Ten-eleven translocation-2-mediated macrophage activation promotes liver regeneration

BACKGROUND

The remarkable regenerative capacity of the liver enables recovery after radical Hepatocellular carcinoma (HCC) resection. After resection, macrophages secrete interleukin 6 and hepatocyte growth factors to promote liver regeneration. Ten-eleven translocation-2 (Tet2) DNA dioxygenase regulates pro-inflammatory factor secretion in macrophages. In this study, we explored the role of Tet2 in macrophages and its function independent of its enzymatic activity in liver regeneration.

METHODS

The model of liver regeneration after 70% partial hepatectomy (PHx) is a classic universal model for studying reparative processes in the liver. Mice were euthanized at 0, 24, and 48 h after PHx. Enzyme-linked immunosorbent assays, quantitative reverse transcription-polymerase chain reaction, western blotting, immunofluorescence analysis, and flow cytometry were performed to explore immune cell infiltration and liver regenerative capability. Molecular dynamics simulations were performed to study the interaction between Tet2 and signal transducer and activator of transcription 1 (Stat1).

RESULTS

Tet2 in macrophages negatively regulated liver regeneration in the partial hepatectomy mice model. Tet2 interacted with Stat1, inhibiting the expression of proinflammatory factors and suppressing liver regeneration. The Tet2 inhibitor attenuated the interaction between Stat1 and Tet2, enhanced Stat1 phosphorylation, and promoted hepatocyte proliferation. The proliferative function of the Tet2 inhibitor relied on macrophages and did not affect hepatocytes directly.

CONCLUSION

Our findings underscore that Tet2 in macrophages negatively regulates liver regeneration by interacting with Stat1. Targeting Tet2 in macrophages promotes liver regeneration and function after a hepatectomy, presenting a novel target to promote liver regeneration and function.

In vivo DNA methylation editing in zebrafish

The CRISPR/dCas9-based epigenome editing technique has driven much attention. Fused with a catalytic domain from Dnmt or Tet protein, the CRISPR/dCas9-DnmtCD or -TetCD systems possess the targeted DNA methylation editing ability and have established a series of in vitro and in vivo disease models. However, no publication has been reported on zebrafish (Danio rerio), an important animal model in biomedicine. The present study demonstrated that CRISPR/dCas9-Dnmt7 and -Tet2 catalytic domain fusions could site-specifically edit genomic DNA methylation in vivo in zebrafish and may serve as an efficient toolkit for DNA methylation editing in the zebrafish model.

IDH2 and TET2 mutations synergize to modulate T Follicular Helper cell functional interaction with the AITL microenvironment

Angioimmunoblastic T cell lymphoma (AITL) is a peripheral T cell lymphoma that originates from T follicular helper (Tfh) cells and exhibits a prominent tumor microenvironment (TME). IDH2 and TET2 mutations co-occur frequently in AITL, but their contribution to tumorigenesis is poorly understood. We developed an AITL mouse model that is driven by Idh2 and Tet2 mutations. Malignant Tfh cells display aberrant transcriptomic and epigenetic programs that impair TCR signaling. Neoplastic Tfh cells bearing combined Idh2 and Tet2 mutations show altered cross-talk with germinal center B cells that promotes B cell clonal expansion while decreasing Fas-FasL interaction and reducing B cell apoptosis. The plasma cell count and angiogenesis are also increased in the Idh2-mutated tumors, implying a major relationship between Idh2 mutation and the characteristic AITL TME. Our mouse model recapitulates several features of human IDH2-mutated AITL and provides a rationale for exploring therapeutic targeting of Tfh-TME cross-talk for AITL patients.

