Sestrin 3 protein enhances hepatic insulin sensitivity by direct activation of the mTORC2-Akt signaling

The multifaceted role of Sestrin 3 (SESN3) in oxidative stress, inflammation and tumorigenesis

The pathogenesis of inflammation and tumors is a focal point of scientific inquiry, with oxidative stress often serving as the primary initiator. Within the human genome, the SESN3 gene encodes the SESN3 protein, a crucial antioxidant stress protein. Acting as a regulatory factor, SESN3 intricately modulates cellular oxidative stress, actively participating in cellular protection and repair mechanisms. Its functions span antioxidative, anti-aging, and anti-tumor properties. The expression of SESN3 is closely linked to cellular and oxidative stress, metabolic status, and specific signaling pathways. This review aims to delve into the origins and functions of SESN3, its role within signaling pathways, and its contributions to inflammation and tumorigenesis.

Beckwith-Wiedemann syndrome and large offspring syndrome involve alterations in methylome, transcriptome, and chromatin configuration

Beckwith-Wiedemann Syndrome (BWS) is the most common epigenetic overgrowth syndrome, caused by epigenetic alterations on chromosome 11p15. In ∼50% of patients with BWS, the imprinted region KvDMR1 (IC2) is hypomethylated. Nearly all children with BWS develop organ overgrowth and up to 28% develop cancer during childhood. The global epigenetic alterations beyond the 11p15 region in BWS are not currently known. Uncovering these alterations at the methylome, transcriptome, and chromatin architecture levels are necessary steps to improve the diagnosis and understanding of patients with BWS. Here we characterized the complete epigenetic profiles of BWS IC2 individuals together with the animal model of BWS, bovine large offspring syndrome (LOS). A novel finding of this research is the identification of two molecular subgroups of BWS IC2 individuals. Genome-wide alternations were detected for DNA methylation, transcript abundance, alternative splicing events of RNA, chromosome compartments, and topologically associating domains (TADs) in BWS and LOS, with shared alterations identified between species. Altered chromosome compartments and TADs were correlated with differentially expressed genes in BWS and LOS. Together, we highlight genes and genomic regions that have the potential to serve as targets for biomarker development to improve current molecular diagnostic methodologies for BWS.

Restoration of Sestrin 3 Expression Mitigates Cardiac Oxidative Damage in Ischemia-Reperfusion Injury Model

Cardiac ischemia-reperfusion injury (IRI) occurs when blood flow is restored to the myocardium after a period of ischemia, leading to oxidative stress and subsequent myocardial cell damage, primarily due to the accumulation of reactive oxygen species (ROS). In our previous research, we identified that miR-25 is significantly overexpressed in pressure overload-induced heart failure, and its inhibition improves cardiac function by restoring the expression of SERCA2a, a key protein involved in calcium regulation. In this study, we aimed to investigate the role of miR-25 in the context of ischemia-reperfusion injury. We found that miR-25 was markedly upregulated under hypoxic conditions in both in vitro and in vivo models. Through in silico analysis, we identified Sestrin3 (SESN3), an antioxidant protein known for its protective effects against oxidative stress, as a novel target of miR-25. Based on these findings, we hypothesized that inhibiting miR-25 would restore Sestrin3 expression, thereby reducing ROS-induced myocardial cell damage and improving cardiac function. To test this hypothesis, we employed two model systems: a hypoxia/reoxygenation (H/R) stress model using H9c2 myoblasts and a surgically induced ischemia-reperfusion injury mouse model. Our results demonstrated that the use of miR-25 inhibitors significantly improved cardiac function and reduced myocardial damage in both models through the restoration of SESN3 expression. In conclusion, our findings suggest that targeting miR-25 may serve as a novel therapeutic modality to alleviate oxidative damage in the heart.

Tanycytes from a bird's eye view: gene expression profiling of the tanycytic region under different seasonal states in the Svalbard ptarmigan

In mammals and birds, tanycytes are known to regulate thyroid hormone conversion, and this process is central to the control of seasonal reproduction. In mammals, this cell type is also implicated in retinoic acid signalling, neurogenesis, and nutritional gatekeeping, all of which have been linked to hypothalamic regulation of energy metabolism. Less is known about these potential wider roles of tanycytes in birds. To address this gap, we combined LASER capture microdissection and transcriptomics to profile the tanycytic region in male Svalbard ptarmigan, a High Arctic species with photoperiod-dependent seasonal rhythms in reproductive activation and body mass. Short photoperiod (SP) adapted birds were transferred to constant light (LL) to trigger breeding and body mass loss. After five months under LL, the development of photorefractoriness led to spontaneous re-emergence of the winter phenotype, marked by the termination of breeding and gain in body mass. The transfer from SP to LL initiated gene expression changes in both thyroid hormone and retinoic acid pathways, as described in seasonal mammals. Furthermore, transcriptomic signatures of cell differentiation and migration were observed. Comparison to data from Siberian hamsters demonstrated that a photoperiod-dependent re-organisation of the hypothalamic tanycytic region is likely a conserved feature. Conversely, the spontaneous development of photorefractoriness showed a surprisingly small number of genes that reverted in expression level, despite reversal of the reproductive and metabolic phenotype. Our data suggest general conservation of tanycyte biology between photoperiodic birds and mammals and raise questions about the mechanistic origins of the photorefractory state.

mTORC2: A neglected player in aging regulation

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase that plays a pivotal role in various biological processes, through integrating external and internal signals, facilitating gene transcription and protein translation, as well as by regulating mitochondria and autophagy functions. mTOR kinase operates within two distinct protein complexes known as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which engage separate downstream signaling pathways impacting diverse cellular processes. Although mTORC1 has been extensively studied as a pro-proliferative factor and a pro-aging hub if activated aberrantly, mTORC2 received less attention, particularly regarding its implication in aging regulation. However, recent studies brought increasing evidence or clues for us, which implies the associations of mTORC2 with aging, as the genetic elimination of unique subunits of mTORC2, such as RICTOR, has been shown to alleviate aging progression in comparison to mTORC1 inhibition. In this review, we first summarized the basic characteristics of mTORC2, including its protein architecture and signaling network. We then focused on reviewing the molecular signaling regulation of mTORC2 in cellular senescence and organismal aging, and proposed the multifaceted regulatory characteristics under senescent and nonsenescent contexts. Next, we outlined the research progress of mTOR inhibitors in the field of antiaging and discussed future prospects and challenges. It is our pleasure if this review article could provide meaningful information for our readers and call forth more investigations working on this topic.

Antioxidant genes in cancer and metabolic diseases: Focusing on Nrf2, Sestrin, and heme oxygenase 1

Reactive oxygen species are involved in the pathogenesis of cancers and metabolic diseases, including diabetes, obesity, and fatty liver disease. Thus, inhibiting the generation of free radicals is a promising strategy to control the onset of metabolic diseases and cancer progression. Various synthetic drugs and natural product-derived compounds that exhibit antioxidant activity have been reported to have a protective effect against a range of metabolic diseases and cancer. This review highlights the development and aggravation of cancer and metabolic diseases due to the imbalance between pro-oxidants and endogenous antioxidant molecules. In addition, we discuss the function of proteins that regulate the production of reactive oxygen species as a strategy to treat metabolic diseases. In particular, we summarize the role of proteins such as nuclear factor-like 2, Sestrin, and heme oxygenase-1, which regulate the expression of various antioxidant genes in metabolic diseases and cancer. We have included recent literature to discuss the latest research on identifying novel signals of antioxidant genes that can control metabolic diseases and cancer.

