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Insulin and Insulin Receptor in Diseases

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Pathology, Diagnostics, and Therapeutics".

Deadline for manuscript submissions: closed (1 August 2018) | Viewed by 78843

Special Issue Editors

Department of Medicine, Georgetown University, Washington, DC 20007, USA
Interests: renal physiology; renal sodium transport; insulin in the kidney; blood pressure regulation; metabolic syndrome; diabetic nephropathy; sex differences in the kidney; renal gluconeogenesis
Special Issues, Collections and Topics in MDPI journals
Endocrinology Section, Department of Clinical and Experimental Medicine, Garibaldi-Nesima Medical Center, University of Catania, Catania, Italy
Interests: insulin receptor isoforms; insulin analogs; intracellular signal transduction of insulin receptor; diabetes and cancer; pregestational diabetes; gestational diabetes; type 1 diabetes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Reduced insulin receptor (Insr) signaling, especially in key metabolic tissues, i.e., the liver, skeletal muscle, and adipose, is associated with type 2 diabetes mellitus due to impaired glucose uptake in cells. However, the Insr may have important roles in other tissues, e.g., vasculature, heart, and kidney with less-defined effects. The human Insr cDNA was first cloned in 1985. The receptor is composed of two subunits: alpha and beta—both derived by the proteolytic processing of a 1382-amino acid pre-proreceptor. Insr signaling proceeds primarily through autophosphorylation on key tyrosine residues with the eventual activation of Akt kinase. On the other hand, phosphorylation of Insr on several serine residues is associated with reduced activation of this signaling cascade.

In addition, the insulin receptor exists in two isoforms (InsrA and InsrB) generated by alternative splicing of the exon 11. The two isoforms may have different tissue expression with different biological effects in several diseases. Dysregulation of the InsrA: InsrB ratio is associated with insulin resistance and increased proliferative activity of normal and neoplastic tissues.

This Special Issue focuses on Insr modifications with disease (expression, post-translational modifications, and downstream signaling), as well as hypothetical, experimental, and tested therapies to restore, alter, or enhance signaling.

We welcome submissions, including original papers and reviews, on this widely-discussed topic.

Dr. Carolyn M. Ecelbarger
Dr. Laura Sciacca
Guest Editors

Manuscript Submission Information

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Keywords

  • metabolic syndrome
  • hypertension
  • insulin resistance
  • type 2 diabetes
  • obesity
  • tyrosine-kinase receptor

Published Papers (11 papers)

