Molecular Mechanisms Of Insulin Resistance Research Articles

Review article: Pathogenesis of MASLD and MASH - role of insulin resistance and lipotoxicity.

Insulin resistance and lipotoxicity are extremely interconnected but fundamental in setting the stage for the development of MASLD/MASH. A comprehensive literature search was performed and key themes were synthesised to provide insight into the underlying molecular mechanisms of insulin resistance and lipotoxicity in the liver, muscle, pancreas and adipose tissue and how organ cross-talk is fundamental to driving disease pathogenesis. Classical thinking postulates that excess FFA load exceeds the storage capacity of adipose tissue, which is predicated upon both genetic and environmental factors. This results in insulin resistance and compensatory hyperinsulinaemia by pancreatic beta cells to overcome target organ insulin resistance. As adipocyte dysfunction worsens, not only are excess FFA delivered to other organs, including skeletal muscle, pancreas and liver but a pro-inflammatory milieu is established with increases in IL-6, TNF-α and changes in adipokine levels (increased leptin and decreased adiponectin). With increased intramuscular lipid accumulation, lipotoxic species decrease insulin signalling, reduce glucose uptake by downregulation of GLUT4 and decrease glycogen synthesis. With this additional reduced capacity, hyperglycaemia is further exacerbated and increased FFA are delivered to the liver. The liver has the largest capacity to oxidise fat and to adapt to these stressors and, therefore, has become the last line of defence for excess lipid storage and utilisation, the capacity of which may be impacted by genetic and environmental factors. However, when the liver can no longer keep up with increasing FFA delivery and DNL, lipotoxic species accumulate with ensuing mitochondrial dysfunction, increased ER stress, oxidant stress and inflammasome activation, all of which drive hepatocyte injury and apoptosis. The resulting wound healing response, marked by stellate cell activation, drives collagen accumulation, progressive fibrosis, and, ultimately, end organ failure and death. This vicious cycle and complex interplay between insulin resistance, hyperinsulinaemia, lipotoxicity and multi-directional cross-talk among different target organs are critical drivers of MASLD/MASH. Targeting tissue-specific insulin resistance and hyperinsulinaemia while decreasing FFA load (lipotoxicity) through dietary and lifestyle changes remain the best upstream interventions.

Cellular and Molecular Mechanisms of Insulin Resistance

Abstract Purpose of Review Although the molecular mechanism of insulin resistance involves multiple factors and several intrinsic and extrinsic mechanisms have been identified, this comprehensive review provides key information on some of the core mechanisms and complex interactions of the molecules involved in the signaling pathways of insulin resistance. Recent Findings Diabetes Mellitus, the most common metabolic disorder, is one of the greatest global medical challenges at present. There has been a significant increase in complications associated with diabetes such as heart disorders, stroke, neuropathy, dyslipidemia, metabolic dysfunction-associated steatotic liver disease, and nephropathy. This calls for immediate strategic action to combat this complex metabolic disorder. Insulin resistance, a characteristic marker of type 2 diabetes is a condition in which the regulation of glucose metabolism in body tissues, such as the liver, adipose tissue, and skeletal muscle, becomes disrupted. It is generally associated with hyperglycemia, hyperinsulinemia, hyperlipidemia, and impaired glucose homeostasis. Summary Understanding the pathophysiological molecular mechanisms involved in insulin resistance is critical for developing new therapeutic strategies to treat this polygenic multifactorial condition. Impairment of insulin action is caused by several factors such as lipotoxicity, increased adiposity, enhanced inflammatory signaling, endoplasmic reticulum stress, adipokines, mitochondrial dysfunction, increased free fatty acids, and dysfunctional insulin signaling.

Exploration of the molecular mechanism of insulin resistance in adipose tissue of patients with type 2 diabetes mellitus through a bioinformatic analysis.

