Biochemical Basis of Sestrin Physiological Activities

Resistance exercise preconditioning prevents disuse muscle atrophy by inhibiting apoptosis and protein degradation via SESN2 in C57BL/6J mice

AIM

To compare the effects of different exercise preconditioning in the context of skeletal muscle atrophy and to investigate the potential involvement of Sestrin2 (SESN2), a stress-inducible protein that can be regulated by exercise, in exercise preconditioning on preventing disuse muscle atrophy.

METHODS

Eight-week-old male C57BL/6J mice were randomly assigned to sedentary groups (SD), aerobic exercise groups (AE), resistance exercise groups (RE), and combined exercise groups (CE) with or without 7 days of immobilization. The duration of the exercise intervention was 10 weeks. The effects of different exercise preconditioning to prevent muscle atrophy were analyzed by evaluating skeletal muscle function and mass. Additionally, to investigate the potential underlying mechanism of exercise-induced protection of skeletal muscle, wild-type and SESN2--/-- mice were randomly divided into sedentary group and resistance exercise preconditioning group. C2C12 cells were treated with SESN2 adenoviruses and MK2206 (an AKT inhibitor) for 48 h to elucidate the underlined mechanism.

RESULTS

RE was more effective in preserving skeletal muscle function, muscle mass and maintaining skeletal muscle protein homeostasis than AE and CE under immobilized condition. Importantly, exercise performance, muscle mass to body weight ratio, and the cross-sectional area of muscle fibers were significantly lower in SESN2-/- mice than wild-type mice after resistance exercise preconditioning. Mechanistically, the absence of SESN2 led to activation of the ubiquitin-proteasome system and induction of apoptosis. In vitro experiments showed that MK2206 treatment mitigated the regulatory effects of overexpression-SESN2 on protein hydrolysis and apoptosis.

CONCLUSION

RE was more effective than AE or CE in preventing disuse muscle atrophy. SESN2 mediated the protective effects of resistance exercise preconditioning on skeletal muscle atrophy.

SESN1 functions as a new tumor suppressor gene via Toll-like receptor signaling pathway in neuroblastoma

AIMS

Neuroblastoma (NB) is the most common extracranial solid tumor in children, with a 5-year survival rate of <50% in high-risk patients. MYCN amplification is an important factor that influences the survival rate of high-risk patients. Our results indicated MYCN regulates the expression of SESN1. Therefore, this study aimed to investigate the role and mechanisms of SESN1 in NB.

METHODS

siRNAs or overexpression plasmids were used to change MYCN, SESN1, or MyD88's expression. The role of SESN1 in NB cell proliferation, migration, and invasion was elucidated. Xenograft mice models were built to evaluate SESN1's effect in vivo. The correlation between SESN1 expression and clinicopathological data of patients with NB was analyzed. RNA-Seq was done to explore SESN1's downstream targets.

RESULTS

SESN1 was regulated by MYCN in NB cells. Knockdown SESN1 promoted NB cell proliferation, cell migration, and cell invasion, and overexpressing SESN1 had opposite functions. Knockdown SESN1 promoted tumor growth and shortened tumor-bearing mice survival time. Low expression of SESN1 had a positive correlation with poor prognosis in patients with NB. RNA-Seq showed that Toll-like receptor (TLR) signaling pathway, and PD-L1 expression and PD-1 checkpoint pathway in cancer were potential downstream targets of SESN1. Knockdown MyD88 or TLRs inhibitor HCQ reversed the effect of knockdown SESN1 in NB cells. High expression of SESN1 was significantly associated with a higher immune score and indicated an active immune microenvironment for patients with NB.

CONCLUSIONS

SESN1 functions as a new tumor suppressor gene via TLR signaling pathway in NB.

Sestrin2 reduces ferroptosis via the Keap1/Nrf2 signaling pathway after intestinal ischemia-reperfusion

Sestrins are metabolic regulators that respond to stress by reducing the levels of reactive oxygen species (ROS) and inhibiting the activity of target of rapamycin complex 1 (mTORC1). Previous research has demonstrated that Sestrin2 mitigates ischemia-reperfusion (IR) injury in the heart, liver, and kidneys. However, its specific role in intestinal ischemia-reperfusion (IIR) injury remains unclear. To elucidate the role of Sestrin2 in IIR injury, we conducted an experimental study using a C57BL/6J mouse model of IIR. We noticed an increase in the levels of Sestrin2 expression and indicators associated with ferroptosis. Our study revealed that manipulating Sestrin2 expression in Caco-2 cells through overexpression or knockdown resulted in a corresponding decrease or increase, respectively, in ferroptosis levels. Furthermore, our investigation revealed that Sestrin2 alleviated ferroptosis caused by IIR injury through the activation of the Keap1/Nrf2 signal pathway. This finding highlights the potential of Sestrin2 as a therapeutic target for alleviating IIR injury. These findings indicated that the modulation of Sestrin2 could be a promising strategy for managing prolonged IIR injury.

Sestrin2 inhibits RANKL-induced osteoclastogenesis through AMPK activation and ROS inhibition

Sestrins are stress-responsive proteins with antioxidant properties. They participate in cellular redox balance and protect against oxidative damage. This study investigated the effects of Sestrin2 (Sesn2) on osteoclast differentiation and function. Overexpressing Sesn2 in osteoclast precursor cells significantly inhibited receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis. This was assessed as reduced expression of various osteoclast markers, including c-Fos, nuclear factor of activated T cells 1 (NFATc1), osteoclast-associated receptor, tartrate-resistant acid phosphatase, and cathepsin K. Conversely, downregulation of Sesn2 produced the opposite effect. Mechanistically, Sesn2 overexpression enhanced AMPK activation and the nuclear translocation of nuclear factor erythroid-derived factor 2-related factor 2 (Nrf2), promoting antioxidant enzymes. Moreover, azithromycin (Azm) induced Sesn2 expression, which suppressed RANKL-induced osteoclast differentiation. Specifically, Azm treatment reduced RANKL-induced production of reactive oxygen species in osteoclasts. Furthermore, intraperitoneal administration of Azm ameliorated RANKL-induced bone loss by reducing osteoclast activity in mice. Taken together, our results suggested that Azm-induced Sesn2 act as a negative regulator of RANKL-induced osteoclast differentiation through the AMPK/NFATc1 signaling pathway. Concisely, targeting Sesn2 can be a potential pharmacological intervention in osteoporosis.

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.

