Insulin receptor structure and its implications for the IGF-1 receptor

Chronically Increased Levels of Circulating Insulin Secondary to Insulin Resistance: A Silent Killer

Despite all the progress made by science in the prevention and treatment of cardiovascular diseases and cancers, these are still the main reasons for hospitalizations and death in the Western world. Among the possible causes of this situation, disorders related to hyperinsulinemia and insulin resistance (Hyperin/IR) are still little-known topics. An analysis of the literature shows that this condition is a multiple risk factor for type 2 diabetes, cardiovascular diseases, cellular senescence and cancer, and neurodegenerative diseases. Hyperin/IR is progressively increasing worldwide, and its prevalence has now exceeded 50% of the general population and in overweight children. Asymptomatic or poorly symptomatic, it can last for many years before manifesting itself as diabetes, cardiovascular disease, neoplasm, cognitive deficit, or dementia, therefore leading to enormous social and healthcare costs. For these reasons, a screening plan for this pathology should be implemented for the purpose of identifying people with Hyperin/IR and promptly starting them on preventive treatment.

Insulin Resistance/Hyperinsulinemia as an Independent Risk Factor That Has Been Overlooked for Too Long

Unfortunately, cardiovascular diseases and cancers are still the leading causes of death in developed and developing countries despite the considerable progress made in the prevention and treatment of diseases. Maybe we missed something? Insulin resistance (IR) with associated hyperinsulinemia (Hypein) is a silent pandemic whose prevalence is continually growing in developed and developing countries, now exceeding 51% of the general population. IR/Hypein, despite the vast scientific literature supporting its adverse action on the development of type 2 diabetes, cardiovascular alterations, tumors, neurological disorders, and cellular senescence, is not yet considered an independent risk factor and, therefore, is not screened in the general population and adequately treated. There are now numerous substances, drugs, and natural substances that, in association with the correction of a wrong lifestyle, can help to reduce IR/Hypein. We are convinced that the time has come to implement a prevention plan against this critical risk factor. Therefore, this manuscript aims to highlight IR/Hypein as an independent risk factor for type 2 diabetes, cardiovascular diseases, cancers, cellular senescence, and neuropsychiatric disorders, supporting our conviction with the available scientific literature on the topic.

Insulin receptor alternative splicing in breast and prostate cancer

Cancer etiology represents an intricate, multifactorial orchestration where metabolically associated insulin-like growth factors (IGFs) and insulin foster cellular proliferation and growth throughout tumorigenesis. The insulin receptor (IR) exhibits two splice variants arising from alternative mRNA processing, namely IR-A, and IR-B, with remarkable distribution and biological effects disparities. This insightful review elucidates the structural intricacies, widespread distribution, and functional significance of IR-A and IR-B. Additionally, it explores the regulatory mechanisms governing alternative splicing processes, intricate signal transduction pathways, and the intricate association linking IR-A and IR-B splicing variants to breast and prostate cancer tumorigenesis. Breast cancer and prostate cancer are the most common malignant tumors with the highest incidence rates among women and men, respectively. These findings provide a promising theoretical framework for advancing preventive strategies, diagnostic modalities, and therapeutic interventions targeting breast and prostate cancer.

Changes of Signaling Pathways in Hypothalamic Neurons with Aging

The hypothalamus is an important regulator of autonomic and endocrine functions also involved in aging regulation. The aging process in the hypothalamus is accompanied by disturbed intracellular signaling including insulin/insulin-like growth factor-1 (IGF-1)/growth hormone (GH), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (AKT)/the mammalian target of rapamycin (mTOR), mitogen activated protein kinase (MAPK), janus kinase (JAK)/signal transducer and activator of transcription (STAT), AMP-activated protein kinase (AMPK), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-ĸB), and nitric oxide (NO). In the current review, I have summarized the current understanding of the changes in the above-mentioned pathways in aging with a focus on hypothalamic alterations.

Insulin receptor-inspired soluble insulin binder

The insulin receptor (IR) is a 320 kDa membrane receptor tyrosine kinase mediating the pleiotropic actions of insulin, leading to phosphorylation of several intracellular substrates including serine/threonine-protein kinase (AKT1), and IR autophosphorylation. Structural details of the IR have been recently revealed. A high-binding insulin site, L1 (Kd =2 nM), consists of two distant domains in the primary sequence of the IR. Our design simplified the L1 binding site and transformed it into a soluble insulin binder (sIB). The sIB, a 17 kDa protein, binds insulin with 38 nM affinity. The sIB competes with IR for insulin and reduces by more than 50% phosphorylation of AKT1 in HEK 293 T cells, with similar effects on IR autophosphorylation. The sIB represents a new tool for research of insulin binding and signaling properties.

Targeting the insulin receptor with hormone and peptide dimers

Insulin is a key hormone involved in the regulation of overall energetic homeostasis of the organism. The dimeric character of the receptor for insulin evokes ideas about its activation or inhibition with peptide dimers that could either trigger or block the structural transition of the insulin receptor, leading to its activation. Herewith, we present the chemical engineering and biological characterization of several series of insulin dimers or dimers of specific peptides that should be able to bind receptors for insulin or insulin growth factor 1. The hormones or peptides in the dimers were interconnected with different linkers, consisting of triazole moieties and 3, 6, 8, 11, or 23 polyethylene glycol units. The prepared dimers were weaker in binding to insulin receptors than human insulin. However, some of the insulin dimers showed preferential binding specificity toward the isoform A of the insulin receptor, and the insulin dimers also stimulated the insulin receptor more strongly than would be consistent with their binding affinities. Our results suggest that designing insulin dimers may be a promising strategy for modulating the ability of the hormone to activate the receptor or to alter its specificity toward insulin receptor isoforms.

Structural models of viral insulin-like peptides and their analogs

The insulin receptor (IR), the insulin-like growth factor-1 receptor (IGF1R), and the insulin/IGF1 hybrid receptors (hybR) are homologous transmembrane receptors. The peptide ligands, insulin and IGF1, exhibit significant structural homology and can bind to each receptor via site-1 and site-2 residues with distinct affinities. The variants of the Iridoviridae virus family show capability in expressing single-chain insulin/IGF1 like proteins, termed viral insulin-like peptides (VILPs), which can stimulate receptors from the insulin family. The sequences of VILPs lacking the central C-domain (dcVILPs) are known, but their structures in unbound and receptor-bound states have not been resolved to date. We report all-atom structural models of three dcVILPs (dcGIV, dcSGIV, and dcLCDV1) and their complexes with the receptors (μIR, μIGF1R, and μhybR), and probed the peptide/receptor interactions in each system using all-atom molecular dynamics (MD) simulations. Based on the nonbonded interaction energies computed between each residue of peptides (insulin and dcVILPs) and the receptors, we provide details on residues establishing significant interactions. The observed site-1 insulin/μIR interactions are consistent with previous experimental studies, and a residue-level comparison of interactions of peptides (insulin and dcVILPs) with the receptors revealed that, due to sequence differences, dcVILPs also establish some interactions distinct from those between insulin and IR. We also designed insulin analogs and report enhanced interactions between some analogs and the receptors.

