Transcription factor Hlx controls a systematic switch from white to brown fat through Prdm16-mediated co-activation

White-to-Beige and Back: Adipocyte Conversion and Transcriptional Reprogramming

Obesity has become a pandemic, as currently more than half a billion people worldwide are obese. The etiology of obesity is multifactorial, and combines a contribution of hereditary and behavioral factors, such as nutritional inadequacy, along with the influences of environment and reduced physical activity. Two types of adipose tissue widely known are white and brown. While white adipose tissue functions predominantly as a key energy storage, brown adipose tissue has a greater mass of mitochondria and expresses the uncoupling protein 1 (UCP1) gene, which allows thermogenesis and rapid catabolism. Even though white and brown adipocytes are of different origin, activation of the brown adipocyte differentiation program in white adipose tissue cells forces them to transdifferentiate into "beige" adipocytes, characterized by thermogenesis and intensive lipolysis. Nowadays, researchers in the field of small molecule medicinal chemistry and gene therapy are making efforts to develop new drugs that effectively overcome insulin resistance and counteract obesity. Here, we discuss various aspects of white-to-beige conversion, adipose tissue catabolic re-activation, and non-shivering thermogenesis.

Vascular endothelial growth factor B improves impaired glucose tolerance through insulin-mediated inhibition of glucagon secretion

BACKGROUND

Impaired glucose tolerance (IGT) is a homeostatic state between euglycemia and hyperglycemia and is considered an early high-risk state of diabetes. When IGT occurs, insulin sensitivity decreases, causing a reduction in insulin secretion and an increase in glucagon secretion. Recently, vascular endothelial growth factor B (VEGFB) has been demonstrated to play a positive role in improving glucose metabolism and insulin sensitivity. Therefore, we constructed a mouse model of IGT through high-fat diet feeding and speculated that VEGFB can regulate hyperglycemia in IGT by influencing insulin-mediated glucagon secretion, thus contributing to the prevention and cure of prediabetes.

AIM

To explore the potential molecular mechanism and regulatory effects of VEGFB on insulin-mediated glucagon in mice with IGT.

METHODS

We conducted in vivo experiments through systematic VEGFB knockout and pancreatic-specific VEGFB overexpression. Insulin and glucagon secretions were detected via enzyme-linked immunosorbent assay, and the protein expression of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) was determined using western blot. Further, mRNA expression of forkhead box protein O1, phosphoenolpyruvate carboxykinase, and glucose-6 phosphatase was detected via quantitative polymerase chain reaction, and the correlation between the expression of proteins was analyzed via bioinformatics.

RESULTS

In mice with IGT and VEGFB knockout, glucagon secretion increased, and the protein expression of PI3K/AKT decreased dramatically. Further, in mice with VEGFB overexpression, glucagon levels declined, with the activation of the PI3K/AKT signaling pathway.

CONCLUSION

VEGFB/vascular endothelial growth factor receptor 1 can promote insulin-mediated glucagon secretion by activating the PI3K/AKT signaling pathway to regulate glucose metabolism disorders in mice with IGT.

A brown fat-enriched adipokine, ASRA, is a leptin receptor antagonist that stimulates appetite

The endocrine control of food intake remains incompletely understood, and whether the leptin receptor-mediated anorexigenic pathway in the hypothalamus is negatively regulated by a humoral factor is unknown. Here we identify an appetite-stimulating factor - ASRA - that acts as a leptin receptor antagonist. ASRA encodes an 8 kD protein that is abundantly and selectively expressed in adipose tissue and to a lesser extent, in liver, and is upregulated during fasting and cold. ASRA protein associates with autophagosomes and its secretion is induced by energy deficiency. Overexpression of ASRA in mice attenuates leptin receptor signaling leading to elevated blood glucose and development of severe hyperphagic obesity, whereas either adipose- or liver-specific ASRA knockout mice display increased leptin sensitivity, improved glucose homeostasis, reduced food intake, and resistance to high fat diet-induced obesity. Furthermore, ASRA is indispensable for cold-evoked feeding response. Recombinant ASRA (rASRA) protein binds to leptin receptor and suppresses leptin receptor signaling in cultured cells. In vivo, rASRA promotes food intake and increases blood glucose in a leptin receptor signaling-dependent manner. Our studies collectively show that ASRA, acting as a peripheral signal of energy deficit, stimulates appetite and regulates glucose metabolism by antagonizing leptin receptor signaling, thus revealing a previously unknown endocrine mechanism that has important implications for our understanding of leptin resistance.

