Ablation of the transcriptional regulator Id1 enhances energy expenditure, increases insulin sensitivity, and protects against age and diet induced insulin resistance, and hepatosteatosis

Zinc Improves Semen Parameters in High-Fat Diet-Induced Male Rats by Regulating the Expression of LncRNA in Testis Tissue

This study aimed to identify differentially expressed LncRNAs in testis tissue of male rats induced by high-fat diet and their changes after zinc supplementation, by constructing a high-fat feeding rat model, and then supplemented with zinc, and observed the expression of LncRNA in three groups of normal, high-fat fed, and zinc-intervened rats. Experimental studies show that the semen parameters of male rats with high-fat diet were decreased but recovered after zinc supplementation, and the related LncRNA also changed. Zinc may improve the high-fat diet-induced reduction of semen parameters by changing the expression of related LncRNA.

Characterization of transcript enrichment and detection bias in single-nucleus RNA-seq for mapping of distinct human adipocyte lineages

Single-cell RNA sequencing (scRNA-seq) enables molecular characterization of complex biological tissues at high resolution. The requirement of single-cell extraction, however, makes it challenging for profiling tissues such as adipose tissue, for which collection of intact single adipocytes is complicated by their fragile nature. For such tissues, single-nucleus extraction is often much more efficient and therefore single-nucleus RNA sequencing (snRNA-seq) presents an alternative to scRNA-seq. However, nuclear transcripts represent only a fraction of the transcriptome in a single cell, with snRNA-seq marked with inherent transcript enrichment and detection biases. Therefore, snRNA-seq may be inadequate for mapping important transcriptional signatures in adipose tissue. In this study, we compare the transcriptomic landscape of single nuclei isolated from preadipocytes and mature adipocytes across human white and brown adipocyte lineages, with whole-cell transcriptome. We show that snRNA-seq is capable of identifying the broad cell types present in scRNA-seq at all states of adipogenesis. However, we also explore how and why the nuclear transcriptome is biased and limited, as well as how it can be advantageous. We robustly characterize the enrichment of nuclear-localized transcripts and adipogenic regulatory lncRNAs in snRNA-seq, while also providing a detailed understanding for the preferential detection of long genes upon using this technique. To remove such technical detection biases, we propose a normalization strategy for a more accurate comparison of nuclear and cellular data. Finally, we show successful integration of scRNA-seq and snRNA-seq data sets with existing bioinformatic tools. Overall, our results illustrate the applicability of snRNA-seq for the characterization of cellular diversity in the adipose tissue.

BMP7 Increases UCP1-Dependent and Independent Thermogenesis with a Unique Gene Expression Program in Human Neck Area Derived Adipocytes

White adipocytes contribute to energy storage, accumulating lipid droplets, whereas brown and beige adipocytes mainly function in dissipating energy as heat primarily via the action of uncoupling protein 1 (UCP1). Bone morphogenic protein 7 (BMP7) was shown to drive brown adipocyte differentiation in murine interscapular adipose tissue. Here, we performed global RNA-sequencing and functional assays on adipocytes obtained from subcutaneous (SC) and deep-neck (DN) depots of human neck and differentiated with or without BMP7. We found that BMP7 did not influence differentiation but upregulated browning markers, including UCP1 mRNA and protein in SC and DN derived adipocytes. BMP7 also enhanced mitochondrial DNA content, levels of oxidative phosphorylation complex subunits, along with PGC1α and p-CREB upregulation, and fragmentation of mitochondria. Furthermore, both UCP1-dependent proton leak and UCP1-independent, creatine-driven substrate cycle coupled thermogenesis were augmented upon BMP7 addition. The gene expression analysis also shed light on the possible role of genes unrelated to thermogenesis thus far, including ACAN, CRYAB, and ID1, which were among the highest upregulated ones by BMP7 treatment in both types of adipocytes. Together, our study shows that BMP7 strongly upregulates thermogenesis in human neck area derived adipocytes, along with genes, which might have a supporting role in energy expenditure.

Acute effects of active breaks during prolonged sitting on subcutaneous adipose tissue gene expression: an ancillary analysis of a randomised controlled trial

Active breaks in prolonged sitting has beneficial impacts on cardiometabolic risk biomarkers. The molecular mechanisms include regulation of skeletal muscle gene and protein expression controlling metabolic, inflammatory and cell development pathways. An active communication network exists between adipose and muscle tissue, but the effect of active breaks in prolonged sitting on adipose tissue have not been investigated. This study characterized the acute transcriptional events induced in adipose tissue by regular active breaks during prolonged sitting. We studied 8 overweight/obese adults participating in an acute randomized three-intervention crossover trial. Interventions were performed in the postprandial state and included: (i) prolonged uninterrupted sitting; or prolonged sitting interrupted with 2-minute bouts of (ii) light- or (iii) moderate-intensity treadmill walking every 20 minutes. Subcutaneous adipose tissue biopsies were obtained after each condition. Microarrays identified 36 differentially expressed genes between the three conditions (fold change ≥0.5 in either direction; p < 0.05). Pathway analysis indicated that breaking up of prolonged sitting led to differential regulation of adipose tissue metabolic networks and inflammatory pathways, increased insulin signaling, modulation of adipocyte cell cycle, and facilitated cross-talk between adipose tissue and other organs. This study provides preliminary insight into the adipose tissue regulatory systems that may contribute to the physiological effects of interrupting prolonged sitting.

