq analyses identify components of the Wnt and Fgf signaling pathways as Prep1 target genes in mouse embryonic stem cells

The Prep1 (Pknox1) homeodomain transcription factor is essential at multiple stages of embryo development. In the E11.5 embryo trunk, we previously estimated that Prep1 binds about 3,300 genomic sites at a highly specific decameric consensus sequence, mainly governing basal cellular functions. We now show that in embryonic stem (ES) cells Prep1 binding pattern only partly overlaps that of the embryo trunk, with about 2,000 novel sites. Moreover, in ES cells Prep1 still binds mostly to promoters, as in total embryo trunk but, among the peaks bound exclusively in ES cells, the percentage of enhancers was three-fold higher. RNA-seq identifies about 1800 genes down-regulated in Prep1-/- ES cells which belong to gene ontology categories not enriched in the E11.5 Prep1i/i differentiated embryo, including in particular essential components of the Wnt and Fgf pathways. These data agree with aberrant Wnt and Fgf expression levels in the Prep1-/- ES cells with a deficient embryoid bodies (EBs) formation and differentiation. Re-establishment of the Prep1 level rescues the phenotype.

Personalized medicine and type 2 diabetes: lesson from epigenetics

Similarly to genetic polymorphisms, epigenetic modifications may alter transcriptional activity and contribute to different traits of the Type 2 diabetes phenotype. The establishment of these epigenetic marks may precede diabetes onset and predict the disease. Current evidence now indicates that epigenetic differences represent markers of diabetes risk. Studies on epigenome plasticity revealed that cytokines and other metabolites, by affecting DNA methylation, may acutely reprogram gene expression and contribute to the Type 2 diabetes phenotype even in the adult life. The available evidence further indicates that epigenetic marks across the genome are subject to dynamic variations in response to environmental cues. Finally, different genes responsible for the interindividual variability in antidiabetic drug response are subjected to epigenetic regulation. Determining how specific epigenetic profiles determine diabetes is a challenging task. In the near future, the identification of epigenetic marks predictive of diabetes risk or response to treatment may offer unanticipated opportunities to personalize Type 2 diabetes management.

Transcription factor PREP1 induces EMT and metastasis by controlling the TGF-β-SMAD3 pathway in non-small cell lung adenocarcinoma

Pre-B-cell leukemia homeobox (Pbx)-regulating protein-1 (Prep1) is a ubiquitous homeoprotein involved in early development, genomic stability, insulin sensitivity, and hematopoiesis. Previously we have shown that Prep1 is a haploinsufficient tumor suppressor that inhibits neoplastic transformation by competing with myeloid ecotropic integration site 1 for binding to the common heterodimeric partner Pbx1. Epithelial-mesenchymal transition (EMT) is controlled by complex networks of proinvasive transcription factors responsive to paracrine factors such as TGF-β. Here we show that, in addition to inhibiting primary tumor growth, PREP1 is a novel EMT inducer and prometastatic transcription factor. In human non-small cell lung cancer (NSCLC) cells, PREP1 overexpression is sufficient to trigger EMT, whereas PREP1 down-regulation inhibits the induction of EMT in response to TGF-β. PREP1 modulates the cellular sensitivity to TGF-β by inducing the small mothers against decapentaplegic homolog 3 (SMAD3) nuclear translocation through mechanisms dependent, at least in part, on PREP1-mediated transactivation of a regulatory element in the SMAD3 first intron. Along with the stabilization and accumulation of PBX1, PREP1 induces the expression of multiple activator protein 1 components including the proinvasive Fos-related antigen 1 (FRA-1) oncoprotein. Both FRA-1 and PBX1 are required for the mesenchymal changes triggered by PREP1 in lung tumor cells. Finally, we show that the PREP1-induced mesenchymal transformation correlates with significantly increased lung colonization by cells overexpressing PREP1. Accordingly, we have detected PREP1 accumulation in a large number of human brain metastases of various solid tumors, including NSCLC. These findings point to a novel role of the PREP1 homeoprotein in the control of the TGF-β pathway, EMT, and metastasis in NSCLC.

