Thyroid hormones regulate Zfp423 expression in regionally distinct adipose depots through direct and cell-autonomous action

The hypothalamic pituitary thyroid axis is a major regulator of many differentiation processes, including adipose tissue. However, it remains unclear whether and how thyroid hormone (TH) signaling contributes to preadipocyte commitment and differentiation into mature adipocytes. Here, we show a cell-autonomous effect of TH on the transcriptional regulation of zinc finger protein 423 (Zfp423), an early adipogenic determination factor, in murine adipose depots. Mechanistically, binding of the unliganded TH receptor to a negative TH responsive element within the Zfp423 promoter activates transcriptional activity that is reversed upon TH binding. Zfp423 upregulation is associated with increased GFP+ preadipocyte recruitment in stromal vascular fraction isolated from white fat of hypothyroid Zfp423GFP reporter mice. RNA sequencing identified Zfp423-driven gene programs that are modulated in response to TH during adipogenic differentiation. Collectively, we identified Zfp423 as a key molecule that integrates TH signaling into the regulation of adipose tissue plasticity.

ZFP423 regulates early patterning and multiciliogenesis in the hindbrain choroid plexus

The choroid plexus (ChP) is a secretory tissue that produces cerebrospinal fluid (CSF) secreted into the ventricular system. It is a monolayer of secretory, multiciliated epithelial cells derived from neuroepithelial progenitors and overlying a stroma of mesenchymal cells of mesodermal origin. Zfp423, which encodes a Kruppel-type zinc-finger transcription factor essential for cerebellar development and mutated in rare cases of cerebellar vermis hypoplasia/Joubert syndrome and other ciliopathies, is expressed in the hindbrain roof plate, from which the IV ventricle ChP arises, and, later, in mesenchymal cells, which give rise to the stroma and leptomeninges. Mouse Zfp423 mutants display a marked reduction of the hindbrain ChP (hChP), which: (1) fails to express established markers of its secretory function and genes implicated in its development and maintenance (Lmx1a and Otx2); (2) shows a perturbed expression of signaling pathways previously unexplored in hChP patterning (Wnt3); and (3) displays a lack of multiciliated epithelial cells and a profound dysregulation of master genes of multiciliogenesis (Gmnc). Our results propose that Zfp423 is a master gene and one of the earliest known determinants of hChP development.

Retinoic acid inhibits white adipogenesis by disrupting GADD45A-mediated Zfp423 DNA demethylation

Retinoic acid (RA), a bioactive metabolite of vitamin A, is a critical mediator of cell differentiation. RA blocks adipogenesis, but mechanisms remain to be established. ZFP423 is a key transcription factor maintaining white adipose identity. We found that RA inhibits Zfp423 expression and adipogenesis via blocking DNA demethylation in the promoter of Zfp423, a process mediated by growth arrest and DNA-damage-inducible protein alpha (GADD45A). RA induces the partnering between retinoic acid receptor (RAR) and tumor suppressor inhibitor of growth protein 1 (ING1), which prevents the formation of GADD45A and ING1 complex necessary for locus-specific Zfp423 DNA demethylation. In vivo, vitamin A supplementation prevents obesity, downregulates Gadd45a expression, and reduces GADD45A binding and DNA demethylation in the Zfp423 promoter. Inhibition of Zfp423 expression due to RA contributes to the enhanced brown adipogenesis. In summary, RA inhibits white adipogenesis by inducing RAR and ING1 interaction and inhibiting Gadd45a expression, which prevents GADD45A-mediated DNA demethylation.

