Insulin Increases Sestrin 2 Content by Reducing Its Degradation through the PI 3 K/mTOR Signaling Pathway

Sestrin2 in diabetes and diabetic complications

Diabetes is a global health problem which is accompanied with multi-systemic complications. It is of great significance to elucidate the pathogenesis and to identify novel therapies of diabetes and diabetic complications. Sestrin2, a stress-inducible protein, is primarily involved in cellular responses to various stresses. It plays critical roles in regulating a series of cellular events, such as oxidative stress, mitochondrial function and endoplasmic reticulum stress. Researches investigating the correlations between Sestrin2, diabetes and diabetic complications are increasing in recent years. This review incorporates recent findings, demonstrates the diverse functions and regulating mechanisms of Sestrin2, and discusses the potential roles of Sestrin2 in the pathogenesis of diabetes and diabetic complications, hoping to highlight a promising therapeutic direction.

A cross-talk between sestrins, chronic inflammation and cellular senescence governs the development of age-associated sarcopenia and obesity

The rapid increase in both the lifespan and proportion of older adults is accompanied by the unprecedented rise in age-associated chronic diseases, including sarcopenia and obesity. Aging is also manifested by increased susceptibility to multiple endogenous and exogenous stresses enabling such chronic conditions to develop. Among the main physiological regulators of cellular adaption to various stress stimuli, such as DNA damage, hypoxia, and oxidative stress, are sestrins (Sesns), a family of three evolutionarily conserved proteins, Sesn1, 2, and 3. Age-associated sarcopenia and obesity are characterized by two key processes: (i) accumulation of senescent cells in the skeletal muscle and adipose tissue and (ii) creation of a systemic, chronic, low-grade inflammation (SCLGI). Presumably, failed SCLGI resolution governs the development of these chronic conditions. Noteworthy, Sesns activate senolytics, which are agents that selectively eliminate senescent cells, as well as specialized pro-resolving mediators, which are factors that physiologically provide inflammation resolution. Sesns reveal clear beneficial effects in pre-clinical models of sarcopenia and obesity. Based on these observations, we propose a novel treatment strategy for age-associated sarcopenia and obesity, complementary to the conventional therapeutic modalities: Sesn activation, SCLGI resolution, and senescent cell elimination.

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.

Association between serum Sestrin2 level and diabetic peripheral neuropathy in type 2 diabetic patients

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a chronic and serious microvascular complication of diabetes linked to redox imbalance. Sestrin2, a novel inducible stress protein, participates in glucose metabolic regulation and redox homeostasis. However, the association between serum Sestrin2 and DPN is unknown.

AIM

To explore the association between serum Sestrin2 and DPN in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 96 T2DM patients and 39 healthy volunteers, matched by age and sex, participated in this cross-sectional study. Clinical features and metabolic indices were identified. Serum Sestrin2 was measured by ELISA. The association between Sestrin2 and DPN was studied. Correlation and logistic regression analyses were used to evaluate the associations of different metabolic indices with Sestrin2 and DPN.

RESULTS

The 96 patients with T2DM were divided into DPN (n = 47) and patients without DPN (n = 49). Serum Sestrin2 was significantly lower in healthy volunteers than in all T2DM patients combined [9.10 (5.41-13.53) ng/mL vs 12.75 (7.44-23.80) ng/mL, P < 0.01]. T2DM patients without DPN also had significantly higher levels of Sestrin2 than healthy volunteers [14.58 (7.93-26.62) ng/mL vs 9.10 (5.41-13.53) ng/mL, P < 0.01]. However, T2DM patients with DPN had lower circulating Sestrin2 levels compared to T2DM patients without DPN [9.86 (6.72-21.71) ng/mL vs 14.58 (7.93-26.62) ng/mL, respectively, P < 0.01]. Bivariate correlation analysis revealed that serum Sestrin2 was positively correlated with body mass index (r = 0.672, P = 0.000), hemoglobin A1c (HbA1c) (r = 0.292, P = 0.000), serum creatinine (r = 0.206, P = 0.016), triglycerides (r = 0.731, P = 0.000), and fasting glucose (r = 0.202, P = 0.040), and negatively associated with estimated glomerular filtration rate (r = -0.230, P = 0.007). After adjustment for sex, age, HbA1c, and diabetes duration, multiple regression analysis revealed that Sestrin2 was independently correlated with body mass index and triglyceride levels (P = 0.000). Logistic regression analyses indicated that Sestrin2, diabetes duration, and high-density lipoprotein were strongly associated with DPN (odds ratio = 0.855, 1.411, and 0.041, respectively).