We aimed to determine the cis-expression Quantitative Trait Loci (cis-eQTL) and trans-eQTL of differentially expressed genes (DEGs) in insulin resistance (IR) related pathways. The expression profile data for insulin sensitivity (IS) and IR in the adipose tissue of patients with type 2 diabetes mellitus (T2DM) were acquired from the Gene Expression Omnibus databases. Then, the Gene set enrichment analysis (GSEA) and Gene set variation analysis (GSVA) methods were performed to identify the significant enrichment of potential Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways between IS and IR groups, and the Wilcoxon rank sum test was carried out to identify the DEGs related to KEGG pathways. Finally, the cis-eQTLs and trans-eQTLs that can affect the expression of DEGs were screened from the eQTLGen database. The GSEA and GSVA analysis indicated that the mTOR signaling pathway, insulin signaling pathway and T2DM had a strong correlation with the pathological process of T2DM. Furthermore, six genes (ACACA, GYS2, PCK1, PRKAR1A, SLC2A4, and VEGFA) were found to be significantly differentially expressed in IR-related pathways. Finally, we have identified a total of 1073 cis-eQTLs and 24 trans-eQTLs. We screened out six genes that were significantly differentially expressed in IR-related pathways, including ACACA, GYS2, PCK1, PRKAR1A, SLC2A4, and VEGFA. Moreover, we discovered that these six genes were affected by 1073 cis-eQTLs and 24 trans-eQTLs.

Insulin Resistance in Mitochondrial Diabetes

Mitochondrial diabetes (MD) is generally classified as a genetic defect of β-cells. The main pathophysiology is insulin secretion failure in pancreatic β-cells due to impaired mitochondrial ATP production. However, several reports have mentioned the presence of insulin resistance (IR) as a clinical feature of MD. As mitochondrial dysfunction is one of the important factors causing IR, we need to focus on IR as another pathophysiology of MD. In this special issue, we first briefly summarized the insulin signaling and molecular mechanisms of IR. Second, we overviewed currently confirmed pathogenic mitochondrial DNA (mtDNA) mutations from the MITOMAP database. The variants causing diabetes were mostly point mutations in the transfer RNA (tRNA) of the mitochondrial genome. Third, we focused on these variants leading to the recently described "tRNA modopathies" and reviewed the clinical features of patients with diabetes. Finally, we discussed the pathophysiology of MD caused by mtDNA mutations and explored the possible mechanism underlying the development of IR. This review should be beneficial to all clinicians involved in diagnostics and therapeutics related to diabetes and mitochondrial diseases.

Current Studies on Molecular Mechanisms of Insulin Resistance.

Diabetes is a metabolic disease that raises the risk of microvascular and neurological disorders. Insensitivity to insulin is a characteristic of type II diabetes, which accounts for 85-90 percent of all diabetic patients. The fundamental molecular factor of insulin resistance may be impaired cell signal transduction mediated by the insulin receptor (IR). Several cell-signaling proteins, including IR, insulin receptor substrate (IRS), and phosphatidylinositol 3-kinase (PI3K), have been recognized as being important in the impaired insulin signaling pathway since they are associated with a large number of proteins that are strictly regulated and interact with other signaling pathways. Many studies have found a correlation between IR alternative splicing, IRS gene polymorphism, the complicated regulatory function of IRS serine/threonine phosphorylation, and the negative regulatory role of p85 in insulin resistance and diabetes mellitus. This review brings up-to-date knowledge of the roles of signaling proteins in insulin resistance in order to aid in the discovery of prospective targets for insulin resistance treatment.

Reduced Tyrosine and Serine-632 Phosphorylation of Insulin Receptor Substrate-1 in the Gastrocnemius Muscle of Obese Zucker Rat.