Transcriptional brakes on the road to adipocyte thermogenesis

White adipocytes represent the principle site for energy storage whereas brown/beige adipocytes emerge from seemingly distinct cellular lineages and burn chemical energy to produce heat. Thermogenic adipocytes utilize cell-type selective master regulatory transcription factors to drive the expression of their adipocyte thermogenic gene program. White adipocytes harbor transcriptional mechanisms to suppress the thermogenic gene program and maintain an energy-storing function. Here, we summarize some of the key developmental and transcriptional mechanisms leading to the postnatal recruitment of thermogenic adipocytes under physiological conditions, with a particular emphasis on the transcriptional "brakes" on the thermogenic gene program. We highlight a number of recent studies, including our own work on the transcription factor, ZFP423, that illustrate the potential to engineer the subcutaneous and visceral white fat lineages to adopt a thermogenic fat cell fate by releasing the inhibition of the adipocyte thermogenic gene program. These transcriptional brakes on adipocyte thermogenesis may represent potential targets of therapeutic interventions designed to combat obesity and associated metabolic disorders.

Warming Induces Significant Reprogramming of Beige, but Not Brown, Adipocyte Cellular Identity

Beige and brown adipocytes generate heat in response to reductions in ambient temperature. When warmed, both beige and brown adipocytes exhibit morphological "whitening," but it is unknown whether or to what extent this represents a true shift in cellular identity. Using cell-type-specific profiling in vivo, we uncover a unique paradigm of temperature-dependent epigenomic plasticity of beige, but not brown, adipocytes, with conversion from a brown to a white chromatin state. Despite this profound shift in cellular identity, warm whitened beige adipocytes retain an epigenomic memory of prior cold exposure defined by an array of poised enhancers that prime thermogenic genes for rapid response during a second bout of cold exposure. We further show that a transcriptional cascade involving glucocorticoid receptor and Zfp423 can drive warm-induced whitening of beige adipocytes. These studies identify the epigenomic and transcriptional bases of an extraordinary example of cellular plasticity in response to environmental signals.

Increased Ifi202b/IFI16 expression stimulates adipogenesis in mice and humans

AIMS/HYPOTHESIS

Obesity results from a constant and complex interplay between environmental stimuli and predisposing genes. Recently, we identified the IFN-activated gene Ifi202b as the most likely gene responsible for the obesity quantitative trait locus Nob3 (New Zealand Obese [NZO] obesity 3). The aim of this study was to evaluate the effects of Ifi202b on body weight and adipose tissue biology, and to clarify the functional role of its human orthologue IFI16.

METHODS

The impact of Ifi202b and its human orthologue IFI16 on adipogenesis was investigated by modulating their respective expression in murine 3T3-L1 and human Simpson-Golabi-Behmel syndrome (SGBS) pre-adipocytes. Furthermore, transgenic mice overexpressing IFI202b were generated and characterised with respect to metabolic traits. In humans, expression levels of IFI16 in adipose tissue were correlated with several variables of adipocyte function.

RESULTS

In mice, IFI202b overexpression caused obesity (Δ body weight at the age of 30 weeks: 10.2 ± 1.9 g vs wild-type mice) marked by hypertrophic fat mass expansion, increased expression of Zfp423 (encoding the transcription factor zinc finger protein [ZFP] 423) and white-selective genes (Tcf21, Tle3), and decreased expression of thermogenic genes (e.g. Cidea, Ucp1). Compared with their wild-type littermates, Ifi202b transgenic mice displayed lower body temperature, hepatosteatosis and systemic insulin resistance. Suppression of IFI202b/IFI16 in pre-adipocytes impaired adipocyte differentiation and triacylglycerol storage. Humans with high levels of IFI16 exhibited larger adipocytes, an enhanced inflammatory state and impaired insulin-stimulated glucose uptake in white adipose tissue.

CONCLUSIONS/INTERPRETATION

Our findings reveal novel functions of Ifi202b and IFI16, demonstrating their role as obesity genes. These genes promote white adipogenesis and fat storage, thereby facilitating the development of obesity-associated insulin resistance.

