The protective role of TET2 in erythroid iron homeostasis against oxidative stress and erythropoiesis

Ferroptosis regulation by methylation in cancer

Epigenetic regulation plays a critical role in cancer development and progression. Methylation is an important epigenetic modification that influences gene expression by adding a methyl group to nucleic acids and proteins. Ferroptosis is a new form of regulated cell death triggered by the accumulation of iron and lipid peroxidation. Emerging evidence have shown that methylation regulation plays a significant role in the regulation of ferroptosis in cancer. This review aims to explore the methylation regulation of ferroptosis in cancer, including reactive oxygen species and iron bio-logical activity, amino acid and lipid metabolism, and drugs interaction. The findings of this review may provide new insights and strategies for the prevention and treatment of cancer.

Iron deficiency and its epigenetic effects on iron homeostasis

Iron deficiency is a common micronutrient deficiency associated with metabolic changes in the levels of iron regulatory proteins, hepcidin and ferroportin. Studies have associated dysregulation of iron homeostasis to other secondary and life-threatening diseases including anaemia, neurodegeneration and metabolic diseases. Iron deficiency plays a critical role in epigenetic regulation by affecting the Fe²⁺/α-ketoglutarate-dependent demethylating enzymes, Ten Eleven Translocase 1-3 (TET 1-3) and Jumonji-C (JmjC) histone demethylase, which are involved in epigenetic erasure of the methylation marks on both DNA and histone tails, respectively. In this review, studies involving epigenetic effects of iron deficiency associated with dysregulation of TET 1-3 and JmjC histone demethylase enzyme activities on hepcidin/ferroportin axis are discussed.

Effects of green tea extract treatment on erythropoiesis and iron parameters in iron-overloaded β-thalassemic mice

β-Thalassemia is characterized by ineffective erythropoiesis leading to chronic anemia. Thus, increased iron absorption from the duodenum and via blood transfusions is required to maintain normal blood hemoglobin (Hb) levels and iron chelators in the removal of excessive iron. Certain agents are also needed for the improvement of stress erythropoiesis and iron dysregulation. Green tea extract (GTE), which is rich in epigallocatechin-3-gallate (EGCG), is known to possess radical scavenging and iron-chelating activities. We aimed to assess the effects of green tea extract on erythroid regulators, iron mobilization and anti-lipid peroxidation in the liver, spleen, and kidneys of iron-loaded β-globin gene knockout thalassemic (BKO) mice. Our results indicate that treatments of green tea extract and/or deferiprone (DFP) diminished levels of plasma erythropoietin (EPO) and erythroferrone (ERFE), and consistently suppressed kidney Epo and spleen Erfe mRNA expressions (p < .05) in iron- loaded BKO mice when compared with untreated mice. Coincidently, the treatments decreased plasma ferritin (Ft) levels, iron content levels in the liver (p < .05), spleen (p < .05), and kidney tissues of iron-loaded BKO mice. Furthermore, lipid-peroxidation products in the tissues and plasma were also decreased when compared with untreated mice. This is the first evidence of the orchestral role of green tea extract abundant with epigallocatechin-3-gallate in improving ineffective erythropoiesis, iron dysregulation and oxidative stress in iron-overloaded β-thalassemic mice.

Vitamin C deficiency reveals developmental differences between neonatal and adult hematopoiesis

