Homozygosity for an allele encoding deacetylated FoxO1 protects macrophages from cholesterol-induced inflammation without increasing apoptosis

Protective mechanism of FoxO1 against early brain injury after subarachnoid hemorrhage by regulating autophagy

INTRODUCTION

Early brain injury (EBI) plays a key role in the devastating outcomes after subarachnoid hemorrhage (SAH). Autophagy and apoptosis may share a common molecular inducer that regulates the process of cell death. FoxO1, as a key regulator of neuronal autophagy which is involved in apoptosis, has not been reported in SAH rats. This work was to investigate the protective and anti-inflammatory effects of FoxO1 on EBI after SAH by regulating autophagy.

METHODS

In this study, we constructed the SAH model. In experiment I, low dose (50 μl of 1 × 10⁸  IU/ml) or high dose (50 μl of 1 × 10¹⁰  IU/ml) of FoxO1 gene overexpressed adenovirus vector was injected into the lateral ventricle of rats before SAH. In experiment II, we reported the effect of FoxO1 overexpress on nerve function recovery, oedema, BBB leakage, neuronal death in rats after SAH through autophagy regulation. Post-SAH evaluation included neurological function score, brain water content, evans blue exosmosis, pathological changes, inflammatory response and apoptosis.

RESULTS

The experiment I showed that either low or high dose of ad-FoxO1 could significantly improve nerve function, reduce cerebral water content and reduce blood-brain barrier (BBB) destruction in rats, indicating that ad-FoxO1 had a protective effect on brain injury in rats EBI after SAH. In addition, ad-FoxO1 promoted autophagy in rat hippocampal tissue, as evidenced by accumulation of LC3II/I and Beclin-1 and degradation of p62. Furthermore, ad-FoxO1 inhibited the inflammatory response and apoptosis of rat hippocampal neurons after SAH. The experiment II showed that both ad-FoxO1 and rapamycin attenuated the injury of nerve function in rats after SAH, and this synergistic effect further reduced cerebral edema and evansblue extravasation, decreased hippocampus neuronal cell apoptosis, and declined inflammatory response. However, this was contrary to the results of chloroquine. These findings suggested that FoxO1 regulated the neural function of EBI after SAH through the autophagy pathway.

CONCLUSIONS

The findings in this study was beneficial for identifying the novel therapeutic target for the treatment of SAH.

Hyperglycaemia up-regulates placental growth factor (PlGF) expression and secretion in endothelial cells via suppression of PI3 kinase-Akt signalling and activation of FOXO1

Placenta growth factor (PlGF) is a pro-inflammatory angiogenic mediator that promotes many pathologies including diabetic complications and atherosclerosis. Widespread endothelial dysfunction precedes the onset of these conditions. As very little is known of the mechanism(s) controlling PlGF expression in pathology we investigated the role of hyperglycaemia in the regulation of PlGF production in endothelial cells. Hyperglycaemia stimulated PlGF secretion in cultured primary endothelial cells, which was suppressed by IGF-1-mediated PI3K/Akt activation. Inhibition of PI3K activity resulted in significant PlGF mRNA up-regulation and protein secretion. Similarly, loss or inhibition of Akt activity significantly increased basal PlGF expression and prevented any further PlGF secretion in hyperglycaemia. Conversely, constitutive Akt activation blocked PlGF secretion irrespective of upstream PI3K activity demonstrating that Akt is a central regulator of PlGF expression. Knock-down of the Forkhead box O-1 (FOXO1) transcription factor, which is negatively regulated by Akt, suppressed both basal and hyperglycaemia-induced PlGF secretion, whilst FOXO1 gain-of-function up-regulated PlGF in vitro and in vivo. FOXO1 association to a FOXO binding sequence identified in the PlGF promoter also increased in hyperglycaemia. This study identifies the PI3K/Akt/FOXO1 signalling axis as a key regulator of PlGF expression and unifying pathway by which PlGF may contribute to common disorders characterised by endothelial dysfunction, providing a target for therapy.