Directing visceral white adipocyte precursors to a thermogenic adipocyte fate improves insulin sensitivity in obese mice

Visceral adiposity confers significant risk for developing metabolic disease in obesity whereas preferential expansion of subcutaneous white adipose tissue (WAT) appears protective. Unlike subcutaneous WAT, visceral WAT is resistant to adopting a protective thermogenic phenotype characterized by the accumulation of Ucp1⁺ beige/BRITE adipocytes (termed ‘browning’). In this study, we investigated the physiological consequences of browning murine visceral WAT by selective genetic ablation of Zfp423, a transcriptional suppressor of the adipocyte thermogenic program. Zfp423 deletion in fetal visceral adipose precursors (Zfp423^loxP/loxP; Wt1-Cre), or adult visceral white adipose precursors (Pdgfrb^rtTA; TRE-Cre; Zfp423^loxP/loxP), results in the accumulation of beige-like thermogenic adipocytes within multiple visceral adipose depots. Thermogenic visceral WAT improves cold tolerance and prevents and reverses insulin resistance in obesity. These data indicate that beneficial visceral WAT browning can be engineered by directing visceral white adipocyte precursors to a thermogenic adipocyte fate, and suggest a novel strategy to combat insulin resistance in obesity.

DOI:http://dx.doi.org/10.7554/eLife.27669.001

Mammals have different types of fat cells in their bodies. White fat cells store energy for later use, and brown and beige fat cells burn energy to help keep the body warm. Individuals who are obese typically have too many white fat cells in and around their belly. This belly fat, also called visceral fat, accumulates around the organs and is believed to contribute to metabolic diseases, such as diabetes and heart disease. Individuals who are obese also have relatively few brown and beige energy-burning fat cells.

Boosting the amount of brown and beige fat in individuals who are obese has been proposed as a potential way to reduce their risk of metabolic disease. One way to do this would be to encourage white visceral fat cells to become more like energy-burning beige or brown fat cells.

Recent research has shown that white fat cells contain higher amounts of a protein called Zfp423 than brown or beige fat cells. This protein turns off the genes that fat cells use to burn energy and so keeps white fat cells in an energy-storing state. Now, Hepler et al. show that genetically modifying mice to turn off the gene that produces Zfp423 specifically in the precursor cells that become white fat cells causes more energy-burning beige cells to appear in their visceral fat.

The genetically modified mice were better able to tolerate cold than normal mice. When placed on a high-fat diet, the modified mice were also less likely to become resistant to the effects of the hormone insulin – a process that can lead to the development of type 2 diabetes and may be linked to heart disease. This suggests that treatments that prevent Zfp423 from working in fat cells could help to treat or prevent diabetes and heart disease in people who are obese. Before such treatments can be developed, further work is needed to investigate how Zfp423 works in more detail, and to confirm that it has the same effects in human fat cells as it does in mice.

DOI:http://dx.doi.org/10.7554/eLife.27669.002

Fetal development of subcutaneous white adipose tissue is dependent on Zfp423

Objective

Zfp423 is a multi zinc-finger transcription factor expressed in preadipocytes and mature adipocytes in vivo. Our recent work has revealed a critical role for Zfp423 in maintaining the fate of white adipocytes in adult mice through suppression of the beige cell thermogenic gene program; loss of Zfp423 in mature adipocytes of adult mice results in a white-to-beige phenotypic switch. However, the exact requirements of Zfp423 in the fetal stages of early adipose development in vivo have not been clarified.

Method

Here, we utilize two models that confer adipose-specific Zfp423 inactivation during fetal adipose development (Adiponectin-Cre; Zfp423^loxP/loxP and Adiponectin-rtTA; TRE-Cre; Zfp423^loxP/loxP). We assess the impact of fetal adipose Zfp423 deletion on the initial formation of adipose tissue and evaluate the metabolic consequences of challenging these animals with high-fat diet feeding.

Results

Deletion of Zfp423 during fetal adipose development results in a different phenotype than is observed when deleting Zfp423 in adipocytes of adult mice. Inactivation of Zfp423 during fetal adipose development results in arrested differentiation, specifically of inguinal white adipocytes, rather than a white-to-beige phenotypic switch that occurs when Zfp423 is inactivated in adult mice. This is likely explained by the observation that adiponectin driven Cre expression is active at an earlier stage of the adipocyte life cycle during fetal subcutaneous adipose development than in adult mice. Upon high-fat diet feeding, obese adipose Zfp423-deficient animals undergo a pathological adipose tissue expansion, associated with ectopic lipid deposition and systemic insulin resistance.

