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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.Forkhead box (FOXO) transcription factors are important mediators of cell stress responses, generally considered to preserve homeostasis and counteract ageing. However, FOXO-mediated mechanisms can also support the survival of cancer and other dysfunctional cells, thereby complicating the link between FOXOs and lifespan extension.

The glycolytic activity of Paneth cells provides lactate, which is required by self-renewing intestinal stem cells for oxidative metabolism to activate p38 MAP kinase, ensuring regeneration of a mature crypt. Metabolism and gut regeneration Small intestine crypts are regenerated throughout life thanks to self-renewing stem cells located at the bottom of crypts. Differentiated Paneth cells provide the signalling molecules that modulate the regenerative properties of these stem cells. The influence of metabolism on the self-renewal of the crypt has not been studied in great detail. Burgering and colleagues now show that, whereas intestinal stem cells rely on mitochondrial activity for their metabolic needs, Paneth cells use glycolysis, a process that provides the lactate that is required by the stem cells for their oxidative metabolism. This activates the p38 MAP kinase to ensure regeneration of a mature crypt. The findings suggest that the metabolism of certain intestinal cells has an important role in supporting stem cell function. The small intestinal epithelium self-renews every four or five days. Intestinal stem cells (Lgr5 + crypt base columnar cells (CBCs)) sustain this renewal and reside between terminally differentiated Paneth cells at the bottom of the intestinal crypt 1 . Whereas the signalling requirements for maintaining stem cell function and crypt homeostasis have been well studied, little is known about how metabolism contributes to epithelial homeostasis. Here we show that freshly isolated Lgr5 + CBCs and Paneth cells from the mouse small intestine display different metabolic programs. Compared to Paneth cells, Lgr5 + CBCs display high mitochondrial activity. Inhibition of mitochondrial activity in Lgr5 + CBCs or inhibition of glycolysis in Paneth cells strongly affects stem cell function, as indicated by impaired organoid formation. In addition, Paneth cells support stem cell function by providing lactate to sustain the enhanced mitochondrial oxidative phosphorylation in the Lgr5 + CBCs. Mechanistically, we show that oxidative phosphorylation stimulates p38 MAPK activation by mitochondrial reactive oxygen species signalling, thereby establishing the mature crypt phenotype. Together, our results reveal a critical role for the metabolic identity of Lgr5 + CBCs and Paneth cells in supporting optimal stem cell function, and we identify mitochondria and reactive oxygen species signalling as a driving force of cellular differentiation.

Reactive Oxygen Species (ROS) derived from mitochondrial respiration are frequently cited as a major source of chromosomal DNA mutations that contribute to cancer development and aging. However, experimental evidence showing that ROS released by mitochondria can directly damage nuclear DNA is largely lacking. In this study, we investigated the effects of H 2 O 2 released by mitochondria or produced at the nucleosomes using a titratable chemogenetic approach. This enabled us to precisely investigate to what extent DNA damage occurs downstream of near- and supraphysiological amounts of localized H 2 O 2 . Nuclear H 2 O 2 gives rise to DNA damage and mutations and a subsequent p53 dependent cell cycle arrest. Mitochondrial H 2 O 2 release shows none of these effects, even at levels that are orders of magnitude higher than what mitochondria normally produce. We conclude that H 2 O 2 released from mitochondria is unlikely to directly damage nuclear genomic DNA, limiting its contribution to oncogenic transformation and aging. Nuclear DNA damage downstream of mitochondrial ROS is often cited to contribute to cancer initiation and aging. However, here the authors show that although H 2 O 2 induces DNA mutations when produced near DNA, it does not when released by mitochondria.

