Role of sestrin2 in peroxide signaling in macrophages

Cellular RNA and DNA sensing pathways are essential for the dose-dependent response of human monocytes to ionizing radiation

Circulating monocytes are important players of the inflammatory response to ionizing radiation (IR). These IR-resistant immune cells migrate to radiation-damaged tissues and differentiate into macrophages that phagocytize dying cells, but also facilitate inflammation. Besides the effect of damage-associated molecular patterns, released from irradiated tissues, the inflammatory activation of monocytes and macrophages is largely dependent on IR-induced DNA damage and aberrant transcriptional activity, which may facilitate expression of type I interferons (IFN-I) and numerous inflammation-related genes. We analyzed the accumulation of dsRNA, dsDNA fragments, and RNA:DNA hybrids in the context of induction of RNA-triggered MAVS-mediated and DNA-triggered STING-mediated signaling pathways, in primary human monocytes and a monocytic cell line, THP1, in response to various doses of gamma IR. We found that exposure to lower doses (<7.5 Gy) led to the accumulation of dsRNA, along with dsDNA and RNA:DNA hybrids and activated both MAVS and STING pathway-induced gene expression and signaling activity of IFN-I. Higher doses of IR resulted in the reduced dsRNA level, degradation of RNA-sensing mediators involved in MAVS signaling and coincided with an increased accumulation of dsDNA and RNA:DNA hybrids that correlated with elevated STING signaling and NF-κB-dependent gene expression. While both pathways activate IFN-I expression, using MAVS- and STING-knockout THP1 cells, we identified differences in the spectra of interferon-stimulated genes (ISGs) that are associated with each specific signaling pathway and outlined a large group of STING signaling-associated genes. Using the RNAi technique, we found that increasing the dose of IR activates STING signaling through the DNA sensor cGAS, along with suppression of the DDX41 helicase, which is known to reduce the accumulation of RNA:DNA hybrids and thereby limit cGAS/STING signaling activity. Together, these results indicate that depending on the applied dose, IR leads to the activation of either dsRNA-induced MAVS signaling, which predominantly leads to the expression of both pro- and anti-inflammatory markers, or dsDNA-induced STING signaling that contributes to pro-inflammatory activation of the cells. While RNA:DNA hybrids boost both MAVS- and STING-mediated signaling pathways, these structures being accumulated upon high IR doses promote type I interferon expression and appear to be potent enhancers of radiation dose-dependent pro-inflammatory activation of monocytes.

The pathogenesis and potential therapeutic targets in sepsis

Sepsis is defined as "a life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection." At present, sepsis continues to pose a grave healthcare concern worldwide. Despite the use of supportive measures in treating traditional sepsis, such as intravenous fluids, vasoactive substances, and oxygen plus antibiotics to eradicate harmful pathogens, there is an ongoing increase in both the morbidity and mortality associated with sepsis during clinical interventions. Therefore, it is urgent to design specific pharmacologic agents for the treatment of sepsis and convert them into a novel targeted treatment strategy. Herein, we provide an overview of the molecular mechanisms that may be involved in sepsis, such as the inflammatory response, immune dysfunction, complement deactivation, mitochondrial damage, and endoplasmic reticulum stress. Additionally, we highlight important targets involved in sepsis-related regulatory mechanisms, including GSDMD, HMGB1, STING, and SQSTM1, among others. We summarize the latest advancements in potential therapeutic drugs that specifically target these signaling pathways and paramount targets, covering both preclinical studies and clinical trials. In addition, this review provides a detailed description of the crosstalk and function between signaling pathways and vital targets, which provides more opportunities for the clinical development of new treatments for sepsis.

Sestrin-2 and hypoxia-ınducible factor-1 alpha levels in major depressive disorder and its subtypes

BACKGROUND

The objective of this study is to measure the levels of sestrin-2 (SESN2) and hypoxia-inducible factor-1 alpha (HIF-1α), which can be determinants in the relevant physiopathology and etiology, assessment of the clinical severity, and identification of new treatment targets in major depressive disorder (MDD) and its subtypes.

METHODS

A total of 230 volunteers, including 153 patients diagnosed with MDD according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), and 77 healthy controls, were included in the study. Of the MDD patients included in the study, 40 had melancholic features, 40 had anxious distress features, 38 had atypical features, and the remaining 35 had psychotic features. All participants were administered the Beck's Depression Inventory (BDI) and Clinical Global Impressions-Severity (CGI-S) scale. Serum SESN2 and HIF-1α levels of the participants were measured using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

The HIF-1α and SESN2 values of the patient group were found to be significantly lower than those of the control group (p < 0.05). The HIF-1α and SESN2 values were significantly lower in patients with melancholic, anxious distress, and atypical features compared to the control group (p < 0.05). The HIF-1α and SESN2 levels did not differ significantly between patients with psychotic features and the control group (p > 0.05).

CONCLUSION

The findings of the study suggested that knowledge of SESN2 and HIF-1α levels may contribute to the explanation of the etiology of MDD, objective assessment of the severity of the disease, and identification of new treatment targets.

Association between the antioxidant properties of SESN proteins and anti-cancer therapies

Since the beginning of SESN protein development, they have attracted highly progressive attention due to their regulatory role in multiple signalling pathways. Through their antioxidant activity and autophagy regulation implication, they can function as powerful antioxidants to reduce oxidative stress in cells. SESN proteins received special attention in the field of regulation of reactive oxygen species level in the cell and its interplay with signalling pathways determining energy and nutrient homeostasis. Since perturbations in these pathways are implicated in cancer onset and development, SESNs might constitute potential novel therapeutic targets of broad interest. In this review, we discuss the impact of SESN proteins on anti-cancer therapy based on naturally occurring compounds and conventionally used drugs that influence oxidative stress and autophagy-induced cellular signalling pathways. The significant changes in reactive oxygen species level and nutrient status in cancer cells generate subsequent biological effect through the regulation of SESN-dependent pathways. Thus, SESN may serve as the key molecule for regulating anti-cancer drugs' induced cellular response.

A review of the signaling pathways of aerobic and anaerobic exercise on atherosclerosis

Atherosclerosis (AS), a chronic inflammatory vascular disease with lipid metabolism abnormalities, is one of the major pathological bases of coronary heart disease. As people's lifestyles and diets change, the incidence of AS increases yearly. Physical activity and exercise training have recently been identified as effective strategies for lowering cardiovascular disease (CVD) risk. However, the best exercise mode to ameliorate the risk factors related to AS is not clear. The effect of exercise on AS is affected by the type of exercise, intensity, and duration. In particular, aerobic and anaerobic exercise are the two most widely discussed types of exercise. During exercise, the cardiovascular system undergoes physiological changes via various signaling pathways. The review aims to summarize signaling pathways related to AS in two different exercise types and provide new ideas for the prevention and treatment of AS in clinical practice.