The Insulin Receptor: An Important Target for the Development of Novel Medicines and Pesticides

The insulin receptor (IR) is a transmembrane protein that is activated by ligands in insulin signaling pathways. The IR has been considered as a novel therapeutic target for clinical intervention, considering the overexpression of its protein and A-isoform in multiple cancers, Alzheimer's disease, and Type 2 diabetes mellitus in humans. Meanwhile, it may also serve as a potential target in pest management due to its multiple physiological influences in insects. In this review, we provide an overview of the structural and molecular biology of the IR, functions of IRs in humans and insects, physiological and nonpeptide small molecule modulators of the IR, and the regulating mechanisms of the IR. Xenobiotic compounds and the corresponding insecticidal chemicals functioning on the IR are also discussed. This review is expected to provide useful information for a better understanding of human IR-related diseases, as well as to facilitate the development of novel small-molecule activators and inhibitors of the IR for use as medicines or pesticides.

The insulin receptor family in the heart: new light on old insights

Insulin was discovered over 100 years ago. Whilst the first half century defined many of the physiological effects of insulin, the second emphasised the mechanisms by which it elicits these effects, implicating a vast array of G proteins and their regulators, lipid and protein kinases and counteracting phosphatases, and more. Potential growth-promoting and protective effects of insulin on the heart emerged from studies of carbohydrate metabolism in the 1960s, but the insulin receptors (and the related receptor for insulin-like growth factors 1 and 2) were not defined until the 1980s. A related third receptor, the insulin receptor-related receptor remained an orphan receptor for many years until it was identified as an alkali-sensor. The mechanisms by which these receptors and the plethora of downstream signalling molecules confer cardioprotection remain elusive. Here, we review important aspects of the effects of the three insulin receptor family members in the heart. Metabolic studies are set in the context of what is now known of insulin receptor family signalling and the role of protein kinase B (PKB or Akt), and the relationship between this and cardiomyocyte survival versus death is discussed. PKB/Akt phosphorylates numerous substrates with potential for cardioprotection in the contractile cardiomyocytes and cardiac non-myocytes. Our overall conclusion is that the effects of insulin on glucose metabolism that were initially identified remain highly pertinent in managing cardiomyocyte energetics and preservation of function. This alone provides a high level of cardioprotection in the face of pathophysiological stressors such as ischaemia and myocardial infarction.

Insulin facilitates corneal wound healing in the diabetic environment through the RTK-PI3K/Akt/mTOR axis in vitro

Diabetic patients can develop degenerative corneal changes, termed diabetic keratopathy, during the course of their disease. Topical insulin has been shown to reduce corneal wound area and restore sensitivity in diabetic rats, and both the insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF-1R) stimulate cell signaling of the PI3K-Akt pathway. The purpose of this study was to assess a mechanism by which improved wound healing occurs by characterizing expression within the PI3K-Akt pathway in corneal epithelial and stromal cells. In vitro scratch tests were used to evaluate wound healing outcomes under variable glucose conditions in the presence or absence of insulin. Protein expression of intracellular kinases in the PI3K pathway, stromal cell markers, and GLUT-1 was evaluated by immunoblotting.TGF-β1 expression was evaluated by ELISA. Insulin promoted in vitro wound healing in all cell types. In human corneal epithelial cells, insulin did not induce PI3K-Akt signaling; however, in all other cell types evaluated, insulin increased expression of PI3K-Akt signaling proteins compared to vehicle control. Fibroblasts variably expressed α-SMA under all treatment conditions, with significant increases in α-SMA and TGF-β1 occurring in a dose-dependent manner with glucose concentration. These results indicate that insulin can promote corneal cellular migration and proliferation by inducing Akt signaling. Exogenous insulin therapy may serve as a novel target of therapeutic intervention for diabetic keratopathy.

Insulin Receptor Genetic Variants Causal Association with Type 2 Diabetes: A Mendelian Randomization Study

Background

Type 2 diabetes (T2D) is a prevalent chronic disease associated with several comorbidities.

Objectives

This study investigated whether the risk of T2D varied with genetically predicted insulin (INS), insulin receptor (INS-R), or insulin-like growth factor 1 receptor (IGF-1R) using genetic variants in a Mendelian randomization (MR) study.

Methods

A 2-sample MR study was conducted using summary statistics from 2 genome-wide association studies (GWASs). Genetic predictors of the exposures (INS, INS-R, and IGF-1R) were obtained from a publicly available proteomics GWAS of the INTERVAL randomized controlled trial of blood donation in the United Kingdom. For T2D, the study leveraged the DIAbetes Meta-ANalysis of Trans-Ethnic association studies (DIAMANTE) consortium. The estimated associations of INS, INS-R, and IGF-1R proteins with T2D were based on independent single nucleotide polymorphisms (SNPs) strongly (P < 5 × 10-6) predicting each exposure. These SNPs were applied to publicly available genetic associations with T2D from the DIAMANTE case (n = 74,124) and control (n = 824,006) study of people of European descent. SNP-specific Wald estimates were meta-analyzed using inverse variance weighting with multiplicative random effects. Sensitivity analysis was conducted using the weighted median (WM) and MR-Egger.

Results

INS-R (based on 13 SNPs) was associated with a lower risk of T2D (OR: 0.95 per effect size; 95% CI: 0.92, 0.98; P = 0.001), with similar estimates from the WM and MR-Egger. Insulin (8 SNPs) and IGF-1R (10 SNPs) were not associated with T2D. However, 1 of the SNPs for INS-R was from the ABO blood group gene.

Conclusions

This study is consistent with a causally protective association of the INS-R with T2D. INS-R in RBCs regulates glycolysis and thus may affect their functionality and integrity. However, a pleiotropic effect via the blood group ABO gene cannot be excluded. The INS-R may be a target for intervention by repurposing existing therapeutics or otherwise to reduce the risk of T2D.

Insulin and the insulin receptor collaborate to promote human gastric cancer

BACKGROUND

Gastric adenocarcinoma is common and consequent mortality high. Presentation and mortality are increased in obese individuals, many of whom have elevated circulating insulin concentrations. High plasma insulin concentrations may promote, and increase mortality from, gastric adenocarcinoma. Tumour promotion activities of insulin and its receptor are untested in gastric cancer cells.

METHODS

Tumour gene amplification and expression were computed from sequencing and microarray data. Associations with patient survival were assessed. Insulin-dependent signal transduction, growth, apoptosis and anoikis were analysed in metastatic cells from gastric adenocarcinoma patients and in cell lines. Receptor involvement was tested by pharmacological inhibition and genetic knockdown. RNA was analysed by RT-PCR and proteins by western transfer and immunofluorescence.