Modulation of Leucine Sensors to Mitigate Antipsychotics-Induced Metabolic Syndrome: A New Vista

Second-generation antipsychotics (SGAs) are currently the mainstay in the pharmacotherapy of some psychiatric disorders, which have improved the quality of life of millions of patients globally. A broad spectrum of activity and diminished liabilities of extrapyramidal side effects have made SGAs better alternatives compared to first-generation antipsychotics. Nevertheless, they display a complex profile of activity by affecting an array of biological targets and, as a result, are associated with a constellation of metabolic abnormalities such as hyperglycemia, dyslipidemia, weight gain, and cardiovascular problems. The SGAs-induced metabolic syndrome's exact mechanism has remained nebulous, but some evidence points the finger at mTOR signaling. In this viewpoint, we propose potential strategies to prevent or alleviate the SGA-induced metabolic adverse effects by modulating the activity of the leucine sensors, Sestrins.

Status of Research on Sestrin2 and Prospects for its Application in Therapeutic Strategies Targeting Myocardial Aging

Cardiac aging is accompanied by changes in the heart at the cellular and molecular levels, leading to alterations in cardiac structure and function. Given today's increasingly aging population, the decline in cardiac function caused by cardiac aging has a significant impact on quality of life. Antiaging therapies to slow the aging process and attenuate changes in cardiac structure and function have become an important research topic. Treatment with drugs, including metformin, spermidine, rapamycin, resveratrol, astaxanthin, Huolisu oral liquid, and sulforaphane, has been demonstrated be effective in delaying cardiac aging by stimulating autophagy, delaying ventricular remodeling, and reducing oxidative stress and the inflammatory response. Furthermore, caloric restriction has been shown to play an important role in delaying aging of the heart. Many studies in cardiac aging and cardiac aging-related models have demonstrated that Sestrin2 has antioxidant and anti-inflammatory effects, stimulates autophagy, delays aging, regulates mitochondrial function, and inhibits myocardial remodeling by regulation of relevant signaling pathways. Therefore, Sestrin2 is likely to become an important target for antimyocardial aging therapy.

Glucose promotes cell growth and casein synthesis via ATF4/Nrf2-Sestrin2- AMPK-mTORC1 pathway in dairy cow mammary epithelial cells

In the dairy industry, glucose (Glu) is used as bioactive substance to increase milk yield. However, the molecular regulation underneath needs further clarification. Here, the regulation and its molecular mechanism of Glu on cell growth and casein synthesis of dairy cow mammary epithelial cells (DCMECs) were investigated. When Glu was added from DCMECs, both cell growth, β-casein expression and the mechanistic target of rapamycin complex 1 (mTORC1) pathway were increased. Overexpression and silencing of mTOR revealed that Glu promoted cell growth and β-casein expression through the mTORC1 pathway. When Glu was added from DCMECs, both Adenosine 5'-monophosphate-activated protein kinase α (AMPKα) and Sestrin2 (SESN2) expression were decreased. Overexpression and silencing of AMPKα or SESN2 uncovered that AMPKα suppressed cell growth and β-casein synthesis through inhibiting mTORC1 pathway, and SESN2 suppressed cell growth and β-casein synthesis through activating AMPK pathway. When Glu was depleted from DCMECs, both activating transcription factor 4 (ATF4) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression were increased. Overexpression or silencing of ATF4 or Nrf2 demonstrated that Glu depletion promoted SESN2 expression through ATF4 and Nrf2. Together, these results indicate that in DCMECs, Glu promoted cell growth and casein synthesis via ATF4/Nrf2-SESN2-AMPK-mTORC1 pathway.

Research progress in the role and mechanism of Leucine in regulating animal growth and development

Leucine, a branched-chain amino acid, is essential in regulating animal growth and development. Recent research has uncovered the mechanisms underlying Leucine's anabolic effects on muscle and other tissues, including its ability to stimulate protein synthesis by activating the mTORC1 signaling pathway. The co-ingestion of carbohydrates and essential amino acids enhances Leucine's anabolic effects. Moreover, Leucine has been shown to benefit lipid metabolism, and insulin sensitivity, making it a promising strategy for preventing and treating metabolic diseases, including type 2 diabetes and obesity. While emerging evidence indicates that epigenetic mechanisms may mediate Leucine's effects on growth and development, more research is needed to elucidate its mechanisms of action fully. Specific studies have demonstrated that Leucine promotes muscle growth and metabolic health in animals and humans, making it a promising therapeutic agent. However, it is essential to note that Leucine supplementation may cause digestive issues or interact with certain medications, and More study is required to determine definitively optimal dosages. Therefore, it is important to understand how Leucine interacts with other nutrients, dietary factors, and lifestyle habits to maximize its benefits. Overall, Leucine's importance in human nutrition is far-reaching, and its potential to prevent muscle loss and enhance athletic performance warrants further investigation.

Regulation of nucleo-cytosolic 26S proteasome translocation by aromatic amino acids via mTOR is essential for cell survival under stress

The proteasome is responsible for removal of ubiquitinated proteins. Although several aspects of its regulation (e.g., assembly, composition, and post-translational modifications) have been unraveled, studying its adaptive compartmentalization in response to stress is just starting to emerge. We found that following amino acid starvation, the proteasome is translocated from its large nuclear pool to the cytoplasm-a response regulated by newly identified mTOR-agonistic amino acids-Tyr, Trp, and Phe (YWF). YWF relay their signal upstream of mTOR through Sestrin3 by disrupting its interaction with the GATOR2 complex. The triad activates mTOR toward its downstream substrates p62 and transcription factor EB (TFEB), affecting both proteasomal and autophagic activities. Proteasome translocation stimulates cytosolic proteolysis which replenishes amino acids, thus enabling cell survival. In contrast, nuclear sequestration of the proteasome following mTOR activation by YWF inhibits this proteolytic adaptive mechanism, leading to cell death, which establishes this newly identified pathway as a key stress-coping mechanism.

Muscular Sestrins: Roles in Exercise Physiology and Stress Resistance

Sestrins are a family of stress-inducible proteins that are critical for stress adaptation and the maintenance of metabolic homeostasis. High expression of Sestrins is observed in skeletal and cardiac muscle tissues, suggesting their significance in the physiological homeostasis of these organs. Furthermore, expression of Sestrins is dynamically controlled in the tissues, based on the level of physical activity and the presence or absence of stress insults. Genetic studies in model organisms have shown that muscular Sestrin expression is critical for metabolic homeostasis, exercise adaptation, stress resistance, and repair and may mediate the beneficial effects of some available therapeutics. The current minireview summarizes and discusses recent findings that shed light on the role of Sestrins in regulating muscle physiology and homeostasis.

