The essential role of FoxO6 phosphorylation in aging and calorie restriction

Mechanistic insights into the role of FOXO in diabetic retinopathy

Diabetes mellitus (DM), a metabolic disorder characterized by insulin-deficiency or insulin-resistant conditions. The foremost microvascular complication of diabetes is diabetic retinopathy (DR). This is a multifaceted ailment mainly caused by the enduring adverse effects of hyperglycaemia. Inflammation, oxidative stress, and advanced glycation products (AGES) are part and parcel of DR pathogenesis. In regulating many cellular and biological processes, the family of fork-head transcription factors plays a key role. The current review highlights that FOXO is a requisite regulator of pathways intricate in diabetic retinopathy on account of its effect on microvascular cells inflammatory and apoptotic gene expression, and FOXO also has the foremost province in regulating cell cycle, proliferation, apoptosis, and metabolism. Blockage of insulin turns into an exaggerated level of glucose in the bloodstream and can upshot into the exaggerated triggering of FOXO1, which can ultimately uplift the production of several factors of apoptosis and inflammation, such as TNF-α, NF-kB, and various others, as well as reactive oxygen species, which can also come up with diabetic retinopathy. The current review also focuses on various therapies which can be used in the future, like SIRT1 signalling, resveratrol, retinal VEGF, etc., which can be used to suppress FOXO over activation and can prevent the progression of diabetic complications viz. diabetic retinopathy.

FoxO transcription factors in mitochondrial homeostasis

Mitochondria play essential roles in cellular energetics, biosynthesis, and signaling transduction. Dysfunctional mitochondria have been implicated in different diseases such as obesity, diabetes, cardiovascular disease, nonalcoholic fatty liver disease, neurodegenerative disease, and cancer. Mitochondrial homeostasis is controlled by a triad of mitochondrial biogenesis, dynamics (fusion and fission), and autophagy (mitophagy). Studies have underscored FoxO transcription factors as key mitochondrial regulators. Specifically, FoxOs regulate mitochondrial biogenesis by dampening NRF1-Tfam and c-Myc-Tfam cascades directly, and inhibiting NAD-Sirt1-Pgc1α cascade indirectly by inducing Hmox1 or repressing Fxn and Urod. In addition, FoxOs mediate mitochondrial fusion (via Mfn1 and Mfn2) and fission (via Drp1, Fis1, and MIEF2), during which FoxOs elicit regulatory mechanisms at transcriptional, posttranscriptional (e.g. via miR-484/Fis1), and posttranslational (e.g. via Bnip3-calcineurin mediated Drp1 dephosphorylation) levels. Furthermore, FoxOs control mitochondrial autophagy in the stages of autophagosome formation and maturation (e.g. initiation, nucleation, and elongation), mitochondria connected to and engulfed by autophagosome (e.g. via PINK1 and Bnip3 pathways), and autophagosome-lysosome fusion to form autolysosome for cargo degradation (e.g. via Tfeb and cathepsin proteins). This article provides an up-to-date view of FoxOs regulating mitochondrial homeostasis and discusses the potential of targeting FoxOs for therapeutics.

Evaluating the beneficial effects of dietary restrictions: A framework for precision nutrigeroscience

Dietary restriction (DR) has long been viewed as the most robust nongenetic means to extend lifespan and healthspan. Many aging-associated mechanisms are nutrient responsive, but despite the ubiquitous functions of these pathways, the benefits of DR often vary among individuals and even among tissues within an individual, challenging the aging research field. Furthermore, it is often assumed that lifespan interventions like DR will also extend healthspan, which is thus often ignored in aging studies. In this review, we provide an overview of DR as an intervention and discuss the mechanisms by which it affects lifespan and various healthspan measures. We also review studies that demonstrate exceptions to the standing paradigm of DR being beneficial, thus raising new questions that future studies must address. We detail critical factors for the proposed field of precision nutrigeroscience, which would utilize individualized treatments and predict outcomes using biomarkers based on genotype, sex, tissue, and age.

