Structure of the insulin receptor substrate IRS-1 defines a unique signal transduction protein

Regulation and function of insulin and insulin-like growth factor receptor signalling

Receptors of insulin and insulin-like growth factors (IGFs) are receptor tyrosine kinases whose signalling controls multiple aspects of animal physiology throughout life. In addition to regulating metabolism and growth, insulin-IGF receptor signalling has recently been linked to a variety of new, cell type-specific functions. In the last century, key questions have focused on how structural differences of insulin and IGFs affect receptor activation, and how insulin-IGF receptor signalling translates into pleiotropic biological functions. Technological advances such as cryo-electron microscopy have provided a detailed understanding of how native and engineered ligands activate insulin-IGF receptors. In this Review, we highlight recent structural and functional insights into the activation of insulin-IGF receptors, and summarize new agonists and antagonists developed for intervening in the activation of insulin-IGF receptor signalling. Furthermore, we discuss recently identified regulatory mechanisms beyond ligand-receptor interactions and functions of insulin-IGF receptor signalling in diseases.

Physiological and pathophysiological actions of insulin in the liver

The liver plays an important role in the control of glucose homeostasis. When insulin levels are low, such as in the fasting state, gluconeogenesis and glycogenolysis are stimulated to maintain the blood glucose levels. Conversely, in the presence of increased insulin levels, such as after a meal, synthesis of glycogen and lipid occurs to maintain the blood glucose levels within normal range. Insulin receptor signaling regulates glycogenesis, gluconeogenesis and lipogenesis through downstream pathways such as the insulin receptor substrate (IRS)-phosphoinositide 3 (PI3) kinase-Akt pathway. IRS-1 and IRS-2 are abundantly expressed in the liver and are thought to be responsible for transmitting the insulin signal from the insulin receptor to the intracellular effectors involved in the regulation of glucose and lipid homeostasis. Impaired insulin receptor signaling can cause hepatic insulin resistance and lead to type 2 diabetes. In the present study, we focus on a concept called "selective insulin resistance," which has received increasing attention recently: the frequent coexistence of hyperglycemia and hepatic steatosis in people with type 2 diabetes and obesity suggests that it is possible for the insulin signaling regulating gluconeogenesis to be impaired even while that regulating lipogenesis is preserved, suggestive of selective insulin resistance. In this review, we review the progress in research on the insulin actions and insulin signaling in the liver.

High-fat diet and neuroinflammation: The role of mitochondria

In recent years, increasing evidence has supported that high-fat diet (HFD) can induce the chronic, low-grade neuroinflammation in the brain, which is closely associated with the impairment of cognitive function. As the key organelles responsible for energy metabolism in the cell, mitochondria are believed to involved in the pathogenesis of a variety of neurological disorders. This review summarizes the current progress in the field of the relationship between HFD exposure and neurodegenerative diseases, and outline the major routines of HFD induced neuroinflammation and its pathological significance in the pathogenesis of neurodegenerative diseases. Furthermore, the article highlights the pivotal role of mitochondrial dysfunction in driving the neuroinflammation in the setting of HFD. Danger-associated molecular patterns (DAMPs) from damaged mitochondria can activate innate immune signaling pathways, while mitochondrial dysfunction itself can lead to metabolic remodeling of inflammatory cells, thus inducing neuroinflammation. More importantly, mitochondrial damage, neuroinflammation, and insulin resistance caused by HFD form a mutually reinforcing vicious cycle, ultimately leading to the death of neurons and promoting the progression of neurodegenerative diseases. Thus, in-depth elucidation of the role and underlying mechanisms of mitochondrial dysfunction in HFD-induced metabolic disorders may not only expand our understanding of the mechanistic linkages between HFD and etiology of neurodegenerative diseases, but also help develop the specific strategies for the prevention and treatment of neurodegenerative diseases.

The role of insulin signaling with FOXO and FOXK transcription factors

Insulin is an essential hormone for animal activity and survival, and it controls the metabolic functions of the entire body. Throughout the evolution of metazoan animals and the development of their brains, a sustainable energy supply has been essential to overcoming the competition for survival under various environmental stresses. Managing energy for metabolism, preservation, and consumption inevitably involves high oxidative stress, causing tissue damage in various organs. In both mice and humans, excessive dietary intake can lead to insulin resistance in various organs, ultimately displaying metabolic syndrome and type 2 diabetes. Insulin signals require thorough regulation to maintain metabolism across diverse environments. Recent studies demonstrated that two types of forkhead-box family transcription factors, FOXOs and FOXKs, are related to the switching of insulin signals during fasting and feeding states. Insulin signaling plays a role in supporting higher activity during periods of sufficient food supply and in promoting survival during times of insufficient food supply. The insulin receptor depends on the tyrosine phosphatase feedback of insulin signaling to maintain adipocyte insulin responsiveness. α4, a regulatory subunit of protein phosphatase 2A (PP2A), has been shown to play a crucial role in modulating insulin signaling pathways by regulating the phosphorylation status of key proteins involved in these pathways. This short review summarizes the current understanding of the molecular mechanism related to the regulation of insulin signals.

CREB3 suppresses hepatocellular carcinoma progression by depressing AKT signaling through competitively binding with insulin receptor and transcriptionally activating RNA-binding motif protein 38

cAMP responsive element binding protein 3 (CREB3), belonging to bZIP family, was reported to play multiple roles in various cancers, but its role in hepatocellular carcinoma (HCC) is still unclear. cAMP responsive element binding protein 3 like 3 (CREB3L3), another member of bZIP family, was thought to be transcription factor (TF) to regulate hepatic metabolism. Nevertheless, except for being TFs, other function of bZIP family were poorly understood. In this study, we found CREB3 inhibited growth and metastasis of HCC in vitro and in vivo. RNA sequencing indicated CREB3 regulated AKT signaling to influence HCC progression. Mass spectrometry analysis revealed CREB3 interacted with insulin receptor (INSR). Mechanistically, CREB3 suppressed AKT phosphorylation by inhibiting the interaction of INSR with insulin receptor substrate 1 (IRS1). In our study, CREB3 was firstly proved to affect activation of substrates by interacting with tyrosine kinase receptor. Besides, CREB3 could act as a TF to transactivate RNA-binding motif protein 38 (RBM38) expression, leading to suppressed AKT phosphorylation. Rescue experiments further confirmed the independence between the two functional manners. In conclusion, CREB3 acted as a tumor suppressor in HCC, which inhibited AKT phosphorylation through independently interfering interaction of INSR with IRS1, and transcriptionally activating RBM38.

Regulation of placental amino acid transport in health and disease

Abnormal fetal growth, i.e., intrauterine growth restriction (IUGR) or fetal growth restriction (FGR) and fetal overgrowth, is associated with increased perinatal morbidity and mortality and is strongly linked to the development of metabolic and cardiovascular disease in childhood and later in life. Emerging evidence suggests that changes in placental amino acid transport may contribute to abnormal fetal growth. This review is focused on amino acid transport in the human placenta, however, relevant animal models will be discussed to add mechanistic insights. At least 25 distinct amino acid transporters with different characteristics and substrate preferences have been identified in the human placenta. Of these, System A, transporting neutral nonessential amino acids, and System L, mediating the transport of essential amino acids, have been studied in some detail. Importantly, decreased placental Systems A and L transporter activity is strongly associated with IUGR and increased placental activity of these two amino acid transporters has been linked to fetal overgrowth in human pregnancy. An array of factors in the maternal circulation, including insulin, IGF-1, and adiponectin, and placental signaling pathways such as mTOR, have been identified as key regulators of placental Systems A and L. Studies using trophoblast-specific gene targeting in mice have provided compelling evidence that changes in placental Systems A and L are mechanistically linked to altered fetal growth. It is possible that targeting specific placental amino acid transporters or their upstream regulators represents a novel intervention to alleviate the short- and long-term consequences of abnormal fetal growth in the future.

