IGF1 Locus Research Articles

Hybrid de novo and haplotype-resolved genome assembly of Vechur cattle - elucidating genetic variation.

Cattle contribute to the nutritional needs and economy of a place. The performance and fitness of cattle depend on the response and adaptation to local climatic conditions. Genomic and genetic studies are important for advancing cattle breeding, and availability of relevant reference genomes is essential. In the present study, the genome of a Vechur calf was sequenced on both short-read Illumina and long-read Nanopore sequencing platforms. The hybrid de novo assembly approach was deployed to obtain an average contig length of 1.97 Mbp and an N50 of 4.94 Mbp. By using a short-read genome sequence of the corresponding sire and dam, a haplotype-resolved genome was also assembled. In comparison to the taurine reference genome, we found 28,982 autosomal structural variants and 16,926,990 SNVs, with 883,544 SNVs homozygous in the trio samples. Many of these SNPs have been reported to be associated with various QTLs including growth, milk yield, and milk fat content, which are crucial determinants of cattle production. Furthermore, population genotype data analysis indicated that the present sample belongs to an Indian cattle breed forming a unique cluster of Bos indicus. Subsequent FST analysis revealed differentiation of the Vechur cattle genome at multiple loci, especially those regions related to whole body growth and cell division, especially IGF1, HMGA2, RRM2, and CD68 loci, suggesting a possible role of these genes in its small stature and better disease resistance capabilities in comparison with the local crossbreeds. This provides an opportunity to select and engineer cattle breeds optimized for local conditions.

Genetic variation at the OLR1, ANXA9, MYF5, LTF, IGF1, LGB, CSN3, PIT1, MBL1,CACNA2D1, and ABCG2 loci in Turkish Grey Steppe, Anatolian Black, and EastAnatolian Red cattle

Native breeds are excellent sources of genetic variation. Anatolian native breeds are relatives of the first cattle domesticated and are ancestors of many European breeds. Therefore, this study aimed to evaluate the genetic variation of OLR1, ANXA9, MYF5, LTF, IGF1, LGB, CSN3, PIT1, MBL1, CACNA2D1, and ABCG2 markers in Turkish Grey Steppe, Anatolian Black, and East Anatolian Red cattle. The analysis included 367 cattle and the genotyping was performed by the PCR-RFLP. Population genetics indices including heterozygosity, the number of effective alleles, the polymorphism information content, fixation index, and the level of possible variability realization, and moreover, the genetic diversity parameters including Shannon?Weaver diversity index and Simpson dominance index were estimated. Hardy?Weinberg equilibrium was evaluated based on the number of individuals per genotype. Native breeds exhibited admissible population genetics and diversity levels. There was no animal with the MYF5-AA, IGF1-CC, LGB-BB, CSN3-BB, CACNA2D1- GG, and ABCG2-AC genotypes in the Anatolian Black breed. The frequencies of the genotypes/alleles favorable for milk production traits were remarkably low in all breeds. These findings could provide useful information on the genetic variation of Anatolian native cattle and the genetic investigations of resistance and health traits in bovine breeding and genetics.

The polymorphism rs35767 at IGF1 locus is associated with serum urate levels

Previous studies suggested that the IGF-1/IGF-1 receptor signaling pathway may contribute to regulate uric acid levels. To confirm this hypothesis, we assessed the effects of the IGF-1-raising genetic variant rs35767 on urate levels in serum and urine, and we investigated IGF-1 ability to modulate the expression of transporters involved in reabsorption and secretion of uric acid in the kidney. The study population included 2794 adult Whites. 24-hour urinary uric acid concentration was available for 229 subjects. rs35767 polymorphism was screened using TaqMan genotyping assays. HEK293 (human embryonic kidney-293) cell line was treated with IGF-1 (1, 5, 10, 50 nM) for 24-hours, and differences in the expression of urate transporters were evaluated via Western Blot and real time rtPCR. Individuals carrying the IGF-1-raising allele (rs35767 T) exhibited significantly lower levels of serum urate according to both additive and recessive models, after correction for gender, age, BMI, glucose tolerance, glomerular filtration rate, and anti-hypertensive treatment. TT genotype carriers displayed higher uricosuria than C allele carriers did, after adjusting for confounders. Exposure of HEK293 cells to IGF-1 resulted in a dose-dependent increase of uric acid transporters deputed to uric acid excretion (MRP4, NPT1 and BCRP), and reduction of GLUT9 expression, the major mediator of uric acid reabsorption, both at mRNA and protein level. We observed a significant association between the functional polymorphism rs35767 near IGF1 with serum urate concentrations and we provide a mechanistic explanation supporting a causal role for IGF-1 in the regulation of uric acid homeostasis.