Knockdown of Tet2 Inhibits the Myogenic Differentiation of Chicken Myoblasts Induced by Ascorbic Acid

Ascorbic acid (also called Vitamin C, VC) strengthens the function of Tets families and directly increases DNA demethylation level to affect myogenic differentiation. However, the precise regulatory mechanism of DNA methylation in chicken myogenesis remains unclear. Results of present study showed that the mRNA expression of MyoD significantly decreased and MyoG and MyHC increased in myoblasts treated with 5 μM 5-azacytidine (5-AZA) and 5 μM VC (p < 0.05). Results also indicated the formation of myotubes was induced by 5-AZA or VC, but this effect was attenuated after knockdown of Tet2. In addition, the protein expression of TET2, DESMIN and MyHC was remarkable increased by the addition of 5-AZA or VC, and the upregulation was inhibited after knockdown of Tet2 (p < 0.05). DNA dot blot and immunofluorescence staining results suggested that the level of 5hmC was significantly increased when treated with 5-AZA or VC, even by Tet2 knockdown (p < 0.05). Moreover, 5-AZA and VC reduced the level of dimethylation of lysine 9 (H3K9me2) and trimethylation of lysine 27 of histone 3 (H3K27me3), and this inhibitory effect was eliminated after Tet2 knockdown (p < 0.05). These data indicated that Tet2 knockdown antagonized the increased levels of 5hmC and H3K27me3 induced by 5-AZA and VC, and eventually reduced myotube formation by modulating the expression of genes involved in myogenic differentiation. This study provides insights that epigenetic regulators play essential roles in mediating the myogenic program of chicken myoblasts.

Tet2 deficiency drives liver microbiome dysbiosis triggering Tc1 cell autoimmune hepatitis

The triggers that drive interferon-γ (IFNγ)-producing CD8 T cell (Tc1 cell)-mediated autoimmune hepatitis (AIH) remain obscure. Here, we show that lack of hematopoietic Tet methylcytosine dioxygenase 2 (Tet2), an epigenetic regulator associated with autoimmunity, results in the development of microbiota-dependent AIH-like pathology, accompanied by hepatic enrichment of aryl hydrocarbon receptor (AhR) ligand-producing pathobionts and rampant Tc1 cell immunity. We report that AIH-like disease development is dependent on both IFNγ and AhR signaling, as blocking either reverts ongoing AIH-like pathology. Illustrating the critical role of AhR-ligand-producing pathobionts in this condition, hepatic translocation of the AhR ligand indole-3-aldehyde (I3A)-releasing Lactobacillus reuteri is sufficient to trigger AIH-like pathology. Finally, we demonstrate that I3A is required for L. reuteri-induced Tc1 cell differentiation in vitro and AIH-like pathology in vivo, both of which are restrained by Tet2 within CD8 T cells. This AIH-disease model may contribute to the development of therapeutics to alleviate AIH.

Tet2 deficiency in immune cells exacerbates tumor progression by increasing angiogenesis in a lung cancer model

Immune cells harboring somatic mutations reportedly infiltrate cancer tissues in patients with solid cancers and accompanying clonal hematopoiesis. Loss‐of‐function TET2 mutations are frequently observed in clonal hematopoiesis in solid cancers. Here, using a mouse lung cancer model, we evaluated the activity of Tet2‐deficient immune cells in tumor tissues. Myeloid‐specific Tet2 deficiency enhanced tumor growth in mice relative to that seen in controls. Single‐cell sequencing analysis of immune cells infiltrating tumors showed relatively high expression of S100a8/S100a9 in Tet2‐deficient myeloid subclusters. In turn, treatment with S100a8/S100a9 promoted Vegfa production by cancer cells, leading to a marked increase in the tumor vasculature in Tet2‐deficient mice relative to controls. Finally, treatment of Tet2‐deficient mice with an antibody against Emmprin, a known S100a8/S100a9 receptor, suppressed tumor growth. These data suggest that immune cells derived from TET2‐mutated clonal hematopoiesis exacerbate lung cancer progression by promoting tumor angiogenesis and may provide a novel therapeutic target for lung cancer patients with TET2‐mutated clonal hematopoiesis.