Bta-miR-330 promotes bovine intramuscular pre-adipocytes adipogenesis via targeting SESN3 to activate the Akt-mTOR signaling pathway

Consumers are more inclined to choose beef with a high intramuscular fat content (IMF), which regulated by lots of factors. It is very significant to find a miRNA that plays a key role in the accumulation of IMF. In our study, we found that bta-miR-330 was highly expressed in Japanese black cattle and differentially expressed at intramuscular pre-adipocytes differentiation processes. Furthermore, we transfected the bta-miR-330 mimic & inhibitor in intramuscular pre-adipocytes. The results showed that bta-miR-330 inhibits the proliferation but promotes the adipogenesis of intramuscular pre-adipocytes. Subsequently, our study showed that bta-miR-330 binds to SESN3, which inhibits the adipogenesis of intramuscular pre-adipocytes. Moreover, we established the mechanism that bta-miR-330 promotes the adipogenesis of intramuscular pre-adipocytes by targeting SESN3 to activate the Akt-mTOR signaling pathway. Overall, our results revealed that bta-miR-330-SESN3-Akt-mTOR axis plays an important role in adipogenesis of intramuscular pre-adipocytes, which provides a molecular basis for increasing IMF content in beef cattle.

Sestrin2 and Sestrin3 protect spermatogenesis against heat-induced meiotic defects†

Heat stress induces testicular oxidative stress, impairs spermatogenesis, and increases the risk of male infertility. Recent studies have highlighted the antioxidative properties of the Sestrins family in reducing cellular oxidative damage. However, the role of Sestrins (Sestrin1, 2, and 3) in the testicular response to heat stress remains unclear. Here, we found that Sestrin2 and 3 were highly expressed in the testis relative to Sestrin1. Then, the Sestrin2-/- and Sestrin3-/- mice were generated by CRISPR/Cas9 to investigate the role of them on spermatogenesis after heat stress. Our data showed that Sestrin2-/- and Sestrin3-/- mice testes exhibited more severe damage manifested by exacerbated loss of germ cells and higher levels of oxidative stress as compared to wild-type counterparts after heat stress. Notably, Sestrin2-/- and Sestrin3-/- mice underwent a remarkable increase in heat-induced spermatocyte apoptosis than that of controls. Furthermore, the transcriptome landscape of spermatocytes and chromosome spreading showed that loss of Sestrin2 and Sestrin3 exacerbated meiotic failure by compromising DNA double-strand breaks repair after heat stress. Taken together, our work demonstrated a critical protective function of Sestrin2 and Sestrin3 in mitigating the impairments of spermatogenesis against heat stress.

Role of sestrins in metabolic and aging-related diseases

Sestrins are a type of highly conserved stress-inducing protein that has antioxidant and mTORC1 inhibitory functions. Metabolic dysfunction and aging are the main risk factors for development of human diseases, such as diabetes, neurodegenerative diseases, and cancer. Sestrins have important roles in regulating glucose and lipid metabolism, anti-tumor functions, and aging by inhibiting the reactive oxygen species and mechanistic target of rapamycin complex 1 pathways. In this review, the structure and biological functions of sestrins are summarized, and how sestrins are activated and contribute to regulation of the downstream signal pathways of metabolic and aging-related diseases are discussed in detail with the goal of providing new ideas and therapeutic targets for the treatment of related diseases.

Sestrin1, 2, and 3 are dispensable for female fertility in mice

BACKGROUND

Sestrins have been implicated in regulating aging in various organs through multiple pathways. However, their roles in ovarian aging remain unrevealed.

METHODS

Female Sestrin1-/-, Sestrin2-/-, and Sestrin3-/- mice were generated using the CRISPR-Cas9 system. Body weights, little sizes, ovarian weights, estrous cyclicity, and follicle number in female mice were observed. ELISA was utilized to measure serum anti-Müllerian hormone (AMH) levels. Real time PCR, western blot, immunofluorescence, and Masson trichrome staining were employed for assessment of aging-related change.

RESULTS

The deletion of Sestrin 1, 2, or 3 had no discernible impact on body weights,or serum AMH levels in female mice at the age of 12 months. And there were no discernible differences in litter sizes or estrous cyclicity which were assessed at the age of 8 months. At the age of 12 months, no significant differences were observed in ovarian weights or follicle numbers among the knockout mice. Consistently, the extent of fibrosis within the ovaries remained comparable across all experimental groups at this age. Additionally, autophagy, apoptosis, DNA damage, and inflammation within the ovaries were also found to be comparable to those in wild-type mice of the same age.

CONCLUSIONS

The loss of Sestrin 1, 2, or 3 does not exert a noticeable influence on ovarian function during the aging process. Sestrin1, 2, and 3 are not essential for female fertility in mice.

The mTORC2 signaling network: targets and cross-talks

The mechanistic target of rapamycin, mTOR, controls cell metabolism in response to growth signals and stress stimuli. The cellular functions of mTOR are mediated by two distinct protein complexes, mTOR complex 1 (mTORC1) and mTORC2. Rapamycin and its analogs are currently used in the clinic to treat a variety of diseases and have been instrumental in delineating the functions of its direct target, mTORC1. Despite the lack of a specific mTORC2 inhibitor, genetic studies that disrupt mTORC2 expression unravel the functions of this more elusive mTOR complex. Like mTORC1 which responds to growth signals, mTORC2 is also activated by anabolic signals but is additionally triggered by stress. mTORC2 mediates signals from growth factor receptors and G-protein coupled receptors. How stress conditions such as nutrient limitation modulate mTORC2 activation to allow metabolic reprogramming and ensure cell survival remains poorly understood. A variety of downstream effectors of mTORC2 have been identified but the most well-characterized mTORC2 substrates include Akt, PKC, and SGK, which are members of the AGC protein kinase family. Here, we review how mTORC2 is regulated by cellular stimuli including how compartmentalization and modulation of complex components affect mTORC2 signaling. We elaborate on how phosphorylation of its substrates, particularly the AGC kinases, mediates its diverse functions in growth, proliferation, survival, and differentiation. We discuss other signaling and metabolic components that cross-talk with mTORC2 and the cellular output of these signals. Lastly, we consider how to more effectively target the mTORC2 pathway to treat diseases that have deregulated mTOR signaling.

Immunoregulation: the interplay between metabolism and redox homeostasis

Regulatory T cells are fundamental for the induction and maintenance of immune homeostasis, with their dysfunction resulting in uncontrolled immune responses and tissue destruction predisposing to autoimmunity, transplant rejection and several inflammatory and metabolic disorders. Recent discoveries have demonstrated that metabolic processes and mitochondrial function are critical for the appropriate functioning of these cells in health, with their metabolic adaptation, influenced by microenvironmental factors, seen in several pathological processes. Upon activation regulatory T cells rearrange their oxidation-reduction (redox) system, which in turn supports their metabolic reprogramming, adding a layer of complexity to our understanding of cellular metabolism. Here we review the literature surrounding redox homeostasis and metabolism of regulatory T cells to highlight new mechanistic insights of these interlinked pathways in immune regulation.

GLP-1 receptor agonists modulate blood glucose levels in T2DM by affecting Faecalibacterium prausnitzii abundance in the intestine

BACKGROUND

Glucagon-like peptide 1 (GLP-1) receptor agonists are a class of medications used to treat type 2 diabetes, including metformin, which is considered first-line therapy for type 2 diabetes. In recent years, GLP-1 receptor agonists (GLP-1 RAs) have been found to alter the composition and structure of gut flora and also promote the production of gut probiotics. However, there have been few clinical studies regarding the effects of GLP-1 RAs on gut flora. In this study, we investigated changes in the abundance of Lactobacillus delbrueckii (L delbrueckii) and Faecalibacterium prausnitzii (F prausnitzii) 1 week after administration of a GLP-1 RA in the clinical treatment of type 2 diabetes. The association with glycemic and body mass index (BMI) correlations was also explored.

METHODS

Twelve newly diagnosed patients with type 2 diabetes were examined for changes in the abundance of L delbrueckii and F prausnitzii by Fluorescence in Situ Hybridization 1 week after administration of GLP-1 RAs. Subjects BMI was measured and fasting glucose changes were detected using the glucose oxidase method, and Spearman correlation analysis was performed to explore their relevance.