Biochemistry of the tale transcription factors PREP, MEIS, and PBX in vertebrates

TALE (three amino acids loop extension) homeodomain transcription factors are required in various steps of embryo development, in many adult physiological functions, and are involved in important pathologies. This review focuses on the PREP, MEIS, and PBX sub-families of TALE factors and aims at giving information on their biochemical properties, i.e., structure, interactors, and interaction surfaces. Members of the three sets of protein form dimers in which the common partner is PBX but they can also directly interact with other proteins forming higher-order complexes, in particular HOX. Finally, recent advances in determining the genome-wide DNA-binding sites of PREP1, MEIS1, and PBX1, and their partial correspondence with the binding sites of some HOX proteins, are reviewed. These studies have generated a few general rules that can be applied to all members of the three gene families. PREP and MEIS recognize slightly different consensus sequences: PREP prefers to bind to promoters and to have PBX as a DNA-binding partner; MEIS prefers HOX as partner, and both PREP and MEIS drive PBX to their own binding sites. This outlines the clear individuality of the PREP and MEIS proteins, the former mostly devoted to basic cellular functions, the latter more to developmental functions.

PREP1 deficiency downregulates hepatic lipogenesis and attenuates steatohepatitis in mice

AIMS/HYPOTHESIS

The aim of this study was to investigate the function of Prep1 (also known as Pknox1) in hepatic lipogenesis.

METHODS

The hepatic lipogenesis pathway was evaluated by real-time RT-PCR and Western blot. Biochemical variables were assessed using a clinical chemistry analyser.

RESULTS

Serum triacylglycerols and liver expression of fatty acid synthase (FAS) were significantly decreased in Prep1 hypomorphic heterozygous (Prep1 (i/+) ) mice compared with their non-hypomorphic littermates. Upstream FAS expression, phosphorylation of protein kinase C (PKC)ζ, liver kinase B1 (LKB1), AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) increased in Prep1 (i/+) mice, while protein and mRNA levels of the lipid phosphatase inhibitor of PKCζ, SH2-containing inositol 5'-phosphatase 2 (SHIP2), was more than 60% reduced. Consistent with these findings, HepG2 cells transfected with Prep1 cDNA exhibited increased triacylglycerol accumulation and FAS expression, with strongly reduced PKCζ, LKB1, AMPK and ACC phosphorylation. Further experiments revealed the presence of both Prep1 and its major partner Pbx1 at the Ship2 (also known as Inppl1) promoter. PBX-regulating protein 1 (PREP1) and pre-B cell leukaemia transcription factor 1 (PBX1) enhanced Ship2 transcription. The PREP1HR mutant, which is unable to bind PBX1, exhibited no effect on Ship2 function, indicating transcriptional activation of Ship2 by the PREP1/PBX1 complex. Treatment with a methionine- and choline-deficient diet (MCDD) induced steatosis in both Prep1 (i/+) and non-hypomorphic control mice. However, alanine aminotransferase increase, intracellular triacylglycerol content and histological evidence of liver steatosis, inflammation and necrosis were significantly less evident in Prep1 (i/+) mice, indicating that Prep1 silencing protects mice from MCDD-induced steatohepatitis.

CONCLUSIONS/INTERPRETATION

Our results indicate that Prep1 silencing reduces lipotoxicity by increasing PKCζ/LKB1/AMPK/ACC signalling, while levels of PREP1 expression may determine the risk of steatohepatitis and its progression.

Pknox1/Prep1 regulates mitochondrial oxidative phosphorylation components in skeletal muscle

The homeodomain transcription factor Prep1 was previously shown to regulate insulin sensitivity. Our aim was to study the specific role of Prep1 for the regulation of energy metabolism in skeletal muscle. Muscle-specific ablation of Prep1 resulted in increased expression of respiratory chain subunits. This finding was consistent with an increase in mitochondrial enzyme activity without affecting mitochondrial volume fraction as assessed by electron microscopy. Metabolic phenotyping revealed no differences in daily energy expenditure or body composition. However, during treadmill exercise challenge, Prep1 ablation resulted in a higher maximal oxidative capacity and better endurance. Elevated PGC-1α expression was identified as a cause for increased mitochondrial capacity in Prep1 ablated mice. Prep1 stabilizes p160 Mybbp1a, a known inhibitor of PGC-1α activity. Thereby, p160 protein levels were significantly lower in the muscle of Prep1 ablated mice. By a chromatin immunoprecipitation-sequencing (ChIP-seq) approach, PREP1 binding sites in genes encoding mitochondrial components (e.g., Ndufs2) were identified that might be responsible for elevated proteins involved in oxidative phosphorylation (OXPHOS) in the muscle of Prep1 null mutants. These results suggest that Prep1 exhibits additional direct effects on regulation of mitochondrial proteins. We therefore conclude that Prep1 is a regulator of oxidative phosphorylation components via direct and indirect mechanisms.