Targeting FoxO transcription factors with HDAC inhibitors for the treatment of osteoarthritis

OBJECTIVES

Osteoarthritis (OA) features ageing-related defects in cellular homeostasis mechanisms in articular cartilage. These defects are associated with suppression of forkhead box O (FoxO) transcription factors. FoxO1 or FoxO3 deficient mice show early onset OA while FoxO1 protects against oxidative stress in chondrocytes and promotes expression of autophagy genes and the essential joint lubricant proteoglycan 4 (PRG4). The objective of this study was to identify small molecules that can increase FoxO1 expression.

METHODS

We constructed a reporter cell line with FoxO1 promoter sequences and performed high-throughput screening (HTS) of the Repurposing, Focused Rescue and Accelerated Medchem (ReFRAME) library . Hits from the HTS were validated and function was assessed in human chondrocytes, meniscus cells and synoviocytes and following administration to mice. The most promising hit, the histone deacetylase inhibitor (HDACI) panobinostat was tested in a murine OA model.

RESULTS

Among the top hits were HDACI and testing in human chondrocytes, meniscus cells and synoviocytes showed that panobinostat was the most promising compound as it increased the expression of autophagy genes and PRG4 while suppressing the basal and IL-1β induced expression of inflammatory mediators and extracellular matrix degrading enzymes. Intraperitoneal administration of panobinostat also suppressed the expression of mediators of OA pathogenesis induced by intra-articular injection of IL-1β. In a murine OA model, panobinostat reduced the severity of histological changes in cartilage, synovium and subchondral bone and improved pain behaviours.

CONCLUSION

Panobinostat has a clinically relevant activity profile and is a candidate for OA symptom and structure modification.

Mechanism of skeletal muscle atrophy after spinal cord injury: A narrative review

Spinal cord injury leads to loss of innervation of skeletal muscle, decreased motor function, and significantly reduced load on skeletal muscle, resulting in atrophy. Factors such as braking, hormone level fluctuation, inflammation, and oxidative stress damage accelerate skeletal muscle atrophy. The atrophy process can result in skeletal muscle cell apoptosis, protein degradation, fat deposition, and other pathophysiological changes. Skeletal muscle atrophy not only hinders the recovery of motor function but is also closely related to many systemic dysfunctions, affecting the prognosis of patients with spinal cord injury. Extensive research on the mechanism of skeletal muscle atrophy and intervention at the molecular level has shown that inflammation and oxidative stress injury are the main mechanisms of skeletal muscle atrophy after spinal cord injury and that multiple pathways are involved. These may become targets of future clinical intervention. However, most of the experimental studies are still at the basic research stage and still have some limitations in clinical application, and most of the clinical treatments are focused on rehabilitation training, so how to develop more efficient interventions in clinical treatment still needs to be further explored. Therefore, this review focuses mainly on the mechanisms of skeletal muscle atrophy after spinal cord injury and summarizes the cytokines and signaling pathways associated with skeletal muscle atrophy in recent studies, hoping to provide new therapeutic ideas for future clinical work.

Nelumbinis Stamen Ameliorates Chronic Restraint Stress-Induced Muscle Dysfunction and Fatigue in Mice by Decreasing Serum Corticosterone Levels and Activating Sestrin2

Nelumbo nucifera Gaertn. is an important aquatic vegetable, and its dried stamen (Nelumbinis stamen, NS) is a valuable nutraceutical usually used as a herbal tea. Here, we used ultrahigh-performance liquid chromatography (UPLC)-quadrupole time-of-flight mass spectrometry and high-performance liquid chromatography (HPLC) to chemically profile NS and quantify their main constituent flavonoids, respectively. In total, 44 components were identified, including organic acids, flavonoids, monoterpene glycosides, and fatty acids. Experimental mice were induced with fatigue by exposure to chronic restraint stress (CRS) for 8 h daily for 15 days and then treated with an aqueous extract of NS (0.5 and 1 g/kg) via gavage. NS significantly mitigated CRS-induced skeletal muscle dysfunction and fatigue in mice possibly by lowering serum corticosterone levels and restoring Sestrin2 expression in the gastrocnemius to regulate metabolism, preserve mitochondrial homeostasis, and promote antioxidant capacity. These results demonstrate that NS can be used as a nutraceutical or supplement for controlling stress-induced muscle dysfunction and fatigue.

Simultaneous loss of TSC1 and DEPDC5 in skeletal and cardiac muscles produces early-onset myopathy and cardiac dysfunction associated with oxidative damage and SQSTM1/p62 accumulation

By promoting anabolism, MTORC1 is critical for muscle growth and maintenance. However, genetic MTORC1 upregulation promotes muscle aging and produces age-associated myopathy. Whether MTORC1 activation is sufficient to produce myopathy or indirectly promotes it by accelerating tissue aging is elusive. Here we examined the effects of muscular MTORC1 hyperactivation, produced by simultaneous depletion of TSC1 and DEPDC5 (CKM-TD). CKM-TD mice produced myopathy, associated with loss of skeletal muscle mass and force, as well as cardiac failure and bradypnea. These pathologies were manifested at eight weeks of age, leading to a highly penetrant fatality at around twelve weeks of age. Transcriptome analysis indicated that genes mediating proteasomal and macroautophagic/autophagic pathways were highly upregulated in CKM-TD skeletal muscle, in addition to inflammation, oxidative stress, and DNA damage signaling pathways. In CKM-TD muscle, autophagosome levels were increased, and the AMPK and ULK1 pathways were activated; in addition, autophagy induction was not completely blocked in CKM-TD myotubes. Despite the upregulation of autolysosomal markers, CKM-TD myofibers exhibited accumulation of autophagy substrates, such as SQSTM1/p62 and ubiquitinated proteins, suggesting that the autophagic activities were insufficient. Administration of a superoxide scavenger, tempol, normalized most of these molecular pathologies and subsequently restored muscle histology and force generation. However, CKM-TD autophagy alterations were not normalized by rapamycin or tempol, suggesting that they may involve non-canonical targets other than MTORC1. These results collectively indicate that the concomitant muscle deficiency of TSC1 and DEPDC5 can produce early-onset myopathy through accumulation of oxidative stress, which dysregulates myocellular homeostasis.Abbreviations: AMPK: AMP-activated protein kinase; CKM: creatine kinase, M-type; COX: cytochrome oxidase; DEPDC5: DEP domain containing 5, GATOR1 subcomplex subunit; DHE: dihydroethidium; EDL: extensor digitorum longus; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; GAP: GTPase-activating protein; GTN: gastrocnemius; MTORC1: mechanistic target of rapamycin kinase complex 1; PLA: plantaris; QUAD: quadriceps; RPS6KB/S6K: ribosomal protein S6 kinase beta; SDH: succinate dehydrogenase; SOL: soleus; SQSTM1: sequestosome 1; TA: tibialis anterior; TSC1: TSC complex subunit 1; ULK1: unc-51 like autophagy activating kinase 1.