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Research

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20 pages, 4341 KiB  
Article
Chronic Exposure to Palmitate Impairs Insulin Signaling in an Intestinal L-cell Line: A Possible Shift from GLP-1 to Glucagon Production
by Agnese Filippello, Francesca Urbano, Stefania Di Mauro, Alessandra Scamporrino, Antonino Di Pino, Roberto Scicali, Agata Maria Rabuazzo, Francesco Purrello and Salvatore Piro
Int. J. Mol. Sci. 2018, 19(12), 3791; https://doi.org/10.3390/ijms19123791 - 28 Nov 2018
Cited by 23 | Viewed by 3947
Abstract
Obesity and type 2 diabetes mellitus (T2DM) are characterized by insulin resistance and impaired glucagon-like peptide-1 (GLP-1) secretion/function. Lipotoxicity, a chronic elevation of free fatty acids in the blood, could affect insulin-signaling in many peripheral tissues. To date, the effects of lipotoxicity on [...] Read more.
Obesity and type 2 diabetes mellitus (T2DM) are characterized by insulin resistance and impaired glucagon-like peptide-1 (GLP-1) secretion/function. Lipotoxicity, a chronic elevation of free fatty acids in the blood, could affect insulin-signaling in many peripheral tissues. To date, the effects of lipotoxicity on the insulin receptor and insulin resistance in the intestinal L-cells need to be elucidated. Moreover, recent observations indicate that L-cells may be able to process not only GLP-1 but also glucagon from proglucagon. The aim of this study was to investigate the effects of chronic palmitate exposure on insulin pathways, GLP-1 secretion and glucagon synthesis in the GLUTag L-cell line. Cells were cultured in the presence/absence of palmitate (0.5 mM) for 24 h to mimic lipotoxicity. Palmitate treatment affected insulin-stimulated GLP-1 secretion, insulin receptor phosphorylation and IRS-1-AKT pathway signaling. In our model lipotoxicity induced extracellular signal-regulated kinase (ERK 44/42) activation both in insulin stimulated and basal conditions and also up-regulated paired box 6 (PAX6) and proglucagon expression (Gcg). Interestingly, palmitate treatment caused an increased glucagon secretion through the up-regulation of prohormone convertase 2. These results indicate that a state of insulin resistance could be responsible for secretory alterations in L-cells through the impairment of insulin-signaling pathways. Our data support the hypothesis that lipotoxicity might contribute to L-cell deregulation. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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13 pages, 3550 KiB  
Article
Chronic Insulin Infusion Down-Regulates Circulating and Urinary Nitric Oxide (NO) Levels Despite Molecular Changes in the Kidney Predicting Greater Endothelial NO Synthase Activity in Mice
by Maurice B. Fluitt, Sophia Rizvi, Lijun Li, Ashley Alunan, Hwal Lee, Swasti Tiwari and Carolyn M. Ecelbarger
Int. J. Mol. Sci. 2018, 19(10), 2880; https://doi.org/10.3390/ijms19102880 - 22 Sep 2018
Cited by 8 | Viewed by 3578
Abstract
Insulin therapy is often needed to overcome insulin receptor resistance in type 2 diabetes; however, the impact of providing additional insulin to already hyperinsulinemic subjects is not clear. We infused male TALLYHO/Jng (TH) mice (insulin resistant) with insulin (50 U/kg·bw/d) or vehicle (control) [...] Read more.
Insulin therapy is often needed to overcome insulin receptor resistance in type 2 diabetes; however, the impact of providing additional insulin to already hyperinsulinemic subjects is not clear. We infused male TALLYHO/Jng (TH) mice (insulin resistant) with insulin (50 U/kg·bw/d) or vehicle (control) by osmotic minipump for 14 days. One group of insulin-infused mice was switched to 4% NaCl diet (high-sodium diet, HSD) in the second week. Blood chemistry revealed a significantly higher anion gap and blood sodium concentrations with insulin infusion, i.e., relative metabolic acidosis. Systolic BP and heart rate were slightly (~5 mm Hg) higher in insulin-infused versus control mice. HSD resulted in a modest and transient rise in mean arterial blood pressure (BP), relative to control or insulin-infused, normal-NaCl-fed mice. In kidney, insulin infusion: (1) increased total and phosphorylated (serine-1177) endothelial nitric oxide synthase (eNOS) band densities; (2) reduced band density of the uncoupled form of eNOS; and (3) increased renal homogenate nitric oxide synthase (NOS) activity. Despite this, plasma and urine levels of nitrates plus nitrites (NOx) fell with insulin infusion, by day 14 (40–50%) suggesting worsening of resistance. Overall, insulin infusion ramps up the cellular means in kidney to increase vasodilatory and natriuretic NO, but in the long term may be associated with worsening of insulin receptor resistance. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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22 pages, 7581 KiB  