Insulin resistance and adipogenesis: role of transcription and secreted factors

Insulin stimulates carbohydrate uptake by cells and induces their conversion into lipids as a more efficient form of energy storage. Insulin resistance is associated with a decrease in glucose uptake by muscle and adipose cells and also with a decrease in glycogen synthesis on retention of glucose synthesis by liver cells. Disorders in the insulin signaling cascade on development of insulin resistance can be caused by both changes in functioning of transcriptional factors and in the secretion profile of hormone-like substances. Diacylglycerols and ceramides responsible for activation of some kinases and phosphatases can directly trigger these changes in muscle and liver cells. In adipose tissue, insulin mainly stimulates adipogenesis (adipocyte differentiation) and lipogenesis (lipid accumulation in the cells). Thus, studies on the action mechanisms of factors influencing adipogenesis can be of help for understanding the molecular mechanisms of insulin resistance.

Myb-binding protein 1A (MYBBP1A) is essential for early embryonic development, controls cell cycle and mitosis, and acts as a tumor suppressor

MYBBP1A is a predominantly nucleolar transcriptional regulator involved in rDNA synthesis and p53 activation via acetylation. However little further information is available as to its function. Here we report that MYBBP1A is developmentally essential in the mouse prior to blastocyst formation. In cell culture, down-regulation of MYBBP1A decreases the growth rate of wild type mouse embryonic stem cells, mouse embryo fibroblasts (MEFs) and of human HeLa cells, where it also promotes apoptosis. HeLa cells either arrest at G2/M or undergo delayed and anomalous mitosis. At mitosis, MYBBP1A is localized to a parachromosomal region and gene-expression profiling shows that its down-regulation affects genes controlling chromosomal segregation and cell cycle. However, MYBBP1A down-regulation increases the growth rate of the immortalized NIH3T3 cells. Such Mybbp1a down-regulated NIH3T3 cells are more susceptible to Ras-induced transformation and cause more potent Ras-driven tumors. We conclude that MYBBP1A is an essential gene with novel roles at the pre-mitotic level and potential tumor suppressor activity.

Epigeneitc silencing of ribosomal RNA genes by Mybbp1a

BACKGROUND

Transcription of the ribosomal RNA gene repeats by Pol I occurs in the nucleolus and is a fundamental step in ribosome biogenesis and protein translation. Due to tight coordination between ribosome biogenesis and cell proliferation, transcription of rRNA and stable maintenance of rDNA clusters are thought to be under intricate control by intercalated mechanisms, particularly at the epigenetic level.

METHODS AND RESULTS

Here we identify the nucleolar protein Myb-binding protein 1a (Mybbp1a) as a novel negative regulator of rRNA expression. Suppression of rDNA transcription by Mybbp1a was linked to promoter regulation as illustrated by its binding to the chromatin around the hypermethylated, inactive rDNA gene promoters. Our data further showed that downregulation of Mybbp1a abrogated the local DNA methylation levels and histone marks associated with gene silencing, and altered the promoter occupancy of various factors such UBF and HDACs, consequently leading to elevated rRNA expression. Mechanistically, we propose that Mybbp1a maintains rDNA repeats in a silenced state while in association with the negative epigenetic modifiers HDAC1/2.

CONCLUSIONS

Results from our present work reveal a previously unrecognized co-repressor role of Mybbp1a in rRNA expression. They are further consistent with the scenario that Mybbp1a is an integral constituent of the rDNA epigenetic regulation that underlies the balanced state of rDNA clusters.

Epigenetic silencing of myogenic gene program by Myb-binding protein 1a suppresses myogenesis

Skeletal myogenesis involves highly coordinated steps that integrate developmental cues at the chromatin of muscle progenitors. Here, we identify Myb-binding protein 1a (Mybbp1a) as a novel negative regulator of muscle-specific gene expression and myoblast differentiation. The mode of action of Mybbp1a was linked to promoter regulation as illustrated by its interaction with MyoD at the genomic regions of silent muscle-specific genes as well as its negative effect on MyoD-mediated transcriptional activity. We propose that Mybbp1a exerts its repressive role by inducing a less permissible chromatin structure following recruitment of negative epigenetic modifiers such as HDAC1/2 and Suv39h1. At the onset of differentiation, Mybbp1a undergoes a promoter disengagement that may be due to the differentiation-responsive, miR-546-mediated downregulation of Mybbp1a expression. Moreover, such alteration gave rise to promoter enrichment of activators and histone acetylation, an epigenetic status amenable to gene activation. Together, these findings unveil a hitherto unrecognized transcriptional co-repressor role of Mybbp1a in proliferating muscle progenitor cells, and highlight an epigenetic mechanism by which Mybbp1a and miR-546 interplay to control myoblast differentiation transition.