Obesity has become a serious health problem in the world, with increased morbidity, mortality, and financial burden on patients and health-care providers. The skeletal muscle is the most extensive tissue, severely affected by a sedentary lifestyle, which leads to obesity and type 2 diabetes. Obesity disrupts insulin signaling in the skeletal muscle, resulting in decreased glucose disposal, a condition known as insulin resistance. Although there is a large body of evidence on obesity-induced insulin resistance in various skeletal muscles, the molecular mechanism of insulin resistance due to a disruption in insulin receptor signaling, specifically in the gastrocnemius skeletal muscle of obese Zucker rats (OZRs), is not fully understood. This study subjected OZRs to a glucose tolerance test (GTT) to analyze insulin sensitivity. In addition, immunoprecipitation and immunoblotting techniques were used to determine the expression and tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and insulin receptor-β (IRβ), and the activation of serine-632-IRS-1 phosphorylation in the gastrocnemius muscle of Zucker rats. The results show that the GTT in the OZRs was impaired. There was a significant decrease in IRS-1 levels, but no change was observed in IRβ in the gastrocnemius muscle of OZRs, compared to Zucker leans. Obese rats had a higher ratio of tyrosine phosphorylation of IRS-1 and IRβ than lean rats. In obese rats, however, insulin was unable to induce tyrosine phosphorylation. Moreover, insulin increased the phosphorylation of serine 632-IRS-1 in the gastrocnemius muscle of lean rats. However, obese rats had a low basal level of serine-632-IRS-1 and insulin only mildly increased serine phosphorylation in obese rats, compared to those without insulin. Thus, we addressed the altered steps of the insulin receptor signal transduction in the gastrocnemius muscle of OZRs. These findings may contribute to a better understanding of human obesity and type 2 diabetes.

Sexual dimorphism in the molecular mechanisms of insulin resistance during a critical developmental window in Wistar rats

BackgroundInsulin resistance (IR) is a condition in which the response of organs to insulin is impaired. IR is an early marker of metabolic dysfunction. However, IR also appears in physiological contexts during critical developmental windows. The molecular mechanisms of physiological IR are largely unknown in both sexes. Sexual dimorphism in insulin sensitivity is observed since early stages of development. We propose that during periods of accelerated growth, such as around weaning, at postnatal day 20 (p20) in rats, the kinase S6K1 is overactivated and induces impairment of insulin signaling in its target organs. This work aimed to characterize IR at p20, determine its underlying mechanisms, and identify whether sexual dimorphism in physiological IR occurs during this stage.MethodsWe determined systemic insulin sensitivity through insulin tolerance tests, glucose tolerance tests, and blood glucose and insulin levels under fasting and fed conditions at p20 and adult male and female Wistar rats. Furthermore, we quantified levels of S6K1 phosphorylated at threonine 389 (T389) (active form) and its target IRS1 phosphorylated at serine 1101 (S1101) (inhibited form). In addition, we assessed insulin signal transduction by measuring levels of Akt phosphorylated at serine 473 (S473) (active form) in white adipose tissue and skeletal muscle through western blot. Finally, we determined the presence and function of GLUT4 in the plasma membrane by measuring the glucose uptake of adipocytes. Results were compared using two-way ANOVA (With age and sex as factors) and one-way ANOVA with post hoc Tukey’s tests or t-student test in each corresponding case. Statistical significance was considered for P values < 0.05.ResultsWe found that both male and female p20 rats have elevated levels of glucose and insulin, low systemic insulin sensitivity, and glucose intolerance. We identified sex- and tissue-related differences in the activation of insulin signaling proteins in p20 rats compared to adult rats.ConclusionsMale and female p20 rats present physiological insulin resistance with differences in the protein activation of insulin signaling. This suggests that S6K1 overactivation and the resulting IRS1 inhibition by phosphorylation at S1101 may modulate to insulin sensitivity in a sex- and tissue-specific manner.1x839z9cy-UAMHakhorVgrVideo

Sirt3 negatively regulates Glut4 in skeletal muscle insulin resistance in old male offspring rats fed with maternal high fat diet