Hematopoiesis, a process that results in the differentiation of all blood lineages, is essential throughout life. The production of 1x10¹² blood cells per day, including 200x10⁹ erythrocytes, is highly dependent on nutrient consumption. Notably though, the relative requirements for micronutrients during the perinatal period, a critical developmental window for immune cell and erythrocyte differentiation, have not been extensively studied. More specifically, the impact of the vitamin C/ascorbate micronutrient on perinatal as compared to adult hematopoiesis has been difficult to assess in animal models. Even though humans cannot synthesize ascorbate, due to a pseudogenization of the L-gulono-γ-lactone oxidase (GULO) gene, its generation from glucose is an ancestral mammalian trait. Taking advantage of a Gulo^-/- mouse model, we show that ascorbic acid deficiency profoundly impacts perinatal hematopoiesis, resulting in a hypocellular bone marrow (BM) with a significant reduction in hematopoietic stem cells, multipotent progenitors, and hematopoietic progenitors. Furthermore, myeloid progenitors exhibited differential sensitivity to vitamin C levels; common myeloid progenitors and megakaryocyte-erythrocyte progenitors were markedly reduced in Gulo^-/- pups following vitamin C depletion in the dams, whereas granulocyte-myeloid progenitors were spared, and their frequency was even augmented. Notably, hematopoietic cell subsets were rescued by vitamin C repletion. Consistent with these data, peripheral myeloid cells were maintained in ascorbate-deficient Gulo^-/- pups while other lineage-committed hematopoietic cells were decreased. A reduction in B cell numbers was associated with a significantly reduced humoral immune response in ascorbate-depleted Gulo^-/- pups but not adult mice. Erythropoiesis was particularly sensitive to vitamin C deprivation during both the perinatal and adult periods, with ascorbate-deficient Gulo^-/- pups as well as adult mice exhibiting compensatory splenic differentiation. Furthermore, in the pathological context of hemolytic anemia, vitamin C-deficient adult Gulo^-/- mice were not able to sufficiently increase their erythropoietic activity, resulting in a sustained anemia. Thus, vitamin C plays a pivotal role in the maintenance and differentiation of hematopoietic progenitors during the neonatal period and is required throughout life to sustain erythroid differentiation under stress conditions.

Insufficient Radiofrequency Ablation Promotes Hepatocellular Carcinoma Metastasis Through N6-Methyladenosine mRNA Methylation-Dependent Mechanism

BACKGROUND AND AIMS

The dynamic N6-methyladenosine (m⁶ A) mRNA modification is essential for acute stress response and cancer progression. Sublethal heat stress from insufficient radiofrequency ablation (IRFA) has been confirmed to promote HCC progression; however, whether m⁶ A machinery is involved in IRFA-induced HCC recurrence remains open for study.

APPROACH AND RESULTS

Using an IRFA HCC orthotopic mouse model, we detected a higher level of m⁶ A reader YTH N6-methyladenosine RNA binding protein 1-3 (YTHDF1) in the sublethal-heat-exposed transitional zone close to the ablation center than that in the farther area. In addition, we validated the increased m⁶ A modification and elevated YTHDF1 protein level in sublethal-heat-treated HCC cell lines, HCC patient-derived xenograft (PDX) mouse model, and patients' HCC tissues. Functionally, gain-of-function/loss-of-function assays showed that YTHDF1 promotes HCC cell viability and metastasis. Knockdown of YTHDF1 drastically restrains the tumor metastasis evoked by sublethal heat treatment in tail vein injection lung metastasis and orthotopic HCC mouse models. Mechanistically, we found that sublethal heat treatment increases epidermal factor growth receptor (EGFR) m⁶ A modification in the vicinity of the 5' untranslated region and promotes its binding with YTHDF1, which enhances the translation of EGFR mRNA. The sublethal-heat-induced up-regulation of EGFR level was further confirmed in the IRFA HCC PDX mouse model and patients' tissues. Combination of YTHDF1 silencing and EGFR inhibition suppressed the malignancies of HCC cells synergically.

CONCLUSIONS

The m⁶ A-YTHDF1-EGFR axis promotes HCC progression after IRFA, supporting the rationale for targeting m⁶ A machinery combined with EGFR inhibitors to suppress HCC metastasis after RFA.

