IRS2 integrates insulin/IGF1 signalling with metabolism, neurodegeneration and longevity

Timing of TORC1 inhibition dictates Pol III involvement in Caenorhabditis elegans longevity

Organismal growth and lifespan are inextricably linked. Target of Rapamycin (TOR) signalling regulates protein production for growth and development, but if reduced, extends lifespan across species. Reduction in the enzyme RNA polymerase III, which transcribes tRNAs and 5S rRNA, also extends longevity. Here, we identify a temporal genetic relationship between TOR and Pol III in Caenorhabditis elegans, showing that they collaborate to regulate progeny production and lifespan. Interestingly, the lifespan interaction between Pol III and TOR is only revealed when TOR signaling is reduced, specifically in adulthood, demonstrating the importance of timing to control TOR regulated developmental versus adult programs. In addition, we show that Pol III acts in C. elegans muscle to promote both longevity and healthspan and that reducing Pol III even in late adulthood is sufficient to extend lifespan. This demonstrates the importance of Pol III for lifespan and age-related health in adult C. elegans.

Metabolic perturbations in pregnant rats exposed to low-dose perfluorooctanesulfonic acid: An integrated multi-omics analysis

Emerging epidemiological evidence has linked per- and polyfluoroalkyl substances (PFAS) exposure could be linked to the disturbance of gestational glucolipid metabolism, but the toxicological mechanism is unclear, especially when the exposure is at a low level. This study examined the glucolipid metabolic changes in pregnant rats treated with relatively low dose perfluorooctanesulfonic acid (PFOS) through oral gavage during pregnancy [gestational day (GD): 1-18]. We explored the molecular mechanisms underlying the metabolic perturbation. Oral glucose tolerance test (OGTT) and biochemical tests were performed to assess the glucose homeostasis and serum lipid profiles in pregnant Sprague-Dawley (SD) rats randomly assigned to starch, 0.03 and 0.3 mg/kg·bw·d groups. Transcriptome sequencing combined with non-targeted metabolomic assays were further performed to identify differentially altered genes and metabolites in the liver of maternal rats, and to determine their correlation with the maternal metabolic phenotypes. Results of transcriptome showed that differentially expressed genes at 0.03 and 0.3 mg/kg·bw·d PFOS exposure were related to several metabolic pathways, such as peroxisome proliferator-activated receptors (PPARs) signaling, ovarian steroid synthesis, arachidonic acid metabolism, insulin resistance, cholesterol metabolism, unsaturated fatty acid synthesis, bile acid secretion. The untargeted metabolomics identified 164 and 158 differential metabolites in 0.03 and 0.3 mg/kg·bw·d exposure groups, respectively under negative ion mode of Electrospray Ionization (ESI-), which could be enriched in metabolic pathways such as α-linolenic acid metabolism, glycolysis/gluconeogenesis, glycerolipid metabolism, glucagon signaling pathway, glycine, serine and threonine metabolism. Co-enrichment analysis indicated that PFOS exposure may disturb the metabolism pathways of glycerolipid, glycolysis/gluconeogenesis, linoleic acid, steroid biosynthesis, glycine, serine and threonine. The key involved genes included down-regulated Ppp1r3c and Abcd2, and up-regulated Ogdhland Ppp1r3g, and the key metabolites such as increased glycerol 3-phosphate and lactosylceramide were further identified. Both of them were significantly associated with maternal fasting blood glucose (FBG) level. Our findings may provide mechanistic clues for clarifying metabolic toxicity of PFOS in human, especially for susceptible population such as pregnant women.

Identification of key regulatory genes and their working mechanisms in type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of beta cells in pancreatic islets. Identification of the key genes involved in T1D progression and their mechanisms of action may contribute to a better understanding of T1D.

METHODS

The microarray profile of T1D-related gene expression was searched using the Gene Expression Omnibus (GEO) database. Then, the expression data of two messenger RNAs (mRNAs) were integrated for Weighted Gene Co-Expression Network Analysis (WGCNA) to generate candidate genes related to T1D. In parallel, T1D microRNA (miRNA) data were analyzed to screen for possible regulatory miRNAs and their target genes. An miRNA-mRNA regulatory network was then established to predict the key regulatory genes and their mechanisms.

RESULTS

A total of 24 modules (i.e., clusters/communities) were selected using WGCNA analysis, in which three modules were significantly associated with T1D. Further correlation analysis of the gene module revealed 926 differentially expressed genes (DEGs), of which 327 genes were correlated with T1D. Analysis of the miRNA microarray showed that 13 miRNAs had significant expression differences in T1D. An miRNA-mRNA network was established based on the prediction of miRNA target genes and the combined analysis of mRNA, in which the target genes of two miRNAs were found in T1D correlated genes.

CONCLUSION

An miRNA-mRNA network for T1D was established, based on which 2 miRNAs and 12 mRNAs were screened, suggesting that they may play key regulatory roles in the initiation and development of T1D.

Protective role of IGF-1 and GLP-1 signaling activation in neurological dysfunctions

Insulin-like growth factor-1 (IGF-1), a pleiotropic polypeptide, plays an essential role in CNS development and maturation. Glucagon-like peptide-1 (GLP-1) is an endogenous incretin hormone that regulates blood glucose levels and fatty acid oxidation in the brain. GLP-1 also exhibits similar functions and growth factor-like properties to IGF-1, which is likely how it exerts its neuroprotective effects. Recent preclinical and clinical evidence indicate that IGF-1 and GLP-1, apart from regulating growth and development, prevent neuronal death mediated by amyloidogenesis, cerebral glucose deprivation, neuroinflammation and apoptosis through modulation of PI3/Akt kinase, mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK/ERK). IGF-1 resistance and GLP-1 deficiency impair protective cellular signaling mechanisms, contributing to the progression of neurodegenerative diseases. Over the past decades, IGF-1 and GLP-1 have emerged as an essential component of the neuronal system and as potential therapeutic targets for several neurodegenerative and neuropsychiatric dysfunctions. There is substantial evidence that IGF-1 and GLP-1 analogues penetrate the blood-brain barrier (BBB) and exhibit neuroprotective functions, including synaptic formation, neuronal plasticity, protein synthesis, and autophagy. Conclusively, this review represents the therapeutic potential of IGF-1 and GLP-1 signaling target activators in ameliorating neurological disorders.

Dynamic Alteration Profile and New Role of RNA m6A Methylation in Replicative and H2O2-Induced Premature Senescence of Human Embryonic Lung Fibroblasts

N6-methyladenosine (m6A) methylation is one of the most common RNA modifications, regulating RNA fate at the posttranscriptional level, and is closely related to cellular senescence. Both models of replicative and premature senescence induced by hydrogen peroxide (H₂O₂) were used to detect m6A regulation during the senescence of human embryonic lung fibroblasts (HEFs). The ROS level accumulated gradually with senescence, leading to normal replicative senescence. H₂O₂-treated cells had dramatically increased ROS level, inducing the onset of acute premature senescence. Compared with replicative senescence, ROS changed the expression profiles for m6A-related enzymes and binding proteins, including higher levels of METTL3, METTL14, WTAP, KIAA1429, and FTO, and lower levels of METTL16, ALKBH5, YTHDC1, and YTHDF1/2/3 in the premature senescence persistence group, respectively. Meanwhile, senescent cells decreased total m6A content and RNA methylation enzymes activity, regardless of replicative or premature senescence. Moreover, specific m6A methylation levels regulated the expression of SIRT3, IRS2, and E2F3 between replicative and premature senescence separately. Taken together, differential m6A epitranscription microenvironment and the targeted genes can be used as epigenetic biomarkers to cell senescence and the related diseases, offering new clues for the prevention and intervention of cellular senescence.

Efficient generation of functional pancreatic β cells from dental-derived stem cells via laminin-induced differentiation

Background

This study was designed to generate functional insulin-producing cells (IPCs) from dental-derived mesenchymal stem cells (MSCs) and further explore their therapeutic potential against diabetes mellitus in vivo. MSCs were isolated from human dental pulp and periodontal ligament and were induced to differentiate into insulin-producing cells (IPCs) using laminin-based differentiation protocol for 14 days. Confirmation of IPCs was performed through real-time PCR analysis and insulin release assay. Then, the generated IPCs were labeled with PKH26 dye prior to transplantation in experimental animals. Twenty-eight days later, blood glucose, serum insulin (INS), c-peptide (CP), and visfatin (VF) levels and pancreatic glucagon (GC) level were estimated. Pancreatic forkhead box protein A2 (Foxa2) and SRY-box transcription factor 17 (Sox17), insulin-like growth factor I (IGF-1), and fibroblast growth factor10 (FGF 10) gene expression levels were analyzed.