RESULTS

INSR expression was higher in tumour than in normal gastric tissue. High tumour expression was associated with worse patient survival. Insulin receptor was detected readily in metastatic gastric adenocarcinoma cells and cell lines. Isoforms B and A were expressed. Pharmacological inhibition prevented cell growth and division, and induced caspase-dependent cell death. Rare tumour INS expression indicated tumours would be responsive to pancreatic or therapeutic insulins. Insulin stimulated gastric adenocarcinoma cell PI3-kinase/Akt signal transduction, proliferation, and survival. Insulin receptor knockdown inhibited proliferation and induced programmed cell death. Type I IGF receptor knockdown did not induce cell death.

CONCLUSIONS

The insulin and IGF signal transduction pathway is dominant in gastric adenocarcinoma. Gastric adenocarcinoma cell survival depends upon insulin receptor. That insulin has direct cancer-promoting effects on tumour cells has implications for clinical management of obese and diabetic cancer patients.

The Effect of Diabetes Mellitus on IGF Axis and Stem Cell Mediated Regeneration of the Periodontium

Periodontitis and diabetes mellitus (DM) are two of the most common and challenging health problems worldwide and they affect each other mutually and adversely. Current periodontal therapies have unpredictable outcome in diabetic patients. Periodontal tissue engineering is a challenging but promising approach that aims at restoring periodontal tissues using one or all of the following: stem cells, signalling molecules and scaffolds. Mesenchymal stem cells (MSCs) and insulin-like growth factor (IGF) represent ideal examples of stem cells and signalling molecules. This review outlines the most recent updates in characterizing MSCs isolated from diabetics to fully understand why diabetics are more prone to periodontitis that theoretically reflect the impaired regenerative capabilities of their native stem cells. This characterisation is of utmost importance to enhance autologous stem cells based tissue regeneration in diabetic patients using both MSCs and members of IGF axis.

A proposed lectin-mediated mechanism to explain the in Vivo antihyperglycemic activity of γ-conglutin from Lupinus albus seeds

Experiments conducted in vitro and in vivo, as well as clinical trials for hypoglycemic therapeutics, support the hypoglycemic properties of the lectin γ-conglutin, a Lupinus seed storage protein, by a mechanism not yet been clarified. Structural studies established that binding of γ-conglutin, in native and denatured form, to insulin occurs by a strong binding that resists rupture when 0.4 M NaCl and 0.4 M galactose are present, suggesting that strong electrostatic interactions are involved. Studies on binding of γ-conglutin in native and denatured form to HepG2 membrane glycosylated receptors were conducted, which reveal that only the native form of γ-conglutin with lectin activity is capable of binding to these receptors. Glycosylated insulin receptors were detected on purified HepG2 cell membranes and characterized by 1D and 2D analyses. Preclinical assays with male mice (CD-1) indicated that native and denatured γ-conglutins display antihyperglycemic effect, decreasing glucose in blood comparable after 120 min to that exhibited by the animal group treated with metformin, used to treat T2D and used as a positive control. Measurement of organ injury/functional biomarkers (hepatic, pancreatic, renal, and lipid profile) was comparable to that of metformin treatment or even better in terms of safety endpoints (pancreatic and hepatic biomarkers).

Molecular Modeling and Bioinformatics Analysis of Drug-Receptor Interactions in the System Formed by Glargine, Its Metabolite M1, the Insulin Receptor, and the IGF1 Receptor

Introduction

Insulin and insulin-like growth factor type 1 (IGF1) regulate multiple physiological functions by acting on the insulin receptor (IR) and insulin-like growth factor type 1 receptor (IGF1R). The insulin analog glargine differs from insulin in three residues (Gly^A21, Arg^B31, Arg^B32), and it is converted to metabolite M1 (lacks residues Arg^B31 and Arg^B32) by in vivo processing. It is known that activation of these receptors modulates pathways related to metabolism, cell division, and growth. Though, the structures and structural basis of the glargine interaction with these receptors are not known.

Aim

To generate predictive structural models, and to analyze the drug/receptor interactions in the system formed by glargine, its metabolite M1, IR, and IGF1R by using bioinformatics tools.

Methods

Ligand/receptor models were built by homology modeling using SWISSMODEL, and surface interactions were analyzed using Discovery Studio® Visualizer. Target and hetero target sequences and appropriate template structures were used for modeling.

Results

Our glargine/IR and metabolite M1/IR models showed an overall symmetric T-shaped conformation and full occupancy with four ligand molecules. The glargine/IR model revealed that the glargine residues Arg^B31 and Arg^B32 fit in a hydrophilic region formed by the α-chain C-terminal helix (αCT) and the cysteine-rich region (CR) domain of this receptor, close to the CR residues Arg270-Arg271-Gln272 and αCT residue Arg717. Regarding IGF1R, homologous ligand/receptor models were further built assuming that the receptor is in a symmetrical T-shaped conformation and is fully occupied with four ligand molecules, similar to what we described for IR. Our glargine/IGF1R model showed the interaction of the glargine residues Arg^B31 and Arg^B32 with Glu264 and Glu305 in the CR domain of IGF1R.

Conclusion

Using bioinformatics tools and predictive modeling, our study provides a better understanding of the glargine/receptor interactions.

Metabolic Hormones Modulate Macrophage Inflammatory Responses

Simple Summary

Macrophages are a type of immune cell which play an important role in the development of cancer. Obesity increases the risk of cancer and obesity also causes disruption to the normal levels of hormones that are produced to coordinate metabolism. Recent research now shows that these metabolic hormones also play important roles in macrophage immune responses and so through macrophages, disrupted metabolic hormone levels may promote cancer. This review article aims to highlight and summarise these recent findings so that the scientific community may better understand how important this new area of research is, and how these findings can be capitalised on for future scientific studies.

Abstract

Macrophages are phagocytotic leukocytes that play an important role in the innate immune response and have established roles in metabolic diseases and cancer progression. Increased adiposity in obese individuals leads to dysregulation of many hormones including those whose functions are to coordinate metabolism. Recent evidence suggests additional roles of these metabolic hormones in modulating macrophage inflammatory responses. In this review, we highlight key metabolic hormones and summarise their influence on the inflammatory response of macrophages and consider how, in turn, these hormones may influence the development of different cancer types through the modulation of macrophage functions.

Targeting obesity-related dysfunction in hormonally driven cancers

Obesity is a risk factor for at least 13 different types of cancer, many of which are hormonally driven, and is associated with increased cancer incidence and morbidity. Adult obesity rates are steadily increasing and a subsequent increase in cancer burden is anticipated. Obesity-related dysfunction can contribute to cancer pathogenesis and treatment resistance through various mechanisms, including those mediated by insulin, leptin, adipokine, and aromatase signalling pathways, particularly in women. Furthermore, adiposity-related changes can influence tumour vascularity and inflammation in the tumour microenvironment, which can support tumour development and growth. Trials investigating non-pharmacological approaches to target the mechanisms driving obesity-mediated cancer pathogenesis are emerging and are necessary to better appreciate the interplay between malignancy, adiposity, diet and exercise. Diet, exercise and bariatric surgery are potential strategies to reverse the cancer-promoting effects of obesity; trials of these interventions should be conducted in a scientifically rigorous manner with dose escalation and appropriate selection of tumour phenotypes and have cancer-related clinical and mechanistic endpoints. We are only beginning to understand the mechanisms by which obesity effects cell signalling and systemic factors that contribute to oncogenesis. As the rates of obesity and cancer increase, we must promote the development of non-pharmacological lifestyle trials for the treatment and prevention of malignancy.

