FoxK1 associated gene regulatory network in hepatic insulin action and its relationship to FoxO1 and insulin receptor mediated transcriptional regulation

OBJECTIVE

Insulin acts on the liver via changes in gene expression to maintain glucose and lipid homeostasis. This study aimed to the Forkhead box protein K1 (FOXK1) associated gene regulatory network as a transcriptional regulator of hepatic insulin action and to determine its role versus FoxO1 and possible actions of the insulin receptor at the DNA level.

METHODS

Genome-wide analysis of FoxK1 binding were studied by chromatin immunoprecipitation sequencing and compared to those for IR and FoxO1. These were validated by knockdown experiments and gene expression analysis.

RESULTS

Chromatin immunoprecipitation (ChIP) sequencing shows that FoxK1 binds to the proximal promoters and enhancers of over 4000 genes, and insulin enhances this interaction for about 75% of them. These include genes involved in cell cycle, senescence, steroid biosynthesis, autophagy, and metabolic regulation, including glucose metabolism and mitochondrial function and are enriched in a TGTTTAC consensus motif. Some of these genes are also bound by FoxO1. Comparing this FoxK1 ChIP-seq data to that of the insulin receptor (IR) reveals that FoxK1 may act as the transcription factor partner for some of the previously reported roles of IR in gene regulation, including for LARS1 and TIMM22, which are involved in rRNA processing and cell cycle.

CONCLUSION

These data demonstrate that FoxK1 is an important regulator of gene expression in response to insulin in liver and may act in concert with FoxO1 and IR in regulation of genes in metabolism and other important biological pathways.

The transcription factor Foxp1 regulates aerobic glycolysis in adipocytes and myocytes

In recent years, lactate has been recognized as an important circulating energy substrate rather than only a dead-end metabolic waste product generated during glucose oxidation at low levels of oxygen. The term "aerobic glycolysis" has been coined to denote increased glucose uptake and lactate production despite normal oxygen levels and functional mitochondria. Hence, in "aerobic glycolysis" lactate production is a metabolic choice, whereas in "anaerobic glycolysis" it is a metabolic necessity based on inadequate levels of oxygen. Interestingly, lactate can be taken up by cells and oxidized to pyruvate and thus constitutes a source of pyruvate that is independent of insulin. Here, we show that the transcription factor Foxp1 regulates glucose uptake and lactate production in adipocytes and myocytes. Over-expression of Foxp1 leads to increased glucose uptake and lactate production. In addition, protein levels of several enzymes in the glycolytic pathway are upregulated, such as hexokinase 2, phosphofructokinase, aldolase, and lactate dehydrogenase. Using chromatin immunoprecipitation and real-time quantitative PCR (ChIP-qPCR) assays, we demonstrate that Foxp1 directly interacts with promoter consensus cis-elements that regulate expression of several of these target genes. Conversely, knock-down of Foxp1 suppresses these enzyme levels and lowers glucose uptake and lactate production. Moreover, mice with a targeted deletion of Foxp1 in muscle display systemic glucose intolerance with decreased muscle glucose uptake. In primary human adipocytes with induced expression of Foxp1, we find increased glycolysis and glycolytic capacity. Our results indicate Foxp1 may play an important role as a regulator of aerobic glycolysis in adipose tissue and muscle.

Human Bone Marrow Adipose Tissue is a Metabolically Active and Insulin-Sensitive Distinct Fat Depot

CONTEXT

Bone marrow (BM) in adult long bones is rich in adipose tissue, but the functions of BM adipocytes are largely unknown. We set out to elucidate the metabolic and molecular characteristics of BM adipose tissue (BMAT) in humans.

OBJECTIVE

Our aim was to determine if BMAT is an insulin-sensitive tissue, and whether the insulin sensitivity is altered in obesity or type 2 diabetes (T2DM).

DESIGN

This was a cross-sectional and longitudinal study.

SETTING

The study was conducted in a clinical research center.

PATIENTS OR OTHER PARTICIPANTS

Bone marrow adipose tissue glucose uptake (GU) was assessed in 23 morbidly obese subjects (9 with T2DM) and 9 healthy controls with normal body weight. In addition, GU was assessed in another 11 controls during cold exposure. Bone marrow adipose tissue samples for molecular analyses were collected from non-DM patients undergoing knee arthroplasty.

INTERVENTION(S)

Obese subjects were assessed before and 6 months after bariatric surgery and controls at 1 time point.

MAIN OUTCOME MEASURE

We used positron emission tomography imaging with 2-[18F]fluoro-2-deoxy-D-glucose tracer to characterize GU in femoral and vertebral BMAT. Bone marrow adipose tissue molecular profile was assessed using quantitative RT-PCR.

RESULTS

Insulin enhances GU in human BMAT. Femoral BMAT insulin sensitivity was impaired in obese patients with T2DM compared to controls, but it improved after bariatric surgery. Furthermore, gene expression analysis revealed that BMAT was distinct from brown and white adipose tissue.

CONCLUSIONS

Bone marrow adipose tissue is a metabolically active, insulin-sensitive and molecularly distinct fat depot that may play a role in whole body energy metabolism.

Lactate: the ugly duckling of energy metabolism

Lactate, perhaps the best-known metabolic waste product, was first isolated from sour milk, in which it is produced by lactobacilli. Whereas microbes also generate other fermentation products, such as ethanol or acetone, lactate dominates in mammals. Lactate production increases when the demand for ATP and oxygen exceeds supply, as occurs during intense exercise and ischaemia. The build-up of lactate in stressed muscle and ischaemic tissues has established lactate's reputation as a deleterious waste product. In this Perspective, we summarize emerging evidence that, in mammals, lactate also serves as a major circulating carbohydrate fuel. By providing mammalian cells with both a convenient source and sink for three-carbon compounds, circulating lactate enables the uncoupling of carbohydrate-driven mitochondrial energy generation from glycolysis. Lactate and pyruvate together serve as a circulating redox buffer that equilibrates the NADH/NAD ratio across cells and tissues. This reconceptualization of lactate as a fuel-analogous to how Hans Christian Andersen's ugly duckling is actually a beautiful swan-has the potential to reshape the field of energy metabolism.

The generation of immune-induced fever and emotional stress-induced hyperthermia in mice does not involve brown adipose tissue thermogenesis

We examined the role of brown adipose tissue (BAT) for fever and emotional stress-induced hyperthermia. Wild-type and uncoupling protein-1 (UCP-1) knockout mice were injected with lipopolysaccharide intraperitoneally or intravenously, or subjected to cage exchange, and body temperature monitored by telemetry. Both genotypes showed similar febrile responses to immune challenge and both displayed hyperthermia to emotional stress. Neither procedure resulted in the activation of BAT, such as the induction of UCP-1 or peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mRNA, or reduced BAT weight and triglyceride content. In contrast, in mice injected with a β₃ agonist, UCP-1 and PGC-1α were strongly induced, and BAT weight and triglyceride content reduced. Both lipopolysaccharide and the β₃ agonist, and emotional stress, induced UCP-3 mRNA in skeletal muscle. A β₃ antagonist did not attenuate lipopolysaccharide-induced fever, but augmented body temperature decrease and inhibited BAT activation when mice were exposed to cold. An α₁ /α_2b antagonist or a 5HT_1A agonist, which inhibit vasoconstriction, abolished lipopolysaccharide-induced fever, but had no effect on emotional stress-induced hyperthermia. These findings demonstrate that in mice, UCP-1-mediated BAT thermogenesis does not take part in inflammation-induced fever, which is dependent on peripheral vasoconstriction, nor in stress-induced hyperthermia. However, both phenomena may involve UCP-3-mediated muscle thermogenesis.