Results

Dental stem cells were successfully differentiated into IPCs that demonstrated increased expression of pancreatic endocrine genes. IPCs released insulin after being subjected to high levels of glucose. In vivo findings uncovered that the implanted IPCs triggered significant decrease in blood glucose, serum VF, and pancreatic GC levels with significant increase in serum INS and CP levels. Furthermore, the implanted IPCs provoked significant upregulation in the expression level of pancreatic genes. Histopathological description of the pancreas tissues revealed that transplantation of IPCs ameliorated the destabilization of pancreas tissue architecture.

Conclusion

This study demonstrates the significant role of the implantation of IPCs generated from dental-derived stem cells in treatment of diabetes mellitus.

Neuroprotective Effects of Cholinesterase Inhibitors: Current Scenario in Therapies for Alzheimer’s Disease and Future Perspectives

Alzheimer’s disease (AD) is a slowly progressive neurodegenerative disease conceptualized as a continuous process, ranging from mild cognitive impairment (MCI), to the mild, moderate, and severe clinical stages of AD dementia. AD is considered a complex multifactorial disease. Currently, the use of cholinesterase inhibitors (ChEI), such as tacrine, donepezil, rivastigmine, and galantamine, has been the main treatment for AD patients. Interestingly, there is evidence that ChEI also promotes neuroprotective effects, bringing some benefits to AD patients. The mechanisms by which the ChEI act have been investigated in AD. ChEI can modulate the PI3K/AKT pathway, which is an important signaling cascade that is capable of causing a significant functional impact on neurons by activating cell survival pathways to promote neuroprotective effects. However, there is still a huge challenge in the field of neuroprotection, but in the context of unravelling the details of the PI3K/AKT pathway, a new scenario has emerged for the development of more efficient drugs that act on multiple protein targets. Thus, the mechanisms by which ChEI can promote neuroprotective effects and prospects for the development of new drug candidates for the treatment of AD are discussed in this review.

Challenges and approaches of drugs such as Memantine, Donepezil, Rivastigmine and Aducanumab in the treatment, control and management of Alzheimer's disease

Alzheimer's disease (AD) is a kinds of neuropsychiatric illnesses that affect the central nervous system. In this disease, the accumulation of amyloid-beta increases, and phosphorylated tau (P-tau) protein, one of the ways to treat this disease is to reduce the accumulation of amyloid-beta. Various studies have demonstrated that pharmacological approaches have considerable effects in the treatment of AD, despite the side effects and challenges. Cholinesterase inhibitors and the NMDA receptor antagonist memantine are presently authorized therapies for AD. Memantine and Donepezil are the most common drugs for the prevention and therapy of AD with mechanisms such as lessened β-amyloid plaque, effect on N-Methyl-D-aspartate (NMDA) receptors. Diminution glutamate and elevated acetylcholine are some of the influences of medications administrated to treat AD, and drugs can also play a role in slowing the progression of cognitive and memory impairment. A new pharmacological approach and strategy is required to control the future of AD. This review appraises the effects of memantine, donepezil, rivastigmine, and aducanumab in clinical trials, in vitro and animal model studies that have explored how these drugs versus AD development and also discuss possible mechanisms of influence on the brain. Research in clinical trials has substantial findings that support the role of these medications in AD treatment and ameliorate the safety and efficacy of AD therapy, although more clinical trials are required to prove their effectiveness.

The neuroprotective effects of intermittent fasting on brain aging and neurodegenerative diseases via regulating mitochondrial function

Intermittent fasting (IF) has been studied for its effects on lifespan and the prevention or delay of age-related diseases upon the regulation of metabolic pathways. Mitochondria participate in key metabolic pathways and play important roles in maintaining intracellular signaling networks that modulate various cellular functions. Mitochondrial dysfunction has been described as an early feature of brain aging and neurodegeneration. Although IF has been shown to prevent brain aging and neurodegeneration, the mechanism is still unclear. This review focuses on the mechanisms by which IF improves mitochondrial function, which plays a central role in brain aging and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. The cellular and molecular mechanisms of IF in brain aging and neurodegeneration involve activation of adaptive cellular stress responses and signaling- and transcriptional pathways, thereby enhancing mitochondrial function, by promoting energy metabolism and reducing oxidant production.

Mechanisms underlying the pathophysiology of type 2 diabetes: From risk factors to oxidative stress, metabolic dysfunction, and hyperglycemia

Type 2 diabetes (T2D) is a complex multifactorial disease that emerges from the combination of genetic and environmental factors, and obesity, lifestyle, and aging are the most relevant risk factors. Hyperglycemia is the main metabolic feature of T2D as a consequence of insulin resistance and β-cell dysfunction. Among the cellular alterations induced by hyperglycemia, the overproduction of reactive oxygen species (ROS) and consequently oxidative stress, accompanied by a reduced antioxidant response and impaired DNA repair pathways, represent essential mechanisms underlying the pathophysiology of T2D and the development of late complications. Mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and inflammation are also closely correlated with insulin resistance and β-cell dysfunction. This review focus on the mechanisms by which oxidative stress, mitochondrial dysfunction, ER stress, and inflammation are involved in the pathophysiology of T2D, highlighting the importance of the antioxidant response and DNA repair mechanisms counteracting the development of the disease. Moreover, we indicate evidence on how nutritional interventions effectively improve diabetes care. Additionally, we address key molecular characteristics and signaling pathways shared between T2D and Alzheimer's disease (AD), which might probably be implicated in the risk of T2D patients to develop AD.

Circular RNA circ_0070441 regulates MPP+-triggered neurotoxic effect in SH-SY5Y cells via miR-626/IRS2 axis

Circular RNAs (circRNAs) was suggested to play crucial regulatory roles in various human diseases, including Parkinson's disease (PD). This research aimed to investigate the function and potential mechanism of circ_0070441 in PD. MPP⁺ (1-methyl-4-phenylpyridinium)-treated SH-SY5Y cells was used as an in vitro cellular PD model. The expressions of circ_0070441, microRNA (miR)-626 and insulin receptor substrate 2 (IRS2) were measured by quantitative real-time polymerase chain reaction (RT-qPCR) or western blot. Cell Counting Kit-8 (CCK-8) assay, Cytotoxicity Detection Kit (Lactate Dehydrogenase), flow cytometry and Caspase-3 Assay Kit were used to detect cell viability, LDH release, cell apoptosis and caspase-3 activity, respectively. The levels of inflammation-related factors were detected by enzyme-linked immunosorbent assay (ELISA). The correlation among circ_0070441, miR-626 and IRS2 were confirmed by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay. The levels of circ_0070441 and IRS2 were increased while miR-626 expression was decreased in MPP⁺-treated SH-SY5Y cells in dose- and time-dependent manners. Depletion of circ_0070441 alleviated MPP⁺-triggered neuronal damage by regulating cell apoptosis and inflammation. Circ_0070441 acted as a sponge for miR-626, and IRS2 was a target of miR-626. Besides, the neuroprotective effects of circ_0070441 knockdown or miR-626 overexpression were partly overturned by the suppression of miR-626 or IRS2 overexpression. Moreover, circ_0070441 upregulated IRS2 expression by interacting with miR-626. In summary, circ_0070441 aggravated MPP⁺-triggered neurotoxic effect in SH-SY5Y cells by regulating miR-626/IRS2 axis.

Hyperuricemia contributes to glucose intolerance of hepatic inflammatory macrophages and impairs the insulin signaling pathway via IRS2-proteasome degradation

AIM

Numerous reports have demonstrated the key importance of macrophage-elicited metabolic inflammation in insulin resistance (IR). Our previous studies confirmed that hyperuricemia or high uric acid (HUA) treatment induced an IR state in several peripheral tissues to promote the development of type 2 diabetes mellitus (T2DM). However, the effect of HUA on glucose uptake and the insulin sensitivity of macrophages and its mechanism is unclear.