Pyometra-associated insulin resistance assessment by insulin binding assay and tyrosine kinase activity evaluation in canine muscle tissue

Diestrus is associated with insulin resistance in bitches and pyometra can further impair insulin sensitivity. This study aimed to compare insulin sensitivity, insulin binding, and tyrosine kinase activity in bitches in anestrus, diestrus, or with pyometra. Patients submitted to elective ovariohysterectomy were divided into anestrus (n = 11) or diestrus (n = 13) according to reproductive history, vaginal cytology, and uterine histology. The group pyometra (n = 8) included bitches diagnosed with the disease based on clinical presentation and abdominal ultrasound findings and further confirmed by uterine histopathology. All patients were submitted to an intravenous glucose tolerance test (IVGTT) before ovariohysterectomy, and rectus abdominis muscle samples were collected during surgery for plasmatic membrane suspension preparation. Muscle-membranes were submitted to cold saturation insulin binding assay for dissociation constant (Kd) and maximum binding capacity (Bmax) determination, as well as exogenous substrate Poly (Glu: Tyr 4:1) phosphorylation assay for basal tyrosine kinase evaluation. Bitches with pyometra showed higher basal insulin (P < 0.001) and higher area under the curve (AUC) for insulin (P = 0.01) and glucose (P < 0.001) response during the IVGTT in comparison with bitches in anestrus or diestrus. Diestrus (P < 0.0001) and pyometra (P = 0.001) were associated with reduced tyrosine kinase activity in comparison with anestrus. No differences were documented in Kd and Bmax results for the low-affinity/high-capacity insulin receptors; however, high-affinity/low-capacity insulin receptors showed higher Kd and Bmax results in bitches in diestrus or with pyometra (P < 0.05) in comparison with anestrus. Despite the pyometra group showed the highest Kd values (P < 0.01), its Bmax results did not differ from the diestrus group (P > 0.05). Diestrus' higher Kd values and reduced tyrosine kinase activity in muscle tissue were compensated by increased total insulin binding capacity. Absent differences in IVGTT results between diestrus and anestrus bitches corroborate this finding. However, in bitches with pyometra, the highest Kd values were not compensated by increased total insulin binding capacity. This finding was associated with insulin resistance and glucose intolerance in IVGTT results. Moreover, pyometra resolution restored insulin sensitivity and glucose tolerance. These features can play a key role in pyometra-associated CDM, as well as in diabetic remission after pyometra resolution.

Effect of the interaction between ribosomal protein L10a and insulin receptor on carbohydrate metabolism

The number of patients with insulin-resistant diabetes has significantly increased. Thus, alternative insulin mimetics are required for such patients. Some evidences indicate that ribosomal protein L10a (RpL10a) is involved in the insulin pathway. In addition, we previously demonstrated that recombinant RpL10a from Fenneropenaeus merguiensis (Fm-RpL10a) could stimulate cell proliferation and trehalose metabolism in RpL10a–over-expressing flies by inducing insulin receptor (InR) expression and some insulin signaling mediators phosphorylation. In this study, we investigated the in silico binding between Fm-RpL10a and InR. The results indicated that Fm-RpL10a bound to InR at residues 635–640 and 697–702 of the FnIII2 domain. This binding was confirmed using a pull-down and immunofluorescence assay. Further analysis indicated that Fm-RpL10a could stimulate glucose utilisation by insulin-resistant cells (IRCs) and healthy cells. Additionally, Fm-RpL10a at a low concentration (1 μg/ml) altered some glucose metabolism-related genes expression in Fm-RpL10a treated IRCs. The qRT-PCR result revealed the up-regulation of Hk1, which encode key enzymes in glycolysis. Conversely, the expression of G6pc3, which participates in gluconeogenesis, was down-regulated. Overall, the results suggest that Fm-RpL10a can alleviate insulin resistance by stimulating insulin signaling via the FnIII2 domain of InR and activate glycolysis. Therefore, Fm-RpL10a may be a candidate insulin mimetic for the treatment of diabetes.

Role of Insulin-Like Growth Factor Receptor 2 across Muscle Homeostasis: Implications for Treating Muscular Dystrophy

The insulin-like growth factor 2 receptor (IGF2R) plays a major role in binding and regulating the circulating and tissue levels of the mitogenic peptide insulin-like growth factor 2 (IGF2). IGF2/IGF2R interaction influences cell growth, survival, and migration in normal tissue development, and the deregulation of IGF2R expression has been associated with growth-related disease and cancer. IGF2R overexpression has been implicated in heart and muscle disease progression. Recent research findings suggest novel approaches to target IGF2R action. This review highlights recent advances in the understanding of the IGF2R structure and pathways related to muscle homeostasis.

Mutations at hypothetical binding site 2 in insulin and insulin-like growth factors 1 and 2 result in receptor- and hormone-specific responses

Information on how insulin and insulin-like growth factors 1 and 2 (IGF-1 and -2) activate insulin receptors (IR-A and -B) and the IGF-1 receptor (IGF-1R) is crucial for understanding the difference in the biological activities of these peptide hormones. Cryo-EM studies have revealed that insulin uses its binding sites 1 and 2 to interact with IR-A and have identified several critical residues in binding site 2. However, mutagenesis studies suggest that Ile-A10, Ser-A12, Leu-A13, and Glu-A17 also belong to insulin's site 2. Here, to resolve this discrepancy, we mutated these insulin residues and the equivalent residues in IGFs. Our findings revealed that equivalent mutations in the hormones can result in differential biological effects and that these effects can be receptor-specific. We noted that the insulin positions A10 and A17 are important for its binding to IR-A and IR-B and IGF-1R and that A13 is important only for IR-A and IR-B binding. The IGF-1/IGF-2 positions 51/50 and 54/53 did not appear to play critical roles in receptor binding, but mutations at IGF-1 position 58 and IGF-2 position 57 affected the binding. We propose that IGF-1 Glu-58 interacts with IGF-1R Arg-704 and belongs to IGF-1 site 1, a finding supported by the NMR structure of the less active Asp-58–IGF-1 variant. Computational analyses indicated that the aforementioned mutations can affect internal insulin dynamics and inhibit adoption of a receptor-bound conformation, important for binding to receptor site 1. We provide a molecular model and alternative hypotheses for how the mutated insulin residues affect activity.

