FoxO1 localizes to mitochondria of adipose tissue and is affected by nutrient stress

Inhibitory Regulation of FOXO1 in PPARδ Expression Drives Mitochondrial Dysfunction and Insulin Resistance

Forkhead box O1 (FOXO1) regulates muscle growth, but the metabolic role of FOXO1 in skeletal muscle and its mechanisms remain unclear. To explore the metabolic role of FOXO1 in skeletal muscle, we generated skeletal muscle-specific Foxo1 inducible knockout (mFOXO1 iKO) mice and fed them a high-fat diet to induce obesity. We measured insulin sensitivity, fatty acid oxidation, mitochondrial function, and exercise capacity in obese mFOXO1 iKO mice and assessed the correlation between FOXO1 and mitochondria-related protein in the skeletal muscle of patients with diabetes. Obese mFOXO1 iKO mice exhibited improved mitochondrial respiratory capacity, which was followed by attenuated insulin resistance, enhanced fatty acid oxidation, and improved skeletal muscle exercise capacity. Transcriptional inhibition of FOXO1 in peroxisome proliferator-activated receptor δ (PPARδ) expression was confirmed in skeletal muscle, and deletion of PPARδ abolished the beneficial effects of FOXO1 deficiency. FOXO1 protein levels were higher in the skeletal muscle of patients with diabetes and negatively correlated with PPARδ and electron transport chain protein levels. These findings highlight FOXO1 as a new repressor in PPARδ gene expression in skeletal muscle and suggest that FOXO1 links insulin resistance and mitochondrial dysfunction in skeletal muscle via PPARδ.

ARTICLE HIGHLIGHTS

Protective Effect and Mechanism of Autophagy in Endothelial Cell Injury Induced by Hyperoxia

OBJECTIVE

Bronchopulmonary dysplasia is a chronic lung disease in premature infants with alveolar simplification and pulmonary vascular development disorder as the main pathological feature and hyperoxia as the main etiology. Autophagy is a highly conserved cytological behavior of self-degrading cellular components and is accompanied by oxidative stress. Studies have reported that autophagy is regulated by FOXO1 posttranslational modification. However, whether autophagy can be involved in the regulation of endothelial cell injury induced by hyperoxia and its mechanism are still unclear.

STUDY DESIGN

We have activated and inhibited autophagy in human umbilical vein endothelial cells under hyperoxia and verified the role of autophagy in endothelial cell-related functions from both positive and negative aspects.

RESULTS

Our research showed that the expression level of autophagy-related proteins decreased, accompanied by decreased cell migration ability and tube formation ability and increased cell reactive oxygen species level and cell permeability under hyperoxia conditions. Using an autophagy agonist alleviated hyperoxia-induced changes and played a protective role. However, inhibition of autophagy aggravated the cell damage induced by hyperoxia. Moreover, the decrease in autophagy proteins was accompanied by the upregulation of FOXO1 phosphorylation and acetylation.

CONCLUSION

We concluded that autophagy was a protective mechanism against endothelial cell injury caused by hyperoxia. Autophagy might participate in this process by coregulating posttranslational modifications of FOXO1.

KEY POINTS

· Hyperoxia induces vascular endothelial cell injury.. · Autophagy may has a protective role under hyperoxia conditions.. · FOXO1 posttranslational modification may be involved in the regulation of autophagy..