Elevated Glucose Levels Preserve Glucose Uptake, Hyaluronan Production, and Low Glutamate Release Following Interleukin-1β Stimulation of Differentiated Chondrocytes

OBJECTIVE

Chondrocytes are responsible for remodeling and maintaining the structural and functional integrity of the cartilage extracellular matrix. Because of the absence of a vascular supply, chondrocytes survive in a relatively hypoxic environment and thus have limited regenerative capacity during conditions of cellular stress associated with inflammation and matrix degradation, such as osteoarthritis (OA). Glucose is essential to sustain chondrocyte metabolism and is a precursor for key matrix components. In this study, we investigated the importance of glucose as a fuel source for matrix repair during inflammation as well as the effect of glucose on inflammatory mediators associated with osteoarthritis.

DESIGN

To create an OA model, we used equine chondrocytes from 4 individual horses that were differentiated into cartilage pellets in vitro followed by interleukin-1β (IL-1β) stimulation for 72 hours. The cells were kept at either normoglycemic conditions (5 mM glucose) or supraphysiological glucose concentrations (25 mM glucose) during the stimulation with IL-1β.

RESULTS

We found that elevated glucose levels preserve glucose uptake, hyaluronan synthesis, and matrix integrity, as well as induce anti-inflammatory actions by maintaining low expression of Toll-like receptor-4 and low secretion of glutamate.

CONCLUSIONS

Adequate supply of glucose to chondrocytes during conditions of inflammation and matrix degradation interrupts the detrimental inflammatory cycle and induces synthesis of hyaluronan, thereby promoting cartilage repair.

Foxc2 is essential for podocyte function

Foxc2 is one of the earliest podocyte markers during glomerular development. To circumvent embryonic lethal effects of global deletion of Foxc2, and to specifically investigate the role of Foxc2 in podocytes, we generated mice with a podocyte-specific Foxc2 deletion. Mice carrying the homozygous deletion developed early proteinuria which progressed rapidly into end stage kidney failure and death around postnatal day 10. Conditional loss of Foxc2 in podocytes caused typical characteristics of podocyte injury, such as podocyte foot process effacement and podocyte microvillus transformation, probably caused by disruption of the slit diaphragm. These effects were accompanied by a redistribution of several proteins known to be necessary for correct podocyte structure. One target gene that showed reduced glomerular expression was Nrp1, the gene encoding neuropilin 1, a protein that has been linked to diabetic nephropathy and proteinuria. We could show that NRP1 was regulated by Foxc2 in vitro, but podocyte-specific ablation of Nrp1 in mice did not generate any phenotype in terms of proteinuria, suggesting that the gene might have more important roles in endothelial cells than in podocytes. Taken together, this study highlights a critical role for Foxc2 as an important gene for podocyte function.

FoxK1 and FoxK2 in insulin regulation of cellular and mitochondrial metabolism

A major target of insulin signaling is the FoxO family of Forkhead transcription factors, which translocate from the nucleus to the cytoplasm following insulin-stimulated phosphorylation. Here we show that the Forkhead transcription factors FoxK1 and FoxK2 are also downstream targets of insulin action, but that following insulin stimulation, they translocate from the cytoplasm to nucleus, reciprocal to the translocation of FoxO1. FoxK1/FoxK2 translocation to the nucleus is dependent on the Akt-mTOR pathway, while its localization to the cytoplasm in the basal state is dependent on GSK3. Knockdown of FoxK1 and FoxK2 in liver cells results in upregulation of genes related to apoptosis and down-regulation of genes involved in cell cycle and lipid metabolism. This is associated with decreased cell proliferation and altered mitochondrial fatty acid metabolism. Thus, FoxK1/K2 are reciprocally regulated to FoxO1 following insulin stimulation and play a critical role in the control of apoptosis, metabolism and mitochondrial function.

Insulin signaling represses Forkhead transcription factor FoxO activity, which contributes to organismal metabolism. Here, the authors use proteomics to identify positively regulated insulin signaling targets FoxK1/K2 and demonstrate their role in lipid metabolism and mitochondrial regulation.

FOXK1 and FOXK2 regulate aerobic glycolysis

Adaptation to the environment and extraction of energy are essential for survival. Some species have found niches and specialized in using a particular source of energy, whereas others-including humans and several other mammals-have developed a high degree of flexibility¹. A lot is known about the general metabolic fates of different substrates but we still lack a detailed mechanistic understanding of how cells adapt in their use of basic nutrients². Here we show that the closely related fasting/starvation-induced forkhead transcription factors FOXK1 and FOXK2 induce aerobic glycolysis by upregulating the enzymatic machinery required for this (for example, hexokinase-2, phosphofructokinase, pyruvate kinase, and lactate dehydrogenase), while at the same time suppressing further oxidation of pyruvate in the mitochondria by increasing the activity of pyruvate dehydrogenase kinases 1 and 4. Together with suppression of the catalytic subunit of pyruvate dehydrogenase phosphatase 1 this leads to increased phosphorylation of the E1α regulatory subunit of the pyruvate dehydrogenase complex, which in turn inhibits further oxidation of pyruvate in the mitochondria-instead, pyruvate is reduced to lactate. Suppression of FOXK1 and FOXK2 induce the opposite phenotype. Both in vitro and in vivo experiments, including studies of primary human cells, show how FOXK1 and/or FOXK2 are likely to act as important regulators that reprogram cellular metabolism to induce aerobic glycolysis.

STK25 regulates oxidative capacity and metabolic efficiency in adipose tissue

Whole-body energy homeostasis at over-nutrition critically depends on how well adipose tissue remodels in response to excess calories. We recently identified serine/threonine protein kinase (STK)25 as a critical regulator of ectopic lipid storage in non-adipose tissue and systemic insulin resistance in the context of nutritional stress. Here, we investigated the role of STK25 in regulation of adipose tissue dysfunction in mice challenged with a high-fat diet. We found that overexpression of STK25 in high-fat-fed mice resulted in impaired mitochondrial function and aggravated hypertrophy, inflammatory infiltration and fibrosis in adipose depots. Reciprocally, Stk25-knockout mice displayed improved mitochondrial function and were protected against diet-induced excessive fat storage, meta-inflammation and fibrosis in brown and white adipose tissues. Furthermore, in rodent HIB-1B cell line, STK25 depletion resulted in enhanced mitochondrial activity and consequently, reduced lipid droplet size, demonstrating an autonomous action for STK25 within adipocytes. In summary, we provide the first evidence for a key function of STK25 in controlling the metabolic balance of lipid utilization vs lipid storage in brown and white adipose depots, suggesting that repression of STK25 activity offers a potential strategy for establishing healthier adipose tissue in the context of chronic exposure to dietary lipids.