Degradation of splicing factor SRSF3 contributes to progressive liver disease

Serine rich splicing factor 3 (SRSF3) plays a critical role in liver function and its loss promotes chronic liver damage and regeneration. As a consequence, genetic deletion of SRSF3 in hepatocytes caused progressive liver disease and ultimately led to hepatocellular carcinoma. Here we show that SRSF3 is decreased in human liver samples with non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), or cirrhosis that was associated with alterations in RNA splicing of known SRSF3 target genes. Hepatic SRSF3 expression was similarly decreased and RNA splicing dysregulated in mouse models of NAFLD and NASH. We showed that palmitic acid-induced oxidative stress caused conjugation of the ubiquitin like NEDD8 protein to SRSF3 and proteasome mediated degradation. SRSF3 was selectively neddylated at lysine11 and mutation of this residue (SRSF3-K11R) was sufficient to prevent both SRSF3 degradation and alterations in RNA splicing. Finally prevention of SRSF3 degradation in vivo partially protected mice from hepatic steatosis, fibrosis and inflammation. These results highlight a neddylation-dependent mechanism regulating gene expression in the liver that is disrupted in early metabolic liver disease and may contribute to the progression to NASH, cirrhosis and ultimately hepatocellular carcinoma.

Meta-analysis of mammary RNA seq datasets reveals the molecular understanding of bovine lactation biology

A better understanding of the biology of lactation, both in terms of gene expression and the identification of candidate genes for the production of milk and its components, is made possible by recent advances in RNA seq technology. The purpose of this study was to understand the synthesis of milk components and the molecular pathways involved, as well as to identify candidate genes for milk production traits within whole mammary transcriptomic datasets. We performed a meta-analysis of publically available RNA seq transcriptome datasets of mammary tissue/milk somatic cells. In total, 11 562 genes were commonly identified from all RNA seq based mammary gland transcriptomes. Functional annotation of commonly expressed genes revealed the molecular processes that contribute to the synthesis of fats, proteins, and lactose in mammary secretory cells and the molecular pathways responsible for milk synthesis. In addition, we identified several candidate genes responsible for milk production traits and constructed a gene regulatory network for RNA seq data. In conclusion, this study provides a basic understanding of the lactation biology of cows at the gene expression level.

Copy number variation (CNV) in the IGF1R gene across four cattle breeds and its association with economic traits

The insulin-like growth factor 1 receptor (IGF1R) plays a vital role in immunomodulation and muscle and bone growth. The copy number variation (CNV) is believed to the reason for many complex phenotypic variations. In this paper, we statistically analyzed the copy number and the expression profiling in different tissue types of the IGF1R gene using the 422 samples from four Chinese beef cattle breeds, and the mRNA of IGF1R was widely expressed in nine tissue types of adult cattle (heart, liver, kidney, muscle, fat, stomach, spleen, lung and testis). Results of CNV and growth traits indicated that the IGF1R CNV was significantly associated with body weight and body height of Jinnan (JN) cattle and was significantly associated with body height and hucklebone width of Qinchuan (QC) cattle, making IGF1R CNV a promising molecular marker to improve meat production in beef cattle breeding. Bioinformatics predictions show that the CNV region is highly similar to the human genome, and there are a large number of transcription factors, DNase I hypersensitive sites, and high levels of histone acetylation, suggesting that this region may play a role in transcriptional regulation, providing directions for further study of the role of bovine CNV and economic traits.

Effects of obesity on insulin: insulin-like growth factor 1 hybrid receptor expression and Akt phosphorylation in conduit and resistance arteries

Insulin and insulin-like growth factor-1 stimulate specific responses in arteries, which may be disrupted by diet-induced obesity. We examined (1) temporal effects of high-fat diet compared to low-fat diet in mice on insulin receptor, insulin-like growth factor-1 receptor, insulin receptor/insulin-like growth factor-1 receptor hybrid receptor expression and insulin/insulin-like growth factor-1-mediated Akt phosphorylation in aorta; and (2) effects of high-fat diet on insulin and insulin-like growth factor-1-mediated Akt phosphorylation and vascular tone in resistance arteries. Medium-term high-fat diet (5 weeks) decreased insulin-like growth factor-1 receptor expression and increased hybrid expression (~30%) only. After long-term (16 weeks) high-fat diet, insulin receptor expression was reduced by ~30%, insulin-like growth factor-1 receptor expression decreased a further ~40% and hybrid expression increased a further ~60%. Independent correlates of hybrid receptor expression were high-fat diet, duration of high-fat diet and plasma insulin-like growth factor-1 (all p < 0.05). In aorta, insulin was a more potent activator of Akt than insulin-like growth factor-1, whereas in resistance arteries, insulin-like growth factor-1 was more potent than insulin. High-fat diet blunted insulin-mediated vasorelaxation ( p < 0.01) but had no effect on insulin-like growth factor-1-mediated vasorelaxation in resistance arteries. Our findings support the possibility that hybrid receptor level is influenced by nutritional and metabolic cues. Moreover, vessel-dependent effects of insulin and insulin-like growth factor-1 on vascular tone and Akt activation may have implications in treating obesity-related vascular disease.

Insulin Receptor Isoforms in Cancer

The insulin receptor (IR) mediates both metabolic and mitogenic effects especially when overexpressed or in clinical conditions with compensatory hyperinsulinemia, due to the metabolic pathway resistance, as obesity diabetes. In many cancers, IR is overexpressed preferentially as IR-A isoform, derived by alternative splicing of exon 11. The IR-A overexpression, and the increased IR-A:IR-B ratio, are mechanisms that promote the mitogenic response of cancer cells to insulin and IGF-2, which is produced locally by both epithelial and stromal cancer cells. In cancer IR-A, isoform predominance may occur for dysregulation at both mRNA transcription and post-transcription levels, including splicing factors, non-coding RNAs and protein degradation. The mechanisms that regulate IR isoform expression are complex and not fully understood. The IR isoform overexpression may play a role in cancer cell stemness, in tumor progression and in resistance to target therapies. From a clinical point of view, the IR-A overexpression in cancer may be a determinant factor for the resistance to IGF-1R target therapies for this issue. IR isoform expression in cancers may have the meaning of a predictive biomarker and co-targeting IGF-1R and IR-A may represent a new more efficacious treatment strategy.

A versatile insulin analog with high potency for both insulin and insulin-like growth factor 1 receptors: Structural implications for receptor binding

Insulin and insulin-like growth factor 1 (IGF-1) are closely related hormones involved in the regulation of metabolism and growth. They elicit their functions through activation of tyrosine kinase–type receptors: insulin receptors (IR-A and IR-B) and IGF-1 receptor (IGF-1R). Despite similarity in primary and three-dimensional structures, insulin and IGF-1 bind the noncognate receptor with substantially reduced affinity. We prepared [d-His^B24, Gly^B31, Tyr^B32]-insulin, which binds all three receptors with high affinity (251 or 338% binding affinity to IR-A respectively to IR-B relative to insulin and 12.4% binding affinity to IGF-1R relative to IGF-1). We prepared other modified insulins with the aim of explaining the versatility of [d-His^B24, Gly^B31, Tyr^B32]-insulin. Through structural, activity, and kinetic studies of these insulin analogs, we concluded that the ability of [d-His^B24, Gly^B31, Tyr^B32]-insulin to stimulate all three receptors is provided by structural changes caused by a reversed chirality at the B24 combined with the extension of the C terminus of the B chain by two extra residues. We assume that the structural changes allow the directing of the B chain C terminus to some extra interactions with the receptors. These unusual interactions lead to a decrease of dissociation rate from the IR and conversely enable easier association with IGF-1R. All of the structural changes were made at the hormones' Site 1, which is thought to interact with the Site 1 of the receptors. The results of the study suggest that merely modifications of Site 1 of the hormone are sufficient to change the receptor specificity of insulin.