FOXO transcription factors as mediators of stress adaptation

The forkhead box protein O (FOXO, consisting of FOXO1, FOXO3, FOXO4 and FOXO6) transcription factors are the mammalian orthologues of Caenorhabditis elegans DAF-16, which gained notoriety for its capability to double lifespan in the absence of daf-2 (the gene encoding the worm insulin receptor homologue). Since then, research has provided many mechanistic details on FOXO regulation and FOXO activity. Furthermore, conditional knockout experiments have provided a wealth of data as to how FOXOs control development and homeostasis at the organ and organism levels. The lifespan-extending capabilities of DAF-16/FOXO are highly correlated with their ability to induce stress response pathways. Exogenous and endogenous stress, such as cellular redox stress, are considered the main drivers of the functional decline that characterizes ageing. Functional decline often manifests as disease, and decrease in FOXO activity indeed negatively impacts on major age-related diseases such as cancer and diabetes. In this context, the main function of FOXOs is considered to preserve cellular and organismal homeostasis, through regulation of stress response pathways. Paradoxically, the same FOXO-mediated responses can also aid the survival of dysfunctional cells once these eventually emerge. This general property to control stress responses may underlie the complex and less-evident roles of FOXOs in human lifespan as opposed to model organisms such as C. elegans.

FoxO1 as a tissue-specific therapeutic target for type 2 diabetes

Forkhead box O (FoxO) proteins are transcription factors that mediate many aspects of physiology and thus have been targeted as therapeutics for several diseases including metabolic disorders such as type 2 diabetes mellitus (T2D). The role of FoxO1 in metabolism has been well studied, but recently FoxO1's potential for diabetes prevention and therapy has been debated. For example, studies have shown that increased FoxO1 activity in certain tissue types contributes to T2D pathology, symptoms, and comorbidities, yet in other tissue types elevated FoxO1 has been reported to alleviate symptoms associated with diabetes. Furthermore, studies have reported opposite effects of active FoxO1 in the same tissue type. For example, in the liver, FoxO1 contributes to T2D by increasing hepatic glucose production. However, FoxO1 has been shown to either increase or decrease hepatic lipogenesis as well as adipogenesis in white adipose tissue. In skeletal muscle, FoxO1 reduces glucose uptake and oxidation, promotes lipid uptake and oxidation, and increases muscle atrophy. While many studies show that FoxO1 lowers pancreatic insulin production and secretion, others show the opposite, especially in response to oxidative stress and inflammation. Elevated FoxO1 in the hypothalamus increases the risk of developing T2D. However, increased FoxO1 may mitigate Alzheimer's disease, a neurodegenerative disease strongly associated with T2D. Conversely, accumulating evidence implicates increased FoxO1 with Parkinson's disease pathogenesis. Here we review FoxO1's actions in T2D conditions in metabolic tissues that abundantly express FoxO1 and highlight some of the current studies targeting FoxO1 for T2D treatment.

PTPMT1 protects cardiomyocytes from necroptosis induced by γ-ray irradiation through alleviating mitochondria injury

Radiation-induced heart disease (RIHD) progresses over time and may manifest decades after the initial radiation exposure, which is associated with significant morbidity and mortality. The clinical benefit of radiotherapy is always counterbalanced by an increased risk of cardiovascular events in survivors. There is an urgent need to explore the effect and the underlying mechanism of radiation-induced heart injury. Mitochondrial damage widely occurs in irradiation-induced injury, and mitochondrial dysfunction contributes to necroptosis development. Experiments were performed using induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and rat H9C2 cells to investigate the effect of mitochondrial injury on necroptosis in irradiated cardiomyocytes and to further elucidate the mechanism underlying radiation-induced heart disease and discover possible preventive targets. After γ-ray irradiation, the expression levels of necroptosis markers were increased, along with higher oxidative stress and mitochondrial injury. These effects could be abated by overexpression of protein tyrosine phosphatase, mitochondrial 1 (PTPMT1). Inhibiting oxidative stress or increasing the expression of PTPMT1 could protect against radiation-induced mitochondrial injury and then decrease the necroptosis of cardiomyocytes. These results suggest that PTPMT1 may be a new target for the treatment of radiation-induced heart disease.NEW & NOTEWORTHY Effective strategies are still lacking for treating RIHD, with unclear pathological mechanisms. In cardiomyocytes model of radiation-induced injuries, we found γ-ray irradiation decreased the expression of PTPMT1, increased oxidative stress, and induced mitochondrial dysfunction and necroptosis in iPSC-CMs. ROS inhibition attenuated radiation-induced mitochondrial damage and necroptosis. PTPMT1 protected cardiomyocytes from necroptosis induced by γ-ray irradiation by alleviating mitochondrial injury. Therefore, PTPMT1 might be a potential strategy for treating RIHD.