Matriptase-2 deficiency protects from obesity by modulating iron homeostasis

Alterations in iron status have frequently been associated with obesity and other metabolic disorders. The hormone hepcidin stands out as a key regulator in the maintenance of iron homeostasis by controlling the main iron exporter, ferroportin. Here we demonstrate that the deficiency in the hepcidin repressor matriptase-2 (Tmprss6) protects from high-fat diet-induced obesity. Tmprss6^−/− mice show a significant decrease in body fat, improved glucose tolerance and insulin sensitivity, and are protected against hepatic steatosis. Moreover, these mice exhibit a significant increase in fat lipolysis, consistent with their dramatic reduction in adiposity. Rescue experiments that block hepcidin up-regulation and restore iron levels in Tmprss6^−/− mice via anti-hemojuvelin (HJV) therapy, revert the obesity-resistant phenotype of Tmprss6^−/− mice. Overall, this study describes a role for matritpase-2 and hepcidin in obesity and highlights the relevance of iron regulation in the control of adipose tissue function.

Iron homeostasis dysfunctions have been associated with several metabolic disorders including obesity, steatosis and diabetes. Here the authors demonstrate that the hepcidin repressor matriptase-2 regulates adiposity and its deficiency protects mice against obesity and promotes lipolysis.

The tumor secretory factor ZAG promotes white adipose tissue browning and energy wasting

Cachexia is a complex tissue-wasting syndrome characterized by inflammation, hypermetabolism, increased energy expenditure, and anorexia. Browning of white adipose tissue (WAT) is one of the significant factors that contribute to energy wasting in cachexia. By utilizing a cell implantation model, we demonstrate here that the lipid mobilizing factor zinc-α₂-glycoprotein (ZAG) induces WAT browning in mice. Increased circulating levels of ZAG not only induced lipolysis in adipose tissues but also caused robust browning in WAT. Stimulating WAT progenitors with ZAG recombinant protein or expression of ZAG in mouse embryonic fibroblasts (MEFs) strongly enhanced brown-like differentiation. At the molecular level, ZAG stimulated peroxisome proliferator-activated receptor γ (PPARγ) and early B cell factor 2 expression and promoted their recruitment to the PR/SET domain 16 (Prdm16) promoter, leading to enhanced expression of Prdm16, which determines brown cell fate. In brown adipose tissue, ZAG stimulated the expression of PPARγ and PPARγ coactivator 1α and promoted recruitment of PPARγ to the uncoupling protein 1 (Ucp1) promoter, leading to increased expression of Ucp1. Overall, our results reveal a novel function of ZAG in WAT browning and highlight the targeting of ZAG as a potential therapeutic application in humans with cachexia.-Elattar, S., Dimri, M., Satyanarayana, A. The tumor secretory factor ZAG promotes white adipose tissue browning and energy wasting.

The cell polarity protein Scrib functions as a tumor suppressor in liver cancer

Scrib is a membrane protein that is involved in the maintenance of apical-basal cell polarity of the epithelial tissues. However, Scrib has also been shown to be mislocalized to the cytoplasm in breast and prostate cancer. Here, for the first time, we report that Scrib not only translocates to the cytoplasm but also to the nucleus in hepatocellular carcinoma (HCC) cells, and in mouse and human liver tumor samples. We demonstrate that Scrib overexpression suppresses the growth of HCC cells in vitro, and Scrib deficiency enhances liver tumor growth in vivo. At the molecular level, we have identified the existence of a positive feed-back loop between Yap1 and c-Myc in HCC cells, which Scrib disrupts by simultaneously regulating the MAPK/ERK and Hippo signaling pathways. Overall, Scrib inhibits liver cancer cell proliferation by suppressing the expression of three oncogenes, Yap1, c-Myc and cyclin D1, thereby functioning as a tumor suppressor in liver cancer.

Cdkn2a deficiency promotes adipose tissue browning

Objectives

Genome-wide association studies have reported that DNA polymorphisms at the CDKN2A locus modulate fasting glucose in human and contribute to type 2 diabetes (T2D) risk. Yet the causal relationship between this gene and defective energy homeostasis remains elusive. Here we sought to understand the contribution of Cdkn2a to metabolic homeostasis.