METHODS

To assess systemic IR, we generated hyperuricemic mice by urate oxidase knockout (UOX-KO). Then, glucose/insulin tolerance, the tissue uptake of 18F-fluorodeoxyglucose, body composition, and energy balance were assessed. Glucose uptake of circulating infiltrated macrophages in the liver was evaluated by glucose transporter type 4 (GLUT-4) staining. Insulin sensitivity and the insulin signaling pathway of macrophages were demonstrated using the 2-NBDG kit, immunoblotting, and immunofluorescence assays. The immunoprecipitation assay and LC-MS analysis were used to determine insulin receptor substrate 2 (IRS2) levels and its interacting protein enrichment under HUA conditions.

RESULTS

Compared to WT mice (10 weeks old), serum uric acid levels were higher in UOX-KO mice (WT, 182.3 ± 5.091 μM versus KO, 421.9 ± 45.47 μM). Hyperuricemic mice with metabolic disorders and systemic IR showed inflammatory macrophage recruitment and increased levels of circulating proinflammatory cytokines. HUA inhibited the nuclear translocation of GLUT-4 in hepatic macrophages, restrained insulin-induced glucose uptake and glucose tolerance, and blocked insulin IRS2/PI3K/AKT signaling. Meanwhile, HUA mediated the IRS2 protein degradation pathway and activated AMPK/mTOR in macrophages. LC-MS analysis showed that ubiquitination degradation could be involved in IRS2 and its interacting proteins to contribute to IR under HUA conditions.

CONCLUSION

The data suggest that HUA-induced glucose intolerance in hepatic macrophages contributed to insulin resistance and impaired the insulin signaling pathway via IRS2-proteasome degradation.

Aging modulated by the Drosophila insulin receptor through distinct structure-defined mechanisms

Mutations of the Drosophila melanogaster insulin/IGF signaling system slow aging, while also affecting growth and reproduction. To understand this pleiotropy, we produced an allelic series of single codon substitutions in the Drosophila insulin receptor, InR. We generated InR substitutions using homologous recombination and related each to emerging models of receptor tyrosine kinase structure and function. Three mutations when combined as trans-heterozygotes extended lifespan while retarding growth and fecundity. These genotypes reduced insulin-stimulated Akt phosphorylation, suggesting they impede kinase catalytic domain function. Among these genotypes, longevity was negatively correlated with egg production, consistent with life-history trade-off theory. In contrast, one mutation (InR353) was located in the kinase insert domain, a poorly characterized element found in all receptor tyrosine kinases. Remarkably, wild-type heterozygotes with InR353 robustly extended lifespan without affecting growth or reproduction and retained capacity to fully phosphorylate Akt. The Drosophila insulin receptor kinase insert domain contains a previously unrecognized SH2 binding motif. We propose the kinase insert domain interacts with SH2-associated adapter proteins to affect aging through mechanisms that retain insulin sensitivity and are independent of reproduction.

From population to neuron: exploring common mediators for metabolic problems and mental illnesses

Major mental illnesses such as schizophrenia (SZ) and bipolar disorder (BP) frequently accompany metabolic conditions, but their relationship is still unclear, in particular at the mechanistic level. We implemented an approach of "from population to neuron", combining population-based epidemiological analysis with neurobiological experiments using cell and animal models based on a hypothesis built from the epidemiological study. We characterized high-quality population data, olfactory neuronal cells biopsied from patients with SZ or BP, and healthy subjects, as well as mice genetically modified for insulin signaling. We accessed the Danish Registry and observed (1) a higher incidence of diabetes in people with SZ or BP and (2) higher incidence of major mental illnesses in people with diabetes in the same large cohort. These epidemiological data suggest the existence of common pathophysiological mediators in both diabetes and major mental illnesses. We hypothesized that molecules associated with insulin resistance might be such common mediators, and then validated the hypothesis by using two independent sets of olfactory neuronal cells biopsied from patients and healthy controls. In the first set, we confirmed an enrichment of insulin signaling-associated molecules among the genes that were significantly different between SZ patients and controls in unbiased expression profiling data. In the second set, olfactory neuronal cells from SZ and BP patients who were not pre-diabetic or diabetic showed reduced IRS2 tyrosine phosphorylation upon insulin stimulation, indicative of insulin resistance. These cells also displayed an upregulation of IRS1 protein phosphorylation at serine-312 at baseline (without insulin stimulation), further supporting the concept of insulin resistance in olfactory neuronal cells from SZ patients. Finally, Irs2 knockout mice showed an aberrant response to amphetamine, which is also observed in some patients with major mental illnesses. The bi-directional relationships between major mental illnesses and diabetes suggest that there may be common pathophysiological mediators associated with insulin resistance underlying these mental and physical conditions.

The inflammatory role of dysregulated IRS2 in pulmonary vascular remodeling under hypoxic conditions

Pulmonary hypertension (PH) is a devastating disease characterized by progressive elevation of pulmonary vascular resistance, right ventricular failure, and ultimately death. We have shown previously that insulin receptor substrate 2 (IRS2), a molecule highly critical to insulin resistance and metabolism, has an anti-inflammatory role in Th2-skewed lung inflammation and pulmonary vascular remodeling. Here, we investigated the hypothesis that IRS2 has an immunomodulatory role in human and experimental PH. Expression analysis showed that IRS2 was significantly decreased in the pulmonary vasculature of patients with pulmonary arterial hypertension and in rat models of PH. In mice, genetic ablation of IRS2 enhanced the hypoxia-induced signaling pathway of Akt and Forkhead box O1 (FOXO1) in the lung tissue and increased pulmonary vascular muscularization, proliferation, and perivascular macrophage recruitment. Furthermore, mice with homozygous IRS2 gene deletion showed a significant gene dosage-dependent increase in pulmonary vascular remodeling and right ventricular hypertrophy in response to hypoxia. Functional studies with bone marrow-derived macrophages isolated from homozygous IRS2 gene-deleted mice showed that hypoxia exposure led to enhancement of the Akt and ERK signaling pathway followed by increases in the pro-PH macrophage activation markers, vascular endothelial growth factor-A and arginase 1. Our data suggest that IRS2 contributes to anti-inflammatory effects by regulating macrophage activation and recruitment, which may limit the vascular inflammation, remodeling, and right ventricular hypertrophy that are seen in PH pathology. Restoring the IRS2 pathway may be an effective therapeutic approach for the treatment of PH and right heart failure.

Glucocorticoid receptor triggers a reversible drug-tolerant dormancy state with acquired therapeutic vulnerabilities in lung cancer

The glucocorticoid receptor (GR) regulates gene expression, governing aspects of homeostasis, but is also involved in cancer. Pharmacological GR activation is frequently used to alleviate therapy-related side-effects. While prior studies have shown GR activation might also have anti-proliferative action on tumours, the underpinnings of glucocorticoid action and its direct effectors in non-lymphoid solid cancers remain elusive. Here, we study the mechanisms of glucocorticoid response, focusing on lung cancer. We show that GR activation induces reversible cancer cell dormancy characterised by anticancer drug tolerance, and activation of growth factor survival signalling accompanied by vulnerability to inhibitors. GR-induced dormancy is dependent on a single GR-target gene, CDKN1C, regulated through chromatin looping of a GR-occupied upstream distal enhancer in a SWI/SNF-dependent fashion. These insights illustrate the importance of GR signalling in non-lymphoid solid cancer biology, particularly in lung cancer, and warrant caution for use of glucocorticoids in treatment of anticancer therapy related side-effects.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

Skeletal muscle transcriptome in healthy aging

Age-associated changes in gene expression in skeletal muscle of healthy individuals reflect accumulation of damage and compensatory adaptations to preserve tissue integrity. To characterize these changes, RNA was extracted and sequenced from muscle biopsies collected from 53 healthy individuals (22-83 years old) of the GESTALT study of the National Institute on Aging-NIH. Expression levels of 57,205 protein-coding and non-coding RNAs were studied as a function of aging by linear and negative binomial regression models. From both models, 1134 RNAs changed significantly with age. The most differentially abundant mRNAs encoded proteins implicated in several age-related processes, including cellular senescence, insulin signaling, and myogenesis. Specific mRNA isoforms that changed significantly with age in skeletal muscle were enriched for proteins involved in oxidative phosphorylation and adipogenesis. Our study establishes a detailed framework of the global transcriptome and mRNA isoforms that govern muscle damage and homeostasis with age.