Smad3 Phospho-Isoform Signaling in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis with insulin resistance, oxidative stress, lipotoxicity, adipokine secretion by fat cells, endotoxins (lipopolysaccharides) released by gut microbiota, and endoplasmic reticulum stress. Together, these factors promote NAFLD progression from steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, and eventually end-stage liver diseases in a proportion of cases. Hepatic fibrosis and carcinogenesis often progress together, sharing inflammatory pathways. However, NASH can lead to hepatocarcinogenesis with minimal inflammation or fibrosis. In such instances, insulin resistance, oxidative stress, and lipotoxicity can directly lead to liver carcinogenesis through genetic and epigenetic alterations. Transforming growth factor (TGF)-β signaling is implicated in hepatic fibrogenesis and carcinogenesis. TGF-β type I receptor (TβRI) and activated-Ras/c-Jun-N-terminal kinase (JNK) differentially phosphorylate the mediator Smad3 to create two phospho-isoforms: C-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L). TβRI/pSmad3C signaling terminates cell proliferation, while constitutive Ras activation and JNK-mediated pSmad3L promote hepatocyte proliferation and carcinogenesis. The pSmad3L signaling pathway also antagonizes cytostatic pSmad3C signaling. This review addresses TGF-β/Smad signaling in hepatic carcinogenesis complicating NASH. We also discuss Smad phospho-isoforms as biomarkers predicting HCC in NASH patients with or without cirrhosis.

Sestrin2 overexpression attenuates osteoarthritis pain via induction of AMPK/PGC-1α-mediated mitochondrial biogenesis and suppression of neuroinflammation

BACKGROUND

Our previous study indicated that reactive oxygen species (ROS) are critically involved in chronic pain. Sestrin2 (Sesn2), a novel stress-inducible protein, is evidenced to reduce the generation of ROS. The study examined the role of Sesn2 in osteoarthritis (OA) pain and delineated the underlying molecular mechanisms.

METHODS

In the present study, we investigated the impact of Sesn2 on mitochondrial biogenesis in a rat model of OA pain. After adeno-associated viral (AAV)-Sesn2EGFP was injected for 14 days, OA was induced by intra-articular injection of monosodium iodoacetate (MIA). We assessed pain behaviors (weight-bearing asymmetry and paw withdrawal threshold) and explored possible mechanisms in the L4-6 spinal cord.

RESULTS

Our results showed that overexpression of Sesn2 in the spinal cord alleviated pain behaviors in OA rats. Moreover, overexpression of Sesn2 increased the activity of AMP-activated protein kinase (AMPK) signaling and significantly restored mitochondrial biogenesis. Besides, Sesn2 overexpression inhibited the activation of astrocytes and microglia, and decreased the production of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the spinal cord of the OA pain rats. These effects were significantly reversed by an AMPK inhibitor.

CONCLUSIONS

Collectively, these results suggest that Sesn2 overexpression ameliorates mechanical allodynia and weight-bearing asymmetry in OA rats via activation of AMPK/PGC-1α-mediated mitochondrial biogenesis in the spinal cord. Moreover, Sesn2 overexpression attenuates OA-induced neuroinflammation at least partly by activating AMPK signaling. Sesn2 may become an encouraging therapeutic strategy for OA pain relief and other disorders.

Serum Sestrin-1 Concentration Is Higher in Frail than Non-Frail Older People Living in Nursing Homes

Given the increasing prevalence of frailty and its implications for public health, the identification of biomarkers to detect frailty is essential. Sestrin-1 is a protein with a protective role in muscle function. This study aimed to determine whether the serum sestrin-1 concentration differed between frail and non-frail populations and to investigate its association with frailty-related variables in 225 older women and men living in nursing homes (Gipuzkoa, Spain). Serum sestrin-1 concentration was measured by ELISA. Frailty, dependence, anthropometry, physical function, and physical activity were determined by validated tests and tools. The associations between sestrin-1 concentration and the other variables were determined using generalized linear models. The differences between frail and non-frail individuals were analyzed by the Mann–Whitney U-test, and receiver operating characteristic (ROC) curves were constructed to calculate the capability of sestrin-1 to detect frailty. Unexpectedly, frail individuals—according to the Fried Frailty Phenotype or the Clinical Frailty Scale—had higher serum sestrin-1 concentrations than non-frail individuals. Furthermore, the higher serum sestrin-1 concentration was associated with the increased frailty scores and dependence as well as the poorer physical function and the less physical activity. Given the contradictory results regarding serum sestrin-1 and frailty, further investigation is required to propose it as a molecular biomarker of frailty.

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.

SESN3 Inhibited SMAD3 to Relieve Its Suppression for MiR-124, Thus Regulating Pre-Adipocyte Adipogenesis

Sestrin-3, together with the other two members Sestrin-1 and Sestrin-2, belongs to the Sestrin family. The Sestrin protein family has been demonstrated to be involved in antioxidative, metabolic homeostasis, and even the development of nonalcoholic steatohepatitis (NASH). However, the adipogenic regulatory role of SESN3 in adipogenesis still needs to be further explored. In this study, we demonstrated SESN3 inhibited porcine pre-adipocyte proliferation, thus suppressing its adipogenesis. Meanwhile, SESN3 has been demonstrated to inhibit Smad3 thus protecting against NASH. Further, for our previous study, we found mmu-miR-124 involved in 3T3-L1 cell adipogenesis regulation. In this study, we also identified that ssc-miR-124 inhibited porcine pre-adipocyte proliferation, thus suppressing its adipogenesis, and the SMAD3 was an inhibitor of ssc-miR-124 by binding to its promoter. Furthermore, the ssc-miR-124 targeted porcine C/EBPα and GR and thus inhibited pre-adipocyte adipogenesis. In conclusion, SESN3 inhibited SMAD3, thus improving ssc-miR124, and then suppressed C/EBPα and GR to regulate pre-adipocytes adipogenesis.