Methods

We first analyzed glucose and energy homeostasis from Cdkn2a-deficient mice subjected to normal or high fat diets. Subsequently Cdkn2a-deficient primary adipose cells and human-induced pluripotent stem differentiated into adipocytes were further characterized for their capacity to promote browning of adipose tissue. Finally CDKN2A levels were studied in adipocytes from lean and obese patients.

Results

We report that Cdkn2a deficiency protects mice against high fat diet-induced obesity, increases energy expenditure and modulates adaptive thermogenesis, in addition to improving insulin sensitivity. Disruption of Cdkn2a associates with increased expression of brown-like/beige fat markers in inguinal adipose tissue and enhances respiration in primary adipose cells. Kinase activity profiling and RNA-sequencing analysis of primary adipose cells further demonstrate that Cdkn2a modulates gene networks involved in energy production and lipid metabolism, through the activation of the Protein Kinase A (PKA), PKG, PPARGC1A and PRDM16 signaling pathways, key regulators of adipocyte beiging. Importantly, CDKN2A expression is increased in adipocytes from obese compared to lean subjects. Moreover silencing CDKN2A expression during human-induced pluripotent stem cells adipogenic differentiation promoted UCP1 expression.

Conclusion

Our results offer novel insight into brown/beige adipocyte functions, which has recently emerged as an attractive therapeutic strategy for obesity and T2D. Modulating Cdkn2a-regulated signaling cascades may be of interest for the treatment of metabolic disorders.

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Cdkn2a deficiency protects mice against high fat diet-induced obesity.

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Cdkn2a modulates brown-like/beige fat gene networks involved in energy production and lipid metabolism.

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Increased CDKN2A expression in human obese adipocytes.

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Increased UCP1 levels in adipocytes differentiated from CDKN2A-silenced hiPS cells.

Acute loss of the hepatic endo-lysosomal system in vivo causes compensatory changes in iron homeostasis

Liver cells communicate with the extracellular environment to take up nutrients via endocytosis. Iron uptake is essential for metabolic activities and cell homeostasis. Here, we investigated the role of the endocytic system for maintaining iron homeostasis. We specifically depleted the small GTPase Rab5 in the mouse liver, causing a transient loss of the entire endo-lysosomal system. Strikingly, endosome depletion led to a fast reduction of hepatic iron levels, which was preceded by an increased abundance of the iron exporter ferroportin. Compensatory changes in livers of Rab5-depleted mice include increased expression of transferrin receptor 1 as well as reduced expression of the iron-regulatory hormone hepcidin. Serum iron indices (serum iron, free iron binding capacity and total iron binding capacity) in Rab5-KD mice were increased, consistent with an elevated splenic and hepatic iron export. Our data emphasize the critical importance of the endosomal compartments in hepatocytes to maintain hepatic and systemic iron homeostasis in vivo. The short time period (between day four and five) upon which these changes occur underscore the fast dynamics of the liver iron pool.

Id1 Promotes Obesity by Suppressing Brown Adipose Thermogenesis and White Adipose Browning

Obesity results from increased energy intake or defects in energy expenditure. Brown adipose tissue (BAT) is specialized for energy expenditure, a process called adaptive thermogenesis. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) controls BAT-mediated thermogenesis by regulating the expression of Ucp1 Inhibitor of differentiation 1 (Id1) is a helix-loop-helix transcription factor that plays an important role in cell proliferation and differentiation. We demonstrate a novel function of Id1 in BAT thermogenesis and programming of beige adipocytes in white adipose tissue (WAT). We found that adipose tissue-specific overexpression of Id1 causes age-associated and high-fat diet-induced obesity in mice. Id1 suppresses BAT thermogenesis by binding to and suppressing PGC1α transcriptional activity. In WAT, Id1 is mainly localized in the stromal vascular fraction, where the adipose progenitor/precursors reside. Lack of Id1 increases beige gene and Ucp1 expression in the WAT in response to cold exposure. Furthermore, brown-like differentiation is increased in Id1-deficient mouse embryonic fibroblasts. At the molecular level, Id1 directly interacts with and suppresses Ebf2 transcriptional activity, leading to reduced expression of Prdm16, which determines beige/brown adipocyte cell fate. Overall, the study highlights the existence of novel regulatory mechanisms between Id1/PGC1α and Id1/Ebf2 in controlling brown fat metabolism, which has significant implications in the treatment of obesity and its associated diseases, such as diabetes.

Interrogating islets in health and disease with single-cell technologies

BACKGROUND

Blood glucose levels are tightly controlled by the coordinated actions of hormone-producing endocrine cells that reside in pancreatic islets. Islet cell malfunction underlies diabetes development and progression. Due to the cellular heterogeneity within islets, it has been challenging to uncover how specific islet cells contribute to glucose homeostasis and diabetes pathogenesis. Recent advances in single-cell technologies and computational methods have opened up new avenues to resolve islet heterogeneity and study islet cell states in health and disease.