RESULTS

There was no significant change in the abundance of L delbrueckii in the intestine (P = .695) and no significant correlation with BMI and fasting glucose levels (R = 0.134, P = .534) after the use of GLP-1 RA (R = -0.098, P = .647); F prausnitzii on the other hand had a significantly higher abundance (P = .002) and a significant negative correlation with fasting glucose level (R = -0.689, P < .001), but no significant correlation with BMI (R = -0.056, P = .796).

CONCLUSION

F prausnitzii may be one of the pathways through which glucose is regulated in the treatment of type 2 diabetes by GLP-1 RAs.

Glucose-Induced Activation of mTORC1 is Associated with Hexokinase2 Binding to Sestrins in HEK293T Cells

BACKGROUND

Sestrins (SESN1-3) act as proximal sensors in leucine-induced activation of the protein kinase mechanistic target of rapamycin (mTOR) in complex 1 (mTORC1), a key regulator of cell growth and metabolism.

OBJECTIVE

In the present study, the hypothesis that SESNs also mediate glucose-induced activation of mTORC1 was tested.

METHODS

Rats underwent overnight fasting, and in the morning, either saline or a glucose solution (4 g⋅kg-1 BW/10 mL⋅kg-1) was administered by oral gavage; mTORC1 activation in the tibialis anterior muscle was assessed. To further assess the mechanism through which glucose promotes mTORC1 activation, wild-type (WT) HEK293T and HEK293T cells lacking either all 3 SESNs (SESNTKO) or hexokinase 2 (HK2KO) were deprived of glucose, followed by glucose addback, and mTORC1 activation was assessed. In addition, glucose-induced changes in the association of the SESNs with components of the GAP activity toward the Rags (GATOR2) complex and with hexokinase 2 (HK2) were assessed by co-immunoprecipitation. One- and two-way ANOVA with Tukey post hoc comparisons were used.

RESULTS

Glucose administration to fasted rats promoted mTORC1 activation. Similarly, glucose readdition (GluAB) to the medium of glucose-deprived WT cells also promoted mTORC1 activation. By contrast, SESNTKO cells demonstrated attenuated mTORC1 activation following GluAB compared with WT cells. Interestingly, HK2 associated with all 3 SESNs in a glucose-dependent manner, i.e., HK2 abundance in SESN immunoprecipitates was high in cells deprived of glucose and decreased in response to GluAB. Moreover, similar to SESNTKO cells, the sensitivity of mTORC1 to GluAB was attenuated in HK2KO cells compared with WT cells.

CONCLUSIONS

The results of this study demonstrate that the SESNs and HK2 play important roles in glucose-induced mTORC1 activation in HEK293T cells. However, unlike leucine-induced mTORC1 activation, the effect was independent of the changes in SESN-GATOR2 interaction, and instead, it was associated with alterations in the association of SESNs with HK2.

Specificity and sensitivity of the SeLECT score in predicting late seizures in patients undergoing intravenous thrombolytic treatment and the effect of diabetes mellitus and leukoaraiosis

BACKGROUND

 Seizures after stroke can negatively affect the prognosis of ischemic stroke and cause a decrease in quality of life. The efficacy of intravenous (IV) recombinant tissue plasminogen activator (rt-PA) treatment in acute ischemic stroke has been demonstrated in many studies, and IV rt-PA treatment has been increasingly used around the world. The SeLECT score is a useful score for the prediction of late seizures after stroke and includes the severity of stroke (Se), large artery atherosclerosis (L), early seizure (E), cortical involvement (C), and the territory of the middle cerebral artery (T). However, the specificity and sensitivity of the SeLECT score have not been studied in acute ischemic stroke patients that received IV rt-PA treatment.

OBJECTIVE

 In the present study, we aimed to validate and develop the SeLECT score in acute ischemic stroke patients receiving IV rt-PA treatment.

METHODS

 The present study included 157 patients who received IV thrombolytic treatment in our third-stage hospital. The 1-year seizure rates of the patients were detected. SeLECT scores were calculated.

RESULTS

 In our study, we found that the SeLECT score had low sensitivity but high specificity for predicting the likelihood of late seizure after stroke in patients administered IV rt-PA therapy. In addition to the SeLECT score, we found that the specificity and sensitivity were higher when we evaluated diabetes mellitus (DM) and leukoaraiosis.

CONCLUSION

 We found that DM was an independent risk factor for late seizures after stroke in a patient group receiving thrombolytic therapy, and late seizures after stroke were less frequent in patients with leukoaraiosis.

Aerobic exercise ameliorates insulin resistance in C57BL/6 J mice via activating Sestrin3

Skeletal muscle insulin resistance (IR) is closely linked to hyperglycemia and metabolic disorders. Regular exercise enhances insulin sensitivity in skeletal muscle, but its underlying mechanisms remain unknown. Sestrin3 (SESN3) is a stress-inducible protein that protects against obesity-induced hepatic steatosis and insulin resistance. Regular exercise training is known to increase SESN3 expression in skeletal muscle. The purpose of this study was to explore whether SESN3 mediates the metabolic effects of exercise in the mouse model of high-fat diet (HFD)-induced IR. SESN3^-/- mice exhibited severer body weight gain, ectopic lipid accumulation, and dysregulation of glucose metabolism after long-term HFD feeding compared with the wild-type (WT) mice. Moreover, we found that SESN3 deficiency weakened the effects of exercise on reducing serum insulin levels and improving glucose tolerance in mice. Exercise training increased pAKT-S473 and GLUT4 expression, accompanied by enhanced pmTOR-S2481 (an indicator of mTORC2 activity) in WT quadriceps that were less pronounced in SESN3^-/- mice. SESN3 overexpression in C2C12 myotubes further confirmed that SESN3 played an important role in skeletal muscle glucose metabolism. SESN3 overexpression increased the binding of Rictor to mTOR and pmTOR-S2481 in C2C12 myotubes. Moreover, SESN3 overexpression resulted in an elevation of glucose uptake and a concomitant increase of pAKT-S473 in C2C12 myotubes, whereas these effects were diminished by downregulation of mTORC2 activity. Taken together, SESN3 is a crucial protein in amplifying the beneficial effects of exercise on insulin sensitivity in skeletal muscle and systemic glucose levels. SESN3/mTORC2/AKT pathway mediated the effects of exercise on skeletal muscle insulin sensitivity.

Insulin-induced mTOR signaling and gluconeogenesis in renal proximal tubules: A mini-review of current evidence and therapeutic potential

Energy is continuously expended in the body, and gluconeogenesis maintains glucose homeostasis during starvation. Gluconeogenesis occurs in the liver and kidneys. The proximal tubule is the primary location for renal gluconeogenesis, accounting for up to 25% and 60% of endogenous glucose production during fasting and after a meal, respectively. The mechanistic target of rapamycin (mTOR), which exists downstream of the insulin pathway, plays an important role in regulating proximal tubular gluconeogenesis. mTOR is an atypical serine/threonine kinase present in two complexes. mTORC1 phosphorylates substrates that enhance anabolic processes such as mRNA translation and lipid synthesis and catabolic processes such as autophagy. mTORC2 regulates cytoskeletal dynamics and controls ion transport and proliferation via phosphorylation of SGK1. Therefore, mTOR signaling defects have been implicated in various pathological conditions, including cancer, cardiovascular disease, and diabetes. However, concrete elucidations of the associated mechanisms are still unclear. This review provides an overview of mTOR and describes the relationship between mTOR and renal.