Sestrin2 induction contributes to anti-inflammatory responses and cell survival by globular adiponectin in macrophages

Adiponectin, an adipose tissue-derived hormone, exhibits a modulatory effect on cell death/survival and possesses potent anti-inflammatory properties. However, the underlying molecular mechanisms remain elusive. Sestrin2, a stress-inducible metabolic protein, has shown cytoprotective and inflammation-modulatory effects under stressful conditions. In this study, we examined the role of sestrin2 signaling in the modulation of cell survival and inflammatory responses by globular adiponectin (gAcrp) in macrophages. We observed that gAcrp induced a significant increase in sestrin2 expression in both RAW 264.7 murine macrophages and primary murine macrophages. Notably, gAcrp treatment markedly increased expression of hypoxia inducible factor-1 α (HIF-1α) and gene silencing of HIF-1α blocked sestrin2 induction by gAcrp. In addition, pretreatment with a pharmacological inhibitor of ERK or PI3K abrogated both sestrin2 and HIF-1α expression by gAcrp, indicating that ERK/PI3K-mediated HIF-1α signaling pathway plays a critical role in sestrin2 induction by gAcrp. Furthermore, sestrin2 induction is implicated in autophagy activation, and knockdown of sestrin2 prevented enhanced cell viability by gAcrp. Moreover, gene silencing of sestrin2 caused restoration of gAcrp-induced expression of anti-inflammatory genes in a gene-selective manner. Taken together, these results indicate that sestrin2 induction critically contributes to cell survival and anti-inflammatory responses by gAcrp in macrophages.

Sestrin2 protects against lethal sepsis by suppressing the pyroptosis of dendritic cells

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sestrin2 (SESN2), a highly evolutionarily conserved protein, is critically involved in the cellular response to various stresses and has been confirmed to maintain the homeostasis of the internal environment. However, the potential effects of SESN2 in regulating dendritic cells (DCs) pyroptosis in the context of sepsis and the related mechanisms are poorly characterized. In this study, we found that SESN2 was capable of decreasing gasdermin D (GSDMD)-dependent pyroptosis of splenic DCs by inhibiting endoplasmic reticulum (ER) stress (ERS)-related nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3)-mediated ASC pyroptosome formation and caspase-1 (CASP-1) activation. Furthermore, SESN2 deficiency induced NLRP3/ASC/CASP-1-dependent pyroptosis and the production of proinflammatory cytokines by exacerbating the PERK–ATF4–CHOP signaling pathway, resulting in an increase in the mortality of septic mice, which was reversed by inhibiting ERS. These findings suggest that SESN2 appears to be essential for inhibiting NLRP3 inflammasome hyperactivation, reducing CASP-1-dependent pyroptosis, and improving sepsis outcomes through stabilization of the ER. The present study might have important implications for exploration of novel potential therapeutic targets for the treatment of sepsis complications.

Exercise improves lipid metabolism disorders induced by high-fat diet in a SESN2/JNK-independent manner

SESN2 and JNK are emerging powerful stress-inducible proteins in regulating lipid metabolism. The aim of this study was to determine the underlying mechanism of SESN2/JNK signaling in exercise to improve lipid disorder induced by high-fat diet (HFD). Our data showed that HFD and SESN2 knockout resulted in abnormalities including elevated body weight, increased fat mass, serum total cholesterol, lipid biosynthesis related proteins, and a concomitant increase of pJNK-Thr183/Tyr185. The above changes were reversed by exercise training. SESN2 silencing or JNK inhibition in palmitate-treated C2C12 further confirmed that SESN2 and JNK play a vital role in lipid biosynthesis. Rescue experiment further demonstrated that SESN2 reduced lipid biosynthesis through inhibition of JNK. SESN2/JNK signaling axis regulates lipid biosynthesis in both animal and cell models with abnormalities of lipid metabolism induced by HFD or palmitate treatment. This study provided evidence that exercise ameliorated lipid metabolic disorder induced by HFD feeding or by SESN2 knockout. SESN2 may improve lipid metabolism through inhibition JNK expression in skeletal muscle cells, providing a molecular mechanism that may represent an attractive target for the treatment of lipid disorder. Novelty: Exercise improved lipid disorder induced by HFD feeding and SESN2 knockout. SESN2 and JNK play a vital role in lipid biosynthesis in vivo and in vitro. SESN2 suppressed JNK to improve lipid metabolism in skeletal muscle cells.

Exercise and Sestrin Mediate Speed and Lysosomal Activity in Drosophila by Partially Overlapping Mechanisms

Chronic exercise is widely recognized as an important contributor to healthspan in humans and in diverse animal models. Recently, we have demonstrated that Sestrins, a family of evolutionarily conserved exercise-inducible proteins, are critical mediators of exercise benefits in flies and mice. Knockout of Sestrins prevents exercise adaptations to endurance and flight in Drosophila, and similarly prevents benefits to endurance and metabolism in exercising mice. In contrast, overexpression of dSestrin in muscle mimics several of the molecular and physiological adaptations characteristic of endurance exercise. Here, we extend those observations to examine the impact of dSestrin on preserving speed and increasing lysosomal activity. We find that dSestrin is a critical factor driving exercise adaptations to climbing speed, but is not absolutely required for exercise to increase lysosomal activity in Drosophila. The role of Sestrin in increasing speed during chronic exercise requires both the TORC2/AKT axis and the PGC1α homolog spargel, while dSestrin requires interactions with TORC1 to cell-autonomously increase lysosomal activity. These results highlight the conserved role of Sestrins as key factors that drive diverse physiological adaptations conferred by chronic exercise.

Sestrins regulate muscle stem cell metabolic homeostasis

The health and homeostasis of skeletal muscle are preserved by a population of tissue-resident muscle stem cells (MuSCs) that maintain a state of mitotic and metabolic quiescence in adult tissues. The capacity of MuSCs to preserve the quiescent state declines with aging and metabolic insults, promoting premature activation and stem cell exhaustion. Sestrins are a class of stress-inducible proteins that act as antioxidants and inhibit the activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling complex. Despite these pivotal roles, the role of Sestrins has not been explored in adult stem cells. We show that SESTRIN1,2 loss results in hyperactivation of the mTORC1 complex, increased propensity to enter the cell cycle, and shifts in metabolic flux. Aged SESTRIN1,2 knockout mice exhibited loss of MuSCs and a reduced ability to regenerate injured muscle. These findings demonstrate that Sestrins help maintain metabolic pathways in MuSCs that protect quiescence against aging.