Sestrin2: multifaceted functions, molecular basis, and its implications in liver diseases

Sestrin2 (SESN2), a highly conserved stress-responsive protein, can be triggered by various noxious stimuli, such as hypoxia, DNA damage, oxidative stress, endoplasmic reticulum (ER) stress, and inflammation. Multiple transcription factors regulate SESN2 expression, including hypoxia-inducible factor 1 (HIF-1), p53, nuclear factor E2-related factor 2 (Nrf2), activating transcription factor 4 (ATF4), ATF6, etc. Upon induction, SESN2 generally leads to activation of adenosine monophosphate-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin complex 1 (mTORC1). To maintain cellular homeostasis, SESN2 and its downstream molecules directly scavenge reactive oxygen species or indirectly influence the expression patterns of key genes associated with redox, macroautophagy, mitophagy, ER stress, apoptosis, protein synthesis, and inflammation. In liver diseases including acute liver injury, fatty liver diseases, hepatic fibrosis, and hepatocellular carcinoma (HCC), SESN2 is abnormally expressed and correlated with disease progression. In NAFLD, SESN2 helps with postponing disease progression through balancing glycolipid metabolism and macroautophagy (lipophagy), and rectifying oxidative damage and ER stress. During hepatic fibrosis, SESN2 represses HSCs activation and intrahepatic inflammation, hindering the occurrence and progress of fibrogenesis. However, the role of SESN2 in HCC is controversial due to its paradoxical pro-autophagic and anti-apoptotic effects. In conclusion, this review summarizes the biological functions of SESN2 in hypoxia, genotoxic stress, oxidative stress, ER stress, and inflammation, and specifically emphasizes the pathophysiological significance of SESN2 in liver diseases, aiming to providing a comprehensive understanding for SESN2 as a potential therapeutic target in liver diseases.

The association between serum Sestrin2 and the risk of coronary heart disease in patients with type 2 diabetes mellitus

Background

Coronary heart disease (CHD) is one of the most common causes of morbidity and mortality in type 2 diabetes mellitus (T2DM). Oxidative stress is one of the important contributors to the pathogenesis of CHD. Sestrin2 is a stress-induced antioxidant protein that plays a important role in T2DM and CHD. However, the relationship between serum Sestrin2 levels and T2DM with CHD remains unclear.

Aim

This study aimed to investigate the relationship between serum Sestrin2 levels and CHD in patients with type 2 diabetes.

Methods

A total of 70 T2DM patients with CHD and 69 T2DM patients were enrolled in this study. Clinical features and metabolic indices were identified. Serum Sestrin2 was measured by ELISA.

Results

Serum Sestrin2 levels in T2DM-CHD groups were significantly lower compared with the T2DM group (11.17 (9.79, 13.14) ng/mL vs 9.46 (8.34, 10.91) ng/mL). Bivariate correlation analysis revealed that serum Sestrin2 levels were negatively correlated with age (r = − 0.256, P = 0.002), BMI (r = − 0.206, P = 0.015), FBG (r = − 0.261, P = 0.002) and Tyg index (r = − 0.207, P < 0.014). Binary logistic regression suggested that low serum Sestrin2 levels were related to the increased risk of T2DM-CHD (P < 0.05). In addition, the receiver operating characteristic analysis revealed that the area under the curve of Sestrin2 was 0.724 (95% CI 0.641–0.808, P < 0.001) to predict T2DM-CHD patients (P < 0.001).

Conclusion

The Sestrin2 levels were highly associated with CHD in diabetes patients. Serum Sestrin2 may be involved in the occurrence and development of diabetic with CHD.

Specific amino acids regulate Sestrin2 mRNA and protein levels in an ATF4-dependent manner in C2C12 myocytes

BACKGROUND

Sestrin2 is a conserved protein in several species, and its expression is upregulated in cells under various environmental stresses. Sestrin2 content is involved in the function of mechanistic target of rapamycin complex 1 (mTORC1) in mouse embryonic fibroblasts and C2C12 cells.

METHODS

C2C12 cells were treated with amino acid-free DMEM (AF-DMEM) for 5 h. The effects of the addition of specific amino acids to AF-DMEM on Sestrin2 mRNA and protein expression were examined using RT-qPCR and western blotting, respectively. The mechanism by which amino acids regulate Sestrin2 mRNA expression was examined using blocking and siRNA experiments.

RESULTS

AF-DMEM increased the mRNA and protein levels of both Sestrin2 and activating transcription factor 4 (ATF4). The addition of a specific amino acid changed Sestrin2 mRNA and protein levels. The response pattern of Sestrin2 to specific amino acids was similar to that of ATF4. ATF4 siRNA reduced Sestrin2 mRNA levels. AF-DMEM increased eukaryotic initiation factor 2α (eIF2α) phosphorylation as early as 10 min after the treatment; however, ATF4 and Sestrin2 were increased 300 min after the treatment. Nuclear factor erythroid 2-related factor 2 and pancreatic and duodenal homeobox 1 siRNA did not affect ATF4 and Sestrin2 mRNA expression.

CONCLUSIONS

Specific Amino acids regulate Sestrin2 levels in an ATF4-dependent manner in C2C12 cells.

GENERAL SIGNIFICANCE

The results of the present study indicate that amino acids regulate levels of Sestrin2, which might cause phenotypic alterations, including mTORC1 activity, in C2C12 cells.

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.

Regulatory Effects of Quercetin on M1/M2 Macrophage Polarization and Oxidative/Antioxidative Balance

Macrophage polarization plays essential and diverse roles in most diseases, such as atherosclerosis, adipose tissue inflammation, and insulin resistance. Homeostasis dysfunction in M1/M2 macrophage polarization causes pathological conditions and inflammation. Neuroinflammation is characterized by microglial activation and the concomitant production of pro-inflammatory cytokines, leading to numerous neurodegenerative diseases and psychiatric disorders. Decreased neuroinflammation can be obtained by using natural compounds, including flavonoids, which are known to ameliorate inflammatory responses. Among flavonoids, quercetin possesses multiple pharmacological applications and regulates several biological activities. In the present study, we found that quercetin effectively inhibited the expression of lipocalin-2 in both macrophages and microglial cells stimulated by lipopolysaccharides (LPS). The production of nitric oxide (NO) and expression levels of the pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, were also attenuated by quercetin treatment. Our results also showed that quercetin significantly reduced the expression levels of the M1 markers, such as interleukin (IL)-6, tumor necrosis factor (TNF)-α, and IL-1β, in the macrophages and microglia. The M1 polarization-associated chemokines, C–C motif chemokine ligand (CCL)-2 and C-X-C motif chemokine ligand (CXCL)-10, were also effectively reduced by the quercetin treatment. In addition, quercetin markedly reduced the production of various reactive oxygen species (ROS) in the microglia. The microglial phagocytic ability induced by the LPS was also effectively reduced by the quercetin treatment. Importantly, the quercetin increased the expression levels of the M2 marker, IL-10, and the endogenous antioxidants, heme oxygenase (HO)-1, glutamate-cysteine ligase catalytic subunit (GCLC), glutamate-cysteine ligase modifier subunit (GCLM), and NAD(P)H quinone oxidoreductase-1 (NQO1). The enhancement of the M2 markers and endogenous antioxidants by quercetin was activated by the AMP-activated protein kinase (AMPK) and Akt signaling pathways. Together, our study reported that the quercetin inhibited the effects of M1 polarization, including neuroinflammatory responses, ROS production, and phagocytosis. Moreover, the quercetin enhanced the M2 macrophage polarization and endogenous antioxidant expression in both macrophages and microglia. Our findings provide valuable information that quercetin may act as a potential drug for the treatment of diseases related to inflammatory disorders in the central nervous system.