Multi-omics analysis identifies FoxO1 as a regulator of macrophage function through metabolic reprogramming

Macrophages are plastic cells that can switch among different states according to bioenergetic or biosynthetic requirements. Our previous work demonstrated that the transcription factor Forkhead Box Protein 1 (FoxO1) plays a pivotal role in regulating the function of macrophages, but the underlying mechanisms are still unclear. Here we identify FoxO1 as a regulator of macrophage function through metabolic reprogramming. Transcriptomic and proteomic analyses showed that the deficiency of FoxO1 results in an alternatively activated (M2) phenotype of macrophages, with lower expression of inflammatory response- and migration-associated genes. Using the high content screening and analysis technology, we found that deletion of FoxO1 in macrophages slows their migration rate and impairs their function to limit tumor cell growth in vitro. Next, we demonstrated that glycolysis is inhibited in FoxO1-deficient macrophages, which leads to the observed functional changes and the reduced tumor suppression capability. This prospective study shows that FoxO1 serves as a bridge between metabolism and macrophage function.

Insulin Action Research and the Future of Diabetes Treatment: The 2017 Banting Medal for Scientific Achievement Lecture

Diabetes is caused by combined abnormalities in insulin production and action. The pathophysiology of these defects has been studied extensively and is reasonably well understood. Their causes are elusive and their manifestations pleiotropic, likely reflecting the triple threat of genes, environment, and lifestyle. Treatment, once restricted to monotherapy with secretagogues or insulin, now involves complex combinations of expensive regimens that stem the progression but do not fundamentally alter the underlying causes of the disease. As advances in our understanding of insulin action and β-cell failure reach a critical stage, here I draw on lessons learned from our research on insulin regulation of gene expression and pancreatic β-cell dedifferentiation to address the question of how we can translate this exciting biology into mechanism-based interventions to reverse the course of diabetes.

Biochemical and cellular properties of insulin receptor signalling

The mechanism of insulin action is a central theme in biology and medicine. In addition to the rather rare condition of insulin deficiency caused by autoimmune destruction of pancreatic β-cells, genetic and acquired abnormalities of insulin action underlie the far more common conditions of type 2 diabetes, obesity and insulin resistance. The latter predisposes to diseases ranging from hypertension to Alzheimer disease and cancer. Hence, understanding the biochemical and cellular properties of insulin receptor signalling is arguably a priority in biomedical research. In the past decade, major progress has led to the delineation of mechanisms of glucose transport, lipid synthesis, storage and mobilization. In addition to direct effects of insulin on signalling kinases and metabolic enzymes, the discovery of mechanisms of insulin-regulated gene transcription has led to a reassessment of the general principles of insulin action. These advances will accelerate the discovery of new treatment modalities for diabetes.

Cellular hormetic response to 27-hydroxycholesterol promotes neuroprotection through AICD induction of MAST4 abundance and kinase activity

The function of the amyloid precursor protein (APP) in brain health remains unclear. This study elucidated a novel cytoprotective signaling pathway initiated by the APP transcriptionally active intracellular domain (AICD) in response to 27-hydroxycholesterol (27OHC), an oxidized cholesterol metabolite associated with neurodegeneration. The cellular response to 27OHC was hormetic, such that low, but not high, doses promoted AICD transactivation of microtubule associated serine/threonine kinase family member 4 (MAST4). MAST4 in turn phosphorylated and inhibited FOXO1-dependent transcriptional repression of rhotekin 2 (RTKN2), an oxysterol stress responder, to optimize cell survival. A palmitate-rich diet, which increases serum 27OHC, or APP ablation, abrogated this response in vivo. Further, this pathway was downregulated in human Alzheimer's Disease (AD) brains but not in frontotemporal dementia brains. These results unveil MAST4 as functional kinase of FOXO1 in a 27OHC AICD-driven, hormetic pathway providing insight for therapeutic approaches against cholesterol associated neuronal disorders.