Oncogenic role of early growth response-1 in liver cancer through the regulation of the microRNA-675/sestrin 3 and the Wnt/β-catenin signaling pathway

Early growth response-1 (EGR1) is a multi-domain protein and an immediate early transcription factor that is induced during liver injury and controls the expression of a variety of genes implicated in metabolism, cell proliferation, and tumorigenesis. Liver cancer (LC) is a highly malignant disease with high mortality worldwide. This study focused on the function of EGR1 in LC development and the mechanism of action. Two LC-related datasets GSE101728 and GSE138178 downloaded from the Gene Expression Omnibus (GEO) database were used for identification of key genes involved in cancer progression. A microarray analysis was conducted to identify differentially expressed microRNAs (miRNAs) after EGR1 knockdown. The target gene of miR-675 was identified by integrated analysis. EGR1 and miR-675 were highly expressed, whereas sestrin 3 (SESN3) was poorly expressed in LC tissues and cells. High EGR1 expression was associated with poor liver function and disease severity in patients with LC. Knockdown of EGR1 weakened proliferation and invasiveness of LC cells. EGR1 bound to the miR-675 promoter and increased its transcription, and miR-675 bound to SESN3 mRNA to induce its downregulation. miR-675 upregulation promoted the malignance of LC cells, but further upregulation of SESN3 reduced invasiveness of cells. SESN3 was enriched in the Wnt/β-catenin signaling. EGR1 and miR-675 activated the Wnt/β-catenin through downregulating SESN3. This study demonstrated that EGR1 promotes the malignant behaviors of LC cells through mediating the miRNA-675/SESN3/Wnt/β-catenin axis.

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.

Aerobic Exercise Improves Mitochondrial Function in Sarcopenia Mice Through Sestrin2 in an AMPKα2-Dependent Manner

Sarcopenia, the age-related loss of skeletal muscle mass and function, contributes to high morbidity and mortality in the older population. Regular exercise is necessary to avoid the initiation and progression of sarcopenia, in which the underlying molecular mechanism is still not clear. Our data revealed that the outcomes induced by sarcopenia, including muscle mass and strength loss, decreased cross-sectional area of gastrocnemius fiber, chronic inflammation, and increased dysfunctional mitochondria, were reversed by regulation exercise. Knockout or silencing of Sestrin2 (Sesn2) resulted in imbalanced mitochondrial fusion and fission, mitochondrial biogenesis, and mitophagy damage in vivo and in vitro, which was attenuated by aerobic exercise or overexpression of Sesn2. Moreover, we found that the effects of Sesn2 on mitochondrial function are dependent on AMP-activated protein kinase α2 (AMPKα2). This study indicates that aerobic exercise alleviates the negative effects resulting from sarcopenia via the Sesn2/AMPKα2 pathway and provides new insights into the molecular mechanism by which the Sesn2/AMPKα2 signaling axis mediates the beneficial impact of exercise on sarcopenia.

Sestrin regulates acute chill coma recovery in Drosophila melanogaster

When chill-susceptible insects are exposed to low temperatures they enter a temporary state of paralysis referred to as a chill coma. The most well-studied physiological mechanism of chill coma onset and recovery involves regulation of ion homeostasis. Previous studies show that changes in metabolism may also underlie the ability to recovery quickly, but the roles of genes that regulate metabolic homeostasis in chill coma recovery time (CCRT) are not well understood. Here, we investigate the roles of Sestrin and Spargel (Drosophila homolog of PGC-1α), which are involved in metabolic homeostasis and substrate oxidation, on CCRT in Drosophila melanogaster. We find that sestrin and spargel mutants have impaired CCRT. sestrin is required in the muscle and nervous system tissue for normal CCRT and spargel is required in muscle and adipose. On the basis that exercise induces sestrin and spargel, we also test the interaction of cold and exercise. We find that pre-treatment with one of these stressors does not consistently confer acute protection against the other. We conclude that Sestrin and Spargel are important in the chill coma response, independent of their role in exercise.

Pharmacokinetic Analysis of Carnosic Acid and Carnosol in Standardized Rosemary Extract and the Effect on the Disease Activity Index of DSS-Induced Colitis

Rosemary extract (RE) is an approved food preservative in the European Union and contains dietary phytochemicals that are beneficial for gastrointestinal health. This study investigated the effects of RE on dextran sodium sulfate (DSS)-induced colitis and also determined the pharmacokinetics of dietary phytochemicals administered to mice via oral gavage. Individual components of rosemary extract were separated and identified by LC–MS/MS. The pharmacokinetics of two major diterpenes from RE, carnosic acid (CA) and carnosol (CL), administered to mice via oral gavage were determined. Then, the effect of RE pre-treatment on the disease activity index (DAI) of DSS-induced colitis in mice was investigated. The study determined that 100 mg/kg RE significantly improved DAI in DSS-induced colitis compared to negative control. Sestrin 2 protein expression, which increased with DSS exposure, was reduced with RE treatment. Intestinal barrier integrity was also shown to improve via fluorescein isothiocyanate (FITC)–dextran administration and Western blot of zonula occludens-1 (ZO-1), a tight junction protein. Rosemary extract was able to improve the DAI of DSS-induced colitis in mice at a daily dose of 100 mg/kg and showed improvement in the intestinal barrier integrity. This study suggests that RE can be an effective preventative agent against IBD.

Hexavalent chromium induced heart dysfunction via Sesn2-mediated impairment of mitochondrial function and energy supply

Hexavalent chromium (Cr(VI)), the most toxic valence state of chromium, is widely present in industrial effluents and wastes. Although previous study has reported that Cr(VI) can cause cytomembrane structure impairment by aggravating lipid peroxidation in the heart, the detailed mechanism of Cr(VI)-induced heart dysfunction is still unclear. Sesn2, a novel antioxidant and stress-inducible molecule, is evidenced to protect against various cardiometabolic diseases such as atherosclerosis and cardiomyopathy. To define the potential mechanism of heart dysfunction induced by chronic Cr(VI) exposure, Wistar rats were intraperitoneal injected with potassium dichromate (K₂Cr₂O₇) for 35 d in the present study. The data showed that chronic K₂Cr₂O₇ exposure caused dose-dependently hematological variations, oxidative stress, dysfunction, and disorganized structure of heart, cardiomyocyte apoptosis, ATP depletion, and mitochondria impairment in rats. In addition, the expressions of Drp1 and Bax were increased by K₂Cr₂O₇. However, the suppression of Mfn2, PGC-1α, Sesn2, nuclear Nrf2, HO-1, and NQO1 protein levels was observed in K₂Cr₂O₇-treated rat hearts. In conclusion, these results demonstrate that chronic K₂Cr₂O₇ exposure dose-dependently causes heart dysfunction, and the molecular mechanism of this event is associated with the loss of Sesn2 mediated mitochondrial function and energy supply impairment.