CONCLUSION

Our results show Sestrin2 is decreased in T2DM patients with DNP. As lower Sestrin2 is independently associated with DPN, Sestrin2 may contribute to progression of DPN in T2DM patients.

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.

Investigation of the levels of circulating miR-29a, miR-122, sestrin 2 and inflammatory markers in obese children with/without type 2 diabetes: a case control study

AIM

The present work investigated serum levels of miR-29a, miR-122 and sestrin2 in obese children with/without type-2-diabetes mellitus (T2DM), and their correlations with inflammatory, metabolic and anthropometric parameters.

METHODS

The study included 298 children, divided into: G1 (control, n = 136), G2 (obese without diabetes, n = 90) and G3 (obese with T2DM, n = 72). Metabolic and anthropometric parameters, miR-29a, miR-122 relative expressions, and sestrin2, high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) levels were measured by their specific methods. The data was processed and analyzed by SPSS V.26 using the corresponding tests. After testing the variables' normality, Kruskal-Wallis one-way-ANOVA, Spearman correlations coefficient were used.

RESULTS

Significant higher serum miR-29a, miR-122, IL-6, hsCRP and TNF-α and lower sestrin2 levels were found in G2 and G3 than G1 and in G3 than G2 (p= > 0.001 for all). Especially in G3, miR-29a and miR-122 levels correlated positively while sestrin2 levels correlated negatively with waist circumference and BMI percentiles, serum levels of LDL-cholesterol, triacylglycerol, total cholesterol, HbA1c%, glucose, insulin, c-peptide, homeostatic model assessment-insulin resistance (HOMA-IR), IL-6, hsCRP and TNF-α.

CONCLUSION

The change in the serum miR-29a, miR-122 and sestrin2 levels in obese children with/without T2DM may suggest a possible role of these biomarkers in the pathogenesis of childhood obesity and their accompanied complications e.g. inflammations and T2DM. Also, further studies are required to test drugs that antagonize the action miR-29a and miR-122 or upregulate sestrin2 in the management of these cases.

The involvement of Sestrin2 in the effect of IGF-I and leucine on mTROC1 activity in C2C12 and L6 myocytes

OBJECTIVE

IGF-I and branched-chain amino acids have been reported to promote muscle hypertrophy via the stimulation of protein synthesis. Sestrin2, the function of which is regulated by leucine, has been reported to attenuate the activity of the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) that stimulates protein synthesis. The objective of this study was to examine whether IGF-I modulates Sestrin2 abundance and to clarify the involvement of Sestrin2 in the effect of IGF-I and leucine on mTROC1.

DESIGN

C2C12 and L6 myocytes were stimulated by leucine (1 mM) with or without pretreatment with IGF-I (100 ng/mL). Phosphorylation of p70 S6 kinase (S6K) and 4E-binding protein 1 (4E-BP1), both of which are targets of the mTORC1, was examined by western blotting. Effects of Sestrin2 small interfering RNA (siRNA) on the actions of leucine and IGF-I were examined. Sestrin2 mRNA and protein levels were also determined after Sestrin2 siRNA.

RESULTS

Leucine increased the phosphorylation of S6K and 4E-BP1 in a dose-dependent manner. Pretreatment with IGF-I for 5 h further increased the stimulatory effect of leucine on the phosphorylation of S6K and 4E-BP1 in C2C12 cells. IGF-I increased Sestrin2 protein and messenger RNA levels. Sestrin2 siRNA increased or tended to increase basal phosphorylation of 4E-BP1 and decreased the leucine-induced phosphorylation in C2C12 and L6 cells, in particular after IGF-I treatment, suggesting the involvement of Sestrin2 in the action of leucine and IGF-I. The net increase in leucine-induced 4E-BP1 phosphorylation appeared to be attenuated by Sestrin2 siRNA. Likewise, Sestrin2 siRNA attenuated leucine-induced S6K phosphorylation in L6 cells. However, Sestrin2 siRNA did not influence leucine-induced S6K phosphorylation in C2C12 cells.

CONCLUSIONS

IGF-I and leucine cooperatively increased mTORC1 activity in C2C12 cells. IGF-I increased Sestrin2. Sestrin2 siRNA experiments showed that Sestrin2 was involved in the effect of leucine and IGF-I on mTORC1 activity in C2C12 and L6 cells, and suggested that increased Sestrin2 by IGF-I pretreatment might play a role in enhancing the effect of leucine on mTORC1.

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.