High fat (HF) diet intake during pregnancy is linked to insulin resistance (IR) in offspring, but the molecular mechanism still needs to be clarified. In the present study, pregnant rats were fed either HF diet (45% energy from fat) or normal control (CON) diet (10% energy from fat) during gestation from day 5–21. Experiments were performed in 20 months old male offspring rats. The results showed that the fasting insulin levels of old male offspring in HF increased compared with CON. However, the fasting glucose levels was unchanged. Besides, the glucose tolerance tests (GTTs) and insulin tolerance tests (ITTs) were impaired, and the AUC of GTT in HF and CON was 44.62±5.12, 33.58±3.98, with significant differences (P<.05). Furthermore, the AUC of ITT in HF and CON was 16.62±2.07 and 12.44±2.28, which showed an obvious difference (P<.05). Additionally, Sirt3 transcript and protein expressions were found up-regulated in both of the HF old male offspring skeletal muscle (1.42-fold) (P<.05) and palmitic acid (PA) treated L6 myotubes (1.32-fold) (P<.05), accompanied with increase in nicotinamide adenine dinucleotide (NAD+) in HF old male offspring skeletal muscle (P<.05). What's more, Glut4 transcript and protein expressions were found decreased significantly in both of the HF old male offspring skeletal muscle (0.45-fold) (P<.01) and PA treated L6 myotubes (0.49-fold) (P<.01). Transfection of Sirt3 gene in differentiated L6 myocytes indicated that Sirt3 negatively regulated Glut4 in L6 cells. However, AcK-103 protein, an indicator of acetylation, was found decreased in HF old male offspring skeletal muscle and L6 myotubes as a result of up-regulation of Sirt3 (P<.05). Thus, our findings suggest that HF diet intake during pregnancy induced IR in the skeletal muscle of old male offspring rats, probably occurred through Sirt3-Glut4 retrograde regulation, providing novel information concerning the molecular mechanism of IR in old male offspring rats.

Reversible insulin resistance in muscle and fat unrelated to the metabolic syndrome in patients with acromegaly.

SummaryBackgroundPatients with active acromegaly exhibit insulin resistance despite a lean phenotype whereas controlled disease improves insulin sensitivity and increases fat mass. The mechanisms underlying this paradox remain elusive, but growth hormone (GH)-induced lipolysis plays a central role. The aim of the study was to investigative the molecular mechanisms of insulin resistance dissociated from obesity in patients with acromegaly.MethodsIn a prospective study, twenty-one patients with newly diagnosed acromegaly were studied at diagnosis and after disease control obtained by either surgery alone (n=10) or somatostatin analogue (SA) treatment (n=11) with assessment of body composition (DXA scan), whole body and tissue-specific insulin sensitivity and GH and insulin signalling in adipose tissue and skeletal muscle.FindingsDisease control of acromegaly significantly reduced lean body mass (p<0.001) and increased fat mass (p<0.001). At diagnosis, GH signalling (pSTAT5) was constitutively activated in fat and enhanced expression of GH-regulated genes (CISH and IGF-I) were detected in muscle and fat. Insulin sensitivity in skeletal muscle, liver and adipose tissue increased after disease control regardless of treatment modality. This was associated with enhanced insulin signalling in both muscle and fat including downregulation of phosphatase and tensin homolog (PTEN) together with reduced signalling of GH and lipolytic activators in fat.InterpretationIn conclusion, the study support that uncontrolled lipolysis is a major feature of insulin resistance in active acromegaly, and is characterized by upregulation of PTEN and suppression of insulin signalling in both muscle and fat.FundingThis work was supported by a grant from the Independent Research Fund, Denmark (7016-00303A) and from the Alfred Benzon Foundation, Denmark.