Methylglyoxal impairs insulin signalling and insulin action on glucose-induced insulin secretion in the pancreatic beta cell line INS-1E

AIMS/HYPOTHESIS

Chronic hyperglycaemia aggravates insulin resistance, at least in part, by increasing the formation of advanced glycation end-products (AGEs). Methylglyoxal (MGO) is the most reactive AGE precursor and its abnormal accumulation participates in damage in various tissues and organs. Here we investigated the ability of MGO to interfere with insulin signalling and to affect beta cell functions in the INS-1E beta cell line.

METHODS

INS-1E cells were incubated with MGO and then exposed to insulin or to glucose. Western blotting was used to study signalling pathways, and real-time PCR to analyse gene expression; insulin levels were determined by radioimmunoassay.

RESULTS

Non-cytotoxic MGO concentrations inhibited insulin-induced IRS tyrosine phosphorylation and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) pathway activation independently from reactive oxygen species (ROS) production. Concomitantly, formation of AGE adducts on immunoprecipitated IRS was observed. Aminoguanidine reversed MGO inhibitory effects and the formation of AGE adducts on IRS. Further, the insulin- and glucose-induced expression of Ins1, Gck and Pdx1 mRNA was abolished by MGO. Finally, MGO blocked glucose-induced insulin secretion and PI3K/PKB pathway activation. These MGO effects were abolished by LiCl, which inhibits glycogen synthase kinase-3 (GSK-3).

CONCLUSIONS/INTERPRETATION

MGO exerted major damaging effects on INS-1E cells impairing both insulin action and secretion. An important actor in these noxious MGO effects appears to be GSK-3. In conclusion, MGO participates not only in the pathogenesis of the debilitating complications of type 2 diabetes, but also in worsening of the diabetic state by favouring beta cell failure.

Prep1 controls insulin glucoregulatory function in liver by transcriptional targeting of SHP1 tyrosine phosphatase

OBJECTIVE

We investigated the function of the Prep1 gene in insulin-dependent glucose homeostasis in liver.

RESEARCH DESIGN AND METHODS

Prep1 action on insulin glucoregulatory function has been analyzed in liver of Prep1-hypomorphic mice (Prep1(i/i)), which express 2-3% of Prep1 mRNA.

RESULTS

Based on euglycemic hyperinsulinemic clamp studies and measurement of glycogen content, livers from Prep1(i/i) mice feature increased sensitivity to insulin. Tyrosine phosphorylation of both insulin receptor (IR) and insulin receptor substrate (IRS)1/2 was significantly enhanced in Prep1(i/i) livers accompanied by a specific downregulation of the SYP and SHP1 tyrosine phosphatases. Prep1 overexpression in HepG2 liver cells upregulated SYP and SHP1 and inhibited insulin-induced IR and IRS1/2 phosphorylation and was accompanied by reduced glycogen content. Consistently, overexpression of the Prep1 partner Pbx1, but not of p160MBP, mimicked Prep1 effects on tyrosine phosphorylations, glycogen content, and on SYP and SHP1 expression. In Prep1 overexpressing cells, antisense silencing of SHP1, but not that of SYP, rescued insulin-dependent IR phosphorylation and glycogen accumulation. Both Prep1 and Pbx1 bind SHP1 promoter at a site located between nucleotides -2,113 and -1,778. This fragment features enhancer activity and induces luciferase function by 7-, 6-, and 30-fold, respectively, in response to Prep1, Pbx1, or both.

CONCLUSIONS

SHP1, a known silencer of insulin signal, is a transcriptional target of Prep1. In liver, transcriptional activation of SHP1 gene by Prep1 attenuates insulin signal transduction and reduces glucose storage.