The Relationship between Oxidative Status and Radioiodine Treatment Qualification among Papillary Thyroid Cancer Patients

Total oxidative status (TOS), total antioxidant capacity (TAC), tumor protein 53 (p53), nuclear factor kappa B (NF-κB), forkhead box protein O1 (FOXO), and sirtuin 1 (SIRT1) play crucial roles in oxidative homeostasis and the progression of papillary thyroid cancer (PTC), as previously demonstrated in the literature. Therefore, profiling these markers among PTC patients may be useful in determining their eligibility for radioiodine (RAI) treatment. Since treatment indications are based on multiple and dynamic recommendations, additional criteria for adjuvant RAI therapy are still needed. In our study, we evaluated the TOS, TAC, and serum concentrations of p53, NF-κB, FOXO, and SIRT1 to analyze the relationship between oxidative status and qualification for RAI treatment. For the purpose of this study, we enrolled 60 patients with PTC allocated for RAI treatment as the study group and 25 very low-risk PTC patients not allocated for RAI treatment as a reference group. The serum TOS and SIRT1 concentrations were significantly higher in the study group compared to the reference group (both p < 0.001), whereas the TAC and p53, NK-κB, and FOXO concentrations were significantly lower (all p < 0.05). We also demonstrated the diagnostic utility of TAC (AUC = 0.987), FOXO (AUC = 0.648), TOS (AUC = 0.664), SIRT1 (AUC = 0.709), p53 (AUC = 0.664), and NF-κB (AUC = 0.651) measurements as indications for RAI treatment based on American Thyroid Association recommendations. Our study revealed that oxidative status-related markers may become additional criteria for RAI treatment in PTC patients.

Fibrinogen-like protein 2 promotes proinflammatory macrophage polarization and mitochondrial dysfunction in liver fibrosis

Fibrinogen-like protein 2 (Fgl2) robustly activates macrophages in response to infection or inflammatory cytokine challenge and is markedly increased in the liver tissues of liver cirrhosis patientswithhepatitisCvirus(HCV) infection. However, the molecular mechanism underlying the involvement of Fgl2 in macrophage function in the pathogenesis of liver fibrosis remains unclear. In this study, we demonstrated that increased hepatic Fgl2 expression was associated with hepatic inflammation and high-grade liver fibrosis in patients with hepatitis B virus (HBV) infection and experimental models. Genetic ablation of Fgl2 alleviated hepatic inflammation and fibrosis progression. Fgl2 promoted M1 macrophage polarization and increased the production of proinflammatory cytokines that contribute to inflammatory damage and fibrosis development. In addition, Fgl2 augmented mitochondrial reactive oxygen species (ROS) production and modulated mitochondrial functions. Fgl2-mediated mtROS were involved in macrophage activation and polarization. We further demonstrated that in macrophages, Fgl2 localized to not only the cytosol but also mitochondria, where it bound to cytosolic and mitochondrial heat shock protein 90 (HSP90). Mechanistically, Fgl2 interacted with HSP90, hindering the interaction of HSP90 with its target protein Akt, significantly inhibiting Akt phosphorylation and downstream FoxO1 phosphorylation. These results reveal different layers of regulation of Fgl2 that are necessary for inflammatory damage and mitochondrial dysfunction in M1-polarized macrophages. Therefore, Fgl2 may be a potent target in liver fibrosis treatment.