Influence of potential nanopollutant fullerene C60 on physiological and biochemical responses in mammals

The progressive development of technologies in the manufacture and application of nanomaterials in almost all spheres of human life causes penetration in an organism and accumulation of nanoparticles in its cells. Determinations of the risk of using nanomaterials and mechanisms of their cytotoxicity are extremely relevant current problems that should be studied. Fullerene C60 is the most widespread nanomaterial proposed to use inhibition of tumour growth, microbial infections, and purposeful drug delivery. However, there are contradictory data on cytotoxic and/or cytoprotective effects of this fullerene. In the present paper, the action of fullerene C60 on glucose metabolism, the composition of the intestinal microbiota, and an acid-reducing balance were studied in rats. It is shown that fullerene C60 dissolved in olive oil (2 mg/kg/day) induces insulin resistance, activates the peroxidation of lipids in the brain of animals, but not in the liver, under conditions of chronic influence. In addition, fullerene C60 induced changes in the composition of the intestinal microbiota in rats. Determined disorders may be a cause of insulin production, as an adaptive response to the needs of metabolic energy under local oxidative stress in the nerve tissue. At the same time, the growth of insulin resistance can be induced by nonspecific molecular damage in biomembranes and macromolecules, including insulin receptors. In this regard, the explanation of the molecular mechanisms of insulin resistance induced by fullerene C60 together with the effect of fullerene dose will be of particular interest in further studies.

Severe insulin resistance syndromes.

Severe insulin resistance syndromes are a heterogeneous group of rare disorders characterized by profound insulin resistance, substantial metabolic abnormalities, and a variety of clinical manifestations and complications. The etiology of these syndromes may be hereditary or acquired, due to defects in insulin potency and action, cellular responsiveness to insulin, and/or aberrations in adipose tissue function or development. Over the past decades, advances in medical technology, particularly in genomic technologies and genetic analyses, have provided insights into the underlying pathophysiological pathways and facilitated the more precise identification of several of these conditions. However, the exact cellular and molecular mechanisms of insulin resistance have not yet been fully elucidated for all syndromes. Moreover, in clinical practice, many of the syndromes are often misdiagnosed or underdiagnosed. The majority of these disorders associate with an increased risk of severe complications and mortality; thus, early identification and personalized clinical management are of the essence. This Review aims to categorize severe insulin resistance syndromes by disease process, including insulin receptor defects, signaling defects, and lipodystrophies. We also highlight several complex syndromes and emphasize the need to identify patients, investigate underlying disease mechanisms, and develop specific treatment regimens.

Sexual dimorphism in insulin resistance in a metabolic syndrome rat model

ObjectiveWe assessed the sex-specific differences in the molecular mechanisms of insulin resistance in muscle and adipose tissue, in a MS rat model induced by a high sucrose diet.MethodsMale, female, and ovariectomized female Wistar rats were randomly distributed in control and high-sucrose diet (HSD) groups, supplemented for 24 weeks with 20% sucrose in the drinking water. At the end, we assessed parameters related to MS, analyzing the effects of the HSD on critical nodes of the insulin signaling pathway in muscle and adipose tissue.ResultsAt the end of the treatment, HSD groups of both sexes developed obesity, with a 15, 33 and 23% of body weight gain in male, female, and OVX groups respectively, compared with controls; mainly related to hypertrophy of peripancreatic and gonadal adipose tissue. They also developed hypertriglyceridemia, and liver steatosis, with the last being worse in the HSD females. Compared to the control groups, HSD rats had higher IL1B and TNFA levels and insulin resistance. HSD females were more intolerant to glucose than HSD males. Our observations suggest that insulin resistance mechanisms include an increase in phosphorylated AKT(S473) form in HSD male and female groups and a decrease in phosphorylated P70S6K1(T389) in the HSD male groups from peripancreatic adipose tissue. While in gonadal adipose tissue the phosphorylated form of AKT decreased in HSD females, but not in HSD males. Finally, HSD groups showed a reduction in p-AKT levels in gastrocnemius muscle.ConclusionA high-sucrose diet induces MS and insulin resistance with sex-associated differences and in a tissue-specific manner.

Gangliosides Contribute to Vascular Insulin Resistance.