Organ-differential Roles of Akt/FoxOs Axis as a Key Metabolic Modulator during Aging

FoxOs and their post-translational modification by phosphorylation, acetylation, and methylation can affect epigenetic modifications and promote the expression of downstream target genes. Therefore, they ultimately affect cellular and biological functions during aging or occurrence of age-related diseases including cancer, diabetes, and kidney diseases. As known for its key role in aging, FoxOs play various biological roles in the aging process by regulating reactive oxygen species, lipid accumulation, and inflammation. FoxOs regulated by PI3K/Akt pathway modulate the expression of various target genes encoding MnSOD, catalases, PPARγ, and IL-1β during aging, which are associated with age-related diseases. This review highlights the age-dependent differential regulatory mechanism of Akt/FoxOs axis in metabolic and non-metabolic organs. We demonstrated that age-dependent suppression of Akt increases the activity of FoxOs (Akt/FoxOs axis upregulation) in metabolic organs such as liver and muscle. This Akt/FoxOs axis could be modulated and reversed by antiaging paradigm calorie restriction (CR). In contrast, hyperinsulinemia-mediated PI3K/Akt activation inhibited FoxOs activity (Akt/FoxOs axis downregulation) leading to decrease of antioxidant genes expression in non-metabolic organs such as kidneys and lungs during aging. These phenomena are reversed by CR. The results of studies on the process of aging and CR indicate that the Akt/FoxOs axis plays a critical role in regulating metabolic homeostasis, redox stress, and inflammation in various organs during aging process. The benefical actions of CR on the Akt/FoxOs axis in metabolic and non-metabolic organs provide further insights into the molecular mechanisms of organ-differential roles of Akt/FoxOs axis during aging.

Protease-activated receptor 2 induces ROS-mediated inflammation through Akt-mediated NF-κB and FoxO6 modulation during skin photoaging

Long-term exposure to ultraviolet irradiation to skin leads to deleterious intracellular effects, including reactive oxygen species (ROS) production and inflammatory responses, causing accelerated skin aging. Previous studies have demonstrated that increased expression and activation of protease-activated receptor 2 (PAR2) and Akt is observed in keratinocyte proliferation, suggesting their potential regulatory role in skin photoaging. However, the specific underlying molecular mechanism of PAR2 and the Akt/NF-κB/FoxO6-mediated signaling pathway is not clearly defined. In this study, we first used the UVB-irradiated photoaged skin of hairless mice and observed an increase in PAR2 and Gαq expression and PI3-kinase/Akt, NF-κB, and suppressed FoxO6. Consequently, increased levels of proinflammatory cytokines and decreased levels of antioxidant MnSOD was observed. Next, to investigate PAR2-specific roles in inflammation and oxidative stress, we used photoaged hairless mice topically applied with PAR2 antagonist GB83 and photoaged PAR2 knockout mice. PAR2 inhibition and deletion significantly suppressed inflammatory and oxidative stress levels, which were associated with decreased IL-6 and IL-1β levels and increased MnSOD levels, respectively. Furthermore, NF-κB phosphorylation and decreased FoxO6 was reduced by PAR2 inhibition and deletion in vivo. To confirm the in vivo results, we conducted PAR2 knockdown and overexpression in UVB-irradiated HaCaT cells. In PAR2 knockdown cells by si-PAR2 treatment, it suppressed Akt/NF-κB and increased FoxO6, whereas PAR2 overexpression reversed these effects and subsequently modulated proinflammatory target genes. Collectively, our data define that PAR2 induces oxidative stress and inflammation through Akt-mediated phosphorylation of NF-κB (Ser536) and FoxO6 (Ser184), which could be a critical upstream regulatory mechanism in ROS-mediated inflammatory response.

Caloric restriction in heart failure: A systematic review

BACKGROUND AND AIMS

Nutrition exerts a determinant role in maintaining cardiac function, regulating insulin and mitochondrial efficiency, that are essential to support energy production for contractility. In patients with heart failure (HF), myocardial tissue efficiency is reduced because of decreased mitochondrial oxidative capacity. In HF conditions, cardiomyocytes shift toward glucose and a reduction in fatty acid utilization. Calorie restriction induces weight loss in obese patients and can be beneficial in some HF patients, although this has generated some controversy. This study aims to evaluate the impact of the CR diet on myocardial efficiency in HF patients.