Insulinlike Growth Factor 1 Gene Variation in Vertebrates.

IGF1-a small, single-chain, secreted peptide in mammals-is essential for normal somatic growth and is involved in a variety of other physiological and pathophysiological processes. IGF1 expression appears to be controlled by several different signaling mechanisms in mammals, with GH playing a key role by activating an inducible transcriptional pathway via the Jak2 protein kinase and the Stat5b transcription factor. Here, to understand aspects of Igf1 gene regulation over a substantially longer timeline than is discernible in mammals, Igf1 genes have been examined in 21 different nonmammalian vertebrates representing five different classes and ranging over ∼500 million years of evolutionary history. Parts of vertebrate Igf1 genes resemble components found in mammals. Conserved exons encoding the mature IGF1 protein are detected in all 21 species studied and are separated by a large intron, as seen in mammals; the single promoter contains putative regulatory elements that are similar to those functionally mapped in human IGF1 promoter 1. In contrast, GH-activated Stat5b-binding enhancers found in mammalian IGF1 loci are completely absent, there is no homolog of promoter 2 or exon 2 in any nonmammalian vertebrate, and different types of "extra" exons not present in mammals are found in birds, reptiles, and teleosts. These data collectively define properties of Igf1 genes and IGF1 proteins that were likely present in the earliest vertebrates and support the contention that common structural and regulatory features in Igf1 genes have a long evolutionary history.

Association of IGF 1 gene polymorphisms with some morphometric traits of Nigerian indigenous sheep breeds

The relationship between IGF 1 gene polymorphisms and some morphometric traits of the Balami, Uda and Yankasa sheep breeds of Nigeria was investigated. Blood samples and morphometric measurements were obtained from 150 sheep (50 for each of the three breeds) at the Maiduguri Livestock market and abattoir while DNA was extracted at the Biotechnology laboratory of the University of Maiduguri. Evaluation of results revealed 2 alleles (A and B) and 3 genotypes (AA, AB and BB) for all the breeds. The Uda and Yankasa breeds had higher frequency of allele B (0.64 and 0.56, respectively) while Balami had higher allele frequency for A (0.61). Balami and Yankasa had high heterozygosity for IGF-1 gene while Uda had high homozygosity for B. For Balami sheep, the genotype BB had higher (P < 0.05) body weight and heart girth (56 kg and 79 cm, respectively) than AB for body weight (45.80 kg) and BB for heart girth (69.67 cm). Conversely, genotype AA had higher body length (94.33 cm) than AB (73.80 cm). IGF 1 gene polymorphisms did not significantly (P < 0.05) affect most morphometric traits of the Yankasa and Uda sheep except height at withers where the genotype AB had higher (P < 0.05) height at withers (71.77 cm) than AA (53.50 cm) for Yankasa sheep. Thus, the three breeds were found to be 100% polymorphic at the regulatory region of IGF-1 locus and this gene may be used as a marker for some morphometric traits in Nigerian indigenous sheep. Keywords : body weight, heart girth, height at withers, breeds, sheep

Association of IGF and IGFBP2 gene polymorphisms with growth and egg traits in Atak-S laying hens

Atak-S laying hens are a high-performance hybrid obtained by crossing of the Rhode Island Red (RIR) X the Barred Plymouth Rock (BR) and are being produced in the Ankara Poultry Research Institute since 1997. Phenotypic and genetic improving studies are continuous for this hybrid. In this study three different SNPs, two from IGF1 and one from IGFBP2 genes, were examined in 150 Atak-S chickens. Genetic association of SNPs were compared to body weight and egg number till 32 weeks of age, body weight at sexual maturity, age at sexual maturity and also egg quality traits such as egg shell breaking strength, shell thickness, Haugh unit, albumen index, yolk index and shape index were statistically analyzed. Only IGF1(a) locus was in agreement with Hardy-Weinberg equilibrium, while, the rest of the loci were not. As a result of the comparisons performed to the three SNPs, it was determined that there was a significant association (P&lt;0.05) between the T364C haplotypes of the IGF1(b) locus and body weight at 32 weeks of age, but there was not any association to the other traits.