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.

Aerobic exercise inhibits inflammatory response in atherosclerosis via Sestrin1 protein

Aerobic exercise plays an important role in prevention and treatment of atherosclerosis. Inflammatory response is the main pathological process during occurrence and development stage of atherosclerosis. SESNs are considered as anti-inflammation protein in atherosclerosis. In current study, a high expression level of SESN1 is identified under the condition of aerobic exercise, further investigation shows levels of IL-1β/IL-6/TNF-α are significantly suppressed compared to those atherosclerosis mice with no aerobic training. Besides, we find that the activation of NF-κB signaling is impeded. Combine with our previous study, SESN1 is considered as the downstream factor of aerobic exercise which tend to inhibit the activation of inflammatory signaling and results in suppressing the expression level of inflammatory factors. Another exciting finding is that MMP9/13 are also suppressed，but the potential mechanism is unclear. Overall, present study sheds light on the significance of aerobic exercise for inflammation and stability of plaque through SESN1 may help developing new clinical treatments of atherosclerosis.

Potential Roles of Sestrin2 in Alzheimer's Disease: Antioxidation, Autophagy Promotion, and Beyond

Alzheimer’s disease (AD) is the most common age-related neurodegenerative disease. It presents with progressive memory loss, worsens cognitive functions to the point of disability, and causes heavy socioeconomic burdens to patients, their families, and society as a whole. The underlying pathogenic mechanisms of AD are complex and may involve excitotoxicity, excessive generation of reactive oxygen species (ROS), aberrant cell cycle reentry, impaired mitochondrial function, and DNA damage. Up to now, there is no effective treatment available for AD, and it is therefore urgent to develop an effective therapeutic regimen for this devastating disease. Sestrin2, belonging to the sestrin family, can counteract oxidative stress, reduce activity of the mammalian/mechanistic target of rapamycin (mTOR), and improve cell survival. It may therefore play a crucial role in neurodegenerative diseases like AD. However, only limited studies of sestrin2 and AD have been conducted up to now. In this article, we discuss current experimental evidence to demonstrate the potential roles of sestrin2 in treating neurodegenerative diseases, focusing specifically on AD. Strategies for augmenting sestrin2 expression may strengthen neurons, adapting them to stressful conditions through counteracting oxidative stress, and may also adjust the autophagy process, these two effects together conferring neuronal resistance in cases of AD.

Sestrin2 in hypoxia and hypoxia-related diseases

Objectives: Sestrin2 is a stress-inducible protein and play an important role in adapting stress states of cells. This article reviewed the role of Sestrin2 in hypoxia and hypoxia-related diseases to provide new perspectives for future research and new therapeutic targets for hypoxia-related diseases.

Methods: A review was conducted through an electronic search of PubMed and Medline databases. Keywords included Sestrin2, ROS, hypoxia, and hypoxia-related disease. Articles from 2008 to 2021 were mostly included and older ones were not excluded.

Results: Sestrin2 is upregulated under various stress conditions, especially hypoxia. Under hypoxic condition, Sestrin2 plays a protective role by reducing the generation of ROS through various pathways, such as adenosine monophosphatea-ctivated protein kinase (AMPK) / mammalian target of rapamycin (mTOR) pathway and nuclear factor-E2-related factor2 (Nrf2) pathway. In addition, Sestrin2 is involved in various hypoxia-related diseases, such as cerebral hypoxic disease, myocardial hypoxic disease, hypoxia-related respiratory disease, and diabetes.

Discussion: Sestrin2 is involved in various hypoxia-related diseases and maybe a therapeutic target. Furthermore, most studies focus on cerebral and myocardial ischemia reperfusion. More researches on hypoxia-related respiratory diseases, kidney injury, and diabetes are needed in future.

The p53/NF-kappaB-dependent induction of sestrin2 by amyloid-beta peptides exerts antioxidative actions in neurons

Accumulation of senile plaques mainly composed of neurotoxic amyloid-beta peptide (Aβ) is a pathological hallmark of Alzheimer's disease (AD). Sestrin2 inducible by various types of stressors is known to promote autophagy and exert antioxidative effects. In this work, we revealed the molecular mechanisms underlying Aβ induction of sestrin2 and tested whether antioxidation, in addition to autophagy regulation, also contributes to its neuroprotective effects in primary rat cortical neurons. We found that Aβ25-35 triggered nuclear translocation of p65 and p50, two subunits of nuclear factor-kappaB (NF-κB), and p53. Aβ25-35-induced sestrin2 expression was abolished by the p65 siRNA, the NF-κB inhibitor SN50, and the p53 inhibitor pifithrin-alpha (PFT-α). Further, Aβ25-35 enhanced binding of p50 and p53 to sestrin2 gene promoter that was abolished respectively by the p50 shRNA and PFT-α. Both p50 shRNA and PFT-α attenuated Aβ25-35-induced expression as well as nuclear translocation of all three transcription factors, namely p65, p50, and p53. Interestingly, p50 binding to the promoters of its target genes required p53 activity, whereas p50 also negatively regulated p53 binding to its target sequences. Suppression of sestrin2 expression by siRNA enhanced Aβ25-35- and Aβ1-42-induced production of reactive oxygen species (ROS), lipid peroxidation, and formation of 8-hydroxy-2-deoxyguanosine (8-OH-dG). In contrast, overexpression of the sestrin2 N-terminal or C-terminal fragments neutralized Aβ25-35-induced ROS production. We concluded that Aβ-induced sestrin2 contributing to antioxidant effects in neurons is in part mediated by p53 and NF-κB, which also mutually affect the expression of each other.

