Rapamycin reverses insulin resistance (IR) in high-glucose medium without causing IR in normoglycemic medium

Inflammation in diabetes complications: molecular mechanisms and therapeutic interventions

At present, diabetes mellitus (DM) has been one of the most endangering healthy diseases. Current therapies contain controlling high blood sugar, reducing risk factors like obesity, hypertension, and so on; however, DM patients inevitably and eventually progress into different types of diabetes complications, resulting in poor quality of life. Unfortunately, the clear etiology and pathogenesis of diabetes complications have not been elucidated owing to intricate whole-body systems. The immune system was responsible to regulate homeostasis by triggering or resolving inflammatory response, indicating it may be necessary to diabetes complications. In fact, previous studies have been shown inflammation plays multifunctional roles in the pathogenesis of diabetes complications and is attracting attention to be the meaningful therapeutic strategy. To this end, this review systematically concluded the current studies over the relationships of susceptible diabetes complications (e.g., diabetic cardiomyopathy, diabetic retinopathy, diabetic peripheral neuropathy, and diabetic nephropathy) and inflammation, ranging from immune cell response, cytokines interaction to pathomechanism of organ injury. Besides, we also summarized various therapeutic strategies to improve diabetes complications by target inflammation from special remedies to conventional lifestyle changes. This review will offer a panoramic insight into the mechanisms of diabetes complications from an inflammatory perspective and also discuss contemporary clinical interventions.

Leucine alleviates cytokine storm syndrome by regulating macrophage polarization via the mTORC1/LXRα signaling pathway

Cytokine storms are associated with severe pathological damage and death in some diseases. Excessive activation of M1 macrophages and the subsequent secretion of pro-inflammatory cytokines are a major cause of cytokine storms. Therefore, promoting the polarization of M2 macrophages to restore immune balance is a promising therapeutic strategy for treating cytokine storm syndrome (CSS). This study was aimed at investigating the potential protective effects of leucine on lipopolysaccharide (LPS)-induced CSS in mice and exploring the underlying mechanisms. CSS was induced by LPS administration in mice, which were concurrently administered leucine orally. In vitro, bone marrow derived macrophages (BMDMs) were polarized to M1 and M2 phenotypes with LPS and interleukin-4 (IL-4), respectively, and treated with leucine. Leucine decreased mortality in mice treated with lethal doses of LPS. Specifically, leucine decreased M1 polarization and promoted M2 polarization, thus diminishing pro-inflammatory cytokine levels and ameliorating CSS in mice. Further studies revealed that leucine-induced macrophage polarization through the mechanistic target of rapamycin complex 1 (mTORC1)/liver X receptor α (LXRα) pathway, which synergistically enhanced the expression of the IL-4-induced M2 marker Arg1 and subsequent M2 polarization. In summary, this study revealed that leucine ameliorates CSS in LPS mice by promoting M2 polarization through the mTORC1/LXRα/Arg1 signaling pathway. Our findings indicate that a fundamental link between metabolism and immunity contributes to the resolution of inflammation and the repair of damaged tissues.

Senescence-associated inflammation and inhibition of adipogenesis in subcutaneous fat in Werner syndrome

Werner syndrome (WS) is a hereditary premature aging disorder characterized by visceral fat accumulation and subcutaneous lipoatrophy, resulting in severe insulin resistance. However, its underlying mechanism remains unclear. In this study, we show that senescence-associated inflammation and suppressed adipogenesis play a role in subcutaneous adipose tissue reduction and dysfunction in WS. Clinical data from four Japanese patients with WS revealed significant associations between the decrease of areas of subcutaneous fat and increased insulin resistance measured by the glucose clamp. Adipose-derived stem cells from the stromal vascular fraction derived from WS subcutaneous adipose tissues (WSVF) showed early replicative senescence and a significant increase in the expression of senescence-associated secretory phenotype (SASP) markers. Additionally, adipogenesis and insulin signaling were suppressed in WSVF, and the expression of adipogenesis suppressor genes and SASP-related genes was increased. Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), alleviated premature cellular senescence, rescued the decrease in insulin signaling, and extended the lifespan of WS model of C. elegans. To the best of our knowledge, this study is the first to reveal the critical role of cellular senescence in subcutaneous lipoatrophy and severe insulin resistance in WS, highlighting the therapeutic potential of rapamycin for this disease.

High glucose exposure drives intestinal barrier dysfunction by altering its morphological, structural and functional properties

High dietary glucose consumption and hyperglycemia can result in chronic complications. Several studies suggest that high glucose (HG) induces dysfunction of the intestinal barrier. However, the precise changes remain unclear. In our study, we used in vitro models composed of Caco-2 and/or HT29-MTX cells in both monoculture and co-culture to assess the effects of long-term HG exposure on the morphological, structural, and functional properties of the intestinal barrier. Cells were grown in medium containing normal physiologic glucose (NG, 5.5 mM) or a clinically relevant HG (25 mM) concentration until 21 days. Results demonstrated that HG induced morphological changes, with the layers appearing denser and less organized than under physiological conditions, which is in accordance with the increased migration capacity of Caco-2 cells and proliferation properties of HT29-MTX cells. Although we mostly observed a small decrease in mRNA and protein expressions of three junction proteins (ZO-1, OCLN and E-cad) in both Caco-2 and HT29-MTX cells cultured in HG medium, confocal microscopy showed that HG induced a remarkable reduction in their immunofluorescence intensity, triggering disruption of their associated structural network. In addition, we highlighted that HG affected different functionalities (permeability, mucus production and alkaline phosphatase activity) of monolayers with Caco-2 and HT29-MTX cells. Interestingly, these alterations were stronger in co-culture than in monoculture, suggesting a cross-relationship between enterocytes and goblet cells. Controlling hyperglycemia remains a major therapeutical method for reducing damage to the intestinal barrier and improving therapies.

Cellular senescence: when growth stimulation meets cell cycle arrest

At the very moment of cell-cycle arrest, the cell is not senescent yet. For several days in cell culture, the arrested cell is acquiring a senescent phenotype. What is happening during this geroconversion? Cellular enlargement (hypertrophy) and hyperfunctions (lysosomal and hyper-secretory) are hallmarks of geroconversion.

Reducing Akt2 in retinal pigment epithelial cells causes a compensatory increase in Akt1 and attenuates diabetic retinopathy

The retinal pigment epithelium (RPE) plays an important role in the development of diabetic retinopathy (DR), a leading cause of blindness worldwide. Here we set out to explore the role of Akt2 signaling-integral to both RPE homeostasis and glucose metabolism-to DR. Using human tissue and genetically manipulated mice (including RPE-specific conditional knockout (cKO) and knock-in (KI) mice), we investigate whether Akts in the RPE influences DR in models of diabetic eye disease. We found that Akt1 and Akt2 activities were reciprocally regulated in the RPE of DR donor tissue and diabetic mice. Akt2 cKO attenuated diabetes-induced retinal abnormalities through a compensatory upregulation of phospho-Akt1 leading to an inhibition of vascular injury, inflammatory cytokine release, and infiltration of immune cells mediated by the GSK3β/NF-κB signaling pathway; overexpression of Akt2 has no effect. We propose that targeting Akt1 activity in the RPE may be a novel therapy for treating DR.

Peripheral tissular analysis of rapamycin's effect as a neuroprotective agent in vivo

Rapamycin is the best-characterized autophagy inducer, which is related to its antiaging and neuroprotective effects. Although rapamycin is an FDA-approved drug for human use in organ transplantation and cancer therapy, its administration as an antiaging and neuroprotective agent is still controversial because of its immunosuppressive and reported side effects. Therefore, it is critical to determine whether the dose that exerts a neuroprotective effect, 35 times lower than that used as an immunosuppressant agent, harms peripheral organs. We validated the rapamycin neuroprotective dosage in a Parkinson's disease (PD) model induced with paraquat. C57BL/6 J mice were treated with intraperitoneal (IP) rapamycin (1 mg/kg) three times per week, followed by paraquat (10 mg/kg) twice per week for 6 weeks, along with rapamycin on alternate days. Rapamycin significantly decreased dopaminergic neuronal loss induced by paraquat. Since rapamycin's neuroprotective effect in a PD model was observed at 7 weeks of treatment; we evaluated its effect on the liver, kidney, pancreas, and spleen. In addition, we prolonged treatment with rapamycin for 14 weeks. Tissue sections were subjected to histochemical, immunodetection, and morphometric analysis. Chronic rapamycin administration does not affect bodyweight, survival, and liver or kidney morphology. Although the pancreas tissular architecture and cellular distribution in Langerhans islets are modified, they may be reversible. The spleen B lymphocyte and macrophage populations were decreased. Notably, the lymphocyte T population was not affected. Therefore, chronic administration of a rapamycin neuroprotective dose does not produce significant tissular alterations. Our findings support the therapeutic potential of rapamycin as a neuroprotective agent.