GH/IGF-1 Signaling and Current Knowledge of Epigenetics; a Review and Considerations on Possible Therapeutic Options.

Epigenetic mechanisms play an important role in the regulation of the Growth Hormone- Insulin-like Growth Factor 1 (GH-IGF1) axis and in processes for controlling long bone growth, and carbohydrate and lipid metabolism. Improvement of methodologies that allow for the assessment of epigenetic regulation have contributed enormously to the understanding of GH action, but many questions still remain to be clarified. The reversible nature of epigenetic factors and, particularly, their role as mediators between the genome and the environment, make them viable therapeutic target candidates. Rather than reviewing the molecular and epigenetic pathways regulated by GH action, in this review we have focused on the use of epigenetic modulators as potential drugs to improve the GH response. We first discuss recent progress in the understanding of intracellular molecular mechanisms controlling GH and IGF-I action. We then emphasize current advances in genetic and epigenetic mechanisms that control gene expression, and which support a key role for epigenetic regulation in the cascade of intracellular events that trigger GH action when coupled to its receptor. Thirdly, we focus on fetal programming and epigenetic regulation at the IGF1 locus. We then discuss epigenetic alterations in intrauterine growth retardation, and the possibility for a potential epigenetic pharmaceutical approach in short stature associated with this fetal condition. Lastly, we review an example of epigenetic therapeutics in the context of growth-related epigenetic deregulation disorders. The advance of our understanding of epigenetic changes and the impact they are having on new forms of therapy creates exciting prospects for the future.

Signatures of adaptive molecular evolution in American pikas (Ochotona princeps)

The American pika (Ochotona princeps) is a small, winter-active mammal inhabiting alpine environments. For alpine mammals, metabolic heat production and cellular mechanisms to cope with hypoxia are critical for survival and reproduction. Thus, because of the pikas' long association with alpine environments, they may have genetically adapted to alpine conditions. Here, we present evidence for positive selection acting at 2 loci within the Ochotona genome. These loci were identified by first assembling a list of 50 candidate genes and collecting sequence data from 2 O. princeps draft genomes available from public databases. We then tested the possibility that positive selection acted on the Ochotona lineage, relative to other mammalian species, using the CODEML program in the PAML package. These analyses indicated positive selection at 4 loci—insulin-like growth factor 1 gene (IGF-1), enoyl-CoA hydratase/3-hydroxyacyl CoA dehydrogenase (EHHADH), inducible nitric oxide synthase 2 (NOS2), and transforming growth factor beta 1 gene (TGF-β1). To test this assumption further, we collected DNA sequence data from the 4 genes of interest from multiple O. princeps individuals across a broad geographic range, as well as individuals from the congeneric collared pika (O. collaris). We used multiple interspecific and intraspecific polymorphism-based tests to test the resulting sequence data for patterns of non-neutral evolution. These tests provide additional support for positive selection acting on the IGF-1 and EHHADH loci.

