Epididymal White Fat Research Articles

Overexpression of PRDM16 improves muscle function after rotator cuff tears

Muscle atrophy, fibrosis, and fatty infiltration are commonly seen in rotator cuff tears (RCTs), which are critical factors that directly determine the clinical outcomes for patients with this injury. Therefore, improving muscle quality after RCT is crucial in improving the clinical outcome of tendon repair. In recent years, it has been discovered that adults have functional beige/brown adipose tissue (BAT) that can secrete batokines to promote muscle growth. PRDM16, a PR-domain-containing protein, was discovered with the ability to determine the brown fat cell fate and stimulate its development. Thus, the goal of this study was to discover the role of PRDM16 in improving muscle function after massive tendon tears using a transgenic mouse model with an elevated level of PRDM16 expression. Transgenic aP2-driven PRDM16-overexpressing mice and C57BL/6J mice underwent unilateral supraspinatus (SS) tendon transection and suprascapular nerve transection (TTDN) as described previously (n=8 in each group). DigiGait was performed to evaluate forelimb function at 6 weeks post the TTDN injury. Bilateral SS muscles, interscapular brown fat, epididymal white fat, and inguinal beige fat were harvested for analysis. The expression of PRDM16 in adipose tissue was detected by Western blot. Masson Trichrome staining was conducted to evaluate the muscle fibrosis, and Oil Red O staining was used to determine the fat infiltration. Muscle fiber type was determined by major histocompatibility complex (MHC) expression via immunostaining. All data were presented in the form of mean±standard deviation. t test and 2-way analysis of variance was performed to determine a statistically significant difference between groups. Significance was considered when P<.05. Western blot data showed an increased expression of PRDM16 protein in both white and brown fat in PRDM16-overexpressing mice compared with wild-type (WT) mice. Even though PRDM16 overexpression had no effect on increasing muscle weight, it significantly improved the forelimbs function with longer brake, stance, and stride time and larger stride length and paw area in mice after RCT. Additionally, PRDM16-overexpressing mice showed no difference in the amount of fibrosis when compared to WT mice; however, they had a significantly reduced area of fatty infiltration. These mice also exhibited abundant MHC-IIx fiber percentage in the supraspinatus muscle after TTDN. Overexpression of PRDM16 significantly improved muscle function and reduced fatty infiltration after rotator cuff tears. Promoting BAT activity is beneficial in improving rotator cuff muscle quality and shoulder function after RCT.

Mfat-1 ameliorates cachexia after hypoxic-ischemic brain damage in mice by protecting the hypothalamus-pituitary-adrenal axis

AimsCachexia, a metabolic syndrome, affects 21 % of patients suffering from ischemic encephalopathy. However, the specific mechanism and prevention measures are still unclear. Omega-3 polyunsaturated fatty acids (n−3 PUFAs) have been proven to reduce inflammatory cytokine levels during ischemic events, but whether they have a protective effect against cachexia after hypoxic-ischemic brain damage (HIBD) remains unclear. Main methodsC57BL/6J wild-type and mfat-1 transgenic male mice were treated with and without HIBD. One day after HIBD, the epididymal white fat, gastrocnemius muscle and hypothalamus were weighed and analyzed the phenotypic changes. RNA sequencing was applied to gastrocnemius muscle to identify differential genes and pathways in HIBD groups. The effect of HPA axis on cachexia post-HIBD was examined via adrenalectomy, dexamethasone (0.1 mg/kg), and corticosterone injection (100 mg/kg). Key findingsThe results showed that the incidence of cachexia in mfat-1 mice, which produce high proportion of n−3 PUFAs, was significantly lower than that in wild-type mice post-HIBD. Cachexia-related factors, such as inflammation, muscle atrophy and lipid metabolism were significantly improved in mfat-1 HIBD. RNA sequencing revealed that catabolic and proteasome pathways were significantly downregulated. In hypothalamus, inflammatory cytokines, lipid peroxidation levels were reduced. Corticosterone, glucocorticoid receptor, and dexamethasone suppression test all showed that mfat-1 improved the dysfunction of the HPA axis post-HIBD. The present study elucidated for the first time that mfat-1 reduced HIBD-induced hyperactivation of the HPA axis in mice by reducing inflammation and oxidative stress and contributed to the reduction of metabolic imbalance in peripheral tissues. SignificanceOur study provides mechanistic information for the development of intervention strategies to prevent cachexia.