Targeting thermogenesis in brown fat and muscle to treat obesity and metabolic disease

Brown fat is emerging as an interesting and promising target for therapeutic intervention in obesity and metabolic disease. Activation of brown fat in humans is associated with marked improvement in metabolic parameters such as levels of free fatty acids and insulin sensitivity. Skeletal muscle is another important organ for thermogenesis, with the capacity to induce energy-consuming futile cycles. In this Review, we focus on how these two major thermogenic organs - brown fat and muscle - act and cooperate to maintain normal body temperature. Moreover, in the light of disease-relevant mechanisms, we explore the molecular pathways that regulate thermogenesis in brown fat and muscle. Brown adipocytes possess a unique cellular mechanism to convert chemical energy into heat: uncoupling protein 1 (UCP1), which can short-circuit the mitochondrial proton gradient. However, recent research demonstrates the existence of several other energy-expending 'futile' cycles in both adipocytes and muscle, such as creatine and calcium cycling. These mechanisms can complement or even substitute for UCP1-mediated thermogenesis. Moreover, they expand our view of cold-induced thermogenesis from a special feature of brown adipocytes to a more general physiological principle. Finally, we discuss how thermogenic mechanisms can be exploited to expend energy and hence offer new therapeutic opportunities.

Acidosis and Deafness in Patients with Recessive Mutations in FOXI1

Maintenance of the composition of inner ear fluid and regulation of electrolytes and acid-base homeostasis in the collecting duct system of the kidney require an overlapping set of membrane transport proteins regulated by the forkhead transcription factor FOXI1. In two unrelated consanguineous families, we identified three patients with novel homozygous missense mutations in FOXI1 (p.L146F and p.R213P) predicted to affect the highly conserved DNA binding domain. Patients presented with early-onset sensorineural deafness and distal renal tubular acidosis. In cultured cells, the mutations reduced the DNA binding affinity of FOXI1, which hence, failed to adequately activate genes crucial for normal inner ear function and acid-base regulation in the kidney. A substantial proportion of patients with a clinical diagnosis of inherited distal renal tubular acidosis has no identified causative mutations in currently known disease genes. Our data suggest that recessive mutations in FOXI1 can explain the disease in a subset of these patients.

Metformin treatment significantly enhances intestinal glucose uptake in patients with type 2 diabetes: Results from a randomized clinical trial

AIMS

Metformin therapy is associated with diffuse intestinal ¹⁸F-fluoro-deoxyglucose (FDG) accumulation in clinical diagnostics using routine FDG-PET imaging. We aimed to study whether metformin induced glucose uptake in intestine is associated with the improved glycaemic control in patients with type 2 diabetes. Therefore, we compared the effects of metformin and rosiglitazone on intestinal glucose metabolism in patients with type 2 diabetes in a randomized placebo controlled clinical trial, and further, to understand the underlying mechanism, evaluated the effect of metformin in rats.

METHODS

Forty-one patients with newly diagnosed type 2 diabetes were randomized to metformin (1g, b.i.d), rosiglitazone (4mg, b.i.d), or placebo in a 26-week double-blind trial. Tissue specific intestinal glucose uptake was measured before and after the treatment period using FDG-PET during euglycemic hyperinsulinemia. In addition, rats were treated with metformin or vehicle for 12weeks, and intestinal FDG uptake was measured in vivo and with autoradiography.

RESULTS

Glucose uptake increased 2-fold in the small intestine and 3-fold in the colon for the metformin group and associated with improved glycemic control. Rosiglitazone increased only slightly intestinal glucose uptake. In rodents, metformin treatment enhanced intestinal FDG retention (P=0.002), which was localized in the mucosal enterocytes of the small intestine.

CONCLUSIONS

Metformin treatment significantly enhances intestinal glucose uptake from the circulation of patients with type 2 diabetes. This intestine-specific effect is associated with improved glycemic control and localized to mucosal layer. These human findings demonstrate directs effect of metformin on intestinal metabolism and elucidate the actions of metformin. Clinical trial number NCT02526615.

Brown Adipose Reporting Criteria in Imaging STudies (BARCIST 1.0): Recommendations for Standardized FDG-PET/CT Experiments in Humans

Human brown adipose tissue (BAT) presence, metabolic activity, and estimated mass are typically measured by imaging [18F]fluorodeoxyglucose (FDG) uptake in response to cold exposure in regions of the body expected to contain BAT, using positron emission tomography combined with X-ray computed tomography (FDG-PET/CT). Efforts to describe the epidemiology and biology of human BAT are hampered by diverse experimental practices, making it difficult to directly compare results among laboratories. An expert panel was assembled by the National Institute of Diabetes and Digestive and Kidney Diseases on November 4, 2014 to discuss minimal requirements for conducting FDG-PET/CT experiments of human BAT, data analysis, and publication of results. This resulted in Brown Adipose Reporting Criteria in Imaging STudies (BARCIST 1.0). Since there are no fully validated best practices at this time, panel recommendations are meant to enhance comparability across experiments, but not to constrain experimental design or the questions that can be asked.

A randomized trial of cold-exposure on energy expenditure and supraclavicular brown adipose tissue volume in humans

OBJECTIVE

To study if repeated cold-exposure increases metabolic rate and/or brown adipose tissue (BAT) volume in humans when compared with avoiding to freeze.

DESIGN

Randomized, open, parallel-group trial.

METHODS

Healthy non-selected participants were randomized to achieve cold-exposure 1hour/day, or to avoid any sense of feeling cold, for 6weeks. Metabolic rate (MR) was measured by indirect calorimetry before and after acute cold-exposure with cold vests and ingestion of cold water. The BAT volumes in the supraclavicular region were measured with magnetic resonance imaging (MRI).

RESULTS

Twenty-eight participants were recruited, 12 were allocated to controls and 16 to cold-exposure. Two participants in the cold group dropped out and one was excluded. Both the non-stimulated and the cold-stimulated MR were lowered within the group randomized to avoid cold (MR at room temperature from 1841±199 kCal/24h to 1795±213 kCal/24h, p=0.047 cold-activated MR from 1900±150 kCal/24h to 1793±215 kCal/24h, p=0.028). There was a trend towards increased MR at room temperature following the intervention in the cold-group (p=0.052). The difference between MR changes by the interventions between groups was statistically significant (p=0.008 at room temperature, p=0.032 after cold-activation). In an on-treatment analysis after exclusion of two participants that reported ≥8days without cold-exposure, supraclavicular BAT volume had increased in the cold-exposure group (from 0.0175±0.015l to 0.0216±0.014l, p=0.049).

CONCLUSIONS

We found evidence for plasticity in metabolic rate by avoiding to freeze compared with cold-exposure in a randomized setting in non-selected humans.