Genetic mapping of principal components of canine pelvic morphology

BackgroundConcentrated breeding effort to produce various body structures and behaviors of dogs to suit human demand has inadvertently produced unwanted traits and diseases that accompany the morphological and behavioral phenotypes. We explored the relationship between pelvic conformation and canine hip dysplasia (HD) because purebred dogs which are predisposed, or not, to HD share common morphologic features, respectively. Thirteen unique bilateral anatomical features of the pelvis were measured on 392 dogs of 51 breeds and 95 mixed breed dogs. Principal components (PCs) were derived to describe pelvic morphology. Dogs were genotyped at ~183,000 single nucleotide polymorphisms and their hip conformation was measured by the Norberg angle and angle of inclination between the femoral neck and diaphysis.ResultsNo associations reached genome wide significance for the Norberg angle when averaged over both hips. PC1 was negatively correlated with the Norberg angle (r = -0.31; P < 0.05) but not the angle of inclination (r = -0.08; P > 0.05). PC1, 2, 4, and 5 differed significantly between male and female dogs confirming pelvic sexual dimorphism. With sex as a covariate, the eigenvector contribution to PC1 reflected the overall size of the pelvis and was significantly associated with the IGF-1 locus, a known contributor to canine body size. PC3, which represented a tradeoff between ilial length and ischial length in which a longer ischium is associated with a shorter ilium, was significantly associated with a marker on canine chromosome 16:5181388 bp. The closest candidate gene is TPK1, a thiamine-dependent enzyme and part of the PKA complex. Associations with the remaining PCs did not reach genome wide significance.ConclusionIGF-1 was associated with the overall size of the pelvis and sex is related to pelvic size. Ilial/ischial proportion is genetically controlled and the closest candidate gene is thiamine-dependent and affects birth weight and development of the nervous system. Dogs with larger pelves tend to have smaller NAs consistent with increased tendency toward HD in large breed dogs. Based on the current study, pelvic shape alone was not strongly associated with canine hip dysplasia.

A polymorphism at IGF1 locus is associated with anemia.

In vitro and in vivo studies suggest that IGF-1 has a role in erythropoiesis. There is evidence that the rs35767 C/T polymorphism near IGF1 is associated with plasma IGF-1 levels. We investigated the effect of this polymorphism on hemoglobin (Hb) concentration and anemia. The study group comprised 3286 adult Whites. The rs35767 polymorphism was screened using a TaqMan allelic discrimination assay. The rs35767 polymorphism was not associated with age, gender, BMI, waist circumference, smoking, blood pressure, plasma glucose, HbA1c, type 2 diabetes, HOMA-IR, hsCRP, eGFR, and lipid profile. Erythrocyte sedimentation rate (ESR), fibrinogen, and fasting insulin levels were significantly lower in TT genotype carriers compared with C allele carriers. Hb concentration was significantly higher in carriers of the TT genotype compared with C allele carriers, and a lower proportion of TT carriers had anemia. As compared with TT genotype carriers, those bearing the CC genotype had a 2.4-fold higher risk of anemia (OR 2.40, 95%CI 1.19-4.82), and those with the CT genotype had a 2.0-fold higher risk of anemia (OR 2.06, 95%CI 1.04-4.11). The association remained significant when fasting insulin, eGFR, smoking, diabetes, ACE inhibitors, sartans or diuretics treatments, use of metformin and pioglitazone were added to the model, but its independence was not retained after inclusion of fibrinogen and ESR values into the model. In conclusion, rs35767 TT allele carriers exhibited significantly higher concentrations of Hb, and lower risk of anemia compared with C allele carriers supporting the idea that IGF-1 plays a role in erythropoiesis homeostasis.

Genetic mapping of canine fear and aggression.

