Inducible disruption of Tet genes results in myeloid malignancy, readthrough transcription, and a heterochromatin-to-euchromatin switch.

The three mammalian TET dioxygenases oxidize the methyl group of 5-methylcytosine in DNA, and the oxidized methylcytosines are essential intermediates in all known pathways of DNA demethylation. To define the in vivo consequences of complete TET deficiency, we inducibly deleted all three Tet genes in the mouse genome. Tet1/2/3-inducible TKO (iTKO) mice succumbed to acute myeloid leukemia (AML) by 4 to 5 wk. Single-cell RNA sequencing of Tet iTKO bone marrow cells revealed the appearance of new myeloid cell populations characterized by a striking increase in expression of all members of the stefin/cystatin gene cluster on mouse chromosome 16. In patients with AML, high stefin/cystatin gene expression correlates with poor clinical outcomes. Increased expression of the clustered stefin/cystatin genes was associated with a heterochromatin-to-euchromatin compartment switch with readthrough transcription downstream of the clustered stefin/cystatin genes as well as other highly expressed genes, but only minor changes in DNA methylation. Our data highlight roles for TET enzymes that are distinct from their established function in DNA demethylation and instead involve increased transcriptional readthrough and changes in three-dimensional genome organization.

Loss of adipose TET proteins enhances ß-adrenergic responses and protects against obesity by epigenetic regulation of ß3-AR expression.

ß-adrenergic receptor (ß-AR) signaling plays predominant roles in modulating energy expenditure by triggering lipolysis and thermogenesis in adipose tissue, thereby conferring obesity resistance. Obesity is associated with diminished ß3-adrenergic receptor (ß3-AR) expression and decreased ß-adrenergic responses, but the molecular mechanism coupling nutrient overload to catecholamine resistance remains poorly defined. Ten-eleven translocation (TET) proteins are dioxygenases that alter the methylation status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine and further oxidized derivatives. Here, we show that TET proteins are pivotal epigenetic suppressors of ß3-AR expression in adipocytes, thereby attenuating the responsiveness to ß-adrenergic stimulation. Deletion of all three Tet genes in adipocytes led to increased ß3-AR expression and thereby enhanced the downstream ß-adrenergic responses, including lipolysis, thermogenic gene induction, oxidative metabolism, and fat browning in vitro and in vivo. In mouse adipose tissues, Tet expression was elevated after mice ate a high-fat diet. Mice with adipose-specific ablation of all TET proteins maintained higher levels of ß3-AR in both white and brown adipose tissues and remained sensitive to ß-AR stimuli under high-fat diet challenge, leading to augmented energy expenditure and decreased fat accumulation. Consequently, they exhibited improved cold tolerance and were substantially protected from diet-induced obesity, inflammation, and metabolic complications, including insulin resistance and hyperlipidemia. Mechanistically, TET proteins directly repressed ß3-AR transcription, mainly in an enzymatic activity-independent manner, and involved the recruitment of histone deacetylases to increase deacetylation of its promoter. Thus, the TET-histone deacetylase-ß3-AR axis could be targeted to treat obesity and related metabolic diseases.

CD8α(-) Dendritic Cells Induce Antigen-Specific T Follicular Helper Cells Generating Efficient Humoral Immune Responses.

Recent studies on T follicular helper (Tfh) cells have significantly advanced our understanding of T cell-dependent B cell responses. However, little is known about the early stage of Tfh cell commitment by dendritic cells (DCs), particularly by the conventional CD8α(+) and CD8α(-) DC subsets. We show that CD8α(-) DCs localized at the interfollicular zone play a pivotal role in the induction of antigen-specific Tfh cells by upregulating the expression of Icosl and Ox40l through the non-canonical NF-κB signaling pathway. Tfh cells induced by CD8α(-) DCs function as true B cell helpers, resulting in significantly increased humoral immune responses against various human pathogenic antigens, including Yersinia pestis LcrV, HIV Gag, and hepatitis B surface antigen. Our findings uncover a mechanistic role of CD8α(-) DCs in the initiation of Tfh cell differentiation and thereby provide a rationale for investigating CD8α(-) DCs in enhancing antigen-specific humoral immune responses for improving vaccines and therapeutics.