SCOPE OF REVIEW

In the past year, a multitude of studies have been published that used single-cell approaches to interrogate the transcriptome and proteome of the different islet cell types. Here, we summarize the conclusions of these studies, as well as discuss the technologies used and the challenges faced with computational analysis of single-cell data from islet studies.

MAJOR CONCLUSIONS

By analyzing single islet cells from rodents and humans at different ages and disease states, the studies reviewed here have provided new insight into endocrine cell function and facilitated a high resolution molecular characterization of poorly understood processes, including regeneration, maturation, and diabetes pathogenesis. Gene expression programs and pathways identified in these studies pave the way for the discovery of new targets and approaches to prevent, monitor, and treat diabetes.

Id2 Mediates Differentiation of Labyrinthine Placental Progenitor Cell Line, SM10

The placenta is an organ that is formed transiently during pregnancy, and appropriate placental development is necessary for fetal survival and growth. Proper differentiation of the labyrinthine layer of the placenta is especially crucial, as it establishes the fetal-maternal interface that is involved in physiological exchange processes. Although previous studies have indicated the importance of inhibitor of differentiation/inhibitor of DNA binding-2 (Id2) helix-loop-helix transcriptional regulator in mediating cell differentiation, the ability of Id2 to regulate differentiation toward the labyrinthine (transport) lineage of the placenta has yet to be determined. In the current study, we have generated labyrinthine trophoblast progenitor cells with increased (SM10-Id2) or decreased (SM10-Id2-shRNA) Id2 expression and determined the effect on TGF-β-induced differentiation. Our Id2 overexpression and knockdown analyses indicate that Id2 mediates TGF-β-induced morphological differentiation of labyrinthine trophoblast cells, as Id2 overexpression prevents differentiation and Id2 knockdown results in differentiation. Thus, our data indicate that Id2 is an important molecular mediator of labyrinthine trophoblast differentiation. An understanding of the regulators of trophoblast progenitor differentiation toward the labyrinthine lineage may offer insights into events governing pregnancy-associated disorders, such as placental insufficiency, fetal growth restriction, and preeclampsia.

Identification of genes for controlling swine adipose deposition by integrating transcriptome, whole-genome resequencing, and quantitative trait loci data

Backfat thickness is strongly associated with meat quality, fattening efficiency, reproductive performance, and immunity in pigs. Fat storage and fatty acid synthesis mainly occur in adipose tissue. Therefore, we used a high-throughput massively parallel sequencing approach to identify transcriptomes in adipose tissue, and whole-genome differences from three full-sibling pairs of pigs with opposite (high and low) backfat thickness phenotypes. We obtained an average of 38.69 million reads for six samples, 78.68% of which were annotated in the reference genome. Eighty-nine overlapping differentially expressed genes were identified among the three pair comparisons. Whole-genome resequencing also detected multiple genetic variations between the pools of DNA from the two groups. Compared with the animal quantitative trait loci (QTL) database, 20 differentially expressed genes were matched to the QTLs associated with fatness in pigs. Our technique of integrating transcriptome, whole-genome resequencing, and QTL database information provided a rich source of important differentially expressed genes and variations. Associate analysis between selected SNPs and backfat thickness revealed that two SNPs and one haplotype of ME1 significantly affected fat deposition in pigs. Moreover, genetic analysis confirmed that variations in the differentially expressed genes may affect fat deposition.

E Proteins and ID Proteins: Helix-Loop-Helix Partners in Development and Disease

The basic Helix-Loop-Helix (bHLH) proteins represent a well-known class of transcriptional regulators. Many bHLH proteins act as heterodimers with members of a class of ubiquitous partners, the E proteins. A widely expressed class of inhibitory heterodimer partners-the Inhibitor of DNA-binding (ID) proteins-also exists. Genetic and molecular analyses in humans and in knockout mice implicate E proteins and ID proteins in a wide variety of diseases, belying the notion that they are non-specific partner proteins. Here, we explore relationships of E proteins and ID proteins to a variety of disease processes and highlight gaps in knowledge of disease mechanisms.

Impaired Thermogenesis and a Molecular Signature for Brown Adipose Tissue in Id2 Null Mice

Inhibitor of DNA binding 2 (ID2) is a helix-loop-helix transcriptional repressor rhythmically expressed in many adult tissues. Our previous studies have demonstrated that Id2 null mice have sex-specific elevated glucose uptake in brown adipose tissue (BAT). Here we further explored the role of Id2 in the regulation of core body temperature over the circadian cycle and the impact of Id2 deficiency on genes involved in insulin signaling and adipogenesis in BAT. We discovered a reduced core body temperature in Id2-/- mice. Moreover, in Id2-/- BAT, 30 genes including Irs1, PPARs, and PGC-1s were identified as differentially expressed in a sex-specific pattern. These data provide valuable insights into the impact of Id2 deficiency on energy homeostasis of mice in a sex-specific manner.