Stanniocalcin2 inhibits the epithelial-mesenchymal transition and invasion of trophoblasts via activation of autophagy under high-glucose conditions

Maternal pregnancy hyperglycemia is often accompanied by placental dysfunction. During placental development, epithelial-mesenchymal transition (EMT) contributes to the transformation of relatively noninvasive trophoblasts into highly invasive extravillous trophoblasts (EVTs). However, the specific role of EMT in placentas under hyperglycemia environments remains relatively unexplored. Stanniocalcin2 (STC2) regulates EMT in many cancers. In this study, we first demonstrated that STC2 expression was upregulated in GDM placenta. We found that STC2 activated autophagy and suppressed EMT in high-glucose-treated EVTs and was associated with a lack of invasiveness. Specifically, STC2 inhibited the interactions between p62/SQSTM1 (p62) and EMT transcription factors to promote the degradation of Twist1 and Snail via a proteasome-dependent pathway. Furthermore, the PI3K/AKT/AMPK signaling pathway was involved in the regulation of autophagy and EMT by STC2. Taken together, our results reveal that STC2 may serve as a potential prognostic biomarker in GDM and sheds light on the regulatory mechanisms of trophoblast invasion.

Endoplasmic reticulum stress downregulates PGC-1α in skeletal muscle through ATF4 and an mTOR-mediated reduction of CRTC2

Background

Peroxisome proliferator-activated receptor γ (PPARγ) coactivator 1α (PGC-1α) downregulation in skeletal muscle contributes to insulin resistance and type 2 diabetes mellitus. Here, we examined the effects of endoplasmic reticulum (ER) stress on PGC-1α levels in muscle and the potential mechanisms involved.

Methods

The human skeletal muscle cell line LHCN-M2 and mice exposed to different inducers of ER stress were used.

Results

Palmitate- or tunicamycin-induced ER stress resulted in PGC-1α downregulation and enhanced expression of activating transcription factor 4 (ATF4) in human myotubes and mouse skeletal muscle. Overexpression of ATF4 decreased basal PCG-1α expression, whereas ATF4 knockdown abrogated the reduction of PCG-1α caused by tunicamycin in myotubes. ER stress induction also activated mammalian target of rapamycin (mTOR) in myotubes and reduced the nuclear levels of cAMP response element-binding protein (CREB)-regulated transcription co-activator 2 (CRTC2), a positive modulator of PGC-1α transcription. The mTOR inhibitor torin 1 restored PCG-1α and CRTC2 protein levels. Moreover, siRNA against S6 kinase, an mTORC1 downstream target, prevented the reduction in the expression of CRTC2 and PGC-1α caused by the ER stressor tunicamycin.

Conclusions

Collectively, these findings demonstrate that ATF4 and the mTOR-CRTC2 axis regulates PGC-1α transcription under ER stress conditions in skeletal muscle, suggesting that its inhibition might be a therapeutic target for insulin resistant states.

Geroscience-guided repurposing of FDA-approved drugs to target aging: A proposed process and prioritization

Common chronic diseases represent the greatest driver of rising healthcare costs, as well as declining function, independence, and quality of life. Geroscience-guided approaches seek to delay the onset and progression of multiple chronic conditions by targeting fundamental biological pathways of aging. This approach is more likely to improve overall health and function in old age than treating individual diseases, by addressing aging the largest and mostly ignored risk factor for the leading causes of morbidity in older adults. Nevertheless, challenges in repurposing existing and moving newly discovered interventions from the bench to clinical care have impeded the progress of this potentially transformational paradigm shift. In this article, we propose the creation of a standardized process for evaluating FDA-approved medications for their geroscience potential. Criteria for systematically evaluating the existing literature that spans from animal models to human studies will permit the prioritization of efforts and financial investments for translating geroscience and allow immediate progress on the design of the next Targeting Aging with MEtformin (TAME)-like study involving such candidate gerotherapeutics.

Dynamic insulin-stimulated mTOR/GSK3 signaling in peripheral immune cells: Preliminary evidence for an association with lithium response in bipolar disorder

INTRODUCTION

A key mechanism of lithium is the inhibition of glycogen synthase kinase-3β (GSK3β) and activation of mammalian target of rapamycin (mTOR), two contributors to insulin signaling. We explored the relationship between these markers and clinical response to lithium in bipolar disorder (BD).

METHODS

Thirty-four subjects with BD who had been taking lithium for ≥2 years and had a maintenance lithium Alda score defined as either high (≥7; n = 20) or low (≤2; n = 14) were included in the study. Baseline protein expression of GSK3β and mTOR (total and phosphorylated (p)) was obtained from a buffy coat. Peripheral blood mononuclear cells (PBMCs) from a subset of each group (n = 11) were stimulated with insulin (10 µg) and change in protein expression was determined using Western blot.

RESULTS

In buffy coat samples, significantly higher levels of pmTOR were present in subjects with an Alda score ≤2 (lithium non-responsive), relative to those with scores ≥7 (lithium-responsive). No differences were observed for pGSK3β. In contrast, functional PBMC responses to 5 min of insulin stimulation demonstrated robust increases in pGSK3β (87.05 ± 43.41%) and pmTOR (105.7 ± 66.48%) in the lithium responsive group only. This contrasted observed decreases in pGSK3β (34.08 ± 16.12%) and pmTOR (37.84 ± 14.39%) 5 mins post-insulin in non-responders.

CONCLUSIONS

Dynamic increases in pmTOR and pGSK3β post-insulin stimulation may reflect an immunometabolic state that facilitates lithium response. Further prospective analyses are needed to replicate and extend these preliminary findings and further investigate the role of insulin signaling in lithium response in BD.

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.

Effects of High Dietary Carbohydrate and Lipid Intake on the Lifespan of C. elegans

Health and lifespan are influenced by dietary nutrients, whose balance is dependent on the supply or demand of each organism. Many studies have shown that an increased carbohydrate–lipid intake plays a critical role in metabolic dysregulation, which impacts longevity. Caenorhabditis elegans has been successfully used as an in vivo model to study the effects of several factors, such as genetic, environmental, diet, and lifestyle factors, on the molecular mechanisms that have been linked to healthspan, lifespan, and the aging process. There is evidence showing the causative effects of high glucose on lifespan in different diabetic models; however, the precise biological mechanisms affected by dietary nutrients, specifically carbohydrates and lipids, as well as their links with lifespan and longevity, remain unknown. Here, we provide an overview of the deleterious effects caused by high-carbohydrate and high-lipid diets, as well as the molecular signals that affect the lifespan of C. elegans; thus, understanding the detailed molecular mechanisms of high-glucose- and lipid-induced changes in whole organisms would allow the targeting of key regulatory factors to ameliorate metabolic disorders and age-related diseases.