The potential role of sestrin 2 in liver regeneration

Liver regeneration is a remarkably complex phenomenon conserved across all vertebrates, enabling the restoration of lost liver mass in a matter of days. Unfortunately, extensive damage to the liver may compromise this process, often leading to the death of affected individuals. Ischemia/reperfusion injury (IRI) is a common source of damage preceding regeneration, often present during liver transplantation, resection, trauma, or hemorrhagic shock. Increased oxidative stress and mitochondrial dysfunction are key hallmarks of IRI, which can jeopardize the liver's ability to regenerate. Therefore, a better understanding of both liver regeneration and IRI is of important clinical significance. In the current review, we discuss the potential role of sestrin 2 (SESN2), a novel anti-aging protein, in liver regeneration and ischemia/reperfusion preceding regeneration. We highlight its beneficial role in protecting cells from mitochondrial dysfunction and oxidative stress as key aspects of its involvement in liver regeneration. Additionally, we describe how its ability to promote the expression of Nrf2 bears significant importance in this context. Finally, we focus on a potential novel link between SESN2, mitohormesis and ischemic preconditioning, which could explain some of the protective effects of preconditioning.

Sestrin 2, a potential star of antioxidant stress in cardiovascular diseases

Physiological reactive oxygen species (ROS) play an important role in cellular signal transduction. However, excessive ROS is an important pathological mechanism in most cardiovascular diseases (CVDs), such as myocardial aging, cardiomyopathy, ischemia/reperfusion injury (e.g., myocardial infarction) and heart failure. Programmed cell death, hypertrophy and fibrosis may be due to oxidative stress. Sestrin 2 (Sesn2), a stress-inducible protein associated with various stress conditions, is a potential antioxidant. Sesn2 can suppress the process of heart damage caused by oxidative stress, promote cell survival and play a key role in a variety of CVDs. This review discusses the effect of Sesn2 on the redox signal, mainly via participation in the signaling pathway of nuclear factor erythroid 2-related factor 2, activation of adenosine monophosphate-activated protein kinase and inhibition of mammalian target of rapamycin complex 1. It also discusses the effect of Sesn2's antioxidant activity on different CVDs. We speculate that Sesn2 plays an important role in CVDs by stimulating the process of antioxidation and promoting the adaptation of cells to stress conditions and/or the environment, opening a new avenue for related therapeutic strategies.

Xanthatin synergizes with cisplatin to suppress homologous recombination through JAK2/STAT4/BARD1 axis in human NSCLC cells

Xanthatin (Xa) is a bicyclic sesquiterpene lactone identified from the plant Xanthium L. with impressive antitumor activity, but the role of Xa in non‐small cell lung cancer (NSCLC) is not known. Here we found that Xa inhibits proliferation, migration, invasion and induces apoptosis in NSCLC cells. RNA sequencing and Gene set enrichment analysis revealed that Xa significantly activates p53 pathway and suppresses E2F targets, G2M checkpoint and MYC targets in A549 cells. Among these changed genes, the down‐regulated gene BARD1 triggered by Xa was identified as a candidate involved in Xa’s antitumor effect because of its vital role in homologous recombination (HR). Further studies demonstrated that Xa inhibits HR through the BARD1/BRCA1/RAD51 axis, which enhances cell sensitivity to cisplatin. Mechanistic studies showed that Xa inhibits BARD1 through the JAK2/STAT4 pathway. Our study revealed that Xa is a promising drug to treat NSCLC, especially in combination with conventional chemotherapy.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

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.

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.

Oleacein Attenuates the Pathogenesis of Experimental Autoimmune Encephalomyelitis through Both Antioxidant and Anti-Inflammatory Effects

Oxidative stress and proinflammatory cytokines are factors affecting multiple sclerosis (MS) disease progression. Oleacein (OLE), an olive secoiridoid, possesses powerful antioxidant and anti-inflammatory activities, which suggests its potential application to treat neuroinflammatory disorders. Herein, we investigated the impact of OLE on the main clinic-pathological features of experimental autoimmune encephalomyelitis (EAE), an animal model for MS, including paralysis, demyelination, central nervous system (CNS) inflammation/oxidative stress and blood-brain barrier (BBB) breakdown.

METHODS

Mice were immunized with the myelin oligodendrocyte glycoprotein peptide, MOG_35-55, to induce EAE, and OLE was administrated from immunization day. Serum, optic nerve, spinal cord and cerebellum were collected to evaluate immunomodulatory activities at a systemic level, as well as within the CNS. Additionally, BV2 microglia and the retinal ganglion cell line RGC-5 were used to confirm the direct effect of OLE on CNS-resident cells.

RESULTS

We show that OLE treatment effectively reduced clinical score and histological signs typical of EAE. Histological evaluation confirmed a decrease in leukocyte infiltration, demyelination, BBB disruption and superoxide anion accumulation in CNS tissues of OLE-treated EAE mice compared to untreated ones. OLE significantly decreased expression of proinflammatory cytokines (IL-13, TNFα, GM-CSF, MCP-1 and IL-1β), while it increased the anti-inflammatory cytokine IL-10. Serum levels of anti-MOG_35-55 antibodies were also lower in OLE-treated EAE mice. Further, OLE significantly diminished the presence of oxidative system parameters, while upregulated the ROS disruptor, Sestrin-3. Mechanistically, OLE prevented NLRP3 expression, phosphorylation of p65-NF-κB and reduced the synthesis of proinflammatory mediators induced by relevant inflammatory stimuli in BV2 cells. OLE did not affect viability or the phagocytic capabilities of BV2 microglia. In addition, apoptosis of RGC-5 induced by oxidative stressors was also prevented by OLE.

CONCLUSION

Altogether, our results show that the antioxidant and anti-inflammatory OLE has neuroprotective effects in the CNS of EAE mice, pointing out this natural product as a candidate to consider for research on MS treatments.

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.

Sestrin1 exerts a cytoprotective role against oxygen-glucose deprivation/reoxygenation-induced neuronal injury by potentiating Nrf2 activation via the modulation of Keap1

Sestrin1 (Sesn1) acts as a stress-inducible protein that performs a remarkable cytoprotective function upon diverse cellular stresses. However, whether Sesn1 exerts a cytoprotective role in neurons following cerebral ischemia/reperfusion injury is unknown. The goal of this work was to evaluate the role of Sesn1 in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced neuronal injury in vitro. The induction of Sesn1 was found in neurons exposed to OGD/R treatment. The silencing of Sesn1 rendered neurons more vulnerable to OGD/R injury, while the up-regulation of Sesn1 ameliorated OGD/R-induced neuronal injury by reducing apoptosis and the generation of reactive oxygen species (ROS). Furthermore, the up-regulation of Sesn1 promoted the activity of the nuclear factor-erythroid 2-related factor 2 (Nrf2) by down-regulating the expression of the Kelchlike ECH-associated protein 1 (Keap1). The restoration of Keap1 or the suppression of Nrf2 remarkably abolished the Sesn1-induced neuroprotection effects in OGD/R-exposed neurons. In summary, our work indicates that Sesn1 is a remarkable neuroprotective protein that potentiates Nrf2 activation via Keap1 to ameliorate OGD/R-induced injury.