Sestrin2 is an endogenous antioxidant that improves contractile function in the heart during exposure to ischemia and reperfusion stress

Sestrin2 (Sesn2) is a stress-inducible protein that plays a critical role in the response to ischemic stress. We recently recognized that Sesn2 may protect the heart against ischemic insults by reducing the generation of reactive oxygen species (ROS). After 45 min of ischemia followed by 24 h of reperfusion, myocardial infarcts were significantly larger in Sesn2 KO hearts than in wild-type hearts. Isolated cardiomyocytes from wild-type hearts treated with hypoxia and reoxygenation (H/R) stress showed significantly greater Sesn2 levels, compared with normoxic hearts (p < 0.05). Intriguingly, the administration of adeno-associated virus 9-Sesn2 into Sesn2 knockout (KO) hearts rescued Sesn2 protein levels and significantly improved the cardiac function of Sesn2 KO mice exposed to ischemia and reperfusion. The rescued levels of Sesn2 in Sesn2 KO hearts significantly ameliorated ROS generation and the activation of ROS-related stress signaling pathways during ischemia and reperfusion. Moreover, the rescued Sesn2 levels in Sesn2 KO cardiomyocytes improved the maximal velocity of cardiomyocyte shortening by H/R stress. Rescued Sesn2 levels also improved peak height, peak shortening amplitude, and maximal velocity of the re-lengthening of Sesn2 KO cardiomyocytes subjected to H/R. Finally, the rescued Sesn2 levels significantly augmented intracellular calcium levels and reduced the mean time constant of transient calcium decay in Sesn2 KO cardiomyocytes exposed to H/R. Overall, these findings indicated that Sesn2 can act as an endogenous antioxidant to maintain intracellular redox homeostasis under ischemic stress conditions.

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.

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.

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.

Sestrin 2 controls the cardiovascular aging process via an integrated network of signaling pathways

As an inevitable biological process, cardiovascular aging is the greatest risk factor for cardiovascular diseases (CVDs). Sestrin 2 (Sesn2), a stress-inducible and age-related protein associated with various stress conditions, plays a pivotal role in slowing this process. It acts as an anti-aging agent, mainly through its antioxidant enzymatic activity and regulation of antioxidant signaling pathways, as well as by activating adenosine monophosphate-activated protein kinase and inhibiting mammalian target of rapamycin complex 1. In this review, we first introduce the biochemical functions of Sesn2 in the cardiovascular aging process, and describe how Sesn2 expression is regulated under various stress conditions. Next, we emphasize the role of Sesn2 signal transduction in a series of age-related CVDs, including hypertension, myocardial ischemia and reperfusion, atherosclerosis, and heart failure, as well as provide potential mechanisms for the association of Sesn2 with CVDs. Finally, we present the potential therapeutic applications of Sesn2-directed therapy and future prospects.

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 as a potential therapeutic target for cardiovascular diseases

Sestrin2 is a cysteine sulfinyl reductase that plays crucial roles in regulation of antioxidant actions. Sestrin2 provides cytoprotection against multiple stress conditions, including hypoxia, endoplasmic reticulum (ER) stress and oxidative stress. Recent research reveals that upregulation of Sestrin2 is induced by various transcription factors such as p53 and activator protein 1 (AP-1), which further promotes AMP-activated protein kinase (AMPK) activation and inhibits mammalian target of rapamycin protein kinase (mTOR) signaling. Sestrin2 triggers autophagy activity to reduce cellular reactive oxygen species (ROS) levels by promoting nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) activation and Kelch-like ECH-associated protein 1 (Keap1) degradation, which plays a pivotal role in homeostasis of metabolic regulation. Under hypoxia and ER stress conditions, elevated Sestrin2 expression maintains cellular homeostasis through regulation of antioxidant genes. Sestrin2 is responsible for diminishing cellular ROS accumulation through autophagy via AMPK activation, which displays cardioprotection effect in cardiovascular diseases. In this review, we summarize the recent understanding of molecular structure, biological roles and biochemical functions of Sestrin2, and discuss the roles and mechanisms of Sestrin2 in autophagy, hypoxia and ER stress. Understanding the precise functions and exact mechanism of Sestrin2 in cellular homeostasis will provide the evidence for future experimental research and aid in the development of novel therapeutic strategies for cardiovascular diseases.

Sestrin2 Mediates IL-4-induced IgE Class Switching by Enhancing Germline ε Transcription in B Cells

Sestrin2 (Sesn2), a metabolic regulator, accumulates in response to a diverse array of cellular stresses. Sesn2 regulates cellular metabolism by inhibiting the mammalian target of rapamycin complex 1 through the AMP-activated protein kinase (AMPK) signaling pathway. Recently, researchers reported that Sesn2 regulates the differentiation and function of innate immune cells and T cells; however, the role of Sesn2 in B cells is largely unknown. In this study, we investigated the role of Sesn2 in Ig class switching and Ig production in mouse B cells. We observed that mouse B cells express Sesn2 mRNA. Interestingly, the expression of germline ε transcripts (GLTε) was selectively decreased in lipopolysaccharide-stimulated Sesn2^−/− splenocytes. Overexpression of Sesn2 increased GLTε promoter activity in B cells. In addition, AICAR (an activator of AMPK) selectively increased IL-4-induced GLTε expression and surface IgE (sIgE) expression in splenocytes. Furthermore, AICAR selectively enhanced IL-4-induced GLTε expression, sIgE expression, and IgE production by anti-CD40-stimulated B cells. We observed that ovalbumin (OVA)-specific IgE concentration was reduced in OVA-challenged Sesn2^−/− mice. Taken together, these results indicate that Sesn2-AMPK signaling selectively enhances IL-4-induced IgE class switching and IgE production by B cells, suggesting that this could be a therapeutic strategy targeting Sesn2 in IgE-mediated allergic diseases.

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.

The regulatory role of HIF-1 in tubular epithelial cells in response to kidney injury

The high sensitivity to changes in oxygen tension makes kidney vulnerable to hypoxia. Both acute kidney injury and chronic kidney disease are almost always accompanied by hypoxia. Tubular epithelial cells (TECs), the dominant intrinsic cells in kidney tissue, are believed to be not only a victim in the pathological process of various kidney diseases, but also a major contributor to kidney damage. Hypoxia inducible factor-1 (HIF-1) is the main regulator of adaptive response of cells to hypoxia. Under various clinical and experimental kidney disease conditions, HIF-1 plays a pivotal role in modulating multiple cellular processes in TECs, including apoptosis, autophagy, inflammation, metabolic pattern alteration, and cell cycle arrest. A comprehensive understanding of the mechanisms by which HIF-1 regulates these cellular processes in TECs may help identify potential therapeutic targets to improve the outcome of acute kidney injury and delay the progression of chronic kidney disease.