Branched-chain Amino Acids: Catabolism in Skeletal Muscle and Implications for Muscle and Whole-body Metabolism

Branched-chain amino acids (BCAAs) are critical for skeletal muscle and whole-body anabolism and energy homeostasis. They also serve as signaling molecules, for example, being able to activate mammalian/mechanistic target of rapamycin complex 1 (mTORC1). This has implication for macronutrient metabolism. However, elevated circulating levels of BCAAs and of their ketoacids as well as impaired catabolism of these amino acids (AAs) are implicated in the development of insulin resistance and its sequelae, including type 2 diabetes, cardiovascular disease, and of some cancers, although other studies indicate supplements of these AAs may help in the management of some chronic diseases. Here, we first reviewed the catabolism of these AAs especially in skeletal muscle as this tissue contributes the most to whole body disposal of the BCAA. We then reviewed emerging mechanisms of control of enzymes involved in regulating BCAA catabolism. Such mechanisms include regulation of their abundance by microRNA and by post translational modifications such as phosphorylation, acetylation, and ubiquitination. We also reviewed implications of impaired metabolism of BCAA for muscle and whole-body metabolism. We comment on outstanding questions in the regulation of catabolism of these AAs, including regulation of the abundance and post-transcriptional/post-translational modification of enzymes that regulate BCAA catabolism, as well the impact of circadian rhythm, age and mTORC1 on these enzymes. Answers to such questions may facilitate emergence of treatment/management options that can help patients suffering from chronic diseases linked to impaired metabolism of the BCAAs.

The prognostic outcome of 'type 2 diabetes mellitus and breast cancer' association pivots on hypoxia-hyperglycemia axis

Type 2 diabetes mellitus and breast cancer are complex, chronic, heterogeneous, and multi-factorial diseases; with common risk factors including but not limited to diet, obesity, and age. They also share mutually inclusive phenotypic features such as the metabolic deregulations resulting from hyperglycemia, hypoxic conditions and hormonal imbalances. Although, the association between diabetes and cancer has long been speculated; however, the exact molecular nature of this link remains to be fully elucidated. Both the diseases are leading causes of death worldwide and a causal relationship between the two if not addressed, may translate into a major global health concern. Previous studies have hypothesized hyperglycemia, hyperinsulinemia, hormonal imbalances and chronic inflammation, as some of the possible grounds for explaining how diabetes may lead to cancer initiation, yet further research still needs to be done to validate these proposed mechanisms. At the crux of this dilemma, hyperglycemia and hypoxia are two intimately related states involving an intricate level of crosstalk and hypoxia inducible factor 1, at the center of this, plays a key role in mediating an aggressive disease state, particularly in solid tumors such as breast cancer. Subsequently, elucidating the role of HIF1 in establishing the diabetes-breast cancer link on hypoxia-hyperglycemia axis may not only provide an insight into the molecular mechanisms underlying the association but also, illuminate on the prognostic outcome of the therapeutic targeting of HIF1 signaling in diabetic patients with breast cancer or vice versa. Hence, this review highlights the critical role of HIF1 signaling in patients with both T2DM and breast cancer, potentiates its significance as a prognostic marker in comorbid patients, and further discusses the potential prognostic outcome of targeting HIF1, subsequently establishing the pressing need for HIF1 molecular profiling-based patient selection leading to more effective therapeutic strategies emerging from personalized medicine.

How the love of muscle can break a heart: Impact of anabolic androgenic steroids on skeletal muscle hypertrophy, metabolic and cardiovascular health

It is estimated 6.4% of males and 1.6% of females globally use anabolic-androgenic steroids (AAS), mostly for appearance and performance enhancing reasons. In combination with resistance exercise, AAS use increases muscle protein synthesis resulting in skeletal muscle hypertrophy and increased performance. Primarily through binding to the androgen receptor, AAS exert their hypertrophic effects via genomic, non-genomic and anti-catabolic mechanisms. However, chronic AAS use also has a detrimental effect on metabolism ultimately increasing the risk of cardiovascular disease (CVD). Much research has focused on AAS effects on blood lipids and lipoproteins, with abnormal concentrations of these associated with insulin resistance, hypertension and increased visceral adipose tissue (VAT). This clustering of interconnected abnormalities is often referred as metabolic syndrome (MetS). Therefore, the aim of this review is to explore the impact of AAS use on mechanisms of muscle hypertrophy and markers of MetS. AAS use markedly decreases high-density lipoprotein cholesterol (HDL-C) and increases low-density lipoprotein cholesterol (LDL-C). Chronic AAS use also appears to cause higher fasting insulin levels and impaired glucose tolerance and possibly higher levels of VAT; however, research is currently lacking on the effects of AAS use on glucose metabolism. While cessation of AAS use can restore normal lipid levels, it may lead to withdrawal symptoms such as depression and hypogonadism that can increase CVD risk. Research is currently lacking on effective treatments for withdrawal symptoms and further long-term research is warranted on the effects of AAS use on metabolic health in males and females.

N-retinylidene-N-retinylethanolamine adduct induces expression of chronic inflammation cytokines in retinal pigment epithelium cells

Blindness due to photoreceptor degeneration is observed in both genetic and acquired eye disorders. Long blue light exposure can contribute to increase levels of oxidative compounds within the retinal pigment epithelium (RPE), enhancing risk of retinal damage. In retina, reactive oxygen species contribute to the activation of inflammatory cascade. If chronic, this inflammatory response can result in photoreceptor death. Therefore, we investigated the effects of the endogenous adduct N-retinylidene-N-retinylethanolamine (A2E) on RPE cells, in order to identify the most dysregulated cytokines and their related inflammatory pathways. RPE cells were exposed to A2E and blue light for 3h and 6h. By transcriptome analysis, we identified differentially expressed genes in A2E-treated cells, when compared to untreated ones. Expression values were quantified by the Limma R package. Enrichment analysis was performed according to the "Reactome" and the Gene Ontology databases. Expression of pro-inflammatory cytokines increased after 3h of A2E treatment and pathways related to IL-6 and IL-1 signaling resulted enriched. Also the up-regulation of genes having a protective role against inflammation was observed. Moreover, our results show that ferroptosis could contribute to RPE degeneration induced by A2E and blue light. Dysregulated genes related to retinal degeneration triggered by oxidative damage and inflammatory response activation identified in this study can be considered as potential biomarkers for targeted therapies.

Insulin sensitivity in long-lived growth hormone-releasing hormone knockout mice

Our previous studies showed that loss-of-function mutation of growth hormone releasing hormone (GHRH) results in increased longevity and enhanced insulin sensitivity in mice. However, the details of improved insulin action and tissue-specific insulin signaling are largely unknown in this healthy-aging mouse model. We conducted hyperinsulinemic-euglycemic clamp to investigate mechanisms underlying enhanced insulin sensitivity in growth hormone (GH) deficient mice. Further, we assessed in vivo tissue-specific insulin activity via activation of PI3K-AKT and MAPK-ERK1/2 cascades using western blot. Clamp results showed that the glucose infusion rate required for maintaining euglycemia was much higher in GHRH^-/- mice compared to WT controls. Insulin-mediated glucose production was largely suppressed, whereas glucose uptake in skeletal muscle and brown adipose tissue were significant enhanced in GHRH^-/- mice compared to WT controls. Enhanced capacity of insulin-induced activation of the PI3K-AKT and MAPK-ERK1/2 signaling were observed in a tissue-specific manner in GHRH^-/- mice. Enhanced systemic insulin sensitivity in long-lived GHRH^-/- mice is associated with differential activation of insulin signaling cascades among various organs. Improved action of insulin in the insulin sensitive tissues is likely to mediate the prolonged longevity and healthy-aging effects of GH deficiency in mice.

From causes of aging to death from COVID-19

COVID-19 is not deadly early in life, but mortality increases exponentially with age, which is the strongest predictor of mortality. Mortality is higher in men than in women, because men age faster, and it is especially high in patients with age-related diseases, such as diabetes and hypertension, because these diseases are manifestations of aging and a measure of biological age. At its deepest level, aging (a program-like continuation of developmental growth) is driven by inappropriately high cellular functioning. The hyperfunction theory of quasi-programmed aging explains why COVID-19 vulnerability (lethality) is an age-dependent syndrome, linking it to other age-related diseases. It also explains inflammaging and immunosenescence, hyperinflammation, hyperthrombosis, and cytokine storms, all of which are associated with COVID-19 vulnerability. Anti-aging interventions, such as rapamycin, may slow aging and age-related diseases, potentially decreasing COVID-19 vulnerability.