Tet2 regulates Barx2 expression in undifferentiated and early differentiated mouse embryonic stem cells

The methylcytosine oxidase TET proteins play important roles in DNA demethylation and development. In developing embryos, TET2 are upregulated during pre-implantation development, and significantly expressed in the trophectoderm and inner cell mass. In this study, we identified Barx2 as a new target of Tet2. Tet2 bound and demethylated the promoter of Barx2 in mouse embryonic stem cells (mESCs) to maintain the expression of Barx2. During mESC differentiation, Tet2 bound the promoter of Barx2 in day 4 embryonic bodies but not in day 8 EBs. However, Barx2 expression remained unchanged. Thus, Tet2 functioned as a demethylase and maintained the expression of Barx2 in undifferentiated and early differentiated mESCs.

Bronchial Epithelial Tet2 Maintains Epithelial Integrity during Acute Pseudomonas aeruginosa Pneumonia

Respiratory epithelial cells are important for pulmonary innate immune responses during Pseudomonas aeruginosa infection. Tet methylcytosine dioxygenase 2 (Tet2) has been implicated in the regulation of host defense by myeloid and lymphoid cells, but whether Tet2 also contributes to epithelial responses during pneumonia is unknown. The aim of this study was to investigate the role of bronchial epithelial Tet2 in acute pneumonia caused by P. aeruginosa To this end, we crossed mice with Tet2 flanked by two Lox-P sites (Tet2^fl/fl mice) with mice expressing Cre recombinase under the bronchial epithelial cell-specific Cc10 promoter (Cc10^Cre mice) to generate bronchial epithelial cell-specific Tet2-deficient (Tet2^fl/fl Cc10^Cre ) mice. Six hours after infection with P. aeruginosa, Tet2^fl/fl Cc10^Cre and wild-type mice had similar bacterial loads in bronchoalveolar lavage fluid (BALF). At this time point, Tet2^fl/fl Cc10^Cre mice displayed reduced mRNA levels of the chemokines Cxcl1, Cxcl2, and Ccl20 in bronchial brushes. However, Cxcl1, Cxcl2, and Ccl20 protein levels and leukocyte recruitment in BALF were not different between groups. Tet2^fl/fl Cc10^Cre mice had increased protein levels in BALF after infection, indicating a disturbed epithelial barrier function, which was corroborated by reduced mRNA expression of tight junction protein 1 and occludin in bronchial brushes. Differences detected between Tet2^fl/fl Cc10^Cre and wild-type mice were no longer present at 24 h after infection. These results suggest that bronchial epithelial Tet2 contributes to maintaining epithelial integrity by enhancing intracellular connections between epithelial cells during the early phase of P. aeruginosa pneumonia.

Effects of Ten-Eleven Translocation-2 (Tet2) on myogenic differentiation of chicken myoblasts

Skeletal muscle development is an orchestrated progress that is primarily regulated by temporospatial expression of myogenic regulatory factors (MRFs). Recent studies demonstrated that DNA demethylation also exerted a critical role in myogenesis. However, the function of Tet2 in the regulation of chicken myogenesis still remains unknown. In the present study, the role of Tet2 in regulating myogenic differentiation was determined by using a model of primary myoblasts from chickens. The expression of Tet2 was significantly elevated during myoblast differentiation. Meanwhile, the level of 5hmC in genomic DNA was increased, but H3K9me2 and H3K27me3 were markedly reduced following differentiation. Knockdown of Tet2 significantly inhibited the formation of multinucleated myotubes, which was accompanied by a reduction of relevant pivotal MRFs. Moreover, the level of 5hmC decreased sharply in Tet2 knockdown myoblasts. Attenuated differentiated myoblasts that resulted from reduced Tet2 also demonstrated an increased level of H3K9me2 and H3K27me3. Collectively, these results indicated that Tet2 played an essential role during myogenesis, which affected demethylation of genomic DNA and histone to regulate expression of MRFs and therefore, contributed to myoblast differentiation.