A Review of Structural Features, Biological Functions and Biotransformation Studies in Adipose Tissues and an Assessment of Progress and Implications

Roles for adipose tissues in energy metabolism, health maintenance and disease onset have been established. Evidence indicates that white, brown and beige fats are quite different in terms of their cellular origin and biological characteristics. These differences are significant in targeting adipocytes to study the pathogenesis and prevention strategies of related diseases. The biotransformations of white, brown and beige fat cells constitute an intriguing topic worthy of further study, and the molecular mechanisms underlying the biotransformations of white, brown and beige fat cells remain to be elucidated. Hence, we herein collected evidence from studies on adipose tissue or adipocytes, and we extracted the structural features, biologic functions, and biotransformations of adipose tissue/adipocytes. The present review aimed to summarize the latest research progress and propose novel research directions with respect to adipose tissue and adipocytes. We posit that this work will provide new insights and opportunities in the effective treatment strategies for obesity, diabetes and other lipid-related diseases. It will also contribute to our knowledge of the basic biologic underpinnings of adipocyte biology.

A brown fat-enriched adipokine Adissp controls adipose thermogenesis and glucose homeostasis

The signaling mechanisms underlying adipose thermogenesis have not been fully elucidated. Particularly, the involvement of adipokines that are selectively expressed in brown adipose tissue (BAT) and beige adipocytes remains to be investigated. Here we show that a previously uncharacterized adipokine (UPF0687 protein / human C20orf27 homolog) we named as Adissp (Adipose-secreted signaling protein) is a key regulator for white adipose tissue (WAT) thermogenesis and glucose homeostasis. Adissp expression is adipose-specific and highly BAT-enriched, and its secretion is stimulated by β3-adrenergic activation. Gain-of-functional studies collectively showed that secreted Adissp promotes WAT thermogenesis, improves glucose homeostasis, and protects against obesity. Adipose-specific Adissp knockout mice are defective in WAT browning, and are susceptible to high fat diet-induced obesity and hyperglycemia. Mechanistically, Adissp binds to a putative receptor on adipocyte surface and activates protein kinase A independently of β-adrenergic signaling. These results establish BAT-enriched Adissp as a major upstream signaling component in thermogenesis and offer a potential avenue for the treatment of obesity and diabetes.

SOX4 promotes beige adipocyte-mediated adaptive thermogenesis by facilitating PRDM16-PPARγ complex

Brown and beige fat protect against cold environments and obesity by catabolizing stored energy to generate heat. This process is achieved by controlling thermogenesis-related gene expression and the development of brown/beige fat through the induction of transcription factors, most notably PPARγ. However, the cofactors that induce the expression of thermogenic genes with PPARγ are still not well understood. In this study, we explored the role of SOX4 in adaptive thermogenesis and its relationship with PPARγ. Methods: Whole transcriptome deep sequencing (RNA-seq) analysis of inguinal subcutaneous white adipose tissue (iWAT) after cold stimulation was performed to identify genes with differential expression in mice. Indirect calorimetry detected oxygen consumption rate and heat generation. mRNA levels were analyzed by qPCR assays. Proteins were detected by immunoblotting and immunofluorescence. Interaction of proteins was detected by endogenous and exogenous Co-IP. ChIP-qPCR, FAIRE assay and luciferase reporter assays were used to investigate transcriptional regulation. Results: SOX4 was identified as the main transcriptional effector of thermogenesis. Mice with either adipocyte-specific or UCP1⁺ cells deletion of SOX4 exhibited significant cold intolerance, decreased energy expenditure, and beige adipocyte formation, which was attributed to decreased thermogenic gene expression. In addition, these mice developed obesity on a high-fat diet, with severe hepatic steatosis, insulin resistance, and inflammation. At the cell level, loss of SOX4 from preadipocytes inhibited the development of beige adipocytes, and loss of SOX4 from mature beige adipocytes reduced the expression of thermogenesis-related genes and energy metabolism. Mechanistically, SOX4 stimulated the transcriptional activity of Ucp1 by binding to PPARγ and activating its transcriptional function. These actions of SOX4 were, at least partly, mediated by recruiting PRDM16 to PPARγ, thus forming a transcriptional complex to elevate the expression of thermogenic genes. Conclusion: SOX4, as a coactivator of PPARγ, drives the thermogenic gene expression program and thermogenesis of beige fat, promoting energy expenditure. It has important physiological significance in resisting cold and obesity.