Elucidating the mechanism of action of alpha-1-antitrypsin using retinal pigment epithelium cells exposed to high glucose. Potential use in diabetic retinopathy

BACKGROUND

Alpha-1-antitrypsin is a protein involved in avoidance of different processes that are seen in diabetic retinopathy pathogenesis. These processes include apoptosis, extracellular matrix remodeling and damage of vessel walls and capillaries. Furthermore, because of its anti-inflammatory effects, alpha-1-antitrypsin has been proposed as a possible therapeutic approach for diabetic retinopathy. Our group tested alpha-1-antitrypsin in a type 1 diabetes mouse model and observed a reduction of inflammation and retinal neurodegeneration. Thus, shedding light on the mechanism of action of alpha-1-antitrypsin at molecular level may explain how it works in the diabetic retinopathy context and show its potential for use in other retinal diseases.

METHODS

In this work, we evaluated alpha-1-antitrypsin in an ARPE-19 human cell line exposed to high glucose. We explored the expression of different mediators on signaling pathways related to pro-inflammatory cytokines production, glucose metabolism, epithelial-mesenchymal transition and other proteins involved in the normal function of retinal pigment epithelium by RT-qPCR and Western Blot.

RESULTS

We obtained different expression patterns for evaluated mediators altered with high glucose exposure and corrected with the use of alpha-1-antitrypsin.

CONCLUSIONS

The expression profile obtained in vitro for the evaluated proteins and mRNA allowed us to explain our previous results obtained on mouse models and to hypothesize how alpha-1-antitrypsin hinder diabetic retinopathy progression on a complex network between different signaling pathways.

GENERAL SIGNIFICANCE

This network helps to understand the way alpha-1-antitrypsin works in diabetic retinopathy and its scope of action.

Drp1 mediates high glucose-induced mitochondrial dysfunction and epithelial-mesenchymal transition in endometrial cancer cells

This study aims to clarify the role and molecular mechanism of dynamin-related protein 1 (Drp1)-mediated mitochondrial homeostasis in high glucose (HG)-induced endometrial cancer (EC). Normal endometrium and tumor tissues of EC patients with normal and HG levels were collected, and Drp1 and p-Drp1 expression levels were detected by immunohistochemistry. Human EC cells were cultured with different glucose concentrations, and Drp1 and p-Drp1 expression levels were evaluated by Western blotting. Cell models of control and siDrp1 groups under normal and HG conditions were established, and subsequent functional experiments were conducted. Histology and in vitro experiments showed that the HG environment increased Drp1 activation, which could lead to mitochondrial dysfunction. Moreover, the imbalance of mitochondrial homeostasis mediated by Drp1 resulted in cell dysfunction, including altered glucose metabolism and increased epithelial-mesenchymal transition (EMT), migration and invasion. All these changes caused by HG could be partially alleviated by Drp1 knockdown. This study revealed that Drp1 was involved in the progression of EC associated with HG, and Drp1 might be a new potential therapeutic target for EC patients with diabetes.

Bisphenol A exposure under metabolic stress induces accelerated cellular senescence in vivo in a p53 independent manner

Senescence is an irreversible process that is a characteristic of age-associated disease like Type 2 diabetes (T2D). Bisphenol-A (BPA), one of the most common endocrine disruptor chemicals, received special attention in the development of insulin resistance and T2D. To understand the role played by BPA in cellular senescence under metabolic stress, zebrafish embryos were exposed to BPA in the absence and presence of hyperglycaemia. Transcriptional levels of the senescence markers p15, p53, Rb1 and β-galactosidase were increased when BPA was combined with metabolic stress. In addition, zebrafish embryos that were exposed to combination of hyperglycaemia and BPA exhibited increased levels of apoptosis. However, cellular senescence remained induced by a combination of hyperglycaemia and BPA exposure even in the absence of a translated p53 protein suggesting that senescence is primarily independent of it but dependent on the p15-Rb1 pathway under our experimental conditions. To confirm that our results hold true in adult mammalian tissues, we validated our embryonic experiments in an adult mammalian metabolic model of skeletal muscle cells. Our work reveals a novel and unique converging role of senescence and apoptosis axis contributing to glucose dyshomeostasis. Thus, we conclude that BPA exposure can exacerbate existing metabolic stress to increase cellular senescence that leads to aggravation of disease phenotype in age-associated diseases like type 2 diabetes.

Rapamycin for longevity: opinion article

From the dawn of civilization, humanity has dreamed of immortality. So why didn't the discovery of the anti-aging properties of mTOR inhibitors change the world forever? I will discuss several reasons, including fear of the actual and fictional side effects of rapamycin, everolimus and other clinically-approved drugs, arguing that no real side effects preclude their use as anti-aging drugs today. Furthermore, the alternative to the reversible (and avoidable) side effects of rapamycin/everolimus are the irreversible (and inevitable) effects of aging: cancer, stroke, infarction, blindness and premature death. I will also discuss why it is more dangerous not to use anti-aging drugs than to use them and how rapamycin-based drug combinations have already been implemented for potential life extension in humans. If you read this article from the very beginning to its end, you may realize that the time is now.

High blood sugar levels but not diabetes mellitus significantly enhance oxaliplatin chemoresistance in patients with stage III colorectal cancer receiving adjuvant FOLFOX6 chemotherapy

Background:

The high prevalence of type 2 diabetes mellitus (DM) among patients with colorectal cancer (CRC) is becoming a serious public health concern worldwide. FOLFOX4 chemotherapy is one of the most widely used adjuvant therapies in patients with stage III colon cancer after surgical resection. However, chemotherapy resistance is associated with a poor prognosis. The prognostic impact of high blood sugar levels on oxaliplatin resistance in CRC patients is an unexplored topic.

Methods:

In total, 157 patients with stage III CRC were classified according to their fasting blood sugar level (⩾126 or <126 mg/dl). Clinicopathological features and oxaliplatin chemoresistance/survival outcome of the two groups were compared. In vitro cell proliferation assay was performed through d-(+)-glucose administration.

Results:

Multivariate analysis results revealed that high blood sugar level was a significantly independent prognostic factor of disease-free survival and overall survival (both p < 0.05), but not DM history. After metformin administration, enhanced proliferation of CRC cells (HT-29, HCT-116, SW480, and SW620) with d-(+)-glucose administration could be reversed and oxaliplatin chemosensitivity considerably increased (p < 0.05). Furthermore, phosphorylation of two glycolysis-related target proteins, SMAD3 and MYC, notably increased under high glucose concentration.

Conclusions:

Hyperglycemia can affect clinical outcomes in stage III CRC patients receiving adjuvant chemotherapy, and the mechanism underlying oxaliplatin resistance is possibly associated with increased phosphorylation of SMAD3 and MYC and upregulation of EHMT2 expression.

Fasting and rapamycin: diabetes versus benevolent glucose intolerance

Rapamycin (Sirolimus) slows aging, extends life span, and prevents age-related diseases, including diabetic complications such as retinopathy. Puzzlingly, rapamycin can induce insulin sensitivity, but may also induce insulin resistance or glucose intolerance without insulin resistance. This mirrors the effect of fasting and very low calorie diets, which improve insulin sensitivity and reverse type 2 diabetes, but also can cause a form of glucose intolerance known as benevolent pseudo-diabetes. There is no indication that starvation (benevolent) pseudo-diabetes is detrimental. By contrast, it is associated with better health and life extension. In transplant patients, a weak association between rapamycin/everolimus use and hyperglycemia is mostly due to a drug interaction with calcineurin inhibitors. When it occurs in cancer patients, the hyperglycemia is mild and reversible. No hyperglycemic effects of rapamycin/everolimus have been detected in healthy people. For antiaging purposes, rapamycin/everolimus can be administrated intermittently (e.g., once a week) in combination with intermittent carbohydrate restriction, physical exercise, and metformin.

UCHL1 regulates muscle fibers and mTORC1 activity in skeletal muscle

AIMS

Skeletal muscle wasting is associated with many chronic diseases. Effective prevention and treatment of muscle wasting remain as a challenging task due to incomplete understanding of mechanisms by which muscle mass is maintained and regulated. This study investigated the functional role of Ubiquitin C-terminal hydrolase L1 (UCHL1) in skeletal muscle.