Bone morphogenetic proteins in inflammation, glucose homeostasis and adipose tissue energy metabolism

Bore morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-β superfamily, a group of secreted proteins that regulate embryonic development. This review summarizes the effects of BMPs on physiological processes not exclusively linked to the musculoskeletal system. Specifically, we focus on the involvement of BMPs in inflammatory disorders, e.g. fibrosis, inflammatory bowel disease, anchylosing spondylitis, rheumatoid arthritis. Moreover, we discuss the role of BMPs in the context of vascular disorders, and explore the role of these signalling proteins in iron homeostasis (anaemia, hemochromatosis) and oxidative damage. The second and third parts of this review focus on BMPs in the development of metabolic pathologies such as type-2 diabetes mellitus and obesity. The pancreatic beta cells are the sole source of the hormone insulin and BMPs have recently been implicated in pancreas development as well as control of adult glucose homeostasis. Lastly, we review the recently recognized role of BMPs in brown adipose tissue formation and their consequences for energy expenditure and adiposity. In summary, BMPs play a pivotal role in metabolism beyond their role in skeletal homeostasis. However, increased understanding of these pleiotropic functions also highlights the necessity of tissue-specific strategies when harnessing BMP action as a therapeutic target.

Can Brown Fat Win the Battle Against White Fat?

A rapid growth in the overweight and obese population in the last few decades suggest that the current diet, exercise, awareness or drug strategies are still not effectively restraining the obesity epidemic. Obesity results from increased energy intake, and the body's energy balance shifts towards energy abundance. Therefore, current research is focused on developing new strategies aimed at increasing energy expenditure. As a result, brown adipose tissue (BAT) is receiving tremendous attention since the major function of BAT is to dissipate energy as heat. For example, mouse models that have increased BAT activity or increased numbers of brown-like adipocytes within the white adipose tissue (WAT) are lean and protected from obesity. Alternatively, mouse models that lack BAT activity are more susceptible to age and diet-induced obesity. However, a significant loss of BAT mass during the natural growth process in humans has created enormous challenges in effectively utilizing this tissue to increase energy expenditure. New strategies are primarily focused on expanding the BAT mass and/or activating the existing BAT. In this regard, recent finding that expression of early B cell factor-2 (Ebf2) reprograms the white pre-adipocytes into brown adipocytes is a significant break-through in developing BAT-mediated strategies to treat obesity. Here we review the major biological functions of WAT and BAT, which play critical but opposing roles in the energy spectrum, energy storage versus energy expenditure, and we evaluate whether activation and/or expansion of BAT is practically achievable to treat obesity in humans.

Negative regulators of brown adipose tissue (BAT)-mediated thermogenesis

Brown adipose tissue (BAT) is specialized for energy expenditure, a process called adaptive thermogenesis. PET-CT scans recently demonstrated the existence of metabolically active BAT in adult humans, which revitalized our interest in BAT. Increasing the amount and/or activity of BAT holds tremendous promise for the treatment of obesity and its associated diseases. PGC1α is the master regulator of UCP1-mediated thermogenesis in BAT. A number of proteins have been identified to influence thermogenesis either positively or negatively through regulating the expression or transcriptional activity of PGC1α. Therefore, BAT activation can be achieved by either inducing the expression of positive regulators of PGC1α or by inhibiting the repressors of the PGC1α/UCP1 pathway. Here, we review the most important negative regulators of PGC1α/UCP1 signaling and their mechanism of action in BAT-mediated thermogenesis.

Up-regulation of the Sirtuin 1 (Sirt1) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) genes in white adipose tissue of Id1 protein-deficient mice: implications in the protection against diet and age-induced glucose intolerance

Id1, a helix-loop-helix (HLH) protein that inhibits the function of basic HLH E protein transcription factors in lymphoid cells, has been implicated in diet- and age-induced obesity by unknown mechanisms. Here we show that Id1-deficient mice are resistant to a high fat diet- and age-induced obesity, as revealed by reduced weight gain and body fat, increased lipid oxidation, attenuated hepatosteatosis, lower levels of lipid droplets in brown adipose tissue, and smaller white adipocytes after a high fat diet feeding or in aged animals. Id1 deficiency improves glucose tolerance, lowers serum insulin levels, and reduces TNFα gene expression in white adipose tissue. Id1 deficiency also increased expression of Sirtuin 1 and peroxisome proliferator-activated receptor γ coactivator 1α, regulators of mitochondrial biogenesis and energy expenditure, in the white adipose tissue. This effect was accompanied by the elevation of several genes encoding proteins involved in oxidative phosphorylation and fatty acid oxidation, such as cytochrome c, medium-chain acyl-CoA dehydrogenase, and adipocyte protein 2. Moreover, the phenotype for Id1 deficiency was similar to that of mice expressing an E protein dominant-positive construct, ET2, suggesting that the balance between Id and E proteins plays a role in regulating lipid metabolism and insulin sensitivity.