Single-Cell Transcriptome Analysis of Colon Cancer Cell Response to 5-Fluorouracil-Induced DNA Damage

DNA damage often induces heterogeneous cell-fate responses, such as cell-cycle arrest and apoptosis. Through single-cell RNA sequencing (scRNA-seq), we characterize the transcriptome response of cultured colon cancer cell lines to 5-fluorouracil (5FU)-induced DNA damage. After 5FU treatment, a single population of colon cancer cells adopts three distinct transcriptome phenotypes, which correspond to diversified cell-fate responses: apoptosis, cell-cycle checkpoint, and stress resistance. Although some genes are regulated uniformly across all groups of cells, many genes showed group-specific expression patterns mediating DNA damage responses specific to the corresponding cell fate. Some of these observations are reproduced at the protein level by flow cytometry and are replicated in cells treated with other 5FU-unrelated genotoxic drugs, camptothecin and etoposide. This work provides a resource for understanding heterogeneous DNA damage responses involving fractional killing and chemoresistance, which are among the major challenges in current cancer chemotherapy.

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.

Elevating sestrin2 attenuates endoplasmic reticulum stress and improves functional recovery through autophagy activation after spinal cord injury

Spinal cord injury (SCI) is a devastating neurological trauma that causes losses of motor and sensory function. Sestrin2, also known as hypoxia inducible gene 95, is emerging as a critical determinant of cell homeostasis in response to cellular stress. However, the role of sestrin2 in the neuronal response to endoplasmic reticulum (ER) stress and the potential mechanism remain undefined. In this study, we investigated the effects of sestrin2 on ER stress and delineated an underlying molecular mechanism after SCI. Here, we found that elevated sestrin2 is a protective process in neurons against chemical ER stress induced by tunicamycin (TM) or traumatic invasion, while treatment with PERK inhibitor or knockdown of ATF4 reduces sestrin2 expression upon ER stress. In addition, we demonstrated that overexpression of sestrin2 limits ER stress, promoting neuronal survival and improving functional recovery after SCI, which is associated with activation of autophagy and restoration of autophagic flux mediated by sestrin2. Moreover, we also found that sestrin2 activates autophagy dependent on the AMPK-mTOR signaling pathway. Consistently, inhibition of AMPK abrogates the effect of sestrin2 on the activation of autophagy, and blockage of autophagic flux abolishes the effect of sestrin2 on limiting ER stress and neural death. Together, our data reveal that upregulation of sestrin2 is an important resistance mechanism of neurons to ER stress and the potential role of sestrin2 as a therapeutic target for SCI. Graphical abstract.

Variation in mobility and exercise adaptations between Drosophila species

Locomotion and mobility have been studied extensively in Drosophila melanogaster but less is known about the locomotor capacity of other Drosophila species, while the response to chronic exercise in other species has yet to be examined. We have shown that adult male D. melanogaster adapt to exercise training with improved running endurance, climbing speed, and flight ability compared to unexercised flies. Here, we examine baseline mobility of D. sechellia, D. simulans, and D. virilis, and their response to chronic exercise training. We found significant interspecific differences in mobility and in the response to exercise. Although there is a significant sex difference in exercise adaptations in D. melanogaster, intraspecific analysis reveals few sex differences in other Drosophila species. As octopamine has been shown to be important for exercise adaptations in D. melanogaster, we also asked if any observed differences could be attributed to baseline octopamine levels. We find that octopamine and tyramine levels have the same rank order as baseline climbing speed and endurance in males, but do not predict the response to chronic exercise in males or females. Future research should focus on determining the mechanisms responsible for the inter- and intraspecific differences in mobility and the response to exercise.

Diagnostic Value of Sestrin2 in Patients with Obstructive Sleep Apnea

Background: Obstructive sleep apnea (OSA) is a serious threat to individual health. Diagnosis of OSA is mainly polysomnography (PSG). However, PSG monitoring is costly and time-consuming. At present, increasing studies are exploring new diagnostic methods for OSA. This study aimed to explore the diagnostic role of Sestrin2 in OSA.

Materials and Methods: Sixty-four subjects were recruited in this study. The concentration of plasma Sestrin2 of all subjects were measured and compared. Spearman's correlation analysis was used to investigate the correlation between plasma Sestrin2 concentration and other factors. Receiver-operating characteristic (ROC) curve was used to investigate the role of Sestrin2 in the diagnosis of OSA, moderate-severe and severe OSA.

Results: Subjects were divided into OSA group (n = 38) and control (n = 26). Levels of Plasma Sestrin2 were significantly higher in OSA patients than in controls. Sestrin2 was positively correlated with oxygen reduction index and negatively correlated with mean oxygen saturation and lowest oxygen saturation. The area under ROC curve (AUC) of Sestrin2 for OSA diagnosis was 0.740 [95% confidence interval (CI), 0.615–0.842], the cutoff value was 1.86 ng/mL, and the sensitivity and specificity were 81.58% and 61.54%, respectively. The AUC of Sestrin2 for the diagnosis of severe OSA was 0.801 (95% CI, 0.682–0.890), and the cutoff value was 5.21 ng/mL exhibiting the sensitivity and specificity of 61.90% and 90.70%, respectively.

Conclusion: Setrin2 is a marker for OSA and may be helpful in the diagnosis of OSA.

Sestrin2 inhibits YAP activation and negatively regulates corneal epithelial cell proliferation

Corneal wound healing is essential for the maintenance of corneal integrity and transparency and involves a series of physiological processes that depend on the proliferation of epithelial cells. However, the molecular mechanisms that control corneal epithelial cell proliferation are poorly understood. Here, we show that Sestrin2, a stress-inducible protein, is downregulated in the corneal epithelium during wound healing and that the proliferation of epithelial basal cells is enhanced in Sestrin2-deficient mice. We also show that YAP, a major downstream effector of the Hippo signaling pathway, regulates cell proliferation during corneal epithelial wound repair and that Sestrin2 suppresses its activity. Moreover, increased levels of reactive oxygen species in the Sestrin2-deficient corneal epithelium promote the nuclear localization and dephosphorylation of YAP, activating it to enhance the proliferation of corneal epithelial cells. These results reveal that Sestrin2 is a negative regulator of YAP, which regulates the proliferative capacity of basal epithelial cells, and may serve as a potential therapeutic target for corneal epithelial damage.