A central process contributing to the phenotype of aging is cellular senescence. We recently identified the FOXO4 – p53 axis as pivotal in maintaining the viability of senescent cells, and that senescent cells can be targeted selectively with the senolytic peptide FOXO4-DRI. Here, we solve the solution NMR structural models of the p53 transactivation domain in complex with the FOXO4 forkhead domain and in complex with FOXO4-DRI. Strikingly, we find that the disordered FOXO4-DRI binds to the disordered p53 TAD2 and forms a transiently folded complex. In this complex, both, the FOXO4-derived region and the cationic cell permeability peptide contribute to the interaction. Furthermore, we show that p53 phosphorylation enhances the affinity for both FOXO4 and FOXO4-DRI. Summarizing we provide a detailed characterization of the interaction of p53 with FOXO4 and FOXO4-DRI which is the basis for development of p53 inhibitors to treat diseases linked to cellular senescence such as cancers. Cellular senescence drives aging, with the p53–FOXO4 axis sustaining senescent cell viability. This study reveals structural insights into p53 binding to FOXO4/FOXO4-DRI, informing the development of p53-targeted senolytics for age related diseases.

The microbiome is a key regulator of host homeostasis and immune activity, in part through the production of metabolites. These microbiota-derived metabolites can modulate both the innate and adaptive immune system, as well as directly target tumour cells, thereby regulating anti-tumour immunity and response to immunotherapy. Here, we describe the current mechanistic knowledge on how these metabolites exert their effects and outline the methodologies used to detect and assess these metabolites. Finally, we summarize microbiota-targeted therapies capable of improving microbial functionality to ultimately enhance immunotherapy responses and improve patient survival.

Fibroblast growth factor 19 (FGF19) is a gut-derived peptide hormone that is produced following activation of Farnesoid X Receptor (FXR). FGF19 is secreted and signals to the liver, where it contributes to the homeostasis of bile acid (BA), lipid and carbohydrate metabolism. FGF19 is a promising therapeutic target for the metabolic syndrome and cholestatic diseases, but enthusiasm for its use has been tempered by FGF19-mediated induction of proliferation and hepatocellular carcinoma. To inform future rational design of FGF19-variants, we have conducted temporal quantitative proteomic and gene expression analyses to identify FGF19-targets related to metabolism and proliferation. Mice were fasted for 16 hours, and injected with human FGF19 (1 mg/kg body weight) or vehicle. Liver protein extracts (containing \"light\" lysine) were mixed 1:1 with a spike-in protein extract from 13C6-lysine metabolically labelled mouse liver (containing \"heavy\" lysine) and analysed by LC-MS/MS. Our analyses provide a resource of FGF19 target proteins in the liver. 189 proteins were upregulated (≥ 1.5 folds) and 73 proteins were downregulated (≤ -1.5 folds) by FGF19. FGF19 treatment decreased the expression of proteins involved in fatty acid (FA) synthesis, i.e., Fabp5, Scd1, and Acsl3 and increased the expression of Acox1, involved in FA oxidation. As expected, FGF19 increased the expression of proteins known to drive proliferation (i.e., Tgfbi, Vcam1, Anxa2 and Hdlbp). Importantly, many of the FGF19 targets (i.e., Pdk4, Apoa4, Fas and Stat3) have a dual function in both metabolism and cell proliferation. Therefore, our findings challenge the development of FGF19-variants that fully uncouple metabolic benefit from mitogenic potential.

β-Catenin is a multifunctional protein that mediates Wnt signaling by binding to members of the T cell factor (TCF) family of transcription factors. Here, we report an evolutionary conserved interaction of β-catenin with FOXO transcription factors, which are regulated by insulin and oxidative stress signaling. β-Catenin binds directly to FOXO and enhances FOXO transcriptional activity in mammalian cells. In Caenorhabditis elegans, loss of the β-catenin BAR-1 reduces the activity of the FOXO ortholog DAF-16 in dauer formation and life span. Association of β-catenin with FOXO was enhanced in cells exposed to oxidative stress. Furthermore, BAR-1 was required for the oxidative stressinduced expression of the DAF-16 target gene sod-3 and for resistance to oxidative damage. These results demonstrate a role for β-catenin in regulating FOXO function that is particularly important under conditions of oxidative stress.