Whey Derivatives and Galactooligosaccharides Stimulate the Wound Healing and the Function of Human Keratinocytes through the NF-kB and FOXO-1 Signaling Pathways

Skin repair requires the activation of keratinocytes and is mediated by controlled inflammation and cell migration and proliferation, ending with the regeneration of well-differentiated cell layers. Whey derivatives contain galactooligosaccharides (GOS), which have potential beneficial effects on wound healing due to their activity as toll-like receptor ligands, although their direct nonprebiotic effects in the skin have not yet been described. In this study, we investigated the effects of different whey-derived products and purified GOS on a human keratinocyte cell line. We found that the inflammatory cytokine interleukin-8 (IL-8) was upregulated by nuclear factor kappa B (NF-kB) signaling triggered by whey derivatives and GOS and that wound healing was accelerated by promoting cell migration and the loss of E-cadherin in the absence of epithelial–mesenchymal transition. Interestingly, the treatments enhanced the mitochondrial function in association with the translocation of the Forkhead Box O1 (FOXO-1) transcription factor. Finally, we detected the increased expression of the differentiation markers induced by GOS and whey derivatives. All together, our results show that GOS-containing products can promote wound closure and skin health by direct activity on keratinocyte functions. Among the preparations tested, the fermented compound produced by autochthonous microorganisms was the most active in modulating keratinocyte activity, supporting the biological value of whey derivatives for health.

Mitochondrial dysfunction and oxidative stress contribute to cognitive and motor impairment in FOXP1 syndrome

FOXP1 haploinsufficiency underlies cognitive and motor impairments in individuals with FOXP1 syndrome. Here, we show that mice lacking one Foxp1 copy exhibit similar behavioral deficits, which may be caused by striatal dysfunction. Indeed, Foxp1^+/− striatal medium spiny neurons display reduced neurite branching, and we show altered mitochondrial biogenesis and dynamics; increased mitophagy; reduced mitochondrial membrane potential, structure, and motility; and elevated oxygen species in the striatum of these animals. As FOXP1 is highly conserved, our data strongly suggest that mitochondrial dysfunction and excessive oxidative stress contribute to the motor and cognitive impairments seen in individuals with FOXP1 syndrome. Thus, mitochondrial homeostasis is critical for normal development and can explain deficits in neurodevelopmental disorders.

FOXP1 syndrome caused by haploinsufficiency of the forkhead box protein P1 (FOXP1) gene is a neurodevelopmental disorder that manifests motor dysfunction, intellectual disability, autism, and language impairment. In this study, we used a Foxp1^+/− mouse model to address whether cognitive and motor deficits in FOXP1 syndrome are associated with mitochondrial dysfunction and oxidative stress. Here, we show that genes with a role in mitochondrial biogenesis and dynamics (e.g., Foxo1, Pgc-1α, Tfam, Opa1, and Drp1) were dysregulated in the striatum of Foxp1^+/− mice at different postnatal stages. Furthermore, these animals exhibit a reduced mitochondrial membrane potential and complex I activity, as well as decreased expression of the antioxidants superoxide dismutase 2 (Sod2) and glutathione (GSH), resulting in increased oxidative stress and lipid peroxidation. These features can explain the reduced neurite branching, learning and memory, endurance, and motor coordination that we observed in these animals. Taken together, we provide strong evidence of mitochondrial dysfunction in Foxp1^+/− mice, suggesting that insufficient energy supply and excessive oxidative stress underlie the cognitive and motor impairment in FOXP1 deficiency.

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.

Mitochondrial regulation and white adipose tissue homeostasis

The important role of mitochondria in the regulation of white adipose tissue (WAT) remodeling and energy balance is increasingly appreciated. The remarkable heterogeneity of the adipose tissue stroma provides a cellular basis to enable adipose tissue plasticity in response to various metabolic stimuli. Regulating mitochondrial function at the cellular level in adipocytes, in adipose progenitor cells (APCs), and in adipose tissue macrophages (ATMs) has a profound impact on adipose homeostasis. Moreover, mitochondria facilitate the cell-to-cell communication within WAT, as well as the crosstalk with other organs, such as the liver, the heart, and the pancreas. A better understanding of mitochondrial regulation in the diverse adipose tissue cell types allows us to develop more specific and efficient approaches to improve adipose function and achieve improvements in overall metabolic health.