Enhanced insulin sensitivity mediated by adipose tissue browning perturbs islet morphology and hormone secretion in response to autonomic nervous activation in female mice

Insulin resistance results in a compensatory increase in insulin secretion to maintain normoglycemia. Conversely, high insulin sensitivity results in reduced insulin secretion to prevent hypoglycemia. The mechanisms for this inverse adaptation are not well understood. We utilized highly insulin-sensitive mice, due to adipocyte-specific overexpression of the FOXC2 transcription factor, to study mechanisms of the reversed islet adaptation to increased insulin sensitivity. We found that Foxc2TG mice responded to mild hyperglycemia with insulin secretion significantly lower than that of wild-type mice; however, when severe hyperglycemia was induced, Foxc2TG mice demonstrated insulin secretion equal to or greater than that of wild-type mice. In response to autonomic nervous activation by 2-deoxyglucose, the acute suppression of insulin seen in wild-type mice was absent in Foxc2TG mice, suggesting impaired sympathetic signaling to the islet. Basal glucagon was increased in Foxc2TG mice, but they displayed severely impaired glucagon responses to cholinergic and autonomic nervous stimuli. These data suggest that the autonomic nerves contribute to the islet adaptation to high insulin sensitivity, which is compatible with a neuro-adipo regulation of islet function being instrumental for maintaining glucose regulation.

Casein Kinase 2--A Kinase that Inhibits Brown Fat Formation

In adipose tissue, there is a delicate balance between storing and expending energy. In this issue, Shinoda et al. (2015) use phosphoproteomics to identify casein kinase 2 (CK2) as a suppressor of brown adipocyte formation, providing insights into how adipose tissue regulates its composition of white versus brown adipocytes.

Human Brown Adipose Tissue: What We Have Learned So Far

Brown adipose tissue (BAT) is a unique tissue that is able to convert chemical energy directly into heat when activated by the sympathetic nervous system. While initially believed to be of relevance only in human newborns and infants, research during recent years provided unequivocal evidence of active BAT in human adults. Moreover, it has become clear that BAT plays an important role in insulin sensitivity in rodents and humans. This has opened the possibility for exciting new therapies for obesity and diabetes. This review summarizes the current state of research with a special focus on recent advances regarding BAT and insulin resistance in human adults. Additionally, we provide an outlook on possible future therapeutic uses of BAT in the treatment of obesity and diabetes.

Characterization of brown adipose tissue by water-fat separated magnetic resonance imaging

BACKGROUND

To evaluate the possibility of quantifying brown adipose tissue (BAT) volume and fat concentration with a high resolution, long echo time, dual-echo Dixon imaging protocol.

METHODS

A 0.42 mm isotropic resolution water-fat separated MRI protocol was implemented by using the second opposite-phase echo and third in-phase echo. Fat images were calibrated with regard to the intensity of nearby white adipose tissue (WAT) to form relative fat content (RFC) images. To evaluate the ability to measure BAT volume and RFC contrast dynamics, rats were divided into two groups that were kept at 4° or 22°C for 5 days. The rats were then scanned in a 70 cm bore 3.0 Tesla MRI scanner and a human dual energy CT. Interscapular, paraaortal, and perirenal BAT (i/pa/pr-BAT) depots as well as WAT and muscle were segmented in the MRI and CT images. Biopsies were collected from the identified BAT depots.

RESULTS

The biopsies confirmed that the three depots identified with the RFC images consisted of BAT. There was a significant linear correlation (P < 0.001) between the measured RFC and the Hounsfield units from DECT. Significantly lower iBAT RFC (P = 0.0064) and significantly larger iBAT and prBAT volumes (P = 0.0017) were observed in the cold stimulated rats.

CONCLUSION

The calibrated Dixon images with RFC scaling can depict BAT and be used to measure differences in volume, and fat concentration, induced by cold stimulation. The high correlation between RFC and HU suggests that the fat concentration is the main RFC image contrast mechanism.

Brown adipose tissue improves whole-body glucose homeostasis and insulin sensitivity in humans

Brown adipose tissue (BAT) has attracted scientific interest as an antidiabetic tissue owing to its ability to dissipate energy as heat. Despite a plethora of data concerning the role of BAT in glucose metabolism in rodents, the role of BAT (if any) in glucose metabolism in humans remains unclear. To investigate whether BAT activation alters whole-body glucose homeostasis and insulin sensitivity in humans, we studied seven BAT-positive (BAT(+)) men and five BAT-negative (BAT(-)) men under thermoneutral conditions and after prolonged (5-8 h) cold exposure (CE). The two groups were similar in age, BMI, and adiposity. CE significantly increased resting energy expenditure, whole-body glucose disposal, plasma glucose oxidation, and insulin sensitivity in the BAT(+) group only. These results demonstrate a physiologically significant role of BAT in whole-body energy expenditure, glucose homeostasis, and insulin sensitivity in humans, and support the notion that BAT may function as an antidiabetic tissue in humans.

Brown adipose tissue and its therapeutic potential

Obesity and related diseases are a major cause of human morbidity and mortality and constitute a substantial economic burden for society. Effective treatment regimens are scarce, and new therapeutic targets are needed. Brown adipose tissue, an energy-expending tissue that produces heat, represents a potential therapeutic target. Its presence is associated with low body mass index, low total adipose tissue content and a lower risk of type 2 diabetes mellitus. Knowledge about the development and function of thermogenic adipocytes in brown adipose tissue has increased substantially in the last decade. Important transcriptional regulators have been identified, and hormones able to modulate the thermogenic capacity of the tissue have been recognized. Intriguingly, it is now clear that humans, like rodents, possess two types of thermogenic adipocytes: the classical brown adipocytes found in the interscapular brown adipose organ and the so-called beige adipocytes primarily found in subcutaneous white adipose tissue after adrenergic stimulation. The presence of two distinct types of energy-expending adipocytes in humans is conceptually important because these cells might be stimulated and recruited by different signals, raising the possibility that they might be separate potential targets for therapeutic intervention. In this review, we will discuss important features of the energy-expending brown adipose tissue and highlight those that may serve as potential targets for pharmacological intervention aimed at expanding the tissue and/or enhancing its function to counteract obesity.

An enzymatic chromatin switch that directs formation of active brown fat

How is the recruitment of brown adipocytes regulated? Ohno et al. (2013) show that the euchromatic histone-lysine N-metyltransferase 1 (EHMT1) is essential for the specification of the brown adipocyte fate, a finding with important implications for the pathophysiology of obesity and obesity-related maladies.

Hyperthyroidism increases brown fat metabolism in humans

CONTEXT

Thyroid hormones are important regulators of brown adipose tissue (BAT) development and function. In rodents, BAT metabolism is up-regulated by thyroid hormones.

OBJECTIVE

The purpose of this article was to investigate the impact of hyperthyroidism on BAT metabolism in humans.

DESIGN

This was a follow-up study using positron emission tomography imaging.

MAIN OUTCOME MEASURES

Glucose uptake (GU) and perfusion of BAT, white adipose tissue, skeletal muscle, and thyroid gland were measured using [18F]2-fluoro-2-deoxy-D-glucose and [15O]H2O and positron emission tomography in 10 patients with overt hyperthyroidism and in 8 healthy participants. Five of the hyperthyroid patients were restudied after restoration of euthyroidism. Supraclavicular BAT was quantified with magnetic resonance imaging or computed tomography and energy expenditure (EE) with indirect calorimetry.