FOXO transcription factors act downstream of PI3K signaling, and FOXO transcriptional activity is inhibited through nuclear exclusion by PKB/AKT-mediated phosphorylation. Many studies have shown FOXO to contribute to organismal homeostasis by mitigating (extra)cellular stress to prevent cell death (reviewed in [1]). Here we show that FOXO3 activation protects cells from ferroptosis, an iron-dependent form of non-apoptotic cell death. In untransformed hTERT-RPE-1 cells, FOXO3 activation reduces ferroptosis in a multilayered manner. First, FOXO3 mediates protection from ferroptosis in part through a p27-induced G1 cell cycle arrest. Second, FOXO3 activation reduces cellular H 2 O 2 levels, thereby limiting substrate availability for the Fenton reaction, which fuels hydroxyl radical formation for lipid peroxidation. Third, FOXO3 activation lowers cellular iron content by reducing TFR1 expression, which, combined with the lowering of cellular H 2 O 2 levels, likely further reduces the formation of hydroxyl radicals through the Fenton reaction. Finally, FOXO3 activation reduces expression of long-chain-fatty-acid—CoA ligase 4 (ACSL4) and Peroxisomal targeting signal 1 receptor (PEX5), proteins involved in lipid metabolism and protection against ferroptosis. Taken together, we show that FOXO3 activation results in protection from ferroptosis, adding to the repertoire of FOXO-controlled cell protection programs.

Key Points More than 100 forkhead transcription factors have been identified, and they are known as FOX (forkhead box) proteins. These proteins are classified in terms of structure, not function, and mutation of various FOX proteins leads to immune dysfunction. FOXP3 regulates the production of CD4 + CD25 + regulatory T cells, which are crucial for the maintenance of self-tolerance. Deletion of the gene encoding FOXP3 results in overproliferation of activated T cells and development of both autoimmune disease and allergy. FOXN1 is crucial for the growth and differentiation of thymic epithelial cells. Deletion or mutation of the gene encoding this transcription factor, as found in the nude mouse, results in athymia. FOXJ1 is a transcriptional activator, and its expression levels are downregulated by lymphocytes from mice prone to systemic lupus erythematosus. FOXJ1 regulates T-cell activation, probably through inhibiting the activation of nuclear factor-κB (NF-κB). FOXO-subfamily members have central roles in the regulation of proliferation and apoptosis of various cell types. In the immune system, FOXO activity tends to be inversely correlated with cellular activation. Deletion of the gene encoding FOXO3A results in lymphoproliferation and multi-organ inflammation. Similar to FOXJ1, this might also occur through modulation of NF-κB activity. It is more than a decade since the discovery of the first forkhead-box (FOX) transcription factor in the fruit fly Drosophila melanogaster . In the intervening time, there has been an explosion in the identification and characterization of members of this family of proteins. Importantly, in the past few years, it has become clear that members of the FOX family have crucial roles in various aspects of immune regulation, from lymphocyte survival to thymic development. This review focuses on FOXP3, FOXN1, FOXJ1 and members of the FOXO subfamily and their function in the immune system.

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease leading to motor neuron loss. Currently mutations in > 40 genes have been linked to ALS, but the contribution of many genes and genetic mutations to the ALS pathogenic process remains poorly understood. Therefore, we first performed comparative interactome analyses of five recently discovered ALS-associated proteins (C21ORF2, KIF5A, NEK1, TBK1, and TUBA4A) which highlighted many novel binding partners, and both unique and shared interactors. The analysis further identified C21ORF2 as a strongly connected protein. The role of C21ORF2 in neurons and in the nervous system, and of ALS-associated C21ORF2 variants is largely unknown. Therefore, we combined human iPSC-derived motor neurons with other models and different molecular cell biological approaches to characterize the potential pathogenic effects of C21ORF2 mutations in ALS. First, our data show C21ORF2 expression in ALS-relevant mouse and human neurons, such as spinal and cortical motor neurons. Further, the prominent ALS-associated variant C21ORF2-V58L caused increased apoptosis in mouse neurons and movement defects in zebrafish embryos. iPSC-derived motor neurons from C21ORF2-V58L-ALS patients, but not isogenic controls, show increased apoptosis, and changes in DNA damage response, mitochondria and neuronal excitability. In addition, C21ORF2-V58L induced post-transcriptional downregulation of NEK1, an ALS-associated protein implicated in apoptosis and DDR. In all, our study defines the pathogenic molecular and cellular effects of ALS-associated C21ORF2 mutations and implicates impaired post-transcriptional regulation of NEK1 downstream of mutant C21ORF72 in ALS.