IGF1 receptor and thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a vexing and poorly understood autoimmune process involving the upper face and tissues surrounding the eyes. In TAO, the orbit can become inflamed and undergo substantial remodeling that is disfiguring and can lead to loss of vision. There are currently no approved medical therapies for TAO, the consequence of its uncertain pathogenic nature. It usually presents as a component of the syndrome known as Graves' disease where loss of immune tolerance to the thyrotropin receptor (TSHR) results in the generation of activating antibodies against that protein and hyperthyroidism. The role for TSHR and these antibodies in the development of TAO is considerably less well established. We have reported over the past 2 decades evidence that the insulin-like growth factorI receptor (IGF1R) may also participate in the pathogenesis of TAO. Activating antibodies against IGF1R have been detected in patients with GD. The actions of these antibodies initiate signaling in orbital fibroblasts from patients with the disease. Further, we have identified a functional and physical interaction between TSHR and IGF1R. Importantly, it appears that signaling initiated from either receptor can be attenuated by inhibiting the activity of IGF1R. These findings underpin the rationale for therapeutically targeting IGF1R in active TAO. A recently completed therapeutic trial of teprotumumab, a human IGF1R inhibiting antibody, in patients with moderate to severe, active TAO, indicates the potential effectiveness and safety of the drug. It is possible that other autoimmune diseases might also benefit from this treatment strategy.

Insulin-like growth factor-1 (IGF1) in systemic lupus erythematosus: relation to disease activity, organ damage and immunological findings

Background Insulin growth factor-1 (IGF1) activates cell proliferation pathways and inhibits apoptosis. IGF1 is involved in tumour growth and required for T-cell independent activation of B cells. Activated B cells and autoantibody production are a hallmark of systemic lupus erythematosus (SLE). To investigate the possible role of IGF1 in SLE, we studied IGF1 across clinical characteristics, immunological biomarkers, disease activity and organ damage in SLE patients. Method In a cross-sectional study, we collected clinical characteristics, medication, disease activity (SLEDAI-2K) and organ damage (SDI) for 94 SLE patients. Autoantibodies and cytokines were measured by ELISA, and levels of IGF1 and IGF binding protein 3 (IGFBP3) by chemiluminescence. Free IGF1 was estimated by the IGF1:IGFBP3 ratio. Healthy controls served as a comparator group. Results There was a significant age-related decline in IGF1, IGFBP3 and free IGF1 (IGF1:IGFBP3 ratio) that was similar in SLE patients and controls with very few outliers. Free IGF1 was inversely related to blood pressure (Rs -0.327, p < 0.01) and HbA1c (Rs -0.31, p < 0.01). Free IGF1 was higher in disease-modifying antirheumatic drug-treated patients ( p < 0.01), but there was no significant association between the IGF1 axis and autoantibody profiles, cytokine levels or SLEDAI-2K or SDI categories. IGF1 correlated inversely with BAFF level and B, natural killer and CD8 + cell counts. Conclusion Free IGF1 levels in SLE patients declined appropriately with age. IGF1 levels were not associated with disease activity, severity or autoantibody levels in SLE. Free IGF1 had positive metabolic effects in SLE and may play an indirect role in dampening the cellular immune response by downregulating B- and T-cell activity.

Expression and purification of functional insulin and insulin-like growth factor 1 holoreceptors from mammalian cells

The insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R) are receptor tyrosine kinases (RTKs) involved in the regulation of many important cellular processes. The current proposed models of activation are derived from structural studies using soluble extracellular domains and cytoplasmic tyrosine kinase domains. Preparations of full length IR and IGF1R have been hampered by the need for unconventional affinity chromatography resins and/or harsh eluting conditions. Here, we present a purification protocol to obtain full-length, detergent solubilized IR and IGF1R at quantities suitable for biochemical and structural characterization. We screened a panel of 24 structurally diverse detergents for optimal ligand activation. The receptors purified in n-dodecyl-β-D-maltoside showed ligand-stimulated autophosphorylation and kinase activity, suggesting an intact transmembrane signaling mechanism. This convenient purification protocol can be used to produce high quantities of IR, IGF1R, or other RTKs, and can be adapted for other challenging membrane proteins.

Equilibrium Ensembles for Insulin Folding from Bias-Exchange Metadynamics

Earliest events in the aggregation process, such as single molecule reconfiguration, are extremely important and the most difficult to characterize in experiments. To this end, we have used well-tempered bias exchange metadynamics simulations to determine the equilibrium ensembles of an insulin molecule under amyloidogenic conditions of low pH and high temperature. A bin-based clustering method that uses statistics accumulated in bias exchange metadynamics trajectories was employed to construct a detailed thermodynamic and kinetic model of insulin folding. The highest lifetime, lowest free-energy ensemble identified consisted of native conformations adopted by a folded insulin monomer in solution, namely, the R-, the R^f-, and the T-states of insulin. The lowest free-energy structure had a root mean square deviation of only 0.15 nm from native x-ray structure. The second longest-lived metastable state was an unfolded, compact monomer with little similarity to the native structure. We have identified three additional long-lived, metastable states from the bin-based model. We then carried out an exhaustive structural characterization of metastable states on the basis of tertiary contact maps and per-residue accessible surface areas. We have also determined the lowest free-energy path between two longest-lived metastable states and confirm earlier findings of non-two-state folding for insulin through a folding intermediate. The ensemble containing the monomeric intermediate retained 58% of native hydrophobic contacts, however, accompanied by a complete loss of native secondary structure. We have discussed the relative importance of nativelike versus nonnative tertiary contacts for the folding transition. We also provide a simple measure to determine the importance of an individual residue for folding transition. Finally, we have compared and contrasted this intermediate with experimental data obtained in spectroscopic, crystallographic, and calorimetric measurements during early stages of insulin aggregation. We have also determined stability of monomeric insulin by incubation at a very low concentration to isolate protein-protein interaction effects.

Conserved insulin signaling in the regulation of oocyte growth, development, and maturation

Insulin signaling regulates various aspects of physiology, such as glucose homeostasis and aging, and is a key determinant of female reproduction in metazoans. That insulin signaling is crucial for female reproductive health is clear from clinical data linking hyperinsulinemic and hypoinsulinemic condition with certain types of ovarian dysfunction, such as altered steroidogenesis, polycystic ovary syndrome, and infertility. Thus, understanding the signaling mechanisms that underlie the control of insulin-mediated ovarian development is important for the accurate diagnosis of and intervention for female infertility. Studies of invertebrate and vertebrate model systems have revealed the molecular determinants that transduce insulin signaling as well as which biological processes are regulated by the insulin-signaling pathway. The molecular determinants of the insulin-signaling pathway, from the insulin receptor to its downstream signaling components, are structurally and functionally conserved across evolution, from worms to mammals-yet, physiological differences in signaling still exist. Insulin signaling acts cooperatively with gonadotropins in mammals and lower vertebrates to mediate various aspects of ovarian development, mainly owing to evolution of the endocrine system in vertebrates. In contrast, insulin signaling in Drosophila and Caenorhabditis elegans directly regulates oocyte growth and maturation. In this review, we compare and contrast insulin-mediated regulation of ovarian functions in mammals, lower vertebrates, C. elegans, and Drosophila, and highlight conserved signaling pathways and regulatory mechanisms in general while illustrating insulin's unique role in specific reproductive processes.