Sestrin2 is involved in asthma: a case-control study

Background

Asthma is a chronic disease that seriously harms the health of patients. Oxidative stress is involved in asthma. As an oxidative stress-inducible protein, sestrin2 is elevated in oxidative stress-related diseases. We aimed to explore whether sestrin2 was involved in asthma.

Methods

Seventy-six subjects (44 in the asthma group, 32 in the control group) were recruited in this study. Plasma sestrin2 levels, peak expiratory flow (PEF), forced expiratory volume in 1 s (FEV₁) % predicted, forced vital capacity (FVC) % predicted and FEV₁/FVC ratio were measured in controls and in asthmatics both during an exacerbation and when controlled after the exacerbation.

Results

The asthma group had a significant higher sestrin2 level than the control group (asthmatics during exacerbation, 1.75 ± 0.53 ng/mL vs. 1.32 ± 0.48 ng/mL, p < 0.001; asthmatics when controlled after the exacerbation, 1.56 ± 0.46 ng/mL vs. 1.32 ± 0.48 ng/mL, p = 0.021, respectively). In addition, sestrin2 was negatively correlated with FEV₁% predicted and FEV₁/FVC ratio in asthmatics during exacerbation (r = − 0.393, p = 0.008; r = − 0.379, p = 0.011; respectively). Moreover, negative correlations between sestrin2 and FEV₁% predicted and FEV₁/FVC ratio also existed in asthmatics when controlled after the exacerbation (r = − 0.543, p < 0.001; r = − 0.433, p = 0.003 respectively). More importantly, multiple linear regression analysis demonstrated that FEV₁% predicted was independently associated with sestrin2 in asthmatics both during exacerbation and when controlled after the exacerbation.

Conclusions

Sestrin2 is involved in asthma. Sestrin2 levels increase in asthmatics both during exacerbation and when controlled after the exacerbation. In addition, sestrin2 is independently associated with FEV₁% predicted.

Macrophage-Driven Biomaterial Degradation Depends on Scaffold Microarchitecture

In situ tissue engineering is a technology in which non-cellular biomaterial scaffolds are implanted in order to induce local regeneration of replaced or damaged tissues. Degradable synthetic electrospun scaffolds are a versatile and promising class of biomaterials for various in situ tissue engineering applications, such as cardiovascular replacements. Functional in situ tissue regeneration depends on the balance between endogenous neo-tissue formation and scaffold degradation. Both these processes are driven by macrophages. Upon invasion into a scaffold, macrophages secrete reactive oxygen species (ROS) and hydrolytic enzymes, contributing to oxidative and enzymatic biomaterial degradation, respectively. This study aims to elucidate the effect of scaffold microarchitecture, i.e., μm-range fiber diameter and fiber alignment, on early macrophage-driven scaffold degradation. Electrospun poly-ε-caprolactone-bisurea (PCL-BU) scaffolds with either 2 or 6 μm (Ø) isotropic or anisotropic fibers were seeded with THP-1 derived human macrophages and cultured in vitro for 4 or 8 days. Our results revealed that macroph age-induced oxidative degradation in particular was dependent on scaffold microarchitecture, with the highest level of ROS-induced lipid peroxidation, NADPH oxidase gene expression and degradation in the 6 μm Ø anisotropic group. Whereas, biochemically polarized macrophages demonstrated a phenotype-specific degradative potential, the observed differences in macrophage degradative potential instigated by the scaffold microarchitecture could not be attributed to either distinct M1 or M2 polarization. This suggests that the scaffold microarchitecture uniquely affects macrophage-driven degradation. These findings emphasize the importance of considering the scaffold microarchitecture in the design of scaffolds for in situ tissue engineering applications and the tailoring of degradation kinetics thereof.

Investigation of Urinary Sestrin2 in Patients with Obstructive Sleep Apnea

Background

Obstructive sleep apnea (OSA) is a disease seriously threatening individual health, which results in serious complications such as hypertension and stroke. These complications are associated with oxidative stress triggered by intermittent hypoxia in OSA. Sestrin2 is a crucial factor involved in oxidative stress. The goal of this study was to investigate if a relationship exists between OSA and Sestrin2.

Methods

We prospectively enrolled 71 subjects, and 16 patients of them with severe OSA completed 4 weeks of nasal continuous positive airway pressure (nCPAP) therapy. We measured and compared the concentration of Sestrin2 in the urine of all subjects, as well as the changes between before and after nCPAP treatment. Additionally, the correlation between Sestrin2 and sleep parameters was analyzed, and the multiple linear regression analysis with stepwise selection was performed to explore the relationship between Sestrin2 and various factors.

Results

A total of 71 subjects were enrolled and divided into two groups: OSA group (n = 41), control group (n = 30). The level of urinary Sestrin2 in OSA patients was significantly higher than that of the control group, and increased with the severity of OSA, while it reduced after nCPAP treatment. Additionally, Sestrin2 was positively correlated with apnea/hypopnea index (AHI), oxygen desaturation index, oxygen saturation < 90% percentage of recording time spent (PRTS) and high-density lipoprotein (HDL), while negatively correlated with the lowest oxygen saturation. Importantly, Sestrin2 was independently associated with AHI, oxygen saturation < 90% PRTS and HDL.

Conclusions

Urinary Sestrin2 is involved in OSA, and is a paramount marker of OSA severity.

Responses of the Differentiated Intestinal Epithelial Cell Line Caco-2 to Infection With the Giardia intestinalis GS Isolate

Giardia intestinalis is a parasitic protist that causes diarrhea in humans, affecting mainly children of the developing world, elderly and immunocompromised individuals. Humans are infected by two major Giardia assemblages (i.e. genetic subtypes), A and B, with the latter being the most common. So far, there is little information on molecular or cellular changes during infections with assemblage B. Here, we used RNA sequencing to study transcriptional changes in Caco-2 intestinal epithelial cells (IECs) co-incubated with assemblage B (GS isolate) trophozoites for 1.5, 3, and 4.5 h. We aimed to identify early molecular events associated with the establishment of infection and followed cellular protein changes up to 10 h. IEC transcriptomes showed a dominance of immediate early response genes which was sustained across all time points. Transcription of inflammatory cytokines (e.g., cxcl1-3, ccl2, 1l1a, and il1b) peaked at 1.5 and 3 h of infection. Compared to co-incubation with assemblage A Giardia, we identified the induction of novel cytokines (cxcl8, cxcl10, csf1, cx3cl1, il12a, il11) and showed that inflammatory signaling is mediated by Erk1/2 phosphorylation (mitogen activated protein kinase, MAPK), nuclear factor kappa B (NFκB) and adaptor protein-1 (AP-1). We also showed that GS trophozoites attenuate P38 (MAPK) phosphorylation in IECs. Low amounts of IL-8, CXCL1 and CCL20 proteins were measured in the interaction medium, which was attributed to cytokine degradation by trophozoite secreted proteases. Based on the transcriptome, the decay of cytokines mRNA mediated by zinc finger protein 36 might be another mechanism controlling cytokine levels at later time points. IEC transcriptomes suggested homeostatic responses to counter oxidative stress, glucose starvation, and disturbances in amino acid and lipid metabolism. A large group of differentially transcribed genes were associated with cell cycle arrest and induction of apoptosis, which was validated at protein level. IEC transcriptomes also suggested changes in tight junction's integrity, microvilli structure and the extracellular mucin layer. This is the first study to illuminate transcriptional and protein regulatory events underlying IECs responses and pathogenesis during Giardia assemblage B infection. It highlights differences compared to assemblage A infections which might account for the differences observed in human infections with the two assemblages.