A mosaic analysis system with Cre or Tomato expression in the mouse

Somatic mutations are the driving force of many age-related diseases such as cancer and hematopoietic failure. A challenge in the field is to evaluate health impact of somatic mutations prior to the appearance of disease symptoms. We describe a genetic tool named MASCOT (mosaic analysis system with Cre or Tomato) for mosaic analysis of somatic mutations that drive clonal hematopoiesis and lymphomagenesis. MASCOT can be applied to mosaic analysis of broad tissue types, and thus provides a valuable tool to aid functional dissection of somatic mutations in studies of development and disease.

Somatic mutations are major genetic contributors to cancers and many other age-related diseases. Many disease-causing somatic mutations can initiate clonal growth prior to the appearance of any disease symptoms, yet experimental models that can be used to examine clonal abnormalities are limited. We describe a mosaic analysis system with Cre or Tomato (MASCOT) for tracking mutant cells and demonstrate its utility for modeling clonal hematopoiesis. MASCOT can be induced to constitutively express either Cre-GFP or Tomato for lineage tracing of a mutant and a reference group of cells simultaneously. We conducted mosaic analysis to assess functions of the Id3 and/or Tet2 gene in hematopoietic cell development and clonal hematopoiesis. Using Tomato-positive cells as a reference population, we demonstrated the high sensitivity of this system for detecting cell-intrinsic phenotypes during short-term or long-term tracking of hematopoietic cells. Long-term tracking of Tet2 mutant or Tet2/Id3 double-mutant cells in our MASCOT model revealed a dynamic shift from myeloid expansion to lymphoid expansion and subsequent development of lymphoma. This work demonstrates the utility of the MASCOT method in mosaic analysis of single or combined mutations, making the system suitable for modeling somatic mutations identified in humans.

Non-catalytic Roles of Tet2 Are Essential to Regulate Hematopoietic Stem and Progenitor Cell Homeostasis

The Ten-eleven translocation (TET) enzymes regulate gene expression by promoting DNA demethylation and partnering with chromatin modifiers. TET2, a member of this family, is frequently mutated in hematological disorders. The contributions of TET2 in hematopoiesis have been attributed to its DNA demethylase activity, and the significance of its nonenzymatic functions has remained undefined. To dissect the catalytic and non-catalytic requirements of Tet2, we engineered catalytically inactive Tet2 mutant mice and conducted comparative analyses of Tet2 mutant and Tet2 knockout animals. Tet2 knockout mice exhibited expansion of hematopoietic stem and progenitor cells (HSPCs) and developed myeloid and lymphoid disorders, while Tet2 mutant mice predominantly developed myeloid malignancies reminiscent of human myelodysplastic syndromes. HSPCs from Tet2 knockout mice exhibited distinct gene expression profiles, including downregulation of Gata2. Overexpression of Gata2 in Tet2 knockout bone marrow cells ameliorated disease phenotypes. Our results reveal the non-catalytic roles of TET2 in HSPC homeostasis.

TET2 promotes anti-tumor immunity by governing G-MDSCs and CD8+ T-cell numbers

The host immune response is a fundamental mechanism for attenuating cancer progression. Here we report a role for the DNA demethylase and tumor suppressor TET2 in host anti-tumor immunity. Deletion of Tet2 in mice elevates IL-6 levels upon tumor challenge. Elevated IL-6 stimulates immunosuppressive granulocytic myeloid-derived suppressor cells (G-MDSCs), which in turn reduce CD8⁺ T cells upon tumor challenge. Consequently, systematic knockout of Tet2 in mice leads to accelerated syngeneic tumor growth, which is constrained by anti-PD-1 blockade. Removal of G-MDSCs by the anti-mouse Ly6g antibodies restores CD8⁺ T-cell numbers in Tet2^-/- mice and reboots their anti-tumor activity. Importantly, anti-IL-6 antibody treatment blocks the expansion of G-MDSCs and inhibits syngeneic tumor growth. Collectively, these findings reveal a TET2-mediated IL-6/G-MDSCs/CD8⁺ T-cell immune response cascade that safeguards host adaptive anti-tumor immunity, offering a cell non-autonomous mechanism of TET2 for tumor suppression.