Article
Hyperinsulinemia Promotes Esophageal Cancer Development in a Surgically-Induced Duodeno-Esophageal Reflux Murine Model
by Diletta Arcidiacono, Arben Dedja, Cinzia Giacometti, Matteo Fassan, Daniele Nucci, Simona Francia, Federico Fabris, Alice Zaramella, Emily J. Gallagher, Mauro Cassaro, Massimo Rugge, Derek LeRoith, Alfredo Alberti and Stefano Realdon
Int. J. Mol. Sci. 2018, 19(4), 1198; https://doi.org/10.3390/ijms19041198 - 14 Apr 2018
Cited by 14 | Viewed by 4465
Abstract
Hyperinsulinemia could have a role in the growing incidence of esophageal adenocarcinoma (EAC) and its pre-cancerous lesion, Barrett’s Esophagus, a possible consequence of Gastro-Esophageal Reflux Disease. Obesity is known to mediate esophageal carcinogenesis through different mechanisms including insulin-resistance leading to hyperinsulinemia, which may [...] Read more.
Hyperinsulinemia could have a role in the growing incidence of esophageal adenocarcinoma (EAC) and its pre-cancerous lesion, Barrett’s Esophagus, a possible consequence of Gastro-Esophageal Reflux Disease. Obesity is known to mediate esophageal carcinogenesis through different mechanisms including insulin-resistance leading to hyperinsulinemia, which may mediate cancer progression via the insulin/insulin-like growth factor axis. We used the hyperinsulinemic non-obese FVB/N (Friend leukemia virus B strain) MKR (muscle (M)-IGF1R-lysine (K)-arginine (R) mouse model to evaluate the exclusive role of hyperinsulinemia in the pathogenesis of EAC related to duodeno-esophageal reflux. FVB/N wild-type (WT) and MKR mice underwent jejunum-esophageal anastomosis side—to end with the exclusion of the stomach. Thirty weeks after surgery, the esophagus was processed for histological, immunological and insulin/Insulin-like growth factor 1 (IGF1) signal transduction analyses. Most of the WT mice (63.1%) developed dysplasia, whereas most of the MKR mice (74.3%) developed squamous cell and adenosquamous carcinomas, both expressing Human Epidermal growth factor receptor 2 (HER2). Hyperinsulinemia significantly increased esophageal cancer incidence in the presence of duodenal-reflux. Insulin receptor (IR) and IGF1 receptor (IGF1R) were overexpressed in the hyperinsulinemic condition. IGF1R, through ERK1/2 mitogenic pattern activation, seems to be involved in cancer onset. Hyperinsulinemia-induced IGF1R and HER2 up-regulation could also increase the possibility of forming of IGF1R/HER2 heterodimers to support cell growth/proliferation/progression in esophageal carcinogenesis. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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3720 KiB  
Article
Rapid Non-Enzymatic Glycation of the Insulin Receptor under Hyperglycemic Conditions Inhibits Insulin Binding In Vitro: Implications for Insulin Resistance
by Tyler Rhinesmith, Thomas Turkette and Robert Root-Bernstein
Int. J. Mol. Sci. 2017, 18(12), 2602; https://doi.org/10.3390/ijms18122602 - 02 Dec 2017
Cited by 8 | Viewed by 4654
Abstract
The causes of insulin resistance are not well-understood in either type 1 or type 2 diabetes. Insulin (INS) is known to undergo rapid non-enzymatic covalent conjugation to glucose or other sugars (glycation). Because the insulin receptor (IR) has INS-like regions associated with both [...] Read more.
The causes of insulin resistance are not well-understood in either type 1 or type 2 diabetes. Insulin (INS) is known to undergo rapid non-enzymatic covalent conjugation to glucose or other sugars (glycation). Because the insulin receptor (IR) has INS-like regions associated with both glucose and INS binding, we hypothesize that hyperglycemic conditions may rapidly glycate the IR, chronically interfering with INS binding. IR peptides were synthesized spanning IR- associated INS-binding regions. Glycation rates of peptides under hyperglycemic conditions were followed over six days using matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. INS conjugated to horse-radish peroxidase was used to determine INS binding to IR peptides in glycated and non-glycated forms. Several IR peptides were glycated up to 14% within days of exposure to 20–60 mM glucose. Rates of IR-peptide glycation were comparable to those of insulin. Glycation of four IR peptides significantly inhibits INS binding to them. Glycation of intact IR also decreases INS binding by about a third, although it was not possible to confirm the glycation sites on the intact IR. Glycation of the IR may therefore provide a mechanism by which INS resistance develops in diabetes. Demonstration of glycation of intact IR in vivo is needed. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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Review