Id transcriptional regulators in adipogenesis and adipose tissue metabolism

Id proteins (Id1-Id4) are helix-loop-helix (HLH) transcriptional regulators that lack a basic DNA binding domain. They act as negative regulators of basic helix-loop-helix (bHLH) transcription factors by forming heterodimers and inhibit their DNA binding and transcriptional activity. Id proteins are implicated in the regulation of various cellular mechanisms such as cell proliferation, cellular differentiation, cell fate determination, angiogenesis and tumorigenesis. A handful of recent studies also disclosed that Id proteins have critical functions in adipocyte differentiation and adipose tissue metabolism. Here, we reviewed the progress made thus far in understanding the specific functions of Id proteins in adipose tissue differentiation and metabolism. In addition to reviewing the known mechanisms of action, we also discuss possible additional mechanisms in which Id proteins might participate in regulating adipogenic and metabolic pathways.

Id proteins regulate capillary repair and perivascular cell proliferation following ischemia-reperfusion injury

Acute kidney injury (AKI) results in microvascular damage that if not normally repaired, may lead to fibrosis. The Id1 and 3 proteins have a critical role in promoting angiogenesis during development, tumor growth and wound repair by functioning as dominant negative regulators of bHLH transcription factors. The goal of this study was to determine if Id proteins regulate microvascular repair and remodeling and if increased Id1 expression results in decreased capillary loss following AKI. The effect of changes in Id expression in vivo was examined using Id1−/−, Id3RFP/+ (Id1/Id3 KO) and Tek (Tie2)-rtTA, TRE-lacz/TRE Id1 (TRE Id1) mice with doxycycline inducible endothelial Id1 and β-galactosidase expression. Id1 and 3 were co-localized in endothelial cells in normal adult kidneys and protein levels were increased at day 3 following ischemia-reperfusion injury (IRI) and contralateral nephrectomy. Id1/Id3 KO mice had decreased baseline capillary density and pericyte coverage and increased tubular damage following IRI but decreased interstitial cell proliferation and fibrosis compared with WT littermates. No compensatory increase in kidney size occurred in KO mice resulting in increased creatinine compared with WT and TRE Id1 mice. TRE Id1 mice had no capillary rarefaction within 1 week following IRI in comparison with WT littermates. TRE Id1 mice had increased proliferation of PDGFRβ positive interstitial cells and medullary collagen deposition and developed capillary rarefaction and albuminuria at later time points. These differences were associated with increased Angiopoietin 1 (Ang1) and decreased Ang2 expression in TRE Id1 mice. Examination of gene expression in microvascular cells isolated from WT, Id1/Id3 KO and TRE Id1 mice showed increased Ang1 and αSMA in Id1 overexpressing cells and decreased pericyte markers in cells from KO mice. These results suggest that increased Id levels following AKI result in microvascular remodeling associated with increased fibrosis.

Id proteins: small molecules, mighty regulators

The family of inhibitor of differentiation (Id) proteins is a group of evolutionarily conserved molecules, which play important regulatory roles in organisms ranging from Drosophila to humans. Id proteins are small polypeptides harboring a helix-loop-helix (HLH) motif, which are best known to mediate dimerization with other basic HLH proteins, primarily E proteins. Because Id proteins do not possess the basic amino acids adjacent to the HLH motif necessary for DNA binding, Id proteins inhibit the function of E protein homodimers, as well as heterodimers between E proteins and tissue-specific bHLH proteins. However, Id proteins have also been shown to have E protein-independent functions. The Id genes are broadly but differentially expressed in a variety of cell types. Transcription of the Id genes is controlled by transcription factors such as C/EBPβ and Egr as well as by signaling pathways triggered by different stimuli, which include bone morphogenic proteins, cytokines, and ligands of T cell receptors. In general, Id proteins are capable of inhibiting the differentiation of progenitors of different cell types, promoting cell-cycle progression, delaying cellular senescence, and facilitating cell migration. These properties of Id proteins enable them to play significant roles in stem cell maintenance, vasculogenesis, tumorigenesis and metastasis, the development of the immune system, and energy metabolism. In this review, we intend to highlight the current understanding of the function of Id proteins and discuss gaps in our knowledge about the mechanisms whereby Id proteins exert their diverse effects in multiple cellular processes.

Brown and beige fat: development, function and therapeutic potential

Adipose tissue, best known for its role in fat storage, can also suppress weight gain and metabolic disease through the action of specialized, heat-producing adipocytes. Brown adipocytes are located in dedicated depots and express constitutively high levels of thermogenic genes, whereas inducible 'brown-like' adipocytes, also known as beige cells, develop in white fat in response to various activators. The activities of brown and beige fat cells reduce metabolic disease, including obesity, in mice and correlate with leanness in humans. Many genes and pathways that regulate brown and beige adipocyte biology have now been identified, providing a variety of promising therapeutic targets for metabolic disease.