PRDM16 Regulating Adipocyte Transformation and Thermogenesis: A Promising Therapeutic Target for Obesity and Diabetes

Given that obesity and diabetes have been major public health concerns and that disease morbidities have been rising continuously, effective treatment for these diseases is urgently needed. Because adipose tissue metabolism is involved in the progression of obesity and diabetes, it might be efficient to target adipocyte metabolic pathways. Positive regulatory domain zinc finger region protein 16 (PRDM16), a transcription factor that is highly expressed in adipocytes, plays a key role in adipose tissue metabolism, such as the browning and thermogenesis of adipocytes, the beigeing of adipocytes, the adipogenic differentiation of myoblasts, and the conversion of visceral adipocytes to subcutaneous adipocytes. Furthermore, clinical and basic studies have shown that the expression of PRDM16 is associated with obesity and diabetes and that PRDM16 signaling participates in the treatment of the two diseases. For example, metformin promotes thermogenesis and alleviates obesity by activating the AMPK/αKG/PRDM16 signaling pathway; rosiglitazone alleviates obesity under the synergistic effect of PRDM16; resveratrol plays an antiobesity role by inducing the expression of PRDM16; liraglupeptide improves insulin resistance by inducing the expression of PRDM16; and mulberry leaves play an anti-inflammatory and antidiabetes role by activating the expression of brown fat cell marker genes (including PRDM16). In this review, we summarize the evidence of PRDM16 involvement in the progression of obesity and diabetes and that PRDM16 may be a promising therapy for obesity and diabetes.

Lack of TRPV1 aggravates obesity-associated hypertension through the disturbance of mitochondrial Ca2+ homeostasis in brown adipose tissue

The combination of obesity and hypertension is associated with high morbidity and mortality; however, the mechanism underlying obesity-induced hypertension remains unclear. In this study, we detected the possible effects of TRPV1, a previously identified antihypertensive calcium (Ca²⁺) channel in adipose tissue, on the occurrence of obesity and hypertension in mice lacking UCP1, a spontaneously genetically manipulated obesity model, by generating TRPV1 and UCP1 double knockout mice. In these mice, obesity and hypertension appeared earlier and were more severe than in mice with the knockout of UCP1 or TRPV1 alone. The knockout of TRPV1 in UCP1 knockout mice further reduced functional brown adipose tissue (BAT) generation; decreased resting oxygen consumption, heat production, and locomotor activities; and was accompanied by severe mitochondrial respiratory dysfunction in BAT. Mechanistically, TRPV1, UCP1, and LETM1 acted as a complex to maintain an appropriate mitochondrial Ca²⁺ level, and TRPV1 knockout caused a compensatory increase in mitochondrial Ca²⁺ uptake via LETM1 activation. However, the compensatory response was blocked in UCP1^−/− mice, resulting in dramatically reduced mitochondrial Ca²⁺ uptake and higher production of ATP and oxidative stress. This study provides in vivo evidence for the critical role of BAT mitochondrial Ca²⁺ homeostasis in obesity-associated hypertension and indicates that the TRPV1/UCP1/LETM1 complex may be an alternative intervention target.

The KRAB Domain-Containing Protein ZFP961 Represses Adipose Thermogenesis and Energy Expenditure through Interaction with PPARα

Adipose thermogenesis plays a pivotal role in whole-body metabolic homeostasis. Although transcriptional mechanisms that promote thermogenesis are extensively studied, the negative regulatory network is still poorly understood. Here, a Krüppel-associated box (KRAB) domain-containing zinc finger protein, ZFP961, as a potent repressor of the thermogenic program is identified. ZFP961 expression is induced by cold and β3-adrenergic agonist in adipose tissue. ZFP961 represses brown fat-selective gene expression and mitochondrial respiration without any effect on general adipogenesis in cultured adipocytes. Adipose-specific knockdown and overexpression of ZFP961 produce remarkable and opposite phenotypes of white fat remodeling. ZFP961 knockout mice display robust inguinal white adipose tissue browning, which is abolished by reexpression of full-length ZFP961, but not by KRAB domain-deleted ZFP961 mutant. ZFP961-deficient mice are cold tolerant and resistant to high-fat diet-induced obesity, hyperglycemia, and hepatic steatosis. ZFP961 suppresses thermogenic gene expression by directly interacting with PPARα and blocking its transcriptional activity, which can be completely negated by the PPARα agonist. The findings uncover ZFP961 as a critical physiological brake that limits adipose thermogenesis and provides insights into the regulatory mechanisms that maintain energy balance and tissue homeostasis.