MAIN METHODS

Mice with skeletal muscle specific gene knockout of UCHL1 and C2C12 myoblast cells with UCHL1 knockdown were used. Muscle fiber types and size were measured using tissue or cell staining. The mammalian target of rapamycin complex 1 (mTORC1) and mTORC2 activities were assessed with the phosphorylation of their downstream targets.

KEY FINDINGS

In mouse skeletal muscle, UCHL1 was primarily expressed in slow twitch muscle fibers. Mice with skeletal muscle specific knockout (skmKO) of UCHL1 exhibited enlarged muscle fiber sizes in slow twitch soleus but not fast twitch extensor digitorum longus (EDL) muscle. Meanwhile, UCHL1 skmKO enhanced mTORC1 activity and reduced mTORC2 activity in soleus but not in EDL. Consistently, in C2C12 cells, UCHL1 knockdown increased the myotube size, enhanced mTORC1 activity, and reduced mTORC2 activities as compared with control cells. UCHL1 knockdown did not change the major proteins of mTOR complex but decreased the protein turnover of PRAS40, an inhibitory factor of mTORC1.

SIGNIFICANCE

These data revealed a novel function of UCHL1 in regulation of mTORC1 activity and skeletal muscle growth in slow twitch skeletal muscle. Given the upregulation of UCHL1 in denervation and spinal muscle atrophy, our finding advances understanding of regulators that are involved in muscle wasting.

Alteration of Sphingolipids in Biofluids: Implications for Neurodegenerative Diseases

Sphingolipids (SL) modulate several cellular processes including cell death, proliferation and autophagy. The conversion of sphingomyelin (SM) to ceramide and the balance between ceramide and sphingosine-1-phosphate (S1P), also known as the SL rheostat, have been associated with oxidative stress and neurodegeneration. Research in the last decade has focused on the possibility of targeting the SL metabolism as a therapeutic option; and SL levels in biofluids, including serum, plasma, and cerebrospinal fluid (CSF), have been measured in several neurodegenerative diseases with the aim of finding a diagnostic or prognostic marker. Previous reviews focused on results from diseases such as Alzheimer's Disease (AD), evaluated total SL or species levels in human biofluids, post-mortem tissues and/or animal models. However, a comprehensive review of SL alterations comparing results from several neurodegenerative diseases is lacking. The present work compiles data from circulating sphingolipidomic studies and attempts to elucidate a possible connection between certain SL species and neurodegeneration processes. Furthermore, the effects of ceramide species according to their acyl-chain length in cellular pathways such as apoptosis and proliferation are discussed in order to understand the impact of the level alteration in specific species. Finally, enzymatic regulations and the possible influence of insulin resistance in the level alteration of SL are evaluated.

High Glucose Promotes Human Glioblastoma Cell Growth by Increasing the Expression and Function of Chemoattractant and Growth Factor Receptors

Diabetes mellitus, characterized by hyperglycemia, is considered as a risk factor of cancers including malignant gliomas. However, the direct effect of high glucose on cancer cell behavior is not clear. We therefore investigated the effect of hyperglycemia on the growth of human glioblastoma (GBM) cells. Our results revealed that high glucose (HG) promoted the proliferation and inhibited the apoptosis of a human GBM cell line U87. Mechanistically, HG upregulated the expression and function of a G-protein coupled chemoattractant receptor (GPCR) formyl peptide receptor 1 (FPR1) and epidermal growth factor receptor (EGFR) on GBM cells, which upon activation by their agonists, promoted cell migration and proliferation. In addition, the invasiveness and the production of VEGF by U87 cells were enhanced under HG conditions, the effects of which were mediated by FPR1 and EGFR agonists. The tumor promoting activity of HG was further substantiated by increased tumorigenicity and growth of xenograft tumors formed by GBM cells in nude mice with induced diabetes mellitus. Thus, our study demonstrates the capacity of HG to promote GBM progression via enhancement of the function of chemoattractant and growth factor receptors.

High Glucose Concentrations Negatively Regulate the IGF1R/Src/ERK Axis through the MicroRNA-9 in Colorectal Cancer

Studies have revealed that people with hyperglycemia have a high risk of colorectal cancer (CRC). Hyperglycemia may be responsible for supplying energy to CRC cells. However, the potential molecular mechanism for this association remains unclear. Furthermore, microRNA-9 (miR-9) has a tumor-suppressive function in CRC. Aberrant reduced expression of miR-9 is involved in the development and progression of malignancy caused by a high glucose (HG) concentration. In this study, we used an HG concentration to activate miR-9 downregulation in CRC cells. Our results indicated that miR-9 decreased the insulin-like growth factor-1 receptor (IGF1R)/Src signaling pathway and downstream cyclin B1 and N-cadherin but upregulated E-cadherin. The HG concentration not only promoted cell proliferation, increased the G1 population, and modulated epithelial-to-mesenchymal transition (EMT) protein expression and morphology but also promoted the cell migration and invasion ability of SW480 (low metastatic potential) and SW620 (high metastatic potential) cells. In addition, low glucose concentrations could reverse the effect of the HG concentration in SW480 and SW620 cells. In conclusion, our results provide new evidence for multiple signaling pathways being regulated through hyperglycemia in CRC. We propose that blood sugar control may serve as a potential strategy for the clinical management of CRC.

Non-alcoholic Fatty Liver Disease Induced by Perinatal Exposure to Bisphenol a Is Associated With Activated mTOR and TLR4/NF-κB Signaling Pathways in Offspring Rats

Accumulating evidence suggests a role of bisphenol A (BPA) in non-alcoholic fatty liver disease (NAFLD), and its mechanism may be related to the up-regulation of lipogenic genes, but the mechanism of BPA induced lipogenic gene expression remains unknown. The aim of this study was to investigate the effects of perinatal exposure to BPA on NAFLD and its mechanisms. Pregnant Sprague-Dawley rats had access to drinking water containing 1 or 10 μg/ml BPA from gestational day 6 to post-natal day 21. For 5 weeks after weaning, offspring drank normal water without BPA. Body weight, lipid profile and the expression of genes or proteins involved in mTOR mediated lipid metabolism and autophagy, as well as inflammatory response were investigated in the 8-wk-old offspring of different genders. The results showed that body weight was increased only in females, however, males, and females from dams treated with BPA had significantly excess visceral adipose tissue, which was consistent with adipocyte hypertrophy. Elevated TG levels and up-regulation of lipogenic genes or proteins in liver, such as sterol regulatory element binding protein 1 (SREBP1), acetyl-CoA carboxylase 1 (ACC1), and fatty acid synthase (FAS) were consistent with increased liver lipid droplets in offspring exposed to BPA. Compared with controls, the protein levels of InsR, p-IRS-1, IRS-1, TSC1, and TSC2 were decreased, p-PI3K, p-Akt (S473), p-Akt (T308), p-mTOR, and mTOR were increased, and the impaired autophagic degradation was evidenced by increased protein levels of p62, although the levels of p-ULK1, Beclin1, and LC3B proteins were increased in liver of BPA-exposed offspring. The levels of TLR4 and NF-κB proteins were also significantly increased, and ERα protein was significantly decreased in BPA-exposed offspring. Our findings indicate that perinatal exposure to BPA causes the development of NAFLD in both female and male offspring, which is associated with up-regulation of lipogenic genes, dysregulated autophagy and activated inflammatory response involving the PI3K/Akt/mTOR and TLR4/NF-κB pathways.

Rapamycin, proliferation and geroconversion to senescence

Rapamycin inhibits cell proliferation, yet preserves (re)-proliferative potential (RPP). RPP is a potential of quiescent cells that is lost in senescent cells. mTOR drives conversion from quiescence to senescence (geroconversion). By suppressing geroconversion, rapamycin preserves RPP. Geroconversion is characterized by proliferation-like levels of phospho-S6K/S6/4E-BP1 in nonproliferating cells arrested by p16 and/or p21. mTOR-driven geroconversion is associated with cellular hyperfunction, which in turn leads to organismal aging manifested by age-related diseases.