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20 pages, 678 KiB  
Review
Insulin and Insulin Receptors in Adipose Tissue Development
by Angelo Cignarelli, Valentina Annamaria Genchi, Sebastio Perrini, Annalisa Natalicchio, Luigi Laviola and Francesco Giorgino
Int. J. Mol. Sci. 2019, 20(3), 759; https://doi.org/10.3390/ijms20030759 - 11 Feb 2019
Cited by 128 | Viewed by 15619
Abstract
Insulin is a major endocrine hormone also involved in the regulation of energy and lipid metabolism via the activation of an intracellular signaling cascade involving the insulin receptor (INSR), insulin receptor substrate (IRS) proteins, phosphoinositol 3-kinase (PI3K) and protein kinase B (AKT). Specifically, [...] Read more.
Insulin is a major endocrine hormone also involved in the regulation of energy and lipid metabolism via the activation of an intracellular signaling cascade involving the insulin receptor (INSR), insulin receptor substrate (IRS) proteins, phosphoinositol 3-kinase (PI3K) and protein kinase B (AKT). Specifically, insulin regulates several aspects of the development and function of adipose tissue and stimulates the differentiation program of adipose cells. Insulin can activate its responses in adipose tissue through two INSR splicing variants: INSR-A, which is predominantly expressed in mesenchymal and less-differentiated cells and mainly linked to cell proliferation, and INSR-B, which is more expressed in terminally differentiated cells and coupled to metabolic effects. Recent findings have revealed that different distributions of INSR and an altered INSR-A:INSR-B ratio may contribute to metabolic abnormalities during the onset of insulin resistance and the progression to type 2 diabetes. In this review, we discuss the role of insulin and the INSR in the development and endocrine activity of adipose tissue and the pharmacological implications for the management of obesity and type 2 diabetes. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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15 pages, 1233 KiB  
Review
The Effects of Systemic and Local Acidosis on Insulin Resistance and Signaling
by Nicola Baldini and Sofia Avnet
Int. J. Mol. Sci. 2019, 20(1), 126; https://doi.org/10.3390/ijms20010126 - 30 Dec 2018
Cited by 31 | Viewed by 7095
Abstract
Most pathological conditions that cause local or systemic acidosis by overcoming the buffering activities of body fluids overlap with those diseases that are characterized by glucose metabolic disorders, including diabetes mellitus, inflammation, and cancer. This simple observation suggests the existence of a strong [...] Read more.
Most pathological conditions that cause local or systemic acidosis by overcoming the buffering activities of body fluids overlap with those diseases that are characterized by glucose metabolic disorders, including diabetes mellitus, inflammation, and cancer. This simple observation suggests the existence of a strong relationship between acidosis and insulin metabolism or insulin receptor signaling. In this review, we summarized the current knowledge on the activity of insulin on the induction of acidosis and, vice versa, on the effects of changes of extracellular and intracellular pH on insulin resistance. Insulin influences acidosis by promoting glycolysis. Although with an unclear mechanism, the lowering of pH, in turn, inhibits insulin sensitivity or activity. In addition to ketoacidosis that is frequently associated with diabetes, other important and more complex factors are involved in this delicate feedback mechanism. Among these, in this review we discussed the acid-mediated inhibiting effects on insulin binding affinity to its receptor, on glycolysis, on the recycling of glucose transporters, and on insulin secretion via transforming growth factor β (TGF-β) activity by pancreatic β-cells. Finally, we revised current data available on the mutual interaction between insulin signaling and the activity of ion/proton transporters and pH sensors, and on how acidosis may enhance insulin resistance through the Nuclear Factor kappa B (NF-κB) inflammatory pathway. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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18 pages, 1714 KiB  
Review
The Emerging Role of Insulin Receptor Isoforms in Thyroid Cancer: Clinical Implications and New Perspectives
by Veronica Vella and Roberta Malaguarnera
Int. J. Mol. Sci. 2018, 19(12), 3814; https://doi.org/10.3390/ijms19123814 - 30 Nov 2018
Cited by 32 | Viewed by 3533
Abstract
Thyroid cancer (TC) is the most common endocrine tumor. Although the majority of TCs show good prognoses, a minor proportion are aggressive and refractory to conventional therapies. So far, the molecular mechanisms underlying TC pathogenesis are incompletely understood. Evidence suggests that TC cells [...] Read more.