Sparcl1 promotes nonalcoholic steatohepatitis progression in mice through upregulation of CCL2

Nonalcoholic fatty liver disease (NAFLD) represents a spectrum of chronic liver disease ranging from simple steatosis (NAFL) to nonalcoholic steatohepatitis (NASH). However, the molecular mechanisms of NASH progression remain incompletely understood. White adipose tissue (WAT) has emerged as an important endocrine organ and contributes not only to the initial stage of NAFLD, but also to its severity. In the current study, through transcriptomic analysis we identified increased expression of Sparcl1, a secreted glycoprotein, in the WAT from NASH mice. Plasma Sparcl1 levels were similarly elevated and positively correlated with hepatic pathological features in NASH patients. Functional studies showed that both chronic injection of recombinant Sparcl1 protein and overexpression of Sparcl1 exaggerated hepatic inflammation and liver injury in mice. In contrast, genetic ablation of Sparcl1, knockdown of Sparcl1 in WAT, and treatment with a Sparcl1-neutralizing antibody dramatically alleviated diet-induced NASH pathogenesis. Mechanistically, Sparcl1 promoted the expression of C-C motif chemokine ligand 2 (CCL2) in hepatocytes through binding to Toll-like receptor 4 (TLR4) and activation of the NF-κB/p65 signaling pathway. Genetically or pharmacologically blocking the CCL2/CCR2 pathway attenuated the hepatic inflammatory response evoked by Sparcl1. Thus, our results demonstrated an important role for Sparcl1 in NASH progression, suggesting a potential target for therapeutic intervention.

HOXC10 Suppresses Browning to Maintain White Adipocyte Identity

Promoting beige adipocyte development within white adipose tissue (WAT) is a potential therapeutic approach to staunch the current obesity epidemic. Previously, we identified homeobox-containing transcription factor HOXC10 as a suppressor of browning in subcutaneous WAT. Here, we provide evidence for the physiological role of HOXC10 in regulating WAT thermogenesis. Analysis of an adipose-specific HOXC10 knockout mouse line with no detectable HOXC10 in mature adipocytes revealed spontaneous subcutaneous WAT browning, increased expression of genes involved in browning, increased basal rectal temperature, enhanced cold tolerance, and improved glucose homeostasis. These phenotypes were further exacerbated by exposure to cold or a β-adrenergic stimulant. Mechanistically, cold and β-adrenergic exposure led to reduced HOXC10 protein level without affecting its mRNA level. Cold exposure induced cAMP-dependent protein kinase-dependent proteasome-mediated degradation of HOXC10 in cultured adipocytes, and shotgun proteomics approach identified KCTD2, 5, and 17 as potential E3 ligases regulating HOXC10 proteasomal degradation. Collectively, these data demonstrate that HOXC10 is a gatekeeper of WAT identity, and targeting HOXC10 could be a plausible therapeutic strategy to unlock WAT thermogenic potentials.

Novel adipokine asprosin modulates browning and adipogenesis in white adipose tissue

Obesity is an increasingly serious epidemic worldwide characterized by an increase in the number and size of adipocytes. Adipose tissue maintains the balance between lipid storage and energy utilization. Therefore, adipose metabolism is of great significance for the prevention, treatment and intervention of obesity. Asprosin, a novel adipokine, is a circulating hormone mainly secreted by white adipose tissue. Previous studies have shown that asprosin plays a role in fasting-induced homeostasis, insulin resistance, and glucose tolerance. However, whether it can regulate the metabolism of adipose tissue itself has not been studied. This study intended to examine the roles and potential mechanisms of asprosin in adipose regulation. We first demonstrated that the expression level of asprosin was significantly downregulated in subcutaneous white adipose tissue (scWAT) of high-fat diet (HFD)-fed or cold-stimulated mice. Overexpression of asprosin in scWAT reduced heat production, decreased expression of the browning marker uncoupling protein 1 (UCP1) and other browning-related genes, along with upregulation of adipogenic gene expression. Mechanistically, we found that Nrf2 was activated upon cold exposure, but this activation was suppressed after asprosin overexpression. In primary cultured adipocytes, adenovirusmediated asprosin overexpression inhibited adipose browning and aggravated lipid deposition, while Nrf2 agonist oltipraz could reverse these changes. Our findings suggest that novel adipokine asprosin negatively regulated browning and elevate lipid deposition in adipose tissue via a Nrf2-mediated mechanism. Asprosin may be a promising target for the prevention and treatment of obesity and other metabolic diseases.