METHODS

On Pubmed and Embase, articles related to the keywords: "chronic heart failure" with "diet," "nutrition," "insulin resistance," and "caloric restriction" have been searched, Studies, including exercise or food supplementation, were excluded.

RESULTS

The retrieved articles showed that weight loss, through the activation of insulin and various kinase pathways, regulates the efficiency of myocardial tissue. In contrast, insulin resistance represents a strong cardiovascular risk factor that reduces myocardial function.

CONCLUSION

CR diet represents the first therapy in overweight HF patients, both with preserved ejection fraction (HFpEF) and with reduced ejection fraction (HFrHF) because reducing body fat, the myocardial function increased. Insulin activity is the critical hormone that regulates mitochondrial function and cardiac efficiency. However, a severely restricted diet may represent a severe risk factor correlated with all-cause mortality, particularly in underweight HF patients. Long-term studies conducted on large populations are necessary to evaluate the effects of CR on myocardial function in HF patients.

FoxO6 inhibits melanogenesis partly by elevating intracellular antioxidant capacity

Of the various transcription factors that play a role in controlling oxidative stress, the role of FoxO proteins in skin aging has recently become of interest. Unlike other FoxOs, FoxO6 remains in the nucleus due to the lack of nuclear export signal, so that it may respond sensitively to intracellular stimuli for the induction of target genes. However, the role of FoxO6 in melanogenesis and its related signaling pathways are unclear. We used UV exposed and intrinsically aged mice that exhibited skin aging. Our data showed that FoxO6 activation was markedly decreased in the skin of aging mice and UVB-exposed hairless mice that exhibited an increase in melanogenesis. The reduced FoxO6 activity was closely associated with the elevation of oxidative stress in the skin of these animal models. To our interest, siRNA-mediated FoxO6 knockdown markedly increased melanin content and related signaling pathways in B16F10 cells even without any stimulation. On the contrary, adenovirus-mediated FoxO6 activation significantly reduced melanin content in UVB-exposed B16F10 cells, which is closely associated with the induction of antioxidant genes including MnSOD and catalase, leading to a decrease in oxidative stress. Furthermore, vitamin C treatment reversed the elevated melanogenesis by the FoxO6 knockdown, indicating that the decreased antioxidant capacity greatly contributes to increased melanogenesis in the FoxO6 knockdown condition. For the upstream of a FoxO6 signaling pathway in melanocytes, FoxO6 phosphorylation by Akt appears to be essential evidenced by the reduction of FoxO6 activity and the increase in melanogenesis by PI3K/AKT inhibitor treatment. Our study suggests that FoxO6 is an antioxidant gene that prevents oxidative stress-induced melanogenesis.

Signaling Network of Forkhead Family of Transcription Factors (FOXO) in Dietary Restriction

Dietary restriction (DR), which is defined as a reduction of particular or total nutrient intake without causing malnutrition, has been proved to be a robust way to extend both lifespan and health-span in various species from yeast to mammal. However, the molecular mechanisms by which DR confers benefits on longevity were not yet fully elucidated. The forkhead box O transcription factors (FOXOs), identified as downstream regulators of the insulin/IGF-1 signaling pathway, control the expression of many genes regulating crucial biological processes such as metabolic homeostasis, redox balance, stress response and cell viability and proliferation. The activity of FOXOs is also mediated by AMP-activated protein kinase (AMPK), sirtuins and the mammalian target of rapamycin (mTOR). Therefore, the FOXO-related pathways form a complex network critical for coordinating a response to environmental fluctuations in order to maintain cellular homeostasis and to support physiological aging. In this review, we will focus on the role of FOXOs in different DR interventions. As different DR regimens or calorie (energy) restriction mimetics (CRMs) can elicit both distinct and overlapped DR-related signaling pathways, the benefits of DR may be maximized by combining diverse forms of interventions. In addition, a better understanding of the precise role of FOXOs in different mechanistic aspects of DR response would provide clear cellular and molecular insights on DR-induced increase of lifespan and health-span.