Modeling microRNA-driven post-transcriptional regulation using exon-intron split analysis in pigs

The contribution of microRNAs (miRNAs) to mRNA post-transcriptional regulation has often been explored by the post hoc selection of downregulated genes and determining whether they harbor binding sites for miRNAs of interest. This approach, however, does not discriminate whether these mRNAs are also downregulated at the transcriptional level. Here, we have characterized the transcriptional and post-transcriptional changes in mRNA expression in two porcine tissues: gluteus medius muscle of fasted and fed Duroc gilts and adipose tissue of lean and obese Duroc-Göttingen minipigs. Exon-intron split analysis of RNA-seq data allowed us to identify downregulated mRNAs with high post-transcriptional signals in fed or obese states, and we assessed whether they harbor binding sites for upregulated miRNAs in any of these two physiological states. We found 26 downregulated mRNAs with high post-transcriptional signals in the muscle of fed gilts and 21 of these were predicted targets of miRNAs upregulated in fed pigs. For adipose tissue, 44 downregulated mRNAs in obese minipigs displayed high post-transcriptional signals, and 25 of these were predicted targets of miRNAs upregulated in the obese state. These results suggest that the contribution of miRNAs to mRNA repression is more prominent in the skeletal muscle system. Finally, we identified several genes that may play relevant roles in the energy homeostasis of the pig skeletal muscle (DKK2 and PDK4) and adipose (SESN3 and ESRRG) tissues. By differentiating transcriptional from post-transcriptional changes in mRNA expression, exon-intron split analysis provides a valuable view of the regulation of gene expression, complementary to canonical differential expression analyses.

The central moTOR of metabolism

The protein kinase mechanistic target of rapamycin (mTOR) functions as a central regulator of metabolism, integrating diverse nutritional and hormonal cues to control anabolic processes, organismal physiology, and even aging. This review discusses the current state of knowledge regarding the regulation of mTOR signaling and the metabolic regulation of the four macromolecular building blocks of the cell: carbohydrate, nucleic acid, lipid, and protein by mTOR. We review the role of mTOR in the control of organismal physiology and aging through its action in key tissues and discuss the potential for clinical translation of mTOR inhibition for the treatment and prevention of diseases of aging.

Exploring New Drug Targets for Type 2 Diabetes: Success, Challenges and Opportunities

There are substantial shortcomings in the drugs currently available for treatment of type 2 diabetes mellitus. The global diabetic crisis has not abated despite the introduction of new types of drugs and targets. Persistent unaddressed patient needs remain a significant factor in the quest for new leads in routine studies. Drug discovery methods in this area have followed developments in the market, contributing to a recent rise in the number of molecules. Nevertheless, troubling developments and fresh challenges are still evident. Recently, metformin, the most widely used first-line drug for diabetes, was found to contain a carcinogenic contaminant known as N-nitroso dimethylamine (NDMA). Therefore, purity and toxicity are also a big challenge for drug discovery and development. Moreover, newer drug classes against SGLT-2 illustrate both progress and difficulties. The same was true previously in the case of glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors. Furthermore, researchers must study the importance of mechanistic characteristics of novel compounds, as well as exposure-related hazardous aspects of current and newly identified protein targets, in order to identify new pharmacological molecules with improved selectivity and specificity.

Targeting mTOR Signaling in Type 2 Diabetes Mellitus and Diabetes Complications

The mechanistic target of rapamycin (mTOR) is a pivotal regulator of cell metabolism and growth. In the form of two different multi-protein complexes, mTORC1 and mTORC2, mTOR integrates cellular energy, nutrient and hormonal signals to regulate cellular metabolic homeostasis. In type 2 diabetes mellitus (T2DM) aberrant mTOR signaling underlies its pathological conditions and end-organ complications. Substantial evidence suggests that two mTOR-mediated signaling schemes, mTORC1-p70S6 kinase 1 (S6K1) and mTORC2-protein kinase B (AKT), play a critical role in insulin sensitivity and that their dysfunction contributes to development of T2DM. This review summaries our current understanding of the role of mTOR signaling in T2DM and its associated complications, as well as the potential use of mTOR inhibitors in treatment of T2DM.

The functions and roles of sestrins in regulating human diseases

Sestrins (Sesns), highly conserved stress-inducible metabolic proteins, are known to protect organisms against various noxious stimuli including DNA damage, oxidative stress, starvation, endoplasmic reticulum (ER) stress, and hypoxia. Sesns regulate metabolism mainly through activation of the key energy sensor AMP-dependent protein kinase (AMPK) and inhibition of mammalian target of rapamycin complex 1 (mTORC1). Sesns also play pivotal roles in autophagy activation and apoptosis inhibition in normal cells, while conversely promoting apoptosis in cancer cells. The functions of Sesns in diseases such as metabolic disorders, neurodegenerative diseases, cardiovascular diseases, and cancer have been broadly investigated in the past decades. However, there is a limited number of reviews that have summarized the functions of Sesns in the pathophysiological processes of human diseases, especially musculoskeletal system diseases. One aim of this review is to discuss the biological functions of Sesns in the pathophysiological process and phenotype of diseases. More significantly, we include some new evidence about the musculoskeletal system. Another purpose is to explore whether Sesns could be potential biomarkers or targets in the future diagnostic and therapeutic process.

Sestrins' Expression in the Liver Is Not Altered by Short-Term Calorie Restriction in Young and Old Rats

INTRODUCTION

Short-term calorie restriction (SCR) may have a positive impact on health. We hypothesized that sestrins, a family of stress-inducible proteins (Sesn1, Sesn2, Sesn3) are involved in the response to SCR in the liver.

METHODS

Young-adult (4-month) and old (24-month) male Wistar rats were either fed ad libitum (control groups) or received 60% of food intake on a daily basis for 30 days (SCR groups). In blood sera, biochemical parameters and fibroblast growth factor 21 (FGF21) concentration were measured (ELISA). Liver samples were collected for analyses of genes' expression (real-time PCR) and protein levels (Western blotting).

RESULTS

SCR caused improvements in blood glucose and lipids and parameters of liver function but did not affect the serum FGF21 concentration. SCR caused changes typically associated with calorie restriction in the gene expression of fatty acid synthase (fasn), ATP-citrate lyase (acly), and sirtuin 1 (sirt1). In the liver of young SCR rats, protein level of Sesn2 tended to increase, while Sesn3 tended to decrease, accompanied by reduced sesn3 expression. In old SCR rats, reduced sesn1 expression was reflected by decreasing trend for Sesn1 content. Activation of AMP-activated protein kinase (phospho-Thr172) and protein content of peroxisome proliferator-activated receptor gamma coactivator 1-alpha were not affected by SCR.

CONCLUSION

Sestrins' hepatic expression is only minimally affected by SCR in young and old rats. We propose that sestrins may not be a major effector of mild SCR in the liver of young or old rats.

Signal Transduction and Molecular Regulation in Fatty Liver Disease

Significance: Fatty liver disease is a major liver disorder in the modern societies. Comprehensive understanding of the pathophysiology and molecular mechanisms is essential for the prevention and treatment of the disease. Recent Advances: Remarkable progress has been made in the recent years in basic and translational research in the field of fatty liver disease. Multiple signaling pathways have been implicated in the development of fatty liver disease, including AMP-activated protein kinase, mechanistic target of rapamycin kinase, endoplasmic reticulum stress, oxidative stress, inflammation, transforming growth factor β, and yes1-associated transcriptional regulator/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). In addition, critical molecular regulations at the transcriptional and epigenetic levels have been linked to the pathogenesis of fatty liver disease. Critical Issues: Some critical issues remain to be solved so that research findings can be translated into clinical applications. Robust and reliable biomarkers are needed for diagnosis of different stages of the fatty liver disease. Effective and safe molecular targets remain to be identified and validated. Prevention strategies require solid scientific evidence and population-wide feasibility. Future Directions: As more data are generated with time, integrative approaches are needed to comprehensively understand the disease pathophysiology and mechanisms at multiple levels from population, organismal system, organ/tissue, to cell. The interactions between genes and environmental factors require deeper investigation for the purposes of prevention and personalized treatment of fatty liver disease. Antioxid. Redox Signal. 35, 689-717.