Identification of protein kinase inhibitors to reprogram breast cancer cells

Direct reversion of cancers into normal-like tissues is an ideal strategy for cancer treatment. Recent reports have showed that defined transcription factors can induce reprogramming of cancer cells into pluripotent stem cells, supporting this notion. Here, we have developed a reprogramming method that uses a conceptually unique strategy for breast cancer cell treatment. We have screened a kinase inhibitor library and found that Rho-associated protein kinase (ROCK) and mammalian target of rapamycin (mTOR) kinase inhibitors can substitute for all transcription factors to be sufficient to reprogram breast cancer cells into progenitor cells. Furthermore, ROCK–mTOR inhibitors could reprogram breast cancer cells to another terminal lineage-adipogenic cells. Genome-wide transcriptional analysis shows that the induced fat-like cells have a profile different from breast cancer cells and similar to that of normal adipocytes. In vitro and in vivo tumorigenesis assays have shown that induced fat-like cells lose proliferation and tumorigenicity. Moreover, reprogramming treatment with ROCK–mTOR inhibitors prevents breast cancer local recurrence in mice. Currently, ROCK–mTOR inhibitors are already used as antitumor drugs in patients, thus, this reprogramming strategy has significant potential to move rapidly toward clinical trials for breast cancer treatment.

Effects of β-caryophyllene on arginine ADP-ribosyltransferase 1-mediated regulation of glycolysis in colorectal cancer under high-glucose conditions

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of the development of colorectal cancer (CRC). A previous study revealed that the levels of arginine-specific mono-ADP-ribosyltransferase 1 (ART1) in CRC tissues from patients with T2DM were higher than in non-diabetic patients. Hyperglycemia, which is a risk factor of cancer, is a common feature of T2DM; however, the effects of ART1 on glycolysis and energy metabolism in CRC cells under high-glucose conditions remains to be elucidated. β-caryophyllene (BCP) has been reported to exert anticancer and hypoglycemic effects. In the present study, CT26 cells were cultured under a high-glucose conditions and the expression levels of relevant factors were detected by western blotting. Cell Counting Kit-8 assay, flow cytometry, Hoechst 33258 staining, ATP assay and lactic acid assay were used to detect the proliferation, apoptosis and energy metabolism of CT26 cells. To observe the effects of ART1 and BCP on tumor growth in vivo, CT26 cell tumors were successfully transplanted into BALB/c mice with T2DM. The results demonstrated that overexpression of ART1 may increase glycolysis and energy metabolism in CT26 CRC cells under high glucose conditions by regulating the protein kinase B/mammalian target of rapamycin/c‑Myc signaling pathway and the expression of glycolytic enzymes. BCP inhibited the effects induced by ART1, which may be due to a BCP-induced reduction in the expression levels of ART1 via nuclear factor-κB. Therefore, ART1 may be considered a therapeutic target for the treatment of diabetic patients with CRC.

High glucose induces formation of tau hyperphosphorylation via Cav-1-mTOR pathway: A potential molecular mechanism for diabetes-induced cognitive dysfunction

The abnormally hyperphosphorylated tau is thought to be implicated in diabetes-associated cognitive deficits. The role of mammalian target of rapamycin (mTOR) / S6 kinase (S6K) signalling in the formation of tau hyperphosphorylation has been previously studied. Caveolin-1 (Cav-1), the essential structure protein of caveolae, promotes neuronal survival and growth, and inhibits glucose metabolism. In this study, we aimed to investigate the role of Cav-1 in the formation of tau hyperphosphorylation under chronic hyperglycemic condition (HGC). Diabetic rats were induced by streptozotocin (STZ). Primary hippocampal neurons with or without molecular intervention such as the transient over-expression or knock-down were subjected to HGC. The obtained experimental samples were analyzed by real time quantitative RT-PCR, Western blot, immunofluorescence or immunohistochemisty. We found: 1) that a chronic HGC directly decreases Cav-1 expression, increases tau phosphorylation and activates mTOR/S6K signalling in the brain neurons of diabetic rats, 2) that overexpression of Cav-1 attenuates tau hyperphosphorylation induced by chronic HGC in primary hippocampal neurons, whereas down-regulation of Cav-1 using Cav-1 siRNA dramatically worsens tau hyperphosphorylation via mTOR/S6K signalling pathway, and 3) that the down-regulation of Cav-1 induced by HGC is independent of mTOR signalling. Our results suggest that tau hyperphosphorylation and the sustained over-activated mTOR signalling under hyperglycemia may be due to the suppression of Cav-1. Therefore, Cav-1 is a potential therapeutic target for diabetes-induced cognitive dysfunction.

Counteraction of Oxidative Stress by Vitamin E Affects Epigenetic Regulation by Increasing Global Methylation and Gene Expression of MLH1 and DNMT1 Dose Dependently in Caco-2 Cells

Obesity- or diabetes-induced oxidative stress is discussed as a major risk factor for DNA damage. Vitamin E and many polyphenols exhibit antioxidative activities with consequences on epigenetic regulation of inflammation and DNA repair. The present study investigated the counteraction of oxidative stress by vitamin E in the colorectal cancer cell line Caco-2 under normal (1 g/l) and high (4.5 g/l) glucose cell culture condition. Malondialdehyde (MDA) as a surrogate marker of lipid peroxidation and reactive oxygen species (ROS) was analyzed. Gene expression and promoter methylation of the DNA repair gene MutL homolog 1 (MLH1) and the DNA methyltransferase 1 (DNMT1) as well as global methylation by LINE-1 were investigated. Results revealed a dose-dependent counteracting effect of vitamin E on H₂O₂-induced oxidative stress. Thereby, 10 μM vitamin E proved to be more efficient than did 50 μM in reducing MDA. Further, an induction of MLH1 and DNMT1 gene expression was noticed, accompanied by an increase in global methylation. Whether LINE-1 hypomethylation is a cause or effect of oxidative stress is still unclear. In conclusion, supplementation of exogenous antioxidants like vitamin E in vitro exhibits beneficial effects concerning oxidative stress as well as epigenetic regulation involved in DNA repair.

Chronic treatment with novel nanoformulated micelles of rapamycin, Rapatar, protects diabetic heart against ischaemia/reperfusion injury

BACKGROUND AND PURPOSE

Enhanced mammalian target of rapamycin (mTOR) signalling contributes to the pathogenesis of diabetes and plays a critical role in myocardial ischaemia/reperfusion (I/R) injury. Rapatar is a novel nanoformulated micellar of rapamycin, a putative inhibitor of mTOR that has been rationally designed to increase water solubility of rapamycin to facilitate p.o. administration and enhance bioavailability. We examined the effect of Rapatar on the metabolic status and protection against myocardial I/R injury in type 2 diabetic mice.

EXPERIMENTAL APPROACH

Adult male db/db mice were treated daily for 10 weeks with Rapatar (0.75 mg·kg-1 ·day-1 , p.o.) or vehicle. Isolated hearts were connected to a Langendorff perfusion system and subjected to global ischaemia (30 min) and reperfusion (1 h).

KEY RESULTS

Rapatar reduced fasting plasma glucose and triglyceride levels, prevented the gain in body weight and also improved glucose tolerance and insulin sensitivity in db/db mice compared with control. Cardiac function was improved following Rapatar treatment in db/db mice. Myocardial infarct size was reduced in Rapatar-treated mice with improved post-ischaemic rate-force product. Western blot analyses demonstrated a significant inhibition of phosphorylation of ribosomal protein S6 (downstream target of mTORC1), but not Akt (Ser473 , target of mTORC2) following chronic treatment with Rapatar. Rapatar also induced phosphorylation of AMPK, STAT3, ERK1/2 and glycogen synthase kinase 3β, without interfering with phosphorylation of p38.

CONCLUSION AND IMPLICATIONS

Our studies indicate that chronic treatment with Rapatar improves metabolic status and cardiac function with a reduction of infarct size following myocardial I/R injury in diabetic mice.