Conclusions

Our results reveal that Zfp423 is essential for the terminal differentiation of subcutaneous white adipocytes during fetal adipose tissue development. Moreover, our data highlight the striking adverse effects of pathological subcutaneous adipose tissue remodeling on visceral adipose function and systemic nutrient homeostasis in obesity. Importantly, these data reveal the distinct phenotypes that can occur when adiponectin driven transgenes are activated in fetal vs. adult adipose tissue.

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Fetal adipose deletion of Zfp423 disrupts terminal differentiation of white adipocytes.

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Inguinal WAT of Zfp423-deficient mice undergoes a pathological expansion in obesity.

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Pathological expansion of subcutaneous adipose triggers systemic insulin resistance.

miR-195a inhibits adipocyte differentiation by targeting the preadipogenic determinator Zfp423

MicroRNAs (miRNAs) play essential roles in various cellular processes including proliferation and differentiation. In this study, we identified miRNA-195a (miR-195a) as a regulator of adipocyte differentiation. Differential expression of miR-195a in preadipocytes and adipocytes suggests its role in lipid accumulation and adipocyte differentiation. Forced expression of miR-195a mimics suppressed lipid accumulation and inhibited expression of adipocyte markers such as PPARγ and aP2 in 3T3-L1 and C3H10T1/2 cells. Conversely, downregulation of miR-195a by anti-miR-195a increased lipid accumulation and expression of adipocyte markers. Target prediction analysis suggested zinc finger protein 423 (Zfp423), a preadipogenic determinator, as a potential gene recognized by miR-195a. In line with this, mimicked expression of miR-195a reduced the expression of Zfp423, whereas anti-miR-195a increased its expression. Predicted targeting sequences in Zfp423 3'UTR, but not mutated sequences fused to luciferase, were regulated by miR-195a. Ectopic Zfp423 expression in 3T3-L1 cells increased lipid accumulation and expression of adipocyte markers, consistent with the observation that miR-195a targets Zfp423, resulting in suppressed adipocyte differentiation. In addition, miR-195a and Zfp423 were inversely correlated in obese fat tissues, raising the possibility of miRNA's role in obesity. Together, our data show that miR-195a is an anti-adipogenic regulator, which acts by targeting Zfp423, and further suggest the roles of miR-195a in obesity and metabolic diseases.

Zfp521 promotes B-cell viability and cyclin D1 gene expression in a B cell culture system

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Knockdown of Zfp521 in BCL1 cell culture reduces viability and promotes apoptosis.

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Genes expressed in B cells are down-regulated in cells with Zfp521 knockdown.

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Cyclin D1 expression is increased in mouse tumors with Zfp521 over-expression.

Leukemia arises due to the dysregulated proliferation of hematopoietic progenitor cells. Errors in the multi-step commitment process result in excessive numbers of immature lymphocytes, causing malignant disease. Genes involved in the differentiation of lymphocytes are often associated with leukemia. One such gene, Zfp521, has been found to cause B-cell leukemia in mice when over-expressed. The role of Zfp521 in B-cell differentiation, and the mechanisms by which it leads to leukemic transformation, are unclear. In this study we report that Zfp521 knockdown causes apoptosis in a B-cell culture system and promotes down-regulation of genes acting at late stages of B-cell differentiation. We identify Pax5 and cyclin D1 as Zfp521 target genes, and suggest that excessive B-cell proliferation observed in mice with retroviral insertions near the Zfp521 gene is due to an up-regulation of cyclin D1 in B-cells. Overall, these results suggest links between dysregulated Zfp521 and B-cell survival.