Decreased Sestrin levels in patients with type 2 diabetes and dyslipidemia and their association with the severity of atherogenic index

PURPOSE

We earlier reported that Sestrin2 regulates monocyte activation and atherogenic events through AMPK-mTOR nexus under high-glucose and dyslipidemic conditions. However, the statuses of Sestrins in diabetes and dyslipidemia are not known. We report here on the status of Sestrins and their association with diabetic dyslipidemia and atherosclerosis.

METHODS

Individuals with normal glucose tolerance (NGT) (n = 46), dyslipidemia (n = 42), and patients with Type 2 diabetes with (n = 41) and without dyslipidemia (n = 40) were recruited from a tertiary diabetes centre, Chennai, India to study the mRNA expression levels of Sestrins (1, 2, and 3) in monocytes by RT-qPCR. Serum levels of Sestrins were measured using ELISA. Atherogenic index of plasma was calculated as log (triglyceride/HDL).

RESULTS

mRNA expressions of Sestrin1 and Sestrin3 were significantly reduced in monocytes under dyslipidemic conditions but not in diabetes condition. Interestingly, Sestrin2 mRNA expression was significantly reduced in all disease conditions including dyslipidemia, and diabetes with and without dyslipidemia. Sestrin2 mRNA levels were negatively correlated with glycemic and lipid parameters and plasma atherogenic index. Furthermore, circulatory Sestrin2 was also found to be significantly decreased in dyslipidemia (415.2 ± 44.7 pg/ml), diabetes (375 ± 45 pg/ml), and diabetes with dyslipidemia (319.2 ± 26.3 pg/ml) compared to NGT (706.3 ± 77 pg/ml) and negatively correlated with glycemic, lipid parameters, and plasma atherogenic index.

CONCLUSION

We report for the first time that Sestrins levels are significantly decreased in diabetes and dyslipidemic conditions. More strikingly, Sestrin2 had a strong association with atherogenic risk factors and severity of atherogenic index and we suggest that Sestrin2 may be used as a biomarker for assessing atherogenesis.

Sestrins as modulators of aging processes and diseases related to age

Sestrins are highly conserved proteins that regulate cell growth, metabolism, survival and proliferation under oxidative stress, genotoxic stress, hypoxia or endoplasmic reticulum stress. Sestrins affect cell signaling by inhibiting the production of reactive oxygen species, activating the AMP-activated protein kinase (AMPK), inhibiting the mTOR pathway and acting as a positive regulator of autophagy. Therefore, their protective role against cancer, metabolic disorders, cardiovascular diseases and neurodegeneration is increasingly being postulated. The article describes the mechanisms of action of sestrins and their meaning in aging and age-related diseases. The latest studies indicating their physiological significance and role in key signaling pathways controlling the cell metabolism and survival under stress conditions were also discussed.

Sestrin Proteins Protect Against Lipotoxicity-Induced Oxidative Stress in the Liver via Suppression of C-Jun N-Terminal Kinases

BACKGROUND & AIMS

Sestrin 1/2/3 (Sesn1/2/3) belong to a small family of proteins that have been implicated in the regulation of metabolic homeostasis and oxidative stress. However, the underlying mechanisms remain incompletely understood. The aim of this work was to illustrate the collective function of Sesn1/2/3 in the protection against hepatic lipotoxicity.

METHODS

We used Sesn1/2/3 triple knockout (TKO) mouse and cell models to characterize oxidative stress and signal transduction under lipotoxic conditions. Biochemical, histologic, and physiological approaches were applied to illustrate the related processes.

RESULTS

After feeding with a Western diet for 8 weeks, TKO mice developed remarkable metabolic associated fatty liver disease that was manifested by exacerbated hepatic steatosis, inflammation, and fibrosis compared with wild-type counterparts. Moreover, TKO mice exhibited higher levels of hepatic lipotoxicity and oxidative stress. Our biochemical data revealed a critical signaling node from sestrins to c-Jun N-terminal kinases (JNKs) in that sestrins interact with JNKs and mitogen-activated protein kinase kinase 7 and suppress the JNK phosphorylation and activity. In doing so, sestrins markedly reduced palmitate-induced lipotoxicity and oxidative stress in both mouse and human hepatocytes.

CONCLUSIONS

The data from this study suggest that Sesn1/2/3 play an important role in the protection against lipotoxicity-associated oxidative stress and related pathology in the liver.

mTOR Signaling in Pulmonary Vascular Disease: Pathogenic Role and Therapeutic Target

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease without a cure. The exact pathogenic mechanisms of PAH are complex and poorly understood, yet a number of abnormally expressed genes and regulatory pathways contribute to sustained vasoconstriction and vascular remodeling of the distal pulmonary arteries. Mammalian target of rapamycin (mTOR) is one of the major signaling pathways implicated in regulating cell proliferation, migration, differentiation, and protein synthesis. Here we will describe the canonical mTOR pathway, structural and functional differences between mTOR complexes 1 and 2, as well as the crosstalk with other important signaling cascades in the development of PAH. The pathogenic role of mTOR in pulmonary vascular remodeling and sustained vasoconstriction due to its contribution to proliferation, migration, phenotypic transition, and gene regulation in pulmonary artery smooth muscle and endothelial cells will be discussed. Despite the progress in our elucidation of the etiology and pathogenesis of PAH over the two last decades, there is a lack of effective therapeutic agents to treat PAH patients representing a significant unmet clinical need. In this review, we will explore the possibility and therapeutic potential to use inhibitors of mTOR signaling cascade to treat PAH.

Regulation and metabolic functions of mTORC1 and mTORC2

Cells metabolize nutrients for biosynthetic and bioenergetic needs to fuel growth and proliferation. The uptake of nutrients from the environment and their intracellular metabolism is a highly controlled process that involves cross talk between growth signaling and metabolic pathways. Despite constant fluctuations in nutrient availability and environmental signals, normal cells restore metabolic homeostasis to maintain cellular functions and prevent disease. A central signaling molecule that integrates growth with metabolism is the mechanistic target of rapamycin (mTOR). mTOR is a protein kinase that responds to levels of nutrients and growth signals. mTOR forms two protein complexes, mTORC1, which is sensitive to rapamycin, and mTORC2, which is not directly inhibited by this drug. Rapamycin has facilitated the discovery of the various functions of mTORC1 in metabolism. Genetic models that disrupt either mTORC1 or mTORC2 have expanded our knowledge of their cellular, tissue, as well as systemic functions in metabolism. Nevertheless, our knowledge of the regulation and functions of mTORC2, particularly in metabolism, has lagged behind. Since mTOR is an important target for cancer, aging, and other metabolism-related pathologies, understanding the distinct and overlapping regulation and functions of the two mTOR complexes is vital for the development of more effective therapeutic strategies. This review discusses the key discoveries and recent findings on the regulation and metabolic functions of the mTOR complexes. We highlight findings from cancer models but also discuss other examples of the mTOR-mediated metabolic reprogramming occurring in stem and immune cells, type 2 diabetes/obesity, neurodegenerative disorders, and aging.

Increased Sestrin3 Contributes to Post-ischemic Seizures in the Diabetic Condition

Seizures are among the most common neurological sequelae of stroke, and diabetes notably increases the incidence of post-ischemic seizures. Recent studies have indicated that Sestrin3 (SESN3) is a regulator of a proconvulsant gene network in human epileptic hippocampus. But the association of SESN3 and post-ischemic seizures in diabetes remains unclear. The present study aimed to reveal the involvement of SESN3 in seizures following transient cerebral ischemia in diabetes. Diabetes was induced in adult male mice and rats via intraperitoneal injection of streptozotocin (STZ). Forebrain ischemia (15 min) was induced by bilateral common carotid artery occlusion, the 2-vessel occlusion (2VO) in mice and 4-vessel occlusion (4VO) in rats. Our results showed that 59% of the diabetic wild-type mice developed seizures after ischemia while no seizures were observed in non-diabetic mice. Although no apparent cell death was detected in the hippocampus of seizure mice within 24 h after the ischemic insult, the expression of SESN3 was significantly increased in seizure diabetic mice after ischemia. The post-ischemic seizure incidence significantly decreased in SESN3 knockout mice. Furthermore, all diabetic rats suffered from post-ischemic seizures and non-diabetic rats have no seizures. Electrophysiological recording showed an increased excitatory synaptic transmission and intrinsic membrane excitability in dentate granule cells of the rat hippocampus, together with decreased I _A currents and Kv4.2 expression levels. The above results suggest that SESN3 up-regulation may contribute to neuronal hyperexcitability and seizure generation in diabetic animals after ischemia. Further studies are needed to explore the molecular mechanism of SESN3 in seizure generation after ischemia in diabetic conditions.