Structure and dynamics of the insulin receptor: implications for receptor activation and drug discovery

Recently, major progress has been made in uncovering the mechanisms of how insulin engages its receptor and modulates downstream signal transduction. Here, we present in detail the current structural knowledge surrounding the individual components of the complex, binding sites, and dynamics during the activation process. A novel kinase triggering mechanism, the 'bow-arrow model', is proposed based on current knowledge and computational simulations of this system, in which insulin, after its initial interaction with binding site 1, engages with site 2 between the fibronectin type III (FnIII)-1 and -2 domains, which changes the conformation of FnIII-3 and eventually translates into structural changes across the membrane. This model provides a new perspective on the process of insulin binding to its receptor and, thus, could lead to future novel drug discovery efforts.

Expression of two insulin receptor subtypes, insra and insrb, in zebrafish (Danio rerio) ovary and involvement of insulin action in ovarian function

Present study reports differential expression of the two insulin receptor (IR) subtypes in zebrafish ovary at various stages of follicular growth and potential involvement of IR in insulin-induced oocyte maturation. The results showed that mRNA expression for IR subtypes, insra and insrb, exhibited higher levels in mid-vitellogenic (MV) and full-grown (FG) rather than pre-vitellogenic (PV) oocytes. Interestingly, compared to the levels in denuded oocytes, mRNAs for both insra and insrb were expressed at much higher level in the follicle layer harvested from FG oocytes. Immunoprecipitation using IRβ antibody could detect a protein band of desired size (∼95kDa) in FG oocyte lysates. Further, IRβ immunoreactivity was detected in ovarian tissue sections, especially at the follicle layer and oocyte membrane of MV and FG, but not PV stage oocytes. While hCG (10IU/ml) stimulation was without effect, priming with insulin (5μM) could promote oocyte maturation of MV oocytes in a manner sensitive to de novo protein and steroid biosynthesis. Compared to hCG, in insulin pre-incubated MV oocytes, stimulation with maturation inducing steroid (MIS), 17α,20β-dihydroxy-4-pregnen-3-one (DHP) elicited higher maturational response. Potential involvement of insulin-mediated action on acquisition of maturational competence and regulation of oocyte maturation was further manifested through up regulation of 20β-hydroxysteroid dehydrogenase (20β-hsd), MIS receptor (mPRα), insulin-like growth factor 3 (igf3) and IGF1 receptor (igf1rb), but not cyp19a expression in MV oocytes. Moreover, priming with anti-IRβ attenuated insulin action on meiotic G2-M1 transition indicating the specificity of insulin action and physiological relevance of IR in zebrafish ovary.

Association of Obesity-Related Metabolic Disruptions With Cancer Risk and Outcome

Over the past 40 years, the prevalence of obesity has increased epidemically worldwide, which raises significant concerns regarding public health and the associated economic burden. Obesity is a major risk factor for several conditions including cardiovascular disease and type 2 diabetes, and recent evidence suggests that obesity negatively affects cancer risk and outcome. The relationship between obesity and cancer is complex and involves multiple factors both at the systemic and cellular level. Indeed, disruptions in insulin metabolism, adipokines, inflammation, and sex hormones all contribute to the adverse effects of obesity in cancer development and progression. The focus of this review will be the impact of these systemic obesity-related factors on cancer biology, incidence, and outcome. Potential therapeutic interventions and current clinical trials targeting obesity and its associated factors will also be discussed.

Combination therapy approaches to target insulin-like growth factor receptor signaling in breast cancer

Insulin-like growth factor receptor (IGF1R) signaling as a therapeutic target has been widely studied and clinically tested. Despite the vast amount of literature supporting the biological role of IGF1R in breast cancer, effective clinical translation in targeting its activity as a cancer therapy has not been successful. The intrinsic complexity of cancer cell signaling mediated by many tyrosine kinase growth factor receptors that work together to modulate each other and intracellular downstream mediators in the cell highlights that studying IGF1R expression and activity as a prognostic factor and therapeutic target in isolation is certainly associated with problems. This review discusses the current literature and clinical trials associated with IGF-1 signaling and attempts to look at new ways of designing novel IGF1R-directed breast cancer therapy approaches to target its activity 
and/or intracellular downstream signaling pathways in IGF1R-expressing breast cancers.

Fasting modulates GH/IGF-I axis and its regulatory systems in the mammary gland of female mice: Influence of endogenous cortistatin

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are essential factors in mammary-gland (MG) development and are altered during fasting. However, no studies have investigated the alterations in the expression of GH/IGF-I and its regulatory systems (somatostatin/cortistatin and ghrelin) in MG during fasting. Therefore, this study was aimed at characterizing the regulation of GH/IGF-I/somatostatin/cortistatin/ghrelin-systems expression in MG of fasted female-mice (compared to fed-controls) and the influence of endogenous-cortistatin (using cortistatin-knockouts). Fasting decreased IGF-I while increased IGF-I/Insulin-receptors expression in MGs. Fasting provoked an increase in GH expression that might be associated to enhanced ghrelin-variants/ghrelin-O-acyl-transferase enzyme expression, while an upregulation of somatostatin-receptors was observed. However, cortistatin-knockouts mice showed a decrease in GH and somatostatin receptor-subtypes expression. Altogether, we demonstrate that GH/IGF-I, somatostatin/cortistatin and ghrelin systems expression is altered in MG during fasting, suggesting a relevant role in coordinating its response to metabolic stress, wherein endogenous cortistatin might be essential for an appropriate response.

Probing Receptor Specificity by Sampling the Conformational Space of the Insulin-like Growth Factor II C-domain

Insulin and insulin-like growth factors I and II are closely related protein hormones. Their distinct evolution has resulted in different yet overlapping biological functions with insulin becoming a key regulator of metabolism, whereas insulin-like growth factors (IGF)-I/II are major growth factors. Insulin and IGFs cross-bind with different affinities to closely related insulin receptor isoforms A and B (IR-A and IR-B) and insulin-like growth factor type I receptor (IGF-1R). Identification of structural determinants in IGFs and insulin that trigger their specific signaling pathways is of increasing importance in designing receptor-specific analogs with potential therapeutic applications. Here, we developed a straightforward protocol for production of recombinant IGF-II and prepared six IGF-II analogs with IGF-I-like mutations. All modified molecules exhibit significantly reduced affinity toward IR-A, particularly the analogs with a Pro-Gln insertion in the C-domain. Moreover, one of the analogs has enhanced binding affinity for IGF-1R due to a synergistic effect of the Pro-Gln insertion and S29N point mutation. Consequently, this analog has almost a 10-fold higher IGF-1R/IR-A binding specificity in comparison with native IGF-II. The established IGF-II purification protocol allowed for cost-effective isotope labeling required for a detailed NMR structural characterization of IGF-II analogs that revealed a link between the altered binding behavior of selected analogs and conformational rearrangement of their C-domains.