The lack of Irs2 induces changes in the immunocytochemical expression of aromatase in the mouse retina

Insulin receptor substrate (Irs) belongs to a family of proteins that mediate the intracellular signaling of insulin and IGF-1. Insulin receptor substrate 2 (Irs2) is necessary for retinal function, since its failure in Irs2-deficient mice in hyperglycemic situation promotes photoreceptor degeneration and visual dysfunction, like in diabetic retinopathy. The expression of P450 aromatase, which catalyzes androgen aromatization to form 17ß-estradiol, increases in some neurodegenerative diseases thus promoting the local synthesis of neuroestrogens that exert relevant neuroprotective functions. Aromatase is also expressed in neurons and glial cells of the central nervous system (CNS), including the retina. To further understand the role of Irs2 at the retinal level, we performed an immunocytochemical study in adult normoglycemic Irs2-deficient mice. For this aim, the retinal immunoexpression of neuromodulators, such as aromatase, glutamine synthetase (GS), and tyrosine hydroxylase (TH) was analyzed, joint to a morphometric and planimetric study of the retinal layers. Comparing with wild-type (WT) control mice, the Irs2-knockout (Irs2-KO) animals showed a significant increase in the immunopositivity to aromatase in almost all of the retinal layers. Besides, Irs2-KO mice exhibited a decreased immunopositive reaction for GS and TH, in Müller and amacrine cells, respectively; morphological variations were also found in these retinal cell types. Furthermore, the retina of Irs2-KO mice displayed alterations in the structural organization, and a generalized decrease in the retinal thickness was observed in each of the layers, except for the inner nuclear layer. Our findings suggest that the absence of Irs2 induces retinal neurodegenerative changes in Müller and amacrine cells that are unrelated to hyperglycemia. Accordingly, in the Irs2-KO mice, the increased retinal immunocytochemical reactivity of aromatase could be associated with an attempt to repair such neural retina injuries by promoting local neuroprotective mediators.

SOX21-AS1 modulates neuronal injury of MMP+-treated SH-SY5Y cells via targeting miR-7-5p and inhibiting IRS2

Parkinson's disease (PD), caused by the decreased number of dopaminergic neurons in the substantia nigra, is identified as the second most familiar age-dependent neurodegenerative disease to the public. Long non-coding RNAs (lncRNAs) have been reported to participate in the development of PD. In our research, the expression of lncRNA SRY-box transcription factor 21 antisense divergent transcript 1 (SOX21-AS1) was up-regulated in 1-methyl-4-phenylpyridinium (MMP⁺)-treated SH-SY5Y cells. In addition, SOX21-AS1 depletion weakened the cell injury induced by MMP⁺. Moreover, SOX21-AS1 knockdown decreased Reactive Oxygen Species (ROS) generation and levels of TNF-α, IL-1β and IL-6, but increased SOD activity. However, SOX21-AS1 up-regulation led to opposite results. Further, SOX21-AS1 could bind with miR-7-5p, whose overexpression relieved MMP⁺-induced cell injury. Additionally, insulin receptor substrate 2 (IRS2) served as the target gene of miR-7-5p, and its expression was positively modulated by SOX21-AS1. Similarly, IRS2 knockdown also had alleviative effects on cell injury stimulated by MMP⁺ treatment. In sum up, our study demonstrated a new regulatory network consisted of SOX21-AS1, miR-7-5p and IRS2 in SH-SY5Y cells, supplying with a better comprehension about the pathogenic mechanism of PD.

Aging Regulated Through a Stability Model of Insulin/Insulin Growth Factor Receptor Function

Mutations of the insulin-like receptor in Drosophila extend lifespan. New research suggests this receptor operates in two modes. The first extends lifespan while slowing reproduction and reducing growth. The second strongly extends lifespan without impairing growth or reproduction; it confers longevity assurance. The mutation that confers longevity assurance resides in the kinase insert domain, which contains a potential SH2 binding site for substrate proteins. We apply a recent model for the function of receptor tyrosine kinases to propose how insulin receptor structure can modulate aging. This concept hypothesizes that strong insulin-like ligands promote phosphorylation of high threshold substrate binding sites to robustly induce reproduction, which impairs survival as a consequence of trade-offs. Lower levels of receptor stimulation provide less kinase dimer stability, which reduces reproduction and extends lifespan by avoiding reproductive costs. Environmental conditions that favor diapause alter the expression of insulin ligands to further repress the stability of the interacting kinase domains, block phosphorylation of low threshold substrates and thus induce a unique molecular program that confers longevity assurance. Mutations of the insulin receptor that block low-phosphorylation site interactions, such as within the kinase insert domain, can extend lifespan while maintaining overall dimer stability. These flies are long-lived while maintaining reproduction and growth. The kinase insert domain of Drosophila provides a novel avenue from which to seek signaling of the insulin/insulin-like growth factor system of humans that modulate aging without impacting reproduction and growth, or incurring insulin resistance pathology.

Selective neuronal vulnerability in Alzheimer's disease

Alzheimer's disease (AD) is defined by a deficiency in specific behavioural and/or cognitive domains, pointing to selective vulnerabilities of specific neurons from different brain regions. These vulnerabilities can be compared across neuron subgroups to identify the most vulnerable neuronal types, regions, and time points for further investigation. Thus, the relevant organizational frameworks for brain subgroups will hold great values for a clear understanding of the progression in AD. Presently, the neuronal vulnerability has yet urgently required to be elucidated as not yet been clearly defined. It is suggested that cell-autonomous and non-cell-autonomous mechanisms can affect the neuronal vulnerability to stressors, and in turn modulates AD progression. This review examines cell-autonomous and non-cell-autonomous mechanisms that contribute to the neuronal vulnerability. Collectively, the cell-autonomous mechanisms seem to be the primary drivers responsible for initiating specific stressor-related neuronal vulnerability with pathological changes in certain brain areas, which then utilize non-cell-autonomous mechanisms and result in subsequent progression of AD. In summary, this article has provided a new perspective on the preventative and therapeutic options for AD.

Oxygen and embryonic growth: the role of insulin-like growth factor signaling

Oxygen is indispensable for the efficient release of chemical energy from nutrient molecules in cells. Therefore, the local oxygen tension is one of the most critical factors affecting physiological processes. In most viviparous species, many pathological conditions result in abnormal oxygen tension in the uterus, which modifies the growth and development of the fetus. Insulin-like growth factor (IGF/Igf) is one of the most important hormones for the regulation of somatic growth in animals. Changes in oxygen levels modulate the activity of the IGF/Igf signaling system, which in turn regulates the embryonic growth rate. In general, there are serious difficulties associated with monitoring and studying rodent embryos in utero. The zebrafish is a convenient experimental model to study the relationship between embryonic growth and environmental conditions. Most importantly, the fish model makes it possible to rapidly evaluate embryonic growth and development under entirely controlled environments without interfering with the mother organism. In this review, firstly an overview is given of the fluctuation of environmental oxygen, the IGF-system, and the advantages of the zebrafish model for studying embryonic growth. Then, the relationships of dynamic environmental oxygen and embryonic growth rate are outlined with a specific focus on the changes in the IGF/Igf-system in the zebrafish model. This review will shed light on the fine-tuning mechanisms of the embryonic IGF/Igf-system under different oxygen levels, including constant normoxia, hypoxia, and re-oxygenation.

Disruption of insulin receptor substrate-2 impairs growth but not insulin function in rats

Insulin receptor substrate (IRS)-2, along with IRS-1, is a key signaling molecule that mediates the action of insulin and insulin-like growth factor (IGF)-I. The activated insulin and IGF-I receptors phosphorylate IRSs on tyrosine residues, leading to the activation of downstream signaling pathways and the induction of various physiological functions of insulin and IGF-I. Studies using IRS-2 knockout (KO) mice showed that the deletion of IRS-2 causes type 2 diabetes due to peripheral insulin resistance and impaired β-cell function. However, little is known about the roles of IRS-2 in other animal models. Here, we created IRS-2 KO rats to elucidate the physiological functions of IRS-2 in rats. The body weights of IRS-2 KO rats at birth were lower compared with those of their WT littermates. The postnatal growth of both male and female IRS-2 KO rats was also suppressed. Compared with male WT rats, the glucose and insulin tolerance of male IRS-2 KO rats were slightly enhanced, whereas a similar difference was not observed between female WT and IRS-2 KO rats. Besides the modestly increased insulin sensitivity, male IRS-2 KO rats displayed the enhanced insulin-induced activation of the mTOR complex 1 pathway in the liver compared with WT rats. Taken together, these results indicate that in rats, IRS-2 plays important roles in the regulation of growth but is not essential for the glucose-lowering effects of insulin.