Insulin in physiological concentrations is important to maintain vascular function. Moreover, vascular insulin resistance contributes to vascular impairment. In the elderly, other factors including hypertension, dyslipidemia, and chronic inflammation amplify senescence of vascular endothelial and smooth muscle cells. In turn, senescence increases the risk for vascular-related diseases such as arteriosclerosis, diabetes, and Alzheimer’s disease. Recently, it was found that GM1 ganglioside, one of the glycolipids localized on the cell membrane, mediates vascular insulin resistance by promoting senescence and/or inflammatory stimulation. First, it was shown that increased GM1 levels associated with aging/senescence contribute to insulin resistance in human aortic endothelial cells (HAECs). Second, the expression levels of gangliosides were monitored in HAECs treated with different concentrations of tumor necrosis factor-alpha (TNFα) for different time intervals to mimic in vivo acute or chronic inflammatory conditions. Third, the levels of insulin signaling-related molecules were monitored in HAECs after TNFα treatment with or without inhibitors of ganglioside synthesis. In this review, we summarize the molecular mechanisms of insulin resistance in aged/senescent and TNFα-stimulated endothelial cells mediated by gangliosides and highlight the possible roles of gangliosides in vascular insulin resistance-related diseases.

Molecular Mechanisms of Insulin Resistance in Polycystic Ovary Syndrome: Unraveling the Conundrum in Skeletal Muscle?

Polycystic ovary syndrome (PCOS) is a common endocrine condition affecting 8% to 13% of women across the lifespan. PCOS affects reproductive, metabolic, and mental health, generating a considerable health burden. Advances in treatment of women with PCOS has been hampered by evolving diagnostic criteria and poor recognition by clinicians. This has resulted in limited clinical and basic research. In this study, we provide insights into the current and future research on the metabolic features of PCOS, specifically as they relate to PCOS-specific insulin resistance (IR), that may affect the most metabolically active tissue, skeletal muscle. PCOS is a highly heritable condition, yet it is phenotypically heterogeneous in both reproductive and metabolic features. Human studies thus far have not identified molecular mechanisms of PCOS-specific IR in skeletal muscle. However, recent research has provided new insights that implicate energy-sensing pathways regulated via epigenomic and resultant transcriptomic changes. Animal models, while in existence, have been underused in exploring molecular mechanisms of IR in PCOS and specifically in skeletal muscle. Based on the latest evidence synthesis and technologies, researchers exploring molecular mechanisms of IR in PCOS, specifically in muscle, will likely need to generate new hypothesis to be tested in human and animal studies. Investigations to elucidate the molecular mechanisms driving IR in PCOS are in their early stages, yet remarkable advances have been made in skeletal muscle. Overall, investigations have thus far created more questions than answers, which provide new opportunities to study complex endocrine conditions.

Molecular mechanisms of insulin resistance and interventional effects of Chinese herbal medicine

It is considered that insulin resistance(IR)and its signaling pathway disorder are one of pathogenesis that causes insulin target-organs/issues lesions and their slow progression. The clinical diagnosis index of IR is the homeostatic model of insulin resistance(HOMA-IR)based on fasting blood-glucose and fasting serum insulin. Furthermore, the emerging IR biomarkers including adiponectin may be the references for clinical diagnosis. The influence factors of IR are obesity, chronic microinflammation and a lack of exercise. The major signaling pathways of IR include insulin receptor substrate 1(IRS1)/phosphatidylinositiol-3-kinase(PI3 K)/serine-threonine kinase(Akt)pathway, mitogen-activated protein kinase(MAPK)pathway and Smad3 pathway. In clinics, insulin sensibility and IR could be increased and improved via promoting insulin secretion and enhancing insulin signaling activation. At present, insulin sensitizers treating IR not only have the classic thiazolidinediones and its ramifications but also have the newly discovered metformin and vitamin D. In addition, it is reported that some extracts from single Chinese herbal medicine(CHM)and Chinese herbal compound prescription such as total flavone from the flowers of Abelmoschl manihot, berberine, astragalus polysaccharides and Huang-qi decoction also have the beneficial effects in ameliorating IR. In the field of chronic kidney disease, targeting a common insulin target-organs/issues lesion, the early renal damage in diabetic mellitus, the intervention studies regarding to regulating podocyte IR signaling pathways by CHM will be one of the significant directions in the future.