Pathogenesis of MASLD and MASH - role of insulin resistance and lipotoxicity

BACKGROUND

Insulin resistance and lipotoxicity are extremely interconnected but fundamental in setting the stage for the development of MASLD/MASH.

AIM/METHODS

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.

RESULTS

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.

CONCLUSIONS

Targeting tissue-specific insulin resistance and hyperinsulinaemia while decreasing FFA load (lipotoxicity) through dietary and lifestyle changes remain the best upstream interventions.

Antidiabetic potency and molecular insights of natural products bearing indole moiety: A systematic bioinformatics investigation targeting AKT1

Diabetic mellitus (DM) is a chronic disorder, and type 2 DM (T2DM) is the most prevalent among all categories (nearly 90%) across the globe every year. With the availability of potential drugs, the prevalence rate has remained uncontrollable, while natural resources showed a promising potency, and exploring such potential candidates at the preclinical stage is essential. An extensive literature search selected 89 marine and plant-derived indole derivatives with anti-inflammatory, antioxidant, lipid-lowering, etc., activities. However, as we know, drugs have not been able to convert from 'lead' to 'mainstream' due to inadequate drug-ability profiles, as our systematic investigation proved and selected herdmanine_A (HERD_A) and penerpene_D (PENE_D) as the most potential antidiabetic candidates from the library of indole derivatives. Based on our previous network pharmacology study, we selected three new target enzymes: Acetyl-CoA carboxylase 2 (ACACB; PDB ID: 3JRX), cyclin-dependent kinase 4 (CDK4; PDB ID: 3G33), and alpha serine/threonine-protein kinase 1 (AKT1; PDB ID: 3O96) to assess the antidiabetic potency of selected indole derivatives through binding energy or docking score. To conduct molecular docking studies with these enzymes, we used the PyRx-AutoDock platform. Furthermore, molecular dynamic simulation at 100 ns, physicochemical analysis, pharmacokinetics, toxicity assessment, and drug-likeness evaluation suggested that HERD_A and penerpene PENE_D were the most potent inhibitors against AKT1 compared to koenimbine (most potential based on the recorded IC50 value) and murrayakonine_A (most potential based on the docking score). In summary, HERD_A and/or PENE_D have the potential to be used as alternative therapeutic agent for the treatment of diabetes after some pharmacological investigation.

Hepatic selective insulin resistance at the intersection of insulin signaling and metabolic dysfunction-associated steatotic liver disease

Insulin resistance (IR) is a major pathogenic factor in the progression of MASLD. In the liver, insulin suppresses gluconeogenesis and enhances de novo lipogenesis (DNL). During IR, there is a defect in insulin-mediated suppression of gluconeogenesis, but an unrestrained increase in hepatic lipogenesis persists. The mechanism of increased hepatic steatosis in IR is unclear and remains controversial. The key discrepancy is whether insulin retains its ability to directly regulate hepatic lipogenesis. Blocking insulin/IRS/AKT signaling reduces liver lipid deposition in IR, suggesting insulin can still regulate lipid metabolism; hepatic glucose metabolism that bypasses insulin's action may contribute to lipogenesis; and due to peripheral IR, other tissues are likely to impact liver lipid deposition. We here review the current understanding of insulin's action in governing different aspects of hepatic lipid metabolism under normal and IR states, with the purpose of highlighting the essential issues that remain unsettled.

Molecular recognition of ITIM/ITSM domains with SHP2 and their allosteric effect

Src homology 2-domain-containing tyrosine phosphatase 2 (SHP2) is a non-receptor protein tyrosine phosphatase that is widely expressed in a variety of cells and regulates the immune response of T cells through the PD-1 pathway. However, the activation mechanism and allosteric effects of SHP2 remain unclear, hindering the development of small molecule inhibitors. For the first time, in this study, the complex structure formed by the intact PD-1 tail and SHP2 was modeled. The molecular recognition and conformational changes of inactive/active SHP2 versus ITIM/ITSM were compared based on prolonged MD simulations. The relative flexibility of the two SH2 domains during MD simulations contributes to the recruitment of ITIM/ITSM and supports the subsequent conformational change of SHP2. The binding free energy calculation shows that inactive SHP2 has a higher affinity for ITIM/ITSM than active SHP2, mainly because the former's N-SH2 refers to the α-state. In addition, a significant decrease in the contribution to the binding energy of certain residues (e.g., R32, S34, K35, T42, and K55) of conformationally transformed SHP2 contributes to the above result. These detailed changes during conformational transition will provide theoretical guidance for the molecular design of subsequent novel anticancer drugs.

Association between insulin receptor substrate 1 gene polymorphism rs1801278 and gestational diabetes mellitus: an updated meta- analysis

OBJECTIVES

we performed this meta- analysis to investigate the impact of insulin receptor substrate 1 (IRS1) gene rs1801278 on susceptibility to gestational diabetes mellitus (GDM).

METHODS

The pooled odds ratio (OR) and 95% confidence interval (95% CI) were calculated, and p value is used to determine statistical significance. Sensitivity analysis was performed under three models (dominant, recessive and allele model), and the pooled ORs and 95%CI were calculated. Funnel plots and Begger's regression test were employed to test the publication bias.

RESULTS

The meta-analysis included 4777 participants (2116 cases and 2661 controls). The IRS1 rs1801278 (C/T) were not significant associated with GDM risk under the dominant and allele models, OR (95%CI) = 1.22 (0.88-1.70) and 1.24 (0.91-1.68), respectively (both p values were more than 0.05). But we also found the IRS1 rs1801278 (C/T) were significant associated with GDM risk under the recessive model, OR (95%CI) = 0.37 (0.16-0.86), p = 0.030. Our results showed that none of the studies affected the quality of the pooled OR. We also found no significant publication bias existed in this meta study for three genetic models, PTT + CT vs. CC = 0.445; PCC+CT vs. TT= 0.095; PC vs. T = 0.697.

CONCLUSION

this meta-analysis indicated that IRS1 rs1801278 (C/T) was associated with the GDM risk under the recessive model but was not associated with the GDM risk under dominant and allele models.

Diabetes mellitus with severe insulin resistance in a young male patient with a heterozygous pathogenic IRS1 frameshift variant

We present the case of a young male patient (height, 158.1 cm [+3.3 standard deviation (SD)]; weight, 63.7 kg [body mass index, 25.5]) with diabetes mellitus and severe insulin resistance associated with a heterozygous pathogenic insulin receptor substrate 1 (IRS1) frameshift mutation. The patient also had severe acanthosis nigricans. Notably, the patient's father was undergoing treatment with high doses of insulin for diabetes mellitus, and had been experiencing angina pectoris. Laboratory data showed a fasting plasma glucose level of 88 mg/dL, hemoglobin A1C (HbA1c) of 7.4%, fasting insulin level of 43.1 µg/mL, and a homeostasis model assessment-insulin resistance (HOMA-IR) score of 9.36, indicating hyperinsulinism. Oral glucose tolerance test revealed a diabetic pattern and insulin hypersecretion. In addition, the patient had hyperlipidemia. Genetic studies revealed a heterozygous frameshift variant of IRS1 [NM_005544.3:c.1791dupG:p.(His598Alafs*13)] in the patient and his father, which can impair the binding and activation of phosphoinositide 3 (PI-3) kinase and defectively mediate the translocation of glucose transporter type 4 (GLUT4) in adipose tissues, possibly leading to glucose intolerance. Therefore, this variant may be disease causing. After confirming IRS1 mutation, metformin was administered, and physical exercise and dietary management were initiated; metformin was well tolerated, and optimal glycemic control was maintained.

Increased Levels of Urine Volatile Organic Compounds Are Associated With Diabetes Risk and Impaired Glucose Homeostasis

CONTEXT

Volatile organic compounds (VOCs) are pervasive environmental pollutants that have been linked to various adverse health effects. However, the effect of ambient VOCs, whether individually or in mixtures, on diabetes remains uncertain and requires further investigation.

OBJECTIVE

This study investigates the effects of ambient VOCs exposure, whether single or mixed, on diabetes mellitus and glucose homeostasis in the general population.