BackgroundFear/anxiety and anger/aggression greatly influence health, quality of life and social interactions. They are a huge burden to wellbeing, and personal and public economics. However, while much is known about the physiology and neuroanatomy of such emotions, little is known about their genetics – most importantly, why some individuals are more susceptible to pathology under stress.ResultsWe conducted genomewide association (GWA) mapping of breed stereotypes for many fear and aggression traits across several hundred dogs from diverse breeds. We confirmed those findings using GWA in a second cohort of partially overlapping breeds. Lastly, we used the validated loci to create a model that effectively predicted fear and aggression stereotypes in a third group of dog breeds that were not involved in the mapping studies. We found that i) known IGF1 and HMGA2 loci variants for small body size are associated with separation anxiety, touch-sensitivity, owner directed aggression and dog rivalry; and ii) two loci, between GNAT3 and CD36 on chr18, and near IGSF1 on chrX, are associated with several traits, including touch-sensitivity, non-social fear, and fear and aggression that are directed toward unfamiliar dogs and humans. All four genome loci are among the most highly evolutionarily-selected in dogs, and each of those was previously shown to be associated with morphological traits. We propose that the IGF1 and HMGA2 loci are candidates for identical variation being associated with both behavior and morphology. In contrast, we show that the GNAT3-CD36 locus has distinct variants for behavior and morphology. The chrX region is a special case due to its extensive linkage disequilibrium (LD). Our evidence strongly suggests that sociability (which we propose is associated with HS6ST2) and fear/aggression are two distinct GWA loci within this LD block on chrX, but there is almost perfect LD between the peaks for fear/aggression and animal size.ConclusionsWe have mapped many canine fear and aggression traits to single haplotypes at the GNAT3-CD36 and IGSF1 loci. CD36 is widely expressed, but areas of the amygdala and hypothalamus are among the brain regions with highest enrichment; and CD36-knockout mice are known to have significantly increased anxiety and aggression. Both of the other genes have very high tissue-specificity and are very abundantly expressed in brain regions that comprise the core anatomy of fear and aggression – the amygdala to hypothalamic-pituitary-adrenal (HPA) axis. We propose that reduced-fear variants at these loci may have been involved in the domestication process.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2936-3) contains supplementary material, which is available to authorized users.

Association of the IGF1 gene with fasting insulin levels.

Insulin-like growth factor 1 (IGF-I) has been associated with insulin resistance. Genome-wide association studies (GWASs) of fasting insulin (FI) identified single-nucleotide variants (SNVs) near the IGF1 gene, raising two hypotheses: (1) these associations are mediated by IGF-I levels and (2) these noncoding variants either tag other functional variants in the region or are directly functional. In our study, analyses including 5141 individuals from population-based cohorts suggest that FI associations near IGF1 are not mediated by IGF-I. Analyses of targeted sequencing data in 3539 individuals reveal a large number of novel rare variants at the IGF1 locus and show a FI association with a subset of rare nonsynonymous variants (PSKAT=5.7 × 10(-4)). Conditional analyses suggest that this association is partly explained by the GWAS signal and the presence of a residual independent rare variant effect (Pconditional=0.019). Annotation using ENCODE data suggests that the GWAS variants may have a direct functional role in insulin biology. In conclusion, our study provides insight into variation present at the IGF1 locus and into the genetic architecture underlying FI levels, suggesting that FI associations of SNVs near IGF1 are not mediated by IGF-I and suggesting a role for both rare nonsynonymous and common functional variants in insulin biology.

NOTCH1 Induces Differential Epigenomic Patterning and Genomic Organization in Fetal Liver- and Adult Bone Marrow-Derived Hematopoietic Progentiors

T-cell acute lymphoblastic leukemia (T-ALL) is a malignancy of immature T-cell progenitors, characterized by activating NOTCH1 mutations in over 50% of children and adult cases. Although intensive multiagent chemotherapy achieves cure in most pediatric patients, the majority of adults succumb quickly to their disease. The basis for this divergence is likely multifactorial, but we sought in this study to investigate whether cell intrinsic features might contribute to the disparate biologies in pediatric and adult patients.In our prior abstract, we modeled pediatric and adult leukemias by transduction of hematopoietic stem/progenitor cells (HSPC) derived from mouse fetal liver (FL) and adult bone marrow (ABM) with activated NOTCH1 virus followed by transplantation into histocompatible recipient animals. We observed that whereas FL- and ABM-derived HSPC generate similar primary acute T-cell leukemias in terms of penetrance, latency, disease burden/distribution, and immunophenotype, FL leukemias exhibit much greater cycling activity than ABM leukemias, yet are dramatically impaired in their ability to propagate disease in secondary and tertiary recipients compared to ABM leukemias. Using a combination of gene expression profiling and in vitro culture assays, we attributed this differential behavior to NOTCH1-induced autocrine IGF signaling that is operative in FL, but not ABM-derived HSPC.Here we report that NOTCH1 mediates its effects on IGF1 in FL-derived HSPC directly by physical occupancy over the IGF1 promoter in a dimerization-dependent fashion. As well, increased NOTCH1 occupancy at the IGF1 promoter region in FL tissues is associated with reduced histone H3K27 trimethylation (a mark of transcriptionally silent chromatin), yet there is equivalent histone H3K4 trimethylation (a mark identifying transcriptionally active promoters) in both FL and ABM tissues, suggesting that NOTCH1 may be responsible for interconverting the IGF1 locus between active and inactive, but poised chromatin states. NOTCH1 occupancy is also associated with enhanced physical interactions between the IGF1 promoter region and distant genomic loci as revealed by circularized chromosome conformation capture (4C) assay and confirmed by chromosome conformation capture (3C) assay, including sites with H3K4 monomethylation (a mark of transcriptional enhancers) suggesting that NOTCH1 promotes "looping in" of distant enhancer elements that drive IGF1 expression in FL tissues. We conclude from these studies that NOTCH1 enacts differential, developmental stage-specific transcriptional programs by a combination of local epigenetic patterning and long-range genomic interactions. These findings support the notion that pediatric and adult T-ALL may potentially be regarded as related, but biologically distinct diseases, and that novel, age-specific therapies that exploit these differences may improve clinical outcomes. DisclosuresNo relevant conflicts of interest to declare.