PRMT5 Promotes EMT Through Regulating Akt Activity in Human Lung Cancer

The type II protein arginine methyltransferase 5 (PRMT5) has been engaged in various human cancer development and progression types. Nevertheless, few studies uncover the biological functions of PRMT5 in the epithelial-mesenchymal transition (EMT) of human lung cancer cells, and the associated molecular mechanisms and signaling cascades are entirely unknown. Here, we show that PRMT5 is the ectopic expression in human lung cancer tissues and cell lines. Further study reveals that silencing PRMT5 by lentivirus-mediated shRNA or blocking of PRMT5 by specific inhibitor GSK591 attenuates the expression levels of EMT-related markers in vivo, using the xenograft mouse model. Moreover, our results show that down-regulation of PRMT5 impairs EGFR/Akt signaling cascades in human lung cancer cells, whereas re-expression of PRMT5 recovers those changes, suggesting that PRMT5 regulates EMT probably through EGFR/Akt signaling axis. Altogether, our results demonstrate that PRMT5 serves as a critical oncogenic regulator and promotes EMT in human lung cancer cells. More importantly, our findings also suggest that PRMT5 may be a potential therapeutic candidate for the treatment of human lung cancer.

Epigenetic Regulators of White Adipocyte Browning

Adipocytes play an essential role in maintaining energy homeostasis in mammals. The primary function of white adipose tissue (WAT) is to store energy; for brown adipose tissue (BAT), primary function is to release fats in the form of heat. Dysfunctional or excess WAT can induce metabolic disorders such as dyslipidemia, obesity, and diabetes. Preadipocytes or adipocytes from WAT possess sufficient plasticity as they can transdifferentiate into brown-like beige adipocytes. Studies in both humans and rodents showed that brown and beige adipocytes could improve metabolic health and protect from metabolic disorders. Brown fat requires activation via exposure to cold or β-adrenergic receptor (β-AR) agonists to protect from hypothermia. Considering the fact that the usage of β-AR agonists is still in question with their associated side effects, selective induction of WAT browning is therapeutically important instead of activating of BAT. Hence, a better understanding of the molecular mechanisms governing white adipocyte browning is vital. At the same time, it is also essential to understand the factors that define white adipocyte identity and inhibit white adipocyte browning. This literature review is a comprehensive and focused update on the epigenetic regulators crucial for differentiation and browning of white adipocytes.

Downregulation of exosomal miR‑1273a increases cisplatin resistance of non‑small cell lung cancer by upregulating the expression of syndecan binding protein

Resistance to platinum‑based drugs, such as cisplatin (CDDP), has been one of the major factors adversely affecting the clinical prognosis of patients with advanced non‑small cell lung cancer (NSCLC). While it has been demonstrated that dysregulation of microRNAs (miRNAs) may contribute to cisplatin resistance in NSCLC, the underlying mechanisms remain largely unclear. In the present study, the effect of exosomal miR‑1273a on cisplatin sensitivity of NSCLC was investigated. Microarray analysis was conducted to analyze the miRNA expression profiles in exosomes isolated from A549 cells treated with or without CDDP, and miR‑1273a was found to be the most prominently downregulated miRNA in CDDP‑treated exosomes. Overexpression of miR‑1273a significantly increased the cytotoxicity of CDDP and induced apoptosis in A549 cells. Syndecan binding protein (SDCBP) was predicted to be a direct target of miR‑1273a by bioinformatics and was found to be downregulated by miR‑1273a in A549 cells. Furthermore, decreased plasma exosomal miR‑1273a and increased plasma SDCBP levels were found to be associated with worse therapeutic outcomes of patients with advanced NSCLC receiving platinum‑based chemotherapy. These findings suggest that miR‑1273a is closely associated with the development of cisplatin resistance and may serve as a potential prognostic biomarker and therapeutic target for NSCLC.