Sestrin2 prevents age-related intolerance to post myocardial infarction via AMPK/PGC-1α pathway

We have revealed that a novel stress-inducible protein, Sestrin2, declines in the heart with aging. Moreover, there is an interaction between Sestrin2 and energy sensor AMPK in the heart in response to ischemic stress. The objective of this study is to determine whether Sestrin2-AMPK complex modulates PGC-1α in the heart and protects the heart from ischemic insults. In order to characterize the role of cardiac Sestrin2-AMPK signaling cascade in aging, C57BL/6 wild type young mice (3-4months), aged mice (24-26months) and young Sestrin2 KO mice were subjected to left anterior descending coronary artery occlusion for in vivo regional ischemia. Intriguingly, ischemic AMPK activation was blunted in aged WT and young Sesn2 KO hearts as compared with young WT hearts. In addition, the AMPK downstream PGC-1α was down-regulated in the aged and Sestrin2 KO hearts during post myocardial infarction. To further determine the regulation of AMPK on mitochondrial functions in aging, the downstream of mitochondrial biogenesis PGC-1α transcriptional factor were measured. The results demonstrated that the PGC-1α downstream effectors TFAM and UCP2 were impaired in the aged and Sestrin2 KO post-MI hearts as compared to the young hearts. While the apoptotic flux markers such as AIF, Bax/Bcl-2 were up-regulated in both aged and Sestrin2 KO hearts versus young hearts. Furthermore, both Sestrin2 KO and aged hearts demonstrated more susceptible to ischemic insults as compared to young hearts. Additionally, the adeno-associated virus (AAV9)-Sestrin2 delivered to the aged hearts via a coronary delivery approach significantly rescued the ischemic tolerance of aged hearts. Taken together, the decreased Sestrin2 levels in aging lead to an impaired AMPK/PGC-1α signaling cascade and an increased sensitivity to ischemic insults.

Sestrin2 and sestrin3 suppress NK-92 cell-mediated cytotoxic activity on ovarian cancer cells through AMPK and mTORC1 signaling

Ovarian cancer is one of the major cancer types. NK-92 cell line, which has consistently and reproducibly high anti-tumor cytotoxicity, may be used for immunotherapy against ovarian cancer. Understanding the mechanisms that regulate the anti-tumor activity of NK-92 cells is important for developing novel therapeutic strategies. In the current study, using an ovarian cancer xenograft mouse model, we identified the up-regulation of sestrin2 (SESN2) and sestrin3 (SESN3) in intratumoral NK-92 cells. Lentivirus-transduced NK-92 cells, which overexpressed SESN2 or SESN3 after doxycycline treatment, exhibited less expression of activating receptors, perforin and granzyme B. Overexpression of SESN2 and SESN3 impaired tumoricidal effect of NK-92 cells both in vitro and in vivo. Furthermore, overexpression of SESN2 and SESN3 inhibited mTORC1 signaling while promoting AMPK signaling in NK-92 cells. Taken together, our data highlights the crucial effects of SESN2 and SESN3 on NK-92 cell-mediated anti-ovarian cancer activity. This study might be valuable for designing a novel therapeutic strategy for ovarian cancer.

Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism

A novel stress-inducible protein, Sestrin2 (Sesn2), declines in the heart with aging. AMPK has emerged as a pertinent stress-activated kinase that has been shown to have cardioprotective capabilities against myocardial ischemic injury. We identified the interaction between Sesn2 and AMPK in the ischemic heart. To determine whether ischemic AMPK activation-modulated by the Sesn2-AMPK complex in the heart-is impaired in aging that sensitizes the heart to ischemic insults, young C57BL/6 mice (age 3-4 mo), middle-aged mice (age 10-12 mo), and aged mice (age 24-26 mo) were subjected to left anterior descending coronary artery occlusion for in vivo regional ischemia. The ex vivo working heart system was used for measuring substrate metabolism. The protein level of Sesn2 in hearts was gradually decreased with aging. Of interest, ischemic AMPK activation was blunted in aged hearts compared with young hearts (P < 0.05); the AMPK downstream glucose uptake and the rate of glucose oxidation were significantly impaired in aged hearts during ischemia and reperfusion (P < 0.05 vs. young hearts). Myocardial infarction size was larger in aged hearts (P < 0.05 vs. young hearts). Immunoprecipitation with Sesn2 Ab revealed that cardiac Sesn2 forms a complex with AMPK and upstream liver kinase B1 (LKB1) during ischemia. Of interest, the binding affinity between Sesn2 and AMPK upstream LKB1 is impaired in aged hearts during ischemia (P < 0.05 vs. young hearts). Furthermore, Sesn2-knockout hearts demonstrate a cardiac phenotype and response to ischemic stress that is similar to wild-type aged hearts (i.e., impaired ischemic AMPK activation and higher sensitivity to ischemia- and reperfusion- induced injury). Adeno-associated virus-Sesn2 was delivered to aged hearts via a coronary delivery approach and significantly rescued the protein level of Sesn2 and the ischemic tolerance of aged hearts; therefore, Sesn2 is a scaffold protein that mediates AMPK activation in the ischemic myocardium via an interaction with AMPK upstream LKB1. Decreased Sesn2 levels in aging lead to a blunted ischemic AMPK activation, alterations in substrate metabolism, and an increased sensitivity to ischemic insults-Quan, N., Sun, W., Wang, L., Chen, X., Bogan, J. S., Zhou, X., Cates, C., Liu, Q., Zheng, Y., Li J. Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism.