Sestrin3 enhances macrophage-mediated generation of T helper 1 and T helper 17 cells in a mouse colitis model

Intestinal macrophages participate in the pathogenesis of inflammatory bowel diseases (IBDs) through secreting pro-inflammatory and tissue-damaging factors as well as inducing the differentiation of T helper 1 (Th1) and T helper 17 (Th17) cells. Elucidating the regulatory mechanisms of intestinal macrophage activity in IBDs is important for developing new therapeutic approaches. In the current study, the expression of Sestrins in myeloid cells and lymphocytes in colonic lamina propria (LP) was evaluated in a murine acute colitis model. We found that Sestrin3 was significantly up-regulated in LP macrophages by the colonic LP microenvironment. In the in vitro experiments, lentivirus-mediated Sestrin3 knockdown significantly reduced the production of IL-12 and IL-23 in activated macrophages, in addition to decreasing the expression of classical pro-inflammatory cytokines such as IL-1β, IL-6 and TNF-α. Additionally, Sestrin3 knockdown impaired macrophage-mediated generation of Th1 and Th17 cells from CD4+ T cells, probably through up-regulating the phosphorylation of mechanistic target of rapamycin complex 1 (mTORC1) in macrophages. In the in vivo experiments, adoptive transfer of Sestrin3-deficient macrophages alleviated the generation of Th1 and Th17 cells in the colonic LP and mesenteric lymph nodes. Furthermore, the adoptive transfer mitigated the severity of colitis, as demonstrated by lower production of pro-inflammatory cytokines and fewer tissue lesions in the colon. Our study suggests that Sestrin3 might be crucial for macrophage-mediated generation of pathogenic Th1 and Th17 cells in IBDs.

Sestrin2 as a Potential Target for Regulating Metabolic-Related Diseases

Sestrin2 is a highly conserved protein that can be induced under a variety of stress conditions, including DNA damage, oxidative stress, endoplasmic reticulum (ER) stress, and metabolic stress. Numerous studies have shown that the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling pathway has a crucial role in the regulation of metabolism. Sestrin2 regulates metabolism via a number of pathways, including activation of AMPK, inhibition of the mTOR complex 1 (mTORC1), activation of mTOR complex 2 (mTORC2), inhibition of ER stress, and promotion of autophagy. Therefore, modulation of Sestrin2 activity may provide a potential therapeutic target for the prevention of metabolic diseases such as insulin resistance, diabetes, obesity, non-alcoholic fatty liver disease, and myocardial ischemia/reperfusion injury. In this review, we examined the regulatory relationship between Sestrin2 and the AMPK/mTOR signaling pathway and the effects of Sestrin2 on energy metabolism.

SESTRINs: Emerging Dynamic Stress-Sensors in Metabolic and Environmental Health

Proper timely management of various external and internal stresses is critical for metabolic and redox homeostasis in mammals. In particular, dysregulation of mechanistic target of rapamycin complex (mTORC) triggered from metabolic stress and accumulation of reactive oxygen species (ROS) generated from environmental and genotoxic stress are well-known culprits leading to chronic metabolic disease conditions in humans. Sestrins are one of the metabolic and environmental stress-responsive groups of proteins, which solely have the ability to regulate both mTORC activity and ROS levels in cells, tissues and organs. While Sestrins are originally reported as one of several p53 target genes, recent studies have further delineated the roles of this group of stress-sensing proteins in the regulation of insulin sensitivity, glucose and fat metabolism, and redox-function in metabolic disease and aging. In this review, we discuss recent studies that investigated and manipulated Sestrins-mediated stress signaling pathways in metabolic and environmental health. Sestrins as an emerging dynamic group of stress-sensor proteins are drawing a spotlight as a preventive or therapeutic mechanism in both metabolic stress-associated pathologies and aging processes at the same time.

Protective response of Sestrin under stressful conditions in aging

The aging at cellular level manifests itself in the form of uncontrolled formation of ROS, chronic inflammation, and increased susceptibility to cellular stress. Aging is often regarded as a risk factor for several diseases due to several age-associated pathological changes in cells. Sestrin (Sesn) is an important molecule for controlling normal cellular physiology and play a significant role in the progression of certain age-associated cellular pathologies. This review deals with the structure, function, regulation, signaling network, and the potential role of Sesn in age-associated cellular pathophysiology. The cellular response mediated by Sesn under stressful conditions and rescue mechanism is discussed. It would be interesting to find out the precise physiological role of Sesn in the regulation of cellular aging. The anti-aging activity of Sesn may benefit to prevent various age-associated diseases and have clinical utility in diagnostic and therapeutic intervention.

Sestrins in Physiological Stress Responses

Sestrins are a family of proteins that respond to a variety of environmental stresses, including genotoxic, oxidative, and nutritional stresses. Sestrins affect multiple signaling pathways: AMP-activated protein kinase, mammalian target of rapamycin complexes, insulin-AKT, and redox signaling pathways. By regulating these pathways, Sestrins are thought to help adapt to stressful environments and subsequently restore cell and tissue homeostasis. In this review, we describe how Sestrins mediate physiological stress responses in the context of nutritional and chemical stresses (liver), physical movement and exercise (skeletal muscle), and chemical, physical, and inflammatory injuries (heart). These findings also support the idea that Sestrins are a molecular mediator of hormesis, a paradoxical beneficial effect of low- or moderate-level stresses in living organisms.

Sestrin family - the stem controlling healthy ageing

Sestrins are a family of stress-responsive antioxidant proteins responsible for regulation of cell viability and metabolism. The best known Sestrin targets are mTORC1 and mTORC2 kinases that control different cellular processes including growth, viability, autophagy, and mitochondrial metabolism. Inactivation of the single Sestrin gene in invertebrates has an adverse impact on their healthspan and longevity, whereas each of the three Sestrin genes in mammals and other vertebrate organisms has a different impact on maintenance of a particular tissue, affecting its stress tolerance, function and regenerative capability. As a result, Sestrins attenuate ageing and suppress development of many age-related diseases including myocardial infarction, muscle atrophy, diabetes, and immune dysfunction, but exacerbate development of chronic obstructive pulmonary disease. Moreover, Sestrins play opposite roles in carcinogenesis in different tissues. Stem cells support tissue remodelling that influences ageing, and Sestrins might suppress ageing and age-related pathologies through control of stem cell biology. In this review, we will discuss the potential link between Sestrins, stem cells, and ageing.

The Synergistic Effect of an ATP-Competitive Inhibitor of mTOR and Metformin on Pancreatic Tumor Growth

BACKGROUND

The mechanistic target of rapamycin complex 1 (mTORC1) is a nutrient-sensing pathway and a key regulator of amino acid and glucose metabolism. Dysregulation of the mTOR pathways is implicated in the pathogenesis of metabolic syndrome, obesity, type 2 diabetes, and pancreatic cancer.

OBJECTIVES

We investigated the impact of inhibition of mTORC1/mTORC2 and synergism with metformin on pancreatic tumor growth and metabolomics.