Gestational caloric restriction improves redox homeostasis parameters in the brain of Wistar rats: a screening from birth to adulthood

Caloric restriction (CR) improves health and life span in animal models. Although CR effects in adult life are well described, little is known about effects on offspring when applied during gestation. Pregnancy is a remarkable period of life, alterations in this stage lead to lifelong consequences, some of which, associated to redox unbalance. Furthermore, gestational overweight is a growing issue that can lead to detrimental outcomes. To address this issue, we divided pregnant rats into control (ad libitum food) and CR groups, which received 20% less food than control. Micronutrients consumption was equalized between groups by oral gavage. Cerebellum, prefrontal cortex, hippocampus, and hypothalamus were evaluated on post-natal day (PND) 0, 7, 21, and 60. We observed increased oxidants content on PND0 in all brain structures, except for the cerebellum. Key enzymatic antioxidant defenses showed decreased activity on PND0. Interestingly, on PND60, we observed a positive modulation of most antioxidant enzymes, especially on the prefrontal cortex and hippocampus. Non-enzymatic antioxidant defenses were decreased at birth and increased during development and adult age. Lipid peroxidation was increased at birth on most structures, and the effect was abolished thereafter. In the prefrontal cortex, lipid peroxidation was unaltered at birth and diminished thereafter, while protein oxidation was increased on PND0 and decreased on PND60. Protein oxidation was also decreased in the cerebellum at adult age. Our results shown controlled gestational CR to improve antioxidant defenses and protect offspring's brain from oxidative stress, especially in adulthood, as a result of developmental metabolic programming.

Downregulation of FOXO6 in breast cancer promotes epithelial-mesenchymal transition and facilitates migration and proliferation of cancer cells

Purpose

Increasing evidence indicates that members of forkhead transcription factor family (FOXO) play key roles in cell proliferation and apoptosis in multiple cancers, including prostate cancer. However, the underlying mechanism of FOXO6 was not yet known. The aim of our work is to investigate the function of FOXO6 in breast cancer.

Methods

In the present study, quantitative real-time polymerase chain reaction and Western blotting analyses were used to detect the expression of FOXO6 in breast cancer tissues and cell lines.

Results

The results revealed that FOXO6 was downregulated in breast cancer tissues and cell lines, compared with adjacent normal tissues and MCF-10A cells, respectively. Moreover, the expression of FOXO6 was associated with the expression of epithelial–mesenchymal transition (EMT) indicator proteins, such as E-cadherin and N-cadherin. Additionally, our findings suggested that FOXO6 expression was negatively associated with tumor size (p=0.002), pathological grade (p=0.018) and lymph node metastasis (p=0.003). Sirt6 has been found to promote cell proliferation and metastasis in several cancers, and quantitative chromatin immunoprecipitation and luciferase reporter assays indicated FOXO6 transcriptionally regulated Sirt6 expression. Furthermore, various functional experiments, including wound healing assay, transwell invasion assay, colony formation assay and Cell Counting Kit-8 assay, revealed that FOXO6 suppressed cell migration, invasion, and proliferation of breast cancer cells.

Conclusion

In conclusion, FOXO6 serves as a tumor suppressor in breast cancer, and suppresses EMT through regulation of Sirt6.