METHODS

Urinary concentrations of VOC metabolites were obtained from the National Health and Nutrition Examination Survey. Survey-weighted logistic regression and generalized linear regression were used to explore the associations between individual VOC exposure and diabetes risk and glucose homeostasis indicators, respectively. Weighted quantile sum (WQS) regression models were applied to assess the combined effects of VOC mixtures.

RESULTS

Out of 8468 participants, 1504 had diabetes mellitus. Eight VOC metabolites showed positive associations with diabetes mellitus (OR, 1.15-1.43; all P < .05), insulin resistance (IR) (OR, 1.02-1.06; P < .05), and other glucose homeostasis indicators (β, 0.04-2.32; all P < .05). Mixed VOC models revealed positive correlations between the WQS indices and diabetes risk (OR = 1.52; 95% CI, 1.29-1.81), IR (OR = 1.36; 95% CI, 1.14-1.62), and other glucose homeostasis indicators (β, 0.17-2.22; all P < .05).

CONCLUSION

Urinary metabolites of ambient VOCs are significantly associated with an increased diabetes risk and impaired glucose homeostasis. Thus, primary prevention policies aimed at reducing ambient VOCs could attenuate diabetes burden.

Diabetic sensory neuropathy and insulin resistance are induced by loss of UCHL1 in Drosophila

Diabetic sensory neuropathy (DSN) is one of the most common complications of type 2 diabetes (T2D), however the molecular mechanistic association between T2D and DSN remains elusive. Here we identify ubiquitin C-terminal hydrolase L1 (UCHL1), a deubiquitinase highly expressed in neurons, as a key molecule underlying T2D and DSN. Genetic ablation of UCHL1 leads to neuronal insulin resistance and T2D-related symptoms in Drosophila. Furthermore, loss of UCHL1 induces DSN-like phenotypes, including numbness to external noxious stimuli and axonal degeneration of sensory neurons in flies' legs. Conversely, UCHL1 overexpression improves DSN-like defects of T2D model flies. UCHL1 governs insulin signaling by deubiquitinating insulin receptor substrate 1 (IRS1) and antagonizes an E3 ligase of IRS1, Cullin 1 (CUL1). Consistent with these results, genetic and pharmacological suppression of CUL1 activity rescues T2D- and DSN-associated phenotypes. Therefore, our findings suggest a complete set of genetic factors explaining T2D and DSN, together with potential remedies for the diseases.

Phosphorylation Codes in IRS-1 and IRS-2 Are Associated with the Activation/Inhibition of Insulin Canonical Signaling Pathways

Insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) are signaling adaptor proteins that participate in canonical pathways, where insulin cascade activation occurs, as well as in non-canonical pathways, in which phosphorylation of substrates is carried out by a diverse array of receptors including integrins, cytokines, steroid hormones, and others. IRS proteins are subject to a spectrum of post-translational modifications essential for their activation, encompassing phosphorylation events in distinct tyrosine, serine, and threonine residues. Tyrosine residue phosphorylation is intricately linked to the activation of the insulin receptor cascade and its interaction with SH2 domains within a spectrum of proteins, including PI3K. Conversely, serine residue phosphorylation assumes a different function, serving to attenuate the effects of insulin. In this review, we have identified over 50 serine residues within IRS-1 that have been reported to undergo phosphorylation orchestrated by a spectrum of kinases, thereby engendering the activation or inhibition of different signaling pathways. Furthermore, we delineate the phosphorylation of over 10 distinct tyrosine residues at IRS-1 or IRS-2 in response to insulin, a process essential for signal transduction and the subsequent activation of PI3K.

Current progression in application of extracellular vesicles in central nervous system diseases

Early diagnosis and pharmacological treatment of central nervous system (CNS) diseases has been a long-standing challenge for clinical research due to the presence of the blood-brain barrier. Specific proteins and RNAs in brain-derived extracellular vesicles (EVs) usually reflect the corresponding state of brain disease, and therefore, EVs can be used as diagnostic biomarkers for CNS diseases. In addition, EVs can be engineered and fused to target cells for delivery of cargo, demonstrating the great potential of EVs as a nanocarrier platform. We review the progress of EVs as markers and drug carriers in the diagnosis and treatment of neurological diseases. The main areas include visual imaging, biomarker diagnosis and drug loading therapy for different types of CNS diseases. It is hoped that increased knowledge of EVs will facilitate their clinical translation in CNS diseases.

Human cytomegalovirus attenuates AKT activity by destabilizing insulin receptor substrate proteins

IMPORTANCE

Human cytomegalovirus (HCMV) requires inactivation of AKT to efficiently replicate, yet how AKT is shut off during HCMV infection has remained unclear. We show that UL38, an HCMV protein that activates mTORC1, is necessary and sufficient to destabilize insulin receptor substrate 1 (IRS1), a model insulin receptor substrate (IRS) protein. Degradation of IRS proteins in settings of excessive mTORC1 activity is an important mechanism for insulin resistance. When IRS proteins are destabilized, PI3K cannot be recruited to growth factor receptor complexes, and hence, AKT membrane recruitment, a rate limiting step in its activation, fails to occur. Despite its penchant for remodeling host cell signaling pathways, our results reveal that HCMV relies upon a cell-intrinsic negative regulatory feedback loop to inactivate AKT. Given that pharmacological inhibition of PI3K/AKT potently induces HCMV reactivation from latency, our findings also imply that the expression of UL38 activity must be tightly regulated within latently infected cells to avoid spontaneous reactivation.

Insulin Receptor Isoforms and Insulin Growth Factor-like Receptors: Implications in Cell Signaling, Carcinogenesis, and Chemoresistance

This comprehensive review thoroughly explores the intricate involvement of insulin receptor (IR) isoforms and insulin-like growth factor receptors (IGFRs) in the context of the insulin and insulin-like growth factor (IGF) signaling (IIS) pathway. This elaborate system encompasses ligands, receptors, and binding proteins, giving rise to a wide array of functions, including aspects such as carcinogenesis and chemoresistance. Detailed genetic analysis of IR and IGFR structures highlights their distinct isoforms, which arise from alternative splicing and exhibit diverse affinities for ligands. Notably, the overexpression of the IR-A isoform is linked to cancer stemness, tumor development, and resistance to targeted therapies. Similarly, elevated IGFR expression accelerates tumor progression and fosters chemoresistance. The review underscores the intricate interplay between IRs and IGFRs, contributing to resistance against anti-IGFR drugs. Consequently, the dual targeting of both receptors could present a more effective strategy for surmounting chemoresistance. To conclude, this review brings to light the pivotal roles played by IRs and IGFRs in cellular signaling, carcinogenesis, and therapy resistance. By precisely modulating these receptors and their complex signaling pathways, the potential emerges for developing enhanced anti-cancer interventions, ultimately leading to improved patient outcomes.

Is Insulin Receptor Substrate4 (IRS4) a Platform Involved in the Activation of Several Oncogenes?

The IRS (insulin receptor substrate) family of scaffold proteins includes insulin receptor substrate-4 (IRS4), which is expressed only in a few cell lines, including human kidney, brain, liver, and thymus and some cell lines. Its N-terminus carries a phosphotyrosine-binding (PTB) domain and a pleckstrin homology domain (PH), which distinguishes it as a member of this family. In this paper, we collected data about the molecular mechanisms that explain the relevance of IRS4 in the development of cancer and identify IRS4 differences that distinguish it from IRS1 and IRS2. Search engines and different databases, such as PubMed, UniProt, ENSEMBL and SCANSITE 4.0, were used. We used the name of the protein that it encodes "(IRS-4 or IRS4)", or the combination of these terms with the word "(cancer)" or "(human)", for searches. Terms related to specific tumor pathologies ("breast", "ovary", "colon", "lung", "lymphoma", etc.) were also used. Despite the lack of knowledge on IRS4, it has been reported that some cancers and benign tumors are characterized by high levels of IRS-4 expression. Specifically, the role of IRS-4 in different types of digestive tract neoplasms, gynecological tumors, lung cancers, melanomas, hematological tumors, and other less common types of cancers has been shown. IRS4 differs from IRS1 and IRS2 in that can activate several oncogenes that regulate the PI3K/Akt cascade, such as BRK and FER, which are characterized by tyrosine kinase-like activity without regulation via extracellular ligands. In addition, IRS4 can activate the CRKL oncogene, which is an adapter protein that regulates the MAP kinase cascade. Knowledge of the role played by IRS4 in cancers at the molecular level, specifically as a platform for oncogenes, may enable the identification and validation of new therapeutic targets.