Disabling MNK protein kinases promotes oxidative metabolism and protects against diet-induced obesity

Objectives

Diet-driven obesity is increasingly widespread. Its consequences pose major challenges to human health and health care systems. There are MAP kinase-interacting kinases (MNKs) in mice, MNK1 and MNK2. Studies have demonstrated that mice lacking either MNK1 or MNK2 were partially protected against high-fat diet (HFD)-induced weight gain and insulin resistance. The aims of this study were to evaluate the phenotype of mice lacking both MNKs when given an HFD, to assess whether pharmacological inhibition of MNK function also protects against diet-induced obesity (DIO) and its consequences and to probe the mechanisms underlying such protection.

Methods

Male wild-type (WT) C57Bl6 mice or mice lacking both MNK1 and MNK2 (double knockout, DKO) were fed an HFD or control diet (CD) for up to 16 weeks.

In a separate study, WT mice were also given an HFD for 6 weeks, after which half were treated with the recently-developed MNK inhibitor ETC-206 daily for 10 more weeks while continuing an HFD. Metabolites and other parameters were measured, and the expression of selected mRNAs and proteins was assessed.

Results

MNK-DKO mice were almost completely protected from HFD-induced obesity. Higher energy expenditure (EE) in MNK-DKO mice was observed, which probably reflects the changes in a number of genes or proteins linked to lipolysis, mitochondrial function/biogenesis, oxidative metabolism, and/or ATP consumption. The MNK inhibitor ETC-206 also prevented HFD-induced weight gain, confirming that the activity of the MNKs facilitates weight gain due to excessive caloric consumption.

Conclusions

Disabling MNKs in mice, either genetically or pharmacologically, strongly prevents weight gain on a calorie-rich diet. This finding likely results from increased energy utilisation, involving greater ATP consumption, mitochondrial oxidative metabolism, and other processes.

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Knockout of MNK1/MNK2 protects mice against diet-induced obesity.

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MNK1/2 DKO mice have higher energy expenditure.

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MNK1/2 DKO increases the expression of genes of lipid and mitochondrial metabolism.

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Pharmacological inhibition of MNKs has similar effects.

Deregulated NKL Homeobox Genes in B-Cell Lymphoma

Recently, we have described physiological expression patterns of NKL homeobox genes in early hematopoiesis and in subsequent lymphopoiesis. We identified nine genes which constitute the so-called NKL-code. Aberrant overexpression of code-members or ectopically activated non-code NKL homeobox genes are described in T-cell leukemia and in T- and B-cell lymphoma, highlighting their oncogenic role in lymphoid malignancies. Here, we introduce the NKL-code in normal hematopoiesis and focus on deregulated NKL homeobox genes in B-cell lymphoma, including HLX, MSX1 and NKX2-2 in Hodgkin lymphoma; HLX, NKX2-1 and NKX6-3 in diffuse large B-cell lymphoma; and NKX2-3 in splenic marginal zone lymphoma. Thus, the roles of various members of the NKL homeobox gene subclass are considered in normal and pathological hematopoiesis in detail.

Cbx4 Sumoylates Prdm16 to Regulate Adipose Tissue Thermogenesis

Transcriptional co-activator Prdm16 controls brown fat development and white fat browning, but how this thermogenic function is modulated post-translationally is poorly understood. Here, we report that Cbx4, a Polycomb group protein, is a SUMO E3 ligase for Prdm16 and that Cbx4-mediated sumoylation of Prdm16 is required for thermogenic gene expression. Cbx4 expression is enriched in brown fat and is induced in adipose tissue by acute cold exposure. Sumoylation of Prdm16 at lysine 917 by Cbx4 blocks its ubiquitination-mediated degradation, thereby augmenting its stability and thermogenic function. Moreover, this sumoylation event primes Prdm16 to be further stabilized by methyltransferase Ehmt1. Heterozygous Cbx4-knockout mice develop metabolic phenotypes resembling those of Prdm16-knockout mice. Furthermore, fat-specific Cbx4 knockdown and overexpression produce remarkable, opposite effects on white fat remodeling. Our results identify a modifying enzyme for Prdm16, and they demonstrate a central role of Cbx4 in the control of Prdm16 stability and white fat browning.