METHODS

Cell lines derived from pancreatic tumors of the KPC (KrasG12D/+; p53R172H/+; Pdx1-Cre) transgenic mice model were implanted into the pancreas of C57BL/6 albino mice (n = 10/group). Two weeks later, the mice were injected intraperitoneally with daily doses of 1) Torin 2 (mTORC1/mTORC2 inhibitor) at a high concentration (TH), 2) Torin 2 at a low concentration (TL), 3) metformin at a low concentration (ML), 4) a combination of Torin 2 and metformin at low concentrations (TLML), or 5) DMSO vehicle (control) for 12 d. Tissues and blood samples were collected for targeted xenometabolomics analysis, drug concentration, and cell signaling.

RESULTS

Metabolomic analysis of the control and treated plasma samples showed differential metabolite profiles. Phenylalanine was significantly elevated in the TLML group compared with the control (+426%, P = 0.0004), whereas uracil was significantly lower (-38%, P = 0.009). The combination treatment reduced tumor growth in the orthotopic mouse model. TLML significantly decreased pancreatic tumor volume (498 ± 104 mm3; 37%; P < 0.0004) compared with control (1326 ± 134 mm3; 100%), ML (853 ± 67 mm3; 64%), TL (745 ± 167 mm3; 54%), and TH (665 ± 182 mm3; 50%) (ANOVA and post hoc tests). TLML significantly decreased tumor weights (0.66 ± 0.08 g; 52%) compared with the control (1.28 ± 0.19 g; 100%) (P < 0.002).

CONCLUSIONS

The combination of mTOR dual inhibition by Torin 2 and metformin is associated with an altered metabolomic profile and a significant reduction in pancreatic tumor burden compared with single-agent therapy, and it is better tolerated.

Effect of Lactobacillus delbrueckii Subsp. lactis PTCC1057 on Serum Glucose, Fetuin-A ,and Sestrin 3 Levels in Streptozotocin-Induced Diabetic Mice

Intake of probiotic bacteria may improve or preserve insulin sensitivity. Fetuin-A and sestrin 3 have emerged as promising candidate biomarkers for crucial roles in insulin signaling pathway. Therefore, the effect of oral supplementation with the probiotic bacterium Lactobacillus delbrueckii subsp. lactis PTCC1057 on proteins involved in insulin signaling pathway was investigated in normal and streptozotocin (STZ)-induced diabetic mice. The 6-8-week-old female mice were divided into a non-diabetic control, diabetic control, and diabetic experimental and non-diabetic experimental groups (5 mice each group). Diabetic and non-diabetic experimental groups treated with 3 × 10⁷ CFU mL^-1 L. delbrueckii subsp. lactis PTCC1057 by gavage feeding approach daily for 28 days. Serum glucose, fetuin-A, and sestrin 3 levels were measured by standard methods. The result showed that oral administration of L. delbrueckii significantly decreased serum glucose in comparison to diabetic control group (P = 0.01). Serum fetuin-A level was higher in diabetic control group than non-diabetic group and oral administration of L. delbrueckii subsp. lactis PTCC1057 significantly decreased fetuin-A level in diabetic experimental group in comparison with non-diabetic groups (P = 0.001). Sestrin 3 level significantly was lower in diabetic control group than non-diabetic control group (P = 0.03) and it significantly increased in diabetic experimental group in comparison with diabetic control group after intervention of L. delbrueckii subsp. lactis PTCC1057 (P = 0.02). The results show that feeding the STZ-induced diabetic mice with L. delbrueckii subsp. lactis PTCC1057 terminated to decrease in fasting blood glucose and fetuin-A level and increase in serum sestrin 3 level. Therefore, the L. delbrueckii subsp. lactis PTCC1057 can be considered as excellent candidate for future studies on diabetes mellitus.

Pathological Consequences of Hepatic mTORC1 Dysregulation

The mammalian target of rapamycin complex 1 (mTORC1) is a central regulator of metabolism that integrates environmental inputs, including nutrients, growth factors, and stress signals. mTORC1 activation upregulates anabolism of diverse macromolecules, such as proteins, lipids, and nucleic acids, while downregulating autolysosomal catabolism. mTORC1 dysregulation is often found in various diseases, including cancer, cardiovascular and neurodegenerative diseases, as well as metabolic syndromes involving obesity and type II diabetes. As an essential metabolic organ, the liver requires proper regulation of mTORC1 for maintaining homeostasis and preventing pathologies. For instance, aberrant hyper- or hypoactivation of mTORC1 disrupts hepatocellular homeostasis and damages the structural and functional integrity of the tissue, leading to prominent liver injury and the development of hepatocellular carcinogenesis. Proper regulation of mTORC1 during liver diseases may be beneficial for restoring liver function and ameliorating the detrimental consequences of liver failure.

Substrate metabolism regulated by Sestrin2-mTORC1 alleviates pressure overload-induced cardiac hypertrophy in aged heart

Sestrin2 (Sesn2) is a stress sensor for the mammalian target of rapamycin complex 1 (mTORC1) pathway. Aging impairs cardiac mTORC1 activation, thereby sensitizing the heart to hypertrophy. C57BL/6 J young wild-type (young WT; 4-6 months), aged WT (24-26 months), and young Sestrin2 knockout mice (Y-Sesn2 KO; 4-6 months) underwent transverse aortic constriction (TAC) for pressure overload. Cardiac expression of Sesn2 decreased with age. At 4 weeks after TAC, aged WT and Y-Sesn2 KO exhibited larger hearts and impaired cardiac function, compared with young WT mice. Augmented phosphorylation of mTOR and downstream effectors; damaged mitochondria and elevated redox markers, as well as and impaired glucose and fatty acid oxidation were observed in aged WT and Y-Sesn2 KO hearts. A pressure overload-induced interaction between Sesn2 and GTPase-activating protein activity toward Rags 2 (GATOR2), which positively regulates mTORC1, was impaired in aged WT hearts. Adeno-associated virus 9-Sesn2 treatment rescued Sesn2 expression, attenuated mTORC1 activation, and increased pressure overload tolerance in aged WT and Y-Sesn2 KO hearts. These results indicated that cardiac Sesn2 acts as a pressure overload sensor for mTORC1. Furthermore, Sesn2 deficiency may cause increased sensitivity to hypertrophy in elderly individuals.

Mitochondrial Dysfunction in Age-Related Metabolic Disorders

Aging is a natural biological process in living organisms characterized by receding bioenergetics. Mitochondria are crucial for cellular bioenergetics and thus an important contributor to age-related energetics deterioration. In addition, mitochondria play a major role in calcium signaling, redox homeostasis, and thermogenesis making this organelle a major cellular component that dictates the fate of a cell. To maintain its quantity and quality, mitochondria undergo multiple processes such as fission, fusion, and mitophagy to eliminate or replace damaged mitochondria. While this bioenergetics machinery is properly protected, the functional decline associated with age and age-related metabolic diseases is mostly a result of failure in such protective mechanisms. In addition, metabolic by-products like reactive oxygen species also aid in this destructive pathway. Mitochondrial dysfunction has always been thought to be associated with diseases. Moreover, studies in recent years have pointed out that aging contributes to the decay of mitochondrial health by promoting imbalances in key mitochondrial-regulated pathways. Hence, it is crucial to understand the nexus of mitochondrial dysfunction in age-related diseases. This review focuses on various aspects of basic mitochondrial biology and its status in aging and age-related metabolic diseases.

The Emerging Role of Sestrin2 in Cell Metabolism, and Cardiovascular and Age-Related Diseases

Sestrins (Sesns), including Sesn1, Sesn2, and Sesn3, are cysteine sulfinyl reductases that play critical roles in the regulation of peroxide signaling and oxidant defense. Sesn2 is thought to regulate cell growth, metabolism, and survival response to various stresses, and act as a positive regulator of autophagy. The anti-oxidative and anti-aging roles of Sesn2 have been the focus of many recent studies. The role of Sesn2 in cellular metabolism and cardiovascular and age-related diseases must be analyzed and discussed. In this review, we discuss the physiological and pathophysiological roles and signaling pathways of Sesn2 in different stress-related conditions, such as oxidative stress, genotoxic stress, and hypoxia. Sesn2 is also involved in aging, cancer, diabetes, and ischemic heart disease. Understanding the actions of Sesn2 in cell metabolism and age-related diseases will provide new evidence for future experimental research and aid in the development of novel therapeutic strategies for Sesn2-related diseases.