Circulating Sphingolipids in Insulin Resistance, Diabetes and Associated Complications

Sphingolipids play an important role in the development of diabetes, both type 1 and type 2 diabetes, as well as in the development of both micro- and macro-vascular complications. Several reviews have been published concerning the role of sphingolipids in diabetes but most of the emphasis has been on the possible mechanisms by which sphingolipids, mainly ceramides, contribute to the development of diabetes. Research on circulating levels of the different classes of sphingolipids in serum and in lipoproteins and their importance as biomarkers to predict not only the development of diabetes but also of its complications has only recently emerged and it is still in its infancy. This review summarizes the previously published literature concerning sphingolipid-mediated mechanisms involved in the development of diabetes and its complications, focusing on how circulating plasma sphingolipid levels and the relative content carried by the different lipoproteins may impact their role as possible biomarkers both in the development of diabetes and mainly in the development of diabetic complications. Further studies in this field may open new therapeutic avenues to prevent or arrest/reduce both the development of diabetes and progression of its complications.

Insulin Resistance and Hypertension: Mechanisms Involved and Modifying Factors for Effective Glucose Control

Factors such as aging, an unhealthy lifestyle with decreased physical activity, snacking, a standard Western diet, and smoking contribute to raising blood pressure to a dangerous level, increasing the risk of coronary artery disease and heart failure. Atherosclerosis, or aging of the blood vessels, is a physiological process that has accelerated in the last decades by the overconsumption of carbohydrates as the primary sources of caloric intake, resulting in increased triglycerides and VLDL-cholesterol and insulin spikes. Classically, medications ranging from beta blockers to angiotensin II blockers and even calcium channel blockers were used alone or in combination with lifestyle modifications as management tools in modern medicine to control arterial blood pressure. However, it is not easy to control blood pressure or the associated complications. A low-carbohydrate, high-fat (LCHF) diet can reduce glucose and insulin spikes, improve insulin sensitivity, and lessen atherosclerosis risk factors. We reviewed articles describing the etiology of insulin resistance (IR) and its impact on arterial blood pressure from databases including PubMed, PubMed Central, and Google Scholar. We discuss how the LCHF diet is beneficial to maintaining arterial blood pressure at normal levels, slowing down the progression of atherosclerosis, and reducing the use of antihypertensive medications. The mechanisms involved in IR associated with hypertension are also highlighted.

Eicosapentaenoic Acid Induces the Inhibition of Adipogenesis by Reducing the Effect of PPARγ Activator and Mediating PKA Activation and Increased COX-2 Expression in 3T3-L1 Cells at the Differentiation Stage

Obesity has received increasing attention in recent years because it is a factor in the development of non-communicable diseases. The current study aimed to analyze how representative fatty acids (FAs) such as palmitic acid, stearic acid, oleic acid, α-linolenic acid (ALA), and eicosapentaenoic acid (EPA) affected adipogenesis when/if introduced at the differentiation stage of 3T3-L1 cell culture. These FAs are assumed to be potentially relevant to the progression or prevention of obesity. EPA added during the differentiation stage reduced intracellular triacylglycerol (TAG) accumulation, as well as the expression of the established adipocyte-specific marker genes, during the maturation stage. However, no other FAs inhibited intracellular TAG accumulation. Coexistence of Δ12-prostaglandin J2, a peroxisome proliferator-activated receptor γ activator, with EPA during the differentiation stage partially attenuated the inhibitory effect of EPA on intracellular TAG accumulation. EPA increased cyclooxygenase-2 (COX-2) expression and protein kinase A (PKA) activity at the differentiation stage, which could explain the inhibitory actions of EPA. Taken together, exposure of preadipocytes to EPA only during the differentiation stage may be sufficient to finally reduce the mass of white adipose tissue through increasing COX-2 expression and PKA activity.

The Activation Mechanism of the Insulin Receptor: A Structural Perspective

The insulin receptor (IR) is a type II receptor tyrosine kinase that plays essential roles in metabolism, growth, and proliferation. Dysregulation of IR signaling is linked to many human diseases, such as diabetes and cancers. The resolution revolution in cryo-electron microscopy has led to the determination of several structures of IR with different numbers of bound insulin molecules in recent years, which have tremendously improved our understanding of how IR is activated by insulin. Here, we review the insulin-induced activation mechanism of IR, including (a) the detailed binding modes and functions of insulin at site 1 and site 2 and (b) the insulin-induced structural transitions that are required for IR activation. We highlight several other key aspects of the activation and regulation of IR signaling and discuss the remaining gaps in our understanding of the IR activation mechanism and potential avenues of future research.

Identification of novel genes associated with exercise and calorie restriction effects in skeletal muscle

Exercise and caloric restriction (CR) significantly increase longevity across a range of species and delay aging-related losses in organ function. Although both interventions enhance skeletal muscle function, the molecular mechanisms underlying these associations are unknown. We sought to identify genes regulated by CR and exercise in muscle, and investigate their relationship with muscle function. To do this, expression profiles of Gene Expression Omnibus datasets obtained from the muscle tissue of calorie-restricted male primates and young men post-exercise were analyzed. There were seven transcripts (ADAMTS1, CPEB4, EGR2, IRS2, NR4A1, PYGO1, and ZBTB43) that were consistently upregulated by both CR and exercise training. We used C2C12 murine myoblasts to investigate the effect of silencing these genes on myogenesis, mitochondrial respiration, autophagy, and insulin signaling, all of which are processes affected by CR and exercise. Our results show that in C2C12 cells, Irs2 and Nr4a1 expression were critical for myogenesis, and five genes (Egr2, Irs2, Nr4a1, Pygo1, and ZBTB43) regulated mitochondrial respiration while having no effect on autophagy. Cpeb4 knockdown increased the expression of genes involved in muscle atrophy and induced myotube atrophy. These findings suggest new resources for studying the mechanisms underlying the beneficial effects of exercise and calorie restriction on skeletal muscle function and lifespan extension.

Molecular Mechanisms for the Vicious Cycle between Insulin Resistance and the Inflammatory Response in Obesity

The comprehensive anabolic effects of insulin throughout the body, in addition to the control of glycemia, include ensuring lipid homeostasis and anti-inflammatory modulation, especially in adipose tissue (AT). The prevalence of obesity, defined as a body mass index (BMI) ≥ 30 kg/m², has been increasing worldwide on a pandemic scale with accompanying syndemic health problems, including glucose intolerance, insulin resistance (IR), and diabetes. Impaired tissue sensitivity to insulin or IR paradoxically leads to diseases with an inflammatory component despite hyperinsulinemia. Therefore, an excess of visceral AT in obesity initiates chronic low-grade inflammatory conditions that interfere with insulin signaling via insulin receptors (INSRs). Moreover, in response to IR, hyperglycemia itself stimulates a primarily defensive inflammatory response associated with the subsequent release of numerous inflammatory cytokines and a real threat of organ function deterioration. In this review, all components of this vicious cycle are characterized with particular emphasis on the interplay between insulin signaling and both the innate and adaptive immune responses related to obesity. Increased visceral AT accumulation in obesity should be considered the main environmental factor responsible for the disruption in the epigenetic regulatory mechanisms in the immune system, resulting in autoimmunity and inflammation.