EnvIRONmental Aspects in Myelodysplastic Syndrome

Systemic iron overload is multifactorial in patients suffering from myelodysplastic syndrome (MDS). Disease-immanent ineffective erythropoiesis together with chronic red blood cell transfusion represent the main underlying reasons. However, like the genetic heterogeneity of MDS, iron homeostasis is also diverse in different MDS subtypes and can no longer be generalized. While a certain amount of iron and reactive oxygen species (ROS) are indispensable for proper hematological output, both are harmful if present in excess. Consequently, iron overload has been increasingly recognized as an important player in MDS, which is worth paying attention to. This review focuses on iron- and ROS-mediated effects in the bone marrow niche, their implications for hematopoiesis and their yet unclear involvement in clonal evolution. Moreover, we provide recent insights into hepcidin regulation in MDS and its interaction between erythropoiesis and inflammation. Based on Tet methylcytosine dioxygenase 2 (TET2), representing one of the most frequently mutated genes in MDS, leading to disturbances in both iron homeostasis and hematopoiesis, we highlight that different genetic alteration may have different implications and that a comprehensive workup is needed for a complete understanding and development of future therapies.

An IDH1-vitamin C crosstalk drives human erythroid development by inhibiting pro-oxidant mitochondrial metabolism

The metabolic changes controlling the stepwise differentiation of hematopoietic stem and progenitor cells (HSPCs) to mature erythrocytes are poorly understood. Here, we show that HSPC development to an erythroid-committed proerythroblast results in augmented glutaminolysis, generating alpha-ketoglutarate (αKG) and driving mitochondrial oxidative phosphorylation (OXPHOS). However, sequential late-stage erythropoiesis is dependent on decreasing αKG-driven OXPHOS, and we find that isocitrate dehydrogenase 1 (IDH1) plays a central role in this process. IDH1 downregulation augments mitochondrial oxidation of αKG and inhibits reticulocyte generation. Furthermore, IDH1 knockdown results in the generation of multinucleated erythroblasts, a morphological abnormality characteristic of myelodysplastic syndrome and congenital dyserythropoietic anemia. We identify vitamin C homeostasis as a critical regulator of ineffective erythropoiesis; oxidized ascorbate increases mitochondrial superoxide and significantly exacerbates the abnormal erythroblast phenotype of IDH1-downregulated progenitors, whereas vitamin C, scavenging reactive oxygen species (ROS) and reprogramming mitochondrial metabolism, rescues erythropoiesis. Thus, an IDH1-vitamin C crosstalk controls terminal steps of human erythroid differentiation.

Recent advances in iron homeostasis and regulation - a focus on epigenetic regulation and stroke

Iron is an element with redox properties. It is active sites of many enzymes and plays an important role in various cellular and biological functions including ATP production and DNA synthesis. However, as a redox element, iron promotes free radical generation and lipid peroxidation, causing oxidative damage and cell death. Iron-mediated oxidation is a central player in ferroptosis, a type of cell death process that is different from apoptosis and necrosis. Thus, iron metabolism and homeostasis are sophisticatedly regulated. There has been exciting progress in understanding iron metabolism and regulation since hepcidin was recognized as the central regulator of iron homeostasis. Hepcidin mainly regulates the iron export function of the ferrous iron permease, ferroportin, which is the only known iron exporter expressed by mammalian cells. Particularly, epigenetic regulation has been a recent focus on iron homeostasis. Epigenetic phenomena have been demonstrated to modulate key proteins including hepcidin in iron metabolism. Here, we review the rapid progress in recent years in understanding molecular mechanisms of iron homeostasis with a focus on epigenetic regulation of hepcidin, ferritin, and ferroptosis. Interactions between methionine oxidation and iron is also discussed. Furthermore, many studies have suggested that the severity of neuronal damage after stroke is proportional to the magnitude of brain iron accumulation. Recent discoveries regarding iron metabolism in stroke is briefly discussed. Understanding the underlying mechanism in iron regulation could provide insight into the treatment of various intractable diseases including stroke.