Ten-eleven translocation methyl-cytosine dioxygenase 2 deficiency exacerbates renal ischemia-reperfusion injury

BACKGROUND

Ten-eleven translocation (Tet) methyl-cytosine dioxygenases (including Tet1/2/3)-mediated 5mC oxidation and DNA demethylation play important roles in embryonic development and adult tissue homeostasis. The expression of Tet2 and Tet3 genes are relatively abundant in the adult murine kidneys while Tet1 gene is expressed at a low level. Although Tet3 has been shown to suppress kidney fibrosis, the role of Tet2 in kidney physiology as well as renal ischemia-reperfusion (IR) injury is still largely unknown.

RESULTS

Tet2^-/- mice displayed normal kidney morphology and renal function as WT mice while the expression of genes associated with tight junction and adherens junction was impaired. At 24 h post-renal IR, Tet2^-/- mice showed higher SCr and BUN levels, more severe tubular damage, and elevated expression of Kim1 and Ngal genes in the kidney in comparison with WT mice. Moreover, the transcriptomic analysis revealed augmented inflammatory response in the kidneys of Tet2^-/- mice.

CONCLUSIONS

Tet2 is dispensable for kidney development and function at baseline condition while protects against renal IR injury possibly through repressing inflammatory response. Our findings suggest that Tet2 may be a potential target for the intervention of IR-induced acute kidney injury (AKI).

Inhibition of Inflammatory Signaling in Tet2 Mutant Preleukemic Cells Mitigates Stress-Induced Abnormalities and Clonal Hematopoiesis

Inflammation is a risk factor for cancer development. Individuals with preleukemic TET2 mutations manifest clonal hematopoiesis and are at a higher risk of developing leukemia. How inflammatory signals influence the survival of preleukemic hematopoietic stem and progenitor cells (HSPCs) is unclear. We show a rapid increase in the frequency and absolute number of Tet2-KO mature myeloid cells and HSPCs in response to inflammatory stress, which results in enhanced production of inflammatory cytokines, including interleukin-6 (IL-6), and resistance to apoptosis. IL-6 induces hyperactivation of the Shp2-Stat3 signaling axis, resulting in increased expression of a novel anti-apoptotic long non-coding RNA (lncRNAs), Morrbid, in Tet2-KO myeloid cells and HSPCs. Expression of activated Shp2 in HSPCs phenocopies Tet2 loss with regard to hyperactivation of Stat3 and Morrbid. In vivo, pharmacologic inhibition of Shp2 or Stat3 or genetic loss of Morrbid in Tet2 mutant mice rescues inflammatory-stress-induced abnormalities in HSPCs and mature myeloid cells, including clonal hematopoiesis.

Dual mechanisms of posttranscriptional regulation of Tet2 by Let-7 microRNA in macrophages

Tet methylcytosine dioxygenase 2 (Tet2) is an epigenetic regulator that removes methyl groups from deoxycytosine residues in DNA. Tet2-deficient murine macrophages show increased lipopolysaccharide (LPS)-induced and spontaneous inflammation at least partially because Tet2 acts to restrain interleukin (IL)-1β and IL-6 expression in induced cells. MicroRNAs have emerged as critical regulatory noncoding RNAs that tune immune cell responses to physiological perturbations and play roles in pathological conditions in macrophages. To determine if a microRNA played any role in Tet2 activity, we examined the interrelationship of Tet2 action and the let-7 microRNA family, utilizing several let-7 microRNA engineered murine models. We first showed that Tet2, but not Tet3, is a direct target of the let-7a-1/let-7d/let-7f-1 (let-7adf) microRNAs in macrophages. We found that overexpression or deletion of the let-7adf gene cluster causes altered IL-6 induction both in tissue culture cells induced by LPS treatment in vitro as well as in a Salmonella infection mouse model in vivo. Mechanistically, let-7adf promotes IL-6 by directly repressing Tet2 levels and indirectly by enhancing a Tet2 suppressor, the key TCA cycle metabolite, succinate. We found that Let-7adf promotes succinate accumulation by regulating the Lin28a/Sdha axis. We thereby identify two pathways of let-7 control of Tet2 and, in turn, of the key inflammatory cytokine, IL-6, thus characterizing a regulatory pathway in which a microRNA acts as a feedback inhibitor of inflammatory processes.