Regulatory mechanisms of Sesn2 and its role in multi-organ diseases

Sestrin2 (Sesn2) is a powerful anti-oxidant that can prevent acute and chronic diseases. The role of Sesn2 has been thoroughly reviewed in liver, nervous system, and immune system diseases. However, there is a limited number of reviews that have summarized the effects of Sesn2 in heart and vascular diseases, and very less literature-based information is available on involvement of Sesn2 in renal and respiratory pathologies. This review summarizes the latest research on Sesn2 in multi-organ stress responses, with a particular focus on the protective role of Sesn2 in cardiovascular, respiratory, and renal diseases, emphasizing the potential therapeutic benefit of targeting Sesn2 in stress-related diseases.

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.

Globular Adiponectin Inhibits Breast Cancer Cell Growth through Modulation of Inflammasome Activation: Critical Role of Sestrin2 and AMPK Signaling

Adiponectin, an adipokine predominantly derived from adipose tissue, exhibits potent antitumor properties in breast cancer cells. However, its mechanisms of action remain elusive. Inflammasomes—intracellular multimeric protein complexes—modulate cancer cell growth in a complicated manner, as well as playing a role in the innate immune system. Herein, we examined the potential role of inflammasomes in the antitumor activity of adiponectin and found that globular adiponectin (gAcrp) significantly suppressed inflammasomes activation in breast cancer cells both in vitro and in vivo conditions, as determined by decreased expression of inflammasomes components, including NOD-like receptor pyrin domain-containing protein 3 (NLRP3) and the apoptosis-associated speck-like protein containing a CARD (ASC), and inhibition of interleukin-1β and caspase-1 activation. Treatment with pharmacological inhibitors of inflammasomes caused decrease in cell viability, apoptosis induction, and G0/G1 cell cycle arrest, suggesting that inflammasomes activation is implicated in the growth of breast cancer cells. In addition, treatment with gAcrp generated essentially similar results to those of inflammasomes inhibitors, further indicating that suppression of breast cancer cell growth by gAcrp is mediated via modulation of inflammasomes. Mechanistically, gAcrp suppressed inflammasomes activation through sestrin2 (SESN2) induction, liver kinase B1 (LKB-1)-dependent AMP-activated protein kinase (AMPK) phosphorylation, and alleviation of endoplasmic reticulum (ER) stress. Taken together, these results demonstrate that gAcrp inhibits growth of breast cancer cells by suppressing inflammasomes activation, at least in part, via SESN2 induction and AMPK activation-dependent mechanisms.

Association of serum sestrin 2 and betatrophin with serum neutrophil gelatinase associated lipocalin levels in type 2 diabetic patients with diabetic nephropathy

Purpose

Understanding the pathogenesis and the molecular mechanisms of diabetic nephropathy (DN) helps its timely detection and prevention. The current work aims tomeasure serum sestrin 2 and betatrophin levels in healthy and type diabetic (T2DM)subjects with/or without diabetic nephropathy (DN) and also to test their correlation with serum neutrophil gelatinase associated lipocalin (sNGAL); indicator of DN.

Methods

This study included 96 subjects; 20 healthy (G1) and 76 T2DM [22 normoalbuminuric (G2), 35 microalbuminuric (G3) and 19 macroalbuminuric (G4)]. Serum sestrin 2, betatrophin and NGAL were measured by their corresponding kits.

Results

Significant low levels of serum sestrin 2 andhigh levels of serum betatrophin were found in T2DM group when compared to G1 (p = 0.002,p > 0.001, respectively) and this difference is manifested in G4 followed, in order, by G3, G2 then G1 (p= > 0.001 for both). Also, serum sestrin2 levels showed significant negative correlations with sNGAL in G1 (r = -0.497, p = 0.026), G2 (r = -0.784, p > 0.001), G3 (r = -0.894, p > 0.001) and G4 (r = -0.896, pp. > 0.001) while serum betatrophin levels showed significant positive correlations with sNGAL in G2 (r = 0.681, p > 0.001), G3 (r = 0.518, p > 0.001) and G4 (r = 0.727, p > 0.001).

Conclusion

Serum sestrin 2 levels decrease significantly while betatrophin levels increase significantly in T2DM patients with DN especially those with macroalbuminuria. These levels have significant effect strengths on the indicator of diabetic nephropathy; sNGAL which might indicate theirvaluablerole in the timely detection and prevention of the development of DN.

Sestrin2: Its Potential Role and Regulatory Mechanism in Host Immune Response in Diseases

Sestrin2 (SESN2), a highly evolutionarily conserved protein, is critically involved in cellular responses to various stresses. SESN2 has a protective effect on physiological and pathological states mainly via regulating oxidative stress, endoplasmic reticulum stress, autophagy, metabolism, and inflammation. In recent years, breakthrough investigations with regard to the regulation and signaling mechanisms of SESN2 have markedly deepened our understanding of its potential role as well as its significance in host response. However, the functions of SESN2 in the immune system and inflammation remain elusive. It has been documented that many immune cells positively express SESN2 and, in turn, that SESN2 might modulate cellular activities. This review incorporates recent progress and aims to provide novel insight into the protective role and regulatory pathway of SESN2, which acts as a potential biomarker and therapeutic target in the context of various diseases.