Sestrin2 Suppresses Classically Activated Macrophages-Mediated Inflammatory Response in Myocardial Infarction through Inhibition of mTORC1 Signaling

Myocardial infarction (MI) triggers an intense inflammatory response that is essential for dead tissue clearance but also detrimental to cardiac repair. Macrophages are active and critical players in the inflammatory response after MI. Understanding the molecular mechanisms by which macrophage-mediated inflammatory response is regulated is important for designing new therapeutic interventions for MI. In the current study, we examined the role of Sestrin2, which is a stress-inducible protein that regulate metabolic homeostasis, in the regulation of inflammatory response of cardiac macrophages after MI. We found that cardiac macrophages upregulated Sestrin2 expression in a mouse MI model. Using a lentiviral transduction system to overexpress Sestrin2 in polarized M1 and M2 macrophages, we revealed that Sestrin2 predominantly functioned on M1 rather than M2 macrophages. Sestrin2 overexpression suppressed inflammatory response of M1 macrophages both in vitro and in vivo. Furthermore, in the mouse MI model with selective depletion of endogenous macrophages and adoptive transfer of exogenous Sestrin2-overexpressing macrophages, the anti-inflammatory and repair-promoting effect of Sestrin2-overexpressing macrophages was demonstrated. Furthermore, Sestrin2 significantly inhibited mTORC1 signaling in M1 macrophages. Taken together, our study indicates the importance of Sestrin2 for suppression of M1 macrophage-mediated cardiac inflammation after MI.

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.

Mitochondrial AKAP1 supports mTOR pathway and tumor growth

Mitochondria are the powerhouses of energy production and the sites where metabolic pathway and survival signals integrate and focus, promoting adaptive responses to hormone stimulation and nutrient availability. Increasing evidence suggests that mitochondrial bioenergetics, metabolism and signaling are linked to tumorigenesis. AKAP1 scaffolding protein integrates cAMP and src signaling on mitochondria, regulating organelle biogenesis, oxidative metabolism and cell survival. Here, we provide evidence that AKAP1 is a transcriptional target of Myc and supports the growth of cancer cells. We identify Sestrin2, a leucine sensor and inhibitor of the mammalian target of rapamycin (mTOR), as a novel component of the complex assembled by AKAP1 on mitochondria. Downregulation of AKAP1 impaired mTOR pathway and inhibited glioblastoma growth. Both effects were reversed by concomitant depletion of AKAP1 and sestrin2. High levels of AKAP1 were found in a wide variety of high-grade cancer tissues. In lung cancer, AKAP1 expression correlates with high levels of Myc, mTOR phosphorylation and reduced patient survival. Collectively, these data disclose a previously unrecognized role of AKAP1 in mTOR pathway regulation and cancer growth. AKAP1/mTOR signal integration on mitochondria may provide a new target for cancer therapy.

More Insight into BDNF against Neurodegeneration: Anti-Apoptosis, Anti-Oxidation, and Suppression of Autophagy

In addition to its well-established neurotrophic action, brain-derived neurotrophic factor (BDNF) also possesses other neuroprotective effects including anti-apoptosis, anti-oxidation, and suppression of autophagy. We have shown before that BDNF triggers multiple mechanisms to confer neuronal resistance against 3-nitropropionic acid (3-NP)-induced mitochondrial dysfunction in primary rat cortical cultures. The beneficial effects of BDNF involve the induction of anti-oxidative thioredoxin with the resultant expression of anti-apoptotic B-cell lymphoma 2 (Bcl-2) as well as erythropoietin (EPO)-dependent stimulation of sonic hedgehog (SHH). We further revealed that BDNF may bring the expression of sulfiredoxin, an ATP-dependent antioxidant enzyme, to offset mitochondrial inhibition in cortical neurons. Recently, we provided insights into another novel anti-oxidative mechanism of BDNF, which involves the augmentation of sestrin2 expression to endow neuronal resistance against oxidative stress induced by 3-NP; BDNF induction of sestrin2 entails the activation of a pathway involving nitric oxide (NO), cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG), and nuclear factor-κB (NF-κB). Apart from anti-apoptosis and anti-oxidation, we demonstrated in our most recent study that BDNF may activate the mammalian target of rapamycin (mTOR) with resultant activation of transcription factor c-Jun, thereby stimulating the expression of p62/sequestosome-1 to suppress heightened autophagy as a result of 3-NP exposure. Together, our results provide in-depth insight into multi-faceted protective mechanisms of BDNF against mitochondrial dysfunction commonly associated with the pathogenesis of many chronic neurodegenerative disorders. Delineation of the protective signaling pathways elicited by BDNF would endow a rationale to develop novel therapeutic regimens to halt or prevent the progression of neurodegeneration.

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.

Biochemical Basis of Sestrin Physiological Activities

Excessive accumulation of reactive oxygen species (ROS) and chronic activation of mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) are well-characterized promoters of aging and age-associated degenerative pathologies. Sestrins, a family of highly conserved stress-inducible proteins, are important negative regulators of both ROS and mTORC1 signaling pathways; however, the mechanistic basis of how Sestrins suppress these pathways remains elusive. In the past couple of years, breakthrough discoveries about Sestrin signaling and its molecular nature have markedly increased our biochemical understanding of Sestrin function. These discoveries have also uncovered new potential therapeutic strategies that may eventually enable us to attenuate aging and age-associated diseases.

Sestrin2: A Promising Therapeutic Target for Liver Diseases

Sestrin2 (Sesn2), a highly conserved antioxidant protein, is induced by various stresses, including oxidative and energetic stress, and protects cells against those stresses. In normal physiological conditions, redox-homeostasis plays an essential role in cell survival and performs the cellular functions to protect the cells against oxidative damage. The liver is susceptible to oxidative stress, since it is responsible for xenobiotic detoxification and energy metabolism. For this reason, oxidative stress is associated with the pathogenesis of liver diseases. Recently, the role of Sesn2 has been investigated in liver injury and related diseases. In this paper, we review the role of Sesn2 in the pathophysiology of liver diseases and the potential clinical applications of Sesn2 as a therapeutic target to prevent/treat liver diseases. This article promotes our understanding of liver disease progression and advances the development of strategies for pharmacological intervention.

The Reactive Oxygen Species in Macrophage Polarization: Reflecting Its Dual Role in Progression and Treatment of Human Diseases

High heterogeneity of macrophage is associated with its functions in polarization to different functional phenotypes depending on environmental cues. Macrophages remain in balanced state in healthy subject and thus macrophage polarization may be crucial in determining the tissue fate. The two distinct populations, classically M1 and alternatively M2 activated, representing the opposing ends of the full activation spectrum, have been extensively studied for their associations with several disease progressions. Accumulating evidences have postulated that the redox signalling has implication in macrophage polarization and the key roles of M1 and M2 macrophages in tissue environment have provided the clue for the reasons of ROS abundance in certain phenotype. M1 macrophages majorly clearing the pathogens and ROS may be crucial for the regulation of M1 phenotype, whereas M2 macrophages resolve inflammation which favours oxidative metabolism. Therefore how ROS play its role in maintaining the homeostatic functions of macrophage and in particular macrophage polarization will be reviewed here. We also review the biology of macrophage polarization and the disturbance of M1/M2 balance in human diseases. The potential therapeutic opportunities targeting ROS will also be discussed, hoping to provide insights for development of target-specific delivery system or immunomodulatory antioxidant for the treatment of ROS-related diseases.