Tet2 Rescues Age-Related Regenerative Decline and Enhances Cognitive Function in the Adult Mouse Brain

Restoring adult stem cell function provides an exciting approach for rejuvenating the aging brain. However, molecular mechanisms mediating neurogenic rejuvenation remain elusive. Here we report that the enzyme ten eleven translocation methylcytosine dioxygenase 2 (Tet2), which catalyzes the production of 5-hydroxymethylcytosine (5hmC), rescues age-related decline in adult neurogenesis and enhances cognition in mice. We detected a decrease in Tet2 expression and 5hmC levels in the aged hippocampus associated with adult neurogenesis. Mimicking an aged condition in young adults by abrogating Tet2 expression within the hippocampal neurogenic niche, or adult neural stem cells, decreased neurogenesis and impaired learning and memory. In a heterochronic parabiosis rejuvenation model, hippocampal Tet2 expression was restored. Overexpressing Tet2 in the hippocampal neurogenic niche of mature adults increased 5hmC associated with neurogenic processes, offset the precipitous age-related decline in neurogenesis, and enhanced learning and memory. Our data identify Tet2 as a key molecular mediator of neurogenic rejuvenation.

Disruption of asxl1 results in myeloproliferative neoplasms in zebrafish

Somatic loss-of-function mutations of the additional sex combs-like transcriptional regulator 1 (ASXL1) gene are common genetic abnormalities in human myeloid malignancies and induce clonal expansion of mutated hematopoietic stem cells (HSCs). To understand how ASXL1 disruption leads to myeloid cell transformation, we generated asxl1 haploinsufficient and null zebrafish lines using genome-editing technology. Here, we show that homozygous loss of asxl1 leads to apoptosis of newly formed HSCs. Apoptosis occurred via the mitochondrial apoptotic pathway mediated by upregulation of bim and bid. Half of the asxl1^+/− zebrafish had myeloproliferative neoplasms (MPNs) by 5 months of age. Heterozygous loss of asxl1 combined with heterozygous loss of tet2 led to a more penetrant MPN phenotype, while heterozygous loss of asxl1 combined with complete loss of tet2 led to acute myeloid leukemia (AML). These findings support the use of asxl1^+/− zebrafish as a strategy to identify small-molecule drugs to suppress the growth of asxl1 mutant but not wild-type HSCs in individuals with somatically acquired inactivating mutations of ASXL1.

Summary: Homozygous loss of asxl1 in zebrafish leads to apoptosis of newly formed HSCs by upregulation of bim and bid. Half of the asxl1^+/− zebrafish had MPNs by 5 months of age.

The role of 5-hydroxymethylcytosine in mitochondria after ischemic stroke

5-Hydroxymethylcytosine (5hmC) exists in DNA, RNA, and mitochondrial DNA (mtDNA) and plays an important role in many diseases. Specifically, 5hmC is involved in promoting gene expression, and this process is regulated by Tet enzymes. In this study, we identified that there is no difference in male mice and female mice at first; then we examined the levels of 5hmC in mtDNA and explored the relationship among 5hmC, mitochondrial gene expression and ATP production after acute brain ischemia. The abundance of mtDNA 5hmC was increased at 1 d and peaked at 2 d after ischemic injury, whereas that of mtDNA 5mC was unchanged. Furthermore, increased mitochondrial Tet2 expression was found to be responsible for the increase in mtDNA 5hmC. Tet2 inhibition decreased the mtDNA 5hmC abundance and increased the ATP levels in mitochondria, suggesting an association between the cellular ATP levels and mtDNA 5hmC abundance. We also demonstrated that mtDNA 5hmC increased the mRNA levels of mitochondrial genes after ischemia/reperfusion (I/R) injury.