RESULTS

Compared with healthy participants, hyperthyroid participants had 3-fold higher BAT GU (2.7±2.3 vs 0.9±0.1 μmol/100 g/min, P=.0013), 90% higher skeletal muscle GU (P<.005), 45% higher EE (P<.005), and a 70% higher lipid oxidation rate (P=.001). These changes were reversible after restoration of euthyroidism. During hyperthyroidism, serum free T4 and free T3 were strongly associated with EE and lipid oxidation rates (P<.001). TSH correlated inversely with BAT and skeletal muscle glucose metabolism (P<.001). Hyperthyroidism had no effect on BAT perfusion, whereas it stimulated skeletal muscle perfusion (P=.04). Thyroid gland GU did not differ between hyperthyroid and euthyroid study subjects.

CONCLUSIONS

Hyperthyroidism increases GU in BAT independently of BAT perfusion. Hyperthyroid patients are characterized by increased skeletal muscle metabolism and lipid oxidation rates.

Two types of brown adipose tissue in humans

During the last years the existence of metabolically active brown adipose tissue in adult humans has been widely accepted by the research community. Its unique ability to dissipate chemical energy stored in triglycerides as heat makes it an attractive target for new drugs against obesity and its related diseases. Hence the tissue is now subject to intense research, the hypothesis being that an expansion and/or activation of the tissue is associated with a healthy metabolic phenotype. Animal studies provide evidence for the existence of at least two types of brown adipocytes. Apart from the classical brown adipocyte that is found primarily in the interscapular region where it constitutes a thermogenic organ, a second type of brown adipocyte, the so-called beige adipocyte, can appear within white adipose tissue depots. The fact that the two cell types develop from different precursors suggests that they might be recruited and stimulated by different cues and therefore represent two distinct targets for therapeutic intervention. The aim of this commentary is to discuss recent work addressing the question whether also humans possess two types of brown adipocytes and to highlight some issues when looking for molecular markers for such cells.

Blunted metabolic responses to cold and insulin stimulation in brown adipose tissue of obese humans

OBJECTIVE

Inactive brown adipose tissue (BAT) may predispose to weight gain. This study was designed to measure metabolism in the BAT of obese humans, and to compare it to that in lean subjects. The impact of weight loss on BAT and the association of detectable BAT with various metabolic characteristics were also assessed.

DESIGN AND METHODS

Using positron emission tomography (PET), cold- and insulin-stimulated glucose uptake and blood flow in the BAT of obese and lean humans were quantified. Further, cold-induced glucose uptake was measured in obese subjects before and after a 5-month conventional weight loss.

RESULTS

Mean responses in BAT glucose uptake rate to both cold and insulin stimulation were twice as large in lean as in obese subjects. Blood flow in BAT was also lower in obese subjects under cold conditions. The increase in cold-induced BAT glucose uptake rate after weight loss was not statistically significant. Subjects with cold-activated detectable BAT were leaner and had higher whole-body insulin sensitivity than BAT-negative subjects, irrespective of age and gender.

CONCLUSIONS

The effects of cold and insulin on BAT activity are severely blunted in obesity, and the presence of detectable BAT may contribute to a metabolically healthy status.

Presence of brown adipocytes in retroperitoneal fat from patients with benign adrenal tumors: relationship with outdoor temperature

CONTEXT

Brown adipose tissue (BAT) is a metabolically highly active organ with increased thermogenic activity in rodents exposed to cold temperature. Recently its presence in the cervical adipose tissue of human adults and its association with a favorable metabolic phenotype have been reported.

OBJECTIVE

The objective of the study was to determine the prevalence of retroperitoneal BAT in human adults.

DESIGN

This was an observational cohort study.

SETTING

The study was conducted at a tertiary referral hospital.

PATIENTS

Fifty-seven patients who underwent surgery for benign adrenal tumors were included in this study.

MAIN OUTCOME MEASURES

Prevalence of retroperitoneal BAT adjacent to the removed adrenal tumor as determined by uncoupling protein 1 (UCP1) protein and mRNA expression was measured.

RESULTS

Using protein and mRNA expression analysis, we detected UCP1 protein in 26 of 57 patients (45.6%) as well as high mRNA expression of genes characteristic for brown adipocytes, independent of the adrenal tumor type. The presence of brown adipocytes within the retroperitoneal fat was associated with a significantly lower outdoor temperature during the month prior to surgery. Importantly, UCP1 expression on both mRNA and protein level was inversely correlated to outdoor temperature, whereas body mass index, sex, age, and diabetes status were not.

CONCLUSIONS

These findings suggest that human retroperitoneal adipose tissue can acquire a BAT phenotype, thereby adapting to environmental challenges. These adaptive processes might provide a valuable therapeutic target in the treatment of obesity and insulin resistance.

Adipose tissue metabolism in 2012: Adipose tissue plasticity and new therapeutic targets

2012 has been a rewarding year for adipocyte research. A new type of brown-like adipocyte—the beige adipocyte—and irisin, a previously unknown hormone that stimulates the formation of such cells, have been discovered. A bipotential adipocyte progenitor giving rise to both brown and white adipocytes has also been identified.

Beige adipocytes are a distinct type of thermogenic fat cell in mouse and human

Brown fat generates heat via the mitochondrial uncoupling protein UCP1, defending against hypothermia and obesity. Recent data suggest that there are two distinct types of brown fat: classical brown fat derived from a myf-5 cellular lineage and UCP1-positive cells that emerge in white fat from a non-myf-5 lineage. Here, we report the isolation of "beige" cells from murine white fat depots. Beige cells resemble white fat cells in having extremely low basal expression of UCP1, but, like classical brown fat, they respond to cyclic AMP stimulation with high UCP1 expression and respiration rates. Beige cells have a gene expression pattern distinct from either white or brown fat and are preferentially sensitive to the polypeptide hormone irisin. Finally, we provide evidence that previously identified brown fat deposits in adult humans are composed of beige adipocytes. These data provide a foundation for studying this mammalian cell type with therapeutic potential. PAPERCLIP:

Adipocyte mitochondrial genes and the forkhead factor FOXC2 are decreased in type 2 diabetes patients and normalized in response to rosiglitazone

BACKGROUND

FOXC2 has lately been implicated in diabetes and obesity as well as mitochondrial function and biogenesis and also as a regulator of mtTFA/Tfam. In this study, the expression of FOXC2 and selected genes involved in mitochondrial function and biogenesis in healthy subjects and in a matched cohort with type 2 diabetes patients before and after treatment with rosiglitazone was determined. Quantitative real time PCR was used to analyze both RNA and DNA from biopsies from subcutaneous adipose tissue.

METHODS

Blood samples and subcutaneous abdominal fat biopsies were collected from 12 T2D patients, of which 11 concluded the study, pre-treatment and 90 days after initiation of rosiglitazone treatment, and from 19 healthy control subjects on the first and only visit from healthy subjects. Clinical parameters were measured on the blood samples. RNA and DNA were prepared from the fat biopsies and gene expression was measured with real time PCR.