Post-translational regulation of muscle growth, muscle aging and sarcopenia

Skeletal muscle makes up 30-40% of the total body mass. It is of great significance in maintaining digestion, inhaling and exhaling, sustaining body posture, exercising, protecting joints and many other aspects. Moreover, muscle is also an important metabolic organ that helps to maintain the balance of sugar and fat. Defective skeletal muscle function not only limits the daily activities of the elderly but also increases the risk of disability, hospitalization and death, placing a huge burden on society and the healthcare system. Sarcopenia is a progressive decline in muscle mass, muscle strength and muscle function with age caused by environmental and genetic factors, such as the abnormal regulation of protein post-translational modifications (PTMs). To date, many studies have shown that numerous PTMs, such as phosphorylation, acetylation, ubiquitination, SUMOylation, glycosylation, glycation, methylation, S-nitrosylation, carbonylation and S-glutathionylation, are involved in the regulation of muscle health and diseases. This article systematically summarizes the post-translational regulation of muscle growth and muscle atrophy and helps to understand the pathophysiology of muscle aging and develop effective strategies for diagnosing, preventing and treating sarcopenia.

Positive selection of somatically mutated clones identifies adaptive pathways in metabolic liver disease

Somatic mutations in nonmalignant tissues accumulate with age and injury, but whether these mutations are adaptive on the cellular or organismal levels is unclear. To interrogate genes in human metabolic disease, we performed lineage tracing in mice harboring somatic mosaicism subjected to nonalcoholic steatohepatitis (NASH). Proof-of-concept studies with mosaic loss of Mboat7, a membrane lipid acyltransferase, showed that increased steatosis accelerated clonal disappearance. Next, we induced pooled mosaicism in 63 known NASH genes, allowing us to trace mutant clones side by side. This in vivo tracing platform, which we coined MOSAICS, selected for mutations that ameliorate lipotoxicity, including mutant genes identified in human NASH. To prioritize new genes, additional screening of 472 candidates identified 23 somatic perturbations that promoted clonal expansion. In validation studies, liver-wide deletion of Tbx3, Bcl6, or Smyd2 resulted in protection against hepatic steatosis. Selection for clonal fitness in mouse and human livers identifies pathways that regulate metabolic disease.

Human cytomegalovirus attenuates AKT activity by destabilizing insulin receptor substrate proteins

The phosphoinositide 3-kinase (PI3K)/AKT pathway plays crucial roles in cell viability and protein synthesis and is frequently co-opted by viruses to support their replication. Although many viruses maintain high levels of AKT activity during infection, other viruses, such as vesicular stomatitis virus and human cytomegalovirus (HCMV), cause AKT to accumulate in an inactive state. To efficiently replicate, HCMV requires FoxO transcription factors to localize to the infected cell nucleus (Zhang et. al. mBio 2022), a process directly antagonized by AKT. Therefore, we sought to investigate how HCMV inactivates AKT to achieve this. Subcellular fractionation and live cell imaging studies indicated that AKT failed to recruit to membranes upon serum-stimulation of infected cells. However, UV-inactivated virions were unable to render AKT non-responsive to serum, indicating a requirement for de novo viral gene expression. Interestingly, we were able to identify that UL38 (pUL38), a viral activator of mTORC1, is required to diminish AKT responsiveness to serum. mTORC1 contributes to insulin resistance by causing proteasomal degradation of insulin receptor substrate (IRS) proteins, such as IRS1, which are necessary for the recruitment of PI3K to growth factor receptors. In cells infected with a recombinant HCMV disrupted for UL38 , AKT responsiveness to serum is retained and IRS1 is not degraded. Furthermore, ectopic expression of UL38 in uninfected cells induces IRS1 degradation, inactivating AKT. These effects of UL38 were reversed by the mTORC1 inhibitor, rapamycin. Collectively, our results demonstrate that HCMV relies upon a cell-intrinsic negative feedback loop to render AKT inactive during productive infection.

Positive selection of somatically mutated clones identifies adaptive pathways in metabolic liver disease

Somatic mutations in non-malignant tissues accumulate with age and insult, but whether these mutations are adaptive on the cellular or organismal levels is unclear. To interrogate mutations found in human metabolic disease, we performed lineage tracing in mice harboring somatic mosaicism subjected to non-alcoholic steatohepatitis (NASH). Proof-of-concept studies with mosaic loss of Mboat7 , a membrane lipid acyltransferase, showed that increased steatosis accelerated clonal disappearance. Next, we induced pooled mosaicism in 63 known NASH genes, allowing us to trace mutant clones side-by-side. This in vivo tracing platform, which we coined MOSAICS, selected for mutations that ameliorate lipotoxicity, including mutant genes identified in human NASH. To prioritize new genes, additional screening of 472 candidates identified 23 somatic perturbations that promoted clonal expansion. In validation studies, liver-wide deletion of Bcl6, Tbx3, or Smyd2 resulted in protection against NASH. Selection for clonal fitness in mouse and human livers identifies pathways that regulate metabolic disease.

Highlights

Mosaic Mboat7 mutations that increase lipotoxicity lead to clonal disappearance in NASH. In vivo screening can identify genes that alter hepatocyte fitness in NASH. Mosaic Gpam mutations are positively selected due to reduced lipogenesis. In vivo screening of transcription factors and epifactors identified new therapeutic targets in NASH.

Insulin Receptor Substrate-1 (IRS1) Regulates Oogenesis and Vitellogenesis in Propylea japonica by Mediating the FOXO Transcription Factor Expression, Independent of JH and 20E Signaling Pathways

The insulin receptor substrate (IRS), as the core cytoplasmic adapter protein in the insulin/insulin-like signaling (IIS) pathway, is an important mediator of cellular signaling. However, it is still unknown how IRS crosstalk with hormone signaling regulates insect growth, development, and reproduction. In this study, we demonstrated that knockdown of IRS1 significantly inhibited oogenesis, vitellogenesis, and the development of nurse cells and follicular epithelial cells. In addition, qRT-PCR results showed that FOXO transcription factors significantly responded to silencing of the IRS1 gene. However, IRS1 silencing had no significant effect on the expression of juvenile hormone/20-hydroxyecdysone (JH/20E)-signaling genes, JH synthesis, and degradation enzyme-related genes and the JH/20E titers. Our results suggested that the IIS pathway regulated ovarian development and Vg production through FOXO, independent of JH and 20E signaling pathways. This study revealed the reproductive regulation mechanism in Propylea japonica, which provides a theoretical basis for large-scale expansion of P. japonica as an environment-friendly biological control strategy.

Exposure to elevated temperature affects the expression of PIWI-interacting RNAs and associated transcripts in mouse testes

BACKGROUND

Exposure to heat waves could result in adverse effects on human health, especially in male testicles. PIWI-interacting RNA (piRNA) is a novel type of small non-coding RNA, which can notably impact mRNA turnover and preserve germline maintenance in germline cells. However, piRNA's expression status when adapting to testicular heat stress remains largely unclear.

OBJECTIVES

To investigate the function and mechanisms of relevant piRNAs during testicular heat stress.

MATERIALS AND METHODS

In this study, a mouse testicular heat stress model was constructed, and the testes were removed for piRNA-sequencing. Bioinformatics analysis was used to discover the differential expressed piRNAs, piRNA clusters, and enriched pathways. A cell heat stress model was constructed to validate the top five upregulated piRNAs. Proliferation and apoptosis assays were utilized to validate the function of selected piRNA. Bioinformatics prediction, western blotting, and immunohistochemistry were used to illustrate the downstream mechanisms.

RESULTS

Through the bioinformatics analysis, we identified the differential expression profile and enriched pathways of piRNAs and piRNA clusters during testicular hyperthermia. Besides, piR-020492 was proved to be upregulated in heat stress mouse testes and a germ cell model. A series of in vitro assays illustrated that an overexpression of piR-020492 could restrain the proliferation and promote the apoptosis of mouse germ cells. Kyoto Encyclopedia of Genes and Genomes analysis of piRNA-generating genes in the testicular heat stress model and piR-020492 targeting genes showed that the overlap pathways are adenosine monophosphate-activated protein kinase (AMPK) and insulin pathways. Validation experiments demonstrated that the key genes of AMPK and insulin pathway exhibit differential expression after an overexpression of piR-020492 or testicular heat stress.