Postbiotics Prepared Using Lactobacillus paracasei CCFM1224 Prevent Nonalcoholic Fatty Liver Disease by Modulating the Gut Microbiota and Liver Metabolism.

Postbiotics are rich in a variety of bioactive components, which may have beneficial effects in inhibiting hepatic lipid accumulation. In this study, we investigated the preventive effects of postbiotics (POST) prepared from Lactobacillus paracasei on non-alcoholic fatty liver disease (NAFLD). Our results showed that when mice ingested a high-fat diet (HFD) and POST simultaneously, weight gain was slowed, epididymal white fat hypertrophy and insulin resistance were suppressed, serum biochemical indicators related to blood lipid metabolism were improved, and hepatic steatosis and liver inflammation decreased. Bacterial sequencing showed that POST modulated the gut microbiota in HFD mice, increasing the relative abundance of Akkermansia and reducing the relative abundance of Lachnospiraceae NK4A136 group, Ruminiclostridium and Bilophila. Spearman's correlation analysis revealed significant correlations between lipid metabolism parameters and gut microbes. Functional prediction results showed that the regulation of gut microbiota was associated with the improvement of metabolic status. The metabolomic analysis of the liver revealed that POST-regulated liver metabolic pathways, such as glycerophospholipid and ether lipid metabolism, pantothenate and CoA biosynthesis, some parts of amino acid metabolism, and other metabolic pathways. In addition, POST regulated the gene expression in hepatocytes at the mRNA level, thereby regulating lipid metabolism. These findings suggest that POST plays a protective role against NAFLD and may exert its efficacy by modulating the gut microbiota and liver metabolism, and these findings may be applied to related functional foods.

Latent transforming growth factor β binding protein 3 controls adipogenesis

Transforming growth factor-beta (TGFβ) is released from cells as part of a trimeric latent complex consisting of TGFβ, the TGFβ propeptides, and either a latent TGFβ binding protein (LTBP) or glycoprotein-A repetitions predominant (GARP) protein. LTBP1 and 3 modulate latent TGFβ function with respect to secretion, matrix localization, and activation and, therefore, are vital for the proper function of the cytokine in a number of tissues. TGFβ modulates stem cell differentiation into adipocytes (adipogenesis), but the potential role of LTBPs in this process has not been studied. We observed that 72 h post adipogenesis initiation Ltbp1, 2, and 4 expression levels decrease by 74–84%, whereas Ltbp3 expression levels remain constant during adipogenesis. We found that LTBP3 silencing in C3H/10T1/2 cells reduced adipogenesis, as measured by the percentage of cells with lipid vesicles and the expression of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ). Lentiviral mediated expression of an Ltbp3 mRNA resistant to siRNA targeting rescued the phenotype, validating siRNA specificity. Knockdown (KD) of Ltbp3 expression in 3T3-L1, M2, and primary bone marrow stromal cells (BMSC) indicated a similar requirement for Ltbp3. Epididymal and inguinal white adipose tissue fat pad weights of Ltbp3−/- mice were reduced by 62% and 57%, respectively, compared to wild-type mice. Inhibition of adipogenic differentiation upon LTBP3 loss is mediated by TGFβ, as TGFβ neutralizing antibody and TGFβ receptor I kinase blockade rescue the LTBP3 KD phenotype. These results indicate that LTBP3 has a TGFβ-dependent function in adipogenesis both in vitro and possibly in vivo. SignificanceUnderstanding the control of mesenchymal stem cell fate is crucial for the potential use of these cells for regenerative medicine.