RESULTS

The expression level of genes in the mitochondrial respiratory complexes I - IV were significantly downregulated in the diabetic patients and restored in response to rosiglitazone treatment. Rosiglitazone treatment also increased the relative number of mitochondria in diabetic patients compared with controls. Furthermore, the transcription factors FOXC2 and mtTFA/Tfam displayed a response pattern identical to the mitochondrial genes.

CONCLUSIONS

FOXC2, mtTFA/Tfam and subunits of the respiratory complexes I - IV show equivalent regulation in gene expression levels in response to TZD treatment. This, together with the knowledge that FOXC2 has a regulatory function of mtTFA/Tfam and mitochondrial biogenesis, suggests that FOXC2 has a possible functional role in the TZD activated mitochondrial response.

Comparison of dorsocervical with abdominal subcutaneous adipose tissue in patients with and without antiretroviral therapy-associated lipodystrophy

OBJECTIVE

Combination antiretroviral therapy (cART) is associated with lipodystrophy, i.e., loss of subcutaneous adipose tissue in the abdomen, limbs, and face and its accumulation intra-abdominally. No fat is lost dorsocervically and it can even accumulate in this region (buffalo hump). It is unknown how preserved dorsocervical fat differs from abdominal subcutaneous fat in HIV-1-infected cART-treated patients with (cART+LD+) and without (cART+LD-) lipodystrophy.

RESEARCH DESIGN AND METHODS

We used histology, microarray, PCR, and magnetic resonance imaging to compare dorsocervical and abdominal subcutaneous adipose tissue in cART+LD+ (n=21) and cART+LD- (n=11).

RESULTS

Albeit dorsocervical adipose tissue in cART+LD+ seems spared from lipoatrophy, its mitochondrial DNA (mtDNA; copies/cell) content was significantly lower (by 62%) than that of the corresponding tissue in cART+LD-. Expression of CD68 mRNA, a marker of macrophages, and numerous inflammatory genes in microarray were significantly lower in dorsocervical versus abdominal subcutaneous adipose tissue. Genes with the greatest difference in expression between the two depots were those involved in regulation of transcription and regionalization (homeobox genes), irrespective of lipodystrophy status. There was negligible mRNA expression of uncoupling protein 1, a gene characteristic of brown adipose tissue, in either depot.

CONCLUSIONS

Because mtDNA is depleted even in the nonatrophic dorsocervical adipose tissue, it is unlikely that the cause of lipoatrophy is loss of mtDNA. Dorsocervical adipose tissue is less inflamed than lipoatrophic adipose tissue. It does not resemble brown adipose tissue. The greatest difference in gene expression between dorsocervical and abdominal subcutaneous adipose tissue is in expression of homeobox genes.

Mice with disrupted type I protein kinase A anchoring in T cells resist retrovirus-induced immunodeficiency

Type I protein kinase A (PKA) is targeted to the TCR-proximal signaling machinery by the A-kinase anchoring protein ezrin and negatively regulates T cell immune function through activation of the C-terminal Src kinase. RI anchoring disruptor (RIAD) is a high-affinity competitor peptide that specifically displaces type I PKA from A-kinase anchoring proteins. In this study, we disrupted type I PKA anchoring in peripheral T cells by expressing a soluble ezrin fragment with RIAD inserted in place of the endogenous A-kinase binding domain under the lck distal promoter in mice. Peripheral T cells from mice expressing the RIAD fusion protein (RIAD-transgenic mice) displayed augmented basal and TCR-activated signaling, enhanced T cell responsiveness assessed as IL-2 secretion, and reduced sensitivity to PGE(2)- and cAMP-mediated inhibition of T cell function. Hyperactivation of the cAMP-type I PKA pathway is involved in the T cell dysfunction of HIV infection, as well as murine AIDS, a disease model induced by infection of C57BL/6 mice with LP-BM5, a mixture of attenuated murine leukemia viruses. LP-BM5-infected RIAD-transgenic mice resist progression of murine AIDS and have improved viral control. This underscores the cAMP-type I PKA pathway in T cells as a putative target for therapeutic intervention in immunodeficiency diseases.

The adipocyte-expressed forkhead transcription factor Foxc2 regulates metabolism through altered mitochondrial function

OBJECTIVE

Previous findings demonstrate that enhanced expression of the forkhead transcription factor Foxc2 in adipose tissue leads to a lean and insulin-sensitive phenotype. These findings prompted us to further investigate the role of Foxc2 in the regulation of genes of fundamental importance for metabolism and mitochondrial function.

RESEARCH DESIGN AND METHODS

The effects of Foxc2 on expression of genes involved in mitochondriogenesis and mitochondrial function were assessed by quantitative real-time PCR. The potential of a direct transcriptional regulation of regulated genes was tested in promoter assays, and mitochondrial morphology was investigated by electron microscopy. Mitochondrial function was tested by measuring oxygen consumption and extracellular acidification rates as well as palmitate oxidation.

RESULTS

Enhanced expression of FOXC2 in adipocytes or in cells with no endogenous Foxc2 expression induces mitochondriogenesis and an elongated mitochondrial morphology. Together with increased aerobic metabolic capacity, increased palmitate oxidation, and upregulation of genes encoding respiratory complexes and of brown fat-related genes, Foxc2 also specifically induces mitochondrial fusion genes in adipocytes. Among tested forkhead genes, Foxc2 is unique in its ability to trans-activate the nuclear-encoded mitochondrial transcription factor A (mtTFA/Tfam) gene--a master regulator of mitochondrial biogenesis. In human adipose tissue the expression levels of mtTFA/Tfam and of fusion genes also correlate with that of Foxc2.

CONCLUSIONS

We previously showed that a high-calorie diet and insulin induce Foxc2 in adipocytes; the current findings identify a previously unknown role for Foxc2 as an important metabo-regulator of mitochondrial morphology and metabolism.

Therapeutic prospects of metabolically active brown adipose tissue in humans

The world-wide obesity epidemic constitutes a severe threat to human health and wellbeing and poses a major challenge to health-care systems. Current therapeutic approaches, relying mainly on reduced energy intake and/or increased exercise energy expenditure, are generally of limited effectiveness. Previously believed to be present only in children, the existence of metabolically active brown adipose tissue (BAT) was recently demonstrated also in healthy human adults. The physiological role of BAT is to dissipate chemical energy, mainly from fatty acids, as heat to maintain body temperature in cold environments. Recent studies indicate that the activity of BAT is negatively correlated with overweight and obesity, findings that raise the exciting possibility of new and effective weight reduction therapies based on increased BAT energy expenditure, a process likely to be amenable to pharmacological intervention.

Brown adipose tissue--a new role in humans?