H2S exposure induces cell death in the broiler thymus via the ROS-initiated JNK/MST1/FOXO1 pathway

Hydrogen sulfide (H₂S) is a common toxic gas in chicken houses that endangers the health of poultry. Harbin has a cold climate in winter, and the conflict between heat preservation and ventilation in poultry houses is obvious. In this study, we investigated the H₂S content in chicken houses during winter in Harbin and found that the H₂S concentration exceeded the national standard in individual chicken houses. Then, a model of H₂S exposure was established in an environmental simulation chamber. We also developed a NaHS exposure model of chicken peripheral blood lymphocytes in vitro. Proteomics analysis was used to reveal the toxicology of thymus injury in broilers, the FOXO signaling pathway was determined to be significantly enriched, ROS bursts and JNK/MST1/FOXO1 pathway activation induced by H₂S exposure were detected, and ROS played an important switch role in the JNK/MST1/FOXO1 pathway. In addition, H₂S exposure-induced thymus cell death involved immune dysregulation. Overall, the present study adds data for H₂S contents in chicken houses, provides new findings for the mechanism of H₂S poisoning and reveals a new regulatory pathway in immune injury.

Cardiac toxicity assessment of pendimethalin in zebrafish embryos

Pendimethalin (PND) is one of the best sellers of selective herbicide in the world and has been frequently detected in the water. However, little is known about its effects on cardiac development. In this study, we used zebrafish to investigate the developmental and cardiac toxicity of PND. We exposed the zebrafish embryos with a serial of concentrations at 3, 4, and 5 mg/L at 5.5-72 h post-fertilization (hpf). We found that PND exposure can reduce the heart rate, survival rate, and body length of zebrafish embryos. Furthermore, we identified many malformations including pericardial and yolk sac edema, spinal deformity, and cardiac looping abnormality. In addition, PND increased the expression of reactive oxygen species and malondialdehyde and reduced the activity of superoxide dismutase (Antioxidant enzymes); We examined the expression of cardiac development-related genes and the apoptosis markers, and found changes of the following marker: vmhc, nppa, tbx5a, nkx2.5, gata4, tbx2b and FoxO1, bax, bcl-2, p53, casp-9, casp-3. Our data showed that activation of Wnt pathway can rescue the cardiac abnormalities caused by PND. Our results provided new evidence for the toxicity of PND and suggested that the PND residual should be treated as a hazard in the environment.

Metformin and Vitamin D Modulate Inflammation and Autophagy during Adipose-Derived Stem Cell Differentiation

Adipose-derived stem cells (ADSCs) came out from the regenerative medicine landscape for their ability to differentiate into several phenotypes, contributing to tissue regeneration both in vitro and in vivo. Dysregulation in stem cell recruitment and differentiation during adipogenesis is linked to a chronic low-grade inflammation and macrophage infiltration inside the adipose tissue, insulin resistance, cardiovascular disease and obesity. In the present paper we aimed to evaluate the role of metformin and vitamin D, alone or in combination, in modulating inflammation and autophagy in ADSCs during adipogenic commitment. ADSCs were cultured for 21 days in the presence of a specific adipogenic differentiation medium, together with metformin, or vitamin D, or both. We then analyzed the expression of FoxO1 and Heat Shock Proteins (HSP) and the secretion of proinflammatory cytokines IL-6 and TNF-α by ELISA. Autophagy was also assessed by specific Western blot analysis of ATG12, LC3B I, and LC3B II expression. Our results showed the ability of the conditioned media to modulate adipogenic differentiation, finely tuning the inflammatory response and autophagy. We observed a modulation in HSP mRNA levels, and a significant downregulation in cytokine secretion. Taken together, our findings suggest the possible application of these molecules in clinical practice to counteract uncontrolled lipogenesis and prevent obesity and obesity-related metabolic disorders.