Alternative translation initiation of Caveolin-2 desensitizes insulin signaling through dephosphorylation of insulin receptor by PTP1B and causes insulin resistance

Insulin resistance, defined as attenuated sensitivity responding to insulin, impairs insulin action. Direct causes and molecular mechanisms of insulin resistance have thus far remained elusive. Here we show that alternative translation initiation (ATI) of Caveolin-2 (Cav-2) regulates insulin sensitivity. Cav-2β isoform yielded by ATI desensitizes insulin receptor (IR) via dephosphorylation by protein-tyrosine phosphatase 1B (PTP1B), and subsequent endocytosis and lysosomal degradation of IR, causing insulin resistance. Blockage of Cav-2 ATI protects against insulin resistance by preventing Cav-2β-PTP1B-directed IR desensitization, thereby normalizing insulin sensitivity and glucose uptake. Our findings show that Cav-2β is a negative regulator of IR signaling, and identify a mechanism causing insulin resistance through control of insulin sensitivity via Cav-2 ATI.

Molecular mechanisms of insulin resistance in 2 cases of primary insulin receptor defect-associated diseases

Defects of the insulin receptor gene ( INSR ) cause wide spectra of congenital insulin resistance. Monoallelic defects result in milder insulin-resistant diabetes mellitus with acanthosis nigricans (IRAN, type A). Whereas, leprechaunism (Donahue syndrome), the most severe condition with lethality during the infantile period is caused by biallelic defects of INSR . We detected 2 missense mutations in 2 cases of leprechaunism and IRAN, type A, and reduced mRNA expression in the leprechaunism case. We performed an in vitro analysis to confirm that the 2 missense mutations are causative. The heterozygote mutations c.3436G>A (p.Gly1146Arg) and c.294C>A (p.Ser98Arg) were identified in a male patient with IRAN, type A and a female patient with leprechaunism, respectively. Gly1146Arg was previously reported in a diabetic case without precise functional analyses, and Ser98Arg is a novel mutation. Gly1146 and Ser98 are located on the tyrosine kinase domain and ligand-binding domain of INSR, respectively, and in vitro analyses (assay for insulin binding and phosphorylation) revealed that each mutation disrupted protein functions and properties. In the leprechaunism case, mutations in INSR other than Ser98Arg were not identified, and qRT-PCR analysis revealed that mRNA expression of INSR in lymphocytes was reduced in the leprechaunism case. Our study indicates that the 2 missense mutations of INSR , Gly1146Arg, and Ser98Arg, are responsible for insulin resistance, and, suggests that mutations not contained within INSR , but leading to decreased INSR expression should be considered for the patients who show insulin resistance without any mutations in the coding sequence of INSR.

Cross-talks via mTORC2 can explain enhanced activation in response to insulin in diabetic patients.