Mesodermal ALK5 controls lung myofibroblast versus lipofibroblast cell fate

Background

Epithelial-mesenchymal cross talk is centerpiece in the development of many branched organs, including the lungs. The embryonic lung mesoderm provides instructional information not only for lung architectural development, but also for patterning, commitment and differentiation of its many highly specialized cell types. The mesoderm also serves as a reservoir of progenitors for generation of differentiated mesenchymal cell types that include αSMA-expressing fibroblasts, lipofibroblasts, endothelial cells and others. Transforming Growth Factor β (TGFβ) is a key signaling pathway in epithelial-mesenchymal cross talk. Using a cre-loxP approach we have elucidated the role of the TGFβ type I receptor tyrosine kinase, ALK5, in epithelial-mesenchymal cross talk during lung morphogenesis.

Results

Targeted early inactivation of Alk5 in mesodermal progenitors caused abnormal development and maturation of the lung that included reduced physical size of the sub-mesothelial mesoderm, an established source of specific mesodermal progenitors. Abrogation of mesodermal ALK5-mediated signaling also inhibited differentiation of cell populations in the epithelial and endothelial lineages. Importantly, Alk5 mutant lungs contained a reduced number of αSMA^pos cells and correspondingly increased lipofibroblasts. Elucidation of the underlying mechanisms revealed that through direct and indirect modulation of target signaling pathways and transcription factors, including PDGFRα, PPARγ, PRRX1, and ZFP423, ALK5-mediated TGFβ controls a process that regulates the commitment and differentiation of αSMA^pos versus lipofibroblast cell populations during lung development.

Conclusion

ALK5-mediated TGFβ signaling controls an early pathway that regulates the commitment and differentiation of αSMA^pos versus LIF cell lineages during lung development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-016-0242-9) contains supplementary material, which is available to authorized users.

ZNF423: Transcriptional modulation in development and cancer

Krüppel-like zinc finger proteins are versatile players in biology that have been implicated in mammalian development and disease. Among these proteins, ZNF423 and its mouse ortholog Zfp423 were initially implicated in midline patterning of the central nervous system but have emerged as critical transcriptional modulators in cancer. Epigenetically uncurbed ZNF423 interferes with lymphopoiesis by sequestration of the essential early B-cell factor 1 (EBF1) causing B-cell maturation arrest, a hallmark of acute lymphoblastic leukemia. Conversely, its presence in neuroblastoma, a primitive neuroectodermal tumor of childhood, allows retinoic acid-induced differentiation and is associated with a favorable outcome of neuroblastoma patients. Such opposing effects may be explained by the cellular context, but also by the multifunctionality of ZNF423 that is mediated by 30 zinc fingers forming various functional domains. This review summarizes current knowledge of ZNF423, focusing on its role in development and cancer.

Aldehyde dehydrogenase-1a1 induces oncogene suppressor genes in B cell populations

The deregulation of B cell differentiation has been shown to contribute to autoimmune disorders, hematological cancers, and aging. We provide evidence that the retinoic acid-producing enzyme aldehyde dehydrogenase 1a1 (Aldh1a1) is an oncogene suppressor in specific splenic IgG1(+)/CD19(-) and IgG1(+)/CD19(+) B cell populations. Aldh1a1 regulated transcription factors during B cell differentiation in a sequential manner: 1) retinoic acid receptor alpha (Rara) in IgG1(+)/CD19(-) and 2) zinc finger protein Zfp423 and peroxisome proliferator-activated receptor gamma (Pparg) in IgG1(+)/CD19(+) splenocytes. In Aldh1a1(-/-) mice, splenic IgG1(+)/CD19(-) and IgG1(+)/CD19(+) B cells acquired expression of proto-oncogenic genes c-Fos, c-Jun, and Hoxa10 that resulted in splenomegaly. Human multiple myeloma B cell lines also lack Aldh1a1 expression; however, ectopic Aldh1a1 expression rescued Rara and Znf423 expressions in these cells. Our data highlight a mechanism by which an enzyme involved in vitamin A metabolism can improve B cell resistance to oncogenesis.