[Progress on epigenetic regulation of iron homeostasis]

Iron homeostasis plays an important role for the maintenance of human health. It is known that iron metabolism is tightly regulated by several key genes, including divalent metal transport-1(DMT1), transferrin receptor 1(TFR1), transferrin receptor 2(TFR2), ferroportin(FPN), hepcidin(HAMP), hemojuvelin(HJV) and Ferritin H. Recently, it is reported that DNA methylation, histone acetylation, and microRNA (miRNA) epigenetically regulated iron homeostasis. Among these epigenetic regulators, DNA hypermethylation of the promoter region of FPN, TFR2, HAMP, HJV and bone morphogenetic protein 6 (BMP6) genes result in inhibitory effect on the expression of these iron-related gene. In addition, histone deacetylase (HADC) suppresses HAMP gene expression. On the contrary, HADC inhibitor upregulates HAMP gene expression. Additional reports showed that miRNA can also modulate iron absorption, transport, storage and utilization via downregulation of DMT1, FPN, TFR1, TFR2, Ferritin H and other genes. It is noteworthy that some key epigenetic regulatory enzymes, such as DNA demethylase TET2 and histone lysine demethylase JmjC KDMs, require iron for the enzymatic activities. In this review, we summarize the recent progress of DNA methylation, histone acetylation and miRNA in regulating iron metabolism and also discuss the future research directions.

Association of Mutations Contributing to Clonal Hematopoiesis With Prognosis in Chronic Ischemic Heart Failure

Question

What is the clinical significance of clonal hematopoiesis of indeterminate potential (CHIP) for chronic heart failure (CHF) owing to ischemic origin?

Findings

In this cohort study, CHIP had a high prevalence in 200 investigated patients with CHF. While no clinical baseline characteristics associated with CHF were different between CHIP carriers and non-CHIP carriers, except for the mean age, harboring mutations in the most prevalent driver genes associated with CHIP, namely DNMT3A and TET2, was associated with a significant and profound increase in death and rehospitalization for heart failure.

Meaning

Clonal hematopoiesis of indeterminate potential is presented as a newly identified risk factor for impaired long-term survival and increased disease progression in patients with CHF that may be well targetable as a valuable approach to precision medicine in patients with CHF carrying specific mutations encoding for clonal hematopoiesis.

Importance

Somatic mutations causing clonal expansion of hematopoietic cells (clonal hematopoiesis of indeterminate potential [CHIP]) are increased with age and associated with atherosclerosis and inflammation. Age and inflammation are the major risk factors for heart failure, yet the association of CHIP with heart failure in humans is unknown.

Objective

To assess the potential prognostic significance of CHIP in patients with chronic heart failure (CHF) owing to ischemic origin.

Design, Setting, and Participants

We analyzed bone marrow–derived mononuclear cells from 200 patients with CHF by deep targeted amplicon sequencing to detect the presence of CHIP and associated such with long-term prognosis in patients with CHF at University Hospital Frankfurt, Frankfurt, Germany. Data were analyzed between October 2017 and April 2018.

Results

Median age of the patients was 65 years. Forty-seven mutations with a variant allele fraction (VAF) of at least 0.02 were found in 38 of 200 patients with CHF (18.5%). The somatic mutations most commonly occurred in the genes DNMT3A (14 patients), TET2 (9 patients), KDM6A (4 patients), and BCOR (3 patients). Patients with CHIP were older and more frequently had a history of hypertension. During a median follow-up of 4.4 years, a total of 53 patients died, and 23 patients required hospitalization for heart failure. There was a significantly worse long-term clinical outcome for patients with either DNMT3A or TET2 mutations compared with non-CHIP carriers. By multivariable Cox proportional regression analysis, the presence of somatic mutations within TET2 or DNMT3A (HR, 2.1; 95% CI, 1.1-4.0; P = .02, for death combined with heart failure hospitalization) and age (HR, 1.04; 95% CI, 1.01-1.07 per year; P = .005) but not a history of hypertension remained independently associated with adverse outcome. Importantly, there was a significant dose-response association between VAF and clinical outcome.

Conclusions and Relevance

Our data suggest that somatic mutations in hematopoietic cells, specifically in the most commonly mutated CHIP driver genes TET2 and DNMT3A, may be significantly associated with the progression and poor prognosis of CHF. Future studies will have to validate our findings in larger cohorts and address whether targeting specific inflammatory pathways may be valuable for precision medicine in patients with CHF carrying specific mutations encoding for CHIP.