Thyroid cancer (TC) is the most common endocrine tumor. Although the majority of TCs show good prognoses, a minor proportion are aggressive and refractory to conventional therapies. So far, the molecular mechanisms underlying TC pathogenesis are incompletely understood. Evidence suggests that TC cells and their precursors are responsive to insulin and insulin-like growth factors (IGFs), and often overexpress receptors for insulin (IR) and IGF-1 (IGF-1R). IR exists in two isoforms, namely IR-A and IR-B. The first binds insulin and IGF-2, unlike IR-B, which only binds insulin. IR-A is preferentially expressed in prenatal life and contributes to development through IGF-2 action. Aggressive TC overexpresses IR-A, IGF-2, and IGF-1R. The over-activation of IR-A/IGF-2 loop in TC is associated with stem-like features and refractoriness to some targeted therapies. Importantly, both IR isoforms crosstalk with IGF-1R, giving rise to the formation of hybrids receptors (HR-A or HR-B). Other interactions have been demonstrated with other molecules such as the non-integrin collagen receptor, discoidin domain receptor 1 (DDR1), and the receptor for the hepatocyte growth factor (HGF), Met. These functional networks provide mechanisms for IR signaling diversification, which may also exert a role in TC stem cell biology, thereby contributing to TC initiation and progression. This review focuses on the molecular mechanisms by which deregulated IR isoforms and their crosstalk with other molecules and signaling pathways in TC cells and their precursors may contribute to thyroid carcinogenesis, progression, and resistance to conventional treatments. We also highlight how targeting these alterations starting from TC progenitors cells may represent new therapeutic strategies to improve the clinical management of advanced TCs. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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24 pages, 575 KiB  
Review
MicroRNAs as Regulators of Insulin Signaling: Research Updates and Potential Therapeutic Perspectives in Type 2 Diabetes
by Laura Nigi, Giuseppina Emanuela Grieco, Giuliana Ventriglia, Noemi Brusco, Francesca Mancarella, Caterina Formichi, Francesco Dotta and Guido Sebastiani
Int. J. Mol. Sci. 2018, 19(12), 3705; https://doi.org/10.3390/ijms19123705 - 22 Nov 2018
Cited by 69 | Viewed by 8140
Abstract
The insulin signaling pathway is composed of a large number of molecules that positively or negatively modulate insulin specific signal transduction following its binding to the cognate receptor. Given the importance of the final effects of insulin signal transduction, it is conceivable that [...] Read more.
The insulin signaling pathway is composed of a large number of molecules that positively or negatively modulate insulin specific signal transduction following its binding to the cognate receptor. Given the importance of the final effects of insulin signal transduction, it is conceivable that many regulators are needed in order to tightly control the metabolic or proliferative functional outputs. MicroRNAs (miRNAs) are small non-coding RNA molecules that negatively modulate gene expression through their specific binding within the 3′UTR sequence of messenger RNA (mRNA), thus causing mRNA decoy or translational inhibition. In the last decade, miRNAs have been addressed as pivotal cellular rheostats which control many fundamental signaling pathways, including insulin signal transduction. Several studies demonstrated that multiple alterations of miRNAs expression or function are relevant for the development of insulin resistance in type 2 diabetes (T2D); such alterations have been highlighted in multiple insulin target organs including liver, muscles, and adipose tissue. Indirectly, miRNAs have been identified as modulators of inflammation-derived insulin resistance, by controlling/tuning the activity of innate immune cells in insulin target tissues. Here, we review main findings on miRNA functions as modulators of insulin signaling in physiologic- or in T2D insulin resistance- status. Additionally, we report the latest hypotheses of prospective therapies involving miRNAs as potential targets for future drugs in T2D. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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20 pages, 6476 KiB  
Review
Insulin Receptor Isoforms in Cancer
by Veronica Vella, Agostino Milluzzo, Nunzio Massimo Scalisi, Paolo Vigneri and Laura Sciacca
Int. J. Mol. Sci. 2018, 19(11), 3615; https://doi.org/10.3390/ijms19113615 - 16 Nov 2018
Cited by 70 | Viewed by 6402
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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17 pages, 1712 KiB  