New targets for pharmacological interventions are of great importance to combat the epidemic of obesity. Brown adipose tissue could potentially represent one such target. Unlike white adipose tissue, brown adipose tissue has the ability to dissipate energy by producing heat rather than storing it as triglycerides. In small mammals, the presence of active brown adipose tissue is pivotal for the maintenance of body temperature and possibly to protect against the detrimental effects of surplus energy intake. Animal studies have shown that expansion and/or activation of brown adipose tissue counteracts diet-induced weight gain and related disorders such as type 2 diabetes mellitus. Several independent studies have now confirmed the presence of functional brown adipose tissue in adult humans, for whom this tissue is probably metabolically beneficial given its association with both low BMI and low total adipose tissue content. Over the past few years, knowledge of the transcriptional control and development of brown adipose tissue has increased substantially. Thus, several possible targets that may be useful for the expansion and/or activation of this tissue by pharmacological means have been identified. Whether or not brown adipose tissue will be useful in the battle against obesity remains to be seen. However, this possibility is certainly well worth exploring.

Human brown adipose tissue

The BAT organ is unique in that it has evolved to safely dissipate large amounts of chemical energy--a quality that might be harnessed to help humans deal with a dangerously hypercaloric environment and still remain in good health.

Overexpression of Foxf2 in adipose tissue is associated with lower levels of IRS1 and decreased glucose uptake in vivo

Many members of the forkhead genes family of transcription factors have been implicated as important regulators of metabolism, in particular, glucose homeostasis, e.g., Foxo1, Foxa3, and Foxc2. The purpose of this study was to exploit the possibility that yet unknown members of this gene family play a role in regulating glucose tolerance in adipocytes. We identified Foxf2 in a screen for adipose-expressed forkhead genes. In vivo overexpression of Foxf2 in an adipose tissue-restricted fashion demonstrated that such mice display a significantly induced insulin secretion in response to an intravenous glucose load compared with wild-type littermates. In response to increased Foxf2 expression, insulin receptor substrate 1 (IRS1) mRNA and protein levels are significantly downregulated in adipocytes; however, the ratio of serine vs. tyrosine phosphorylation of IRS1 seems to remain unaffected. Furthermore, adipocytes overexpressing Foxf2 have a significantly lower insulin-mediated glucose uptake compared with wild-type adipocytes. These findings argue that Foxf2 is a previously unrecognized regulator of cellular and systemic whole body glucose tolerance, at least in part, due to lower levels of IRS1. Foxf2 and its downstream target genes can provide new insights with regard to identification of novel therapeutic targets.

Pilot study of sentinel-node-based adoptive immunotherapy in advanced colorectal cancer

Background

Despite optimal surgical treatment and modern adjuvant therapies, 50% of patients diagnosed with colorectal cancer die within 5 years. Immunotherapy offers an appealing complement to traditional chemotherapy, with possible long-term protection against tumor recurrences through immunological memory. We have conducted a pilot study of a novel adoptive immunotherapy, using autologous, in vitro expanded lymphocytes isolated from the tumor-draining sentinel lymph node.

Study Design

Sentinel nodes were recovered from 16 patients with disseminated or locally advanced, high-risk colorectal cancer. Single-cell suspensions of sentinel-node-acquired lymphocytes were clonally expanded in vitro in the presence of autologous tumor extract and returned as a transfusion. Patients were followed with clinical and radiological evaluations. Long-term survival was compared with traditionally treated controls.

Results

Sentinel-node-acquired CD4⁺ Th1-lymphocytes could be clonally expanded in vitro and safely administered to all 16 patients without side-effects. In four out of nine stage IV patients, complete tumor regression occurred. Median survival time in the stage IV patients (n = 9) was 2.6 years, as compared with 0.8 years in conventionally treated controls. A dose-dependent effect with regards to reduced tumor burden and long-term survival was observed.

Conclusion

Sentinel-node-based adoptive immunotherapy is feasible; the method has shown no apparent side-effects and appears to convey therapeutic antitumor effects. Further studies are justified to determine its efficacy and precise role in the treatment of colorectal cancer.

Functional brown adipose tissue in healthy adults

Using positron-emission tomography (PET), we found that cold-induced glucose uptake was increased by a factor of 15 in paracervical and supraclavicular adipose tissue in five healthy subjects. We obtained biopsy specimens of this tissue from the first three consecutive subjects and documented messenger RNA (mRNA) and protein levels of the brown-adipocyte marker, uncoupling protein 1 (UCP1). Together with morphologic assessment, which showed numerous multilocular, intracellular lipid droplets, and with the results of biochemical analysis, these findings document the presence of substantial amounts of metabolically active brown adipose tissue in healthy adult humans.

The forkhead transcription factor Foxi1 is a master regulator of vacuolar H-ATPase proton pump subunits in the inner ear, kidney and epididymis

The vacuolar H(+)-ATPase dependent transport of protons across cytoplasmic membranes in FORE (forkhead related) cells of endolymphatic epithelium in the inner ear, intercalated cells of collecting ducts in the kidney and in narrow and clear cells of epididymis require expression of several subunits that assemble into a functional multimeric proton pump. We demonstrate that expression of four such subunits A1, B1, E2 and a4 all co-localize with the forkhead transcription factor Foxi1 in a subset of epithelial cells at these three locations. In cells, of such epithelia, that lack Foxi1 we fail to identify any expression of A1, B1, E2 and a4 demonstrating an important role for the transcription factor Foxi1 in regulating subunit availability. Promoter reporter experiments, electrophoretic mobility shift assays (EMSA) and site directed mutagenesis demonstrate that a Foxi1 expression vector can trans-activate an a4-promoter reporter construct in a dose dependent manner. Furthermore, we demonstrate using chromatin immunoprecipitation (ChIP) assays that Foxi1-dependent activation to a large extent depends on cis-elements at position -561/-547 in the a4 promoter. Thus, we provide evidence that Foxi1 is necessary for expression of at least four subunits in three different epithelia and most likely is a major determinant for proper assembly of a functional vacuolar H(+)-ATPase complex at these locations.

Emergence of the sensory nervous system as defined by Foxs1 expression

Peripheral sensory neurons are derived from two distinct structures, the ectodermal placodes and the neural crest. Here, we establish the forkhead family transcription factor Foxs1 as an early sensory neuronal marker. Early embryonic Foxs1 expression was present in all the sensory nervous system regardless of cellular origin, but was not found in other placode and neural crest-derived cell types. Foxs1 expression was turned on in the sensory neuron precursors of the trunk. Consistently, expression of Sox10, that is present in undifferentiated multipotent neural crest cells (NCCs), was mutually exclusive to Foxs1. Acquirement of Foxs1 expression was used to study the emergence of the dorsal root ganglion (DRG) sensory neurons. Migrating pioneering Foxs1 expressing NCCs were found at the anterior dorsal somitic lip at the 18-somite stage. These cells showed limited proliferation and migrated to form a cluster in the ventral aspect of the coalescing ganglion, surrounded by Foxs1(-)/Sox10(+) migrating NCCs retaining a high rate of proliferation. Sensory neurogenesis of the Foxs1(-)/Sox10(+) precursors occurred within the condensed DRG starting with neurogenin-1 (Ngn1) and Brn3a expression. These data define a sequential emergence of neuronal precursors of the sensory nervous system with different molecular characteristics, starting during migration and continuing well after DRG condensation.