When β-cells fail: lessons from dedifferentiation

Diabetes is caused by a combination of impaired responsiveness to insulin and reduced production of insulin by the pancreas. Until recently, the decline of insulin production had been ascribed to β-cell death. But recent research has shown that β-cells do not die in diabetes, but undergo a silencing process, termed "dedifferentiation." The main implication of this discovery is that β-cells can be revived by appropriate treatments. We have shown that mitochondrial abnormalities are a key step in the progression of β-cell dysfunction towards dedifferentiation. In normal β-cells, mitochondria generate energy required to sustain insulin production and its finely timed release in response to the body's nutritional status. A normal β-cell can adapt its mitochondrial fuel source based on substrate availability, a concept known as "metabolic flexibility." This capability is the first casualty in the progress of β-cell failure. β-Cells lose the ability to select the right fuel for mitochondrial energy production. Mitochondria become overloaded, and accumulate by-products derived from incomplete fuel utilization. Energy production stalls, and insulin production drops, setting the stage for dedifferentiation. The ultimate goal of these investigations is to explore novel treatment paradigms that will benefit people with diabetes.

Posttranslational modulation of FoxO1 contributes to cardiac remodeling in post-ischemic heart failure

OBJECTIVE

Forkhead box protein O1 (FoxO1) plays a key role in energy homeostasis, stress response and autophagy and is dysregulated in diabetes and ischemia. We investigated cardiac FoxO1 expression and posttranstranslational modifications after myocardial infarction (MI) and further tested if active posttranstranslational modulation of FoxO1 can alter cardiac remodeling in postischemic heart failure.

METHODS

Non-diabetic and diabetic C57BL/6 mice were subjected to MI by ligation of left anterior descending artery. In selected experiments we combined this model with intramyocardial injection of adenovirus expressing different isoforms of FoxO1. We used Millar catheter, histology, Western blot and metabolomics for further analyses.

RESULTS

We show that after MI total cardiac FoxO1 is downregulated and partly recovers after 7 days. This downregulation is accompanied by fundamental posttranslational modifications of FoxO1, particularly acetylation. Adenovirus experiments revealed smaller infarction size and improved heart function in mice expressing a constitutively deacetylated variant of FoxO1 compared to a wild type variant of FoxO1 in both non-diabetic (MI size: -13.4 ± 3.5%; LVDP: +29.1 ± 9.4  mmHg; p < 0.05) and diabetic mice (MI size: -17.6 ± 3.7%; LVDP: +10.9 ± 3.6  mmHg; p < 0.05). Metabolomics analyses showed alterations in metabolites connected to muscle breakdown, collagen/elastin and energy metabolism between the two groups.

CONCLUSION

First, our results demonstrate that myocardial ischemia is associated with downregulation and posttranslational modification of cardiac FoxO1. Second, we show in a mouse model of postischemic heart failure that posttranslational modulation of FoxO1 alters heart function involving collagen and protein metabolism. Therefore, posttranslational modifications of FoxO1 could be an option to target remodeling processes in postischemic heart failure.

Distinct role of FoxO1 in M-CSF- and GM-CSF-differentiated macrophages contributes LPS-mediated IL-10: implication in hyperglycemia

Macrophages are a heterogeneous population of immune cells that are essential for the initiation and containment inflammation. There are 2 well-established populations of inflammatory macrophages: classically activated M1 and alternatively activated M2 macrophages. The FoxO family of transcription factors plays key roles in a number of cellular processes, including cell growth, metabolism, survival, and inflammation. In this study, we determined whether the expression of FoxO1 contributes polarization of macrophages toward the M2-like phenotype by enhancing IL-10 cytokine expression. We identified that FoxO1 is highly expressed in M-CSF-derived (M2-like) macrophage subsets, and this M2-like macrophages showed a preferential FoxO1 enrichment on the IL-10 promoter but not in GM-CSF-derived (M1-like) macrophages during classic activation by LPS treatment, which suggests that FoxO1 enhances IL-10 by binding directly to the IL-10 promoter, especially in BMMs. In addition, our data show that macrophages in the setting of hyperglycemia contribute to the macrophage-inflammatory phenotype through attenuation of the contribution of FoxO1 to activate IL-10 expression. Our data identify a novel role for FoxO1 in regulating IL-10 secretion during classic activation and highlight the potential for therapeutic interventions for chronic inflammatory conditions, such as atherosclerosis, diabetes, inflammatory bowel disease, and arthritis.