Janus-faced Sestrin2 controls ROS and mTOR signalling through two separate functional domains

Sestrins are stress-inducible metabolic regulators with two seemingly unrelated but physiologically important functions: reduction of reactive oxygen species (ROS) and inhibition of the mechanistic target of rapamycin complex 1 (mTORC1). How Sestrins fulfil this dual role has remained elusive so far. Here we report the crystal structure of human Sestrin2 (hSesn2), and show that hSesn2 is twofold pseudo-symmetric with two globular subdomains, which are structurally similar but functionally distinct from each other. While the N-terminal domain (Sesn-A) reduces alkylhydroperoxide radicals through its helix–turn–helix oxidoreductase motif, the C-terminal domain (Sesn-C) modified this motif to accommodate physical interaction with GATOR2 and subsequent inhibition of mTORC1. These findings clarify the molecular mechanism of how Sestrins can attenuate degenerative processes such as aging and diabetes by acting as a simultaneous inhibitor of ROS accumulation and mTORC1 activation.

Sestrins are conserved stress-inducible metabolic regulators implicated in the prevention of agerelated diseases. Here, Kim et al. report the crystal structure of human Sestrin2 and propose a molecular mechanism for how Sestrin2 functions to prevent ROS accumulation and inhibit mTORC1 activity.

Roles of Sestrin2 and Ribosomal Protein S6 in Transient Global Ischemia-Induced Hippocampal Neuronal Injury

Recent studies suggested that sestrin2 is a crucial modulator for the production of reactive oxygen species (ROS). In addition, sestrin2 may also regulate ribosomal protein S6 (RpS6), a molecule important for protein synthesis, through the effect of mammalian target of rapamycin (mTOR) complex that is pivotal for longevity. However, the roles of sestrin2 in cerebral ischemia, in which oxidative stress is one of the major pathogenic mechanisms, are still less understood. In this study, we hypothesized that sestrin2 may protect hippocampal CA1 neurons against transient global ischemia (TGI)-induced apoptosis by regulating RpS6 phosphorylation in rats. We found that sestrin2 expression was progressively increased in the hippocampal CA1 subfield 1–48 h after TGI, reaching the maximal level at 24 h, and declined thereafter. Further, an increased extent of RpS6 phosphorylation, but not total RpS6 protein level, was observed in the hippocampal CA1 subfield after TGI. The sestrin2 siRNA, which substantially blocked the expression of TGI-induced sestrin2, also abolished RpS6 phosphorylation. TGI with reperfusion may induce oxidative stress with the resultant formation of 8-hydroxy-deoxyguanosine (8-OHdG). We found that sestrin2 siRNA further augmented the formation of 8-OHdG induced by TGI with reperfusion for 4 h. Consistently, sestrin2 siRNA also enhanced apoptosis induced by TGI with reperfusion for 48 h based on the analysis of DNA fragmentation by agarose gel electrophoresis, DNA fragmentation sandwich ELISA, and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. Together these findings indicated that TGI-induced sestrin2 expression contributed to RpS6 phosphorylation and neuroprotection against ischemic injury in the hippocampal CA1 subfield.

Nuclear Factor-kappaB-Dependent Sestrin2 Induction Mediates the Antioxidant Effects of BDNF Against Mitochondrial Inhibition in Rat Cortical Neurons

Brain-derived neurotrophic factor (BDNF), in addition to its neurotrophic action, also possesses antioxidant activities. However, the underlying mechanisms remain to be fully defined. Sestrin2 is a stress-responsive gene implicated in the cellular defense against oxidative stress. Currently, the potential functions of sestrin2 in nervous system, in particular its correlation with neurotrophic factors, have not been well established. In this study, we hypothesized that BDNF may enhance sestrin2 expression to confer neuronal resistance against oxidative stress induced by 3-nitropropionic acid (3-NP), an irreversible mitochondrial complex II inhibitor, and characterized the molecular mechanisms underlying BDNF induction of sestrin2 in primary rat cortical cultures. We found that BDNF-mediated sestrin2 expression in cortical neurons required formation of nitric oxide (NO) with subsequent production of 3',5'-cyclic guanosine monophosphate (cGMP) and activation of cGMP-dependent protein kinase (PKG). BDNF induced localization of nuclear factor-kappaB (NF-κB) subunits p65 and p50 into neuronal nuclei that required PKG activities. Interestingly, BDNF exposure led to formation of a protein complex containing at least PKG-1 and p65/p50, which bound to sestrin2 promoter with resultant upregulation of its protein products. Finally, BDNF preconditioning mitigated production of reactive oxygen species (ROS) as a result of 3-NP exposure; this antioxidative effect of BDNF was dependent upon PKG activity, NF-κB, and sestrin2. Taken together, our results indicated that BDNF enhances sestrin2 expression to confer neuronal resistance against oxidative stress induced by 3-NP through attenuation of ROS formation; furthermore, BDNF induction of sestrin2 requires activation of a pathway involving NO/PKG/NF-κB.

Gossypol Acetic Acid Prevents Oxidative Stress-Induced Retinal Pigment Epithelial Necrosis by Regulating the FoxO3/Sestrin2 Pathway

The late stage of dry age-related macular degeneration (AMD), or geographic atrophy (GA), is characterized by extensive retinal pigment epithelial (RPE) cell death, and a cure is not available currently. We have recently demonstrated that RPE cells die from necrosis in response to oxidative stress, providing a potential novel mechanism for RPE death in AMD. In this study, we screened U.S. Food and Drug Administration-approved natural compounds and identified gossypol acetic acid (GAA) as a potent inhibitor of oxidative stress-induced RPE cell death. GAA induces antioxidative response and inhibits accumulation of excessive reactive oxygen species in cells, through which it prevents the activation of intrinsic necrotic pathway in response to oxidative stress. Sestrin2 (SESN2) is found to mediate GAA function in antioxidative response and RPE survival upon oxidative stress. Moreover, Forkhead box O3 transcription factor (FoxO3) is further found to be required for GAA-mediated SESN2 expression and RPE survival. Mechanistically, GAA promotes FoxO3 nuclear translocation and binding to the SESN2 enhancer, which in turn increases its transcriptional activity. Taken together, we have identified GAA as a potent inhibitor of oxidative stress-induced RPE necrosis by regulating the FoxO3/SESN2 pathway. This study may have significant implications in the therapeutics of age-related diseases, especially GA.