Fat-specific Dicer deficiency accelerates aging and mitigates several effects of dietary restriction in mice

Aging increases the risk of type 2 diabetes, and this can be prevented by dietary restriction (DR). We have previously shown that DR inhibits the downregulation of miRNAs and their processing enzymes - mainly Dicer - that occurs with aging in mouse white adipose tissue (WAT). Here we used fat-specific Dicer knockout mice (AdicerKO) to understand the contributions of adipose tissue Dicer to the metabolic effects of aging and DR. Metabolomic data uncovered a clear distinction between the serum metabolite profiles of Lox control and AdicerKO mice, with a notable elevation of branched-chain amino acids (BCAA) in AdicerKO. These profiles were associated with reduced oxidative metabolism and increased lactate in WAT of AdicerKO mice and were accompanied by structural and functional changes in mitochondria, particularly under DR. AdicerKO mice displayed increased mTORC1 activation in WAT and skeletal muscle, where Dicer expression is not affected. This was accompanied by accelerated age-associated insulin resistance and premature mortality. Moreover, DR-induced insulin sensitivity was abrogated in AdicerKO mice. This was reverted by rapamycin injection, demonstrating that insulin resistance in AdicerKO mice is caused by mTORC1 hyperactivation. Our study evidences a DR-modulated role for WAT Dicer in controlling metabolism and insulin resistance.

Rapamycin treatment benefits glucose metabolism in mouse models of type 2 diabetes

Numerous studies suggest that rapamycin treatment promotes insulin resistance, implying that rapamycin could have negative effects on patients with, or at risk for, type 2 diabetes (T2D). New evidence, however, indicates that rapamycin treatment produces some benefits to energy metabolism, even in the context of T2D. Here, we survey 5 mouse models of T2D (KK, KK-Ay, NONcNZO10, BKS-db/db, TALLYHO) to quantify effects of rapamycin on well-recognized markers of glucose homeostasis within a wide range of T2D environments. Interestingly, dietary rapamycin treatment did not exacerbate impaired glucose or insulin tolerance, or elevate circulating lipids as T2D progressed. In fact, rapamycin increased insulin sensitivity and reduced weight gain in 3 models, and decreased hyperinsulinemia in 2 models. A key covariate of this genetically-based, differential response was pancreatic insulin content (PIC): Models with low PIC exhibited more beneficial effects than models with high PIC. However, a minimal PIC threshold may exist, below which hypoinsulinemic hyperglycemia develops, as it did in TALLYHO. Our results, along with other studies, indicate that beneficial or detrimental metabolic effects of rapamycin treatment, in a diabetic or pre-diabetic context, are driven by the interaction of rapamycin with the individual model's pancreatic physiology.

USP9X deubiquitylating enzyme maintains RAPTOR protein levels, mTORC1 signalling and proliferation in neural progenitors

USP9X, is highly expressed in neural progenitors and, essential for neural development in mice. In humans, mutations in USP9X are associated with neurodevelopmental disorders. To understand USP9X’s role in neural progenitors, we studied the effects of altering its expression in both the human neural progenitor cell line, ReNcell VM, as well as neural stem and progenitor cells derived from Nestin-cre conditionally deleted Usp9x mice. Decreasing USP9X resulted in ReNcell VM cells arresting in G0 cell cycle phase, with a concomitant decrease in mTORC1 signalling, a major regulator of G0/G1 cell cycle progression. Decreased mTORC1 signalling was also observed in Usp9x-null neurospheres and embryonic mouse brains. Further analyses revealed, (i) the canonical mTORC1 protein, RAPTOR, physically associates with Usp9x in embryonic brains, (ii) RAPTOR protein level is directly proportional to USP9X, in both loss- and gain-of-function experiments in cultured cells and, (iii) USP9X deubiquitlyating activity opposes the proteasomal degradation of RAPTOR. EdU incorporation assays confirmed Usp9x maintains the proliferation of neural progenitors similar to Raptor-null and rapamycin-treated neurospheres. Interestingly, loss of Usp9x increased the number of sphere-forming cells consistent with enhanced neural stem cell self-renewal. To our knowledge, USP9X is the first deubiquitylating enzyme shown to stabilize RAPTOR.

High blood sugar levels significantly impact the prognosis of colorectal cancer patients through down-regulation of microRNA-16 by targeting Myb and VEGFR2

The high prevalence of type 2 diabetes mellitus in colorectal cancer patients is a crucial public health issue worldwide. The deregulation of microRNAs has been shown to be associated with the progression of CRC; however, the effects of high blood sugar levels on miR deregulation and, in turn, CRC remain unexplored. In this study, 520 CRC patients were classified into two groups according to their blood sugar levels (≧110 or <110 mg/dL). Clinicopathologic features, clinical outcomes, and serum miR-16 levels of the two groups were then analyzed, while cell cycles, cell proliferation, migration, and cellular miR-16 expression were investigated via D-(+)-glucose administration. Additionally, the target genes of miR-16 were identified. Through multivariate analysis, both the disease-free survival and overall survival of the CRC patients were found to be associated with the UICC stage, perineural invasion, and blood glucose levels (P < 0.05). Serum miR-16 levels were significantly lower in the high blood glucose patients than in the normal blood glucose patients (P = 0.0329). With D-(+)-glucose administration, the proliferation and migration of CRC cells in vitro increased remarkably (P < 0.05), while their accumulation in the G1 phase decreased significantly. Cellular miR-16 expression was suppressed by D-(+)-glucose administration. The expression levels of two target genes, Myb and VEGFR2, were affected significantly by miR-16, while glucose administration inhibited miR-16 expression and enhanced tumor cell proliferation and migration. Hyperglycemia can impact the clinical outcomes of CRC patients, likely by inhibiting miR-16 expression and the expression of its downstream genes Myb and VEGFR2.

Effect of everolimus on the glucose metabolic pathway in mouse skeletal muscle cells (C2C12)

INTRODUCTION

Everolimus selectively inhibits mammalian target of rapamycin complex 1 (mTORC1) and exerts an antineoplastic effect. Metabolic disturbance has emerged as a common and unique side effect of everolimus.

OBJECTIVES

We used targeted metabolomic analysis to investigate the effects of everolimus on the intracellular glycometabolic pathway.

METHODS

Mouse skeletal muscle cells (C2C12) were exposed to everolimus for 48 h, and changes in intracellular metabolites were determined by capillary electrophoresis time-of-flight mass spectrometry. mRNA abundance, protein expression and activity were measured for enzymes involved in glycometabolism and related pathways.

RESULTS

Both extracellular and intracellular glucose levels increased with exposure to everolimus. Most intracellular glycometabolites were decreased by everolimus, including those involved in glycolysis and the pentose phosphate pathway, whereas no changes were observed in the tricarboxylic acid cycle. Everolimus suppressed mRNA expression of enzymes related to glycolysis, downstream of mTOR signaling enzymes and adenosine 5'-monophosphate protein kinases. The activity of key enzymes involved in glycolysis and the pentose phosphate pathway were decreased by everolimus. These results show that everolimus impairs glucose utilization in intracellular metabolism.

CONCLUSIONS

The present metabolomic analysis indicates that everolimus impairs glucose metabolism in muscle cells by lowering the activities of glycolysis and the pentose phosphate pathway.

Epigallocatechin gallate affects glucose metabolism and increases fitness and lifespan in Drosophila melanogaster

In this study, we tested whether a standardized epigallocatechin-3-gallate (EGCG) rich green tea extract (comprising > 90% EGCG) affects fitness and lifespan as well as parameters of glucose metabolism and energy homeostasis in the fruit fly, Drosophila melanogaster. Following the application of the green tea extract a significant increase in the mean lifespan (+ 3.3 days) and the 50% survival (+ 4.3 days) as well as improved fitness was detected. These effects went along an increased expression of Spargel, the homolog of mammalian PGC1α, which has been reported to affect lifespan in flies. Intriguingly, in flies, treatment with the green tea extract decreased glucose concentrations, which were accompanied by an inhibition of α-amylase and α-glucosidase activity. Computational docking analysis proved the potential of EGCG to dock into the substrate binding pocket of α-amylase and to a greater extent into α-glucosidase. Furthermore, we demonstrate that EGCG downregulates insulin-like peptide 5 and phosphoenolpyruvate carboxykinase, major regulators of glucose metabolism, as well as the Drosophila homolog of leptin, unpaired 2. We propose that a decrease in glucose metabolism in connection with an upregulated expression of Spargel contribute to the better fitness and the extended lifespan in EGCG-treated flies.