Elevated FOXO6 expression correlates with progression and prognosis in gastric cancer

The FOXO6 correlated with tumor progression in a wide range of carcinomas, yet little is known in gastric cancer. The expression of FOXO6 and matrix metallopeptidase 9 (MMP-9) was assessed by immunohistochemistry in 192 gastric carcinoma specimens. The correlation between FOXO6 expression with MMP-9, clinicopathological/prognostic value in gastric cancer was examined. FOXO6 overexpression was significantly associated with depth of invasion, lymph node metastasis and stage of disease. In univariate and multivariate analyses, FOXO6 was an independent prognostic factor for both overall survival (OS) and recurrence-free survival (RFS). Moreover, FOXO6 over-expression was correlated with poor prognosis in patients subgroups stratified by tumor size, depth of invasion and lymph node metastasis. FOXO6 expression was increased in both prominent serosal invasion group and lymph node metastasis group. In addition, FOXO6 expression was positively correlated with MMP-9 among 192 gastric cancer tissues. Patients with FOXO6 over-expression had poor OS and shorter RFS in low and high invasiveness groups. Furthermore, stratified analysis showed that the TNM stage I patients with high FOXO6 expression had poor prognosis than those with low FOXO6 expression. In conclusion, FOXO6 overexpression promotes tumor aggressiveness and prognosis, and could be a promising target for prognostic prediction in gastric cancer patients.

Evidence that a mitochondrial death spiral underlies antagonistic pleiotropy

The antagonistic pleiotropy (AP) theory posits that aging occurs because alleles that are detrimental in older organisms are beneficial to growth early in life and thus are maintained in populations. Although genes of the insulin signaling pathway likely participate in AP, the insulin‐regulated cellular correlates of AP have not been identified. The mitochondrial quality control process called mitochondrial autophagy (mitophagy), which is inhibited by insulin signaling, might represent a cellular correlate of AP. In this view, rapidly growing cells are limited by ATP production; these cells thus actively inhibit mitophagy to maximize mitochondrial ATP production and compete successfully for scarce nutrients. This process maximizes early growth and reproduction, but by permitting the persistence of damaged mitochondria with mitochondrial DNA mutations, becomes detrimental in the longer term. I suggest that as mitochondrial ATP output drops, cells respond by further inhibiting mitophagy, leading to a further decrease in ATP output in a classic death spiral. I suggest that this increasing ATP deficit is communicated by progressive increases in mitochondrial ROS generation, which signals inhibition of mitophagy via ROS‐dependent activation of insulin signaling. This hypothesis clarifies a role for ROS in aging, explains why insulin signaling inhibits autophagy, and why cells become progressively more oxidized during aging with increased levels of insulin signaling and decreased levels of autophagy. I suggest that the mitochondrial death spiral is not an error in cell physiology but rather a rational approach to the problem of enabling successful growth and reproduction in a competitive world of scarce nutrients.

Bipolar disorder risk gene FOXO6 modulates negative symptoms in schizophrenia: a neuroimaging genetics study

BACKGROUND

Despite being diagnostically associated uniquely with schizophrenia, negative symptoms are also observed in bipolar disorder (BD). Genome-wide association studies (GWAS) have uncovered a number of shared risk genes between schizophrenia and BD. The objectives of this study were to examine whether previously identified risk genes for BD are associated with negative symptom severity within a first-episode schizophrenia (FES) cohort and to examine whether such genes influence brain morphology.

METHODS

Patients experiencing FES were genotyped for 21 previously identified BD risk genes; a series of univariate analyses of covariance examined the association between negative symptom severity, as measured using the Scale for the Assessment of Negative Symptoms (SANS), and genotype. A subset of participants underwent a structural 1.5 T MRI T₁ scan, analyzed for surface area and cortical thickness changes via the CIVET pipeline and LPBA40 atlas.

RESULTS

We included 133 patients with FES in our analysis; 61 of them underwent structural MRI. We observed a significant association between negative symptom severity and the BD risk gene FOXO6 (rs4660531). Individuals with the CC genotype presented significantly higher negative symptoms (Cohen d = 0.46, F = 5.854, p = 0.017) and significantly smaller surface area within the right middle orbitofrontal gyrus (Cohen d = 0.69, F = 7.289, p = 0.009) than carriers of allele A.

LIMITATIONS

Limitations of this study include its modest sample size and lack of a control sample.