MiR-125b-2 knockout increases high-fat diet-induced fat accumulation and insulin resistance

Obese individuals are more susceptible to comorbidities than individuals of healthy weight, including cardiovascular disease and metabolic disorders. MicroRNAs are a class of small and noncoding RNAs that are implicated in the regulation of chronic human diseases. We previously reported that miR-125b plays a critical role in adipogenesis in vitro. However, the involvement of miR-125b-2 in fat metabolism in vivo remains unknown. In the present study, miR-125b-2 knockout mice were generated using CRISPR/CAS9 technology, resulting in mice with a 7 bp deletion in the seed sequence of miR-125b-2. MiR-125b-2 knockout increased the weight of liver tissue, epididymal white fat and inguinal white fat. MiR-125b-2 knockout also increased adipocyte volume in HFD-induced obese mice, while there were no significant differences in body weight and feed intake versus mice fed a normal diet. Additionally, qRT-PCR and western blot analysis revealed that the expression of the miR-125b-2 target gene SCD-1 and fat synthesis-associated genes, such as PPARγ and C/EBPα, were significantly up-regulated in miR-125b-2KO mice (P < 0.05). Moreover, miR-125b-2KO altered HFD-induced changes in glucose tolerance and insulin resistance. In conclusion, we show that miR-125b-2 is a novel potential target for regulating fat accumulation, and also a candidate target to develop novel treatment strategies for obesity and diabetes.

Gochujang prepared using rice and wheat koji partially alleviates high-fat diet-induced obesity in rats.

The aim of this study was to compare whether gochujang products prepared using giant embryo rice koji (rice gochujang, RG) and wheat koji (wheat gochujang, WG) have anti‐obesity effects on rats fed a high‐fat diet (HFD), who served as a model for obesity. The nutritional composition of RG and WG including proximate constituents, amino acid and fatty acid compositions were investigated. Consequently, the secondary fermented metabolites were analyzed in RG and WG by ultrahigh‐performance liquid chromatography and mass spectrometry. Rats were fed a HFD containing 10% RG powder (HFD‐RG) or 10% WG powder (HFD‐WG) for 8 weeks. Body weight gain, weights of liver, epididymal, retroperitoneal, perirenal, and total white fat pads, and levels of serum triglyceride (TG), total cholesterol, low‐density lipoprotein cholesterol, and leptin were lower in all gochujang groups than in the HFD group. Furthermore, RG and WG treatment decreased the hepatic TG content and lipid accumulation and significantly reduced the size of epididymal adipocytes. These effects are probably mediated through inhibition of hepatic fatty acid synthase, acetyl CoA carboxylase, malic enzyme, and adipose tissue lipoprotein lipase activities. The anti‐obesity effect was slightly greater in the HFD‐RG group than in the HFD‐WG group. This effect may be attributed to secondary metabolites, such as capsaicin, genistein, daidzein, soyasaponin, and lysophosphatidylcholines, contained in gochujang prepared using giant embryo rice or wheat koji.

TSH promotes adiposity by inhibiting the browning of white fat

ABSTRACT Adiposity is caused by an imbalance between energy intake and consumption. Promotion of the browning of white fat increases energy expenditure and could combat adiposity. Thyroid-stimulating hormone (TSH) has been confirmed to positively correlate with adiposity. However, the putative connection between TSH and white adipose browning has never been explored. In this study, we sought to assess the effect of TSH on white adipose tissue browning and energy metabolism. Subclinical hypothyroidism mice, thyroid-specific Tshr-knockout mice injected with TSH, adipocyte-specific and global Tshr-knockout micewere subjected to morphological, physiological, genetic or protein expression analyses and metabolic cages to determine the role of TSH on the browning of white adipose tissue and metabolism. 3T3-L1 and primary SVF cells were used to verify the effects and mechanism of TSH on the browning of white adipocytes. We show that increased circulation TSH level decreases energy expenditure, promotes adiposity, impairs glucose and lipid metabolism. Knockout of Tshr decreases adiposity, increases energy expenditureand markedly promotes the development of beige adipocytesin both epididymal and inguinal subcutaneous white fat via a mechanism that likely involves AMPK/PRDM16/PGC1α. Our results reveal an important role of TSH in regulating energy balance and adiposity by inhibiting the browning of white fat.