DISCUSSION AND CONCLUSION

In conclusion, our findings revealed the expression profile of piRNAs in testicular heat stress and illustrated the function and mechanisms of piR-020492 in germ cells, which could provide novel insights into the mechanism of hyperthermia-induced testicular injury.

Cell cycle control by the insulin-like growth factor signal: at the crossroad between cell growth and mitotic regulation

In proliferating cells and tissues a number of checkpoints (G1/S and G2/M) preceding cell division (M-phase) require the signal provided by growth factors present in serum. IGFs (I and II) have been demonstrated to constitute key intrinsic components of the peptidic active fraction of mammalian serum. In vivo genetic ablation studies have shown that the cellular signal triggered by the IGFs through their cellular receptors represents a non-replaceable requirement for cell growth and cell cycle progression. Retroactive and current evaluation of published literature sheds light on the intracellular circuitry activated by these factors providing us with a better picture of the pleiotropic mechanistic actions by which IGFs regulate both cell size and mitogenesis under developmental growth as well as in malignant proliferation. The present work aims to summarize the cumulative knowledge learned from the IGF ligands/receptors and their intracellular signaling transducers towards control of cell size and cell-cycle with particular focus to their actionable circuits in human cancer. Furthermore, we bring novel perspectives on key functional discriminants of the IGF growth-mitogenic pathway allowing re-evaluation on some of its signal components based upon established evidences.

Role of Exosomes Derived from Adipose Tissue under Obese Conditions in Skeletal Muscle and Liver Cells: Commonalities and Differences

SCOPE

To determine the correlation between obesity and insulin resistance in skeletal muscle and liver tissues, this study isolates exosomes from adipose tissue under obese conditions and investigates the effect of adipose tissue-derived exosomes (Ad-exosomes) in mouse muscle (C2C12 cells) and liver cell lines (AML12 cells).

METHODS AND RESULTS

The study isolates exosomes from the adipose tissue of normal diet-fed mice or high-fat diet (HFD)-fed obese mice and confirms the uptake into differentiated C2C12 and AML12 cells. Ad-exosomes from HFD-fed mice induce insulin resistance, triglyceride (TG) accumulation, endoplasmic reticulum stress, and inflammation in both C2C12 and AML12 cells. Interestingly, the study finds that the TG accumulation induces by Ad-exosomes from HFD-fed obese mice is dramatically increased in AML12 cells compared with that in the differentiated C2C12 cells, and glucose uptake following the same treatment is decreased in C2C12 cells and increased in AML12 cells. In addition, Ad-exosomes from HFD-fed obese mice cause not only TG accumulation but also lipogenesis in AML12 cells.

CONCLUSIONS

The results suggest that Ad-exosomes from HFD-fed obese mice cause insulin resistance in both the muscles and liver, but their effects on metabolism during the development of insulin resistance vary between tissues.

The skeletal muscle fiber periphery: A nexus of mTOR-related anabolism

Skeletal muscle anabolism is driven by numerous stimuli such as growth factors, nutrients (i.e., amino acids, glucose), and mechanical stress. These stimuli are integrated by the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signal transduction cascade. In recent years, work from our laboratory and elsewhere has sought to unravel the molecular mechanisms underpinning the mTOR-related activation of muscle protein synthesis (MPS), as well as the spatial regulation of these mechanisms within the skeletal muscle cell. These studies have suggested that the skeletal muscle fiber periphery is a region of central importance in anabolism (i.e., growth/MPS). Indeed, the fiber periphery is replete with the substrates, molecular machinery, and translational apparatus necessary to facilitate MPS. This review provides a summary of the mechanisms underpinning the mTOR-associated activation of MPS from cell, rodent, and human studies. It also presents an overview of the spatial regulation of mTORC1 in response to anabolic stimuli and outlines the factors that distinguish the periphery of the cell as a highly notable region of skeletal muscle for the induction of MPS. Future research should seek to further explore the nutrient-induced activation of mTORC1 at the periphery of skeletal muscle fibers.

Architecture of the outbred brown fat proteome defines regulators of metabolic physiology

Brown adipose tissue (BAT) regulates metabolic physiology. However, nearly all mechanistic studies of BAT protein function occur in a single inbred mouse strain, which has limited the understanding of generalizable mechanisms of BAT regulation over physiology. Here, we perform deep quantitative proteomics of BAT across a cohort of 163 genetically defined diversity outbred mice, a model that parallels the genetic and phenotypic variation found in humans. We leverage this diversity to define the functional architecture of the outbred BAT proteome, comprising 10,479 proteins. We assign co-operative functions to 2,578 proteins, enabling systematic discovery of regulators of BAT. We also identify 638 proteins that correlate with protection from, or sensitivity to, at least one parameter of metabolic disease. We use these findings to uncover SFXN5, LETMD1, and ATP1A2 as modulators of BAT thermogenesis or adiposity, and provide OPABAT as a resource for understanding the conserved mechanisms of BAT regulation over metabolic physiology.

Insulin Resistance and High Blood Pressure: Mechanistic Insight on the Role of the Kidney

The metabolic effects of insulin predominate in skeletal muscle, fat, and liver where the hormone binds to its receptor, thereby priming a series of cell-specific and biochemically diverse intracellular mechanisms. In the presence of a good secretory reserve in the pancreatic islets, a decrease in insulin sensitivity in the metabolic target tissues leads to compensatory hyperinsulinemia. A large body of evidence obtained in clinical and experimental studies indicates that insulin resistance and the related hyperinsulinemia are causally involved in some forms of arterial hypertension. Much of this involvement can be ascribed to the impact of insulin on renal sodium transport, although additional mechanisms might be involved. Solid evidence indicates that insulin causes sodium and water retention, and both endogenous and exogenous hyperinsulinemia have been correlated to increased blood pressure. Although important information was gathered on the cellular mechanisms that are triggered by insulin in metabolic tissues and on their abnormalities, knowledge of the insulin-related mechanisms possibly involved in blood pressure regulation is limited. In this review, we summarize the current understanding of the cellular mechanisms that are involved in the pro-hypertensive actions of insulin, focusing on the contribution of insulin to the renal regulation of sodium balance and body fluids.

The Role of Insulin Receptor Substrate Proteins in Bronchopulmonary Dysplasia and Asthma: New Potential Perspectives

Insulin receptor substrates (IRSs) are proteins that are involved in signaling through the insulin receptor (IR) and insulin-like growth factor (IGFR). They can also interact with other receptors including growth factor receptors. Thus, they represent a critical node for the transduction and regulation of multiple signaling pathways in response to extracellular stimuli. In addition, IRSs play a central role in processes such as inflammation, growth, metabolism, and proliferation. Previous studies have highlighted the role of IRS proteins in lung diseases, in particular asthma. Further, the members of the IRS family are the common proteins of the insulin growth factor signaling cascade involved in lung development and disrupted in bronchopulmonary dysplasia (BPD). However, there is no study focusing on the relationship between IRS proteins and BPD yet. Unfortunately, there is still a significant gap in knowledge in this field. Thus, in this review, we aimed to summarize the current knowledge with the major goal of exploring the possible roles of IRS in BPD and asthma to foster new perspectives for further investigations.