Comprehensive Transcriptome Analysis of mRNA Expression Patterns of Early Embryo Development in Goat under Hypoxic and Normoxic Conditions

Simple Summary

Oxygen plays a vital role in the development of early embryos, no matter whether it is too high or low, it will adversely affect the early embryo development, but the mechanisms involved in these effects are still unclear. RNA-seq was performed to compare 8-cell-stage and blastocyst-stage goat embryos under hypoxic and normoxic conditions, the mRNA expression mechanisms of 8-cell- and blastocyst-stage embryos were systematically analyzed under hypoxic and normoxic conditions. Functional enrichment analysis indicated that these differentially expressed genes (DEGs) were mainly related to biological processes and function regulation. In conclusion, we can infer that oxidative stress regulates early embryo development by affecting the expression of zygotic genes and transcription factors, and those stress genes play a potential role in adaptation to normoxic environments in goat embryos.

Abstract

It has been reported that hypoxic environments were more suitable for the in vitro development of mammalian embryos, but the underlying mechanisms were still unclear. In the present study, RNA-seq was performed to compare 8-cell-stage and blastocyst-stage goat embryos under hypoxic and normoxic conditions; zygotes were checked at 72 and 168 h to 8-cell stage (L8C) and blastocyst stage (LM) in hypoxic conditions and 8-cell stage (H8C) and blastocyst stage (HM) in normoxic conditions. In the H8C and L8C groups, 399 DEGs were identified, including 348 up- and 51 down-regulated DEGs. In the HM and LM groups, 1710 DEGs were identified, including 1516 up- and 194 down-regulated DEGs. The expression levels of zygotic genes, transcription factors, and maternal genes, such as WEE2, GDF9, HSP70.1, BTG4, and UBE2S showed significant changes. Functional enrichment analysis indicated that these DEGs were mainly related to biological processes and function regulation. In addition, combined with the pathway–gene interaction network and protein–protein interaction network, twenty-two of the hub genes were identified and they are mainly involved in energy metabolism, immune stress response, cell cycle, receptor binding, and signal transduction pathways. The present study provides comprehensive insights into the effects of oxidative stress on early embryo development in goats.

Redox regulation of the insulin signalling pathway

The peptide hormone insulin is a key regulator of energy metabolism, proliferation and survival. Binding of insulin to its receptor activates the PI3K/AKT signalling pathway, which mediates fundamental cellular responses. Oxidants, in particular H₂O₂, have been recognised as insulin-mimetics. Treatment of cells with insulin leads to increased intracellular H₂O₂ levels affecting the activity of downstream signalling components, thereby amplifying insulin-mediated signal transduction. Specific molecular targets of insulin-stimulated H₂O₂ include phosphatases and kinases, whose activity can be altered via redox modifications of critical cysteine residues. Over the past decades, several of these redox-sensitive cysteines have been identified and their impact on insulin signalling evaluated. The aim of this review is to summarise the current knowledge on the redox regulation of the insulin signalling pathway.

Structure, mechanism, and regulation of mitochondrial DNA transcription initiation

Mitochondria are specialized compartments that produce requisite ATP to fuel cellular functions and serve as centers of metabolite processing, cellular signaling, and apoptosis. To accomplish these roles, mitochondria rely on the genetic information in their small genome (mitochondrial DNA) and the nucleus. A growing appreciation for mitochondria's role in a myriad of human diseases, including inherited genetic disorders, degenerative diseases, inflammation, and cancer, has fueled the study of biochemical mechanisms that control mitochondrial function. The mitochondrial transcriptional machinery is different from nuclear machinery. The in vitro re-constituted transcriptional complexes of Saccharomyces cerevisiae (yeast) and humans, aided with high-resolution structures and biochemical characterizations, have provided a deeper understanding of the mechanism and regulation of mitochondrial DNA transcription. In this review, we will discuss recent advances in the structure and mechanism of mitochondrial transcription initiation. We will follow up with recent discoveries and formative findings regarding the regulatory events that control mitochondrial DNA transcription, focusing on those involved in cross-talk between the mitochondria and nucleus.