The Continuing Evolution of Insulin-like Growth Factor Signaling

The insulin-like growth factors (IGFs; IGF1/IGF2), known for their regulation of cell and organismal growth and development, are evolutionarily conserved ligands with equivalent peptides present in flies ( D. melanogaster), worms ( C. elegans) among others. Two receptor tyrosine kinases, the IGF1 receptor and the insulin receptor mediate the actions of these ligands with a family of IGF binding proteins serving as selective inhibitors of IGF1/2. This treatise reviews recent findings on IGF signaling in cancer biology and central nervous system function. This includes overexpression of IGF1 receptors in enhancing tumorigenesis, acquired resistance and contributions to metastasis in multiple cancer types. There is accumulating evidence that insulin resistance, a hallmark of type 2 diabetes, occurs in the central nervous system, independent of systemic insulin resistance and characterized by reduced insulin and IGF1 receptor signaling, and may contribute to dementias including Alzheimer’s Disease and cognitive impairment. Controversy over the role(s) of IGF signaling in cancer and whether its inhibition would be of benefit, still persist and extend to IGF1’s role in longevity and central nervous system function.

Insulin Signaling Via Progesterone-Regulated Insulin Receptor Substrate 2 is Critical for Human Uterine Decidualization

Decidualization, the process by which fibroblastic human endometrial stromal cells (HESC) differentiate into secretory decidual cells, is a critical event during the establishment of pregnancy. It is dependent on the steroid hormone progesterone acting through the nuclear progesterone receptor (PR). Previously, we identified insulin receptor substrate 2 (IRS2) as a factor that is directly regulated by PR during decidualization. IRS2 is an adaptor protein that functionally links receptor tyrosine kinases, such as insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R), and their downstream effectors. IRS2 expression was induced in HESC during in vitro decidualization and siRNA-mediated downregulation of IRS2 transcripts resulted in attenuation of this process. Further use of siRNAs targeted to IR or IGF1R transcripts showed that downregulation of IR, but not IGF1R, led to impaired decidualization. Loss of IRS2 transcripts in HESC suppressed phosphorylation of both ERK1/2 and AKT, downstream effectors of insulin signaling, which mediate gene expression associated with decidualization and regulate glucose uptake. Indeed, downregulation of IRS2 resulted in reduced expression and membrane localization of the glucose transporters GLUT1 and GLUT4, resulting in lowered glucose uptake during stromal decidualization. Collectively, these data suggest that the PR-regulated expression of IRS2 is necessary for proper insulin signaling for controlling gene expression and glucose utilization, which critically support the decidualization process to facilitate pregnancy. This study provides new insight into the mechanisms by which steroid hormone signaling intersects with insulin signaling in the uterus during decidualization, which has important implications for pregnancy complications associated with insulin resistance and infertility.

Release of insulin produced by the choroid plexis is regulated by serotonergic signaling

The choroid plexus (ChP) is a highly vascularized tissue found in the brain ventricles, with an apical epithelial cell layer surrounding fenestrated capillaries. It is responsible for the production of most of the cerebrospinal fluid (CSF) in the ventricular system, subarachnoid space, and central canal of the spinal cord, while also constituting the blood-CSF barrier (BCSFB). In addition, epithelial cells of the ChP (EChP) synthesize neurotrophic factors and other signaling molecules that are released into the CSF. Here, we show that insulin is produced in EChP of mice and humans, and its expression and release are regulated by serotonin. Insulin mRNA and immune-reactive protein, including C-peptide, are present in EChP, as detected by several experimental approaches, and appear in much higher levels than any other brain region. Moreover, insulin is produced in primary cultured mouse EChP, and its release, albeit Ca2+ sensitive, is not regulated by glucose. Instead, activation of the 5HT2C receptor by serotonin treatment led to activation of IP3-sensitive channels and Ca2+ mobilization from intracellular storage, leading to insulin secretion. In vivo depletion of brain serotonin in the dorsal raphe nucleus negatively affected insulin expression in the ChP, suggesting an endogenous modulation of ChP insulin by serotonin. Here, we show for the first time to our knowledge that insulin is produced by EChP in the brain, and its release is modulated at least by serotonin but not glucose.

Insulin receptor substrate 2 (IRS2) deficiency delays liver fibrosis associated with cholestatic injury

Insulin receptor substrate 2 (IRS2) is a key downstream mediator of insulin and insulin-like growth factor 1 (IGF1) signalling pathways and plays a major role in liver metabolism. The aim of this study was to investigate whether IRS2 had an impact on the hepatic fibrotic process associated with cholestatic injury. Bile duct ligation (BDL) was performed in wild-type (WT) and Irs2-deficient (IRS2KO) female mice. Histological and biochemical analyses, together with fibrogenic and inflammatory responses were evaluated in livers from mice at 3, 7 and 28 days following BDL. We also explored whether activation of human hepatic stellate cells (HSCs) induced by IGF1 was modulated by IRS2. IRS2KO mice displayed reduced disruption of liver histology, such hepatocyte damage and excess deposition of extracellular matrix components, compared with WT mice at 3 and 7 days post-BDL. However, no histological differences between genotypes were found at 28 days post-BDL. The less pro-inflammatory profile of bile acids accumulated in the gallbladder of IRS2KO mice after BDL corresponded with the reduced expression of pro-inflammatory markers in these mice. Stable silencing of IRS2 or inhibition of ERK1/2 reduced the activation of human LX2 cells and also reduced induction of MMP9 upon IGF1 stimulation. Furthermore, hepatic MMP9 expression was strongly induced after BDL in WT mice, but only a slight increase was found in mice lacking IRS2. Our results have unravelled the signalling pathway mediated by IGF1R–IRS2–ERK1/2–MMP9 as a key axis in regulating HSC activation, which might be therapeutically relevant for targeting liver fibrosis.

Summary: IRS2 is a key mediator of IGF1R signalling in hepatic stellate cell activation in cholestatic liver injury.

Insulin-Driven PI3K-AKT Signaling in the Hepatocyte Is Mediated by Redundant PI3Kα and PI3Kβ Activities and Is Promoted by RAS

Phosphatidylinositol-3-kinase (PI3K) activity is aberrant in tumors, and PI3K inhibitors are investigated as cancer therapeutics. PI3K signaling mediates insulin action in metabolism, but the role of PI3K isoforms in insulin signaling remains unresolved. Defining the role of PI3K isoforms in insulin signaling is necessary for a mechanistic understanding of insulin action and to develop PI3K inhibitors with optimal therapeutic index. We show that insulin-driven PI3K-AKT signaling depends on redundant PI3Kα and PI3Kβ activities, whereas PI3Kδ and PI3Kγ are largely dispensable. We have also found that RAS activity promotes AKT phosphorylation in insulin-stimulated hepatocytes and that promotion of insulin-driven AKT phosphorylation by RAS depends on PI3Kα. These findings reveal the detailed mechanism by which insulin activates AKT, providing an improved mechanistic understanding of insulin signaling. This improved model for insulin signaling predicts that isoform-selective PI3K inhibitors discriminating between PI3Kα and PI3Kβ should be dosed below their hyperglycemic threshold to achieve isoform selectivity.

Target gene identification and functional characterization of miR-1704 in chicken

MiRNAs are small non-coding RNAs that negatively regulate gene expression at the post-transcriptional level. SNPs in miRNA genes may lead to phenotypic variation by altering miRNA expression and their targets. In this study, miR-1704 expression profiles in nine tissues at 1 d, 6 weeks and 16 weeks old Gushi chickens were detected. MiR-1704 was widely expressed in the detection of tissues. The expression in 1 d and 6 weeks old was low abundance, while its expression at 16 weeks was very high. An rs14668705 (C > G) SNP was detected within the pre-miR-1704 in an F₂ resource population of Gushi chicken crossed with Anka broiler. Bioinformatic analysis indicated that the C > G mutation could introduce a base-pair mismatch and cause the change of free energy. Experiments further revealed that the rs14668705 in precursor miR-1704 could significantly affect mature miR-1704 biogenesis and was significantly associated with body weight at the age of 0, 6, 8, 10, and 12 weeks, shank circumference at 4, 8, and 12 weeks, carcass weight, and semi-evisceration weight (p < 0.05). Insulin receptor 2 (IRS2) gene, one of the potential targets of miR-1704 was identified and further confirmed. These data suggested that miR-1704 targeted IRS2 and have an effect on body weight in chicken.