TSH Promotes Adiposity by Inhibiting the Browning of White Fat

Background: Adiposity is caused by an imbalance between energy intake and consumption. Promotion of the browning of white fat increases energy expenditure and could be a promising therapy for adiposity. Thyroid-stimulating hormone (TSH) has been confirmed to positively correlate with adiposity. However, the putative connection between TSH and white adipose browning has never been explored. In this study, we sought to assess the effect of TSH on white adipose tissue browning and energy metabolism. Methods: Subclinical hypothyroidism mice, thyroid-specific Tshr-knockout mice injected with TSH, adipocyte-specific Tshr-knockout mice, global Tshr-knockout mice and their littermates were subjected to morphological, physiological, genetic or protein expression analyses and metabolic cages to determine the role of TSH on the browning of white adipose tissue and metabolism. To activate thermogenesis, some mice were exposed to cold condition for 4 weeks. 3T3-L1 cells and primary SVF cells were used to verify the effects of TSH on the browning of white adipocytes and its mechanism. Findings: We show that TSH decreases energy expenditure, promotes body weight gain, impairs glucose tolerance and lipid metabolism in subclinical hypothyroidism mice and thyroid-specific Tshr-knockout mice injected with TSH. Adipose-specific or global knockout of Tshr decreases adiposity, resists diet-induced obesity and increases energy expenditure. The knockout of Tshr markedly promotes the development of beige adipocytes and increases expression of UCP1 and other thermogenic genes in both epididymal and inguinal subcutaneous white fat via a mechanism that likely involves AMPK/PRDM16/PGC1α. Interpretation: Our results reveal an important role of TSH in regulating energy balance and adiposity by inhibiting the browning of white fat. Funding: This work was supported by grants from the National Natural Science Foundation (81400828) and the Natural Science Foundation of Shandong Province (ZR2014HQ057). This study was also supported by Projects of the Medical and Health Technology Development Program in Shandong Province (2016WS0427) and Shandong Key R&D Program (2017GSF18129). Declaration of Interest: The authors have no competing financial interests to declare. Ethical Approval: All animal experimental protocols were approved by the Animal Care Committee of School of Medicine, Shandong University.

PO-043 The Effects of One-Time High Intensity Intermittent Training on Expression of LC3 Gene in Rats’ White Adipose Tissue

Objective To investigate the effect of one-time high-intensity intermittent exercise in white fat autophagy in obese rats and provide a theoretical basis of the molecular mechanism of exercise fat loss.&#x0D; Methods Eighteen male 3-weeks-old rats were selected and divided into control group fed with normal diet (C), high-fat diet group fed with high fat diet (H). After 16 weeks, there were twelve obesity rats that divided into diet group (HS) and exercise group (HE). The other six control group rats of 19 weeks age were used as the standard (CS group). OE group did the high intensity intermittent exercise once. The CS group and the CS group were kept quietly. Three groups were taken subcutaneous white adipose tissue(S) and epididymal white adipose tissue (E) immediately after exercise. Mensurate the expression of LC3 gene in the tissue using the fluorescent quantitative PCR.&#x0D; Results 1. The expression of LC3 mRNA from white fat tissue was different to the tissues, which the expression of epididymal white adipose tissue of each group was higher than that in subcutaneous white adipose tissue (P &lt;0.01). 2. Compared with CS group, the expression of epididymal white fat adipose tissue LC3 mRNA decreased (P&lt;0.01) and the expression of the subcutaneous white adipose tissue increased from HS group (P &lt;0.05). 3. Compared with OS group, the expression of epididymal white fat adipose tissue LC3 mRNA decreased (P&lt;0.05) and the expression of subcutaneous white adipose tissue decreased from OS group.&#x0D; Conclusions The expression of LC3mRNA in epididymal white fat adipose tissue of rats was significantly higher than that of subcutaneous white fat. The changes of LC3mRNA expression of adipose tissue caused by high-fat diet have tissue differences. One-time high-intensity intermittent exercise can reduce the expression of LC3mRNA in fat tissue of obese rats. Its regulatory mechanism needs to be further studied.