Dominant-negative p53-overexpression in skeletal muscle induces cell death and fiber atrophy in rats

The tumor suppressor p53 is thought to play a key role in the maintenance of cell size and homeostasis, but relatively little is known about its role in skeletal muscle. Based on its ability to suppress cell growth, we hypothesized that inhibiting the function of wild-type p53 through the overexpression of a dominant-negative p53 mutant (DDp53) could result in muscle fiber hypertrophy. To test this hypothesis, we electroporated adult rat tibialis anterior muscles with DDp53 and collected the tissue three weeks later. We confirmed successful overexpression of DDp53 on a histological and biochemical level and found pronounced changes to muscle architecture, metabolism, and molecular signaling. Muscle mass, fiber cross-sectional area, and fiber diameter significantly decreased with DDp53 overexpression. We found histopathological changes in DDp53 transfected muscle which were accompanied by increased levels of proteins that are associated with membrane damage and repair. In addition, DDp53 decreased oxidative phosphorylation complex I and V protein levels, and despite its negative effects on muscle mass and fiber size, caused an increase in muscle protein synthesis as assessed via the SUnSET technique. Interestingly, the increase in muscle protein synthesis was concomitant with a decrease in phospho-S6K1 (Thr389). Furthermore, the muscle wasting in the DDp53 electroporated leg was accompanied by a decrease in global protein ubiquitination and an increase in proteasome activity. In conclusion, overexpression of a dominant-negative p53 mutant in skeletal muscle results in decreased muscle mass, myofiber size, histological muscle damage, a metabolic phenotype, and perturbed homeostasis between muscle protein synthesis and degradation.

Orphan nuclear receptor NUR77 relieves insulin resistance in HTR-8/SVneo trophoblast cells through activation of autophagy and insulin signaling

Gestational diabetes mellitus (GDM) is a common pregnancy complication with a high incidence in women. Orphan nuclear receptor NUR77 is involved in regulating glucose metabolism. However, its role in GDM has not been fully elucidated yet. In this study, an animal model of GDM was established by feeding mice with a high-fat diet (HFD) before and during pregnancy. NUR77 expression was abnormally upregulated in placenta tissues of GDM mice. We performed gain- and loss-of-function studies of NUR77 in HTR-8/SVneo cells. Cells were incubated with 1 × 10^-6 M insulin for 48 h to induce insulin resistance (IR). The expression of NUR77 was downregulated in HTR-8/SVneo cells following IR induction. Overexpression of NUR77 promoted cell proliferation, migration, and invasion. Notably, NUR77 promoted glucose uptake and enhanced insulin sensitivity in vitro. NUR77 increased the ratio of p-insulin receptor β (IRβ)^Tyr1361/IRβ, p-insulin receptor substrate (IRS)-1^Tyr612/IRS-1, p-Akt/Akt and decreased p-IRS-1^Ser307/IRS-1, as well as lowered the expression of glucose transport protein type 1 (GLUT1) and elevated GLUT4. These results suggest the involvement of IRβ/IRS/Akt/GLUT4 signaling activation in the regulatory effects of NUR77 on IR in HTR-8/SVneo cells. Silencing of NUR77 displayed opposite effects. Besides, NUR77 enhanced the expression of autophagy-related protein Beclin 1 and the ratio of LC3II/LC3I. Further study demonstrated that the inhibitory effect of NUR77 on IR was partially attributed to the activation of autophagy. Therefore, we demonstrate that NUR77 enhances insulin sensitivity in HTR-8/SVneo cells likely through activating IRβ/IRS/Akt/GLUT4 pathway and regulating autophagy.

[The insulin receptor discovery is 50 years old - A review of achieved progress]

The isolation of insulin from the pancreas and its purification to a degree permitting its safe administration to type 1 diabetic patients were accomplished 100 years ago at the University of Toronto by Banting, Best, Collip and McLeod and constitute undeniably one of the major medical therapeutic revolutions, recognized by the attribution of the 1923 Nobel Prize in Physiology or Medicine to Banting and McLeod. The clinical spin off was immediate as well as the internationalization of insulin's commercial production. The outcomes regarding basic research were much slower, in particular regarding the molecular mechanisms of insulin action on its target cells. It took almost a half-century before the determination of the tri-dimensional structure of insulin in 1969 and the characterization of its cell receptor in 1970-1971. The demonstration that the insulin receptor is in fact an enzyme named tyrosine kinase came in the years 1982-1985, and the crystal structure of the intracellular kinase domain 10 years later. The crystal structure of the first intracellular kinase substrate (IRS-1) in 1991 paved the way for the elucidation of the intracellular signalling pathways but it took 15 more years to obtain the complete crystal structure of the extracellular receptor domain (without insulin) in 2006. Since then, the determination of the structure of the whole insulin-receptor complex in both the inactive and activated states has made considerable progress, not least due to recent improvement in the resolution power of cryo-electron microscopy. I will here review the steps in the development of the concept of hormone receptor, and of our knowledge of the structure and molecular mechanism of activation of the insulin receptor.

Insulin receptor substrate 1(IRS1) is related with lymph node metastases and prognosis in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the leading causes of cancer-related mortality globally with a high risk of lymph node metastasis (LNM). In this study, weighted gene co-expression network analysis (WGCNA) showed the identification of 10 modules among which the significant module (turquoise), including 1352 genes, was correlated with LNM. A group 52 overlapping differentially expressed genes (DEGs) was identified based on the comparison of turquoise module with GSE23400 and GSE20347 datasets. Using Ctyohubba plugin, we identified 7 hub genes (ACTG2, SORBS1, MYH11, CXCL12, CNN1, IRS1 and CXCL8). IRS1 displayed significant correlation with metastasis. The decreased expression of IRS1 was also a predictor of poor OS of ESCC patients whereas the hub genes namely ACTG2, MYH11, CXCL8, CXCL12, IRS1 and CNN1 were associated with RFS of ESCC patients. These findings suggest that the altered expression of these hub genes are associated with prognosis and thus can be used as potential biomarkers for ESCC. Moreover, immunohistochemical staining and cell functional experiments displayed that the overexpression of IRS1 was negatively associated with metastasis in ESCC. In general, our research revealed several novel genes in ESCC especially the association of IRS1 with LNM in ESCC, which could provide novel insights into the initiation and progression of ESCC.

Insulin, Muscle Glucose Uptake, and Hexokinase: Revisiting the Road Not Taken

Research conducted over the last 50 yr has provided insight into the mechanisms by which insulin stimulates glucose transport across the skeletal muscle cell membrane Transport alone, however, does not result in net glucose uptake as free glucose equilibrates across the cell membrane and is not metabolized. Glucose uptake requires that glucose is phosphorylated by hexokinases. Phosphorylated glucose cannot leave the cell and is the substrate for metabolism. It is indisputable that glucose phosphorylation is essential for glucose uptake. Major advances have been made in defining the regulation of the insulin-stimulated glucose transporter (GLUT4) in skeletal muscle. By contrast, the insulin-regulated hexokinase (hexokinase II) parallels Robert Frost's "The Road Not Taken." Here the case is made that an understanding of glucose phosphorylation by hexokinase II is necessary to define the regulation of skeletal muscle glucose uptake in health and insulin resistance. Results of studies from different physiological disciplines that have elegantly described how hexokinase II can be regulated are summarized to provide a framework for potential application to skeletal muscle. Mechanisms by which hexokinase II is regulated in skeletal muscle await rigorous examination.

Identification of Immune-Related Breast Cancer Chemotherapy Resistance Genes via Bioinformatics Approaches

Chemotherapy resistance in breast cancer is an important factor affecting the prognosis of breast cancer patients. We computationally analyzed the differences in gene expression before and after chemotherapy in breast cancer patients, drug-sensitive groups, and drug-resistant groups. Through functional enrichment analysis, immune microenvironment analysis, and other computational analysis methods, we identified PRC1, GGTLC1, and IRS1 as genes that may mediate breast cancer chemoresistance through the immune pathway. After validation of certain other clinical datasets and in vitro cellular assays, we found that the above three genes influenced drug resistance in breast cancer patients and were closely related to the tumor immune microenvironment. Our finding that chemoresistance in breast cancer could be influenced by the mediation of tumor immunity expanded our knowledge of how to address this problem and could guide future research involving chemoresistance.