Sestrins are evolutionarily conserved mediators of exercise benefits

Exercise is among the most effective interventions for age-associated mobility decline and metabolic dysregulation. Although long-term endurance exercise promotes insulin sensitivity and expands respiratory capacity, genetic components and pathways mediating the metabolic benefits of exercise have remained elusive. Here, we show that Sestrins, a family of evolutionarily conserved exercise-inducible proteins, are critical mediators of exercise benefits. In both fly and mouse models, genetic ablation of Sestrins prevents organisms from acquiring metabolic benefits of exercise and improving their endurance through training. Conversely, Sestrin upregulation mimics both molecular and physiological effects of exercise, suggesting that it could be a major effector of exercise metabolism. Among the various targets modulated by Sestrin in response to exercise, AKT and PGC1α are critical for the Sestrin effects in extending endurance. These results indicate that Sestrin is a key integrating factor that drives the benefits of chronic exercise to metabolism and physical endurance.

Sestrin prevents atrophy of disused and aging muscles by integrating anabolic and catabolic signals

A unique property of skeletal muscle is its ability to adapt its mass to changes in activity. Inactivity, as in disuse or aging, causes atrophy, the loss of muscle mass and strength, leading to physical incapacity and poor quality of life. Here, through a combination of transcriptomics and transgenesis, we identify sestrins, a family of stress-inducible metabolic regulators, as protective factors against muscle wasting. Sestrin expression decreases during inactivity and its genetic deficiency exacerbates muscle wasting; conversely, sestrin overexpression suffices to prevent atrophy. This protection occurs through mTORC1 inhibition, which upregulates autophagy, and AKT activation, which in turn inhibits FoxO-regulated ubiquitin-proteasome-mediated proteolysis. This study reveals sestrin as a central integrator of anabolic and degradative pathways preventing muscle wasting. Since sestrin also protected muscles against aging-induced atrophy, our findings have implications for sarcopenia.

The GATOR2-mTORC2 axis mediates Sestrin2-induced AKT Ser/Thr kinase activation

Sestrins represent a family of stress-inducible proteins that prevent the progression of many age- and obesity-associated disorders. Endogenous Sestrins maintain insulin-dependent AKT Ser/Thr kinase (AKT) activation during high-fat diet-induced obesity, and overexpressed Sestrins activate AKT in various cell types, including liver and skeletal muscle cells. Although Sestrin-mediated AKT activation improves metabolic parameters, the mechanistic details underlying such improvement remain elusive. Here, we investigated how Sestrin2, the Sestrin homolog highly expressed in liver, induces strong AKT activation. We found that two known targets of Sestrin2, mTOR complex (mTORC) 1 and AMP-activated protein kinase, are not required for Sestrin2-induced AKT activation. Rather, phosphoinositol 3-kinase and mTORC2, kinases upstream of AKT, were essential for Sestrin2-induced AKT activation. Among these kinases, mTORC2 catalytic activity was strongly up-regulated upon Sestrin2 overexpression in an in vitro kinase assay, indicating that mTORC2 may represent the major link between Sestrin2 and AKT. As reported previously, Sestrin2 interacted with mTORC2; however, we found here that this interaction occurs indirectly through GATOR2, a pentameric protein complex that directly interacts with Sestrin2. Deleting or silencing WDR24 (WD repeat domain 24), the GATOR2 component essential for the Sestrin2-GATOR2 interaction, or WDR59, the GATOR2 component essential for the GATOR2-mTORC2 interaction, completely ablated Sestrin2-induced AKT activation. We also noted that Sestrin2 also directly binds to the pleckstrin homology domain of AKT and induces AKT translocation to the plasma membrane. These results uncover a signaling mechanism whereby Sestrin2 activates AKT through GATOR2 and mTORC2.

Sestrin 3 Protects Against Diet-Induced Nonalcoholic Steatohepatitis in Mice Through Suppression of Transforming Growth Factor β Signal Transduction

Sestrin 3 (Sesn3) belongs to the three-member sestrin protein family. Sestrins have been implicated in antioxidative stress, adenosine monophosphate-activated protein kinase and mammalian target of rapamycin signal transduction, and metabolic homeostasis. However, the role of Sesn3 in the development of nonalcoholic steatohepatitis (NASH) has not been previously studied. In this work, we generated Sesn3 whole-body knockout and liver-specific transgenic mice to investigate the hepatic function of Sesn3 in diet-induced NASH. With only 4 weeks of dietary treatment, Sesn3 knockout mice developed severe NASH phenotype as characterized by hepatic steatosis, inflammation, and fibrosis. Strikingly, after 8-week feeding with a NASH-inducing diet, Sesn3 transgenic mice were largely protected against NASH development. Transcriptomic analysis revealed that multiple extracellular matrix-related processes were up-regulated, including transforming growth factor β (TGF-β) signaling and collagen production. Further biochemical and cell biological analyses have illustrated a critical control of the TGF-β-mothers against decapentaplegic homolog (Smad) pathway by Sesn3 at the TGF-β receptor and Smad3 levels. First, Sesn3 inhibits the TGF-β receptor through an interaction with Smad7; second, Sesn3 directly inhibits the Smad3 function through protein-protein interaction and cytosolic retention. Conclusion: Sesn3 is a critical regulator of the extracellular matrix and hepatic fibrosis by suppression of TGF-β-Smad3 signaling.

p53-inducible SESTRINs might play opposite roles in the regulation of early and late stages of lung carcinogenesis

SESTRINs (SESN1-3) are proteins encoded by an evolutionarily conserved gene family that plays an important role in the regulation of cell viability and metabolism in response to stress. Many of the effects of SESTRINs are mediated by negative and positive regulation of mechanistic target of rapamycin kinase complexes 1 and 2 (mTORC1 and mTORC2), respectively, that are often deregulated in human cancers where they support cell growth, proliferation, and cell viability. Besides their effects on regulation of mTORC1/2, SESTRINs also control the accumulation of reactive oxygen species, cell death, and mitophagy. SESN1 and SESN2 are transcriptional targets of tumor suppressor protein p53 and may mediate tumor suppressor activities of p53. Therefore, we conducted studies based on a mouse lung cancer model and human lung adenocarcinoma A549 cells to evaluate the potential impact of SESN1 and SESN2 on lung carcinogenesis. While we observed that expression of SESN1 and SESN2 is often decreased in human tumors, inactivation of Sesn2 in mice positively regulates tumor growth through a mechanism associated with activation of AKT, while knockout of Sesn1 has no additional impact on carcinogenesis in Sesn2-deficient mice. However, inactivation of SESN1 and/or SESN2 in A549 cells accelerates cell proliferation and imparts resistance to cell death in response to glucose starvation. We propose that despite their contribution to early tumor growth, SESTRINs might suppress late stages of carcinogenesis through inhibition of cell proliferation or activation of cell death in conditions of nutrient deficiency.

Sestrins as a Therapeutic Bridge between ROS and Autophagy in Cancer

The regulation of Reactive Oxygen Species (ROS) levels and the contribution therein from networks regulating cell metabolism, such as autophagy and the mTOR-dependent nutrient-sensing pathway, constitute major targets for selective therapeutic intervention against several types of tumors, due to their extensive rewiring in cancer cells as compared to healthy cells. Here, we discuss the sestrin family of proteins—homeostatic transducers of oxidative stress, and drivers of antioxidant and metabolic adaptation—as emerging targets for pharmacological intervention. These adaptive regulators lie at the intersection of those two priority nodes of interest in antitumor intervention—ROS control and the regulation of cell metabolism and autophagy—therefore, they hold the potential not only for the development of completely novel compounds, but also for leveraging on synergistic strategies with current options for tumor therapy and classification/stadiation to achieve personalized medicine.