Body weight predicts Nicotinamide N-Methyltransferase activity in mouse fat

ABSTRACT Aim: Nicotinamide N-methyltransferase (NNMT) is a novel regulator of energy homeostasis in adipose tissue. NNMT expression is higher in obese mice than in lean mice, and NNMT knockdown prevents diet-induced obesity. Little is known about the regulation of enzyme activity during the development of obesity. The aim of this study was to analyze NNMT activity in tissues of mice with incipient and established obesity. Methods: A fluorescence-based, sensitive, low-volume, high-throughput method was developed to assay NNMT activity. C57BL/6 mice were fed a high-fat diet for 4 weeks (incipient obesity) and for 12 weeks (established obesity). Tissues and serum were harvested and analyzed. Results: NNMT activity was highest in subcutaneous white fat (55.0 µU/mg), followed by epididymal white fat (35.6 µU/mg), brown adipose tissue (7.8 µU/mg), liver (7.6 µU/mg), and lung (7.3 µU/mg). Little activity was detected in heart, skeletal muscle, and kidney. No activity was found in serum samples. Body weight predicted NNMT activity in white fat, but not in brown fat or any other tissue, and only in incipient obesity. With established obesity, this association was lost. Conclusions: As obesity develops, body weight predicts NNMT activity in white adipose tissue, but not in any other tissue, consistent with a specific role of adipose-tissue NNMT in the regulation of body weight.

Erythropoietin (EPO) ameliorates obesity and glucose homeostasis by promoting thermogenesis and endocrine function of classical brown adipose tissue (BAT) in diet-induced obese mice

Erythropoietin (EPO), clinically used as a hematopoietic drug, has received much attention due to its nonhematopoietic effects. EPO reportedly has beneficial effects on obesity and diabetes mellitus. We investigated whether interscapular brown adipose tissue (iBAT: main part of classical BAT) could play a role in EPO’s anti-obesity and anti-diabetic effects in diet-induced obese mice. Four-week-old male C57BL/6J mice were fed a high-fat diet (HFD-Con), and half were additionally given an intraperitoneal injection of recombinant human EPO (200 IU/kg) (HFD-EPO) thrice a week for four weeks. At 8 weeks, EPO-injected mice showed significantly reduced body weight with reduced epididymal and subcutaneous white fat mass and unchanged caloric intake and locomotor activity. HOMA-IR (insulin resistance index) and glucose levels during intraperitoneal glucose tolerance test (IPGTT) were significantly lower in HFD-EPO mice than in HFD-Con mice. EPO-injected mice also showed increased oxygen consumption, indicative of metabolic rate, and skin temperature around iBAT tissue masses. EPO significantly upregulated the PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16), a transcriptional factor with a crucial role in brown adipocyte differentiation. EPO significantly increased phosphorylated signal transducer and activator of transcription 3 (STAT3), which is downstream of erythropoietin receptor (EpoR) and known to stabilize PRDM16. EPO’s suppression of myocyte enhancer factor 2c (Mef2c) and microRNA-133a (miR-133a) via β3-adrenergic receptor caused PRDM16 upregulation. EPO-mediated enhancement of EpoR/STAT3 and β-adrenergic receptor/Mef2c/miR-133 pathways dramatically increases total uncoupling protein 1 (UCP1), an essential enzyme for BAT thermogenesis. Furthermore, EPO activated BAT’s endocrine functions. EPO facilitated fibroblast growth factor 21 (FGF21) production and excretion in iBAT, associated with reduction of liver gluconeogenesis-related genes. Thus, EPO’s improvement of obesity and glucose homeostasis can be attributed to increased iBAT thermogenic capacity and activation of BAT’s endocrine functions.

De Novo Reconstruction of Adipose Tissue Transcriptomes Reveals Long Non-coding RNA Regulators of Brown Adipocyte Development

Brown adipose tissue (BAT) protects against obesity by promoting energy expenditure via uncoupled respiration. To uncover BAT-specific long non-coding RNAs (lncRNAs), we used RNA-seq to reconstruct de novo transcriptomes of mouse brown, inguinal white, and epididymal white fat and identified ∼1,500 lncRNAs, including 127 BAT-restricted loci induced during differentiation and often targeted by key regulators PPARγ, C/EBPα, and C/EBPβ. One of them, lnc-BATE1, is required for establishment and maintenance of BAT identity and thermogenic capacity. lnc-BATE1 inhibition impairs concurrent activation of brown fat and repression of white fatgenes and is partially rescued by exogenous lnc-BATE1 with mutated siRNA-targeting sites, demonstrating a function in trans. We show that lnc-BATE1 binds heterogeneous nuclear ribonucleoprotein U and that both are required for brown adipogenesis. Our work provides an annotated catalog for the study of fat depot-selective lncRNAs and establishes lnc-BATE1 as a regulator of BAT development and physiology.