Molecular characterization and expression analysis of protein enhancer of sevenless 2B from Artemia sinica at early embryonic development and during immune response to bacterial stimulation

Protein enhancer of sevenless 2B, E(sev)2B, is a key adapter protein in the Ras/MAPK signaling pathway which has been reported to be involved in innate immunity. In this study, the gene that encodes AsE(sev)2B was isolated from A. sinica. It was found to contain a 636 bp open reading frame encoding 211 amino acids with a calculated molecular mass of 24.357 kDa and a predicted isoelectric point of 5.39. The predicted protein contains a N-terminal Src homology 3 domain (SH3), a central Src homology 2 domain (SH2), and a C-terminal Src homology 3 domain (SH3). Homology analysis revealed that AsE(sev)2B shares 49%-95% identity with E(sev)2B homologs from other species. In this study, the expression pattern and location of AsE(sev)2B during different stages of embryonic development and bacterial challenge were investigated by means of real-time qPCR, Western blotting and immunohistochemistry. Results showed that the highest expression level of AsE(sev)2B was at 0 h. After challenged by Gram-positive bacteria and Gram-negative bacteria, AsE(sev)2B was remarkably upregulated at 10⁶ cellsL^-1 bacterial concentrations. These results suggested that AsE(sev)2B plays a vital role during early embryonic development and in immune responses against bacterial challenge.

In vivo genome-wide binding interactions of mouse and human constitutive androstane receptors reveal novel gene targets

The constitutive androstane receptor (CAR; NR1I3) is a nuclear receptor orchestrating complex roles in cell and systems biology. Species differences in CAR's effector pathways remain poorly understood, including its role in regulating liver tumor promotion. We developed transgenic mouse models to assess genome-wide binding of mouse and human CAR, following receptor activation in liver with direct ligands and with phenobarbital, an indirect CAR activator. Genomic interaction profiles were integrated with transcriptional and biological pathway analyses. Newly identified CAR target genes included Gdf15 and Foxo3, important regulators of the carcinogenic process. Approximately 1000 genes exhibited differential binding interactions between mouse and human CAR, including the proto-oncogenes, Myc and Ikbke, which demonstrated preferential binding by mouse CAR as well as mouse CAR-selective transcriptional enhancement. The ChIP-exo analyses also identified distinct binding motifs for the respective mouse and human receptors. Together, the results provide new insights into the important roles that CAR contributes as a key modulator of numerous signaling pathways in mammalian organisms, presenting a genomic context that specifies species variation in biological processes under CAR's control, including liver cell proliferation and tumor promotion.

Dual Therapy with Liraglutide and Ghrelin Promotes Brain and Peripheral Energy Metabolism in the R6/2 Mouse Model of Huntington's Disease

Neuronal loss alongside altered energy metabolism, are key features of Huntington’s disease (HD) pathology. The orexigenic gut-peptide hormone ghrelin is known to stimulate appetite and affect whole body energy metabolism. Liraglutide is an efficient anti-type 2 diabetes incretin drug, with neuroprotective effects alongside anorectic properties. Combining liraglutide with the orexigenic peptide ghrelin may potentially promote brain/cognitive function in HD. The R6/2 mouse model of HD exhibits progressive central pathology, weight loss, deranged glucose metabolism, skeletal muscle atrophy and altered body composition. In this study, we targeted energy metabolism in R6/2 mice using a co-administration of liraglutide and ghrelin. We investigated their effect on brain cortical hormone-mediated intracellular signalling pathways, metabolic and apoptotic markers, and the impact on motor function in HD. We here demonstrate that liraglutide, alone or together with ghrelin (subcutaneous daily injections of 150 µg/kg (ghrelin) and 0.2 mg/kg (liraglutide), for 2 weeks), normalized glucose homeostatic features in the R6/2 mouse, without substantially affecting body weight or body composition. Liraglutide alone decreased brain cortical active GLP-1 and IGF-1 levels in R6/2 mice, alongside higher ADP levels. Liraglutide plus ghrelin decreased brain insulin, lactate, AMP and cholesterol levels in R6/2 mice. Taken together, our findings encourage further studies targeting energy metabolism in HD.

Metformin treatment ameliorates diabetes-associated decline in hippocampal neurogenesis and memory via phosphorylation of insulin receptor substrate 1

Age‐related reduction in adult hippocampal neurogenesis is correlated with cognitive impairment. Diabetes is a chronic systemic disease that negatively affects adult neural stem cells and memory functions in the hippocampus. Despite growing concern regarding the potential role of diabetic drugs in neural abnormalities, their effects on progressive deterioration of neurogenesis and cognitive functions remain unknown. Here, we show that the combination of aging and diabetes in mice causes a marked decrease in hippocampal neurogenesis along with memory impairment and elevated neuroinflammation. Prolonged treatment with metformin, a biguanide antidiabetic medication, promotes cell proliferation and neuronal differentiation and inhibits aging‐ and diabetes‐associated microglial activation, which is related to homeostatic neurogenesis, leading to enhanced hippocampal neurogenesis in middle‐aged diabetic mice. Although chronic therapy with metformin fails to achieve recovery from hyperglycemia, a key feature of diabetes in middle‐aged diabetic mice, it improves hippocampal‐dependent spatial memory functions accompanied by increased phosphorylation of adenosine monophosphate‐activated protein kinase (AMPK), atypical protein kinase C ζ (aPKC ζ), and insulin receptor substrate 1 (IRS1) at selective serine residues in the hippocampus. Our findings suggest that signaling networks acting through long‐term metformin‐stimulated phosphorylation of AMPK, aPKC ζ/λ, and IRS1 serine sites contribute to neuroprotective effects on hippocampal neurogenesis and cognitive function independent of a hypoglycemic effect.

Effect of gastric bypass combined with ileal transportation on type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a chronic progressive disease, which manifests as an endocrine disorder. Among the different methods of surgery available to treat patients with T2DM, Roux-en-Y gastric bypass (RYGBP) and ileal transposition (IT) are the most commonly performed. The aim of the present study was to investigate the effects of RYGBP combined with IT on rats with T2DM. A total of 8 healthy male rats were used as a control group and 40 GK rats were randomly divided into 5 groups: A diabetes mellitus (DM) group, a sham operative group (SO), a RYGBP group, an IT group and a RYGBP+IT group. The results demonstrated that fasting blood glucose, triglyceride, total cholesterol and gastric inhibitory polypeptide levels in all treatment groups were significantly lower than those of the SO and DM groups. Furthermore, levels TC and TG in the RYGBP+IT group were significantly lower than in the RYGBP and IT groups. Levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase mRNA and IRS-2 protein in all treatment groups were also significantly lower than those of the SO group; and they were significantly lower in the RYGBP+IT group compared with the RYGBP and IT groups. The expression of phosphorylated Akt in the treatment groups was significantly higher than the SO group and was significantly higher in the RYGBP+IT group compared with the RYGBP and IT groups. These results indicate that RYGBP and IT surgical treatment can induce T2DM remission by mediating the expression of insulin-related factors to reverse insulin resistance. The current study also indicated that the effect of RYGBP combined with IT may be developed as a novel first-line method of treating T2DM.