Direct interaction between the PRDM3 and PRDM16 tumor suppressors and the NuRD chromatin remodeling complex

Aberrant isoform expression of chromatin-associated proteins can induce epigenetic programs related to disease. The MDS1 and EVI1 complex locus (MECOM) encodes PRDM3, a protein with an N-terminal PR-SET domain, as well as a shorter isoform, EVI1, lacking the N-terminus containing the PR-SET domain (ΔPR). Imbalanced expression of MECOM isoforms is observed in multiple malignancies, implicating EVI1 as an oncogene, while PRDM3 has been suggested to function as a tumor suppressor through an unknown mechanism. To elucidate functional characteristics of these N-terminal residues, we compared the protein interactomes of the full-length and ΔPR isoforms of PRDM3 and its closely related paralog, PRDM16. Unlike the ΔPR isoforms, both full-length isoforms exhibited a significantly enriched association with components of the NuRD chromatin remodeling complex, especially RBBP4. Typically, RBBP4 facilitates chromatin association of the NuRD complex by binding to histone H3 tails. We show that RBBP4 binds to the N-terminal amino acid residues of PRDM3 and PRDM16, with a dissociation constant of 3.0 μM, as measured by isothermal titration calorimetry. Furthermore, high-resolution X-ray crystal structures of PRDM3 and PRDM16 N-terminal peptides in complex with RBBP4 revealed binding to RBBP4 within the conserved histone H3-binding groove. These data support a mechanism of isoform-specific interaction of PRDM3 and PRDM16 with the NuRD chromatin remodeling complex.

Neuregulin 4 Is a Novel Marker of Beige Adipocyte Precursor Cells in Human Adipose Tissue

Background: Nrg4 expression has been linked to brown adipose tissue activity and browning of white adipocytes in mice. Here, we aimed to investigate whether these observations could be translated to humans by investigating NRG4 mRNA and markers of brown/beige adipocytes in human visceral (VAT) and subcutaneous adipose tissue (SAT). We also studied the possible association of NRG4 with insulin action.

Methods: SAT and VAT NRG4 and markers of brown/beige (UCP1, UCP3, and TMEM26)-related gene expression were analyzed in two independent cohorts (n = 331 and n = 59). Insulin resistance/sensitivity was measured using HOMA_IR and glucose infusion rate during euglycemic hyperinsulinemic clamp.

Results: In both cohort 1 and cohort 2, NRG4 and thermogenic/beige-related gene expression were significantly increased in VAT compared to SAT. Adipogenic-related genes followed an opposite pattern. In cohort 1, VAT NRG4 gene expression was positively correlated with BMI and expression of UCP1, UCP3, TMEM26, and negatively with adipogenic (FASN, PPARG, and SLC2A4)- and inflammatory (IL6 and IL8)-related genes. In SAT, NRG4 gene expression was negatively correlated with HOMA_IR and positively with UCP1 and TMEM26 gene expression. Multiple linear regression analysis revealed that expression of TMEM26 gene was the best predictor of NRG4 gene expression in both VAT and SAT. Specifically, NRG4 and TMEM26 gene expression was significantly increased in VAT, but not in SAT stromal vascular fraction cells (p < 0.001). In cohort 2, the significant association between NRG4 and TMEM26 gene expression in both VAT and SAT was confirmed, and SAT NRG4 gene expression also was positively correlated with insulin action and the expression of UCP1.

Conclusion: Current findings suggest NRG4 gene expression as a novel marker of beige adipocytes in human adipose tissue.

Increased FGF21 in brown adipose tissue of tyrosine hydroxylase heterozygous mice: implications for cold adaptation

Tyrosine hydroxylase (TH) catalyzes the first step in catecholamines synthesis. We studied the impact of reduced TH in brown adipose tissue (BAT) activation. In adult heterozygous (Th^+/- ) mice, dopamine and noradrenaline (NA) content in BAT decreased after cold exposure. This reduced catecholaminergic response did not impair cold adaptation, because these mice induced uncoupling protein 1 (UCP-1) and maintained BAT temperature to a similar extent than controls (Th^+/+ ). Possible compensatory mechanisms implicated were studied. Prdm16 and Fgf21 expression, key genes in BAT activation, were elevated in Th^+/- mice at thermoneutrality from day 18.5 of embryonic life. Likewise, plasma FGF21 and liver Fgf21 mRNA were increased. Analysis of endoplasmic reticulum (ER) stress, a process that triggers elevations in FGF21, showed higher phospho-IRE1, phospho-JNK, and CHOP in BAT of Th^+/- mice at thermoneutrality. Also, increased lipolysis in BAT of cold-exposure Th^+/- mice was demonstrated by increased phosphorylation of hormone-sensitive lipase (HSL), as well as diacylglycerol (DAG) and FFA content. Overall, these results indicate that the mild effects of Th haploinsufficiency on BAT function are likely due to compensatory mechanisms involving elevations in Fgf21 and Prdm16 and through adaptive changes in the lipid profile.