Insulin binding characteristics in canine muscle tissue: effects of the estrous cycle phases

Abstract: Hormonal fluctuations during the different estrous cycle are a well-recognized cause of insulin resistance in bitches, and little is known about insulin receptor binding or post-binding defects associated with insulin resistance in dogs. To evaluate insulin binding characteristics in muscle tissue of bitches during the estrous cycle, 17 owned bitches were used in the study (six in anestrus, five in estrus, and six in diestrus). An intravenous glucose tolerance test (IVGTT) was performed in all patients by means of injection of 1mL/kg of a glucose 50% solution (500mg/kg), with blood sample collection for glucose determination at 0, 3, 5, 7, 15, 30, 45 and 60 minutes after glucose infusion. Muscle samples, taken after spaying surgery, were immediately frozen in liquid nitrogen and then stored at -80 ºC until the membranes were prepared by sequential centrifugation after being homogenized. For binding studies, membranes were incubated in the presence of 20,000cpm of human 125I-insulin and in increasing concentrations of unlabeled human regular insulin for cold saturation. The IVGTT showed no differences among bitches during the estrous cycle regarding baseline glycemia or glycemic response after glucose infusion. Two insulin binding sites - high-affinity and low-affinity ones - were detected by Scatchard analysis, and significant statistical differences were observed in the dissociation constant (Kd1) and maximum binding capacity (Bmax1) of the high-affinity binding sites. The Kd1 for the anestrus group (6.54±2.77nM/mg of protein) was smaller (P<0.001) than for the estrus (28.54±6.94nM/mg of protein) and diestrus (15.56±3.88nM/mg of protein) groups. Bmax1 in the estrus (0.83±0.42nM/mg of protein) and diestrus (1.24±0.24nM/mg of protein) groups were also higher (P<0.001) than the values observed in anestrus (0.35±0.06nM/mg of protein). These results indicate modulation of insulin binding characteristics during different phases of the estrous cycle in dogs, showing that muscle insulin binding affinity for its receptor is reduced during estrus and diestrus. However, this poor hormone-receptor affinity is compensated for by a greater total binding capacity, once there is no difference in patients' glycemic response after an intravenous glucose load.

Insulin receptor isoforms: an integrated view focused on gestational diabetes mellitus

The human insulin receptor (IR) exists in two isoforms that differ by the absence (IR-A) or the presence (IR-B) of a 12-amino acid segment encoded by exon 11. Both isoforms are functionally distinct regarding their binding affinities and intracellular signalling. However, the underlying mechanisms related to their cellular functions in several tissues are only partially understood. In this review, we summarize the current knowledge in this field regarding the alternative splicing of IR isoform, tissue-specific distribution and signalling both in physiology and disease, with an emphasis on the human placenta in gestational diabetes mellitus (GDM). Furthermore, we discuss the clinical relevance of IR isoforms highlighted by findings that show altered insulin signalling due to differential IR-A and IR-B expression in human placental endothelium in GDM pregnancies. Future research and clinical studies focused on the role of IR isoform signalling might provide novel therapeutic targets for treating GDM to improve the adverse maternal and neonatal outcomes.

Polymorphism in exon 2 encoding the putative ligand binding pocket of the bovine insulin-like growth factor 1 receptor affects milk traits in four different cattle breeds

As a member of the somatotropic axis, insulin-like growth factor I receptor (IGF1R) seems to be a promising candidate gene. Two silent polymorphisms, identified by MspI and TaqI restriction enzymes, were selected within exon 2, encoding the majority of the putative ligand binding pocket. A total of 1169 cows of four pure breeds (Polish Holstein Friesian, Montbeliarde, Jersey and Holstein Friesian) were genotyped. The T (IGF1R/e2/MspI) and G (IGF1R/e2/TaqI) alleles were found to be prevalent. Three combinations of genotypes (TT/GG, TT/AG and CT/GG) were associated with the highest productivity (milk, protein and fat yields) among all breeds under study, as opposed to individuals carrying the worst CC/AA combination. In view of the specific structure of the ligand binding pocket and the significance of insulin-like growth factor I signalling promoting the development and differentiation in a variety of tissues (not only limited to mammary gland), the existence of missense mutation is unlikely. Potential mutations are likely limited to mRNA transcription and further post-transcriptional modifications. Further investigations should follow searching for the most useful IGF1R haplotypes, associated with higher milk production traits, exerting at the same time positive or neutral impact on health and welfare of individuals.

Are all regions of folded proteins that undergo ligand-dependent order-disorder transitions targets for allosteric peptide mimetics?

Although the classical view of how proteins function relied on well folded structures, it is now recognized that the functions of many proteins are dependent on being intrinsically disordered. The primary consideration in this work is the intermediate group of proteins that are overall well folded, but which contain small regions that undergo order-disorder transitions. In particular, the current focus is on those order-disorder transitions that are energetically coupled to ligand binding. As exemplified by the case of human liver pyruvate kinase (hL-PYK), peptides that mimic the sequence of the order-disorder region can be used as allosteric regulators of the enzyme. On the basis of this example and others reported in the literature, we propose that a similar use of peptides that mimic protein regions that experience ligand-dependent order-disorder transitions can be a generalized initiation point for the development of allosteric drugs.

Genomic organization and expression of insulin receptors in grass carp, Ctenopharyngodon idellus

Insulin receptors have been demonstrated to be involved in embryogenesis, food intake regulation and glucose metabolism in several fish, while more researchis needed for further understanding. In this study, the complete coding sequence (CDS) of insulin receptor a (insra) gene and insulin receptor b (insrb) gene in grass carp were obtained, the CDS were 4068 bp and 4514 bp in length, encoding 1355 aa protein and 1351 aa protein. Both of insra and insrb in grass carp showed high amino acid identities with other fish. Insra and insrb genes were widely expressed in all tested tissues with an overlapping but distinct expressions. The high levels of insra mRNA were distributed in hindgut and heart tissues. The insrb gene showed the highest expression levels in liver and hindgut. We also proved that two forms of grass carp insulin receptors participate in the regulation of blood glucose and might act differently. Phylogenetic analysis confirmed that different isoforms of fish insulin receptors are derived from two distinct genes, which was inconsistent with the generation of mammalian insulin receptors. Synteny analyses of insulin receptor genes showed that genes surrounding the insulin receptor genes were conserved in fish. Arhgef18, PEX11G, humanC19orf45 genes were highly conserved among mammal species. However, no conserved synteny was observed among fish, mammals, avians and amphibians.