Review
Type 2 Diabetes Mellitus and Alzheimer’s Disease: Role of Insulin Signalling and Therapeutic Implications
by Andrea Tumminia, Federica Vinciguerra, Miriam Parisi and Lucia Frittitta
Int. J. Mol. Sci. 2018, 19(11), 3306; https://doi.org/10.3390/ijms19113306 - 24 Oct 2018
Cited by 157 | Viewed by 12817
Abstract
In the last two decades, numerous in vitro studies demonstrated that insulin receptors and theirs downstream pathways are widely distributed throughout the brain. This evidence has proven that; at variance with previous believes; insulin/insulin-like-growth-factor (IGF) signalling plays a crucial role in the regulation [...] Read more.
In the last two decades, numerous in vitro studies demonstrated that insulin receptors and theirs downstream pathways are widely distributed throughout the brain. This evidence has proven that; at variance with previous believes; insulin/insulin-like-growth-factor (IGF) signalling plays a crucial role in the regulation of different central nervous system (CNS) tasks. The most important of these functions include: synaptic formation; neuronal plasticity; learning; memory; neuronal stem cell activation; neurite growth and repair. Therefore; dysfunction at different levels of insulin signalling and metabolism can contribute to the development of a number of brain disorders. Growing evidences demonstrate a close relationship between Type 2 Diabetes Mellitus (T2DM) and neurodegenerative disorders such as Alzheimer’s disease. They, in fact, share many pathophysiological characteristics comprising impaired insulin sensitivity, amyloid β accumulation, tau hyper-phosphorylation, brain vasculopathy, inflammation and oxidative stress. In this article, we will review the clinical and experimental evidences linking insulin resistance, T2DM and neurodegeneration, with the objective to specifically focus on insulin signalling-related mechanisms. We will also evaluate the pharmacological strategies targeting T2DM as potential therapeutic tools in patients with cognitive impairment. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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20 pages, 2499 KiB  
Review
The Biased G-Protein-Coupled Receptor Agonism Bridges the Gap between the Insulin Receptor and the Metabolic Syndrome
by Iryna Liauchonak, Fady Dawoud, Yatin Riat, Bessi Qorri, Manpreet Sambi, Justin Jain, Regina-Veronicka Kalaydina, Nicole Mendonza, Komal Bajwa and Myron R. Szewczuk
Int. J. Mol. Sci. 2018, 19(2), 575; https://doi.org/10.3390/ijms19020575 - 17 Feb 2018
Cited by 10 | Viewed by 7201
Abstract
Insulin signaling, as mediated through the insulin receptor (IR), plays a critical role in metabolism. Aberrations in this signaling cascade lead to several pathologies, the majority of which are classified under the umbrella term “metabolic syndrome”. Although many of these pathologies are associated [...] Read more.
Insulin signaling, as mediated through the insulin receptor (IR), plays a critical role in metabolism. Aberrations in this signaling cascade lead to several pathologies, the majority of which are classified under the umbrella term “metabolic syndrome”. Although many of these pathologies are associated with insulin resistance, the exact mechanisms are not well understood. One area of current interest is the possibility of G-protein-coupled receptors (GPCRs) influencing or regulating IR signaling. This concept is particularly significant, because GPCRs have been shown to participate in cross-talk with the IR. More importantly, GPCR signaling has also been shown to preferentially regulate specific downstream signaling targets through GPCR agonist bias. A novel study recently demonstrated that this GPCR-biased agonism influences the activity of the IR without the presence of insulin. Although GPCR-IR cross-talk has previously been established, the notion that GPCRs can regulate the activation of the IR is particularly significant in relation to metabolic syndrome and other pathologies that develop as a result of alterations in IR signaling. As such, we aim to provide an overview of the physiological and pathophysiological roles of the IR within metabolic syndrome and its related pathologies, including cardiovascular health, gut microflora composition, gastrointestinal tract functioning, polycystic ovarian syndrome, pancreatic cancer, and neurodegenerative disorders. Furthermore, we propose that the GPCR-biased agonism may perhaps mediate some of the downstream signaling effects that further exacerbate these diseases for which the mechanisms are currently not well understood. Full article
(This article belongs to the Special Issue Insulin and Insulin Receptor in Diseases)
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