Peripheral and Central Effects of Memantine in a Mixed Preclinical Mice Model of Obesity and Familial Alzheimer's Disease

There is growing evidence that obesity associated with type 2 diabetes mellitus (T2DM) and aging are risk factors for the development of Alzheimer's disease (AD). However, the molecular mechanisms through which obesity interacts with β-amyloid (Aβ) to promote cognitive decline remains poorly understood. Memantine (MEM), a N-methyl-D-aspartate receptor antagonist, is currently used for the treatment of AD. Nonetheless, few studies have reported its effects on genetic preclinical models of this neurodegenerative disease exacerbated with high-fat diet (HFD)-induced obesity. Therefore, the present research aims to elucidate the effects of MEM on familial AD HFD-induced insulin resistance and learning and memory impairment. Furthermore, it aspires to determine the possible underlying mechanisms that connect AD to T2DM. Wild type and APPswe/PS1dE9 mice were used in this study. The animals were fed with either chow or HFD until 6 months of age, and they were treated with MEM-supplemented water (30 mg/kg) during the last 12 weeks. Our study demonstrates that MEM improves the metabolic consequences produced by HFD in this model of familial AD. Behavioural assessments confirmed that the treatment also improves animals learning abilities and decreases memory loss. Moreover, MEM treatment improves brain insulin signalling upregulating AKT, as well as cyclic adenosine monophosphate response element binding (CREB) expression, and modulates the amyloidogenic pathway, which, in turn, reduced the accumulation of Aβ. Moreover, this drug increases the activation of molecules involved with insulin signalling in the liver, such as insulin receptor substrate 2 (IRS2), which is a key protein regulating hepatic resistance to insulin. These results provide new insight into the role of MEM not only in the occurrence of AD treatment, but also in its potential application on peripheral metabolic disorders where Aβ plays a key role, as is the case of T2DM.

Central IGF1 improves glucose tolerance and insulin sensitivity in mice

Insulin-like growth factor 1 (IGF1) is a key factor for tissue growth and fuel metabolism. The potential function of central IGF1 remains unclear. We previously observed that IGF1 expression is increased in the hypothalamus of obese mice lacking STAT5 in the central nervous system (CNS). In this study, we explored the potential metabolic function of central IGF1 by intracerebroventricular (ICV) injection of IGF1, over-expression of central IGF1 by administering an adeno-associated virus (AAV), and ICV injection of an anti-IGF1 antibody. Mice that over-expressed central IGF1 displayed increased appetite, improved glucose tolerance and insulin sensitivity, decreased Pomc levels in the hypothalamus, and increased UCP1 expression in brown fat tissue. This is the first study demonstrating that central IGF1 regulates several important metabolic functions.

Neurotrophic and Neuroregenerative Effects of GH/IGF1

Introduction. Human neurodegenerative diseases increase progressively with age and present a high social and economic burden. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are both growth factors exerting trophic effects on neuronal regeneration in the central nervous system (CNS) and peripheral nervous system (PNS). GH and IGF-1 stimulate protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells, and favor neuronal survival, inhibiting apoptosis. This study aims to evaluate the effect of GH and IGF-1 on neurons, and their possible therapeutic clinical applications on neuron regeneration in human subjects. Methods. In the literature, we searched the clinical trials and followed up studies in humans, which have evaluated the effect of GH/IGF-1 on CNS and PNS. The following keywords have been used: “GH/IGF-1” associated with “neuroregeneration”, “amyotrophic lateral sclerosis”, “Alzheimer disease”, “Parkinson’s disease”, “brain”, and “neuron”. Results. Of the retrieved articles, we found nine articles about the effect of GH in healthy patients who suffered from traumatic brain injury (TBI), and six studies (four using IGF-1 and two GH therapy) in patients with amyotrophic lateral sclerosis (ALS). The administration of GH in patients after TBI showed a significantly positive recovery of brain and mental function. Treatment with GH and IGF-1 therapy in ALS produced contradictory results. Conclusions. Although strong findings have shown the positive effects of GH/IGF-1 administration on neuroregeneration in animal models, a very limited number of clinical studies have been conducted in humans. GH/IGF-1 therapy had different effects in patients with TBI, evidencing a high recovery of neurons and clinical outcome, while in ALS patients, the results are contradictory. More complex clinical protocols are necessary to evaluate the effect of GH/IGF-1 efficacy in neurodegenerative diseases. It seems evident that GH and IGF-1 therapy favors the optimal recovery of neurons when a consistent residual activity is still present. Furthermore, the effect of GH/IGF-1 could be mediated by, or be overlapped with that of other hormones, such as estradiol and testosterone.

Impaired Insulin Signaling is Associated with Hepatic Mitochondrial Dysfunction in IR+/--IRS-1+/- Double Heterozygous (IR-IRS1dh) Mice

Mitochondria play a pivotal role in energy metabolism, but whether insulin signaling per se could regulate mitochondrial function has not been identified yet. To investigate whether mitochondrial function is regulated by insulin signaling, we analyzed muscle and liver of insulin receptor (IR)^+/−-insulin receptor substrate-1 (IRS-1)^+/− double heterozygous (IR-IRS1dh) mice, a well described model for insulin resistance. IR-IRS1dh mice were studied at the age of 6 and 12 months and glucose metabolism was determined by glucose and insulin tolerance tests. Mitochondrial enzyme activities, oxygen consumption, and membrane potential were assessed using spectrophotometric, respirometric, and proton motive force analysis, respectively. IR-IRS1dh mice showed elevated serum insulin levels. Hepatic mitochondrial oxygen consumption was reduced in IR-IRS1dh animals at 12 months of age. Furthermore, 6-month-old IR-IRS1dh mice demonstrated enhanced mitochondrial respiration in skeletal muscle, but a tendency of impaired glucose tolerance. On the other hand, 12-month-old IR-IRS1dh mice showed improved glucose tolerance, but normal muscle mitochondrial function. Our data revealed that deficiency in IR/IRS-1 resulted in normal or even elevated skeletal muscle, but impaired hepatic mitochondrial function, suggesting a direct cross-talk between insulin signaling and mitochondria in the liver.

Insulin-Like Growth Factor 1: At the Crossroads of Brain Development and Aging

Insulin-like growth factor 1 (IGF1) is a polypeptide hormone structurally similar to insulin. It is central to the somatotropic axis, acting downstream of growth hormone (GH). It activates both the mitogen-activated protein (MAP) kinase and PI3K signaling pathways, acting in almost every tissue in the body to promote tissue growth and maturation through upregulation of anabolic processes. Overall GH and IGF1 signaling falls with age, suggesting that it is this reduced IGF1 activity that leads to age-related changes in organisms. However, mutations that reduce IGF1-signaling activity can dramatically extend the lifespan of organisms. Therefore, the role of IGF1 in the overall aging process is unclear. This review article will focus on the role of IGF1 in brain development and aging. The evidence points towards a role for IGF1 in neurodevelopment both prenatally and in the early post-natal period, and in plasticity and remodeling throughout life. This review article will then discuss the hallmarks of aging and cognitive decline associated with falls in IGF1 levels towards the end of life. Finally, the role of IGF1 will be discussed within the context of both neuropsychiatric disorders caused by impaired development of the nervous system, and neurodegenerative disorders associated with aging. IGF1 and its derivatives are shown to improve the symptoms of certain neuropsychiatric disorders caused by deranged neurodevelopment and these effects have been correlated with changes in the underlying biology in both in vitro and in vivo studies. On the other hand, studies looking at IGF1 in neurodegenerative diseases have been conflicting, supporting both a role for increased and decreased IGF1 signaling in the underlying pathogenesis of these diseases.

IGF1 neuronal response in the absence of MECP2 is dependent on TRalpha 3

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder in which the MECP2 (methyl CpG-binding protein 2) gene is mutated. Recent studies showed that RTT-derived neurons have many cellular deficits when compared to control, such as: less synapses, lower dendritic arborization and reduced spine density. Interestingly, treatment of RTT-derived neurons with Insulin-like Growth Factor 1 (IGF1) could rescue some of these cellular phenotypes. Given the critical role of IGF1 during neurodevelopment, the present study used human induced pluripotent stem cells (iPSCs) from RTT and control individuals to investigate the gene expression profile of IGF1 and IGF1R on different developmental stages of differentiation. We found that the thyroid hormone receptor (TRalpha 3) has a differential expression profile. Thyroid hormone is critical for normal brain development. Our results showed that there is a possible link between IGF1/IGF1R and the TRalpha 3 and that over expression of IGF1R in RTT cells may be the cause of neurites improvement in neural RTT-derived neurons.