Pleiotropic Effects of Cavin-1 Deficiency on Lipid Metabolism

Mice and humans lacking caveolae due to gene knock-out or inactivating mutations of cavin-1/PTRF have numerous pathologies including markedly aberrant fuel metabolism, lipodystrophy, and muscular dystrophy. We characterized the physiologic/metabolic profile of cavin-1 knock-out mice and determined that they were lean because of reduced white adipose depots. The knock-out mice were resistant to diet-induced obesity and had abnormal lipid metabolism in the major metabolic organs of white and brown fat and liver. Epididymal white fat cells from cavin-1-null mice were small and insensitive to insulin and β-adrenergic agonists resulting in reduced adipocyte lipid storage and impaired lipid tolerance. At the molecular level, the lipolytic defects in white fat were caused by impaired perilipin phosphorylation, and the reduced triglyceride accumulation was caused by decreased fatty acid uptake and incorporation as well as the virtual absence of insulin-stimulated glucose transport. The livers of cavin-1-null mice were mildly steatotic and did not accumulate more lipid after high-fat feeding. The brown adipose tissues of cavin-1-null mice exhibited decreased mitochondria protein expression, which was restored upon high fat feeding. Taken together, these data suggest that dysfunction in fat, muscle, and liver metabolism in cavin-1-null mice causes a pleiotropic phenotype, one apparently identical to that of humans lacking caveolae in all tissues.

The fractalkine/Cx3CR1 system is implicated in the development of metabolic visceral adipose tissue inflammation in obesity

Diet-induced obesity and related peripheral and central inflammation are major risk factors for metabolic, neurological and psychiatric diseases. The chemokine fractalkine (Cx3CL1) and its receptor Cx3CR1 play a pivotal role in recruitment, infiltration and proinflammatory polarization of leukocytes and micoglial cells, however, the role of fractalkine signaling in the development of metabolic inflammation is not fully resolved. To address this issue, fractalkine receptor deficient (Cx3CR1 gfp/gfp) mice were exposed to normal or fat-enriched diet (FatED) for 10weeks and physiological-, metabolic- and immune parameters were compared to those animals in which the fractalkine signaling is maintained by the presence of one functioning allele (Cx3CR1 +/gfp). Mice with intact fractalkine signaling develop obesity characterized by increased epididymal white fat depots and mild glucose intolerance, recruit leukocytes into the visceral adipose tissue and display increased expression of subset of pro- and anti-inflammatory cytokines when exposed to fat-enriched diet. By contrast, Cx3CR1-deficient (gfp/gfp) mice gain significantly less weight on fat-enriched diet and have smaller amount of white adipose tissue (WAT) in the visceral compartment than heterozygote controls. Furthermore, Cx3CR1 gfp/gfp mice fed a fat-enriched diet do not develop glucose intolerance, recruit proportionally less number of gfp-positive cells and express significantly less MCP-1, IL-1α and TNFα in the WAT than control animals with fat-enriched diet induced obesity. Furthermore, heterozygote obese, but not fractalkine receptor deficient mice express high levels of anti-inflammatory IL-10 and arginase1 markers in the visceral fat. The effect of fat-enriched diet on cytokine expression pattern was specific for the WAT, as we did not detect significant elevation of interleukin-1, tumor necrosis factor-alpha and monocyte chemotacting protein (MCP-1) expression in the liver or in the hypothalamus in either genotype. These results highlight the importance of fractalkine signaling in recruitment and polarization of adipose tissue immune cells and identify fractalkine as a target to fight obesity-induced inflammatory complications.