Genetic and Epigenetic Modulation of Growth Hormone Sensitivity Studied With the IGF-1 Generation Test.

Context:Like all hormones, GH has variable physiological effects across people. Many of these effects initiated by the binding of GH to its receptor (GHR) in target tissues are mediated by the expression of the IGF1 gene. Genetic as well as epigenetic variation is known to contribute to the individual diversity of GH-dependent phenotypes through two mechanisms. The first one is the genetic polymorphism of the GHR gene due to the common deletion of exon 3. The second, more recently reported, is the epigenetic variation in the methylation of a cluster of CGs dinucleotides located within the proximal part of the P2 promoter of the IGF-1 (IGF1) gene, notably CG-137.Objective:The current study evaluates the relative contribution of these two factors controlling individual GH sensitivity by measuring the response of serum IGF-1 to a GH injection (IGF-1 generation test) in a sample of 72 children with idiopathic short stature.Results:Although the d3 polymorphism of the GHR contributed 19% to the variance of the IGF-1 response, CG-137 methylation in the IGF-1 promoter contributed 30%, the combined contribution of the two factors totaling 43%.Conclusion:Our observation indicates that genetic and epigenetic variation at the GHR and IGF-1 loci play a major role as independent modulators of individual GH sensitivity.

Minireview: mechanisms of growth hormone-mediated gene regulation.

GH exerts a diverse array of physiological actions that include prominent roles in growth and metabolism, with a major contribution via stimulating IGF-1 synthesis. GH achieves its effects by influencing gene expression profiles, and Igf1 is a key transcriptional target of GH signaling in liver and other tissues. This review examines the mechanisms of GH-mediated gene regulation that begin with signal transduction pathways activated downstream of the GH receptor and continue with chromatin events at target genes and additionally encompasses the topics of negative regulation and cross talk with other cellular inputs. The transcription factor, signal transducer and activator of transcription 5b, is regarded as the major signaling pathway by which GH achieves its physiological effects, including in stimulating Igf1 gene transcription in liver. Recent studies exploring the mechanisms of how activated signal transducer and activator of transcription 5b accomplishes this are highlighted, which begin to characterize epigenetic features at regulatory domains of the Igf1 locus. Further research in this field offers promise to better understand the GH-IGF-1 axis in normal physiology and disease and to identify strategies to manipulate the axis to improve human health.