Glial cells and energy balance

The search for new strategies and drugs to abate the current obesity epidemic has led to the intensification of research aimed at understanding the neuroendocrine control of appetite and energy expenditure. This intensified investigation of metabolic control has also included the study of how glial cells participate in this process. Glia, the most abundant cell type in the central nervous system, perform a wide spectrum of functions and are vital for the correct functioning of neurons and neuronal circuits. Current evidence indicates that hypothalamic glia, in particular astrocytes, tanycytes and microglia, are involved in both physiological and pathophysiological mechanisms of appetite and metabolic control, at least in part by regulating the signals reaching metabolic neuronal circuits. Glia transport nutrients, hormones and neurotransmitters; they secrete growth factors, hormones, cytokines and gliotransmitters and are a source of neuroprogenitor cells. These functions are regulated, as glia also respond to numerous hormones and nutrients, with the lack of specific hormonal signaling in hypothalamic astrocytes disrupting metabolic homeostasis. Here, we review some of the more recent advances in the role of glial cells in metabolic control, with a special emphasis on the differences between glial cell responses in males and females.

Harnessing the Power of SIRT1 and Non-coding RNAs in Vascular Disease

Noncommunicable diseases (NCDs) contribute to a significant amount of disability and death in the world. Of these disorders, vascular disease is ranked high, falls within the five leading causes of death, and impacts multiple other disease entities such as those of the cardiac system, nervous system, and metabolic disease. Targeting the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) pathway and the modulation of micro ribonucleic acids (miRNAs) may hold great promise for the development of novel strategies for the treatment of vascular disease since each of these pathways are highly relevant to cardiac and nervous system disorders as well as to metabolic dysfunction. SIRT1 is vital in determining the course of stem cell development and the survival, metabolism, and life span of differentiated cells that are overseen by both autophagy and apoptosis. SIRT1 interfaces with a number of pathways that involve forkhead transcription factors, mechanistic of rapamycin (mTOR), AMP activated protein kinase (AMPK) and Wnt1 inducible signaling pathway protein 1 (WISP1) such that the level of activity of SIRT1 can become a critical determinant for biological and clinical outcomes. The essential fine control of SIRT1 is directly tied to the world of non-coding RNAs that ultimately oversee SIRT1 activity to either extend or end cellular survival. Future studies that can further elucidate the crosstalk between SIRT1 and non-coding RNAs should serve well our ability to harness the power of SIRT1 and non-coding RNAs for the treatment of vascular disorders.

Brain Insulin Signaling Is Increased in Insulin-Resistant States and Decreases in FOXOs and PGC-1α and Increases in Aβ1-40/42 and Phospho-Tau May Abet Alzheimer Development

Increased coexistence of Alzheimer disease (AD) and type 2 diabetes mellitus (T2DM) suggests that insulin resistance abets neurodegenerative processes, but linkage mechanisms are obscure. Here, we examined insulin signaling factors in brains of insulin-resistant high-fat-fed mice, ob/ob mice, mice with genetically impaired muscle glucose transport, and monkeys with diet-dependent long-standing obesity/T2DM. In each model, the resting/basal activities of insulin-regulated brain protein kinases, Akt and atypical protein kinase C (aPKC), were maximally increased. Moreover, Akt hyperactivation was accompanied by hyperphosphorylation of substrates glycogen synthase kinase-3β and mammalian target of rapamycin and FOXO proteins FOXO1, FOXO3A, and FOXO4 and decreased peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) expression. Akt hyperactivation was confirmed in individual neurons of anterocortical and hippocampal regions that house cognition/memory centers. Remarkably, β-amyloid (Aβ1-40/42) peptide levels were as follows: increased in the short term by insulin in normal mice, increased basally in insulin-resistant mice and monkeys, and accompanied by diminished amyloid precursor protein in monkeys. Phosphorylated tau levels were increased in ob/ob mice and T2DM monkeys. Importantly, with correction of hyperinsulinemia by inhibition of hepatic aPKC and improvement in systemic insulin resistance, brain insulin signaling normalized. As FOXOs and PGC-1α are essential for memory and long-term neuronal function and regeneration and as Aβ1-40/42 and phospho-tau may increase interneuronal plaques and intraneuronal tangles, presently observed aberrations in hyperinsulinemic states may participate in linking insulin resistance to AD.

Increased oxidative stress and apoptosis in the hypothalamus of diabetic male mice in the insulin receptor substrate-2 knockout model

Insulin receptor substrate-2-deficient (IRS2(-/-)) mice are considered a good model to study the development of diabetes because IRS proteins mediate the pleiotropic effects of insulin-like growth factor-I (IGF-I) and insulin on metabolism, mitogenesis and cell survival. The hypothalamus might play a key role in the early onset of diabetes, owing to its involvement in the control of glucose homeostasis and energy balance. Because some inflammatory markers are elevated in the hypothalamus of diabetic IRS2(-/-) mice, our aim was to analyze whether the diabetes associated with the absence of IRS2 results in hypothalamic injury and to analyze the intracellular mechanisms involved. Only diabetic IRS2(-/-) mice showed increased cell death and activation of caspase-8 and -3 in the hypothalamus. Regulators of apoptosis such as FADD, Bcl-2, Bcl-xL and p53 were also increased, whereas p-IκB and c-FLIPL were decreased. This was accompanied by increased levels of Nox-4 and catalase, enzymes involved in oxidative stress. In summary, the hypothalamus of diabetic IRS2(-/-) mice showed an increase in oxidative stress and inflammatory markers that finally resulted in cell death via substantial activation of the extrinsic apoptotic pathway. Conversely, non-diabetic IRS2(-/-) mice did not show cell death in the hypothalamus, possibly owing to an increase in the levels of circulating IGF-I and in the enhanced hypothalamic IGF-IR phosphorylation that would lead to the stimulation of survival pathways. In conclusion, diabetes in IRS2-deficient male mice is associated with increased oxidative stress and apoptosis in the hypothalamus.

Novel nervous and multi-system regenerative therapeutic strategies for diabetes mellitus with mTOR

Throughout the globe, diabetes mellitus (DM) is increasing in incidence with limited therapies presently available to prevent or resolve the significant complications of this disorder. DM impacts multiple organs and affects all components of the central and peripheral nervous systems that can range from dementia to diabetic neuropathy. The mechanistic target of rapamycin (mTOR) is a promising agent for the development of novel regenerative strategies for the treatment of DM. mTOR and its related signaling pathways impact multiple metabolic parameters that include cellular metabolic homeostasis, insulin resistance, insulin secretion, stem cell proliferation and differentiation, pancreatic β-cell function, and programmed cell death with apoptosis and autophagy. mTOR is central element for the protein complexes mTOR Complex 1 (mTORC1) and mTOR Complex 2 (mTORC2) and is a critical component for a number of signaling pathways that involve phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), AMP activated protein kinase (AMPK), silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), Wnt1 inducible signaling pathway protein 1 (WISP1), and growth factors. As a result, mTOR represents an exciting target to offer new clinical avenues for the treatment of DM and the complications of this disease. Future studies directed to elucidate the delicate balance mTOR holds over cellular metabolism and the impact of its broad signaling pathways should foster the translation of these targets into effective clinical regimens for DM.

Lipoic acid improves neuronal insulin signalling and rescues cognitive function regulating VGlut1 expression in high-fat-fed rats: Implications for Alzheimer's disease

The concept of central insulin resistance and dysfunctional insulin signalling in sporadic Alzheimer's disease (AD) is now widely accepted and diabetes is recognized as one of the main risk factors for developing AD. Moreover, some lines of evidence indicated that VGlut1 is impaired in frontal regions of AD patients and this impairment is correlated with the progression of cognitive decline in AD. The present work hypothesizes that ketosis associated to insulin resistance could interfere with the normal activity of VGlut1 and its role in the release of glutamate in the hippocampus, which might ultimately lead to cognitive deficits. High fat diet (HFD) rats showed memory impairments and both peripheral (as shown by increased fasting plasma insulin levels and HOMA index) and hippocampal (as shown by decreased activation of insulin receptor, IRS-1 and pAkt) insulin pathway alterations, accompanied by increased ketone bodies production. All these effects were counteracted by α-lipoic acid (LA) administration. VGlut1 levels were significantly decreased in the hippocampus of HFD rats, and this decrease was reversed by LA. Altogether, the present results suggest that HFD induced alterations in central insulin signalling could switch metabolism to produce ketone bodies, which in turn, in the hippocampus, might lead to a decreased expression of VGlut1, and therefore to a decreased release of glutamate and hence, to the glutamatergic deficit described in AD. The ability of LA treatment to prevent the alterations in insulin signalling in this model of HFD might represent a possible new therapeutic target for the treatment of AD.