A Novel Therapeutic Approach to Treating Obesity through Modulation of TGFβ Signaling

Obesity results from disproportionately high energy intake relative to energy expenditure. Many therapeutic strategies have focused on the intake side of the equation, including pharmaceutical targeting of appetite and digestion. An alternative approach is to increase energy expenditure through physical activity or adaptive thermogenesis. A pharmacological way to increase muscle mass and hence exercise capacity is through inhibition of the activin receptor type IIB (ActRIIB). Muscle mass and strength is regulated, at least in part, by growth factors that signal via ActRIIB. Administration of a soluble ActRIIB protein comprised of a form of the extracellular domain of ActRIIB fused to a human Fc (ActRIIB-Fc) results in a substantial muscle mass increase in normal mice. However, ActRIIB is also present on and mediates the action of growth factors in adipose tissue, although the function of this system is poorly understood. In the current study, we report the effect of ActRIIB-Fc to suppress diet-induced obesity and linked metabolic dysfunctions in mice fed a high-fat diet. ActRIIB-Fc induced a brown fat-like thermogenic gene program in epididymal white fat, as shown by robustly increased expression of the thermogenic genes uncoupling protein 1 and peroxisomal proliferator-activated receptor-γ coactivator 1α. Finally, we identified multiple ligands capable of reducing thermogenesis that represent likely target ligands for the ActRIIB-Fc effects on the white fat depots. These data demonstrate that novel therapeutic ActRIIB-Fc improves obesity and obesity-linked metabolic disease by both increasing skeletal muscle mass and by inducing a gene program of thermogenesis in the white adipose tissues.

Knockdown of NPY Expression in the Dorsomedial Hypothalamus Promotes Development of Brown Adipocytes and Prevents Diet-Induced Obesity

Hypothalamic neuropeptide Y (NPY) has been implicated in control of energy balance, but the physiological importance of NPY in the dorsomedial hypothalamus (DMH) remains unclear. Here we report that knockdown of NPY expression in the DMH by adeno-associated virus-mediated RNAi reduced fat depots in rats fed regular chow and ameliorated high-fat diet-induced hyperphagia and obesity. DMH NPY knockdown resulted in development of brown adipocytes in inguinal white adipose tissue through the sympathetic nervous system. This knockdown increased uncoupling protein 1 expression in both inguinal fat and interscapular brown adipose tissue (BAT). Consistent with the activation of BAT, DMH NPY knockdown increased energy expenditure and enhanced the thermogenic response to a cold environment. This knockdown also increased locomotor activity, improved glucose homeostasis, and enhanced insulin sensitivity. Together, these results demonstrate critical roles of DMH NPY in body weight regulation through affecting food intake, body adiposity, thermogenesis, energy expenditure, and physical activity.

Vitamin A Deficiency Increases Protein Catabolism and Induces Urea Cycle Enzymes in Rats

Chronic vitamin A deficiency induces a substantial delay in the rates of weight and height gain in both humans and experimental animals. This effect has been associated with an impaired nutrient metabolism and loss of body protein. Therefore, we analyzed the effect of vitamin A deficiency on endogenous proteolysis and nitrogen metabolism and its reversibility with all-trans retinoic acid (RA). Male weanling rats, housed in pairs, were pair-fed a vitamin A-deficient (VAD) or control diet until they were 60 d old. A group of deficient rats were further treated with daily intraperitoneal injections of all-trans RA for 10 d. Final body and tissue (i.e. liver and heart) weights were significantly lower and tissue:body weight ratios were similar in VAD rats and in controls. Conversely, the epididymal white fat:body weight ratio and the plasma concentrations of alanine aminotransferase and adiponectin were significantly higher in VAD rats, which also had hepatic macrovesicular lipid accumulations. Plasma and gastrocnemius muscle 3-methylhistidine, urine nitrogen, and plasma and urine urea concentrations were all significantly higher in the VAD group. The expression of the genes encoding urea cycle enzymes and their activities increased in VAD livers. These changes were partially reverted by all-trans RA. We propose that fuel partitioning in vitamin A deficiency may shift from fatty acids to protein catabolism as an energy source. Our results emphasize the importance of vitamin A on the energy balance control system and they provide an explanation for the role of vitamin A in protein turnover, development, and growth.