Ablation of the ID2 gene results in altered circadian feeding behavior, and sex-specific enhancement of insulin sensitivity and elevated glucose uptake in skeletal muscle and brown adipose tissue

Inhibitor of DNA binding 2 (ID2) is a helix-loop-helix transcriptional repressor rhythmically expressed in many adult tissues. Our earlier studies have demonstrated a role for ID2 in the input pathway, core clock function and output pathways of the mouse circadian system. We have also reported that Id2 null (Id2−/−) mice are lean with low gonadal white adipose tissue deposits and lower lipid content in the liver. These results coincided with altered or disrupted circadian expression profiles of liver genes including those involved in lipid metabolism. In the present phenotypic study we intended to decipher, on a sex-specific basis, the role of ID2 in glucose metabolism and in the circadian regulation of activity, important components of energy balance. We find that Id2−/− mice exhibited altered daily and circadian rhythms of feeding and locomotor activity; activity profiles extended further into the late night/dark phase of the 24-hr cycle, despite mice showing reduced total locomotor activity. Also, male Id2−/− mice consumed a greater amount of food relative to body mass, and displayed less weight gain. Id2−/− females had smaller adipocytes, suggesting sexual-dimorphic programing of adipogenesis. We observed increased glucose tolerance and insulin sensitivity in male Id2−/− mice, which was exacerbated in older animals. FDG-PET analysis revealed increased glucose uptake by skeletal muscle and brown adipose tissue of male Id2−/− mice, suggesting increased glucose metabolism and thermogenesis in these tissues. Reductions in intramuscular triacylglycerol and diacylglycerol were detected in male Id2−/− mice, highlighting its possible mechanistic role in enhanced insulin sensitivity in these mice. Our findings indicate a role for ID2 as a regulator of glucose and lipid metabolism, and in the circadian control of feeding/locomotor behavior; and contribute to the understanding of the development of obesity and diabetes, particularly in shift work personnel among whom incidence of such metabolic disorders is elevated.

Identification of a loss-of-function mutation in Ube2l6 associated with obesity resistance

We previously mapped a locus on BALB/c chromosome 2 associated with protection from leptin-deficiency-induced obesity. Here, we generated the corresponding congenic mouse strain by introgression of a segment of C57BL/6J chromosome 2 to the BALB/c background to confirm the genotype-phenotype associations. We found that the BALB/c alleles decreased fat mass expansion by limiting adipocyte hyperplasia and adipocyte hypertrophy. This was concomitant to an increase in adipocyte triglyceride lipase (ATGL)-mediated triglyceride breakdown and prolongation of ATGL half-life in adipose tissue. In addition, BALB/c alleles on chromosome 2 exerted a cell-autonomous role in restraining the adipogenic potential of preadipocytes. Within a 9.8-Mb critical interval, we identified a nonsynonymous coding single nucleotide polymorphism in the gene coding for the ubiquitin-conjugating enzyme E2L6 (Ube2l6, also known as Ubch8) and showed that the BALB/c allele of Ube2l6 is a hypomorph leading to the lack of UBE2L6 protein expression. Ube2l6 knockdown in 3T3-L1 adipocytes repressed adipogenesis. Thus, altered adipogenic potential caused by Ube2l6 knockdown is likely critically involved in BALB/c obesity resistance by inhibiting adipogenesis and reducing adipocyte numbers. Overall, we have identified a loss-of-function mutation in Ube2l6 that contributes to the chromosome 2 obesity quantitative trait locus.

Decreased body fat, elevated plasma transforming growth factor-β levels, and impaired BMP4-like signaling in biglycan-deficient mice

Biglycan (BGN), a small leucine-rich proteoglycan, binds the pro-fibrotic cytokine transforming growth factor β (TGFβ) and inhibits its bioactivity in vitro. Nevertheless, it is controversial whether BGN plays an inhibitory role in vivo. Therefore, the purpose of this study was to evaluate the effect of BGN deficiency on TGFβ activity in vivo by studying 1-year-old Bgn null and wild-type (WT) mice on an Ldlr-null background. Phenotypic and metabolic characterization showed that the Bgn null mice had lower body weight, shorter body length, and shorter femur length (all p < 0.05). Surprisingly, the Bgn null mice also exhibited a striking reduction in percent body fat compared to WT mice (p == 0.006), but no changes were observed in plasma triglycerides, total cholesterol, or glycohemoglobin. Both total and bioactive TGFβ1 concentrations in plasma were markedly elevated in Bgn null mice compared to WT mice (4-fold and 11-fold increase, respectively, both p < 0.001), but no changes were found in hepatic levels of mRNA for Tgfβ1 or its receptors. Bgn null mice exhibited elevated expression of hepatic fibronectin protein (p = 0.034) without changes in hepatic or renal histology, and Bgn null mice had decreased urinary albumin/creatinine ratio (p = 0.01). Two key downstream targets of bone morphogenetic protein 4-like signaling, SMAD1/3/5 phosphorylation and Id2 gene expression, were found dramatically reduced in Bgn null livers (p = 0.034). Thus, BGN deficiency decreases body fat in this hyperlipidemic mouse model without changing liver or kidney histology. Overall, we propose that this unexpected phenotype arises from the effects of BGN deficiency in vivo to elevate TGFβ levels while decreasing bone morphogenetic protein 4-like signaling.