RBX1-mediated ubiquitination of SESN2 promotes cell death upon prolonged mitochondrial damage in SH-SY5Y neuroblastoma cells

Sestrins are evolutionary conserved stress-inducible genes which regulate the axis of cell survival and cell death. Suppression of Sestrin 2 (SESN2) has been linked with increase in oxidative stress and cell death but mechanistic details related to regulation of SESN2 during mitochondrial damage remain unknown. Our study shows that prolonged CCCP-induced mitochondrial damage decreases SESN2 levels and viability of SH-SY5Y cells while overexpression of SESN2 significantly rescues the viability of cells. Further, we demonstrate that Ring box protein 1 (RBX1) is a novel interactive partner and E3 ligase for SESN2 which mediates its K-48-linked ubiquitination upon extensive mitochondrial damage. Downregulation of RBX1 causes stabilization in levels of SESN2. Notably, silencing of RBX1 expression substantially declines cell death and generation of mitochondrial ROS in response to prolonged mitochondrial damage. Taken together, we suggest that SESN2 is critical to protect cells against detrimental effect of mitochondrial damage and RBX1 is a negative regulator of SESN2 which hampers its stabilization.

Sestrin2 as a Novel Biomarker and Therapeutic Target for Various Diseases

Sestrin2 (SESN2), a highly conserved stress-inducible metabolic protein, is known to repress reactive oxygen species (ROS) and provide cytoprotection against various noxious stimuli including genotoxic and oxidative stress, endoplasmic reticulum (ER) stress, and hypoxia. Studies demonstrate that the upregulation of Sestrin2 under conditions of oxidative stress augments autophagy-directed degradation of Kelch-like ECH-associated protein 1 (Keap1), which targets and breaks down nuclear erythroid-related factor 2 (Nrf2), a key regulator of various antioxidant genes. Moreover, ER stress and hypoxia are shown to induce Sestrins, which ultimately reduce cellular ROS levels. Sestrin2 also plays a pivotal role in metabolic regulation through activation of the key energy sensor AMP-dependent protein kinase (AMPK) and inhibition of mammalian target of rapamycin complex 1 (mTORC1). Other downstream effects of Sestrins include autophagy activation, antiapoptotic effects in normal cells, and proapoptotic effects in cancer cells. As perturbations in the aforementioned pathways are well documented in multiple diseases, Sestrin2 might serve as a potential therapeutic target for various diseases. Thus, the aim of this review is to discuss the upstream regulators and the downstream effectors of Sestrins and to highlight the significance of Sestrin2 as a biomarker and a therapeutic target in diseases such as metabolic disorders, cardiovascular and neurodegenerative diseases, and cancer.

Sensing the Environment Through Sestrins: Implications for Cellular Metabolism

Sestrins are a family of stress-responsive genes that have evolved to attenuate damage induced by stress caused to the cell. By virtue of their antioxidant activity, protein products of Sestrin genes prevent the accumulation of reactive oxygen species within the cell, thereby attenuating the detrimental effects of oxidative stress. In parallel, Sestrins participate in several signaling pathways that control the activity of the target of rapamycin protein kinase (TOR). TOR is a crucial sensor of intracellular and extracellular conditions that promotes cell growth and anabolism when nutrients and growth factors are abundant. In addition to reacting to stress-inducing insults, Sestrins also monitor the changes in the availability of nutrients, which allows them to serve as a key checkpoint for the TOR-regulated signaling pathways. In this review, we will discuss how Sestrins integrate signals from numerous stress- and nutrient-responsive signaling pathways to orchestrate cellular metabolism and support cell viability.

The potential of sestrins as therapeutic targets for diabetes

Sestrins (Sesn1/2/3) belong to a small protein family that has versatile biological functions. In addition to initially characterized oxidoreductase activity, sestrins also have oxidoreductase-independent functions, including activation of AMP-activated protein kinase, inhibition of the mechanistic target of rapamycin complex 1 (mTORC1) and activation of mTORC2. As these kinases are important for metabolic regulation, sestrins have a favorable profile as potential therapeutic targets for metabolic diseases such as diabetes. Recent data are in line with such a notion. In this editorial, I have attempted to provide a brief update on the major findings in regard to sestrins in metabolism.