The molecular mechanisms of insulin resistance in Type 2 diabetes have been extensively studied in primary human adipocytes, and mathematical modelling has clarified the central role of attenuation of mammalian target of rapamycin (mTOR) complex 1 (mTORC1) activity in the diabetic state. Attenuation of mTORC1 in diabetes quells insulin-signalling network-wide, except for the mTOR in complex 2 (mTORC2)-catalysed phosphorylation of protein kinase B (PKB) at Ser473 (PKB-S473P), which is increased. This unique increase could potentially be explained by feedback and interbranch cross-talk signals. To examine if such mechanisms operate in adipocytes, we herein analysed data from an unbiased phosphoproteomic screen in 3T3-L1 adipocytes. Using a mathematical modelling approach, we showed that a negative signal from mTORC1-p70 S6 kinase (S6K) to rictor–mTORC2 in combination with a positive signal from PKB to SIN1–mTORC2 are compatible with the experimental data. This combined cross-branch signalling predicted an increased PKB-S473P in response to attenuation of mTORC1 – a distinguishing feature of the insulin resistant state in human adipocytes. This aspect of insulin signalling was then verified for our comprehensive model of insulin signalling in human adipocytes. Introduction of the cross-branch signals was compatible with all data for insulin signalling in human adipocytes, and the resulting model can explain all data network-wide, including the increased PKB-S473P in the diabetic state. Our approach was to first identify potential mechanisms in data from a phosphoproteomic screen in a cell line, and then verify such mechanisms in primary human cells, which demonstrates how an unbiased approach can support a direct knowledge-based study.

Molecular mechanisms of insulin resistance in chronic kidney disease

Insulin resistance refers to reduced sensitivity of organs to insulin-initiated biologic processes that result in metabolic defects. Insulin resistance is common in patients with end-stage renal disease but also occurs in patients with chronic kidney disease (CKD), even when the serum creatinine is minimally increased. Following insulin binding to its receptor, auto-phosphorylation of the insulin receptor is followed by kinase reactions that phosphorylate insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3K) and Akt. In fact, low levels of Akt phosphorylation (p-Akt) identifies the presence of the insulin resistance that leads to metabolic defects in insulin-initiated metabolism of glucose, lipids and muscle proteins. Besides CKD, other complex conditions (e.g., inflammation, oxidative stress, metabolic acidosis, aging and excess angiotensin II) reduce p-Akt resulting in insulin resistance. Insulin resistance in each of these conditions is due to activation of different, E3 ubiquitin ligases which specifically conjugate ubiquitin to IRS-1 marking it for degradation in the ubiquitin-proteasome system (UPS). Consequently, IRS-1 degradation suppresses insulin-induced intracellular signaling, causing insulin resistance. Understanding mechanisms of insulin resistance could lead to therapeutic strategies that improve the metabolism of patients with CKD.

PCBP2 regulates hepatic insulin sensitivity via HIF-1α and STAT3 pathway in HepG2 cells

Elevated free fatty acids (FFAs) are fundamental to the pathogenesis of hepatic insulin resistance. However, the molecular mechanisms of insulin resistance remain not completely understood. Transcriptional dysregulation, post-transcriptional modifications and protein degradation contribute to the pathogenesis of insulin resistance. Poly(C) binding proteins (PCBPs) are RNA-binding proteins that are involved in post-transcriptional control pathways. However, there are little studies about the roles of PCBPs in insulin resistance. PCBP2 is the member of the RNA-binding proteins and is thought to participate in regulating hypoxia inducible factor-1 (HIF-1α) and signal transducers and activators of transcription (STAT) pathway which are involved in regulating insulin signaling pathway. Here, we investigated the influence of PCBP2 on hepatic insulin resistance. We showed that the protein and mRNA levels of PCBP2 were down-regulated under insulin-resistant conditions. In addition, we showed that over-expression of PCBP2 ameliorates palmitate (PA)-induced insulin resistance, which was indicated by elevated phosphorylation of protein kinase B (AKT) and glycogen synthase kinase 3β (GSK3β). We also found that over-expression of PCBP2 inhibits HIF1α and STAT3 pathway. Furthermore, glucose uptake was found to display a similar tendency with the phosphorylation of Akt. The expressions of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), two key gluconeogenic enzymes, were down-regulated following Over-expression of PCBP2. Accordingly, PA-induced intracellular lipid accumulation was suppressed in over-expression of PCBP2 HepG2 cells. In addition, we found that over-expression of PCBP2 inhibits HIF1α and STAT3 pathway. Our results demonstrate that PCBP2 was involved in hepatic insulin sensitivity might via HIF-1α and STAT3 pathway in HepG2 cells.