Combined therapy for acute hepatic failure

Acute hepatic failure (AHF) is a devastating clinical syndrome characterized by rapid impairment of liver functions and development of encephalopathy, multiple organ failure, and in most cases cerebral edema. AHF has a high mortality rate. Although advances in drug treatment, artificial liver and liver transplantation have significantly improved the prognosis of AHF, there is still a lack of effective treatment for AHF because of its complicated etiopathogenesis, rapid progression and less clinical knowledge about managing the disease. There is an urgent need to develop effective treatments for AHF. This article aims to review recent advances in the treatment of AHF.

Nutritional and metabolic abnormalities and nutrition support therapy in patients with liver failure

Nutritional and metabolic damage is an important manifestation of severe liver disease and is significantly associated with prognosis. In this paper, we review nutritional and metabolic abnormalities and nutritional support therapy in patients with liver failure by summarizing the indicators for evaluating the nutritional and metabolic status and the features of nutrients and energy metabolism. We point out that resting energy expenditure can be measured using CCM-D nutrition metabolism test system in liver failure patients. Energy supply is primarily contributed by fat oxidation in patients with chronic liver failure, and their respiratory quotient is significantly lower than the predicted values. In addition, we discuss nutritional support intervention methods and intake for different stages of liver failure. Our aim is to raise the awareness of clinicians for malnutrition in patients with liver failure to formulate individualized nutrition support therapy.

Genetic control of ATGL-mediated lipolysis modulates adipose triglyceride stores in leptin-deficient mice

Dissecting the genetics of complex traits such as obesity allows the identification of causal genes for disease. Here, we show that the BALB/c mouse strain carries genetic variants that confer resistance to obesity induced by leptin-deficiency or a high-fat diet (HFD). We set out to identify the physiological and genetic bases underlying this phenotype. When compared with C57BL6/J ob/ob mice (B6), BALB/c ob/ob mice exhibited decreased food intake, increased thermogenic capacity, and improved fat catabolism, each of which can potentially modify obesity. Interestingly, analysis of F1 ob/ob (progeny of B6 ob/+ × BALB/c ob+) mice revealed that obesity resistance in BALB/c ob/ob mice principally relied upon improved fat mobilization. This was mechanistically explained by increased adipose triglyceride lipase (ATGL) content in adipocytes, along with increased lipolysis and fatty acid oxidation. We conducted a genome-wide scan and defined a quantitative trait locus (QTL) on chromosome 2. BALB/c alleles on chromosome 2 not only associated with the obesity resistance phenotype but also supported increased ATGL content in adipose tissue. In summary, our study provides evidence that leptin-independent control of adipocyte lipolysis rates directly modifies the balance of macronutrient handling and is sufficient to regulate fat mass in the absence of alterations in food intake and energy expenditure.-Marcelin, G., S-M. Liu, X. Li, G. J. Schwartz, and S. Chua.

A tale with a Twist: a developmental gene with potential relevance for metabolic dysfunction and inflammation in adipose tissue

The Twist proteins (Twist-1 and -2) are highly conserved developmental proteins with key roles for the transcriptional regulation in mesenchymal cell lineages. They belong to the super-family of bHLH proteins and exhibit bi-functional roles as both activators and repressors of gene transcription. The Twist proteins are expressed at low levels in adult tissues but may become abundantly re-expressed in cells undergoing malignant transformation. This observation prompted extensive research on the roles of Twist proteins in cancer progression and metastasis. Very recent studies indicate a novel role for Twist-1 as a potential regulator of adipose tissue (AT) remodeling and inflammation. Several studies suggested that developmental genes are important determinants of obesity, fat distribution and remodeling capacity of different adipose depots. Twist-1 is abundantly and selectively expressed in the adult AT and its constitutive expression is significantly higher in subcutaneous (SAT) vs. visceral (VAT) fat in both mice and humans. Moreover, Twist1 expression is strongly correlated with BMI and insulin resistance in humans. However, the functional roles and transcriptional downstream targets of Twist1 in AT are largely unexplored. The purpose of this review is to highlight the major findings related to Twist1 expression in different fat depots and cellular components of AT and to discuss the potential mechanisms suggesting a role for Twist1 in AT metabolism, inflammation and remodeling.