"The adipocyte: a multifunctional cell"

The beautiful Thorskog Castle just north of Göteborg on the Swedish west coast was the venue for the 134th Nobel Symposium, entitled "The Adipocyte: A Multifunctional Cell." For three splendid summer days, some 50 scientists working on various aspects of adipocyte biology convened under the auspices of the Nobel Foundation.

Epididymal expression of the forkhead transcription factor Foxi1 is required for male fertility

An essential aspect of male reproductive capacity is the immediate availability of fertilization-ready spermatozoa. To ensure this, most mammals rely on post-testicular sperm maturation. In epididymis, germ cells are matured and stored in a quiescent state that readily can be altered to produce active spermatozoa. This depends on active proton secretion into the epididymal lumen. We have identified Foxi1 as an important regulator of gene expression in narrow and clear cells-the major proton secretory cells of epididymal epithelia. Foxi1 appears to be required for the expression of the B1-subunit of the vacuolar H+ -ATPase proton pump and for carbonic anhydrase II as well as the chloride/bicarbonate transporter pendrin. Using transfection experiments, we have identified a Foxi1 binding cis-element in the ATP6V1B1 (encoding the B1-subunit) promoter that is critical for reporter gene activation. When this site is mutated to eliminate Foxi1 binding, activation is also abolished. As a consequence of defect Foxi1-dependent epididymal sperm maturation, we demonstrate that spermatozoa from Foxi1 null males fail to reach the female genital tract in sufficient number to allow fertilization.

Eya1 regulates the growth of otic epithelium and interacts with Pax2 during the development of all sensory areas in the inner ear

Members of the Eyes absent (Eya) gene family are important for auditory system development. While mutations in human EYA4 cause late-onset deafness at the DFNA10 locus, mutations in human EYA1 cause branchio-oto-renal (BOR) syndrome. Inactivation of Eya1 in mice causes an early arrest of the inner ear development at the otocyst stage. To better understand the role of Eya1 in inner ear development, we analyzed the cellular and molecular basis of the early defect observed in the Eya1 mutant embryos. We report here that Eya1-/- otic epithelium shows reduced cell proliferation from E8.5 and increased cell apoptosis from E9.0, thus providing insights into the cellular basis of inner ear defect which occurred in the absence of Eya1. Previous studies have suggested that Pax, Eya and Six genes function in a parallel or independent pathway during inner ear development. However, it remains unknown whether Pax genes interact with Eya1 or Six1 during inner ear morphogenesis. To further evaluate whether Pax genes function in the Eya1-Six1 pathway or whether they interact with Eya1 or Six1 during inner ear morphogenesis, we have analyzed the expression pattern of Eya1, Pax2 and Pax8 on adjacent sections of otic epithelium from E8.5 to 9.5 by in situ hybridization and the inner ear gross structures of Pax2, Eya1 and Six1 compound mutants at E17.5 by latex paintfilling. Our data strongly suggest that Pax2 interacts with Eya1 during inner ear morphogenesis, and this interaction is critical for the development of all sensory areas in the inner ear. Furthermore, otic marker analysis in both Eya1-/- and Pax2-/- embryos indicates that Eya1 but not Pax2 regulates the establishment of regional specification of the otic vesicle. Together, these results show that, while Eya1 exerts an early function essential for normal growth and patterning of the otic epithelium, it also functionally synergizes with Pax2 during the morphogenesis of all sensory areas of mammalian inner ear.

Reduced PDE4 expression and activity contributes to enhanced catecholamine-induced cAMP accumulation in adipocytes from FOXC2 transgenic mice

Overexpression of forkhead transcription factor FOXC2 in white adipose tissue (WAT) leads to a lean phenotype resistant to diet-induced obesity. This is due, in part, to enhanced catecholamine-induced cAMP-PKA signaling in FOXC2 transgenic mice. Here we show that rolipram treatment of adipocytes from FOXC2 transgenic mice did not increase isoproterenol-induced cAMP accumulation to the same extent as in wild type cells. Accordingly, phosphodiesterase-4 (PDE4) activity was reduced by 75% and PDE4A5 protein expression reduced by 30-50% in FOXC2 transgenic WAT compared to wild type. Thus, reduced PDE4 activity in adipocytes from FOXC2 transgenic mice contributes to amplified beta-AR induced cAMP responses observed in these cells.

Comparative lymphatic, ocular, and metabolic phenotypes of Foxc2 haploinsufficient and aP2-FOXC2 transgenic mice

FOXC2 mutations cause the lymphatic/ocular disorder Lymphedema-Distichiasis (LD), and Foxc2 haploinsufficient mice mimic this disorder. To determine if FOXC2 overexpression might also cause lymphatic and/or ocular abnormalities, we performed dynamic lymphatic imaging (Evans blue dye), ocular tissue examination, and metabolic profiles in mice: transgenic for FOXC2 with an adipocyte (aP2) promoter (aP2-FOXC2 Tg), heterozygous for targeted disruption of Foxc2 (Foxc2+/-), or compound heterozygous and transgenic (Foxc2+/-, Tg) compared to wild-type controls (WT). Foxc2+/-; aP2-FOXC2 Tg; and Foxc2+/-, Tg, exhibited LD's distinctive hyperplastic lymphatic phenotype characterized by increased number of lymphatic channels and lymph nodes as well as retrograde lymph reflux. Foxc2+/-, and Foxc2+/-, Tg but not aP2-FOXC2 Tg or WT showed an abnormal ocular phenotype. Previously described alterations in brown/ white fat distribution and lean phenotype in aP2-FOXC2 transgenics were confirmed. AP2-FOXC2 Tg immunohistochemistry disclosed aberrant FOXC2 expression in ectopic sites, especially embryonic heart. Lymphatic system links with fat metabolism are discussed.

Lack of the central nervous system- and neural crest-expressed forkhead gene Foxs1 affects motor function and body weight

To gain insight into the expression pattern and functional importance of the forkhead transcription factor Foxs1, we constructed a Foxs1-beta-galactosidase reporter gene "knock-in" (Foxs1beta-gal/beta-gal) mouse, in which the wild-type (wt) Foxs1 allele has been inactivated and replaced by a beta-galactosidase reporter gene. Staining for beta-galactosidase activity reveals an expression pattern encompassing neural crest-derived cells, e.g., cranial and dorsal root ganglia as well as several other cell populations in the central nervous system (CNS), most prominently the internal granule layer of cerebellum. Other sites of expression include the lachrymal gland, outer nuclear layer of retina, enteric ganglion neurons, and a subset of thalamic and hypothalamic nuclei. In the CNS, blood vessel-associated smooth muscle cells and pericytes stain positive for Foxs1. Foxs1beta-gal/beta-gal mice perform significantly better (P < 0.01) on a rotating rod than do wt littermates. We have also noted a lower body weight gain (P < 0.05) in Foxs1beta-gal/lbeta-gal males on a high-fat diet, and we speculate that dorsomedial hypothalamic neurons, expressing Foxs1, could play a role in regulating body weight via regulation of sympathetic outflow. In support of this, we observed increased levels of uncoupling protein 1 mRNA in Foxs1beta-gal/beta-gal mice. This points toward a role for Foxs1 in the integration and processing of neuronal signals of importance for energy turnover and motor function.