Tet2 Regulates Osteoclast Differentiation by Interacting with Runx1 and Maintaining Genomic 5-Hydroxymethylcytosine (5hmC)

As a dioxygenase, Ten-Eleven Translocation 2 (TET2) catalyzes subsequent steps of 5-methylcytosine (5mC) oxidation. TET2 plays a critical role in the self-renewal, proliferation, and differentiation of hematopoietic stem cells, but its impact on mature hematopoietic cells is not well-characterized. Here we show that Tet2 plays an essential role in osteoclastogenesis. Deletion of Tet2 impairs the differentiation of osteoclast precursor cells (macrophages) and their maturation into bone-resorbing osteoclasts in vitro. Furthermore, Tet2-/- mice exhibit mild osteopetrosis, accompanied by decreased number of osteoclasts in vivo. Tet2 loss in macrophages results in the altered expression of a set of genes implicated in osteoclast differentiation, such as Cebpa, Mafb, and Nfkbiz. Tet2 deletion also leads to a genome-wide alteration in the level of 5-hydroxymethylcytosine (5hmC) and altered expression of a specific subset of macrophage genes associated with osteoclast differentiation. Furthermore, Tet2 interacts with Runx1 and negatively modulates its transcriptional activity. Our studies demonstrate a novel molecular mechanism controlling osteoclast differentiation and function by Tet2, that is, through interactions with Runx1 and the maintenance of genomic 5hmC. Targeting Tet2 and its pathway could be a potential therapeutic strategy for the prevention and treatment of abnormal bone mass caused by the deregulation of osteoclast activities.

[The effect of DNA hydroxymethylase Tet2 on γ globin activation in the treatment of β-thalassemia]

Objective: To study the function of ten-eleven translocation 2 (Tet2) in γ globin gene expression in patients with β- thalassemia. Methods: Gamma globin expression was induced by 5-azacytidine and Tet2 gene expression was knocked down by short hairpin RNA (shRNA) in a human immortalized myelogenous leukemia K562 cell line. The global 5-hydroxymethylcytosine (5hmC) level was measured by an ELISA kit. 5hmC level of γ globin gene was quantified by sulfite sequencing. The mRNA level of Tet2, γ globin, and related transcription factors Nfe4 and Klf1 were quantified by real-time PCR. Results: Tet2 knockdown resulted in a decreased global 5hmC level from 0.14% to 0.03% as of the control group in K562 cells. The expression of γ globin was enhanced after 5-azacytidine treatment in vitro. However, γ globin mRNA level in Tet2 knockdown cells was only 55% as that in control group. The CG sites on γ globin gene were unmethylated. As Tet2 was down-regulated, the expression levels of Nfe4 and Klf1 decreased by about 80% and increased to 3.5 folds, respectively. Conclusions: Tet2 appears to maintain 5hmC level and facilitates γ globin gene activation. Moreover, Tet2 more likely regulates γ globin expression via affecting transcription factors rather than the gene itself. Thus, Tet2 could be a potential therapeutic target for β thalassemias.

An epigenetic switch repressing Tet1 in gonadotropes activates the reproductive axis

The TET enzymes catalyze conversion of 5-methyl cytosine (5mC) to 5-hydroxymethyl cytosine (5hmC) and play important roles during development. TET1 has been particularly well-studied in pluripotent stem cells, but Tet1-KO mice are viable, and the most marked defect is abnormal ovarian follicle development, resulting in impaired fertility. We hypothesized that TET1 might play a role in the central control of reproduction by regulating expression of the gonadotropin hormones, which are responsible for follicle development and maturation and ovarian function. We find that all three TET enzymes are expressed in gonadotrope-precursor cells, but Tet1 mRNA levels decrease markedly with completion of cell differentiation, corresponding with an increase in expression of the luteinizing hormone gene, Lhb We demonstrate that poorly differentiated gonadotropes express a TET1 isoform lacking the N-terminal CXXC-domain, which represses Lhb gene expression directly and does not catalyze 5hmC at the gene promoter. We show that this isoform is also expressed in other differentiated tissues, and that it is regulated by an alternative promoter whose activity is repressed by the liganded estrogen and androgen receptors, and by the hypothalamic gonadotropin-releasing hormone through activation of PKA. Its expression is also regulated by DNA methylation, including at an upstream enhancer that is protected by TET2, to allow Tet1 expression. The down-regulation of TET1 relieves its repression of the methylated Lhb gene promoter, which is then hydroxymethylated and activated by TET2 for full reproductive competence.