Tumor suppressor maspin as a rheostat in HDAC regulation to achieve the fine-tuning of epithelial homeostasis

Maspin, a class II tumor suppressor, is often downregulated during tumor progression and its depletion from the nucleus is associated with poor prognosis. Recently, we reported that reintroduction of maspin is sufficient for redifferentiation of prostate cancer cells to epithelial phenotype, a reversal of epithelial-to-mesenchymal transition. We have linked this effect of maspin with its ability to directly inhibit HDAC1, thereby influencing the acetylation state of transcription factors and other proteins. Maspin overexpression leads to changes in the expression level of a large number of proteins and these changes are often microenvironment specific. In this review, we summarize the epigenetic effects of maspin and provide comprehensive bioinformatic analysis of microarray-derived gene expression changes caused by maspin in different microenvironments. The analysis was performed on multiple levels, including identification of statistically enriched gene ontology groups, detection of overreprepresented transcription factors binding sites in promoters of differentially expressed genes, followed by searching for key nodes of regulatory networks controlling these transcription factors. The results are consistent with our hypothesis that maspin serves as an endogenous regulator of HDAC activity and suggest that the effect of maspin is primarily mediated by TGFβ, β-catenin/E-cadherin pathways, and network key nodes such as Abl kinase, p62, IL1, and caspases 6 and 8.

Expanded granulocyte/monocyte compartment in myeloid-specific triple FoxO knockout increases oxidative stress and accelerates atherosclerosis in mice

RATIONALE

Increased neutrophil and monocyte counts are often associated with an increased risk of atherosclerosis, but their relationship to insulin sensitivity is unknown.

OBJECTIVE

To investigate the contribution of forkhead transcription factors (FoxO) in myeloid cells to neutrophil and monocyte counts, atherosclerosis, and systemic insulin sensitivity.

METHODS AND RESULTS

Genetic ablation of the 3 genes encoding FoxO isoforms 1, 3a, and 4, in myeloid cells resulted in an expansion of the granulocyte/monocyte progenitor compartment and was associated with increased atherosclerotic lesion formation in low-density lipoprotein receptor knockout mice. In vivo and ex vivo studies indicate that FoxO ablation in myeloid cells increased generation of reactive oxygen species. Accordingly, treatment with the antioxidant N-acetyl-l-cysteine reversed the phenotype, normalizing atherosclerosis.

CONCLUSIONS

Our data indicate that myeloid cell proliferation and oxidative stress can be modulated via the FoxO branch of insulin receptor signaling, highlighting a heretofore-unknown link between insulin sensitivity and leukocytosis that can affect the predisposition to atherosclerosis.

Increased atherosclerosis and endothelial dysfunction in mice bearing constitutively deacetylated alleles of Foxo1 gene

Complications of atherosclerosis are the leading cause of death of patients with type 2 (insulin-resistant) diabetes. Understanding the mechanisms by which insulin resistance and hyperglycemia contribute to atherogenesis in key target tissues (liver, vessel wall, hematopoietic cells) can assist in the design of therapeutic approaches. We have shown that hyperglycemia induces FoxO1 deacetylation and that targeted knock-in of alleles encoding constitutively deacetylated FoxO1 in mice (Foxo1(KR/KR)) improves hepatic lipid metabolism and decreases macrophage inflammation, setting the stage for a potential anti-atherogenic effect of this mutation. Surprisingly, we report here that when Foxo1(KR/KR) mice are intercrossed with low density lipoprotein receptor knock-out mice (Ldlr(-/-)), they develop larger aortic root atherosclerotic lesions than Ldlr(-/-) controls despite lower plasma cholesterol and triglyceride levels. The phenotype is unaffected by transplanting bone marrow from Ldlr(-/-) mice into Foxo1(KR/KR) mice, indicating that it is independent of hematopoietic cells and suggesting that the primary lesion in Foxo1(KR/KR) mice occurs in the vessel wall. Experiments in isolated endothelial cells from Foxo1(KR/KR) mice indicate that deacetylation favors FoxO1 nuclear accumulation and exerts target gene-specific effects, resulting in higher Icam1 and Tnfα expression and increased monocyte adhesion. The data indicate that FoxO1 deacetylation can promote vascular endothelial changes conducive to atherosclerotic plaque formation.