A Fasting Insulin–Raising Allele at IGF1 Locus Is Associated with Circulating Levels of IGF-1 and Insulin Sensitivity

BackgroundA meta-analysis of genome-wide data reported the discovery of the rs35767 polymorphism near IGF1 with genome-wide significant association with fasting insulin levels. However, it is unclear whether the effects of this polymorphism on fasting insulin are mediated by a reduced insulin sensitivity or impaired insulin clearance. We investigated the effects of the rs35767 polymorphism on circulating IGF-1 levels, insulin sensitivity, and insulin clearance. Methodology/Principal FindingsTwo samples of adult nondiabetic white Europeans were studied. In sample 1 (n=569), IGF-1 levels were lower in GG genotype carriers compared with A allele carriers (190±77 vs. 218±97 ng/ml, respectively; P=0.007 after adjusting for age, gender, and BMI). Insulin sensitivity assessed by euglycaemic-hyperinsulinemic clamp was lower in GG genotype carriers compared with A allele carriers (8.9±4.1 vs. 10.1±5.1 mg x Kg-1 free fat mass x min-1, respectively; P=0.03 after adjusting for age, gender, and BMI). The rs35767 polymorphism did not show significant association with insulin clearance. In sample 2 (n=859), IGF-1 levels were lower in GG genotype carriers compared with A allele carriers (155±60 vs. 164±63 ng/ml, respectively; P=0.02 after adjusting for age, gender, and BMI). Insulin sensitivity, as estimated by the HOMA index, was lower in GG genotype carriers compared with A allele carriers (2.8±2.2 vs. 2.5±1.3, respectively; P=0.03 after adjusting for age, gender, and BMI).Conclusion/SignificanceThe rs35767 polymorphism near IGF1 was associated with circulating IGF-1 levels, and insulin sensitivity with carriers of the GG genotype exhibiting lower IGF-1 concentrations and insulin sensitivity as compared with subjects carrying the A allele.

A polymorphism at IGF1 locus is associated with carotid intima media thickness and endothelium-dependent vasodilatation

ObjectiveWhether IGF-1 has a protective or a detrimental role in vascular homeostasis remains unsettled. There is evidence that the C/T polymorphism rs35767 near the promoter region of the IGF1 gene located in chromosome 12 is associated with plasma IGF-1 levels. We investigated the effects of this polymorphism on circulating IGF-1 levels, carotid intima media thickness (cIMT) and endothelial-dependent vasodilation. MethodsTwo samples of adult nondiabetic Whites were studied. Sample 1 comprised 1124 individuals in whom cIMT was measured by ultrasonography. Sample 2 included 162 drug-naïve hypertensive individuals in whom endothelium-dependent and endothelium-independent vasodilation were assessed by intra-arterial infusion of acetylcholine (ACh), and sodium nitroprusside (SNP), respectively. IGF-1 was determined by chemiluminescent immunoassay. rs35767 polymorphism was screened using a TaqMan allelic discrimination assay. ResultsIn sample 1, IGF-1 levels were higher in subjects carrying the T allele compared with CC carriers (178 ± 78 vs. 166 ± 60 ng/mL, respectively; P = 0.007 adjusted for age, gender, and BMI). cIMT was lower in subjects carrying the T allele compared with CC carriers (0.71 ± 0.20 vs. 0.76 ± 0.22 mm, respectively; P < 0.0001 adjusted for age, gender, and BMI). In sample 2, maximally ACh-stimulated forearm blood flow was higher in subjects carrying the T allele compared with CC carriers (343 ± 191 vs. 281 ± 125%, respectively; P = 0.02 adjusted for age, gender, and BMI). ConclusionSubjects carrying the T allele exhibited significantly higher levels of circulating IGF-1, lower values of cIMT, and higher endothelium-dependent vasodilatation compared with CC carriers. These findings support the idea that IGF-1 plays a role in the pathogenesis of atherosclerosis.

Hepatic-Specific Accessibility of Igf1 Gene Enhancers Is Independent of Growth Hormone Signaling