Vitamin C down-regulate apo(a) expression via Tet2-dependent DNA demethylation in HepG2 cells

Lipoprotein(a)[Lp(a)] is a risk factor for coronary heart diseases. However, the metabolism of this protein remains poorly understood. Efficient and specific drugs that can decrease high plasma levels of Lp(a) have not been developed yet. Vitamin C is responsible for maintaining the catalytic activity of a group of iron and 2-oxoglutarate (2OG)-dependent dioxygenases and induces the generation of 5-hydroxymethylcytosine (5hmC) via Ten-eleven translocation (Tet) dioxygenases. In addition, It has been reported vitamin C deficiency induces atherosclerosis and increases Lp(a) and apo(a) plasma levels in Lp(a)+ mice. However, the mechanism is still unclear. In this study, we investigated the effects of vitamin C on apo(a) expression and the possible molecular mechanism of vitamin C that influences apolipoprotein(a) [apo(a)] biosynthesis in HepG2 cells. Results showed that vitamin C significantly inhibited the expression and secretion levels of apo(a). Vitamin C can also increase ELK1 expression and hydroxymethylation of ELK1 promoter and the globle DNA in HepG2 cells. In addition, the effects of vitamin C inhibiting the apo(a) expression were attenuated by ELK1siRNA and Tet2siRNA. These results suggested vitamin C down-regulate apo(a) expression via Tet2-dependent DNA demethylation in HepG2 cells.

MBD3L2 promotes Tet2 enzymatic activity for mediating 5-methylcytosine oxidation

Ten-eleven translocation (Tet) proteins are key players involved in the dynamic regulation of cytosine methylation and demethylation. Inactivating mutations of Tet2 are frequently found in human malignancies, highlighting the essential role of Tet2 in cellular transformation. However, the factors that control Tet enzymatic activity remain largely unknown. Here, we found that methyl-CpG-binding domain protein 3 (MBD3) and its homolog MBD3-like 2 (MBD3L2) can specifically modulate the enzymatic activity of Tet2 protein, but not Tet1 and Tet3 proteins, in converting 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC). Moreover, MBD3L2 is more effective than MBD3 in promoting Tet2 enzymatic activity through strengthening the binding affinity between Tet2 and the methylated DNA target. Further analysis revealed pronounced decreases in 5mC levels at MBD3L2 and Tet2 co-occupied genomic regions, most of which are promoter elements associated with either cancer-related genes or genes involved in the regulation of cellular metabolic processes. Our data add new insights into the regulation of Tet2 activity by MBD3 and MBD3L2, and into how that affects Tet2-mediated modulation of its target genes in cancer development. Thus, they have important applications in understanding how dysregulation of Tet2 might contribute to human malignancy.

Genome engineering of mammalian haploid embryonic stem cells using the Cas9/RNA system

Haploid embryonic stem cells (ESCs) are useful for studying mammalian genes because disruption of only one allele can cause loss-of-function phenotypes. Here, we report the use of haploid ESCs and the CRISPR RNA-guided Cas9 nuclease gene-targeting system to manipulate mammalian genes. Co-transfection of haploid ESCs with vectors expressing Cas9 nuclease and single-guide RNAs (sgRNAs) targeting Tet1, Tet2, and Tet3 resulted in the complete disruption of all three genes and caused a loss-of-function phenotype with high efficiency (50%). Co-transfection of cells with vectors expressing Cas9 and sgRNAs targeting two loci on the same chromosome resulted in the creation of a large chromosomal deletion and a large inversion. Thus, the use of the CRISPR system in combination with haploid ESCs provides a powerful platform to manipulate the mammalian genome.