Decoding the rosetta stone of mitonuclear communication

Cellular homeostasis in eukaryotic cells requires synchronized coordination of multiple organelles. A key role in this stage is played by mitochondria, which have recently emerged as highly interconnected and multifunctional hubs that process and coordinate diverse cellular functions. Beyond producing ATP, mitochondria generate key metabolites and are central to apoptotic and metabolic signaling pathways. Because most mitochondrial proteins are encoded in the nuclear genome, the biogenesis of new mitochondria and the maintenance of mitochondrial functions and flexibility critically depend upon effective mitonuclear communication. This review addresses the complex network of signaling molecules and pathways allowing mitochondria-nuclear communication and coordinated regulation of their independent but interconnected genomes, and discusses the extent to which dynamic communication between the two organelles has evolved for mutual benefit and for the overall maintenance of cellular and organismal fitness.

Omics Integration for Mitochondria Systems Biology

Significance: Elucidation of the central importance of mitophagy in homeostasis of cells and organisms emphasizes that mitochondrial functions extend far beyond short-term needs for energy production. In mitochondria systems biology, the mitochondrial genome, proteome, and metabolome operate as a functional network in coordination of cell activities. Organization occurs through subnetworks that are interconnected by membrane potential, transport activities, allosteric and cooperative interactions, redox signaling mechanisms, rheostatic control by post-translational modifications, and metal ion homeostasis. These subnetworks enable use of varied energy precursors, defense against environmental stressors, and macromolecular rewiring to titrate energy production, biosynthesis, and detoxification according to cell-specific needs. Rewiring mechanisms, termed mitochondrial reprogramming, enhance fitness to respond to metabolic resources and challenges from the environment. Maladaptive responses can cause cell death. Maladaptive rewiring can cause disease. In cancer, adaptive rewiring can interfere with effective treatment. Recent Advances: Many recent advances have been facilitated by the development of new omics tools, which create opportunities to use data-driven analysis of omics data to address these complex adaptive and maladaptive mechanisms of mitochondrial reprogramming in human disease. Critical Issues: Application of omics integration to model systems reveals a critical role for metal ion homeostasis broadly impacting mitochondrial reprogramming. Importantly, data show that trans-omics associations are more robust and biologically relevant than single omics associations. Future Directions: Application of omics integration to mitophagy research creates new opportunities to link the complex, interactive functions of mitochondrial form and function in mitochondria systems biology.

Adipose Tissue and FoxO1: Bridging Physiology and Mechanisms

Forkhead box O class proteins (FoxOs) are expressed nearly in all tissues and are involved in different functions such as energy metabolism, redox homeostasis, differentiation, and cell cycle arrest. The plasticity of FoxOs is demonstrated by post-translational modifications that determine diverse levels of transcriptional regulations also controlled by their subcellular localization. Among the different members of the FoxO family, we will focus on FoxO1 in adipose tissue, where it is abundantly expressed and is involved in differentiation and transdifferentiation processes. The capability of FoxO1 to respond differently in dependence of adipose tissue subtype underlines the specific involvement of the transcription factor in energy metabolism and the “browning” process of adipocytes. FoxO1 can localize to nuclear, cytoplasm, and mitochondrial compartments of adipocytes responding to different availability of nutrients and source of reactive oxygen species (ROS). Specifically, fasted state produced-ROS enhance the nuclear activity of FoxO1, triggering the transcription of lipid catabolism and antioxidant response genes. The enhancement of lipid catabolism, in combination with ROS buffering, allows systemic energetic homeostasis and metabolic adaptation of white/beige adipocytes. On the contrary, a fed state induces FoxO1 to accumulate in the cytoplasm, but also in the mitochondria where it affects mitochondrial DNA gene expression. The importance of ROS-mediated signaling in FoxO1 subcellular localization and retrograde communication will be discussed, highlighting key aspects of FoxO1 multifaceted regulation in adipocytes.