RBM4a modulates the impact of PRDM16 on development of brown adipocytes through an alternative splicing mechanism

Brown adipocytes (BAs) exhibit an energy-expending signature that is important in balancing metabolic homeostasis. In this study, results of transcriptome analyses revealed the reprogrammed splicing profile of the PR domain containing 16 (PRDM16) gene, a key transcription factor involved in brown adipogenesis, throughout development of wild-type brown adipose tissues (BATs). Moreover, discriminative splicing patterns of PRDM16 transcripts were noted in embryonic and postnatal RBM4a^-/- BATs. Overexpression of RBM4a enhanced the relative levels of PRDM16^{-ex 16} transcripts by simultaneously interacting with exonic and intronic CU elements, which encoded the PRDM16_S isoform containing a distinct C-terminus. The presence of the overexpressed PRDM16_S isoform showed a stronger effect than the overexpressed PRDM16_L isoform on enhancing transcriptional activity of the RBM4a and the PGC-1α promoter. Overexpression of the PRDM16_S isoform exerted more-prominent effects on enhancing the BAT-related gene program and energy expenditure compared to those of PRDM16_L-overexpressing cells. Our studies demonstrated that RBM4a-regulated alternative splicing constituted another regulatory mechanism for strengthening the influence of PRDM16 on the development of brown adipocytes.

A metabolic interplay coordinated by HLX regulates myeloid differentiation and AML through partly overlapping pathways

The H2.0-like homeobox transcription factor (HLX) regulates hematopoietic differentiation and is overexpressed in Acute Myeloid Leukemia (AML), but the mechanisms underlying these functions remain unclear. We demonstrate here that HLX overexpression leads to a myeloid differentiation block both in zebrafish and human hematopoietic stem and progenitor cells (HSPCs). We show that HLX overexpression leads to downregulation of genes encoding electron transport chain (ETC) components and upregulation of PPARδ gene expression in zebrafish and human HSPCs. HLX overexpression also results in AMPK activation. Pharmacological modulation of PPARδ signaling relieves the HLX-induced myeloid differentiation block and rescues HSPC loss upon HLX knockdown but it has no effect on AML cell lines. In contrast, AMPK inhibition results in reduced viability of AML cell lines, but minimally affects myeloid progenitors. This newly described role of HLX in regulating the metabolic state of hematopoietic cells may have important therapeutic implications.

HLX transcription factor regulates haematopoietic stem and progenitor cell (HSPC) differentiation and is overexpressed in acute myeloid leukemia. Here the authors show that HLX overexpression leads to myeloid differentiation block in zebrafish and human HSPCs by direct regulation of metabolic pathways.

Ifi27 is indispensable for mitochondrial function and browning in adipocytes

Brown adipose tissue (BAT) is specialized for energy expenditure, but the signaling pathways that regulate BAT metabolism and activity are incompletely understood. Interferon (IFN) signaling is a sophisticated defense mechanism to counteract viral infection. IFNs and interferon-stimulated genes (ISGs) are reported to exert profound effects on adipocytes. IFN-α inducible protein 27 (Ifi27/ISG12a) is a BAT-enriched gene, yet no any studies on its roles in BAT have been reported. Here, we show that Ifi27 protein localizes to mitochondria and the expression of Ifi27 can be induced by β3-adrenergic activation in adipose tissues. Knockdown of Ifi27 leads to reduced expression of key enzymes of tricarboxylic acid cycle (TCA), the subunits of electron transport chain (ETC) and uncoupling protein 1 (Ucp1) in brown and beige adipocytes. Moreover, the browning of subcutaneous white fat induced by β3-adrenergic agonist is also dramatically blocked. Ectopic expression of Ifi27 in brown adipocytes has the opposite effects. Together, these data indicate that Ifi27 regulates mitochondrial function and browning in adipocytes.