The diverse roles of IGF-1 in physiology include acting as the endocrine intermediate to elicit the anabolic actions of GH. The majority of serum IGF-1 is synthesized in liver, where GH stimulates Igf1 gene transcription via the transcription factor, signal transducer and activator of transcription (Stat)5b. We and others have identified multiple Stat5-binding domains at the Igf1 locus that function in gene regulation, but it remains unclear whether the roles of these domains are tissue specific. Survey of the chromatin landscape of regulatory domains can provide insight about mechanisms of gene regulation, with chromatin accessibility regarded as a hallmark feature of regulatory domains. We prepared chromatin from liver, kidney, and spleen of C57BL/6 mice, and used formaldehyde-associated isolation of regulatory elements to assess chromatin accessibility at the major Igf1 promoter and 7 -binding enhancers. Whereas the promoters of other prototypical tissue-specific genes are open in a tissue-specific way, the major Igf1 promoter is open in all 3 tissues, albeit moderately more so in liver. In contrast, chromatin accessibility at Igf1 Stat5-binding domains is essentially restricted to liver, indicating that the enhancers are driving extensive differences in tissue expression. Furthermore, studies with Ghrhr(lit/lit) mice reveal that prior GH exposure is not necessary to establish open chromatin at these domains. Lastly, formaldehyde-associated isolation of regulatory elements of human liver samples confirms open chromatin at IGF1 Promoter 1, but unexpectedly, homologous Stat5-binding motifs are not accessible. We conclude that robust GH-stimulated hepatic Igf1 gene transcription utilizes tissue-specific mechanisms of epigenetic regulation that are established independent of GH signaling.

Genetic variation at the IGF1 locus shows association with post-stroke outcome and to circulating IGF1

In humans, serum IGF1 (s-IGF1) is associated with outcome after ischemic stroke (IS). Therefore variation at the IGF1 locus could also associate with both IS and s-IGF1. We investigated whether genetic variation at the IGF1 locus is associated with i) s-IGF1, ii) IS occurrence, iii) IS severity, and iv) post-stroke outcome. Patients (n=844; 66% males, mean age 56 years) and community controls (n=668) were included from the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS). Post-stroke outcome was evaluated with the modified Rankin Scale at 3 and 24 months after index stroke, and baseline stroke severity with the Scandinavian Stroke Scale. s-IGF1 was determined in patients and after random selection in 40 of the controls. Eleven single nucleotide polymorphisms (SNPs) were selected in the IGF1 gene. In healthy controls the major allele of rs7136446 was associated with higher s-IGF1, whereas in patients no such association was found. No SNP was associated with IS, nor with stroke severity. After multivariate correction for presence of diabetes, smoking, and hypertension, the major allele of rs7136446 was associated with favorable functional outcome 24-months post-stroke (odds ratio 1.46; 95% CI 1.09-1.96). Variation in rs7136446 of the IGF1 gene associates with post-stroke outcome in relatively young IS patients. Also, rs7136446 associates with s-IGF1 in controls but not in IS, which indicates that IS perturbs a normal genetic impact on s-IGF1 levels.

Anabolic effects of IGF-1 signaling on the skeleton

This review focuses on the anabolic effects of IGF-1 signaling on the skeleton, emphasizing the requirement for IGF-1 signaling in normal bone formation and remodeling. We first discuss the genomic context, splicing variants, and species conservation of the IGF-1 locus. The modulation of IGF-1 action by growth hormone (GH) is then reviewed while also discussing the current model which takes into account the GH-independent actions of IGF-1. Next, the skeletal phenotypes of IGF-1-deficient animals are described in both embryonic and postnatal stages of development, which include severe dwarfism and an undermineralized skeleton. We then highlight two mechanisms by which IGF-1 exerts its anabolic action on the skeleton. Firstly, the role of IGF-1 signaling in the modulation of anabolic effects of parathyroid hormone (PTH) on bone will be discussed, presenting in vitro and in vivo studies that establish this concept and the proposed underlying molecular mechanisms involving Indian hedgehog (Ihh) and the ephrins. Secondly, the crosstalk of IGF-1 signaling with mechanosensing pathways will be discussed, beginning with the observation that animals subjected to skeletal unloading by hindlimb elevation are unable to mitigate cessation of bone growth despite infusion with IGF-1 and the failure of IGF-1 to activate its receptor in bone marrow stromal cell cultures from unloaded bone. Disrupted crosstalk between IGF-1 signaling and the integrin mechanotransduction pathways is discussed as one of the potential mechanisms for this IGF-1 resistance. Next, emerging paradigms on bone-muscle crosstalk are examined, focusing on the potential role of IGF-1 signaling in modulating such interactions. Finally, we present a future outlook on IGF research.