Characterization of the regulatory region of the zebrafish Prep1.1 gene: analogies to the promoter of the human PREP1

Prep1 is a developmentally essential TALE class homeodomain transcription factor. In zebrafish and mouse, Prep1 is already ubiquitously expressed at the earliest stages of development, with important tissue-specific peculiarities. The Prep1 gene in mouse is developmentally essential and has haploinsufficient tumor suppressor activity [1]. We have determined the human Prep1 transcription start site (TSS) by primer extension analysis and identified, within 20 bp, the transcription start region (TSR) of the zebrafish Prep1.1 promoter. The functions of the zebrafish 5′ upstream sequences were analyzed both by transient transfections in Hela Cells and by injection in zebrafish embryos. This analysis revealed a complex promoter with regulatory sequences extending up to −1.8, possibly −5.0 Kb, responsible for tissue specific expression. Moreover, the first intron contains a conserved tissue-specific enhancer both in zebrafish and in human cells. Finally, a two nucleotides mutation of an EGR-1 site, conserved in all species including human and zebrafish and located at a short distance from the TSS, destroyed the promoter activity of the −5.0 Kb promoter. A transgenic fish expressing GFP under the −1.8 Kb zebrafish promoter/enhancer co-expressed GFP and endogenous Prep1.1 during embryonic development. In the adult fish, GFP was expressed in hematopoietic regions like the kidney, in agreement with the essential function of Prep1 in mouse hematopoiesis. Sequence comparison showed conservation from man to fish of the sequences around the TSS, within the first intron enhancer. Moreover, about 40% of the sequences spread throughout the 5 Kbof the zebrafish promoter are concentrated in the −3 to −5 Kb of the human upstream region.

Down syndrome fibroblasts and mouse Prep1-overexpressing cells display increased sensitivity to genotoxic stress

PREP1 (PKNOX1) maps in the Down syndrome (DS) critical region of chromosome 21, is overexpressed in some DS tissues and might be involved in the DS phenotype. By using fibroblasts from DS patients and by overexpressing Prep1 in F9 teratocarcinoma and Prep1^i/i MEF to single out the role of the protein, we report that excess Prep1 increases the sensitivity of cells to genotoxic stress and the extent of the apoptosis directly correlates with the level of Prep1. The apoptotic response of Prep1-overexpressing cells is mediated by the pro-apoptotic p53 protein that we show is a direct target of Prep1, as its depletion reverts the apoptotic phenotype. The induction of p53 overcomes the anti-apoptotic role of Bcl-X_L, previously shown to be also a Prep1 target, the levels of which are increased in Prep1-overexpressing cells as well. Our results provide a rationale for the involvement of PREP1 in the apoptotic phenotype of DS tissues and indicate that differences in Prep1 level can have drastic effects.

Genome-wide association study of biochemical traits in Korcula Island, Croatia

AIM

To identify genetic variants underlying biochemical traits--total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, uric acid, albumin, and fibrinogen, in a genome-wide association study in an isolated population where rare variants of larger effect may be more easily identified.

METHODS

The study included 944 adult inhabitants of the island of Korcula, as a part of larger DNA-based genetic epidemiological study in 2007. Biochemical measurements were performed in a single laboratory with stringent internal and external quality control procedures. Examinees were genotyped using Human Hap370CNV chip by Illumina, with a genome-wide scan containing 346027 single nucleotide polymorphisms (SNP).

RESULTS

A total of 31 SNPs were associated with 7 investigated traits at the level of P<1.00 x 10(-5). Nine of SNPs implicated the role of SLC2A9 in uric acid regulation (P=4.10 x 10(-6)-2.58 x 10(-12)), as previously found in other populations. All 22 remaining associations fell into the P=1.00 x 10(-5)-1.00 x 10(-6) significance range. One of them replicated the association between cholesteryl ester transfer protein (CETP) and HDL, and 7 associations were more than 100 kilobases away from the closest known gene. Nearby SNPs, rs4767631 and rs10444502, in gene kinase suppressor of ras 2 (KSR2) on chromosome 12 were associated with LDL cholesterol levels, and rs10444502 in the same gene with total cholesterol levels. Similarly, rs2839619 in gene PBX/knotted 1 homeobox 1 (PKNOX1) on chromosome 21 was associated with total and LDL cholesterol levels. The remaining 9 findings implied possible associations between phosphatidylethanolamine N-methyltransferase (PEMT) gene and total cholesterol; USP46, RAP1GDS1, and ZCCHC16 genes and triglycerides; BCAT1 and SLC14A2 genes and albumin; and NR3C2, GRIK2, and PCSK2 genes and fibrinogen.

CONCLUSION

Although this study was underpowered for most of the reported associations to reach formal threshold of genome-wide significance under the assumption of independent multiple testing, replications of previous findings and consistency of association between the identified variants and more than one studied trait make such findings interesting for further functional follow-up studies. Changed allele frequencies in isolate population may contribute to identifying variants that would not be easily identified in much larger samples in outbred populations.