Chromatin modulators are emerging as attractive drug targets, given their widespread implication in human cancers and susceptibility to pharmacological inhibition. Here we establish the histone methyltransferase G9a/EHMT2 as a selective regulator of fast proliferating myeloid progenitors with no discernible function in hematopoietic stem cells (HSCs). In mouse models of acute myeloid leukemia (AML), loss of G9a significantly delays disease progression and reduces leukemia stem cell (LSC) frequency. We connect this function of G9a to its methyltransferase activity and its interaction with the leukemogenic transcription factor HoxA9 and provide evidence that primary human AML cells are sensitive to G9A inhibition. Our results highlight a clinical potential of G9A inhibition as a means to counteract the proliferation and self-renewal of AML cells by attenuating HoxA9-dependent transcription.

Group 2 innate lymphoid cells (ILC2s) are tissue resident in the lung and activated by inhaled allergens via epithelial-derived alarmins including IL-33. Activated ILC2s proliferate, produce IL-5 and IL-13, and induce eosinophilic inflammation. Here, we report that intranasal IL-33 or the protease allergen papain administration resulted in increased numbers of ILC2s not only in the lung but also in peripheral blood and liver. Analyses of IL-33 treated parabiosis mice showed that the increase in lung ILC2s was due to proliferation of lung resident ILC2s, whereas the increase in liver ILC2s was due to the migration of activated lung ILC2s. Lung-derived ILC2s induced eosinophilic hepatitis and expression of fibrosis-related genes. Intranasal IL-33 pre-treatment also attenuated concanavalin A-induced acute hepatitis and cirrhosis. These results suggest that activated lung resident ILC2s emigrate from the lung, circulate, settle in the liver and promote type 2 inflammation and attenuate type 1 inflammation.

The development of cell therapy for repairing damaged or diseased skeletal muscle has been hindered by the inability to significantly expand immature, transplantable myogenic stem cells (MuSCs) in culture. To overcome this limitation, a deeper understanding of the mechanisms regulating the transition between activated, proliferating MuSCs and differentiation-primed, poorly engrafting progenitors is needed. Here, we show that methyltransferase Setd7 facilitates such transition by regulating the nuclear accumulation of β-catenin in proliferating MuSCs. Genetic or pharmacological inhibition of Setd7 promotes in vitro expansion of MuSCs and increases the yield of primary myogenic cell cultures. Upon transplantation, both mouse and human MuSCs expanded with a Setd7 small-molecule inhibitor are better able to repopulate the satellite cell niche, and treated mouse MuSCs show enhanced therapeutic potential in preclinical models of muscular dystrophy. Thus, Setd7 inhibition may help bypass a key obstacle in the translation of cell therapy for muscle disease.

Innate lymphoid cells (ILCs) are emerging as important regulators of homeostatic and disease-associated immune processes. Despite recent advances in defining the molecular pathways that control development and function of ILCs, the epigenetic mechanisms that regulate ILC biology are unknown. Here, we identify a role for the lysine methyltransferase G9a in regulating ILC2 development and function. Mice with a hematopoietic cell-specific deletion of G9a (Vav.G9a(-/-) mice) have a severe reduction in ILC2s in peripheral sites, associated with impaired development of immature ILC2s in the bone marrow. Accordingly, Vav.G9a(-/-) mice are resistant to the development of allergic lung inflammation. G9a-dependent dimethylation of histone 3 lysine 9 (H3K9me2) is a repressive histone mark that is associated with gene silencing. Genome-wide expression analysis demonstrated that the absence of G9a led to increased expression of ILC3-associated genes in developing ILC2 populations. Further, we found high levels of G9a-dependent H3K9me2 at ILC3-specific genetic loci, demonstrating that G9a-mediated repression of ILC3-associated genes is critical for the optimal development of ILC2s. Together, these results provide the first identification of an epigenetic regulatory mechanism in ILC development and function.

Extracellular matrix (ECM) gives structure, support, and is the niche for several cells found in skeletal muscle. ECM is mainly produced by muscle connective tissue (CT) fibroblasts during development and regeneration. Stromal fibroadipogenic progenitors (FAPs) are CT fibroblasts-like mesenchymal progenitors (MPs) with important roles in regeneration and degeneration. Chronic damage restrains the normal regenerative behavior of muscle fibroblasts/FAPs. Thus, the isolation and study of these mesenchymal progenitors are of crucial importance for understanding their behavior and biology. We investigated whether adult muscle CT fibroblasts (hereafter referred to as adherent fibroblasts [aFbs]) cultured via pre-plating strategy belong to a heterogeneous population of FAPs. By combining microscopy, western blot analyses, flow cytometry, and FACS we determined that aFbs isolated from skeletal muscle largely overlap with FAPs. In addition, we used the PDGFRαEGFP mice in order to corroborate our results with EGFP+ FAPs. Moreover, our strategy allows the isolation of activated EGFP+ FAPs from the murine DMD model PDGFRαEGFP; mdx and PDGFRαEGFP denervated mice. Here we report that 1 h 30 min of pre-plating strategy allows the isolation and culture of a highly enriched population of aFbs. These cells are phenotypically and biochemically a FAPs-like population of adherent cells. In addition, aFbs respond in the same fashion as FAPs to Nilotinib, an inducer of FAPs apoptosis. Moreover, flow cytometry characterization of these aFbs suggests that 85% of them express the MP marker PDGFRα, and isolation of aFbs from the PDGFRαEGFP mice suggests that 75% of them show high EGFP expression. Furthermore, TGF-β1 induces aFbs proliferation, myofibroblast differentiation, and ECM production. We were also able to isolate activated aFbs from skeletal muscle of the DMD mice and from the PDGFRαEGFP mice 2-days after denervation. Our findings suggest that the in vitro pre-plating strategy allows the isolation and culture of a relatively pure aFbs population, which resembles FAPs in vitro.

Solid tumors produce proteins that can induce the accumulation of bone marrow-derived cells in various tissues, and these cells can enhance metastatic tumor growth by several mechanisms. 4T1 murine mammary tumors are known to produce granulocyte colony-stimulating factor (G-CSF) and increase the numbers of immunosuppressive CD11b+Gr1+ myeloid-derived suppressor cells (MDSCs) in tissues such as the spleen and lungs of tumor-bearing mice. While surgical resection of primary tumors decreases MDSC levels in the spleen, the longevity and impact of MDSCs and other immune cells in the lungs after tumor resection have been less studied.