Identification of neuronal subpopulations that project from hypothalamus to both liver and adipose tissue polysynaptically

The autonomic nervous system regulates fuel availability and energy storage in the liver, adipose tissue, and other organs; however, the molecular components of this neural circuit are poorly understood. We sought to identify neural populations that project from the CNS indirectly through multisynaptic pathways to liver and epididymal white fat in mice using pseudorabies virus strains expressing different reporters together with BAC transgenesis and immunohistochemistry. Neurons common to both circuits were identified in subpopulations of the paraventricular nucleus of the hypothalamus (PVH) by double labeling with markers expressed in viruses injected in both sites. The lateral hypothalamus and arcuate nucleus of the hypothalamus and brainstem regions (nucleus of the solitary tract and A5 region) also project to both tissues but are labeled at later times. Connections from these same sites to the PVH were evident after direct injection of virus into the PVH, suggesting that these regions lie upstream of the PVH in a common pathway to liver and adipose tissue (two metabolically active organs). These common populations of brainstem and hypothalamic neurons express neuropeptide Y and proopiomelanocortin in the arcuate nucleus, melanin-concentrating hormone, and orexin in the lateral hypothalamus and in the corticotrophin-releasing hormone and oxytocin in the PVH. The delineation of this circuitry will facilitate a functional analysis of the possible role of these potential command-like neurons to modulate autonomic outflow and coordinate metabolic responses in liver and adipose tissue.

Rats Fed Fructose-Enriched Diets Have Characteristics of Nonalcoholic Hepatic Steatosis1–3

Nonalcoholic steatohepatitis (NASH) and nonalcoholic fatty liver disease are increasing in adults and are likely to be increasing in children. Both conditions are hepatic manifestations of metabolic syndrome. Experimental animals fed fructose-enriched diets are widely recognized as good models for metabolic syndrome. However, few reports have described the hepatic pathology of these experimental animals. In this study, 5-wk-old Wistar specific pathogen-free rats, which are a normal strain, were fed experimental diets for 5 wk. We then evaluated the degree of steatohepatitis. The 5 diet groups were as follows: cornstarch (70% wt:wt) [control (C)], high-fructose (70%) (HFr), high-sucrose (70%) (HS), high-fat (15%) (HF), and high-fat (15%) high-fructose (50%) (HFHFr) diets. The macrovesicular steatosis grade, liver:body weight ratio, and hepatic triglyceride concentration were significantly higher in the HFr group than in the other 4 groups. However, the HFr group had a significantly lower ratio of epididymal white fat:body weight than the other 4 groups and had a lower final body weight than the HF and HFHFr groups. The HF group had a greater final body weight than the C, HFr, and HS groups, but no macrovesicular steatosis was observed. The HFr group had a significantly higher grade of lobular inflammation than the other 4 groups. The distribution of lobular inflammation was predominant over portal inflammation, which is consistent with human NASH. In conclusion, rats fed fructose-enriched diets are a better model for NASH than rats fed fat-enriched diets.

The role of LMNA in adipose: a novel mouse model of lipodystrophy based on the Dunnigan-type familial partial lipodystrophy mutation

We investigated the role of LMNA in adipose tissue by developing a novel mouse model of lipodystrophy. Transgenic mice were generated that express the LMNA mutation that causes familial partial lipodystrophy of the Dunnigan type (FPLD2). The phenotype observed in FPLD-transgenic mice resembles many of the features of human FPLD2, including lack of fat accumulation, insulin resistance, and enlarged, fatty liver. Similar to the human disease, FPLD-transgenic mice appear to develop normally, but after several weeks they are unable to accumulate fat to the same extent as their wild-type littermates. One poorly understood aspect of lipodystrophies is the mechanism of fat loss. To this end, we have examined the effects of the FPLD2 mutation on fat cell function. Contrary to the current literature, which suggests FPLD2 results in a loss of fat, we found that the key mechanism contributing to the lack of fat accumulation involves not a loss, but an apparent inability of the adipose tissue to renew itself. Specifically, preadipocytes are unable to differentiate into mature and fully functional adipocytes. These findings provide insights not only for the treatment of lipodystrophies, but also for the study of adipogenesis, obesity, and insulin resistance.