AKT inhibition overcomes rapamycin resistance by enhancing the repressive function of PRAS40 on mTORC1/4E-BP1 axis

The mTORC1 inhibitors, rapamycin and its analogs, are known to show only modest antitumor activity in clinic, but the underlying mechanisms remain largely elusive. Here, we found that activated AKT signaling is associated with rapamycin resistance in breast and colon cancers by sustained phosphorylation of the translational repressor 4E-BP1. Treatment of tumor cells with rapamycin or the AKT inhibitor MK2206 showed a limited activity in inhibiting 4E-BP1 phosphorylation, cap-dependent translation, cell growth and motility. However, treatment with both drugs resulted in profound effects in vitro and in vivo. Mechanistic investigation demonstrated that the combination treatment was required to effectively inhibit PRAS40 phosphorylation on both Ser183 and Thr246 mediated by mTORC1 and AKT respectively, and with the combined treatment, dephosphorylated PRAS40 binding to the raptor/mTOR complex was enhanced, leading to dramatic repression of mTORC1-regulated 4E-BP1 phosphorylation and translation. Knockdown of PRAS40 or 4E-BP1 expression markedly reduced the dependence of tumor cells on AKT/mTORC1 signaling for translation and survival. Together, these findings reveal a critical role of PRAS40 as an integrator of mTORC1 and AKT signaling for 4E-BP1-mediated translational regulation of tumor cell growth and motility, and highlight PRAS40 phosphorylation as a potential biomarker to evaluate the therapeutic response to mTOR/AKT inhibitors.

Metabolic Activity of Radish Sprouts Derived Isothiocyanates in Drosophila melanogaster

We used Drosophila melanogaster as a model system to study the absorption, metabolism and potential health benefits of plant bioactives derived from radish sprouts (Raphanus sativus cv. Rambo), a Brassicaceae species rich in glucosinolates and other phytochemicals. Flies were subjected to a diet supplemented with lyophilized radish sprouts (10.6 g/L) for 10 days, containing high amounts of glucoraphenin and glucoraphasatin, which can be hydrolyzed by myrosinase to the isothiocyanates sulforaphene and raphasatin, respectively. We demonstrate that Drosophila melanogaster takes up and metabolizes isothiocyanates from radish sprouts through the detection of the metabolite sulforaphane-cysteine in fly homogenates. Moreover, we report a decrease in the glucose content of flies, an upregulation of spargel expression, the Drosophila homolog of the mammalian PPARγ-coactivator 1 α, as well as the inhibition of α-amylase and α-glucosidase in vitro. Overall, we show that the consumption of radish sprouts affects energy metabolism in Drosophila melanogaster which is reflected by lower glucose levels and an increased expression of spargel, a central player in mitochondrial biogenesis. These processes are often affected in chronic diseases associated with aging, including type II diabetes mellitus.

Tumor promoter-induced cellular senescence: cell cycle arrest followed by geroconversion

Phorbol ester (PMA or TPA), a tumor promoter, can cause either proliferation or cell cycle arrest, depending on cellular context. For example, in SKBr3 breast cancer cells, PMA hyper-activates the MEK/MAPK pathway, thus inducing p21 and cell cycle arrest. Here we showed that PMA-induced arrest was followed by conversion to cellular senescence (geroconversion). Geroconversion was associated with active mTOR and S6 kinase (S6K). Rapamycin suppressed geroconversion, maintaining quiescence instead. In this model, PMA induced arrest (step one of a senescence program), whereas constitutively active mTOR drove geroconversion (step two). Without affecting Akt phosphorylation, PMA increased phosphorylation of S6K (T389) and S6 (S240/244), and that was completely prevented by rapamycin. Yet, T421/S424 and S235/236 (p-S6K and p-S6, respectively) phosphorylation became rapamycin-insensitive in the presence of PMA. Either MEK or mTOR was sufficient to phosphorylate these PMA-induced rapamycin-resistant sites because co-treatment with U0126 and rapamycin was required to abrogate them. We next tested whether activation of rapamycin-insensitive pathways would shift quiescence towards senescence. In HT-p21 cells, cell cycle arrest was caused by IPTG-inducible p21 and was spontaneously followed by mTOR-dependent geroconversion. Rapamycin suppressed geroconversion, whereas PMA partially counteracted the effect of rapamycin, revealing the involvement of rapamycin-insensitive gerogenic pathways. In normal RPE cells arrested by serum withdrawal, the mTOR/pS6 pathway was inhibited and cells remained quiescent. PMA transiently activated mTOR, enabling partial geroconversion. We conclude that PMA can initiate a senescent program by either inducing arrest or fostering geroconversion or both. Rapamycin can decrease gero-conversion by PMA, without preventing PMA-induced arrest. The tumor promoter PMA is a gero-promoter, which may be useful to study aging in mammals.

The synergistic inhibition of breast cancer proliferation by combined treatment with 4EGI-1 and MK2206

Cap-dependent translation is a potential cancer-related target (oncotarget) due to its critical role in cancer initiation and progression. 4EGI-1, an inhibitor of eIF4E/eIF4G interaction, was discovered by screening chemical libraries of small molecules. 4EGI-1 inhibits cap-dependent translation initiation by impairing the assembly of the eIF4E/eIF4G complex, and therefore is a potential anti-cancer agent. Here, we report that 4EGI-1 also inhibits mTORC1 signaling independent of its inhibitory role on cap-dependent translation initiation. The inhibition of mTORC1 signaling by 4EGI-1 activates Akt due to both abrogation of the negative feedback loops from mTORC1 to PI3K and activation of mTORC2. We further validated that mTORC2 activity is required for 4EGI-1-mediated Akt activation. The activated Akt counteracted the anticancer effects of 4EGI-1. In support of this model, inhibition of Akt potentiates the antitumor activity of 4EGI-1 both in vitro and in a xenograft mouse model in vivo. Our results suggest that a combination of 4EGI-1and Akt inhibitor is a rational approach for the treatment of cancer.

Insulin resistance in the liver: deficiency or excess of insulin?

In insulin-resistant states (obesity, pre-diabetes, and type 2 diabetes), hepatic production of glucose and lipid synthesis are heightened in concert, implying that insulin deficiency and insulin excess coexists in this setting. The fact that insulin may be inadequate or excessive at any one point in differing organs and tissues has many biologic ramifications. In this context the concept of metabolic compartmentalization in the liver is offered herein as one perspective of this paradox. In particular, we focus on the hypothesis that insulin resistance accentuates differences in periportal and perivenous hepatocytes, namely periportal glucose production and perivenous lipid synthesis. Subsequently, excessive production of glucose and accumulation of lipids could be expected in the livers of patients with obesity and insulin resistance. Overall, in this review, we provide our integrative perspective regarding how excessive production of glucose in periportal hepatocytes and accumulation of lipids in perivenous hepatocytes interact in insulin resistant states.

Gerosuppression in confluent cells

The most physiological type of cell cycle arrest - namely, contact inhibition in dense culture - is the least densely studied. Despite cell cycle arrest, confluent cells do not become senescent. We recently described that mTOR (target of rapamycin) is inactive in contact-inhibited cells. Therefore, conversion from reversible arrest to senescence (geroconversion) is suppressed. I this Perspective, we further extended the gerosuppression model. While causing senescence in regular cell density, etoposide failed to cause senescence in contact-inhibited cells. A transient reactivation of mTOR favored geroconversion in etoposide-treated confluent cells. Like p21, p16 did not cause senescence in high cell density. We discuss that suppression of geroconversion in confluent and contact-inhibited cultures mimics gerosuppression in the organism. We confirmed that levels of p-S6 were low in murine tissues in the organism compared with mouse embryonic fibroblasts in cell culture, whereas p-Akt was reciprocally high in the organism.

Fasting levels of hepatic p-S6 are increased in old mice

TOR is involved in aging in a wide range of species from yeast to mammals. Here we show that, after overnight fasting, mTOR activity is higher in the livers of 28 months old female mice compared with middle-aged mice. Taken together with previous reports, our data predict that the life-extending effect of calorie restriction (CR) may be diminished, if CR is started in very old age. In contrast, rapamycin is known to be effective, even when started late in life.