The FOXO's Advantages of Being a Family: Considerations on Function and Evolution

The nematode Caenorhabditis elegans possesses a unique (with various isoforms) FOXO transcription factor DAF-16, which is notorious for its role in aging and its regulation by the insulin-PI3K-AKT pathway. In humans, five genes (including a protein-coding pseudogene) encode for FOXO transcription factors that are targeted by the PI3K-AKT axis, such as in C. elegans. This common regulation and highly conserved DNA-binding domain are the pillars of this family. In this review, I will discuss the possible meaning of possessing a group of very similar proteins and how it can generate additional functionality to more complex organisms. I frame this discussion in relation to the much larger super family of Forkhead proteins to which they belong. FOXO members are very often co-expressed in the same cell type. The overlap of function and expression creates a certain redundancy that might be a safeguard against the accidental loss of FOXO function, which could otherwise lead to disease, particularly, cancer. This is one of the points that will be examined in this "family affair" report.

Aconitase 2 inhibits the proliferation of MCF-7 cells promoting mitochondrial oxidative metabolism and ROS/FoxO1-mediated autophagic response

Background

Deregulation of the tricarboxylic acid cycle (TCA) due to mutations in specific enzymes or defective aerobic metabolism is associated with tumour growth. Aconitase 2 (ACO2) participates in the TCA cycle by converting citrate to isocitrate, but no evident demonstrations of its involvement in cancer metabolism have been provided so far.

Methods

Biochemical assays coupled with molecular biology, in silico, and cellular tools were applied to circumstantiate the impact of ACO2 in the breast cancer cell line MCF-7 metabolism. Fluorescence lifetime imaging microscopy (FLIM) of NADH was used to corroborate the changes in bioenergetics.

Results

We showed that ACO2 levels are decreased in breast cancer cell lines and human tumour biopsies. We generated ACO2- overexpressing MCF-7 cells and employed comparative analyses to identify metabolic adaptations. We found that increased ACO2 expression impairs cell proliferation and commits cells to redirect pyruvate to mitochondria, which weakens Warburg-like bioenergetic features. We also demonstrated that the enhancement of oxidative metabolism was supported by mitochondrial biogenesis and FoxO1-mediated autophagy/mitophagy that sustains the increased ROS burst.

Conclusions

This work identifies ACO2 as a relevant gene in cancer metabolic rewiring of MCF-7 cells, promoting a different utilisation of pyruvate and revealing the potential metabolic vulnerability of ACO2-associated malignancies.

Conventional and unconventional interactions of the transcription factor FOXL2 uncovered by a proteome-wide analysis

Beyond the study of its transcriptional target genes, the identification of the various interactors of a transcription factor (TF) is crucial to understand its diverse cellular roles. We focused on FOXL2, a winged-helix forkhead TF important for ovarian development and maintenance. FOXL2 has been implicated in diverse cellular processes, including apoptosis, the control of cell cycle or the regulation of steroid hormone synthesis. To reliably identify partners of endogenous FOXL2, we performed a proteome-wide analysis using co-immunoprecipitation in the murine granulosa cell-derived AT29c and the pituitary-derived alpha-T3 cell lines, using three antibodies targeting different parts of the protein. Following a stringent selection of mass spectrometry data on the basis of identification reliability and protein enrichment, we identified a core set of 255 partners common to both cell lines. Their analysis showed that we could co-precipitate several complexes involved in mRNA processing, chromatin remodeling and DNA replication and repair. We further validated (direct and/or indirect) interactions with selected partners, suggesting an unexpected role for FOXL2 in those processes. Overall, this comprehensive analysis of the endogenous FOXL2 interactome sheds light on its numerous and diverse interactors and unconventional cellular roles.