Links between Insulin Resistance and Periodontal Bacteria: Insights on Molecular Players and Therapeutic Potential of Polyphenols

Type 2 diabetes is a metabolic disease mainly associated with insulin resistance during obesity and constitutes a major public health problem worldwide. A strong link has been established between type 2 diabetes and periodontitis, an infectious dental disease characterized by chronic inflammation and destruction of the tooth-supporting tissue or periodontium. However, the molecular mechanisms linking periodontal bacteria and insulin resistance remain poorly elucidated. This study aims to summarize the mechanisms possibly involved based on in vivo and in vitro studies and targets them for innovative therapies. Indeed, during periodontitis, inflammatory lesions of the periodontal tissue may allow periodontal bacteria to disseminate into the bloodstream and reach tissues, including adipose tissue and skeletal muscles that store glucose in response to insulin. Locally, periodontal bacteria and their components, such as lipopolysaccharides and gingipains, may deregulate inflammatory pathways, altering the production of pro-inflammatory cytokines/chemokines. Moreover, periodontal bacteria may promote ROS overproduction via downregulation of the enzymatic antioxidant defense system, leading to oxidative stress. Crosstalk between players of inflammation and oxidative stress contributes to disruption of the insulin signaling pathway and promotes insulin resistance. In parallel, periodontal bacteria alter glucose and lipid metabolism in the liver and deregulate insulin production by pancreatic β-cells, contributing to hyperglycemia. Interestingly, therapeutic management of periodontitis reduces systemic inflammation markers and ameliorates insulin sensitivity in type 2 diabetic patients. Of note, plant polyphenols exert anti-inflammatory and antioxidant activities as well as insulin-sensitizing and anti-bacterial actions. Thus, polyphenol-based therapies are of high interest for helping to counteract the deleterious effects of periodontal bacteria and improve insulin resistance.

Research Progress on Neuroprotection of Insulin-like Growth Factor-1 towards Glutamate-Induced Neurotoxicity

Insulin-like growth factor-1 (IGF-1) and its binding proteins and receptors are widely expressed in the central nervous system (CNS), proposing IGF-1-induced neurotrophic actions in normal growth, development, and maintenance. However, while there is convincing evidence that the IGF-1 system has specific endocrine roles in the CNS, the concept is emerging that IGF-I might be also important in disorders such as ischemic stroke, brain trauma, Alzheimer’s disease, epilepsy, etc., by inducing neuroprotective effects towards glutamate-mediated excitotoxic signaling pathways. Research in rodent models has demonstrated rescue of pathophysiological and behavioral abnormalities when IGF-1 was administered by different routes, and several clinical studies have shown safety and promise of efficacy in neurological disorders of the CNS. Focusing on the relationship between IGF-1-induced neuroprotection and glutamate-induced excitatory neurotoxicity, this review addresses the research progress in the field, intending to provide a rationale for using IGF-I clinically to confer neuroprotective therapy towards neurological diseases with glutamate excitotoxicity as a common pathological pathway.

Shared Molecular Mechanisms among Alzheimer’s Disease, Neurovascular Unit Dysfunction and Vascular Risk Factors: A Narrative Review

Alzheimer’s disease (AD) is the most common type of dementia, affecting 24 million individuals. Clinical and epidemiological studies have found several links between vascular risk factors (VRF), neurovascular unit dysfunction (NVUd), blood-brain barrier breakdown (BBBb) and AD onset and progression in adulthood, suggesting a pathogenetic continuum between AD and vascular dementia. Shared pathways between AD, VRF, and NVUd/BBB have also been found at the molecular level, underlining the strength of this association. The present paper reviewed the literature describing commonly shared molecular pathways between adult-onset AD, VRF, and NVUd/BBBb. Current evidence suggests that VRF and NVUd/BBBb are involved in AD neurovascular and neurodegenerative pathology and share several molecular pathways. This is strongly supportive of the hypothesis that the presence of VRF can at least facilitate AD onset and progression through several mechanisms, including NVUd/BBBb. Moreover, vascular disease and several comorbidities may have a cumulative effect on VRF and worsen the clinical manifestations of AD. Early detection and correction of VRF and vascular disease by improving NVUd/BBBd could be a potential target to reduce the overall incidence and delay cognitive impairment in AD.

The impact of the gut microbiota on the reproductive and metabolic endocrine system

As the gut microbiota exerts various effects on the intestinal milieu which influences distant organs and pathways, it is considered to be a full-fledged endocrine organ. The microbiota plays a major role in the reproductive endocrine system throughout a woman's lifetime by interacting with estrogen, androgens, insulin, and other hormones. Imbalance of the gut microbiota composition can lead to several diseases and conditions, such as pregnancy complications, adverse pregnancy outcomes, polycystic ovary syndrome (PCOS), endometriosis, and cancer; however, research on the mechanisms is limited. More effort should be concentrated on exploring the potential causes and underlying the mechanisms of microbiota-hormone-mediated disease, and providing novel therapeutic and preventive strategies.As the gut microbiota exerts various effects on the intestinal milieu which influences distant organs and pathways, it is considered to be a full-fledged endocrine organ. The microbiota plays a major role in the reproductive endocrine system throughout a woman's lifetime by interacting with estrogen, androgens, insulin, and other hormones. Imbalance of the gut microbiota composition can lead to several diseases and conditions, such as pregnancy complications, adverse pregnancy outcomes, polycystic ovary syndrome (PCOS), endometriosis, and cancer; however, research on the mechanisms is limited. More effort should be concentrated on exploring the potential causes and underlying the mechanisms of microbiota-hormone-mediated disease, and providing novel therapeutic and preventive strategies.

Hypoglycemia due to PI3K/AKT/mTOR signaling pathway defects: two novel cases and review of the literature

INTRODUCTION

The PI3K/AKT/mTOR signaling pathway is important for the regulation of multiple biological processes, including cellular growth and glucose metabolism. Defects of the PI3K/AKT/mTOR signaling pathway are not usually considered among the genetic causes of recurrent hypoglycemia in childhood. However, accumulating evidence links hypoglycemia with defects of this pathway.

CASE REPORTS AND REVIEW

We describe here two cases of macrocephaly and hypoglycemia bearing genetic defects in genes involved in the PI3K/AKT/mTOR pathway. The first patient was diagnosed with a PTEN hamartoma tumour syndrome (PTHS) due to the de novo germline missense mutation c.[492 + 1G > A] of the PTEN gene. The second patient presented the autosomal dominant mental retardation-35 (MDR35) due to the heterozygous missense mutation c.592G > A in the PPP2R5D gene. A review of the literature on hypoglycemia and PI3K/AKT/mTOR signaling pathway defects, with a special focus on the metabolic characterization of hypoglycemia, is included.

CONCLUSIONS

PI3K/AKT/mTOR pathway defects should be included in the differential diagnosis of patients with hypoglycemia and macrocephaly. Clinical suspicion and molecular confirmation are important, not just for an accurate genetic counselling but also for defining the follow-up management, including cancer surveillance. The biochemical profile of hypoglycemia varies among patients. While most patients are characterized by low plasmatic insulin levels, hyperinsulinemia has also been observed. Large patient cohorts are needed to gain a comprehensive profile of the biochemical patterns of hypoglycemia in such defects and eventually guide targeted therapeutic interventions.

Insulin Resistance and Cancer: In Search for a Causal Link

Insulin resistance (IR) is a condition which refers to individuals whose cells and tissues become insensitive to the peptide hormone, insulin. Over the recent years, a wealth of data has made it clear that a synergistic relationship exists between IR, type 2 diabetes mellitus, and cancer. Although the underlying mechanism(s) for this association remain unclear, it is well established that hyperinsulinemia, a hallmark of IR, may play a role in tumorigenesis. On the other hand, IR is strongly associated with visceral adiposity dysfunction and systemic inflammation, two conditions which favor the establishment of a pro-tumorigenic environment. Similarly, epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNA, in IR states, have been often associated with tumorigenesis in numerous types of human cancer. In addition to these observations, it is also broadly accepted that gut microbiota may play an intriguing role in the development of IR-related diseases, including type 2 diabetes and cancer, whereas potential chemopreventive properties have been attributed to some of the most commonly used antidiabetic medications. Herein we provide a concise overview of the most recent literature in this field and discuss how different but interrelated molecular pathways may impact on tumor development.