CONCLUSION

Lacking the FOXO6 risk allele was associated with an increase in negative symptoms and surface area reduction in the right orbitofrontal gyrus - an area previously associated with negative symptoms - suggesting that presence of the FOXO6 risk allele confers resistance against negative symptoms and associated neuroanatomical changes in individuals with FES.

Expression of FOXO6 is Associated With Oxidative Stress Level and Predicts the Prognosis in Hepatocellular Cancer: A Comparative Study

The aim of this study was to explore the association of Forkhead box O6 (FOXO6) expression with oxidative stress level and prognosis of hepatocellular cancer (HCC).The case group included tissues of HCC from 128 patients who were hospitalized in Division of Hepatobiliary and Pancreatic Surgery, Department of Surgery of First Affiliated Hospital, School of Medicine, Zhejiang University. The control group included normal liver tissues from 74 patients. RT-PCR and Western blot were used to test expressions of FOXO6, heme oxygenase (HO)-1, glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT). Dihydroethidium (DHE) was dyed to observe reactive oxygen species (ROS) level. Immunohistochemistry was used to test FOXO6 expression. FOXO6 was silenced in HepG2 cells to detect cell proliferation and apoptosis. The expressions of ROS, HO-1, GPx, SOD, CAT, p27, and cyclin D1 were also detected to further explore the possible mechanism.The expressions of FOXO6, HO-1, GPx, SOD, and CAT in HCC tissue was significantly higher than those in normal and adjacent HCC tissues (P <0.05). The tumor size, TNM stage, Alpha-fetoprotein (AFP) level, the presence or absence of hepatitis B surface antigen (HbsAg), and differentiation degree were related to FOXO6 expression level (all P <0.05). COX analysis showed that high FOXO6 expression, male, positive HBsAg, advanced TNM staging, high expression of AFP, and low degree of differentiation were all risk factors for prognosis in HCC (P <0.05). Compared with the blank group (C group, without transfection) and the negative control (NC) group, the mRNA expressions of ROS, FOXO6, HO-1, SOD, GPx, and CAT were decreased (P <0.05). si-RNA group had significantly decreased proliferation speed during 24 to 72 hours (P <0.05), whereas si-FOXO6 group had remarkably increased G0/G1 staged cells and decreased S-staged cells (P <0.05). The si-FOXO6 group showed notably increased apoptosis rate (P <0.05) and p27 expressions as well as decreased cyclin D1 expressions (P <0.05).FOXO6 was highly expressed in HCC tissue and was related to oxidative stress levels. Furthermore, FOXO6 expression can be used as a biomarker for deterioration and prognosis of liver cancer, which may provide a novel treatment target for HCC therapy.

Ageing and microvasculature

A decline in the function of the microvasculature occurs with ageing. An impairment of endothelial properties represents a main aspect of age-related microvascular alterations. Endothelial dysfunction manifests itself through a reduced angiogenic capacity, an aberrant expression of adhesion molecules and an impaired vasodilatory function. Increased expression of adhesion molecules amplifies the interaction with circulating factors and inflammatory cells. The latter occurs in both conduit arteries and resistance arterioles. Age-related impaired function also associates with phenotypic alterations of microvascular cells, such as endothelial cells, smooth muscle cells and pericytes. Age-related morphological changes are in most of cases organ-specific and include microvascular wall thickening and collagen deposition that affect the basement membrane, with the consequent perivascular fibrosis. Data from experimental models indicate that decreased nitric oxide (NO) bioavailability, caused by impaired eNOS activity and NO inactivation, is one of the causes responsible for age-related microvascular endothelial dysfunction. Consequently, vasodilatory responses decline with age in coronary, skeletal, cerebral and vascular beds. Several therapeutic attempts have been suggested to improve microvascular function in age-related end-organ failure, and include the classic anti-atherosclerotic and anti-ischemic treatments, and also new innovative strategies. Change of life style, antioxidant regimens and anti-inflammatory treatments gave the most promising results. Research efforts should persist to fully elucidate the biomolecular basis of age-related microvascular dysfunction in order to better support new therapeutic strategies aimed to improve quality of life and to reduce morbidity and mortality among the elderly patients.